CIF: Medium: Delay, Reliability, Rate Tradeoffs in Wireless Broadcast Channels

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Greater demands are being placed on our wireless networks: not only must they support a growing number of voice and data applications where data rate is of prime importance, but wireless networks are also increasingly being used in delay- and reliability-sensitive technologies including tele-medicine, tele-conferencing, interactive-gaming, and sending delay-sensitive control information for spectrum sharing, real-time energy management, and autonomous vehicles. However, arbitrarily high data rates, low delays and high reliabilities cannot be achieved simultaneously over noisy and time-varying wireless channels. This research will seek to characterize, in a technology-agnostic manner, the fundamental (Delay, Reliability, Rate) tradeoffs in communications over the last-hop of wireless networks, where one base-station wishes to communicate independent messages to many users. The results will provide fundamental performance benchmarks and algorithmic prototypes for industries working towards these ambitious goals. The project also seeks to broaden participation through activities designed to increase enrollment and engagement of students from under-represented groups in computing.The (Delay, Reliability, Rate) tradeoffs will be characterized from information and communication theoretic perspectives. From an information theoretic perspective, the capacity region has long been the central focus, characterizing the number of messages that can be reliably (with vanishingly small probability of error) be communicated to the users simultaneously as the number of channel uses (and hence delay) tends to infinity. Such metrics ignore latency constraints present in practical systems. This research aims to characterize the set of messages that can be communicated to each user in a broadcast setting when the delay is finite and one tolerates some error. Transmission schemes must be carefully re-thought to incorporate these latency and reliability constraints, in particular when the channels to the users change over time as in a wireless channel. The information theoretic study will be complemented by more practically motivated communication theoretic (Delay Reliability, Rate) tradeoffs for the tractable multi-layer erasure channel (that extends simple erasure channels studied in the communications and networking communities) and then the practically relevant Gaussian fading broadcast channel.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.