Link adaptation evaluation for WLAN using a voice quality metric

Link adaptation, the process of adapting a mobile user´s link speed as channel conditions change, is investigated for IEEE 802.11a wireless local area networks (WLANs). An ideal algorithm using channel signal-to-noise ratio and a practical algorithm based on acknowledgement message (ACK) reception are discussed, and their performance is compared to cases without link adaptation. The analysis is performed by simulating a combination voice and data WLAN system, and voice call quality is judged using a unique quality metric. The metric contains two scores: a packet loss percentage and an estimate of the number of audible imperfections based on the pattern of packet loss. System capacity estimates result from applying the metric, and are used to compare the link adaptation schemes.