  Interference alignment aims to achieve maximum degrees of freedom in an
interference system. For achieving Interference alignment in interfering
broadcast systems a closed-form solution is proposed in [1] which is an
extension of the grouping scheme in [2]. In a downlink scenario where there are
a large number of users, the base station is required to select a subset of
users such that the sum rate is maximized. To search for the optimal user
subset using brute-force approach is computationally exhaustive because of the
large number of possible user subset combinations. We propose a user selection
algorithm achieving sum rate close to that of optimal solution. The algorithm
employs coordinate ascent approach and exploits orthogonality between the
desired signal space and the interference channel space in the reciprocal
system to select the user at each step. For the sake of completeness, we have
also extended the sum rate approach based algorithm to Interfering broadcast
channel. The complexity of both these algorithms is shown to be linear with
respect to the total number of users as compared to exponential in brute-force
search.
