# Method for Detecting Abnormal Activity in a Group of Mobile Robots
## 3 Network Model for a Group of Mobile Robots  
Figure 2 shows the network diagram implemented for conducting experimental research and collecting statistical information. It was assumed that the network node was a mobile robot. The mobile robot was a land mobile, which performed the task of movement toward the goal of a certain trajectory. The central server, a node with IP address (Internet Protocol Address) 192.168.1.2, performed the following tasks: providing goals for the mobile robots, and accumulating information. The monitoring mode for the Wi-Fi module of the central server was configured to implement these functions. The wireless mesh network was configured between nodes. The Wi-Fi modules of mobile nodes were configured in ad hoc mode to realize the mesh network topology. Network nodes exchanged packets over wireless communication channels, and the 802.11 n standard was used [27]. This standard allowed setting up an ad hoc network between nodes. Routing protocols, such as AODV and optimized link state routing (OLSR), allowed extending the functionality of the ad hoc network and led to the mesh network creation. Network nodes could communicate with each other directly and, if necessary, via a neighbor through routing protocols. The connections between nodes in Figure 2 only partially show the complete communication scheme. In fact, nodes could communicate with each other through the routing protocol. In this network model, the OLSR routing protocol was used. The UDP protocol was used to transfer data at the transport layer [28]. The TCP protocol was used to transfer control commands and critical information. Nodes with addresses 10.0.0.1-10.0.0.10 formed a segment of the mesh network, and node 192.168.1.2 was a central server which received all traffic that transmitted over the mesh network. In addition, node 192.168.1.2 transmitted control commands to the network nodes. Figure 2: Model of wireless network for a group of mobile robots. Also, three types of nodes were assumed according to their behavior in the network:  
* Trusted node--network node that is not conducting an attack and is not under attack. It performs its functions properly. * Malicious, attacker, intruder node--network node that is conducting the active attack. It could be the internal or external network node. * Victim node--network node that is under attack from the malicious node. Nodes received targets from a central server and then distributed them among themselves. The group control subsystem was implemented to solve the problem of goal distribution. The goal distribution algorithm was chosen in Reference [29]. The main steps of the algorithm are presented below. Step 1. Detection optimal plan for the goal distribution via a pairwise exchange between robots. At this step, the robots \"changed\" in pairs of goals to find out whether the replacement of the goals would lead to an increase in the functionality. Step 2. Improving the plan via the pair-wise exchange of the goals. After completion of all the replacements, steps 1 and 2 were performed again successively, until all values at the next iteration of the execution of step 1 were obtained. Then, step 3 was performed. Step 3. The meaning of this step was to try each robot to improve their choice of goals by organizing a sequence of substitutions of goals. To do this, each robot determined whether replacing its goal with another goal improved the quality of the chosen target, performed until the most profitable target was chosen. Step 4. Determination of the sequence of possible goal replacements in the robot group from all values. The maximum absolute value was selected and transmitted to all other the group of robots. Then, the feasibility of replacing goals with robots was determined. To do this, the robots calculated the improvement of the functionality in this step.