Satellite payload and method of operation thereof

Abstract

The present application relates to a method for operating a payload having reception and transmission capabilities in Earth orbit, the method including receiving GNSS signals from a GNSS in a GNSS frequency band and transmitting navigation signals in the GNSS frequency band towards Earth. The reception and transmission are performed in a time division duplex (TDD) mode, with alternating time slots for receiving GNSS signals and time slots for transmitting navigation signals. The present application further relates to a corresponding payload and a satellite including such a payload.

Description

[Technical Field]

[0001] This application relates to the field of satellite communications and space-based positioning. In particular, this application relates to a method of operating a payload having receiving and transmitting capabilities, a corresponding payload, and a satellite equipped with such a payload. [Background technology]

[0002] Conventional global navigation satellite systems (GNSS) may suffer from problems such as limited visibility of a sufficient number of GNSS satellites from the user terminal due to, for example, low power of the GNSS signals when they arrive at the ground and / or interference from terrestrial emissions in the GNSS frequency bands, and low signal-to-noise ratio (SNR) of the GNSS signals at the location of the user terminal. Summary of the Invention [Problem to be solved by the invention]

[0003] Therefore, there is a need for improved techniques for positioning, particularly techniques that increase the availability and / or accuracy of positioning. [Means for solving the problem]

[0004] Taking into account some or all of these needs, the present disclosure proposes a method (e.g., a navigation or positioning method) for operating a payload with receiving and transmitting capabilities in Earth orbit, a payload and a satellite, having the features of the respective independent claims.

[0005] One aspect of the present disclosure relates to a method for operating a payload (e.g., a satellite payload, a satellite navigation payload) having receiving and transmitting capabilities in Earth orbit. The method may include receiving GNSS signals from a GNSS in a GNSS frequency band. The method may further include transmitting navigation signals toward Earth in the GNSS frequency band. The navigation signals may be based at least in part on the received GNSS signals. The receiving and transmitting may be performed in a time division duplex (TDD) mode having alternating time slots for receiving GNSS signals and time slots for transmitting navigation signals. Furthermore, the receiving and / or transmitting may be performed in two or more GNSS frequency bands. Additional transmissions may be performed in non-GNSS frequency bands. It should be understood that the term GNSS signals may cover navigation or augmentation signals (e.g., SBAS signals) of any higher-orbit satellite, and the term GNSS may cover any higher-orbit satellite navigation or augmentation system (e.g., SBAS).

[0006] By providing navigation signals as described above, the availability of navigation services may be improved along with the received power on the ground. Furthermore, additional benefits may be gained from frequency diversity and / or measurement diversity.

[0007] In some embodiments, the duty cycle of the TDD mode may be synchronized with the GNSS timing epoch, which may be derived (e.g., calculated) from the on-board ODTS using the GNSS signal.

[0008] In some embodiments, the method may further include performing at least one of orbit determination and time synchronization for the satellite payload based on the GNSS signals. The orbit determination and time synchronization (ODTS) may use an on-board filter, such as a Kalman filter, and / or a precise point positioning (PPP) algorithm. It may generally be based on content / information transmitted with the GNSS signals. The ODTS may include the timing of the GNSS. It can also provide an estimate of the epoch.

[0009] In some embodiments, TDD synchronization of the TDD mode duty cycle to the timing epochs of the GNSS may be performed based on the results of at least one of the orbit determination and the time synchronization.

[0010] In some embodiments, at least one of the orbit determination and time synchronization may be based on high precision corrections received with the GNSS signals. Additionally or alternatively, at least one of the orbit determination and time synchronization may use information regarding the authenticity of the GNSS signals. Additionally or alternatively, at least one of the orbit determination and time synchronization may use information regarding the integrity of the GNSS signals.

[0011] In some embodiments, at least one of the orbit determination and time synchronization may be based on one or more of a Space Based Augmentation System (SBAS) message received along with the GNSS signal, ranging authentication and / or message authentication of the GNSS signal, a High Accuracy Service (HAS) message received along with the GNSS signal, and / or an Integrity Support Message (ISM) received along with the GNSS signal.

[0012] In some embodiments, the method may further include maintaining signal tracking of the GNSS signal(s) during a time slot for transmitting the navigation signals to avoid reacquisition based on a result of at least one of the orbit determination and the time synchronization. In particular, the signal tracking may be maintained to avoid reacquisition of the GNSS signal tracking when transmission of the navigation signals by the payload stops and reception of the GNSS signals by the payload resumes. Maintaining signal tracking may include, for example, maintaining a tracking algorithm within a pull-in boundary or a lock indicator boundary of the tracking loop and / or extrapolating tracking parameters and states to prevent the tracking loop from leaving the pull-in range or losing lock during a time slot when reception of the GNSS signals is interrupted and the navigation signals are transmitted.

[0013] In some embodiments, the method may further include demodulating the GNSS signal to obtain GNSS content transmitted together with the GNSS signal. The method may further include including at least a portion of the GNSS content in a navigation message transmitted together with the navigation signal in the GNSS frequency band towards Earth. The GNSS content thus obtained may, for example, relate to a (low latency) GNSS message.

[0014] In some embodiments, the GNSS content may relate to one or more of an SBAS message, a SAR return link message, an ISM, an HAS message, an emergency warning message, and / or an authentication message.

[0015] In some embodiments, the GNSS frequency band may be a first GNSS frequency band, and the method may further include transmitting, in a frequency division duplex (FDD) mode, a second navigation signal toward Earth in a second GNSS frequency band different from the first GNSS frequency band or in a non-GNSS frequency band. The transmission and / or reception in the second GNSS frequency band may be continuous.

[0016] In some embodiments, the method may further include performing radio occultation based on the GNSS signals received in the time slots for receiving GNSS signals in the TDD mode.

[0017] In some embodiments, the method comprises performing reflectivity measurements based on the received GNSS signals, e.g., reflected off the Earth's surface, in a time slot for receiving GNSS signals in TDD mode. It may further include performing.

[0018] In some embodiments, the method may further include performing operations to detect and / or locate unwanted emissions in GNSS frequency bands. Locating unwanted emissions may, in some implementations, involve multilateration using multiple satellite payloads.

[0019] In some embodiments, the method may further include performing radio interference estimation in a time slot for receiving GNSS signals in TDD mode.

[0020] In some embodiments, the navigation signals may be navigation signals for code-based ranging measurements, carrier-based ranging measurements, and / or Doppler measurements at the receiver, and / or for low-complexity acquisition at the receiver. In some embodiments, the navigation signals may be navigation signals for code-based ranging measurements, carrier-based ranging measurements, and / or Doppler measurements at the receiver.

[0021] In some embodiments, the method may further include receiving an uplink signal from the user equipment for two-way navigation services. The two-way navigation services may be related to one or more of a time transfer between the user equipment and a payload, a time transfer between the user equipment and another user equipment, a time limit for the user equipment, a demarcation of the user equipment's location, and / or a verification of the user equipment's location by the payload.

[0022] In some embodiments, the payload may be a satellite payload carried on a satellite in low Earth orbit (LEO).

[0023] In some embodiments, several payloads may be provided onboard each spacecraft in a layer of a multi-layered satellite navigation system. The multi-layered satellite navigation system may include, for example, one or more satellites in MEO, one or more satellites in LEO, and / or one or more satellites in GEO. Thereby, several payloads may be distributed across a layer of a multi-layered satellite navigation system comprising, for example, one or more satellites in LEO. The spacecraft (e.g., satellites) in a given layer may be positioned in different orbital planes, at different inclinations, and / or at different altitudes.

[0024] In some embodiments, the configuration of the uplink signal may depend on prior reception of a downlink navigation message via one or more of a signal from the payload, a signal from another payload, and / or a GNSS signal.

[0025] In some embodiments, the GNSS frequency band may be one of bands E1, E6, E5, E5a and E5b defined for Galileo, or one of bands L1, L2 and L5 defined for GPS.

[0026] Another aspect of the present disclosure relates to a satellite payload having receiving and transmitting capabilities, which may be configured to perform a method according to any of the aforementioned aspects or embodiments thereof.

[0027] Another aspect of the present disclosure relates to a satellite comprising a satellite payload according to the aforementioned aspect.

[0028] Another aspect relates to a satellite navigation system comprising one or more payloads according to the above aspect.

[0029] It will be understood that apparatus features and method steps may be interchanged in many ways. In particular, details of a disclosed apparatus or system (e.g., a satellite payload, a satellite, or a satellite constellation) can be implemented by a corresponding method of operating the apparatus / system or portions thereof, and vice versa, as will be understood by those skilled in the art. Furthermore, it will be understood that any of the above statements made with respect to an apparatus / system equally apply to the corresponding method, and vice versa.

[0030] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram illustrating a schematic example of a framework in which the techniques according to the present disclosure may be applied. [Figure 2] 1 is a flowchart illustrating an example method of operating a payload according to an embodiment of the present disclosure. [Figure 3] 1 is a diagram illustrating a schematic example of using TDD mode in a terrestrial communication system; [Figure 4] FIG. 2 is a diagram illustrating a schematic example of using TDD mode in a satellite navigation scenario according to an embodiment of the present disclosure. [Figure 5A] FIG. 2 illustrates a schematic diagram of an example of timing synchronization for TDD transmission timeslots, according to an embodiment of the present disclosure. [Figure 5B] FIG. 2 illustrates a schematic diagram of an example of timing synchronization for TDD transmission timeslots, according to an embodiment of the present disclosure. [Figure 6] 3 is a flowchart illustrating an example of an optional step for the method of FIG. 2, according to an embodiment of the present disclosure. [Figure 7] FIG. 1 is a block diagram that schematically illustrates a procedure for assisting tracking of a GNSS signal received in TDD mode with information derived from continuous reception of another GNSS signal, in accordance with an embodiment of the present disclosure. [Figure 8]3 is a flowchart illustrating an example of a further optional step for the method of FIG. 2 according to an embodiment of the present disclosure. [Figure 9] FIG. 2 is a diagram illustrating a schematic example of a scheme for relaying GNSS message content to a navigation signal, according to an embodiment of the present disclosure. [Figure 10] 3 is a flowchart illustrating an example of a further optional step for the method of FIG. 2 according to an embodiment of the present disclosure. [Figure 11] FIG. 1 is a diagram illustrating a schematic of an example framework for performing radio occultation according to an embodiment of the present disclosure. [Figure 12] FIG. 1 illustrates a schematic diagram of an example framework for performing radio frequency interference estimation according to an embodiment of the present disclosure. [Figure 13] FIG. 1 illustrates a schematic diagram of an example framework for integrating bidirectional signaling functions, according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0032] overview The present disclosure relates to payloads (e.g., satellite payloads), methods of operating such payloads (e.g., navigation or positioning methods), and corresponding satellites. One example of such a satellite is a LEO satellite for providing positioning, navigation, and timing (PNT) services, or LEO-PNT satellite for short. While the present disclosure frequently refers to LEO-PNT satellites and payloads, this should not be construed as limiting in any way; rather, the present disclosure relates to suitable satellites and payloads other than LEO-PNT satellites and payloads, as will be understood by those skilled in the art, and for reasons of brevity refers to LEO-PNT as a non-limiting example. It is understood that when the disclosure refers to LEO-PNT satellites, payloads, and methods of operating them, other suitable satellites and payloads are also intended to be included.

