The Problem of Using Landmarks for the Navigation of Mobile Autonomous Robots on Unknown Terrain

Navigation of mobile autonomous robots on unknown terrain in the absence of GPS is extremely difficult. The general aim of the chapter is to analyze the possibilities of reliable detecting landmarks and determining their coordinates for navigation purposes. It is shown that the method of solving such a problem is the complex use of the meters operating on different physical principles. The main attention is paid to the radar method of measuring the angular coordinates of the landmarks by an antenna with a small size. For a radar with a wide antenna pattern, the possibility of angular resolving of two or more closely spaced landmarks is estimated. The most reliable method providing angular resolution is the creation of a synthesized aperture of antennae in the process of linear movement of a robot. The possibilities of such antennae are analyzed, considering random phase distortions and errors.

Introduction

Navigation of mobile autonomous robots (MAR) in the unknown terrain is most easily provided using GPS. However, in some cases, such navigation is significantly complicated by the lack of satellites visibility. In the close vicinity of the buildings, hills, mountains, etc. GPS accuracy drops down due to unavailability of useful signal. In such situations, the landmarks for MAR navigation may be single concentrated objects that occur on the ground. As a rule, the non-contact remote methods, which are realized using of radar, ultrasound, infrared and laser systems, as well as systems of technical vision, are used for the landmarks detection by mobile autonomous robots. Each system has limitations due to various factors, such as weather conditions, daily changes, landmark type, presence of noise, etc. Thus, the most rational approach to MAR navigation is the complex use (fusion) of systems built on various physical principles or systems that differ significantly in their characteristics. An alternative approach is to use systems that have proven well in other branches. One such system is presented in the chapter of the book. After detecting a single landmark, its coordinates are determined. If, within the width of the antenna pattern, there are two landmarks that are not resolved by the range, the interference field of the reflected waves has a non-spherical fluctuating phase front. The errors of measuring the azimuth of these landmarks can increase significantly. Consequently, there is a problem of angular resolution of landmarks. The particular purpose of the chapter is to estimate the possibilities of angular resolution of landmarks and determining their coordinates for robotic navigation tasks and to suggest ways of increasing this resolution by radar methods using frequency range VHF or UHF.