MAC PROTOCOLS FOR COOPERATIVE DIVERSITY IN WLAN

Abstract

In recent year, there has been high research attention in the field of user cooperation in wireless communication networks. Here a survey of cooperative diversity enabled medium access control protocols for WLANs are presented. Cooperative diversity is a promising technique which can combat fading and improve reliability in wireless environment. It developed as an alternative to MIMO systems where nearby terminals share their antennas and resources and hence create a Virtual MIMO (VMIMO) system. These terminals cooperate with the transmitter and receiver to transmit multiple copies of the same data to the receiver through independent fading channels. These multiple copies of the data can be combined at the receiver using appropriate techniques to recover the original packet correctly. This improves the reliability of the wireless channel by exploiting the spatial diversity. MAC protocols play an important role in realizing this concept by effectively coordinating transmissions between source, relay and destination nodes. For this reason, the research community has proposed a large number of cooperative MAC protocols to realize this concept. Most of these protocols are contention based and hence are based on IEEE 802.11 DCF mode. These protocols can be classified in to different categories based on condition for cooperation, optimal helper selection procedure, etc. The protocols discussed here belongs to a category in which the decision for cooperation based on a cooperation condition, preparation of potential helper lists and optimal helper selection are done by the source itself. An overview of these protocols including handshaking schemes, medium access schemes, and features are discussed.