Research On The Carrier Sensing Scheme For The Contention And Interference Control In Wireless Ad Hoc Networks

The wireless ad hoc network is a distributed multi-hop network which is composed of several mobile nodes with wireless transceiver devices, and it is very useful in complex environments without deploying the infrastructure and base stations.In wireless ad hoc networks, contention is a method to share the channel for nodes, and interference comes from the interplay of simultaneous transmissions in a region. The space occupied by transmissions determines the number of local contending nodes and local channel contention level, which refers to the exposed terminal problems; while the interference is mainly from surrounding nodes of receiver, which refers to the hidden and extend hidden terminal problems. These two issues seriously affect the performance and transmission capacity of networks. Currently, the challenges of contention and interference problems focus on the designing of a Medium Access Control (MAC) protocol, which effectively allocates channel resources and reduces conflicts, interference and data retransmission. In this dissertation, we analyze and study the carrier sensing, hidden terminal, exposed terminal, contention and interference problems in the physical layer and MAC protocol in the networks.The main work consists of two parts:1) The coordinated dynamic carrier sensing scheme based on local optimization. The distributed coordination function (DCF) focuses on the feature of the ongoing transmitting links to enhance link throughput, however the lack of coordinated adjusting surrounding nodes may reduce the aggregate throughput of entire networks. In this part, we are concerned with the delayed transmissions from exposed terminals and interference and collision from hidden terminals, and classify the neighboring areas to which nodes around a given transmission link into three areas: a hidden area, an exposed area and an overlapped area. The proposed coordinated dynamic physical carrier sense (CDPCS) scheme adjustes the carrier sensing thresholds of neighbors at the same time to achieve local optimization and the improvement of performance.2) The optimal physical carrier sensing based on exposed terminal mitigation. We mainly focus on the trade-off between the hidden terminal and the exposed terminal problems to improve the overall network performance. We first establish the Exposed Terminal Considered Throughput Penalty Function. Then, a heuristic PCS adaptation algorithm is proposed to search for the optimal PCS range within a reasonable time. Based on the models and the optimal theory, the algorithm updates the PCS threshold by calculating the transmission duration time, in which the network overhead is much less because of no cost of information exchange and center control.