Date of Award

January 2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical Engineering

First Advisor

Saleh Faruque

Abstract

Multilevel orthogonal coded modulation technique is a combination of orthogonal channel coding and M-ary modulation, where two or more codes are used simultaneously to detect and correct multiple errors with bandwidth efficiency. The concept, principles, and simulations of the multilevel orthogonal coding combined with M-ary modulations is presented in this thesis. In multilevel orthogonal coding, both information and orthogonal code blocks are split into multiple levels. The information data in each level are mapped to the corresponding orthogonal codes. The outputs of the encoders are then grouped to form symbols suitable for input to spectrally efficient multilevel modulations. The modulated symbols are then transmitted to the channel. At the receiver, the decoding is performed using the correlative decoder. The correlative decoding is also performed in multiple levels independently. At each level of decoding, the incoming orthogonal codes with errors are cross-correlated with the known set of orthogonal code blocks. Then the code set that gives the smallest correlation value, at each level, is chosen as the desired orthogonal code output. The implementing of multilevel encoding and decoding structure increases the error correcting capability of the system significantly, allowing multiple numbers of error corrections. Also, error correction capability of orthogonal codes improves with increasing the code lengths. Combining longer codes in multilevel structures the system shows better error performance. Additionally, the multilevel encoding outputs are suitable for performing multilevel modulation (M-ary modulation), which allows the transmissions of a large number of bits per symbol. This makes the systems to have minimum transmission bandwidths that increase the throughput.

The encoding and decoding structures for three code rates: rate ݬ rate ެ and rate 1, for different orthogonal code lengths are presented and simulated. The transmission bandwidths, bandwidth efficiencies are calculated and error performance analyses of systems are conducted. M-ary Phase Shift Keying (PSK) and M-ary Quadrature Amplitude Modulation (QAM) modulation techniques are chosen as modulation techniques to simulate and analyze the performances in MATLAB. To show the application of MOCM, multilevel orthogonal coded M-ary PSK modulation transmitted in optical wireless communication systems using ambient light cancellation technology is also presented. To simulate the error performances, additive white Gaussian noise channel is used at various signal-to-noise ratios (SNR). The number of errors before decoding and after decoding is counted and tabulated. The number of bit error corrected at specified signal to noise ratio is also tabulated. Error performance curves are plotted and coding gains are observed. The results show the performance improvement of the systems compared to uncoded systems. Also, the coded systems are bandwidth efficient. Thus, the multilevel orthogonal coded modulation systems provide higher error correction capability with bandwidth efficiency.

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