[0033] Generally, LEO-PNT (as a non-limiting example of satellites, payloads, and methods according to the present disclosure) aims to augment and / or complement satellite navigation systems in Medium Earth Orbits (MEO; e.g., 2,000-35,786 km above sea level), inclined geosynchronous orbits (IGSO), and geostationary orbits (GEO), such as GNSS and SBAS, with additional signals transmitted from payloads deployed in LEO, whose transmissions are governed by GNSS time and whose positions at the time of transmission are referenced to the GNSS reference frame.

[0034] 1 illustrates an exemplary framework in which techniques according to embodiments of the present disclosure may be employed. In this framework, a satellite (e.g., a LEO satellite, a LEO-PNT satellite) 10 receives higher-orbit navigation or augmentation system signals (e.g., MEO GNSS signals, GEO augmentation signals, SBAS signals, etc.) from one or more higher-orbit satellite navigation or augmentation system (e.g., GNSS, SBAS, etc.) satellites 20, e.g., in the L-band. Both satellites can transmit signals to user equipment on the ground or within the Earth's atmosphere. The signals from satellite 10 may be referred to as navigation signals (e.g., LEO-PNT signals), and the signals from satellite 20 may be referred to as GNSS signals, without any limitation intended.

[0035] LEO-PNT can augment and / or complement satellite navigation in a variety of ways depending on the intended user and their needs, including providing signals that enable user equipment to derive positioning, velocity, and timing-related measurements (e.g., ranging, Doppler, and carrier phase measurements) and signals that deliver navigation-related data to user equipment.

[0036] LEO-PNT signals enhance a user's experience of GNSS signals, e.g., with respect to performance such as accuracy, availability, robustness and resilience, and convergence time of high-precision PVT solutions (e.g., PPP algorithms) when GNSS signals are impaired due to challenging environments (e.g., signal reflections by obstacles, buildings or natural obstructions, higher attenuation under canopies or inside buildings, higher noise floors, etc.) LEO-PNT signals may also enable user equipment to derive positioning, navigation, and timing information and solutions using only those signals and / or in combination with GNSS signals and / or in combination with other information sources such as dead reckoning, cellular communication systems, and any combination thereof.

[0037] The LEO-PNT signal's contribution to improved performance is made possible by features including: An increase in the number of satellites available to user equipment (compared to dedicated GNSS satellites) to combine with other sources of PNT signals, such as transmitters from GNSS in MEO, IGSO and GEO systems, and terrestrial cellular systems (e.g., 4G / 5G, WIFI). This is useful in difficult environments to improve the number of satellites available for positioning-navigation-timing and the resulting geometry of the signals processed by user equipment to derive a position-velocity-timing solution. Providing user equipment with a signal with increased received power, which allows for improved signal acquisition and tracking performance (e.g., reduced acquisition time and energy consumption, improved carrier cycle slip and loss of lock statistics, improved multipath estimation and mitigation as the latter algorithms work better with the higher signal-to-noise ratio of line-of-sight signals, improved data demodulation and availability), and improved coverage in environments affected by increased propagation loss (e.g., canopies, indoors). Measurement diversity. The faster movement of the payload transmitting the LEO-PNT signal introduces a different error behavior in the measurement of the signal by the user equipment when compared to the signal from the MEO. This signature difference, a source of diversity, is due to different noise, error statistics, This translates to multipath, faster decorrelation of measurements, etc., which user equipment algorithms can exploit to improve performance (accuracy, convergence time, availability when combined with dead reckoning sensors, etc.). Frequency diversity. LEO-PNT signals can be transmitted on carriers in frequency bands similar to GNSS frequency bands, or additionally or alternatively, on frequency bands different from GNSS frequency bands. The latter benefits the user experience and the performance accessible to user equipment. Frequencies lower than current GNSS frequencies (e.g., signals on carrier frequencies lower than 1 GHz) would feature better propagation, less attenuation under canopies or inside buildings, and consequently improved performance for use cases in these conditions. Frequencies significantly higher than current GNSS frequencies (e.g., higher than 5 GHz) typically feature increased signal bandwidth (a source of improved ranging accuracy and robustness) and are less affected by propagation through the ionosphere, resulting in improved accuracy and robustness. Examples include UHF, S-band, C-band, and Ku / K / Ka-band frequency bands.

[0038] Frequency diversity is beneficial for LEO-PNT signals and targeting capabilities. Nevertheless, transmitting LEO-PNT signals in the same band as GNSS signals is also beneficial. In fact, it allows user equipment to receive LEO-PNT signals using the same RF front-end and potentially similar baseband processor as used for GNSS signals, which significantly simplifies user equipment and, therefore, adoption of LEO-PNT signals.

[0039] Furthermore, in addition to frequency diversity, transmitting at multiple frequencies also allows for mitigation of ionospheric effects (e.g., a combination of two or more frequencies) and helps support greater accuracy of a user's position, velocity, and time (PVT). Therefore, it may be desirable for LEO-PNT signals to be transmitted in two, or even three, frequency bands in common with GNSS (e.g., E1, E6, and E5 for Galileo, or L1, L2, and L5 for GPS, or a combination of two or three of these, etc.).

[0040] Related to PNT applications, distribution of data with content supporting user algorithms and / or user experience via LEO-PNT signals can also be advantageous. Indeed, LEO-PNT signals experience lower free-space loss, which can result in a higher SNR, which can enable higher throughput and / or higher availability compared to signals from MEO. Furthermore, the time lapse during which signals from LEO are obstructed to users on Earth, for example by buildings or natural obstructions, is shorter compared to MEO signals. This contributes to reducing the delay or time required to properly demodulate all necessary information.

[0041] Examples of such data relevant to PNT applications include (but are not limited to) data related to orbit and clock data of navigation signals (e.g., GNSS, LEO, etc.), corrections thereto (e.g., PPP corrections), information necessary to estimate the reliability of signal integrity (e.g., SBAS, integrity support messages for the ARAIM concept), information necessary to authenticate the source of data and / or signals (e.g., OSNMA from Galileo), information related to emergency warnings (e.g., EWS messages), and other information relevant to the application derived from the user equipment's PVT solution. These data may be uploaded to the LEO-PNT payload by a ground-to-space link, a satellite communication link, or advantageously received directly on-board via signals arriving from higher-orbit navigation or augmentation system signals, such as MEO GNSS signals or augmentation signals from GEO (e.g., SBAS).

[0042] LEO-PNT signals are signals that utilize the properties of the signal or the proximity of the payload to Earth, being in LEO, or a combination of both, to communicate with GNSS in the areas described below. It can also complement satellite navigation and terrestrial navigation systems.

[0043] LEO-PNT signals and systems can contribute to supporting positioning with very low energy per fix, which is beneficial for increasing the battery life of asset tracking devices.

[0044] Additional capabilities include support for bidirectional PNT links, involving processing by the LEO-PNT payload of signals uplinked by user equipment. LEO-PNT satellites' proximity to Earth and the low equivalent isotropic radiated power (EIRP) required for terrestrial user terminals can facilitate the provision of new bidirectional services. Some possible bidirectional services include two-way time and frequency satellite transfer using LEO satellites, emergency call detection and location, and user position verification, where uplink or bidirectional signals from the user are utilized to verify the user's position by processing on the LEO-PNT satellite or ground segment. In some cases, it may be appropriate to consider placing the uplink carrier frequency in a band nearby (e.g., adjacent) to the GNSS band to reduce the complexity of the user terminal and LEO-PNT payload antennas.

[0045] LEO-PNT systems may also support ancillary functions related to GNSS signals received from LEO, such as GNSS radio occultation (RO), GNSS reflectometry, and monitoring the radio frequency spectrum to detect and locate RF interference that may be generated on Earth in the GNSS frequency bands.

[0046] LEO-PNT satellites can carry GNSS radio occultation (GNSS-RO) equipment to collect measurements from low-altitude GNSS satellites and downlink them to the ground (e.g., via telemetry, tracking, and control (TTC), and possibly one or more inter-satellite link (ISL) hops). Alternatively or additionally, the estimation process can be performed on the LEO-PNT payload, and the results can be transmitted to the user via LEO-PNT signals. The principles of radio occultation can be extended beyond GNSS signals to incorporate other signals received by the LEO-PNT payload and occulted by the atmosphere, particularly LEO-PNT signals received from other LEO-PNT satellites or signals from ISLs between LEO-PNT satellites. Information derived from radio occultation measurements (e.g., GNSS-RO, ISL-RO, or LEO-PNT-RO) may be provided and utilized by other systems or infrastructures involved in providing satellite navigation services (e.g., terrestrial SBAS, GNSS systems, GNSS augmentation systems, etc.), along with additional data (e.g., from their respective ground segments), to derive corrections for atmospheric effects on GNSS signal propagation (e.g., SBAS ionospheric correction messages, GNSS broadcast ionospheric correction messages, GNSS precise ionospheric products supporting the PPP algorithm, etc.).

