Optimal synchronization and selection of symbols at the reception of QPSK radio signal

The article deals with the problem of constructing algorithms for joint phase and symbol synchronization, as well as character extraction when receiving a radio signal with quadrature phase modulation with time offset (OQPSK). Optimal algorithms for solving this problem are based on the maximum likelihood method. The likelihood function is derived from the functional of the two-dimensional probability density for the components of the complex envelope of the input process. The results of calculations of the energy losses in the selected symbols and error performance in a closed tracking algorithms the phase and delay. In contrast to the widely used practice of methods discussed algorithms ensure reliable tracking and selection of symbols for small values of the energy relationship without suppressing of the weak signal due to noise, that it is particularly important in radio deep space communications.