## 1 Introduction
investigated the enhancement of positioning accuracy using GNSS collaborative positioning receivers in urban regions [27]. GNSS users have considered differential positioning the sole accurate positioning technique for many decades. Differential positioning provides the highest accuracy with many limitations. The limitations primarily involve the requirement for a reference station with known coordinates, restrictions on the distance between the rover and the reference station, and the necessity for simultaneous observations between the reference and rover stations. PPP is a cost-effective standalone positioning technique, requiring a single GNSS receiver. PPP uses un-differenced, differenced single-frequency, and differenced dual-frequency pseudo-range and carrier-phase observations along with precise satellite orbit and clock products to produce decimeter-to-sub-centimeter positioning in real-time and post-processing [28; 29; 30; 31; 32; 33]. PPP is considered a strong alternative for differential positioning as it provides an accuracy that matches the need for enormous static and kinematic applications. PPP requires only one receiver to collect observations at an unknown station, while the differential technique requires two receivers to gather observations simultaneously, one at a known position station and the other at an unknown station. Robot localization using the GNSS-PPP technique is considered a promising cost-effective tool compared with other techniques that need more investigation from researchers [34; 35]. The GNSS-PPP technique can be used for real-time robot localization applications [17; 36]. This technique enables the design of cyber-physical system (CPS)-based mobile robots according to RAMI 4.0 [37; 38]. An architecture of CPS-based mobile robots for localization purposes is proposed in Figure 1. The choice of an architectural design comprising five layers (physical, sensing, network, and control) draws an analogy with the successful and efficient modeling and implementation of CPS in CNC machine tools [39]. GSM and GNSS (GPS/GLONASS) receiver modules have become increasingly affordable. The implementation of an Arduino unit including GPS and GSM modules, along with a basic Arduino board, costs approximately USD 125 for a single frequency. Typically, single GNSS-based module (GPS or GLONASS) devices supporting dual-frequency functionality are relatively more expensive (about 82%) than single-frequency ones. A multi-GNSS Arduino unit with a dual frequency typically costs around 76% more than a single-GNSS unit. Notably, prices may also vary based on the brand and optional features of the devices. The widespread adoption of this architecture for mobile robot localization based on an online IoT system in industrial applications has faced setbacks due to constraints on position accuracy [40]. Researchers have continued their efforts for more than two decades to increase the accuracy provided by PPP. PPP accuracy depends mainly on the used GNSS systems (single or mixed), observation type (single or dual), duration of observations, satellite geometry, and processing software capabilities [41; 42; 43; 44; 45; 46; 47]. Kinematic PPP could be used for different applications in strategic fields such as transport, mobile robots, infrastructure, hydrography, and precision agriculture. Also, it is useful in areas where the GNSS infrastructure is not completely developed [48]. Kinematic PPP is considered a hot topic for research, and there is a great research effort dedicated to improving the accuracy of kinematic PPP. Many researchers proved that kinematic PPP provides less accuracy than static PPP because of limitations in collected observations for each station. Static PPP could involve hundreds of collected observations at each station [33], while kinematic PPP deals only with one observation at each station. Figure 1: The architecture of CPS-based mobile robots for localization function.