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WO2003009488A2 - Variable data rate and multi-power level cdma modem - Google Patents

Variable data rate and multi-power level cdma modem Download PDF

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Publication number
WO2003009488A2
WO2003009488A2 PCT/IL2002/000585 IL0200585W WO03009488A2 WO 2003009488 A2 WO2003009488 A2 WO 2003009488A2 IL 0200585 W IL0200585 W IL 0200585W WO 03009488 A2 WO03009488 A2 WO 03009488A2
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WO
WIPO (PCT)
Prior art keywords
sequence
data
generator
sub
spreaders
Prior art date
Application number
PCT/IL2002/000585
Other languages
French (fr)
Other versions
WO2003009488A3 (en
Inventor
Dov Zahavi
David Mansour
Ezra Zamir
Simha Erlich
Original Assignee
Elbit Systems Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Elbit Systems Ltd. filed Critical Elbit Systems Ltd.
Priority to AU2002319887A priority Critical patent/AU2002319887A1/en
Publication of WO2003009488A2 publication Critical patent/WO2003009488A2/en
Publication of WO2003009488A3 publication Critical patent/WO2003009488A3/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/10—Code generation
    • H04J13/12—Generation of orthogonal codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
    • H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
    • H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
    • H04B2201/70703—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation using multiple or variable rates
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/0077—Multicode, e.g. multiple codes assigned to one user

