混合式自動請求重傳機制應用於移動與協同通訊系統下之效能分析

Performance analysis of applying HARQ scheme in mobile and cooperative communication systems

江元弘(Yuan-Hong Jiang)

指導教授 ： 林信標

國立臺北科技大學/電資學院/電腦與通訊研究所/碩士(2009年)

https://doi.org/10.6841/NTUT.2009.00374

摘要

多輸入多輸出架構藉由在傳送與接收端使用多根天線傳送訊號，提高資料傳輸速率與系統效能，為近年來最為熱門的技術之ㄧ。正交分頻多工技術的使用可使資料於傳送過程中只經歷平坦衰減通道，擁有較佳對抗頻率選擇性衰減能力。混合式自動請求重傳為一種重傳之機制，藉由透過錯誤偵測方式來決定是否對資料進行重傳，在重傳階段則結合前次之錯誤解碼資料，進而降低資料之錯誤率。對於協同系統之應用而言，利用中繼站使用者來輔助傳輸，可藉由空間分集方式改善其系統效能。
本論文分別探討混合式自動請求重傳機制應用於移動以及協同通訊系統之效能與吞吐量分析，並在探討後提出在兩種應用方案下之改良方式。在移動通訊系統中，論文中使用基於訊號干擾比之改良式干擾消除法，利用載波干擾之分佈特性，找出干擾較嚴重之影響範圍並搭配重傳機制，有效的對干擾進行壓制及消除。在協同傳輸架構之方案下，本論文則提出了一種將重傳概念用於協同架構下，利用中繼站使用者來輔助重傳，而使用者在每個時間皆傳送新的資料，對時間資源進行有效率的運用。
在移動情況下，當Normalized Doppler為15 %、使用16-QAM調變下，則在第一次重傳時可改善將近5.5 dB左右之系統效能，優於一般之並列式干擾消除法。對於使用協同傳輸架構而言，當子載波數為64、搭配強迫為零等化器時，則整體系統吞吐量最大可改善13 %。

關鍵字

多輸入多輸出 ； 正交分頻多工 ； 混合式自動請求重傳 ； 協同通訊系統

並列摘要

Multiple Input Multiple Output (MIMO) structure, one of the most popular transmission techniques recently, upgrades the system performance and data rate by transmitting signals through multiple antennas at transmitter and receiver. Orthogonal Frequency Division Multiplexing (OFDM) technique can let the transmitted data only experiencing the flat fading channel, which has better capability of resisting frequency selective fading. Hybrid Automatic Repeat reQuest (HARQ) scheme is a retransmission method which through error detection determines whether the data retransmission is required or not. At the retransmission stage, HARQ combines the former error decoded data and then decreases the data inaccuracy. For the application of cooperative system, relay-assisted transmission improves the system performance through the spatial diversity gain.
In this paper, we analyze the system performance and throughput by applying the HARQ scheme in mobile and through cooperative communication systems. We will propose the improved method after discussing both applicable cases. In mobile communication system scenario, we propose an improved Parallel Interference Cancellation (PIC) method on the basis of the Signal-to-Interference Ratio (SIR), find the comparatively severely interfered terms through the property of Inter Carrier Interference (ICI) distribution, collocate the retransmission scheme, and effectively compress and eliminate the interference. For the cooperative transmission systems, we also propose a cooperative transmission scheme, retransmitting the previously packet by using the relay, and the user always transmits the new packet every time slot to make the best utilization of time.
Under mobile condition, while the Normalized Doppler is equal to 15 % and 16-QAM modulation is applied, the proposed method improves about 3.5 dB of system performance after the first retransmission, which is superior to the conventional PIC method. For the cooperative transmission structure, the maximum overall system throughput improves 13 % by using 64 subcarriers and Zero Forcing (ZF) equalizer.

並列關鍵字

MIMO ； OFDM ； HARQ ； Cooperative communication systems

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