Intelligent reflecting surface (IRS) is a promising technology to boost the efficiency of wireless energy transfer (WET) systems. However, for a multiuser WET system, simultaneous multi-beam energy transmission is generally required to achieve the maximum performance, which may not be implemented by using the IRS having only a single set of coefficients. As a result, it remains unknowns how to exploit the IRS to approach such a performance upper bound. To answer this question, we aim to maximize the total harvested energy of a multiuser WET system subject to the user fairness constraints and the non-linear energy harvesting model. We first consider the static IRS beamforming scheme, which shows that the optimal IRS reflection matrix obtained by applying semidefinite relaxation is indeed of high rank in general as the number of energy receivers (ERs) increases, due to which the resulting rank-one solution by applying Gaussian Randomization may lead to significant loss. To achieve the multi-beam gain, we then propose a general time-division based novel framework by exploiting the IRS's dynamic passive beamforming. Moreover, it is able to achieve a good balance between the system performance and complexity by controlling the number of IRS shift patterns. Finally, we also propose a time-division multiple access (TDMA) based passive beamforming design for performance comparison. Simulation results demonstrate the necessity of multi-beam transmission and the superiority of the proposed dynamic IRS beamforming scheme over existing schemes.
翻译:智能反射表面(IRS)是提高无线能源传输系统效率的一个大有希望的技术。然而,对于多用户WET系统来说,通常需要同时进行多波束能源传输才能实现最大性能,而使用IRS的单一一组系数可能无法实现最大性能。因此,目前尚不清楚如何利用IRS来接近这种性能上限。为了回答这个问题,我们的目标是最大限度地利用多用户WET系统的总节能,但需遵守用户公平性限制和非线性能源收获模式。我们首先考虑静态IRS波束成型计划,它表明通过采用半定型放松措施获得的最佳IRS反射矩阵表确实具有很高的等级,因为能源接收者的数量会增加。因此,通过应用高调的随机随机随机调整,因此可能导致重大损失。为了实现多波束增益,我们然后提议一个基于时间配置的通用新框架框架,利用IRS的动态性能级IRS成型和无线能源采集模型模型。此外,我们也可以通过当前动态变压的系统变动性变变变的多重性格式,从而实现目前性变的SD格式。我们以SD格式的SDFID格式的进度。最后,我们能够以显示基于SDFID格式的S格式的S的S-IDFLM的性能。