Does the IEEE 802.11 MAC protocol work well in multihop wireless adhoc networks?

The IEEE 802.11 MAC protocol is the standard for wireless LANs; it is widely used in testbeds and simulations for wireless multihop ad hoc networks. However, this protocol was not designed for multihop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multihop connectivity is one of the most prominent features. In this article we focus on the following question: can the IEEE 802.11 MAC protocol function well in multihop networks? By presenting several serious problems encountered in an IEEE 802.11-based multihop network and revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multihop ad hoc networks. We thus doubt whether the WaveLAN-based system is workable as a mobile ad hoc testbed     

Extended sliding frame R-Aloha: Medium access control (MAC) protocol for mobile networks

Proliferation of mobile communication devices necessitates a reliable and efficient medium access control (MAC) protocol. In this paper, A MAC protocol, called extended sliding frame reservation Aloha (ESFRA), based on sliding frame R-Aloha (SFRA) is proposed for network access technique. ESFRA is particularly designed to solve the mobile hidden station (MHS) problem in a mobile ad hoc network (MANET) by including relative locations of transmitting stations in the packet frame information header. The MHS problem is unique in mobile networks and occurs if a mobile station enters in a collision free zone of any ongoing communication and disturbs this communication with its transmission. In addition to the MHS problem, ESFRA simultaneously solves hidden station, exposed station, and neighborhood capture problems typically observed in wireless networks. A Markov model of ESFRA is developed and provided here to estimate throughput, delay and collision probabilities of the proposed protocol. The Markov modeling is extended to the analysis of SFRA and IEEE 802.11 to compare these competing MAC protocols with ESFRA. The analysis shows that ESFRA decreases frame transmission delay, increases throughput, and reduces collision probabilities compared to IEEE 802.11 and SFRA. ESFRA improves the network throughput 28 percent compared to that of IEEE 802.11, and 33 percent compared to that of SFRA. The improved performance is obtained at the expense of the synchronization compared to IEEE 802.11, but there is virtually no extra cost compared to SFRA.     

Distributed protocols for ad hoc wireless LANs: a learning-automata-based approach

An ad hoc learning-automata-based protocol for wireless LANs, capable of operating efficiently under bursty traffic conditions, is introduced. According to the proposed protocol, the mobile station that is granted permission to transmit is selected by means of learning automata. At each station, the learning automaton takes into account the network feedback information in order to update the choice probability of each mobile station. The proposed protocol is compared via simulation to TDMA and IEEE 802.11 under bursty traffic conditions. Ad hoc learning-automata-based protocol (AHLAP) is shown to exhibit superior performance compared to TDMA in all cases. Compared to IEEE 802.11, the burstier the network traffic, the larger the performance increase of AHLAP. Furthermore, the implementation of AHLAP is more easier than that of IEEE 802.11.     

Towards providing optimal energy‐efficiency and throughput for IEEE 802.11 WLANs

IEEE 802.11 wireless network standard has become one of the most used wireless networking technologies for smart devices as it offers mobility support and low cost deployment. However, these devices deeply rely on the energy provided by their batteries, which results in limited running time. IEEE 802.11 network standard provides stations with carrier sense multiple access with collision avoidance for the medium access. Yet it results in stations to consume an important amount of power. Therefore, minimizing WiFi‐based energy consumption in smart devices has been received substantial attention in both academia and industry. Accordingly, this paper * proposes a novel beacon‐based energy‐efficient collision‐free medium access control protocol for any type of IEEE 802.11 stations, regardless of being stationary or mobile, or having different amount of traffic flow, transmission rates, or traffic types. The proposed scheme is valid for all types of low or wide bandwidth, single or multiuser multiple‐input multiple‐output WLAN channels, such as IEEE 802.11a\b\g\n\ac. In the proposed scheme, energy saving is achieved, enabling stations to transmit on the right time and maintaining stations in the doze state during a predetermined sleep_time interval after each successful frame transmission, by making use of modified control and management frames of the standard IEEE 802.11 protocol. The proposed scheme reduces the probability of collisions and may allow stations to enter the collision‐free state, regardless of the number of stations on the channel and their traffic types. Widespread simulations have been executed to validate the efficiency of the proposed method. The results demonstrate that the proposed method significantly increases overall throughput and reduces power consumption of stations over IEEE 802.11 WLANs.     

