WO2000052871A1 - Emetteur-recepteur a gain de codage reglable - Google Patents

Emetteur-recepteur a gain de codage reglable Download PDF

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Publication number
WO2000052871A1
WO2000052871A1 PCT/US1999/025233 US9925233W WO0052871A1 WO 2000052871 A1 WO2000052871 A1 WO 2000052871A1 US 9925233 W US9925233 W US 9925233W WO 0052871 A1 WO0052871 A1 WO 0052871A1
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WO
WIPO (PCT)
Prior art keywords
coding gain
receive
rate
transmit
data
Prior art date
Application number
PCT/US1999/025233
Other languages
English (en)
Inventor
Terry L. Cole
Original Assignee
Legerity, Inc.
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 Legerity, Inc. filed Critical Legerity, Inc.
Publication of WO2000052871A1 publication Critical patent/WO2000052871A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0059—Convolutional codes
    • H04L1/006—Trellis-coded modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0044—Arrangements for allocating sub-channels of the transmission path allocation of payload

Definitions

  • This invention relates generally to communication systems, and, more particularly, to a transceiver with an adjustable coding gain to control the complexity of the transceiver processing algorithms.
  • DSL technologies leave the POTS service undisturbed.
  • Traditional analog voice band interfaces use the same frequency band, 0-4 Kilohertz (kHz), as telephone service, thereby preventing concurrent voice and data use.
  • a DSL interface operates at frequencies above the voice channels from 100 kHz to 1.1 Megahertz (MHz).
  • MHz Megahertz
  • DSL systems use digital signal processing (DSP) to increase throughput and signal quality through common copper telephone wire.
  • DSL systems provide a downstream data transfer rate from the DSL Point-of-Presence (POP) to the subscriber location at speeds of about 1.5 Megabits per second (MBPS).
  • POP Point-of-Presence
  • MBPS Megabits per second
  • the transfer rate of 1.5 MBPS, for instance, is fifty times faster than a conventional 28.8 kilobits per second (KBPS) transfer rate.
  • DSL Digital Subscriber Line
  • Asymmetrical Digital Subscriber Line (ADSL) technology is described in ANSI T1.413 Issue 2.
  • ADSL modems use two competing modulation schemes: discrete multi-tone (DMT) and carrierless amplitude/phase modulation (CAP).
  • DMT is the standard adopted by the American National Standards Institute.
  • the technology employed by DMT ADSL modems is termed discrete multi-tone.
  • the standard defines 256 discrete tones. Each tone represents a carrier signal that can be modulated with a digital signal for transmitting data.
  • the specific frequency for a given tone is 4.3125 kHz times the tone number.
  • Tones 1-7 are reserved for voice band and guard band (i.e., tone 1 is the voice band and tones 2-7 are guard bands). Data is not transmitted near the voice band to allow for simultaneous voice and data transmission on a single line.
  • the guard band helps isolate the voice band from the ADSL data bands.
  • a splitter may be used to isolate any voice band signal from the data tones.
  • Tones 8-32 are used to transmit data upstream (i.e., from the user), and tones 33-256 are used to transmit data downstream (i.e., to the user).
  • all the data tones 8-256 may be used for downstream data, and upstream data present on tones 8-32 would be detected using echo cancellation. Because more tones are used for downstream communication than for upstream communication, the transfer is said to be asymmetric.
  • the modems on both sides of the connection sense and analyze which tones are less affected by impairments in the telephone line. Each tone that is accepted is used to carry information. Accordingly, the maximum capacity is set by the quality of the telephone connection.
  • a central office (CO) modem communicates with a customer premise (CP) modem.
  • the CP modem is typically installed in a home or office.
  • Techniques have been developed to increase the transfer rate and/or accuracy of the modem data exchange. These techniques typically trade a more complicated processing algorithm for such improvements. The increased complexity results in greater demands on the digital signal processor (DSP) used to implement the modem functionality.
  • DSP digital signal processor
  • Exemplary techniques known in the art for providing such an improvement include constellation encoding with trellis coding, Reed-Solomon forward error correction coding, and spectrum overlap (i.e., transmit and receive signal spectrums overlap and are separated by echo cancellation).
  • constellation encoding with trellis coding e.g., Reed-Solomon forward error correction coding
  • spectrum overlap i.e., transmit and receive signal spectrums overlap and are separated by echo cancellation.
  • coding gain techniques Collectively, these techniques to increase data rate and/or decrease error rate, and others like them, are hereinafter referred to as coding gain techniques.
