Back to the list of graduate studentsRadial basis Function Equalizer for Mobile Channels
by
P. Roohi Larijani
M. Eng., 1994
Abstract
Excessive delay spread in mobile channels causes severe inter symbol-interference. The problem can be corrected by adaptive equalizers that implicitly estimates the channel impulse response and filter the received signal through the inverse channel. For reliable communications, the adaptive filter should be able to converge quickly, and maintain its convergence in the presence of occasional errors and fading hits.
Least Mean Square (LMS) adaptation algorithm is commonly used to adapt equalizer weights because of its simplicity. The LMS algorithm, in its stochastic gradient form, adapts the equalizers weights using a small step fixed size and hence it is too slow to cope with rapid variations in the channel impulse response.
In this thesis we introduce a new adaptation algorithm for the decision feedback equalizers. The adaptation of the equalizer taps is based on a new cost function which adjusts the step size automatically to speed up the convergence. The choice of the cost function in this algorithm is derived from a simple geometrical interpretation of the equalization process under multipath conditions.
To evaluate the equalizer performance, analytical method and direct computer simulation are used. In analytical approach mathematical expressions for convergence speed and steady state error level are derived. Analytical results are confirmed by simulation.