EP0919087A4 - Systeme, dispositif et procede de communication selon un code composite - Google Patents

Systeme, dispositif et procede de communication selon un code composite

Info

Publication number
EP0919087A4
EP0919087A4 EP97954558A EP97954558A EP0919087A4 EP 0919087 A4 EP0919087 A4 EP 0919087A4 EP 97954558 A EP97954558 A EP 97954558A EP 97954558 A EP97954558 A EP 97954558A EP 0919087 A4 EP0919087 A4 EP 0919087A4
Authority
EP
European Patent Office
Prior art keywords
information
subconstellation
signal
decoding
signal points
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP97954558A
Other languages
German (de)
English (en)
Other versions
EP0919087A1 (fr
Inventor
George D Forney Jr
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Motorola Solutions Inc
Original Assignee
Motorola 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 Motorola Inc filed Critical Motorola Inc
Publication of EP0919087A1 publication Critical patent/EP0919087A1/fr
Publication of EP0919087A4 publication Critical patent/EP0919087A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/25—Error detection or forward error correction by signal space coding, i.e. adding redundancy in the signal constellation, e.g. Trellis Coded Modulation [TCM]
    • H03M13/256—Error detection or forward error correction by signal space coding, i.e. adding redundancy in the signal constellation, e.g. Trellis Coded Modulation [TCM] with trellis coding, e.g. with convolutional codes and TCM
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/25—Error detection or forward error correction by signal space coding, i.e. adding redundancy in the signal constellation, e.g. Trellis Coded Modulation [TCM]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
    • H04L25/40—Transmitting circuits; Receiving circuits
    • H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
    • H04L25/4917—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using multilevel codes
    • H04L25/4927—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using multilevel codes using levels matched to the quantisation levels of the channel

