Medium Access Control for QoS Provisioning in Vehicle-to-Infrastructure Communication Networks

The emerging vehicular networks are targeted to provide efficient communications between mobile vehicles and fixed roadside units (RSU), and support mobile multimedia applications and safety services with diverse quality of service (QoS) requirements. In this paper, we propose a busy tone based medium access control (MAC) protocol with enhanced QoS provisioning for life critical safety services. By using busy tone signals for efficient channel preemption in both contention period (CP) and contention free period (CFP), emergency users can access the wireless channel with strict priority when they compete with multimedia users, and thus achieve the minimal access delay. Furthermore, through efficient transmission coordination on the busy tone channel, contention level can be effectively reduced, and the overall network resource utilization can be improved accordingly. We then develop an analytical model to quantify the medium access delay of emergency messages. Extensive simulations with Network Simulator (NS)-2 validate the analysis and demonstrate that the proposed MAC can guarantee reliable and timely emergency message dissemination in a vehicular network.     

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.     

用于VANET紧急消息传输的改进二元分割广播协议

摘要：针对车辆自组织网络（vehicular Ad Hoc network,VANET）中紧急消息的传输,提出一个改进的二元分割广播（MBPAB）协议。协议将通信范围迭代划分成小的区域,寻找离发送节点最远区域内的车辆,对紧急消息执行转发,通过减少转发跳数,提高消息传播速度。通过引入MAC（medium access control）子层的微型分布式帧间间隔（mini-DIFS）,赋予对紧急消息以更高的优先级接入通信信道。仿真结果表明,在VANET 中, MBPAB协议与现有的广播协议相比,在通信时延和消息传播速度方面有更好的性能表现。     

Enhancing secrecy rates in a wiretap channel

Reliable communication imposes an upper limit on the achievable rate, namely the Shannon capacity. Wyner's wiretap coding ensures a security constraint and reliability, but results in a decrease of achievable rate. To mitigate the loss in secrecy rate, we propose a coding scheme in which we use sufficiently old messages as key and prove that multiple messages are secure with respect to all the information possessed by the eavesdropper. We also show that we can achieve security in the strong sense. Next, we study a fading wiretap channel with full channel state information of the eavesdropper's channel and use our coding/decoding scheme to achieve a secrecy capacity close to the Shannon capacity of the main channel (in the ergodic sense). Finally, we study a case where the transmitter does not have instantaneous information of the channel state of the eavesdropper, but only its distribution.     

Using network coding to achieve the capacity of deterministic relay networks with relay messages

In this paper, we derive the capacity of the deterministic relay networks with relay messages. We consider a network that consists of five nodes, four of which can only communicate via the fifth one. However, the fifth node is not merely a relay as it may exchange private messages with the other network nodes. First, we develop an upper bound on the capacity region based on the notion of a single‐sided genie. In the course of the achievability proof, we also derive the deterministic capacity of a four‐user relay network (without private messages at the relay). The capacity achieving schemes use a combination of two network coding techniques: the simple ordering scheme and detour scheme. In the simple ordering scheme, we order the transmitted bits at each user such that the bi‐directional messages will be received at the same channel level at the relay, while the basic idea behind the detour scheme is that some parts of the message follow an indirect paths to their respective destinations. This paper, therefore, serves to show that user cooperation and network coding can enhance throughput, even when the users are not directly connected to each other. Finally, we make a conjecture about the capacity region of the general K‐node relay network with relay messages. Copyright © 2016 John Wiley & Sons, Ltd.     

Industrial IEEE 802.3 networks with short delivery time for urgentmessages

Two solutions are investigated for introducing priority mechanisms in the CSMA/CD (carrier-sense multiple access with collision detection) protocol defined in the IEEE 802.3 standard to provide short delivery times for urgent messages even when the overall traffic on the channel is heavy. Thus the CSMA/CD protocol, attractive because of its low cost, also becomes suitable for a class of industrial control applications. The proposed schemes can easily be implemented by using already-available chips and boards because they are based on the dynamic management of a transmission parameter, the slot time; this feature is already present in the standard IEEE 802.3, where it is set statically when the network is configured. The first configuration considered implements a message priority scheme, where the priority level for the station can be updated at each new message transmission, varying the slot time according to the message characteristics. The second configuration introduces a fixed-station-priority mechanism which allows each node in the network to be assigned to a specific priority class     

