## 1 Introduction
This includes the signal analysis and positioning performance. The former studies of Galileo signals were devoted to phase and code noise, multipath, and cross-correlation [9; 10; 11; 12; 13]. The latter issue, applied to both single-system and multi-constellation single-point positioning, was investigated in [14; 15; 16; 17; 18]. Moreover, at this point we should acknowledge several studies devoted to precise positioning including both absolute (PPP) and relative (RTK) algorithm development and performance assessment. Example of single-system and combined PPP results may be found in [19; 20; 21; 22; 23], while the application of GIOVE and IOV Galileo signals to RTK was examined in [13; 24]. In [25], single-frequency RTK positioning was analysed; in [26] selected methods for GPS + Galileo signals integration were studied and assessed, while [27] was devoted to Galileo IOV + FOC. At this point, it should be noted that the aforementioned studies did not include Galileo E14 and E18 satellites. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & & **GSAT0201 (5-Doresa)** & **GSAT0202 (6-Milena)** \\ \cline{3-4}
**PRN Number/NORAD ID** & **Nominal Orbit** & **E18/40128** & **E14/40129** \\
**Launch Date** & & **22 August 2014** & **22 August 2014** \\
**Signal Transmission Date** & & **29 November 2014** & **17 March 2015** \\ \hline Semi-major axis (km) & 29,599.8 & 27,978 & 27,978 \\ Eccentricity & 0.0001 & 0.15601 & 0.15167 \\ Revolution period (h) & 14.08 & 12.97 & 12.97 \\ Inclination (\({}^{\circ}\)) & 56 & 49.775 & 49.874 \\ Minimum orbital height (km) & 23,220 & 17,382 & 17,382 \\ Maximum orbital height (km) & 23,240 & 25,818 & 25,818 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Selected parameters of E14 and E18 Galileo FOC satellites’ orbits [8]. Moreover, most of these studies, based on real signals, were also limited to close-range RTK--single short baselines. Therefore, in order to extend knowledge in this field, in this paper we analyse the potential use of Galileo satellites with highly eccentric orbits in medium-range instantaneous RTK positioning. Nowadays, RTK positioning is considered a highly effective and reliable method of precise coordinate determination and so is a standard in many commercial and scientific applications. However, the starting point, which was a single-baseline single-system RTK positioning, suffered from several disadvantages such as limited baseline length and longer time to fix during higher ionosphere activity. Within the last decades, several advances in the RTK algorithms were introduced. These led to the development of the network-RTK mode, utilising atmospheric corrections derived from active reference networks. Taking advantage of these new algorithms, it was possible to extend the distance between reference sites and user receivers, and thus extend the service coverage area. This resulted in so-called wide area RTK, with baseline length up to dozens and even hundreds of kilometres (see [28; 29; 30; 31]). Simultaneously, to support Positioning, Navigation and Timing applications (PNT), unprecedented interest was directed to algorithm and methodology development for combining multi-constellation signals. Several contributions were devoted not only to algorithm development and assessment [26; 32], but also to characterisation of the inter GPS-Galileo system biases both in precise relative (RTK) and absolute methods (PPP) [33; 34; 35; 36; 37]. Thus, the RTK method can be considered as under extensive development and being used for a growing number of applications. The main objective of this paper is to evaluate the applicability of the E14 & E18 satellites to precise GNSS positioning. In this contribution we focus on relative kinematic positioning as an instantaneous solution in multi-baseline mode. The prerequisite of precise relative positioning is the correct ambiguity resolution. As expected, reliable single-epoch ambiguity resolution is obviously challenging [38; 39; 40; 41].