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        OFDM系統(tǒng)中子信道聯(lián)合預(yù)編碼技術(shù)的信號檢測算法研究

        2015-11-09 21:13:31蔣海云等
        現(xiàn)代電子技術(shù) 2015年21期

        蔣海云等

        摘 要: 正交頻分復(fù)用技術(shù)將多徑衰落信道劃分為多個(gè)相對平坦的子信道,使得接收機(jī)在信道估計(jì)等恢復(fù)技術(shù)上復(fù)雜度大大降低。OFDM系統(tǒng)采用子信道聯(lián)合預(yù)編碼技術(shù)能有效解決由于成片子載波衰落引起的數(shù)據(jù)丟失問題。由于獨(dú)立信道的線性預(yù)編碼技術(shù)在發(fā)送端不需要信道反饋信息,因此降低了發(fā)送設(shè)備復(fù)雜度,減少了系統(tǒng)延時(shí),該編碼方案適用于從用戶端到基站的數(shù)據(jù)傳輸。通過理論分析推導(dǎo)了當(dāng)系統(tǒng)采用獨(dú)立信道的線性預(yù)編碼技術(shù)時(shí),接收端不能采用迫零均衡(ZF)的線性檢測算法,實(shí)驗(yàn)仿真表明,當(dāng)采用迫零均衡檢測算法時(shí),當(dāng)且僅當(dāng)預(yù)編碼矩陣為酉矩陣時(shí)系統(tǒng)能達(dá)到未經(jīng)預(yù)編碼系統(tǒng)的性能。

        關(guān)鍵詞: OFDM系統(tǒng); 子信道聯(lián)合預(yù)編碼; 迫零均衡檢測算法; 星座調(diào)制信息

        中圖分類號: TN92?34 文獻(xiàn)標(biāo)識(shí)碼: A 文章編號: 1004?373X(2015)21?0046?03

        Research on signal detection algorithm of sub?channel joint precoding technology in OFDM system

        JIANG Haiyun, XIONG Chunlin, WEI Jibo

        (School of Electronic Science and Engineering, National University of Defense Technology, Changsha 410000, China)

        Abstract: The multipath fading channel is divided into multiple relatively flat sub?channels by OFDM, which makes the receiver′s complexity in channel estimation reduced greatly. OFDM system with sub?channel joint precoding technology can effectively solve the problem of data loss caused by numerous carrier wave fading. Since the linear precoding technology of independent channel doesn′t need feedback information of the channel in sending end, which can reduce the complexity of the transmitting device and system delay, this precoding scheme is suitable for data transmission from the client to the base station. In this paper, a conclusion that the linear detection algorithm of zero forcing equilibrium can′t be adopted for receiving end when the linear precoding technology of independent channel is applied by the system is derived according to the theoretical analysis. The experimental simulation results show that the system can achieve the performance without precoding when the precoding matrix is unitary matrix and zero forcing equilibrium detection algorithm is adopted.

        Keywords: OFDM system; sub?channel joint precoding; zero forcing equilibrium detection algorithm; constellation modulation information

        0 引 言

        無線通信技術(shù)的迅猛發(fā)展極大地改變了人們生產(chǎn)生活方式,正交頻分復(fù)用技術(shù)[1](OFDM)作為無線通信的關(guān)鍵技術(shù)之一,在很大程度上降低了通信系統(tǒng)的復(fù)雜度。在多用戶通信過程中,從用戶端到基站的上行鏈路數(shù)據(jù)傳輸要求用戶設(shè)備盡可能簡化。在OFDM系統(tǒng)中,使用子信道聯(lián)合預(yù)編碼技術(shù)[2?4]能帶來性能上的提升。獨(dú)立信道的線性預(yù)編碼[5?6]是一類重要的預(yù)編碼方案,在發(fā)送端使用發(fā)送數(shù)據(jù)符號的統(tǒng)計(jì)特性設(shè)計(jì)預(yù)編碼矩陣,不需要已知信道信息,因此無需信道反饋,降低了發(fā)送端設(shè)備的復(fù)雜度,減少了傳輸延時(shí)。因此獨(dú)立信道的預(yù)編碼方案適用于用戶端到基站的數(shù)據(jù)傳輸。

