  Intelligent Reflecting Surface (IRS) is a promising technology for next
generation wireless networks. Despite substantial research in IRS-aided
communications, the assumed antenna and channel models are typically simplified
without considering site-specific characteristics, which in turn critically
affect the IRS deployment and performance in a given environment. In this
paper, we first investigate the link-level performance of active or passive IRS
taking into account the IRS element radiation pattern (ERP) as well as the
antenna radiation pattern of the access point (AP). Then the network-level
coverage performance is evaluated/optimized in site-specific multi-building
scenarios, by properly deploying multiple IRSs on candidate building facets to
serve a given set of users or Points of Interests (PoIs). The problem is
reduced to an integer linear programming (ILP) based on given link-level
metrics, which is then solved efficiently under moderate network sizes.
Numerical results confirm the impact of AP antenna/IRS element pattern on the
link-level performance. In addition, it is found that active IRSs, though
associated with higher hardware complexity and cost, significantly improve the
site-specific network coverage performance in terms of average ergodic rate and
fairness among the PoIs as well as the range of serving area, compared with
passive IRSs that have a much larger number of elements.