[0047] LEO-PNT satellites may also carry GNSS reflectometry (GNSS-R) equipment to collect measurements from GNSS signals reflected from the Earth's surface and downlink them to the ground (e.g., via TTC and possibly one or more ISL hops), so that this information can be used for Earth observation purposes (e.g., measuring wave height and wind speed) or to locate ships or assets on Earth.

[0048] GNSS receivers onboard LEO-PNT satellites can be used to collect measurements from GNSS satellites and downlink them to the ground (e.g., via TTC and possibly one or more ISL hops), so that this information can be used to improve the capabilities and performance of GNSS systems and services implemented by user equipment. This includes improved clock and ephemeris information for GNSS systems, monitoring the quality of GNSS signals, and detecting faults and integrity issues with signals from GNSS. Data collected by GNSS receivers onboard LEO-PNT satellites can be used to monitor GNSS integrity (e.g., using algorithms like RAIM). This can be processed on board the satellite to detect problems and notify users in real time via LEO-PNT signals.

[0049] The transmission time of the LEO-PNT signal, as well as the location of the transmitting source (e.g., satellite, LEO-PNT payload antenna phase center, etc.) needs to be determined and communicated to the user equipment to enable the user equipment to calculate its position (e.g., by trilateration). Orbit Determination and Clock Synchronization (ODTS) with respect to the GNSS frame can be highly relevant to optimizing the use of LEO-PNT signals in combination with GNSS signals and facilitating adoption by manufacturers and users already familiar with GNSS-based technologies.

[0050] Many applications of LEO-PNT signals and systems may require high accuracy of positioning and therefore low user equivalent distance error, and ODTS can contribute to this. Furthermore, in many applications, LEO-PNT signals and their sources need to be trustworthy. Trustworthiness in this context is understood to consider concepts of integrity known to the GNSS community (e.g., knowledge of measurement statistics and the probability that errors will exceed certain alert limits), as well as concepts of authenticity of the information carried by LEO-PNT signals (e.g., knowledge of the authenticity of the signal's origin and the risk of tampering with the signals or their content).

[0051] Taking into account some or all of the above considerations, a driver for a LEO-PNT payload may include one or more of the following: Transmission of at least one LEO-PNT signal (and possibly two, or even three) in a band common to GNSS signals, and optionally (e.g., preferably) at least one LEO-PNT signal in a band different from the band of the GNSS signals. - Calculation of information and indicators regarding high-precision ODTS and its reliability Accessing navigation messages from GNSS and SBAS signals and relaying some of their content to users Receiving signals in GNSS bands to support ancillary functions such as GNSS radio occultation, GNSS reflectometry, RFI monitoring, and collection of GNSS measurements to improve GNSS-related products (e.g., GNSS ODTS, integrity, etc.), and / or receiving signals in GNSS bands or bands adjacent to GNSS bands to support processing of incoming uplinks from user equipment. Transmission of LEO-PNT signals referenced to GNSS time and position frames derived from high-precision ODTS of LEO-PNT payloads and signals, and association of ODTS with information and metrics of ODTS reliability for users, including integrity and authentication. Receiving uplink signals from users to provide two-way navigation services

[0052] Important Features and Implementation Options A typical architecture of a LEO-PNT system includes a LEO-PNT payload on one or more satellites in LEO, optionally an ensemble of ground functions and capabilities for monitoring, control, and operation of the LEO-PNT mission (e.g., ground control and mission segments), and a user segment containing user equipment.

[0053] A LEO-PNT space segment can include or consist of a set of Earth-orbiting satellites in multiple orbital planes that can be at single or multiple inclinations and single or multiple altitudes. A LEO-PNT space segment can be implemented as a dedicated constellation, as hosted payloads on other satellites, or in a hybrid approach that combines payload-dedicated satellites with payloads hosted on other satellites. A LEO-PNT constellation can be, for example, a constellation of satellites in a particular area (e.g., urban canyons in densely populated regions of the world, polar latitudes, etc.). To optimize coverage, it can consist of multiple satellites distributed in multiple orbital planes which can be at one or more inclinations and one or more altitudes, allowing for different distributions of capabilities on these planes.

[0054] Payloads may also include support functions such as TTC functions and interfaces with equipment. LEO-PNT satellites may include ISL transceivers and antennas to exchange data with other LEO-PNT satellites in view and / or to derive inter-satellite ranging (ISR) measurements. ISLs may be based on radio frequency (RF) and / or optical technology and can operate between satellites on the same plane (intra-plane), different planes (inter-plane), or a combination of both. Using a TTC link to manage mission data, information, and parameters of a LEO-PNT payload may have the advantage of simplicity, but at the cost of increased latency compared to ISLs.

[0055] Considering the drivers listed in the Overview section, the core capabilities of a LEO-PNT system and payload may include the following capabilities: Accurate and reliable ODTS calculation Making the content of the navigation message available to the LEO-PNT payload for relaying on the LEO-PNT signal Generation of LEO-PNT signals necessary to enable LEO-PNT system services and functions (e.g., ranging, data distribution, etc.) in various bands, including GNSS bands, governed by the aforementioned ODTS. Receiving and processing signals uplinked by user equipment when integrating bidirectional capabilities into LEO-PNT systems and payloads Ability to support auxiliary functions such as GNSS radio occultation, GNSS reflectometry, and RFI monitoring

[0056] This may mean one or more of the following characteristics of the LEO-PNT payload: Simultaneous transmission and reception of signals in the GNSS band High-precision ODTS calculation Calculation of information and indicators on the reliability of ODTS The generation of LEO-PNT signals in various bands, including GNSS, governed by this ODTS to enable user equipment to derive relevant PVT-related measurements, the LEO-PNT signals including data related to the ODTS, its reliability, and additional data, some of which originates from external sources. Receiving uplink signals from users to provide two-way navigation services

[0057] As those skilled in the art will appreciate, the ODTS of LEO satellites can be estimated using a variety of methods and concepts. One method involves a network of ground-based sensor stations deriving distance and / or range-rate and / or carrier-phase measurements from signals arriving from LEO satellites and LEO-PNT payloads, similar to concepts operating on the GNSS ground segment. Differential corrections can also be applied to ODTS derived from TTC stations, but are only valid for users in the vicinity of the differential stations (e.g., similar to the GNSS concepts of differential GNSS (DGNSS) and real-time kinematics (RTK)). These methods may include or require additional on-board and ground-based hardware (e.g., high-performance and potentially complex clock systems to maintain stability over long periods of time, low-latency links to the ground, and networks of sensor stations). ODTS can also be derived from processing measurements from links between LEO-PNT satellites (e.g., ISLs).

[0058] Assuming that the LEO-PNT satellites are in orbit under GNSS and therefore receive GNSS signals in good conditions, an advantageous solution is to use measurements from the reception of GNSS signals by the on-board receiver. The goal of the LEO-PNT receiver is to coordinate LEO-PNT signal transmission and reference position for accurate and reliable ODTS performed onboard in real time. Furthermore, this receiver can be integrated into the LEO-PNT payload to optimize performance (e.g., processing time synchronization) as well as to reduce interface, size, weight, etc. The ODTS can use, for example, a real-time precision on-board orbit determination (P2OD) algorithm that uses both pseudorange and carrier phase measurements with floating ambiguity or integer ambiguity resolution (IAR) capabilities.

[0059] The ODTS process can improve its accuracy to tens of centimeters to better than 10s of centimeters using data and / or corrections (e.g., orbital data, clock corrections, inter-signal bias, inter-frequency bias, ionospheric corrections, code bias, phase bias, etc.). For this, certain information that is not integrated into the so-called clock and ephemeris data or standard navigation messages of GNSS signals (e.g., LNAV, CNAV, CNAV-2 from GPS, I / NAV and F / NAV from Galileo) needs to be considered and made available to the on-board ODTS functionality.

[0060] The integrity of the ODTS solution can be derived, for example, by implementing the concepts of autonomous receiver integrity monitoring (RAIM) or advanced RAIM (ARAIM), or by using integrity information generated by SBAS augmentation systems, or a combination of these. The authenticity of navigation messages, including clock and ephemeris data of GNSS signals, also needs to be accessible to the LEO-PNT payload in order to calculate authentic ODTS information.

[0061] The data required to deliver accurate and reliable information from GNSS signals may not be contained in the navigation messages of those signals (e.g., GPS messages for L1C / A, L2C, L5, and L1C, and Galileo's I / NAV and F / NAV). Corrections to improve accuracy and integrity and to verify the authenticity of the navigation messages used in the ODTS can be made available onboard, as in the case of terrestrial users, using sidelink or non-GNSS links (e.g., PPP corrections received over an Internet link, Assisted GNSS protocols from terrestrial cellular networks, so-called L-band correction services delivered over satellite communication systems), or via uplink telecommand, or via an ISL connected to the ground to provide this information. In all cases, this may involve additional equipment onboard, as well as additional reliance of the onboard ODTS on external technologies, information sources, or service providers.

[0062] While the aforementioned links can have several advantages, they can also entail significant drawbacks, including additional complexity and dependency for the LEO-PNT system. LEO-PNT payloads can advantageously utilize additional information contained in certain GNSS and SBAS signals to access the information necessary to derive ODTS reliability. This includes receiving SBAS signals, receiving Galileo HAS corrections broadcast on E6B signals, and receiving authentication features carried by GNSS signals, such as navigation message authentication and encrypted signals (e.g., Galileo's OSNMA and CAS, GPS's Chimera). The primary advantage of LEO-PNT payloads is their simplicity, as reception of these signals and information can be integrated into GNSS-equipped receivers.

[0063] Similarly, certain information relayed to users via LEO-PNT signals may be received directly from certain signals and messages from systems such as GNSS (e.g., GPS) and SBAS.

