认知车载网中基于TDMA/CSMA的混合多信道MAC协议研究

在传统车载自组网(Vehicular Ad Hoc Network, VANET)中采用认知无线电(Cognitive Radio, CR)技术可以解决无线电频谱资源短缺的问题,该技术形成了新兴的认知车载网络(CR-VANET),其关键技术之一是设计高效可靠的介质访问控制(Medium Access Control, MAC)协议。MAC协议在很大程度上影响着车载移动环境的吞吐量,丢包率和传输时延等性能,基于认知车载网中MAC协议的要求,提出了一种TDMA与CSMA相结合的多信道MAC协议(CRTC-MAC)。在固定时隙分配时采用基于无竞争的TDMA访问策略,在动态时隙分配时采用基于竞争的CSMA接入方案,并在此基础之上对传统的TDMA和CSMA访问方式进行了改进。性能分析和仿真结果表明,所提出的MAC协议能有效降低节点间数据包传输时所产生的碰撞,改善网络性能。     

车载自组织网络协作MAC协议研究

车载自组织网络(Vehicular Ad Hoc Network,VANET)的关键技术之一就是 设计一个高效的媒体接入控制(Medium Access Control,MAC)协议。MAC协议因对网络的吞吐量、时延和丢包率等具有重大影响而成为研究热点。针对车载自组织网络对MAC协议的特殊性要求,提出了一种基于协作方案的TDMA MAC协议,即C-TDMA MAC。该协议中,当源节点到目的节点间直接传输失败时,其邻近辅助节点利用未被预留的时隙协作重传其先前侦听到的数据包到目的节点,而不影响其它数据包的正常传输。数值分析和仿真结果表明,所提出的协议提高了数据包成功传输的概率。     

基于竞争允许TDMA的无线传感器MAC层协议

无线传感器网络在许多重要领域有着广泛的应用，而传感网的媒体访问控制子层(MAC)协议对传感器网络的运行和性能具有重要影响。该文概述了目前存在的传感网MAC协议的设计思想，在SMAC协议的基础上，将TDMA和CSMA两种思想结合起来并与SMAC协议同步机制相统一，提出了一个新的基于竞争允许TDMA的无线传感器网络MAC协议。模拟结果显示，与SMAC协议相比，该协议在数据包延迟、能量消耗及数据包的接收率等性能上有很大提高。     

Provably secure and efficient identification and key agreement protocol with user anonymity

Many authentication and key agreement protocols were proposed for protecting communicated messages. In previous protocols, if the user?s identity is transmitted in plaintext, an adversary can tap the communications and employ it to launch some attacks. In most protocols with user anonymity, they focus on satisfaction of several security requirements. From a client?s point of view, those protocols are not admired since the cost of storage, computation and communication is high. In pervasive computing, a client usually uses a limited-resource device to access multiple servers. The storage and computation are very important issues especially in this kind of environments. Also, for a convenience of designing protocol, most protocols use timestamps to prevent the replay attack. As we know, the serious time synchronization problem exists in timestamp-based protocols. Finally, most protocols do not have formal proofs for the security. In this paper, we propose a secure and efficient identification and key agreement protocol with user anonymity based on the difficulty of cracking the elliptic curve Diffie–Hellman assumption. In addition, we also propose an augmented protocol for providing the explicit mutual authentication. Compared with the related protocols, the proposed protocols? computation cost is lower and the key length is shorter. Therefore, our protocols are suitable even for applications in low power computing environments. Finally, we formally prove the security of the proposed protocols by employing the random oracle model.     

Topology-transparent reservation time division multiple access in multihop ad hoc networks

In this paper, an optimal topology-transparent reservation time division multiple access (OTTR-TDMA) protocol is proposed for multihop ad hoc networks. Our MAC protocol is based on a slotted TDMA architecture in which every slot is divided into reservation phase and data transmission phase. Every node not only transmits data in its assigned slots that are computed by Chlamtac’s algorithm, but it also utilizes free slots among its non-assigned slots through reservation. Through theoretical analysis, we derive the proper parameter for the best performance. We compare our protocol with other TDMA protocols and find that it gives better performance. Simulation results show that they are consistent with our analytical results.     

