Wirelessly powered backscatter communication (WPBC) has been identified as a promising technology for low-power communication systems, which can reap the benefits of energy beamforming to improve energy transfer efficiency. However, existing studies on energy beamforming fail to simultaneously take energy supply and information transfer in WPBC into account. This paper takes the first step to fill this gap, by considering the restrictive relationship between the energy harvesting rate and achievable rate with estimated backscatter channel state information (BS-CSI). To ensure reliable communication and user fairness, we formulate the energy beamforming design as a max-min optimization problem by maximizing the minimum achievable rate for all backscatter tags subject to the energy constraint. We derive the closed-form expression of the energy harvesting rate, as well as the lower bound of the achievable rate for maximum-ratio combining (MRC) and zero-forcing (ZF) receivers. Our numerical results indicate that our scheme significantly outperforms state-of-the-art energy beamforming schemes. Additionally, the achievable rate of our scheme approaches more than $90\%$ of the rate limit achieved via beamforming with perfect CSI for both receivers.

中文翻译：

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反向散射多用户网络中能量波束形成的联合能量收集和信息传输

无线供电反向散射通信 (WPBC) 已被确定为低功率通信系统的一项有前途的技术，它可以利用能量波束成形的好处来提高能量传输效率。然而，现有的能量波束形成研究未能同时考虑到 WPBC 中的能量供应和信息传输。本文采取了填补这一空白的第一步，通过考虑能量收集速率和可实现速率与估计的反向散射信道状态信息 (BS-CSI) 之间的限制关系。为了确保可靠的通信和用户公平，我们通过最大化所有受能量约束的反向散射标签的最小可实现速率，将能量波束成形设计制定为最大-最小优化问题。我们推导出能量收集速率的封闭形式表达式，以及最大比合并 (MRC) 和迫零 (ZF) 接收器可实现速率的下限。我们的数值结果表明，我们的方案明显优于最先进的能量波束成形方案。此外，我们方案的可实现速率接近通过具有完美 CSI 的波束成形为两个接收器实现的速率限制的 90% 以上。