Multi-hop Mesh Networks Research Articles

Network Estimation and Packet Delivery Prediction for Control over Wireless Mesh Networks

AbstractMuch of the current theory of networked control systems uses simple point-to-point communication models as an abstraction of the underlying network. As a result, the controller has very limited information on the network conditions and performs suboptimally. This work models the underlying wireless multihop mesh network as a graph of links with transmission success probabilities, and uses a recursive Bayesian estimator to provide packet delivery predictions to the controller. The predictions are a joint probability distribution on future packet delivery sequences, and thus capture correlations between successive packet deliveries. We look at finite horizon LQG control over a lossy actuation channel and a perfect sensing channel, both without delay, to study how the controller can compensate for predicted network outages.

User density sensitive P2P streaming in wireless mesh networks

Link rate allocation is very important for supporting high video playback rate in Peer-to-Peer video streaming. Although many studies can be found on resource allocation in P2P streaming in wired networks, very few studies have studied the problem in wireless networks, especially in Wireless multi-hop Mesh Networks (WMNs), which is still challenging. To maximize the users’ satisfaction of P2P streaming in WMNs, this paper focuses on link rate allocation problem and proposes a fully distributed algorithm to efficiently utilize the upload and download bandwidth of wireless mesh nodes. We first build an efficient P2P streaming system based on the experimental results from real deployment of our wireless mesh testbed. Then we design an efficient distributed algorithm based on the solution to a linear optimization model, which optimizes towards a user-density-related objective to decide the best streaming rates among peers. Our scheme is resilient to network dynamics that is characteristic in wireless multi-hop peer-to-peer networks. The simulation experiments demonstrate the significant performance enhancement by using the proposed rate allocation algorithm in WMNs.

LokVaani

In this work, we consider the goal of enabling effective voice communication in a TDMA, multi-hop mesh network, using low cost and low power platforms. We consider two primary usage scenarios: (1) enabling a local voice communication within a village-like setting, in developing regions (2) supporting an on-site local communication among a team of users e.g. during emergency response systems. While there is plentiful literature on the use of TDMA for multi-hop wireless mesh networks, a practical multi-hop TDMA system remains elusive. Our contributions in this regard are three-fold. (1) We demonstrate the working of an 802.15.4-based low-cost, low-power, local communication system (referred as Lo3) using custom made handsets and off-the-shelf platforms. (2) We show the practicability of LiT: a full-fledged TDMA-based multi-hop, multi-channel MAC protocol for real-time applications; especially on resource constrained platforms, (3) We present implementation-based evaluations results of LiT and show that our protocol achieves practical synchronization, and robust operation in the face of wireless packet errors. As the part of the demo, we showcase LokVaani: an interactive voice application for local communication with the help of Lo3 prototype.

MARS: Link-layer rate selection for multicast transmissions in wireless mesh networks

IEEE 802.11 devices dynamically choose among different modulation schemes and bit-rates for frame transmissions. This rate adaptation, however, is restricted only to unicast frames. Multicast (and broadcast) frames are constrained to use a fixed low bit-rate modulation, resulting in low throughput for multicast streams. Availability of high bandwidth and efficient use of the medium is crucial to support multimedia multicast streaming applications such as IPTV, especially in multihop mesh networks. To address this problem, we propose a rate adaptation algorithm for multicast transmissions in these networks. The proposed algorithm, MARS, is distributed in nature, and relies on local network measurements to select a transmission bit-rate for a given multicast group. The algorithm also facilitates the joint use of bit-rate selection and link-layer mechanisms such as acknowledgements and retransmissions to improve reliability of high throughput multicast streams. Based on implementation and evaluation on a testbed, the algorithm provides up to 600% gain in throughput compared to traditional 802.11 networks in some scenarios. Additionally, the algorithm can support multicast streams while consuming a small fraction (20%) of the resources compared to the basic 802.11 operation.

