Frame Delay and Loss Analysis for Video Transmission over time-correlated 802.11A/G channels

摘要

This paper presents simulation results for the transmission of unicast MAC frames over 802.11a/g. Fading channel models at various Doppler frequencies are developed to generate time-correlated SNR waveforms. These are then used together with a bit accurate MAC/PHY simulator to estimate the frame loss rate, the transmission delay, and the jitter for a steady flow of transmit frames. Time correlated channels are required to correctly simulate the bursty nature of packet loss in a wireless channel. The Doppler spread is shown to have a strong effect on the performance of the ARQ mechanism in the MAC layer. Delay is computed as the sum of the transmission delay and the accumulated queuing delay in the MAC buffer. Delay and frame loss are compared for time correlated and time uncorrelated fading channels. Compared to the slow fading case, in a fast fading channel fewer retransmissions are required and the end-to-end delay is significantly reduced. When channel conditions are poor the simulated delay and frame loss rate are seriously underestimated when time uncorrelated fading is assumed. To analyze the performance of video codecs, we show that a time correlated channel model must be combined with a dedicated 802.11a/g MAC/PHY simulation.