Wireless LAN MAC protocols

The MAC (Medium Access Control) protocols can be roughly categorized into three broad classes [16]. The fixed assignment set will have schemes like TDMA, CDMA and FDMA. These protocols lack the flexibility in allocating resources and thus have problems with configuration changes. This makes them unsuitable for dynamic and bursty wireless packet data networks. The random assignment class consisting of ALOHA[1] and CSMA is very flexible instead and is what is predominantly used in wireless LAN protocols. The demand assignment with schemes like Token Ring, GAMA[20] and PRMA[7] attempt to combine the nice features of both the above but special effort is needed to implement them in the wireless case (Eg. Token Ring needs to know its neighbors). There are systems designed using one or more of these classes. For instance cellular networks use ALOHA to get the code when entering a cell and CDMA for subsequent communication. For the purposes of this paper we restrict ourselves to second (more interesting) class of random assignment. To have a reasonable working set at hand, we do not consider protocols proposed in the context of wireless ATM; these deal with ATM specific issues like different traffic types.