Energy Efficient Coded Random Access for the Wireless Uplink

We discuss the problem of designing channel access architectures for enabling fast, low-latency, grant-free, and uncoordinated uplink for densely packed wireless nodes. Specifically, we study random-access codes, previously introduced for the AWGN MAC, in the practically more relevant case of Raylei...

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Bibliographic Details
Published in:IEEE transactions on communications Vol. 68; no. 8; pp. 4694 - 4708
Main Authors: Kowshik, Suhas S., Andreev, Kirill, Frolov, Alexey, Polyanskiy, Yury
Format: Journal Article
Language:English
Published: New York IEEE 01.08.2020
The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subjects:
Asymptotic properties
Coding
Decoding
Encoding
error correcting codes
Fading
Fading channels
Information theory
internet of things
Iterative decoding
Iterative methods
machineto-machine communications
multiaccess communication
Network latency
Phase transitions
Protocols
Random access
Random noise
Receivers
ISSN:0090-6778, 1558-0857
Online Access:Get full text
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Summary:We discuss the problem of designing channel access architectures for enabling fast, low-latency, grant-free, and uncoordinated uplink for densely packed wireless nodes. Specifically, we study random-access codes, previously introduced for the AWGN MAC, in the practically more relevant case of Rayleigh fading, when channel gains are unknown to the decoder. We propose a random coding achievability bound, which we analyze both non-asymptotically and asymptotically. As a candidate practical solution, we propose an explicit iterative coding scheme. The performance of such a solution is surprisingly close to the finite blocklength bounds. Our main findings are twofold. First, just like in the AWGN MAC, we see that jointly decoding a large number of users leads to a surprising phase transition effect, where, at spectral efficiencies below a critical threshold, a perfect multi-user interference cancellation is possible. Second, while the presence of Rayleigh fading significantly increases the minimal required energy-per-bit, the inherent randomization introduced by the channel makes it much easier to attain the optimal performance via iterative schemes. We hope that a principled definition of the random-access model, together with their information-theoretic analysis, will open the road towards unified benchmarking and performance comparison of various random-access solutions for the 5G/6G.
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ISSN:0090-6778
1558-0857
DOI:10.1109/TCOMM.2020.3000635