Advances in ALOHA random multiple access techniques

Since the 1970s random multiple access techniques have made big progress and found a wide application in modern communication systems. In this paper we review the evolution of ALOHA random multiple access techniques: from pure ALOHA to Spread ALOHA. We introduce the principle of Spread ALOHA, investigate the relationship between spread‐spectrum CDMA and Spread ALOHA, and discuss the prospective applications of Spread ALOHA. Copyright © 2000 John Wiley & Sons, Ltd.     

一种应用于无人机编队通信的防碰撞方法

无人机编队自组网络类似于Ad Hoc网络,针对无人机编队飞行过程中产生的信息碰撞问题,研究了Ad Hoc网络中最典型的ALOHA协议,对时隙ALOHA算法进行改进。改进的时隙ALOHA将信道分成若干个离散的时隙段,给每个时隙段分配一部分节点进行传输数据。仿真结果表明:在对信道分成2个时隙段,竞争窗口K=2,吞吐量为0.368时,改进后的时隙ALOHA算法中数据包的平均传输次数为1.35,归一化时延约为5.32。与改进前的时隙ALOHA算法相比,系统的归一化传输时延降低,提高了无人机编队飞行时信息传输的有效性。     

RFID系统中改进的动态帧时隙ALOHA算法

在RFID系统中,多标签引起的冲突一直是影响系统性能的问题。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,可以动态改变帧宽度,同时对标签进行分组,从而获得较高的系统效率。     

WCDMA移动通信系统抗时隙屏蔽式干扰研究

针对时隙屏蔽式干扰对WCDMA移动通信系统的干扰问题,理论分析了不同条件下干扰对用户平均接入概率和系统归一化吞吐量的影响,提出了两种方法以改善系统抗干扰性,即选择子信道使得两相邻接入时隙间距大于前导码和消息部分发送间距,干扰对系统和用户不产生影响;缩短前导码和消息部分发送间距可以提高系统的抗干扰能力。实验仿真验证了分析的准确性和系统抗干扰的有效性。     

A cooperative Bayesian and lower bound estimation in dynamic framed slotted ALOHA algorithm for RFID systems

A novel estimation scheme that combines Bayesian and lower bound estimating radio frequency identification tag population size is proposed. The developed methodology is based on the fusion between the Bayesian and lower bound estimating techniques. It turns out that the fusion rule is built up thanks to an existing linear relationship between the cited techniques. Simulation results show that the developed technique significantly improves the accuracy of the estimating tag quantity and presents less estimation error. Also, the resulting advanced dynamic framed slotted ALOHA protocol considerably improves the performance and efficiency of the radio frequency identification anti‐collision compared with the most recent protocols using others estimating methods.     

RFID防碰撞算法的研究

随着物联网技术的高速发展,作为其关键技术之一的RFID显得愈为重要。标签碰撞的应用在RFID系统中是不可避免的,因此RFID防碰撞算法是RFID系统中一个重要问题,直接决定了RFID系统可以识别多个标签的能力。目前防碰撞算法在时域上主要可以分为非确定性算法（ALOHA算法）和确定性算法（树形算法）两大类。本文分析了现存的两大类算法中主流的防碰撞算法,总结出两大类算法的优点以及存在的问题。通过MATLAB仿真进一步证明此结论,并总结未来研究中需要继续关注的问题与方向。     

扩展ALOHA随机多址通信技术

在回顾ALOHA随机多址技术发展过程的基础上，着重阐述了新一代ALOHA随机多址技术-扩展ALOHA的基本原理，最后指出其应用前景。     

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.     

ALOHA算法在RFID反碰撞问题中的应用

RFID(RadioFrequencyIdentification)—射频识别技术是一种利用射频信号自动识别目标对象并获取相关信息的技术,现在已经涉及到人们日常生活的各个方面,被称为21世纪最有前途的技术之一。但是,它在应用中存在碰撞问题,使数据读取不正确。论文对最简单的反碰撞算法ALOHA算法进行了研究,在识别时间和重发次数之间作一下折衷,确定如何选择退避时间。     

Contention-based MAC protocols with erasure coding for wireless data networks

Contention-based medium access control (MAC) protocol is a key component for the success of wireless data networks. Conventional random access protocols like ALOHA and Carrier Sense Multiple Access (CSMA) suffer from packet collision which leads to low throughput. Aimed at improving the throughput performance, we propose to integrate erasure coding with contention-based MAC protocols for recovering collided packets. To demonstrate the effectiveness of this approach, we focus on combining erasure coding with slotted ALOHA and slotted non-persistent CSMA in this paper. The performances of the resulting protocols are evaluated by both analytical model and simulation. Simulation results match very well with analytical results and show that the system throughput is increased for low to medium traffic loading. Packet loss ratio is also improved considerably with our scheme when the maximum number of packet retransmission times is limited. However, the delay for our scheme is higher due to the longer waiting time in our scheme for recovering collided packets. It is also shown that delay can be significantly reduced if we choose appropriate coding parameters though throughput will be sacrificed.