移动式UHF RFID阅读器防碰撞问题研究与测试验证

In UHF RFID system, reader collision is more often occur in mobile reader mode compared with fixed reader circumstance, because mobile reader usually move around so that the reader work in dense mode. In this project, the characteristic of mobile reader collision will be studied, and an improved anti-collision algorithm is being proposed based on the accurate collision model. By using frequency hopping along with collision probability and backoff process, high channel use rate of multiple channel access can be achieved, and the throughput is increased. Listen Before Talk(LBT) defined in ETSI 302 208-1 is improved by adding received signal strength detection, to solve not only reader-to-reader collision but multiple reader-to-tag collision, thus achieve high reading rate. The algorithm is implemented by FPGA and will be tested on preliminary test platform. The expected outcomes include a set of scientific modeling methodology and the implementation of the algorithm as well as verification, which will provide the theoretical and experimental basis for improving mobile reader collision performance of UHF RFID system. The research achievement will push forward the engineering applications of UHF RFID.

超高频射频识别（UHF RFID）系统中，移动式阅读器与固定式相比，更容易进入密集阅读器工作模式，产生阅读器碰撞问题。本课题将研究移动式阅读器产生碰撞问题的特点，在建立准确的碰撞模型基础上，提出一种改进算法以提高系统的防碰撞性能。通过采用跳频方法，并引入碰撞概率参数和退避机制，实现高信道利用率的多信道通信，进而有效提高系统识别标签的吞吐率；另外，对ETSI 302 208-1协议定义的LBT占用信道方式进行了改进，通过增加对接收干扰信号强度的判断，不仅解决了"阅读器-阅读器"碰撞问题，也有效避免了"阅读器-标签"碰撞，实现系统的高速识别。该算法通过FPGA实现，并在前期研发的测试平台上进行测试、验证。本课题的预期研究成果将提供一套科学的碰撞建模方法，通过对算法的仿真、实现和测试验证，为提高RFID系统的防碰撞性能提供理论基础和实验依据，推动UHF RFID系统的工程应用。

本课题针对移动式阅读器产生的碰撞问题进行了研究。遵照ISO/18000-6C标准、EPC C1G2协议、欧洲规范ETSI 302 208-1和中国800/900MHz射频识别应用技术规定，采用Simulink仿真工具搭建了移动式UHF RFID系统的多信道通信模型，分析移动式多标签、多阅读器不同场景下的碰撞类型，建立了较完善的防碰撞模型。提出的采用概率分布模型预测标签数量以快速调整Q值的Q++算法和基于探测帧算法，可有效解决移动式多标签识别系统中的阅读器-标签碰撞问题，使得标签在密集场合识别速率提高10%以上；采用信道选择和引入随机功率变化控制算法，可有效解决阅读器-阅读器碰撞问题。提出的算法通过Xilinx Virtex4 xc4vx35 FPGA进行了硬件实现和测试，所搭建的测试平台具有灵活性高、可操作性强等优点。通过实际应用场景中的测试，表明所提出的防碰撞算法可在一定程度上解决不同类型的碰撞问题，提高标签的识别效率，为提高移动式UHF RFID系统的防碰撞性能提供理论基础和实验依据，具有一定的实际应用推广价值。