Multiple Access Protocols with Smart Antennas in Multihop Ad Hoc Rural-Area Networks

Multihop ad hoc networking is a very appealing technology for the deployment of wireless data networks. It eliminates the need for network planning and the reliance on fixed infrastructure. Multihop ad hoc networks are designed with a self-configuring capability and are able to adapt to the addition or removal of network radio units (nodes). This capability makes them simple to install, allowing unskilled users to quickly set up the network. These characteristics make multihop ad hoc networks very attractive for both civilian and military applications, e.g. in rescue operations. The type of multihop ad hoc networks studied in this thesis consist of identical nodes using the same frequency band for transmission. To control the Multiple Access Interference produced by sharing the same radio channel, a Medium Access Control (MAC) protocol must be used. Much work has been done in the MAC protocols area but the work has concentrated on generic nodes, whereas this thesis considers nodes with smart antennas, an enhanced capability. To fully exploit the additional capability the design of the MAC protocol needs to be considered. Hence, the results of a system level study into MAC protocols and smart antennas is presented in this thesis. Two different MAC protocols were examined, Spatial Time Division Multiple Access (STDMA) which shows much potential in multihop ad hoc networks and Carrier Sense Multiple Access Collision Avoidance (CSMA/CA) with handshaking which currently has much popularity as a result of its adoption in the IEEE 802.11 standard. STDMA is a conflict-free MAC protocol where links or nodes are scheduled to transmit in periodical slots making the integration of smart antennas relatively simple. Routing was found to be critical when utilizing smart antennas and a new procedure to create the link schedule is presented. In addition, it is shown that the terrain roughness influence the network connectivity. However, for the same network connectivity similar performance was obtained independently of the terrain roughness. Although STDMA has been found to be efficient and fair, the drawback is that it does not offer a quick response to peak rates for bursty data traffic. CSMA/CA with handshaking protocol provides a quick response to bursty traffic. The handshaking procedure within this MAC allows the use of smart antennas at both the transmitter and the receiver. How to effectively use smart