CN1225211A - Method and apparatus for implementing a wireine transmission connection - Google Patents

Abstract

The invention concerns a method and apparatus for implementing a wireline transmission connection, especially a VDSL transmission connection. The transmission connection is implemented in electric form so that a separate frequency range is reserved for either transmission direction. To allow efficient filtration of radio-frequency interferences by using as simple an apparatus as possible, the frequency band of the transmission line (13) is divided into sub-bands limited by international radio amateur frequency bands (AB1...AB6) and the transmission connection is implemented in at least some of these sub-bands (a) by generating for each sub-band to be used a carrier wave with its own modulator and (b) by dividing the bits of the bit stream (DATA_IN) to be transmitted between the modulators of the transmission direction in question so that each carrier wave is modulated with some of these bits.

Description

Implement the method and apparatus that wire transmission connects

The present invention relates generally to the enforcement that a kind of electric wire transmission connects, relate in particular to a kind of enforcement of transmission connection of employing VDSL (very high bit rate digital subscriber line road) technology.

Optical fiber is a kind of self-explantory selection as the main line network transmission medium, because the main line connection needs transmittability at a high speed usually, for optical cable, used transmission range is than length and have ready-made route usually.Even connect (circuit between local switch and user) for the user, situation is also in rapid change, because from individual consumer's viewpoint, adopt that multimedia is implemented and need the miscellaneous service of high transfer rate more also will become the business of various routines.

Yet when construction can provide the future network of broadband services, expectability did not have very big expense to save, because the expense that its expense is mainly installed from optical cable.But everybody also wants to build optical fiber as much as possible in user network, because obviously this will be essential in future.Yet the expense of upgrading user network is very high, and in fact will be referred to the time of many decades in this problem aspect the time.Desire extends to user network with optical fiber, the maximum really obstacle of huge expense.

For above-mentioned reasons, in order how to seek traditional subscriber's line (metal wire to) is used for the method for high speed data transfer (promptly apparently higher than the basic access rate 144kbit/s of ISDN transmission rate), taked multiple more efficiently than before measure.Existing ADSL (Asymmetrical Digital Subscriber Line) and HDSL (high bitrate digital subscriber line road) technology provides many new possibilities for metal wire subtend user terminal transmission of high-rate data and video along telephone network really.

It is asymmetric that the ADSL transmission connects, that is, the transmission rate from the network to user is apparently higher than the transmission rate from user-to-network.This be because, the ADSL technology is mainly used in various so-called " as required " business.In fact, in ADSL transmission connected, the transmission rate from the network to user was on the order of magnitude of 2...6Mbit/s, from the transmission rate of user-to-network then on the order of magnitude of 16...640kbit/s (for single control channel).

The HDSL transmission technology relates to the transmission of 2Mbit/s stages of digital signal metal wire centering.HDSL represents a kind of symmetrical technology, and promptly the transmission rate on the both direction equates.Independently the HDSL transceiver system comprises a plurality of transceivers that adopt ECT echo cancellation technique, the bidirectional transmission path that constitutes is interconnected by lead by one between these transceivers.In the HDSL transmission system, the number of this standalone transceiver system can be one or two or three that walk abreast, and under two or three pairs of parallel situations, the speed that adopts during each parallel transmission connects is the sub-speed of 2Mbit/s thus; If have three pairs parallel then be 784kbit/s, have two pairs parallelly then to be 1168kbit/s.All signals of transmission 2Mbit/s level in a HDSL system how in international recommendation, have been defined, for example the VC-12 signal of SDH network or according to G.703/G.704 2048kbit/s all signals of suggestion of CCITT.

Though can only obtain to be generally the speed of 1...2Mbit/s magnitude by above-mentioned solution, for subscriber cable, find a kind of technology of the ATM of permission level bit rate.In fact the ETSI of International Standard Association (ETSI) is formulating a kind of VDSL equipment code.Its purpose is, connects and can transmit all cells of ATM between a telephone network and a user terminal in the VDSL transmission that the metal wire centering of telephone network is realized.

Adopt the VDSL technology, all subscriber's lines in all telephone networks are brought into use high-frequency, thereby the radio frequency interference that subscriber's line (be generally maskless line to) is caused becomes a big problem.

