  In this paper, we study the resource allocation for an intelligent reflecting
surface (IRS)-assisted uplink system, where the base station is equipped with
multiple antennas. We propose to jointly optimize the transmit power of the
users, active beamforming at the base station, and passive beamforming at the
IRS to maximize the overall system energy efficiency while maintaining users'
minimum rate constraints. This problem belongs to a highly intractable
non-convex bi-quadratic programming problem, for which an iterative solution
based on block coordinate descent is proposed. Extensive simulations are
conducted to demonstrate the effectiveness of the proposed scheme and the
benefits of having more elements at the IRS.
