The work reported in this thesis deals with aspects of synchronisation and tracking in direct sequence spread spectrum systems used in ranging and communications applications. This is regarded as a major design problem in such systems and several novel solutions are presented. Three main problem areas have been defined: i) reduction of the acquisition time of code sychronisation in the spread spectrum receiver; ii) reduction of the receiver complexity; iii) improvement of the signal to noise ratio performance of the system by better utilisation of the power spectrum in the main lobe of the transmitted signal. Greater tolerance to Doppler shift effects is also important. A general review of the spread spectrum concept and past work is first given in Chapter One, and common methods of synchronisation and tracking are reviewed in Chapter Two. There, current performance limitations are also included. In Chapter Three a novel method is given for increasing the speed of synchronisation between locally generated and received codes, using a technique of controlling the loop's error curve during acquisition. This method is applied to different width delay lock loops, and a significant increase in maximum search rate is obtained. The effect of the width of the discriminator characteristics and damping ratio on the maximum search rate are also examined. The technique is applied to data modulated spread spectrum systems which use either synchronous or asynchronous data communication systems. All methods have been tested experimentally and found to perform as predicted theoretically. Several novel spread sprectrum configurations are given in Chapter Four which employ multi-level sequences. Some configurations have reduced the complexity and cost of the spread spectrum receivers. Others show some improvement in the maximum search rate as well as the signal to noise ratio performance. Some of these configurations have been implemented experimentally. In Chapter Five, the generation and properties of the composite (Kronecker) sequences are explained. Several types of component sequences are examined. And the reception of these composite sequences are discussed. In particular, a technique is introduced for achieving a rapid acquisition of phase synchronisation using these codes. The effect of white Gaussian noise on the acquisition performance of the delay lock loop is given in Chapter Six. Experimental results are obtained for both digital and analogue correlators. Chapter Seven gives a final summary of the conclusions, and further work suggestions.
|Date of Award||1985|