[论文解读] Rate-Splitting Multiple Access for Multi-antenna Downlink Communication Systems: Spectral and Energy Efficiency Tradeoff

Gui Zhou, Yijie Mao+1 more|arXiv (Cornell University)|Jan 9, 2020

Advanced Wireless Communication Technologies被引用 4

一句话总结

该论文提出了一种针对多天线下行链路系统中具有速率相关电路功耗的速率复用多址接入（RSMA）的联合频谱效率（SE）与能量效率（EE）优化框架。通过加权和法与加权功率法将多目标问题转化为单目标子问题，并针对两用户系统采用低复杂度算法，针对K用户系统采用连续凸逼近（SCA）方法，该方法相较于SDMA和NOMA在收敛速度和SE-EE权衡性能方面表现更优。

ABSTRACT

Rate-splitting (RS) has recently been recognized as a promising physical-layer technique for multi-antenna broadcast channels (BC). Due to its ability to partially decode the interference and partially treat the remaining interference as noise, RS is an enabler for a powerful multiple access, namely rate-splitting multiple access (RSMA), that has been shown to achieve higher spectral efficiency (SE) and energy efficiency (EE) than both space division multiple access (SDMA) and non-orthogonal multiple access (NOMA) in a wide range of user deployments and network loads. As SE maximization and EE maximization are two conflicting objectives, the study of the tradeoff between the two criteria is of particular interest. In this work, we address the SE-EE tradeoff by studying the joint SE and EE maximization problem of RSMA in multiple input single output (MISO) BC with rate-dependent circuit power consumption at the transmitter. To tackle the challenges coming from multiple objective functions and rate-dependent circuit power consumption, we first propose two methods to transform the original problem into a single-objective problem, namely, weighted-sum method and weighted-power method. A successive convex approximation (SCA)-based algorithm is then proposed to jointly optimize the precoders and RS message split of the transformed problem. Numerical results show that our algorithm converges much faster than existing algorithms. In addition, the performance of RS is superior to or equal to non-RS strategy in terms of both SE and EE and their tradeoff.

研究动机与目标

• 解决在实际速率相关电路功耗约束下，多天线下行链路系统中频谱效率（SE）与能量效率（EE）之间的基本权衡问题。
• 克服RSMA预编码设计中因速率相关电路功耗而引发的多目标优化与非凸性挑战。
• 开发高效算法，联合最大化SE与EE，且无需对预设SE约束进行可行性检查。
• 证明RSMA在SE与EE性能及其权衡方面优于传统SDMA与NOMA。

提出的方法

• 利用加权和法与加权功率法，将多目标SE-EE优化问题转化为两个单目标子问题。
• 通过求解转换后的单目标问题，为两用户MISO BC场景提出一种低复杂度闭式解算法。
• 采用基于连续凸逼近（SCA）的算法将解扩展至K用户系统，以处理非凸预编码优化问题。
• 将发射机的电路功耗建模为速率相关函数，以反映实际硬件约束。
• 利用Karush-Kuhn-Tucker（KKT）条件与部分一阶近似，推导SCA框架下的最优性条件。
• 应用内逼近技术迭代优化解，确保收敛至原始问题的驻点。

实验结果

研究问题

• RQ1 在具有速率相关电路功耗的多天线下行链路系统中，如何联合优化SE与EE的冲突目标？
• RQ2 在实际硬件约束下，RSMA相较于SDMA与NOMA在SE与EE权衡方面有何性能增益？
• RQ3 能否为具有联合SE-EE优化的两用户RSMA系统推导出具有闭式解的低复杂度算法？
• RQ4 基于SCA的K用户系统算法在收敛速度与性能方面相较于现有方法表现如何？
• RQ5 速率相关电路功耗对SE-EE权衡及最终预编码设计有何影响？

主要发现

• 所提出的基于SCA的算法收敛速度显著快于现有算法，展现出更高的计算效率。
• 在广泛的用户部署与网络负载条件下，RSMA在频谱效率与能量效率方面均优于SDMA与NOMA。
• 通过加权和法与加权功率法实现的联合SE-EE优化，成功避免了固定SE约束带来的可行性问题。
• 对于两用户情况，所提出的低复杂度算法实现了闭式解，支持实时实现。
• K用户SCA算法收敛至原始非凸问题的驻点，确保了可靠的性能表现。
• 数值结果证实，RSMA在SE-EE权衡方面表现更优，其性能在所有信噪比（SNR）范围内持续优于或匹配SDMA与NOMA。