A digital receiver structure based on a multilevel correlative spreading code

Correlative level coding provides spectral reshaping of a pulse train such that the transmit spectrum can be limited within the Nyquist bandwidth without degrading the eye-pattern of the recovered waveform. This coding technique, also known as partial-response signaling, has desirable properties that protect the signal against interceptors using a symbol rate detector based on a squaring circuit. Any waveform that has its power spectrum confined within the Nyquist bandwidth does not expose its clock signal to a square-law circuit. A digital receiver structure has been developed based on a multilevel correlative spreading code, and the fine acquisition performance of its timing and carrier phase synchronization has been evaluated by simulation. A phase modulated signal spread by a multilevel spreading code looks more like noise than does one spread by a PN code