The someone advises, adopts a kind of for example adaptive channel equalizer to help eliminate radio frequency interference in receiver.Yet this just needs a kind of accurate and expensive analog to digital converter, because these interference that also must be converted into digital form may be very strong.In addition, produce very rapidly owing to disturb, its frequency change is also very fast, therefore is difficult to regulate this equalizer.

The another kind of known method of eliminating strong radio frequency interference is, adopt the multi-carrier modulation of certain mode, wherein produce several carrier waves by a kind of single modulated process (for example discrete multitone sound DMT or discrete wavelet multitone DWMT), and this production process is realized as follows, that is, do not distribute bit waiting for transmission for it for those carrier waves that have interference.DMT is a kind of method that is connected by the enforcement ADSL of ANSI (ANSI) definition, wherein produces a plurality of such subchannels (carrier wave) with same modulated process, these channels equally spaced be distributed in the frequency domain and width identical.When wanting to eliminate the interference that is caused by fixing information source (for example ham radio emission), the subchannel that is arranged in interference band (for example amateur radio band) can not use fully.In International PCT patent application WO-A-95/28773, such a solution has been described.

One big major defect of this solution is that it causes the execution mode of a kind of complexity and costliness or causes the poor efficiency utilization of frequency range.This be because, the effective utilization of discontinuous frequency range needs many narrow subchannels, its number is very high.The number that increases subchannel will make system complicated more.When a plurality of DMT subchannels are overlapping on frequency domain top, also can reduce band utilization efficient, thus in order to eliminate interference, all carrier frequency outside the frequency band that is exposed to interference are quit work.The enforcement of these multi-carrier modulation methods also is very complicated (formation of all signals and detection all are very complicated processes).

Another shortcoming based on the solution of DTM is, in order to eliminate the various distortions that channel causes, must increase filling bit (being called the circulation lead code) to the emission data.Therefore, DMT has also wasted the capacity on the time domain.

The objective of the invention is to, have the solution of superperformance by a kind of very simple transmission connection implementation method (especially the VDSL transmission connects) that makes is provided, thereby improve above-mentioned various shortcoming.

Solution of the present invention by a kind of basis defines in each claim independently can reach this purpose.

The present invention is at first based on following viewpoint: though the application of multi-carrier modulator (DMT) is defined as a kind of transmission means in ADSL standard for example, and for a kind of similarly still more enforcement of the connection (VDSL connection) of high speed, this also is a kind of conspicuous possibility, but when available frequency band is discontinuous, when some narrow frequency range is unavailable, this is not to implement the effective or the simplest mode that transmission connects.Secondly, the present invention is also based on following viewpoint: the radio frequency interference that amateur radio station causes is strong especially, because all subscriber's lines of the usually close all telephone networks in the position of amateur radio station.

For these reasons, the present invention can not come from following thinking: must produce a plurality of carrier waves on whole frequency, shielding some carrier wave then passes into disuse it, and be based on following thinking: at the poorest interference band of estimating (promptly, the all frequency ranges of international ampere radio) under the effect, the available transmission frequency range is split into a plurality of frequency sub-band of obvious separation, each frequency sub-band has single-carrier modulated process or the modulator of oneself, and each single-carrier modulated process or modulator are assigned with (at a high speed) waiting for transmission bit stream.Thus in this article, a frequency sub-band means to have its edge and the transmission band that the international ampere radio frequency band joins at least.

This thinking is exactly under the effect of all frequency ranges of ham radio, but will be divided into the frequency sub-band of a plurality of modulating datas for all frequency ranges that this connection is prepared.Each carrier wave is produced by its oneself modulator.On frequency domain a plurality of channels are separated from each other like this, each channel can be handled independently of each other.Be adjusted to the frequency range that each channel is prepared independently according to carrier frequency and symbol rate thus.

In a kind of the method according to this invention, can utilize certain simple modulator approach, preferably for example QAM (quadrature amplitude modulation) or CAP (carrierless amplitude and phase place) modulation.

Hereinafter, will the present invention and useful all embodiment thereof more at large be described with reference to all examples shown in the appended illustration, wherein

Fig. 1 has set forth the transmission system that a kind of VDSL of utilization connects;

Fig. 2 has set forth a kind of frequency division method that adopts in VDSL connects;

Fig. 3 has set forth a kind of according to transmission principle of the present invention;

Figure 4 shows that a kind of division according to a useful embodiment of the present invention all frequency sub-band between each transmission direction;

Figure 5 shows that a kind of according to the citation form that is used to implement the device that VDSL connects of the present invention;

Figure 6 shows that a useful embodiment of device shown in Figure 5.

