Study On One DS-SS PN Code Acquisition System

In modern communications, direct sequence spread spectrum(DS-SS)communication is widely used in military carrier communications because of its high noise resistance,low interception probability and good security. This dissertation constructs DS-SS base band simulation system according to the structure of software defined radio. Pseudonoise (PN) code acquisition is a key technology in SS communication. Since fading channels and hostile jamming would worsen the performance of PN acquisition system, the carrier SS requires one form of effective acquisition scheme. An adaptive serial search PN code acquisition scheme is proposed, in which the detection threshold is set by the instantaneous received power estimation during the correlation period. The adaptive power estimation threshold instantaneously reflects the feature of fading channel and time varying signal noise ratio (SNR). The proposed scheme improves the detection probability at low SNR. When the performace measure is mean acquisition time, threshold based on constant false alarm rate (CFAR) criteria is optimal. Through the conditional probability analysis of acquisition dicision variable under hypotheses of synchronized and nonsynchronized PN code, the CFAR charateristic of the proposed adaptive acquisition system can be obtained. This dessertation simulates the DS-SS system using adaptive acquisition scheme and proves the results of theoretical analysis. This dessertation analyses the features of hostile jamming of DS-SS communication under military electronic countermeasure environment. The pulse jamming with centralized power would increase acquisition time and worsen the performance of acquistion system. Thus, the anti pulse jamming is an important performance metrics of DS-SS. This thesis analyses the statistical property of pulse jamming noise and obtains the value of worst case jamming duty factor. The proposed scheme is shown to be optimum under pulsed noise jamming in the sense that it forces the pulsed jammer to be a full-time jammer. Based on the software defined radio universal platform applied in military carrier communication, the optimized simulation system with the adaptive acquisition scheme can be deployed in military carrier DS-CDMA.