基于语音时隙机制的车载自组网MAC协议

在节点高速运动的车载组网多跳通信中,如何快速选择下一跳中继节点是目前无线自组网亟待解决的问题。为此,提出一种基于类语音时隙划分信道竞争机制的时分复用协议,采用类似语音优先权接入的语音突发方式解决多跳中继选择问题。仿真结果表明,在不同节点分布的运动场景下,使用语音突发方式的MAC协议较传统的时分复用随机接入方式具有更短的接入延时与更低的网络开销。     

A Learning Automata-Based Cognitive Radio for Clustered Wireless Ad-Hoc Networks

In current wireless networks, the radio systems are regulated by a fixed spectrum assignment strategy. This policy partitions the whole radio spectrum into a fixed number of radio ranges, each exclusively assigned to a specific user. Such a spectrum assignment strategy leads to an undesirable condition under which some systems only use a small portion of the allocated spectrum while the others have very serious spectrum insufficiency. The learning automata-based cognitive radio which is proposed in this paper is a highly potential technology to address the spectrum scarcity challenges in wireless ad hoc networks. This paper proposes a learning automata-based dynamic frame length TDMA scheme for slot assignment in clustered wireless ad-hoc networks with unknown traffic parameters, where the intra-cluster communications are scheduled by a TDMA scheme, and a CDMA scheme is overlaid on the TDMA to handle an interference-free inter-cluster communication. In this method, each cluster-head is responsible for a collision-free slot assignment within the cluster and determines the input traffic parameters of its own cluster members. It then takes these traffic parameters into consideration for an optimal channel access scheduling in the cluster. The medium access control layer in each cluster is based on a time division multiple access (TDMA) scheme, in which each host is assigned a fraction of the TDMA frame proportional to its traffic load. The simulation experiments show the superiority of our proposed slot assignment algorithm over the existing methods in terms of the channel utilization, control overhead, and throughput, specifically, under bursty traffic conditions.     

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。     

Queueing analysis of buffered slotted multiple access protocols

Much of the literature on the performance evaluation of multiple access protocols has assumed a buffer capacity of one unit. This assumption is not realistic. In practice the buffer capacities used are larger than one unit in order to reduce the probability of packet rejection. This is more crucial for multiple access protocols, which allow moderate to high values of the expected throughput (URN, Random TDMA etc.).In this paper, a model appropriate for the analysis of buffered slotted multiple access schemes is proposed. The method can be applied to several multiple access protocols such as the URN protocol, the ALOHA protocol, Random TDMA etc. The cases of infinite and finite buffer capacity are examined separately but under the same basic assumptions. The analysis is based on the assumption that each user process can be modelled as an M/G/1 queueing system. The proposed method requires a small amount of computation and is characterized by a high speed, a fact that simplifies the buffer's design as well. The solution obtained is extremely accurate and exhibits excellent agreement with simulation results, which corroborate the accuracy of the model. The special case when the buffer capacity is equal to 1 is examined. In that case, the present approach also allows for computation of the packet delay distribution.     

DTS: Dynamic TDMA scheduling for Networked Control Systems

Networked Control Systems (NCSs) are pervasively applied in modern industry. With increasing functionalities, modern NCSs tend to have dynamic workload by holding a variety of applications via a shared network. To handle workload variations and provide performance guarantees, dynamic network scheduling scheme is highly desired in NCSs. In this paper, we propose a network scheduling scheme, referred to as DTS, that can make on-the-fly decisions to schedule the applications in NCSs. DTS aims at NCSs that use time-triggered network as shared medium and Time division multiple access (TDMA) as network access method. DTS dynamically changes the network accessing sequence of the applications in a way to provide optimal system performance and maintain control stability in NCSs. DTS adopts a decentralized schedule mechanism where each application can make its local schedule decision, enhancing the scalability of NCSs. Simulation results demonstrate the effectiveness of the proposed scheme by improving the network bandwidth and providing better system performance in NCS comparing with the existing time-triggered scheduling schemes.     

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。     

Asynchronous inter-network interference avoidance for wireless body area networks

This paper considers the internetwork interference problem in environments with multiple wireless body area networks (WBANs). We propose an asynchronous internetwork interference avoidance scheme (abbreviated as AIIA), which is based on the hybrid multiple access of carrier sense multiple access with collision avoidance (CSMA/CA) and time division multiple access (TDMA). In AIIA, the gateway device of each WBAN maintains a table, called an AIIA table, which includes the timing offset and TDMA transmission schedule information corresponding to the interfering WBANs. By referring to the table, the conflicting TDMA schedule can be checked and updated by itself, in asynchronous and distributed manners. Extensive simulations are conducted to demonstrate the feasibility and effectiveness of AIIA.     

基于TDMA方式WMN中一种链路调度机制研究

基于TDMA方式的无线网状网中,链路调度对网络性能起着重要作用.针对固定顺序的待调度链路集,提出求解最优调度周期的启发式算法;基于链路顺序对算法性能的影响,从全局优化的角度对全网链路进行排序,提出基于遗传算法的最优链路调度机制.仿真结果表明,该算法能快速收敛于全网链路的最小调度周期,具有比现有算法更高的传输效率和更低的实施复杂度.     