Definitions

  • the invention relates generally to communication systems and, more particularly, to communicating information using a new type of code called a composite code, for example, on a PCM modem connection using the public switched telephone network (PSTN).
  • PSTN public switched telephone network
  • Voiceband modems are very popular largely because of their leverage of existing telephone network infrastructure. In short, a user needs to make only a relatively small investment for a modem and has to pay relatively modest line charges.
  • a conventional PSTN arrangement 100 is shown in Fig. 1. What are typically interpreted as analog signals enter and exit the network 100 at "local loops" 140 and 150. Each signal on loop 140 and 150 is received by a corresponding line interface 120 and 130, or local switch, and each line interface communicates with another via a backbone digital network 110. Under conventional operation, an information signal 175 is sent to a first site 170, which emits an analog signal, for example, representative of a voice signal or binary information, on the locai loop 140.
  • the line interface 120 filters, samples, and quantizes the analog signal and outputs a sequence of octets 125, representative of the analog signal 140.
  • the PCM quantization rules, used for the quantizing, are known and pre-specified, e.g., ⁇ -law or A-law. (Appendix A lists the values for ⁇ -law).
  • the backbone 110 receives the octet sequence 125 and transmits and routes the data to various line interfaces, e.g., 130. Eventually an octet sequence 125', which is similar but not necessarily identical to the original octet sequence 125, is transmitted to the line interface 130 corresponding to the destination site 160.
  • the line interface 130 essentially inverse quantizes and further processes the received octet sequence 125' to create on loop 150 an analog signal that is an "approximate representation" of the originally-transmitted signal 140. Signal 150 is then transmitted to the site 160, where it may be used to recreate a voice signal or the binary information.
  • PCM modems and PCM Modem arrangements
  • a first site 270 such as an Internet server site, communicates with a digital adapter 220, or digital modem, by sending signals over a high- speed link 240.
  • the digital adapter 220 sends a sequence of octets 225 to backbone 110, which, in turn, sends a sequence of octets 225' to conventional line interface 130.
  • Octets 225' may differ from octets 225 because of robbed bit signaling, for example.
  • Line interface 130 then inverse quantizes octets 225' and transmits line interface signals on downstream, user-end loop 250.
  • Analog adapter 260 also known as PCM modem
  • a reverse path from analog adapter 260 to digital adapter 220 may be constructed using conventional modem techniques, for example, V.34 technology, or other technologies can be employed.
  • the PCM modem arrangement considers the same operations as a form of baseband modulation. That is, the line interface 130 produces a signal on the loop whose amplitude varies depending on the information received by the line interface.
  • the modulation technique is akin to PAM, but unlike PAM, and as further described below, the signal constellation involved is unevenly- spaced. This uneven spacing is a consequence of the PCM quantization rules being non-linear.
  • the most desirable feature of the PCM modem arrangement is that, unlike the conventional arrangement of Fig. 1 , the conventional local switch 120 is avoided and, therefore, its capacity-limiting, quantization noise is also avoided.
  • each transmitted signal level is detected independently of other signals at the receiver.
  • the performance of an uncoded system is therefore governed by the minimum distance d m j n between the set of levels that may be transmitted.
  • the set of levels that may be transmitted is the "signal constellation.”
  • a decoder such as the well-known Viterbi algorithm uses these dependencies in sequence decoding to achieve a "coding gain.”
  • V.32 modems use a two-dimensional (2D) trellis code to achieve a coding gain of about 3.6 dB
  • V.34 modems use one of three four-dimensional (4D) trellis codes to achieve a coding gain of from about 4.2 to 4.7 dB.
  • Trellis coding may be found in the literature, for example, Ezio BIGLIERI ET AL, INTRODUCTION TO TRELLIS- CODED MODULATION WITH APPLICATIONS (MacMillan 1991) and JOHN G. PROAKIS, DIGITAL COMMUNICATIONS 511-526 (McGraw Hill 1995).
  • a method, adapters, and a system are provided for communicating information.
  • a first set of signal points define a first subconstellation
  • a second set of signal points define a second subconstellation, wherein the first subconstellation is characterized with a different minimum distance between adjacent signal points than the minimum distance for the second subconstellation.
  • Information to be communicated is mapped to one of the first and second subconstellations. If the information maps to the first subconstellation, the information is transmitted according to a first transmission scheme; and if the information maps to the second subconstellation, the information is transmitted according to a second transmission scheme.
  • information mapped to the first constellation may be transmitted as coded information, for example, using a trellis code.
  • information mapped to the second constellation may be transmitted as uncoded information.
  • the first and second signal constellation are constructed using signal points from PCM quantization rules for PSTNs. From the pre-specified constellation, at least two subconstellations are chosen. One, the "outer subconstellation,” includes a subset of the PSTN quantization levels. At least one other "inner subconstellation” includes another subset of the PSTN quantization levels. The outer subconstellation includes signal points sufficiently separated so that coding is not needed for their transmission.
