Graduate Thesis Or Dissertation
 

Adaptive digital transceiver for rayleigh fading channels

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gf06g497j

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  • This thesis presents an adaptive modulation scheme using a Walsh-code modulator. The Walsh-code modulator consists of a dynamic demultiplexer and predetermined sets of orthogonal Walsh-Hadamard codes. The demultiplexer can demultiplex the input bit stream into a maximum of thirty-two sub-streams. The Walsh- Hadamard codes are used to spread the spectrum of the demultiplexed sub-streams. The Walsh-code modulator produces a multi-level pulse amplitude modulated (PAM) signal by summing the spread sub-streams. The number of levels contained in the constellation of the PAM signal varies, based on the number of demultiplexed substreams. The error rate performance of different constellations produced by the Walsh-code modulator, differ when transmitted through a Rayleigh fading plus additive white Gaussian noise (AWGN) channel. As the level of fading experienced in the channel fluctuates, a desired level of error rate performance can be maintained by switching constellations, while trying to use the maximum number of sub-streams, or links, to transmit the data. Simulation results show the performance of several constellations when transmitted through an AWGN channel and a Rayleigh fading plus AWGN channel. Also, mapping of the PAM signal onto a quadrature amplitude modulation (QAM) constellation, in order to improve the performance of the system is discussed. It is found that for a Rayleigh fading plus AWGN channel, at a given error performance level, the amount of gain in signal-to-noise ratio (SNR), from the largest constellation to the smallest constellation, is 8dB for the symbol error rate (SER) and 14dB for the bit error rate (BER).
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file details Jeffery_R_Hughes.pdf 2017-08-01 Pubblico Scaricare