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Optimized Policies for the Retransmission Probabilities in Slotted Aloha

Chakraborty, Anshuk and Bhatnagar, Shalabh (2010) Optimized Policies for the Retransmission Probabilities in Slotted Aloha. In: Simulation, 86 (4). pp. 247-261.

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Official URL: http://sim.sagepub.com/cgi/content/abstract/86/4/2...


In this paper, we study the behaviour of the slotted Aloha multiple access scheme with a finite number of users under different traffic loads and optimize the retransmission probability q(r) for various settings, cost objectives and policies. First, we formulate the problem as a parameter optimization problem and use certain efficient smoothed functional algorithms for finding the optimal retransmission probability parameter. Next, we propose two classes of multi-level closed-loop feedback policies (for finding in each case the retransmission probability qr that now depends on the current system state) and apply the above algorithms for finding an optimal policy within each class of policies. While one of the policy classes depends on the number of backlogged nodes in the system, the other depends on the number of time slots since the last successful transmission. The latter policies are more realistic as it is difficult to keep track of the number of backlogged nodes at each instant. We investigate the effect of increasing the number of levels in the feedback policies. Wen also investigate the effects of using different cost functions (withn and without penalization) in our algorithms and the corresponding change in the throughput and delay using these. Both of our algorithms use two-timescale stochastic approximation. One of the algorithms uses one simulation while the other uses two simulations of the system. The two-simulation algorithm is seen to perform better than the other algorithm. Optimal multi-level closed-loop policies are seen to perform better than optimal open-loop policies. The performance further improves when more levels are used in the feedback policies.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Sage Publications.
Keywords: closed-loop optimization; optimal retransmission probability; slotted Aloha; smoothed functional algorithms
Department/Centre: Division of Electrical Sciences > Computer Science & Automation
Depositing User: Ms G Yashodha
Date Deposited: 08 Jun 2010 09:08
Last Modified: 08 Jun 2010 09:08
URI: http://eprints.iisc.ac.in/id/eprint/26993

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