A new anti‐collision protocol based on information of collided tags in RFID systems

Radio frequency identification (RFID) technology has recently become an integral part of a wide range of applications. One of the challenges in RFID systems is the tag anti‐collision issue, for which several anti‐collision tag identification protocols have been proposed. This paper proposes a novel slotted ALOHA‐based RFID tag anti‐collision algorithm which can be employed for tag identification. The main idea of this algorithm is to use the information available in collision slots, called collided data, to identify tags uniquely. For this purpose, the collision slots that include only two tags are selected. Then, the non‐conflict bits in these slots are used to possibly identifying the tags. Because in the proposed algorithm readers use both single slots and also the collision slots for tag identification, the performance is increased significantly compared with other protocols. Results of the study indicate that in the proposed algorithm, the optimal frame size for an individual tag number is equal to the half of tags number and the efficiency of the proposed protocol is improved to about 73%. Copyright © 2015 John Wiley & Sons, Ltd.     

ALOHA随机多址通信技术--从纯ALOHA到扩展ALOHA

自７０ 年代以来, 随机多址通信技术取得了很大的进展, 在移动通信、卫星通信和计算机通信领域得到了广泛应用。本文在回顾ＡＬＨＯＨＡ 随机多址技术发展过程的基础上, 探讨了ＡＬＯＨＡ 的吞吐率与信道效率之间的关系, 阐述了新一代ＡＬＯＨＡ随机多址技术———扩展ＡＬＯＨＡ的基本原理, 最后指出其应用前景     

超高频RFID系统的CRC分组ALOHA算法优化

标签冲突增加了射频识别(RFID)系统的时间开销和能量损耗,降低了识别速度,随着标签数量的不断增加,冲突更加明显,系统性能急剧下降。为了解决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标签分组的帧时隙ALOHA优化算法。该算法首先通过标签自身携带的循环冗余校验(CRC) 码将标签分组,记录标签组的组号,按照组号的顺序依次识别,从而减少同时响应阅读器命令的标签数量;针对识别过程中的时隙选择冲突问题,可以通过混沌系统产生均匀分布的伪随机数,对进入识别状态的标签随机选择时隙号,使标签在一帧内选择的时隙分布更加均匀,从而减少标签碰撞的次数。与传统算法的对比实验中：当待识别标签数量相等时,优化算法识别完标签所需命令数更少,且所用命令数与标签数目呈近似线性关系;当待识别的标签数量小于256时,优化算法的标签识别速度提高率稳定在50%;当待识别的标签数量大于256时,优化算法能使标签识别速度提高率达80%。理论分析与实验结果表明,优化算法识别标签的速度更快,且随着标签数量的增加,其优势更明显。     

新的基于分组处理的射频识别标签防碰撞算法

针对现有几种基于二叉树的防碰撞算法识别时延较长、数据传输量大的情况,提出一种新颖的防碰撞算法。算法采用分组策略,读写器按顺序依次识别每个分组,减少了每次应答标签的数量和碰撞发生的概率;此外,把标签ID分为两段识别,第一段为前7位,剩余部分为第二段,标签ID分段处理能减少冗余数据的传输。仿真结果表明,该算法相比其他几种算法,查询次数少,数据传输量仅为动态二叉树搜索(DBS)算法的1/6,识别效率有较大幅度提高。     

大气环境对天然气管道泄漏扩散影响的模拟

目前天然气作为清洁能源得到了广泛的应用,同时天然气的输送主要依靠管道运输,所以对天然气管道的泄漏研究显得尤为必要。当天然气管道发生泄漏后,天然气的扩散范围会受到大气环境的影响,为此本文选用基于高斯扩散模型的ALOHA软件研究了不同大气环境下天然气管道扩散的危险范围。为了验证软件模拟结果的可靠性,将软件模拟结果与公式计算值进行对比。通过ALOHA软件对不同大气环境下天然气管道泄漏后的危险区域进行模拟分析,得出大气环境中温度、风速、湿度、大气稳定度对天然气管道泄漏的影响。结果表明,ALOHA软件的计算结果是可靠的,大气温度的增加会增大危险范围,风速的加快有利于危险范围的缩小,大气越不稳定危险范围越小,湿度对于危险范围基本没有影响。     

ALOHA标签防碰撞算法综述

ALOHA防碰撞算法是无线射频识别技术RFID（Radio Frequency Identification）中一种重要的标签防碰撞算法,该算法设计简单,容易实现,但系统吞吐率较低。其算法不断被研究改进,针对ALOHA算法及其改进算法加以详细的总结,对现在的研究方法加以理论推导、实验模拟,其中对动态帧时隙ALOHA（DFSA）算法中关键环节标签估计算法进行详细归纳。最后结合如今现状提出下一步研究方向。     

RFID系统防碰撞算法的研究及其改进

射频识别技术中,防碰撞问题是提高系统读取效率的关键问题。文章在传统防碰撞算法的基础上,提出一种优化的基于动态帧时隙ALOHA的防碰撞（Improved dynamic framed slotted ALOHA,IDFSA）算法。实验结果表明：IDFSA算法大幅度地提高了系统的时隙利用率和读取效率。     

Throughput and delay analysis of multi-channel wireless infrastructure networks

Wireless infrastructure networks (WINs) provide ubiquitous connectivity to mobile nodes in metro areas. The nodes in such backbone networks are often equipped with multiple transceivers to allow for concurrent transmissions in multiple orthogonal channels. In this study, we develop an analytical model for the estimation of the delay and throughput performance of wireless infrastructure networks employing slotted ALOHA channel access and slotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) over multiple channels. The analytical model, which takes into account the correlation due to multi-hop transmissions, approximates the performance observed through simulations accurately.     

食品质量追溯中RFID多标签识别防碰撞算法

针对食品质量追溯中批量标签识别存在的标签碰撞问题,结合帧时隙ALOHA算法和最小均方误差预编码技术提出了一种RFID多标签识别防碰撞算法。该算法在进行多标签识别前,先通过预编码技术对待识别标签进行分组,有效降低多标签间的碰撞。仿真试验表明,改进算法有效提升了RFID多标签识别性能,具有一定的实用价值。     

Delay‐insensitive identification of neighbors using unslotted and slotted protocols

For many applications, it is desirable for a node to be able to identify the neighbor nodes currently within range. However, the identification procedures for terrestrial communication networks (TCNs) are inefficient when implemented in long‐delay networks (LDNs) such as underwater acoustic networks or satellite networks, where the propagation time of a packet cannot be neglected. Here, we propose a time‐efficient and power‐efficient procedure, which is insensitive to propagation delay, for identifying neighbors in an LDN by optimizing the network offered load using either unslotted or slotted protocols. The procedure is adapted to the scenario when node cardinality and distribution are either known or unknown in advance. We achieve improvements as high as 80% in time and 45% in power consumption for our proposed approach compared with approaches developed previously for TCN. Furthermore, we analyze our proposed approach with the inclusion of the capture effect and packet receive time variations. We also provide a closed form formula for finding the optimum guard time and a procedure to estimate the packet receive time variations. Copyright © 2012 John Wiley & Sons, Ltd.