ON THE CAPACITY OF THE BLOCKWISE INCOHERENT MPSK CHANNEL

The capacity of M-ary phase-shift keying (MPSK) over an additive white Gaussian noise (AWGN) channel with carrier phase unknown but constant over L symbols is investigated. It is shown that capacity-achieving c hannel inputs are uniformly distributed and independent MPSK symbols. Capacity over a range of signal-to-noise ratio (SNR) and L is presente d for binary phase shift keying (BPSK) and quaternary phase-shift keyi ng (QPSK). Upper and lower easy-to-compute bounds on capacity are deri ved. It is proven that for large L the coherent capacity is approached . An analytic asymptotic expression for low L SNR is derived exhibitin g the expected quadratic dependence on the SNR.