WO2008151518A1 - Procédé et dispositif de détection d'information dans un système ofdm - Google Patents

Procédé et dispositif de détection d'information dans un système ofdm Download PDF

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Publication number
WO2008151518A1
WO2008151518A1 PCT/CN2008/001119 CN2008001119W WO2008151518A1 WO 2008151518 A1 WO2008151518 A1 WO 2008151518A1 CN 2008001119 W CN2008001119 W CN 2008001119W WO 2008151518 A1 WO2008151518 A1 WO 2008151518A1
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WO
WIPO (PCT)
Prior art keywords
data symbols
data
equal
posterior probability
detected
Prior art date
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PCT/CN2008/001119
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English (en)
Chinese (zh)
Inventor
Zhendong Luo
Dawei Huang
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Lucent Technologies 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 Lucent Technologies Inc. filed Critical Lucent Technologies Inc.
Publication of WO2008151518A1 publication Critical patent/WO2008151518A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03171—Arrangements involving maximum a posteriori probability [MAP] detection
    • 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
    • H04L1/0045—Arrangements at the receiver end
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375—Passband transmission
    • H04L2025/03414—Multicarrier

Definitions

  • the present invention relates to signal detection in an OFDM system, and in particular to a detection method and apparatus for an OFDM system capable of generating a posterior probability of transmitted data symbols directly from a received signal with higher computational efficiency.
  • OFDM Orthogonal Frequency Division Multiplexing
  • FIG. 1 shows a schematic block diagram of a transmitter and receiver of an OFDM system according to the prior art, wherein dashed boxes 11 and 27 represent channel coding units and channel coding units for the coding system. That is, for an uncoded system, the OFDM system does not include the two parts described above.
  • the transmitter includes: a channel encoder 11, a symbol mapper 12, a pilot insertion unit 13, a power distribution unit 14, an inverse FFT unit 15, an inserted CP unit 16, and a radio frequency/intermediate frequency (RF/).
  • IF radio frequency/intermediate frequency Modulator 17 and modules such as transmit antennas.
  • the channel coder 11 encodes the data information from the source to generate coded bits
  • the symbol mapper 12 maps the coded bits into corresponding data symbols in the signal constellation
  • the pilot insertion unit 13 inserts a guide into the data symbols.
  • the frequency symbol is further adjusted by the power distribution unit 14 for the transmission power of each transmitted symbol, and then processed by the inverse FFT unit 15 and processed by the insertion of the CP unit 16 to generate a baseband transmission signal, which is then modulated by the RF/IF modulator. Finally, it is transmitted by the transmitting antenna.
  • the receiver includes: a receiving antenna, an RP/IF demodulator 21, and a time-frequency.
  • the radio frequency receiving signal is received by the receiving antenna, and then processed by the RF/IF demodulator 21 to generate a baseband received signal, and the time frequency synchronizing unit 22 keeps the time and frequency of the receiver consistent with the received signal, in the CP removing unit.
  • channel estimation unit 25 estimates channel state information (CSI) using the pilot signal
  • signal detector 26 A hard decision result (for an uncoded system and a hard decision decoding system) that produces data symbols from the received signal using the estimated CSI, or soft information that produces data symbols (for a soft decoding system).
  • signal detector 26 produces the final transmitted data; for an encoding system (including a hard decision decoding system and a soft decoding system), channel decoder 27 utilizes the information provided by the signal detector to ultimately Restore the transmitted data. Finally, the recovered transmission data is sent to the sink.
  • Non-Patent Document 1 T. Cui and , C. Tellambura, "Joint Data Detection and Channel Estimation for OFDM Systems," IEEE Trans. Commun., vol. 54, no. 4, pp. 902-915, Apri. 2006
  • a robust hard decision algorithm is proposed, which combines channel estimation with hard decision detection to improve the performance of OFDM receivers.
  • the method proposed in the above Non-Patent Document 1 is so complicated that it cannot be applied to an actual OFDM system.
  • the method cannot provide soft information of data symbols, so it cannot interface with a soft channel decoder such as a turbo decoder to improve reception performance.
  • Non-Patent Document 2 (SY Park, Y. G Kim, and CG ang, "Iterative receiver for joint detection and channel estimation in OFDM systems under mobile radio channels," IEEE Trans. Vehicular Technology, vol. 53, no. 2 , pp. 450-460, Mar. 2004) proposed soft iterative joint channel estimation, A combination of detection and decoding, which effectively improves the performance of the OFDM system by Turbo processing between the channel estimator, the detector and the decoder. Nonetheless, the method essentially utilizes inaccurate CSI estimates generated by the channel estimator to generate soft information, the performance of which is still compromised by channel estimation errors. Summary of the invention
  • An object of the present invention is to provide a detection method and apparatus for an OFDM system capable of generating a posterior probability of a transmitted data symbol directly from a received signal with higher computational efficiency without performing a channel estimation operation.
  • a signal detecting method for an OFDM system comprising the steps of: a) inputting a receiving vector including a plurality of received signals, wherein, one of a plurality of data symbols to be detected is to be detected When the symbol is equal to one of its candidate values, the received vector is considered to be subject to a multi-dimensional complex Gaussian distribution under the condition that the channel and other data symbols are unknown; b) the probability density function of the multi-dimensional complex Gaussian distribution is used to calculate the known reception Under the condition of the vector, each data symbol to be detected is equal to the posterior probability of its respective candidate value.
