Doctor of Philosophy
Electrical and Computer Engineering
Rao, Raveendra K.
Design, analysis, and performance of Multicarrier (MC) and Multicarrier-Code Division Multiple Access (MC-CDMA) systems are considered. Specifically, Multicarrier Modulation (MCM) such as Orthogonal Frequency Division Multiplexing (OFDM) is used in these systems with emphasis on energy efficiency. These systems are examined for their performances over frequency-selective and frequency-non-selective channels. Methods are proposed for reduction of energy costs of an OFDM system. They are: i) Clipping (CL) based on symbol statistics; ii) Partial Transmit Sequence (PTS) using Magic square pattern and adjacent partitioning; and iii) Selective Mapping (SLM) and Tone Reservation (TR) with reduced complexity. These methods are described and algorithms are presented for computation of Peak-to-Average Power Ratio (PAPR). Using extensive simulations, Complementary Cumulative Distribution Functions (CCDFs) of PAPR of OFDM signals for Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), and -QPSK are obtained as a function of number of subcarriers in the system. It is shown that PAPR reductions up to can be achieved using the proposed methods for a 128-subcarrier OFDM system. These reductions amount to increased energy efficiency of High Power Amplifier (HPA) up to 23.794% in an OFDM system.
Bit Error Rate (BER) performances of OFDM system with and without the proposed PAPR reduction techniques are considered over both frequency-selective and frequency-non-selective Rayleigh fading channels. Power Penalty (PP) required over these channels are assessed for BPSK, QPSK, and -QPSK mappers in an OFDM system. It is observed that at BER, PP required is of the order of for frequency-non-selective and for frequency-selective Rayleigh fading channels.
Finally, using a complex spreading sequence, a hybrid of OFDM and CDMA systems referred to as MC-CDMA system is proposed and is investigated for its PAPR properties using the three proposed PAPR reduction techniques. BER performance of MC-CDMA system is determined over frequency-selective and frequency-non-selective Rayleigh fading channels. It is shown that PAPR of MC-CDMA system is a function of the spreading sequence, and the PAPR reduction method used. A PAPR of can be achieved when the proposed complex pseudo-random (PN) sequence is used.
Keywords: Energy-Efficient, OFDM, MC-CDMA, Clipping, PTS, SLM, TR, PAPR, PSD, BER.
Summary for Lay Audience
The digital communication technology industry is among the biggest industries worldwide with more than $1 trillion in annual revenues. Moreover, after the extension of the Internet to wireless users and devices such as users of smart phones, laptops, and home and industrial appliances, automobiles etc., the Internet of Things (IoT) paradigm is the trend in coming years, which implies most users and devices will be connected to the Internet using wired/wireless digital communication technology. The number of IoT connected devices is projected to be about 75.44 billion worldwide by 2025. Thus, it has become important to design digital communication systems that are energy-efficient and reliable for high-speed data transfer. A multicarrier system using Orthogonal Frequency Division Multiplexing (OFDM) is a digital communication system widely employed for transferring data between users/devices. Also, in a multicarrier environment this OFDM system is combined with a Code Division Multiple Access (CDMA) system referred to as Multi-Carrier CDMA (MC-CDMA) system. In this thesis, energy-efficient design of OFDM and MC-CDMA systems are considered. These systems are examined for their Peak-to-Average Power Ratio (PAPR) and Bit Error Rate (BER) performances over various types of wireless communication channels. Several methods are proposed for reduction of energy costs of an OFDM and MC-CDMA systems. They are: i) Clipping (CL) based on symbol statistics; ii) Partial Transmit Sequence (PTS) using Magic square pattern with improved partitioning; and iii) Low-Complexity Selective Mapping (SLM) and Tone Reservation (TR) techniques. It is shown that PAPR reductions up to can be achieved using these techniques in an OFDM system. These reductions amount to 23.794% increase in energy efficiency of the system. Also, it is shown that a PAPR reductions up to can be achieved in an MC-CDMA system with proposed PAPR reduction techniques. These reductions amount to 6.5% increase in energy efficiency of the system
Ali, Moftah, "Energy-Efficient Multicarrier and Multicarrier-CDMA Systems" (2019). Electronic Thesis and Dissertation Repository. 6657.
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