Advanced Baseband

The European satellite navigation system, Galileo will provide several signals that are freely available. These new Open Service (OS) signals make it possible to build a dual frequency navigation receiver that does not require the user to subscribe to a premium service. A dual frequency receiver can reduce the navigation errors caused by Ionospheric delays. The Galileo OS signals are transmitted in the L1 and E5 band and have a different signal structure to that of GPS and a much higher bandwidth.

The EU forecasts a rapid adoption of dual-system GNSS receivers which support both GPS and Galileo. By 2011, more than 50% of the installed base of GNSS receivers will support Galileo. This in turn means that the majority of new GNSS receivers sold are dual system GNSS receivers. The predicted fast adoption depends significantly on the success of the deploying the Galileo systems and promised technical benefits turning into reality.

Some of the benefits with the Galileo signals include improved urban coverage, lower cross correlation when compared to GPS, higher sensitivity and indoor coverage.

The GREAT project is developing a ‘fast track’ Galileo advanced baseband, capable of operating with both the Galileo and GPS signals in the L1-E5a dual band. A detailed study of the E5a signals is also a part of this work package. The key working tasks include the following:

• Define base band system structure for the integrated Galileo / GPS receiver. Optimize system concept for power consumption, and silicon area
• Study the impact of inclusion of the E5 frequency next to L1 with respect to silicon cost, size and power consumption and compare to the potential performance enhancements over an L1-only architecture
• Define concept for integration of GPS and Galileo pseudo-range measurements into acquisition, tracking, and navigation solution
• Develop software algorithms and IP (HDL) for tracking and acquisition of GPS C/A-Code and Galileo BOC(1,1) signals
• Develop software algorithms for the combined processing of GPS and Galileo measurements in the navigation solution

The algorithm development for the Galileo baseband will be based on the existing algorithms for the GPS. The performance of the resulting algorithms will be simulated and their power and silicon area effectiveness will be analysed.  

System performance requirements will be defined based on several application scenarios such as the standalone GPS, assisted GPS, standalone Galileo/GPS and assisted Galileo/GPS. The requirements to the ability of the receiver to acquire and track signals under different environmental conditions are defined based on the environmental scenarios such as the open sky, partly obstructed view, with strong and weak signals and the deep indoor scenario with weak signals only.

The different signal characteristics demand more sophisticated navigation solution algorithms to optimize position accuracy and availability under demanding environmental conditions.

This advanced baseband technology for GNSS receivers, developed by the GREAT project keeps the system costs low, which is one of the crucial requirements for a mass market receiver. This technology of a ‘fast track’ Galileo baseband consumes less power, supporting different Galileo system services and the complete receiver shall be able to compute positions from mixed constellations (e.g. 3D position from 2 GPS and 2 Galileo satellites).

As the major portion of GNSS receivers will be integrated in handheld devices (e.g. mobile phones, smart phones, PDA's and handhelds for recreational use), they have to work reliably in difficult signal environments. The advanced baseband caters to these needs of fast acquisition, high acquisition and tracking sensitivity, high positioning accuracy and for smaller dimensions.