Improvement of Channel Assignment Scheme for WiMax Mesh Networks

The IEEE 802.16 standard, also known as Worldwide Interoperability for Microwave Access (WiMax), provides a mechanism for deploying high-speed wireless mesh network in metropolitan areas, and Quality of Service (QoS) is thus very important for WiMax networks. While being scheduled at the same time, the multiple links may interfere with one another that makes it challenging to provide QoS in multi-hop WiMax mesh networks. In this paper, we propose the LMDFS (Layered Maximum Degree First Select) algorithm for channel assignment in multi-channel single-transceiver WiMax mesh network. The goal is to eliminate the interference, to allow multiple non-interfering links to be scheduled at the same time and to increase the throughput of traffic flows. The simulation results show that this proposed algorithm greatly reduces the length of scheduling and improves the throughput and the average delay from network nodes to the BS in insufficient channels.

Recent Advances in Wireless Communications and Networking

The annual International Conference on Communications and Networking in China (CHINACOM) aims to provide a forum that brings together Chinese and international researchers and practitioners to showcase recent advances in communications networking research. CHINACOM 2008 is the third edition of this event, which was successfully held in Hangzhou, China, in August 2008. This special issue includes a collection of six outstanding research papers selected from CHINACOM 2008, which is a result of several stages of filtration and selection. First, out of the 822 submissions from 36 countries/regions in 5 continents, among which over 500 submissions were from mainland China, less than 270 papers, including some invited papers, were accepted for presentation, representing an acceptance rate of about 33%. Among the 270 papers, 15 papers have been invited to extend and enhance their work for further consideration for publication in this special issue and six of them have finally been included in the special issue. We would like to use this opportunity to appreciate all the reviewers who volunteered their time and professional expertise to help us reach the selection decisions. The papers included in this special issue cover a diversity of topics in wireless communications and networking. In the first paper, “BTAC: A Busy Tone Based Cooperative MAC Protocol for Wireless Local Area Networks”, Sayed et al. proposed and analyzed a busy tone based cooperative medium access control (MAC) protocol, called BTAC, for multi-rate wireless local area networks (WLANs) based on the concept of cooperative communications. The analytical and simulation results show that the BTAC protocol is simple, robust, and fully compatible with the IEEE 802.11b standard, and can achieve better throughput and delay performance than the standard distributed coordination function (DCF) protocol and the recently proposed CoopMAC protocol. In the second paper, “Achieving End-to-end Fairness in 802.11e Based Wireless Multi-Hop Mesh Networks without Coordination,” Li et al. studied the fairness issue in using 802.11 at the MAC layer and proposed the use of 802.11e’s TXOP mechanism to restore/perform fair resource allocation. The proposed TXOP based mechanism is implementable on standard hardware in a simple and fully decentralized way without a need for message passing. J. Zheng (*) National Mobile Communications Research Laboratory, Southeast University, Nanjing, Jiangsu, China e-mail: junzheng@seu.edu.cn

An effective scheduling scheme for multi-hop multicast in wireless mesh networks

With the utilization of concurrent transmission strategy, a throughput-enhanced scheduling scheme is devised for multicast service in wireless multi-hop mesh networks. Since the performance of a multicast mechanism is constrained in a wireless setting due to the interference among local wireless transmissions, the interference relationships are first characterized by introducing a graph transformation method. Based on the graph transformation, the multicast scheduling problem is converted to the graph coloring problem, and then a capacity greedy algorithm is designed to provide concurrent transmission scheduling so that the demanded multicast transmission rate can be achieved. Moreover, the necessary and sufficient conditions of multicast schedulable feasibility are derived. Through corresponding simulations, it is shown that the proposed strategy can enhance the throughput of wireless multi-hop multicast systems significantly.

Fine-Granularity Transmission Distortion Modeling for Video Packet Scheduling Over Mesh Networks

Packet scheduling is a critical component in multi-session video streaming over mesh networks. Different video packets have different levels of contribution to the overall video presentation quality at the receiver side. In this work, we develop a fine-granularity transmission distortion model for the encoder to predict the quality degradation of decoded videos caused by lost video packets. Based on this packet-level transmission distortion model, we propose a content-and-deadline-aware scheduling (CDAS) scheme for multi-session video streaming over multi-hop mesh networks, where content priority, queuing delays, and dynamic network transmission conditions are jointly considered for each video packet. Our extensive experimental results demonstrate that the proposed transmission distortion model and the CDAS scheme significantly improve the performance of multi-session video streaming over mesh networks.

