Analysis and Investigation of LDPC Coded OFDM Based Wireless and Optical Wireless Communication Systems

Abstract

Optical wireless communication (OWC) technology is one of the maximum promising opportunity for inscribing the “last mile” bottleneck in arriving broadband access markets. OWC offers a flexible networking solution with a license-free spectrum of nearly unlimited data rate, low cost of installation and ease of implementation. But, significant demands in the design and implementation of indoor and outdoor OWC systems need to be addressed. These include multipath propagations in both indoor or outdoor OWC, inter symbol-interference (ISI) that affects the quality of transmission, dispersion, and reduction in data rates. These necessitate the use of forward error correction (FEC) and a more bandwidth-efficient scheme. Similarly, the presence of thermal noise and background noise results in bit error rate (BER) deterioration in indoor or outdoor OWC. Due to noise and multipath propagation in both indoor or outdoor OWC, the transmitted signal is affected causing erroneous bits which can be solved using FEC scheme like LDPC, Block code, Convolutional code and Turbo code etc. In outdoor OWC, due to random refractive index variation, turbulence is introduced.
Turbulence results in irradiance fluctuation, which is known as scintillation. The solution to this problem is to use coding. LDPC coded OFDM link shows a promising solution to be used for both indoor and outdoor OWC systems to eradicate problems due to ISI, dispersion, reduced data rates while providing more bandwidth efficiency.
This thesis investigates the systems based on LDPC coded BPSK and QAM modulated oFDM with subcarrier intensity modulation (SIM) over various scenarios. Since, SIM suffers from a high peak-to-average power ratio (PAPR), which translates into poor power efficiency, the thesis also investigates an SLM-based PAPR reduction scheme with optimized phase sequences to be used in indoor OWC system for PAPR reduction.