An efficient joint channel assignment and QoS routing protocol for IEEE 802.11 multi-radio multi-channel wireless mesh networks

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Abstract

With the emerging of video, voice over IP (VoIP) and other real-time multimedia services, more and more people pay attention to quality of service (QoS) issues in terms of the bandwidth, delay and jitter, etc. As one effective way of broadband wireless access, it has become imperative for wireless mesh networks (WMNs) to provide QoS guarantee. Existing works mostly modify QoS architecture dedicated for ad hoc or sensor networks, and focus on single radio and single channel case. Meanwhile, they study the QoS routing or MAC protocol from view of isolated layer. In this paper, we propose a novel cross-layer QoS-aware routing protocol on OLSR (CLQ-OLSR) to support real-time multimedia communication by efficiently exploiting multi-radio and multi-channel method. By constructing multi-layer virtual logical mapping over physical topology, we implement two sets of routing mechanisms, physical modified OLSR protocol (M-OLSR) and logical routing, to accommodate network traffic. The proposed CLQ-OLSR is based on a distributed bandwidth estimation scheme, implemented at each node for estimating the available bandwidth on each associated channel. By piggybacking the bandwidth information in HELLO and topology control (TC) messages, each node disseminates information of topology and available bandwidth to other nodes in the whole network in an efficient way. From topology and bandwidth information, the optimized path can be identified. Finally, we conduct extensive simulation to verify the performance of CLQ-OLSR in different scenarios on QualNet platform. The results demonstrate that our proposed CLQ-OLSR outperforms single radio OLSR, multi-radio OLSR and OLSR with differentiated services (DiffServ) in terms of network aggregate throughput, end-to-end packet delivery ratio, delay and delay jitter with reasonable message overheads and hardware costs. In particular, the network aggregate throughput for CLQ-OLSR can almost be improved by 300% compared with the single radio case.

Introduction

While various wireless networks evolve into the next generation to provide better services, a key technology, wireless mesh networks (WMNs), has emerged in recent years (Akyildiz et al., 2005). As is shown in Fig. 1, there are two types of nodes in WMNs: mesh routers and mesh clients, where mesh routers form the backbone with minimal mobility. Each node operates as both hosts and routers, forwarding packets for other nodes that may not be within direct transmission range of destination nodes. WMNs are dynamically self-organized and self-configured, with nodes in networks automatically establishing and maintaining mesh connectivity among themselves. These features bring many characteristics such as low up-front cost, ease deployment, enhanced capacity and service coverage (Bruno et al., 2005).

Recently, diversities of real-time traffic flows (e.g., voice and audio) have been flooding into the wireless networks. In particular, most of the applications have high QoS demand. Here the concept of QoS is defined as the agreement committed by the network to satisfy some predetermined service constraints for users in terms of available bandwidth, packets delivery ratio, delay and jitter, etc. Therefore, with the development of wireless technology, the ability for WMNs to supply real-time traffic with QoS guarantee has become a significant issue. However, the QoS mechanism is still a challenging task in WMNs due to many factors. Most of all, wireless links are constantly established and broken, thus the link quality would fluctuate owing to channel fading and interference from other transmitting devices.

WMNs have potential capacity enhancement and stable topology structure. However, the mesh architecture, nodes configuration of multi-radio multi-channel, time-varying wireless environment, and high demand of QoS in real-time multimedia applications frequently make users unsatisfactory with current network performance. Therefore one of the most imperative problems in research of backbone WMNs is how to develop related algorithms and protocols to ensure higher QoS (Xue and Ganz, 2002).

In the past few years, the field of QoS routing has been a hot topic in QoS research of WMNs. Previous studies mostly focus on single radio and single channel case, which largely limits the capacity of wireless networks. In fact, there are several wireless channels available in IEEE 802.11 specifications, e.g., the IEEE 802.11 g can provide four orthogonal channels available. If these spectrum resources could be taken full advantage of, the throughput enhancement would be remarkable. Also, with the rapid advance of hardware technique, the cost of wireless device has become lower and lower. Consequently, this offers potential urge to adopt the multi-radio technique in equipments.

At present, traditional OSI network architecture has been still employed in the protocol stack design of WMNs. However, more favorable idea for wireless networks is cross-layer design, which implies that the overall optimization of wireless networks can be achieved by sharing the information of different layers. So cross-layer design is not a complete denial of traditional five-layer reference model, but blurs the strict boundaries between layers, to make coordination and integration of feature parameters dispersed in different layers.

