I'm developing a Multi-user MIMO communication model in MATLAB where a base station communicates with 2 users. The model uses OFDM (QPSK) modulation. Channel model, precoding and covolutional encoder is also used. Iam sending single stream of data to each user and I'm trying to plot the receive constellation diagram for my analysis. At the receiver side, I have single antenna users. Ideally, I'm supposed to get a rectangle lattice configuration for QPSK, however am getting weird geometrical designs which am not able to understand why. I tried to check at the transmitter side how the constellation would be and it seems to be okay. I would be glad if anyone can help me out to debug this issue.