Joint Kalman channel estimation and equalization for the UMTS FDD downlink

Abstract
The performance of a digital mobile receiver operating in time-varying frequency-selective propagation environments is significantly affected by the accuracy of the employed channel estimation. In the frequency-division duplex (FDD) downlink of the universal mobile telecommunication system (UMTS) a code-multiplexed pilot signal is continuously broadcast in order to enable the mobile terminal to estimate the parameters of the transmission channel. However, multipath propagation destroys the code-orthogonality between user and pilot signals resulting in strong multiple-access interference (MAI). Conventional channel estimation techniques do not take into account this impairment. An algorithm consisting of a modified extended Kalman filter is presented which estimates the channel parameters as well as the MAI jointly. The output of the filter can directly be used to retrieve the equalized desired user signal. It is shown by simulations that this algorithm has superior performance compared to the standard Rake receiver as well as decoupled Kalman channel estimation and equalizer structures, especially in fast fading frequency-selective environments.

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