Trellis Coded Modulation for Two-User Unequal-Rate Gaussian MAC

In this paper, code pairs based on trellis coded modulation are proposed over PSK signal sets for a two-user Gaussian multiple access channel. In order to provide unique decodability property to the receiver and to maximally enlarge the constellation constrained (CC) capacity region, a relative angle of rotation is introduced between the signal sets. Subsequently, the structure of the sum alphabet of two PSK signal sets is exploited to prove that Ungerboeck labelling on the trellis of each user maximizes the guaranteed minimum squared Euclidean distance, d 2 g,min in the sum trellis. Hence, such a labelling scheme can be used systematically to construct trellis code pairs for a two-user GMAC to approach any rate pair within the capacity region.