Receiving device for a navigation system

Description of the offer:

Receivers that enable the attitude or the pointing direction of a vehicle are already known. Such attitude can be determined by using the signals transmitted by Global Navigation Satellite Systems (GNSS). Geostationary navigation overlay systems (GNOS) and the European Geostationary Navigation Overlay System (EGNOS) can also be used.

Determining the attitude of any vehicle (space vehicle, aircraft, ship, etc) requires the existence of accurate differential phase measurements of carriers coming from at least two GNSS satellites and received, in general, via a minimum of three non-aligned antennas rigidly mounted on the vehicle. Nevertheless, for two axis attitude determination, also known as “pointing direction” determination, it is possible to determine the attitude with only two antennas.

In addition to knowing simultaneously the position of the receiver and the positions of the transmitters as obtained by tracking and demodulating the GNSS signals, such differential phase measurements allow determining the attitude of the vehicle with accuracies that can be better than one minute of arc, under appropriate conditions.

Current existing solutions present some drawback, as a matter of fact using parallel architectures allow tracking signals continuously, obtaining low random noise in the differential carrier phase measurements. However, given that the signals must pass through different analog devices, unknown bias necessarily arises. On the contrary, in multiplex architectures, measurements are obtained using a single channel which is switched periodically between the various antennas. This eliminates the effects of bias, but considerably increases random noise levels. Each of those architectures thus presents drawbacks in terms of results obtained, or in terms of implementation.

The basic concept of the present invention is to eliminate at least for the most part at least some of the above specified drawbacks by means of an architecture that combines a continuous receiver chain with a multiplex receiver chain. The architecture corresponding to the present invention implements a concept that combines a non-switched receiver section that includes a processor and which is used as a reference channel, together with a receiver section employing antenna signal multiplexing and which includes another processor. A digital signal processor and a frequency synthesizer drive both processors.

The hardware of the presented technology includes a reference antenna and two slave antennas, connected via low-noise preamplifiers to a multiplexer which has an output from which the first processor recovers a navigational parameter. A second processor is fed continuously with the reference antenna whose signal recovers a reference signal representing a parameter of the antenna position. The reference signal is taken into consideration by a digital signal processor operating on the multiplexed signals. The switching time at the reference signal input to the multiplexer is shorter than at the inputs from the other antennas.

Innovations and advantages of the offer:

The innovation of this invention relies in he fact that the receiver is characterized in that switching time allocated by the multiplexer to the input that receives the signal from the reference antenna is shorter than switching time allocated by the multiplexer to other inputs receiving signals from other antennas. So, the receiver is characterized by:

• A first processor comprising the first RF/IF converter downstream from the multiplexer and a first analog-to-digital converter
• A second processor comprising the second RF/IF converter disposed downstream from the reference antenna and a second analog-to-digital converter
• Frequency synthesizer common to the first and second processors and producing a local oscillator signal and a clock signal which are applied respectively firstly to at least the first and second RF/IF converters and to at least the first and second analog-to-.digital converters.
• The proposed innovative receiver comprises a processor block with two sections including a) a baseband converter; b) a numerically controlled carrier oscillator having an output connected to an input of the baseband converter; c) a numerically- controlled code oscillator; d) a code generator; e) a correlator receiving the signal output in baseband from the baseband converter; f) an accumulator receiving the correlation signals as inputs and generating early, punctual and late loop control signals as outputs.

This processor includes a digital processor receiving the loop control signals generated by the accumulator of the reference section and by the accumulator of the slave section.

Domain of Application:

This technological innovation was conceived as an application to improve navigation systems especially for satellites applications. Nevertheless it could be extended to any navigation system, as from earth vehicles to aircrafts, ships, etc.