  • n-dimensional trellis codes are used for transmitting information mapped to the first subconstellation.
  • Another aspect of the invention provides mechanisms for recovering from lost synchronism when decoding an n-dimensional code.
  • Another aspect of the invention provides mechanisms for avoiding catastrophic effects from lost synchronism when decoding an n-dimensional code.
  • Fig. 1 shows a conventional PSTN having local loops
  • Fig. 2 is an architectural diagram of a PCM modem arrangement according to an exemplary embodiment of the invention.
  • Fig. 3 is a trellis diagram associated with a trellis code used for inner signal points of a composite code according to an exemplary embodiment of the invention
  • Fig. 4 is another trellis diagram associated with a trellis code used for inner signal points and having state transitions for outer signal points of a composite code according to an exemplary embodiment of the invention
  • Fig. 5 is an architectural diagram of the relevant part of an analog adapter according to an exemplary embodiment of the invention.
  • Fig. 6 is an architectural diagram of the relevant part of a digital adapter according to an exemplary embodiment of the invention.
  • An exemplary embodiment of the invention uses a new type of code called a composite code.
  • a transmitter, or a digital adapter 220, and a PCM modem, or an analog adapter 260 may be implemented to encode and decode information using the exemplary code.
  • exemplary embodiments of the invention can attain the same transmission rate as uncoded transmission with improved noise resistance. For example, an exemplary embodiment attains a 1.8 dB nominal coding gain over the baseline uncoded constellation above at 56 kb/s, and up to 4.8 dB may be attainable with more complexity.
  • the composite codes used in exemplary embodiments use subsets of the ⁇ -law or A- law quantization levels that are grouped to form at least two subconstellations. Each subconstellation is then associated with a corresponding transmission and decoding scheme tailored to the characteristics of that subconstellation.
  • One embodiment forms a composite code by combining one- dimensional trellis coded modulation and uncoded modulation in the following manner.
  • a subset of the 255 detectable ⁇ -law levels are used to create two subconstellations: a subconstellation of outer points with minimum distance d 0 , and a subconstellation of inner points with minimum distance dj ⁇ d 0 .
  • All outer points are chosen to have larger magnitude than all inner points, and as a consequence of the PCM quantization rules, the outer points also have larger distances to adjacent outer points than the distances between adjacent inner points.
  • the separation between the maximum inner point and minimum outer point is chosen to be at least d 0 .
  • the inner subconstellation is chosen to approximate a normal evenly- spaced pulse amplitude modulation (PAM) constellation.
  • PAM pulse amplitude modulation
  • Exemplary inner subconstellation 1 level at 12;
  • trellis codes may be used with such an inner subconstellation to achieve a large minimum distance between coded sequences.
  • a simple one-dimensional (1 D) 4-state Ungerboeck trellis code may be used.
  • the inner subconstellation may be 4-way partitioned into four subsets A, B, C, D in a periodic ABCDABCD . . . pattern as follows: 231 A -231 D
  • the digital adapter 220 and analog adapter 260 could use the exemplary 4-state trellis diagram shown in Fig. 3 in conjunction with the above constellations.
  • the encoder operates as follows.
  • the digital adapter 220 receives information on link 240 and maps 7 bits of the information, at a time, into one of 128 values, of which
  • 118 values are associated with unique outer points; and • 10 values are associated with two inner points, one in A or C and one in B or D, in such a way that each of the 20 inner points is associated with a unique value.
  • the negative of an A point is a D point
  • the negative of a B point is a C point.
  • the 10 of the 128-bit 7-tuples that designate an inner point designate one of the 10 inner subconstellation magnitudes.
  • the state of the trellis decoder then allows either only A and C points, or alternatively B and D points to be sent; thus the state can be used together with the magnitude to select the sign of a signal point with that magnitude to satisfy the constraints of the code trellis.
  • the data 7-tuple and the trellis state together select one of these 20 inner points to be transmitted. If on the other hand the input 7-tuple corresponds to one of the 118 outer point values, then the corresponding outer point is simply sent uncoded.
  • the minimum distance of the trellis code is 66
  • the minimum distance of the uncoded outer subconstellation is 64
  • the minimum distance between the inner and outer subconstellations is 64
  • the minimum distance between any two sequences in the composite coding scheme is 64.
  • the above composite coding arrangement creates some delay and buffering issues not found in conventional trellis coding and uncoded transmission schemes. More particularly, if the analog adapter 260 detects a signal level in the outer subconstellation, an immediate decision can be made, since the outer subconstellation is uncoded. However, if the analog adapter 260 detects a signal level in the inner subconstellation, then the received signal magnitude must be decoded according to the inner trellis code (e.g., using the Viterbi algorithm). Such decoding inherently introduces some delay. Therefore, in order to put out the decoded received bits in the same order in which they were transmitted, the receiver needs to:
