Date of Award

Summer 2000

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering - (M.S.)

Department

Electrical and Computer Engineering

First Advisor

Yeheskel Bar-Ness

Second Advisor

Alexander Haimovich

Third Advisor

Haibin Zhu

Abstract

High Peak to Average Power Ratio is a main problem in Orthogonal Frequency Division Multiplexing(OFDM) system and Orthogonal Frequency Division Multiplexing -Code Division Multiple Access (OFDM-CDMA) system. Considering a compensated High Power Amplifier(HPA), in order to keep linearity for amplification, Input Back-Off(IBO) of the HP-A, has to be increased for handling a high PAPR. Higher 1130 will make HPA less efficient. Additionally, a signal with high PAPR will suffer clipping when PAPR is larger than 1130 of the HPA. Clipping can cause the distortion of the signal and deteriorate the performance of the system. Reduction of PAPR is a main issue for OFDM and OFDM-CDMA application. In this thesis, some coding schemes are discussed to reduce PAPR. Of all possible code words for transmission, some code words with lower PAPR are chosen for transmission. Some redundancies are added to the end of the original code words to form these lower PAPR code words, though the net bit rate will decrease as a tradeoff. To reduce PAPR block coding scheme and cyclic coding scheme are discussed first. An odd parity bit is added as a redundancy bit. Also the code rate is 3/4. A novel block coding scheme with bit position control is discussed, where the position of the redundancy bit in the original code words is chosen by a feedback selection. For multiuser application, OFDM-CDMA is discussed. Walsh- Hadard (WH) and Complementary (CP) and Gold code sequences are used as the spreading sequences. These coding schemes used in OFDM system are also used before spreading to reduce PAPR in OFDM-CDMA system.

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