JP2002507076A - Gigabit Ethernet transceiver - Google Patents

Abstract

(57) [Summary] A communication line having a plurality of twisted wire pairs and a plurality of transmitters (A, B, C, D, E, F, G, H) and a plurality of receivers (A, B, C, D, E, F, G, H), one receiver at each end of each twisted wire pair, Form part of a communication system with threshold errors. Each receiver receives a combined signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated, and a plurality of noise signals. A plurality of adaptive filters are responsive to the combined signal. Each adaptive filter has a plurality of taps each having a coefficient. Each tap is switchable between an active and an inactive state. The controller provides for adjusting the transfer function of the at least one adaptive filter by selectively deactivating taps while ensuring that errors in the communication system do not exceed a threshold error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] This is a co-pending application Ser. No. 09 / 037,328 (March 9, 1998)
Title, "Apparatus and method for reducing noise in a communication system", Os
car E. Agazzi), 09 / 0978,466 (May 14, 1998)
, "Initiation Protocol for High Throughput Communication System", Osc
arE. Agazzi and John L. Creight, 09 / 098,9
No. 33 (filed May 14, 1998, entitled "Startup Protocol for High Throughput Communication System", inventor Oscar E. Agazzi), and 09/143,
No. 476, filed on Aug. 28, 1998, entitled "Apparatus and Method for Reducing Power Dissipation in Communication Systems", inventor Oscar E. Agazzi, John L.
Creight, and Mehdi Hatamian).

BACKGROUND OF THE INVENTION The present invention relates to systems and methods for reducing noise present in signals received and processed by devices in a communication system, and to such noise in communication systems having high throughput. Systems and methods for reducing energy consumption. The present invention also relates to systems and methods for reducing power dissipation of devices in a communication system, and to systems and methods for reducing such power dissipation in communication systems having high throughput. The invention further relates to an activation protocol for initiating a successful transmission between a transceiver in a high throughput communication system. As used in the context of this disclosure, "high throughput" includes, but is not limited to, 1 gigabit (GB) / sec.

A basic communication system is illustrated in FIG. The system includes a hub and a plurality of computers serviced by the hub in a local area network (LAN). Although four computers are shown by way of example, different numbers of computers may be included in the system. Each computer is typically separated from the hub by a distance on the order of about 100 meters (100 meters). Computers are also remote from each other. The hub is connected to each computer by a communication line. Each communication line includes an unshielded twisted pair wire or cable. Generally, the wires or cables are formed from copper. Four unshielded twisted pair wires are provided for each communication line between each computer and hub. The system shown in FIG. 1 operates with several categories of unshielded twisted-pair cable, designated as categories 3, 4, 6, and 7 in the telecommunications industry. Category 3 cables are of the lowest quality (and lowest cost), and categories 6 and 7 are of the highest quality (and highest cost).

[0004] Associated with each communication system is "throughput." System throughput is the speed at which the system processes data, and is usually expressed in bits per second.
Most communication systems have a throughput of 10 megabits (Mb) / sec or 100 Mb / sec. In the rapidly evolving area of communication system technology, 1 Gb / s full-duplex communication over existing Category 5 unshielded twisted-pair cable is possible. This system is commonly referred to as "Gigabit Ethernet".

[0005] A portion of a typical Gigabit Ethernet is shown in FIG. Gigabit Ethernet provides for the transmission of a digital signal between one computer and a hub and the reception of that signal at another computer and a hub. A similar system is provided for each computer. This system has a gigabit media independent interface (
gigabit medium independent interface
, GMII), which receives data in byte-wide format at a specified rate, for example, 125 MHz, and performs scrambling, coding, and various coding functions in a physical coding sub-layer.
layer, PCS). The PCS encodes bits from the GMII into a five-step pulse amplitude modulation (PAM) signal. The five symbol levels are-
2, -1, 0, +1 and +2. Communication between the computer and the hub is 2
This is achieved using four unshielded twisted pair wires or cables operating at 50 Mb / sec and eight transceivers, one at each end of the unshielded twisted pair. Full duplex bidirectional operation dictates the use of a hybrid circuit at the two ends of each unshielded twisted pair. This hybrid controls access to the communication line, thereby enabling full-duplex bidirectional operation between the transceiver at each end of the communication line.

A common problem associated with communication systems utilizing multiple unshielded twisted pairs and multiple transceivers is that crosstalk and echo noise or impairment signals are introduced into the transmitted signal. Noise is inherent in all such communication systems, independent of system throughput. However, the effects of such impairment signals are greater in Gigabit Ethernet. The impairment signals include echo, near-end crosstalk (NEXT), and far-end crosstalk (FEXT) signals. As a result of such a fault signal, the performance of the transceiver, especially the receiver, is degraded.

[0007] NEXT is a fault signal resulting from the capacitive and inductive coupling of the signal from the near-end transmitter to the input of the receiver. The NEXT impairment signal encountered by the receiver in transceiver A is shown in FIG. The receiver A is trying to detect the direct signal from the transmitter E, but the crosstalk signals from the transmitters B, C, and D appear in the receiver A as noise. As each receiver in the system experiences the same effect, the signal passing through the receiver experiences degradation due to the NEXT impairment signal. FIG. 3 illustrates only the NEXT impairment signal experienced by receiver A for clarity.

[0008] Similarly, due to the bidirectional nature of the communication system, an echo impairment signal is generated by each transmitter, even at a receiver contained in the same transceiver as the transmitter. The echo impairment signal encountered by the receiver in each transceiver is shown in FIG. The receiver is trying to detect the signal from the transmitter at the opposite end of the communication line, but the crosstalk signal from the transmitter appears to the receiver as noise. Since each receiver in the system experiences the same effect, the signal passing through the receiver will experience signal distortion due to the echo impairment signal.

[0009] Far-end crosstalk (FEXT) is a disturbance arising from the capacitive coupling of the signal from the far-end transmitter to the input of the receiver. The FEXT impairment signal encountered by the receiver in transceiver A is shown in FIG. Receiver A is trying to detect the direct signal from transmitter E,
Crosstalk signals from the transmitters F, G, and H appear at the receiver A as noise. Since each receiver in the system experiences the same effect, the signal passing through the receiver will experience signal distortion due to the FEXT impairment signal. In FIG. 5, for clarity, only the FEXT failure experienced by receiver A is illustrated.

As a result of such a noise disturbance signal, the performance of the communication system is degraded. The signal carried by the system is distorted and the system experiences a high signal error rate. Accordingly, the art provides methods and apparatus for compensating for degradation in communication system performance caused by noise impairment signals, and for reducing this type of noise in high-throughput systems such as Gigabit Ethernet. And there is a need to provide equipment. Aspects of the present invention satisfy these needs.

[0011] Four transceivers at one end of a communication line are illustrated in FIG. Transceiver components are shown as overlapping blocks, with each layer corresponding to one transceiver. The GMII, PCS and hybrid of FIG.
And hybrid, and is considered to be independent of the transceiver. The combination of the transceiver and the hybrid forms one "channel" of the communication system. Thus, FIG. 6 illustrates four channels, each operating in a similar manner. The transmitter portion of each transceiver includes a pulse shaping filter and a digital-to-analog (D / A) converter. The receiver portion of each transceiver includes an analog-to-digital (A / D) converter, a first-in first-out (FIFO) buffer, a feedforward equalizer (FFE).
) And a detector. The receiver portion also includes a timing recovery system and a near-end noise reduction system including a NEXT cancellation system and an echo canceller. NEXT cancellation systems and echo cancellers typically include a large number of adaptive filters.

The characteristics of the communication line, for example, the length are determined by the NE which effectively cancels NEXT and echo noise.
This can affect the capabilities of the XT cancellation system and the echo canceller.
Normal cable response measurements and simulations show that in order to provide a sufficient level of cancellation of these interferers, a "long" echo and N
An EXT canceller is required. The term "long" is used to describe a canceller with a large number of taps required by the characteristics of the cable.
For example, FIG. 7 shows the echo impulse response of a 100 m cable having a characteristic impedance of 85 ohm and 100 ohm termination. The rated characteristic impedance is 100 ohms, but manufacturing standards allow for a 15% tolerance. This impedance mismatch can result in reflections at the far end of the cable and secondary pulses with a delay of about 1 microsecond. Due to the long delay, approximately 140 taps (125 taps for a 1 microsecond delay, plus 2) are needed to cancel this pulse.
About 15 additional taps to cancel the next pulse).

The echo impulse response often has additional reflections at intermediate delays. In addition, the unequal return loss of the cable causes a continuous change in characteristic impedance along the cable, which can result in many small reflections at the midpoint. The implication of such intermediate reflections is that the echo canceller should not be configured to cancel only the initial and final reflections, but rather to cover the entire range of impulse responses. As a result of the change in cable characteristics, the change in cable impulse response also varies. Furthermore, the response of an individual cable may change as a result of its operating environment. For example, a change in operating temperature may change the impulse response of the cable. Therefore, it is difficult to pre-calculate the locations where taps are needed and incorporate these locations into the design of the echo and NEXT canceller. FIG. 8 shows the NEXT impulse response of a 100 m cable. As shown, the NEXT response is also long, requiring a large number of taps in the NEXT canceller making up the NEXT cancellation system. N
The combination of EXT and echo canceller is
Most of the SP operation is consumed.

[0014] The high number of taps required to achieve satisfactory performance in such a system results in a high degree of power dissipation. Such high power dissipation is undesirable in that it renders high-throughput communication systems, especially Gigabit Ethernet, inoperable and unmarketable. Accordingly, the art provides a method and apparatus for reducing power dissipation in a communication system utilizing multiple taps, while providing a gigabit transmission system.
There is a need to provide a method and apparatus for reducing this type of power dissipation in high throughput systems such as Ethernet. Aspects of the present invention satisfy these needs.

One of the most important steps in the operation of a Gigabit Ethernet transceiver is activation. At this stage, the adaptive filters contained in the transceiver converge, the timing recovery subsystem acquires frequency and phase synchronization, compensates for the delay differences between the four wire pairs, and ensures that the pair matches and polarities. Be acquired. Upon successful completion of activation, normal operation of the transceiver can begin.

In one start-up protocol, known as "blind start", the transceiver converges its adaptive filter and timing recovery system simultaneously while also acquiring timing synchronization. The disadvantage of this activation is that a high level of interaction is required between the various adaptation and acquisition algorithms in the transceiver. This high level of interaction reduces the reliability of the convergence and synchronization operations that occur during startup.

Thus, the art is susceptible to activation for use in high-throughput communication systems such as Gigabit Ethernet, using an optimal sequence of operations and minimizing the interaction between various adaptation and acquisition algorithms. There is a need to provide a protocol. Aspects of the present invention satisfy these needs. SUMMARY OF THE INVENTION Briefly and generally speaking, the present invention relates to systems and methods for reducing noise and power dissipation in communication systems. The invention also relates to an activation protocol for use in a communication system.

In a first aspect, the invention relates to a communication system having a predetermined threshold error. The communication system includes a communication line having a plurality of twisted wire pairs, a plurality of transmitters, one transmitter at each end of each twisted wire pair, and each end of each twisted wire pair. Includes a plurality of receivers, one receiver comprising a combination comprising a direct signal from a transmitter at the opposite end of the associated twisted wire pair and a plurality of noise signals. Receive the signal. The system also includes a plurality of adaptive filters responsive to the combined signal, each having a plurality of taps each having a coefficient, each tap being switchable between an active and an inactive state. The system further includes periodically adjusting the transfer function of the at least one adaptive filter by selectively deactivating taps while ensuring that errors in the communication system do not exceed a threshold error. A control device is included.

