分优先级ALOHA协议

卫星通信系统具有长的传播时延，其随机多址协议性能的改善非常困难。针对长传播时延的通信系统，我们提出了一种分优先级的ＡＬＯ－ＨＡ协议。研究结果表明，这种协议可以以较小的代价简单有效地改善卫星随机多址系统的时延性能。文章给出了协议性能与设计参数选择的关系。     

CDMA随机接入系统与S—ALOHA系统的性能对比分析

传统的Ｓ－ＡＬＤＨＡ随机接入协议用于通信网络,其理论上的极限通过量为３６％,但在这种情况下,系统的时延随着负荷的增加也变得越来越大,因此传统Ｓ－ＡＬＯＨＡ方式不适合于时延要求较高的通信系统,本文通过研究系统在较低负荷的情况发现采用ＣＤＭＡ技术的随机接入方法在占用相同的系统带宽的条件下,可以获得与传统Ｓ＿ＡＬＯＨＡ方式相同的通过量,而时延却大大降低,而且随着ＣＤＭＡ领域抗干扰技术的发展,它的系统性能     

CDMA随机接入系统与S—ALOHA系统的性能对比分析

传统的Ｓ－ＡＬＤＨＡ随机接入协议用于通信网络，其理论上的极限通过量为３６％，但在这种情况下，系统的时延随着负荷的增加也变得越来越大，因此传统Ｓ－ＡＬＯＨＡ方式不适合于时延要求较高的通信系统，本文通过研究系统在较低负荷的情况发现采用ＣＤＭＡ技术的随机接入方法在占用相同的系统带宽的条件下，可以获得与传统Ｓ＿ＡＬＯＨＡ方式相同的通过量，而时延却大大降低，而且随着ＣＤＭＡ领域抗干扰技术的发展，它的系统性能     

HFC网络CDMA时隙ALOHA接入系统性能分析

同步ＣＤＭＡ（Ｓ－ＣＤＭＡ）解决了双向ＨＦＣ系统上行信道的噪声和容量问题,基于Ｓ－ＣＤＭＡ的ＨＦＣ是一代的ＨＦＣ系统,初始接入ＣＤＭＡ终端是采用时隙ＡＬＯＨＡ技术完成接入进程的,把ＣＤＭＡ技术与时隙ＡＬＯＨＡ技术相结合,会使原来的时隙ＡＬＯＨＡ技术的吞吐量得到一定的改善。本文提出了一种ＨＦＣ网络ＣＤＭＡ－时隙ＡＬＯＨＡ接入系统,分析了该系统的吞吐量性能和接入时延性能,并给出了实验结果与分析。     

一种适于卫星定位与通信系统的扩频ALOHA信道模型

随着人们对通信需求的不断增长，带来了如何有效地利用频率问题，同时也产生了越来越多的多址技术。本文将扩频技术与随机ＡＬＯＨＡ通信方式相结合，提出了一种适于卫星定位与通信系统的扩频ＡＬＯＨＡ信道模型。并对此信道的信道利用率进行了计算，得到了好的结果。全文还对定位与通信构成一体化系统的可实现性做了详细描述。最后，简单介绍了双星定位及通信系统的定位原理。     

时隙ALOHA技术在移动卫星通信系统中的新发展

本文主要介绍近年来，时隙ＡＬＯＨＡ技术在移动卫星通信中的一些新的发展趋势。介绍了在移动卫星通信信道中，ＡＬＯＨＡ技术在稳定控制，提高系统吞吐量和为大容量话音服务等方面的一些新颖的技术设想及初步的分析结果。     

ALOHA技术及其在VSAT网络中的应用

一、ＡＬＯＨＡ技术的工作原理 ＡＬＯＨＡ原是美国夏威夷大学为计算机之间的数据信息传输与交换设计的一种在地面通信网中进行的数据分组广播通信方式，于１９７３年第一次将该技术用于卫星通信系统。经过反复实验，证明这种技术应用于卫星通信完全可行。其基本工作原理是： ＶＳＡＴ数据传输包括许多个远端小站，每个小站有一个发射控制单元。首先，将数据分成若干段，给每一个数据段的前边加上一个报头，其中含有发、收方的地址及某些控制比特在每个数据段后面再加上检错码，就构成了一个信息包（Ｐａｃｋｅｔ）。传输控制单元以线路的最…     

卫星分组话音／数据扩频时隙ALOHA的性能分析

本文讨论了卫星分组话音／数据综合的扩频时隙ＡＬＯＨＡ的性能，并认为该协议较适合于卫星分组话音／数据综合的通信网中，给出了在扩频多址干扰为改进型高斯分布和某一时隙用户数有限的前提下，系统吞吐量的近似解析表达式和平均时延表达式，这比通常的标准高斯分布和无限用户的假设更精确，模拟说明结果性能是优越的。     

