The fault-tolerant routing problem is important consideration in the design of heterogeneous wireless sensor networks (H-WSNs) applications, and has recently been attracting growing research interests. In order to maintain
The complex networks have attracted growing research interests in topology structure and dynamic problems. Many kinds of system can be described with the complex network model, and these models are constructed by several nodes connected with each other, such as the Internet and the wireless sensor networks (WSNs). Due to the ability of collecting data from the environment and reporting it back to the sink without human supervision [
However, in practical applications, unpredictable events such as environmental impairment, communication link broken, and battery depletion may cause the sensor devices to fail, partitioning the network and disrupting network functions. Therefore, fault tolerance becomes a critical issue for the successful communication of H-WSNs. It is expected that the network topology broken by software or hardware failure of sensor nodes could be automatically reconstructed and self-healed by the fault-tolerant routing technology so as to be recovered from path failure and ensured the performance of the communication tasks.
The objective of this paper is to solve the fault-tolerant routing problem for the H-WSNs while maintaining
The main contributions of this paper are as follows: firstly, we formulate the
The remainder of this paper is organized as follows: Section
Fault-tolerant routing protocols proposed for WSNs can be classified into three groups: (1) proactive routing, called disjoint multipath, in which several paths from source node to sink are calculated, maintained in advance, and stored in a routing table, but greater energy consumption and the requirement to predict the global topology information are the disadvantages [
One of the common fault-tolerant routing solutions is to establish disjoint multipath with proactive routing mechanism. Disjoint multipath constructs a number of alternative paths which are node/links disjoint with the primary path and other alternative paths. Thus, a failure in any or all nodes/links on the primary path does not affect the alternative paths. Using this multipath scheme in a network with
A considerable amount of work has also been done on the hybrid routing scheme, which combines multipath scheme and reactive routing scheme. In this scheme, multiple paths are calculated and maintained in advance, and then, alternative paths are created on demand. EARQ (energy-aware routing for real-time and reliable communication) is a hybrid routing scheme proposed by Heo and Hong [
Our work differs from the above existing ones [
The similar hybrid routing schemes for the H-WSNs are as follows: CPEQ (cluster-based periodic, event-driven, and query-based protocol) [
In this paper, we propose an ICPSOA-based fault-tolerant routing algorithm, which reconstructs the network topology of H-WSNs and provides a fast recovery from path failure with alternative path. We also compare the performance of the protocols of EARQ, CPEQ, and ICE with that of our approach. As we known, EARQ is an effective fault-tolerant routing protocol for homogeneous WSNs, while ICE and CPEQ are for H-WSNs to provide routing recovery from path failure. In this way, we can evaluate the fault-tolerant routing recovery mechanism with different network types.
The EA-based bionic randomized algorithm has become the important tools for solving complex optimization problems because of its intelligence and widely used and global search ability. But the algorithm dealing with fault-routing problem of WSNs should support the characteristic of energy saving. In general, better fault-tolerant performance always needs more energy consumption. Therefore, we choose light-weight algorithm based on the particle swarm optimization algorithm (PSOA), which has a simple structure and is easy to realize.
The PSOA is a new EA based method to search an optimal solution in the high-dimensional problem space [
In the standard PSOA (SPSOA), each particle is a potential solution to the problem. Assume
The SPSOA also exhibits several disadvantages: it sometimes posses the problem of converging to undesired local optimum, for the diversity of population decreases in the latter iteration of evolution; optimizing stops when reaching a likely optimal solution, and thus the accuracy of the algorithm is limited. Therefore, a cooperative PSOA (CPSOA), which uses cooperative behavior of multiple swarms to improve the SPSOA, is proposed in [
For this reason, we draw on good diversity characteristic of immune mechanism and develop an immune CPSOA (ICPSOA), in which each particle is considered as an antibody. Particle clone is used to generate a new population with offspring. Mutation is used to diversify the search process. Immune restrain is considered to restrain the inferior ones in order to keep the stable population. Immune memory is used to store the feasible solutions [
The architecture for the model of H-WSNs contains two types of wireless sensor devices as shown in Figure
The architecture of H-WSNs.
Therefore, in-network data transmission can be performed by forming a spanning tree among all the tree nodes. As shown in Figure
Assume that the network has the following characters: (1) the H-WSNs is a static network, where the nodes will not move after deployment, (2) every node knows its own position and that of the macronodes and the sink. The location can be obtained by GPS or localization protocols for estimating the location of a node, (3) the wireless transmission energy of macronode can be adjusted based on the distance between the receiver and itself, (4) the adjacent nodes would acquire the state information of their 1-hop neighbors and the links between them through periodically broadcast. The meanings of used symbols is provided in Table
The main symbols.
The | |
The number of the sensor nodes in | |
The state information of all the nodes in | |
One of the source nodes in | |
The root node (macronode) in | |
The set of all the possible paths between | |
The | |
The failed relay node of | |
The child node of | |
The parent node of | |
The | |
The optimal path of | |
The |
The subtree
As illustrated in Figure
We use the simple fault model proposed in [
We introduce the energy model adopted in [
As described in Section
The architecture of the ICPSOA for the H-WSNs.
