In this section, we compare the performance of our proposed protocol ACECR to other two protocols AOMDA [3] and EAAR [6]. AOMDA protocol extends the single path AODV protocol to compute multiple paths, which always offers a superior overall routing performance than ADOV in a variety of mobility and traffic conditions. EAAR is an ACO-based energy-aware routing protocol, which not only incorporates the effect of power consumption in routing a packet, but also exploits the multi-path transmission properties of ant swarms and use min-max energy to calculate pheromone value; hence, it increases the battery life of a node. Mobility is a natural characteristic of ad hoc networks, it is imperative to use a mobility model that accurately represents the mobile nodes that will eventually utilize the given protocol. The choice of a mobility model can have a significant effect on the performance of an ad hoc network routing protocol. Many mobility models have been reviewed in [11], the mobility models are designed to describe movement pattern of mobile nodes including their locations, velocities and accelerations over time [12]. A mobility prediction-based routing protocol is proposed for DTNs in [13], which will be future research direction for ant conlony-based routing in MANETs. To the best of our knowledge, there is no research on ACO-based energy control routing protocols for different mobility models in ad hoc networks.
In this paper, we do not propose a new mobility model, our target is to measure the influence of the different mobility models to ant colony-based energy control protocols. We discuss following three different mobility models for three ant colony-based energy control protocols in ad hoc networks:
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(1)
Random walk mobility model (Randwalk): each node moves from its existing location to a new location by randomly choosing an arbitrary direction and speed from a specified range [11].
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Random waypoint mobility model (Randway): this model is equivalent to the random walk model except that the modification in speed and direction is done after predefined pause time [11].
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(3)
Reference point group mobility (RPGM): this mobility model represents the random motion of a group of nodes as well as the random motion of each individual node within the group [14]. Group movements are based upon the path traveled by the logical center for the group.
Performance evaluation of routing protocols
NS-2 simulator is used to evaluate the performance of different protocols. There are 100 nodes in a network, which move over a square 1000m∗1000m flat space. For RPGM model, we divided all nodes into four groups, there are 25 nodes in each group. Node’s MAC layer uses IEEE-802.11 DCF media access control protocol, the radio transmission range and the interference range of nodes are all set to be 200 meter. Each node has a total energy of 100J. Mobile nodes are assumed to move randomly according to the random walk, random waypoint, and RPGM mobility models. The speeds of nodes are set to be 1.5,5,10,15, and 20 per second, each node starts moving from a randomly selected initial position to a target position, which is also selected randomly in the simulation. Each packet size is 512-bytes, 10 constant-bit-rate (CBR) flows are generated randomly at a rate of 10 packets per second for 1000 s to test the performance of protocols.
In our simulation experiment, the following metrics are used for our performance study:
Data packet delivery ratio
The percentage of the number of data packets correctly delivered to the number of data packets sent by source nodes.
Figure 2 shows the packet delivery ratio of AOMDV, EAAR, and ACECR protocols at different speeds in different mobility models, where the packet delivery ratio for three routing protocols decreases when the speeds of nodes increase. We observe that the packet delivery ratio for ACECR and EAAR protocols is better than AOMDV protocol, because ACECR and EAAR protocols are energy control routing protocols, they can balance the energy use of the network, and reduce the link break caused by dead nodes. Since both average energy and the minimum energy of a path is considered in ACECR, it can select a path with more residual energy on global view, EAAR only considers the residual energy of nodes instead of paths, the packet delivery ratio for ACECR protocols is higher than that for AOMDV protocol.
Average end-to-end delay
The average time between transmission of data packets at sources and successful reception at receivers.
Figure 3 shows the average end-to-end delay of data packets from source nodes to their destination nodes for AOMDV, EAAR and ACECR in different mobility models, the end-to-end delays decrease with increase of node mobile speeds, because the increase of node mobile speeds will make network topology change, which will cause data buffer and route rediscovery. The average end-to-end delay for ACECR and EAAR protocols is less than AOMDV protocol, because ACECR and EAAR protocols are energy control routing protocols, and ant colony-based energy control routing protocol is multi-path routing protocols, they can balance the energy use of the network, and reduce the route rediscovery.
Routing load ratio
The percentage of the number of control packets sent and forwarded by all nodes to the number of all packets (control and data packets) propagated by nodes.
The communication overhead has profound impact on the performance of routing protocols, it represents the total size of exchanging packets in the network. The control packets increase the communication overhead and reduce the throughput of the network. Figure 4 shows that routing overhead of ACECR and EAAR protocols is higher than AOMDV protocol, since ACECR and EAAR protocols are multi-path routing protocols, they use pheromone updating to maintain the route selection.
Energy consumption evaluation of nodes
Figure 5 shows the dead node ratio for AOMDV, EAAR, and ACECR protocols at different simulation times when nodes are moving at 15-m/s speed. In Fig. 5, the longer the simulation time is, the more there is dead nodes in the network, the ratio of dead nodes of ACECR and EAAR protocols is less than that of AOMDV protocol, since both average energy and minimum energy of a path is considered in ACECR, it can select a path with more residual energy on global view, EAAR only considers the residual energy of nodes instead of paths, AOMDV does not deal with energy balancing problem.
Figure 6 shows the dead node ratio for ACECR protocols under in Randway, Randwalk, and RPGM mobility models at different simulation times when nodes are moving at 15-m/s speed. In Fig. 6, the more stable is the network topology, the less is the dead node ratio. If network topology is unstable, it will rediscover the routing paths and will consume more energy of nodes.
Figure 7 shows the relation between dead node ratio and node moving speed for ACECR protocols under Randway models. In Fig. 7, the higher is the speed of nodes, the more is the dead node ratio, this is because the increase of node moving speed will make network topology is unstable, it will rediscover the routing paths and will consume more energy of nodes.