Pn code acquisition with adaptive antenna array and adaptive threshold for cdma wireless communications

Abstract

A pseudonise (PN) code acquisition scheme employs all elements of a smart antenna array and an adaptive threshold. The basic structure is the combination of a conventional PN correlation searcher, an adaptive beamformer, and an adaptive threshold setting circuit. During each observation interval, the adaptive beamformer adaptively updates the weight vector for the smart antenna elements using the accumulated received signal despread with trial PN code phase error as input, preferably at the chip rate. A spatially correlated signal is then formed by weighting an accumulated value of the signal received by each antenna in the array over the observation period with the corresponding final weight of smart antenna weight vector as calculated by the adaptive beamformer. This spatially correlated signal is then compared to a threshold to determine whether PN code acquisition has occurred. In preferred embodiments, an adaptive threshold setting algorithm is employed to adapt to varying environment for efficient PN code acquisition. The adaptive threshold setting circuit accumulates the signal received by each element over the observation period, multiplies the accumulated values by the updated weight vector and combines the weighted values to an average estimated power. The average estimated power is then employed to scale a fixed reference threshold to create the adaptive threshold.