Media Access Control for Ad Hoc Networks with Adaptive Antenna Arrays

In the past several years ad hoc networking has received a lot of attention from the wireless research community and from industry. Unlike classical cellular networks where communications is highly asymmetric, ad hoc networks form when similar stations come into close proximity and spontaneously communicate. For this reason ad hoc networks must form their own infrastructure in a dynamic and distributed fashion, without any centralized coordination. The applications often quoted for ad hoc networks include combat systems, disaster area networks and campus/conference networks. As wireless communications is increasingly embedded into various objects and devices, the role of ad hoc networking is expected to expand.Much of commercial wireless communications is predominantly omni directional. In the past decade however, adaptive antenna arrays (AAAs) have been widely studied for use in mobile applications [2–5]. Unfortunately, multiple antenna systems have only slowly found their way into commercial applications mainly due to their cost and poor support from legacy air interfaces, especially those based on frequency division duplexing. The cost of multiple antenna systems has been dropping steadily in the past few years and it is now widely anticipated that adaptive antenna arrays will eventually find use in future ad hoc networks. The potential benefits of using AAAs in ad hoc networks include increased network capacity, improved service quality, increased wireless range extension and improved low power node operation.In this chapter, we will review much of the recent work associated with the merging of adaptive antenna arrays and ad hoc networks. Our discussion will focus on this combination from a media access control protocol viewpoint. We will focus on how these types of protocols must be changed to accommodate AAAs compared with the classical omni directional antenna case.