Error control strategies for the wireless channel

The requirements of emerging new communications services differ in many critical ways from traditional voice applications. The effect of errors on voice transmission and techniques to overcome them are relatively well understood. On the other hand, the impact of errors on multimedia transmissions is not fully understood. The Gilbert-Elliott (1960, 1963) model is adequate for characterizing the bursty errors that occur over a communication channel. The channel "seen" by applications is the physical channel as modified by the error correcting mechanisms used at the physical level. Therefore, correlations in the residual error process are relevant to the design of encoding algorithms. We study the residual error process and characterize the block error process beyond the marginal statistics. A Markovian model for the block errors is considered and shown to be adequate. Derivations of the parameters of the block error process an presented in terms of the parameters of the bit/symbol error process. For voice transmissions the use of interleaving and a moderate amount of error correction is found to be desirable, but at higher data speeds, an effective interleaving strategy is found to require very large memory.