正交時空區塊碼之頻域等化及其基於訓練機制之多輸入多輸出的擇頻通道估測

Abstract

針對正交時空區塊碼應用於多輸入多輸出之擇頻通道上的問題，吾人於本文中提出了一個嶄新且完整的推導方式；另著墨於此架構下所能達到的最大之多重增益－包括來自於天線以及多重路徑所貢獻者。藉由多次的模擬實驗結果發現，吾人可以得到一個於實際考量下為合理的假設，進而由此推導錯誤率分析。錯誤率分析的推導結果證實了吾人所提出之架構確實是有能力達到完整的多重增益。另一方面，藉由接收端的頻域等化機制以及所提出之傳輸架構，吾人可以進一步找到基於訓練機制時最佳的通道估測所需之相對應的訊號設計模式。本論文之結果為線性等化器能否達到完整的多重增益提供了一個正面的佐證。

We propose an instructive derivation for the generalized block-level orthogonal space-time block encoder, capable of achieving full spatial diversity via frequency- selective fading environment provided that channel order is known. Instead of dealing with special case and then extending the results intuitively, we provide an alternative by starting with the general signal model with multiple transmit and multiple receive antennas, from which a general form of block-level orthogonality is established. In particular, transmit diversity with more than two transmit antennas can be achieved without compromise by means of frequency-domain equalization, in contrast to the QO-STBC-based approach. Pairwise error probability analysis is derived, under certain assumption which is numerically supported by simulation results, for analytical verifications of our claim on full diversity, inclusive of transmit-receive diversity and the multipath one. Moreover, the encoder structure enables us to generalize a training-based channel estimation technique, originally proposed for flat-fading scenario, to the frequency-selective fading scenario. Surprisingly we even obtain similar optimality criteria for optimal training block design which in our case, the signal block are fixed as OSTBC-based and the design derivation reduces to derive optimal power constraint over the training blocks. The optimality criteria for the training blocks are easy to satisfy when randomness of signal constellation is not a concern. Simulation results validate our discussion of the behaviors of the least-squares and linear MMSE channel estimates.