Investigation into variable shift keying using direct sequence spread spectrum techniques

Abstract

This thesis reports the research done into a relatively unknown modulation scheme called VPSK (Variable Phase Shift Keying) and the use of DSSS (Direct Sequence Spread Spectrum) techniques to achieve carrier synchronization and hence coherent demodulation in the receiver. VPSK is a new and relatively unknown modulation scheme in which data bits are encoded using patented algorithms designed by Millerand Walker. VPSK modulation is a SSBSC (Single Sideband Suppressed Carrier) modulation scheme with good bandwidth efficiency. Data is coherently demodulated in the receiver. In existing VPSK systems, the locally generated carrier in the receiver is synchronized to an integer multiple of the symbol clock frequency to allow coherent demodulation. This coherent method of demodulation is not optimum if the channel over which information must be transmitted is a non-Gaussian channel, or has multi-path characteristics.