Satellite payload and method for operating same

Abstract

The invention relates to a method for operating a payload with receiving and transmitting capabilities on the earth orbit. The method includes receiving a GNSS signal from a GNSS in a GNSS frequency band; and transmit a navigation signal to the earth in the GNSS frequency band. Wherein the receiving and transmitting are performed in a time division duplex (TDD) mode, and the time slots for receiving the GNSS signal and transmitting the navigation signal are alternated. The application also relates to a corresponding payload and a satellite comprising such a payload.

Description

Technical Field

[0001] The present invention relates to the field of satellite communication and space-based positioning. In particular, the present invention relates to a method for operating a payload having receiving and transmitting capabilities, a corresponding payload, and a satellite containing such a payload. Background Art

[0002] Conventional Global Navigation Satellite Systems (GNSS) may have some issues, such as not being able to see a sufficient number of GNSS satellites from a user terminal and a low GNSS signal-to-noise ratio (SNR) at the user terminal location, for example due to low power of the GNSS signal when it reaches the ground and / or interference from terrestrial transmissions in the GNSS frequency band.

[0003] Therefore, there is a need for improved positioning technology. In particular, there is a need for such technology that can improve the availability and / or accuracy of positioning. Summary of the invention

[0004] In view of some or all of these needs, the present disclosure proposes a method of operating a payload with receiving and transmitting capabilities in Earth orbit (e.g., a navigation or positioning method), a payload, and a satellite, which have the features of each independent claim.

[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 a GNSS signal from a GNSS in a GNSS frequency band. The method may also include transmitting a navigation signal to the Earth in a GNSS frequency band. The navigation signal may be based at least in part on the received GNSS signal. The steps of receiving and transmitting may be performed in a time division duplex, TDD, mode, wherein the time slots for receiving GNSS signals and transmitting navigation signals alternate. In addition, receiving and / or transmitting may be performed in two or more GNSS frequency bands. Additional transmissions may be performed in non-GNSS frequency bands. Here, it should be understood that the term GNSS signal may cover any higher orbit satellite navigation or augmentation signal (e.g., SBAS signal), 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 and the ground receiving power can be improved. In addition, frequency diversity and / or measurement diversity can bring additional benefits.

[0007] In some embodiments, the duty cycle of the TDD mode may be synchronized with a timing epoch of the GNSS. The timing epoch of the GNSS may be derived (eg, calculated) from the onboard ODTS using GNSS signals.

[0008] In some embodiments, the method may further include performing at least one of orbit determination and time synchronization of the satellite payload based on the GNSS signals. Orbit determination and time synchronization (ODTS) may use onboard filters, 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. ODTS may also generate an estimate of the GNSS timing epoch.

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

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

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

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

[0013] In some embodiments, the method may further comprise demodulating the GNSS signal to obtain GNSS content transmitted with the GNSS signal. The method may further comprise including at least part of the GNSS content in a navigation message transmitted to the earth in a GNSS frequency band together with the navigation signal. For example, the GNSS content obtained in this manner may be associated with a (low latency) GNSS message.

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

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

[0016] In some embodiments, the method may further include performing radio occultation based on the received GNSS signal in a time slot in which the GNSS signal in the TDD mode is received.

[0017] In some embodiments, the method may further include performing reflection measurements (eg, reflection to the earth's surface) based on the received GNSS signals in the time slots in which the GNSS signals in the TDD mode are received.

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

[0019] In some embodiments, the method may further include performing radio interference estimation in time slots in which GNSS signals in TDD mode are received.

[0020] In some embodiments, the navigation signal may be a navigation signal for code-based ranging measurements, carrier-based ranging measurements, and / or Doppler measurements at the receiver and / or low complexity acquisition at the receiver. In some embodiments, the navigation signal may be a navigation signal 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 device for a two-way navigation service. The two-way navigation service may involve one or more of: a time transfer between the user device and the payload; a time transfer between the user device and another user device; a time limit for the user device; a location limit for the user device; and / or verification of the location of the user device by the payload.

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

[0023] In some embodiments, multiple payloads may be provided on respective spacecraft in a layer of a multi-layer satellite navigation system. For example, a multi-layer 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. Thus, several payloads may be distributed, for example, on a layer of a multi-layer satellite navigation system including one or more satellites in LEO. Spacecraft (e.g., satellites) in a given layer may be arranged in different orbital planes, at different inclinations, and / or at different altitudes.

[0024] In some embodiments, the composition of the uplink signal may depend on previous reception of a downlink navigation message by one or more of: a signal from a payload; a signal from another payload; and / or a GNSS signal.

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

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

[0029] It should be understood that device features and method steps can be interchanged in a variety of ways. In particular, as will be appreciated by those skilled in the art, details of a disclosed device or system (e.g., a satellite payload, a satellite, or a satellite constellation) can be implemented by a corresponding method of operating the device / system or a portion thereof, and vice versa. Furthermore, any statement above regarding a device / system should be understood to apply equally to the corresponding method, and vice versa.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Example embodiments of the present disclosure are explained below with reference to the accompanying drawings, in which:

[0032] Figure 1 schematically illustrates an example of a framework to which techniques according to the present disclosure may be applied;

[0033] Figure 2 is a flowchart illustrating an example of a method of operating a payload according to an embodiment of the present disclosure;

[0034] Figure 3schematically illustrates an example of using TDD mode in a terrestrial telecommunication system;

[0035] Figure 4 An example of using the TDD mode in a satellite navigation scenario according to an embodiment of the present disclosure is schematically shown;

[0036] Figure 5A and Figure 5B An example of timing synchronization of TDD transmission time slots according to an embodiment of the present disclosure is schematically shown;

[0037] Figure 6 The present invention is shown in Figure 2 A flowchart of examples of optional steps of the method;

[0038] Figure 7 is a block diagram schematically illustrating a process of assisting tracking of a GNSS signal received in a TDD mode by using information obtained from continuously receiving another GNSS signal according to an embodiment of the present disclosure;

[0039] Figure 8 The present invention is shown in Figure 2 Flowchart of examples of further optional steps of the method;

[0040] Fig. 9 An example of a scheme for relaying GNSS message content to a navigation signal according to an embodiment of the present disclosure is schematically shown;

[0041] Fig.10 The present invention is shown in Figure 2 Flowchart of examples of further optional steps of the method;

[0042] Fig.11 An example of a framework for performing radio occultation according to an embodiment of the present disclosure is schematically shown;

[0043] Fig.12 An example of a framework for performing radio frequency interference estimation according to an embodiment of the present disclosure is schematically shown; and

[0044] Fig.13 An example of a framework for integrating a bidirectional signaling function according to an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0045] Overview

[0046] The present disclosure relates to payloads (e.g., satellite payloads), methods of operating such payloads (e.g., navigation or positioning methods), and corresponding satellites. An example of such a satellite is a LEO satellite for providing positioning, navigation, and timing (PNT) services, or LEO-PNT satellites for short. Although the present disclosure may often refer to LEO-PNT satellites and payloads, this should never be construed as limiting. On the contrary, as will be appreciated by those skilled in the art, the present disclosure may relate to suitable satellites and payloads other than LEO-PNT satellites and payloads, and for the sake of brevity, LEO-PNT is used as a non-limiting example. It should be understood that when the present disclosure refers to LEO-PNT satellites, payloads, and methods of operating the same, it is also intended to include other suitable satellites and payloads.

[0047] Broadly speaking, LEO-PNT (as a non-limiting example of satellites, payloads, and methods according to the present disclosure) is intended to augment and / or supplement satellite navigation systems, such as GNSS and SBAS, in medium Earth orbit (MEO; e.g., between 2,000 and 35,786 km in altitude), inclined geosynchronous orbit (IGSO), and geostationary orbit (GEO) with additional signals transmitted by payloads deployed in LEO, the transmission of which follows GNSS time and the position of which at the time of transmission is referenced to a GNSS reference frame.

[0048] Figure 1 An example framework in which the technology according to an embodiment of the present disclosure may be employed is schematically shown. In this framework, a satellite (e.g., a LEO satellite, a LEO-PNT satellite) 10 receives a higher orbit navigation or augmentation system signal (e.g., a MEOGNSS signal, a GEO augmentation signal, a SBAS signal, 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 may transmit signals to user equipment on the ground or in the Earth's atmosphere. The signal from the satellite 10 may be referred to as a navigation signal (e.g., a LEO-PNT signal), and the signal from the satellite 20 may be referred to as a GNSS signal, but is not limited thereto.

[0049] LEO-PNT can enhance and / or supplement satellite navigation in various ways, depending on the target user and their needs. This includes providing signals that allow user equipment to obtain positioning velocity / timing related measurements (e.g., ranging, Doppler and carrier phase measurements) and signals that transmit navigation related data to user equipment.

