Robustness of multiplexing protocols for audio-visual services over wireless networks
The protocols used to multiplex the various streams in an audio-visual service (such as MPEG 2 systems and ITU-T H.223) have an important impact on the quality of the service. The fact that wireless channels are often associated with high bit-error rates which are often bursty means that the multiplexing protocols should be designed to be robust against such errors. We suggest two departures from traditional practice which can improve significantly the performance of a packet-oriented multiplex for use with audio-visual services: (1) where the packet header is protected against errors using forward error correcting codes, the use of a synchronization codeword (or flag) is often unnecessary, and (2) for channels where errors tend to occur in bursts, the occurrence of errors in the header can be reduced by transmitting the header information twice (at both ends of the packet) with a low level of FEC protection instead of using the same number of bits to obtain an increased level of protection using a single code word. The value of these approaches is confirmed by simulations.