Achieving End-to-end Fairness in 802.11e Based Wireless Multi-Hop Mesh Networks Without Coordination

To mitigate the damaging impacts caused by interference and hidden terminals, it has been proposed to use orthogonal channels in wireless multi-hop mesh networks. We demonstrate however that even if these issues are completely eliminated with perfectly assigned channels, gross unfairness can still exist amongst competing flows which traverse multiple hops. We propose the use of 802.11e's TXOP mechanism to restore/enforce fairness. The proposed scheme is simple, implementable using off-the-shelf devices and fully decentralised (requires no message passing).

Many-to-One Throughput Capacity of IEEE 802.11 Multihop Wireless Networks

This paper investigates the many-to-one throughput capacity (and by symmetry, one-to-many throughput capacity) of IEEE 802.11 multihop networks, in which many sources send data to a sink. An example of a practical scenario is that of a multihop mesh network connecting source and relay nodes to an Internet gateway. In the trivial case where all source nodes are just one hop from the sink, the system throughput can approach Ls, where Ls is the throughput capacity of an isolated link consisting of just one transmitter and one receiver. In the nontrivial case where some source nodes are more than one hop away, one can still achieve a system throughput of Ls by sacrificing and starving the non-one-hop source nodes-however, this degenerates to an unacceptable trivial solution. We could approach the problem by the following partitioning: preallocate some link capacity aLs (0 les a les 1) at the sink to the one-hop source nodes and then determine the throughput for the source nodes that are two or more hops away based on the remaining capacity L = (1 - a)Ls. The throughput of the one-hop nodes will be around aLs. This paper investigates the extent to which the remaining capacity L can be used efficiently by the source traffic that is two or more hops away. We find that for such source traffic, a throughput of L is not achievable under 802.11. We introduce the notion of networks,rdquo a general class of regularly structured networks that allow us to investigate the system throughput by varying the distances between nodes and other operating parameters. When all links have equal length, we show that 2L/3 is the upper bound for general networks, including random topologies and canonical networks. When the links are allowed to have different lengths, we show that the throughput capacity of canonical networks has an analytical upper bound of 3L/4. The tightness of the bound is confirmed by simulations of 802.11 canonical networks, in which we obtain simulated throughputs of 0.74L when the source nodes are two hops away and 0.69L when the source nodes are many hops away. We conjecture that 3L/4 is also the upper bound for general networks. Our simulations show that 802.11 networks with random topologies operated with AODV routing typically achieve throughputs far below 3L/4. Fortunately, by properly selecting routes near the gateway (or by properly positioning the relay nodes leading to the gateway) to fashion after the structure of canonical networks, the throughput can be improved by more than 150 percent: indeed, in a dense network, deactivating some of the relay nodes near the sink can lead to a higher throughput.

Multi-hop mesh networking for UWB WPANs with QoS support

Currently there are two competing proposals for Ultra-WideBand (UWB): one is DS-UWB based on IEEE 802.15.3 MAC and the other is Multi-Band OFDM Alliance (MBOA). Because of the short-range characteristics of high-speed UWB networks (around 10 m), it is highly desirable to have a multi-hop, range extension technology for future wireless personal area networks. Moreover, QoS is essential to support real-time applications over multi-hop paths in UWB networks. This paper first proposes a mesh network architecture and a simple, low-cost method for establishing communications across multiple piconets via multi-hop connections in 802.15.3 networks. It can be used to extend network coverage through connecting piconets on multiple channels. We then describe a simple, measurement-based admission control scheme for contention access in MBOA UWB networks, which allows high throughputs and low delays for QoS traffic by limiting the traffic load in the network. The admission control decision is based on both on-line measurement and a well-known analytical model of contention-based channel access.

