多輸入多輸出正交分頻多工系統中基於編碼可靠度混合重傳機制及適應性調變編碼之聯合設計

Abstract

編碼混合重傳機制(Hybrid Automatic Repeat Request, HARQ)為一種結合順向錯誤更正(Forward Error Correction, FEC)與自動重送機制(Automatic Repeat Request, ARQ)的錯誤更正技術；並被認為是第四代高速通訊在無線通道雜訊干擾下，解決錯誤更正問題之可行技術，而編碼可靠度混合重傳(reliability-based HARQ, RB-HARQ)機制為一新式編碼混合重傳機制，僅需重傳信賴度較低的位元，較傳統機制提供更優異效能表現且更具適應性；本論文研究主題之ㄧ，即為根據不同服務品質要求，針對編碼可靠度混合重傳機制提出一套適應性選擇重傳封包長度的演算法。另一方面，多輸入多輸出正交分頻多工(Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing, MIMO-OFDM)系統被認為是符合第四代高速通訊需求的最佳解決方案之ㄧ；MIMO為使用多天線於傳送和接收端的可靠通訊技術，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；本論文中研究主題之二，即為針對MIMO-OFDM系統提出一種結合編碼可靠度混合重傳機制與調變編碼的跨層適應性收發架構，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。吾人根據媒體存取層不同的服務品質要求，包含容許最大延遲時間及封包錯誤率，適應性的調整重傳次數、重傳封包長度、傳輸功率、傳輸速率、調變型態等系統參數，達到最佳的性能。最後，吾人藉由電腦模擬驗證上述架構在寬頻無線接取通道環境中具有優異的傳輸表現。

Hybrid automatic repeat request (HARQ) that combines ARQ and forward error correction (FEC) is a promising error-correcting technique for wireless communications. In reliability-based HARQ (RB-HARQ), the bits that are to be retransmitted are adaptively selected at the receiver based on the estimated bit reliabilities at the output of a soft decoder. This technique has the potential of improving system throughput. In this thesis, we propose an adaptive algorithm which can accordingly choose the sizes of retransmissions under the quality of service (QoS) constraints such as the maximum number of retransmissions allowed per packet and packet loss probability. Multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) is suitable for the increasing demand of the high-performance 4G broadband wireless communications with multiple antennas at both the transmitter and receiver sides. In this thesis, we then consider a new wireless communication system combining both MIMO-OFDM and RB-HARQ techniques and propose an adaptive MIMO-OFDM transceiver architecture along with a specifically designed loading procedure to dynamically adjust the transmission parameters such as retransmission size, number of retransmission, modulation order and transmit power over spatial and frequency channels, according to the instantaneous channel statistics, to meet the target QoS. Finally, we evaluate of the performance of the proposed systems, and confirm that it functions well in a typical broadband wireless access environment.