By selectively deactivating the taps of at least one adaptive filter, the present invention reduces the power consumption of the filter and thus the total power consumption of the communication system. In a more detailed aspect, the communication system further includes a plurality of noise reduction systems each comprising at least one adaptive filter. One noise reduction system is associated with each receiver and provides at least one duplicate noise impairment signal. The system also includes a plurality of devices, one associated with each receiver. Each device is responsive to the combined signal received by the receiver and a duplicate noise impairment signal provided by a noise reduction system associated with the receiver and substantially removing at least one noise signal from the combined signal. In another aspect, the noise signal includes a plurality of far-end crosstalk (one from each transmitter at the opposite end of the communication line, other than the transmitter at the opposite end of the twisted wire pair with which the receiver is associated). FEXT) impairment signal, and the noise reduction system includes a FEXT cancellation system that provides a duplicate FEXT impairment signal as one of the duplicate noise impairment signals. In yet another aspect, the noise signal includes multiple near-end crosstalk (NEXT) signals from each transmitter at the same end of the communication line, other than the transmitter at the same end of the twisted wire pair with which the receiver is associated. A) NEXT cancellation system that provides a duplicate NEXT impairment signal as one of the duplicate noise impairment signals. In yet another aspect, the noise signal includes an echo impairment signal received from the same terminating transmitter of the associated twisted wire pair with the receiver, and the noise reduction system includes one of the duplicate noise impairment signals. One includes an echo canceller that provides a duplicate echo impairment signal. In another detailed aspect, the controller includes means for setting the state of each tap, means for calculating a current error of the system, and means for comparing the current error to a threshold error. In yet another aspect, means for setting the state of each tap include means for specifying a tap threshold for each tap, means for comparing the tap coefficient absolute value and the tap threshold for each tap, Means for deactivating taps having a coefficient whose value is less than the tap threshold.

In a second aspect, the present invention operates a communication system having a communication line having a plurality of twisted wire pairs and a plurality of transceivers at each end of each twisted wire pair. Is the way. Each transceiver has a receiver and a transmitter. Each receiver receives a combined signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated, and a plurality of noise signals. Each transceiver further includes a plurality of adaptive filters responsive to the combined signal. Each adaptive filter has a plurality of taps each having a coefficient. Each tap is switchable between an active and an inactive state. The method includes the steps of specifying a system threshold and transmitting at least one adaptive filter by selectively deactivating taps while ensuring that system error does not exceed the threshold error. Periodically adjusting the function.

In a more detailed aspect, the method further comprises generating at least one duplicated noise impairment signal for each receiver, and at least one generating at least one noise signal-free output signal. Combining one duplicate noise impairment signal with the combined signal. In another aspect, adjusting the transfer function includes setting a state of each tap, calculating a current error of the system, and combining the current error with a threshold error. It is. In another aspect, one transceiver of the communication system acts as a master, and another transceiver acts as a slave. Each transceiver has a noise reduction system, a timing recovery system, and at least one equalizer. The method further includes performing a first stage in which the slave timing recovery system and the equalizer are trained and the master noise reduction system is trained, and wherein the master timing recovery system and the equalizer are trained and the slave timing recovery system and the equalizer are trained. Performing a second phase in which the noise reduction system is trained and performing a third phase in which the master noise reduction system is trained. In another aspect,
One transceiver of the communication system acts as a master, and another transceiver acts as a slave. Each transceiver has a noise reduction system, a timing recovery system, and at least one equalizer. The method further includes performing a first phase in which the slave timing recovery system and the equalizer are trained and the master noise reduction system is trained, and wherein the master timing recovery system is trained in both frequency and phase. Performing a second phase in which the master equalizer is trained and the slave noise reduction system is trained; the master noise reduction system is retrained and the master timing recovery system is retrained for phase to recover the slave timing Performing a third stage in which the system is retrained for both frequency and phase.

In a third aspect, the invention comprises a communication line having a plurality of twisted wire pairs, a plurality of transmitters, one at each end of each twisted wire pair, a plurality of transmitters, It is a communication system including a receiver. One receiver is for each twisted wire
At each end of the pair. Each receiver receives a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and one or more far-end crosstalk (FEXT) signals from each of the remaining transmitters at the opposite end of the communication line. ) Receive a combination signal including a failure signal.
The system also includes multiple FEXT cancellation systems, one associated with each receiver. Each FEXT cancellation system provides a duplicate FEXT failure signal. The system further includes a plurality of delay devices, one associated with each receiver. Each delay device is responsive to the combined signal received by its receiver,
Delay the combination signal. Also included are multiple first devices, one associated with each receiver. Each first device is responsive to the output of the delay device associated with the receiver and the duplicated FEXT impairment signal provided by the FEXT cancellation system associated with the receiver and substantially removing the FEXT impairment signal from the combined signal. .

By providing a plurality of FEXT cancellation systems for generating a duplicate FEXT fault signal and a plurality of devices for combining the duplicate FEXT fault signal with a combined signal,
The present invention substantially cancels out the FEXT impairment signal from the combined signal. Therefore, signal degradation due to noise in the communication system is reduced, and transmitted information is more reliably recovered.

In a more detailed aspect, the FEXT cancellation system includes means for receiving a signal from each receiver at the same end of the communication system other than the receiver with which the FEXT canceller is associated. The FEXT cancellation system also includes means for generating an individual duplicate FEXT fault signal for each received signal, and means for combining the individual duplicate FEXT impairment signals to generate a duplicate FEXT impairment signal. In another aspect, when the direct signal arrives after the FEXT signal, the delay device delays the combined signal by an amount approximately equal to the time delay between the FEXT impairment signal and the direct signal reaching the receiver. In another aspect, when the direct signal arrives after the FEXT impairment signal, the delay device may include an amount that is approximately equal to the time delay between the FEXT impairment signal and the direct signal arriving at the receiver, and that the combined signal may have other signals. The combination signal is delayed by the larger amount that synchronizes with the combination signal from the receiver.

In a fourth aspect, the invention relates to a method for reducing noise in a communication system. The system includes a communication line having a plurality of twisted wire pairs. The system also includes multiple transmitters, one at each end of each twisted wire pair. The system further includes a plurality of receivers, one at each end of each twisted wire pair. Each receiver receives a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and one or more far-end crosstalk (FEXT) signals from each of the remaining transmitters at the opposite end of the communication line.
) Receive a combination signal including a failure signal. The method includes, for each receiver, generating a duplicated FEXT impairment signal and combining the duplicated FEXT impairment signal with the combined signal to generate an output signal having few FEXT impairment signals.

In a fifth aspect, the present invention provides a method for reducing power dissipation in a communication system having a plurality of adaptive filters with a plurality of taps, each tap being switchable between an active and an inactive state. With methods to reduce. The method includes the steps of: a) specifying an acceptable error of the system; b) setting a tap threshold for each active tap; and c) for each active tap, the absolute value of the active tap. Deactivating taps having a coefficient less than a tap threshold set for d) calculating a system error; and e) comparing the calculated system error to an acceptable system error. , F) increasing the tap threshold for each active tap if the calculated system error is less than the allowable system error; and g) maintaining the calculated system error without exceeding the allowable system error. Repeating steps c) to f) until approaching an acceptable system error Murrell.

In a sixth aspect, the invention is a communication system having at least one adaptive filter in which each tap is switchable between an active and an inactive state, each tap having a plurality of taps having coefficients. With a method to reduce power dissipation. The method includes the steps of: a) calculating an initial system error; b) setting a tap error threshold for each active tap; and c) for each active tap, the absolute value for the active tap. Deactivating taps having coefficients smaller than a set tap error threshold; d) calculating a next system error; e) determining a difference between the next system error and the initial system error. If not, increasing the tap error threshold for each active tap; and f) steps c) to e) until the difference between the next system error and the initial system error exceeds a predetermined value. Is repeated.

In a seventh aspect, the invention is for use in a communication system having a master transceiver at one end of a twisted wire pair and a slave transceiver at an opposite end of the twisted wire pair. Startup protocol. Each transceiver has a near-end noise reduction system, a far-end noise reduction system, a timing recovery system, and at least one equalizer. The protocol includes, during a first phase, maintaining the master in a half-duplex mode that transmits signals but receives no signals, and a half-duplex mode that receives signals from the master but does not transmit any signals. Maintaining the slave at the same time; converging the master near-end noise reduction system; and adjusting the frequency and phase of the signal received by the slave such that the frequency and phase are synchronized with the frequency and phase of the signal transmitted by the master. And converging the slave equalizer. And maintaining the slave in a half-duplex mode transmitting signals but not receiving any signals during the second stage; and placing the master in a half-duplex mode receiving signals from the slaves but not transmitting any signals. Maintaining; freezing the frequency and phase of the slave; converging the slave near-end noise reduction system; and the signal received by the master such that the phase is synchronized with the phase of the signal transmitted by the slave. And converging the master equalizer. And maintaining the slave in a full-duplex mode such that the slave transmits and receives signals during the third phase; and maintaining the master in a full-duplex mode such that the master transmits and receives signals. And reconverging the master near-end noise reduction system.

In an eighth aspect, the invention comprises a master transceiver at one end of the communication line and a slave transceiver at the opposite end of the communication line, wherein each transceiver is a near-end noise reduction system, An activation protocol for use in an edge noise reduction system, a timing recovery system, and a communication system having at least one equalizer. The protocol includes, during a first phase, maintaining the master in a half-duplex mode that transmits signals but receives no signals, and a half-duplex mode that receives signals from the master but does not transmit any signals. Maintaining the slave at the same time; converging the master near-end noise reduction system; and adjusting the frequency and phase of the signal received by the slave such that the frequency and phase are synchronized with the frequency and phase of the signal transmitted by the master. And converging the slave equalizer. The protocol further includes, during the second phase, maintaining the slave in a half-duplex mode using the free-running clock to transmit signals but not receive any signals, and receive signals from the slave but do not receive any signals. Maintaining the master in half-duplex mode with no signal transmission, converging the slave near-end noise reduction system, and receiving by the master such that the frequency and phase are synchronized with the frequency and phase of the signal transmitted by the slave. Adjusting the frequency and phase of the resulting signal and converging the master equalizer. The protocol also includes, during the third phase, maintaining the slave in full-duplex mode, such that the slave transmits and receives signals, and changing the master to full-duplex mode, such that the master transmits and receives signals. And re-converging the master near-end noise reduction system; adjusting the phase of the signal received by the master such that the phase is synchronized with the phase of the signal transmitted by the slave; And adjusting the frequency and phase of the signal received by the slave such that the phase is synchronized with the frequency and phase of the signal transmitted by the master.

By dividing the start-up protocol into three stages, the convergence of the equalizer and the timing recovery system is separated from the convergence of the noise reduction system. Thus, the interaction between the various adaptation and acquisition algorithms in the transceiver is reduced, and the convergence and synchronization operations are more reliable. These and other aspects and advantages of the present invention will become apparent from the following more detailed description when viewed in conjunction with the accompanying drawings, which illustrate preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The discussion herein is for the purpose of explanation and understanding of the present invention and is believed to be specifically directed to Gigabit Ethernet. However, it is understood that the concepts and claims of the present invention also apply to other types of communication systems than Gigabit Ethernet.

