GNSS and UMTS Technology Demonstrator
Background & Objectives
Positioning based on a mobile radio network (currently GSM in Europe but in the near future UMTS) reaches high levels of availability in urban environments. The received signal by the mobile terminal is strong when compared to GNSS and can easily penetrate walls and reach inside buildings. However, accuracy is usually poor and typically GNSS positioning provides between 10-50 times greater accuracy than mobile phone positioning. Thus it is clear that by merging both these systems in an efficient way, advantages could be taken from the strengths of each individual system, overcoming their respective deficiencies. The GUTD concept is a processing system which allows the study of the synergies identified at signal processing level and navigation level, because these are the enablers of the combination of UMTS technology into a mass-market receiver.
The system is implemented in MATLAB® and VHDL. The first provides the means for studying the signal processing algorithms, hybridisation of the systems and identification of synergies of these algorithms. The second is focusing on the hardware feasibility for the high data-rate processing, in particular at the level of signal processing. These functions have been used to run simulations which are representative of simple cases, in which GNSS and UMTS signals are brought together. Signal processing has proven that the signal was acquired and tracked, and symbols from base-band signal have been extracted from both GNSS and UMTS base-band signals. At the level of the hybridisation, the partial tight coupling approach was adopted and the measurements were combined, leading to a computed position solution.
GUTD conducts a feasibility analysis of the hybridisation between Galileo and UMTS systems with the goal of assessing the increase of position availability. The synergies between both systems are studied at two critical levels: signal processing and navigation.
Signal processing: the analysis of the receiver architectures shows that both receivers use acquisition and tracking blocks at baseband level. Navigational level: the hybridisation between GNSS and UMTS at navigation level is achieved by running simulations on three scenarios
- GNSS and UMTS,
- there are more measurements from one than the other, and
- only two TDOAs are available for each system.
This approach has proven the increase of availability of the position at the receiver by using both GNSS and UMTS systems following a hybrid approach. The work plan of this project involved parallel activities for:
- scientific investigation and specification of algorithms;
- software development.
VHDL was also implemented and tested in comparison against software functions. In the end, simulations were performed and results analysis in the light of the expected results which bring up synergies.
The synergies between the Galileo and UMTS systems are studies at two critical levels: signal processing and navigation. At a signal processing level, the objective was to study the synergies in terms of baseband receiver architectures, considering that both systems employ a CDMA scheme, use PN codes to spread the signal spectrum and rely on correlation processes to track the incoming signal and recover data. At a navigational level, the synergy of GNSS/ UMTS uses tight partial hybridisation algorithms, being a trade off between performance and complexity. The idea is to exploit the generalisation of the explicit closed-form estimator used in the Fang estimator for the generic case of independent TDOA measurements.
Work performed & results
The results show that the simulator is able to track the code delay and carrier phase of the signals using different signal to noise ratios; hence proving the synergies between the GNSS and UMTS receiver architectures. Also, in parallel implementation of the signal processing under MATLAB®, the development of the high-rate signal processing functions in a hardware description language (VHDL) has been performed. In addition to the low-rate signal processing functions commonly computed into processors (software), this hardware implementation constitutes the core of a receiver on which the GNSS/UMTS synergy has been applied. This approach has proven the increase of the position’s availability at the receiver by using both GNSS and UMTS systems following a hybrid approach. The VHDL development and results show that a future receiver (based on FPGA or ASIC), using both GNSS and UMTS signal processing to improve the positioning with a limited increasing of logic, is feasible.