As mentioned above, the ETSI of International Standard Association is formulating a kind of VDSL equipment code.Fig. 1 has set forth a kind of structure of system of the VDSL of utilization connection.This system configuration is compatible mutually with so-called FTTC (optical fiber is to control (curb)/rack) structure.Rack or control appliance 11 connect via the high speed fibre of reference number 12 expression and receive data.Existing metallic circuit (copper cash to) also arrives the user through same rack from switch.These copper cash are to representing with reference number 13.High-speed data is merged on the subscriber's line being arranged in the optical network unit of rack (ONU), thereby the user still can use old arrowband POTS/ISDN business, but in addition the user can also use the high speed full-duplex data to connect.With (passive) filter of carrying out all VDSL signals and all narrow band signal frequency division these arrowbands and broadband services are separated from each other.Between ONU and network terminal NT, constitute VDSL and connect main body.The network terminal is usually located in terminal use (user's) the building, and link to each other with the subscriber terminal equipment of for example common simulation phone or ISDN phone (reference number 15), perhaps the terminal equipment (te) that utilizes broadband services with for example microcomputer (reference number 16) links to each other.The network terminal provides various uni interfaces (user-to-network interface) according to standard for the terminal use.This interface is represented with reference symbol INT1.Represent with reference symbol INT2 by the broadband VDSL interface that optical network unit provides.

Because the present invention only relates to a kind of VDSL that implements and connects between ONU and network terminal NT, will be not described further system shown in Figure 1 herein.For example more at large describing the VDSL system among the ETSI report DTR/TM-03068, the reader can find more detailed description there if desired.

In ETSI, should follow the bit rate of the following VDSL of being used for transmission in essence:

-down direction (from the network to user): 52,26,13 and 6.5Mbit/s

-up direction (from user-to-network): 26,13,6.5 and 2.3Mbit/s.

Realize frequency division according to Fig. 2, on low frequency, reserved space (frequency range A) for existing P OTS or ISDN business like this.All VDSL channels are transferred to frequency range B, and its low side limiting frequency representative value is 300...600kHz, and high-end limiting frequency is preferably about 18MHz, and this point can be seen hereinafter.Hereinafter also will further describe the frequency sub-band that VDSL is connected between the different transmission directions divides.

According to the present invention, the bit stream that sends to the VDSL connection is divided into the several carrier waves that are positioned at this frequency range, and they are arranged in all frequency sub-band that limited by all frequency ranges of international ampere radio like this.Thus, this transmitter contains several parallel modulators, adopts a kind of suitable known modulation method in modulator, for example QAM modulation.In each modulator, use an independent frequency, make corresponding carrier wave be positioned at required frequency sub-band.

Represented all frequency ranges of international ampere radio in the following table, the low side limiting frequency of this frequency range is represented on wherein left hurdle, and the high-end limiting frequency of this frequency range is represented on right hurdle.

The low side limiting frequency (MHz) of frequency range	The high-end limiting frequency (MHz) of frequency range
		????????1.810	?????????2.000
????????3.500	?????????3.800
		????????7.000	?????????7.100
???????10.100	????????10.150
		???????14.000	????????14.350
???????18.068	????????18.168
		???????21.000	????????21.450
???????24.890	????????24.990
		???????28.000	????????29.700

Each above-mentioned frequency values shows that in the method according to the invention, all carrier waves are arranged in following frequency sub-band, and determines its low side and high-end limiting frequency according to all frequency ranges of all ham radioes:

The frequency sub-band number	Low side limiting frequency (MHz)	High-end limiting frequency (MHz)
			???????1.	??????0.3	?????1.810
???????2.	??????2.000	?????3.500
			???????3.	??????3.800	?????7.000
???????4.	??????7.100	????10.100
			???????5.	?????10.150	????14.000
???????6.	?????14.350	????18.068
			???????7.	?????18.168	????21.000
???????8.	?????21.450	????24.890
			???????9.	?????24.990	????28.000