Bidirectional Packet Aggregation and Coding for Efficient VoIP Transmission in Wireless Multi-Hop Networks

This paper proposes bidirectional packet aggregation and coding (BiPAC), a packet mixing technique which jointly applies packet aggregation and network coding in order to increase the number of supportable VoIP sessions in wireless multi-hop mesh networks. BiPAC applies network coding for aggregated VoIP packets by exploiting bidirectional nature of VoIP sessions, and largely reduces the required protocol overhead for transmitting short VoIP packets. We design BiPAC and related protocols so that the operations of aggregation and coding are well-integrated while satisfying the required quality of service by VoIP transmission, such as delay and packet loss rate. Our computer simulation results show that BiPAC can increase the number of supportable VoIP sessions maximum by around 87% as compared with the case when the packet aggregation alone is used, and 600% in comparison to the transmission without aggregation/coding. We also implement BiPAC in a wireless testbed, and run experiments in an actual indoor environment. Our experimental results show that BiPAC is a practical and efficient forwarding method, which can be implemented into the current mesh hardware and network stack.

DTSMA: Distributed time-spread multiple access for wireless mesh networks with IEEE 802.16d MAC protocol

This paper studies the use of IEEE 802.16d mesh MAC protocol for multi-hop networking in an indoor domestic environment. The mesh network is expected to support time-sensitive audio–video applications with stringent QoS requirement. In the literature, time-spread multiple access (TSMA) is a promising technology to provide a minimum throughput guarantee in a multi-hop mesh network with dynamic topology. However, existing TSMA schemes require the number of nodes in the entire network and their global maximum node degree, be known a priori to a central controller. The requirement is not practical. In view of this problem, this paper proposes a distributed time-spread multiple access (DTSMA) scheme. The proposed DTSMA has the following main contributions: (a) A method for each node to determine locally its polynomial coefficients without a priori global knowledge of node number and maximum node degree, and (b) A method to distribute to neighbours the locally determined polynomial coefficients, and to resolve collision between two sets of identical polynomial coefficients from two neighbouring nodes. The proposed DTSMA has been evaluated through extensive simulations to confirm that it can indeed preserve the capability of providing a minimum throughput guarantee in the absence of the a priori global knowledge. In benchmark against the de facto distributed coordinated scheduling (DCS) in the original IEEE 802.16d mesh MAC protocol under various domestic wireless channel conditions, DTSMA outperforms in terms of packet delivery ratio and average end-to-end packet delay which are important metrics for time-sensitive audio–video applications. Simulation results also show that DTSMA outperforms TSMA in terms of average end-to-end packet delay and average delay jitter when the severity of propagation impairment is high.

Understanding Performance for Two 802.11 Competing Flows

It is well known that 802.11 suffers from both inefficiency and unfairness in the face of competition and interference. This paper provides a detailed analysis of the impact of topology and traffic type on network performance when two flows compete with each other for airspace. We consider both TCP and UDP flows and a comprehensive set of node topologies. We vary these topologies to consider all combinations of the following four node-to-node interactions: (1) nodes unable to read or sense each other, (2) nodes able to sense each other but not able to read each other’s packets and nodes able to communicate with (3) weak and with (4) strong signal. We evaluate all possible cases through simulation and show that the cases can be reduced to 9 UDP and 10 TCP 802.11 g models with similar efficiency/fairness characteristics. We also validate our simulation results with extensive experiments conducted in a laboratory testbed. These more detailed models improve on previous work such as hidden-/exposed-terminal categorization and are thus better suited as a basis for adaptive techniques to improve performance in 802.11 multi-hop WLAN or Mesh Networks.

Implementing TCP flow-level fairness using 802.11e in a multi-radio mesh testbed

TCP is known to be subject to poor performance in multi-hop mesh networks. While most work has focused on interference and related issues, we note that cross-layer interactions can also induce considerable unfairness. In this paper, we propose a simple 802.lie scheme to mitigate these interactions and regulate TCP fairness in a flexible manner. The practical effectiveness of the approach is confirmed in a multi- hop, multi-radio testbed.

