Abstract
Multi-path routing, a routing technique that enables data transmission over multiple paths, is an effective strategy in achieving reliability in wireless sensor networks. However, multi-path routing does not guarantee deterministic transmission. This is because more than one path is available for transferring data from the source node to the destination node. A hybrid multi-path routing algorithm is proposed for industrial wireless mesh networks for improving reliability and determinacy of data transmission, as well as to effectively deal with link failures. The proposed algorithm adopts the enhanced Dijkstra’s algorithm for searching the shortest route from the gateway to each end node for first route setup. A virtual pheromone distinct from the regular pheromone is introduced to realize pheromone diffusion and updating. In this way, multiple routes are searched based on the ant colony optimization algorithm. The routes used for data transmission are selected based on their regular pheromone values, facilitating the delivery of data through better routes. Link failures are then handled using route maintenance mechanism. Simulation results demonstrate that the proposed algorithm outperforms traditional algorithms in terms of average end-to-end delay, packet delivery ratio, and routing overhead; moreover, it has a strong capacity to cope with topological changes, thereby making it more suitable for industrial wireless mesh networks.
Keywords:
Multi-path routing; Industrial wireless mesh networks; Enhanced Dijkstra’s algorithm; Ant colony optimization algorithm
1. Introduction
In recent years, wireless technology has gained great interest in industrial applications. With harsh industrial control environment, however, wireless networks are required to comply with several requirements pertaining to reliable communication. Missing or delaying the process data may severely degrade the quality of control; thus at least two paths should be available from source to destination nodes in the wireless sensor networks (WSNs). WirelessHART is a well-known wireless mesh communication standard that is specifically designed for process measurement and control applications. It requires multi-path routing algorithms to provide reliable and deterministic communication. This standard has been approved by the HART Communication Foundation in September 2007 [
1].
Numerous routing algorithms have been proposed for WSNs in the past. Routing algorithm can be divided into three distinct categories, namely, proactive algorithm (including destination sequenced distance vector) [
2], reactive algorithm (including ad hoc on-demand distance vector routing) [
3], and hybrid algorithm (including zone routing protocol) [
4]. In proactive algorithm, nodes attempt to maintain routes to all other nodes at all times, while keeping track of all topological changes. However, this scenario becomes difficult when multiple nodes are present or when the nodes are mobile. In reactive algorithm, nodes only gather routing information when a data session to a new destination starts or when a route in use fails. In general, reactive algorithms are more scalable because they greatly reduce routing overhead. However, such algorithms may suffer from oscillations in performance because they are unprepared for disruptive events. Consequently, according to actual applications, the hybrid algorithm combines the best features of the proactive and reactive algorithms.
Multi-path routing schemes, which are developed based on the three categories of routing algorithms, can search multiple paths through a single-route discovery process. A source node chooses a path among multiple paths, after which it transfers data packets using the chosen path. If a link on the path is broken, the source node chooses another path and continues to transfer data instead of initiating an additional discovery process. New route discovery process is initiated after all paths have failed, thereby reducing the number of flooding initiations. Recently, several multi-path routing schemes have been proposed, which include multi-path dynamic source routing [
5], split multi-path routing [
6], and ad hoc on-demand multi-path distance vector (AOMDV) [
7].
The abovementioned routing algorithms are known as the shortest path algorithms. Recently, many researchers have considered quality of service (QoS) in routing algorithms for WSNs, which magnifies the difficulties associated with some optimization goals. Gelenbe and Lent [
8] proposed an energy-efficient routing algorithm for ad hoc networks based on the cognitive packet network (CPN) [
9,
10] protocol. The CPN algorithm is a fast, adaptive routing algorithm that uses smart packets for QoS-based path finding to minimize power consumption. QoS-aware multi-path routing algorithms have also been proposed in [
11]– [
13], in which QoS routing problems are formulated as different optimization problems (e.g., video quality and energy awareness). However, meeting QoS requirements in WSNs introduces certain overhead to routing protocols in terms of energy consumption, intensive computations, and significantly large storage. Thus, the energy conservation in industrial wireless mesh networks is achieved by the time division multiple access scheduling algorithm. The proposed routing algorithm aims to gain reliable and low-delay communications without high flooding.
In this article, a hybrid multi-path routing algorithm called DAWMNet is proposed for industrial wireless mesh networks, which combines Dijkstra’s algorithm and the ant colony optimization (ACO) algorithm. Dijkstra’s algorithm achieves the first route setup, whereas the ACO algorithm is responsible for route exploration and maintenance. DAWMNet aims to achieve load balance as well as reliable and deterministic transmission with minimal flooding problem. Simulation results demonstrate that the proposed algorithm outperforms the traditional approaches in terms of average end-to-end delay, packet delivery ratio, and routing overhead in number of packets. Moreover, the proposed algorithm has a strong capacity to cope with topological changes.
The reminder of this article is organized as follows. The network model and some related routing schemes are briefly introduced in Section 2. The proposed algorithm, DAWMNet, is established in Section 3. The performance evaluation of the proposed algorithm is presented in Section 4. The conclusions and future work are presented in Section 5.
2. Network model and challenges
2.1. WirelessHART technology
WirelessHART is a secure and robust mesh networking technology, which operates in the 2.4-GHz ISM radio band. It utilizes IEEE 802.15.4 compatible direct-sequence spread spectrum radios with channel hopping on a packet via packet basis. WirelessHART is a user-friendly, reliable, and interoperable wireless mesh sensor protocol used for process measurement and control applications [
14]. Figure
1 shows the architecture of the network, which contains the three principal elements listed below.
(1) WirelessHART field devices are connected to the process or plant equipment.
(2) The WirelessHART gateway acts as a bridge connecting the network manager to field devices and can also convert one protocol to another. One or more gateways should be present in a WirelessHART network.
(3) The WirelessHART network manager is the “brain” of the whole network, which is responsible for configuring the network, scheduling communications between nodes, managing routing tables, and monitoring the health status of network. Redundant network managers are supported; however, only a single active network manager is required per WirelessHART network.
Figure 1. The network structure of a WirelessHART network. The WirelessHART network with field devices deployed as mesh topology. The network consists of a network manager, a gateway, and 13 field nodes. All data packets generated by the field nodes flow to the gateway. For example, the packets from node
d travel through the intermediate nodes to the gateway. Based on the enhanced Dijkstra’s algorithm, once the first route setup is completed, each node has one shortest path to the gateway, which is marked as a blue line.
2.2. Routing schemes in WirelessHART
The two methods for routing packets in WirelessHART networks are graph routing and source routing. Graph routing requires the network manager to pre-configure the routing table for each potential destination. For redundancy, in a properly configured network, all nodes have at least two paths to destination nodes. When using graphs, nodes only obtain the information about their next-hop node not the global information. In comparison, source routing requires information on network topology, because packets may go to an arbitrary destination without an explicit configuration of intermediate nodes. Graph routing is ideal for both upstream and downstream communications, whereas source routing is only intended for network diagnostics.
However, given that WirelessHART provides little guidance on route discovery and route establishment, this article focuses on the improvements of graph routing to meet demands of industrial applications.
2.3. Related routing protocols
Several solutions to implement multi-path routing scheme in WSNs have been proposed, and some of which are used in this study.
Auto-configuring mesh
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