Multi-hop Wireless Mesh Networks Research Articles

CAC-OLSR: Extending OLSR to Provide Admission Control in Wireless Mesh Networks

This work presents an admission control mechanism for multi-hop wireless mesh networks based on the IEEE 802.11 standard and the OLSR routing protocol. This mechanism, called CAC-OLSR, aims at ensuring that traffic flows with quality of service (QoS) requirements, especially voice and video, are only admitted in the mesh network if it has available resources in order to provide flow requirements. In addition, QoS requirements of previously admitted traffic flows cannot be violated. The proposal was evaluated with NS-2 and Evalvid simulations.

Interference-aware QoS multicast routing for smart grid

In the smart grid Wide Area Control Systems (WACS), controller sends command & control message (C & C) messages to remote devices. The reliability and stability of WACS heavily depends on whether the remote devices react promptly. In other words, the end-to-end transmission delay of the C & C messages plays a significant role in ensuring the performance of WACS. Multihop wireless mesh networks are considered as suitable networking infrastructure for providing data communication in smart grid. Nevertheless, due to the interference nature of wireless networks, identifying paths with minimum end-to-end delay is not trivial. This paper deals with the issue of identifying the multicast tree with minimum end-to-end transmission delay for multicasting a C & C message from the controller to a set of remote devices. Our proposal particularly considers the specific communication requirement from smart grid. The contributions of this paper are: (1) we formulate the problem of calculating multicast tree delay as an integer linear programming; (2) we propose a delay estimation method; (3) we propose a new routing algorithm to identify a multicast tree with the minimum delay. Through extensive numerical experiments, we demonstrate that the proposed routing algorithm outperforms the existing multicast tree routing algorithm.

An incentive-based mechanism for fair bidirectional transmissions in wireless mesh networks

The previous studies almost focus on the fairness problem of the uplink traffic in wireless mesh networks. This paper studies the fairness problem for bidirectional traffic in multi-hop wireless mesh networks containing selfish nodes. Unlike the transmission of uplink traffic, where transit packets are dropped at intermediate Transit Access Points (TAPs), almost all downlink traffic is dropped at the gateway. To resolve the problem, this paper presents an incentive-based mechanism (IBM) under which the optimal strategies of selfish TAPs and the gateway are the corresponding actions that enforce fairness. Moreover, this paper formulates the target throughput of each TAP in the network, proves the feasibility of the target throughputs for the uplink and downlink traffic of each TAP, and uses IBM to ensure that all selfish TAPs and the gateway follow the fairness model truthfully. Finally, the simulation results show that the proposed mechanisms are accurate and truthful.

Harnessing the High Bandwidth of Multiradio Multichannel 802.11n Mesh Networks

There has been an increasing interest in deploying wireless mesh networks (WMNs) for communication and video surveillance purposes thanks to its low cost and ease of deployment. It is well known that a major drawback of WMN is multihop bandwidth degradation, which is primarily caused by contention and radio interference. The use of mesh nodes with multiple radios and channels has been regarded as a straightforward solution to the problem in the research community. However, we demonstrate in this paper through real-world experiments that such an approach cannot resolve the multihop TCP throughput degradation problem in IEEE 802.11n mesh networks. With extensive experimentation, we verify that the degradation is principally caused by the increase in TCP Round-Trip Time (RTT) when the number of hops increases. TCP throughput is fundamentally limited inversely by the RTT. We find that the multihop TCP throughput (up to five hops) when using 802.11n is no better than when using 802.11a, despite the much higher data rate 802.11n. We attempt to use multiple parallel TCP connections as a remedy to the problem, and it turns out that the wireless bandwidth can be fully utilized with a sufficient number of parallel streams. In general, our results give a key message that TCP tuning (e.g., setting the correct TCP buffers and use of parallel streams) is of paramount importance in high-bandwidth multihop wireless mesh networks that employ the latest wireless standards. These tuning techniques have to be implemented into commercial products to fully leverage the ever advancing wireless technologies to support the growing demand of multihop communications in wireless mesh networks.

Designing Interference based Routing Metric In Wireless Mesh Network and Comparison According to Various Tunable Parameters

Achieving good performance in wireless mesh network (WMN), implementation of routing metrics is very important. Multiple channels among the multiple radio improve the capacity of the network. Interference based routing metric such as Weighted Cumulative Expected Transmission Time (WCETT), Weighted Cumulative Consecutive Expected Transmission Time (WCCETT), are being proposed in multi-channel multi-hop wireless mesh networks. In this paper we proposed a new interference based routing metric called Modified Weighted Cumulative Consecutive Expected Transmission Time (ModWCCETT) with respect to the selection of less interference path with more channel availability in wireless mesh network. The theoretic analysis and calculations verify the better performance with respect to the other routing metrics.

