Spatially-Coupled Random Access on Graphs

Abstract

In this paper we investigate the effect of spatial coupling applied to the recently-proposed coded slotted ALOHA (CSA) random access protocol. Thanks to the bridge between the graphical model describing the iterative interference cancelation process of CSA over the random access frame and the erasure recovery process of low-density parity-check (LDPC) codes over the binary erasure channel (BEC), we propose an access protocol which is inspired by the convolutional LDPC code construction. The proposed protocol exploits the terminations of its graphical model to achieve the spatial coupling effect, attaining performance close to the theoretical limits of CSA. As for the convolutional LDPC code case, large iterative decoding thresholds are obtained by simply increasing the density of the graph. We show that the threshold saturation effect takes place by defining a suitable counterpart of the maximum-a-posteriori decoding threshold of spatially-coupled LDPC code ensembles. In the asymptotic setting, the proposed scheme allows sustaining a traffic close to 1 [packets/slot].

To be presented at IEEE ISIT 2012, Boston

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• Exploiting Capture Effect in Frameless ALOHA for Massive Wireless Random Access
• Poisson Receivers: a Probabilistic Framework for Analyzing Coded Random Access
• Multiple Access Analog Fountain Codes
• Finite-Length Analysis of Spatially-Coupled Regular LDPC Ensembles on Burst-Erasure Channels
• On the Stability Regions of Coded Poisson Receivers with Multiple Classes of Users and Receivers
• Fixed-Symbol Aided Random Access Scheme for Machine-to-Machine Communications