# Evaluation of Low-Cost GNSS Receiver under Demanding Conditions in RTK Network Mode
## 1 Introduction  
Geodetic measurement techniques are one of the basic solutions for monitoring displacements and deformations of buildings and ground surfaces [1, 2]. They provide the representation of observation results in an external, absolute reference system. Among them, an important role is played by the GNSS (Global Navigation Satellite System) technology. Its contemporary applications have been reviewed in detail by [PERSON] and [PERSON] [3]. In particular, for continuous monitoring real-time observations are especially important [4]. Achieving the highest possible accuracy is possible thanks to the development of effective error mitigation methods and noise modeling [5]. Thus, high-precision geodetic GNSS receivers are commonly used for construction sites that require high measurement accuracy. These solutions are often found for continuous monitoring of high buildings [6], bridges [7] or dams [8]. Various satellite positioning techniques developed over several decades have provided sufficient accuracy for many monitoring cases. However, in recent years there has been a significant progress in this field through the increasing availability of low-cost receivers. They are an alternative to geodetic-grade receivers and can be divided into two groups: low-cost receivers equipped with patch antennas and ultra-low-cost hardware, used e.g., in mobile phones [9, 10]. These solutions significantly reduce the cost of observation in relation to precise geodetic equipment. They allow the use of a large number of measurement sensors on the surveyed object, especially in a situation where, due to the possible destruction of the monitored object, they should be treated as \"throwawayinstrumentation\" [11]. Low-cost equipment has been found to be sufficiently accurate for some applications in geodetic monitoring of natural hazards [12]. The suitability of these devices for monitoring over short baselines at accuracy levels better than 3 mm has also been confirmed by [PERSON] et al. [13]. On the other hand, studies performed by [PERSON] et al. [14] demonstrated the accuracy of the RTK solution using low-cost receivers on the level of 5.5 mm and 11 mm for the horizontal (Hz) and vertical (V) components, respectively. This result turned out to be 2-3 times worse compared to geodetic-grade equipment. Another application is the determination of positions of moving vehicles, especially with the additional use of inertial sensors [15; 16]. Low-cost receivers have been also included in various applications such as landslide monitoring [17] or detection of water vapor time variations [18]. All in all, the implementation of such devices should be preceded by studies in the field of positioning accuracy. Since low-cost GNSS receivers, and especially dual-frequency ones, have been available for a short time, the number of studies on their accuracy is quite small. Since their appearance on the market, they have become the subject of research, both in terms of determining the position using the static [19] and kinematic [20] methods. Comprehensive research of low-cost single-frequency receivers was performed by [PERSON] et al. [21]. Three of the five receivers achieved horizontal position accuracies better than 2.6 cm in RTK mode, under favorable observing conditions. However, the authors found significant limitations on an accurate position using single-frequency receivers for dynamic applications. Three years ago, the ZED-F9P low-cost dual-frequency GNSS receiver, manufactured by the Swiss company u-blox, appeared on the market. As a standard it is equipped with an ANN-MB-00 patch antenna with a ground plane. It provides signal tracking for all of the GNSS systems (GPS, GLONASS, Galileo and BeiDou). The accuracy of the RTK receiver is specified at 1 cm + 1 ppm CEP (Circular Error Probable) for horizontal and vertical positions. This value is independent of the number of satellite navigation systems used, i.e., it is the same for both 4 systems (GPS + GLO + GAL + BDS) and one (GPS) [22].