  Existing works on IRS have mainly considered IRS being deployed in the
environment to dynamically control the wireless channels between the BS and its
served users. In contrast, we propose in this paper a new integrated IRS BS
architecture by deploying IRSs inside the BS antenna radome. Since the distance
between the integrated IRSs and BS antenna array is practically small, the path
loss among them is significantly reduced and the real time control of the IRS
reflection by the BS becomes easier to implement. However, the resultant near
field channel model also becomes drastically different. Thus, we propose an
element wise channel model for IRS to characterize the channel vector between
each single antenna user and the antenna array of the BS, which includes the
direct (without any IRS reflection) as well as the single and double
IRS-reflection channel components. Then, we formulate a problem to optimize the
reflection coefficients of all IRS reflecting elements for maximizing the
uplink sum rate of the users. By considering two typical cases with/without
perfect CSI at the BS, the formulated problem is solved efficiently by adopting
the successive refinement method and iterative random phase algorithm (IRPA),
respectively. Numerical results validate the substantial capacity gain of the
integrated IRS BS architecture over the conventional multi antenna BS without
integrated IRS. Moreover, the proposed algorithms significantly outperform
other benchmark schemes in terms of sum rate, and the IRPA without CSI can
approach the performance upper bound with perfect CSI as the training overhead
increases.
