基于最优化原理的RFID系统中的ALOHA防碰撞算法研究

无线射频识别(RFID)系统中的多个标签同时应答时会引起数据碰撞现象,使阅读器能正确读取信息所使用算法称为防碰撞算法.本文研究了目前RFID系统中常用的防碰撞算法,包括时隙ALOHA(S-ALOHA),纯ALOHA(P-ALOHA)和帧ALOHA(F-ALOHA),同时基于最优化原理对ALOHA防碰撞算法进行了改进.仿真结果表明采用最优化原理改进的ALOHA算法相比较现有RFID系统中常用的ALOHA防碰撞算法有明显的优越性,使得系统获得最佳的传输时隙及数据包大小,得到高吞吐率,低错误率,从而提高系统的工作效率.     

BIS：一种降低空时隙开销的RFID防碰撞算法

提出了一种优化的基于时隙ALOHA的随机型防碰撞算法--BIs算法.该算法在帧开始前扫描空时隙的位置,并结合标签估算算法实现对帧长的动态调度,最大限度地减少空时隙的时间开销,以实现提高多标签读取效率的目标.仿真结果表明,在不考虑误码的理想情况下,采用该算法的系统效率最高可以达到81%,高于ALOHA算法的理想系统效率,识别速度与一般的时隙ALOHA算法和二进制算法相比有较大幅度的提高.     

一种改进的动态帧时隙ALOHA算法

射频识别系统的最大缺点之一是当标签碰撞时的低标签识别效率。传统的射频识别防碰撞算法在标签数量庞大时,解读标签所需的时隙数会成倍增加。为了解决这一问题,文章提出一种改进的动态时隙ALOHA算法,它根据标签数调整每帧中的时隙数,以使系统能以高吞吐量工作,缩短读取时间,提高了整个系统的效率。     

改进型帧时隙ALOHA防碰撞算法研究

为进一步提高RFID系统中电子标签防碰撞算法的识别效率,对帧时隙ALOHA防碰撞算法的性能进行分析,提出一种结合精确标签估计和二进制搜索的改进型帧时隙ALOHA算法.将识别过程分为标签估计和标签识别两个阶段,在标签估计算法中引入碰撞概率上、下限参数,并精确估计标签数量对初始帧时隙大小进行优化;在标签识别阶段,利用二进制搜索算法对时隙内的碰撞标签进行快速识别.通过对识别过程进行仿真结果表明:改进的算法改善了防碰撞性能,提高了RFID系统的标签识别效率.     

一种改进的RFID标签防碰撞算法

在已有RFID标签防碰撞ALOHA算法基础上,提出了一种改进的带中断机制的动态帧时隙ALOHA(ⅡDFSA)算法,一方面通过优化设置系统效率临界因子和参考碰撞时空比,比较系统效率判断是否改变帧的大小;另一方面通过比较碰撞时空比来判断帧大小的改变方向,从而有效降低标签识别时间,提高识别效率。计算机仿真结果表明,与传统的动态帧时隙ALOHA算法相比,当标签数低于200和高于800时,采用ⅡDFSA算法可以有效降低系统总识别时间,提高系统效率。当标签数介于200~800之间时,与传统的动态帧时隙ALOHA算法相当。     

基于间隔估计法的RFID防碰撞算法

多个应答器的碰撞问题是影响超高频射频识别(RFID)系统读取效率的一个关键问题。从EPC Class1 Generation2(C1G2)RFID系统帧长受约束特点出发,分析了帧时隙ALOHA防碰撞机制及其经典应答器估计方法的特点。提出了应答器间隔估计方法(IEM)以及基于该方法的EPC C1G2 RFID防碰撞算法,并给出了仿真结果。与现有基于经典应答器估计方法的射频识别系统防碰撞算法相比较,提出的防碰撞算法减少了识别时间,提高了系统的识别效率。     

一种基于不等长时隙的射频识别防碰撞算法

该文提出了一种基于不等长时隙的射频识别(Radio Frequency Identification, RFID)动态帧时隙ALOHA (Dynamic Framed-Slotted ALOHA, DFSA)防碰撞算法。算法考虑到大量碰撞时隙和空闲时隙对系统效率的影响,采用帧内时隙长度不等的优化策略,由时隙优化参数和未读标签数确定帧长,通过优化的切比雪夫不等式法进行标签估计,并基于马尔科夫链分析标签识别过程,来实现读取周期的控制。分析和仿真结果表明,该算法比时隙优化前的DFSA算法效率更高,平均识别时间更短,标签数估计比下限值法、Schoute法和碰撞率法更准确。     

