(A) DS/CDMA code acquisition scheme robust to residual code phase offset variation

Abstract

In this thesis, we first investigate the effect of residual code phase offset on the DS/CDMA code acquisition scheme using a noncoherent I-Q matched filter receiver. We then propose a new code acquisition scheme which is robust to the variation of the residual code phase offset and outperforms the conventional scheme. In practice, residual code phase offset is unavoidable and may cause serious performance degradation. The output of the noncoherent I-Q matched filter is the correlation between two PN code sequences, the received and locally generated code sequences. Therefore, when the code phase offset between the two sequences is within one chip duration, the sum of two successive outputs has a constant value regardless of the residual code phase offset if the noise is absent. Based on this observation, we propose a new code acquisition scheme, and investigate the performance of the scheme. As the mean acquisition time is an important performance measure in code acquisition, we obtain a closed-form expression of the mean acquisition time by the flow graph technique. We also derive the detection and false alarm probabilities for calculating the mean acquisition time. The proposed code acquisition scheme is analyzed in additive white Gaussian noise and multiple access interference environment. Finally, numerical results are given to show that the proposed scheme is more robust to the variation of the residual code phase offset and has better performance than the conventional scheme on the average.