Convolver-Aided Synchronization in a Direct-Sequence Spread Spectrum Communication System

A commonly used method for the code ac- quisition phase in direct-sequence spread spectrum sys- tems is serial search of the relative positions of received signal and locally generated reference waveform in dis- crete steps of a fraction of a code chip. However, if no a priori timing information is available to the receiver, uniform search over the long pseudonoise (PN) code pe- riods generally employed in anti-jam and anti-intercept communications may lead to acquisition times that are prohibitive. The initial uncertainty can be reduced with the aid of shorter code segments which are processed in matched filters. In order to maintain low probability of exploitation by unintended parties these code segments should be easily variable. Thus programmable matched filtering is required, which advantageously can be per- formed by surface acoustic wave (SAW) convolvers. In the presented system convolvers with I6 ~s integration time and an input 3-dB bandwidth of 90 MHz, centered at 300 MHe, correlate 800-chip PN code patterns. The resulting processing gain is 29 dB. The system operates at a code chip rate of 50 MHz which is determined by the bandwidth of the available convolvers. Performance in additive white Gaussian noise and in CW interference is presented.