Patent ID: 6473415
Filing Date: 2002-10-29
Classification: H04B

Abstract:
An interference canceling method of a multi-mode subtraction type in an asynchronous multipath channels of code division multiple access (CDMA) system, including the steps of:storing a received intermediate frequency (IF) signal, which passed through a root pulse shaping filter and transformed into a baseband signals, to a buffer; inputting the signal outputted in the buffer to each finger of each detector; processing a pseudo-random noise (PN) code acquisition and tracking process in a timing circuit by using the inputted baseband signal; generating a PN code equivalent with a PN code used in the transmitted signal in a PN code generator by using timing information outputted in the timing circuit; demodulating the baseband signal in a demodulator by using the generated PN code and a walsh code; estimating an amplitude and a phase and a power value of channel parameters in channel and power estimator; deciding a ranking of the power values, and selecting a proper IC mode among various IC modes according to a total number of users in service, a hardware speed and a power spread of received signals, and closing a switch 1 (SW1) within each finger of each detector according to a selected IC mode, in a mode selector and a switch controller; combining a signal outputted in L fingers in a maximal ratio combining method, for combining without omitting the power of L multipath signals of each user in a maximal ratio combiner; multiplying a scale value to the combined signal for making a tentative bit decision most approximately to a bit passed through asynchronous multipath fading channels in a scale factor, and doing processing in a clipper; respreading an output signal of the clipper by using a generated PN code and walsh code in a pilot and data spreader of the finger having the closed switch 1 (SW1), and regenerating the baseband signal by multiplying the estimated channel parameters to the output signal of the pilot and data spreader in a estimated channel processor, transforming the regenerated baseband signal into a pulse shaped baseband signal in a pulse shaping filter; adding the pulse shaped baseband signals in an adder; subtracting the added signal from the baseband signal stored in a buffer, and generating an interference-subtracted resultant signal in a subtractor; adding the pulse shaped baseband signals of the finger having the closed switch 1 (SW1) to the interference-subtracted resultant through a feedback path, and generating a clean input signal in an adder; carrying on recursively the interference canceling process on a basis of the clean input signal with a single stage; and deciding the transmitted bit information in a channel decoder and a bit decider by using a signal obtained by a completion of the interference canceling method.