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。     

变速率分组SAMA系统性能研究

以扩频ALOHA(SAMA)多址访问技术为研究对象,研究了变速率方式对分组无线通信系统性能的影响,提出自适应变速率分组算法,提高了系统性能。     

HFC网上行信道的一种接入解决方案

提出了一种基于多码分组CDMA的HFC网络上行信道ALOHA多址接入方式.介绍了这种多址接入方式的接入模型、实现方法及系统的组成,分析了ALOHA-CDMA信道的吞吐量,还分析了这种接入方武的特点、存在问题及解决方法.仿真结果表明该方案可改善HFC网络上行信道的吞吐性能和信道利用率.     

Ad hoc网络的扩频多址接入协议的研究与展望

Ad hoc网络将成为未来网络体系的基本组成部贩而扩频通信技术因其具有频带利用率高、抗干扰能力强等特点,被确认为移动通信系统首选的多址接入方式.鉴于此,本文介绍了扩频技术、Ad hoc网络以及其所面临的问题,对几种能有效解决Ad hoc网络存在的问题的扩频多址接入控制协议进行了分析比较,给出了研究过程中得出的结论.     

天地一体化信息网络中信令技术的研究

为了解决天地一体化信息网络中信令相关技术难点以及信令信道的建设,提出了在天基骨干节点搭载S频段相控阵载荷的解决方法。对几个关键技术进行了重点分析:在物理层,提出了基于开环的信令数据时频快速同步技术、基于非相干的分组数据解调技术;在链路层,采用扩频ALOHA方式解决广域用户随机接入问题。仿真结果表明,基于多符号联合检测的分组数据解调技术比理想相干解调仅损失0.5dB,扩频ALOHA多址随着扩频增益增大,容量也相应增加。     

UWB系统多址接入方法的比较研究

研究UWB系统多址接入技术的主要目的是在尽量减少多址之间的干扰,降低接收机的复杂度,实现低功耗、低成本。从误码率理论分析、性能仿真和接收机结构等几个方面对混沌序列扩频与伪随机序列扩频、伪混沌跳时与传统跳时多址接入方式进行比较研究。结果表明,在系统误码率方面,伪随机序列扩频优于混沌序列扩频,传统跳时优于伪混沌跳时;在接收机复杂度方面,混沌序列扩频和传统跳时较好。     

无线传感器网络中基于NDMA的跨层协作多包接收

本文研究了协作分集下的NDMA(网络辅助分集多址接入)机制,针对无线传感器网络特点和信道矩阵满秩性要求设计中继选择准则,提出了一个新的跨层协作多包接收机制.该机制在抗信道衰落的同时可有效限制数据包重传次数,从而大大提高多包接收的效率.对新机制的性能仿真以及该机制与NDMA、联合NDMA、时隙ALOHA之间的性能对比证实了新机制的有效性.     

面向5G的非正交多址接入技术

为了满足未来5G在频谱效率和连接数等方面的需求,非正交多址接入技术日益受到产业界的重视.从多用户信息论的角度,首先,探讨非正交多址接入与正交多址的理论性能比较及其逼近多用户信道容量界的有效途径;其次,对功率域、星座域、码域3种非正交多址方案的设计原理、信号处理和性能增益进行了深入分析;最后,从网络运营的角度剖析了非正交多址接入技术的应用场景、对系统设计带来的影响和网络后向兼容性等问题.     

CDMA时隙式非坚持CSMA多用户通信系统在电力线网络中的仿真研究

多通道随机通信系统的研究是一个新的课题,在以往的研究中,大多集中在固定分配多址接入方式,而本文引入了随机多址接入技术,以便在突发性事件中保持良好的性能,并采用蒙特卡罗方法对CDMA-时隙式非坚持CSMA多用户通信系统在不同因素影响下的网络吞吐量进行了仿真研究,证明了在随机多址接入技术中采用CDMA技术,可以明显改善系统的性能。     

扩频通信与扩频调制技术

Y2001-62866-132 0119103FHSS-MA 通信系统的联合最佳里德-索洛蒙编码率和用户数=Jointly optimal RS code rate and number ofusers for FHSS-MA communication system[会,英]/Zheng,X.-F.& Zhou,B.//2000 International Con-ference on Communication Technology Proceedings Vol.Ⅰ of Ⅱ.—132～139(HC)本文描述了用里德-索洛蒙码(RS)的跳频扩频多址通信系统,研究了通过 RS 码率和用户数目联合最佳使通过量最大的方法,结论说明,若通过最佳化仅考虑其正规通过量,FHSS-MA 网络如同使用 ALOHA 或时隙 ALOHA 规约的一般多址通信系统进行工作。参2     