一种解决短距离无线接入冲突的方法

基于无线跳频理论和TDMA的思想，针对一类小数据量、子站随机访问的短距离无线通信业务，提出了一种解决短距离无线接入冲突的方法。通过一个具体的应用实例表明该方法能有效解决多个子站同时想接入主站时所发生的冲突。     

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。     

基于协作中继的多点广播码分多址信息系统设计

为了提高多群多点广播中继网络系统的性能,提出一种改进的协作中继多点广播码分多址(CDMA)系统设计。该方案利用协作中继辅助的分布式波束形成 实现单天线基站多播,获得了较好的空间分集增益。在该系统中,多个基站利用多个中继节点向多个目的地的各个小组传播消息;利用CDMA技术来减少中继节点以及目的地节点的多址干扰(MAI)障碍,同时每个中继节点作为线性预编码波束合成器,可以在合适的代码空间重塑基站信号;对线性波束形成矩阵进行优化,使得中继节点的功率最小化,从而满足QoS在信号干扰噪声比方面的要求。系统性能仿真对比实验的结果表明,提出的改进方案明显优于传统的正交复用方案(FDMA / TDMA)。     

On-demand chaotic neural network for broadcast scheduling problem

This paper presents a novel approach to optimizing network packet transfer scheme through introducing a new method for on-demand chaotic noise injection strategy for the Broadcast Scheduling Problem (BSP). Packet radio networks have many applications, while finding an optimized scheduling to transmit data is proven to be a NP-hard problem. The objective of the proposed method is to find an optimal time division multiple access (TDMA) frame, based on maximizing the channel utilization. The proposed method benefits from an on-demand noise injection policy, which injects noise based on the status of neuron and its neighborhoods. The method is superior to other Noise Chaotic Neural Networks (NCNN) that suffer from blind injection policy. The experimental result shows that, in most cases, the proposed on-demand noise injection algorithm finds the best solution with minimal average time delay and maximum channel utilization.     

面向工业无线网络的动态TDMA系统设计与实现

随着工业4.0的发展, 不同种类的新型工业应用被部署到工厂中, 这对现有工业无线技术提出了实时性和高速率的要求. 为了同时满足这两种需求, 本文在支持高速率的IEEE802.11的基础上, 提出了基于软件定义的动态时分多址(Time division multiple access, TDMA)机制无线接入系统. 首先, 为了提供时延有界的传输服务, 设计并实现了基于MAC (Medium access control)层的动态TDMA接入机制. 然后, 为了满足工业无线网络中的动态变化的带宽需求, 考虑设备数据量的动态变化, 在SDN (Software defined network)控制器上通过基于最小二乘法的线性回归算法预测设备时隙需求, 再将动态时隙分配问题转化为优化问题以最大化网络中所有设备动态时隙需求. 最后, 通过仿真对比TDMA时隙分配算法的性能, 并在实际网络环境中开展系统部署与测试. 结果表明, 相对于其他TDMA接入机制, 动态TDMA机制在保障时延有界的同时能有效提升传输性能.     

MASCARA中的调度算法—PRADOS

WAND（Wireless ATM Network Demonstrate）是欧洲ACTS（Advanced Communication Technologies and Services）支持的项目之一。在WAND中采用一种基于集线器式、自适应TDMA方式的MAC协议—MASCARA,它通过预约与竞争相结合的方法,为无线ATM（WATM）终端提供具有QoS保证的宽带无线接入。文章着重分析了MASCARA中基于时延的优先权调节调度（PRADOS）算法,并给出了几种不同情况下的算法性能仿真结果。     

An efficient cluster-based CDMA/TDMA scheme for wireless mobile ad-hoc networks: A learning automata approach

In this paper, we design a dynamic frame length CDMA/TDMA scheme for clustered wireless ad hoc networks with unknown traffic parameters. In this scheme, the collision-free intra-cluster communications are organized by the cluster-heads using a TDMA scheme, and a CDMA scheme is overlaid on the TDMA to organize the interference-free inter-cluster communications. Therefore, to design such a scheme, we encounter three important problems, namely cluster formation, code assignment, and slot assignment. In this paper, we propose three algorithms to solve the addressed problems based on learning automata. In our scheme, by the proposed clustering algorithm, the wireless hosts are grouped into non-overlapping clusters. Then, by the proposed code assignment algorithm (considering the concept of code spatial reuse), an interference-free code is assigned to each cluster. Finally, by the slot assignment algorithm, each cluster member is assigned a fraction of TDMA frame proportional to its traffic load. The simulation results show that the proposed CDMA/TDMA scheme outperforms the existing methods in terms of almost all metrics of interest, specifically, under bursty traffic conditions.     

Learning automata-based bus arbitration for shared-medium ATM switches

Although new high-bandwidth network technologies are being introduced and widely deployed, asynchronous transfer mode (ATM) is still considered one of the most important network technologies currently in use. A number of ATM switch architectures have been proposed in the literature. However, industry has shown that is better to use the well-known shared-medium technique in the design of these ATM switches. In this paper, four variations of a new distributed scheme are proposed for the arbitration of a shared bus of an ATM switch. These schemes are based on learning automata. By taking advantage of the bursty nature of ATM traffic, the new arbitration scheme demonstrates superb performance compared to the time division multiple access (TDMA) scheme.     

