Multi-user parallel interface canceler apparatus

A multi-user parallel interference canceler apparatus for repeatedly performing a hard decision over a plurality of stages to improve channel estimation precision, comprising:

• a plurality of interference estimation units arranged in units of stages to be equal in number to users;
• a plurality of decision error estimation units arranged in units of stages;
• a plurality of combiners arranged in units of stages;
• and
• a plurality of receivers arranged in a last stage in units of users,
• wherein each of said interference estimation units comprises:
• a plurality of despreading processing units each for receiving a received signal or a residual signal in a preceding stage and a symbol replica signal, calculating a reception symbol signal and an estimated value of a transmission path characteristic from the received signal or residual signal and the symbol replica signal, and outputting the reception symbol signal, the estimated value of the transmission path characteristic, and the symbol replica signal from the preceding stage;
• a first combiner (a RAKE combiner) for combining phase-corrected reception symbol signals corresponding to the respective fingers in said plurality of despreading processing units at a maximum ratio;
• a decision unit for making a hard decision about the reception symbol signal combined by said RAKE combiner;
• a plurality of replica generation units for respectively receiving the estimated values of the transmission path characteristics output from said plurality of despreading processing units, the symbol replica signals from the preceding stage, and the hard decision results obtained by said decision units, calculating symbol replica signals and chip replica signals in a current stage from the estimated values of the transmission path characteristics, the symbol replica signals from the preceding stage, and the hard decision results obtained in said decision units, and outputting the symbol replica signals and the chip replica signals;
• a second combiner for combining the chip replica signals output from said plurality of replica generation units;
• a first switch for outputting “0” as the chip replica signal, if the hard decision in the current stage differs from that in the preceding stage and the hard decision in the current stage is wrong, in accordance with a control signal output as a decision result from said decision error estimation units for checking, on the basis of a signal obtained by despreading the received signal or residual signal from the preceding stage which is input to said despreading processing unit, the symbol replica signal input from the preceding stage to said despreading processing unit, and the hard decision result in said decision unit, whether the hard decision in the current stage coincides with that in the preceding stage and the hard decision in the current stage is wrong, and otherwise outputting the chip replica signal generated by said replica generation unit;
• and
• a second switch for outputting the symbol replica signal in the preceding stage in accordance with the control signal if the hard decision in the current stage differs from that in the preceding stage and the hard decision in the current stage is wrong, and otherwise outputting the symbol replica signal generated by said replica generation unit.

A method of improving channel estimation precision in a multi-user parallel interference canceler apparatus, said method comprising:

• in each of a stage comprising a plurality of interference estimation units equal to a number of users, providing a decision error estimation module;
• providing into each said decision error estimation module from each interference estimation unit in said stage a despread result, symbol replicas signals, and a hard decision result;
• providing said hard decision result to be an output of each said decision error estimation module, said hard decision result output to become an input into a subsequent stage decision error estimation module indicating a hard decision result of a preceding stage;
• deciding, in each said decision error estimation module and for each said user, whether an erroneous hard decision has been made;
• and
• stopping processing in said stage for any user determined to have a decision error.