Definitions

  • the present invention relates generally to digital communication systems. More specifically, the present invention relates to a variable bandwidth and variable signal power level modem.
  • Modems also known as modulators-demodulators, are well known in the art of communications. There are various modulation methods presently known and various modems which operate using one or more of these modulation methods. Among the methods presently used are Quadrature Amplitude Modulation (QAM), Quadrature Phase Shift Keying (QPSK), and Spread Spectrum methods (both direct sequence-CDMA and frequency hopping). Modems may transmit and receive data over various mediums including coax cable, twisted pair, fiber-optic strands, and in air (effectively no medium). [003] Each of the mediums over which modems may communicate has its own benefits and drawbacks. Drawbacks of a given transmission medium may include signal attenuation and noise interference. In communication applications where signal interference is a factor which needs to be overcome or minimized, both data rate and signal power regulation may be required. For the most part, however, modems of the prior art operate at fixed bandwidths and with fixed signal power limitations.
  • the present invention is a wireless Direct Sequence Spread Spectrum ("DSSS") or Code Division Multiple Access (“CDMA”) modem including a controller which may regulate the number of modulators and/or spreaders allocated to sources of data streams based on data-rate requirements and/or based on signal power requirements. All spreading sequences may belong to the same family of orthogonal sequences.
  • a source of a data stream may be a multiplex of several sources like IP data, video, etc.
  • may spurted among few modulators each may transmit a portion of the data stream and may use an associated spreading sequence that belongs to same family.
  • the modem controller may increase the number of Modulators that this user receives.
  • the modem controller may increase the power of the modulator(s) that transmit the same source data stream, or portion of it.
  • the variation at the power of the modulators may be such that the over all power of all the modulators remains the same.
  • the wireless modem may be used as part of a point to multi-point or mesh communication system.
  • a modem at a central hub may communicate with two or more remote wireless modems over a common carrier signal, also referred to as a communications channel or frequency band.
  • the common communication channel or frequency band may be partitioned into multiple communication sub-channels, where each sub-channel may be allocated to one or more users and associated with a modulator and an orthogonal spreading sequence.
  • the bandwidth received by a remote modem may be increased by receiving one or more sub-channels.
  • a sub-channel's power may be increased where the over all power of all transmitted sub channels remains the same.
  • FIG. 1 is a block diagram of several transmitters and several receivers operated and constructed according to an embodiment of the present invention
  • FIG. 2 is a block diagram of any one of the transmitters shown in Fig. 1, operated and constructed according to an embodiment of the present invention
  • Fig. 3 is a block diagram representing the timing alignment of transmitted sub-channels according to an embodiment of the present invention.
  • Fig. 4 is a block diagram of a transmit data format according to an embodiment of the present invention.
  • Fig. 5 is a block diagram of any one of the receivers shown in Fig. 1, operated and constructed according to an embodiment of the present invention.
  • This apparatus may be specially constructed for the desired purposes, or it may comprise a general purpose computer or Digital Signal Processor ("DSP") selectively activated or reconfigured by a computer program stored in the computer.
  • DSP Digital Signal Processor
  • Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs) electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards, or any other type of media suitable for storing electronic instructions, and capable of being coupled to a computer system bus.
  • ROMs read-only memories
  • RAMs random access memories
  • EPROMs electrically programmable read-only memories
  • EEPROMs electrically erasable and programmable read only memories
  • the present invention is a wireless Direct Sequence Spread Spectrum ("DSSS”) or Code Division Multiple Access (“CDMA”) modem.
  • the wireless Direct Sequence Spread Spectrum (“DSSS”) or Code Division Multiple Access (“CDMA”) modem may include a controller which may regulate the number of modulators and/or spreaders allocated to a source data stream based on predetermined parameters, for example, data-rate requirements and/or based on signal power requirements.
  • the modem controller may split the source data between wo or more modulators and their associated spreaders, each spreader may use a separate orthogonal spreading sequence.
  • the modem controller may increase the number of Modulators that this user receives.
  • the modem controller may increase the power of the modulator(s) that transmit the same source data stream, or portion of it.
  • the variation at the power of each of the modulators may be such that the over all power of all the modulators remains the same.
