Technical Program

Paper Detail

Paper Title Energy efficient random access for the quasi-static fading MAC
Paper IdentifierFR2.R8.3
Authors Suhas S Kowshik, Massachusetts Institute of Technology, United States; Kirill Andreev, Alexey Frolov, Skolkovo Institute of Science and Technology, Russia; Yury Polyanskiy, Massachusetts Institute of Technology, United States
Session Energy Efficient Communications
Location Conseil, Level 5
Session Time Friday, 12 July, 11:40 - 13:00
Presentation Time Friday, 12 July, 12:20 - 12:40
Manuscript  Click here to download the manuscript
Abstract 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 extend the concept of random-access code introduced by one of authors in ISIT'2017 to the practically more relevant case of the AWGN multiple-access channel (MAC) subject to Rayleigh fading, unknown to the decoder. We derive bounds on the fundamental limits of random-access coding and propose an alternating belief-propagation scheme as a candidate practical solution. The latter's performance was found to be surprisingly close to the information-theoretic bounds. It is curious, thus, that while fading significantly increases the minimal required energy-per-bit $E_b/N_0$ (from about 0-2 dB to about 8-11 dB), it appears that it is much easier to attain the optimal performance over the fading channel with a practical scheme by leveraging the inherent randomization introduced by the channel. Finally, we mention that while a number of candidate solutions (MUSA, SCMA, RSMA etc) are being discussed for the 5G, the information-theoretic analysis and benchmarking has not been attempted before (in part due to lack of common random-access model). Our work may be seen as a step towards unifying performance comparisons of these methods.