[0050] LEO-PNT signals enhance the user experience of GNSS signals, such as in terms of accuracy, availability, robustness and resilience, convergence time of high-precision PVT solutions (e.g., PPP algorithms), when GNSS signals are impaired, for example, due to challenging environments (e.g., reflections of signals from obstacles, buildings or natural obstacles, higher attenuation under tree canopies or inside buildings, higher noise floor, etc.). LEO-PNT signals may also enable user devices to obtain positioning-navigation-timing information and solutions using these signals alone, and / or in combination with GNSS signals, and / or in combination with other information sources (e.g., dead reckoning, cellular communication systems, and any combination thereof).

[0051] The contribution of LEO-PNT signals to performance improvements can be achieved through the following capabilities:

[0052] ● Increased number of satellites available to user equipment (compared to GNSS-only satellites) to combine them with other PNT signal sources, such as GNSS in MEO, systems in IGSO and GEO, transmitters from terrestrial cellular systems (e.g. 4G / 5G, WIFI). This is very useful in challenging environments to increase the number of satellites available for positioning-navigation-timing and the geometry of the signals processed by the user equipment to derive a position-velocity-timing solution.

[0053] ● Provides signals with higher received power to user equipment. This improves signal acquisition and tracking performance (e.g., reduced acquisition time and energy consumption, improved statistics of carrier cycle hopping and loss of lock, improved estimation and mitigation of multipath, as the algorithms involved in the latter perform better at higher signal-to-noise ratios for line-of-sight signals, improved data demodulation and availability), and allows for improved coverage in environments affected by increased propagation losses (e.g., tree canopy, indoors).

[0054] ● Measurement diversity. The faster motion of the payload transmitting the LEO-PNT signal compared to the signal from MEO causes the errors in the measurements made by the user equipment on the signal to behave differently. This difference in characteristics, a source of diversity, translates into different noise and error statistics from multipath, faster measurement decorrelation, etc., which the user equipment algorithms can exploit to improve performance (accuracy, convergence time, usability when combined with dead reckoning sensors, etc.).

[0055] ● Frequency diversity. LEO-PNT signals can be transmitted on carriers in similar frequency bands as GNSS, or in addition or as an alternative, on frequency bands different from GNSS bands. The latter benefits the user experience and performance accessible to user devices. Frequencies below current GNSS frequencies (e.g., signals with carrier frequencies below 1 GHz) will have better propagation and lower attenuation under tree canopies or inside buildings, improving performance for use cases in these situations. Frequencies much higher than current GNSS frequencies (e.g., above 5 GHz) typically have larger signal bandwidths (a source of improved ranging accuracy and stability) and are less affected by propagation through the ionosphere, providing better accuracy and stability. Examples include bands in UHF, S-band, C-band, and Ku / K / Ka-band.

[0056] Frequency diversity is beneficial for LEO-PNT signals and targeting capabilities. Nevertheless, it is also beneficial to transmit LEO-PNT signals in the same band as GNSS signals. In fact, it allows the LEO-PNT signals to be received on the user equipment using the same RF front end and possibly a similar baseband processor (as used for GNSS signals), which greatly simplifies the user equipment and thus the adoption of LEO-PNT signals.

[0057] In addition to frequency diversity, multi-frequency transmission also helps mitigate ionospheric effects (e.g., dual-frequency or multi-frequency combination) and supports higher user position, velocity, and time (PVT) accuracy. Therefore, LEO-PNT signals are preferably transmitted on 2 (possibly 3) frequency bands shared with GNSS (e.g., Galileo's E1, E6, and E5, GPS's L1, L2, and L5, or a combination of 2 or 3 thereof, etc.).

[0058] It can also be advantageous to propagate content data related to PNT applications and support user algorithms and / or user experience via LEO-PNT signals. In fact, LEO-PNT signals experience lower free space losses, resulting in high SNR, thus enabling higher throughput and / or higher availability compared to MEO signals. In addition, LEO signals are blocked for shorter time intervals for users on Earth, such as by buildings or natural obstacles, compared to MEO signals. This helps reduce the latency or time required to properly demodulate all the necessary information.

[0059] 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 to these data (e.g. PPP corrections), information required to estimate the reliability of signal integrity (e.g. SBAS, integrity support messages of ARAIM concept), information required to verify the origin of data and / or signals (e.g. OSNMA of Galileo), other information relevant to the application derived from PVT solutions of user equipment, such as information related to emergency warnings (e.g. EWS messages). These data can be uploaded to LEO-PNT payloads via ground-to-air links, satellite communication links, or received directly on board via signals from higher orbiting navigation or augmentation systems (e.g. MEO GNSS signals or augmentation signals from GEO (e.g. SBAS)).

[0060] LEO-PNT signals can also complement GNSS, satellite navigation, and terrestrial navigation systems in the areas described below, using characteristics that exploit the nature of the signal or the proximity of the payload to the Earth, being in LEO, or a combination of both.

[0061] LEO-PNT signals and systems can help support positioning with very low energy per position fix, which helps extend the battery life of asset tracking devices.

[0062] Other capabilities may include support for bidirectional PNT links, where the LEO-PNT payload processes the signal for the user equipment uplink. The closer proximity of LEO-PNT satellites to the Earth facilitates the provision of new bidirectional services due to the lower equivalent isotropic radiated power (EIRP) required for ground user terminals. Some possible bidirectional services include bidirectional time and frequency satellite transmissions using LEO satellites, detection and location of emergency calls, and user position verification, where the user's position is verified using an uplink signal from the user or a bidirectional signal through processing on the LEO-PNT satellite or ground segment. In some cases, it may be relevant to consider placing the carrier frequency of the uplink in a band close to (e.g., adjacent to) the GNSS band to reduce the complexity of the user terminal and LEO-PNT payload antennas.

[0063] LEO-PNT systems can also provide assistance functions related to GNSS signals received from LEO, such as: GNSS Radio Occultation (RO), GNSS reflectometry, and monitoring of the radio spectrum to detect and locate RF interference that may be generated in GNSS bands on Earth.

[0064] LEO-PNT satellites may carry GNSS radio occultation (GNSS-RO) instruments 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, an estimation process may be run on the LEO-PNT payload and its results transmitted to the user via the LEO-PNT signal. The principle of radio occultation may be extended beyond GNSS signals to incorporate other signals received by the LEO-PNT payload and obscured by the atmosphere, in particular LEO-PNT signals received from other LEO-PNT satellites, or signals from ISLs between LEO-PNT satellites. Other systems or infrastructures involved in providing satellite navigation services (e.g. SBAS, GNSS systems, ground-based GNSS augmentation systems, etc.) can provide and use information obtained from radio occultation measurements (e.g. GNSS-RO, ISL-RO or LEO-PNT-RO) and additional data (e.g. from their respective ground segments) to derive corrections for the effects of the atmosphere on GNSS signal propagation (e.g. SBAS ionospheric correction messages, GNSS broadcast ionospheric correction messages, GNSS precise ionospheric products supporting PPP algorithms, etc.).

[0065] LEO-PNT satellites may also carry GNSS reflectometry (GNSS-R) instruments to collect measurements from GNSS signals reflected from the Earth's surface and downlink them to the ground (e.g., via the 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 for geolocating vessels or assets on Earth.

[0066] GNSS receivers on LEO-PNT satellites may be used to collect measurement data from GNSS satellites and downlink it to the ground (e.g., via TTC and possibly one or more ISL hops) so that the information may be used to improve the functionality and performance of GNSS systems and services implemented by user equipment. This includes improving the clock and ephemeris information of the GNSS system, monitoring the quality of the GNSS signals, and detecting impairments and integrity issues of the GNSS signals. Data collected by GNSS receivers on board airborne LEO-PNT satellites may be processed onboard to detect GNSS integrity issues (e.g., using algorithms like RAIM) and notify users in real time via LEO-PNT signals.

[0067] The transmission time of LEO-PNT signals and the location of the transmission source (e.g., satellite, phase center of LEO-PNT payload antenna, etc.) need to be determined and communicated to the user equipment so that the user equipment can calculate the position (e.g., through trilateration). Orbit determination and clock synchronization (ODTS) referenced to a GNSS frame can be highly relevant to optimizing the use of LEO-PNT signals in conjunction with GNSS signals and facilitating adoption by manufacturers and users who are already familiar with GNSS-based technologies.

[0068] Many applications of LEO-PNT signals and systems may require high precision positioning and therefore low user equivalent range errors (to which ODTS may contribute). In addition, for many applications it may be required that the LEO-PNT signals and their sources are trustworthy. In the present context, trustworthiness is understood as taking into account the notions of integrity known to the GNSS community (e.g., knowledge of measurement statistics and the probability that an error exceeds a certain alarm limit) and the notion of authenticity of the information carried by the LEO-PNT signals (e.g., authenticity of the signal's origin and knowledge of the risk of tampering with the signal or its content).