Broadcast-First Service Scheduling Scheme for Vehicle-Roadside Communication

In recent years, the research of vehicular ad-hoc networks (VANET) has become increasingly popular. More and more vehicles want their requests to be served from roadside units (RSU) in VANET, thus the service scheduling of RSU becomes an important task, especially when a large number of vehicles drive past the RSU and access data. Obviously, different kinds of request messages have different degrees of emergency, in other words, request messages have different priorities while scheduling. In order to provide a more effective and appropriate scheme, in this paper we study the scheduling of service algorithm in VANET, and proposed a novel broadcast-first service scheduling scheme. That scheme is on the basis of existing priority schemes, and takes channel bandwidth and processing capability of RSU into consideration so as to cope with the challenges in vehicle-roadside data access. Finally we conduct our experimental scenario, and simulation results show that our algorithm performs better than other existing algorithms by the comparison.     

A Collision Alleviation Scheme for IEEE 802.11p VANETs

IEEE 802.11p protocol, also known as Wireless Access for the Vehicular Environment provides dedicated short range communication for future Vehicular Ad Hoc Networks (VANETs). According to the IEEE 802.11p standard, the highest priority traffic transmission often suffers from the consecutive collisions in bursty arrival or congested scenarios because of the naive pre-assumption of a low level of congestion in the system, and thus results in emergent messages delayed. In this paper, we propose a simple, but yet well performing collision alleviation scheme to alleviate intensive collisions between highest priority access categories which usually used to schedule emergency message since safety is the most critical and promising issue in VANET. In addition to theoretical analysis, simulations are conducted to evaluate its performance. The simulation results show that the proposed scheme can not only increase the achievable channel throughput of the legacy protocol at most 15%, but also reduce the average packet access delay of the legacy protocol at least 5% and the packet collision probability at most 60% in congested VANET environments.     

AP-Initiated Reservations for Performance Enhancement in 802.11 MAC

In the infrastructure mode of the IEEE 802.11 Wireless Local Area Networks (WLANs), usually an Access Point (AP) requires more transmission opportunities than mobile stations, since the AP relays all the data traffic among mobile stations. However, the current MAC protocol gives AP the same opportunity with mobile stations for channel accessing, and it may introduce unfairness in the infrastructure mode of WLANs. In this paper, aiming at resolving the unfairness problem and enhancing the network performance, we propose an AP-initiated reservation scheme. Our scheme gives a high priority for AP’s channel accessing and allows AP to transmit multiple frames at once. We develop an analytical model to study the performance of proposed scheme, and also perform extensive simulations. Both the analytical and simulation results show that proposed scheme significantly enhances the performance of 802.11 MAC.     

Throughput analysis of the IEEE 802.4 priority scheme

The IEEE 802.4 token bus standard defines an optional priority scheme to handle multiple classes of data. It allocates the channel bandwidth among different priority classes of messages by a set of timers at each station. An analytical model for the priority scheme is presented. The model relates the throughput of each priority class of messages to the traffic intensities of different classes, the target rotation times, and the high-priority token holding time. The network is assumed to be symmetric with respect to its parameters and the traffic distribution among nodes. Simulation results are used to evaluate the accuracy of the model. The model provides means of evaluating the network throughput and can be used to determine the time values to meet the throughput requirements of different classes of traffic     

Multiple preemptive EDCA for emergency medium access control in distributed WLANs

The increasingly use of wireless local area networks (WLANs) in public safety and emergency network services demands for a strict quality of service (QoS) guarantee especially a large number of users report an emergency for immediate channel access. Unfortunately, the traditional IEEE 802.11e-based enhanced distributed channel access (EDCA) does not support a strict QoS guarantee for life saving emergency traffic under high loads. Previous studies have attempted to enhance the performance of EDCA called the Channel Preemtive EDCA (CP-EDCA) which is a promising idea to support emergency traffic in WLANs. However, CP-EDCA supports a single emergency traffic only (i.e. no emergency service differentiation) with high delays for increased traffic loads. To overcome this problem, we propose a class of EDCA protocol called Multiple Preemption EDCA (MP-EDCA) as a candidate to support multiple emergency traffics under high loads. Each MP-EDCA node can support up to four emergency traffics (life, health, property and environment) with different priorities in addition to support background (non-emergency) traffic. The proposed protocol privileged the high priority life-saving emergency traffic to preempt the services of low priority ones without much starvation in the network to maintain a strict QoS guarantee. The paper evaluates the performance of MP-EDCA through an extensive analysis of simulation outcome. The results obtained show that MP-EDCA outperforms CP-EDCA in achieving lower medium access control and emergency node delays.     

