Pulse-Width Modulation of Spread Spectrum Carriers

摘要

Spread spectrum techniques can produce results in communication and navigation systems that are not possible with standard signal formats. The results of particular interest are the ability to screen messages from eavesdroppers, high resolution ranging and the rejection of interference. Three modulation schemes that exploit these spread spectrum properties are analyzed in this thesis. All three techniques use pulse-width modulation to encode sampled analog voice signals onto a digital phase coded carrier. The performance analysis assumes transmission in the presence of white Gaussian noise and CW jamming. The performance analysis uses maximum likelihood estimation to define the sample parameter estimate and associated error variance when probability density functions can be defined for the receiver sample outputs. When the density function is not available a second moment analysis is used to define the expected signal-to-noise ratio. The results are extended to include the introduction of signal dependent code noise into the receiver resulting from the degradation of the orthogonal code word structure. The impact of code noise on system performance is seen to grow with the number of users squared and the received signal energy. (Author)