Adaptive S-ALOHA CDMA as an alternative way of integrating services in mobile environments

Code-division multiple-access (CDMA) schemes appear to be very promising ac cess techniques for coping with the requirements of third-generation mobile systems, mainly because of their flexibility. This paper proposes an adapt ive S-ALOHA DS-CDMA access scheme as a method for integrating nonreal-time (i.e., Internet applications) and real-time (i.e., voice) services in a mul ticell scenario by exploiting the potentials of CDMA under time-varying cha nnel load conditions. The adaptive component makes data terminals autonomou sly change their transmission rate according to the total (voice+data) chan nel occupancy, so that the minimum possible data delay, which can be analyt ically obtained by defining a birth-death process, is almost always achieve d. Moreover, by means of a simplified cellular model, the proposed algorith m revealed the same behavior, i.e., it tries to select the most suitable tr ansmission rate at any time slot, when it is affected by intercell interfer ence and even by power control imperfections. Finally, in order to gain mor e insight into the potentials of such an access strategy, the adaptive S-AL OHA CDMA scheme is then compared to a reservation time-division multiple-ac cess (TDMA)-based protocol (PRMA++), showing the benefits of the CDMA-based solution in terms of capacity, flexibility, and data delay performance.