This research is conducted by Martin Heusse, Franck Rousseau, Cilles Berger-Sabbatel, Andrzej Duda on analyzing the performance of the IEEE 802.11b wireless local area networks. Degraded transmitting rate is caused by CSMA/CA channel access method.

Overview

The performance of the IEEE 802.11b wireless local area networks have degraded performances when some mobile hosts use a lower bit rate than the others, which is caused by CSMA/CA channel access method. When one host changes it modulation type which degrades bit rate, it occupies the channel for a longer time, causing other hosts still using higher bit rate to be penalized. The paper Performance Anamoly of 802.11b analyzes how such anomaly works.

Transmission Overhead

Consider there is only a single host in a 802.11b cell transmitting a single data frame. The overall transmission time is expressed as:

$$T = t_{tr} + t_{ov}$$

where the constant overhead

$$t_{ov} = DIFS + t_{pr} + SIFS + t_{pr} + t_{ack}$$

The transmission process can be represented by the graph

When there are multiple hosts attempting to transmit, a host will execute the exponential backoff algorithm - it waits for a random interval to avoid saturating the channel, resulting in extra time spent in the contention...