[0069] Given some or all of the above considerations, drivers for LEO-PNT payloads may include one or more of the following:

[0070] ● Transmit at least one LEO-PNT signal in a common band with GNSS signals (possibly 2, or even 3), and optionally (e.g., preferably) transmit at least one LEO-PNT signal in a different band than the GNSS signals

[0071] ● Calculate high-precision ODTS and information and indicators about its reliability

[0072] ● Access navigation messages from GNSS and SBAS signals to forward parts of their content to the user,

[0073] ● Receive signals in GNSS bands to support assistance functions such as GNSS radio occultation, GNSS reflectometry, RFI monitoring, collecting GNSS measurements to improve GNSS related products (e.g. GNSS ODTS, integrity, etc.) and / or receive signals in GNSS bands or bands near the GNSS bands to support processing uplinks from user equipment

[0074] ● Transmitting LEO-PNT signals referenced to GNSS time and position frames from the LEO-PNT payload and high-precision ODTS of the signals, and correlating the ODTS with information and metrics about the trustworthiness of the ODTS to the user, including integrity and authentication

[0075] ● Receive uplink signals from users to provide two-way navigation services

[0076] Key Features and Implementation Options

[0077] The typical architecture of a LEO-PNT system involves a LEO-PNT payload on one or more satellites in LEO, optionally a set of functions and capabilities on the ground (e.g., ground control and mission segment) for monitoring, controlling and operating the LEO-PNT mission, and a user segment including user equipment.

[0078] The LEO-PNT space segment may include or consist of a set of satellites orbiting the Earth in multiple orbital planes, which may be at one or more inclinations and one or more altitudes. The LEO-PNT space segment may be implemented as a dedicated constellation or as payloads hosted on other satellites, or may be implemented using a hybrid approach that combines payloads on dedicated satellites with payloads hosted on other satellites. The LEO-PNT constellation consists of multiple satellites distributed in multiple orbital planes, which may be at one or more inclinations and one or more altitudes, for example, to optimize coverage in specific areas (e.g., urban canyons in densely populated areas of the world, polar latitudes, etc.), and may allow for capabilities to be distributed in different ways across these planes.

[0079] The payload may also involve supporting functions, such as interfaces with TTC functions and equipment. LEO-PNT satellites may include ISL transceivers and antennas to exchange data and / or obtain inter-satellite ranging (ISR) measurements with other LEO-PNT satellites within the field of view. ISLs may be based on radio frequency (RF) and / or optical technologies and may operate between satellites in the same plane (in-plane) or in different planes (inter-plane), or a combination of both. Using TTC links to manage mission data and information and parameters for LEO-PNT payloads may have the advantage of simplicity, but at the expense of increased latency compared to ISLs.

[0080] Taking into account the drivers listed in the overview section, the core capabilities of LEO-PNT systems and payloads may include the following:

[0081] ● Accurate and reliable ODTS calculation

[0082] ● Provide the content of the navigation message to the LEO-PNT payload in order to relay the LEO-PNT signal

[0083] Generate the necessary LEO-PNT signals to enable the services and functions of the LEO-PNT system (e.g. ranging, data dissemination, etc.) in various bands including GNSS bands and in compliance with the above ODTS

[0084] ● Receive and process signals uplinked by user equipment in the case of bidirectional capabilities integrated into LEO-PNT systems and payloads

[0085] ● Support for auxiliary performance functions such as GNSS radio occultation, GNSS reflectometry and RFI monitoring

[0086] This could mean that the LEO-PNT payload has one or more of the following capabilities:

[0087] ●Simultaneously transmit and receive GNSS band signals

[0088] ●Calculate high-precision ODTS

[0089] ● Calculate information and indicators about the credibility of ODTS

[0090] ● Generate LEO-PNT signals in various bands including GNSS that comply with this ODTS requirement to enable user equipment to derive relevant PVT-related measurements, and these LEO-PNT signals contain ODTS-related data, ODTS credibility, and other data, some of which is derived from external sources

[0091] ● Receive uplink signals from users to provide two-way navigation services

[0092] As will be appreciated by those skilled in the art, various methods and concepts may be used to estimate the ODTS of LEO satellites. One method involves a network of ground sensor stations that derive range and / or range rate and / or carrier phase measurements from signals from LEO satellites and LEO-PNT payloads, similar to the concepts operating in the GNSS ground segment. Differential corrections may also be applied to the ODTS obtained from TTC stations, but only for users near the differential stations (e.g., similar to the differential GNSS (DGNSS) and real-time kinematic (RTK) concepts of GNSS). These methods may involve or require additional onboard and ground hardware (e.g., high performance and potentially complex clock systems to maintain long term stability, low latency ground links, and sensor station networks). ODTS may also be derived from measurement processing of links between LEO-PNT satellites (e.g., ISLs).

[0093] Given that LEO-PNT satellites are located in orbit below GNSS and therefore receive the latter’s signals under good conditions, an advantageous solution could be to constrain the transmission of LEO-PNT signals and the reference position to an accurate and reliable onboard ODTS using measurements of the onboard receiver when receiving GNSS signals. Furthermore, this receiver could be integrated into the LEO-PNT payload to optimize performance (e.g., time synchronization of processing), as well as to reduce interfaces, size, weight, etc. For example, the ODTS could use a real-time Precision On-board Orbit Determination (P2OD) algorithm using pseudorange and carrier phase measurements with floating ambiguities or integer ambiguity resolution (IAR).

[0094] The ODTS process can improve its accuracy from tens of centimeters to more than ten centimeters using data and / or corrections (e.g., orbit data, clock corrections, inter-signal bias, inter-frequency bias, ionospheric corrections, code bias, phase bias, etc.). To do this, specific information may need to be considered and provided to the onboard ODTS function that is not integrated in the so-called clock and ephemeris data or in the standard navigation messages of the GNSS signals (e.g., LNAV, CNAV, CNAV-2 for GPS, I / NAV and F / NAV for Galileo).

[0095] The integrity of the ODTS solution can be derived by, for example, implementing Receiver Autonomous Integrity Monitoring (RAIM) or Advanced RAIM (ARAIM) concepts, using integrity information generated by SBAS augmentation systems, or a combination of both. LEO-PNT payloads may also need to have access to the authenticity of navigation messages containing GNSS signal clock and ephemeris data to calculate authentic ODTS information.

[0096] The data required for GNSS signals to provide accurate and reliable information may not be contained in the navigation information of these signals (e.g. GPS information on Galileo’s L1C / A, L2C, L5 and L1C, I / NAV and F / NAV). Corrections used to improve the accuracy and integrity of the navigation information used in the ODTS and to confirm its authenticity may be provided onboard via sidelink or non-GNSS links, as in the case of ground users (e.g. PPP corrections received via an Internet link, Assisted-GNSS protocols from terrestrial cellular networks, so-called L-band correction services provided through satellite communication systems), or by uplink telecontrol commands or through ISLs, which will connect to the ground to obtain this information. In all cases, this may involve additional equipment onboard and additional reliance of the airborne ODTS on external technologies, information sources or service providers.

[0097] While the above links may have some advantages, they may also present significant disadvantages, including additional complexity and dependency on LEO-PNT systems. LEO-PNT payloads can take advantage of the additional information contained in specific GNSS and SBAS signals to access the information needed to derive the trustworthiness of the ODTS. This includes receiving SBAS signals, receiving Galileo HAS corrections broadcast on the E6B signal, and receiving authentication features carried by GNSS signals, such as navigation message authentication and encryption signals (e.g. OSNMA and CAS for Galileo, Chimera for GPS). A key advantage of the LEO-PNT payload may be its simplicity, as the reception of these signals and information can be integrated into GNSS airborne receivers.

[0098] Likewise, specific information delivered to users via LEO-PNT signals may be received directly from specific signals and messages from systems such as GNSS (e.g., Galileo, GPS) and SBAS.

[0099] Measurements and data obtained from specific GNSS signals received via LEO-PNT payloads provide many advantages and value-added features. This requires the onboard GNSS receiver to receive identified GNSS signals and data in specific frequency bands, such as E1 / L1 (SBAS, Galileo OSNMA), E6 (Galileo HAS, CAS), E5 (for common dual-frequency measurements between Galileo and GPS, SBASDFMC), receive dual-frequency signals for radio occultation, receive multiple GNSS bands for signal quality monitoring and interference detection, and transmit LEO-PNT signals, some of which are also in GNSS bands.

[0100] In order to generate relevant LEO-PNT signals in the GNSS band while receiving information and obtaining measurements from GNSS and SBAS signals, the conditioning of receiving and transmitting signals operating in the GNSS band may be critical to the foreseen LEO-PNT concept. In addition, the functions that enable the key features of the LEO-PNT payload (such as high-precision ODTS, assistance functions using GNSS bands, etc.) may be affected by this conditioning and therefore also need to be customized according to this conditioning to provide optimal performance.