Fig. 3 has set forth according to transmission principle of the present invention, its mode is the power spectral density (PSD) that is presented at the signal that receives when adopting six different QAM modulated carrier C1...C6 (above-mentioned frequency sub-band 1...6) from a VDSL connects, make minimum two be used for the up direction transmission and remaining two be used for the down direction transmission.The all frequency ranges of ham radio are represented with the rectangle of reference symbol AB1...AB6 representative.Each value is corresponding with the calculation by computer that 400m connection distance is carried out among the figure.The power density that this VDSL connects is-60dBm/Hz that its additional additive white Gaussian (AWGN) is in-the 115dBm/Hz level.Suppose that through-put power is 0dBm and bandwidth when being 4kHz, the height of all rectangle AB1...AB6 is corresponding to the amount of calculation of disturbing.

By adopting six minimum frequency sub-band (frequency sub-band 1-6), can implement all transmission rates that above-mentioned VDSL connects.On down direction, preferably adopt minimum frequency sub-band (No. 1), because in the ADSL system, on this direction, also use these low frequencies.Be connected with VDSL according to the present invention even in same cable, exist ADSL to connect simultaneously, also can avoid near-end crosstalk (NEXT) in this way.The result who adopts Shannon's law that subscriber's line is investigated shows, when being the transmission direction of "the philosophers," referring to the philosophers or their works, outside the Confucianists's Frequency Band Selection according to following table, can realize best that the above-mentioned transmission rate of mentioning in the above-mentioned ETSI report is connected distance with target.(Shannon's law C=B * log ₂(1+S/N) provided the theoretical value of maximum information transmission capacity C in the channel, wherein bandwidth is B and signal to noise ratio is S/N.)

Frequency sub-band number	Transmission direction
		????1	Down direction
????2	Up direction
		????3	Down direction
????4	Up direction
		????5	Down direction
????6	Down direction

By adopting Shannon's law at first to calculate different transmission range (300m, 500m and 1500m) time different frequency sub-band capacity, come to be all transmission direction chooser frequency ranges according to required bit rate in its total capacity and the transmission direction discussed then, realize thus dividing by the frequency range of all transmission directions.Should be noted that since frequency when improving the decay of cable increase sharply, therefore compare with the frequency range of equal bandwidth under the upper frequency, the frequency range of lower frequency correspondingly has better signal to noise ratio, and also has higher message transmission capacity according to Shannon's law.So for transmission capacity, can not be at for example change of direction between the frequency sub-band 3 and 4, though these two frequency ranges have almost equal bandwidth.

Another advantage that above-mentioned frequency range is divided is that it can be used for being connected with asymmetrical of symmetry, may have various types of connections thus in same cable, and each is not crosstalked between connecting.In Fig. 4, also set forth this useful frequency range and divided, wherein planned each frequency sub-band of up direction.

Similarly observe and show, iff symmetry operation or only asymmetric operation is just enough, also can implement VDSL and connect, (frequency range B, Fig. 2) all frequency sub-band of low side adopt up direction, and high-end all frequency sub-band adopt down direction for frequency range thus.If can only adopt symmetry to connect, then for the channel distribution of up/down direction, the 3.5...3.8MHz amateur radio band is a good dividing frequency.On the other hand, if think that asymmetric operation is very important, can point out that in a similar manner the 1.810...2.000MHz amateur radio band is a suitable dividing frequency.Place 3.5...3.8MHz frequency range place can realize the symmetrical bit rate of a 26Mbit/s and the symmetrical bit rate of a 52Mbit/s on down direction crossover frequency.

Fig. 5 has shown the basic comprising according to device of the present invention.The figure illustrates the two ends of the VDSL connection of in a transmission direction, seeing.The high-speed bit stream DATA-IN of VDSL transmission connection that is passed to be passed is (according to above-mentioned, for example, this speed be 52 or 26Mbit/s) be imported into symbol and form piece 41, this piece forms all symbols of all bits and by their input modulator pieces 42 are given different carrier waves with all symbols, modulator block 42 comprises a plurality of parallel QAM modulator A1...An that works in different carrier frequency, as shown in Figure 3.Piece 41 directly sends to the symbol of its formation the input of corresponding modulator.Because different carrier has different signal to noise ratios, the bit number that each symbol uses for different modulators can be different.The signal to noise ratio of carrier wave is good more, then can use many more bit numbers (closeer planisphere).

