Investigation of performance sensitivity of OFDM systems to multipath fading channel parameters

Pao Yue-kong Library Electronic Theses Database

Investigation of performance sensitivity of OFDM systems to multipath fading channel parameters

 

Author: Wong, Mei-lung
Title: Investigation of performance sensitivity of OFDM systems to multipath fading channel parameters
Degree: M.Sc.
Year: 2000
Subject: Wireless communication systems
Multimedia systems
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Electronic and Information Engineering
Pages: viii, 72 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1527630
URI: http://theses.lib.polyu.edu.hk/handle/200/1009
Abstract: Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission technique that has been developed and applied to broadband multimedia services such as ADSL, DAB and DVB-T etc. This report presents the need of a multicarrier transmission technique to solve the ISI problem due to multipath propagation and provide an overview of OFDM, a discussion of the principle of orthogonality and explain how the cyclic prefix is implemented to achieve subcarriers orthogonality. The use of discrete Fourier Transform to implement OFDM modulation and demodulation is discussed. Understanding the behavior of the OFDM signal that transmits over the channels is very important, as the performance of a mobile radio system is related to the channel characteristics. Different kind of channel such as additive white Gaussian noise (AWGN), multipath delay and Jakes' based Rayleigh fading channel are simulated in the report. Although OFDM has ability to solve the multipath fading problem, but it has some disadvantages such as difficult to synchronize the starting point of the OFDM symbol and it also suffers from frequency error between the transmitter and receiver. Because frequency drift that will make OFDM system loss the orthogonality between subcarriers. The impact of the carrier frequency offset and sampling frequency error on the OFDM system are evaluated in this report. Some signal error patterns have been simulated to see the possibilities of reducing bit error rate (BER). In additional to frequency error sensitivity in the OFDM system, the OFDM output signal will be nonlinear distorted in the power amplifier device due to it's wide transmission amplitude range. The envelope distribution of the OFDM signal is simulated to observe the Peak to Average Power Ratio (PAPR) problem. The OFDM system and the fading channels are modeled and implemented by means of using Matlab. The programs are described to show how to develop the models and solve the problems encountered during the simulation development.

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