Interference canceling method and apparatus of a multi-mode subtraction type in asynchronous multipath channels of code division multiple access system

An interference canceling apparatus of a multi-mode subtraction type in asynchronous multipath channels of code division multiple access (CDMA) system, comprising:

• a root pulse shaping filter that transforms a received intermediate frequency signal into a baseband signal;
• a buffer for storing the baseband signal transformed through the root pulse shaping filter;
• a timing circuit of each finger that processes a PN code acquisition and tracking process with the baseband signal outputted in the buffer as a input signal;
• a PN code generator that generates a PN code equivalent with a PN code used in the transmitted signal by using timing information outputted in the timing circuit;
• a demodulator that demodulates the baseband signal by using the generated PN code and a walsh code;
• a channel and power estimator that estimates an amplitude and a phase and a power value of channel parameters;
• a mode selector and switch controller that decides a ranking of the power values, and selects a proper interference canceling mode among a various interference canceling modes according to a number of users and a channel environment and hardware speed, and closes a switch 1 (SW1) within each finger of each detector according to a selected interference canceling mode;
• a maximal ratio combiner that combines a signal outputted in L fingers in a maximal ratio combining method, for combining without omitting a power of L multipath signals of each user;
• a scale factor that multiplies a scale value to a combined signal for making a tentative bit decision most approximately to a bit passed through the asynchronous multipath channels;
• a clipper for clipper processing;
• a pilot and data spreader that respreads an output signal of the clipper by using the generated PN code and walsh code at the finger having the closed switch 1 (SW1);
• an estimated channel processor that regenerates the baseband signal by multiplying the estimated channel parameters to the output signal of the pilot and data spreader;
• a pulse shaping filter that transforms the regenerated baseband signal into a pulse shaped baseband signal;
• an adder that adds the pulse shaped baseband signal;
• a subtractor that subtracts the added signal from the baseband signal stored in the buffer and generates an interference-subtracted resultant signal;
• an adder of each finger that adds the pulse shaped baseband signal of the finger having the closed switch 1 (SW1) to an interference-subtracted resultant through a feedback path, and generates a clean input signal;
• an interference canceler that carries on recursively an interference canceling process on a basis of the clean input signal with a single stage;
• and
• a channel decoder and a bit decider that decides the transmitted bit information by using the signal which is obtained by a completion of interference canceling process.