A Distributed Mechanism for Power Saving in IEEE 802.11 Wireless LANs

The finite battery power of mobile computers represents one of the greatest limitations to the utility of portable computers. Furthermore, portable computers often need to perform power consuming activities, such as transmitting and receiving data by means of a random-access, wireless channel. The amount of power consumed to transfer the data on the wireless channel is negatively affected by the channel congestion level, and significantly depends on the MAC protocol adopted. This paper illustrates the design and the performance evaluation of a new mechanism that, by controlling the accesses to the shared transmission channel of a wireless LAN, leads each station to an optimal Power Consumption level. Specifically, we considered the Standard IEEE 802.11 Distributed Coordination Function (DCF) access scheme for WLANs. For this protocol we analytically derived the optimal average Power Consumption levels required for a frame transmission. By exploiting these analytical results, we define a Power Save, Distributed Contention Control (PS-DCC) mechanism that can be adopted to enhance the performance of the Standard IEEE 802.11 DCF protocol from a power saving standpoint. The performance of an IEEE 802.11 network enhanced with the PS-DCC mechanism has been investigated by simulation. Results show that the enhanced protocol closely approximates the optimal power consumption level, and provides a channel utilization close to the theoretical upper bound for the IEEE 802.11 protocol capacity. In addition, even in low load situations, the enhanced protocol does not introduce additional overheads with respect to the standard protocol.     

Busy tone contention protocol: a new high‐throughput and energy‐efficient wireless local area network medium access control protocol using busy tone

Design of an efficient wireless medium access control (MAC) protocol is a challenging task due to the time‐varying characteristics of wireless communication channel and different delay requirements in diverse applications. To support variable number of active stations and varying network load conditions, random access MAC protocols are employed. Existing wireless local area network (WLAN) protocol (IEEE 802.11) is found to be inefficient at high data rates because of the overhead associated with the contention resolution mechanism employed. The new amendments of IEEE 802.11 that support multimedia traffic (IEEE 802.11e) are at the expense of reduced data traffic network efficiency. In this paper, we propose a random access MAC protocol called busy tone contention protocol (BTCP) that uses out‐of‐band signals for contention resolution in WLANs. A few variants of this protocol are also proposed to meet the challenges in WLAN environments and application requirements. The proposed BTCP isolate multimedia traffics from background data transmissions and gives high throughput irrespective of the number of contending stations in the network. As a result, in BTCP, admission control of multimedia flows becomes simple and well defined. Studies of the protocol, both analytically and through simulations under various network conditions, have shown to give better performance in comparison with the IEEE 802.11 distributed coordination function. Copyright © 2011 John Wiley & Sons, Ltd.     

IEEE 802.11 goodput analysis for mixed real-time and data traffic for home networks

Increasingly, wireless networks are being used to provide connection services for devices running applications with very different quality of service requirements. Although this issue has been addressed by the IEEE 802.11e standard, the fact is that most networks deployed in home/office environments nowadays use IEEE 802.11a/b/g standard devices. Unfortunately, administrators often do not set configuration parameters of network devices to maximize resources performance, thus providing poor quality of service. In this paper, two IEEE 802.11a/b/g analytical performance evaluation models for mixed traffic Ad Hoc and infrastructure WLANs are presented, assuming that some network devices are executing single applications, like VoIP, videoIP or network browsing. In our analysis, network devices are grouped according to the expected traffic pattern of the applications they are running. Then, global and individual group goodput are calculated assuming a congested network. Based upon the outcome of this analysis for different settings of the device configuration parameters, it is shown that the performance of a standard home/office IEEE 802.11 wireless network can be significantly improved by choosing appropriate values of these parameters.     

IEEE802.11s路由协议漏洞与攻击

IEEE802.11s是IEEE关于无线Mesh网络的规范。802.11s虽然沿用了IEEE802.11i的安全规范,但是对于路由协议的安全并没有做过多的定义,由此产生了一定的安全隐患。文章分析了IEEE802.11s标准(草案)中的路由协议的漏洞,并针对IEEE802.11s中使用的混合无线网状网协议(HybridWirelessMeshProtocol,HWMP)设计了两种攻击方式,从而破坏无线网状网络的可用性。通过在自行设计的路由器平台上实现无线攻击,并分析攻击对网络造成的影响来验证安全漏洞的存在性和可利用性。     

Performance evaluation of multihop ad hoc WLANs

Ongoing technological advances in portable devices, coupled with the need for continuous connectivity while mobile, have made ad hoc networks a compelling research and development topic, particularly in a challenging multimedia multihop scenario. The ability of IEEE 802.11's ad hoc mode of operation, as a dominating wireless local area network (WLAN) protocol, to serve multihop networks requires thorough investigation. In this article, through considering crucial real-life physical phenomena and avoiding as many confining assumptions as possible, system performance measures such as delay and packet failure rate are evaluated. As a result, the importance of adequate selection of the system parameters toward performance improvement is underscored. Moreover, the simulation results imply that by complementing through priority provisions, coordination, route reservation, clustering, and optimum channel coding considerations, the IEEE 802.11 medium access control (MAC) protocol can survive in a multihop scenario. The custom simulation environment developed features modularity, comprising traffic generator, mobility, wireless channel, and IEEE 802.11 protocol modules, and is capable of accommodating many more of the physical phenomena involved.     

