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

Abstract

Abstract-Code-division multiple-access (CDMA) schemes appear to be very promising access techniques for coping with the requirements of third-generation mobile systems, mainly because of their flexibility. This paper proposes an adaptive 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 multicell scenario by exploiting the potentials of CDMA under time-varying channel load conditions. The adaptive component makes data terminals autonomously change their transmission rate according to the total (voice+data) channel occupancy, so that the minimum possible data delay, which can be analytically obtained by defining a birth-death process, is almost always achieved. Moreover, by means of a simplified cellular model, the proposed algorithm revealed the same behavior, i.e., it tries to select the most suitable transmission rate at any time slot, when it is affected by intercell interference and even by power control imperfections. Finally, in order to gain more insight into the potentials of such an access strategy, the adaptive S-ALOHA CDMA scheme is then compared to a reservation time-division multiple-access (TDMA)-based protocol (PRMA++), showing the benefits of the CDMA-based solution in terms of capacity, flexibility, and data delay performance.

An Analytical Framework for the Design and Performance Evaluation of Realistic Aloha-CDMA Systems

“…Voice and data traffic is modeled by Bernoulli process models with fixed packet length where no new packet is generated during backlog mode of data users. An adaptive slotted Aloha DS-CDMA access scheme is proposed in Sallent et al [17] for voice and data services where data terminals change their transmission rate according to the total (voice data) channel occupancy to obtain the minimum possible data delay. The analysis is done under the assumption of a Poisson arrival process and exponentially distributed message length for conventional S-Aloha DS-CDMA system and the adaptive scheme is studied via simulation.…”

Throughput Analysis of Adaptive Slotted-ALOHA CDMA over a Multipath Fading Channel with Capture Effects

“…Moreover, as a result of the proportional increase in the number of users, which at the end leads to the increase in competition amongst users, the data rate shall decline. To address this problem, the so-called adaptive S-ALOHA CDMA has been proposed [4,5]. The optimum behaviour and low-complexity cost have been achieved by employing Markov Chain based adaptive S-ALOHA CDMA algorithm [4].…”

“…Due to variations in signal strengths amongst users, the throughputs of CDMA S-ALOHA shall decline [4][5][6][7][8]. As a result, in order to enhance the throughputs, capture effect technique (e.g., see [4][5][6][7][8][9]) has been proposed. Capture effects also shall enable a packet can be properly received in the presence of other packets in the same time slots.…”

“…S-ALOHA adaptive CDMA enables users to send the data using various transmission rates (4v bit/s, 2v nit/s v bit/ s) based on its current traffic conditions such that throughputs shall increase and the amount of delay can be suppressed [4][5][6][7]. Research on S-ALOHA adaptive CDMA based on BPSK modulation technique over AWGN channel with capture effects results in the bigger throughputs of the systems [8][9][10][11][12][13][14][15][16][17].…”

“…In order to calculate the throughputs of the system, adaptive transmission rate with Markov chain model was employed. The total number of users' sent packet due to [4,5,7] can be depicted as follows: …”