Decision statistics for noncoherent serial PN code acquisition in chip-asynchronous DS/SS systems

In this paper, we propose optimal and suboptimal serial code acquisition schemes for chip-asynchronous direct-sequence spread-spectrum (DS/SS) communications. The conventional serial code acquisition scheme individually compares each value of the correlator outputs with a threshold. Such a scheme is optimum, however, only under the chip-synchronous assumption that it is actually very difficult to detect prior to the acquisition at the receiver because the signal-to-noise ratios before despreading are very low. In this paper an optimal serial code acquisition scheme is derived based on the maximum-likelihood criterion under the more realistic and general chip-asynchronous environments. A suboptimal scheme, which is simpler but yields comparable performance to the optimal one, is also derived based on the criterion of local detection power. Numerical results show that, under the chip-asynchronous environments, both the optimal and suboptimal serial code acquisition schemes outperform the conventional serial code acquisition scheme