Trellis Coded Quadrature-Quadrature Phase Shift Keying

Integrated modulation and coding due to Ungerboeck observed no significant effect of dimensionality of signal space on the coding gain; it appeared unlikely that signals in more than two dimensions could have advantages. In this paper, it is pointed out that the utilization of all available signal space dimensions may bring further improvement in the coding gain. A four dimensional signal space due to newly developed Quadrature-Quadrature Phase Shift Keying (Q²PSK) is considered and a hand designed 7/8 rate trellis on Q²PSK signal space is studied. With two and eight states in the trellis, coding gains of 2.43 and 5.45 dB are obtained. With the same number of states in Ungerboeck's two dimensional 8-PSK trellis, the coding gains are 1.1 and 3.6 dB respectively. In low intersymbol interference situation, the bandwidth efficiency of this coded Q²PSK is approximately 1.75 times that of Ungerboeck's coded 8-PSK.