Short-Packet Communications: Fundamental Performance and Key Enablers
Licentiate thesis, 2019
Several key enablers for URLLC communications have been designated in the literature. A non-exhaustive list contains: multiple transmit and receive antennas (MIMO), short transmission-time intervals (TTI), increased bandwidth, and feedback protocols. Furthermore, it is not only important to introduce additional diversity by means of the above examples, one must also guarantee that the scarce number of channel uses are used in an optimal way. Therefore, protocols for how to convey meta-data such as control information and pilot symbols are needed as are efficient short-packet channel codes.
This thesis focuses on the performance of reliable short-packet communications. Specifically, we provide converse (upper) bounds and achievability (lower) bounds on the maximum coding rate, based on finite-blocklength information theory, for systems that employ the key enablers outlined above. With focus on the Rician and Rayleigh block-fading channels, we are able to answer, e.g., how to optimally utilize spatial and frequency diversity, how far from optimal short-packet channel codes perform, and whether feedback-based schemes are preferable over non-feedback schemes.
More specifically, in Paper A, we study the performance impact of MIMO and a shortened TTI in both uplink and downlink under maximum-likelihood decoding and Rayleigh block-fading. Based on our results, we are able to study the trade-off between bandwidth, latency, spatial diversity, and error probability. Furthermore, we give an example of a pragmatic design of a pilot-assisted channel code that comes within 2.7 dB of our achievability bounds. In Paper B, we partly extend our work in Paper A to the Rician block-fading channel and to practical schemes such as pilot-assisted transmission with nearest neighbor decoding. We derive achievability bounds for pilot-assisted transmission with several different decoders that allow us to quantify the impact, on the achievable performance, of pilots and mismatched decoding. Furthermore, we design short-packet channel codes that perform within 1 dB of our achievability bounds. Paper C contains an achievability bound for a system that employs a variable-length stop-feedback (VLSF) scheme with an error-free feedback link. Based on the results in Paper C and Paper B, we are able to compare non-feedback schemes to stop-feedback schemes and assess if, and when, one is superior to the other. Specifically, we show that, for some practical scenarios, stop-feedback does significantly outperform non-feedback schemes.
short-packet channel codes.
Chalmers, Electrical Engineering, Communication and Antenna Systems, Communication Systems
Short Packets over Block-Memoryless Fading Channels: Pilot-Assisted or Noncoherent Transmission?
IEEE Transactions on Communications,; Vol. 67(2019)p. 1521-1536
Low-Latency Short-Packet Transmissions: Fixed Length or HARQ?
2018 IEEE Globecom Workshops, GC Wkshps 2018 - Proceedings,; (2019)
Paper in proceedings
Low-latency Ultra-Reliable 5G Communications: Finite-blocklength bounds and coding schemes
SCC 2017 - 11th International ITG Conference on Systems, Communications and Coding,; (2019)
Paper in proceedings
Theory and practice for optimum spectral efficiency for ad-hoc wireless networks with strict requirements on latency and reliability
Swedish Research Council (VR), 2015-01-01 -- 2018-12-31.
Areas of Advance
Information and Communication Technology
Chalmers University of Technology
Opponent: Mattias Andersson, Ericsson Research