EP0737394A1 - Constellation a modulation d'amplitude en quadrature, faisant preuve de coherence en presence d'un bruit de phase; codeur et decodeur pour cette constellation - Google Patents

Constellation a modulation d'amplitude en quadrature, faisant preuve de coherence en presence d'un bruit de phase; codeur et decodeur pour cette constellation

Info

Publication number
EP0737394A1
EP0737394A1 EP95933569A EP95933569A EP0737394A1 EP 0737394 A1 EP0737394 A1 EP 0737394A1 EP 95933569 A EP95933569 A EP 95933569A EP 95933569 A EP95933569 A EP 95933569A EP 0737394 A1 EP0737394 A1 EP 0737394A1
Authority
EP
European Patent Office
Prior art keywords
constellation
qam constellation
points
qam
ratio
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.)
Ceased
Application number
EP95933569A
Other languages
German (de)
English (en)
Inventor
Monisha Ghosh
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.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
Philips Electronics NV
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 Koninklijke Philips Electronics NV, Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Publication of EP0737394A1 publication Critical patent/EP0737394A1/fr
Ceased legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/3405—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power

Definitions

  • the invention relates to the a QAM transmission system, a transmitter, a receiver and a QAM signal B.
  • Related Art
  • Quadrature Amplitude Modulation (QAM) schemes (like 64 QAM) have traditionally been associated with coherent detection. Such schemes are used in environments that require high spectral efficiency and good performance in the presence of Additive White Gaussian Noise (AWGN). Coherent detection suffers in environments which have degradations other than AWGN, such as phase noise.
  • AWGN Additive White Gaussian Noise
  • Phase noise in particular results in a high error floor.
  • Phase noise typically results from tuners and can be reduced only by extremely stringent requirements on oscillators. Such stringent requirements are incompatible with affordability in the area of consumer electronics.
  • Non-coherent detection is usually used in such environments to reduce cost.
  • non-coherent detection which requires differential encoding and decoding, is usually associated with Phase Shift Keying (PSK), such as disclosed in D. Divsalar et al., "Multiple-symbol differential detection of MPSK", IEEE Trans. Comm. , vol. 38, no. 3, pp. 300-308, March 1990.
  • PSK Phase Shift Keying
  • information is present solely in the phase of the transmitted signal, unlike QAM where both the envelope and the phase carry information. Accordingly, PSK performs worse than QAM in the presence of phase noise.
  • the error signal for the adaptation algorithm is obtained by comparing the equalizer output with the transmitted constellation.
  • the transmitted constellation of Makrakis et al. is much denser than the original QAM constellation which degrades equalizer performance. Moreover, such a scheme does not lend itself to differentially coherent demodulation.
  • Fig. 1 shows a constellation according to the invention.
  • Fig. 2 shows simulated performance of the constellation in comparison with rectangular QAM in the presence of white Gaussian phase noise.
  • Fig. 3 shows theoretical performance of the constellation in the presence of white phase noise with a Tikhonov distribution.
  • Fig. 4 shows an encoder according to the invention.
  • Fig. 5 shows a decoder according to the invention.
  • the constellation of Fig. 1 includes the following 64 points, expressed in polar coordinates, with angles in radians
  • the constellation has 8 concentric circles, each having 8 points. The points on adjacent circles are offset from each other by 22.5° or radians.
  • the values d j ,...,d 8 are radii of the concentric circles. This constellation results in a minimum distance between constellation points of d min .
  • the constellation minimizes an energy value F which is determined according to the following equation In (1) d 2 (x i 0) is the squared distance of the point x-, of the constellation to the origin
  • a quantity which is widely used to compare constellations is the energy efficieny. This is the ratio between the average power of the points of the constellation and the minimum squared distance between points of the constellation. The smaller this ratio, the better the energy efficiency and performance of the constellation in AWGN and coherent detection. For the constellation described above, , which is 0.62dB worse than the
  • the constellation of the invention is, however, 3.696 dB better than the Webb constellation cited above.
  • the small difference in performance between the constellation of the invention and a rectangular constellation, in the presence of AWGN, is offset by the superior performance of the invention in phase noise environments.
  • Fig. 2 shows simulated performance of the proposed and rectangular 64 QAM constellations in white Gaussian phase noise. From this it can be seen that the constellation of Fig. 1 is roughly comparable to rectangular 64 QAM in the presence of AWGN but significantly better in the presence of 2° rms phase noise.
  • the rectangular 64 QAM saturates at a bit error rate (BER) of 10 -5 irrespective of signal to noise ratio (SNR), with phase noise.
  • SNR signal to noise ratio
  • the circular constellation though 2dB worse at a BER of 10 -6 than with AWGN, does not saturate until the BER drops to about 10 -9 .
  • the reader is referred to Fig. 3 where the performance of the constellation of the invention is shown in the presence of phase noise with a Tikhonov distribution.
  • the encoded constellation be the same as the uncoded constellation.
  • mapping ensures that the transmitted sequence x k has symbols from the same constellation as the data sequence a k .
  • the amplitude of each transmitted symbol is the same as the corresponding data symbol, i.e.
  • FIG. 4 An encoder which encodes according to the invention is shown in Fig. 4.
  • multiplier 402. Encoded symbol x k is available at an output of multiplier 402.
  • the output of multiplier 402 is also fed back to delay 403.
  • the output of delay 403 is variously supplied, directly to multiplier 404, to element 405, and to element 406.
  • Element 405 provides an output which is one over the magnitude of the input of element 405.
  • maximizing ⁇ (k) with respect to a k , a k-1 , and a k-2 jointly will give an estimate of a k and a k-1 but will only give an estimate of
  • Such a maximization operation will involve 64 ⁇ 64 ⁇ 8 comparisons for every two data symbols decoded. This number of comparisons allows the various points of the signal constellation to be tried in place of a k , a k-1 , and a k-2 until a maximum is found.
  • the second step which makes decisions for the present symbol based on the decisions made for past symbols, only involves 64 comparisons per data symbol, which is considerably less than the number in the first step.
  • FIG. 5 A decoder operating according to these principles is shown in Fig. 5. Box 500 is shown which produces . Identical boxes produce ,
  • Box 550 outputs S k by choosing symbol i ⁇ for which
  • a received symbol y k is input at 501.
  • Delay element 502 produces delayed input signal y k-1.
  • Delay element 503 produces delayed input signal y k-2
  • a feedback loop via delay element 504 provides the previous estimated symbol â k-1 .
  • Delay element 505 provides delayed estimated symbol â k-2 .
  • Elements 506 and 507 generate from â k-1 and â k-2 , respectively.
  • Elements 506 and 507 can be look up tables operating according to equation (8) above.
  • Element 508 takes one over the absolute value of its input and therefore outputs .
  • Multiplier 509 fed by elements 506, 507, and â k- 1 ,
  • Multiplier 510 fed by elements 508, 509, and y k , outputs
  • Multiplier 515 is fed by ai and the output of element 510.
  • Multipliers 515 and 516 are fed by a 1 because this is the box for estimating the value .
  • the box which estimates will be fed by a i at the elements which correspond to multipliers 515 and 516.
  • the output of multiplier 515 is therefore Multiplier 511, fed by element 507, y k-1 , and â k-1 , outputs
  • Element 512 takes the absolute value of â k-2 .
  • Multiplier 513 fed by
  • Adder 516 is fed by elements 514 and 515 and therefore outputs
  • Box 517 takes the absolute value of the output of box 516.
  • Adder 516 fed by
  • Multiplier 518 multiplies the output of element 516 by 0.5.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