AN ENHANCEMENT OF RTS/CTS CONTROL HANDSHAKE IN CSMA/CA BASED MAC PROTOCOL FOR AN EFFICIENT PACKET DELIVERY OVER MULTIHOP WIRELESS MESH NETWORK (WMN)

The Carrier Sense Multiple Access with Collision Av oidance (CSMA/CA) based Medium Access Control (MAC) protocol uses a short request-to-send (RTS) and clear-to-send (CTS) contr ol packets prior of actual data packet transmission . The function of the CSMA/CA based MAC protocol in wireless communication is to facilitate wireless nodes (i.e. laptop, PC, smart p hones and etc) to access a wireless medium efficiently. Besides, it is also efficiently manage the wireless medium when more wire less nodes involving in transmission activity in the network. This protocol allows all wireless nodes in the network to commun icate between each other without collision. Since collisions may only occurr ed on the RTS control packets thus it can reduce th e actual data collision on the medium. The RTS/CTS control handshake provides bett er performance and reduce the duration of collision especially when long data packets are transmitted over wireless medium. Howev er, even though the CSMA/CA based MAC protocol work ing effectively and provides better throughput performance over single hop communication but it performance degrade signif icantly when directly applied in multihop Wireless Mesh Network (WMN). Th e reason behind this poor performance is due to the inefficient packet delivery of CSMA/CA based MAC protocol in multihop network. The exchange of RTS and CTS signaling that required at each hop throughout the multihop network eventually will cause the larg e overheads and subsequently degrade network throug hput. Therefore, in this paper, an enhancement of RTS/CTS handshake has been proposed in order reduces the signaling overheads and ultimately allows a smooth packet delivery in the multihop network with out any collision. In this work, the multihop netw ork performances are evaluated analytically in terms of throughput and overhead. I t is proven that the new method of RTS/CTS handshak e provides significant improvement in throughput and overhead.

An Adaptive Channel Scheduling Design for Multi-Hop Handoff Delay Reduction in Internet-Based Wireless Mesh Networks

Seamless handoff support is an essential issue to ensure continuous communications in multi-hop wireless mesh networks (WMNs). Due to the multi-hop transmission of network-layer handoff signaling packets, the handoff performance in WMNs can be largely degraded by the long queueing delay and medium access delay at each mesh router, especially when the backbone traffic volume is high. However, this issue is ignored in existing handoff solutions and multi-channel allocation schemes. In this paper, we address the seamless handoff support from a different perspective and propose a novel channel allocation design in hierarchical WMNs to reduce the queueing delay and medium access delay of handoff signaling packets over multi-hop wireless links and to improve the average channel utilization simultaneously. Both analytical and OPNET simulation results show that the performance of the average channel utilization and total handoff delay can be improved significantly using our proposed channel allocation scheme under various scenarios, as compared to other existing channel allocation and handoff solutions in multi-hop WMNs.

A Simulation-Based Performance Analysis of a Cluster-based Routing Scheme for Wireless Mesh Networks

The cluster-based routing protocol (CBRP) is a grouping mechanism that supports unicast and multicast path discovery for low congestion and packet loss in routing mechanisms for multi-hop wireless mesh networks. No simulation analyses or comparisons with other routing protocols have been reported. In this paper, we have evaluated the performance of the CBRP and compared it to AODV and OLSR through software simulations. The scheme indicates several better performance levels in terms of the channel capacity, path discovery, packet delivery ratio, and end-to-end delay, at the sacrifice of routing overhead degradation.

Fair packet scheduling in Wireless Mesh Networks

In this paper we study the interactions of TCP and IEEE 802.11 MAC in Wireless Mesh Networks (WMNs). We use a Markov chain to capture the behavior of TCP sessions, particularly the impact on network throughput due to the effect of queue utilization and packet relaying. A closed form solution is derived to numerically determine the throughput. Based on the developed model, we propose a distributed MAC protocol called Timestamp-ordered MAC (TMAC), aiming to alleviate the unfairness problem in WMNs. TMAC extends CSMA/CA by scheduling data packets based on their age. Prior to transmitting a data packet, a transmitter broadcasts a request control message appended with a timestamp to a selected list of neighbors. It can proceed with the transmission only if it receives a sufficient number of grant control messages from these neighbors. A grant message indicates that the associated data packet has the lowest timestamp of all the packets pending transmission at the local transmit queue. We demonstrate that a loose ordering of timestamps among neighboring nodes is sufficient for enforcing local fairness, subsequently leading to flow rate fairness in a multi-hop WMN. We show that TMAC can be implemented using the control frames in IEEE 802.11, and thus can be easily integrated in existing 802.11-based WMNs. Our simulation results show that TMAC achieves excellent resource allocation fairness while maintaining over 90% of maximum link capacity across a large number of topologies.

