68 research outputs found
Downlink and Uplink Intelligent Reflecting Surface Aided Networks: NOMA and OMA
Intelligent reflecting surfaces (IRSs) are envisioned to provide
reconfigurable wireless environments for future communication networks. In this
paper, both downlink and uplink IRS-aided non-orthogonal multiple access (NOMA)
and orthogonal multiple access (OMA) networks are studied, in which an IRS is
deployed to enhance the coverage by assisting a cell-edge user device (UD) to
communicate with the base station (BS). To characterize system performance, new
channel statistics of the BS-IRS-UD link with Nakagami- fading are
investigated. For each scenario, the closed-form expressions for the outage
probability and ergodic rate are derived. To gain further insight, the
diversity order and high signal-to-noise ratio (SNR) slope for each scenario
are obtained according to asymptotic approximations in the high-SNR regime. It
is demonstrated that the diversity order is affected by the number of IRS
reflecting elements and Nakagami fading parameters, but the high-SNR slope is
not related to these parameters. Simulation results validate our analysis and
reveal the superiority of the IRS over the full-duplex decode-and-forward
relay.Comment: Accepted for publication in the IEEE Transactions on Wireless
Communication
Opportunistic Reflection in Reconfigurable Intelligent Surface-Assisted Wireless Networks
This paper focuses on multiple-access protocol design in a wireless network
assisted by multiple reconfigurable intelligent surfaces (RISs). By extending
the existing approaches in single-user or single-RIS cases, we present two
benchmark schemes for this multi-user multi-RIS scenario. Inspecting their
shortcomings, a simple but efficient method coined opportunistic multi-user
reflection (OMUR) is proposed. The key idea is to opportunistically select the
best user as the anchor for optimizing the RISs, and non-orthogonally
transmitting all users' signals simultaneously. A simplified version of OMUR
exploiting random phase shifts is also proposed to avoid the complexity of RIS
channel estimation.Comment: IEEE PIMRC 2023, Toronto, Canada. arXiv admin note: text overlap with
arXiv:2303.09183. text overlap with arXiv:2309.0632
User Pairing and Power Allocation for IRS-Assisted NOMA Systems with Imperfect Phase Compensation
In this letter, we analyze the performance of the intelligent reflecting
surface (IRS) assisted downlink non-orthogonal multiple access (NOMA) systems
in the presence of imperfect phase compensation. We derive an upper bound on
the imperfect phase compensation to achieve minimum required data rates for
each user. Using this bound, we propose an adaptive user pairing algorithm to
maximize the network throughput. We then derive bounds on the power allocation
factors and propose power allocation algorithms for the paired users to achieve
the maximum sum rate or ensure fairness. Through extensive simulations, we show
that the proposed algorithms significantly outperform the state-of-the-art
algorithms
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