Optimized Rotations for LDPC-coded Gray-mapped MPSK Constellations with Signal Space Diversity

Rotation of the signal constellation together with in-phase and quadrature channel interleaving (signal space diversity) is known to provide good performance gains over fading channels for multi level modulation methods. This paper studies the extension of such schemes with a low density parity check (LDPC) code. It is shown that for both coded and un-coded Gray-mapped MPSK modulation formats with signal space diversity on a Rayleigh fading channel, a well-considered choice of the rotation angle may lead to a significant gain over the conventional un-rotated constellation. However, the optimum rotation angle for the coded scheme may be different from the corresponding optimization angle of the un-coded scheme