Multiuser Trellis Shaping for Space-Time Codes in Vector Gaussian Broadcast Channel

Multiuser trellis shaping for space-time trellis codes (STTC) is proposed to realize dirty paper coding (DPC) in downlink multiuser channel, which is sometimes referred to as vector Gaussian broadcast channel. Our proposal considers not only the current transmit signal, but also the entire sequence of the signal for multiple users to achieve the higher capacity. In our proposal, the STTC is transmitted to each user and preceding is used to pre-subtract the interference among the users. An increase in transmit power due to the preceding is reduced by trellis shaping that adds trellis codewords to the information sequence for each user. The shaping code and the STTC are separated in order to systematically design both codes in our system. Simulation results indicate that the shaping gain of more than 3 dB is achieved by applying the different shaping codes for each user, and that frame error rate of the proposed scheme shows better performance than that of the conventional Tomlinson-Harashima precoding.