Efficient filter design for IS-95 CDMA systems

Abstract

An efficient filter design method for the design of a relatively complex low pass filter specified in the IS-95 code division multiple access (CDMA) standard is presented The described circuit details and algorithm have been tested by means of computer simulation and hardware experimental result. Using field programmable gate array (FPGA) technology, a low power and gate count finite impulse response (FIR) filter design for the transmitter is realized. For the receiver, canonical digit representation of signed numbers are used to reduce the complexities in multiply operations. The critical spectral degradation due to quantization error of the sample and due to truncation of coefficient accuracy is simulated. Practical design guidelines are provided. The described design details demystify the challenging concept and difficulty in an IS-95 standardized filter. In addition, through the use of the implemented filter hardware for the modulator, spectral regrowth in nonlinear amplified IS-95 CDMA is demonstrated and is shown to correlate very closely with computer simulation. This work leads to a cross-correlative technique that will improve spectral regrowth for CDMA systems. Similar methods are being employed in Feher's (1995) family of PSK modulation schemes, a technique which yields lower spectral regrowth in nonlinearly amplified channels.