The Lower Shifting of the Thresholds between 802.11a PHY Rate Modes Selection over Frequency Selective Fading Channels

Due to channel fading effects, the SNR (signal-to-noise ratio) of receiving packets forms a probabilistic distribution with the target SNR of the mobile station as the approximate mean. Performance of the packet error rates (PERs) of different received SNR values, given that the target SNR is fixed, is investigated over frequency selective fading channels. Both an analytical upper bound and a statistical average (via simulation) of the PER of individual received SNR value were obtained. This paper demonstrates that lower target SNR values gives better PER performance under the same received SNR This observation has a significant impact on the determinations of the SNR thresholds for 802.11a link adaptation. Numerical results have shown that the link adaptation thresholds between two comparative rate modes should be decreased with the lowering of target SNR values. Finally, the lower shifting of the thresholds between PHY rate modes selection of 802.11a link adaptation for different target SNR values over ETSI/BRAN channel-A model is presented.