Maximizing delay-constrained throughput in multi-channel DS-CDMA ALOHA networks through power diversity and successive decoding

Abstract

We study multi-channel ALOHA networks (e.g., satellite-based networks) for online transaction processing, striving to maximize attainable throughput while meeting a deadline with near certainty. This captures the service provider's fixed costs and per-transaction revenue, the user's delay consciousness and ALOHA's probabilistic nature. Specifically, we consider CDMA channels and successive-decoding receivers. Interestingly, judicious use of power diversity is shown to be extremely effective: with a single transmission, capacity is doubled relative to that with power equalization. With the deadline permitting as few as one or two retransmission attempts upon failure, the probability of not meeting it can be virtually diminished (10 -5 and 10 -8 , respectively) while approaching the throughput attainable without delay constraints. This also holds for limited mean transmission power. Thus, the effect of power diversity in conjunction with CDMA depends strongly on the type of receiver and on the exact performance measure, and the proposed approach is worth considering for next-generation systems.

Rejuvenating ALOHA: Motivation, approaches and insights

“…The work of [14] was motivated by the observation that more sophisticated receivers that employ successive decoding can mitigate the problem caused by power diversity in con junction with CDMA. Indeed, it is shown that power diversity, in conjunction with optimized power levels and selection probabilities, can yield a significant throughput increase.…”

“…Additionally, frequency-hopped CDMA (FH-CDMA) has been shown to have near-far resistance even with a single-user receiver [16]. As in [15], [14] embarks from the basic CDMA K-user channel model consisting of the sum of antipodally modulated signature sequences embedded in additive white Gaussian noise.…”

“…in [14] were obtained through exhaustive search. One may argue that this is too computationally expensive and therefore cannot be used in practice.…”

“…r thr is the lowest SIR that still enables successful decoding of a packet by the receiver. r thr is a function of the decoding scheme used, and its derivation is not provided in [14].…”

“…To prevent the failure of all the remain ing signals after the first decoding failure in the non-linear receiver, another variant of an SIC receiver was considered in [14]: when the decoding of a user fails, it is subtracted linearly.…”