  • the wireless modem may be used as part of a point to multi-point or mesh communication system.
  • a modem at a central hub may communicate with two or more remote wireless modems over a common carrier signal, also referred to as a communications channel or frequency band.
  • the common communication channel or frequency band may be partitioned into multiple communication sub-channels, where each sub-channel may be allocated to one or more users and may be associated with a modulator and a spreading sequences, where each spreader may use an orthogonal spreading sequence.
  • the modem controller may increase the number of Modulators that this user receives.
  • a sub-channel's power may be increased such as the power of all the modulators remains the same.
  • Fig. 1 there is shown a simplified block diagram of several transmitter users, 12 ⁇ to 12K, and several receivers, 14i to 14 , which may be used as part of a communication system or network 10 according to the an embodiment of the present invention.
  • the communication system 10 may transfer data over one or more carrier frequencies, frequency bands or communication channels. Each communication channel may be parsed in multiple communication sub-channels.
  • the topology of the network may be, for example, either that of a point to multi-point (also known as star) network, where a single hub may communicate with multiple users simultaneously, or the topology may be that of a mesh network, where users can communicate directly between themselves.
  • Each user of the network or system may have transmitter user 12 and receiver 14.
  • a hub may have multiple transmitter users 12 and multiple receivers 14, where each receiver/transmitter pair is associated with one or more users.
  • other network topology configuration may be used.
  • DSSS direct sequence spread spectrum
  • CDMA code division multiple access
  • a given carrier signal or frequency band may be termed "communication channels”, and the total bandwidth (“TBW”) or total data rate (“TDR”) from a transmitter of the communication channel may be parsed into two or more sub-channels, where each sub-channel may be associated with one a separate orthogonal spreading sequences.
  • All the spreading sequences used by a single transmitter may belong to a single set of orthogonal spreading sequences, and the bandwidth or data rate associated with a given spreading sequence, termed the basic data rate ("BDR") may be approximately equal to the TDR divided by the total number of orthogonal spreading sequences in the set of orthogonal spreading sequences.
  • BDR basic data rate
  • Each sub-channel may have a data rate that is substantially equal to BDR. For example, if the total available bandwidth on a 812MHz carrier signal is 5Mhz and a set of 10 orthogonal spreading sequences are used as part of a DSSS/CMDA communications system using the 812MHz carrier signal, the basic data rate would be 0.5Mbits for 0.5Mhz bandwidth.
  • DSSS or CDMA communication methodology is well known in the communications field.
  • the practice of using separate orthogonal spreading sequences or codes to split a single carrier signal, bandwidth or channel capable of supporting a maximum data rate into multiple communication sub-channels, is also well known.
  • the present invention may be implemented using any or all DSSS/CDMA standards known today or to be devised in the future.
  • System 10 may include a hub with one or more transmitter users 12, transmitter .iser 12] to transmitter 12 ⁇ , and L users, where each user may have at least one receiver 14. Each user's receiver is shown as 141 to user 14 .
  • Each transmitter user 12 may transmit some source data or data stream Dk, at a data rate DRk, having a transmission p ⁇ w ei PT - AS an example, transmitter 12j may transmit data stream D at data rate DR] and at a power level PTi.
  • the use of allocated spreading sequences may allow multi-user communication on the same carrier frequency, band or channel.
  • Each user in a communication network may be assigned a unique ID, much like an IP address which may be assigned in an Internet Protocol ("IP") Network.
  • IP Internet Protocol
  • Each user may also be assigned one or more orthogonal spreading sequences, depending on each user's bandwidth needs and reception conditions (receive signal strength).
  • a transmitter user 12i (1 ⁇ i ⁇ K) may adjust the assignment and allocation of spreading sequences for a particular sub-channel based on a detected signal strength of this sub-channelat the input of a corresponding receiver 14j (1 ⁇ j ⁇ L) .
  • the power of a given sub-channel e.g. a forward channel from a transmitter 121 at the hub to user 14j
  • the total power of all subchannels may remain the same.
  • the particular approach may depand, for example, on QoS (Quality of Service) considerations.
  • the present invention may provide data rate and signal power flexibility between a transmitter and a corresponding receiver.
  • the data at each sub-channel may be sent according to the DNB-S format, and filtering of multicast data may be achieved using a user's ID, IP addresses, PID numbers or some other method.
  • Transmitter 12 may include a data source 20, a preamble generator 22, one or more DNB-S modulators 24, one or more direct sequence spreaders 26, a sequences generator 27 and a timing generator 28.