  • the specific algorithms used to implement these and other coding gain techniques are known to those of ordinary skill in the art, and they are not discussed in greater detail herein for clarity purposes.
  • the ADSL standard includes exemplary techniques for accomplishing coding gain.
  • the DSP must be equipped to handle the processing load under worst case conditions (e.g., line length, noise, distortion, etc.).
  • the modem communicates whether or not it supports trellis coding or echo cancellation. Thereafter, the DSP must be able to support the coding gain techniques regardless of line conditions. For example, trellis coding is known to allow communication on longer lines. The complexity of trellis coding is proportional to the number of tones and the bit rate of the connection. If the developer of a modem wishes to includes trellis coding, the DSP must be capable of performing trellis coding on both short (high bit rate, high number of tones) and long (lower bit rate, less tones) lines. This significantly increases the cost of a modem equipped with trellis coding.
  • the present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
  • a transceiver including a receive unit, a transmit unit, and control logic.
  • the receive unit is adapted to receive data at a receive rate.
  • the transmit unit is adapted to transmit data at a transmit rate.
  • the control logic is adapted to receive a first coding gain parameter.
  • At least one of the receive and transmit units is adapted to implement a coding gain technique based on at least the first coding gain parameter and at least one of the receive rate and the transmit rate.
  • a method for determining use of a coding gain technique in a transceiver.
  • the transceiver is capable of receiving data at a receive rate and transmitting data at a transmit rate.
  • the method includes receiving a first coding gain parameter.
  • the coding gain technique is implemented based on at least the first coding gain parameter and at least one of the receive rate and the transmit rate.
  • FIG. 1 is a block diagram of a communications system in accordance with the present invention
  • Figure 2 is a simplified block diagram of a modem in accordance with the present invention.
  • Figure 3 is a simplified functional block diagram of the modem of Figure 2. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
  • the communications system 10 includes a first modem 15 coupled to a second modem 20 through a connection 25.
  • the first modem 15 is located at a customer premise 30, and the second modem 20 is part of a central office 35.
  • the connection 25 is an ordinary twisted pair connection, as is common in present-day telephone networks.
  • other connection types e.g., wireless, cellular, etc.
  • the second modem 20 may not be part of the central office 35, but rather the second modem 20 may be installed in a second customer premise (not shown).
  • the modems 15, 20 are described as they might be implemented under the ADSL standard. It is contemplated that the techniques described herein may be applied to other communication protocols, depending on the specific implementation.
  • the second modem 20 acts as a gateway to a larger communications network (not shown), such as a local or wide area network, or the Internet.
  • a larger communications network such as a local or wide area network, or the Internet.
  • the first modem 15 establishes a connection to the communications network (not shown) through the second modem 20.
  • the first and second modems 15 and 20 complete a training process whereby an initial bit loading technique is employed to establish the throughput available for communication between the modems 15, 20.
  • the modems 15, 20 negotiate coding gain options.
  • the present invention is described as it may be implemented in a modem, it is contemplated that, in light of this disclosure, the invention may be applied to any type of transceiver, including, but not limited to, a modem or some other wired or wireless communication device.
  • the modem 100 may be the first modem 15 or the second modem 20.
  • the modem 100 includes a digital interface 101 for interfacing with the system (not shown) (i.e., computer or communications system to which the modem 100 is connected).
  • the digital interface 101 receives digital data for transmission by the modem 100 and provides digital data received by the modem 100.
  • a processing unit 102 and memory 103 provide processing resources for implementing the algorithms (i.e., coding, modulating, demodulating, etc.) required to operate the modem 100.
  • An analog interface 104 connects the modem 100 to an external connection, such as a phone line (not shown).
  • a simplified functional block diagram of a modem 100 is provided.
  • the modem 100 includes transmit, receive, and control functional blocks 105, 110, 115.
  • the transmit block 105 includes an encoding unit 120 adapted to receive outgoing digital data over a data-out line 122.
  • the encoding unit 120 performs functions such as cyclic redundancy checking (CRC), scrambling, forward error correction (Reed-Solomon coding), and interleaving.
  • CRC cyclic redundancy checking
