ULTRALOW POWER GNSS RECEIVER

Abstract

A system for updating almanac data in low-power GNSS mobile devices (30-34), including a server that keeps a local copy of the almanacs stored in each of the devices and evaluates repeatedly the quality of the almanac of each of the mobile devices (30-34). The evaluation comprises predicting the Doppler shifts for all the satellites potentially receivable by the mobile device using the orbital parameters in the copy and comparing the result with an accurate determination of the same Doppler shifts based on real orbital data.

Claims

1. A system comprising an almanac update server and a plurality of GNSS-capable devices in a low-power wide-area network, wherein the GNSS capable nodes can determine their position based on signals from a plurality of geolocalization space vehicles, and the almanac update server has access to the real positions and speeds of the space vehicles, wherein the devices store orbital data of space vehicles for the purpose of predicting Doppler shills of said space vehicles, and the almanac update server is arranged to maintain a copy of the orbital data stored in the devices, and to compute, for each device and space vehicle: a predicted Doppler shill based on the orbital data stored in the digital copy of the device an actual Doppler shift based on position and speed of the space vehicle derived from another source of orbital data. and, wherein the almanac update server evaluates the quality of the almanacs of each of the mobile devices using the copies and, based on the evaluated quality of the almanac, decides whether to transmit updated almanac data to the mobile devices.

2. The system of claim 1, the evaluation of the quality of the almanacs comprises the computation of a predicted Doppler shift of a selected space vehicle received by a selected device based on the copy of its almanac in the almanac update server, the difference between the predicted Doppler shift with the actual Doppler shift of the selected space vehicle received by the selected device, the comparison of the difference against a determined threshold.

3. The system of claim 2, wherein the almanac update server is arranged to select a subset of updated orbital parameters of the selected space vehicle that bring the difference below the threshold, and to transmit the subset to the selected device.

4. The system of claim 1, comprising an A-GNSS server arranged to receive intermediate localization results from the GNSS-capable devices and to compute a position of the GNSS-capable devices based on the intermediate localization results.

5. The system of claim 4, wherein the intermediate localization results include identification codes of acquired space vehicles and delays of the respective ranging codes or pseudo-ranges to the acquired space vehicles.

6. The system of claim 1, comprising a plurality of almanac update servers and/or a plurality of A-GNSS servers in one low-power wide-area network.

7. The system of claim 1, wherein the updated orbital data consist in a proper subset of orbital parameters of the space vehicle.

8. The system of claim 1, wherein the low-power wide-area network is a LoRaWAN network.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The invention will be better understood with the aid of the description of an embodiment given by way of example and illustrated by the FIGURE that shows a diagram of the system of the invention.

DETAILED DESCRIPTION OF POSSIBLE EMBODIMENTS OF THE INVENTION

[0035] With reference to the FIGURE, the system of the invention is inside a LPWAN 10 that could be a LoRa network and, in that LPWAN, at least one almanac update server 20 and a plurality of GNSS-capable devices 30-34, and preferably one or more A-GNSS servers 25.

[0036] The number of GNSS devices in a LPWAN network like LoRaWAN can be more than several thousand. When several devices are present, it may be advantageous to deploy a plurality of almanac update servers 20, and A-GNSS servers 25, each of them taking care of a subset of the GNSS devices.

[0037] The almanac update server 20 and the a-GNSS server 25 are drawn as separate blocks to underline their separate function but they could be realized by software modules running in a common server and share any number of software and hardware resources. The almanac update server 20 and the a-GNSS server 25 may be embedded in LPWAN access points, with a LPWAN physical interface, or be realized by separate computers, communicating with the other nodes in the network 10 through a not represented proxy, or in any other suitable way.

[0038] Each of the devices 30-34 has a GNSS radio receiver that can receive and demodulate the radio signals broadcast by a plurality of space vehicles. The FIGURE represents five satellites 110-114 controlled by a ground control station 100 and an internet server 205 that publishes the orbital position of all the satellites in real time. The satellites 110-114, the ground control station 100, and the internet server 205 are not part of the system of the invention but interoperate with it. Although the drawing shows five satellites managed by a single ground centre and a single internet server to avoid clutter, real numbers are much higher and the infrastructures managing the GPS, BeiDou, Glonass, and Galileo constellations is highly complex, comprising several control centres and control stations.

[0039] As mentioned in the introduction, devices 30-34 operate with the assistance of the A-GNSS server 25. The devices (32 and 33 in the FIGURE) for which a position fix is required acquire the signals broadcast of a number sufficient (at least 4, put preferably more) of satellites and upload an intermediate localization result to the A-GNSS server 25 (arrow 80). The intermediate result may include the identification code of the acquired satellites, and the delays of the respective ranging codes (pseudo-ranges).

[0040] The A-GNSS server computes the position of the devices that have requested a fix from the uploaded intermediate results. The positions may be retransmitted to the original device, if necessary, or used in any other way. The server 25 makes use of the real and accurate position of the satellites that are available from server 205.

[0041] As mentioned in the introduction, the mobile devices 20-34 need not know the orbital parameters of the satellites to compute their position, because this task is delegated to the server 25, but a certain knowledge of the orbital parameters is essential to reduce the acquisition time, either because the receiver will search only the satellites that are expected to be visible above the horizon at any given moment, and because the span of frequencies searched can be reduced by a prediction of the Doppler shift. Server 20 is responsible for ensuring that the mobile devices 30-34 always have sufficient information on the satellite's positions and speed.

[0042] Server 20 provides almanac data to the mobile devices 30-34, requesting it, for example, from the internet server 205, or from any reliable source. At the same time, the server keeps, for each of the devices that it manages, a copy of the almanac in its internal memory 203. All the updates to the almanac in the mobile nodes 30-34 are reflected in corresponding changes of the copies such that the two are always identical.

[0043] The server 20 evaluates repeatedly the quality of the almanac of each of the mobile devices 30-34, using its local copies. The evaluation comprises predicting the Doppler shifts for all the satellites potentially receivable by the mobile device using the orbital parameters in the copy 302 and comparing the result with an accurate determination of the same Doppler shifts based on real orbital data, for example obtained by the server 205.

[0044] Thanks to this comparison, the server 20 can determine at any moment and for each device, if the orbital data already known to the device are good enough to acquire quickly all the possible satellites or, on the contrary if some satellites would be impossible or too difficult to acquire because the difference between the predicted Doppler shift and the real Doppler shift has exceeded a given threshold. In the latter case, the server schedules a partial almanac update, that will be downloaded to the interested device at the first available opportunity (arrows 70).

[0045] Importantly, the partial update interests only a fraction of the almanac data. On top of that, satellite updates are limited, most of the times, to a few parameters of the orbital model of that satellite. Based on the digital twin state the server decides which minimal set of parameters of that SV must be updated to achieve correct Doppler prediction.

REFERENCE SYMBOLS IN THE DRAWING

[0046] 10 LPWAN network

[0047] 20 almanac update server

[0048] 25 A-GNSS server

[0049] 30-34 GNSS-capable devices

[0050] 70 download of an almanac update

[0051] 80 upload of intermediate result

[0052] 100 ground control station

[0053] 110-114 satellites or Space Vehicles

[0054] 203 twin copies of almanacs

[0055] 205 Internet server