[0064] Many benefits and value-added capabilities can result from measurements and data obtained from reception of specific GNSS signals by LEO-PNT payloads. This includes, for example, E1 / L1 (SBAS, Galileo, etc.) The requirements for the reception of well-defined GNSS signals and data available in specific frequency bands by the onboard GNSS receiver include: E6 (Galileo OSNMA), E6 (Galileo HAS, CAS), E5 (Dual-frequency measurements common between Galileo and GPS, SBAS DFMC), reception of dual-frequency signals for radio occultation, reception of several GNSS bands for signal quality monitoring and interference detection, transmission of LEO-PNT signals, some of which in GNSS bands.

[0065] Adaptation of signal reception and transmission operating in GNSS bands to receive information and derive measurements from GNSS and SBAS signals while generating associated LEO-PNT signals in the GNSS bands can thus aid in foreseen LEO-PNT concepts. Furthermore, functionality enabling key features of LEO-PNT payloads (e.g., high-precision ODTS, auxiliary functions using GNSS bands, etc.) may be affected by this adaptation and therefore also need to be tailored to provide optimal performance.

[0066] Payload implementation example The core functionality of the LEO-PNT payload may include: The ability to receive and process signals coming from MEO satellites (e.g., GNSS), GEO satellites (e.g., SBAS), e.g., in the L-band, and possibly from other orbits above LEO, such as IGSO systems, or general high-orbit satellite navigation or augmentation signals from high-orbit satellite navigation or augmentation systems. Ability to calculate accurate and reliable ODTS The ability to generate the LEO-PNT signals in various bands, including GNSS, required to enable LEO-PNT system services and functions (e.g., ranging, data dissemination, etc.), and coordinate them into the accurate and reliable ODTS described above. Ability to receive signals uplinked by user equipment when bidirectional functionality is integrated into the LEO-PNT system and payload Ability to support auxiliary capabilities such as GNSS-RO, GNSS reflectometry, and RFI monitoring

[0067] Therefore, payloads must receive and transmit signals operating in the GNSS bands (GNSS frequency bands). Feasible ways to implement these functions while avoiding crosstalk between transmission and reception in the GNSS bands can be helpful in payload design and operation.

[0068] The above refers to navigation or augmentation signals of higher-orbit satellites that are received and processed by payloads according to embodiments of the present disclosure. These signals relate to navigation signals received from satellite navigation or augmentation systems (e.g., GNSS, SBAS) in higher orbits (e.g., orbits above LEO). Furthermore, these signals may be received from higher-orbit satellite navigation or augmentation systems in the L-band. They are generally said to be received in the frequency band used by GNSS or augmentation systems (e.g., SBAS). While the present disclosure frequently refers to GNSS signals, it is understood that the present disclosure equally relates to navigation or augmentation signals of higher-orbit satellites, including, but not limited to, GNSS and / or SBAS signals.

[0069] Simultaneous transmission and reception of signals in the GNSS band GNSS (as a non-limiting example of a high-orbit satellite navigation system or augmentation system) is representative of most satellite navigation systems and may therefore be considered typical and representative of current satellite navigation systems. GNSS signals (as a non-limiting example of a high-orbit satellite navigation signal or augmentation signal) are transmitted continuously, and as a result, the signals, associated payloads, and receiver capabilities are designed accordingly for continuous operation.

[0070] The LEO-PNT payloads (as a non-limiting example of a payload or satellite payload) described in this disclosure can transmit and receive signals in the GNSS bands. Transmission of signals from a LEO-PNT payload can affect the operation of nearby receive functions on the same payload. The transmissions can at least significantly increase the noise floor in the receive band, potentially preventing correct processing of signals intended to be received to support the LEO-PNT payload, and can saturate hardware functions in the receiver (e.g., saturating LNAs, operating well beyond the linear region of most of the receive functions involved, etc.), potentially degrading them.

[0071] A feasible solution to support transmit and receive operation in the GNSS bands is to allocate transmit and receive to different frequency bands, which in the context of this disclosure is referred to as frequency division duplex (FDD) mode. Compatibility between the transmission of LEO-PNT signals (e.g., in the L-band) and the reception of GNSS signals by the onboard GNSS receiver when operating in FDD mode can be ensured by one or more of the following: Out-of-band emission filters for LEO-PNT signal transmitters Out-of-band rejection filters in GNSS receivers Digital signal processing (DSP) at the GNSS receiver level for interference cancellation (e.g., self-interference cancellation (SIC) techniques), knowing the exact nature and content of the transmitted signal

[0072] The transmit and receive antennas may be designed to minimize their coupling and thus minimize crosstalk between the transmitter and receiver. Additionally or alternatively, the transmit and receive antennas may be placed as far away from each other as possible, if the size and capacity of the satellite permits. All of these techniques may require additional hardware (e.g., to accommodate filters) and / or additional footprint, which may introduce certain capacity constraints that are typically undesirable. Furthermore, they constrain the design of frequency plans for LEO-PNT payloads in the GNSS bands, limiting the choice of those bands in which to operate in reception and those in which to operate in transmission, which may be undesirable for achieving optimal performance and ease of implementation for user equipment.

[0073] In contrast to the above, the present disclosure proposes introducing (and optimally configuring) alternating transmit and receive functions on the same GNSS frequency band within a LEO-PNT payload, one alternating with the other according to a period and duty cycling. This technique, described in more detail below, is referred to throughout this disclosure as time division duplex (TDD).

[0074] One embodiment of a method 200 for operating a payload having receive and transmit capabilities (e.g., a satellite payload, a LEO-PNT payload) is described with reference to the flowchart of FIG. 2. The method 200 may be performed in Earth orbit, such as in LEO. Furthermore, the method 200 may be said to correspond to a positioning or navigation method. Although additional steps not shown in FIG. 2 are described below, the method 200 may include at least steps S210 and S220. Notably, these steps, or a sequence thereof, may be performed consecutively.

[0075] In step S210, a GNSS signal is received from a GNSS in a GNSS frequency band.

[0076] Although reference is made herein to GNSS signals, it is understood that this step generally relates to receiving navigation or augmentation signals from higher orbit satellites. These signals relate to navigation signals received from satellite navigation or augmentation systems (e.g., GNSS, SBAS) in higher orbits (e.g., orbits above LEO). Accordingly, it should be understood that any techniques presented herein similarly relate to navigation or augmentation signals from higher orbit satellites, including, but not limited to, GNSS and / or SBAS signals.

[0077] The aforementioned GNSS signals (as non-limiting examples of navigation or augmentation signals of high-earth-orbit satellites) may be received from high-earth-orbit satellite navigation systems or augmentation systems in frequency bands used by the GNSS or augmentation systems, referred to as GNSS frequency bands. For example, the GNSS signals may be received in the L-band. More specifically, in some implementations, the GNSS frequency band may be, for example, one of bands E1, E6, E5, E5a, and E5b defined for Galileo, or one of bands L1, L2, and L5 defined for GPS.

[0078] In step S220, navigation signals are transmitted toward Earth at GNSS frequencies. Importantly, the navigation signals are transmitted in the same frequency band (e.g., the same carrier frequency) as the GNSS signals received in step S210. In particular, this is understood to include the case where the transmitted frequency band is in the vicinity of the received GNSS frequency band and is close enough so that the spectra of the transmitted and received signals overlap in the frequency domain. In some implementations, the navigation signals may be transmitted in a frequency band that overlaps with the GNSS frequency band.

[0079] The navigation signals transmitted in step S220 may be navigation signals for code-based ranging measurements, carrier-based measurements, and / or Doppler measurements at a receiver (e.g., user equipment), and / or low-complexity acquisition at the receiver. In this sense, the navigation signals may provide the same functions as GNSS signals.

[0080] Furthermore, the navigation signals may be based at least in part on GNSS signals. For example, the navigation signals (or their content) may be derived at least in part on the GNSS signals (or their content). For example, the navigation signals may be based at least in part on the results of ODTS in the payload. Furthermore, the navigation signals may include GNSS content that is derived from the GNSS signals and relayed via the transmitted navigation signals. This is described in further detail below.

[0081] In the above, the reception in step S210 and the transmission in step S220 are performed in TDD mode, alternating between time slots for receiving GNSS signals and time slots for transmitting navigation signals, i.e., for a given TDD time slot, only one of the reception or transmission functions is active in the same frequency band, and in the subsequent TDD time slot, only the other of the reception or transmission functions is active in the same frequency band.

[0082] 2, the method 200 may include an optional step of transmitting a second navigation signal (which may be performed continuously) towards the Earth in a second GNSS frequency band different from the GNSS frequency band or in a non-GNSS frequency band. The transmission of the second navigation signal may be performed in FDD mode, in the sense that the second navigation signal is transmitted continuously, but in a frequency band different from the receiving frequency band (i.e., the GNSS frequency band).

[0083] In general, the reception in step S210 and / or the transmission in step S220 may be performed in two or more (distinct) GNSS frequency bands. The additional transmission in step S220 may optionally be performed in a non-GNSS frequency band. It is understood that the TDD mode applies to any (GNSS) frequency band used by the payload for both reception and transmission in the same frequency band.

[0084] Traditionally, TDD is applied in terrestrial cellular networks between base stations and user equipment. An example of the use of TDD in communications between a base station 310 and a user equipment (UE) 320 is shown schematically in Figure 3. Here, continuous time is (virtually) divided into a sequence of consecutive time slots 330, 340, of which time slot 330 A subset is used for transmission by the base station 310 (and reception by the UE 320), and a complementary subset of time slots 340 is used for transmission by the UE 320 (and reception by the base station 310). In this configuration, the time slots 330 in which the base station 310 transmits (or can transmit) alternate with the time slots 340 in which the UE 320 transmits (or can transmit).

[0085] Traditionally, TDD has not typically been used in satellite communication systems for various reasons, which make practical implementations of TDD less attractive than FDD. Furthermore, as shown in Figure 3, TDD is typically implemented in telecommunications systems between two nodes (e.g., a base station and user equipment) exchanging signals over a bidirectional communication link.

