Optical-OFDM-aided wireless communications

Abstract

Orthogonal Frequency-Division Multiplexing (OFDM) has compelling benefit in Optical Wireless Communications (OWC). Hence, we analyse the Layered Asymmetrically Clipped Optical OFDM (LACO-OFDM), which is one of the most advanced Optical OFDM (O-OFDM) schemes, and improve its overall system performance. We commence in Chapter 1 with a review of the development of OWC and O-OFDM, discussing its Spectral Efficiency (SE) and Power Efficiency (PE). Then, LACO-OFDM introduced for striking a trade-off between the attainable SE and PE. This is followed by a literature review of its recent development. A more detailed tutorial on LACO-OFDM is then given in Chapter 2, relying on detailed examples. To further study the properties of LACO-OFDM, Chapter 3 analyses its 1) Probability Density Function (PDF) and its statistical moments; 2) Bit Error Ratio (BER); and 3) Peak-to-Average Power Ratio (PAPR). As a further advance, we propose a toneinjection aided PAPR reduction design for LACO-OFDM, which in turn improves the BER performance. Simulations are provided for verifying both the analytical BER performance and the PAPR distribution of LACO-OFDM. The results show that the expressions derived match well with the simulations. Furthermore, the PAPR reduction method proposed attains a 5 dB PAPR reduction at the 10−3 probability-point of the complementary cumulative distribution function, as well as a better BER performance than the original LACO-OFDM scheme. For the sake of improving the BER performance, multi-class channel coded LACOOFDM is proposed in Chapter 4, where the channel capacity of the system is derived based on our mutual information analysis. We conceive a multi-class channel encoding scheme integrated with the layered transmitter. At the receiver, both the coded and uncoded likelihood ratios (LLRs) are extracted for inter-layer interference cancellation and symbol detection, respectively. Simulations are conducted and the results show that our design approaches the achievable rate within 1.1 dB for 16QAM 4-layer LACOOFDM with the aid of a half-rate 8-iteration turbo code at BER = 10−3 , outperforming its conventional counterpart by about 3.6 dB. iv In Chapter 5, we propose algorithms for optimising the Discrete-input Continuousoutput Memoryless Channel (DCMC) capacity of LACO-OFDM. Then, an algorithm is proposed for maximising the capacity for twin-layer LACO-OFDM by optimising the power sharing between the layers. This is followed by the conception of a more general algorithm applicable to LACO-OFDM having an arbitrary number of layers. Numerical results are provided for quantifying the capacity improvement attained by the proposed algorithm. Moreover, an adaptive layer-activation scheme is proposed for adjusting the number of layers to be used for maximising the capacity at different SNRs.

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Identifiers

ORCID for Xiaoyu Zhang: orcid.org/0000-0002-0793-889X

ORCID for Lajos Hanzo: orcid.org/0000-0002-2636-5214

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