Impact of the acquisition searching strategy on the detection and false alarm probabilities in a CDMA receiver

Fine delay and Doppler frequency estimation is a stringent problem of all block-based transmission, such as Orthogonal Frequency Division Multiplexing (OFDM) and Code Division Multiple Access (CDMA). In particular the first stage of each CDMA system, in presence of relevant Doppler shift, consists in a bi-dimensional search leading to a raw estimation of code delay and Doppler frequency. This stage is called acquisition and results extremely critical, both because of the catastrophic consequences of an erroneous estimation and because of the required high computational load. For this reason different acquisition strategies have been developed in order to increase the system performance and reduce the computational complexity. This paper studies the performance of three widely used acquisition strategies. The concept of system probabilities is introduced and used as comparison term. The case of Global Navigation Satellite System (GNSS) is considered as a critical application of CDMA modulation, nevertheless the results are general and apply to all CDMA systems.