  • a signal detecting apparatus for an OFDM system comprising: means for inputting a reception vector including a plurality of received signals, wherein one of a plurality of data symbols to be detected is to be detected When the data symbol is equal to one of its candidate values, the received vector is considered to be subject to a multi-dimensional complex Gaussian distribution under the condition that the channel and other data symbols are unknown; the probability density function for calculating using the multi-dimensional complex Gaussian distribution is known A device in which each data to be detected is equal to the posterior probability of its respective candidate value under the condition of receiving a vector.
  • the posterior probability of the transmitted data symbols can be accurately calculated without the need for channel estimation in the OFDM system.
  • the detection method and apparatus of the present invention can achieve near optimality with a complexity proportional to the number of subcarriers.
  • 1(a) and 1(b) are schematic block diagrams showing a transmitter and a receiver of an OFDM system according to the prior art
  • FIG. 2 shows a schematic block diagram of a transmitter and a receiver of a 0; FDM system in accordance with an embodiment of the present invention
  • 3(a) and 3(b) illustrate the operation of a detector in a receiver of an OFDM system in different situations according to an embodiment of the present invention
  • FIG. 4 illustrates BER performance of a detector in the case of a QPSK constellation and 16 pilot symbols per data block, in accordance with an embodiment of the present invention
  • FIG. 5 illustrates BER performance of a detector in the case of a 16QAM constellation and 16 pilot symbols per data block, in accordance with an embodiment of the present invention
  • FIG. 6 illustrates BER performance of a detector in a QPSK constellation diagram and 4 pilot symbols per data block, in accordance with an embodiment of the present invention
  • Figure ⁇ shows the BER performance of a detector in the case of a 16QAM constellation and 4 pilot symbols per data block, in accordance with an embodiment of the present invention.
  • ⁇ , and H represent the transpose, conjugate and conjugate transpose of the matrix, respectively; det (.) represents the determinant of the matrix; ⁇ represents the identity matrix; diag (.) represents the diagonalization of the vector; V a ) represents the variance of the random variable; Bu
  • the input-output relationship on each subcarrier is equivalent to a flat fading channel and can be expressed as:
  • N Represents the total number of subcarriers, representing the power amplification factor of the symbol,
  • 1, and
  • f ⁇ 2 . Note: also It is called channel state information (CSI).
  • CSI channel state information
  • a set of N transmitted symbols is defined as a block of data.
  • One data block can contain W symbols on any time slot and subcarrier. However, it is generally considered that one data block is composed of one or more consecutive OFDM symbols. Each OFDM symbol is composed of transmitted symbols on each subcarrier. Each transmitted symbol may be a data symbol, a pilot symbol, or a mixture of both.
  • the detector according to the present embodiment will operate on every data block, i.e., each data block is treated as a basic processing unit.
  • h n , y n > ⁇ ⁇ and respectively represent and corresponding Complex channel gain, received signal, noise, and power amplification factor.
  • pilot assisted estimation is widely used in practical systems and in various standards.
  • a system that uses pilot assisted estimation is called a pilot assist system.
  • Each data block in a system has K inserted symbols.
  • Pnt , y 3 ⁇ 4 5 and respectively represent the corresponding transmit power and received signal. Complex channel gain and noise.
  • the detector of this embodiment can be used in any OFDM system, not just for pilot assisted OFDM systems.
  • FIG. 2 shows a schematic block diagram of a transmitter and receiver of an OFDM system in accordance with an embodiment of the present invention.
  • a receiver according to an embodiment of the present invention includes: a receiving antenna, an RF/IF demodulator 21, a time-frequency synchronization unit 22, a CP removing unit 23, an FFT unit 24, a signal detector 26', and a channel translation. Module 27 and other modules.
  • the receiver does not have a channel estimation unit.
  • the signal detector 26 does not require an estimate of the CSI to directly generate a posteriori probability of the data symbol.
  • the signal The detector 26' produces a hard decision result of the data symbols based on the maximum a posteriori probability criterion.
  • the signal detector 26' inputs the posterior probability of the generated data symbols to the soft decoder for subsequent soft translation. code.
  • the other modules of the receiver are identical to the traditional receiver.
  • the receiver according to the embodiment of the present invention is different from the prior art in that the channel estimation unit is removed, and the signal detector 26' directly performs a soft iterative detection operation based on the output of the FFT unit 24 to generate The posterior probability (APP) of a data symbol, also known as soft information.
  • APP The posterior probability
  • This soft information will be used for subsequent hard decisions or input to the soft channel decoder for soft decoding, such as Turbo decoding.
  • the channel decoder in Figure 2 is only available in the case of an encoding system. That is, for an uncoded system, there is no channel coder and channel decoder 27.
  • the signal input to the signal detector is a baseband signal demodulated by OFDM, that is, a received signal on each subcarrier.
  • OFDM frequency division multiple access
  • these signals are the superposition of received data signals and noise or the superposition of pilot signals and noise; for systems using embedded pilots (also known as semi-blind systems), these signals are data Signals, pilot signals, and noise are added together.
