| 摘要(英) |
Cyclic redundancy check (CRC) scheme, which was particularly designed for medium access control (MAC) layer to detect erroneous frames, has been widely used in wired and wireless networks. Due to the limited information carried in the CRC field, receiver is not able to correct any erroneous frame and receiver drops all the erroneous frames automatically. To provide reliable communications on an error-prone communication link, retransmission scheme is often adopted to cooperate with the CRC scheme. From theoretical viewpoint, erroneous frame still possesses useful information which could be helpful for receiver to figure out the original data frame in case that retransmission is failed again. As a solution, we propose a new error recovery scheme at the MAC layer, namely CRC based error corrector (CEC), which simply amends legacy CRC error checker to become a CRC-based error corrector. The key concept of CEC is to compare all received erroneous frames and thereby derive the positions of differentiated bits among them. According to the positions of unmatched bits, all possible data frames are formed and rechecked by a fabric with a number of CRC encoders. As all error bits are detectable by the comparator, the original data frame is found. The error recoverable probability (ERP) of CEC is analyzed in this thesis. For evaluations, we also develop two types of hardware based CEC, namely CEC-I scheme and CEC-II scheme, as they equip different numbers of CRC encoders. As confirmed by performance evaluations, the proposed CEC with limited hardware cost can easily achieve excellent performance in term of the mean number of retransmissions per frame. |
| 參考文獻 |
[1] IEEE 802.16-2004, IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems, IEEE 802.16-2004, Oct. 2004
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[8] R. Lee, “Cyclic Code Redundancy,” Digital Design, pp. 77-85, Jul. 1981.
[9] A. Perez, “Byte-wise CRC Calculations,” IEEE Micro, Jun. 1983, pp. 40-50.
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[11] E. O. Elliott “Estimates of Error Rates for Codes on Burst-noise Channels,” Bell Svst. Tech. J., vol. 42, pp.1977-1997, Sept. 1963. |
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