Finger Allocation for Advanced WCDMA Uplink

In this paper, we study alternative finger allocation algorithms for high speed uplink packet access (HSUPA) mode of wideband code division multiple access (WCDMA) receiver. Higher order modulation methods and additional data channels require advanced receiver structures and good quality signal estimates. Multipath radio channel disperses the signal energy in time, and in the receiver, finger allocation algorithm is needed to find the timing instants containing resolvable signal components. We present two finger allocation methods which offer fast response to the changes in channel, collect the most of the signal energy, and still keep the computational burden within limits. The receiver uses a chip rate minimum mean-squared error frequency domain equalizer (MMSE-FDE) for detection of the signal. Avoiding the Rake type two-phase finger allocation and tracking, we employ the impulse response measurement (IRM) values for finger allocation. Fingers are frequently re-allocated, and no separate finger tracking is needed. Allocation takes place either based on a threshold comparison, or by attempting to maximize the collected signal energy with a fixed number of fingers. These methods can also be combined. Performance results of the finger allocation algorithms are provided via simulations, and also a complexity comparison between the presented methods is given.