The Variometric Approach Applied to the Carrier-Phases of a Multi-Constellation Chipset for Smartphone and LBS Applications

In the past, the possibility to access to dual frequency GNSS was achievable only with expensive and high quality receivers, in environment and conditions that are different from the everyday lifestyle. The use of dual-frequency is relevant because it allows increasing the accuracy and the reliability on the user’s position estimation. The technological evolution has brought today the possibility to extend the advantages of the high accuracy positioning to a larger number of users and applications. The way of providing these benefits goes through GNSS receiver devices designed to enhance the Location Based Services (LBS) applications for smartphones, clothes, tablets and watches. These solutions open the door to a large number of high-accuracy applications including lane-level navigation, mobile augmented reality (AR), autonomous driving, navigation of visually impaired and physically disabled people, micro geo-fencing, extremely precise analyses of the athletes’ performance in various sports and smart city asset management. The main objective of this work is to investigate on precise positioning with a GPS and Galileo enabled chipset embedded in a smartphone. Sapienza research team, as member of the GSA GNSS Raw Measurements Task Force, with contribution by Politecnico di Milano, is investigating the area of real time precise positioning with single frequency, focusing on the benefits of multi-constellation GNSS and raw data quality provided by a smartphone. The analysis is carried out with code- and carrier-based algorithms in different scenarios. Currently the smartphones use only one frequency (L1): this is an important constraint in the design of the precise positioning algorithm mainly due to ionospheric effect. Hence, the work is based in two main algorithms: the first uses the carrier phase differential approach (Static or Kinematic) in conjunction of a reference GNSS networks; the second is based on the variometric approach using the VADASE algorithm, using the carrier phase but without external data. Modern GNSS chipsets are multiconstellations (GPS, GLONASS, Galileo, Beidou) and after the release of the N version of the Android operating system, the raw data are obtainable from a phone or tablet. However, from a technical point of view, the raw data, especially the carrier-phase, are not directly available in standard format and must be properly parsed. Moreover, based on these parsed data, the work analyses the main errors. The primary error source on smartphones lies not in the GNSS chipset, which actually offers great performance in terms of tracking availability and code-based accuracy, but in the antenna, whose chief failing is its poor multipath suppression. High accuracy positioning requires a stable antenna position for referring the position. However, moving smartphones are constantly changing attitude (which affects the antenna gain also), altitude (e.g. when the smartphone is kept in hand along the body or in front of the face for reading) and obstruction conditions. In order to quantify the impact of these scenarios, tests have been conducted. The use of multi-constellation smartphone allows to increase the accuracy and the availability of the solution. In particular, the smartphone can reach decimetre accuracy in static condition and sub-metre when used in urban vehicle scenario; furthermore, the variometric approach is able to track the smartphone displacement with cm/sec velocity accuracy. 30 New dual-frequency GNSS receiver devices, designed to enhance Location Based Services (LBS) applications, use L1E1 and L5E5 GPS and Galileo frequencies to compute the position more accurately in both urban and open area environments. These receivers offer several benefits: the measurements from the two frequency can combined obtaining a new a iono-free measurement that completely remove the ionospheric effect; thanks to the narrower BOC (Binary Offset Carrier) modulation and to the higher chipping rate of L5E5 signals, the code- and carrier-phases from L5E5 frequency are less noisy than those in L1E1, they are more robust against multipath reflections, and, more in general, they increase the quality of the satellites’ tracking and the detection of cycle slips. The use of two frequencies allows to decrease the time the resolve the carrier-phases‘ ambiguities, speeding up the transition from positioning based on code-phase tracking to positioning based on carrier-phase tracking. Finally, the signals transmitted in L5E5 are easier to track due the higher transmitting power, allowing an higher sensitivity that can be useful different scenarios such as urban canyon, presence of foliage and light indoor environment. In this context, the article presents also some preliminary results, in terms of accuracy and availability, of precise positioning’ algorithms applied to a dual-frequency multi-constellation GNSS chipset designed for LBS.