Adaptive digital transceiver for rayleigh fading channels
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).
Advisor:Magalla, Mario E.
School:Oregon State University
School Location:USA - Oregon
Source Type:Master's Thesis
Keywords:coding theory amplitude modulation radio transmitter receivers
Date of Publication:12/09/2003