Since the received signal levels in mobile communications are unknown and the location is varying, acquisition schemes for pseudonoise (PN) sequences with fixed thresholds cannot provide satisfactory performance. This fixed-threshold scheme may cause too many false alarms or result in a low detection probability for a selected threshold value. We present an adaptive acquisition scheme for PN sequences which estimate the background power level, multiply it with a threshold coefficient to keep the false alarms constant, and use it as a threshold.

This paper analyzes the bit error rate (BER) for quadrature amplitude modulation (QAM) with L-fold maximal ratio combining (MRC) space diversity in Rayleigh fading channel. The formula is obtained by averaging the bit error probability of M-ary QAM in an additive white Gaussian noise channel over a chi-square distribution with 2L degrees of freedom. This formula overcomes the limitations of the earlier work, which has been limited only to deriving a BER for QAM with two branch MRC space diversity. The BER performance of quadrature phase shift keying with MRC diversity is obtained from the derived formula by setting M=4.