  This paper investigates an intelligent reflecting surface (IRS) aided
cooperative communication network, where the IRS exploits large reflecting
elements to proactively steer the incident radio-frequency wave towards
destination terminals (DTs). As the number of reflecting elements increases,
the reflection resource allocation (RRA) will become urgently needed in this
context, which is due to the non-ignorable energy consumption. The goal of this
paper, therefore, is to realize the RRA besides the active-passive beamforming
design, where RRA is based on the introduced modular IRS architecture. The
modular IRS consists with multiple modules, each of which has multiple
reflecting elements and is equipped with a smart controller, all the
controllers can communicate with each other in a point-to-point fashion via
fiber links. Consequently, an optimization problem is formulated to maximize
the minimum SINR at DTs, subject to the module size constraint and both
individual source terminal (ST) transmit power and the reflecting coefficients
constraints. Whereas this problem is NP-hard due to the module size constraint,
we develop an approximate solution by introducing the mixed row block
$\ell_{1,F}$-norm to transform it into a suitable semidefinite relaxation.
Finally, numerical results demonstrate the meaningfulness of the introduced
modular IRS architecture.
