Dynamic spreading gain control in multiservice CDMA networks

摘要

In this paper, we consider a direct-sequence code divisionnmultiple access (DS-CDMA) network consisting of a single radio accessnpoint and a collection of wireless terminals. The network offers twonclasses of service: class-1 (real-time) and class-2 (reliable). We areninterested in studying the effect of dynamic spreading gain controln(SGC) on the dynamics of multiple access interference (MAI), spectralnefficiency, and the quality of service (QoS) experienced by each servicenclass. We first consider a time-slotted system in which class-2nterminals operate in a random access fashion. We show that under optimaln(throughput maximizing) dynamic SGC: (1) the optimal retransmissionnprobability is equal to one, and (2) the optimal spreading gainnincreases linearly, or equivalently, the transmission rate decreasesninverse linearly, as the MAI level increases. We then model the systemnas a continuous-time finite-source queueing system with processornsharing, and obtain an explicit (closed-form) expression for thenstationary distribution of the number of active class-1 and class-2nterminals, that is, the MAI level. This distribution is used to derivenexpressions for various QoS measures and define a capacity or admissiblenregion. The results obtained by simulation and analysis are in extremelynclose agreement. This work contributes to a better understanding of thenrelationships between QoS, multiple access interference, and allocationnof radio resources in DS-CDMA networks