  • Reed-Solomon coding forward error correction
  • interleaving interleaving.
  • the complexity of the processing algorithm for the encoding unit 120 depends, at least in part, on the codeword length specified for the forward error correction function. As stated above, the actual algorithms used to implement these functions are known to those of ordinary skill in the art.
  • the data in binary form is grouped into sets referred to as frames.
  • a plurality of frames i.e., 68 in the illustrated embodiment
  • the transmit block 105 also includes a modulator 125 that receives the data frames from the encoding unit 120 and modulates a carrier or carriers with the data.
  • the modulator 125 performs tone ordering, constellation encoding, gain scaling, and an inverse discrete Fourier transform (IDFT) function to provide time domain waveform samples.
  • IDFT inverse discrete Fourier transform
  • a cyclic prefix (CP) unit 130 performs cyclic prefix insertion (i.e., a subset of the output samples from the modulator 125 is replicated and prepended to the existing output samples to provide an overlap and allow for better symbol alignment).
  • a buffer 132 stores the samples received from the CP unit 130.
  • a digital to analog (D/A) converter and filter 135 converts the samples from the CP unit 130 to an analog waveform suitable for transmission over the connection 25 through an external line interface 140.
  • the complexity of the processing algorithm for the modulator 125 depends, at least in part, on the type of constellation encoding algorithm used (i.e., with or without trellis coding).
  • the receive block 110 includes an analog to digital (A/D) converter and filter 145 that receives an analog waveform over the connection 25 and samples the analog waveform to generate a time domain digital signal.
  • An alignment and equalizing unit 150 performs functions known in the art, such as symbol alignment and time domain equalization. In time domain equalization, because the tones are at different frequencies, certain frequencies travel faster than others, and as such, all the tones do not arrive at same time. The time domain equalization function of the alignment and equalizing unit 150 delays the faster tones to compensate for the propagation speed differences.
  • the alignment and equalizing unit 150 also performs gain control to increase the amplitude of the received signal.
  • a demodulator 155 receives the time domain samples from the alignment and equalizing unit 150 and converts the time domain data to frequency domain data.
  • the demodulator 155 also performs an echo cancellation function to derive the received signal if the transmit and receive spectrums of the modem 100 and the interfacing modem (not shown) overlap.
  • the demodulator 155 performs a slicing function to determine constellation points from the constellation encoded data, a demapping function to map the identified constellation point back to bits, and a decoding function (e.g., Viterbi decoding if trellis constellation coding is employed).
  • the complexity of the processing algorithm for the demodulator 155 depends, at least in part, on whether trellis coding was used by the transmitter (not shown) of the interfacing modem (not shown) and whether echo cancellation is required. In the case where the modem operates using the ADSL protocol, the demodulator 155 also performs tone deordering to reassemble the bytes that were divided among the available tones.
  • a decoding unit 160 in the receive block 110 performs forward error correction, CRC checking, and descrambling functions on the data_ received from the demodulator 155.
  • the reconstructed data provided by the decoding unit 160 represents the sequential binary data that was sent by the interfacing modem (not shown).
  • the reconstructed data is provided to a data-in line 165.
  • complexity of the processing algorithm for the decoding unit 160 depends, at least in part, on the codeword length specified for the forward error correction function.
  • the control block 115 includes control logic 170 and a configuration register 175.
  • the configuration register stores data useful for configuring the modem 100.
  • the control logic 170 determines relevant attributes of the connecting channel and establishes transmission and processing characteristics suitable for that channel.
  • the transmit unit 105 shares with its corresponding far-end receive unit (not shown) certain transmission settings that it expects to encounter. For example, the transmit unit
  • the transmit unit 105 communicates to its far-end receive unit (not shown) the number of bits and relative power levels to be used on each DMT tone.
  • the transmit unit 105 also communicates a configuration message signal based on the information contained in the configuration register 175.
  • the configuration message signal includes vendor identification information, transmit power level, trellis coding option, echo canceling option, Reed-Solomon codeword length, etc.