A novel congestion control in hybrid ATM/TDMA networks

A new congestion control scheme is analyzed for an ATM multiplexer node. This scheme is based on the leaky bucket and virtual leaky bucket techniques, and utilizes the interaction between the ATM and higher layers, in a hybrid asynchronous transfer mode/time division multiple access (ATM/TDMA) network. The transport users are assumed to be generic ATM sources, who modulate their end-to-end flow control parameters, i.e. protocol data unit size in case of video and voice users, and window size in case of data users, based on the congestion status. Simple analytical formulas are derived for congestion criteria, to represent the required bandwidth to support various classes of service, i.e. video, voice, data, etc. with their own performance requirements. An ATM multiplexer node buffer is analyzed using a modulated poisson process queuing model with bulk arrival and bulk service of cells. The ATM multiplexer node congestion performance criteria, i.e. the mean probabilities of ATM multiplexer node congestion, cell generation, cell discarding, buffer content and buffer overflow, are evaluated with and without the congestion control schemes.     

Analysis of a Hybrid Access Scheme for Buffered Users-Probabilistic Time Division

A new multiple access scheme is proposed and evaluated. The proposed scheme combines desirable features of the ordinary time-division (TDMA) and the random access (RA) schemes. It is shown that by adjusting the value of a single parameter a, the proposed access method can vary continuously from one extreme (TDMA) to the other (RA). The average delay per packet and the throughput can be improved for intermediate values of the load factor. Furthermore, the method can control the channel instability.     

An efficient broadcast scheduling algorithm for TDMA ad-hoc networks

In this paper, we propose an efficient algorithm to find a collision-free time slot schedule in a time division multiple access frame. In order to minimize the system delay, the optimal schedule must be defined as the one that has the minimum frame length and provides the maximum slot utilization. The proposed algorithm is based on the sequential vertex coloring algorithm. Numerical examples and comparisons with the algorithm in previous research have shown that the proposed algorithm can find near-optimal solutions in respect of the system delay.Scope and purposeAn ad-hoc network was introduced in order to apply packet switching communication to a shared radio channel. Using a radio channel as the broadcast medium to interconnect users, an ad-hoc network provides flexible data communication services among a large number of geographically distributed, possibly mobile, radio units. In an ad-hoc network, since all users share a single channel by multiple access protocol, unconstrained transmission may lead to the time overlap of two or more packet receptions, called collision, resulting in damaged useless packets at the destination. Collided packets increase the system delay because they must be retransmitted. Therefore, the transmission for each station must be scheduled to avoid any collision, that is, collision-free transmission should be guaranteed. The time division multiple access (TDMA) technology can be used to schedule collision-free transmission. In this paper, we propose an efficient algorithm to find a collision-free time slot schedule in a TDMA ad-hoc network.     

Side-Channel Analysis for the Authentication Protocols of CDMA Cellular Networks

Time-division multiple access (TDMA) and code-division multiple access (CDMA) are two technologies used in digital cellular networks. The authentication protocols of TDMA networks have been proven to be vulnerable to side-channel analysis (SCA), giving rise to a series of powerful SCA-based attacks against unprotected subscriber identity module (SIM) cards. CDMA networks have two authentication protocols, cellular authentication and voice encryption (CAVE) based authentication protocol and authentication and key agreement (AKA) based authentication protocol, which are used in different phases of the networks. However, there has been no SCA attack for these two protocols so far. In this paper, in order to figure out if the authentication protocols of CDMA networks are sufficiently secure against SCA, we investigate the two existing protocols and their cryptographic algorithms. We find the side-channel weaknesses of the two protocols when they are implemented on embedded systems. Based on these weaknesses, we propose specific attack strategies to recover their authentication keys for the two protocols, respectively. We verify our strategies on an 8-bit microcontroller and a real-world SIM card, showing that the authentication keys can be fully recovered within a few minutes with a limited number of power measurements. The successful experiments demonstrate the correctness and the effectiveness of our proposed strategies and prove that the unprotected implementations of the authentication protocols of CDMA networks cannot resist SCA.     