Overview of Communication System A communication system incorporating features of the present invention is shown generally at 10 in FIG. The system 10 includes a hub 12 and a plurality of computers serviced by the hub in a local area network (LAN). Although four computers 14 are shown by way of example, different numbers of computers may be used without departing from the scope of the invention. Each computer 14 is separated from hub 12 by a distance on the order of about 100 meters (100 m). Computers 14 are also remote from each other.

The hub 12 is connected to each computer 14 by a communication line 16. The communication line 16 includes a plurality of unshielded twisted pair wires or cables. Generally, the wires or cables are formed from copper. Four unshielded twisted pair wires are provided between each computer in system 10 and hub 12. The system shown in FIG. 1 operates with several categories of twisted pair cable, designated as categories 3, 4, 5, 6, and 7 in the telecommunications industry. Category 3 cables are of the lowest quality (and lowest cost), and categories 6 and 7 are of the highest quality (and highest cost). Gigabit Ethernet uses Category 5 cable.

FIG. 2 illustrates in detail a portion of the communication system of FIG. 1 including one communication line 16 and one computer 14 and part of the hub 12. The communication line 16 has 250
Four unshielded twisted pair wires 18 operating at Mb / sec / pair are included. A transceiver 20 including a transmitter (TX) 22 and a receiver (RX) 24 is located at each unshielded end of each twisted pair 18. There is a hybrid 26 between each transceiver 20 and its associated unshielded twisted pair 18. Hybrid 26 is an interface to communication line 16 that allows full-duplex bidirectional operation between transceivers 20 at each end of the communication line. The hybrid also functions to isolate the transmitter and receiver associated with the transceiver from one another.

The communication system includes a gigabit media independent interface (GMII) 28
Includes a standard connector called. The GMII 28 has 8 transmission and reception directions.
This is a bit width data path. Clocked at a suitable frequency, such as 125 MHz, the GMII produces a net throughput of bidirectional data at a suitable rate, such as 250 Mb / sec / pair. GMII provides a symmetric interface in both transmit and receive directions. The physical coding sublayer (PCS) 30 comprises the GMII 28 and the transceiver 2
Receive and transmit data between zeros. The PCS 30 transmits data to the transceiver or G
It performs functions such as scrambling and encoding / decoding data before being transferred to any of the MIIs. The PCS converts the bits from GMII into 5-level pulse amplitude modulation (P
AM) signal. The five symbol levels are -2, -1, 0, +1 and +2
It is. The PCS also controls some functions of the transceiver, such as skew control as described below.

Transceiver Circuit Four transceivers 20 are illustrated in detail in FIG. The components of the transceiver 20 include:
Each layer is shown as an overlapping block corresponding to one transceiver. G in FIG.
The MII 28, PCS 30 and hybrid 26 correspond to the GMII, PCS and hybrid of FIG. 2 and are considered to be separate from the transceiver. The combination of transceiver 20 and hybrid 26 forms one "channel" of the communication system. Thus, FIG. 9 illustrates four channels each operating in a similar manner.

The transmitter portion of each transceiver 20 includes a pulse shaping filter 32 and a digital-to-analog (D / A) converter 34. In the preferred embodiment of the present invention, D / A converter 34 operates at 125 MHz. The pulse shaping filter 32 receives one one-dimensional (1-D) symbol from the PCS. This symbol is called the TXDatax symbol 36 when x is 1 to 4 corresponding to each of the four channels. TXDatax symbol 3
6 represents 2-bit data. The PCS generates one 1-D symbol for each channel. The symbol of each channel is in the form 0.75+
Passes through a 0.25z ^-1 spectral shaping filter, limiting emissions to within FCC requirements. This simple filter shapes the spectrum so that the power spectral density at the transmitter output is lower than that of a communication system operating at 100 Mb / s over two pairs of Category 5 twisted pair wire. The symbols are then converted to analog signals by a D / A converter 34, which also serves as a low pass filter. The analog signal gains access to unshielded twisted pair wire 18 through hybrid circuit 26.

A signal detector 41, an A / D converter 42, a FIFO,
44, including a digital adaptive equalizer system, a timing recovery circuit and a noise reduction circuit. Digital adaptive equalizer systems include a feedforward equalizer (FFE).
) 46, two devices 50, 56, a skew adjuster 54 and two detectors 58, 6
0 is included. The function of these components is described below in connection with the present invention.
The noise reduction circuit includes a NEXT cancellation system 38 and an echo canceller 3
8 and a FEXT cancellation system 70 are included.

A / D converter 42 provides a digital conversion of the signal received from hybrid 26 at a suitable frequency, such as 125 MHz, which is equal to the baud rate of the signal. A / D converter 42 samples the analog signal with the analog sample clock signal provided by decision-oriented timing recovery circuit 64. FI
FO 44 receives the digitally converted signal from A / D converter 42 and stores it on a first-in, first-out basis. FIFO 44 transfers the individual signals to FFE 46 by means of digital sample clock signal 80 provided by timing recovery circuit 64. FFE 46 receives the digital signal from FIFO 44 and filters the signal. The FFE 46 is a least-mean-square (LMS) adaptive filter, and performs channel equalization and prior intersymbol interference (ISI) cancellation to correct signal distortion.

As noted, the signal is introduced into the A / D converter 42 and then transmitted to the FIFO 44 and the FF.
The signal introduced into E46 has several components. Such components include direct signals received directly from transmitter 22 at the opposite end of unshielded twisted pair wire 18 to which receiver 24 is associated. It also includes one or more NEXT, echo, and FEXT impairment signals from other transmitters 22, as previously described. A signal that includes a direct signal and one or more impairment signals is called a "combination signal."

The FFE 46 transfers the combination signal 48 to a second device 50, which is usually a summing device. In the second device 50, the combined signal 48 is combined with the output of the NEXT cancellation system 38 and the echo canceller 40 to produce a signal with little NEXT and echo impairment signals. This signal is called "first soft decision" 52.
The signal detector 41 detects a signal from the second device 50 and transfers the signal to the skew adjuster 54. Upon signal detection, signal detector 41 initiates various system operations, one of which includes transitions between stages of the activation protocol, as described below. The skew adjuster 54 receives the first soft decision 52 from the second device 50 and outputs a signal called “second soft decision” 66. The skew adjuster 54 is 2
Perform one function. First, a second soft decision 66 from all receivers in the system
Delays the first soft decision 52 to synchronize to compensate for differences in the length of the unshielded twisted pair 18. Second, the first so that the second soft decision 66 arrives at the first device 56 at approximately the same time as the output of the FEXT cancellation system 70.
Adjust the delay of the soft decision 52. Skew adjuster 54 receives skew control signal 82 from PCS 30.

The skew adjuster 54 forwards the second soft decision 66 to the first device 56, which is typically a summing device. In the first device 56, the second soft decision 66 is combined with the output of the FEXT cancellation system 70 to generate a signal with little FEXT impairment signal. This signal is called "third soft decision" 68. The first detector 58 is a first
A third soft decision 68 is received from device 56. The first detector 58 provides an output signal, or "final decision" 72. The first detector 58 is a slicer that generates a final decision 72 corresponding to the analog signal level of magnitude closest to the level of the third soft decision 68. The first detector 58 is also a symbol-by-symbol detector or a sequential detector, such as a Viterbi decoder, that operates based on the order of the signals over all four channels.

In one configuration of the transceiver, the first detector 58 is a symbol-by-symbol detector. A group of detectors 58 for each symbol, one for each channel, is shown in FIG. Each first detector 58 includes a slicer 98, an adaptive feedback filter 100, and an adder 102.
Is included. Summer 102 combines the third soft decision 68 with the output of adaptive feedback filter 100 and provides an output, which is introduced into slicer 98. The output of slicer 98 is introduced to adaptive feedback filter 100. The first detector 58 outputs the output corresponding to the discrete level from the set [−2, −1, 0, 1, 2] that is closest to the difference between the third soft decision 68 and the output of the feedback filter 100. A signal 72 is provided. Adaptive feedback filter 100 corrects the distortion of third soft decision 68. This filter 100 is a past slicer 98
Is used to estimate the subsequent ISI caused by the channel. This IS
I is canceled from the third soft decision 68 to form the final decision signal 72.

In another configuration of the transceiver, the first detector 58 is a combination of a sequential decoder and a decision feedback equalizer (DFE), commonly using an architecture known as a multiple DFE architecture (MDFE) sequential detector. It is. Sequential decoder 58 sees all signals from all four channels simultaneously and with successive samples from each channel over several periods of time. The sequential decoder receives as input each first
At least one signal is received from device 56. The sequential decoder 58 is generally responsive to the order of the output signal from the first device 56, (1) passes the signal in an acceptable order, and (2) constrains established by the coding standards associated with the system. Discard the unacceptable order of the signal. An acceptable order follows the sign constraint, and an unacceptable order violates the sign constraint.

The second detector 60 (FIG. 9) receives the first soft decision 52 from the second device 50.
The second detector 60 is a symbol-by-symbol detector similar to the first detector 58 (FIG. 10). This provides an output signal 74 corresponding to a discrete level from the set [−2, −1, 0, 1, 2] that is closest to the difference between the first soft decision 52 and the output of the feedback filter 100. I do. The second detector 60 produces an output signal 74 that does not utilize FEXT cancellation, so that this determination has a higher error rate than with the first detector 58 utilizing FEXT cancellation. Due to this fact, this decision is called a "provisional decision". Subsequent ISI present in the input to the second detector 60
It is important to note that is canceled using an adaptive feedback filter 100 (FIG. 10) housed in a second detector that receives the tentative decision 74 as input. The coefficient of the adaptive feedback filter 100 is calculated by the first detector 58 (
It is the same as that of the adaptive feedback filter related to FIG. 9).

The third device 62, which is typically a summing device, receives the first soft decision signal 52 from the second device 50 and the tentative decision signal 74 from the second detector 60. In the third device 62, the first soft decision 52 is combined with the tentative decision signal 74 to generate an error signal 76, which is introduced into the timing recovery circuit 64. The timing recovery circuit 64 receives the tentative decision 74 from the second detector 60 and the error signal 76 from the third device 62. Using these signals as inputs, the timing recovery circuit 64
An analog clock synchronization signal 78 introduced to the A / D converter 42, and a FIFO 44
And outputs a digital clock synchronization signal 80 to be introduced into the digital clock. As previously mentioned, these signals control the rate at which A / D converter 42 samples the analog input received from hybrid 26 and the rate at which the FIFO transfers digital signals to FFE 46.