码分多址时器ALOHA分组无线网吞吐量分析

本文讨论码分多址时隙ＡＬＯＨＡ分组无线移动数据网，给出了在非理想功率控制下系统性能的定量分析。在非理想功率控制下，我们运用对数正态概率模型及Ｓｃｈｗａｒｔｚ－Ｙｅｈ近似方法来描述多用户接入干扰功率电平的随机变化，在此基础上，我们分析和计算了在不同控制误差和不同信道负载下系统的比特误码概率、数据包成功接收概率以及吞吐量等性能指标，并与基于等功率模型（即理想功率控制）的传统结果进行了比较。     

动态多通道卫星话音／数据综合的S－ALOHA性能分析

本文分析了一种新的多通道话音／数据综合ＶＳＡＴ系统的Ｓ－ＡＬＯＨＡ性能，并给出了数值计算结果；从中可看到该协议既能提供较高的吞吐量，又能有效地减小话音时延，并能协调话音和数据之间对性能要求的差异，文中考虑了Ｓ－ＡＬＯＨＡ中分组达到时间抖动的影响．文中还讨论了话音在重负载的条件下可占用数据通道的动态分配方案，并给出了动态分配的算法。     

Diversity reservation ALOHA

A multiaccess protocol suitable for packet satellite broadcast channels is introduced in this paper. The proposed protocol, called diversity reservation ALOHA (DRA) combines the essential features of announced retransmission random access (ARRA). diversity ALOHA, and a reservation scheme with a slotted ALOHA reservation channel to achieve the goals of improved delay-throughput characteristics and high channel utilization. Two versions of DRA protocols are analyzed. In scheme 1, called DRA with reservation cleared (DRA-RC), no global queue information is required for a user to access the channel. In this version, even a successful transmission of reservation requests will be cleared from the system if it causes overflow. The second scheme, called DRA with reservation delayed (DRA-RD), establishes a global queue distributed at users' terminals, so that users with successful transmission of reservation requests are assured of access rights although transmission may be delayed to later fames. Important system performance measures, such as activity-factor-throughput characteristics, for DRA-RC and DRA-RD are compared with those of ARRA. Examples of numerical results show that with system parameters properly chosen, substantial increases in attainable channel utilization are possible. Furthermore, the use of diversity for reservation allows a smaller packet delay especially under light traffic conditions. The analysis is validated in light of the simulation results.     

Cooperative-diversity slotted ALOHA

We propose a cooperative-diversity technique for ad hoc networks based on the decode-and-forward relaying strategy. We develop a MAC protocol based on slotted ALOHA that allows neighbors of a transmitter to act as relays and forward a packet toward its final destination when the transmission to the intended recipient fails. The proposed technique provides additional robustness against fading, packet collisions and radio mobility. Network simulations confirm that under heavy traffic conditions, in which every radio always has packets to send, the proposed cooperative-diversity slotted-ALOHA protocol can provide a higher one-hop and end-to-end throughput than the standard slotted-ALOHA protocol can. A similar advantage in end-to-end delay can be obtained when the traffic is light. As a result, the proposed cooperative-diversity ALOHA protocol can be used to improve these measures of Quality of Service (QoS) in ad hoc wireless networks. John M. Shea (S’92–M’99) received the B.S. (with highest honors) in Computer Engineering from Clemson University in 1993 and the M.S. and Ph.D. degrees in electrical engineering from Clemson University in 1995 and 1998, respectively. Dr. Shea is currently an Associate Professor of electrical and computer engineering at the University of Florida. Prior to that, he was an Assistant Professor at the University of Florida from July 1999 to August 2005 and a post-doctoral research fellow at Clemson University from January 1999 to August 1999. He was a research assistant in the Wireless Communications Program at Clemson University from 1993 to 1998. He is currently engaged in research on wireless communications with emphasis on error-control coding, cross-layer protocol design, cooperative diversity techniques, and hybrid ARQ. Dr. Shea was selected as a Finalist for the 2004 Eta Kappa Nu Outstanding Young Electrical Engineer Award. He received the Ellersick Award from the IEEE Communications Society in 1996. Dr. Shea was a National Science Foundation Fellow from 1994 to 1998. He is an Associate Editor for the IEEE Transactions on Vehicular Technology. Tan F. Wong received the B.Sc. degree (1st class honors) in electronic engineering from the Chinese University of Hong Kong in 1991, and the M.S.E.E. and Ph.D. degrees in electrical engineering from Purdue University in 1992 and 1997, respectively. He was a research engineer working on the high speed wireless networks project in the Department of Electronics at Macquarie University, Sydney, Australia. He also served as a post-doctoral research associate in the School of Electrical and Computer Engineering at Purdue University. Since August 1998 he has been with the University of Florida, where he is currently an associate professor of electrical and computer engineering. He serves as Editor for Wideband and Multiple Access Wireless Systems for the IEEE Transactions on Communications and as the Editor for the IEEE Transactions on Vehicular Technology.     

Dynamic Frame Length ALOHA

Adding frame structure to slotted ALOHA makes it very convenient to control the ALOHA channel and eliminate instability. The frame length is adjusted dynamically according to the number of garbled, successful, and empty timeslots in the past. Each terminal that has a packet to transmit selects at random one of thentimeslots of a frame. Dynamic frame length ALOHA achieves a throughput (expected number of successful packets per timeslot) of 0.426 which compares favorably with the1/e (approx0.368)upper bound of ordinary slotted ALOHA.     

