Channel Assignment and Routing in Multiradio Wireless Mesh Networks using Smart Ants

Extended Abstract

Fawaz Bokhari Department of Computer Science and Engineering

The University of Texas at Arlington Texas, US

fawaz.bokhari@mavs.uta.edu

Abstract—We present our initial work on the design and implementation of an efficient channel assignment and routing architecture for multi-radio and multichannel wireless mesh networks (WMNs). Our proposed scheme is derived from the principle of Ant Colony Optimization (ACO) in which smart ants (agents) perform the routing and channel assignment to stochastically solve a dynamic network optimization problem. We extend the ACO framework by implementing two modules namely a channel assignment module and a routing module with the objective of minimizing the overall network inference in multi-radio mesh networks. The main focus in our work is to take advantage of the particular characteristics of ACO framework and exploit them in designing a joint channel assignment and routing scheme for WMNs keeping in view the unique characteristics and requirements of these networks.

I. INTRODUCTION Wireless mesh networks (WMN) have emerged as a

promising technology for the provision of last mile broadband Internet access infrastructure in both urban and rural environments. Such networks are characterized as fixed backbone WMNs where relay nodes are generally static and are mostly supplied by a permanent power source [1]. With the availability of off-the-shelf, low cost, commodity networking hardware, it is possible to incorporate multiple radio interfaces operating in different radio channels on a single mesh router; thus forming a multi-radio mesh network. This enables a potential large improvement in the capacity of mesh networks compared to single-radio mesh networks.

However, one of the unique characteristics of multi-radio mesh networks is the presence of interference among the nodes mainly due to the shared nature of wireless medium and overlapped channels of neighboring nodes. Therefore, in order to effectively mitigate the overall network interference, there is a need to design a joint routing and channel assignment scheme whereas the channel assignment determines the network topology of a network and routing discovers the data paths to route the flows based on the network topology being determined by the channel assignment.

Routing and channel assignment in WMNs has been an active area of research for the last several years. Various approaches have been proposed for joint channel assignment and routing based on intelligent techniques such as multi-agent

technology and genetic algorithms. There is another framework for solving hard optimization problems called Ant Colony Optimization (ACO) [2] which is a meta-heuristic approach for solving such problems. The ACO approach has not been used so far for solving joint channel assignment and routing problem in multi-radio WMNs.

ACO algorithms draw their inspiration from the behavior of real ants, which are known to find the shortest path between their nest and a food source by a process where they deposit pheromones along trails (acting like a local message exchange in a communication network). Ants generally start out moving at random, however, when they encounter a previously laid trail, they can decide to follow it, thus reinforcing the trail with their own pheromone substance. This collective behavior is a form of autocatalytic process where the more ants follow a trail, the more attractive that trail becomes to be followed by future ants. This process is thus characterized as a positive feedback loop, where the probability with which an ant chooses a path increases with the number of ants that previously chose the same path [2]. Hence, in ACO artificial ants probabilistically build a solution iteratively by taking into account pheromone trails or/and local heuristic information as well. Since, artificial ants move stochastically instead of deterministically, therefore it allows them to explore wide variety of possible solutions of a problem independently and in parallel. Similarly, ACO based solutions are known to produce a good suboptimal solution in a very short period of time. These characteristics of ACO has become a source of inspiration for us in designing a joint channel assignment and routing algorithm for WMNs with the objective of minimizing the overall network interference and at the same time exploits the characteristics of ACO framework in terms of robustness, efficiency, self-organization and automatic load balancing.

II. JOINT CHANNEL ASSIGNMENT AND ROUTING ARCHITECTURE

We have designed an efficient channel assignment and routing architecture based on ACO framework for multi-radio WMNs. In order to fully exploit the characteristics of ACO framework and also to make it compatible for WMNs, we implement two custom designed modules namely routing module (RM) and channel assignment module (CAM). Figure 1 shows the architecture of our joint channel assignment and

Fourth Annual PhD Forum on Pervasive Computing and Communications

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routing scheme. We explain the working of our architecture along with the two custom designed modules below.

A. Routing Module Our routing module is based on a routing protocol called

AntMesh that we proposed in [3, 4] which is specifically designed for multi radio WMNs. Our routing module further extends the ACO framework by implementing two estimation modules i.e. a link and a path estimation module to effectively utilize the space/channel diversity typically common in multi radio mesh networks.