Performance Evaluation of Wireless Controller Area Network (WCAN) Using Token Frame Scheme

In this paper, a proposed new wireless protocol so-called wireless controller area network is introduced. WCAN is an adaptation of its wired cousin, controller area network protocol. The proposed WCAN uses token frame scheme in providing channel access to nodes in the system. This token frame method follows the example used in wireless token ring protocol which is a wireless network protocol that reduces the number of retransmissions as a result of collisions. This scheme based on CAN protocol allows nodes to share a common broadcast channel by taking turns in transmitting upon receiving the token frame that circulates around the network for a specified amount of time. The token frame allows nodes to access the network one at a time, giving ‘fair’ chance to all nodes instead of competing against one another. This method provides high throughput in a bounded latency environment. The proposed WCAN protocol has been developed and simulated by means of QualNet simulator. The performances of this proposed protocol are evaluated from the perspective of throughput, end-to-end delay and packet delivery ratio, and are compared against the IEEE 802.11 protocol. Simulation results show that the proposed WCAN outperforms IEEE 802.11 based protocol by 62.5 % in terms of throughput with increasing network size. Also, it shows an improvement of 6 % compared to IEEE 802.11 standard at a higher data interval rate.     

基于平面路由的无线Mesh网切换技术

通过对无线Mesh网络区别于传统无线局域网的特性的分析,以及无线Mesh网的链路层切换机制、网络层切换机制的深入研究,提出了一种基于平面路由和移动IP的无线Mesh网络快速切换机制,并在该机制下给出了2种具体的实现方案。仿真分析表明,上述方案都充分利用了无线Mesh网络的特性,能够有效降低切换时延、减少数据包丢失率,基本可实现无线Mesh网络的无缝切换,并且能够保证与现有的IEEE802.11协议标准兼容。     

Secure and efficient scheme for fast initial link setup against key reinstallation attacks in IEEE 802.11ah networks

IEEE 802.11ah is a recently released IEEE standard to specify a wireless communication system with a long‐range, low‐power, and low data transmission rate over smart devices used in Internet of Things (IoT) systems. This new standard belongs to IEEE 802.11 wireless local area networks (WLANs) protocol family. It requires lightweight protocols to support the low‐power and low‐latency features of the IoT devices. On the other hand, an upcoming solution of fast initial link setup (FILS) specified by IEEE 802.11ai standard is a brand‐new approach aiming to establish fast and secure links among devices in WLANs to meet this new demand. It is natural and feasible to apply it to the 802.11ah networks to support massively deployed wireless nodes. However, security concerns on the link connection by the FILS scheme have not been fully eliminated, especially in the authentication process. It has been explored that a type of recently revealed malicious attack, key reinstallation attack (KRA) might be a threat to the FILS authentication. To prevent the success of the KRAs, in this paper, we proposed a secure and efficient FILS (SEF) protocol as the optional substitute of the FILS scheme. The SEF scheme is designed to eradicate potential threats from the KRAs without degrading the network performance.     

基于干扰图的无线自组织网络MAC协议

由于IEEE802．11MAC协议采用了简单的干扰模型，因此产生了隐藏终端和暴露终端这两个严重影响无线自组织网络性能的问题。文章提出了一种新的基于干扰图（Conflict Graph）的MAC协议——CG-MAC来提高无线自组织网络的吞吐量。通过仿真实验，该协议能够同时解决隐藏终端和暴露终端问题．很大程度地提高了网络性能。     

一种自组网功率控制算法及分析

无线自组网中的移动节点大多依靠电池提供能量,因此能量是影响无线自组网性能的一个很大的瓶颈,作为事实上的无线自组网媒体接入协议,802.11并没有动态调整传输功率的能力,大大限制了网络的生存时间。采用功率控制可以提高节点的功率使用效率,减少相邻节点间的干扰,改善网络的性能。在802.11基础上提出一种基于信噪比的动态传输功率控制算法。通过进行计算机仿真,与802.11协议相比,在保持吞吐量性能的前提下,大大减少了节点的功率消耗,提高了节点的能量利用率。     

IEEE 802.11 Wireless Local Area Networks

The draft IEEE 802.11 wireless local area network (WLAN) specification is approaching completion. In this article, the IEEE 802.11 protocol is explained, with particular emphasis on the medium access control sublayer. Performance results are provided for packetized data and a combination of packetized data and voice over the WLAN. Our performance investigation reveals that an IEEE 802.11 network may be able to carry traffic with time-bounded requirements using the point coordination function. However, our findings suggest that packetized voice traffic must be handled in conjunction with an echo canceler     

