We introduce an opportunistic interference mitigation (OIM) protocol, where a
user scheduling strategy is utilized in K-cell uplink networks with
time-invariant channel coefficients and base stations (BSs) having M
antennas. Each BS opportunistically selects a set of users who generate the
minimum interference to the other BSs. Two OIM protocols are shown according to
the number S of simultaneously transmitting users per cell: opportunistic
interference nulling (OIN) and opportunistic interference alignment (OIA).
Then, their performance is analyzed in terms of degrees-of-freedom (DoFs). As
our main result, it is shown that KM DoFs are achievable under the OIN
protocol with M selected users per cell, if the total number N of users in
a cell scales at least as SNR(Kβ1)M. Similarly, it turns out that
the OIA scheme with S(<M) selected users achieves KS DoFs, if N scales
faster than SNR(Kβ1)S. These results indicate that there exists a
trade-off between the achievable DoFs and the minimum required N. By deriving
the corresponding upper bound on the DoFs, it is shown that the OIN scheme is
DoF optimal. Finally, numerical evaluation, a two-step scheduling method, and
the extension to multi-carrier scenarios are shown.Comment: 18 pages, 3 figures, Submitted to IEEE Transactions on Communication