[0086] In contrast, this disclosure proposes using TDD for reception and transmission by a given payload, and it should be noted that TDD can be adapted to satellite payloads (e.g., LEO-PNT) as an attractive alternative to FDD for accommodating Rx / Tx in the same frequency band. An example of using TDD for Rx / Tx of a payload 410 that can transmit to a UE 420 is shown schematically in FIG. 4. Again, continuous time is (virtually) divided into a sequence of consecutive time slots 430, 440, of which a subset of time slots 430 are used for reception by the payload 410 and a complementary subset of time slots 440 are used for transmission by the payload 410 to the UE 420. In this configuration, time slots 430 in which the payload 410 receives (e.g., GNSS signals) alternate with time slots 440 in which the payload 410 transmits (e.g., navigation signals).

[0087] Adapting a TDD mode for a payload in accordance with the present disclosure may include applying TDD to receiving signals broadcast or transmitted by a set of transmitters (e.g., GNSS, SBAS, interferers) and transmitting LEO-PNT signals to a user receiver (i.e., a user of the LEO-PNT signal). This differs from the use of TDD in terrestrial communication systems where the transmitter and receiver are part of the same two-way link.

[0088] In the example of TDD over GNSS bands, the LEO-PNT payload receives signals in the GNSS bands while transmission of LEO-PNT signals on the GNSS bands is switched off, and vice versa, as explained above. Furthermore, the LEO-PNT payload transmits LEO-PNT signals on the GNSS bands while reception on the GNSS bands is switched off. Furthermore, the TDD adjustments on the receive side apply to signals that are transmitted continuously and therefore are not duty-cycled (or designed for duty-cycled processing, unlike telecommunications signals that may be designed with a TDD implementation in mind) before reaching the LEO-PNT payload front-end.

[0089] For example, the transmission of the TDD signal in the LEO-PNT payload in step S220 may be performed by turning off the signal at the input of the analog chain, for example by blanking the digital-to-analog converter and setting the signal to zero. An alternative may be blanking the signal at the input of an amplifier or chain of amplifiers, or turning off the amplifier, or a combination of these measures.

[0090] Receiving a signal in a TDD signal, for example, in the LEO-PNT payload in step S210, may be performed, for example, by turning off the signal at the output of the receiver's analog front end, e.g., blanking an analog-to-digital converter and setting the signal to zero. An alternative may be to blank the signal at the input of the analog front end (e.g., a low noise amplifier (LNA)) or elsewhere within the analog front end.

[0091] Exemplary durations for TDD patterns range from 1 ms to tens of ms. A shorter pattern period may ease implementation and performance at the receiver level, but may result in a more complex implementation of the transmit chain. A longer pattern period may ease implementation, but puts additional stress on the receiver algorithm and requires additional complexity to maintain good performance.

[0092] An exemplary duty cycling for TDD may be 50%. A lower transmit percentage provides more time to receive the signal at the LEO-PNT payload, and therefore a higher SNR at the receiver at the LEO-PNT payload, but a lower average power and SNR provided to the user of the LEO-PNT signal. Conversely, a higher transmit percentage increases the average power and SNR delivered to the user, but reduces the SNR available to the receiver of the LEO-PNT payload.

[0093] An example of TDD reception and transmission in the E5 GNSS frequency band is shown in Table 1.

[0094] [Table 1] Table 1 TDD for one GNSS frequency band

[0095] The implementation of TDD mode in a LEO-PNT payload does not necessarily preclude the use of FDD mode. For example, the two modes may be advantageously combined when transmission and reception are performed simultaneously in multiple bands. An example is shown in Table 2, where TDD reception and transmission are performed in the E5 GNSS frequency band, and the payload also continuously receives GNSS signals in the E6 GNSS frequency band.

[0096] [Table 2] Table 2. TDD and FDD for each GNSS frequency band

[0097] Another example is shown in Table 3, where TDD reception and transmission are performed in the E5 GNSS frequency band, and the payload also continuously transmits signals in the S-band.

[0098] [Table 3] Table 3. FDD continuous transmission and TDD receive / transmit

[0099] When operating transmissions on multiple bands, transmission (or reception) on multiple bands can be performed simultaneously or alternately. Alternating transmissions on several bands, and consequently, alternating reception on several bands, can be advantageous to optimize the operation of the transmission chain. For example, For example, not all amplifiers draw current at the same time, and the receiver always processes one signal at any given time, which facilitates signal processing and optimizes the resulting performance (e.g., helps keep tracking loops locked, maintains carrier phase continuity, etc.). Examples are shown in Tables 4, 5, and 6.

[0100] [Table 4] Table 4. Optimized TDD RX and / or TX in several frequency bands

[0101] [Table 5] Table 5. Optimized TDD Rx and Tx (one Tx and two Rx simultaneously) for several frequency bands

[0102] [Table 6] Table 6. Optimized TDD Rx and Tx (two Tx and one Rx simultaneously) in several frequency bands

[0103] Additional tuning of the TDD mode to the payload according to the present disclosure includes synchronizing the TDD pattern (e.g., duty cycling, period) to GNSS time derived from the onboard ODTS and / or optimizing the receive algorithms to restore received signal quality despite discontinuous reception. This may also involve leveraging a combination of TDD parameters (e.g., synchronization to GNSS time) and information about the transmitter geometry (e.g., GNSS satellite ephemeris) and the LEO-PNT payload (e.g., onboard ODTS).

[0104] Therefore, the above-described method 200 may further include one or more of the steps of method 600, which will be described with reference to the flowchart of Figure 6. Method 600 includes steps S610, S620, and S630, each of which may be any step of the above-described method 200. Also, these steps may be performed consecutively.

[0105] In step S610, at least one of orbit determination and time synchronization of the satellite payload is performed based on the GNSS signals.

[0106] The details of ODTS are explained below.

[0107] In step S620, the TDD pattern (e.g., the TDD mode duty cycle and / or the TDD mode period length) is disciplined (e.g., synchronized) to the GNSS timing epoch. In some implementations, this may be based on the results of at least one of the orbit determination and time synchronization in step S610.

[0108] The TDD pattern may be synchronized on the same GNSS epoch across several or all LEO-PNT satellites. This means that navigation signals transmitted from different LEO-PNT satellites do not arrive at a user on Earth at the same time due to the spread in propagation times from the various satellites to the user. An example of such a situation is shown schematically in FIG. 5A, where each line indicates a transmit time slot 510 associated with a different payload and in which a navigation signal is transmitted, and a corresponding time slot 520 (originating from the transmit time slot 510) in which this navigation signal is received at a given UE. In this example, the TDD transmit time slots 510 for different payloads are synchronized, but the time slots 520 in which the respective navigation signals transmitted in the transmit time slots 510 by different (spatially separated) payloads are received at the UE are spread in time. This approach may be advantageously implemented to spread the transmit power over time and thus reduce the equivalent power flux density (EPFD) level of the signal received on Earth, thus facilitating compliance with ITU regulations.

[0109] The TDD pattern can be synchronized across several satellites in a LEO-PNT constellation with specific timing offsets determined so that signals from various satellites arrive simultaneously at user equipment in a particular region on Earth. An example of such a situation is shown schematically in FIG. 5B, where TDD transmission time slots 510 for different payloads are spread over time according to timing offsets (e.g., delays) determined according to the respective relative distances between the payloads and the UE or UE region of interest, but the time slots 520 in which the respective navigation signals transmitted in the transmission time slots 510 by the different payloads are received are aligned with respect to the UE of interest. This approach can be advantageously implemented to allow the receiver to turn on its front end only at certain epochs when a signal is expected to be received.

[0110] LEO-PNT payloads use information derived from their on-board orbit determination to A time offset to be applied to the TDD pattern can be determined to align signals at the receiver level in a given area or region. To switch on at the epoch when the LEO-PNT signal is expected, the user equipment needs to estimate the propagation time from the LEO-PNT payload to its location. Meanwhile, the LEO-PNT payloads can use information derived from their onboard orbit determination to determine a time offset to be applied to the TDD pattern to align signals at the receiver level in a given area or region on the ground.

[0111] Reception of GNSS signals and messages received in TDD mode GNSS and SBAS signals (or, in general, higher-orbit satellite navigation or augmentation signals) are designed for continuous transmission and, for example, continuous reception by user equipment. The same considerations apply to the physical layer of the data content of these signals. Duty-cycle reception of these signals can affect the stability of the algorithms used, as well as the quality (e.g., accuracy, reliability / completeness, etc.) of the measurements made. This can be particularly important for GNSS receivers in LEO-PNT payloads, whose purpose is to deliver accurate and reliable ODTS-supporting information for the payload and LEO-PNT signals.

[0112] Turning off reception of signals in the analog domain to protect the RF front end may not be sufficient to avoid any interference. During time intervals when reception (of GNSS signals) is off and transmission (of navigation signals) is active, it may also be necessary to force digital signals at the inputs of baseband processing states (e.g., digital downconversion of GNSS signals, carrier removal, and correlators) to zero. Means for achieving such blanking may generally be in place within the GNSS receiver, configured to protect GNSS reception from the effects of pulsed distance measuring equipment (DME) signals in the E5 band, for example. Nevertheless, such blanking is typically performed with a blanking duration shorter than the pseudorandom noise (PRN) code period and symbol period of the message and therefore does not require specific optimization of the acquisition and tracking algorithms or message demodulation and decoding.

[0113] In some implementations, LEO-PNT payloads may operate with duty cycling periods longer than those of typical GNSS PRN periods and / or symbol durations, and therefore algorithms for receiving GNSS signals in TDD mode during this duty cycling operation may require further adaptation to limit the effective SNR, as well as impairments to measurement accuracy, quality, and integrity, and maintain a good level of performance for an accurate and reliable algorithm, as will be understood by those skilled in the art.

[0114] Typical acquisition (e.g., search engines and matched filters involved in signal acquisition) and tracking algorithms (e.g., delay-locked loops (DLLs), frequency-locked loops (FLLs), phase-locked loops (PLLs)) assume continuous reception of the GNSS signal and therefore assume that each sample at baseband contains relevant information about the GNSS signal. This may not be the case for signals received in TDD mode, as samples are blanked (zeroed) during payload transmission periods. Adaptation and optimization of the GNSS receiver algorithms in LEO-PNT payloads can aim to accommodate and possibly compensate for this lack of information.