  • a composite code trellis diagram may be constructed by starting with a conventional trellis diagram for the known trellis code, whose branches correspond to transmission of inner points, and adding branches corresponding to outer points that do not cause the encoder state to change.
  • a trellis diagram for inner points such as the one of Fig. 3, the trellis diagram of Fig. 4 may be constructed.
  • the thin-line branches correspond to inner points; for clarity the labels are omitted.
  • the thick-line branches correspond to outer points.
  • the modified trellis diagram indicates that transmissions of outer points do not change the encoder state.
  • a transmitter that encodes using this trellis diagram 400 and a receiver that simply decodes this trellis code using the standard Viterbi algorithm with a fixed decoding delay will be equivalent to the composite encoder and decoder described previously.
  • the "constellation expansion" of the exemplary 1 D trellis code embodiment, described above, is a factor of 2. This constrains the amount of gain that can be achieved with 1 D codes in this application.
  • the constellation expansion due to trellis coding can be reduced to about 50% or 25%, respectively.
  • Ungerboeck 2D code, a Wei 4D code, or Ungerboeck- or Wei- type codes such as those used in V.32 or V.34 may be used
  • the uncoded outer subconstellation and the coded inner subconstellation may be used as follows. One bit per sample determines whether we use the inner or outer subconstellation. If outer, then we transmit the remaining 6 bits using the 64-point uncoded outer subconstellation. If inner, then we transmit the remaining 6 bits using the 92-point coded inner subconstellation. The simplicity of this scheme results from the inner and outer scheme both supporting the same number (6) of bits per sample.
  • n parallel decoders at all times, and always choose the path with the best metric. (Implementing n parallel decoders is straightforward for those skilled in the art.) More elegantly, this may be realized by a novel single Viterbi algorithm search through a "super-trellis" containing one state for each of the n possible block phases and each of the states in a 1 D trellis for the original code. While this approach will resynchronize faster and more seamlessly than the one first mentioned, it will of course take about n times as much computation in normal operation.
  • This decoder logic will implement Viterbi decoding of the trellises of Figs. 3-4.
  • the decoder logic may be separated into distinct decoders to correspond to the decoding of signal points in the first and second subconstellations.
  • n parallel decoders may be used to recover from decoding errors.
  • the decoding logic will also include delay logic, described above, to ensure that the decoded outputs correspond to the sequence of inputs.
  • analog adapter 260 receives a baseband signal 250 that is an equivalent of the transmitted octet 225 and that the above description referred to them as signal points regardless of a binary or baseband representation.
  • baseband signal 250 that is an equivalent of the transmitted octet 225
  • the above description referred to them as signal points regardless of a binary or baseband representation.
  • Those skilled in the art will further appreciate the applicability of the above logic and new code to other receiver techniques, e.g., sub-optimum decoders.
  • a transmitter or digital adapter 220
  • Information received from link 240 is mapped by mapper 610 to a relevant subconstellation (in the diagram the transmitter includes two modulators, one for an inner subconstellation and one for an outer subconstellation). Then, depending on which subconstellation is determined as associated with the signal, the signal is modulated by a corresponding modulation technique. For example, for signai points mapped to the outer constellation, the modulation 620 would be for uncoded information, according to the exemplary embodiments described above. For signal points mapped to the inner constellation, the modulation 630 would be for coded information.
  • this coding could be 1 D or nD trellis coding, but the principles of the invention are not limited to just these codes.
  • Control logic 640 besides controlling the above may implement various control functions. For example, in the case of nD codes and depending upon the embodiment of the invention, control logic 640 may constrain the first and second modulators in the above described manners to avoid catastrophic effects from occurring as a result of decoding errors at the analog adapter 260.
  • the digital adapter may include logic for grouping information received from link 240 into a pre-specified number of bits, e.g., 7 bits. This logic is known and well understood. Analogously, the trellis coding logic described above is well understood, though the combination and use of them with the particular subconstellations is novel.
  • the signal constellation may be partitioned into more than two subconstellations.
  • the inner-inner constellation can then support 5 bits per sample with a 2D Ungerboeck-type trellis code; the outer-inner subconstellation can support 5 bits per sample with a simple mod-2 lattice code based on a binary single-parity-check code such as the (6, 5, 2) or (8, 7, 2) code; and the outer subconstellation can support 6 bits per sample, as before. Selection may be made by using one bit per sample to choose the outer subconstellation or not, and, if not, a second bit to choose between the inner-inner and outer-inner subconstellations.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Probability & Statistics with Applications (AREA)
  • Theoretical Computer Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

