利用適應性濾波器為設計用於多輸入多輸出之時空柵狀編碼系統之渦輪等化器

Abstract

時空柵狀編碼是一個使用多根傳送天線的頻寬節省技術•當使用在寬頻的傳送系統時，通道的頻率選擇特性會造成不可忽略的影響。信號之間的互相干擾(ISI)以及同通道中的外來干擾(CCI)都會降低時空柵狀編碼所帶來的的效能增長•在這個論文裡，我們的目的是設計與建立一種接收的技巧，讓時空柵狀編碼系統即使經歷了具有頻率選擇效應的多輸入多輸出通道，仍能正確的接受資訊。我們設計了一個渦輪等化器，使用一根或兩根接受天線來接受多根傳送天線的訊號。等化的動作是用一個簡單的適應性濾波器為主的等化器。濾波器的係數是用一個名稱為”最少平均平方”的適應性演算法來獲得。在每次遞迴時，等化器和解碼器產生出外質的訊息，然後這些外質的訊息會在下次遞迴的時候被拿來使用，就像渦輪碼一樣。我們用兩根、三根、四根的傳送天線來跑模擬，藉此來觀察傳送天線數目對系統效能的增進。關於不同大小的交錯器對我們的渦輪等化器的影響，我們也用模擬來觀察。這些模擬結果顯示出，我們提出的渦輪等化器，配上適當大小的交錯器，能夠有效的對抗多路徑造成的不好影響以及同通道中的干擾。

Space-time trellis code (STTC) is a bandwidth-efficient technique utilizing multiple transmit antennas. When it is applied to wideband systems, the channel’s frequency-selective characteristics are not negligible. The inter-symbol interference (ISI) and the co-channel interference (CCI) will deteriorate the system performance improvement provided by STTC. In this thesis, our goal is to develop a receiving scheme for space-time trellis coded system over frequency-selective multiple-input-multiple-output (MIMO) channels. We design the turbo-equalization with one or two receive antennas to recover all symbols from multiple transmit antennas. Equalization is performed using a simple adaptive filter-based equalizer. The filter coefficients of the equalizer are obtained using an adaptive algorithm called “least-mean-squared (LMS)”. At each iteration, extrinsic information is extracted from the detection and decoding units and is then used at the next iteration as in turbo-decoding. Simulations of two, three and four transmit antennas are conducted to see the performance improvement provided by the different number of transmit antennas. Simulations with different interleaver sizes are also conducted to observe the effect of the interleavers on a turbo system. The simulation results show that the proposed turbo-equalizer with an appropriate interleaver size can successfully combat the multipath effects and the co-channel interference