Power and bandwidth efficiency of wireless mesh networks

As a prevalent network topology, mesh, has been actively researched and developed as a key solution to improve the performance and services of wireless communications. In this study, the authors carry out a comprehensive analysis of the bandwidth efficiency (BE) in b/s/Hz and power efficiency (PE) in b/s/Hz/W of carrier sense multiple access with collision avoidance, the basic medium access control protocol for wireless mesh networks (WMNs). Analysis results show that the suboptimal, not the maximal, power and BE can be achieved simultaneously under the same conditions, for example, the number of competing nodes and contention windows. Hence, the authors present a heuristic bandwidth-PE tradeoff design. Simulation results show that the authors proposed protocol works well in both single-hop and multi-hop WMNs.

Effects of physical channel separation on application flows in a multi-radio multi-hop wireless mesh network: An experimental study on BilMesh testbed

In this paper, we introduce BilMesh, an indoor 802.11b/g mesh networking testbed we established, and we report about our performance experiments conducted on multi-hop topologies with single-radio and multi-radio relay nodes. We investigate and report the effects of using multi-radio, multi-channel relay nodes in the mesh networking infrastructure in terms of network and application layer performance metrics. We also study the effects of physical channel separation on achievable end-to-end goodput perceived by the applications in the multi-radio case by varying the channel separation between the radio interfaces of a multi-radio relay node. We have observed that the difference between TCP and UDP goodput performances together with the delay and jitter performance depends on the hop count. We also observed that assigning overlapping channels with a central frequency separation of 5–15MHz may render the CSMA mechanism used in 802.11 MAC ineffective and hence reduce the overall network performance. Finally, we provide some suggestions that can be considered while designing related protocols and algorithms to deal with the observed facts.

The Convergence Scheme on Network Utility Maximization in Wireless Multicast Networks

With the ever-increasing wireless data application recently, considerable efforts have been focused on the designof distributed explicit rate scheme based on Network Utility Maximization (NUM) or wireless multi-hop meshnetworks. This paper describes a novel wireless multi-hop multicast flow control scheme for wireless meshnetworks via 802.11, which is based on the distributed self-turning Optimal Proportional plus Second-orderDifferential (OPSD) controller. The control scheme, which is located at the sources in the wireless multicastnetworks, can ensure short convergence time by regulating the transmission rate. We further analyze thetheoretical aspects of the proposed algorithm. Simulation results demonstrate the efficiency of the proposedscheme in terms of fast response time, low packet loss and error ration.

A Cross-Layer Design Scheme between Spectrum Decision and Routing in Cognitive Wireless Mesh Networks

Spectrum sharing technologies can achieve the maximum usage of spectrum resources flexibly and high-efficiently, which relieves the current spectrum crunch situation availably. In a multi-hop cognitive wireless mesh network scenario coexisting with a TDMA/FDMA cellular network, an effective scheme of cross-layer design between link-layer spectrum decision and network-layer routing is proposed, on the basis of the combination of spectrum underlay and spectrum overlay. Simulation results verify that the scheme outperforms distinctly the shortest path based random spectrum decision algorithm on network end-to-end performance.

Energy and Throughput Optimization of Wireless Mesh Networks With Continuous Power Control

Providing high data rates with minimum energy consumption is a crucial challenge for next generation wireless networks. There are few papers in the literature which combine these two issues. This paper focuses on multi-hop wireless mesh networks using a MAC layer based on Spatial Time Division Multiple Access (S-TDMA). We develop an optimization framework based on linear programming to study the relationship between throughput and energy consumption. Our contributions are two-fold. First, we formulate and solve, using column generation, a new MILP to compute offline energy-throughput tradeoff curve. We use a physical interference model where the nodes can perform continuous power control and can use a discrete set of data rates. Second, we highlight network engineering insights. We show, via numerical results, that power control and multi-rate functionalities allow optimal throughput to be reached, with lower energy consumption, using a mix of single hop and multi-hop routes.