L'invention porte sur un système, un dispositif (200) et un procédé de communication selon un code en treillis (300) de signaux de bande de base choisis parmi un ensemble fixe de points de signaux de bande de base. Un premier ensemble de points de signaux forme une première sous-constellation et un second ensemble, une seconde sous-constellation. La première sous-constellation se caractérise par une distance minimale entre des points de signaux adjacents différente de la distance minimale de la seconde sous-constellation. Dans un agencement de modem MIC (modulation par impulsions et codage) (200), les première et seconde sous-constellations comprennent respectivement des ensembles de points de signaux sélectionnés parmi les règles de quantification du réseau téléphonique public commuté (RTPC), et la première sous-constellation a une distance minimale inférieure à la seconde.
EP97954558A 1997-01-17 1997-12-12 Systeme, dispositif et procede de communication selon un code composite Withdrawn EP0919087A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US78543497A 1997-01-17 1997-01-17
US785434 1997-01-17
PCT/US1997/022920 WO1998032257A1 (fr) 1997-01-17 1997-12-12 Systeme, dispositif et procede de communication selon un code composite

Publications (2)

Publication Number Publication Date
EP0919087A1 EP0919087A1 (fr) 1999-06-02
EP0919087A4 true EP0919087A4 (fr) 2001-08-16

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EP97954558A Withdrawn EP0919087A4 (fr) 1997-01-17 1997-12-12 Systeme, dispositif et procede de communication selon un code composite

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EP (1) EP0919087A4 (fr)
AU (1) AU5898098A (fr)
TW (1) TW371825B (fr)
WO (1) WO1998032257A1 (fr)

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EP1038379B1 (fr) * 1997-12-29 2008-07-30 Motorola, Inc. Methode et appareil pour selectionner un point d'une constellation pour chaque groupe de bits de donnees transmis par un modem pcm analogique
EP0977410B1 (fr) * 1998-07-30 2003-02-19 Infineon Technologies AG Procédé pour générer des ensembles de codes des signaux MIC
FR2784528A1 (fr) * 1998-10-13 2000-04-14 Koninkl Philips Electronics Nv Methode de construction d'un ensemble de constellations destine a etre utilise pour transmettre des donnees entre un emetteur et un recepteur
US6414989B1 (en) 1999-09-10 2002-07-02 Conexant Systems, Inc. Upstream PCM transmission for a modem system
US7391816B2 (en) * 2003-09-17 2008-06-24 Intel Corporation Decoding upstream V.92-encoded signals
US9191148B2 (en) 2007-06-05 2015-11-17 Constellation Designs, Inc. Methods and apparatuses for signaling with geometric constellations in a Raleigh fading channel
US8265175B2 (en) 2007-06-05 2012-09-11 Constellation Designs, Inc. Methods and apparatuses for signaling with geometric constellations
WO2008151308A1 (fr) 2007-06-05 2008-12-11 Barsoum Maged F Méthodologie de conception et procédé et appareil de signalisation de constellations optimisées avec une capacité
US12289192B2 (en) 2008-12-30 2025-04-29 Constellation Designs, LLC Systems and methods for receiving data transmitted using non-uniform QAM 256 constellations
US12425885B2 (en) 2010-07-08 2025-09-23 Constellation Designs, LLC Systems and methods for receiving data transmitted using non-uniform QAM 256 constellations via fading channels
JP5911517B2 (ja) * 2011-03-15 2016-04-27 インテル・コーポレーション 低メモリアクセス動きベクトル導出
EP4604091A1 (fr) * 2024-02-15 2025-08-20 Minimax Viking Patent Management GmbH Procédé de communication d'une lecture précise d'un détecteur environnemental dans un système de protection contre l'incendie sur une boucle de communication numérique

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Also Published As

Publication number Publication date
TW371825B (en) 1999-10-11
EP0919087A1 (fr) 1999-06-02
WO1998032257A1 (fr) 1998-07-23
AU5898098A (en) 1998-08-07

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