  • the data source 20 may either be a data channel from some outside data source or may a locally generated data.
  • the source data may include redundancy bits produced by a Forward Error Correction (FEC) algorithm (e.g Turbo FEC).
  • FEC Forward Error Correction
  • the timing of the data supplied may be controlled by the timing generator 28.
  • Preamble generator 22 may be used to generate a preamble signal which may enable receiver 14 (Fig. 1) to synchronize to the received signal's time of arrival in burst mode transmissions. In a non-burst/continuous transmission mode, receiver 14 may synchronize to the received signal itself.
  • Each DNB-S modulator 24 may perform real or complex base-band data modulation and conversion to IF (Intermediate Frequency).
  • the DNB-S modulators may be standard DNB-S modulators.
  • Direct sequence Spreaders 26 may perform spreading by real/complex multiplication with the spreading sequence supplied by the sequences generator. Chip pulse shape filtering may also be performed by the direct sequence Spreader26. At each transmitter, the outputs of the direct sequence spreaders 26 may be weighted (given specific power) and summed up such as to keep the total output power constant. Below is an equation for calculating output power. (1)
  • Sequences generator 27 may provide orthogonal sequences for spreading modulated source data, which spreading may be aligned according to a timing signal provided by the timing generator 28.
  • Fig 3 there is shown a diagram exemplifying sub-channels with data spreading.
  • the sub-channel that carries information Di may use spreading sequence
  • D ⁇ may be spread by sequence Si, the same for D ⁇ 2 , etc.
  • the sub-channel that carries mform tinn D 2 may use spreading sequence S 2 .
  • Bit D ] may be spread by
  • the sub-channel that carries information D may use spreading sequence SM- Bit DM I may be spread by sequence S , the same for DM2, etc.
  • sequences SI...S M may be that they have to be orthogonal, or with minimal cross correlation.
  • time alignment may be required, in which all the sequences change at the same time, as depicted in Fig. 3.
  • Fig 4 diagram of a transmit data format.
  • the preamble may be required for the receiver in some applications to synchronize on the start of transmission.
  • the data payload may be spread as depicted in Fig. 3.
  • Dn.. DMI are grouped together, and after that D ⁇ 2 .. DM 2 , and so on.
  • Timing generator 28 may supply the proper timing signal for the data modulation and direct sequence spreading according to Figs. 3 and 4, thereby allowing multi-users on the same bandwidth.
  • Receiver 14 may include a band pass filter and amplifier (BPF & AMP) 30, a RF splitter 32, one or more direct sequence de-spreaders 34, data demodulators 36, a preamble acquisition 38, timing tracking loop 40, sequences generator 42, and routing & data filtering 44.
  • BPF & AMP band pass filter and amplifier
  • BPF & AMP 30 may perform RF front-end amplification and band pass filtering.
  • RF splitter 32 may perform splitting of the received signal and may apply its output to the direct sequence despreaders 34, which despreaders may perfo ⁇ n real/complex multiplication of the received signal with the sequence supplied by the sequences generator.
  • Data demodulator 36 may perform real/complex base-band data demodulation, including down conversion and coherent phase tracking when applicable.
  • the outputs of each of the data demodulators may be applied to a base-band processing block may include FEC decoding algorithm, IP assembly and data filtering.
  • a performance measure process which may indicate a signal strength of the received sub-channel may be performed at the base-band processing block.
  • the performance measure may include error detection and a calculation of bit error rate value.
  • the performance measure may be averaged over some period of time, and if the resulting average is below a predefined threshold, an indication to boost the sub-channel's signal power may be sent via a return channel to the corresponding transmitter producing the signal.
  • the signal power or strength may be boosted according to the present invention. That is, an indication may be sent, via the return channel, to the transmitter at the hub to increase the power of the sub channel that may received by this receiver until the performance measure for this channel is above a given threshold.
  • the hub may use a resource allocation system (equivalent of DAMA) to decide which (if any) of sub-channel to disconnect when one or more of the subchamiels needs a boost for its transmitted power.
  • Preamble acquisition unit 38 may perform a search for a preamble by correlation with the M sub-channels' signals and comparing to a predefined threshold. When the preamble is found, the system may enter track mode, until the end of reception or until signal loss.
  • Timing tracking loop 40 may perform time tracking of the sub-channel's sequences timing and may supply advance/retard commands to the sequences generator 38.
  • Sequences generator 42 may generate the orthogonal sequences required for despreading a sub-channel.
  • the sequence generator may produced spreading sequences aligned in time according to commands from the timing tracking loop 40.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

