# Simple Ultrasonic-Based Localization System for Mobile Robots
## 2 Localization Options  
For every mobile robot, it is crucial to be able to orient itself in its environment. Avoiding dangerous situations such as collisions and hazardous conditions (temperature, radiation, exposure to weather conditions, etc.) is paramount. If a robot has goals associated with specific locations within its environment, it must be able to find these places. Without always knowing its location, a robot becomes uncontrollable. Therefore, localization is an essential task for autonomous navigation [2; 19]. The solution to the question \"Where am 1?\" is complex and pivotal for robot control. Hence, many sensors working on different principles have found application in this area. Often, localization solutions are so complex that using a single sensor is insufficient. It is frequently necessary to use a group of sensors, which may operate on various physical principles. Each of the potential sensors has its advantages and disadvantages, so it is essential to understand their nature to determine where and how individual sensors can be used [2]. The Global Positioning System (GPS) is a system for global positioning. The basic principle of using the system involves determining the position by measuring the time points of receiving a synchronized signal from navigation satellites by the consumer's antenna. To determine three-dimensional coordinates, a GPS receiver requires four equations: \"distance equals the product of the speed of light and the difference between the times of signal reception by the consumer and the time of synchronous emission from the satellite\" [8]. Global Navigation Satellite Systems (GNSS) are satellite systems built to determine position, velocity, and time on Earth regardless of meteorological conditions. Solving the problem of mobile robot localization using a GNSS system involves utilizing a sensor capable of receiving signals from such systems. Since it is a satellite system orbiting the Earth, such a sensor can only be used in outdoor environments. The position of the measured point is determined at the intersection of spherical surfaces, whose radius is determined by the distance between the satellites and this point. The distance between the satellite and the measured point is derived from the flight time of the radio signal from the satellite to the receiver. By comparing times from multiple satellites, it is possible to determine the position of the measured point. Geometrically, to determine the position of a robot, it is necessary to know the position of at least three satellites. However, these data must have the same timestamp and must be synchronized. In other words, to determine the distance between another satellite and the robot, time information must be used, and therefore, to calculate the robot's position, it is necessary to know the position of at least four satellites. To achieve higher accuracy in determining the position, it is important to use as many visible satellites as possible, which must also be appropriately distributed in the sky [2]. There are differences between GPS, GLONASS, Galileo, etc., as each of them was designed at different times and technological advancements. However, these systems are not suitable for indoor localization [9; 10]. Indoor localization systems are of a local nature. Here, it is possible to use either systems based on BTS (Base Transceiver Station) signals, or more localized ones such as Wi-Fi transmitters used in buildings, or specially used Bluetooth modules. However, all these systems exhibit relatively low precision, ranging from tens to hundreds of centimeters [20; 21; 22]. Currently, there are systems based on HF (High-Frequency) signals for internal use that localize with an accuracy of \(<\)10 cm and are suitable for industrial use [23]. There are also ultrasound-based systems that achieve sufficient accuracy (\(\pm\)2 cm) and relatively low cost [24]. However, we use a different principle of tag placement in space.