## 2 Materials and Methods
### Data Acquisition and WiFi Communication System  
The GPS receiver was placed in the rear right corner of each robot. The digital compass was placed in front of the mobile robot. In the study, it was seen that the digital compass did not work when placed close to the GPS receiver. The industrial computer was placed inside the body of the mobile robot. The RS-232 serial communication protocol was used for connecting the industrial computer and other electronic devices and both the GPS receiver and the digital compass have serial communication ports. The serial communication speed of the GPS receiver and the digital compass with the industrial computer was set at 19,200 baud. NMEA (National Marine Electronics Association) 0183 protocol is a combined electrical and data specification for using communication between electronic devices such as GPS receivers, digital compass, and many other types of devices. The NMEA 0183 standard uses a simple ASCII (American Standard Code for Information Interchange), serial communications protocol that defines how data are transmitted in a \"message\" from one \"device\" to multiple \"devices\" at a time. There are more than 80 different types of NMEA sentences for sending GPS data. Each sentence starts with a \"g\" sign and the next five characters determine the sentence type. The $GPRMC sentence type is the most important sentence and included spatial and temporal data for the navigating of the mobile robots. In this study, the GPRMC sentence was used to collect latitude, longitude, and speed data of the mobile robot. Spatial data are expressed in decimal degrees or degrees, minutes, and seconds in GPRMC sentences. Although these formats are sufficient for many applications, they should be converted to UTM (Universal Transverse Mercator) coordinates for mobile robot navigation applications, mathematical calculations, and mapping. Similarly, the HMR3000 digital compass communicates with the industrial computer using a standard serial RS 232 connection using the NMEA 0183 output sentence at 19,200 baud. The NMEA 0183 sentence specifications sent by the GPS receiver and the digital compass are shown in Table 1.  
Figure 2: Hardware components used in communication systems. The IEEE (Institute of Electrical and Electronics Engineers) 802.11 standard defines the WLAN system for providing connectivity between computers or any wireless devices capable to connect WiFi over public areas networks [30]. The IEEE 802.11b/g supports high data speeds using a 2.4 GHz frequency band and provides the speed for maximum data transmission is 5 to 54 Mbps. The computer used in this study has a built-in 802.11b/g WLAN mini PCI module. For this reason, IEEE 802.11b/g was used for communication among mobile robots. The designed mobile multi-robot system is based on the client-server model, which allows the participation of different mobile robots and the creation of a multi-robot network. The designed system consists of a mobile robot server and one or more mobile robot clients. The robot server is responsible for authenticating the connection, listening for the incoming connections, accepting mobile robot client connections, reading the incoming data, collecting all mobile robots' spatio-temporal data in an array, and sending out this array data to all robots. The mobile robot client is responsible for sending its spatio-temporal data to the server and requesting other mobile robots' spatio-temporal data from the server. Multi-robot wireless communication model is shown in Figure 3.  
The client-server model is one of the most usable communication rules in networked systems. In this model, clients communicate with one server at a time. On the other hand, a server communicates with multiple clients at any point in time There are two types of communication protocol used for client-server model, they are TCP/IP (Transmission Control Protocol/Internet Protocol) communication and UDP/IP (User Datagram Protocol/Internet Protocol) communication.