This paper investigates the problem of resource allocation for a wireless
communication network with distributed reconfigurable intelligent surfaces
(RISs). In this network, multiple RISs are spatially distributed to serve
wireless users and the energy efficiency of the network is maximized by
dynamically controlling the on-off status of each RIS as well as optimizing the
reflection coefficients matrix of the RISs. This problem is posed as a joint
optimization problem of transmit beamforming and RIS control, whose goal is to
maximize the energy efficiency under minimum rate constraints of the users. To
solve this problem, two iterative algorithms are proposed for the single-user
case and multi-user case. For the single-user case, the phase optimization
problem is solved by using a successive convex approximation method, which
admits a closed-form solution at each step. Moreover, the optimal RIS on-off
status is obtained by using the dual method. For the multi-user case, a
low-complexity greedy searching method is proposed to solve the RIS on-off
optimization problem. Simulation results show that the proposed scheme achieves
up to 33\% and 68\% gains in terms of the energy efficiency in both single-user
and multi-user cases compared to the conventional RIS scheme and
amplify-and-forward relay scheme, respectively.

这篇论文研究了具有分布式可重构智能表面（RIS）的无线通信网络的资源分配问题，提出了两种迭代算法来最大化网络的能量效率，并展示了所提出方案在单用户和多用户情况下相较传统 RIS 方案和放大转发中继方案可获得高达 33％和 68％的性能提升。

分布式可重构智能表面的能效无线通信

Energy-Efficient Wireless Communications with Distributed Reconfigurable  Intelligent Surfaces

As a recently proposed idea for future wireless systems, intelligent
reflecting surface (IRS) can assist communications between entities which do
not have high-quality direct channels in between. Specifically, an IRS
comprises many low-cost passive elements, each of which reflects the incident
signal by incurring a phase change so that the reflected signals add coherently
at the receiver. In this paper, for an IRS-aided wireless network, we study the
problem of power control at the base station (BS) for physical-layer
broadcasting under quality of service (QoS) constraints at mobile users, by
jointly designing the transmit beamforming at the BS and the phase shifts of
the IRS units. Furthermore, we derive a lower bound of the minimum transmit
power at the BS to present the performance bound for optimization methods.
Simulation results show that, the transmit power at the BS approaches the lower
bound with the increase of the number of IRS units, and is much lower than that
of the communication system without IRS.

本文提出了一种基于智能反射面的无线网络，研究了在 QoS 约束下，通过联合设计基站的发射波束和 IRS 元件的相位调节进行物理层广播的功率控制问题，并导出了用于优化方法的性能下界。仿真结果表明，随着 IRS 单元数量的增加，基站的发射功率接近下限，并且比没有使用 IRS 的通信系统的发射功率低得多。

智能反射面辅助网络：物理层广播功率控制

Intelligent Reflecting Surface Aided Network: Power Control for  Physical-Layer Broadcasting

Transmit beamforming is a versatile technique for signal transmission from an
array of $N$ antennas to one or multiple users [1]. In wireless communications,
the goal is to increase the signal power at the intended user and reduce
interference to non-intended users. A high signal power is achieved by
transmitting the same data signal from all antennas, but with different
amplitudes and phases, such that the signal components add coherently at the
user. Low interference is accomplished by making the signal components add
destructively at non-intended users. This corresponds mathematically to
designing beamforming vectors (that describe the amplitudes and phases) to have
large inner products with the vectors describing the intended channels and
small inner products with non-intended user channels.
While it is fairly easy to design a beamforming vector that maximizes the
signal power at the intended user, it is difficult to strike a perfect balance
between maximizing the signal power and minimizing the interference leakage. In
fact, the optimization of multiuser transmit beamforming is generally a
nondeterministic polynomial-time (NP) hard problem [2]. Nevertheless, this
lecture shows that the optimal transmit beamforming has a simple structure with
very intuitive properties and interpretations. This structure provides a
theoretical foundation for practical low-complexity beamforming schemes.
(See this lecture note for the complete abstract/introduction)

本文介绍了传输波束成形技术的应用及其在无线通信中对于信号传输和干扰抑制的意义，同时也探讨了多用户优化所面临的非确定性多项式时间复杂度的问题。