Heino Gerlach

Joint Kalman channel estimation and equalization for the UMTS FDD downlink

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.

Adaptive block-equalizers for the UTRA-FDD downlink

Novel and simple concepts for adaptive block-equalizers to be used in the downlink of the Universal Mobile Telecommunication System (UMTS) terrestrial radio access (UTRA) with frequency-division duplex (FDD) are presented. The adaptation of the block-equalizers using modified least-squares (LS) or minimum mean-square error (MMSE) schemes is based on the continuously transmitted, code-multiplexed common pilot channel (CPICH). In contrast to classical adaptive filter approaches, the number of coefficients to be adapted corresponds to the number of propagation channel paths and is thus independent of the chosen block size. In time-varying multipath propagation scenarios, a remarkable performance gain in terms of uncoded bit-error rate is obtained with respect to block-equalizers constructed using conventionally estimated channel impulse responses.

Performance of Kalman equalization for the UMT FDD downlink in two-path fading channels

The performance of a discrete Kalman filter used as a chip-level channel equalizer in the downlink of the universal mobile telecommunication system (UMTS) with frequency-division duplex (FDD-UMTS) is analyzed in terms of chip estimation error and bit-error probability. The dependence of the chip estimation error on the signal-to-noise ratio, the transmission channel characteristics, and the filter length is derived and discussed for a two-path frequency-selective static channel. It is shown by simulation that the result for the chip error is also valid for two-path frequency-selective fading channels. A semianalytical approach is utilized to derive the bit-error probability of the Kalman equalizer, and the expression is verified by simulations in a fast-fading FDD-UMTS environment.