[0115] Using the precise knowledge of when transmission is active and reception needs to be switched off, the receiver can force all samples of the digital baseband series to zero for a time interval equal to the payload transmission time interval. Since these samples do not carry information, the receiver can also advantageously suspend baseband processing such as correlation, numerically controlled oscillator (NCO), etc. This reduces power consumption in the payload. This can contribute to

[0116] Due to the smooth orbits of GNSS and LEO satellites and stable onboard clocks, tracking algorithms can take advantage of predictable signal dynamics (e.g., range rate, etc.) to extrapolate their estimates during blanking periods in TDD mode.

[0117] Therefore, the above-described method 200 may further include a step of ensuring signal tracking of GNSS signals during TDD transmission periods when GNSS signals are blanked. For example, step S630 of method 600 of FIG. 6 (as part of method 200) may be a step of maintaining signal tracking of GNSS signals during a time slot for transmitting navigation signals to avoid reacquisition based on at least one result of orbit determination and time synchronization. The purpose of step S630 is to avoid reacquisition of GNSS signal tracking when transmission of navigation signals stops and reception of GNSS signals resumes. In some embodiments, step S630 may include maintaining a tracking algorithm within the bounds of a lock indicator. Additionally or alternatively, step S630 may include extrapolating tracking parameters and / or states to keep the tracking loop from leaving the pull-in range or losing lock during a time slot when reception of GNSS signals is interrupted and navigation signals are transmitted.

[0118] When a LEO-PNT payload receives multiple GNSS frequencies from the same GNSS satellite, the payload can alternate blanking between frequencies arriving from the same GNSS satellite (e.g., receiving E1 while blanking E6) rather than blanking all signals simultaneously. For example, it can be said that for each alternating time slot, reception in at least one GNSS frequency band is active to aid in signal tracking of GNSS signals in other GNSS frequency bands in that time slot where reception is not active. Examples of alternating blanking between different GNSS frequencies are provided in Tables 4, 5, and 6. An algorithm operating on unblanked band A can aid an algorithm operating on blanked band B while A is unblanked, and vice versa. As will be appreciated by those skilled in the art, the aiding information can be further adapted or adjusted to account for different frequencies between A and B and their effects on Doppler, the ionosphere, etc.

[0119] An example of how a tracking algorithm can be aided by information from reception in another frequency band is shown schematically in Figure 7. In this example, a first GNSS signal 701 is continuously received at frequency A and processed by a first processing loop, and a second GNSS signal 711 is received at frequency B in TDD mode (i.e., with duty cycle reception) and processed by a second processing loop. Carrier removal is performed for both GNSS signals in respective carrier removal blocks 702, 712 based on the output of the respective NCOs 706, 716. After carrier removal, the resulting signals are fed to respective correlators 703, 713, after which error estimation is performed in respective error estimators 704, 714. After error estimation, the resulting signals are fed to respective loop filters 705, 715, the outputs of which are provided to the respective NCOs 706, 716, thus closing the first and second processing loops. To assist in signal tracking of the second GNSS signal, the output of the loop filter 705 of the first processing loop may also be provided to the NCO 716 of the second processing loop via summer 730, after any scaling and / or adaptation in scaling / adaptation block 720.

[0120] Additionally, as described above, for example, for step S630, algorithms (e.g., in acquisition and tracking) may be aided by information derived from the on-board ODTS (e.g., the ODTS performed in step S610). This is because using accurate on-board ODTS Although it works best with ODTS, it can also provide benefits when accurate ODTS is not or not yet available and only a coarse ODTS estimate is available for the LEO-PNT payload (e.g., two line elements received by the TC, long-term extrapolation of the ODTS, etc.). Aiding in this context may include, but is not limited to, aiding the DLL, FLL, and / or PLL with range-rate estimates from the ODTS and / or using prior knowledge of the arrival times of the GNSS signals (e.g., to reduce the search space in acquisition).

[0121] The demodulation, decoding, and estimation of bits contained in GNSS signals received by a LEO-PNT payload in TDD mode may also be adapted and / or optimized to limit performance degradation resulting from TDD mode for GNSS signals. The receiver may advantageously utilize interleaving and channel coding of GNSS signals (when present on those signals) and adapt the associated reception algorithms to TDD mode.

[0122] A good estimate of the carrier phase is important for the demodulation of the data symbols. The correlator outputs or matched filter outputs for the pilot and data components of modern GNSS signals are combined together in non-coherent demodulation (e.g., by using prompt correlator outputs for the pilot and data components) to complement or replace typical demodulation using a PLL, allowing residual carrier phase on the data symbols to be erased even when the PLL is not operating optimally due to TDD.

[0123] Interleaving and channel coding in modern GNSS signals can largely compensate for the effects of blanking and the absence of information for some samples. In particular, the decoding algorithms operating on the received symbols can be optimized to take into account the nature of TDD and the fact that some symbols are forced to zero due to TDD operation. The receiver can maintain soft-decision inputs to the decoder for symbols received while the receiver is not blanked, and force hard-decision inputs to the decoder for symbols received during blanking.

[0124] In order to fully benefit from the interleaving and decoding mechanisms embedded in modern GNSS signals, it may be desirable to have a duty cycling period that is shorter than the duration of the interleaving, or the duration of the channel code block, and it may also be desirable to have a duty cycling period that is shorter than the duration of the bits carried by the GNSS signal.

[0125] High-precision ODTS using GNSS signals and data The precise ODTS of a satellite can be derived in several ways that are currently used in typical space systems, especially satellite navigation systems. One such method can use measurements from GNSS signals, possibly combined with PPP corrections broadcast by, for example, the Galileo HAS service.

[0126] Thus, at least one of the orbit determination and time synchronization (e.g., ODTS) performed in step S610 of method 600 may be based on high precision corrections received along with or from GNSS signals (as an example of a higher orbit navigation or augmentation system).

[0127] The ODTS of a LEO-PNT satellite can be performed in real time by, for example, an on-board computer (OBC) running a reduced dynamic orbit filter that processes GNSS measurements. The ODTS reduced dynamic orbit filter models the most important forces acting on the satellite (e.g., Earth gravity model, solar and lunar gravity model, atmospheric drag, solar radiation pressure, etc.). The ODTS is based on the floating antenna. A real-time precision on-board orbit determination (P2OD) algorithm using both pseudorange and carrier phase measurements with viguity or integer ambiguity resolution (IAR) capability can be used.

[0128] Thus, LEO-PNT signals (or generally navigation signals in the context of this disclosure) may be governed by and referenced to an on-board, real-time or near real-time calculated ODTS that includes information combining broadcast GNSS navigation messages and precision products of the Galileo High Accuracy Service (HAS) received, for example, from Galileo E6B.

[0129] Nevertheless, leveraging multiple sources of range / range-rate measurements (e.g., multi-GNSS, ISR, TTC measurements) and data / corrections when available, in addition to the corrections and data delivered by the HAS, can improve system availability against outages of some of these sources.

[0130] When the onboard GNSS receiver processes GNSS signals from a given GNSS in single-frequency mode and both pseudorange and carrier phase measurements are available, a GRAPHIC combination can be used to remove the ionospheric contribution. When GNSS signals from a given GNSS are tracked in single-frequency mode and only pseudorange measurements are available, ionospheric corrections are used, which can be further adapted to the LEO altitude if necessary. Considering the fact that there is still only a residual ionosphere above LEO-PNT satellites (compared to the complete ionosphere for ground users), profiler ionospheric models (e.g., NeQuikG) can achieve better performance.

[0131] The ODTS process may use different weightings for different measurements from different sources (e.g., frequencies, satellites) based on the data / corrections used for each of them. These different weightings may allow for different accuracy and may improve the performance of the ODTS solution, for example, in terms of the accuracy and / or availability of the ODTS solution.

[0132] Using the orbit and clock estimates of LEO-PNT satellites obtained from the onboard ODTS process, orbit and clock products can be generated in real time or near real time and delivered to LEO-PNT receivers via data contained in the LEO-PNT signal (navigation signal). These products can be derived by applying curve fitting (e.g., using Keplerian elements, standard polynomials, B-splines, Chebyshev polynomials, and / or any variants of these) to the orbit and clock estimates, depending on the required validity of the resulting products.

[0133] Reliability of ODTS information The ODTS may implement an integrity function to determine whether the error in the GNSS measurements and / or ODTS solution is within a given range of values for a given probability of missed detection.

[0134] Thus, at least one of the orbit determination and time synchronization (eg, ODTS) performed in step S610 of method 600 may use information about the integrity of the GNSS signals.

[0135] For example, the integrity function of ODTS can be implemented by using one or a combination of the following: Use of SBAS integrity data received by onboard GNSS receivers or via terrestrial networks Autonomous receiver integrity, utilizing redundancy between GNSS and possibly ISR measurements Monitoring (RAIM) technology Advanced Receiver Autonomous Integrity Monitoring (ARAIM) techniques by receiving and processing Integrity Support Messages (ISM), which are advantageously emitted from GNSS or SBAS signals and systems instead of via additional links such as uplink TC or ISL. · Any of the above or a combination of several of the above in conjunction with the aforementioned orbital filter / reduced dynamic orbital filter

[0136] Alternatively or additionally, at least one of the orbit determination and time synchronization (eg, ODTS) performed in step S610 of method 600 may use information about the authenticity of the GNSS signals.

[0137] For example, an ODTS process may implement authentication functionality that utilizes one or more of the following: Authentication functions carried by GNSS signals, such as navigation message authentication and encryption signals (e.g., Galileo's OSNMA and CAS, GPS Chimera). Processing of baseband signals to assess the consistency of correlation functions and performing consistency checks on the state of baseband processing functions and their raw measurements (code, carrier phase, Doppler, signal-to-noise ratio, etc.) Processing of GNSS signals received on two or more antennas to detect mismatches in angle of arrival / angle of arrival signatures. Reception on several antennas can be performed simultaneously and intermittently, e.g., by switching between antennas with a duty cycle. Any combination of the above

[0138] The aforementioned techniques can operate continuously or intermittently to reduce processing complexity and computational power. For example, processing of the encrypted signal can be performed using duty cycling, at snapshots of a specific duration (e.g., up to tens of milliseconds), or for longer periods of up to several seconds or tens of seconds.