The link estimation module measures the cost of a node’s local links in terms of the packet delay taking into account the queuing delay of a node to realistically capture traffic load

The path estimation module has been designed to meet the needs and characteristics of WMNs in order to reduce both inter and intra flow interference.

B. Channel Assignment Module In [3, 4], we have assumed that the channel assignment is

done a priori and the routing protocol does not take into consideration the underlying channel assignment scheme. However, in a multi-radio multi-channel WMN, routing and channel assignment are interdependent because an efficient channel assignment scheme can greatly reduce interference among close by transmissions which helps the routing protocol to distribute the traffic among the nodes as the interference is already determined by the channel assignment scheme. Therefore, we argue that the routing and channel assignment should be jointly optimized to improve the overall network performance in terms of reduced interference which results in efficient load balancing among the nodes in the network. Our proposed architecture is distributed in nature, hence, no centralized control is required to assign the channels and discover the paths, and therefore, no traffic flows information is required a-priori by our algorithm.

The channel assignment module (CAM) is implemented by each node and is distributed in nature. A smart ant is generated periodically to find a shortest path from that node to a particular destination. The smart ant stochastically moves from one node to another unless it reaches the destination and upon then, it deterministically tracks back to the source node. While on its way back, the ant packet updates the routing and channel assignment modules on each intermediate node and the source node. Smart ants in our proposed architecture iteratively build a solution to improve the overall network performance. The routing module selects the paths for the flow from source to

destination, and thus assigns traffic to each radio and link, while channel assignment module determines the channel that a radio interface should use. Depending upon the load on a particular node and the link quality which is measured and maintained by the link estimation module of the routing module, the channel assignment module is initialized that would send an ant to the network to switch the interfaces/channels on the links along the path from the source to the destination. This will ensure that the channel assignment is dynamically adjusted according to the traffic patterns on each node determined by our routing module.

III. OUTLINE OF FUTURE WORK We intend to address some of the challenges in effectively

realizing a practical distributed joint channel assignment and routing algorithm for multi-radio mesh networks. One of the challenges is the network connectivity. How the proposed architecture ensures that the network remains connected when there is a channel switch on some links of the network needs to be studied. Similarly, the signaling overhead to measure the updated traffic and link characteristics on each node plays an important role in defining the efficiency of proposed architecture.

IV. CONCLUSION Within the scope of this extended abstract, we proposed an

efficient channel assignment and routing architecture for multi-radio and multichannel wireless mesh networks (WMNs). As the foundation of our proposed architecture, we use Ant Colony Optimization (ACO) in which smart ants (agents) perform the routing and channel assignment to stochastically solve a dynamic network optimization problem with the objective of minimizing the overall network interference. We extend the ACO framework by implementing two custom designed modules i.e., a channel assignment module to efficiently assign channels to the links and a routing module to find less interference and channel diverse paths.

ACKNOWLEDGMENT I would like to thank my PhD advisor, Dr. Gergely Zaruba

for his continues support throughout this research. I would also like to thank my university for providing me the platform and facility to conduct my research in its fullest manner.

REFERENCES [1] A. Raniwala and T.-C. Chiueh, “Architecture and algorithms for an

IEEE 802.11-based multi-channel wireless mesh network,” Proc. of the IEEE INFOCOM, 2005, pp. 2223-34.

[2] M. Dorigo and G. Di Caro, and L.M. Gambardella, “Ant algorithms for discrete optimization. Arfitcial Life,” 5(2): 137-172, 1999

[3] F. Bokhari and G. Záruba, “AMIRA: interference-aware routing using ant colony optimization in wireless mesh networks,” Proceedings of the IEEE Wireless Communications and Netwrking Conference (WCNC), pp. 2577-2582, April. 2009.

[4] F. Bokhari and G. Záruba, “AntMesh: an efficient data forwarding scheme for load balancing in multi-radio infrastructure mesh networks,” Proceedings of 4th IEEE International Workshop on Enabling Technologies and Standards for Wireless Mesh Netowrking (MeshTech’10), November 8-12, 2010.

Figure 1: Joint Channel Assignment and Routing Architecture

Ant Colony Optimization

(ACO)

Routing Module

(RM)

Channel Assignment Module

(CAM)

Path Estimation Module

(inter/intra – flow interference)

Link Estimation Module

(Delay+Load)

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