The performance of the ALOHA and CSMA MAC protocols are analyzed in spatially distributed wireless networks. The main system objective is correct reception of packets, and thus the analysis is performed in terms of outage probability. In our network model, packets belonging to specific transmitters arrive randomly in space and time according to a 3-D Poisson point process, and are then transmitted to their intended destinations using a fully-distributed MAC protocol. A packet transmission is considered successful if the received SINR is above a predefined threshold for the duration of the packet. Accurate bounds on the outage probabilities are derived as a function of the transmitter density, the number of back offs and retransmissions, and in the case of CSMA, also the sensing threshold. The analytical expressions are validated with simulation results. For continuous-time transmissions, CSMA with receiver sensing (which involves adding a feedback channel to the conventional CSMA protocol) is shown to yield the best performance. Moreover, the sensing threshold of CSMA is optimized. It is shown that introducing sensing for lower densities (i.e., in sparse networks) is not beneficial, while for higher densities (i.e., in dense networks), using an optimized sensing threshold provides significant gain. JAVA- Improving the Performance of Wireless Ad Hoc Networks Through MAC Layer Design
EXISTING SYSTEM:
The design of wireless ad hoc networks, various techniques is applied to efficiently allocate the scarce resources available for the communication links. Using an appropriate medium access control (MAC) protocol is one such technique. Taking into account the system’s quality of service (QoS) requirements, a MAC protocol for ad hoc networks shares the medium and the available resources in a distributed manner, and allows for efficient interference management. Due to the poor performance of unslotted ALOHA, a new MAC protocol, termed Carrier-Sensing Multiple Access (CSMA), was proposed by Kleinrock and Tobagi in [9] more than 30 years ago. By introducing channel sensing and the ability to back off from transmissions, the performance of wireless networks was greatly improved. Moreover, several modifications were proposed in order to overcome the inherent hidden and exposed node problems of CSMA. By allowing some kind of communication between the TX and its RX, throughput improvement was achieved. In the following subsections,we extend the work to consider point-to-point wireless ad hoc networks, and we evaluate the OP performance of CSMA.
PROPOSED SYSTEM:
In this proposed system performance of the ALOHA and CSMA MAC protocols in terms of outage probability (OP) ad hoc network model represents a communication system in which TX-RX pairs are randomly placed on a 2-D plane, and packets arrive continuously in time based on a 1-D PPP. Within our SINR-based model, we derive expressions for the OP of slotted and unslotted ALOHA, CSMA with TX sensing (CSMATX) and CSMA with RX sensing (CSMARX). Our derived analytical expressions are consistent with the simulations, and an intuitive understanding is established on the benefits of CSMA over ALOHA. An interesting result is that when no backoffs or retransmissions are allowed, CSMATX actually performs worse than unslotted ALOHA for low densities due to the exposed node problem. By allowing the RX to sense the channel in CSMARX and inform its TX over a control channel whether or not to initiate its transmission, the performance of the conventional CSMA is significantly improved.