As part of the present invention, there is a transmitter including a sequence generator to produce two or more substantially orthogonal sequences and two or more spreaders to spread a modulated data signal according to a sequence produced by the sequence generator. Each said spreader may use a sequence substantially orthogonal to a sequence used by the other spreader, and the modulated data signal spread by each spreader may be derived from a sub-channel that is a portion of a single data stream.

Description

VARIABLE DATA RATE AND MULTI-POWER LEVEL MODEM
Field of Invention
[001] The present invention relates generally to digital communication systems. More specifically, the present invention relates to a variable bandwidth and variable signal power level modem.
Background
[002] Modems, also known as modulators-demodulators, are well known in the art of communications. There are various modulation methods presently known and various modems which operate using one or more of these modulation methods. Among the methods presently used are Quadrature Amplitude Modulation (QAM), Quadrature Phase Shift Keying (QPSK), and Spread Spectrum methods (both direct sequence-CDMA and frequency hopping). Modems may transmit and receive data over various mediums including coax cable, twisted pair, fiber-optic strands, and in air (effectively no medium). [003] Each of the mediums over which modems may communicate has its own benefits and drawbacks. Drawbacks of a given transmission medium may include signal attenuation and noise interference. In communication applications where signal interference is a factor which needs to be overcome or minimized, both data rate and signal power regulation may be required. For the most part, however, modems of the prior art operate at fixed bandwidths and with fixed signal power limitations.
Summary of the Present Invention
[004] The present invention is a wireless Direct Sequence Spread Spectrum ("DSSS") or Code Division Multiple Access ("CDMA") modem including a controller which may regulate the number of modulators and/or spreaders allocated to sources of data streams based on data-rate requirements and/or based on signal power requirements. All spreading sequences may belong to the same family of orthogonal sequences. A source of a data stream (may be a multiplex of several sources like IP data, video, etc.) may spurted among few modulators each may transmit a portion of the data stream and may use an associated spreading sequence that belongs to same family. In order to increase the bandwidth or data-rate at which a source data stream may be transmitted to a particular user, the modem controller may increase the number of Modulators that this user receives. In order to increase the power at which the source data stream (or portion of the data that belongs to this stream) may be transmitted, the modem controller may increase the power of the modulator(s) that transmit the same source data stream, or portion of it. The variation at the power of the modulators may be such that the over all power of all the modulators remains the same. [005] In some embodiments of the present invention, the wireless modem may be used as part of a point to multi-point or mesh communication system. As part of a point to multi-point system, a modem at a central hub may communicate with two or more remote wireless modems over a common carrier signal, also referred to as a communications channel or frequency band. The common communication channel or frequency band may be partitioned into multiple communication sub-channels, where each sub-channel may be allocated to one or more users and associated with a modulator and an orthogonal spreading sequence. The bandwidth received by a remote modem may be increased by receiving one or more sub-channels. A sub-channel's power may be increased where the over all power of all transmitted sub channels remains the same.
Brief Description of the Drawings
[006] The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which: [007] Fig. 1 is a block diagram of several transmitters and several receivers operated and constructed according to an embodiment of the present invention;
[008] Fig. 2 is a block diagram of any one of the transmitters shown in Fig. 1, operated and constructed according to an embodiment of the present invention;
[009] Fig. 3 is a block diagram representing the timing alignment of transmitted sub-channels according to an embodiment of the present invention; [0010] Fig. 4 is a block diagram of a transmit data format according to an embodiment of the present invention; and
[0011] Fig. 5 is a block diagram of any one of the receivers shown in Fig. 1, operated and constructed according to an embodiment of the present invention.
[0012] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.
Detailed Description of The Invention
[0013] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without tliese specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.
[0014] Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing tenns such as "processing", "computing", "calculating", "determining", or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices. [0015] Embodiments of the present invention may include apparatuses for performing the operations herein. This apparatus may be specially constructed for the desired purposes, or it may comprise a general purpose computer or Digital Signal Processor ("DSP") selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs) electrically programmable read-only memories (EPROMs), electrically erasable and programmable read only memories (EEPROMs), magnetic or optical cards, or any other type of media suitable for storing electronic instructions, and capable of being coupled to a computer system bus.
[0016] The processes and displays presented herein are not inherently related to any particular computer or other apparatus. Various general purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the desired method. The desired structure for a variety of these systems will appear from the description below. In addition, embodiments of the present invention are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the inventions as described herein.
