An Improved Intelligent Hybrid Spread Spectrum MAC Protocol for Interference Management in Wireless Ad hoc Networks

Abstract

Wireless Ad hoc Network (WANET) is a decentralized setup of randomly dispersed and mobile nodes that do not depend on a pre-existing infrastructure. These nodes tend to contend for scarce resources (time, space, bandwidth). This contention causes interference which is one of the most significant degradation factor in communication. Successful communication needs an efficient Medium Access Control (MAC) protocol for enhancing the Transmission Capacity, which is defined as the maximum permissible density of concurrent transmissions in an area, constraint to a specified outage probability. This objective can be achieved by managing interferers around an intended receiver to obtain a desired threshold of signal to interference plus noise ratio (SINR). If the required threshold is not met, an outage occurs. Existing MAC schemes like Carrier Sense Multiple Access (CSMA), Random back off and Guard Zone-based protocols, achieve interference mitigation through suppressing some of active nodes. This prevents nodes from transmission in a certain space during specified time which compromises the Transmission Capacity. Intelligent Hybrid Spread Spectrum (IHSS) MAC is one of existing schemes which used Direct Sequence Spread Spectrum (DSSS) for network wide nodes and Slow Frequency Hopping (SFH) to maintain orthogonality between communications with in a zone around each receiver. Normalized outcome of IHSS MAC showed superior performance over previous schemes. In this research, an improved IHSS MAC scheme is proposed which enhances the Transmission Capacity of ad hoc network where nodes are randomly distributed in space, according to homogeneous Poisson Point Process (PPP). Proposed method employs frequency hopping, based on assigned orthogonal codes, to minimize the effect of interference between simultaneous transmissions. Results depict the improved outcome and help in establishing the tradeoffs between various network parameters, as per network designer’s requirement.