多細胞多用戶正交分頻多工系統之同步多輸入多輸出通道估計

Abstract

在多細胞多用戶多輸入多輸出正交分頻多工 (orthogonal frequency-division multiplexing; OFDM) 的蜂巢環境中，通過首先將來自所有細胞的多個接收到的含有不同恆定振幅 (constant-amplitude; CA) 領航序列的OFDM探測信號分離出來，並在每個基站接收端聯合估計通道響應，實現同步通道估計 (simultaneous channel estimation; SCE)。 本論文在分析多細胞情況下基於最小平方法之同步通道估計的平均均方誤差時，考慮了在獨立的上行瑞利或萊斯多路徑通道下，每個基站接收端以及多個接收到的探測信號之間存在時間偏移的情況。在時域存在多個接收到的探測信號時，SCE系統能夠有效抑制各種接收到的探測信號之間的互相干擾，前提是每個細胞內使用的領航序列子集都是由在時域上滿足最小循環移位距離 ϖ_min 的條件下可循環移位的CA序列(cyclically-shiftable constant-amplitude; CSCA) ，也就是ϖ_min-允許的CSCA序列所組成，且來自不同子集的CA序列彼此間都是正交的。 因此，在本論文中構建了一個修改相位模型分配 (modified phase-model-assigning; MPMA) 序列家族，此家族由正交的 ϖ_min-允許的CSCA序列子家族組成，並將其與由非正交的 ϖ_min-允許的CSCA序列子家族所組成的Zadoff-Chu和Yu-Lee序列家族以及由正交的 ϖ_min-允許的CSCA序列子家族所組成的退化相位模型分配 (degenerated phase-model-assigning; DPMA) 序列家族進行了比較。採用MPMA序列家族的系統在SCE中可以提供了比採用Zadoff-Chu, Yu-Lee和DPMA序列家族更高的估計精確度。

In multicell multiuser multiple-input multiple-output orthogonal frequency-division multiplexing (OFDM) cellular environments, simultaneous channel estimation (SCE) is achieved by first separating multiple received sounding OFDM signals carrying different constant-amplitude (CA) pilot sequences from all cells and then estimating channel responses jointly at each base station receiver. Multicell least-square-based SCE is analytically studied herein in terms of average mean-square-error for each base station receiver operating under independent uplink Rician/Rayleigh multipath channels and in the presence of time offsets among multiple received sounding signals. The SCE system is shown to suppress the mutual interference among various received sounding signals effectively when the pilot sequence subset for each cell consists of all CA sequences that are cyclically shiftable with a minimum cyclic shift distance ϖ_min in time domain (namely, ϖ_min-permissible CSCA sequences), and sequences from different subsets are mutually orthogonal. Thus, a modified phase-model-assigning (MPMA) sequence family is constructed herein of orthogonal ϖ_min-permissible CSCA sequence subfamilies, and compared with Zadoff-Chu and Yu-Lee sequence families that are comprised of nonorthogonal ϖ_min-permissible CSCA sequence subfamilies and the degenerated phase-model-assigning sequence family which consists of orthogonal ϖ_min-permissible CSCA subfamilies. The system adopting the MPMA family is demonstrated to provide higher estimation accuracy in SCE than the systems adopting the other three sequence families.