L'invention concerne une constellation à modulation d'amplitude en quadrature, symétrique de manière circulaire, réduisant le bruit de phase. Les points de cette constellation se trouvent sur des cercles concentriques et la constellation peut être codée et décodée de façon cohérente ou non cohérente. Le codeur différentiel utilisé à cet effet n'opère pas par soustraction directe. Un décodeur différentiel pour la constellation peut faire appel à un ensemble de mesures estimées pour récupérer le signal original.
EP95933569A 1994-10-21 1995-10-20 Constellation a modulation d'amplitude en quadrature, faisant preuve de coherence en presence d'un bruit de phase; codeur et decodeur pour cette constellation Ceased EP0737394A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US32706594A 1994-10-19 1994-10-19
US327065 1994-10-21
PCT/IB1995/000893 WO1996013111A1 (fr) 1994-10-21 1995-10-20 Constellation a modulation d'amplitude en quadrature, faisant preuve de coherence en presence d'un bruit de phase; codeur et decodeur pour cette constellation

Publications (1)

Publication Number Publication Date
EP0737394A1 true EP0737394A1 (fr) 1996-10-16

Family

ID=23274990

Family Applications (1)

Application Number Title Priority Date Filing Date
EP95933569A Ceased EP0737394A1 (fr) 1994-10-21 1995-10-20 Constellation a modulation d'amplitude en quadrature, faisant preuve de coherence en presence d'un bruit de phase; codeur et decodeur pour cette constellation

Country Status (4)

Country Link
EP (1) EP0737394A1 (fr)
JP (1) JPH09507374A (fr)
CN (1) CN1140521A (fr)
WO (1) WO1996013111A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3140974B2 (ja) * 1996-03-31 2001-03-05 富士通株式会社 判定方法及びプリコーダ装置
ES2196221T3 (es) * 1997-08-05 2003-12-16 Sony Int Europe Gmbh Circuito para deshacer la correlacion de qam.
MXPA04008840A (es) * 2002-03-19 2004-11-26 Thomson Licensing Sa Algoritmo de rebanado para esquemas de ecualizacion de modulacion de multiples niveles.
JP2007503734A (ja) * 2003-08-22 2007-02-22 コーニンクレッカ　フィリップス　エレクトロニクス　エヌ　ヴィ 下位互換性のあるマルチキャリア送信システム
CN1863182B (zh) * 2005-09-30 2010-12-08 华为技术有限公司 移动通信系统中提高信号传输速率的方法

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2428946A1 (fr) * 1978-06-13 1980-01-11 Ibm France Procede et dispositif pour initialiser un egaliseur adaptatif a partir d'un signal de donnees inconnu dans un systeme de transmission utilisant la modulation d'amplitude en quadrature
GB2118003B (en) * 1982-02-02 1985-07-31 Racal Milgo Ltd Differential encoder and decoder for transmitting binary data

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9613111A1 *

Also Published As

Publication number Publication date
CN1140521A (zh) 1997-01-15
WO1996013111A1 (fr) 1996-05-02
JPH09507374A (ja) 1997-07-22

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