[0139] Additionally, the aforementioned processes can be advantageously combined with orbit filters or reduced dynamic orbit filters to leverage the short-term stability of on-board clocks (e.g., oven-controlled crystal oscillators, chip-scale atomic clocks, miniature atomic clocks) to improve integrity check statistics or assist in reliable resolution during the above-mentioned duty cycling and times when reliability processes are not being performed.

[0140] The resulting information, i.e., an indication of the reliability of the ODTS solution and the reliability of the reference of the LEO-PNT signal to the ODTS, may be communicated to the user equipment via data contained in the LEO-PNT signal (navigation signal).

[0141] In any case, at least one of the orbit determination and time synchronization (eg, ODTS) performed in step S610 is based on one or more of the following: SBAS messages received along with GNSS signals Ranging authentication and / or message authentication of GNSS signals HAS messages received together with the GNSS signals, and / or ISM messages received with GNSS signals

[0142] Relay of navigation-related data Relaying GNSS messages (or generally GNSS content) to a LEO-PNT signal (or generally a navigation signal transmitted in step S220 of method 200) involves extracting specific messages from fields and pages of associated data components of the GNSS signal and introducing them, in real time or with a delay, into fields and pages of data components of the transmitted LEO-PNT signal. can be considered and adjusted to use TDD mode.

[0143] Therefore, the above-described method 200 may further include one or more of the steps of method 800, which will be described with reference to the flowchart of Figure 8. Method 800 includes steps S810 and S820, both of which may be optional steps of the above-described method 200. These steps may also be performed consecutively.

[0144] In step S810, the GNSS signal (e.g., received in step S210) or the GNSS message contained therein is demodulated to obtain GNSS content transmitted with the GNSS signal. The GNSS content thus obtained may, for example, relate to one or more (low-latency) GNSS messages.

[0145] In step S820, at least a portion of the GNSS content is included in a navigation message that is transmitted along with the navigation signal in the GNSS frequency band towards Earth, and the payload is thus said to relay the GNSS content to any receiver of the navigation signal.

[0146] Among these, the GNSS content acquired in step S810 and relayed in step S820 may relate to one or more of the following: SBAS Message SAR return link message Integrity Support Message (ISM) High Accuracy Service (HAS) messages Emergency warning messages, and / or Authentication message

[0147] If the duty cycling period is shorter than the period of the received symbols, the LEO-PNT payload can estimate each symbol of the data component of the received GNSS signal and directly introduce the associated value as a symbol of the data component of the LEO-PNT signal. This imposes bypassing decoding and may impose hard decisions on the received symbols, which may result in suboptimal estimation performance, but minimizes the delay of the relay mechanism of the LEO-PNT payload.

[0148] More advantageously, the LEO-PNT payload can decode and estimate all or part of the pages of the GNSS signal received in TDD mode, select the pages, fields, and bits to be relayed, and encode and introduce them as symbols in the data component of the LEO-PNT signal. An example of such a procedure is shown schematically in the block diagram of FIG. 9, where the horizontal axis indicates time relative to GNSS signal pages 905-(N-1), 905-N, 905-(N+1), etc. After each page is received in receive block 910, it is demodulated in demodulator block 920 and its symbols are decoded. The resulting data is coded in code block 930 and transmitted in transmit block 940 in TDD mode along with the navigation signal in a sequence of TDD time slots 945.

[0149] In doing so, the LEO-PNT payload may retain any of the formatting, coding, interleaving, bit and symbol rates used by the incoming GNSS signals, or may implement a different conversion of bits to symbols of the data components. For example, the channel code, channel code redundancy ratio, and data rate of the LEO-PNT signals may be modified and optimized to suit the properties of the LEO signals. The data or symbol rate may be increased to take advantage of the higher signal-to-noise ratio of the LEO signals, accelerating the dissemination of relevant data to users and reducing end-to-end delays compared to when the rates of GNSS signals are used.

[0150] auxiliary abilities The design of receivers and equipment processing GNSS signals involved in radio occultation (GNSS-RO), reflectometry (GNSS-R), and space-based GNSS interference monitoring (RFI monitoring) assumes that signals are received continuously for the time that the occultation or reflection lasts.

[0151] This assumption does not apply to GNSS-RO, GNSS-R, and RFI signals received by a LEO-PNT payload that includes these functions in addition to transmitting LEO-PNT signals in TDD mode. As with the reception of GNSS signals for ODTS, the algorithms for GNSS-RO, GNSS-R, and RFI monitoring functions need to be adapted for TDD to limit interference and performance degradation.

[0152] A typical solution for GNSS-RO, GNSS-R, and RFI monitoring may be similar to the algorithms described above for received signals for ODTS, such as aiding between channels and frequency bands, aiding with ODTS information, and assuming coarse knowledge of the location of the source (e.g., occulted GNSS satellites).

[0153] Therefore, the above-described method 200 may further include one or more of the steps of method 1000, which will be described with reference to the flowchart of Figure 10. Method 1000 includes steps S1010 or S1020, both of which may be optional steps of the above-described method 200 and may be performed independently of each other, or these steps may be performed sequentially.

[0154] In step S1010, radio occultation is performed based on the GNSS signals received in the time slots for receiving GNSS signals in TDD mode.

[0155] In step S1020, operations are performed to detect and / or locate unwanted emissions in the GNSS frequency band. Here, locating the unwanted emissions may include multilateration using multiple satellite payloads. Further, this step may include or correspond to, for example, performing radio frequency interference (RFI) estimation in a time slot for receiving GNSS signals in TDD mode.

[0156] 11 schematically illustrates an example framework for performing RO (e.g., via step S1010) according to an embodiment of the present disclosure. In this framework, a LEO-PNT satellite 1120 receives a signal (e.g., a GNSS signal) transmitted by a GNSS satellite 1120 after the signal passes through the Earth's ionosphere 1130. The received GNSS signal can be used to infer information about the state of the ionosphere 1130.

[0157] 12 illustrates generally an example framework for performing RFI estimation (e.g., via step S1020) in accordance with an embodiment of the present disclosure. In this framework, one or more LEO-PNT satellites 1210 receive signals from the ground (e.g., ground-based emitters 1220) in the GNSS frequency bands and estimate RFI and / or locate interference sources (e.g., via multilateration).

[0158] Signal Design and Generation The LEO-PNT design is intended and / or optimized to enable user equipment to derive relevant (e.g., optimal) positioning-velocity-timing related measurements from the navigation signals. Furthermore, it is intended and / or optimized to deliver data to user equipment regarding ODTS, its reliability, and additional data, some of which originates from external sources. Each LEO-PNT signal (navigation signal) may be composed of multiple signal components, including, but not limited to: One or more data components modulated by the navigation message One or more pilot components that are not modulated by the navigation message One or more pseudopilot components that deviate from a pure pilot with low entropy information Optionally, intermodulation products when constant envelope modulation (CEM) multiplexing is used

[0159] LEO-PNT signal generation can be fully digital, utilizing, for example, software-defined radio (SDR) technology and architectures, allowing for software and firmware upgrades in orbit. This can allow for updates to LEO-PNT signal characteristics in space during the life of the system, and even the addition of, for example, new signals.

[0160] When a LEO-PNT signal is composed of multiple signal components, they may be linearly multiplexed (e.g., simply added) or multiplexed using techniques to reduce the peak-to-average power ratio (PAPR) at the input of the payload's high power amplifier (HPA) in the transmit chain.

[0161] One or more of the LEO-PNT signal components may include a time dissemination function that allows for dissemination of absolute time (e.g., time of week) and / or resolves time uncertainties (e.g., after using time assistance data). Signal sizing and time synchronization mechanisms may take advantage of the shorter distances to LEOs and feature shorter codes that are easier to acquire / detect / synchronize with (e.g., a 10 ms code allows for resolution of ambiguities for slant ranges up to 3000 km).

[0162] LEO-PNT signals can be designed for various multiple access schemes on the downlink and / or uplink. CDMA-DSSS is widely adopted for GNSS and may be well suited for LEO PNT signals, although alternative schemes, or combinations thereof (e.g., FDMA+DSSS), may also be considered. (Note that shorter PRN / narrowband signals may be more attractive and, for these, FDMA may outperform CDMA for ease of acquisition and use for asset tracking.) LEO-PNT signals may use direct sequence spread spectrum (DSSS) or chirp spread spectrum (CSS) to optimally spread the signal within the allocated bandwidth and optimize processing complexity in the user equipment for the allocated bandwidth and sampling frequency (e.g., reduced acquisition and tracking complexity, improved synchronization, and ranging performance).

[0163] LEO-PNT broadcast signals may also utilize bandwidth-efficient modulation, such as continuous phase modulation (CPM), to reduce out-of-band emissions and improve spectral compatibility with signals in adjacent bands.

[0164] LEO-PNT signals may include cryptographic features to ensure the authenticity of broadcast navigation messages and ranging codes, or to support controlled access to corresponding services, or a combination of both.

[0165] LEO-PNT signals may carry data messages protected by error control coding and / or erasure coding techniques, with or without bit interleaving.

[0166] LEO-PNT constellations may, for example, implement spatial diversity techniques among multiple satellites to improve capacity or availability to user equipment for delivery of data messages.

[0167] Integration of two-way signaling for PNT An exemplary framework 1300 for integrating bidirectional signaling between one or more LEO payloads and one or more user equipment (UE) is shown generally in Figure 13. The framework includes a set of GNSS satellites 20 (e.g., in MEO), a UE 30, and a set of payloads hosted on satellites 10, e.g., in LEO.

[0168] A bidirectional exchange in this framework may include signal items (1), (2) and (3) described below.