  • the control logic 170 determines the coding gain parameters that can be supported by the modem 100 and the interfacing modem (not shown). There are numerous methods by which the control logic 170 may determine the coding gain techniques to support, and an illustrative sample of some of these methods are provided. In light of this disclosure, other evaluation techniques to determine the coding gain techniques may be developed.
  • a first example illustrates how the control logic 170 may decide under what conditions to support trellis coding.
  • the modem 100 cannot support worst case trellis coding, but has enough processing resources (e.g., DSP cycles, memory, power, etc.) to support trellis coding on a limited basis (i.e., long lines with less tones and bits).
  • the control logic 170 stores a multi-bit trellis coding option parameter (TC Param) 180 in the configuration register 175.
  • the value of the trellis coding option parameter 180 corresponds to the ability of the modem 100 to handle trellis coding under different environments.
  • the specific bit value stored in the configuration register 175 for the trellis coding option parameter 180 is application dependent, and a variety of schemes are possible.
  • a high trellis coding option parameter 180 indicates that the modem 100 is capable of handling trellis coding under near worst case conditions.
  • a low trellis coding option parameter 180 indicates that the modem 100 is only capable of supporting trellis coding under less strenuous operating conditions
  • the trellis coding option parameter 180 may be based on actual measurements of the line conditions, such as estimated line lengths based on attenuation or estimated line capacity based on noise measurement, etc. Alternatively, the trellis coding option parameter 180 may be based on a worst case condition.
  • the modem 100 may be capable of supporting trellis coding if the transfer rate is less than 256 kbps.
  • the modem 100 may be capable of supporting trellis coding if the number of tones being used is less than 96, for example.
  • the trellis coding option parameter 180 may be based on an estimate of the actual processing resources available. Techniques for estimating processing resources (e.g., DSP cycles, memory, power, etc.) are known in the art.
  • Table 1 illustrates an exemplary relationship between the trellis coding option parameter 180 and the bandwidth at which trellis coding is supported.
  • the thresholds at which to support coding gain techniques may be based on available processing resources, worst case throughput, etc.
  • the number of bits in the trellis coding option parameter 180 may be varied depending on the degree of control required.
  • a similar table may be developed for other coding gain techniques.
  • the modem 100 may retrain with the interfacing modem (not shown) and specify a different trellis coding option parameter 180, including a trellis coding option parameter 180 that specifies no trellis coding.
  • control logic 170 determines the availability of echo cancellation or to specify the Reed-Solomon codeword length.
  • the control logic 170 stores a multi-bit echo cancellation option parameter (EC Param) 185, and a Reed-Solomon option parameter (RS Param) 190 in the configuration register 175.
  • the control logic 170 might choose some combination of coding gain techniques, depending on the specific characteristics of the connection. For example, the control logic 170 might elect to support trellis coding and not echo cancellation. It is contemplated that the modem 100 may negotiate with the interfacing modem (not shown) to determine the greatest common coding gain parameters supported.
  • the modem 100 can support trellis coding at a transfer rate of 1024 kbps, but the interfacing modem can only support trellis coding for connections less than 512 kbps, the lower of the two trellis coding option parameters 180 may be selected for use.
  • the modem 100 can support a 32-bit Reed-Solomon codeword length, but the interfacing modem (not shown) can only support a 16-bit codeword length, the lesser codeword length is selected.
  • Determining the conditions under which to support coding gain techniques has numerous advantages. Using negotiated coding gain parameters, rather that fixed, on/off parameters increases the flexibility for upgrade paths.
  • the modem 100 may operate with the highest common coding gain options, and if, for example, the interfacing modem (not shown) is upgraded, the modem 100 will adjust to the new operating environment and possibly increase its performance. Coding gain techniques can be implemented in products sooner because the threshold at which the modem 100 supports the techniques can be varied. Products can also be easily upgraded to increase the coding gain threshold from long loops, to medium loops, to all loops without requiring a new standard.
  • a modem 100 having a DSP (not shown) that cannot support the approximately 240 tone worst case processing load and at the same time support trellis coding can be configured to support trellis coding with, for example, 50 tones.
  • the threshold can be raised to support trellis coding with additional tones.

