## 2 A Short Review of the Contributions in This Special Issue  
The purpose of this Special Issue is to cover issues related to navigation, positioning, and wireless communication, with particular application to companion robots, including methods and issues that may have a direct or indirect impact on the completion of tasks by such robots, e.g., communication with road infrastructure (robot-to-infrastructure (R2I)), communication with pedestrians, communication interfaces, risk analysis, cybersecurity issues, and reliability aspects. There were eight submissions to the Special Issue of which four received positive reviews and were accepted for publication. In Reference [1], the issue of noises in double-differenced GNSS observations was analyzed. The authors claim that precise data-processing from the GNSS reference station network is based on a combination of double-differenced carrier phase and code observations, which allows for most of the measurement errors to be removed or reduced. On the other hand, creating observation differences between two receivers and two satellites increases the measurement noise of the observations by a factor of 2. That is why, in this paper, the authors prepared a complex analysis of the noise type in double-differenced GNSS (GPS, GLONASS and Galileo) observations, both carrier phase and code observations, with a 1-s sampling interval. A couple of methods were used for the research, such as the Autocorrelation Function (ACF) method, the Lomb-Scargle (L-S) periodogram method, and the Allan Variance (AVAR) method. The weekly set of measurement data was analyzed. The results were as follows:  
* Depending on the system and type of observation, the noise level and type of noise are significantly different;
* Among the code measurements, the lowest noise levels were obtained for the GPS C5Q and Galileo C7Q/C8Q observations, with the standard deviations not exceeding \(\pm\)10 cm;
* The noisiest observations were obtained for the GLONASS C1C and C2C signals, which had standard deviations of about \(\pm\)90 cm and \(\pm\)45 cm. Reference [2] aims to analyze the space segment (BDS-2 and BDS-3) of the BeiDou Navigation Satellite System (BDS), focusing on the occurrence of periodic, repetitive signals in the clock products, and determine whether the signals coincide with the orbital periods or their multiples. A couple of tools were used for analysis, such as the Lomb-Scargle (L-S) power spectrum (to determine the periods present in the BDS clock products), and continuous wavelet transform (CWT) (to produce a time\(-\)frequency representation showing the more complex behaviour of the satellite clock products). The results were as follows:  
* The BDS-2 satellite clocks have significantly higher noise than the satellite clocks of BDS-3;
* The number of designated periods is higher, but their reliability is significantly lower;* BDS-3 satellites have only been in operation for a very short time; thus, this was the first analysis to include their data. With reference to the topic of this issue, in Reference [3], a comparative analysis of the GNSS, LiDAR Point Clouds, DTMs, databases, maps, and historical sources was prepared to identify the position of mountains peaks. The global navigation satellite system (GNSS) geodetic measurements were used as a reference for this research. The GNSS measurements were carried out with Xiaomi Mi 8 smartphones and the raw recorded data were further used for calculations in the post-processing mode. Some other data sources included global and local databases, models and topographic maps. A comparison of Polish and Slovak point clouds for two peaks were presented in the article, with the results showing that there is a possibility of using large-area laser scanning to determine the maximum heights of mountain peaks. In Reference [4], the safe communication between the companion robot and infrastructure is discussed, as the authors see a list of challenges in the robot's communication with the environment, which are widely described in the literature.