1. Introduction
Comparison of different automatic identification technologies
首先明确一下比较对象。human identification（cost too high）是人力识别就不用说了。
fingerprint identification:
- stability 稳定，精确度高；
- high speed, 快速匹配；
- security issues: 容易被复制。
face recognition:
- easy to be influenced by surroundings, hair, age…
speech recognition:
- easy to use and accept by user;
- not involve privacy;
- due to international standards, is hard to promoting
1d barcode:
- limit storage capacity, 点线组合少;
- need to combine with database;
- barcode size is large;
- poor fault tolerance, 本来就需要摄像头可见，如果被污损遮挡很容易就无法识别;
2d barcode recognition:
- larger storage capacity;
- high information density;
- powerful fault tolerance;
- support for encryption 容量大了就支持更多编码解码等安全措施了。
rfid：
- low cost;
- low power consumption;
- high accuracy;
- non-contract, fast speed; 不用接触（哪怕是visual，薄纱条码）
- certain computing and storage capabilities;
主要考虑各个的缺点，人脸和声音特征点多速度慢，而且人脸容易被影响，声音由于国际标准技术难以提升；条码需要视觉可见；指纹容易被盗取。
The main features of RFID
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Non-contact automatic and rapid identification 快速薄纱复杂的人脸和声音，无接触薄纱条码和指纹
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Permanently store a certain amount of data 永久存储一定量数据
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Simple logical processing 其包含的简单逻辑电路允许做一定的逻辑处理，比如安全协议、算法
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Reflection signal strength is affected by the distance and other factors significantly 信号受到距离，读写器功率，其他信号，其他标签的干扰
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Low cost, can be deployed at a large scale
Constraints of RFID technology
Core technologies of RFID
Anti-collision mechanism：rfid并不支持传统的cmsa/ca无线通信协议，需要采取一些措施防碰撞（reader-reader, tag-reader, tag-tag)
Efficient information storage, retrieval and mining: 尽量节能的信息存储，检索，挖掘
Make full use of the attenuation laws of backscatter signal to assist in positioning and mobile behavior sensing: 我们知道rfid信号会随着距离衰减。反之我们也可以利用这一点来定位物体位置和移动行为感知。
Security certification and privacy protection: 如何利用逻辑门电路校验安全性。
The advantage of RFID in IoT, and the development trend
充电方式：Backscatter, small node and indefinitely time of endurance. but rely on reader, one to many centralized communication 利用无线电 ratio signal 充电的方式
ptp communication: 建立 channel awareness technologies 使得支持被动点对点通信来建立分布式系统
Combine with Sensors: 开发更多应用方式。
RFID and IoT:
- embed intelligence in the physical object, so that simple physical objects can also “say”.
- allows a physical object to be uniquely identified in a way similar to the “IP address” of a computing node in the Internet.
- provides a low-cost communication way to achieve effective communication between nodes.
- makes the physical objects in a passive environment achieve “passive intelligence“, providing fundamental guarantee for the “thing-thing connection”