[0169] (1) At least one of the following: One or more GNSS satellites 20 transmit GNSS navigation signals 1310 that are received by the UE 30. One or more payloads transmit navigation signals 1320 in TDD and / or FDD mode that are received by the UE 30. In response to and / or prompted by the received signal, the UE 30 constructs an uplink message 1330 and transmits that uplink message 1330 to one or more payloads receiving the uplink signal 1330 in TDD and / or FDD mode.

[0170] (2) Uplink signals 1330 are received by the payload in TDD and / or FDD mode and provide two-way PNT services to the user, including, for example, one or more of the following: Time transfer between two UEs Time Boundary ·Position boundaries Payload-based location verification

[0171] (3) If data from more than one payload is required to provide two-way PNT services, the information received in the multiple payloads may be fused and processed in at least one of the following ways (not shown in Figure 13): One of the payloads (e.g., through an ISL or via a ground station) Ground Station UE30 through additional downlink in TDD and / or FDD mode

[0172] Thus, the above-described method 200 may further include the optional step of receiving an uplink signal from the user equipment for two-way navigation services related to, for example, one or more of: time transfer between the user equipment and a payload, time transfer between the user equipment and another user equipment, time bounds for the user equipment, location bounds for the user equipment, and / or verification of the location of the user equipment by the payload.

[0173] Here, the configuration of the uplink signal 1330 may depend on prior reception of downlink navigation messages 1310, 1320 via one or more of a signal from the payload, a signal from another payload, and / or a GNSS signal.

[0174] Further Examples As mentioned above, a payload according to an embodiment of the present disclosure may be a satellite payload, such as, for example, a payload carried on a satellite in LEO or a LEO-PNT satellite.

[0175] In other embodiments, multiple payloads may be provided and distributed across several spacecraft. For example, the payloads may be distributed across spacecraft (e.g., satellites) in one tier of a multi-tier satellite navigation system. The multi-tier satellite navigation system may include one or more satellites in MEO, one or more satellites in LEO, and / or one or more satellites in GEO. Multiple payloads may be provided, for example, in a multi-tier satellite navigation system. The payloads may be provided at one tier (or across tiers) of the satellite system, with each payload provided to a respective one of the satellites in the LEO.

[0176] Although LEO-PNT payloads have been illustratively mentioned, the present disclosure relates to any payload (e.g., satellite payload, distributed payload) having the necessary capabilities (e.g., receive, transmit, and possibly processing capabilities for the purpose of providing PNT functionality), and it will be understood that such payloads may be configured to perform any or all of the methods described above.

[0177] Additionally, the present disclosure also relates to satellites (eg, LEO satellites, LEO-PNT satellites) that include the above-described payloads (eg, satellite payloads).

[0178] interpretation It will be understood that any module, unit, or block described above may be implemented by one computer processor or by each computer processor, etc. The above modules, units, or blocks may further be implemented in a cloud-based manner.

[0179] Furthermore, it should be noted that the description and drawings merely illustrate the principles of the proposed method and system. Those skilled in the art will be able to implement various configurations not explicitly described or shown herein, but which embody the principles of the present invention and are within the spirit and scope of the present invention. Moreover, all examples and embodiments outlined herein are expressly intended to be primarily for illustrative purposes only, to aid the reader in understanding the principles of the proposed method and system. Furthermore, all statements herein providing principles, aspects, and embodiments of the present invention, as well as specific examples thereof, are intended to encompass equivalents thereof.

[0180] With respect to the flowcharts described throughout this disclosure, it should be understood that the order of the steps is not necessarily fixed by the flowchart; rather, steps may be performed in any order, or even in parallel, so long as any input to those steps from other steps is available.

[0181] Enumerated exemplary embodiments Aspects and implementations of the present disclosure can also be understood from the following enumerated exemplary embodiments (EEE), which are not claims.

[0182] EEE1. 1. A satellite-based positioning method, comprising: receiving, by a radio receiver, navigation signals in a GNSS frequency band; determining a position of the radio receiver based on the navigation signals; Receiving the navigation signals is performed in a time division duplex (TDD) mode, with time slots in which the navigation signals are present and time slots in which they are not present alternating with each other.

[0183] EEE2. The method according to EEE1, wherein the navigation signal is a non-GNSS navigation signal.

[0184] EEE3. The method of EEE1 or EEE2, wherein the navigation signal is a LEO-PNT signal.

[0185] EEE4. 10. The method of any one of the preceding claims, wherein the navigation signal is a navigation signal for code-based ranging measurements, carrier-based measurements, and / or Doppler measurements at a receiver, and / or low-complexity acquisition at a receiver.

[0186] EEE5. receiving, by the radio receiver, GNSS signals from a GNSS in the GNSS frequency band; 10. The method of any one of the preceding EEE, wherein determining the position of the wireless receiver is further based on the GNSS signals.

[0187] EEE6. The method according to EEE5, wherein the GNSS frequency band is one of the bands E1, E6, E5, E5a, E5b defined for Galileo, or one of the bands L1 to L5 defined for GPS.

[0188] EEE9. demodulating the navigation signal; extracting GNSS content from the demodulated navigation signal; 8. The method of claim 6, wherein determining the location of the wireless receiver is further based on the extracted GNSS content.

[0189] EEE10. The GNSS content relates to high precision corrections, as defined in EEE9.

[0190] EEE13. A computer program product which, when executed by a computer coupled to a radio receiver, causes the computer to carry out a method according to any one of the preceding EEE.

[0191] EEE14. A computer-readable storage medium storing a computer program according to EEE13.

Claims

1. 1. A method of operating a payload having receive and transmit capabilities in Earth orbit, comprising: receiving GNSS signals from a GNSS in a GNSS frequency band; transmitting a navigation signal in the GNSS frequency band towards Earth; The method, wherein the receiving and transmitting are performed in a time division duplex (TDD) mode having alternating time slots for receiving the GNSS signals and time slots for transmitting the navigation signals.

2. The method of claim 1 , wherein the duty cycle of the TDD mode is synchronized with a timing epoch of a GNSS.

3. The method of claim 1 , further comprising performing at least one of orbit determination and time synchronization for the satellite payload based on the GNSS signals.

4. The duty cycle of the TDD mode is synchronized with a timing epoch of a GNSS; 4. The method of claim 3, wherein synchronization of the duty cycle of the TDD mode to the timing epoch of the GNSS is performed based on results of at least one of orbit determination and time synchronization.

5. The method of claim 3 , wherein at least one of orbit determination and time synchronization is based on high precision corrections received with the GNSS signals.

6. The method of claim 3 , wherein at least one of orbit determination and time synchronization uses information about GNSS signal authenticity.

7. The method of claim 3 , wherein at least one of orbit determination and time synchronization uses information about GNSS signal integrity.

8. At least one of the orbit determination and the time synchronization an SBAS message received along with the GNSS signal; ranging authentication and / or message authentication of said GNSS signals; an HAS message received together with the GNSS signal; and / or an ISM message received along with the GNSS signal; The method of claim 3 , based on one or more of the following:

9. 4. The method of claim 3, further comprising: maintaining signal tracking of the GNSS signal during a time slot for transmitting the navigation signal to avoid loss of lock and / or reacquisition based on a result of the at least one of orbit determination and time synchronization.

10. demodulating the GNSS signal to obtain GNSS content transmitted with the GNSS signal; The method of claim 1 , further comprising: including at least a portion of the GNSS content in a navigation message transmitted along with the navigation signal in the GNSS frequency band towards Earth.

11. The GNSS content is SBAS messages, SAR return link message, Integrity Support Message (ISM), High Accuracy Service (HAS) messages, Emergency warning messages, and / or Authentication messages, The method of claim 10 based on one or more of the following:

12. 2. The method of claim 1, further comprising transmitting a second navigation signal toward Earth in a frequency division duplex (FDD) mode in a second GNSS frequency band different from the GNSS frequency band or in a non-GNSS frequency band.

13. The method of claim 1 , further comprising performing radio occultation based on the received GNSS signals in the time slots for receiving the GNSS signals in the TDD mode.

14. The method of claim 1 , further comprising: performing reflectivity measurements based on the received GNSS signals in the time slots for receiving the GNSS signals in the TDD mode.

15. 2. The method of claim 1, further comprising performing operations to detect and / or locate unwanted emissions in the GNSS frequency band in the time slots for receiving the GNSS signals in the TDD mode.

16. The method of claim 1 , further comprising: performing radio interference estimation in the time slots for receiving the GNSS signals in the TDD mode.

17. 2. The method of claim 1, wherein the navigation signal is a navigation signal for one or more of code-based ranging measurements, carrier-based measurements and Doppler measurements at a receiver, and / or low-complexity acquisition at the receiver.

18. receiving an uplink signal from a user equipment for two-way navigation services; The two-way navigation service a time transfer between the user equipment and the payload; time transfer between the user equipment and another user equipment; a time limit on the user device; Bounding the location of the user equipment; and / or verifying the location of the user equipment by the payload; The method of claim 1 , wherein the method is associated with one or more of the following:

19. The method of claim 1 , wherein the payload is a satellite payload carried on a satellite in low Earth orbit (LEO).

20. The method of claim 1 , wherein multiple payloads are provided to respective spacecraft in one or more tiers of a multi-tier satellite navigation system.

21. The method of claim 20, further comprising receiving an uplink signal from a user equipment for two-way navigation services; The two-way navigation service a time transfer between the user equipment and the payload; time transfer between the user equipment and another user equipment; a time limit on the user device; Bounding the location of the user equipment; and / or verifying the location of the user equipment by the payload; relates to one or more of the following: The uplink signal has a configuration of: a signal from the payload; a signal from another payload, and / or GNSS signal, 21. The method of claim 20, wherein the method relies on prior reception of a downlink navigation message by one or more of:

22. 2. The method of claim 1, wherein the GNSS frequency band is one of bands E1, E6, E5, E5a and E5b defined for Galileo, or one of bands L1, L2 and L5 defined for GPS.

23. 1. A satellite payload having receive and transmit capabilities, comprising: A satellite payload configured to carry out a method according to any one of claims 1 to 22.

24. A satellite comprising a satellite payload according to claim 23.

25. A satellite navigation system comprising one or more payloads according to claim 23.

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