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。     

本地多点分配接入系统的现状与发展

１本地多点分配接入系统（ＬＭＤＳ）简介宽带网络和无线接入是未来通信网络的两个重要发展方向。传统的电信公司和ＣＡＴＶ公司为了实现网络的宽带化,采用ｘＤＳＬ、ＨＦＣ、ＳＤＨ及ＡＰＯＮ等有线线路设备和技术,组建本地宽带网络。但这些方案和技术都因其昂贵的成本、...     

ANYMEDIA^TM宽带接入系统

１何为ＡｎｙＭｅｄｉｅＴＭ？ＡｎｙＭｅｄｉａＴＭ是朗讯科技最新推出的第四代接入网产品－ＡｎｙＭｅｄｉａＴＭ接入系统的注册商标,ＡｎｙＭｅｄｉａＴＭ可以通过铜线、光纤或无线等任何物理媒体传输,支持话音、数据及视频等任意信息媒体,支持ＡＤＳＬ、ＨＤＳＬ、ＳＤＳＬ及ＶＤＳＬ等“变铜为金”的ｘＤＳＬ技术,以及网络结构由ＦＴＴＣ、ＦＴＴＢ最终发展为基于ＡＴＭＰＯＮ的ＦＴＴＨ。ＡｎｙＭｅｄｉａ（实际上是一个公共的接入平台。目前是采用光纤逐步拓展网络,并同时充分利用铜线宝贵资源,最终发展为实现全程光纤化的全业…     

宁波GSM系统LAC调整方案

宁波ＧＳＭ系统ＬＡＣ状况 目前宁波ＧＳＭ系统共有ＬＡＣ区２２个,每个ＢＳＣ分配一个ＬＡＣ（除市区ＢＳＣ２３,ＢＳＣ２４外）,这样,某些ＢＳＣ的Ｌｏｃａｔｉｏｎ－Ｕｐｄａｔｅ占ＯＫ－ＡＣＣ－ＰＲＯＣ的比例（后称ＬＵ－ＲＡＴＥ）相当高,如余姚ＢＳＣ８,其ＬＵ－ＲＡＴＥ高达７９．４２％,其ＳＤＣＣＨ负荷相当重,且已导致ＳＤＣＣＨ拥塞,具体每个ＢＳＣ的ＬＵ次数,ＬＵ－ＲＡＴＥＰＡＧＥ－ＲＥＱＵＥＳＴＳ／ＰＡＧＥ－ＲＥＳＰＯＮＳＥ,ＰＡＧＥＳ－ＰＥＲ－ＳＥＣＯＮＤ,ＳＤ－ＣＯＮＧＥＳＴＩＯＮ－ＲＡＴＥ,…     

世纪之交的接入网技术与发展展望

目前,接入网已成为全网带宽的瓶颈,宽带化和ＩＰ化是接入网大势所趋。本文讨论了近来发展势头较好的接入网技术：ＡＤＳＬ（ＵＤＳＬ）和ＶＤＳＬ、ＨＦＣ、ＰＯＮ和ＡＰＯＮ、ＳＤＨ接入、ＬＭＤＳ、不可见光纤无线系统以及以太网等;同时指出要构筑公共的接入平台来综合多元经的接入技术。另外,中国接入网也正开始从窄带向宽带方式转变,但制造业在宽带接入技术研发方面滞后于人。     

无线局域网中的预约CDMA接入技术

在传统的无线ＭＡＣ接入协议（如ＡＬＯＨＡ,ＣＳＭＡ／ＣＡ,ＴＤＭＡ和ＣＤＭＡ）的基础上,重点探讨了基于码分多址的预约ＣＤＭＡ无线多址接入协议。该协议的在无线局域网接入时,无论在时间延迟还是吞吐量特性方面均比传统的无线接入协议有很大的改善。     

新一代宽带无线接入技术—LMDS

随着信息高速公路的兴起,光纤与其他高速传输线路已将大多数大中城市与经济中心连在一起,但如何以宽带高速的方式将广大本地用户与中小商业用户连接到骨干网,还是一大难题。针对这一难题,近年来涌现了多种宽带接入技术,这些技术主要分为有线和无线两大类。有线接入主要有数字用户线ＤＳＬＨＤＳＬ、ＡＤＳＬ、ＶＤＳＬ等、利用现有ＣＡＴＶ网的Ｃａｂｌｅ Ｍｏｄｅｍ接入技术和光纤接入技术光纤数字环路、载波系统ＤＬＣ、基于ＡＴＭ的无源光网络ＰＯＮ等。有线接入的优点是带宽相对宽裕,传输质量较好,但是有线接入的成本本…     

无线宽带通信系统

本文重点介绍了无线宽通信系统的宽带接入技术如无线ＬＡＮ，无线ＡＴＭ，ＬＭＤＳ和ＭＭＤＳ。另外，还介绍了以ＴＤＭＡ和ＣＤＭＡ为基础的多媒体无线通信中的新技术，如自适应调ＯＦＤＭ／ＳＳ等。     