An urn occupancy approach for cognitive radio networks in DTVB white spaces

The paradigm of cognitive radio recently received considerable interest to address the so called ‘spectrum scarcity’ problem. In the USA, the Federal Communications Commission issued the regulatory for the use of cognitive radio in the TV white space spectrum. The primary objective is the design of cognitive devices able to combine the use of spectrum sensing and GEO-location information with the concept of the cognitive control channel to manage the cognitive devices. The recent standard ECMA-392 defines physical layer techniques and medium access control protocols to enable a cognitive network managed in a fully distributed fashion. In this work, we pursue the design of an efficient medium access control protocol for the cognitive control channel to flexibly and reliably exchange messages inside the cognitive radio network. In particular, we explore how the cognitive devices can raise their awareness of spectrum vacancies of spectrum vacancies by means of sensing when the distributed beaconing defined by ECMA-392 is used. Our main contributions are the following: (1) we propose a proprietary medium access control protocol based on the Standard ECMA-392; (2) we model the behavior of the cognitive radio network by means of an innovative urn model approach, (3) we investigate the access of the cognitive devices to the frequency channels with and without spoofing attacks and (4) we investigate the ability of the cognitive devices to identify frequency holes accounting for perfect and imperfect spectrum sensing, as well as we study the network throughput.     

A Power-Efficient Distributed TDMA Scheduling Algorithm with Distance-Measurement for Wireless Sensor Networks

This paper describes a power-efficient distributed TDMA slot scheduling algorithm which the slot allocation priority is controlled by distance measurement information in details. In our former proposed scheme, L-DRAND+, an extension of Lamport’s bakery algorithm for prioritized slot allocation based on the distance measurement information between nodes and a packet-based transmission power control had been applied. In this paper, we propose its enhanced scheme with a weighted rule control and state machines refinements of L-DRAND+, named L-DRAND++. This aims at the achievement of media access control methods which can construct a local wireless network practically by limiting the scope, and eliminate the redundant power consumption in the network. The proposed scheme can be shown as a possible replacement of DRAND algorithm for Z-MAC scheme in a distance-measurement-oriented manner. In addition, to evaluate the ordered node sequence determined by the algorithm, node sequence metric is proposed. By using the metric, we can evaluate protocol behaviors according to the environmental situation around the node.     

基于预警优先级的ZigBee传感网络MAC层退避算法

针对无线传感器网络中有预警信息的高优先级数据包需要尽快传输,且IEEE 802.15.4协议本身不支持任何优先级传输机制的情况,提出了一种基于预警优先级的非时隙CSMA/CA自适应调整阶梯退避算法,并建立了离散时间马尔可夫分析模型,比较分析了网络中不同优先级节点的信道接入概率、网络吞吐量和传输延时,仿真结果表明,本文改进的自适应调整阶梯退避机制对提高无线传感器网络中高优先级数据包的实时传输性能具有积极的作用。     

Optimal channel access for TCP performance improvement in cognitive radio networks

Cognitive radio (CR) is a promising technology to improve spectrum utilization. Most of previous work on CR networks concentrates on maximizing transmission rate in the physical layer. However, the end-to-end transmission control protocol (TCP) performance perceived by secondary users is also a very important factor in CR networks. In this paper, we propose a novel multi-channel access scheme in CR networks, where the channel access is based on the TCP throughput in the transport layer. Specifically, we formulate the channel access process in CR network as a restless bandit system. With this stochastic optimization formulation, the optimal channel access policy is indexable, meaning that the channels with highest indices should be selected to transmit TCP traffic. In addition, we exploit cross-layer design methodology to improve TCP throughput, where modulation and coding at the physical layer and frame size at the data-link layer are considered together with TCP throughput in the transport layer to improve TCP performance. Simulation results show the effectiveness of the proposed scheme.     

