Uppsala universitet

A Grid Approach to Tracking of Mobile Radio Channels in D-AMPS 1900

Magnus Falkenström

Master Thesis, Report UPTEC 97 035E, 93 pages, February 1997.

Adaptive equalization, with focus on estimation of mobile radio channels, specified by the D-AMPS 1900 standard, is studied. The considered channel estimators, referred to as WLMS algorithms, utilize and incorporate a priori information about second order moment characteristics of the mobile radio channels.

In this study, autoregressive (AR) models are used to describe this priori knowledge. The potential tracking performance gain by using a grid of WLMS algorithms, instead of a single algorithm, is investigated. The specific choice of estimator is determined by the experienced signal-to-noise ratio and Doppler frequency, which both have to be estimated. The utility of using WLMS estimators based on higher order AR-models is of particular interest.

The overall goal with the grid approach is to maximize the performance over a large operation area with maintained low computational complexity. Guidelines on how to match WLMS algorithms with respect to SNR and Doppler frequency, from a theoretical point of view, are given. Different approaches to robustify WLMS algorithms are considered. The bit error performance obtained by using a grid of multi-step estimators together with Viterbi detectors, implemented as interference rejection combiners (IRC), is investigated.

The initialization stage of each burst has proved to be crucial for the performance, especially for algorithms based on higher order AR-models, due to their poor transient behaviour. If the effect of the initialization stage is eliminated, a grid of algorithms based on higher order AR-models can improve the performance substantially. The gain can be up to 60 %, compared to an algorithm based on a lower order AR-model tuned to the correct signal-to-noise ratio and Doppler frequency.


Thesis Advisors:
Mikael Sternad and Lars Lindbom

Related publications:
PhD Thesis by L Lindbom 1995, presenting the general design methodology.
Paper by Lindbom, Ahlen, Sternad and Falkenström on tracking of IS-136 channels.

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