Enhanced MAC protocol to support multimedia traffic in cognitive wireless mesh networks

With the advanced physical layer techniques such as multiple-input and multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM), transmission real-time 2D/3D contents and applications becomes more and more necessary in wireless networks for the amazing growing in demand of customers. However, the low efficiency of medium access control (MAC) protocol degrades the performance of real-time traffic greatly in multihop, wireless and mobile environment. Focusing on supporting real-time multimedia traffic in cognitive wireless mesh networks (WMNs), an enhanced MAC protocol is proposed. And the contribution of this paper is twofold: (1) An efficient carrier sense multiple access with collision avoidance (CSMA/CA) compatible time division multiple access (TDMA)-like MAC protocol called T-MAC is proposed, which aims to improve the system performance by allocating more channel access time in centralized manner and decreasing overhead. (2) An optimal adaptive scheduling scheme is proposed to support real-time multimedia applications and guarantee QoS for different priority traffic, which aims to find the optimized schedule among all possible sequences of concurrent transmissions by minimizing the occupied resources. Detailed simulation results and comparison with IEEE 802.11e MAC scheme show that the proposed T-MAC can effectively improve quality of service (QoS) for multimedia traffic in terms of throughput, end-to-end delay and packet loss rate, which also manifests that T-MAC is an efficient multimedia applications transmission scheme for mobile terminals and MAPs in cognitive WMNs.     

Loss probability estimation and control for OFDM/TDMA wireless systems considering multifractal traffic characteristics

In this paper, we analyze the queueing performance in terms of loss rate of an OFDM (orthogonal frequency-division multiplexing)/TDMA (time division multiplexing access) based wireless system taking into account the multifractal behavior of the wireless traffic flows. To this end, first, we show evidences of multifractal characteristics on wireless traffic traces. These findings motivated us to propose a traffic policing and control scheme based on a multifractal envelope process in order to maintain the traffic flows well-behaved, i.e., in accordance to the desired QoS parameters. Furthermore, by assuming a multifractal traffic model, we derive a data loss probability equation for wireless traffic flows that was applied to the OFDM/TDMA based wireless system. Simulations and comparisons to other methods were carried out in order to verify the efficiency of the proposed traffic policing scheme as well as of the loss probability estimation approach.     

Link-level traffic scheduling for providing predictive QoS in wireless multimedia networks

A set of centralized burst-level cell scheduling schemes, namely, First Come First Served with Frame Reservation (FCFS-FR), FCFR-FR+, Earliest Deadline First with Frame Reservation (EDF-FR), EDF-FR+, and Multitraffic Dynamic Reservation (MTDR), are investigated for transmission of multiservice traffic over time division multiple access (TDMA)/time division duplex (TDD) channels in wireless ATM (WATM) networks. In these schemes, the number of time slots allocated to a virtual circuit (VC) during a frame-time is changed dynamically depending on the traffic type, system traffic load, the time of arrival (TOA)/time of expiry (TOE) value of the data burst and data burst length. The performances of these schemes are evaluated by computer simulation for realistic voice, video and data traffic models and their quality-of-service (QoS) requirements in a wireless mobile multimedia network. Both the error-free and the correlated fading channel conditions are considered. Simulation results show that the EDF-FR+ and MTDR schemes outperform the other schemes and can provide high channel utilization with predictive QoS guarantee in a multiservice traffic environment even in the presence of bursty channel errors. The EDF-FR+ scheme is found to provide better cell multiplexing performance than the MTDR scheme, Such a scheme would be easy to implement and would also result in a power conservative TDMA/TDD medium access control (MAC) protocol for broadband wireless access. Burst-level cell scheduling schemes such as EDF-FR+ can be easily adapted as MAC protocols in the emerging differentiated services (DS) enhanced wireless Internet protocol (IP) networks.     

改进的VANET分布式自适应时分多址分配机制

在车载自组织网（Vehicular Ad-hoc Network,VANET）环境下,针对多节点同时接入信道时的竞争冲突问题,将分布式时分多址（Time Division Multiple Access,TDMA）和空分多址（Space Division Multiple Access,SDMA）思想相结合,提出改进的分布式自适应时分多址分配机制（Modified Decentralized Adaptive TDMA Scheduling mechanism,MDATS）.MDATS协议的节点通过帧信息（Frame Information,FI）的交互,获取两跳范围内其他节点时隙使用情况,从而筛选出空闲时隙集.竞争区域将根据空闲时隙数在空间上均分成多个逻辑区段,节点则根据所处的逻辑区段与空闲时隙的对应关系确定竞争使用的时隙.该协议通过对空闲时隙在空间上的分散化,降低同时接入节点之间的竞争冲突.仿真结果表明,MDATS协议与其他类似MAC协议相比,能够达到更高的信道接入成功率、更低的接入时延性能以及更高的时隙利用率.