An efficient and secure authentication protocol for RFID systems

The use of radio frequency identification (RFID) tags may cause privacy violation of users carrying an RFID tag. Due to the unique identification number of the RFID tag, the possible privacy threats are information leakage of a tag, traceability of the consumer, denial of service attack, replay attack and impersonation of a tag, etc. There are a number of challenges in providing privacy and security in the RFID tag due to the limited computation, storage and communication ability of low-cost RFID tags. Many research works have already been conducted using hash functions and pseudorandom numbers. As the same random number can recur many times, the adversary can use the response derived from the same random number for replay attack and it can cause a break in location privacy. This paper proposes an RFID authentication protocol using a static identifier, a monotonically increasing timestamp, a tag side random number and a hash function to protect the RFID system from adversary attacks. The proposed protocol also indicates that it requires less storage and computation than previous existing RFID authentication protocols but offers a larger range of security protection. A simulation is also conducted to verify some of the privacy and security properties of the proposed protocol.     

基于CSMA-CA机制的P-GFSA防碰撞算法设计

RFID系统由标签和阅读器组成,往往标签的数量远远大于阅读器,这样就容易产生标签碰撞问题。因此,标签防碰撞算法的性能直接决定了RFID系统中阅读器识别标签的能力和采集数据的速度。在分析了传统防碰撞算法的基础上,本文提出一种基于CSMA-CA机制的预分组GFSA防碰撞算法,并在有源RFID系统上实现。经过测试,该算法适合有源RFID系统,在大量标签处于动态的环境下,性能好于传统算法。     

A power control technique for anti-collision schemes in RFID systems

The emerging technology of Radio Frequency IDentification (RFID) has enabled a wide range of automated tracking and monitoring applications. However, the process of interrogating a set of RFID tags usually involves sharing a wireless communication medium by an RFID reader and many tags. Tag collisions result in a significant delay to the interrogation process, and such collisions are hard to overcome because of the limited capabilities of passive RFID tags and their inability to sense the communication medium. While existing anti-collision schemes assume reading all tags at once which results in many collisions, we propose a novel approach in which the interrogation zone of an RFID reader is divided into a number of clusters (annuli), and tags of different clusters are read separately. Therefore, the likelihood of collisions is reduced as a result of reducing the number of tags that share the same channel at the same time.In this paper, we consider two optimization problems whose objective is minimizing the interrogation delay. The first one aims at finding the optimal clustering scheme assuming an ideal setting in which the transmission range of the RFID reader can be tuned with high precision. In the second one, we consider another scenario in which the RFID reader has a finite set of discrete transmission ranges. For each problem, we present a delay mathematical analysis and devise an algorithm to efficiently find the optimal number of clusters. The proposed approach can be integrated with any existing anti-collision scheme to improve its performance and, hence, meet the demand of large scale RFID applications. Simulation results show that our approach makes significant improvements in reducing collisions and delay.     

Capture-aware Bayesian RFID Tag Estimate for Large-scale Identification

Dynamic framed slotted Aloha algorithm is one of popular passive radio frequency identification (RFID) tag anticollision algorithms. In the algorithm, a frame length requires dynamical adjustment to achieve higher identification efficiency. Generally, the adjustment of the frame length is not only related to the number of tags, but also to the occurrence probability of capture effect. Existing algorithms could estimate both the number of tags and the probability of capture effect. Under large-scale RFID tag identification, however, the number of tags would be much larger than an initial frame length. In this scenario, the existing algorithm's estimation errors would substantially increase. In this paper, we propose a novel algorithm called capture-aware Bayesian estimate, which adopts Bayesian rules to accurately estimate the number and the probability simultaneously. From numerical results, the proposed algorithm adapts well to the large-scale RFID tag identification. It has lower estimation errors than the existing algorithms. Further, the identification efficiency from the proposed estimate is also higher than the existing algorithms.      

基于分段搜索的多RFID标签抗冲突方法*

由于二元树抗冲突方法消耗的识别时间随标签数量呈线性增长,因而提高巨量（>100）标签的抗冲突识别的效率对于推动RFID的应用显得尤为重要。对此本文提出一种分段搜索清点RFID标签的抗冲突方法,通过减少清点过程中标签对阅读器回传数据的位数,达到减少传输耗时的目的。将其与现有的动态二进制搜索法对比,仿真结果表明,当标签突破一定数量,对于特定的分段方式,该算法能够显著降低清点过程的时间消耗。     