Novel Advanced Broadcast Scheme for Efficient Safety Message Collision Alleviation in Vehicular Networks

Safety message broadcasting may cause a broadcast storm in vehicular ad-hoc network without an effective feedback mechanism. In particular, with increasing number of vehicles, serious collisions and incurred long delays are not acceptable for emergency safety messages. In this paper, we proposed an advanced broadcast scheme by the functionality of distributed coordination function and multi-channel operation in dedicated short range communication to decrease collision probability and increase received ratio of safety messages. The proposed scheme can increases safety message transmission efficiency and reduce the latency by delicately designing a rebroadcast probability, choosing the channel and selecting the backoff timer. After broadcasting in the control channel, transmitters return to their original service channel. Then, the vehicles receiving the safety message should inform the others in the same service channel to switch to the control channel for the safety message. Afterwards, the vehicles broadcast the safety message once and go back to the original service channel. This method can inform the other vehicles in different channels to increase the broadcast penetration. The proposed scheme can work without global positioning system (GPS). However, GPS can adapt the rebroadcast probability on hot spots to enhance the efficiency of the proposed scheme. Through detailed simulations, the proposed scheme is shown to be more efficient compared to the existing ones.     

Dynamic control plane management for software‐defined networks

Software‐defined network (SDN) is an emerging network paradigm that allows flexible network management by providing programmability from a separated control plane. Because of the centralized management scheme that SDN adopts, intensive control plane overhead incurs as the scale of SDN increases. The control plane overhead is mainly caused by a massive amount of control messages generated during data plane monitoring and reactive flow instantiation. By far, very few works have addressed the overhead issue on reaction flow instantiation; therefore, we mainly focus on alleviating such overhead in this work. To achieve this goal, we propose a new control plane management (CPMan) method. CPMan aims to realize the following two objectives: first, reduce the number of control messages exchanged through the control channel and second, evenly distribute the control workload across multiple controllers to mitigate the potential performance bottleneck. To realize the former, we propose a lightweight feedback loop‐based control scheme, whereas for the latter, we propose a dynamic switch‐to‐controller (DSC) placement scheme. To show the feasibility of our proposal, we implemented a prototype of the two proposed schemes on top of a carrier‐grade SDN controller and validated its performance in an emulated network. We achieved approximately 57.13% overhead reduction with feedback loop‐based control scheme, while achieved approximately 98.68% balance ratio with DSC placement scheme. Copyright © 2016 John Wiley & Sons, Ltd.     

A distributed network coded control channel for multihop cognitive radio networks

Designing a solution for multihop cognitive radio networks poses several challenges such as the realization of the control channel, the detection of primary users, and the coordination of secondary users for dynamic spectrum access purposes. In this article we discuss these challenges and propose a solution that aims to meet most of them. The proposed solution is completely distributed, and does not need dedicated spectrum resources for control purposes, but rather leverages on a virtual control channel that is implemented by having users exchange control information whenever they meet in a particular channel, using network coding techniques for better dissemination performance. Due to these aspects, our proposal represents a significant improvement over existing dynamic spectrum access and multichannel MAC solutions. We discuss the effectiveness of our scheme in multihop cognitive ad hoc networks, where secondary users need to opportunistically access the spectrum at those locations and times at which it is not used by primary users. Finally, we report the results of an evaluation study assessing the performance of the proposed scheme with respect to different system and scenario parameters.     

应急通信网络中的异构网络互联问题及实现机制研究

应急通信网络要充分发挥功效,必须要有效解决各类网络之间的异构互联问题。本文给出了一种支持异构网络互联的应急通信网络结构,提出了无线自组网基于连接共享接入Internet的方案,详细说明了互联网关选择和允许控制机制,并分析了控制消息开销。     

Belief Propagation Decoding of Polar Codes Using Intelligent Post-Processing

Polar code is a channel coding method that has been proved to be able to reach Shannon capacity in the binary discrete memoryless channel. Because of the superior performance and low encoding and decoding complexity, polar code has attracted extensive attention in the industry and been chosen as the channel coding scheme for the control channel in the scenario of EMBB in 5G mobile communication. In this work, we propose an intelligent BP decoding algorithm of polar code based on smart post-processing. We employ the neural network to classify the output data of regular BP decoding into “good-bit” and “bad-bit” categories. We also design a strategy to search the bits, which are most probably incorrect from the “bad-bit” group for post-processing. Then, we can invert the “bad-bit” to correct the residual error in the Belief Propagation (BP) iterative process. Simulation results prove that the proposed algorithm can achieve at least 0.5dB error correction performance enhancement compared with the regular BP decoding with slight computation complexity and energy consumption increase.