This work presents a study of the adaptive equalization techniques
designed to improve the bit error rates of digital transmissions degraded by
intersymbol interference in radio communication. This thesis considers the
following structures: the linear transversal equalizer (LTE), the decision feedback
equalizer (DFE), the lattice equalizer, and the maximum likelihood sequence
estimation (MLSE) equalizer. Least mean square (LMS) and recursive least
squares (RLS) algorithms are used as the adaptive algorithms for these equalizers.
Lattice-DFE, DFE, and MLSE with an RLS algorithm are recommended to be
implemented in mobile systems because of their better performances. A two-ray
Rayleigh fading channel model is used to simulate the mobile channels. The
results show that adaptive equalization can significantly improve the performance
of mobile communications if the channel does not change too fast. The simulation
shows that if the delay (T) of the second ray is too small, the adaptive
equalization will degrade the BER performance, and the value of T at which the
adaptive equalizer can improve the BER is determined by the speed of the mobile
channel variation. Also, simulation results obtained by using SIRCIM, a real
world indoor channel simulator, shows that adaptive equalization has good
performance in slowly varying channels. An equalizer working in indoor high data
rate systems has a BER less than 10-3 at 15 dB Eb/No• The SMRCIM urban
channel model is also developed and implemented for equalization simulation.
Finally, equalization structures for differential modulation techniques are
proposed.
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