Performance of truncated type-II hybrid ARQ schemes with noisy feedback over block fading channels

This paper considers truncated type-II hybrid automatic repeat-request (ARQ ) schemes with noisy feedback over block fading channels. With these ARQ te chniques, the number of retransmissions is limited, and, similar to forward error correction (FEC), error-free delivery of data packets cannot he guar anteed. Bounds on the average number of transmissions, the average coding r ate as well as the reliability of the schemes are derived using random codi ng techniques, and the performance is compared with FEC. The random coding bounds reveal the achievable performance with block codes and maximum-likel ihood soft-decision decoding. Union upper bounds and simulation results sho w that over block fading channels, these bounds can be closely approached w ith simple terminated convolutional codes and soft-decision Viterbi decodin g. Truncated type-II hybrid ARQ and the corresponding FEC schemes have the same probability of packet erasure; however, the truncated ARQ schemes offe r a trade-off between the average coding rate and the probability of undete cted error. Truncated ARQ schemes have significantly higher average coding rates than FEC at high and medium signal-to-noise ratio even with noisy fee dback. Truncated ARQ can he viewed as adaptive FEC that adapts to the insta ntaneous channel conditions.