As previously mentioned, the symbols transmitted by transmitter 22 (FIG. 2) in the communication system cause NEXT, echo and FEXT impairments in the received signal of each channel. Since each receiver 24 has access to the data of the other three channels that cause this interference, it is possible to substantially cancel each of these effects. NEX
T cancellation is achieved using three adaptive NEXT cancellation filters 84 as shown in the block diagram of FIG. Each NEXT cancellation system 38
Receives three TXDatax symbols 36 from each transmitter on the same end of the communication line 18 as the receiver with which the NEXT cancellation system is associated. Each NEXT cancellation system 38 includes three filters 84, one for each TXDatax symbol 36. These filters 84 model the impulse response of the NEXT noise from the transmitter and are implemented, for example, as an adaptive transversal filter (ATF) utilizing the LMS algorithm. The filter 84 is connected to each TXDat
Create a copy of the NEXT fault signal for the ax symbol 36. Summing unit 86 combines the three individually duplicated NEXT failure signals 92 to form NEXT cancellation system 38.
Generate a copy of the NEXT impairment signal contained in the combined signal received by the associated receiver. The duplicate NEXT impairment signal 88 is introduced to the second device 50 (FIG. 9) where it is combined with the combined signal 48 to provide a first NEXT impairment signal having substantially no NEXT impairment signal.
A soft decision signal 52 is generated.

Echo cancellation is achieved by an adaptive echo cancellation filter 85 as shown in the block diagram of FIG. Each echo canceller 40 receives a TXDatax symbol 36 from a transmitter at the same end as the receiver with which the echo canceller of twisted wire pair 18 is associated. As shown in FIG. 12, each echo canceller 40 includes one filter 85. This filter 85 models the impulse response of the echo noise from the transmitter and is implemented, for example, as an ATF using the LMS algorithm. This filter is an echo canceller 4
0 produces a copy of the echo impairment signal contained in the combined signal received by the associated receiver. The duplicate echo impairment signal 90 is introduced to the second device 50 (FIG. 9) and combined with the combined signal 48 to generate a first soft decision signal 52 with little echo impairment signal.

As shown in the configuration diagram of FIG. 13, the FEXT cancellation includes three adaptive FEXTs.
Achieved by a T-cancel filter 87. Each FEXT cancellation system 70 receives three tentative decision symbols 74, one from each receiver at the same end as the receiver with which the FEXT cancellation system of the communication line is associated. Each FEXT
Cancellation system 70 includes three filters 87, one for each provisional decision symbol 74. These filters 87 model the impulse response of the FEXT noise from the transmitter and are implemented, for example, as ATFs utilizing the LMS algorithm. The filter 87 performs FEX for each of the individual provisional decision symbols 74.
A copy of the T fault signal 96 is generated. Summing unit 108 combines the three individually duplicated FEXT impairment signals 96 to produce a duplicate of the FEXT impairment signal contained in the combined signal 48 received by the associated receiver with the FEXT cancellation system. Duplicate FEXT impairment signal 94 is introduced to first device 56 (FIG. 9) where it is combined with second combined signal 66 to form third soft decision signal 6 with little FEXT impairment signal.
8 is generated. The high error rate of the tentative decision 74 does not degrade the performance of the FEXT cancellation system 70 since the decision used to cancel FEXT is statistically independent of the final decision 72 made by the receiver in which FEXT is canceled. It is important to note that

The symbols provided by the first detector 58 may be used by the PCS before being introduced into GMII.
Decoded and descrambled by 30 receiving sections. Changes in how the wire pairs are twisted can cause delays through the four channels of up to 50 nanoseconds. As a result, symbols may not be synchronized across the four channels. As mentioned earlier, if the first detector is a sequential detector, the PCS
Also determines the relative skew of the four streams of 1-D symbols, and the first detector 58
The skew adjuster 54 adjusts the symbol delay before reaching, so that the sequential decoder can operate on properly configured four-dimensional (4-D) symbols. In addition, the cable plant may introduce wire swapping or pair swapping between pairs of four unshielded twisted pairs, so that PCS3
0 also determines and corrects such conditions.

Noise Reduction As mentioned earlier, FEXT is a disturbance that results from the capacitive coupling of the signal from the far-end transmitter to the input of the receiver, as shown in FIG. Crosstalk signals from transmitters F, G and H appear as noise to receiver A trying to detect the signal from transmitter E. A similar situation applies to all other receivers with respect to the signal from the appropriate transmitter located at the opposite end of the line.

The FEXT noise experienced by receiver A and generated by transmitter F depends on the characteristics of the cable, and some impulse response that models the coupling characteristics of the unshielded twisted pair used by transmitter F and receiver A. And can be modeled as the convergence of the data symbols transmitted by F. Normally measured FEXT impulse response 1
04 is shown in FIGS. Similar statements can be made for all other possible receiver and transmitter combinations. Thus, there are a total of 12 FEXT impulse responses describing FEXT noise signals from transmitters E, F, G and H to receivers A, B, C and D. These twelve impulse responses are not identical, but each have a similar general shape to that shown in FIGS.

Although FEXT is also an obstacle for many communication systems other than Gigabit Ethernet, in those systems the receiver may not be physically co-located and / or experience FEXT A given receiver typically does not have access to symbols detected by other receivers, since the other receivers operate at a rate that is not synchronized with the receiver's data rate. Aspects of the present invention take advantage of the fact that in a gigabit Ethernet transceiver, decisions corresponding to all four channels are available to four receivers and the decisions are synchronized.

In operation, there may be a delay associated with transmitting a signal over a communication line. Synchronization of signals in the system is very important for effective cancellation of noise. It is important that the duplicate noise impairment signal arrives at the summing device almost simultaneously with the combined signal and / or the soft decision signal. Regarding the FEXT impairment signal, the second soft decision signal 66 is generated because the impairment occurs at the transmitter at the opposite end of the receiver.
Is liable to occur between the time at which the data arrives at the first device 56 and the time at which the duplicate FEXT fault signal 94 arrives. In some channels, as illustrated in FIG.
In some cases, the group delay of the XT signal 104 is smaller than the group delay of the desired signal 106. In this case, the tentative decision 74 provided by receivers B, C and D of FIG. 5 is not effective in canceling the FEXT failure because it arrives too late at receiver A's FEXT cancellation system 70.

To compensate for this delay, the present invention utilizes a skew adjuster 54, which, as mentioned earlier, includes the direct signal arriving at the receiver and the FE associated with that receiver.
Delay the first soft decision signal 52 by a time approximately equal to or greater than the time delay between XT impairment signals. If the output is delayed by an amount greater than the time delay, the situation illustrated in FIG. 16 results, but the FEXT cancellation system 7
The adaptive feedback filter 87 in FIG.
4 to compensate for the excessive delay caused by delaying the second soft decision signal 6.
6 and almost simultaneously with the first device 56 (FIG. 9).

The third soft decision 68 resulting from FEXT cancellation allows the first detector 58 to make a more reliable final decision 72 with a much lower error rate. Computer simulations show that the typical improvement achievable by the invention described in this application is about 25 dB if the signal to noise ratio at the input of the first detector 58 before FEXT cancellation is about 25 dB. 2-3 dB. This corresponds to a reduction of the symbol error rate by a factor of 1000 or more.

If there is no delay associated with transmitting the signal over the communication line, the FEXT fault signal 1
Both 04 and the direct signal 106 arrive at the receiver almost simultaneously, as shown in FIG. In this situation, the skew adjuster 54 is set to zero. In the alternative,
An embodiment of the invention having only one detector 110 and one summing device 112, as shown in FIG. 17, is used. In this configuration, the summing device 112 is
The XT, echo and FEXT impairment signals 88, 90, 94 and the combined signal 48 are received to generate a first soft decision 52 with few impairment signals. This first soft decision 52 is introduced to the detector 110 and the third device 62. Detector 110 may include a single symbol-by-symbol detector or both a symbol-by-symbol detector and a sequential detector. For a symbol-by-symbol detector, the final decision 72 and the second output 114 of the detector 110 are the same. For both symbol-by-symbol and sequential detectors, the final output is provided by the sequential detector and introduced into PCS 30. The second output 114 is provided by a symbol-by-symbol detector and is provided to the timing recovery circuit 64 and the third device 62 for use in determining the error signal 76.

Power Dissipation Reduction As mentioned earlier, the NEXT cancellation system, the echo canceller and the FEXT cancellation system use ATF to effectively cancel noise from the combined signal. An example of the ATF used is shown in FIG. The ATF 120 includes a plurality of taps 122 each including a multiplexer 124 and an adder 126. Associated with each tap 122 is a coefficient C _n , where n is 0-x−1 when x is the number of taps in the ATF. The circuitry associated with each tap includes a 1-bit storage (not shown) that allows activation and deactivation of the tap. The value of the coefficient C _n is adjusted by the LMS algorithm as mentioned before. Tap 12
The register 128 is inserted between the two. These registers 128 provide data to taps 122 at time intervals that match the clock signal.

As shown by the echo and NEXT impulse responses, as shown in FIGS. 7 and 8, all taps 122 in the NEXT and echo cancellers 38, 40 contribute significantly to the performance of the communication system. Do not mean. Aspects of the invention include:
Determining which taps 122 do not contribute significantly to the reduction of the mean square error (MSE) of the system and deactivating those taps, thereby removing them from the filtering calculations, greatly reducing the power dissipation of the system. Further, as shown by the impulse responses of FIGS. 7 and 8, it is difficult to avoid the need to configure long span NEXT and echo cancellers 38,40. Since the individual cable response may differ from that shown in FIGS. 7 and 8, the required tap 1
22 may be more or less than required by the cables of FIGS. As previously mentioned, it is difficult to determine a priori which taps 122 are needed for an individual cable.

According to aspects of the present invention, NEXT, echo and FEXT cancellers 38, 40
, 70 comprise an ATF 120 utilizing a sufficient number of taps 122 to provide sufficient cancellation for the worst case expected impulse response. this is,
As in the example of FIG. 7, 140 taps 122 may be required, and longer cables may require more taps. To reduce power dissipation, taps 122 are inspected after convergence, and taps that are found not to contribute significantly to the performance of the system are deactivated. When the tap 122 is deactivated, it is removed from NEXT, echo, and FEXT replication calculations and adaptations, and the contribution to the overall system power dissipation is substantially eliminated.

When the system is initially converged, all taps 122 are active and NE
The XT, echo and FEXT cancelers 38, 40, 70 are converged along their entire length. After convergence, taps 122 are examined using the tap scanning algorithm shown in FIG. 19 to determine which taps can be deactivated. Step S
At 1, an acceptable level of error S _ea is specified for the system. In step S2, a tap coefficient threshold T _th is set for each active tap. Although individual taps may each have a unique tap threshold T _th , in a preferred embodiment of the present invention, all taps have approximately equal tap coefficients. Since the initial value of the tap coefficient threshold T _th is low enough, only a few taps 122 are deactivated and the performance of the system is not significantly affected. In a preferred embodiment of the invention, the tap coefficient threshold T _th is initially set to a value equal to the tap coefficient C _n having the minimum absolute value. Also, an appropriate value can be determined by simulation.
This initial value is not important as long as the tap scanning procedure is first applied and low enough to avoid significant degradation in system performance.

In step S3, a tap coefficient C for each active tap_nIs the tap coefficient threshold T_thIs compared to Tap coefficient C_nIs the tap coefficient threshold T_{t h} If so, tap 122 is deactivated in step S4. This procedure is repeated for each tap 122 in the filter 120. Preferably a tap
The decision to deactivate 122 is made sequentially from the input of filter 120
Done in a typical way. In step S5, the system error S_ecIs calculated. This
Is the tap coefficient C_nIs multiplied by the average energy signal to calculate the MSE of each active tap 122 first. Tap
The error of the filter 120 associated with 122 is obtained by summing the individual tap errors.
It is determined. The system error is then summed by summing the errors of the individual filters.
It is determined.

