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On the Capacity of the Fading AWGN Broadcast Channel without CSITx with Channel Output Feedback



  1. NSF CISE Grant #1900911 “CIF: Medium: Delay, reliability, rate tradeoffs in wireless broadcast channels

Problem Statement and Motivation 

  • The exact capacity of the fading Gaussian broadcast channel without channel state information at the transmitter is an open problem.  In this work we consider the same model but with channel output feedback.
  • We aim to determine, exactly or to within a constant additive gap, the capacity of this channel model, as well as its maximal rate region when the block-length is large but finite.
  • This model finds applications in future wireless networks that will serve many users, each needing only a relatively small number of bits that must be delivered with a very strict latency requirement and with high reliability.

Technical Approach

  • An approximate capacity result for the fading Gaussian broadcast channel without channel state information at the transmitter has been derived based on using a so-called “deterministic approximation” (i..e, by neglecting the Gaussian noise). In this work we used the same approach to derive the capacity for the case when channel output feedback is present.
  • We derived capacity inner and outer bounds.
  • The inner bounds generalize past results for the two-user erasure BC; the novelty lies in the use of inter-user & inter-layer network coding retransmissions (for those packets that have only been received by the unintended user), where each random linear combination may involve packets intended for any user originally sent on any of the layers.
  • The outer bound uses the classical approach of enhancing the channel to a physically degraded one (for which channel output feedback is useless) for which the capacity without feedback is known.
  • Analytical and numerical examples show that the proposed bounds meet for some parameter regimes.

Key Achievements and Future Goals

  • Siyao Li, Daniela Tuninetti, and Natasha Devroye, “On the Capacity Region of the Layered Packet Erasure Broadcast Channel with Feedback,” Proceedings of the 2019 IEEE International Conference on Communications (ICC 2019).
  • Siyao Li, Daniela Tuninetti, Natasha Devroye, and Hulya Seferoglu “On The Stability Region of the Layered Packet Erasure Broadcast Channel with Output Feedback,”Proceedings of the 2019 IEEE Information Theory Workshop (ITW 2019). SUBMITTED.
  • Daniela Tuninetti, Besma Smida, Hulya Seferoglu, and Natasha Devroye “On Gaussian Broadcast Channels with Hard Deadlines,” Proceedings of the 2018 IEEE International Conference on Communications (ICC 2018).
  • Zohreh Ovasi, Natasha Devroye, Besma Smida, Hulya Seferoglu and Daniela Tuninetti “On Erasure Broadcast Channels with Hard Deadlines,” Proceedings of the 2018 IEEE International Conference on Communications (ICC 2018), Workshop: 5G & Beyond – Enabling Technologies and Applications focus on the Tactile Internet (5G TACNET).

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