蔣海云等
摘 要: 正交頻分復用技術將多徑衰落信道劃分為多個相對平坦的子信道,使得接收機在信道估計等恢復技術上復雜度大大降低。OFDM系統(tǒng)采用子信道聯合預編碼技術能有效解決由于成片子載波衰落引起的數據丟失問題。由于獨立信道的線性預編碼技術在發(fā)送端不需要信道反饋信息,因此降低了發(fā)送設備復雜度,減少了系統(tǒng)延時,該編碼方案適用于從用戶端到基站的數據傳輸。通過理論分析推導了當系統(tǒng)采用獨立信道的線性預編碼技術時,接收端不能采用迫零均衡(ZF)的線性檢測算法,實驗仿真表明,當采用迫零均衡檢測算法時,當且僅當預編碼矩陣為酉矩陣時系統(tǒng)能達到未經預編碼系統(tǒng)的性能。
關鍵詞: OFDM系統(tǒng); 子信道聯合預編碼; 迫零均衡檢測算法; 星座調制信息
中圖分類號: TN92?34 文獻標識碼: 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
無線通信技術的迅猛發(fā)展極大地改變了人們生產生活方式,正交頻分復用技術[1](OFDM)作為無線通信的關鍵技術之一,在很大程度上降低了通信系統(tǒng)的復雜度。在多用戶通信過程中,從用戶端到基站的上行鏈路數據傳輸要求用戶設備盡可能簡化。在OFDM系統(tǒng)中,使用子信道聯合預編碼技術[2?4]能帶來性能上的提升。獨立信道的線性預編碼[5?6]是一類重要的預編碼方案,在發(fā)送端使用發(fā)送數據符號的統(tǒng)計特性設計預編碼矩陣,不需要已知信道信息,因此無需信道反饋,降低了發(fā)送端設備的復雜度,減少了傳輸延時。因此獨立信道的預編碼方案適用于用戶端到基站的數據傳輸。
1 獨立信道的線性預編碼技術采用迫零檢測算
法的性能分析
帶預編碼的OFDM系統(tǒng)簡化框圖[7]如圖1所示。
圖1在數學上可建模[7]為:
矩陣的系統(tǒng)性能對比
3 結 語
本文從理論和實驗仿真兩方面分析證明了獨立信道的預編碼技術不適合采用迫零均衡檢測算法。文獻[14]從最大化最小子載波信噪比準則出發(fā)對獨立信道的預編碼技術進行了研究,文獻[7,9?10]從獲得分集增益和編碼增益角度出發(fā)設計出了獨立信道的預編碼矩陣,仿真結果表明,當接收端采用最大似然檢測(ML)算法或球狀譯碼(SD)等多符號聯合檢測算法時,文獻[7]和文獻[14]提出的預編碼方案較未預編碼方案性能上有較大提升。因此,當采用多符號聯合檢測算法時,獨立信道的預編碼技術對于提升OFDM系統(tǒng)傳輸性能有重要的意義。
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