  • the detector according to the present embodiment does not require channel estimation, directly calculates the posterior probability distribution of the data symbols, and outputs the final result after a plurality of iterations. If the system uses a soft decoder, the detector outputs a posterior probability distribution for each data symbol. If the system is not programmed The code is either a hard decision decoder, and the detector outputs the decision result of the data symbol obtained according to the maximum posterior probability criterion.
  • the operation of the detector according to an embodiment of the present invention is described below.
  • the key to the detector according to an embodiment of the invention is a core detection algorithm for calculating the APP of the data symbol without channel estimation.
  • the probability density function of the received signal vector y which is often referred to as a likelihood function; is a prior probability density function of the received signal vector, which is constant for different m;
  • Each element of the received signal vector y is a random variable formed by a channel, a data symbol or a pilot symbol, and noise.
  • y is considered to obey (or approximately obey) the multidimensional complex Gaussian distribution.
  • equation (9) is a simplified form of equation (7) under the condition that the transmitted data symbols are a priori
  • equation (10) is a simplification of equation (7) under the condition that the data symbols are constant modulus. form.
  • R ⁇ can be thought of as the matrix R when ⁇ - ⁇ Jf.
  • R and R r beau Snim differ only in the elements on the nth and nth columns.
  • det(R) and y3 ⁇ 4" as intermediate variables, the rank 1 update formula and the block matrix are further inferred using the determinant and matrix inversion. Determinant and inversion formula, The proposed simplified algorithm is thus obtained.
  • Det(R) and y ff R- can be regarded as constants, which can be omitted from the calculation and do not need to calculate their results.
  • FIG. 3 is a flow chart showing a soft iterative detection process performed by a signal detector in a receiver of an OFDM system in accordance with an embodiment of the present invention.
  • i represents the index of the number of iterations
  • N represents the total number of iterations.
  • Figure 3(a) shows the detection flow for an uncoded system or a hard decision decoding system.
  • the so-called updated condition refers to using the APP of the data symbol generated by the detector in the previous iteration to calculate the current The mean and variance of the data symbols required in the iteration.
  • Figure 3(b) shows the flow for a soft decoding system.
  • the updated condition refers to the calculation of the mean and variance of the data symbols required in the current iteration using the APP of the data symbols generated by the decoder in the previous iteration.
  • ⁇ ( ) is usually a constant.
  • Vector y receives signals from the received signal of the symbol to be detected and the pilot Composition.
  • y) p (x n ⁇ s n , m
  • n ( (h' ) is a subarray consisting of a matrix column and elements of the ..., 3 ⁇ 4 rows.
  • equation (23) can be simplified to
  • the complexity of the first iteration after simplification is 0 (Nf + NM). Where f is the number of pilot symbols in each data block.
  • CSI channel state information
  • AMC adaptive modulation and coding
  • V are determined by the APP generated by the detector or soft decoder at the last iteration.
  • an encoding system it can be generated by encoding and mapping the data bits output by the decoder.
  • ⁇ 2 can be calculated by the method proposed in Non-Patent Document 3 (IEEE Std 802.16e-2005 and IEEE Std 802.16-2004/Cor 1-2005 (Amendment and Corrigendum to IEEE Std 802.16-2004), Feb. 2006). This document is incorporated by reference in its entirety. The following discusses how to determine Rh .
  • Non-Patent Document 4 (D. J.
  • Non-Patent Document 5 A. avcic and B. Yang, "A new efficient Subspace tracking algorithm based on singular value decomposition,” in Proc. 1994 IEEE Int. Conf. Acoustics, Speech, and Signal Processing, vol. IV, 1994, pp.
  • the fast rank 1 singular value decomposition update algorithm for subspace tracking can be applied to the calculation of U and D.
  • Their computational complexity is only 0 (H). Since the channel is statistically invariant over a relatively long period of time, the estimated parameters are relatively relatively Precise.
  • Figures 4 through 7 show the simulation results of the above algorithm in several cases.
  • an uncoded pilot assisted OFDM system with 256 subcarriers is considered.
  • the channel is a 6-path typical city (TU) fading channel (COST207) with a channel bandwidth of 10 MHz and an OFDM symbol duration of 32 ⁇ with a cyclic prefix of 6.4 ⁇ .
  • TU typical city
  • COST207 OFDM symbol duration
  • All transmitted symbols including data symbols and pilot symbols
  • the pilot symbols for each data block are 16.
  • the constellation used in Figures 4 and 6 is QPSK
  • the constellation used in Figures 5 and 7 is 16QAM. .
  • ML-MMSE represents the performance of a maximum likelihood detector using minimum mean square error (MMSE) channel estimation, which is a very common OFDM reception scheme in practice.
  • MMSE minimum mean square error
  • the performance of ML-MMSE is always far from the optimal performance, which is caused by the error of channel estimation.
  • the performance of the above iterative detection method is similar to ML-MMSE. However, as the number of iterations increases, its performance quickly approaches optimal performance. As shown in Figures 6 and 7, although the inserted pilot symbols are sparse, the soft iterative detection method according to an embodiment of the present invention can still achieve near optimal performance.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Probability & Statistics with Applications (AREA)
  • Power Engineering (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Error Detection And Correction (AREA)
  • Radio Transmission System (AREA)