公用市话交换网中的IP旁路技术

ＩＰ旁路技术 不同的ＩＰ接入方式 互联网接入的方式根据不同的网络平台有多种,公用市话交换网（ＰＳＴＮ）主要采用铜线（双绞线）和光纤,如３３．６Ｋ／５６Ｋ ＭＯＤＥＭ、ＩＳＤＮ、ＡＤＳＬ、ＦＴＴＨ等;而广电的网络可以采用Ｃａｂｌｅ Ｍｏｄｅｍ;对于新兴的运营商则可以大量的采用光纤到户、光纤到小区、辅助以局域网／城域网技术和无线的ＬＭＤＳ方式。 以上的接入方式大致可分为两类：一类是传统运营商体系的传统接入方式;另一类是新兴运营商和新兴的接入方式（如,ＡＤＳＬ、ＦＴＴＨ、Ｃａｂｌｃ Ｍｏｄｅｍ、 ＬＭＤＳ）…     

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     

Stability and throughput analysis of unslotted CDMA‐ALOHA with finite number of users and code sharing

We consider a system comprising a finite number of nodes, with infinite packet buffers, that use unslotted ALOHA with Code Division Multiple Access (CDMA) to share a channel for transmitting packetised data. We propose a simple model for packet transmission and retransmission at each node, and show that saturation throughput in this model yields a sufficient condition for the stability of the packet buffers; we interpret this as the capacity of the access method. We calculate and compare the capacities of CDMA‐ALOHA (with and without code sharing) and TDMA‐ALOHA; we also consider carrier sensing and collision detection versions of these protocols. In each case, saturation throughput can be obtained via analysis of a continuous time Markov chain. Our results show how saturation throughput degrades with code‐sharing. Finally, we also present some simulation results for mean packet delay. Our work is motivated by optical CDMA in which “chips” can be optically generated, and hence the achievable chip rate can exceed the achievable TDMA bit rate which is limited by electronics. Code sharing may be useful in the optical CDMA context as it reduces the number of optical correlators at the receivers. Our throughput results help to quantify by how much the CDMA chip rate should exceed the TDMA bit rate so that CDMA‐ALOHA yields better capacity than TDMA‐ALOHA. This revised version was published online in June 2006 with corrections to the Cover Date.     

Slotted ALOHA and code division multiple access techniques forland-mobile satellite personal communications

The throughput and delay characteristics of a land-mobile satellite channel are analyzed for both slotted ALOHA. And slotted direct-sequence CDMA (code division multiple access), using binary phase shift keying (BPSK) modulation and forward error correction coding (FEC). In the case of CDMA, the application of path diversity techniques-maximal ratio combining and selection diversity-is also taken into account. Packet success probabilities are derived for both slow and fast fading, in order to evaluate the throughput and delay. Numerical results are presented for arbitrary code lengths and for specific values of the number of resolvable paths. It is shown that CDMA can offer a substantial improvement over slotted ALOHA, especially when the chip time is less than the delay spread     

Asynchronous fiber optic local area network using CDMA and optical correlation

An experimental fiber optic local area network utilizing code division multiple access (CDMA) and fiber optic delay-line signal processing is reported. The throughput-delay characteristics are compared to ALOHA and CSMA/CD. Since CDMA allows many users to access the network simultaneously, it can achieve higher throughput with no delay.     

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。     

Performance analysis of a slotted CDMA ALOHA network

ALOHA is a simple and efficient way of allowing many machines with bursty data streams to communicate with a central computer. For cases where machines are equally likely to transmit to one another, CDMA ALOHA, which allows for full connectivity, may be a better multiple access protocol than slotted ALOHA through a central machine. This paper first describes a model for a fully connected, full duplex, and slotted CDMA ALOHA network where the receiver-based code access protocol is used. The stations can send data to, and receive data from, different stations simultaneously. The model is analyzed using discrete-time Markov chain, and some numerical results are presented. For a system with a large number of users where Markov analysis is impractical, equilibrium point analysis is used to predict the stability of the system and determine the throughput as well as the delay performance of the system when it is stable. It is shown that a CDMA slotted ALOHA network has a much better performance compared to simple slotted ALOHA networks.     

时隙ALOHA DS/CDMA系统与多载波时隙ALOHA系统吞吐性能的比较研究

该文对同样带宽下时隙 ALOHA DS/CDMA系统和多载波时隙 ALOHA系统的吞吐量进行了理论计算、比较和仿真。结果表明,在总负载较大时,采用高纠错能力的时隙 ALOHA DS/CDMA系统可以在吞吐量上有更好的性能。但若网络负载过重,时隙ALOHA DS/CDMA系统的吞吐性能较多载波时隙ALOHA的系统下降快;码字总数受限会带来码字选择的冲突,从而降低系统的吞吐性能。     

扩频ALOHA多址系统吞吐量和时延性能分析

该文深入地研究了扩频ALOHA多址(SAMA)系统的信道接入性能,推导了通用的扩频ALOHA多址系统平均误比特率公式,给出了扩频ALOHA系统吞吐量和时延性能表达式,同时还分析了信道编码对系统性能的改进,给出了相应的仿真和数值结果。结论表明,扩频ALOHA多址系统可以显著提高传统ALOHA系统的吞吐量和时延性能,提高程度随扩频增益增加而增加,引入信道编码可以进一步提高网络性能。     

A controlled multiaccess protocol for packet satellitecommunication

This protocol is fully distributed and no onboard processing is required for the satellite. A control parameter f is used to adaptively control the packet transmission rate such that maximum system capacity can be attained and the average delay is always minimized for a given throughput. The controlled protocol is found to give a smaller average delay than slotted ALOHA even when the throughput is as low as 0.05. On the other hand, under heavy traffic conditions, it can provide a throughput close to unity and an average delay not much more than one round-trip propagation delay. The system performance is also robust, in the sense that a 15% error in throughput estimation results in no more than a 3% increase of the overall average packet delay