Existing achievements mostly modify QoS architecture dedicated for ad hoc or sensor networks, and focus on single radio and single channel case. Meanwhile, they study the QoS routing or MAC protocol from view of isolated layer. Therefore, with cross-layer idea and multi-radio multi-channel technique as the background, this paper proposes a QoS-aware routing protocol, cross-layer based QoS-aware OLSR (CLQ-OLSR), to provide QoS guarantee for real-time applications. In the proposal, each node is equipped with multiple radios, to each of which a different available channel would be assigned without overlapping. We assume that the number of available channels is equal or more than the number of radios on each node. One of radios is running M-OLSR to accommodate best-effort traffic, while the remaining radios are left to be responsible for delivering real-time multimedia data. Each node calculates the channel busy state in neighborhood region and derives its available bandwidth. By piggybacking the bandwidth information in HELLO and TC messages, each node disseminates information about topology and available bandwidth to other nodes all over the networks in an efficient way. Best-effort packets are carried along the physical path maintained by the routing tables, while real-time packets are sent along the optimized logical path, which is constructed by using the obtained topology and bandwidth information. Since the logical path is different from the physical path, packets are encapsulated by addresses sequences of logical route, so that they can traverse the logical path from source to destination. For channel assignment, each intermediate node receiving an encapsulated real-time packet greedily chooses the best channel based on channel usage lists for efficient use of wireless resources and collision avoidance.

In this paper, we investigate the mechanism of how to establish QoS routing for real-time traffic in IEEE 802.11 multi-radio multi-channel WMNs and make the following contributions:

  • (1)

    First, we propose a new method for estimating link available bandwidth that can take into account the activities of the nodes’ neighbors and adapt to change of channel conditions dynamically.

  • (2)

    Then, we design a cross-layer QoS-aware routing protocol by integration of bandwidth estimation, routing table construction and logical path establishment. In particular, the body part illustrates how to construct the logical routing to deliver the real-time packet hop-by-hop.

  • (3)

    Finally, we implement the proposed CLQ-OLSR routing protocol based on OLSR in QualNet simulator. Extensive simulation experiments demonstrate that the CLQ-OLSR outperforms single radio OLSR, multi-radio OLSR and OLSR with DiffServ in terms of network aggregate throughput, end-to-end packet delivery ratio, end-to-end delay and end-to-end delay jitter at the expense of reasonable overheads.

The rest of the paper is organized as follows: after describing the related works in Section 2, we present the system model in Section 3. Section 4 describes the proposed CLQ-OLSR in details, and Section 5 presents our extensive simulation results. We finally conclude our paper in section 6.

Section snippets

Related works

In the beginning, the bandwidth constrained routing problem was extensively explored in wired networks to achieve load balancing and traffic engineering, especially in the MPLS networks (Guerin et al., 1997, Wang and Crowcroft, 1996, Kodialam and Lakshman, 2000, Suri et al., 2003, Ricciato and Monaco, 2005). In these literatures, the common solution is to find a feasible path on the constructed topology by removing all links that do not meet the bandwidth requirement. Although this method could

System model

We consider the multi-radio multi-channel WMNs with the IEEE 802.11 DCF MAC protocol. In our model, there are N nodes which are all stationary and act as traffic aggregation access points, providing network connectivity to mobile end-users within their coverage ranges. Packets are forwarded via multi-hop relaying manner. Each node i is equipped with Ri heterogeneous radios, and the number of radios on each node may be different. By heterogeneous radios, we mean that the wireless capability,

Physical routing mechanism

Our proposed CLQ-OLSR includes two parts: physical routing and logical routing. Here, physical routing denotes the modified OLSR (M-OLSR) protocol with bandwidth estimation function, while logical routing represents another independent path establishment mechanism basing on topology and bandwidth information. The layered stack architecture of CLQ-OLSR is shown in Fig. 2. In this section, we shall interpret how the physical routing layer works in detail.

The physical routing not only inherits the

Performance evaluations

To verify the effectiveness of the proposed CLQ-OLSR, we conduct extensive simulations on QualNet Developer 5.0.2 platform in this section. The main simulation parameters settings are listed in Table 1. Here note that the configuration of related simulation parameters can refer to Kajioka et al. (2011), Kandris et al. (2011), Liu and Liao (2009), and Hou et al. (2012).

Particularly, the key performance metrics of throughput, delay, delay jitter, packet delivery ratio and the number of control

Conclusion

In this paper, we study the problem of how to provide QoS guarantee in WMNs, and design a QoS-aware routing protocol CLQ-OLSR to provide QoS guarantee for real-time applications. By constructing multi-layer virtual logical mapping over physical topology, we implement two sets of routing mechanisms—physical M-OLSR protocol and logical routing. Physical M-OLSR protocol functions on best-effort interface for routing table construction and bandwidth estimation, while logical routing on real-time

Acknowledgments

The preliminary work of this paper was presented at the International Conference on Communication Technology (ICCT) 2012. This work was supported in part by the National Natural Science Foundation of China (61172051, 61071124, 60903211), the Fok Ying Tung Education Foundation (121065), the Program for New Century Excellent Talents in University (NCET-11-0075), the Fundamental Research Funds for the Central Universities (N110204001, N100304009), and the Specialized Research Fund for the Doctoral

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