The mixed signal (SiGe BiCMOS) technologies have been under interest in the specific area of signal generation due to good achievable signal quality. Meanwhile, the technology has been improved to reach higher operating frequencies and lower noise figures, too. The SiGe is very well suited for digital receiver implementation at L-band.The advantage of SiGe over GaAs in space use is foreseen in the high degree of integration due to the feasibility of mixing analogue and digital functions on a single chip. This means that the complete microwave system (e.g.

Provision of integrity in harsh terrestrial environment is very difficult due to the increasing rate of failure induced by the local effects. Analysis of these events shall be performed together with the possible countermeasure and detection mechanism in order to minimise the integrity impact maximising service availability and continuity. Ground Integrity Channel as EGNOS and GALILEO will only cover the system events so usage of local solutions is mandatory to cope with the local threats.

Given that a navigation signal is weak when received by a GNSS receiver on earth it can be easily interfered by other signals. Field campaigns, performed up to now, at numerous locations, have shown that the level of interference in Galileo E5 and E6 could be, quite often, significantly higher than the typical level of interference in Galileo E1. In the frame of the ESA GSP activity Interference Information Systems (IIS) several concepts for interference mitigation were proposed and preliminary assessed from a theoretical and conceptual perspective; amongst them the following:1.

Communication links between GNSS satellites are required if the constellation shall operate for an extended time without ground contact. Under such circumstances, jamming resistance is considered a critical requirement and optical links can provide the ultimate protection from ground-to-space jamming. At the same time, low cost, high reliability and small size, mass and power are important to be implemented on a GNSS constellation. The activity shall review the requirements on intersatellite links based on the GNSS architecture.

Communication links between GNSS satellites are required if the constellation shall operate for an extended time without ground contact. Under such circumstances, jamming resistance is considered a critical requirement and optical links can provide the ultimate protection from ground-to-space jamming. At the same time, low cost, high reliability and small size, mass and power are important to be implemented on a GNSS constellation. The activity shall review the requirements on intersatellite links based on the GNSS architecture.

Carrier phase measurements are more precise than pseudorange measurements and are used for high precision services. The quality of the carrier phase measurements influences directly the Galileo/EGNOS Ground-Segment navigation and integrity algorithms output quality, as well as the GPS/Galileo professional and mass market user positioning accuracy. Unfortunately, phase tracking can be severely stressed under ionospheric scintillation (under severe scintillation, phase may change too fast for being tracked by the receiver).

Current optical design of optical instruments is based on conic or aspheric surfaces of revolution (both on-axis and off-axis). Free-form surfaces (surfaces with no axis of symmetry) can now be manufactured thanks to recent advances in Single Point Diamond Turning. Despite this technological breakthrough the theory is unfortunately not at the same level. Free-form surfaces cannot be represented properly in an optical design software and cannot be used for efficient optimisation algorithms.

Studies on high-sensitivity Rx have already focussed on weak-signal (e.g.

The accuracy of tropospheric excess path length estimation in a GNSS receiver can be increased by using an estimate of current or short-term evolution of atmospheric conditions. This information can be provided by ground or space based sensors and numerical weather prediction systems (like ECMWF for a global scale or HIRLAM/MM5 for regional scale). The models and algorithms to process this type of information and convert it into a message for local augmentation systems need to be develped.

The accuracy of tropospheric excess path length estimation in a GNSS receiver can be increased by using an estimate of current or short-term evolution of atmospheric conditions. This information can be provided by ground or space based sensors and numerical weather prediction systems (like ECMWF for a global scale or HIRLAM/MM5 for regional scale). The models and algorithms to process this type of information and convert it into a message for local augmentation systems need to be develped.