[0101] Example Payload Implementation

[0102] Core capabilities of LEO-PNT payloads may include:

[0103] The ability to receive and process signals from MEO satellites (e.g. GNSS), GEO satellites (e.g. SBAS), for example in the L-band, and possibly from satellites in other orbits above LEO (e.g. IGSO systems), or high-orbit satellite navigation or augmentation signals, typically from high-orbit satellite navigation or augmentation systems

[0104] ●Calculate accurate and reliable ODTS function

[0105] ● The ability to generate LEO-PNT signals in various bands including GNSS that are necessary to enable the services and functions of the LEO-PNT system (e.g. ranging, data dissemination, etc.) and constrain them to the above-mentioned accurate and reliable ODTS

[0106] ● Capability to receive uplink signals from user equipment in case of bidirectional functionality integrated in LEO-PNT system and payload

[0107] ●Supports auxiliary performance functions such as GNSS-RO, GNSS reflectometry and RFI monitoring

[0108] Therefore, the payload must receive and transmit signals operating in the GNSS band (GNSS frequency band). A feasible method to achieve these functions while avoiding crosstalk between transmission and reception in the GNSS band may be critical to the design and operation of the payload.

[0109] The above content relates to higher orbit satellite navigation or augmentation signals received and processed by the payload 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). In addition, these signals can be received from higher orbit satellite navigation or augmentation systems in the L-band. Typically these signals can be considered to be received in a frequency band used by a GNSS or augmentation system (e.g., SBAS). Although the present disclosure often mentions GNSS signals, it is understood that it also relates to higher orbit satellite navigation or augmentation signals, including but not limited to GNSS signals and / or SBAS signals.

[0110] Simultaneous transmission and reception in the GNSS band

[0111] GNSS (as a non-limiting example of a high-orbit satellite navigation or augmentation system) represents the majority of satellite navigation systems and can therefore be considered typical and representative of current satellite navigation systems. GNSS signals (as a non-limiting example of a high-orbit satellite navigation or augmentation signal) are continuously transmitted, and therefore the signals, associated payloads, and reception functions are accordingly designed for continuous operation.

[0112] The LEO-PNT payloads described in this disclosure (as non-limiting examples of payloads or satellite payloads) are capable of transmitting and receiving signals in the GNSS bands. Signal transmissions from a LEO-PNT payload may affect the operation of nearby receive functions on the same payload. The transmissions may at least significantly increase the noise floor in the receive band, potentially preventing proper processing of signals intended to be received to support the LEO-PNT payload, may saturate hardware functions in the receiver (e.g., saturation of the LNA, operation well beyond the linear region of most of the receive functions involved, etc.), and may degrade them.

[0113] A feasible solution to support transmission and reception operation in the GNSS band is to allocate transmission and reception to different frequency bands, which will be referred to as frequency division duplex (FDD) mode in the context of this disclosure. When operating in FDD mode, compatibility between LEO-PNT signal transmission (e.g., in the L-band) and reception of GNSS signals by an onboard GNSS receiver can be ensured by one or more of the following:

[0114] ●Out-of-band emission filter for LEO-PNT signal transmitter

[0115] ●Out-of-band rejection filter for GNSS receivers

[0116] Digital signal processing (DSP) at the GNSS receiver level for interference cancellation (e.g., self-interference cancellation (SIC) techniques) to understand the exact nature and content of the transmitted signal

[0117] The transmit and receive antennas can be designed to minimize their coupling, thereby minimizing crosstalk between the transmitter and receiver. Additionally or alternatively, the transmit and receive antennas can be mounted as far apart from each other as possible, if the size of the satellite and the accommodation space permit. All of these techniques may require additional hardware and / or additional space (e.g., to accommodate filters) and may introduce specific accommodation constraints that are often not ideal. In addition, they also constrain the frequency planning design of LEO-PNT payloads in GNSS bands, limiting the choice of those bands to operate in when receiving and those bands to operate in when transmitting, which may not be conducive to achieving optimal performance and facilitating the implementation of user equipment.

[0118] In contrast to the above, the present disclosure proposes to introduce (and optimally configure) alternating transmit and receive functions on the same GNSS frequency band in the LEO-PNT payload, one function alternating with the other according to a certain period and duty cycle. This technique will be described in more detail below and will be referred to as time division duplex (TDD) throughout the disclosure.

[0119] Reference now Figure 2The flowchart of the present invention describes an example of a method 200 for operating a payload having receiving and transmitting capabilities (e.g., a satellite payload, a LEO-PNT payload). The method 200 can be performed, for example, in an Earth orbit (e.g., LEO). In addition, it can be said that the method 200 corresponds to a positioning or navigation method. Although the following description will be Figure 2 Although additional steps are not shown in the figure, the method 200 may at least include steps S210 and S220. It should be noted that these steps or their sequences may be performed continuously.

[0120] exist Step S210 , a GNSS signal received from a GNSS in a GNSS frequency band.

[0121] Although GNSS signals are mentioned here, it is understood that this step generally involves receiving higher orbit satellite navigation or augmentation signals. These signals involve navigation signals received from satellite navigation or augmentation systems (e.g., GNSS, SBAS) in higher orbits (e.g., orbits above LEO). Therefore, it is understood that any technology proposed herein also involves higher orbit satellite navigation or augmentation signals, including but not limited to GNSS signals and / or SBAS signals.

[0122] The above-mentioned GNSS signals (as non-limiting examples of high-orbit satellite navigation or augmentation signals) can be received from a high-orbit satellite navigation or augmentation system in a frequency band used by the GNSS or augmentation system, which frequency band will be referred to as a GNSS frequency band. For example, the GNSS signal can be received in the L band. More specifically, in some embodiments, the GNSS frequency band can be, for example, one of the E1, E6, E5, E5a, and E5b bands defined for Galileo, or one of the L1, L2, and L5 bands defined for GPS.

[0123] In step S220, a navigation signal is transmitted toward the earth in a GNSS frequency band. Importantly, the navigation signal is transmitted in the same frequency band (e.g., at the same carrier frequency) as the GNSS signal received in step S210. Notably, this is understood to include situations where the transmission frequency band is located near the receiving GNSS frequency band, close enough so that the frequency spectra of the transmitted and received signals overlap in the frequency domain. In some embodiments, the navigation signal may be transmitted in a frequency band that overlaps the GNSS frequency band.

[0124] The navigation signal transmitted at step S220 may be a navigation signal used for code-based ranging measurement, carrier-based measurement and / or Doppler measurement at a receiver (e.g., user equipment) and / or low-complexity acquisition at the receiver. In this sense, the navigation signal may provide the same functionality as a GNSS signal.

[0125] In addition, the navigation signal may be based at least in part on the GNSS signal. For example, the navigation signal (or its content) may be derived at least in part based on the GNSS signal (or its content). For example, the navigation signal may be based at least in part on the results of the ODTS at the payload. In addition, the navigation signal may include GNSS content derived from the GNSS signal and relayed by the transmitted navigation signal. Further details of this will be described below.

[0126] In the above, the reception in step S210 and the transmission in step S220 are performed in TDD mode, wherein the time slots for receiving GNSS signals and transmitting navigation signals are alternated. That is, for a given TDD time slot, only one of the receiving function or the transmitting function is active in the same frequency band, and in a subsequent TDD time slot, only the other of the receiving function or the transmitting function is active in the same frequency band.

[0127] In addition, although Figure 2 Although not shown in the figure, method 200 may include an optional step of transmitting a second navigation signal to the earth in a second GNSS frequency band or a non-GNSS frequency band different from the GNSS frequency band (this step may also be performed continuously). The transmission of the second navigation signal may be performed in FDD mode, i.e., the second navigation signal is continuously transmitted, but the transmission frequency band is different from the reception frequency band (i.e., the GNSS frequency band).

[0128] Typically, the reception in step S210 and / or the transmission in step S220 may be performed in two or more (different) GNSS frequency bands. The additional transmission in step S220 may optionally be performed in a non-GNSS frequency band. It will be appreciated that the TDD mode is applicable to any (GNSS) frequency band in which the payload is used for reception and transmission in the same frequency band.

[0129] Traditionally, TDD is used in terrestrial cellular networks, between base stations and user equipment. Figure 3 Schematically illustrates an example of using TDD in communications between a base station 310 and a user equipment (UE) 320. Here, continuous time is (in practice) divided into a series of consecutive time slots 330, 340, where a subset of the time slots 330 is used for transmission by the base station 310 (and reception by the UE 320), and a complementary subset of the 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).

[0130] Traditionally, TDD has not been used in satellite telecommunication systems for a variety of reasons, which makes its practical implementation less attractive than FDD. Figure 3As shown, TDD is typically implemented in a telecommunication system between two nodes (eg, a base station and a user equipment) that exchange signals via a bidirectional communication link.

[0131] In contrast, the present disclosure proposes the use of TDD for both reception and transmission of a given payload and notes that TDD can be tailored for satellite payloads (e.g., LEO-PNT) as an attractive alternative to FDD for accommodating Rx / Tx in the same frequency band. Figure 4 Schematically, an example of using TDD in the Rx / Tx of a payload 410 transmittable to a UE 420 is shown. Again, continuous time is (effectively) divided into a series of consecutive time slots 430, 440, wherein a subset of the time slots 430 is used for reception of the payload 410, and a complementary subset of the time slots 440 is used for transmission of the payload 410 to the UE 420. In this configuration, time slots 430 for reception of the payload 410 (e.g., GNSS signals) alternate with time slots 440 for transmission of the payload 410 (e.g., navigation signals).