[0017] The present invention is a wireless Direct Sequence Spread Spectrum ("DSSS") or Code Division Multiple Access ("CDMA") modem. According to some embodiments of the present invention the wireless Direct Sequence Spread Spectrum ("DSSS") or Code Division Multiple Access ("CDMA") modem may include a controller which may regulate the number of modulators and/or spreaders allocated to a source data stream based on predetermined parameters, for example, data-rate requirements and/or based on signal power requirements. The modem controller may split the source data between wo or more modulators and their associated spreaders, each spreader may use a separate orthogonal spreading sequence. In order to increase the bandwidth or data-rate at which a source data stream is to be transmitted to a particular user (a remote modem), the modem controller may increase the number of Modulators that this user receives. In order to increase the power at which the source data stream (or portion of the data that belongs to this stream) is to be transmitted, the modem controller may increase the power of the modulator(s) that transmit the same source data stream, or portion of it. The variation at the power of each of the modulators may be such that the over all power of all the modulators remains the same.In some embodiments of the present invention, the wireless modem may be used as part of a point to multi-point or mesh communication system. As part of a point to multi-point system, a modem at a central hub may communicate with two or more remote wireless modems over a common carrier signal, also referred to as a communications channel or frequency band. The common communication channel or frequency band may be partitioned into multiple communication sub-channels, where each sub-channel may be allocated to one or more users and may be associated with a modulator and a spreading sequences, where each spreader may use an orthogonal spreading sequence. In order to increase the bandwidth or data-rate at which a source data stream is to be transmitted to a particular user (a remote modem), the modem controller may increase the number of Modulators that this user receives. A sub-channel's power may be increased such as the power of all the modulators remains the same. [0018] The present invention may be applicable to a variety of data communication systems and networks, including terrestrial and satellite point to multi-point or mesh networks. The following description may be applicable to any such communication systems.
[0019] Turning now to Fig. 1, there is shown a simplified block diagram of several transmitter users, 12χ to 12K, and several receivers, 14i to 14 , which may be used as part of a communication system or network 10 according to the an embodiment of the present invention. The communication system 10 may transfer data over one or more carrier frequencies, frequency bands or communication channels. Each communication channel may be parsed in multiple communication sub-channels. The topology of the network may be, for example, either that of a point to multi-point (also known as star) network, where a single hub may communicate with multiple users simultaneously, or the topology may be that of a mesh network, where users can communicate directly between themselves. Each user of the network or system may have transmitter user 12 and receiver 14. In a star or point to multi-point network, a hub may have multiple transmitter users 12 and multiple receivers 14, where each receiver/transmitter pair is associated with one or more users. In some embodiments of the present invention other network topology configuration may be used.
[0020] According to some embodiments of the present invention, direct sequence spread spectrum ("DSSS") or code division multiple access ("CDMA") may be used as the communication method between the transmitter users 12 and receivers 14. A given carrier signal or frequency band may be termed "communication channels", and the total bandwidth ("TBW") or total data rate ("TDR") from a transmitter of the communication channel may be parsed into two or more sub-channels, where each sub-channel may be associated with one a separate orthogonal spreading sequences. All the spreading sequences used by a single transmitter may belong to a single set of orthogonal spreading sequences, and the bandwidth or data rate associated with a given spreading sequence, termed the basic data rate ("BDR") may be approximately equal to the TDR divided by the total number of orthogonal spreading sequences in the set of orthogonal spreading sequences. Each sub-channel may have a data rate that is substantially equal to BDR. For example, if the total available bandwidth on a 812MHz carrier signal is 5Mhz and a set of 10 orthogonal spreading sequences are used as part of a DSSS/CMDA communications system using the 812MHz carrier signal, the basic data rate would be 0.5Mbits for 0.5Mhz bandwidth. DSSS or CDMA communication methodology is well known in the communications field. The practice of using separate orthogonal spreading sequences or codes to split a single carrier signal, bandwidth or channel capable of supporting a maximum data rate into multiple communication sub-channels, is also well known. The present invention may be implemented using any or all DSSS/CDMA standards known today or to be devised in the future.
[0021]System 10 may include a hub with one or more transmitter users 12, transmitter .iser 12] to transmitter 12κ, and L users, where each user may have at least one receiver 14. Each user's receiver is shown as 141 to user 14 . Each transmitter user 12 may transmit some source data or data stream Dk, at a data rate DRk, having a transmission pυw ei PT - AS an example, transmitter 12j may transmit data stream D at data rate DR] and at a power level PTi. The data rate DRk at which a transmitter may transmit an associated data stream Dk may be a multiple of the transmitters subchannels basic data rate BDR, where DRk = m * BDR, m ? M (M = the max number of spread sequences in an orthogonal set of spreading sequences). It is noted that one or more subchannels can be received by more then a single user.
[0022] In some embodiments of the present invention, the use of allocated spreading sequences may allow multi-user communication on the same carrier frequency, band or channel. Each user in a communication network according to embodiments of the present invention may be assigned a unique ID, much like an IP address which may be assigned in an Internet Protocol ("IP") Network. Each user may also be assigned one or more orthogonal spreading sequences, depending on each user's bandwidth needs and reception conditions (receive signal strength).
[0023] In cases the strength of a signal received by a user is below some threshold value, it may be possible to trade off data rate for quality of reception. A transmitter user 12i (1< i < K) may adjust the assignment and allocation of spreading sequences for a particular sub-channel based on a detected signal strength of this sub-channelat the input of a corresponding receiver 14j (1< j < L) . The power of a given sub-channel (e.g. a forward channel from a transmitter 121 at the hub to user 14j) may be increased. However, the total power of all subchannels may remain the same. Therefore, when a power of a subchannel is increased, either the power of the other sub-channels may be reduced, or the number of the sub-channels may be to be reduced, or both. The particular approach may depand, for example, on QoS (Quality of Service) considerations.
[0024] Therefore, the present invention may provide data rate and signal power flexibility between a transmitter and a corresponding receiver. According to some embodiments of the present invention, the data at each sub-channel may be sent according to the DNB-S format, and filtering of multicast data may be achieved using a user's ID, IP addresses, PID numbers or some other method.