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  • Engineering & Computer Science (AREA)
  • Quality & Reliability (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Telephonic Communication Services (AREA)

Abstract

Un émetteur-récepteur (100) comprend une unité de réception (110), une unité d'émission (105), et une logique de commande (170). L'unité de réception (110) est conçue pour recevoir de données à un certain débit de réception. L'unité d'émission (105) est conçue pour émettre des données à un certain débit d'émission. La logique de commande (170) est conçue pour recevoir un premier paramètre de gain de codage. Au moins une des unités de réception et d'émission (110, 105) est conçue pour la mise en oeuvre d'une technique à gain de codage basée sur au moins le premier paramètre de gain de codage et sur au moins un des débit de réception et d'émission. Un procédé de détermination de l'utilisation de la technique à gain de codage dans un émetteur-récepteur (100) est décrit. L'émetteur récepteur (100) est capable de recevoir des données à au moins un débit de réception et d'émettre des données à un débit d'émission. Le procédé consiste à recevoir un premier paramètre de gain de codage. La technique à gain de codage est mise en oeuvre en fonction d'au moins un premier paramètre de gain de codage, à au moins un des débits de réception et d'émission.
PCT/US1999/025233 1999-03-02 1999-10-27 Emetteur-recepteur a gain de codage reglable WO2000052871A1 (fr)

Applications Claiming Priority (2)

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US26075099A 1999-03-02 1999-03-02
US09/260,750 1999-03-02

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4701923A (en) * 1985-01-14 1987-10-20 Oki Electric Industry Co., Ltd. Adaptively coded data communication system with half duplex and/or full duplex function
WO1997013388A1 (fr) * 1995-10-02 1997-04-10 Telefonaktiebolaget Lm Ericsson (Publ) Systeme et procede de codage, de modulation et d'attribution de creneau temporel souples dans un reseau de telecommunications radio
EP0841771A1 (fr) * 1996-11-12 1998-05-13 Alcatel Protocole d'initialisation pour débits de données adaptatifs et émetteur-récepteur correspondant
US5757813A (en) * 1995-10-18 1998-05-26 Telefonaktiebolaget Lm Ericsson Method for achieving optimal channel coding in a communication system
EP0905948A2 (fr) * 1997-09-25 1999-03-31 Motorola, Inc. Adaptation de débit pour ligne d'abonné numérique assymétrique en employant un nombre variable de sousporteuses

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4701923A (en) * 1985-01-14 1987-10-20 Oki Electric Industry Co., Ltd. Adaptively coded data communication system with half duplex and/or full duplex function
WO1997013388A1 (fr) * 1995-10-02 1997-04-10 Telefonaktiebolaget Lm Ericsson (Publ) Systeme et procede de codage, de modulation et d'attribution de creneau temporel souples dans un reseau de telecommunications radio
US5757813A (en) * 1995-10-18 1998-05-26 Telefonaktiebolaget Lm Ericsson Method for achieving optimal channel coding in a communication system
EP0841771A1 (fr) * 1996-11-12 1998-05-13 Alcatel Protocole d'initialisation pour débits de données adaptatifs et émetteur-récepteur correspondant
EP0905948A2 (fr) * 1997-09-25 1999-03-31 Motorola, Inc. Adaptation de débit pour ligne d'abonné numérique assymétrique en employant un nombre variable de sousporteuses

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