[0132] According to the present disclosure, customizing the TDD mode to accommodate the payload may include applying TDD to the reception of signals broadcast or transmitted by a specific set of transmitters (e.g., GNSS, SBAS, interference sources) and the transmission of LEO-PNT signals to user receivers (i.e., users of LEO-PNT signals). This is different from using TDD in terrestrial telecommunication systems, where the transmitter and receiver are part of the same bidirectional link.

[0133] In the example of TDD on the GNSS band, the LEO-PNT payload receives signals in the GNSS band while turning off transmission of the LEO-PNT signals on the GNSS band, and vice versa, as described above. In addition, the LEO-PNT payload transmits LEO-PNT signals on the GNSS band while turning off reception on the GNSS band. In addition, the TDD customization on the receiving end will be for the signal that is continuously transmitted, so it is not duty cycled before reaching the LEO-PNT payload front end (nor is it designed for duty cycle processing, unlike telecommunication signals that may be designed with TDD implementation in mind).

[0134] The transmission of the TDD signal in the LEO-PNT payload (e.g., at step S220) can be achieved by shutting down the signal at the analog chain input, shielding, for example, the digital-to-analog converter and setting the signal to zero. An alternative solution could be to shield the signal at the amplifier or amplifier chain input, or to shut down the amplifier, or a combination of these measures.

[0135] The reception of the signal in the TDD signal in the LEO-PNT payload (e.g., at step S210) can be achieved, for example, by turning off the signal at the output of the receiver analog front end, shielding, for example, the analog-to-digital converter, and setting the signal to zero. An alternative solution may be to shield the signal at the input of the analog front end (e.g., a low noise amplifier (LNA)) or somewhere in the analog front end.

[0136] Example periods for TDD patterns can range from 1 millisecond to tens of milliseconds. Shorter pattern periods will facilitate implementation and performance at the receiver level, but may result in more complex implementation of the transmit chain. Longer pattern periods may facilitate implementation, but will put additional stress on the receiver algorithm and require additional complexity to maintain good performance.

[0137] An example duty cycle for TDD might be 50%. The lower the percentage on the transmit side, the longer the LEO-PNT payload signal is on the receive side, and therefore the higher the SNR on the receive side of the LEO-PNT payload, but the lower the average power and SNR available to the LEO-PNT signal user. Conversely, the higher the percentage on the transmit side, the higher the average power and SNR available to the user, but the lower the SNR available to the LEO-PNT payload receiver.

[0138] Table 1 shows examples of TDD reception and transmission for the E5 GNSS band.

[0139]

[0140] Table 1 TDD of a GNSS frequency band

[0141] The implementation of TDD mode in LEO-PNT payloads is not necessarily independent of FDD mode. For example, when transmitting and receiving simultaneously in multiple bands, the two modes can be advantageously combined. An example of this is shown in Table 2, where TDD reception and transmission are performed in the E5 GNSS band and the payload also continuously receives GNSS signals in the E6 GNSS band.

[0142]

[0143] Table 2 TDD and FDD for each GNSS frequency band

[0144] Another example is shown in Table 3, where TDD reception and transmission are performed in the E5 GNSS band, and the payload also continuously transmits signals in the S band.

[0145]

[0146] Table 3 FDD continuous transmission and TDD reception / transmission

[0147] When transmitting on multiple bands, it is possible to transmit (receive) on the multiple bands simultaneously or alternately. Alternating between transmitting on the multiple bands, and therefore receiving on the multiple bands, may be beneficial to optimize the operation of the transmit chain. For example, not all amplifiers will consume current at the same time, and the receiver will always be processing a signal at any time, which facilitates signal processing and optimizes the final performance (e.g., helps keep the tracking loop locked, maintain carrier phase continuity, etc.). Examples of this are shown in Table 4, Table 5, and Table 6.

[0148]

[0149] Table 4 Optimized TDD R for multiple frequency bands X and / or T X

[0150]

[0151] Table 5 Optimized TDD Rx and Tx for multiple bands (1Tx and 2Rx at the same time)

[0152]

[0153] Table 6 Optimized TDD Rx and Tx for multiple bands (simultaneous 2Tx and 1Rx)

[0154] According to the present disclosure, additional customization of the TDD mode to accommodate the payload includes synchronizing the TDD mode (e.g., duty cycle, period) to the GNSS time derived from the onboard ODTS and / or optimizing the reception algorithm to restore the quality of the received signal (although the reception is discontinuous). This may also involve utilizing the parameters of TDD (e.g., synchronization with GNSS time) and a combination of information about the transmitter geometry (e.g., ephemeris of GNSS satellites) and the LEO-PNT payload (e.g., onboard ODTS).

[0155] Therefore, the above method 200 may also include one or more steps of method 600, which will now be referred to. Figure 6 The method 600 includes steps S610, S620 and S630, each of which can be an optional step of the above method 200. These steps can also be performed continuously.

[0156] exist Step S610 In the embodiment of the present invention, at least one of orbit determination and time synchronization of a satellite payload is performed based on the GNSS signal.

[0157] The details of ODTS will be described below.

[0158] In step S620, the TDD mode (e.g., the duty cycle of the TDD mode and / or the cycle length of the TDD mode) is normalized (e.g., synchronized) to the timing epoch of the GNSS. In some implementations, this may be based on the result of at least one of the orbit determination and time synchronization in step S610.

[0159] TDD mode can be synchronized across multiple LEO-PNT satellites or across all LEO-PNT satellites at the same GNSS epoch. This means that navigation signals transmitted by different LEO-PNT satellites will not arrive at the ground user at the same time due to the propagation time dispersion from each satellite to the user. Figure 5A An example of this is schematically shown, where each line is associated with a different payload, and shows a transmission slot 510 in which a navigation signal is transmitted, and a corresponding time slot 520 in which this navigation signal (originating from the transmission slot 510) is received at a given UE. In this example, the TDD transmission slots 510 at the different payloads are synchronized, but the time slots 520 in which the UE receives the corresponding navigation signals transmitted in the transmission slots 510 by the different (spatially separated) payloads will be spread out over time. This approach can be advantageously implemented to spread the transmitted power over time, thereby reducing the equivalent power flux density (EPFD) level of the signal received on Earth, thereby facilitating compliance with ITU regulations.

[0160] The TDD mode can synchronize multiple satellites in the LEO-PNT constellation with a specific timing offset, which is determined in such a way that the signals from each satellite can reach the user equipment in a specific area on the earth at the same time. Figure 5B An example of this is schematically shown, where TDD transmission slots 510 at different payloads are distributed over time according to timing offsets (e.g., delays) determined according to respective relative distances between the payloads and the UE or area of ​​interest to the UE, but the slots 520 receiving respective navigation signals transmitted by the different payloads in the transmission slots 510 will be aligned with the UE of interest. This approach can be advantageously implemented to allow the receiver to turn on the front end only during specific periods when it is expected to receive a signal.

[0161] The LEO-PNT payload can use information derived from its onboard orbit determination to determine the time offset applied to the TDD mode in order to align the signal at the receiver level in a predefined area or region on the Earth. In order to turn on during the period when the LEO-PNT signal is expected, the user equipment needs to estimate the propagation time from the LEO-PNT payload to its location. On the other hand, the LEO-PNT payload can use information derived from its onboard orbit determination to determine the time offset applied to the TDD mode in order to align the signal at the receiver level in a predefined area or region on the Earth.

[0162] Reception of GNSS signals and messages received in TDD mode

[0163] GNSS and SBAS signals (or generally, high-orbit satellite navigation or augmentation signals) are designed for continuous transmission and assume continuous reception by user equipment, etc. The same considerations apply to the physical layer of the data content of these signals. The duty cycle reception of these signals may affect the stability of the algorithms used and the quality of the measurements made (e.g., accuracy, reliability / integrity, etc.). This may be particularly important for GNSS receivers for LEO-PNT payloads, as their purpose is to provide accurate and reliable ODTS information to support the payload and LEO-PNT signals.

[0164] Turning off signal reception in the analog domain to protect the RF front end may not be sufficient to avoid any damage. It may also be necessary to force the digital signals at the input of the baseband processing states (e.g., digital down-conversion, carrier removal, and correlators for GNSS signals, etc.) to zero during the time interval when reception (GNSS signals) is turned off and transmission (navigation signals) is active. Means to implement such shielding may typically be present in a GNSS receiver, which is configured, for example, to protect GNSS reception from pulse ranging equipment (DME) signals in the E5 band. However, such shielding is typically implemented with a shielding duration that is shorter than the pseudo-random noise (PRN) code period and symbol period of the message, so that no specific optimization of the acquisition and tracking algorithms and the message demodulation and decoding is required.

[0165] In some embodiments, as will be appreciated by those skilled in the art, LEO-PNT payloads may operate with duty cycle periods that are longer than typical GNSS PRN periods and / or symbol durations, and therefore, algorithms for receiving GNSS signals in TDD mode during such duty cycle operations may require further tuning to limit impairment to the effective SNR and the accuracy, quality, and integrity of the measurements, and to maintain performance at a good level to enable accurate and trustworthy algorithms.

