Rate unity trellis codes with quadrature-quadrature phase shift keying (Q2PSK) signals

Trellis coding with a spectrally efficient 4D signal set due to newly developed Q²PSK (quadrature-quadrature phase-shift keying) is addressed. Some simple hand designed trellis codes at rate unity are presented. A sixteen state code provides a coding gain of 6.02 dB. With the same number of states in Ungerboeck´s 8-PSK, trellis (1982), the gain is 4.1 dB. In low intersymbol interference situations, the bandwidth efficiency of this coded Q²PSK is twice that of coded 8-PSK; if both operate at 2 bits/s/Hz and an error event probability of 10^-5, the coded Q²PSK provides a savings of about 4 dB over the coded 8-PSK