When the preferred forms that adopts according to Fig. 4, selecting symbol rate is very useful (a kind of simple device embodiments) to the enforcement of this device, thereby for example carrier wave C4 has the symbol rate that is in a ratio of twice with carrier wave C2 on up direction, and carrier wave C3, C5 and C6 have the symbol rate that is in a ratio of twice with carrier wave C1 on down direction.Because transmission occurs on the different directions, so carrier wave C3 and C4 need not to have equal symbol rate.On the other hand, if the channel distribution of up/down direction is positioned at the 3.5...3.8MHz amateur radio band, can select identical symbol rate with each carrier wave on the down direction for up direction.If limiting frequency is positioned at the 1.81...2.0MHz amateur radio band, only use a frequency sub-band at up direction so.In the case, should select the symbol rate of down direction like this, make frequency surpass select on all frequency ranges of 3.8MHz one with minimum 2.0...3.5MHz frequency range on speed be in a ratio of the symbol rate of twice.

If on transmitter, adopt above-mentioned all bits are assigned to different carrier waves adaptively get on, then be worth increasing a brief cycle of training at the initial period of this connection, in order to research on each carrier wave to suitable what bits that adopt of each symbol.

All QAM modulators are modulated to all signals on the different carrier frequency, and these frequencies are arranged in some of above-mentioned all frequency sub-band 1...9, preferably are positioned at the center of the frequency range that comes into question in each case in itself.Because qam mode is a most general present modulation system, for example in cable modem, is therefore no longer further described in this article.If the reader has this interest, can the IEEE in the Pentech in London publishing house and New York publishing house by William Webb, the publication that LajosHanzo showed: modern quadrature amplitude modulation obtains the more detailed description to QAM among the ISBN 0-7803-1098-5 (list of references 1).

All output signals from all modulators are imported in the summer 43, herein all signals are carried out the digitlization summation.This numeral summing signal is continued to be input to line adapter unit 44, and this unit typically comprises a digital to analog converter, one be promoted to an accurate level in order to the output level with signal in order to the filter of removing all harmonic components that occur in the digital signal, one line drive circuit, one successively in order to the hybrid circuit that will transmit and receive branch road and be separated from each other out, one line converter and (passive) filter (POTS/ISDN splitter) in order to POTS/ISDN signal and VDSL signal are separated from each other out.The output of this filter and channel (line to) link to each other.

At receiving terminal, signal at first links to each other with line adapter unit 45, and this unit typically comprises above-mentioned (passive) filter (POTS/ISDN splitter), one in order to will transmit and receive hybrid circuit, an adjustable amplifier level, a filter stage and analog to digital converter that branch is separated from each other out.This filter stage preferably contains a plurality of so-called notch filters that are operated in all frequency ranges of ham radio.Because summer and line adapter unit can be realized according to every common technology, therefore describe its structure in this article no longer further.

The all numeric words that receive from line adapter unit 45 also are connected to demodulator unit 46, and this unit comprises n parallel qam demodulator B1...Bn, thereby constitute n modulator/demodulator to (for example all carrier wave C1, C3, C5 and C6, so n=4).The all symbol words that receive from the demodulator output are imported into symbol recognition circuit 47, and this circuit constitutes the original bit stream DATA_OUT of all symbol words of base band.

If the various time-delays of all carrier waves cause variety of issue when rebuilding primary signal, then can measure all time delays respectively for each carrier wave, and in reception, can utilize this information to guarantee the correct reception order of all symbols in the starting stage that connects.

Can further revise said apparatus according to the various useful embodiment that for example hereinafter occurs.

About this method, it is very useful adopting trellis coding (trellis-coded) modulation (TCM), amplify because can obtain coding in this way, and the performance difference between can balanced each carrier wave.Well-known trellis coded modulation is a kind of coded system of great use, and especially along in the transmission of telephone line, so this also is a kind of very useful selection.

