Joint protocol-channel decoding for robust aggregated packet recovery at wimax MAC layer

In many communication protocols, small packets are aggregated into larger packets (bursts) at some layer of the protocol stack before being forwarded to the lower layer. Upon reception, the beginning of the burst has to be detected, and it has to be segmented to recover the small packets. Usually, this task is performed by hard decision on the received data. Obviously, if the burst is affected by transmission errors, many packets are likely to be erroneously segmented. Error detection and retransmission are usually employed to solve this problem, reducing the throughput. This paper proposes a robust aggregated packet header recovery mechanism able to significantly reduce the segmentation error. This technique is applied to the IEEE 802.16 PHY layer, where MAC bursts are segmented into MAC packets. The aggregation of MAC packets is modeled as a Markov process. The possible successions of MAC packets forming a burst are described by a trellis. A BCJR-like algorithm then provides a posteriori probabilities of packet boundaries. Simulation results show that the proposed method outperforms the conventional hard decision decoder by more than 8 dB in SNR.