Analysis of Priority R‐ALOHA (PR‐ALOHA) protocol

With the exception of required time synchronization, the Reservation‐ALOHA (R‐ALOHA) protocol is simple to implement and suitable for medium access control in ad hoc wireless networks. In this paper, we propose an innovative protocol, referred to as Reservation ALOHA with priority (PR‐ALOHA) that provides differentiated services on the basis of traffic priority. To date, the carrier sense multiple access/collision avoidance (CSMA/CA) protocol has been widely used for this purpose by employing an interframe spacing (IFS) for priority service, that is, nodes ready for packet transmissions are required to wait for an IFS amount of time, where a shorter IFS is used to gain faster access to the radio channel. However, sensing and collision avoidance mechanisms make CSMA/CA unsuitable for delay‐sensitive applications, that is, congested scenarios with high traffic. In contrast, the proposed PR‐ALOHA protocol may be considered a good candidate for such applications. In this paper, the performance of the PR‐ALOHA protocol is investigated analytically and by simulation. Its comparison with regular R‐ALOHA is also carried out. Modeling and simulation results of PR‐ALOHA show that PR‐ALOHA improves the performance of high‐priority traffic with limited effect on normal network traffic. Thus, PR‐ALOHA may be useful in vehicular communications, where traffic may be separated into emergency messages having high priority and multimedia messages having low priority. Copyright © 2013 John Wiley & Sons, Ltd.     

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。     

主动重发的DS／CDMA ALOHA

针对DS/CDMA ALOHA系统,本文提出了一种主动复发方案,并对主动重发时延为无限和有限值的情况分别进行了分析和研究,研究结果表明,主动重发时延为一个时隙时即可获得接近理想情况的性能。从理论计算和仿真实验的结果可以看到,这种新方案可以有效地改善DS/CDMA ALOHA协议的性能。     

Stabilization of slotted ALOHA spread-spectrum communicationnetworks

A method is presented for stabilizing slotted ALOHA frequency-hop communication networks by controlling code rate. In particular, the stabilization of a fully connected network in which a finite number of transmitter-receiver pairs exchange packets of information encoded by Reed-Solomon codes is considered. A principle of flow balance to stability analysis is adopted, and it is shown that network stability can be ensured by controlling code rate. The requirement on code rate for ensuring network stability is examined. In addition, the mean delay and the mean channel throughput of the network are discussed     

On Improving Utilization in ALOHA Networks

By the simple expedient of dividing users into two groups-one transmitting at high power and the other at low powerthe maximum utilization of a slotted ALOHA communication system can be increased from 36.8 percent to about 53 percent. Similar comments apply to the unslotted ALOHA case. An extension to more than two power groups also is described.     

Performance comparison of a slotted ALOHA DS/SSMA network and amultichannel narrow-band slotted ALOHA network

Throughput, delay, and stability for two slotted ALOHA packet radio systems are compared. One system is a slotted direct-sequence spread-spectrum multiple-access (DS/SSMA) network where each user employs a newly chosen random signature sequence for each bit in a transmitted packet. The other system is a multiple-channel slotted narrow-band ALOHA network where each packet is transmitted over a randomly selected channel. Accurate packet success probabilities for the code-division multiple-access (CDMA) system are computed using an improved Gaussian approximation technique which accounts for bit-to-bit error dependencies. Average throughput and delay results are obtained for the multiple-channel slotted ALOHA system and CDMA systems with block error correction. The first exit time (FET) is computed for both systems and used as a measure of the network stability. The CDMA system is shown to have better performance than the multiple-channel ALOHA system in all three areas     

Perfect-Capture ALOHA for Local Radio Communications

We consider a set of uncoordinated users employing an ALOHA protocol to transmit packets to a central base station in a local radio environment, e.g., in an urban area or within a building. Because of the different distances between the various users and the base station, the signals received from different users have substantially different power levels. This near/far phenomenon gives rise to a capture effect at the receiver such that when several packets are transmitted simultaneously, the receiver has a good chance of accurately detecting the packet arriving with the highest energy. Moreover, capture can be made near perfect in this environment through the use of properly design spread-spectrum signaling technique that enables the receiver to differentiate among the arriving packets based on both power differences and differing arrival times. We investigate variations to the conventional ALOHA protocols that take advantage of perfect capture to reduce the delays and increase the throughputs of all users, including the furthest one. Three protocols are introduced and compared, which we call "persistent ALOHA with capture" (PAC), "gated ALOHA with capture" (GAC), and "gated ALOHA with capture/exhausted" (GAC/E). Two goals are considered in the comparison: an equatable delay profile among the users, and a small expected number of simultaneously transmitted packets. The latter is quite relevant for the practical implementation of a perfect-capture receiver. We conclude that the GAC/E protocol is most desirable from the twin points of view of delay profile and receiver implementation.