On the use of learning automata in the control of broadcast networks: a methodology

Due to its fixed assignment nature, the well-known time division multiple access (TDMA) protocol suffers from poor performance when the offered traffic is bursty. In this paper, an adaptive TDMA protocol, which is capable of operating efficiently under bursty traffic conditions, is introduced. According to the proposed protocol, the station which is granted permission to transmit at each time slot is selected by means of learning automata (LA). The choice probability of the selected station is updated by taking into account the network feedback information. The system which consists of the LA and the network is analyzed and it is proven that the choice probability of each station asymptotically tends to be proportional to the probability that this station is not idle. Although there is no centralized control of the stations and the traffic characteristics are unknown and time-variable, each station tends to take a fraction of the bandwidth proportional to its needs. Furthermore, extensive simulation results are presented, which indicate that the proposed protocol achieves a significantly higher performance than other well-known TDMA protocols when operating under bursty traffic conditions.     

Steady-state and transient delay analysis of ARQ protocols

A technique for the performance evaluation of ARQ protocols is presented. General distributions for the packet interarrival times at the transmitter are assumed. Two specific ARQ protocols, the stop-and-wait ARQ and the continuous ARQ are examined in particular. Both the transient and steady-state behaviour are obtained. A simple iterative scheme is proposed for the computation of the delay experienced by the packets and for the packet interdeparture time distribution. The latter result can be applied to the analysis of networks using an ARQ protocol in their datalink control layer. This method is demonstrated for the special case of a network consisting of N nodes connected in tandem. Analytical results are compared with simulation runs and excellent agreement is observed.     

中小型Ad hoc网络信道接入协议研究

在介绍了Ad hoc网络的概念及特点的基础上,系统地论述了Ad hoc网络的多址接入技术,并针对基于时分多址接入的网络系统提出了一种改进的无线自组网信道接入协议--信道预约多址接入协议.该协议通过对物理信道的动态划分,将控制信道与业务信道相分离,实现了网络控制信息和业务信息的无冲突发送,改善了网络的信道利用率和传输的可靠性.     

一种用于多跳分布式无线网络的多址接入协议及其性能分析

为多跳分布式无线网络提出了一套灵活而有效的自适应获取冲突避免(AACA)的多址接入协议．它综合了多信道和随机附带预约的思想，有效地解决了多跳网络环境下出现的隐藏终端和暴露终端问题以及由于节点的移动而造成的侵入终端问题．在该协议中，各节点自适应预约所要使用的空闲业务信道，预约之后的通信过程不会受到其它节点的干扰．AACA协议有三种形式，即AACA-SDT／MDT／RDT协议，它们使用任意确定数目的信道，在总带宽相同的情况下表现出比单信道RTS／CTS协议更好的网络性能．     

Performance study of SRMA multiple access protocols

In this paper we are concerned with packet broadcast networks in which users communicate with the central station. The key problem is multiple access of a shared broadcast channel. The performance of a family of SRMA (split-channel reservation multiple access) protocols for multiple access proposed by Tobagi and Kleinrock (1976) is studied. We analyse the performance of SRMA-RM (request message) and modified SRMA-RAM (request answer message) protocols in terms of the throughput and the average packet delay. Bounds on the throughput are also established for both protocols.     

无线传感器网络TDMA MAC协议的对比和改进研究

无线传感器网络MAC协议对网络的生命期有着重要影响,为找到适合一定环境所使用的MAC协议,必须对不同的MAC协议进行必要的分析。从数据帧着手,分析了不同的基于TDMA的调度式MAC协议的差异。针对原有TDMA MAC协议数据传输量不高、实现难度大等问题,提出相应的改进方法,并对三个基于LEACH的TDMA MAC协议进行了仿真实现,仿真结果与数据分析的结果一致。     

基于跨层竞争的同步MAC协议研究

在无线传感器网络(WSNs)中,基于跨层竞争的同步媒体接入控制(MAC)在一周期内可安排多个数据包的多跳传输,传统的协议在同一个数据窗口传输请求数据包和确认数据包,降低了数据窗口的多跳流量的建立,也降低了在多跳场景中的数据包传输率和传输时延性能.本文提出了基于新的基于跨层竞争的同步MAC(CLC-MAC)协议,CLC-MAC协议引用新的周期结构,且其包含两个独立窗口,并由该窗口分别传输数据请求包和确认包,即请求包在数据窗口传输,而确认包在休眠窗口传输.实验数据表明:与先锋路由帧MAC(PRMAC)协议相比,CLC-MAC协议的端到端传输时延和数据包传输率的性能均得到了提高.     

