Efficient pilot-assisted channel estimation for random access in IMT-2000/UMTS

In this paper various efficient channel estimation techniques are employed for the random access channel of third-generation wideband CDMA (3G WCDMA) specified by 3GPP for IMT-2000/UMTS. The quality of channel estimates is important in order to adjust the tap weights of RAKE receivers in base stations. Schemes using slot-based as well as symbol-based pilot-assisted channel estimates applying different kinds of interpolation methods and post-filters for interference and noise suppression are considered. Results of link level simulations for typical indoor and vehicular fading channels are discussed and compared with the respective performance in case of ideal (undistorted) channel weights. The analysis criterion is the frame error rate (FER) vs. average signal-to-noise-ratio E_b/N₀. It turns out that symbol-based channel estimation can lead to significant improvements of 1-10 dB compared to conventional approaches without post-filters, especially for high speed scenarios (>200 km/h). Good performance as well as low-complexity for all random access deployment scenarios gives a non-causal forward-backward-multiplication-method (FBMM) filter