Error tolerant MAC extension for speech communications over 802.11 WLANs

The IEEE 802.11 MAC standard currently tolerates no errors in delivered packets. In this paper we study the performance of an error tolerant extension to the standard MAC that exploits the unequal perceptual importance of speech bitstreams. More in detail, we differentiate the CRC coverage on the speech payload in order to enable the delivery of partially corrupted packets. In our experiments, network drivers of a wireless receiver have been modified to test three different CRC strategies. GSM AMR-WB speech transmissions in various channel conditions have been evaluated in terms of packet losses, goodput, and user perceived quality. Results show that accepting erroneous packets more than halves the number of lost packets with respect to the standard MAC implementation. However error detection on the speech payload can not be completely disabled. Only if the most perceptually important bits are protected, speech quality is improved in every channel condition achieving quality gains up to 0.4 points of the MOS scale.