Differential detection of the OQPSK signal: coding and decoding

The authors consider the differential detection of the OQPSK (offset quadrature phase-shift keying) signal and propose a method for the differential coding of the binary message as well as a suitable decoding technique. It is shown that the coding of OQPSK for differential detection can be done either by double differential encoding of the binary message m(t) before driving the demultiplexer at the transmitter or by differential coding on each channel I(t) and Q(t) obtained by demultiplexing the message m(t). On the receiver side, it is shown that it is possible to use two lines of BPSK (binary PSK) differential detection. Doing so makes possible a decision on the polarity of the received data by simultaneous sampling of the inphase and quadrature channels. Like the minimum shift keying signal, the OQPSK signal can be detected with a delay of one or two bit time duration