[论文解读] Multi-user Scheduling Schemes for Simultaneous Wireless Information and Power Transfer Over Fading Channels

Rania Morsi, Diomidis S. Michalopoulos+1 more|arXiv (Cornell University)|Jan 9, 2014

Energy Harvesting in Wireless Networks参考文献 16被引用 4

一句话总结

本文针对具有同时无线信息与能量传输（SWIET）的多用户下行链路系统，提出了基于顺序的信噪比（SNR）和归一化SNR（N-SNR）调度方案。通过调度第j个信道质量最佳的用户（而非最佳用户），系统能够控制遍历容量与采集能量之间的权衡。j值越小，能量采集越多，但吞吐量越低，从而实现能量效率操作，潜在实现通过动态电压调节降低立方功率。

ABSTRACT

In this paper, we study downlink multi-user scheduling for a time-slotted system with simultaneous wireless information and power transfer. In particular, in each time slot, a single user is scheduled to receive information, while the remaining users opportunistically harvest the ambient radio frequency energy. We devise novel online scheduling schemes in which the tradeoff between the users' ergodic rates and their average amount of harvested energy can be controlled. In particular, we modify the well-known maximum signal-to-noise ratio (SNR) and maximum normalized-SNR (N-SNR) schedulers by scheduling the user whose SNR/N-SNR has a certain ascending order (selection order) rather than the maximum one. We refer to these new schemes as order-based SNR/N-SNR scheduling and show that the lower the selection order, the higher the average amount of harvested energy in the system at the expense of a reduced ergodic sum rate. The order-based N-SNR scheduling scheme provides proportional fairness among the users in terms of both the ergodic achievable rate and the average harvested energy. Furthermore, we propose an order-based equal throughput (ET) fair scheduler, which schedules the user having the minimum moving average throughput out of the users whose N-SNR orders fall into a given set of allowed orders. We show that this scheme provides the users with proportionally fair average harvested energies. In this context, we also derive feasibility conditions for achieving ET with the order-based ET scheduler. Using the theory of order statistics, the average per-user harvested energy and ergodic achievable rate of all proposed scheduling schemes are analyzed and obtained in closed form for independent and non-identically distributed Rayleigh, Ricean, Nakagami-m, and Weibull fading channels. Our closed-form analytical results are corroborated by simulations.

研究动机与目标

• 解决多用户SWIET系统中系统容量与能量采集之间的权衡问题。
• 将传统调度方案（如最大SNR、轮询）扩展至联合优化信息与能量传输。
• 通过引入可调参数j控制速率-能量权衡，实现比例公平与能量效率。
• 分析在非同分布的Ricean和Rayleigh衰落信道下的遍历容量与平均采集能量。

提出的方法

• 通过选择SNR按升序排列的第j个用户的方案，提出基于顺序的SNR调度。
• 提出基于顺序的N-SNR调度，即选择相对于其平均值的第j个归一化SNR的用户进行调度。
• 应用顺序统计理论，推导出在非同分布Rayleigh衰落信道下遍历容量与平均采集能量的闭式表达式。
• 分析基准方案：在联合WIET下的轮询（RR）与等吞吐量（ET）调度。
• 通过系统级仿真验证分析结果，并评估不同衰落条件下性能权衡。
• 评估用户数N与调度顺序j对系统容量与总采集能量的影响。

实验结果

研究问题

• RQ1 与调度最佳用户相比，调度第j个最佳用户的SWIET系统中，遍历容量与平均采集能量如何变化？
• RQ2 在基于顺序的调度下，用户数N对系统速率-能量性能有何影响？
• RQ3 与绝对SNR调度相比，基于顺序的N-SNR方案在公平性与能量效率方面表现如何？
• RQ4 基准方案（RR与ET）与所提出的基于顺序的方案在容量与能量采集方面存在多大性能差距？

主要发现

• 在基于顺序的SNR/N-SNR调度中，j值越小，平均采集能量越高，但遍历系统容量越低，从而实现可调制的速率-能量权衡。
• 基于顺序的N-SNR方案在具有不同信道条件的用户间实现了比例公平，而最大SNR方案则倾向于强信道用户。
• 当j=1时，随着用户数N增加，平均采集能量上升，但因选择最弱信道导致多用户干扰损失，遍历容量下降。
• 当j=N时，由于选择最强信道带来多用户分集增益，遍历容量随N增加而提升，同时总采集能量也增加。
• 对于中间j值（如j=N/2），当N≥8时系统容量几乎保持不变，表明实现了平衡的权衡。
• 绝对SNR与归一化SNR调度之间的性能差异极小，但N-SNR调度在公平性方面表现更优，因此在实际应用中更受青睐。