  Intelligent reflecting surface (IRS), which is capable to adjust propagation
conditions by controlling phase shifts of the reflected waves that impinge on
the surface, has been widely analyzed for enhancing the performance of wireless
systems. However, the reflective properties of widely studied IRSs restrict the
service coverage to only one side of the surface. In this paper, to extend the
wireless coverage of communication systems, we introduce the concept of
intelligent omni-surface (IOS)-assisted communication. More precisely, IOS is
an important instance of reconfigurable intelligent surface (RIS) that is
capable to provide service coverage to the mobile users (MUs) in a reflective
and a transmissive manner. We consider a downlink IOS-assisted communication
system, where a multi-antenna small base station (SBS) and an IOS perform
beamforming jointly, to improve the received power of multiple MUs on both
sides of the IOS, through different reflective/transmissive channels. To
maximize the sum-rate, we formulate a joint IOS phase shift design and SBS
beamforming optimization problem, and propose an iterative algorithm to solve
the resulting non-convex program efficiently. Both theoretical analysis and
simulation results show that an IOS significantly extends the service coverage
of the SBS when compared to an IRS.