In step S 6, the calculated system error S _ec is compared with the specified allowable system error S _ea . If the calculated system error S _ec is smaller than the allowable system error S _ea , the tap threshold T _th of each active tap is increased by a small amount in step S7, and steps S3 to S6 are repeated. As a result, some additional taps 122 are deactivated, but the increase in tap threshold T _th is small, so that the number of deactivated taps is usually not very large. The calculated system error S _ec is, step S3~S6 are repeated until approaching an acceptable system error S _ea without exceeding the allowable system error. If the calculated system error S _ec is greater than the allowable system error S _ea , the tap scanning algorithm stops.

As an alternative to deciding whether to deactivate taps based on the MSE of the communication system, a decision may be made based on the MSE of the individual filters. In this embodiment of the invention, an acceptable level of error F _ea of the filter is specified. As described previously, the individual taps are deactivated and the calculated filter error F _ec is calculated. If the deactivation of the tap does not cause the calculated filter error F _ec to exceed the allowable filter error F _ea , the tap remains inactive.

In yet another embodiment of the present invention, the contribution of each deactivated tap to the filter and thus the MSE of the system is calculated. If the tap's contribution to the MSE is determined to be an allowed amount, the tap remains deactivated. This method is generally preferred during initial startup of a system where the overall system MSE is large because the filter coefficients in the system are in a non-convergent state. Once the filter coefficients of the system have initially converged, the decision to deactivate the tap is generally made based on the tap's contribution to the MSE of the system as described earlier in connection with FIG.

The end result of the tap scanning algorithm is that in a normal channel of a communication system,
A number of taps 122 are deactivated and power dissipation is reduced by a large percentage. As an example, a computer simulation of a tap scanning algorithm in which the echo response operates on the channel shown in FIG. 7 is presented in FIG.
This figure shows the MSE to signal ratio for both master and slave as a function of time during the initial convergence of the system. At time t = 360,000 baud, the tap scanning algorithm is started so that the MSE to signal ratio increases to a predetermined target of 24 dB. FIG. 21 shows taps of the echo canceller after convergence at the threshold of 24 dB, and FIG. 22 shows taps of the threshold of 26 dB. 0 deactivated taps
As shown. In FIG. 21, the total number of active taps of the echo canceller is 22. Similarly, the three NEs forming the NEXT cancellation system
The number of active taps 122 of the XT canceller (not shown) is 6, 2 respectively.
And 0. In FIG. 22, the total number of active taps of the echo canceller is 47. Similarly, active NEXT cancellers (not shown)
The number of taps 122 is 6, 2 and 0, respectively.

With the 24 dB threshold, only 30 of the 440 initial active taps remain active after the tap scanning algorithm is applied, maintaining a 5 dB margin for the required bit error rate. . As can be seen from FIGS. 21 and 22, the taps 122 that remain active occur at sparse locations, and the location of the taps is highly dependent on the individual cable response, so during the design of NEXT and the echo canceller. It would be difficult to assign these taps statistically.

In another embodiment of the present invention, the tap scanning algorithm monitors changes in the MSE during the progress of the tap scanning algorithm. The algorithm is not the MSE itself,
The change in the MSE is applied until it exceeds a predetermined value, for example 1 dB. If the MSE to signal ratio before the scan is applied is 25 dB, the final MSE to signal ratio is 24
dB, and many taps are deactivated. This embodiment of the tap scanning algorithm is shown in FIG. In step S10, an initial system error S _ei is calculated. In step S11, an allowable system error difference _De is designated. In step S12, a tap coefficient threshold _Tth is set for each active tap. As with other tap scanning algorithms, the value of the tap threshold T _th is low enough so that only a few taps 122 are deactivated and the performance of the system is not significantly affected.

[0069] In step S13, the absolute value of the tap coefficients C _n for each active tap is compared with the tap coefficient threshold T _th. If the tap coefficient C _n is smaller than the tap coefficient threshold T _th , the tap 122 is deactivated in step S14. This process is repeated for each tap 122 in the filter 120. Preferably, tap 12
The decision to deactivate 2 is made in a sequential manner starting from the input of the filter 120. In step S15, the following error S _es of the system is calculated.

In step S 16, the next error S _es of the system is compared with the initial system error S _ei . If the difference between the next system error S _es and the initial system error S _ei is smaller than a predetermined value, the tap coefficient threshold T _th is increased by a small amount in step 17;
Steps S13 to S16 are repeated. As a result, add some tap 1
22 is deactivated. The difference between the following system error S _es an initial system error S _ei until exceeding a predetermined value, step S13~S16 are repeated.

In some cases, the NEXT, echo, and FEXT impulse responses may change during normal operation, for example, as a result of temperature changes. Accordingly, it is preferable to periodically activate the previously deactivated tap 122 and recheck that the absolute value of the tap coefficient C _n is less than or equal to the tap threshold T _th , preferably in a sequential manner. desirable. If the tap coefficient C _n is greater than the tap threshold T _th , the tap 122 remains active, otherwise it is deactivated. Similarly, the tap 122 that was active may _fall below the tap threshold T _th , in which case the tap is deactivated. All of this can be achieved by periodic reapplication of the sequential tap scanning algorithm during normal operation.

In an alternative embodiment of the present invention, a selected number, eg, 10 taps 122 located at the input of the filter 120 are not subject to deactivation. Usually there is a large skew rate in these first few taps 122, which means that the numerical values can change significantly if the sampling phase changes. This sampling phase changes dynamically as a result of jitter, and the previously deactivated tap 122
May be significant. By keeping some taps at the input of the filter active, potential degradation in the presence of jitter is avoided.

When the total number of taps is very large, for example, 440, the power dissipation may be large during the initial convergence transient before the tap scanning algorithm has the potential to deactivate the tap. Even if the average power dissipation of the system is greatly reduced, the peak power dissipation is not reduced. The preferred embodiment of the present invention provides NEXT, echo and F
This is compensated by converging the EXT canceller stepwise. For example, two at a time
Blocks of zero taps are converged, after which the tap scanning algorithm is applied to those taps on a block-by-block basis. For example, the first block of 20 taps has a low MS
As a result of the fact that it is not large enough to provide E, the MSE during initial convergence
If is large, tap 1 deactivated as a measure of whether to end the algorithm
It is better to monitor the sum of the squares of the twenty-two coefficients.

Activation Protocol One of the most important stages of the operation of the communication system is the activation of the transceiver. At this stage, the FFE 46 (FIG. 9) of the receiver portion of each transceiver and the echo canceller 4
0, NEXT cancellation system 38, FEXT cancellation system 70,
The adaptive filters included in timing recovery system 64 and detector 58 converge. During convergence, the actual output of the adaptive filter is compared to the expected output of the filter to determine an error. The error is reduced to almost zero by adjusting the coefficients of the algorithm that defines the transfer function of the filter. Similarly, the timing recovery system is converged by adjusting the frequency and phase of the phase locked loop and local oscillator included in the timing recovery system such that the signal to noise ratio of the channel is optimized. In addition, the difference in delay between the four wire pairs is compensated to obtain pair match and polarity. Successful activation ensures that the transceiver can begin normal operation.

According to an aspect of the present invention, each transceiver channel operates in a loop time manner, as shown in FIG. The transceivers 20 at the two ends of each twisted wire pair 18 have two different roles as far as synchronization is concerned. One of the transceivers, called master 130, transmits data using an independent clock GTX_CLK provided through GMII interface 28 (FIG. 9). This clock signal is fixed in both frequency and phase and is provided to the master transceiver 130 in each of the four transceiver channels of the communication system. In practice, the transmit clock used by master 130 may be a filtered version of GTX_CLK obtained using a very narrow bandwidth phase locked loop to reduce jitter. The other terminating transceiver 20, called slave 132, of twisted wire pair 18 includes a timing recovery system 64 (FIG. 9) located at receiver 24.
) Using the master 130 to control both the frequency and phase of its receive and transmit clocks.
Synchronize with the signal received from The slave 132 transmit clock always maintains a fixed phase relationship with the slave receive clock. The reception clock of the master 130 is synchronized in phase, not frequency, with the signal received from the slave transmitter 22.
That is, after the initial acquisition period, the master 130 receive clock follows the master transmit clock with a phase difference determined by the loop round trip delay. This phase relationship is
The master 130 receive clock may change dynamically due to the need to track the jitter present in the signal received from the slave 132.

Fixed Slave Transmit Clock The sequence of events during the activation protocol of the present invention is shown in FIG. The protocol consists of three stages 134, 136, 138, during which the receiver is trained, for example, the adaptive filter is converged, the timing synchronization is obtained, etc., after which normal operation is performed in the fourth stage 140 Is started. In a first step 134, the master starts transmitting to the slave using the transmit clock signal, both frequency and phase fixed. The master trains the near-end noise reduction system by converging the adaptive filters included in the echo canceller and NEXT cancellation system (E). At the same time, the slave trains the equalizer and the far-end noise reduction system by converging the adaptive filters included in the DFE, FFE and FEXT cancellation systems (D). While training the equalizer and far-end noise reduction system, the slave simultaneously acquires both frequency and phase timing synchronization (
T). The slave then also guarantees a differential delay between the four twisted wire pairs, identifies the four pairs, and corrects the polarity of the pairs.

In one embodiment of the protocol, a first stage 134 on both the master and the slave
The transition from to the second stage 136 takes place after a fixed period of time. However, in the preferred embodiment, when the slave detects that its receiver has converged (D) the adaptive filters included in the DFE, FFE and FEXT cancellation systems and has acquired timing synchronization (T), the first A transition is made from step 134 to a second step 136. As mentioned earlier, the master receiver includes a signal detector 41 (FIG. 9) that detects the energy in the line coming from the slave. The master transitions from the first step 134 to the second step 136 upon detecting this energy from the slave. Thus, the slave has the initiative when transitioning from the first stage 134 to the second stage 136,
The master follows when detecting a signal from the slave.

The convergence of the echo canceller and the NEXT cancellation system during the first stage 134 at the master is performed with the aim of allowing the signal detector of the master to detect the signal from the slave. Without proper echo and NEXT cancellation, the signal detector may be triggered by echo and NEXT noise present in the receiver. After the transition has taken place, the master discards the echo canceller and NEXT cancellation system coefficients resulting from the convergence in the first stage 134. This is done by resetting the echo canceller and the adaptive filter in the NEXT cancellation system. Since the correct sampling phases of the four receivers of the master are obtained in the third stage 138, the coefficients of the echo canceller and NEXT cancellation system obtained in the first stage 134 are the final values reacquired in the third stage 138 It is important to note that this can be different.

In the second step 136, the slave trains the near-end noise reduction system by converging the echo canceller and the adaptive filters included in the NEXT cancellation system (E). At the same time, the master trains the equalizer and the far-end noise reduction system by converging the adaptive filters included in the DFE, FFE and FEXT cancellation systems (D). While training the equalizer and the far-end noise reduction system, the master simultaneously acquires phase-only timing synchronization (P). The master also then compensates for the differential delay between the four twisted wire pairs, identifies the four pairs, and corrects the polarity of the pairs. In the second stage, the slave saves the timing recovery state variables obtained in the first stage 134 and freezes the frequency and phase. Doing this ensures that when the master resumes transmission at the start of the third phase 138, the slave samples the signal coming from the master to the slave in the correct phase. The slave also freezes the coefficients of the DFE, FFE and FEXT cancellation systems obtained in the first step 134.

