用於多路徑衰落環境中擷取訊號之波束空間分集結合器

Abstract

在無線通訊環境下，波束分集技術能夠有效的對抗多路徑衰落．所謂波束 分集系統乃是多個具有不同場型的天線波束能形成不同的接收分支在不同 接收分支所發生的衰落現象是互不相關．如此技術有一個缺乏適應性的抑 制同通道干擾的缺點．在本論文中，吾人提出一個用於區域性訊號接收的 適應性場型分集結合器．此方法主要觀念乃在於一區域內形成多個波束場 型以達到分集來接收衰落訊號．再藉由選擇適當的加權向量使得在此工作 區域內能完成有效的分集結合,並徹底的抑制區域外的同通道干擾．然而, 這只能對抗平坦衰落通道．若在頻率選擇性衰落通道，此波束場型分集結 合器必須結合等化器使用以對抗碼際干擾．電腦模擬結果顯示，在具有多 干擾源及衰落現象之傳播下，結合吾人所提的適應性波束空間分集結合器 及等化器將是一適當解決方案 The beam diversity technique is effective in combating multipath in wireless communications. In a beam diversity system, multiple receiving branches are formed with multiple antenna beams with distinctive patterns. Thesebeams are synthesized in such a fashion that the fading phenomena observed at different branches are nearly uncorrelated. The disadvantage of such a system is the lack of adaptivity for cochannel interference (CCI) suppression. In this thesis, an adaptive beam diversity combiner is proposed for sectorized signal reception. The diversity branches are formed with several adaptive beamformers whose response patterns encompass an angular sector in the field-of-view of the receiver. With a set of juidiciously chosen weight vectors, effective diversity combining can be achieved inside the sector, and out-of-sector CCI can be suppressed via nulling. To enchance its tracking capability, the decision-directed mode is employed upon the convergence of the combiner. In a frequency selective fading channel in which intersymbol interference (ISI) is present,a joint operation of the decision-directed optimum combiner and linear equalizer is necessary, and will be discussed in the thesis. Finally, simulation results based on the GSM signal model are given to confirm the efficacy of the proposed beam diversity combiner/equalizer.