Adaptive rate controller for mobile ad hoc networks

Mobile devices in the IEEE 802.11 wireless local area network (WLAN) have the ability to transmit data frames at one of four transmission rates 1Mb/s, 2Mb/s, 5.5Mb/s and 11Mb/s. This is because the commercial WLAN transceivers are equipped with several modulation schemes. According to the characteristics of the modulation scheme, a higher transmission rate will result in a smaller transmission range and longer time consumption on data frame transmission. If the channel environment is relatively clear and the transmission distance is short, one should choose a higher transmission rate for data transmission to maximise channel utilisation. On the contrary, a lower transmission rate should be selected to minimise the frame loss and frame error probabilities if the bit error rate is high. Therefore, the problem of choosing a proper transmission rate to accommodate a varying environment is a new and valuable problem in the wireless LANs. To our knowledge, it is very difficult and impractical to formalise an indoor environment since the channel status is quite unstable and unpredictable. Instead, we propose an adaptive rate controller (ARC), which employs the powerful fuzzy set function, for intelligently selecting the transmission rate for frame transmissions. This fuzzy control function refers the received signal strength indicator (RSSI), the frame error rate (FER) and the medium access control (MAC) delay to make a correct decision. Simulation results demonstrate that the proposed fuzzy controller indeed enhances the network throughput and the access delay.