摘 要:無線OFDM通信系統(tǒng)中信道的時變特性非常明顯,載波間正交性遭到破壞,出現(xiàn)載波間相互干擾(ICI),給系統(tǒng)均衡帶來了極大困難?;诘刃?shù)字基帶模型下ICI分析,在現(xiàn)有的 OFDM協(xié)議標(biāo)準中,存在一些空閑載波。利用這些空閑子載波信息,研究了一種適用于時變信道 OFDM 系統(tǒng)的稀疏矩陣均衡器結(jié)構(gòu)。該算法具有 ICI 消除與均衡效果良好,計算量適中,頻譜利用率高的特點。關(guān)鍵詞:時變信道; OFDM系統(tǒng); ICI; 系統(tǒng)均衡; MMSE算法
中圖分類號:TN602文獻標(biāo)識碼:A
文章編號:1004-373X(2010)15-0092-04
Research and Design of Equalizer in OFDM System
HUANG Jun-you
(Sichuan Information Technology College, Guangyuan 628017, China)
Abstract: The time-varying characteristic of channel in wireless OFDM communication system is obvious, the destroyed orthogonality between carrier may cause the inter-carrier interference (ICI), which leads to a great difficulty for system equalization. A number of free carrier are existed in current OFDM protocol standards based on the ICI analysis under equivalent digital base-band model. A structure of sparse matrix equalizer applicable to time-varying channels for OFDM system is studied by using the information of idle sub-carrier. ICI elimination and equalization of the algorithm have good effect, suitable calculation and high spectral efficiency.Keywords: time-varying channel; OFDM system; ICI; system equalization; MMSE algorithm
0 引 言
傳統(tǒng)OFDM 系統(tǒng)設(shè)計,假設(shè)信道參數(shù)在一個OFDM 符號周期內(nèi)不變化,信號通過頻率選擇性衰落信道后載波間的正交性保持不變,接收機通過簡單的單抽頭頻域均衡即可補償信道失真。無線OFDM 通信系統(tǒng)信道時變特性更明顯,當(dāng)信道參數(shù)隨時間快速變化時,正交頻分復(fù)用通信系統(tǒng)(OFDM)載波間的正交性遭到破壞,出現(xiàn)載波間的相互干擾(ICI),傳統(tǒng)的單抽頭頻域均衡器不再適用[1]??熳冃诺乐械?OFDM 系統(tǒng)均衡接收常采用兩種方法:先對接收信號進行ICI消除,恢復(fù)載波間的正交性,然后再進行單抽頭頻域均衡;采用最小均方誤差(MMSE)均衡來補償信道失真[2]。
1 等效數(shù)字基帶模型下ICI分析
模型如圖1所示。設(shè)系統(tǒng)有N個載波,發(fā)送設(shè)備先對發(fā)送符號進行串/并變換,得到長度為 N 的數(shù)據(jù)矢量,第i個數(shù)據(jù)矢量表示為:S(i)=[si,0,si,1,…,si,N-1]T,對數(shù)據(jù)矢量進行N點快速傅里葉逆變換(N-IFFT),得到時域數(shù)據(jù),在此數(shù)據(jù)前面插入長度為M 的循環(huán)前綴CP,得到長度為N+M的OFDM 數(shù)據(jù)幀,經(jīng)并/串變換,信號在信道中傳輸?!?br>