无源RFID自适应帧时隙防碰撞算法研究

射频识别RFID作为一种重要的物联网终端数据采集技术,系统的吞吐率直接影响着数据采集终端的性能,但目前广泛应用于无源RFID系统的帧时隙类防碰撞算法吞吐率普遍较低.本文着重分析了影响无源RFID帧时隙类ALOHA防碰撞算法性能两类因素：帧长和碰撞时隙的处理方式,通过构建和求解帧长调整和标签碰撞的数学模型,给出了无源RFID帧时隙类ALOHA防碰撞算法的具体优化途径和方案：帧长自适应调整和碰撞实时散列.在此基础上提出了自适应二进制散列帧时隙ALOHA防碰撞算法-ABSFSA.实验结果表明ABSFSA算法在同等条件下可以有效减少无效时隙,明显将RFID系统的吞吐率稳定提高到45%.本文的研究工作为无源RFID帧时隙类防碰撞算法的优化提供了可供参考的数学模型,同时对提升物联网数据采集终端的性能具有一定的应用价值.     

分组自适应分配时隙的RFID防碰撞算法研究

为了解决射频识别(Radio Frequency IDentification,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,提出一种基于分组自适应分配时隙的RFID防碰撞算法(GAAS).首先让阅读器对标签随机所选的时隙进行扫描统计,并将其发送给每一个标签,标签再进行相应地时隙调整,使阅读器跳过空闲时隙和碰撞时隙,自适应地分配有效时隙,进而对标签进行快速识别.当未识别标签数比较大时,算法采用分组以及动态调整帧长等策略,以减少时隙处理的时间.仿真结果表明:GAAS算法提高了系统的识别效率和稳定性,降低了传输开销.特别是当标签数超过1000时,该算法的吞吐率仍保持在71%以上,比传统的帧时隙ALOHA-256算法和分组动态帧时隙ALOHA算法的系统效率分别提高了300%和97.2%.     

基于ALOHA算法的RFID防碰撞技术研究

在RFID系统中,由于多标签引起的冲突一直是影响系统性能的主要问题。ALOHA算法是解决标签碰撞问题最有效的方法之一。当系统中标签数过多时,帧时隙ALOHA算法和动态帧时隙ALOHA算法,都会降低系统效率。因此我们提出一种利用二进制树形分组的时隙ALHOA算法。由于只需要对标签进行简单分组就可以有效的提高ALOHA算法的效率,所以此方法更具有实际意义。     

改进动态帧时隙ALOHA算法

ALOHA型算法是一种防碰撞算法,适用于标签数目较少的情况。当标签数目逐渐增大时,通常需要指数倍增长的时隙数才能识别出这些标签。文中提出了一种改进的动态帧时隙ALOHA算法,它首先估计未被识别的标签数,然后调整相应帧长,从而获得最佳系统效率。仿真结果显示,当标签数为500时,文中所提出算法较传统算法的系统时延减少为原来的1／2。     

RFID系统防碰撞协议研究设计与优化

碰撞问题是影响射频识别(RFID)系统读取效率的关键问题。该文提出了两种新的防碰撞协议CDCA协议和CDCA-2D协议,并且对两种协议进行了详细的理论分析和优化。新协议将RFID系统的读取过程分为两个阶段,利用第1阶段的碰撞检测信息实现在第2个阶段的无碰撞通信。仿真结果表明,和目前国际上流行的RFID防碰撞算法相比,两种新协议极大地提高了读取的效率。     

短距离无线通信系统的冲突信号分离与解码

短距离通信是物联网中常用的通信方式,多是一传感节点对多物理节点的情形,由于其采用无线共享信道,因此多个信源一起传输必导致冲突发生。通常,该冲突采用随机多址方法解决,但通信效率并不高。采用信号分离和编解码技术可直接从冲突信号中恢复出信源,因此可显著提高通信效率,但该方法需要预知或估计信号衰落系数才能保证良好的性能。本文提出一种有限符号分离的维特比解码方法,该方法通过估计字典矩阵,无需预知衰落系数就能准确提高恢复冲突信号。实验中,我们分别用仿真和软件无线电构建了一个基于FM0码的超高频短距离无线通信系统,实验结果表明本文提出的方法吞吐量达到了约0.61,相比传统的ALOHA系统吞吐量提高了约0.25。      

Gen2‐Based Tag Anti‐collision Algorithms Using Chebyshev's Inequality and Adjustable Frame Size

Arbitration of tag collision is a significant issue for fast tag identification in RFID systems. A good tag anti‐collision algorithm can reduce collisions and increase the efficiency of tag identification. EPCglobal Generation‐2 (Gen2) for passive RFID systems uses probabilistic slotted ALOHA with a Q algorithm, which is a kind of dynamic framed slotted ALOHA (DFSA), as the tag anti‐collision algorithm. In this paper, we analyze the performance of the Q algorithm used in Gen2, and analyze the methods for estimating the number of slots and tags for DFSA. To increase the efficiency of tag identification, we propose new tag anti‐collision algorithms, namely, Chebyshev's inequality, fixed adjustable framed Q, adaptive adjustable framed Q, and hybrid Q. The simulation results show that all the proposed algorithms outperform the conventional Q algorithm used in Gen2. Of all the proposed algorithms, AAFQ provides the best performance in terms of identification time and collision ratio and maximizes throughput and system efficiency. However, there is a tradeoff of complexity and performance between the CHI and AAFQ algorithms.     

