The paper presents an IRS-aided multiuser communication system that simultaneously serves high-mobility and low-mobility users.
For high-mobility users, the system employs a novel transmit diversity scheme by dynamically adjusting the IRS's common phase-shift in real time, without requiring any channel state information (CSI). This is achieved by designing a new space-time code at the IRS-integrated base station (BS).
For low-mobility users, the system incorporates conventional active/passive precoding at the IRS-integrated BS, assuming their CSI is known. Notably, the passive precoding gain of the IRS remains unchanged when dynamically tuning its common phase-shift to enable transmit diversity for high-mobility users.
The paper formulates an optimization problem to minimize the total transmit power at the BS, subject to individual signal-to-interference-plus-noise ratio (SINR) constraints for both high-mobility and low-mobility users. An efficient alternating optimization algorithm is developed to solve this non-convex problem, by iteratively optimizing the IRS's reflect precoding and the BS's transmit precoding.
Simulation results demonstrate the superior performance of the proposed IRS-aided multiuser communication system compared to other benchmarks, by virtue of the new architecture of the IRS-integrated BS and the co-design of transmit diversity and active/passive precoding.
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