[0166] Typical acquisition (e.g., search engines and matched filters involved in signal acquisition) and tracking algorithms (e.g., delay locked loop (DLL), frequency locked loop (FLL), phase locked loop (PLL)) assume continuous reception of GNSS signals and therefore assume that every sample in the baseband contains relevant information about the GNSS signal. This may not be the case for signals received in TDD mode, as the samples are masked (forced to zero) during the transmission of the payload. Adjustments and optimizations of GNSS receiver algorithms in LEO-PNT payloads may be designed to accommodate and potentially compensate for this lack of information.

[0167] With the exact information of when transmission is active and when reception needs to be turned off, the receiver can force all samples of the digital baseband sequence to zero at a time interval equal to the transmission time interval of the payload. Since these samples do not carry information, the receiver can also advantageously suspend baseband processing such as correlators, numerically controlled oscillators (NCOs), etc. This may help reduce the power consumption of the payload.

[0168] Since GNSS and LEO satellites have smooth trajectories and stable onboard clocks, tracking algorithms can exploit predictable signal dynamics (e.g., rate of range change, etc.) to extrapolate their estimates during the blackout period of TDD mode.

[0169] Therefore, the method 200 may further include a step of ensuring that the GNSS signal is tracked during the TDD transmission period when the GNSS signal is shielded. Figure 6 Step S630 of method 600 (as part of method 200) may be a step of maintaining signal tracking of the GNSS signal during a time slot for transmitting the navigation signal to avoid reacquisition based on a result of at least one of orbit determination and time synchronization. The purpose of step S630 is to avoid reacquisition of GNSS signal tracking when transmission of the navigation signal ceases and reception of the GNSS signal resumes. In some embodiments, step S630 may involve maintaining the tracking algorithm within the boundaries of a lock indicator. Additionally or alternatively, step S630 may involve inferring tracking parameters and / or states to maintain the tracking loop to prevent the tracking loop from leaving the acquisition range or losing lock during the time slot when GNSS signal reception is interrupted and the navigation signal is transmitted.

[0170] If the LEO-PNT payload receives multiple GNSS frequencies from the same GNSS satellite, the payload may not shield all signals at the same time, but instead alternate shielding between frequencies from the same GNSS satellite (e.g., receiving E1 while shielding E6, etc.). For example, it can be said that for each alternating time slot, reception in at least one GNSS frequency band is active to assist in signal tracking of GNSS signals in other GNSS frequency bands in the time slots in which reception is inactive. Tables 4, 5, and 6 give examples of alternating shielding between different GNSS frequencies. An algorithm running on unshielded band A can assist an algorithm running on band B, where band B is shielded and A is not shielded, and vice versa. As is known to those skilled in the art, the assistance information can be further adjusted or adjusted to take into account the different frequencies between A and B and their effects on Doppler, ionosphere, etc.

[0171] Figure 7An example of how the tracking algorithm can be aided by information received in another frequency band is schematically shown. In this example, a first GNSS signal 701 is continuously received on frequency A and processed by a first processing loop, while a second GNSS signal 711 is received on frequency B in TDD mode (i.e., in duty cycle reception) and processed by a second processing loop. Carrier removal is performed on the two GNSS signals at respective carrier removal blocks 702, 712 based on the output of respective NCOs 706, 716. After carrier removal, the resulting signals are fed to respective correlators 703, 713, whereupon error estimation is performed at 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 respective NCOs 706, 716, thereby 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 an adder 730 after optional scaling and / or adaptation at the scaling / adaptation block 720 .

[0172] Additionally, as described above, for example, with respect to step S630, the algorithm (e.g., in acquisition and tracking) may be assisted with information obtained from an onboard ODTS (e.g., the ODTS executed in step S610). This works best when using an accurate onboard ODTS, but may also provide benefits if an accurate ODTS is not available or not yet available and the LEO-PNT payload has only a coarse ODTS estimate available (e.g., two-line elements received by the TC, long-term extrapolation of the ODTS, etc.). In this case, assistance may include, but is not limited to, using range rate estimates from the ODTS to assist the DLL, FLL, and / or PLL and / or using a priori knowledge of GNSS signal arrival times (e.g., to reduce the search space in acquisition).

[0173] The demodulation, decoding and estimation of bits contained in GNSS signals received by the LEO-PNT payload in TDD mode may also be adjusted and / or optimized to limit the performance degradation caused by the TDD mode to the GNSS signals. Advantageously, the receiver may take advantage of the interleaving and channel coding of GNSS signals (when present on these signals) and adjust the associated reception algorithms to accommodate the TDD mode.

[0174] A good estimate of the carrier phase can be important for demodulation of data symbols. The correlator outputs or matched filter outputs on the pilot and data components of modern GNSS signals can be combined together in non-coherent demodulation (e.g., by using the pilot and data components to prompt the output of the correlator) to supplement or replace typical demodulation using a PLL and to remove residual carrier phase on data symbols even if the PLL is not operating optimally due to TDD.

[0175] The interleaving and channel coding of modern GNSS signals can significantly compensate for the effects of masking certain samples and missing information. In particular, the decoding algorithm running on the received symbols can be optimized to take into account the nature of TDD and the fact that certain symbols are forced to zero due to TDD operation. The receiver can maintain soft decision inputs to the decoder for received symbols when the receiver is not masked and force hard decision inputs to the decoder for received symbols during masking.

[0176] In order to fully exploit the interleaving and decoding mechanisms embedded in modern GNSS signals, it may be desirable for the duty cycle period to be shorter than the duration of an interleaving or channel coding block. It may also be desirable for the duty cycle period to be shorter than the duration of a bit carried by the GNSS signal.

[0177] High-precision ODTS using GNSS signals and data

[0178] The precise ODTS of a satellite can be derived by a number of methods currently used in typical space systems, especially satellite navigation systems. One such method may use measurements from GNSS signals, possibly combined with PPP corrections broadcast by, for example, the Galileo HAS service.

[0179] Thus, at least one of the orbit determination and time synchronization (e.g., ODTS) performed in step S610 of method 600 can be based on high precision corrections received with GNSS signals, or high precision corrections received from GNSS (as an example of a higher orbit navigation or augmentation system).

[0180] The ODTS for LEO-PNT satellites can be executed in real time by an onboard computer (OBC), for example, running a simplified dynamic orbit filter that processes GNSS measurements. The simplified dynamic orbit filter of the ODTS model simulates the most significant forces acting on the satellite (e.g., Earth gravity model, Sun and Moon gravity model, atmospheric drag, solar radiation pressure, etc.). The ODTS can use a real-time precise onboard orbit determination (P2OD) algorithm that uses pseudorange and carrier phase measurements with either floating ambiguities or integer ambiguity resolution (IAR) capabilities.

[0181] Thus, LEO-PNT signals (or generally, navigation signals in the context of the present disclosure) can be trained and referenced to an ODTS computed onboard in real time or near real time involving information combined with broadcast GNSS navigation messages, such as precise products from the Galileo High Accuracy Service (HAS) received from Galileo E6B.

[0182] Nonetheless, utilizing multiple sources of range / range rate measurements (e.g., multi-GNSS, ISR, TTC measurements) and available data / corrections in addition to the corrections and data provided by the HAS can improve system availability in the event of outages of some sources.

[0183] When the onboard GNSS receiver processes the GNSS signals from a given GNSS in single-frequency mode and both pseudorange and carrier phase measurements are available, the GRAPHIC combination can be used to remove the ionospheric contribution. When tracking the GNSS signals from a given GNSS in single-frequency mode and only pseudorange measurements are available, the ionospheric correction can be used and, if necessary, further adapted to the LEO altitude. Given that there is still only a residual ionosphere above the LEO-PNT satellites (compared to the complete ionosphere for ground users), profiler ionospheric models (e.g. NeQuikG) can achieve better performance.

[0184] The ODTS process may use different weights for different measurements from different sources (e.g., frequency, satellite) and based on the data / corrections used for each measurement. These different weights may account for different accuracies and may improve the performance of the ODTS solution, e.g., in terms of accuracy and / or availability of the ODTS solution.

[0185] The LEO-PNT satellite orbit and clock estimates produced by the onboard ODTS process can be used to generate orbit and clock products in real time or near real time and propagated to LEO-PNT receivers via data contained in the LEO-PNT signal (navigation signal). These products can be derived by curve fitting the orbit and clock estimates, depending on the required validity of the resulting products (e.g., using Kepler elements, standard polynomials, B-splines, Chebyshev polynomials, and / or any variants of these).

[0186] Credibility of ODTS information

[0187] The ODTS may implement an integrity function to determine whether the errors of the GNSS measurements and / or the ODTS solution are within a given value and at a given probability of miss detection.

[0188] Therefore, at least one of the orbit determination and the time synchronization (eg, ODTS) performed in step S610 of the method 600 may use information about the GNSS signal integrity.