On a Mixed Mode Multiple Access Scheme for Packet-Switched Radio Channels

We extend the study of access schemes for packet-switched radio channels as an alternative to conventional wire communications for data transmission among users. Among the various multiple access schemes previously implemented or proposed, ALOHA presents many advantages, especially for a large population of bursty users. However, more than 60% of the ALOHA channel capacity is wasted. In this paper we introduce a separate large carrier-sensing user who "steals" slots which remain unused by the background of ALOHA users. This leads to a new multiple-access scheme: the Mixed ALOHA Carrier Sense (MACS) access scheme, whose performance We analyze. The total channel utilization is significantly increased with MACS, and the delaythroughput performance of both the large user and the background of ALOHA users is shown to be better with MACS than with a "split channel" mode in which the large user and the ALOHA users are each permanently assigned a portion of the channel.     

Packet Switching in Radio Channels: Part IV--Stability Considerations and Dynamic Control in Carrier Sense Multiple Access

In two companion papers a method for multiplexing a population of terminals communicating with a central station over a packet-switched radio channel was introduced; this method is known as Carrier Sense Multiple Access (CSMA). CSMA, as with ALOHA multiaccess broadcast channels, has the unfortunate property that the throughput falls to zero as the channel load increases beyond a critical value. The dynamic behavior and stability of slotted ALOHA channels have been studied extensively and have led to a definition of stability. In this paper, similar techniques are used to analyze CSMA, which is shown to have a behavior not unlike that of ALOHA. However, contrary to ALOHA channels where steady-state performance is badly degraded when true stability is to be guaranteed, hence requiring dynamic control, we find that CSMA provides excellent stable performance even with as large a population as 1000 terminals. Furthermore, we study a simple adaptive retransmission control procedure which provides a significantly improved channel performance which is insensitive to the population size.     

Pereormance analysis of slotted ALOHA for land mobile satellite networks

The ALOHA protocol has been proposed for accessing reservation channels in demand-assigned channel access protocols for land mobile satellite communications networks. This paper provides a rigorous performance analysis of both the slotted ALOHA protocol and two-packet replication ALOHA protocol taking into account the effects of the fading multipath communications environment. Throughput, delay and stability of these two protocols are determined using a Gilbert channel error model with memory. Comparison of slotted ALOHA and two-packet replication ALOHA shows that a smaller average delay can be achieved by replication. Moreover average throughput is improved in some cases. However replication reduces stability.     

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.     

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     

The ALOHA systems in shadowed mobile radio channels with slow orfast fading

The influence of receiver capture on the performance of the ALOHA protocol in the presence of shadowing is investigated. The combined effect of Rayleigh fading, log-normal shadowing, and spatial distribution of mobile users is also studied. It is shown that shadowing is similar to fading and near/far phenomena, in that it makes the capture effect possible and provides ALOHA systems with substantial improvements in throughput. It is also confirmed that the superimposed Rayleigh fading, log-normal shadowing, and spatial distribution can further enhance the capture effect, resulting in a ALOHA system with higher throughput. The fast fading effect in ALOHA systems is explored. A very fast fading case is examined which may be considered to be equivalent to interleaving in slow fading. It is found that an ALOHA system under fast fading conditions also benefits from the capture results in higher throughput     

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.     

The effect of multipath interference on the performance of packetradios

The effect of multipath interference on the performance of packet radios is investigated. The protocols considered include pure ALOHA and slotted ALOHA. Signal reception with and without capture effect is considered in the analysis. Mathematical expressions of system throughput and packet delay have been successfully obtained for each protocol. Numerical calculations are used to demonstrate when the multipath interference can be ignored and when it can be disastrous     

Hybrid ALOHA: A Novel MAC Protocol

This paper considers cross-layer medium access control (MAC) protocol design in wireless networks. Taking a mutually interactive MAC-PHY perspective, we aim to design an MAC protocol that is in favor of the physical (PHY) layer information transmission, and the improved PHY, in turn, can improve the MAC performance. More specifically, we propose a novel MAC protocol, named hybrid ALOHA, which makes it possible for collision-free channel estimation and simultaneous multiuser transmission. The underlying argument is as follows: As long as good channel estimation can be achieved, advanced signal processing does allow effective signal separation given that the multiuser interference is limited to a certain degree. Comparing with traditional ALOHA, there are more than one pilot subslots in each hybrid ALOHA slot. Each user randomly selects a pilot subslot for training sequence transmission. Therefore, it is possible for different users to transmit their training sequences over nonoverlapping pilot subslots and achieving collision-free channel estimation. Relying mainly on the general multipacket reception (MPR) model, in this paper, quantitative analysis is conducted for the proposed hybrid ALOHA protocol in terms of throughput, stability, as well as delay behavior. It is observed that significant performance improvement can be achieved in comparison with the traditional ALOHA protocol based either on the collision model or the MPR model.