Intelligent reflecting surfaces (IRS) have been proposed as a revolutionary
technology owing to its capability of adaptively reconfiguring the propagation
environment in a cost-effective and hardware-efficient fashion. While the
application of IRS as a passive reflector to enhance the performance of
wireless communications has been widely investigated in the literature, using
IRS as a passive transmitter recently is emerging as a new concept and
attracting steadily growing interest. In this paper, we propose two novel
IRS-based passive information transmission systems using advanced symbol-level
precoding. One is a standalone passive information transmission system, where
the IRS operates as a passive transmitter serving multiple receivers by
adjusting its elements to reflect unmodulated carrier signals. The other is a
joint passive reflection and information transmission system, where the IRS not
only enhances transmissions for multiple primary information receivers (PIRs)
by passive reflection, but also simultaneously delivers additional information
to a secondary information receiver (SIR) by embedding its information into the
primary signals at the symbol level. Two typical optimization problems, i.e.,
power minimization and quality-of-service (QoS) balancing, are investigated for
the proposed IRS-based passive information transmission systems. Simulation
results demonstrate the feasibility of IRS-based passive information
transmission and the effectiveness of our proposed algorithms, as compared to
other benchmark schemes.Comment: 14 pages, 11 figures, major revisio