[0025] Turning now to Fig. 2, there is shown a block diagram of transmitter 12 according to some embodiment of the present invention. Transmitter 12 may include a data source 20, a preamble generator 22, one or more DNB-S modulators 24, one or more direct sequence spreaders 26, a sequences generator 27 and a timing generator 28.
The data source 20 may either be a data channel from some outside data source or may a locally generated data. The source data may include redundancy bits produced by a Forward Error Correction (FEC) algorithm (e.g Turbo FEC). The timing of the data supplied may be controlled by the timing generator 28. Preamble generator 22 may be used to generate a preamble signal which may enable receiver 14 (Fig. 1) to synchronize to the received signal's time of arrival in burst mode transmissions. In a non-burst/continuous transmission mode, receiver 14 may synchronize to the received signal itself. [0026] Each DNB-S modulator 24 may perform real or complex base-band data modulation and conversion to IF (Intermediate Frequency). In some embodiment's of the present method, the DNB-S modulators may be standard DNB-S modulators. Direct sequence Spreaders 26 may perform spreading by real/complex multiplication with the spreading sequence supplied by the sequences generator. Chip pulse shape filtering may also be performed by the direct sequence Spreader26. At each transmitter, the outputs of the direct sequence spreaders 26 may be weighted (given specific power) and summed up such as to keep the total output power constant. Below is an equation for calculating output power. (1)
M
∑tkSkWk = P k=\
Where
tk - Toggle function: 1 (if branch k is connected), 0 (if branch k is disconnected)
Sk - Output of data spreader k
Wk - Weighting function (or power gain) of branch k
P - Total power of transmitter.
[0027] It is noted that sometimes, in order not to pass the limit of max power P, some of the branches may be disconnected. In that case the total data rate out from the transmitter may be reduced.
[0028] Sequences generator 27 may provide orthogonal sequences for spreading modulated source data, which spreading may be aligned according to a timing signal provided by the timing generator 28.
[0029] Turning now to Fig 3, there is shown a diagram exemplifying sub-channels with data spreading. The sub-channel that carries information Di may use spreading sequence
Si. hi: Dπ may be spread by sequence Si, the same for Dι2, etc. The sub-channel that carries mform tinn D2 may use spreading sequence S2. Bit D ] may be spread by
; ., : ιiL S2, the same for D22, etc. The sub-channel that carries information D may use spreading sequence SM- Bit DMI may be spread by sequence S , the same for DM2, etc.
[0030] The selection criteria for sequences SI...SM may be that they have to be orthogonal, or with minimal cross correlation. To exploit the full advantage of the orthogonality of the sequences time alignment may be required, in which all the sequences change at the same time, as depicted in Fig. 3.
[0031] Reference is now made to Fig 4, diagram of a transmit data format. The preamble may be required for the receiver in some applications to synchronize on the start of transmission. The data payload may be spread as depicted in Fig. 3. Dn.. DMI are grouped together, and after that Dι2 .. DM2 , and so on.
[0032] Timing generator 28 may supply the proper timing signal for the data modulation and direct sequence spreading according to Figs. 3 and 4, thereby allowing multi-users on the same bandwidth.
[0033] Turning now to Fig. 5, there is shown a block diagram of a receiver 14 according to some embodiment of the present invention. Receiver 14 may include a band pass filter and amplifier (BPF & AMP) 30, a RF splitter 32, one or more direct sequence de-spreaders 34, data demodulators 36, a preamble acquisition 38, timing tracking loop 40, sequences generator 42, and routing & data filtering 44.
[0034] BPF & AMP 30 may perform RF front-end amplification and band pass filtering. RF splitter 32 may perform splitting of the received signal and may apply its output to the direct sequence despreaders 34, which despreaders may perfoπn real/complex multiplication of the received signal with the sequence supplied by the sequences generator. Data demodulator 36 may perform real/complex base-band data demodulation, including down conversion and coherent phase tracking when applicable. The outputs of each of the data demodulators (including soft information) may be applied to a base-band processing block may include FEC decoding algorithm, IP assembly and data filtering.
[0035] A performance measure process, which may indicate a signal strength of the received sub-channel may be performed at the base-band processing block. The performance measure may include error detection and a calculation of bit error rate value. The performance measure may be averaged over some period of time, and if the resulting average is below a predefined threshold, an indication to boost the sub-channel's signal power may be sent via a return channel to the corresponding transmitter producing the signal. The signal power or strength may be boosted according to the present invention. That is, an indication may be sent, via the return channel, to the transmitter at the hub to increase the power of the sub channel that may received by this receiver until the performance measure for this channel is above a given threshold. It is noted that increasing the power of one or more spreaded sub-channels at the transmitter may force it to reduce the number of the spreading channels according to Equation (1). The hub may use a resource allocation system (equivalent of DAMA) to decide which (if any) of sub- channel to disconnect when one or more of the subchamiels needs a boost for its transmitted power. Preamble acquisition unit 38 may perform a search for a preamble by correlation with the M sub-channels' signals and comparing to a predefined threshold. When the preamble is found, the system may enter track mode, until the end of reception or until signal loss. [0036] Timing tracking loop 40 may perform time tracking of the sub-channel's sequences timing and may supply advance/retard commands to the sequences generator 38.
[0037] Sequences generator 42 may generate the orthogonal sequences required for despreading a sub-channel. The sequence generator may produced spreading sequences aligned in time according to commands from the timing tracking loop 40.
[0038] It will be appreciated by those skilled in the art that the above described invention may provide for multiple-user on the same carrier frequency, f equency bandwidth or channel by parsing the channel into sub-channels having variable data rates and variable signal power strengths. [0039] It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the claims that follow:

