Localizing RFID-tagged objects by a mobile robot plays an important role in many Internet of Things (IoT) applications. Existing RFID localization systems are infeasible, since they either demand bulky RFID infrastructures or cannot achieve sufficient localization accuracy. In this article, a portable localization (POLO) system is developed for a mobile robot to locate RFID-tagged objects. POLO consists of an RFID reader, a tag array, and a lightweight receiver. The reader is used for interrogating the RFID tag on an object. The tag array is designed to reflect the RFID signal from an object into multipath signals. The receiver captures such signals and estimates their multipath channel coefficients by a tag-array-assisted channel estimation (TCE) mechanism. Such channel coefficients are further exploited to determine the object’s direction by a spatial smoothing direction estimation (SSDE) algorithm. To resist the impact of multipath reflections from surroundings, more spatial information is exploited by placing the tag elements densely and collecting the channel coefficients during the robot’s movement. Based on the object’s direction, POLO guides the robot to approach the object. When the object is in proximity, its 3-D location is finally determined by a near-range positioning (NRP) algorithm. Moreover, POLO is designed to be compatible with commercial RFID systems. POLO is prototyped and evaluated via extensive experiments. Results show that the average angular error is within 1 degree when the object is in the far range (2–6 m), and the average location error is within 6 cm while the object is in the near range (~1 m).

中文翻译：

---

移动机器人的便携式 RFID 定位方法


通过移动机器人定位带有 RFID 标签的物体在许多物联网 (IoT) 应用中发挥着重要作用。现有的 RFID 定位系统不可行，因为它们要么需要庞大的 RFID 基础设施，要么无法实现足够的定位精度。在本文中，为移动机器人开发了便携式定位（POLO）系统来定位带有 RFID 标签的物体。 POLO 由 RFID 读取器、标签阵列和轻型接收器组成。阅读器用于询问物体上的 RFID 标签。标签阵列旨在将来自物体的 RFID 信号反射为多路径信号。接收器捕获此类信号并通过标签阵列辅助信道估计（TCE）机制估计其多径信道系数。通过空间平滑方向估计（SSDE）算法进一步利用此类通道系数来确定对象的方向。为了抵抗周围环境多径反射的影响，通过密集放置标签元件并收集机器人运动过程中的通道系数来利用更多的空间信息。 POLO根据物体的方向引导机器人接近物体。当物体接近时，其 3D 位置最终由近距离定位 (NRP) 算法确定。此外，POLO 的设计与商业 RFID 系统兼容。 POLO 是通过大量实验进行原型设计和评估的。结果表明，当物体在远距离（2-6 m）时，平均角度误差在1度以内；当物体在近距离（~1 m）时，平均位置误差在6 cm以内。