  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.