Claims

ClaimsWhat is claimed:
1. A transmitter comprising:
a data splitter, said data splitter being adapted to split the
modulated data source into one or more sub-channels
a sequence generator, said sequence generator being adapted to
produce two or more substantially orthogonal sequences;
two or more spreaders, said spreaders being adapted to spread a
modulated data signal according to a sequence produced by said sequence generator; and
wherein each said spreader uses a sequence substantially orthogonal to a sequence used by the other said spreader, and the
modulated data signal spread by each said spreader is derived from a
sub-channel.
2.The transmitter according to claim 1 , wherein the modulated data signals
for each of said spreaders are derived from separate data segments of
the single data stream.
3.The transmitter according to claim 1 , wherein the modulated data signals
for each of said spreaders are derived from the same data segment of the
single data stream.
4.The transmitter according to claim 1 , further comprising a preamble generator to produce a preamble for segments of the single data stream.
5.The transmitter according to claim 4, further comprising a timing generator to produce a timing signal for said preamble generator, wherein said timing generator produces a timing signal based on a characteristic of the single data stream.
6.A receiver comprising:
a sequence generator, said sequence generator being adapted to produce two or more substantially orthogonal sequences;
two or more de-spreaders , said de-spreaders being adapted to despread a received data signal according to a sequence produced by said sequence generator; and
wherein each said de-spreader uses a sequence substantially orthogonal to a sequence used by the other said despreader, and the received signal despread by each said despreader being derived from a sub-channel that is a portion of a single data stream.
7.The receiver according to claim 6, further comprising a demodulator to demodulate the output of said despreads.
S.The receiver according to claim 7, wherein the demodulated output of said two or more despreaders is combined in serial.
9.The receiver according to claim 7, wherein the demodulated output of said two or more despreaders is combined in parallel.
lO.The receiver according to claim 7, further comprising a preamble acquisition unit to acquire a preamble from an output of said demodulator.
11. The receiver according to claim 10, further comprising a timing tracking loop to produce a timing signal for said sequence generator, wherein said timing tracking loop produces a timing signal based on an output of said preamble acquisition unit and a characteristic of the received data signal.
PCT/IL2002/000585 2001-07-18 2002-07-17 Variable data rate and multi-power level cdma modem WO2003009488A2 (en)

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Applications Claiming Priority (2)

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IL144419 2001-07-18
IL14441901A IL144419A0 (en) 2001-07-18 2001-07-18 Multi-mode modem

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2404534A (en) * 2003-07-26 2005-02-02 Motorola Inc CDMA transmitter which inputs the same signal to at least two parallel spreading elements and applies identical spreading codes at these spreading elements
US20120320900A1 (en) * 2011-05-19 2012-12-20 Empire Technology Development Llc Transmitting or receiving data via code division multiple access using highly correlated spreading codes assigned to a user

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5734646A (en) * 1995-10-05 1998-03-31 Lucent Technologies Inc. Code division multiple access system providing load and interference based demand assignment service to users
JP3385299B2 (en) * 1996-05-20 2003-03-10 三菱電機株式会社 Spread spectrum communication equipment

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2404534A (en) * 2003-07-26 2005-02-02 Motorola Inc CDMA transmitter which inputs the same signal to at least two parallel spreading elements and applies identical spreading codes at these spreading elements
GB2404534B (en) * 2003-07-26 2005-08-10 Motorola Inc A code division multiple access transmitter and a method of oepration therefor
US20120320900A1 (en) * 2011-05-19 2012-12-20 Empire Technology Development Llc Transmitting or receiving data via code division multiple access using highly correlated spreading codes assigned to a user
US8867515B2 (en) * 2011-05-19 2014-10-21 Empire Technology Development Llc Transmitting or receiving data via code division multiple access using highly correlated spreading codes assigned to a user

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WO2003009488A3 (en) 2003-03-27
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