Multiplexing VBR video and training sequences on wireless fading channels

A time slotted multiple access scheme that shares bandwidth between source and training signals is proposed for the transmission of variable bit rate (VBR) video signals over non-ideal channels. The error performance is examined using finite state Markov chains that model both the VBR source traffic and the time variation of fading channels. The characteristic time-scale of the fade duration, the step-size parameter of the LMS equalizer training algorithm, and the number of training sequences allocated per time slot jointly influence the error performance. The consideration of the physical layer characteristics in the design of higher layer protocols enhances the performance of conventional application layer based preventive and reactive error control schemes. Simulation results for fast and slow fading channels show that the proposed channel access scheme can lead to an order of magnitude decrease in the bit error ratio if the combination of training overhead and step-size parameter are chosen judiciously with respect to the fading time-scale. In addition, the multiplexing efficiency of VBR encoded video is shown to be useful for limiting the channel access delays when training overhead is increased.