Design and Detection of Non-Coherent Unitary Constellations for SIMO Systems for Short Packet Communications
Date
2023-12-21
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-1347-9164
Type
Thesis
Degree Level
Masters
Abstract
Ultra-reliable low-latency communications (URLLC) have been a crucial part of 5G and upcoming 6G networks to cater to mission-critical applications with stringent demands for high reliability and minimal latency. Short packet communications (SPC) have been employed to meet the requirement of low latency. Coherent communications require the transmission of pilot symbols to obtain accurate instantaneous channel state information (CSI), thus suffering from spectral efficiency (SE) loss in SPC. These challenges motivate the use of non-coherent communications, which do not require instantaneous CSI, as an alternative paradigm for coherent communications in SPC.
Among different schemes of non-coherent communications, unitary multi-symbol constellations and multi-level unitary multi-symbol constellations have been investigated to improve the error performance of communication systems. In the literature, there have been two approaches to design and detect unitary constellations and multi-level unitary constellations. The first one is the unstructured constellations with maximum-likelihood (ML) detection, which can achieve optimal error performance but suffer from high complexity in both design and detection. As a result, this approach is not practical for many practical applications. The other approach is the structured unitary constellations with simplified detectors, which can have low complexity in design and detection, therefore being practical. However, the structured constellations sacrifice the optimal error performance of the unstructured constellations. Hence, in this thesis, we focus on the structured unitary and multi-level unitary constellations with low complexity while improving the error performance to meet the reliability requirement of communication systems.
Firstly, we investigate the design of multi-level unitary constellations for block Rayleigh fading channels. By using the Kullback-Leibler (KL) divergence as the design criterion, we formulate a multiple-symbol constellation optimization problem, which turns out to have high computational complexity to construct and detect. We exploit the structure of the formulated problem and decouple the constellation into a Cartesian product of a unitary constellation design and a multi-level design. The proposed multi-level design has low complexity in both construction and detection and is compatible with any type of unitary constellation in the literature. Simulation results show that our multi-level design performs better than traditional pilot-based schemes and other existing low-complexity single-level designs in low SNR regimes.
Secondly, we propose a novel structure of unitary constellations for block Rayleigh fading channels. Our proposed structure involves a Cartesian product of an amplitude vector and a phase-shift keying (PSK) vector, which reduces the design complexity compared to the unstructured unitary constellations. Furthermore, the structure allows iterative detection of amplitude vectors and phase vectors, which reduces the complexity of the ML detector. We adopt the sort-decision-feedback-differential-detection (sort-DFDD) to further reduce the complexity of detecting the PSK vector when compared to the ML detector. Furthermore, we adopt a posterior probability as a reliability criterion to improve the error performance of sort-DFDD, which results in near-optimal error performance in the case of the PSK constellations with equal modulation order. This detector is called Posteriori-based-reliability-sort-DFDD (PR-sort-DFDD) and has polynomial complexity. We also propose an improved detector called improved-PR-sort-DFDD to detect a more generalized PSK structure, i.e.,PSK symbols with unequal modulation orders. This detector also approaches the optimal error performance with polynomial complexity. Through simulation, we demonstrate the superiority of our proposed multi-symbol unitary constellation over competing low-complexity unitary constellations and traditional pilot-based schemes.
Description
Keywords
Constellation design, non-coherent communications.
Citation
Degree
Master of Science (M.Sc.)
Department
Electrical and Computer Engineering
Program
Electrical Engineering