Similar to the transition from the first stage 134 to the second stage 136, the second stage 136
The transition to step 138 occurs after a fixed predetermined period. First, second and third
Although the duration of steps 134, 136, 138 is fixed, the duration is not necessarily equal for all steps. However, in a preferred embodiment, when the master detects that the receiver has converged (D) the adaptive filters included in the DFE, FFE and FEXT cancellation systems and has acquired timing synchronization (P), the second stage The transition is made from 136 to a third stage 138. Like the master, the slave receiver
A signal detector 41 (FIG. 9) for detecting energy in the line coming from the master is included. Upon detecting this energy from the master, the slave transitions from the second stage 136 to a third stage 138. Thus, the master has the initiative when transitioning from the second stage 136 to the third stage, and the slave follows when detecting a signal from the master.

In the third step 138, the slave sends the echo canceller and the NEXT cancel
Freezes the coefficients of the system and maintains the steady-state conditions while the operating characteristics of the slave are not adjusted. Similarly, the master freezes the coefficients of the DFE, FFE and FEXT cancellation systems and the phase of its clock signal. The master also retains the near-end noise reduction system by reconverging the echo canceller and the NEXT cancellation system during the third stage 138 (E). In the third stage 138,
It is important to note that the master already knows the correct frequency at which the receiver will operate, since the slave will resume transmission using the clock recovered from the signal transmitted from the master. "Relative sampling phase" of four receivers
That is, the difference between the sampling phases of the three receivers and one receiver arbitrarily used as a reference is also known since it has been obtained in the second stage 136. However, the "total sampling phase" of the receiver, ie, the sampling phase of the receiver arbitrarily selected as a reference, is not known and must be obtained in a third step 138. When both the master and the slave complete the training operation, they exchange messages indicating that they are ready to send valid data. In a fourth step 140, all coefficients of the previously frozen adaptive filter are unfrozen and ready to transmit data.

Self-Running Slave Transmit Clock The sequence of events during the activation protocol of the present invention is shown in FIG. The protocol consists of three stages 144, 146, 148, during which the receiver is trained, for example, the adaptive filter is converged, the timing synchronization is obtained, etc., the normal operation in the fourth stage 150 Is started. The start-up protocol is initiated by the master when the master starts transmitting signals to the slave using a transmit clock signal that has both a fixed frequency and a fixed phase. In a first step 144, the master trains the near-end noise reduction system by converging the echo canceller and the adaptive filters included in the NEXT cancellation system (E). As previously mentioned, the slave receiver includes a signal detector 41 (FIG. 9) that detects energy in the line coming from the master. Upon detecting a signal from the master, the slave trains the equalizer and the far-end noise reduction system by converging the adaptive filters included in the DFE, FFE and FEXT cancellation systems (D).
While training the equalizer and the far-end noise reduction system, the slave simultaneously acquires both frequency and phase timing synchronization (T). The slave then also compensates for the differential delay between the four twisted wire pairs, identifies the four pairs, and corrects the polarity of the pairs.

In one embodiment of the protocol, the first stage 144 on both master and slave
The transition from to the second stage 146 takes place after a fixed predetermined period. However, in the preferred embodiment, when the slave detects that its receiver has converged (D) the adaptive filters included in the DFE, FFE and FEXT cancellation systems and has acquired timing synchronization (T), the first A transition is made from step 144 to a second step 146. The master receiver also includes a signal detector 41 (FIG. 9) that detects energy in the line coming from the slave. The master transitions from the first step 144 to the second step 146 upon detecting this energy from the slave. Thus, the slave has the initiative when transitioning from the first stage 144 to the second stage 146, and the master follows when it detects a signal from the slave.

The convergence of the echo canceller and the NEXT cancellation system during the first stage 144 at the master is performed with the purpose of allowing the signal detector of the master to detect the signal from the slave. Without proper echo and NEXT cancellation, the signal detector may be triggered by echo and NEXT noise present in the receiver. After the transition has taken place, the master discards the echo canceller and NEXT cancellation system coefficients resulting from the convergence in the first step 144. This is done by resetting the adaptive filters in the echo canceller and NEXT cancellation system. Since the correct sampling phases of the four receivers of the master are obtained in the third stage 148, the echo canceller and NEXT cancellation system coefficients obtained in the first stage 144 are the same as the final values reacquired in the third stage 148. It is important to note that may vary.

In a second step 146, the slave trains the near-end noise reduction system by converging the adaptive filters included in the echo canceller and NEXT cancellation system (E). The slave also receives the D
Freeze the coefficients of the FE, FFE and FEXT cancellation systems. At the same time, the master trains the equalizer and the far-end noise reduction system by converging the adaptive filters included in the DFE, FFE and FEXT cancellation systems (D). While training the equalizer and far-end noise reduction system, the master simultaneously acquires both frequency and phase timing synchronization (T). The master also then compensates for the differential delay between the four twisted wire pairs, identifies the four pairs, and corrects the polarity of the pairs. A slave may deviate from any stable clock that has a frequency offset below a predetermined limit, such as 200 ppm, as compared to the master transmit clock. In a second step 146, the slave transceiver transmits using the free running clock. As a result, the master acquires both frequency and phase synchronization in a second step 146. Although phase synchronization is a normal function performed by the master in any form of start-up protocol, frequency synchronization is not a normal master function, but rather a timing recovery state variable when transitioning from the first stage 144 to the second stage 146. Is performed only in the second stage 146 of startup, which aims to perform proper operation with a slave transceiver that does not save

Similar to the transition from the first step 144 to the second step 146, the second step 146
The transition to step 148 occurs after a fixed predetermined period. First, second and third
The duration of steps 144, 146, 148 is fixed, but the duration is not necessarily equal for all steps. However, in a preferred embodiment, when the master detects that the receiver has converged (D) the adaptive filters included in the DFE, FFE and FEXT cancellation systems and has acquired timing synchronization (T), the second stage A transition is made from 146 to a third stage 148. The master starts sending signals to the slave. Upon detecting this signal from the master, the slave transitions from the second step 146 to the third step 148. Accordingly, the master can move from the second stage 144 to the third stage 14
8, the slave has the initiative, and the slave follows when detecting a signal from the master.

In the third step 148, the slave sends the echo canceller and the NEXT cancel
Freeze the coefficients of the system and maintain the near-end noise reduction system at steady state conditions. The slave also regains both frequency and phase timing synchronization at the third step 148 since the timing recovery state variables were not saved during the transition to the second step 146 (T). In a third step 148, the master freezes the coefficients of the DFE and FEXT cancellation system and the frequency of the clock signal. The master also
Retrain the near end noise reduction system by reconverging the echo canceller and NEXT cancellation system (E). The master also regains phase-only timing synchronization (P). Note that in the third step 148, the slave resumes transmission using the clock recovered from the signal transmitted by the master, so that the master already knows the correct frequency at which the receiver operates. is important. The "relative sampling phase" of the four receivers, that is, the difference between the three receivers and the sampling phase of one receiver, which is optionally used as a reference, is also known since it was obtained in the second stage 146. I have. However, the "total sampling phase" of the receiver, ie, the sampling phase of the receiver arbitrarily selected as a reference, is not known and must be obtained in a third step 148. When both the master and the slave complete the training operation, they exchange messages indicating that they are ready to send valid data. In a fourth step 150, all coefficients of the previously frozen adaptive filter are unfrozen and ready to transmit data.

Although the present invention has been disclosed and illustrated with reference to specific embodiments, the principles involved therein are to be understood in numerous other embodiments which will be apparent to those of ordinary skill in the art. Can be used with Accordingly, the invention is limited only as indicated by the scope of the appended claims.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a communication system providing a plurality of computers connected to a hub by communication lines to form a local area network (LAN).

FIG. 2 Gigabit Media Independent Interface (GMII), Physical Coding Sublayer (P
FIG. 1 is a schematic configuration diagram of a communication system that provides a plurality of unshielded twisted pair wires each having a transceiver at each end.

FIG. 3 is a schematic configuration diagram of a part of the communication system of FIG. 2, showing a NEXT failure signal received by a receiver A from adjacent transmitters B, C, and D;

FIG. 4 is a schematic configuration diagram of a part of the communication system of FIG. 2, showing an echo interference signal received by a receiver A from a transmitter A.

5 is a schematic block diagram of a portion of the communication system of FIG. 2, showing a FEXT fault signal received by receiver A from opposing transmitters F, G, and H.

FIG. 6 is a schematic configuration diagram of a communication system including a plurality of transceivers each having a NEXT cancellation system, an echo canceller, a feedforward equalizer, a digital adaptive filter system including one detector, and a timing recovery circuit. is there.

FIG. 7 shows an impulse response of an echo signal passing through a 100 m communication line.

FIG. 8 shows an impulse response of a NEXT signal passing through a 100 m communication line.

FIG. 9 is a communication including a plurality of transceivers each having a NEXT cancellation system, an echo canceller and a FEXT cancellation system, a digital adaptive filter system including a plurality of detectors and skew adjusters, and a timing recovery circuit. FIG. 1 is a schematic configuration diagram of a system.

FIG. 10 is a schematic block diagram of the symbol-by-symbol detector of FIG. 9 each including a plurality of slicers, a feedback filter, and an adder, and receiving a soft decision as input.

11 is a schematic block diagram of the NEXT cancellation system of FIG. 9, each including a plurality of adaptive transversal filters (ATFs) and adders, and receiving a transmission signal from an adjacent transmitter as an input.

12 is a schematic configuration diagram of the echo canceller of FIG. 9, each including an ATF and receiving a transmission signal from the same transmitter as an input.

FIG. 13 is a schematic block diagram of the FEXT cancellation system of FIG. 9 for receiving a transmission signal from an opposite transmitter as an input, each including a plurality of ATFs and an adder.

FIG. 14 shows the direct impulse response arriving at the receiver after the FEXT impulse response.

FIG. 15 shows a direct impulse response and a FEXT impulse response arriving at the receiver almost simultaneously.

FIG. 16 shows the direct impulse response arriving at the receiver before the FEXT impulse response.

FIG. 17 is a schematic configuration of a communication system including a plurality of transceivers each having a NEXT cancellation system, an echo canceller and a FEXT cancellation system, a digital adaptive filter system including one detector, and a timing recovery circuit; FIG.

FIG. 18 illustrates an AT including a cascade of taps present in the NEXT cancellation system of FIG. 11, the echo canceller of FIG. 12, and the FEXT cancellation system of FIG.
It is the schematic of F.

FIG. 19 is a flowchart illustrating one embodiment of a method for reducing power dissipation.

FIG. 20 shows the mean squared error (MSE) to signal ratio as a function of time during initial convergence of the communication system.

FIG. 21 shows echo canceller taps that are active after convergence for a communication system having an error threshold of 24 dB.

FIG. 22 shows the echo canceller taps that are active after convergence for a communication system having an error threshold of 26 dB.

FIG. 23 is a flowchart illustrating another embodiment of a method for reducing power dissipation.

FIG. 24 is a schematic configuration diagram showing a master-slave relationship between transceivers of each transceiver channel of FIG. 2;

FIG. 25 is a timing diagram illustrating the steps of one embodiment of the activation protocol.

FIG. 26 is a timing diagram illustrating the steps of another embodiment of the activation protocol.