<Emphasis Type="Bold">Ppssm:push/pull smooth video streaming multicast protocol design and implementation for an overlay network</Emphasis>

IP multicast is one of the best techniques for video streaming on the Internet. It faces issues with respect to address allocation, routing, authorization, group management, security, and scalability. By default, local Internet Service Providers did not enable IP multicast services, because of the cost incurred in using multicast-enabled routers. To solve these issues some of the IP layer functionalities have been shifted to the Application Layer, thus leading to Application Layer Multicast (ALM) protocols. However, ALM protocols face issues related to synchronous data delivery, scalability, link stress, link stretch and node failures. Some of the existing protocols are CoolStreaming, and mTreebone. A novel ALM protocol based Push/Pull Smooth video Streaming Multicast (PPSSM) protocol is proposed in this paper, to increase the throughput and reduce the packet loss rate. The PPSSM protocol involves three stages, such as tree-mesh construction, dynamic buffer management and network coding techniques. In the tree-mesh construction, a tree consists of stable nodes and a mesh consists of unstable nodes. The proposed PPSSM optimizes the stable nodes in the tree, which minimizes or eliminates the pull operations from the unstable mesh overlay nodes, by exploring the potential of the stable nodes. Dynamic buffer management is achieved by setting the optimal buffer threshold value, using the optimization of the sensitivity parameters, such as packet loss and packet workload/delay by the Infinitesimal Perturbation Analysis and Stochastic Approximation algorithms. In addition to the tree-mesh construction and buffer management, the introduction of the network coding technique will enhance the throughput and minimize the packet loss and delay. Finally, the performance of the proposed PPSSM protocol is compared with those of CoolStreaming, and mTreebone, and it shows improvement in respect of throughput, packet loss, and average decoding time.     

Performance simulation of wireless multimedia systems using NC-PRMA/DA and SNC-PRMA/DA protocols

A noncollision packet reservation multiple access with dynamic allocation (NC-PRMA/DA) scheme is proposed and investigated as a suitable candidate protocol for wireless multimedia communications. Access requests of the existing users in NC-PRMA/DA are conveyed to the base station in a noncollision manner by using a time-frequency signaling scheme. In addition, the scheduling NC-PRMA/DA (SNC-PRMA/DA) scheme, which is NC-PRMA/DA with packet scheduling, is also presented. Mixed voice, variable-rate video, and data traffic is used to demonstrate the efficiency of the proposed schemes for a single-cell environment. Simulation results show that our proposed NC-PRMA/DA and SNC-PRMA/DA protocols outperform the existing PRMA/DA protocol.     

多跳分布式无线网络环境下自适应获取冲突避免的多址接入协议

该文为多跳移动的分布式无线网络提出了一种新型的媒质接入控制（MAC）协议，即公共－发送信道式自适应获取冲突避免（AACA－CT）协议，在该协议中，每个节点预先监测记录周邻节点的信道使用情况，从而自适应地为自己选择发送信道，并且利用在公共信道上发送的RTS分组唤起收方使用各自的发送信道而实现无冲突的通信，它的主要思想在于资源预约可以简便地利用半双工无线电台以异步方式灵活，有效地在多个频段，多个跳频（FH）码或多个直接序列扩频（DSSS）码上实现，而且不依赖于功能强大的基站或中心控制器以及有线骨干网的帮助，性能分析和仿真结果表明，它能有效地克服隐藏终端和暴露终端问题，并且可以完全解决侵入终端问题。     

基于状态响应的分组预约多址接入协议研究

为了克服经典PRMA-HS协议中的双稳态问题和分组发送允许概率的静态性缺点,提出了一种基于状态响应的改进型分组预约多址接入协议.该协议能够利用卫星基站反馈信息,根据系统状态实时调整分组发送允许概率,使系统始终处在最佳状态.利用计算机对理想信道和随机误差信道条件下的协议性能进行了仿真,实验结果表明,采用状态响应机制能够克服经典PRMA-HS协议的双稳态问题,提高了协议的稳定性,增加了系统容量,降低了分组丢弃率.