A HYBRID MULTILEVEL ERROR CONTROL SCHEME FOR WIRELESS ATM NETWORKS

Abstract

In this thesis, a Hybrid Multilevel Error Control (HMEC) scheme for ·wireless ATM (WATM) is described. The main techniques adopted in the scheme include error detection, error correction, and cell recovery combined with an early-stop ARQ scheme. The main idea of the HMEC scheme is that the information from a source is segmented into a number of blocks, each with m cells. The cells are protected using the techniques of error detection and error correction, then these m cells are encoded again into k (k?m) cells. At the receiver, cells containing uncorrectable errors are dropped. When the number of such dropped cells is more than k - m in one block, subsequent corrupted cells are retransmitted using the ARQ protocol. On the other hand, the transmission of one block may be finished using early-stop ARQ as long as m out of the k cells are received correctly. In either case, the original information of a block can be reconstructed from the m received cells. In this thesis, the throughput efficiency of the HMEC protocol in white Gaussian channels and Rayleigh fading channels is analyzed; the analysis models in random error channels and IVlarkov transmission error channels are given: a novel analysis method -- '·event-split-insert' for Markov transmission error channels is proposed; a set of simulations is clone and the simulation results are discussed in depth. From the theoretical analysis and simulations, we can see that the HMEC scheme is superior to some conventional error control schemes. The HMEC .scheme is able to improve performance of wireless ATM networks in terms of reliability and efficiency- reducing the probability of cell retransmission and maintaining a higher throughput over a wide range of channel error rate if proper protocol parameters are chosen. Therefore, the HMEC scheme is an efficient error control scheme for wireless ATM networks.