Implementation of ARS-STR in STR for Effective Energy Transmission

Wireless mesh networks (WMNs) have emerged as a key technology for next generation wireless networking. Because of their advantages over other wireless networks, WMNs are undergoing rapid progress and inspiring numerous applications. In multi-hop wireless mesh networks (WMNs) experience frequent link failures caused by channel interference, dynamic obstacles and/or applications bandwidth demands. These failures cause severe performance degradation in WMNs or require expensive, manual network management for their real-time recovery. This paper presents an Autonomous network Reconfiguration System (ARS-STR) that enables a multi-radio WMN to autonomously recover from local link failures to preserve network performance. ARS-STR also improves channel efficiency.

Efficient Beacon Collision Detection/Avoidance Mechanism in WLAN-Based Mesh Networks

Every node in wireless multi-hop mesh networks periodically transmits its own beacon and then monitors the existence or activity of other nodes by checking their beacons. So, the loss of beacon message in wireless multi-hop mesh networks causes the inefficient network overhead. This paper proposed a dynamic beacon collision detection and avoidance (BCDA) mechanism that can actively adapt to beacon collision status due to node movement. Each node checks the collision status by comparing the received beacon timing information from neighboring nodes with that of its own. It is shown from the performance evaluations that the proposed BCDA mechanism provides the decrease of beacon collision ratio and the throughput enhancement.

Selective opportunistic routing based on QoS in wireless mesh network

Multi-hop wireless mesh networks are becoming a new attractive communication paradigm. In this paper, a new metric for selecting next hop, selective opportunistic routing based on quality of services (SOR-QoS) is proposed. It takes a number of criteria under consideration in order to minimise the expected number of transmissions and the overhead which is occurring in most opportunistic routing protocols. Simulation results show that the proposed SOR-QoS metric achieves higher improvement in the performance over the conventional forwarder list metrics in all network situations.

Convergence rate control for distributed multi-hop wireless mesh networks

Control message delay is a major factor affecting distributed network utility maximization (NUM) in practical wireless mesh networks, and the inherent delay of the control response leads to severe oscillations and slow convergence. However, existing NUM techniques either fail to pay attention to the convergence rate or achieve suboptimal results. This paper proposes a novel technique to solve the reverse impact of inherent control delay in the distributed NUM of wireless mesh networks with noisy feedback by overcoming the slow convergence induced by control delay in conjunction with feedback noise. A self-tuning algorithm reduces the number of required iterations for convergence while also providing an optimum value in distributed networks, and substantive simulations prove this improved convergence performance within a distributed multi-hop wireless mesh network. A theoretical explanation built from the viewpoint of control theory is also put forward to describe the model.

A Survey on Bandwidth Guaranteed Routing Techniques in Wireless Mesh Networks

A Wireless Mesh Network is defined as an infrastructure network working with in as ad hoc mode.In a multi-hop wireless mesh network, it is always preferable to choose a path with higher throughput between a pair of source /destination nodes to fully exploit the network capacity. Since Wireless Mesh Networks have emerged as a practical solution for the wireless extension of the broadband internet, finding high throughput path is important. This paper surveys the different routing approaches for wireless mesh network that using bandwidth as routing metric. It discusses the problem statement, approach and the result obtaining on these methods.

Minimizing Interference in Wireless Mesh Networks Based Telemedicine System

Problem statement: It has been always a challenging task for the researchers to incorporate information technology advancements in the medical profession. In order to guarantee a reliable network infrastructure that supports the employment of wireless technology and mobile devices, a hybrid infrastructure that integrates wireless networks with the traditional wired Local Area Networks (LANs) is needed. The wired network will provide the stability to the network, improve the overall performance of the hybrid network and provide an alternative to the mobile routes, hence increasing the degree of redundancy and reliability. In recent years, Wireless Mesh Networks (WMN) have become more popular than ever. WMN has advantage of robust fault tolerance. Even if some of the mesh nodes are incapable, there exist many other alternative nodes to serve relay. In addition, multi-hop of WMN can not only spread coverage but also save both cabling cost and human resource. Health care can drastically benefit by incorporating technological advancements, particularly wireless mesh technology. In this study we have presented a telemedicine system for rural and urban scenario based on WMN so that the medical community gets benefited by state of art broadband connectivity. Also in this study we have addressed a critical issue of performance degradation in WMN due to interference and varying load. Approach: For this we have proposed a routing protocol AODV LBIARM. We have incorporated our routing metric Load Balancing Interference Aware Routing Metric (LBIARM) in AODV protocol to minimize the interference and cater for varying traffic load in multi hop WMN based telemedicine system, thereby maximizing network throughput. Results and Conclusion: This protocol is evaluated by simulating in Opnet Modeler 16.1 PL1. We have found that our proposed protocol performs better than AODV WCETT and AODV HOP-COUNT.