Fig. 6 has shown a kind of like this embodiment, and wherein symbol forms unit 51 and also carries out trellis coding.Because trellis coding is well-known technology, so this paper no longer is further described it.If desired, can in for example above-mentioned list of references 1, find more detailed description.Since carry out trellis coding at transmitting terminal, thus for example decoding process of Veterbi decoding adopted at receiving terminal, because this is about trellis coding decoding process commonly used.In list of references 1 and more fully at for example Benedetto of Prentice-Hall company publication, Biglieri, the publication that Castellani showed: all described viterbi algorithm among the theoretical ISBN 0-13-214313-5025 of Digital Transmission.

Can also adopt " gain calibration " method, be different carrier waves and adopt different transmission levels, evaluate the performance difference between different carrier.In fact, the gross power of transmitter can be restricted to a certain determined value (for example, 10dBm), this helps demarcating the through-put power of different carrier, thus make all carrier waves the position bit error probability identical.For this purpose, the output of each modulator is linked to each other with an adjustable amplifier AMP1...AMPn according to Fig. 6, thus the multiplication factor that the control section 48 of permission transmitter is individually regulated each carrier wave.Under opening situation, receiver is notified transmitter all signal to noise ratios that it has measured, regulates the multiplication factor of all amplifier AMP1...AMPn according to the control section of these value transmitters, thereby the bit error rate of each carrier wave is all equated.

Though above described the present invention with reference to all examples shown in the drawings, apparent the present invention also not only is confined to this, but can be revised in the scope of the inventive concept in aforesaid and the appended claims.For example, among the above-mentioned embodiment, each frequency sub-band contains a carrier wave.Though this is the most useful implementation method, on principle, each frequency sub-band also can use a plurality of carrier waves.Though all frequency ranges of ham radio are international, the boundary of some frequency range may have some and changes in different countries, and this shows and need not given frequency range boundary (being used for Europe usually at least) is interpreted as fully accurate boundary.

Claims (10)

1. in order to implement a kind of method of two-way wire transmission connection, wherein should transmission connect, thereby be independent frequency scope of each transmission direction reservation from this transmission line (13) with electrical form enforcement,

It is characterized in that,

The frequency range of this transmission line (13) is divided into the frequency sub-band that is limited by all frequency ranges of international ampere radio (AB1...AB6), and implements this transmission connection on some in these frequency sub-band at least, and its execution mode is

(a) modulator with itself is that each frequency sub-band to be used produces a carrier frequency,

(b) will between all modulators in the transmission direction that comes into question, divide by all bits of this bit stream waiting for transmission (DATA_IN), and make each carrier wave all be modulated by some bit in all bits.

2. the method for claim 1 is characterized in that, uses 1-2 carrier wave in the direction from user-to-network, and use 1-5 carrier wave on the direction from the network to user.

3. method as claimed in claim 2, it is characterized in that, in all available frequency sub-band, use six minimum frequency sub-band, make that be that the frequency sub-band of 3.5MHz and 10.1MHz transmits from the data of user-to-network in upper limiting frequency, and from the network to the user's data, on upper limiting frequency is the frequency sub-band of 1.81MHz, 7.0MHz, 14.0MHz and 18.068MHz, transmit.

4. the method for claim 1 is characterized in that, only uses a carrier wave between two amateur radio bands, and uses a plurality of symbol rates in the carrier modulation process.

5. the method for claim 1 is characterized in that, adopts adaptive bit to distribute at different carrier waves.

6. the method for claim 1 is characterized in that, at the different transmission power level of different carrier use of identical traffic direction.

7. the method for claim 1 is characterized in that, adopts trellis coded modulation in transmitter.

8. the method for claim 1 is characterized in that, it is that a kind of VDSL connects that this transmission connects.

9. implement the device that two-way wire transmission connects with electrical form, this device all comprises (a) in order to form the device (41) of a plurality of input bit symbols (DATA_IN) in each transmission direction, (b) in order to modulating device (42) according to established all symbol-modulated carrier waves, thereby this device uses an independent frequency scope for each transmission direction, it is characterized in that, this modem devices comprises n parallel modulator, select the frequency of each modulator to make them constitute several carrier waves (C1...C6), all be positioned on its oneself the frequency sub-band at each carrier wave on this frequency range of this transmission line, at least one end of each frequency sub-band is connected mutually with an international ampere radio frequency band.

10. device as claimed in claim 9,

It is characterized in that each modulator (A1...An) all is equipped with an adjustable amplifier (AMP1...AMPn), in order to the power level of independent each carrier wave of adjusting.

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