
Energy Efficiency Research on Cell-Free Massive MIMO-WPT Systems with Mixed-Resolution DACs
ZHANG Yao, ZHAO Hai-tao, XIA Wen-chao, YANG Long-xiang, ZHU Hong-bo
ACTA ELECTRONICA SINICA ›› 2023, Vol. 51 ›› Issue (10) : 2765-2774.
Energy Efficiency Research on Cell-Free Massive MIMO-WPT Systems with Mixed-Resolution DACs
A downlink cell-free massive multiple-input multiple-output wireless power transfer (MIMO-WPT) system using the mixed-resolution digital-to-analog converter (DAC) architecture is studied, where the user equipments (UEs) harvest the ratio-frequency energy from downlink signal sent by the access points (APs). Using the additive quantization noise model to construct the energy signal after quantization and introducing a power consumption model to characterize the power consumed by mixed-resolution DACs, closed-form expressions of both harvested energy (HE) and energy efficiency (EE) are derived. These expressions facilitate analyzing the impacts of key parameters, such as the resolution of DACs, the proportion of high-resolution DACs, the number of APs/UEs, and the transmit power of APs on downlink WPT performance. Aside from this, an EE maximization power control algorithm based on the accelerated projected gradient (APG) technique is proposed. Specifically, the APG-based power control algorithm is a first-order optimization method and can determine the optimal solution in closed form, thus benefiting from low computational complexity and short runtime. Experimental results show that compared with the full low-resolution DAC structure, the mixed-resolution DAC architecture can significantly improve both HE and EE. Besides, for mixed-resolution DAC architectures with different proportions of high-resolution DACs, an optimal EE can be approached along with a better SE when the resolution of DACs (except high-resolution DACs) is set to 5 bits. Moreover, in communication scenarios with medium and low signal-to-noise ratios, it is reasonable to increase the AP transmit power to boost the system EE. At last, in cell-free massive MIMO-WPT systems with a large number of UEs, the proposed APG-based power control algorithm not only enhances the EE related to the equal power control scheme by about 19.5% but also significantly reduces the runtime compared to the interior-point-based power control algorithm.
cell-free massive multiple-input multiple-output / wireless power transfer / mixed-resolution digital-to-analog converter / energy efficiency / accelerated projected gradient {{custom_keyword}} /
算法1 求解问题 |
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输入: 输出: 1. 设 2. WHILE 3. 4. 5. 6. 7. 8. 设 9. END WHILE 10. 令 |
表1 仿真参数值 |
参数 | 设定值 |
---|---|
噪声功率 | -126 dBW |
AP和UE最大发射功率 | 2 W, 0.1 W |
能量转换效率 | 0.8 |
导频长度 | K/2 |
| 0.002 W, 0.02 W |
| 0.388 |
转换器功率 | 3 V |
最低有效位单位电流源 | 10 µA |
转换器中每个开关寄生电容 | 1 pF |
噪声的拐点频率 | 1 MHz |
系统带宽 | 20 MHz |
阴影衰落标准差 | 8 dB |
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