──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number 09 / 078,933 (32) Priority date May 14, 1998 (May 14, 1998) (33) Priority claim country United States (US) ( 31) Priority number 09 / 143,476 (32) Priority date August 28, 1998 (August 28, 1998) (33) Priority country United States (US) (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ , TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW , MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZW ( 72) Inventor Hatamian, Madey USA 92926, California, Mission Bijo, Pacific Hills Drive 25681 F-term (reference) 5K046 AA01 BA07 BB05 HH02 HH24 HH55 HH71 HH72 HH77 HH78

Claims (66)

[Claims] 1. A communication system having a predetermined threshold error, the communication system comprising: a communication line having a plurality of twisted wire pairs; and a plurality of transmitters, wherein one of the transmitters A plurality of transmitters, one at each end of each twisted wire pair, and a plurality of receivers, one of the receivers at each end of each twisted wire pair, wherein each of the receivers comprises: A plurality of receivers for receiving a combined signal including a direct signal from the transmitter at the opposite end of the associated twisted wire pair and a plurality of noise signals; and responsive to the combined signal A plurality of adaptive filters, each of the adaptive filters having a transfer function and a plurality of taps, each of the taps having a coefficient, each of the taps being switchable between an active and an inactive state. A plurality of adaptive filters, selectively deactivating at least one of the taps while ensuring that errors in the communication system do not exceed the predetermined threshold error, A control device for periodically adjusting at least one of said transfer functions. 2. A plurality of noise reduction systems, wherein one of said noise reduction systems is associated with one of said receivers, said noise reduction systems each providing at least one duplicated noise impairment signal. And a plurality of devices, wherein one of said devices is associated with one of said receivers, each of said devices for substantially removing at least one of said noise signals from said combined signal. 2. The communication of claim 1, comprising a plurality of devices responsive to the combined signal received by the receiver and the duplicated noise impairment signal provided by the noise reduction system associated with the receiver. system. 3. The transmitter of claim 2, wherein the noise signal comprises a plurality of far end crosstalk (FEXT) impairment signals, one of the FEXT impairment signals being the transmitter at the opposite end of the twisted wire pair with which the receiver is associated. A FEXT cancellation system wherein each of the transmitters at the opposite end of the communication line is provided with a duplicate FEXT impairment signal as one of the duplicate noise impairment signals. The communication system according to claim 2, comprising: 4. The FEXT cancellation system comprises: means for receiving a signal from each of the receivers at the same end of the communication line other than the receiver with which the FEXT cancellation system is associated; The communication system according to claim 3, comprising: means for generating an individually duplicated FEXT fault signal for each; and means for combining the individual duplicated FEXT fault signals to generate the duplicated FEXT fault signal. 5. The noise signal includes a plurality of near-end crosstalk (NEXT) impairment signals, wherein one of the NEXT impairment signals is other than the transmitter at the same end of the twisted wire pair with which the receiver is associated. From each of the transmitters at the same end of the communication line, wherein the noise reduction systems each include a NEXT cancellation system that provides a duplicate NEXT impairment signal as one of the duplicate noise impairment signals. A system according to any one of claims 2 to 4. 6. The NEXT cancellation system comprising: means for receiving a signal from each of the transmitters at opposite ends of the communication line other than the transmitter with which the NEXT cancellation system is associated; The communication system according to claim 5, comprising: means for generating an individual duplicate NEXT fault signal for each; and means for combining the individual duplicate NEXT fault signals to generate the duplicate NEXT fault signal. 7. The noise signal comprises an echo impairment signal received from the transmitter at the same end of the twisted wire pair with which the receiver is associated, and wherein the noise reduction systems each include the duplicate noise impairment signal. The communication system according to claim 2, wherein one of the signals includes an echo canceller that provides a duplicate echo impairment signal. 8. The echo canceller comprises: means for receiving a signal from the transmitter with which the echo canceller is associated; means for processing the received signal to generate the duplicate echo impairment signal. The communication system according to claim 7. 9. The control device further includes: means for setting a state of each tap; means for calculating a current error of the system; and means for comparing the current error with the predetermined threshold error. A communication system according to any one of the preceding claims, comprising: 10. The means for setting the state of each tap, the means for specifying a tap threshold for each tap, the means for comparing the absolute value of the tap coefficient for each tap with the tap threshold, Means for deactivating taps having a coefficient whose absolute value is smaller than said tap threshold. 11. The communication system of claim 10, wherein said means for setting the state of each tap further comprises means for periodically activating a previously deactivated tap. 12. The communication system according to claim 10, further comprising means for increasing said tap threshold when said current error is smaller than said threshold error. 13. A communication line having a plurality of twisted wire pairs and a plurality of transceivers, one of said transceivers being at each end of each of said twisted wire pairs, wherein said transceiver is Each having a receiver and a transmitter, the receiver each including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated, and a plurality of noise signals. Receiving a combined signal, wherein the transceiver further comprises a plurality of adaptive filters responsive to the combined signal, wherein the adaptive filters each have a plurality of taps having coefficients, each of the taps being in an active and inactive state. A method of operating the communication system in a communication system switchable between: a step of specifying a threshold error for the system; While ensuring that error systems out does not exceed the predetermined threshold error,
Periodically adjusting at least one transfer function of the adaptive filter by selectively deactivating at least one of the taps. 14. Further, for each of the receivers, generating at least one duplicated noise impairment signal; and generating the output signal substantially free of at least one of the noise signals. Combining a fault signal with the combination signal. 15. The transmitter of claim 1, wherein the noise signal comprises a plurality of far end crosstalk (FEXT) impairment signals, wherein one of the FEXT impairment signals is the transmitter at the opposite end of the twisted wire pair with which the receiver is associated. Generating the at least one of the duplicated noise impairment signals from each of the transmitters at opposite ends of the communication line other than generating a duplicated FEXT impairment signal. Item 1
4. The method according to 4. 16. The method of generating a duplicate FEXT fault signal comprises receiving a signal from each of the receivers at the same end of the communication line other than the receiver for which the duplicate FEXT fault signal is to be generated. 16. The method of claim 15, comprising: generating an individual duplicate FEXT impairment signal for each of the received signals; and combining the individual duplicate FEXT impairment signals to generate the duplicate FEXT impairment signal. The described method. 17. The noise signal comprises a plurality of near-end crosstalk (NEXT) impairment signals, one of the NEXT impairment signals being other than the transmitter at the same end of the twisted wire pair with which the receiver is associated. 15. The method of claim 14, wherein generating the at least one of the duplicate noise impairment signals from each of the transmitters at the same end of the communication line comprises generating a duplicate NEXT impairment signal. ~
The method according to claim 16. 18. The method according to claim 18, wherein the step of generating a duplicate NEXT fault signal comprises: the transmitter at the opposite end of the communication line other than the transmitter associated with the receiver for which the duplicate NEXT fault signal is to be generated. Receiving a signal from each of the following; generating an individually duplicated NEXT impairment signal for each received signal; combining the individual duplicated NEXT impairment signal to generate the duplicated NEXT impairment signal; The method according to claim 17. 19. The noise signal includes an echo impairment signal received from the transmitter at the same end of the twisted wire pair with which the receiver is associated, generating at least one of the duplicate noise impairment signals. 19. The method according to any one of claims 14 to 18, wherein said steps include generating a duplicate echo impairment signal. 20. The method of generating a duplicate echo impairment signal comprising: receiving a signal from the transmitter associated with the receiver for which the duplicate echo impairment signal is to be generated; Processing the received signal to generate. 21. The step of adjusting the transfer function further comprising: setting a state of each tap; calculating a current error for the system; and setting the current error to the specified threshold. 21. A method as claimed in any one of claims 13 to 20, comprising comparing with. 22. The step of setting the state of each tap, the steps of: specifying a tap threshold for each tap; and comparing the absolute value of the tap coefficient with each tap threshold for each tap; Deactivating taps having a coefficient whose absolute value is less than said tap threshold. 23. The method of claim 22, wherein setting the state of each tap further comprises periodically deactivating previously deactivated taps. 24. One transceiver acts as a master, another transceiver acts as a slave, each transceiver has a noise reduction system, a timing recovery system and at least one equalizer, The method further comprises: performing a first phase in which the timing recovery system of the slave and the equalizer are trained and the noise reduction system of the master is trained; and Performing a second phase in which the equalizer is trained and the noise reduction system of the slave is trained; and performing a third phase in which the noise reduction system of the master is retrained. A method according to any one of claims 13 to 23. 25. The method of claim 24, further comprising: transitioning from the first stage to the second stage; and transitioning from the second stage to the third stage. 26. The step of transitioning from the first stage to the second stage, comprising: transmitting a signal from the slave to the master; detecting the signal at the master; and transmitting the signal from the master. Discontinuing. 27. The method of claim 26, wherein said transmitting said signal from said slave occurs upon completion of said training of said timing recovery system and said equalizer of said slave. 28. The step of transitioning from the second step to the third step, comprising: transmitting a signal from the master to the slave; detecting the signal at the slave; and transmitting the signal from the slave. 27. The method of claim 25, further comprising the steps of: 29. The method of claim 28, wherein said transmitting said signal from said master occurs upon completion of said training of said timing recovery system and said equalizer of said master. 30. One transceiver serving as a master, another transceiver serving as a slave, each transceiver having a noise reduction system, a timing recovery system, and at least one equalizer; The method further comprises performing a first phase in which the timing recovery system and the equalizer of the slave are trained and the noise reduction system of the master is trained; Performing a second phase in which the equalizer of the master is trained and the noise reduction system of the slave is trained, and the noise reduction system of the master is retrained. , The phase of the timing recovery system of the master Performing a third phase in which the timing recovery system of the slave is retrained in both frequency and phase. 24. The method of claim 23, further comprising: . 31. The method according to claim 31, further comprising: starting the first stage; transitioning from the first stage to the second stage; and transitioning from the second stage to the third stage. Item 30. The method according to Item 30, 32. The step of initiating the first step comprises: transmitting a signal from the master to the slave; detecting the signal at the slave; and wherein the slave is transmitting, Stopping the transmission from the slave. 33. The step of transitioning from the first stage to the second stage, comprising: transmitting a signal from the slave to the master; detecting the signal at the master; and transmitting the signal from the master. Stopping. 34. The method of claim 33, wherein said transmitting said signal from said slave occurs upon completion of said training of said timing recovery system and said equalizer of said slave. 35. The step of transitioning from the second step to the third step, comprising: transmitting a signal from the master to the slave; detecting the signal at the slave; and transmitting the signal from the slave. Continuing. 36. The method of claim 35, wherein said transmitting said signal from said master occurs upon completion of said training of said timing recovery system and said equalizer of said master. 37. A communication system, comprising: a communication line having a plurality of twisted wire pairs; and a plurality of transmitters, one transmitter at each end of each twisted wire pair. A transmitter and a plurality of receivers, one receiver at each end of each twisted wire pair, and each receiver having an opposite end of the twisted wire pair with which the receiver is associated Receivers that receive a combined signal including a direct signal from the transmitter of claim 1 and a plurality of far end crosstalk (FEXT) impairment signals, one from each of the remaining transmitters at the opposite end of the communication line. A plurality of FEXT cancellation systems, one associated with each receiver, each FEXT cancellation system providing a duplicate FEXT failure signal.
