射频识别，RFID（Radio Frequency Identification）技术，又称无线射频识别，是一种通信技术，可通过无线电讯号识别特定目标并读写相关数据，而无需识别系统与特定目标之间建立机械或光学接触。
RFID is a wireless system that identifi es tags attached to the object of interest. An RFID system consists of a reader and RFID tags. RFID systems are divided into two categories, according to whether they use passive or active tags [13] . Passive tags do not contain a power source and thus are suitable for short - range applications.
RFID是一种无线系统，可识别附着在感兴趣对象上的标签。 RFID系统由阅读器和RFID标签组成。 RFID系统根据它们是使用被动还是有源标签分为两类[13]。 无源标签不包含电源，因此适用于短程应用。
Passive RFID tags are equipped with an antenna that is excited by output signals at specific frequencies, and these tags are activated by the power of the received signal.
An active RFID system is in fact a full transceiver system including processors, antennas, and batteries. Thus, an active tag contains both a radio transponder and a power source for the transponder.
无源RFID标签配备有由特定频率的输出信号激发的天线，并且这些标签由接收信号的功率激活。
有源RFID系统实际上是包括处理器，天线和电池的完整收发器系统。 因此，有源标签包含无线电应答器和应答器的电源。
An RFID reader constantly sends RF electromagnetic waves, which are received by the RFID tag in its vicinity. The RFID tag modulates the wave adding its identifi cation information and sends it back to the reader. The reader converts the modulated signal into digital form to determine the tag identity. Active tags are ideally suitable for the identifi cation of high - volume products moving through a processing unit.
RFID读取器不断发送RF电磁波，其由附近的RFID标签接收。 RFID标签调制波，添加其识别信息并将其发送回读卡器。 读取器将调制信号转换为数字形式以确定标签标识。 有源标签非常适合识别通过处理单元移动的大批量产品。
RFID as a Positioning System:
RFID can be used to localize the position of a target object. An active RFID tag can be attached to the object, which transmits a
signal to the RFID reader. The concept of trilateration, as shown in Figure 1.2 a, is used along with the RSSI technique to localize the position of the tag. Because the objects to be positioned using RFID are usually in an enclosed environment, there are multipath effects, which decrease the accuracy of the system. In order to increase the accuracy of RFID - based positioning system, the system utilizes additional readers and reference tags.
RFID可用于定位目标对象的位置。 有源RFID标签可以附着到物体上，该物体将信号发送到RFID读取器。 如图1.2a所示，三边测量的概念与RSSI技术一起用于定位标签的位置。 因为使用RFID定位的对象通常处于封闭环境中，所以存在多径效应，这降低了系统的准确性。 为了提高基于RFID的定位系统的准确性，该系统利用额外的读取器和参考标签。
However, these additional readers increase the cost of the system. In order to keep the costs down, Ni et al. [14] proposed an innovative approach that employs the idea of installing extra fi xed reference tags. This approach is called location identifi cation based on dynamic active RFID calibration (LANDMARC). In a manner similar to the geographic landmarks we use in our daily lives, the fi xed tags serve as reference points in the system.
但是，这些额外的阅读器会增加系统的成本。 为了降低成本，Ni等人。 [14]提出了一种创新方法，采用安装额外固定参考标签的想法。 这种方法称为基于动态有源RFID校准（LANDMARC）的位置识别。 以类似于我们日常生活中使用的地理标志的方式，固定标签用作系统中的参考点。