Exclusion and Guard Zones in DC-CDMA Ad Hoc Networks

TL;DR

This paper analyzes how exclusion and CSMA guard zones affect interference management and capacity in DS-CDMA ad hoc networks, providing formulas and tradeoff insights for network design.

Contribution

It introduces a comprehensive analysis of exclusion and CSMA guard zones in DS-CDMA networks, including closed-form outage probability expressions and capacity tradeoffs.

Findings

Exclusion zones maintain constant active mobiles, enhancing capacity.

CSMA guard zones deactivate mobiles within their range, reducing interference.

Design parameters like spreading factor and guard-zone radius influence outage probability.

Abstract

The central issue in direct-sequence code-division multiple-access (DS-CDMA) ad hoc networks is the prevention of a near-far problem. This paper considers two types of guard zones that may be used to control the near-far problem: a fundamental exclusion zone and an additional CSMA guard zone that may be established by the carrier-sense multiple-access (CSMA) protocol. In the exclusion zone, no mobiles are physically present, modeling the minimum physical separation among mobiles that is always present in actual networks. Potentially interfering mobiles beyond a transmitting mobile's exclusion zone, but within its CSMA guard zone, are deactivated by the protocol. This paper provides an analysis of DS-CSMA networks with either or both types of guard zones. A network of finite extent with a finite number of mobiles and uniform clustering as the spatial distribution is modeled. The analysis applies a closed-form expression for the outage probability in the presence of Nakagami fading, conditioned on the network geometry. The tradeoffs between exclusion zones and CSMA guard zones are explored for DS-CDMA and unspread networks. The spreading factor and the guard-zone radius provide design flexibility in achieving specified levels of average outage probability and transmission capacity. The advantage of an exclusion zone over a CSMA guard zone is that since the network is not thinned, the number of active mobiles remains constant, and higher transmission capacities can be achieved.