SWIFT: Instantaneous Feedback-based Adaptive Communications and Networks

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This research program investigates instantaneous feedback-based adaptive communications (IFAC) for next generation wireless communication systems. The proposed IFAC enables sub-bit-level real-time adaptation of the wireless communication signal to exploit dynamic tradeoffs in spectral efficiency, reliability, and latency based on the instantaneous feedback from the receiver. Most conventional systems are designed for message-level link adaptation based on the average noise power without utilizing sub-bit-level noise observation. Such message-level feedback schemes are suboptimal for emerging and future applications that require ultra-reliable low latency communication (URLLC) in massive machine-type communication networks where the number of devices can be much greater than that of today's consumer mobile cellular networks. This research program will investigate the feasibility of instantaneous feedback-based wireless communication systems to attain a superior performance closer to the theoretical channel capacity and reliability limit, outperforming state-of-the-art conventional approaches. The proposed IFAC has great potential as a critical enabling technology for the next generation (beyond 5G) URLLC that targets 100 micro-second latency and 99.99999% reliability for short message transmission. Attaining such stringent URLLC goals with IFAC can enable various classes of new applications including autonomous micro-robots, intelligent automated factories, and virtual/augmented reality systems for people with disabilities. The proposed research program includes undergraduate- and graduate-level curricula development as an integral part. It will contribute to new course materials that cover interdisciplinary topics that range from the wireless communication theory and data-driven reinforcement learning to real-time hardware system prototyping.The proposed IFAC scheme is inspired by an early result by Viterbi in 1965 that utilizes instantaneous feedback for reliable communications. The term "instantaneous" in the proposed IFAC indicates that the feedback latency is negligible as it is significantly shorter than the average symbol length. In the original Viterbi's work, instantaneous feedback was a theoretical assumption that was not realizable in practical systems at that time. However, the proposed research aims at demonstrating the feasibility of end-to-end real-time systems to show that instantaneous feedback is indeed possible thanks to the advancement of digital integrated circuit technologies that attained astonishing 9 orders of magnitude (a factor of a billion) improvement since 1965. IFAC is a rate-less scheme that adapts to the channel realization at the sub-bit level to optimize the spectral efficiency, error rate, and/or the latency given the target outage probability. This research program will study various IFAC schemes that are constructed with an application-specific optimization criterion as a Markov decision process or reinforcement learning problem for the instantaneous feedback decision at the receiver. IFAC can enable highly adaptive, online learning based novel methods for massive machine-type communication, accomplishing superior efficiency and performance that are unattainable from conventional wireless communication schemes.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.