New PN code acquisition schemes for low Earth orbit satellites

Abstract

A new approach to PN code acquisition, for CDMA LEO satellite systems experiencing high code Doppler and code Doppler rate, is presented and analysed. The approach is based on transforming the two dimensional code Doppler (D) and delay (t) uncertainty region (D,t) into a new uncertainty region (T/sub c/,t) where T/sub c/ is the period of the correlation pulses at the output of a sliding correlator. When Doppler rate is present the three dimensional uncertainty region (D, R/sub t/,t) is transformed into a new one (T/sub c/, R/sub t/,t) where R/sub d/ and R/sub t/ are Doppler rate and correlation pulse period rate respectively. The main motivation for this work is to find new algorithms which are suitable for all digital receiver implementation. In the implementation of these new algorithms rather complex FFT hardware components are now replaced by much simpler components such as accumulators. These algorithms make CDMA techniques feasible in the communication between LEO satellite and small ground based user terminals. Personal communications based on LEO satellites is an option that has been considered extensively for rural areas. A comprehensive performance study of the new PN code acquisition system is presented and discussed. >