基于标签分布状态参数的射频识别系统可靠性评估方法研究

The Internet of Things (IOT) is emerging as the major trend in shaping the development of the next generation of information networks. As one of the crucial terminal parts, radio frequency identification (RFID) plays an important role in many occasions, such as supply chain management, access control to buildings, localization of people, mobile healthcare, et al. Therefore, the reliability of RFID systems becomes a key factor of IOT.. Passive ultra-high-frequency (UHF) RFID, due to its larger reading region, higher speed of operation, cost-effectiveness and ease of use, is widely employed in intelligent perception layer of smart grid. Based on the hypothesis that the neighboring tags have no effect on each other’s performance, there are lots of studies addressing the methods for reliability evaluation of passive UHF RFID systems at present. However, in most practical applications of IOT, RFID tags are placed on objects that are densely co-located. When the tags are placed in dense circumstance, the close displacement of tags causes the phenomenon of mutual coupling and generates mutual impedance among tag antennas, which varying impedance matching condition of passive tags, and degrading the performance of RFID system eventually. . Based on the previous research foundation, this project proposes a reliability evaluation method of passive UHF RFID systems on account of the distribution parameters of tags. The main research contents are as follows: Firstly, based on the principle of passive UHF RFID technology and the transformer model, analytic expression of mutual impedance is derived when the interference tags are located in reactive near-field region of the target tag. Secondly, by using of the theory of backscatter modulation, the mechanism of impedance mismatching between antenna and chip impendance caused by mutual coupling is illuminated. Then, utilizing the parameters of power transmission coefficient and reverse link modulation factor, the variation of system performance is discussed, and then the estimation methods for the evaluation indicators of RFID systems are presented. Finally, the relevance among the evaluation indicators is explored and the reliability evaluation method for RFID systems based on the distribution parameters of tags is proposed. With the study of this project, the performance degeneration of passive UHF RFID systems selected in real application environment can be acquired accurately, and the advanced methodology and reference for optimization deployment of RFID devices in practical applications is provided.

现有射频识别系统系统可靠性评估方法均假设标签呈稀疏分布，无需考虑邻近标签散射电磁波对目标标签的电磁干扰；而实际应用中标签分布状态未知，标签密集分布时标签天线间存在电磁干扰影响。本项目拟以标签天线与芯片阻抗匹配关系为切入点，研究标签分布状态不规则时的系统可靠性评估方法。通过分析天线感应近场电磁耦合机理，结合感应电动势法和变压器模型，推导标签天线近场互阻抗解析式；基于反向散射调制原理，揭示不同标签分布状态下标签灵敏度、谐振频率及反向散射功率的变化规律；确定标签密集分布时系统信道统计模型及链路预算模型的关键参数，优化防碰撞模型建模方法，提出基于标签分布状态参数的系统性能指标估计方法；分析系统性能指标随分布状态变化的规律，研究不同性能指标的关联性，提出基于标签分布状态参数的RFID系统可靠性评估方法。本项目研究可为RFID设备最优化署提供参考依据，具有重要的科学研究意义和实际应用价值。

射频识别（RFID）系统利用射频通信技术实现阅读器与标签间的信息传输，完成对目标物的识别、定位、监控及跟踪等功能。实际应用中，标签分布情况与系统信道参数影响系统可靠性，对RFID系统性能分析与评估提出了新的要求。本项目在RFID系统信道分析与建模、近场区标签互耦效应分析、标签防碰撞及系统识别范围评估等方面展开研究。.无线信道传播效率是影响ETC系统性能的主要因素之一。考虑客车与轿车外形差异，定义了ETC系统信道传播损耗系数，提出一种基于两径模型的ETC系统信道传播损耗建模方法。测试结果表明：ETC天线极化方式影响车载标签单元（OBU）接收功率，OBU距离地面高度越高，其接收功率越大；OBU识别范围小于10m时，轿车引擎盖的电磁波反射引起垂直极化波衰减损耗突变，为保证OBU的成功识别，ETC天线距离地面高度应大于5.35m。.实际应用中，ETC系统受标签部署方式和电波随机多径传播制约，难以准确估计标签识别范围。针对ETC应用场景具有几何共性的特点，基于电波传播的几何光学方法，通过对标签接收多径射线的构成进行分析，融入场景几何特征和天线射频特征参数，提出了一种标签识别范围的预测方法。实际场景测试与仿真表明：所提出方法能较精确预测标签在三维空间中的接收功率分布和识别范围，且精确性高于对数正态等经验模型，而复杂性低于电磁场的商用仿真软件。.标识与传感融合符合智能电网、环境监测等应用需求，已成为RFID技术的一种发展趋势。基于标签性能分析与建模研究基础，设计了一种低成本、低功耗，具有传感功能的无源超高频标签。接口电路部分基于锁相环原理，采用全数字电容-数字直接转换结构，能够工作在接近工艺阈值电压下。测试结果表明，该湿度传感器在常温下1V电源电压时的功耗为92nw，传感分辨率为0.15 °C/LSB，在−30 °C至70 °C范围内的传感精度为−0.7/0.6 °C。.项目研究成果对于RFID系统性能的提升及应用的深入拓展具有重要科学研究意义与潜在应用价值。