一种自适应帧长RFID标签防碰撞算法

无线识别技术基于无线射频标签与无线读卡器的信息交互,实现无需人工干预的标签识别,因此无线识别技术受到现代化物流的重视。由于中转站货物数量庞大,而读卡器的硬件设计必须考虑实现复杂度,因此在识别货物的无线标签过程中存在无线标签信息碰撞的现象。目前,概率性标签防碰撞算法的标签识别率较低,面对大量待识别标签的工作效率有限。本文提出一种自适应帧长的无线识别标签防碰撞算法AFA,分析结果表明该算法可以自适应调整检测帧长度,提高标签识别率。     

基于分组动态帧时隙的RFID防碰撞算法

为了解决射频识别(RFID)系统中的多标签防碰撞问题,在分析帧时隙ALOHA算法的基础上,提出一种基于分组动态帧时隙的RFID防碰撞算法。当标签数量庞大时,该算法可以通过分组限制响应标签数量达到较高的识别效率。仿真结果表明,当标签数为1 000时,与传统算法相比,该算法能使时隙利用率提高80%以上。     

RSSI在RFID读写器中的应用

基于接收信号强度指示(RSSI)测距的定位方法容易实现、开销少,适合在射频识别(RFID)系统中使用。由此提出一种RSSI在UHF频段下RFID读写器中的实现方式。使用合适的测量方法,通过对无线电传播路径损耗模型及大量实测数据的分析,证明得到的标签RSSI可以用于对无源标签的实时距离定位。     

基于虚拟参考标签的RFID定位系统构建方法

针对现有RFID定位系统在位置服务单一、部署大量RFID设备相互间产生信号干扰而影响定位精度等方面的不足,利用经典信号传播模型在定位区域内构造虚拟参考标签空间,进而构建了一种基于虚拟参考标签空间的移动对象定位方法。实际测试表明,本系统具有较高的定位精度,可以有效克服部署大量参考标签及定位读写器引起的设备干扰问题,定位精度在中心区域达到0.31m~1. 65m,在外围区域误差为1. 48m~3.72m。     

RFID读写器网络的跟踪算法研究

针对读写器密集分布且位置固定,标签在其读写范围内移动的RFID系统需要对标签进行识别和跟踪的问题,提出一种改进的虚拟路由跟踪算法,对移动的标签进行跟踪,分析当标签同时被多个读写器读取或被读写器漏读时数据出现异常的处理方法。结果证明该算法可减少误差引入的来源,并且在处理异常情况时不受读写器个数的限制,保证当标签被多个读写器同时读取或被读写器漏读时,仍能够对标签进行跟踪,使得RFID读写器网络有较好的鲁棒性。     

Battery-free wireless identification and sensing

The Wireless Identification and Sensing Platform (WISP) project explores an approach to provide power for sensor networks, based on passive radio-frequency-identification technology. In traditional passive RFID systems, ambient high-power readers interrogate battery-free devices, called tags, that modulate the interrogating signal to communicate a unique identifier to the reader. The WISP project aims to augment RFID tags with sensors so that tags can also send sensed data to the readers. We call these augmented tags wisps. Basing wisps on RFID has some immediate advantages. RFID tags communicate to ambient readers over distances of up to eight meters. Solutions compatible with RFID standards might therefore find quicker acceptance and see faster improvement than other solutions.     

一种改进的四叉树RFID防碰撞算法

针对随机ALOHA算法效率较低,确定性树型方法要求区域内标签数量不变的问题,提出一种改进的四叉树RFID防碰撞算法。在阅读器阅读范围内的标签根据不同的问询命令修改自身应答概率进行分组。阅读器采用比较碰撞位的四叉树算法识别应答概率为1的标签。通过公式推导证明了算法采用四叉树识别的合理性。实例说明和仿真结果显示,该算法能减少阅读器和标签之间的查询次数和通信量,有效提高阅读器的识别效率。     

改进ALOHA算法在RFID多目标识别中的应用

RFID系统中,由于多标签引起的冲突一直是影响系统性能的大问题。ALOHA算法是运用比较普遍的一种防冲突算法,在标签数目较少的情况下,现有的ALOHA算法也有较高的效率,但是随着标签数目的急剧增加,算法时间也成指数往上增长,本文提出一种改进的ALOHA算法,在标签总数未知的情况下,动态估计标签数目,以选择合适的窗口大小,获得较高的系统效率。仿真结果表明,跟传统ALOHA算法相比,性能有明显改善。     

多天线RFID系统标签碰撞问题研究

提出两种基于盲源分离方法的标签防碰撞算法,解决标签密集的多天线RFID系统中的标签碰撞问题。在一个确定的时隙内,当发射反向反馈信号的标签数目不超过阅读器天线的数目时,这些标签可以通过盲源分离算法被阅读器成功识别;否则,这些标签不能被阅读器识别。这些未被识别的标签再随机选择相同帧内其他的任意一个时隙,向阅读器发送返回信号,直到所有标签被成功识别出来。仿真结果表明,新算法能使得RFID系统获得更加高效的吞吐率,能比基于ALOHA的标签防碰撞算法具有更小的时耗,尤其是当标签数目较大时更加显著。     