A T cancellation system; and a plurality of delay devices, one associated with each receiver, each delay device responsive to the combined signal received by the receiver to delay the combined signal. A delay device; and a plurality of first devices, one associated with each receiver, each first device associated with the receiver for substantially removing the FEXT impairment signal from the combined signal. A communication system comprising: a first device responsive to an output of a delay device and the duplicate FEXT failure signal provided by the FEXT cancellation system associated with the receiver. 38. The FEXT cancellation system comprising: means for receiving a signal from each of the receivers at the same end of the communication line other than the receiver with which the FEXT cancellation system is associated; and for each received signal. 38. The communication system of claim 37, comprising: means for generating an individual duplicate FEXT fault signal; and means for combining the individual duplicate FEXT fault signal to generate the duplicate FEXT fault signal. 39. When the direct signal reaches the receiver after the FEXT impairment signal, the delay device is substantially equal to a time delay between the FEXT impairment signal and the direct signal reaching the receiver. 39. The communication system of claim 38, wherein the combination signal is delayed by an amount. 40. The communication system according to claim 38, wherein said delay device delays said combined signal such that said combined signal is synchronized with said combined signal from another receiver. 41. When the direct signal arrives at the receiver after the FEXT impairment signal, the delay device gives the combined signal a time between the FEXT impairment signal and the direct signal arrive at the receiver. 39. The communication system of claim 38, wherein the delay is the greater of an amount approximately equal to the delay and an amount such that the combined signal is synchronized with the combined signal from another receiver. 42. When the direct signal arrives at the receiver after the FEXT impairment signal, the delay device causes the delay to be greater than the time delay between the FEXT impairment signal and the direct signal arriving at the receiver. Delays the combined signal while the F
An EXT cancellation system may include the replica FE in an amount approximately equal to the large amount.
39. The communication system of claim 38, wherein the communication system delays the XT fault signal. 43. When the FEXT impairment signal arrives at the receiver after the direct signal, the FEXT cancellation system causes the direct signal and the FEXT
The replica FE by an amount approximately equal to the time delay during which the impairment signal reaches the receiver.
39. The communication system of claim 38, wherein the communication system delays the XT fault signal. 44. A plurality of analog-to-digital (A / D) converters, one associated with each receiver, each A / D converter providing a digital conversion of the combined signal. A plurality of A / D converters responsive to the combined signal received by the receiver; and a plurality of equalizer systems, one associated with each receiver, and each equalizer system comprising: A plurality of equalizer systems responsive to the digitally-converted combined signal to provide an adaptive equalization of the digitally-converted combined signal; and a plurality of first-in-first-out (FIFO) devices, one associated with each receiver and one for each FIFO. 38. The communication system of claim 37, wherein the device comprises a plurality of FIFO devices for receiving an output of the A / D converter and transferring the output to the equalizer system on a FIFO basis. 45. Responsive to an output signal of each first device to provide a first detector output signal corresponding to an analog signal level closest to the level of the output signal of the first device. A first detector responsive to an output signal of each equalizer system to provide a second detector output signal corresponding to an analog signal level of magnitude closest to the level of the output signal of the equalizer. The communication system according to claim 44, further comprising a second detector. 46. A communication line having a plurality of twisted wire pairs, a plurality of transmitters, one transmitter at each end of each of said twisted wire pairs, A plurality of receivers, one receiver being the twisted
At each end of each of the wire pairs, each receiver has a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated, and a direct signal at the opposite end of the communication line. A plurality of far-end crosstalk (FEX), one from each of the remaining transmitters
T) A method for reducing noise in a communication system comprising a plurality of receivers receiving a combined signal including a fault signal, the method comprising: for each receiver, generating a duplicate FEXT fault signal; To generate an output signal with few FEXT impairment signals, the duplicate FEXT
Combining a T impairment signal with said combined signal. 47. The method according to claim 47, wherein the step of generating the duplicated FEXT fault signal comprises: receiving a signal from each of the receivers other than the receiver from which the duplicated FEXT fault signal is generated; 47. The method of claim 46, further comprising: generating an individual duplicate FEXT impairment signal; and combining the individual duplicate FEXT impairment signal to form the duplicate FEXT impairment signal. 48. The method of claim 46, wherein combining the duplicated FEXT impairment signal with the combined signal comprises subtracting the duplicated FEXT impairment signal from the combined signal. 49. The communication system further comprises a plurality of coupling devices,
One associated with each receiver, each combining device comprising a plurality of combining devices responsive to the combined signal and the duplicated FEXT impairment signal, wherein the direct signal reaches the receiver after the FEXT impairment signal When combining the duplicated FEXT impairment signal with the combination signal comprises: combining the combined FEXT impairment signal with the combination signal at the combining device by an amount substantially equal to the time delay between the arrival of the FEXT impairment signal and the direct signal at the receiver Delaying the arrival of the signal; and subtracting the duplicated FEXT impairment signal from the combined signal.
47. The method according to claim 46. 50. The communication system further comprises a plurality of coupling devices,
One associated with each receiver, each combining device comprising a plurality of combining devices responsive to the combined signal and the duplicated FEXT impairment signal, wherein the direct signal reaches the receiver after the FEXT impairment signal When combining the duplicated FEXT impairment signal with the combined signal comprises: combining the combined FEXT impairment signal with the combined signal by an amount greater than a time delay between the arrival of the FEXT impairment signal and the direct signal at the receiver. Delaying the arrival of the duplicate FEXT impairment signal by the coupling device by an amount substantially equal to the large amount; and subtracting the duplicate FEXT impairment signal from the combination signal. Including,
47. The method according to claim 46. 51. The communication system further comprises a plurality of coupling devices,
One associated with each receiver, each combining device comprising a plurality of combining devices responsive to the combined signal and the duplicated FEXT impairment signal, wherein the FEXT impairment signal arrives at the receiver after the direct signal When combining the duplicated FEXT impairment signal with the combined signal comprises: combining the duplicated FEXT impairment signal with the combined FEXT impairment signal at the combiner by an amount substantially equal to the time delay between the arrival of the direct signal and the FEXT impairment signal at the receiver. Delaying the arrival of a fault, and subtracting the duplicate FEXT fault signal from the combined signal;
47. The method according to claim 46. 52. A method for reducing power dissipation in a communication system having a plurality of adaptive filters with a plurality of taps, wherein each tap is switchable between an active and an inactive state, each having a coefficient. The method comprises: a) specifying an allowable error for the system; b) setting a tap threshold for each active tap; c) for each active tap the absolute value is Deactivating taps having a coefficient less than the tap threshold of active taps; d) calculating a system error; e) comparing the calculated system error with the allowable system error. F) if the calculated system error is smaller than the allowable system error, Increasing the tap threshold for the active tap; and g) until the calculated system error approaches the allowable system error without exceeding the allowable system error. ). 53. The method of claim 52, wherein the decision to deactivate a tap is made in a sequential manner starting at the input of the filter. 54. The method of claim 52, further comprising: periodically activating previously deactivated taps; and repeating steps b) -g). 55. The method of claim 54, wherein the previously deactivated taps are activated in a sequential manner starting from an input of the filter. 56. The method of claim 52, wherein calculating the system error comprises: determining an error for each individual filter; and summing the errors for the individual filters. 57. The method of claim 56, wherein calculating the error of the filter comprises: determining an error for each individual tap; and summing the errors of the individual taps. 58. The method of claim 57, wherein the error of each individual tap is a mean square error for the tap and is determined by multiplying the absolute value of the tap coefficient by an average energy signal. 59. Specifying an acceptable level of error for the taps; calculating, for each active tap, the error of deactivating the taps; Deactivating the tap if less than the allowable error. 60. The method of claim 59, wherein said steps are performed before steps a) -g). 61. A method for reducing power dissipation in a communication system having at least one adaptive filter with a plurality of taps, wherein each tap is switchable between an active and an inactive state, and each tap is a coefficient. The method comprises: a) calculating an initial system error; b) setting a tap error threshold for each active tap; c) for each active tap, the absolute value is Deactivating taps having a coefficient less than the tap error threshold set for the active tap; d) calculating a next system error; e) the next system error and the initial system. If the difference between the errors is less than a predetermined value, increase the tap error threshold for each active tap. Steps and, f) until the difference between the said following system error initial system error exceeds the predetermined value, the method comprising the step of repeating steps c) ~ step e) to. 62. The method of claim 61, wherein the decision to deactivate a tap is made in a sequential manner starting at the input of the filter. 63. The method of claim 61, wherein each tap threshold is initially set equal to a tap coefficient having a minimum absolute value. 64. The method of claim 61, wherein said tap error threshold is set substantially the same for each tap in said filter. 65. A start-up protocol for use in a communication system having a master transceiver at one end of a twisted wire pair and a slave transceiver at an opposite end of the twisted wire pair, Each transceiver has a near-end noise reduction system, a far-end noise reduction system, a timing recovery system, and at least one equalizer, wherein the protocol, during a first stage, transmits a signal but does not receive any signal Maintaining the master in a half-duplex mode; maintaining the slave in a half-duplex mode receiving signals from the master but not transmitting any signals; converging the master near-end noise reduction system. Received by the slave such that the frequency and phase are synchronized with the frequency and phase of the signal transmitted by the master Adjusting the frequency and phase of the signal to be transmitted; converging the equalizer of the slave; and maintaining the slave in a half-duplex mode that transmits a signal but receives no signal during a second stage. , Maintaining the master in a half-duplex mode that receives signals from the slave but does not transmit any signals; freezing the frequency and phase of the slave; and Converging; adjusting a phase of a signal received by the master such that a phase is synchronized with a phase of a signal transmitted by the slave; converging the equalizer of the master; Maintaining the slave in a full-duplex mode such that the slave transmits and receives signals during three phases , Activation protocol includes the step of maintaining the master to full-duplex mode as the master transmits and receives a signal, and the step of refocusing the master near-end noise reduction system. 66. A start-up protocol for use in a communication system having a master transceiver at one end of a communication line and a slave transceiver at an opposite end of the communication line, wherein each transceiver is a near end. A noise reduction system, a far-end noise reduction system, a timing recovery system, and at least one equalizer, wherein the protocol comprises: in a first stage, a half-duplex mode transmitting a signal but receiving no signal; Maintaining a master; maintaining the slave in a half-duplex mode that receives signals from the master but does not transmit any signals; converging the master near-end noise reduction system; Adjust the frequency and phase of the signal received by the slave to be synchronized with the frequency and phase of the signal transmitted by the master. And converging the equalizer of the slave; and maintaining the slave in a half-duplex mode transmitting a signal but receiving no signal during a second stage, wherein the slave Transmitting using a free-running clock; maintaining the master in a half-duplex mode receiving signals from the slave but not transmitting any signals; and converging the slave near-end noise reduction system. Adjusting the frequency and phase of the signal received by the master such that the frequency and phase are synchronized with the frequency and phase of the signal transmitted by the slave; and converging the equalizer of the master. And maintaining the slave in a full-duplex mode such that the slave transmits and receives signals during a third phase. Maintaining the master in full-duplex mode such that the master transmits and receives signals; reconverging the master near-end noise reduction system; and phase transmitted by the slave. Adjusting the phase of the signal received by the master to be synchronized with the phase of the signal; and the signal received by the slave such that the frequency and phase are synchronized with the frequency and phase of the signal transmitted by the master. Adjusting the frequency and phase of the power-on sequence.