Coherent serial acquisition schemes for PN sequences with data modulation

The performance of acquisition schemes for direct-sequence spread-spectrum systems in the presence of data modulation is investigated. The authors treat the phase of the incoming sequence as a signal parameter to be estimated in additive white Gaussian noise. The optimal coherent acquisition scheme based on the maximum-likelihood method is derived. A practical serial search scheme is proposed as an approximation to the optimal scheme. Numerical results show that the performance of the proposed scheme is significantly better than that of the conventional scheme when there is data modulation