| Summary: | 碩士 === 國立中山大學 === 通訊工程研究所 === 92 === There are two important techniques, automatic repeat request (ARQ) and forward error control (FEC), in error control systems. ARQ uses redundancy for detecting errors. While an error is detected in a transmitted code word, the receiver requests the transmitter to re-transmit the corrupted code word and the transmitted code word with detected error is discarded. However, the transmitted code word with detected error still contains a lot of information. ARQ schemes require a feedback channel. FEC relies on the controlled use of redundancy in the transmitted code word to detect and correct errors. Whether the decoding of the received code word is successful, no further processing is performed at the receiver. Therefore, FEC requires only a one-way link between the transmitter and receiver. In error control systems, a powerful FEC, turbo coding, was first proposed in 1993. Its performance was investigated by simulation to be close to the Shannon limit.
Hybrid ARQ (HARQ) systems after properly combining the ARQ techniques and FEC techniques, can be classified into type-I, type-II and type-III, and its performance can be elevated far more than ARQ systems. HARQ adopts the FEC methods to detect and correct the error patterns caused in the process of transmission. While errors are detected in the demodulated signals at receiver and fail to be corrected, the receiver will activate ARQ mechanism to request the transmitter to retransmit related information to achieve an error-free transmission.
In this thesis, a feasible type-II hybrid ARQ algorithm is proposed. Performance of the proposed algorithm is evaluated and analyzed by computer simulations. Compared with the traditional HARQ algorithms, the proposed algorithm can offer better performance in delay time and number of retransmissions with approximate throughput.
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