Date of Award

12-17-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Systems Engineering

First Advisor

Seshadri Mohan

Abstract

Efficiently utilizing the available spectrum is crucial due to the growing demand for high throughput. One potential solution is to enhance Spectral Efficiency (SE) at the waveform level, enabling higher data rates beyond what Orthogonal Frequency Division Multiplexing (OFDM) can achieve. As an initial step towards a solution, we introduce the principle of Spectral Sampling and Signal Decomposition (SSSD). SSSD has the capability to break down the OFDM signal into its spectral components. By sampling the OFDM signal spectrum at a number of points double the number of subcarriers and decomposing it, a system of linear equations can be constructed and solved for the transmitted symbols. The SSSD can be used to model the OFDM signal at every point in frequency domain. Based on SSSD, we propose a new reception scheme referred to as Highly Immune-Orthogonal Frequency Division Multiplexing (HI-OFDM). The HI-OFDM harvest the benefits of SSSD by extracting multiple copies of the received signal to achieve enhancements in terms of SE and Bit Error Rate (BER) in comparison to the OFDM. HI-OFDM preserves the inherent advantages of OFDM and surpasses its performance metrics. Specifically, HI-OFDM offers high immunity against noise and achieves higher modulation orders by reducing the noise effect and delivering a significant improvement in terms of Signal-to-Noise Ratio (SNR) without compromising the BER. In this dissertation, we establish the foundation for SSSD and HI-OFDM first then validate it through simulation which shows that an enhancement in SE by 33% and 66% can be obtained using 3 and 10 SSSD receivers respectively. A higher enhancement also possible by employing a higher number of SSSD receivers. We propose a simple receiver design based on SSSD principle to receive the non-orthogonal Spectrally Efficient Frequency Division Multiplexing (SEFDM) signal. The use of the SSSD receiver differ from the traditional SEFDM approaches by using the interfering carriers as useful signals. We demonstrate the performance of the SSSD receiver through simulations for different compression ratio, showcasing its capability to extract the SEFDM signal and also to accommodate various pulse shapes beyond the conventional rectangular pulse. However, the results also reveal a significant challenge posed by severely ill-conditioned matrix.

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