RFID系统实时高效ALOHA防冲突算法研究与仿真

简要介绍了当前几种主要的ALOHA算法基本思想和系统效能,详细讨论了间接估算自适应帧时隙（DFSA）算法的原理和帧长度调整方法,并就DFSA算法对未识读标签的估计方法进行了统计分析,最后基于MatLab对各种算法性能进行了仿真。结果表明,间接估算DFSA算法较其它算法更能使RFID系统保持较高的系统效率,能够实时准确地识别标签。     

基于先验知识的自适应多叉树防碰撞算法

为提高无线射频识别(RFID)系统快速识别大量标签的能力,提出一种基于先验知识的自适应多叉树防碰撞算法。利用标签访问的规律性和标签分布的随机性,在不同的搜索深度,根据已有的先验知识和碰撞比特信息估计待识别的标签数量,从而动态地自适应选择搜索叉树。通过有效减少碰撞和空闲时隙数,大幅提高读写器搜索和识别标签的能力。理论分析与仿真实验结果表明,该算法能克服传统自适应多叉树防碰撞算法的缺点,合理选择初始搜索叉树,尤其在待识别标签数量较多的场合,可有效提高RFID系统的吞吐率。     

超高频RFID标签一致性的近场检测技术

超高频RFID标签一致性直接影响RFID系统中采集数据的识别率和准确率。采用接收信号强度指示RSSI(Received Signal Strength Indicator)技术及数理统计,采集标签反射信号强度,设定标准差阈值,作为标签一致性检测参数。研制弯折偶极子近场天线,实现0.1 mm近距离标签识读。利用屏蔽效应,在全自动卷筒式RFID标签套装上设置打点标识机构,对标签批量标记,可实现对柔性超高频RFID标签的高速、批量一致性检测。     

基于多处碰撞位探测的标签防碰撞算法研究

在无线射频识别系统（RFID）中,当阅读器向范围内的标签发送命令以后,标签向阅读器发送反馈信号,当有两个或者两个以上的标签做出了相同的反馈信息,就会产生标签碰撞。解决碰撞问题提高标签识别效率对RFID的应用具有重要意义。针对目前一些已有算法存在查询次数过多且吞吐率不高的问题,该文提出一种基于多处碰撞位探测的标签防碰撞算法(Multiple Collision Bits Detection, MCBD)。该算法通过阅读器发送的探测命令,获取标签发生碰撞位的比特值,再结合查询命令直接识别出标签。仿真实验结果显示MCBD算法降低了识别标签所需的查询次数,提高了吞吐率。该文算法的创新在于可以对单独或者连续的碰撞位都一并处理,充分利用标签的ID信息,对RFID标签识别的研究具有一定意义。     

自适应树形分组的盲分离射频识别系统防碰撞算法

针对单天线射频识别(RFID)系统中阅读器不能同时识别多个标签造成标签识别率较低的问题,结合多天线技术及基于标签ID号序列的二叉树时隙分组提出了一种自适应树形分组的盲分离RFID系统防碰撞算法.首先根据RFID系统中天线的个数调整阅读器查询码码长并发送查询信号,将符合条件的响应标签分配到相应的时隙中,使每一个时隙中的标签数小于或者等于阅读器的天线数,满足盲源分离(BSS)的多天线系统识别标签的条件,从而达到同时且快速识别多个标签的目的.仿真结果表明,与同样采用多天线技术的基于位隙动态分组的盲分离(BSDBG)算法相比,当天线个数为4~32时,所提算法的标签识别速度提高了20%~69%,标签识别率提高了60%~88%,同时该算法复杂度低,硬件开销小,实现相对简单,有利于推广和使用.     

基于支持向量回归机的RFID室内定位研究

基于接收信号强度的射频识别(RFID)定位是一种低成本、便于实现的室内定位方法,针对在RFID室内定位系统中使用参考标签法存在的小样本问题,提出一种基于支持向量回归机(SVR)的RFID室内定位算法。结合无源超高频RFID系统工作原理,在Matlab环境下,对比经典的LANDMARC方法,测试了基于支持向量回归机的定位算法性能,以及互耦效应、多径效应对该算法定位结果的影响。仿真结果表明,相较于LANDMARC方法,所提方法在不增加参考标签数量的情况下定位精度至少提高了25%。