Co-channel interference mitigation detectors for multirate transmission in TD-CDMA systems

In this paper, we address the problem of downlink detection in a mobile radio time division/code division multiple access multirate communication system employing a linear modulation. We focus on the detection of a group of intracell codes (ranging from a single one to all the active codes) rejecting both interference coming from the complementary set of undesired intracell codes and co-channel intercell interference. We investigate efficient implementations of linear nonadaptive multiuser detection realized by either joint or separate intersymbol interference and multiple access interference (MAI) mitigation using the zero-forcing or minimum mean square error criteria. The proposed detection schemes employ a tunable-complexity structured description of the MAI for the purpose of detection and interference mitigation. Specifically, the receivers always envision an intracell interference mitigation and data detection capability, while intercell interference is treated differently depending on operating environments. If a statistical description of the intercell interference is available, the receiver realizes group detection in the presence of possibly nonwhite Gaussian noise. Soft hand-over procedures are also proposed wherein direct suppression of intercell interference is possible as well as group detection of the data of the neighboring cells. A unified and finite complexity implementation of the proposed detection schemes based on a sliding window formulation is provided. The numerical results validate the proposed receiver structures showing that a structured description of the observation always leads to a detector with superior performance.