On Frame Asynchronous Coded Slotted ALOHA: Asymptotic, Finite Length, and Delay Analysis
Journal article, 2017

We consider a frame asynchronous coded slotted ALOHA (FA-CSA) system for uncoordinated multiple access, where users join the system on a slot-by-slot basis according to a Poisson random process and, in contrast to standard frame synchronous CSA (FS-CSA), users are not frame-synchronized. We analyze the performance of FA-CSA in terms of packet loss rate and delay. In particular, we derive the (approximate) density evolution that characterizes the asymptotic performance of FACSA when the frame length goes to infinity. We show that, if the receiver can monitor the system before anyone starts transmitting, a boundary effect similar to that of spatially-coupled codes occurs, which greatly improves the iterative decoding threshold. Furthermore, we derive tight approximations of the error floor (EF) for the finite frame length regime, based on the probability of occurrence of the most frequent stopping sets. We show that, in general, FA-CSA provides better performance in both the EF and waterfall regions as compared to FS-CSA. Moreover, FACSA exhibits better delay properties than FS-CSA.

Coded slotted ALOHA

frame asynchronous

spatially coupled codes

error floor

finite length analysis

density evolution

packet loss rate

uncoordinated multiple access

random access


Erik Sandgren

Chalmers, Signals and Systems

Alexandre Graell i Amat

Chalmers, Signals and Systems, Communication, Antennas and Optical Networks

Fredrik Brännström

Chalmers, Signals and Systems, Communication, Antennas and Optical Networks

IEEE Transactions on Communications

0090-6778 (ISSN) 15580857 (eISSN)

Vol. 65 2 691-704 7762138

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Areas of Advance

Information and Communication Technology

Subject Categories


Communication Systems



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9/8/2019 1