我們設計一個適用於室內之高生產量的4x4多輸入輸出正交分頻多工調變的無線通訊傳輸系統之通道回傳方案，並將其硬體設計完成。此無線通訊系統傳送機與接收機星座圖對應可支援到16QAM，多輸入輸出系統支援到4根傳送天線對應4根接收天線。此無線收發機可以支援三種不同子載波數的正交分頻多工調變系統分別對應到128、256與512個子載波模組。我們將原本需要回傳4x4x512個通道資訊壓縮至4x4x120個通道資訊，約為原來的20%。在通道回授模組設計中，我們採用對訊號使用Raised-Cosine濾波器過濾，可以有效抑制雜訊對系統效能的影響，在頻域上針對數位訊號使用Raised-Cosine係數與訊號做摺積(Convolution)。量化的部分我們針對802.11ac的架構將原本矩陣回傳的方式修改為以頻域方向的回傳，利用通道的相關性來進行Encoding可以提升分組方式的效能。在傳送機端我們先將原本Encoding後的通道資訊decoding回原來的資訊，再利用這些資訊使用內插器還原至原本需要的4x4x512個通道資訊。另外，這套通道回傳系統的效能，將直接影響傳送機使用排序後QR分解加上THP的precoding架構的效能。在硬體設計上我們考量到利用次取樣特性降低接收端(使用者端)複雜度，改變802.11ac規格之回傳編碼分組方式增加回傳效能，以及利用共用記憶體降低記憶體配置，我們設計的通道回傳方式可以在多輸入輸出系統在系統模擬上得到良好的效能。 Channel feedback reduction and channel interpolation of a precoded MIMO-OFDM baseband transceiver for indoor high-throughput wireless communication systems is presented. It is important to keep the quality of channel estimation but reduce the channel feedback overhead in precoded MIMO-OFDM systems. This system uses 16-QAM constellation and spatial multiplexing up to four antennas. We use the Tomlinson-Harashima precoding (THP) to get rid of interference at the transmitter. The performance of THP highly depends on on the accuracy of channel estimates. Thus, channel feedback encoding quantization is employed together with subsampling of the channel state information among the total transmission band. The transmitter then reconstructs the channel state information by frequency-domain interpolation. Simulation results show that improvement of channel feedback encoding and a sub-sampling ratio of 1/4 can approach the BER performance with perfect channel feedback. In hardware design, we use sub-sampling technology to reduces the complexity of the transceiver, provement encoding of 802.11ac specifications to increase the channel feedback performance, and reduce the memory allocation by sharing memory.
