A Study on the Optimal Degree-of-Freedoms of Cellular Networks: Opportunistic Interference Mitigation

We introduce an opportunistic interference mitigation (OIM) protocol for cellular networks, where a user scheduling strategy is utilized in uplink K-cell environments with time-invariant channel coefficients and base stations (BSs) having M receive antennas. In the OIM scheme, each BS opportunistically selects a set of users who generate the minimum interference to the other BSs. We consider two OIM protocols according to the number S of simultaneously transmitting users per cell. Then, their performance is analyzed in terms of degrees-of-freedom (DoFs). As our main result, it is shown that KS DoFs are achievable if and only if the total number N of users in a cell scales at least as SNR(K-1)S. These results indicate that there exists a trade-off between the achievable number of DoFs and the scaling parameter N by tuning the number S of selected users. By showing an upper bound on the DoFs, it is also shown that the OIM scheme with M selected users is DoF-optimal. Finally, numerical evaluation is performed.