Non coherent demodulation of BPSK secure symbols

From the communication channel and implementation aspects of communications, the transmission environment may be sufficiently degraded that introduces practical difficulties in acquiring and tracking a coherent demodulation reference signal. Coherent receivers require exact knowledge of the channel phase for optimum performance. Due to the difficult task of estimating the channel phase, non-coherent as well as differential detection is an attractive alternative to coherent detection. A conventional differential detector uses the signal received in the previous symbol interval as a phase reference for the received signal in the current interval. As long as the phase distortion introduced by channel varies slowly relative to the symbol rate, conventional differential detection will work quite well. This assumption is not always true, and, in addition, differentially coherent detection is based on the premise that there is no intersymbol interference (ISI) in the received signal. In this paper we present a new modulation technique which allows to transmit coherent secure symbols and demodulate them incoherently. The main advantages is the use of simpler receiver while still having information carried by the phase of the radio signal. In practise, an incoherent detector can be used, while having optimum performance as a coherent detector. No reference signal or symbol is needed to automatically compensate the total phase rotation at the receiver. It will be shown that the total phase rotation can be easily and accurately estimated (and compensated) at the receiver side, without relying on any phase reference from a transmitted pilot signal or from the received modulated signal.