[0189] For example, the integrity functionality of ODTS may be implemented by using one or more of the following:

[0190] ● SBAS integrity data received using an onboard GNSS receiver or via a ground network

[0191] Receiver Autonomous Integrity Monitoring (RAIM) technology, which exploits redundancy between GNSS measurements and possible ISR measurements

[0192] ● Advanced Receiver Autonomous Integrity Monitoring (ARAIM) technology, by receiving and processing Integrity Support Messages (ISM). ISM advantageously comes from GNSS or SBAS signals and systems, rather than through additional links such as uplink TC or ISL

[0193] ● Any one or combination of the above associated with the above track filter / simplified dynamic track filter

[0194] Alternatively or additionally, at least one of the orbit determination and the time synchronization (eg, ODTS) performed in step S610 of the method 600 may use information on the authenticity of the GNSS signal.

[0195] For example, the ODTS process may utilize one or more of the following to implement authentication functionality:

[0196] Authentication features carried by GNSS signals, such as navigation message authentication and encrypted signals (e.g., OSNMA and CAS for Galileo, Chimera for GPS),

[0197] ● Processing of baseband signals to assess the consistency of correlation functions and to perform consistency checks on the state of the baseband processing functions and their raw measurements (code, carrier phase, Doppler, signal-to-noise ratio, etc.),

[0198] ● Processing GNSS signals received on two or more antennas to detect inconsistencies in the angle of arrival / angle of arrival characteristics. Reception on multiple antennas can be done simultaneously or intermittently, for example by switching between antennas with a certain duty cycle.

[0199] ●Any combination of the above

[0200] The above techniques can be run continuously or intermittently to reduce processing complexity and computing power. For example, the processing of encrypted signals can be performed in a duty cycle manner, processing snapshots of a certain duration (e.g., up to tens of milliseconds), or processing at longer intervals, such as a few seconds or tens of seconds.

[0201] In addition, the above processing can be advantageously combined with an orbital filter or a simplified dynamic orbital filter and utilize the short-term stability of an onboard clock (e.g., an oven-controlled crystal oscillator, a chip-scale atomic clock, a micro-atomic clock) to improve the statistics of the consistency check or to obtain a trusted solution during the above-mentioned duty cycle and when no credibility processing is performed.

[0202] The resulting information, an indication of the confidence of the ODTS solution and the confidence of the LEO-PNT signal's reference to the ODTS, can then be communicated to the user equipment via data contained in the LEO-PNT signal (navigation signal).

[0203] Regardless, at least one of the orbit determination and time synchronization (e.g., ODTS) performed in step S610 may be based on one or more of the following:

[0204] SBAS messages received together with GNSS signals;

[0205] ● Ranging authentication and / or message authentication of GNSS signals;

[0206] ● HAS messages received with GNSS signals; and / or

[0207] ●ISM messages received together with GNSS signals.

[0208] Relay of navigation related data

[0209] Relaying GNSS messages (or GNSS content in general) to the LEO-PNT signal (or in general, the navigation signal transmitted in step S220 of method 200) includes retrieving specific messages from the fields and pages of the relevant data component of the GNSS signal and introducing them into the fields and pages of the data component of the transmitted LEO-PNT signal in real time or delayed. Different methods for performing relaying can be considered and customized to use TDD mode.

[0210] Therefore, the above method 200 may also include one or more steps of method 800, which will now be referred to. Figure 8 The method 800 includes steps S810 and S820, both of which can be optional steps of the above method 200. These steps can also be performed continuously.

[0211] In step S810, a GNSS signal (eg, received in step S210) or a GNSS message contained therein is demodulated to obtain GNSS content transmitted with the GNSS signal. For example, the GNSS content obtained in this manner may be associated with one or more (low latency) GNSS messages.

[0212] exist Step S820 , at least part of the GNSS content is included in the navigation message that is transmitted to the Earth in the GNSS frequency band along with the navigation signal. Thus, it can be said that the payload relays the GNSS content to any receiver of the navigation signal.

[0213] The GNSS content obtained in step S810 and relayed in step S820 may be related to one or more of the following:

[0214] SBAS messages;

[0215] ●SAR returns link message;

[0216] Integrity Support Message (ISM);

[0217] High Accuracy Service (HAS) messages;

[0218] ● Emergency warning messages; and / or

[0219] ●Authentication message.

[0220] If the duty cycle period is shorter than the period of the received symbol, the LEO-PNT payload may estimate each symbol of the data component of the received GNSS signal and introduce the correlation value directly as the symbol of the data component of the LEO-PNT signal. This forces decoding to be bypassed and may impose hard decisions on the received symbols, which may result in suboptimal estimation performance, but will minimize the latency of the LEO-PNT payload's relay mechanism.

[0221] Advantageously, the LEO-PNT payload can decode and estimate all or part of the pages of the received GNSS signal in TDD mode, select the pages, fields and bits to be relayed, and encode and introduce them as symbols of the data component of the LEO-PNT signal. Fig. 9 An example of such a process is schematically shown in the block diagram of FIG. 1 , where the horizontal axis represents time relative to GNSS signal pages 905-(N-1), 905-N, 905-(N+1), etc. After receiving the corresponding page at the receiving block 910, it is demodulated at the demodulator block 920 and its symbols are decoded. The resulting data is encoded at the encoding block 930 and transmitted in TDD mode along with the navigation signal at the transmitting block 940 in a sequence of TDD time slots 945.

[0222] In this way, the LEO-PNT payload can retain any format, encoding, interleaving, bit and symbol rate used by the incoming GNSS signal, or implement different transformations to convert bits into data component symbols. For example, the channel code on the LEO-PNT signal, the redundancy rate of the channel code, and the data rate can be modified and optimized to accommodate the characteristics of the LEO signal. The higher signal-to-noise ratio of the LEO signal can be exploited to increase the data or symbol rate to speed up the dissemination of relevant data to the user and reduce end-to-end latency compared to using the GNSS signal rate.

[0223] Accessibility

[0224] The design of receivers and instruments processing GNSS signals involved in radio occultation (GNSS-RO), reflectometry (GNSS-R) and GNSS space interference monitoring (RFI monitoring) assumes that the signal is received continuously during the duration of the occultation or reflection.

[0225] This assumption does not apply to GNSS-RO, GNSS-R, and RFI signals received by a LEO-PNT payload that contains these functions in addition to transmitting LEO-PNT signals in TDD mode. Just like receiving GNSS signals for ODTS, the algorithms for GNSS-RO, GNSS-R, and RFI monitoring functions need to be tailored for TDD to limit interference and performance degradation.

[0226] A typical solution for GNSS-RO, GNSS-R, and RFI monitoring may be similar to the algorithm described above for ODTS received signals, such as aiding between channels and bands, aiding with ODTS information, and assuming a rough knowledge of the location of the source (e.g., obscured GNSS satellites, etc.).

[0227] Therefore, the above method 200 may also include one or more steps of the method 1000, which will now be referred to as Fig.10 The method 1000 includes step S1010 or S1020, both of which are optional steps of the method 200 and can be performed independently of each other. These steps can also be performed continuously.

[0228] exist Step S1010 In the present invention, radio masking is performed based on the GNSS signal received in the time slot in which the GNSS signal in the TDD mode is received.

[0229] exist Step S1020 , performing operations of detecting and / or locating unwanted emissions in the GNSS frequency band. Here, locating the unwanted emissions may involve multi-lateration using multiple satellite payloads. In addition, this step may involve or correspond to performing radio interference (RFI) estimation, for example, in a time slot in which a GNSS signal in TDD mode is received.

[0230] Fig.11 An example of a framework for performing RO (e.g., through step S1010) according to an embodiment of the present disclosure is schematically shown. In this framework, the LEO-PNT satellite 1120 receives a signal (e.g., a GNSS signal) transmitted by the GNSS satellite 1120 after the signal passes through the Earth's ionosphere 1130. The received GNSS signal can be used to infer state information of the ionosphere 1130.

[0231] Fig.12An example of a framework for performing RFI estimation (e.g., through step S1020) according to an embodiment of the present disclosure is schematically shown. In the framework, one or more LEO-PNT satellites 1210 receive signals from the ground (e.g., ground-based transmitters 1220) in the GNSS frequency band and estimate RFI and / or locate interference sources (e.g., through multilateration).

[0232] Signal design and generation

[0233] LEO-PNT is designed and / or optimized to enable user equipment to obtain relevant (e.g., best) position-velocity-timing related measurements from navigation signals. It is also designed and / or optimized to disseminate data related to the ODTS and its credibility, as well as other data (some of which comes from external sources) to user equipment.

[0234] Each LEO-PNT signal (navigation signal) can be composed of multiple signal components, including but not limited to:

[0235] ●One or more data components, modulated by the navigation message

[0236] ●One or more pilot components, not modulated by the navigation message

[0237] ●One or more quasi-pilot components, deviating from the pure pilot with low entropy information

[0238] - Optionally, intermodulation products if Constant Envelope Modulation (CEM) multiplexing is used.

[0239] LEO-PNT signal generation can be fully digital, for example using software defined radio (SDR) technology and architecture, allowing software and firmware upgrades after entering orbit. This can allow the signal characteristics of the LEO-PNT in space to be updated during the system life cycle, for example even adding new signals.