Optimal MAC packet size in networks without cut-through routing

This paper presents an analytical method of optimal breaking of a transmission control protocol (TCP)/Internet protocol (IP) message into medium access control (MAC) packets in networks without cut-through routing (such as networks compliant with the IEEE 802.11 wireless local area network standard). The method accounts for the transmission delay of acknowledgement frames, the sliding window flow control in TCP/IP protocol, error control via retransmissions, and heterogeneity of transport parameters (link-to-link and upstream-downstream) along a multihop network path. Mathematically, the problem consists in minimizing the TCP/IP message transaction time, a nonlinear function of the MAC packet size, in the presence of a set of linear restrictions. Throughput calculations illustrating this method are performed using IEEE 802.11 data.     

无线现场总线参数配置研究

为了使工业现场总线能够在更复杂的环境中得到应用,研究人员开始试图将无线通信技术融入到工业现场总线中去。以Profibus和IEEE802.11这两种具有代表性的通信标准,在介绍无线现场总线的基本概念和体系结构的基础上,建立时间模型,对令牌持有时间、退避时间元、转发时延等网络参数的配置进行优化。     

A ubiquitous mobile communication architecture for next-generation heterogeneous wireless systems

Rapid progress in research and development of wireless networking and communication technologies have created different types of wireless systems (e.g., Bluetooth, IEEE 802.11, UMTS, and satellite networks). These systems are envisioned to coordinate with each other to provide ubiquitous high-data-rate services to mobile users. In this article, the architecture for ubiquitous mobile communications (AMC) is introduced that integrates these heterogeneous wireless systems. AMC eliminates the need for direct service level agreements among service providers by using a third party, a network interoperating agent. Instead of deploying a totally new infrastructure, AMC extends the existing infrastructure to integrate heterogeneous wireless systems. It uses IP as the interconnection protocol. By using IP as the gluing protocol, transparency to the heterogeneities of the individual systems is achieved in AMC. Third-party-based authentication and billing algorithms are designed for AMC. New mobility management protocols are also developed to support seamless roaming between different wireless systems.     

A group-based channel assignment protocol for rate separation in IEEE 802.11-based multi-radio multi-rate ad hoc networks

Today’s IEEE 802.11 devices support multiple channels and data rates. Utilizing multiple channels and data rates can increase the performance of IEEE 802.11 networks. However, the multi-channel design to exploit available channels is one of the challenging issues. Moreover, performance anomaly occurs in IEEE 802.11 multi-rate networks when high-rate and low-rate links share a common channel, which degrades the overall network capacity significantly. In this paper, we introduce an extension of conflict graph, called rate conflict graph (RCG), to understand the performance anomaly problem in IEEE 802.11 multi-rate networks. Then, we propose a group-based channel assignment (GCA) protocol for IEEE 802.11-based multi-radio multi-rate single-hop ad hoc networks. In GCA, each node is equipped with multiple IEEE 802.11 interfaces, and links are subdivided into multiple groups, called component groups, by obeying the interface constraints. Then, GCA utilizes RCG and a heuristic algorithm to separate different data rate links via multiple channels so that the performance anomaly problem is addressed. Our extensive simulation results reveal that GCA achieves improved performance over existing channel assignment protocols designed to consider performance anomaly.     

Design of a lightweight authentication scheme for IEEE 802.11p vehicular networks

With the growing popularity of vehicle-based mobile devices, vehicular networks are becoming an essential part of wireless heterogeneous networks. Therefore, vehicular networks have been widely studied in recent years. Because of limited transmission range of wireless antennas, mobile vehicles should also switch their access points to maintain the connections as conventional mobile nodes. Considering the inherent characteristics of vehicular networks such as dynamic topology and high speed, the question of how to implement handoff protocol under real-time scenarios is very important. IEEE 802.11p protocol is designed for vehicular networks for the long distance transmission. To reduce handoff latency for 802.11p protocol, the authentication phase is waived during the handoff. However, security is also very important for wireless communications, and authentication can forbid access from malicious nodes and prevent wireless communications from potential attacks. Thus, in this paper, a lightweight authentication scheme is introduced to balance the security requirements and the handoff performance for 802.11p vehicular networks. In our scheme, the access points are divided into different trust groups, and the authentication process is completed in a group-based method. Once a vehicle is authenticated by an access point group, during the handoff within the same group, few extra authentication operations are needed. As a result, there is no extra overhead introduced to the authentication servers. Simulation results demonstrate that our authentication scheme only introduces small handoff latency and it is ideal for vehicular networks.