The principle of the ICPSOA is to search, respectively, in different
In Algorithm
Particle’s
In this step, each particle can be considered as an antibody, resulting in the clonal mutation set
For the particles replacement rule, we need to calculate the antigen stimulus degree of the original particles and select clonal mutation particles. The Euclidean distance between any particle
Therefore, the stimulus degree of antibody particle is
After that, each particle is compared with stimulus threshold; the higher one will maintain in the subswarm, and the lower one will be replaced (called restrain). The process of this step is as shown in Algorithm
If the solution is satisfied with the termination criterion,
In this step, the velocity and position of the particle is updated as (
Update velocity and position of each sub swarm’s particle
Equation (
Inertia weight
The computational complexity is an important issue in designing our optimization algorithms. In the
Therefore, the computational complexity of the ICPSOA is
The ICPSOA is the kernel of fault-tolerant routing protocol. As shown in Figure
If an intermediate node
Each intermediate node in the subtree repeats Step
If
During this process,
To evaluate the performance of the ICPSOA, we design a corresponding simulation scenario upon Matlab. The simulation experiment is constructed on Windows XP with Intel Pentium 4 processor (2.4 GHz) and 2 GB RAM. The goal of the simulation is to show that the ICPSOA can provide a more stable transport environment in an error-prone network. The results are also compared to the protocols of ICE, CPEQ, and EARQ.
In Table
Simulation parameters.
Simulation parameter | Value |
---|---|
Network area | 10000 m × 10000 m |
Number of sensor node | 50–500 |
Number of macronode | 10 |
Available energy on sensors | 120 J |
Sensing radius of sensor node | 300 m |
Communication radius of sensor node | 600 m |
Communication radius of macronode | 3500 m |
Bandwidth of sensor node | 250 kb/s |
Number of disjoint multipath | 3 |
Number of simulation rounds | 500 |
Number of packet in each round | 1 |
Size of packet in each round | 400 bits |
Probability of node failure | 0.02 |
Energy consumption of sending circuit | 40 nJ/bit |
Energy consumption of receiving circuit | 80 nJ/bit |
Energy consumption of sending amplifier | 200 pJ/bit/m2 |
Channel attenuation index | 2 |
Energy consumption of data fusion | 4 nJ/bit |
Energy consumption of updating routing table | 2 nJ/bit |
To illustrate the effect of the proposed protocol, we take a snapshot during a simulation. Figure
Snapshot of establishing the alternative path using ICPSOA.
The simulation ends after 1000 rounds. We compare the number of alive nodes per round for these four protocols. As shown in Figure
Experimental results for number of alive nodes per round with variant scale of network. (a) Size of 50 nodes. (b) Size of 250 nodes.
As shown in Figure
Experimental results for energy depletion ratio per round with variant scale of networks. (a) Size of 50 nodes. (b) Size of 250 nodes.
Figure
Experimental results for average delay of packet delivery.
Figure
Experimental results for average successful packet delivery ratio with variant failure probability. (a)
We should also compare the performance trend of the three algorithms with different probability of node failure
We propose the ICPSOA-based fault-tolerant routing protocol for H-WSNs, which focuses on a solution to the problem of energy depletion and packet delivery of nodes, by trying to reconstruct the topology structure and recover the routing for the path failure and achieve energy conservation by avoiding unnecessary retransmission. The conserved energy can be used to increase the quantity of information received by the sink. The experiment presents the promising ability of the ICPSOA, and better solutions of fault tolerance and prolonging the network lifetime can be obtained by the ICPSOA-based protocol than the protocols of EARQ, ICE and CPEQ. The results have illustrated the advantage of H-WSNs and backup disjoint multipath, which can reduce the risk of data delivery loss and energy consumption on the path exploring. It also aims at shortening delay of packet delivery, evening energy dissipation among the nodes by constructing the optimal alternative paths in the H-WSNs with the swarm intelligence algorithm. The strength of the ICPSOA is its simplicity, robustness and effectiveness for fast routing recovery compared to other approaches and makes the ICPSOA a potential solution to meet the requirements of critical conditions monitoring applications.
As for future studies, the following directions are under the way: firstly, the proposed protocol ignores the fault-tolerant routing between macronode-macronode communications, which could be considered to form a more complete protocol architecture; secondly, we should further reduce the computational complexity of the proposed ICPSOA such that it converges faster to a better solution, providing robustness against failure in the network.
This work was supported in part by the Key Project of the National Nature Science Foundation of China (no. 61134009), the National Nature Science Foundation of China (no. 60975059), Specialized Research Fund for the Doctoral Program of Higher Education from Ministry of Education of China (no. 20090075110002), Specialized Research Fund for Shanghai Leading Talents, Project of the Shanghai Committee of Science and Technology (nos. 11XD1400100, 11JC1400200, 10JC1400200, 10DZ0506500).