適用於多輸入多輸出無線區域網路之適應性調變編碼及傳送模式選擇之跨層設計

Abstract

多輸入多輸出(Multiple-Input Multiple-Output, MIMO)為使用多天線於傳送和接收端的可靠通訊技術，並被認為是符合第四代高速通訊需求的最佳方案之一。另一方面，正交分頻多工（Orthogonal Frequency Division Multiplexing, OFDM）為一種具高頻譜效益，並能有效克服多路徑衰落效應的調變技術。在本論文中，吾人針對MIMO-OFDM提出一種跨層設計之適應性收發架構，使其能夠隨時間動態地在頻率與空間通道上調整傳輸參數，如：調變階數、通道編碼以及傳輸能量，吾人更進一步的透過同時考慮實體層與媒體存取層之共同設計，將MIMO技術向上延伸至媒體存取層，依據不同的品質要求，進行調整及修正系統參數與選用適當的MIMO傳輸技術，適切調整及修正重傳次數、封包長度、傳輸功率、傳輸速率、調變型態等系統參數，以便充分地利用空間、時間以及頻率通道上的特性以維持系統的目標錯誤率，達到最佳的性能。此種架構的特色之一在於可視需要彈性地獲取多樣與多工兩種增益，且針對上層之需求根據通道狀況選擇適當之傳送模式與參數。另外，不同的通道環境會造成不同的多路徑衰落效應。基於此一觀點，吾人將探討結合智慧型天線與MIMO之通訊系統架構，針對不同的環境效應，選取最適合之傳輸技術。吾人將進一步針對MIMO提出一種適應性傳收架構，以便充分利用無線通道的特性。最後，吾人藉由電腦模擬驗證上述架構在室內無線環境中具有優異的傳輸表現。

Multiple-input multiple-output (MIMO) is a promising technique suited to the increasing demand for high-performance 4G broadband wireless communications with multiple antennas at both transmitter and receiver side. In this thesis, we consider a new wireless communication system combining MIMO and OFDM, called the MIMO-OFDM system. To fully exploit the channel properties in the space-time-frequency wireless channels, we propose an adaptive MIMO-OFDM transceiver architecture along with a designed loading procedure to dynamically adjust the transmission parameters such as modulation order, channel coding and transmit power over spatial and frequency channels, according to the instantaneous channel statistics, to meet the target BER. Such transceiver scheme enjoys both the diversity and multiplexing gain in a flexible manner. Furthermore, we evaluate different error control and adaptation mechanisms available at different layers, namely MAC retransmission strategy, physical-layer channel coding, modulation order, MIMO mode, and adaptive packetization strategies. Besides, In a wireless transmission environment, the transmitted signal is scattered by various environmental objects causing different multi-path fading effects. With this point of view, we here consider a wireless communication system combining smart antenna or MIMO techniques. Depending on the channel condition, the optimal transmission technique is selected to combat channel impairments. Finally, we evaluate the performance of the proposed systems, and confirm that they work well in a typical indoor environment.