In multiple access channels, when users know each other channels, precoders can be designed utilizing channel information to cancel the interference at the receiver without sacrificing the diversity or the complexity of the system. In a recent work, it was shown that when there are only two users, a receiver can completely cancel the interference and provide full diversity for each user. Unfortunately, the scheme only works for two users. In this paper, we extend the scheme to 4 users. In other words, we propose a system to achieve interference cancellation and full diversity with low complexity for 4 users. We also provide simulation results that confirm our analysis.