Soft-decision decoding techniques for permutation modulation in powerline and visible light communication
Date
2020
Authors
Kolade, Oluwafemi Ibrahim
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Abstract
As the realization of smart cities and connected internet of things (IoT) devices becomes imminent, the spectral requirements of the volume of devices requiring data communication will exceed the avail-able radio frequency spectrum. Alternative means of communication such as powerline and visible light communication (VLC) are proposed as supplementary data links to radio frequency communication. Powerline communication (PLC) is essential to the deployment of smart grids since the equipment’s powerlines can also be used for communication. Since indoor illumination units are powered by powerlines, a natural integration exists between the powerline and visible light unit, extending the indoor VLC unit to the grid via the powerline. However, the PLC channel becomes noisy due to ‘burst’ impulses introduced into the channel by other powered equipment. VLC units on the other hand, exist in a cluster of light emitting diodes (LEDs), hence the presence of cross-talk interference among the emitting transmitters. In this research, the channel model of an amplify-and-forward (AF) hybrid PLC-VLC system is de-signed using the Fritchman model, a semi-hidden Markov model. Measurements are obtained from an indoor testbed for multicarrier, orthogonal frequency division multiplexing (OFDM) modulation with binary phase shift keying (BPSK). With adequate knowledge of the channel’s error distribution, adequate coding such as permutation codes (PC) and permutation trellis codes (PTC) are recommended to mitigate the bursts of errors in the channel when combined with M-ary frequency shift keying (M-FSK). The combination of codewords with distinct properties are then used to novelistically increase the data rate of a permutation coded multiple-input multiple-output (MIMO) VLC scheme. In order to improve the bit error rate (BER) of PC and PTC with M-FSK, novel soft-decision techniques are presented. Soft-decision is possible by interpreting the output of the channel as an assignment problem, hence the use of optimization algorithms for detection. The optimization algorithms are then used to mitigate the effects of impulse noise in permutation-coded OFDM-MFSK and avoid channel estimation errors in space-time shift keying (STSK)
Description
A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy, 2020