Performance of enhanced multi-code spread slotted Aloha (EMCSSA) with voice and data

We present an analytical framework which enables the MCSSA protocol defined and analyzed by Dastangoo, Vojcic and Daigle (see IEEE GLOBECOM ´98) to support differentiated services (e.g., voice and data). The underlying principles to the MCSSA protocol consist of two elements. The first element concerns the users´ random selection from a finite number of resources (i.e., channels or spread spectrum (SS) codes). The second is the simultaneous transmission of users´ packets. These elements are realized through two stages of packet acquisition (Stage-I) and packet transmission (Stage-II). Therefore, a successful transmission depends not only upon the success in Stage-I, but also the success in Stage-II. To support multi-traffic classes requires several modifications to Stage-I of the MCSSA protocol. Naturally, voice traffic must be given preferential treatment over the data traffic, since the quality of service (QoS) of the former suffers more from excess access/queueing delays. In EMCSSA, we develop a priority mechanism in Stage-I which enables the voice users to contend, acquire, and reserve SS codes for the duration of their calls. Since the users´ access to the resources in EMCSSA is distributed on a per-slot basis, each user´s activity should be known to all. This is realized through a multi-level information feedback in Stage-I. We set the stage for both infinite population (Poisson/binomial model) and finite population (Markov model) cases. However, we only present the former. To assess the performance of the proposed protocol, we evaluate a commonly used performance metric: the average throughput