基于时隙ALOHA的RFID防冲突算法及其系统实现方案的分析研究

无线射频识别系统要实现同时阅读现场多个RFID标签的关键技术在于找到防冲突算法来解决RFID标签发送数据的冲突问题。本文首先对基于时隙ALOHA的各种防冲突算法进行研究比较和分析,然后给出仿真结果;接着,说明各种不同的标签预测方法和信息帧设置调整方法对系统响应时间和识别效率的影响;最后,针对自适应调整方法的防冲突算法及其实现方案进行了进一步仿真分析。     

基于CDMA技术的新型防碰撞算法

标签碰撞是射频识别（RFID）技术的常见问题,该问题影响了RFID系统通信过程中数据传输的完整性.在分析已有防碰撞方法的基础上,根据帧时隙分组ALOHA算法,结合码分多址技术,提出了新型的标签防碰撞算法.该算法能够有效减小标签之间的碰撞概率,缩短读写器操作时间,提高吞吐率,很适合应用于具有较大数量标签的RFID系统中.     

Optimal Dynamic Framed Slotted ALOHA Based Anti-collision Algorithm for RFID Systems

In Radio Frequency IDentification (RFID) system, one of the most important issues that affect the data integrity is the collision resolution between the tags when these tags transmit their data to reader. In majority of tag anti-collision algorithm, Dynamic Framed Slotted Aloha (DFSA) has been employed as a popular collision resolution algorithm to share the medium when multiple tags respond to the reader’s signal command. According to previous works, the performance of DFSA algorithm is optimal when the frame size equals to the number of un-identified tags inside the interrogation zone. However, based on our research results, when the frame size equals to number of tags, collision occurs frequently, and this severely affects the system performance because it causes power consumption and longer tag reading time. Since the proper choice of the frame size has a great influence on overall system performance, in this paper we develop an analytical model to study the system throughput of DFSA based RFID systems, and then we use this model to search for an optimal frame size that maximizes the system throughput based on current number of un-identified tags. In addition to theoretical analysis, simulations are conducted to evaluate its performance. Comparing with the traditional DFSA anti-collision algorithm, the simulation results show that the proposed scheme reaches better performance with respect to the tag collision probability and tag reading time.     

Reading Rate Improvement for UHF RFID Systems with Massive Tags by the Q Parameter

To implement an ultra high frequency (UHF) RFID system, the first problem that an enterprise faces is the assurance of stable and extremely high reading rates. Empirical investigations indicated many hardware and environment factors can affect the reading rates. Unfortunately, even if all of the hardware and environment factors have been resolved, reading a large number of RFID tags in a single run is still a challenge. For RFID systems with massive tags, signal collision is the major factor to reduce system reading rate. To diminish the influence induced by signal collision, this study examined the anti-collision technology applied in EPCglobal UHF Gen II standards and proposed the method of adapting the Q parameter of control module in UHF RFID interrogator. Finally, we conducted field simulation to monitor relative reading rates under different conditions with different tag numbers, speeds passing through portal and Q values. Following by experimental results, this study provided the criteria to determine optimal Q value by activating system. With proper Q value, stable and extremely high reading rates in one-time reading of a large number of RFID tags (100 and above) can be achieved.     

Carrier sense multiple access with improvised collision avoidance and short-term fairness

In this paper, we present a simple method to simultaneously enhance collision avoidance efficiency and short-term fairness of a most popular contention based medium access control protocol, carrier sense multiple access with collision avoidance. The key idea here is to adaptively tune the shape of contention slot selection distribution over the temporal contention window during ongoing collision resolution process which, in the legacy scheme, used to be flat throughout. The tuning mechanism is such designed that it not only maximizes the selection likelihood of relatively less collision prone contention slots over the contention window but also compensates the idle delay that the contending stations have suffered in their recent access attempt. Through rigorous numerical and simulation based analysis, the proposed scheme is shown to enhance the performance of a IEEE 802.11 based distributed wireless network in terms of network throughput efficiency and packet transmission delay while allowing individual stations to share the channel fairly even in short time scale.