        1 獨(dú)立信道的線性預(yù)編碼技術(shù)采用迫零檢測算

        法的性能分析

        帶預(yù)編碼的OFDM系統(tǒng)簡化框圖[7]如圖1所示。

        圖1在數(shù)學(xué)上可建模[7]為:

        矩陣的系統(tǒng)性能對比

        3 結(jié) 語

        本文從理論和實(shí)驗(yàn)仿真兩方面分析證明了獨(dú)立信道的預(yù)編碼技術(shù)不適合采用迫零均衡檢測算法。文獻(xiàn)[14]從最大化最小子載波信噪比準(zhǔn)則出發(fā)對獨(dú)立信道的預(yù)編碼技術(shù)進(jìn)行了研究,文獻(xiàn)[7,9?10]從獲得分集增益和編碼增益角度出發(fā)設(shè)計(jì)出了獨(dú)立信道的預(yù)編碼矩陣,仿真結(jié)果表明,當(dāng)接收端采用最大似然檢測(ML)算法或球狀譯碼(SD)等多符號聯(lián)合檢測算法時(shí),文獻(xiàn)[7]和文獻(xiàn)[14]提出的預(yù)編碼方案較未預(yù)編碼方案性能上有較大提升。因此,當(dāng)采用多符號聯(lián)合檢測算法時(shí),獨(dú)立信道的預(yù)編碼技術(shù)對于提升OFDM系統(tǒng)傳輸性能有重要的意義。

        參考文獻(xiàn)

        [1] PROAKIS J G. Digital communication [M]. New York: McGraw?Hill, 1995.

        [2] MIYAKAWA H, HARASHIMA H. Matched?transmission technique for channels with Inter?symbol interference [J]. IEEE Transactions on Communications, 1972, 20(4): 774?780.

        [3] TOMLISON M. New automatic equalizer employing modulo arithmetic [J]. Electronic Letter, 1971, 7: 138?139.

        [4] SAMPATH H, STOICA P, PAULRAJ A. Generalized linear precoder and decoder design for MIMO channels using the weighted MMSE criterion [J]. IEEE Transactions on Communications, 2001, 49(12): 2198?2206.

        [5] LIN Y P, PHOONG S M. Perfect discrete multitone modulation with optimal transceivers [J]. IEEE Transactions on Signal Processing, 2010, 48(6): 1702?1711.

        [6] SCAGLIONE A, GIANNAKIS G B, BARBAROSSA S. Redundant filterbank precoders and equalizers part I: unification and optimal designs [J]. IEEE Transactions on Signal Processing, 1999, 47(7): 1988?2006.

        [7] LIU Zhiqiang, XIN Yan, GIANNAKIS G B. Linear constellation?precoding for OFDM with maximum multipath diversity and coding gains [J]. IEEE Transactions on Communications, 2003, 51(3): 294?309.

        [8] 孫鍇,黃威.MIMO?OFDM無線通信技術(shù)及MATLAB實(shí)現(xiàn)[M].北京:電子工業(yè)出版社,2013.

        [9] WANG Z, GIANNAKIS G B. Wireless multicarrier communications: where Fourier meets Shannon [J] IEEE Signal Proces?sing Magazine, 2000, 17(3): 29?48.

        [10] XIN Y, WANG Z D, GIANNAKIS G B. Space?time diversity systems based on linear constellation precoding [J]. IEEE Transactions on Wireless Communication, 2013, 2(2): 294?309.

        [11] 張賢達(dá).矩陣分析與應(yīng)用[M].北京:清華大學(xué)出版社,2004.

        [12] AVRIEL M. Nonlinear programming: analysis and methods [M]. New Jersey: Prentice Hall Inc., 1976.

        [13] LUENBERGER D G. Linear and nonlinear programming [M]. 2nd ed. London: Addison?Wesley, 1984.

        [14] LIN Yuanpei, PHOONG S M. BER minimized OFDM systems with channel independent precoders [J]. IEEE Transactions on Signal Processing, 2003, 51(9): 2369?2380.

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