A segmented matched filter for CDMA code phase acquisition

Abstract

This paper presents a segmented transversal matched filter (SMF) capable of performing code phase acquisition for a direct sequence spread spectrum (DS-SS) system in the presence of Doppler frequency shift and high co-user noise. Traditional acquisition methods such as serial search, sequential estimation, and I-Q matched filters are either too slow, incapable of overcoming high co-user noise, or unable to handle phase rotations due to Doppler shifts. The SMF has a high acquisition speed because it retains the signal history. A new code phase candidate can be tested as each new code chip is received. The segmentation of the SMF's correlation function allows it to handle several cycles of phase rotation caused by carrier frequency offset (Doppler). Presented here is a 512 bit, 16 segment (32 bits per segment) SMF implemented as a mixed analog/digital integrated circuit (IC). Several ICs may be cascaded to extend the effective filter length.