Design of an access mechanism for a high speed distributed wireless LAN

Abstract

The medium used by indoor wireless LANs is a shared, scarce resource. Hence, efficient use of this medium is important, which in turn requires an efficient MAC protocol. Moreover, next generation wireless LANs will have to support data rates from 10 to 100 Mbits/s. At these data rates, turnaround times in half-duplex radios are a large overhead. This makes the current wireless standards inefficient. However, busy-tone solutions can get around this problem. In spite of their better performance, the busy-tone protocols are not widely used because of the hardware cost, i.e., the requirement of two transceivers-one each for the data and feedback channel. A novel wireless transceiver architecture which mitigates this hardware cost by overlaying the data channel and the feedback channel in the same frequency band is designed. It is shown that this transceiver can be built with current technology. Based on this wireless transceiver, a new MAC protocol called wireless collision detect (WCD) is proposed. This protocol uses a carrier detect signal to decrease the collision probability and receiver initiated feedback to handle hidden nodes. We derive a mathematical expression for the throughput of the protocol. The simulation results match the analysis. At 100 Mbits/s, WCD achieves 77% efficiency with 192 byte packets. For this scenario, the throughput of the IEEE 802.11 MAC protocol and RI-BTMA is 3% and 52%, respectively.