Load aware traffic engineering for mesh networks

Wireless Mesh Network (WMN) is a multi-hop mesh network that consists of mesh routers and mesh clients, where mesh routers are static and form the backbone of the mesh network. The static nature of mesh nodes imposes requirements for designing routing metrics that support high-throughput and low packet delay. This article considers the problem of Interference-Load Aware routing in multi-channel Wireless Mesh Networks. We propose a new Interference-Load Aware routing metric, ILA, that finds paths with reduced inter-flow and intra-flow interference. The aim of this metric is to route the traffic through congestion free areas and balance the load amongst the network nodes. We incorporate this new metric in the well known AODV routing protocol and study the performance of ILA through simulations. We show that the proposed metric is able to adapt to changes in interfering traffic better than existing link metrics such as ETT, WCETT and MIC. We also demonstrate that our metric delivers high-throughput in multi-channel networks.

On the feasibility of IEEE 802.11 multi-channel multi-hop mesh networks

Several scientific works have considered the possibility to build Wireless Mesh Networks (WMN) using multi-channel IEEE 802.11 architectures. At the basis of these works is the notion of “non-overlapping” channels, i.e. with a frequency separation equal or greater than 25 MHz. It is now a common assumption that multiple independent transmissions over these channels can coexist without mutual interference even in physical proximity. In this work we demonstrate that this assumption does not hold in general. Through an extensive set of experiments we illustrate the presence of cross-channel interference between “non-overlapping” channels at relay nodes due to the “near-far” effect. We analyze in what manner the MAC layer reacts to such an interference and how this problem extends to higher layers, with detrimental effects on the global throughput. The central problem is that cross-channel interference is not handled adequately by the MAC layer, and in some cases single-channel multi-hop settings perform better than multi-channel. Our results highlight a serious mismatch between some routing and channel assignment schemes proposed recently by the research community, assuming full separation between non-overlapping channels, and what is achievable in practice. More generally, as the presence of cross-channel interference can not be neglected at relay nodes, our findings point to a fundamental problem in building Multi-channel Multi-hop WMN based on IEEE 802.11b/g technology.

Design of a Networked Monitoring System for Home Automation

This paper presents the design and implementation of a networked monitoring system for home automation. The proposed system architecture organizes the deployed sensor nodes to form a multihop mesh network in the home environment. Multiple communication interfaces are designed to enable local and remote user interactions through Internet or Bluetooth. This system offers a complete, flexible and reusable solution for various home monitoring and control applications.

A Distributed End-to-End Reservation Protocol for IEEE 802.11-Based Wireless Mesh Networks

This paper presents an end-to-end reservation protocol for quality-of-service (QoS) support in the medium access control layer of wireless multihop mesh networks. It reserves periodically repeating time slots for QoS-demanding applications, while retaining the distributed coordination function (DCF) for best effort applications. The key features of the new protocol, called "distributed end-to-end allocation of time slots for real-time traffic (DARE), are distributed setup, interference protection, and scheduling of real-time data packets, as well as the repair of broken reservations and the release of unused reservations. A simulation-based performance study compares the delay and throughput of DARE with those of DCF and the priority-based enhanced distributed channel access (EDCA) used in IEEE 802.11e. In contrast to DCF and EDCA, DARE has a low, nonvarying delay and a constant throughput for each reserved flow

Multichannel mesh networks: challenges and protocols

Supporting high throughput is an important challenge in multihop mesh networks. Popular wireless LAN standards, such as IEEE 802.11, provision for multiple channels. In this article, we consider the use of multiple wireless channels to improve network throughput. Commercially available wireless network interfaces can typically operate over only one channel at a time. Due to cost and complexity constraints, the total number of interfaces at each host is expected to be smaller than the total channels available in the network. Under this scenario, several challenges need to be addressed before all the available channels can be fully utilized. In this article, we highlight the main challenges, and present two link-layer protocols for utilizing multiple channels. We also present a new abstraction layer that simplifies the implementation of new multichannel protocols in existing operating systems. This article demonstrates the feasibility of utilizing multiple channels, even if each host has fewer interfaces than the number of available channels.