Research Online: Optimizing performance of dual-frequency mass-market chips

By Paolo Crosta, Paolo Zoccarato, Rafael Lucas and Gerarda De Pasquale, European Space Agency

Test set-up. (Image: Authors)

Most mass-market manufacturers have already developed a dual-frequency chip or will soon do so. What is still not completely clear is the main benefit of adding the second frequency. Is it beneficial just for correcting ionospheric error?

Will it provide an improvement of the ranging error thanks to the wideband nature of the signal broadcast on the second frequency and their multipath rejection capabilities? Is it improving the measurement quality by means of a higher transmitting power?

Could it be exploited as a source of data for the provision of accurate orbit and clock corrections? What is the best PVT algorithm to apply to a multi-constellation dual-frequency mass-market chip?

To answer these questions, an evaluation kit of the Broadcom chip BCM4775 has been tested — the first dual-frequency mass-market chip commercially available.

Results show:

• the code noise (multipath) is often the main source of error, hiding the benefits of more accurate clocks and orbital data.
• wide-band signals are very beneficial for multipath rejection. Position fix based on E5a-L5-only measurements even with fewer satellites can outperform L1-E1-only in tests performed this September (impact of the new Galileo satellites).
• after deactivation of the duty-cycle tracking on Android phones, the carrier phase measurements are improved and we do not experience any longer filter resets in the position Kalman filter.

More information at www.ion.org/publications/browse.cfm.