Instantaneous degrees of freedom of downlink interference channels with multiuser diversity

Independent channel fading across different users in a wireless network enables the system to exploit multiuser diversity. In this paper, we investigate the impact of user scheduling on the instantaneous degrees of freedom of multiple interfering cellular networks. Particularly, we consider a homogeneous multiple cellular downlink scenario with multiple users per cell. We show that if the number of users in a cell scales faster than linearly with SNR, the instantaneous degrees of freedom with multiuser diversity increases and converges to L in both mean-square (m.s.) sense and almost sure (a.s.) sense for an L-cell downlink interference channel, even though very limited channel feedback is needed. Each user is equipped with L-1 antennas to capture the multidimensional out-of-cell interference from other base stations, while the base station has a single antenna. The user scheduling strategy that achieves L instantaneous degrees of freedom is to poll users experiencing only a small amount of out-of-cell interference. The instantaneous degrees of freedom with multiuser diversity and its convergence mode are compared to those of conventional interference alignment. Furthermore, the user scaling law is relaxed when ergodic throughout is analyzed.