Abstract

La présente invention concerne un procédé de détection d'information dans un système OFDM comportant les étapes suivantes. A) le vecteur incluant plusieurs signaux reçu est fourni en entrée au récepteur, quand un symbole de plusieurs symboles à détecter est égal à l'une des valeurs candidates, le vecteur devrait respecter la distribution gaussienne complexe multidimensionnelle quand les conditions concernant les canaux et les autres données sont inconnues. B) La probabilité postérieure de chaque donnée qui est égale à chaque valeur candidate peut être calculée avec la fonction de densité de la probabilité de la distribution gaussienne complexe multidimensionnelle. Ainsi, la probabilité postérieure des données peut être calculée avec exactitude quand les conditions du canal n'auraient pas été évaluées. Le rendement de la détection peut être proche des résultats optimaux, et la complexité est en rapport direct avec le nombre de porteuses.
PCT/CN2008/001119 2007-06-08 2008-06-10 Procédé et dispositif de détection d'information dans un système ofdm WO2008151518A1 (fr)

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CN2007101119304A CN101320994B (zh) 2007-06-08 2007-06-08 Ofdm系统的信号检测方法和设备
CN200710111930.4 2007-06-08

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CN101789816B (zh) * 2009-01-22 2012-12-05 北京信威通信技术股份有限公司 一种ofdma多天线系统的符号检测方法及装置
CN101986572B (zh) * 2009-07-29 2013-10-16 中兴通讯股份有限公司 正交频分复用系统中随机接入信号的检测方法与装置
CN103730123A (zh) * 2012-10-12 2014-04-16 联芯科技有限公司 噪声抑制中衰减因子的估计方法和装置
CN103200138B (zh) * 2013-04-03 2016-01-20 北京航空航天大学 噪声方差估计方法
CN105207753B (zh) * 2015-08-26 2018-10-16 北京润科通用技术有限公司 一种误码率测量方法、误码率测量系统及功率控制系统
CN107404346A (zh) * 2016-05-18 2017-11-28 北京信威通信技术股份有限公司 一种接收信号检测方法及系统

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CN1462533A (zh) * 2001-05-11 2003-12-17 三星电子株式会社 正交频分复用系统中的信道解码装置和方法
US6678339B1 (en) * 2000-02-02 2004-01-13 Agere Systems Inc. Globally optimum maximum likelihood estimation of joint carrier frequency offset and symbol timing error in multi-carrier systems
CN1547339A (zh) * 2003-12-05 2004-11-17 清华大学 Ofdm系统用的高效的迭代编码多用户检测方法
US20070064687A1 (en) * 2005-09-22 2007-03-22 Sanyo Electric Co., Ltd. Radio apparatus

Patent Citations (4)

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Publication number Priority date Publication date Assignee Title
US6678339B1 (en) * 2000-02-02 2004-01-13 Agere Systems Inc. Globally optimum maximum likelihood estimation of joint carrier frequency offset and symbol timing error in multi-carrier systems
CN1462533A (zh) * 2001-05-11 2003-12-17 三星电子株式会社 正交频分复用系统中的信道解码装置和方法
CN1547339A (zh) * 2003-12-05 2004-11-17 清华大学 Ofdm系统用的高效的迭代编码多用户检测方法
US20070064687A1 (en) * 2005-09-22 2007-03-22 Sanyo Electric Co., Ltd. Radio apparatus

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