Positioning with Impulse Radio Improving Satellite
Background & Objectives
The dramatic impact of environments like urban canyons and indoor areas on GNSS signal reception have led to the development of innovative concepts in order to overcome the imitations of navigation satellite systems. Satellite signals suffer from dramatic attenuation and multipath phenomena in indoor environments leading to either degradation or a total loss of the positioning information. POSIRIS intends to increase the Galileo services into indoor localities through the use of an alternative radiated signal relaying the outdoor level of performance to this restricted environment.
The POSIRIS concept is based on an innovative combination of GNSS signals and a new technology known to be adaptable to indoor environments - the Impulse Radio Ultra Wideband (IR-UWB) technology. Indeed, IR-UWB signals are claimed to present adequate propagation properties in an indoor environment, offer good wall-penetration capacity and allow multipath discrimination.
The work was divided into three phases. Consolidation phase: The goals of this phase were to complete the specification of the POSIRIS system and to refine the development process and organisation issues in a project plan. The scope of the project has been specified in order to demonstrate the feasibility of the POSIRIS signal generation with the help of a relay prototype. Work related to the prototype development has been achieved in the phase referred to as the implementation phase. Implementation phase: The implementation phase included two types of activities managed in parallel. The first was based on a paper study to perform a trade-off on the potential solutions leading to the identification of a complete system design. The second focused on the activities leading to the development required for the emission of the POSIRIS signal.
Added to the technical part of the project, activities related to business and marketing were performed. A business plan document has been achieved. In parallel to this market consideration, a study on the technology transfer gave the opportunity to complete a survey on UWB technology. A review of standardisation and promoting bodies allowed identifying the actors which would be useful for assisting the technology transfer phase of the future POSIRIS product. One of the main issues that came out of this study was the impact of regulation. Since the UWB devices are emitting signals that overlay other systems, the regulation bodies (CEPT in Europe and FCC in the USA) defined an emission mask to avoid any potential interference. This emission mask is a critical issue for the POSIRIS signal definition. Technology transfer phase:
GNSS solutions suffer from signal attenuations and lack of visibility in urban or other masking areas, giving unsatisfactory performances. The POSIRIS concept intends to extend the positioning and navigation functions into indoor environments since satellite-based systems are limited to outdoor/light indoor environments. The origin of the concept to be studied during the POSIRIS project was based on Pole Star R&D department identifying complementarities between GNSS and a new technology referred to as UWB.
Using UWB signal characteristics, i.e. fine timing resolution and indoor propagation, a network of relays sends satellite synchronisation signals inside buildings, which allows the user terminal to track and acquire in-view GPS satellites. These signals are also processed by the user terminal to compute the deep indoor position. A first relay prototype will be developed during the project with the aim of completing the first POSIRIS signal studies and UWB channel propagation characterisation.
Work performed & results
One part of the POSIRIS relay prototype has been developed. The relay architecture is divided into two subsystems, the GNSS subsystem and the UWB transmitter. The GNSS subsystem is composed of two main modules, the typical component of a GNSS receiver and the POSISIR core. The GNSS receiver was selected in order to offer the highest access level of the inner signal processing. The POSIRIS core has been implemented on a FPGA that runs the applications designed for the process of the GNSS inputs data to generate the output POSIRIS logical signal. A UWB transmitter (Tx) has been developed. The objective of the UWB Tx was to generate a short pulse (3ns) triggered by the input signal supplied by the GNSS subsystem. Once the relay beacon prototype interfaces have been validated, the impact of the antenna and propagation channel will be investigated. A large set of parameters (pulse repetition frequency, phase, burst length, etc.) have been tested. These measurements led to highlighting the needs of the complete indoor channel characterisation following its dramatic impact on signal reception. Indeed, the first link budget analysis shows the need for a good knowledge of UWB signal propagation properties to design a processing gain process at receiver level.