[0240] In cases where the LEO-PNT signal consists of multiple signal components, they can be multiplexed linearly (e.g., simply added) or multiplexed using techniques to reduce the peak-to-average power ratio (PAPR) at the input of the payload high power amplifier (HPA) in the transmission chain.

[0241] One or more LEO-PNT signal components may include a time propagation feature that allows propagation of absolute time (e.g., time of week) and / or resolution of time uncertainties (e.g., after application of time assistance data). Signal magnitude and time synchronization mechanisms may take advantage of the shorter range to LEO to employ shorter codes (e.g., a 10 ms code may resolve ambiguities up to 3000 km slant range), which are easier to acquire / detect / synchronize.

[0242] LEO-PNT signals may be designed for various multiple access schemes on the downlink and / or uplink. While CDMA-DSSS is widely used for GNSS and may be well suited for LEO-PNT signals, alternatives or combinations thereof (e.g., FDMA+DSSS) may also be considered (e.g., for ease of acquisition and for asset tracking, note that shorter PRN / narrowband signals are more attractive, for which FDMA may be preferred over CDMA). LEO-PNT signals may use direct sequence spread spectrum (DSSS) or chirp spread spectrum (CSS) to best spread the signal in the allocated bandwidth and optimize the processing complexity of the allocated bandwidth and sampling frequency in the user equipment (e.g., reducing acquisition and tracking complexity, improving synchronization and ranging performance).

[0243] LEO-PNT broadcast signals can also utilize bandwidth-efficient modulation, such as continuous phase modulation (CPM), to reduce out-of-band emissions and improve spectral compatibility with adjacent band signals.

[0244] LEO-PNT signals may include encryption capabilities to ensure the authenticity of broadcast navigation messages and ranging codes, or to support access control to corresponding services, or both.

[0245] LEO-PNT signals may carry data messages protected by error control coding and / or erasure coding techniques, with or without bit interleaving.

[0246] LEO-PNT constellations may implement spatial diversity techniques, for example between multiple satellites, to increase capacity or improve the availability of data messages to user devices.

[0247] PNT two-way signaling integration

[0248] Fig.13 An example framework 1300 for integrating bidirectional signaling between one or more LEO payloads and one or more user equipments (UEs) is schematically shown. The framework includes a set of GNSS satellites 20 (e.g., in MEO), UE 30, and a set of payloads carried on satellites 10, e.g., in LEO.

[0249] Bidirectional exchanges in this framework may involve signal items (1), (2) and (3) described below.

[0250] (1) At least one of the following:

[0251] ● One or more GNSS satellites 20 transmit GNSS navigation signals 1310, which are received by UE 30

[0252] ● One or more payloads transmit navigation signals 1320 in TDD and / or FDD mode, which are received by UE 30

[0253] Based on and / or prompted by the received signal, the UE 30 composes an uplink message 1330 and transmits the uplink message 1330 to one or more payloads receiving the uplink signal 1330 in TDD and / or FDD mode

[0254] (2) Uplink signals 1330 are received by the payload in TDD and / or FDD mode to provide bidirectional PNT services to the user, such as one or more of the following:

[0255] ●Time transmission between two UEs

[0256] ●Time limit

[0257] ●Location limit

[0258] ● Payload-based position verification

[0259] (3) If data from multiple payloads is required to provide bidirectional PNT services, the signals received at the multiple payloads may be fused and processed in at least one of the following ways: Fig.13 Not shown):

[0260] ● One of the payloads (e.g., via ISL or via a ground station)

[0261] Ground station

[0262] ● UE 30 via additional downlink in TDD and / or FDD mode

[0263] Therefore, the above-mentioned method 200 may also include an optional step of receiving an uplink signal from a user device to perform a two-way navigation service, for example, wherein the two-way navigation service involves one or more of the following: time transfer between the user device and a payload; time transfer between the user device and another user device; time boundaries of the user device; location boundaries of the user device; and / or verification of the location of the user device by the payload.

[0264] Among other things, the composition of the uplink signal 1330 may depend on the previous reception of the downlink navigation messages 1310, 1320, one or more of: a signal from a payload; a signal from another payload; and / or a GNSS signal.

[0265] Further implementation examples

[0266] As described above, the payload according to an embodiment of the present disclosure may be a satellite payload, such as a payload carried on a LEO satellite or a LEO-PNT satellite, for example.

[0267] In other implementations, multiple payloads may be provided and distributed across multiple spacecraft. For example, the payloads may be distributed across spacecraft (e.g., satellites) in a layer of a multi-layer satellite navigation system. The multi-layer 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 layer (or across layers) of a multi-layer satellite navigation system, with each payload provided on a corresponding one of the satellites in LEO.

[0268] Although exemplary reference has been made to LEO-PNT payloads, the present disclosure relates to any payload (e.g., satellite payload, distributed payload) having the required capabilities (e.g., receive capability, transmit capability, and possibly processing capability to provide PNT functionality). It is understood that such payloads are configured to perform any or all of the methods described above.

[0269] Furthermore, the present disclosure also relates to a satellite (eg, a LEO satellite, a LEO-PNT satellite) including the above-mentioned payload (eg, a satellite payload).

[0270] explain

[0271] It should be understood that any of the above modules, units or blocks can be implemented by a computer processor or a corresponding computer processor, etc. The above modules, units or blocks can also be implemented in a cloud-based manner.

[0272] It should also be noted that the description and drawings illustrate only the principles of the proposed method and system. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the present invention and are included within the spirit and scope of the present invention. In addition, all examples and embodiments summarized in this document are primarily intended to be used for illustrative purposes only to help the reader understand the principles of the proposed method and system. In addition, all statements of the principles, aspects, and embodiments of the present invention and specific examples thereof are provided herein and are intended to encompass their equivalents.

[0273] With respect to the flowcharts described in the present disclosure, it should be understood that the order of the steps is not necessarily fixed by the flowchart; rather, the steps may be performed in any order, even in parallel, as long as any input to those steps is available from other steps.

[0274] Listed Example Embodiments

[0275] Aspects and embodiments of the present disclosure may also be understood from the following enumerated example embodiments (EEE), which are not claims.

[0276] EEE1. A satellite-based positioning method, the method comprising:

[0277] receiving, by means of a radio receiver, navigation signals in a GNSS frequency band;

[0278] determining the position of the radio receiver based on the navigation signal,

[0279] The receiving of the navigation signal is performed in a time division duplex, TDD, mode, wherein the navigation signal is present or absent in alternating time slots.

[0280] EEE2. A method according to EEE1, wherein the navigation signal is a non-GNSS navigation signal.

[0281] EEE3. A method according to EEE1 or EEE2, wherein the navigation signal is a LEO-PNT signal.

[0282] EEE4. A method according to any one of the preceding EEEs, wherein the navigation signal is a navigation signal for code-based ranging measurements, carrier-based measurements and / or Doppler measurements at the receiver and / or low-complexity acquisition at the receiver.

[0283] EEE5. A method according to any one of the preceding EEEs, further comprising:

[0284] receiving, by a radio receiver, a GNSS signal in a GNSS frequency band from the GNSS,

[0285] The determination of the position of the radio receiver is also based on GNSS signals.

[0286] 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. EEE6.

[0287] EEE9. A method according to EEE5 or any claim dependent thereon, further comprising:

[0288] demodulating navigation signals; and

[0289] Extract GNSS content from the demodulated navigation signal,

[0290] Therein, determining the position of the radio receiver is also based on the extracted GNSS content.

[0291] EEE10. A method according to EEE9, wherein the GNSS content involves high precision corrections.

[0292] EEE13. A computer program for causing a computer coupled to a radio receiver to perform a method according to any one of the preceding EEEs when the computer program is executed by the computer.

[0293] EEE14. A computer-readable storage medium storing a computer program according to EEE13.

Claims

1. A method of operating a payload having receiving and transmitting capabilities in Earth orbit, the method comprising: receiving a GNSS signal from the GNSS in a GNSS frequency band; as well as Transmits navigation signals to the Earth in the GNSS frequency band, Wherein reception and transmission are performed in time division duplex, TDD, mode, wherein the time slots for receiving the GNSS signal and transmitting the navigation signal are alternated.

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

3. The method according to claim 1 or 2, further comprising: At least one of orbit determination and time synchronization is performed for the satellite payload based on the GNSS signals.

4. The method according to claim 3, when claim 3 refers to claim 2, wherein: The synchronization of the duty cycle of the TDD mode with the timing epoch of the GNSS is performed based on a result of at least one of the orbit determination and the time synchronization.

5. The method according to claim 3 or 4, wherein: At least one of the orbit determination and the time synchronization is based on high precision corrections received with the GNSS signals.

6. The method according to any one of claims 3 to 5, wherein: At least one of the orbit determination and the time synchronization uses information about the authenticity of the GNSS signals.

7. The method according to any one of claims 3 to 6, wherein: At least one of the orbit determination and the time synchronization uses information about the integrity of the GNSS signals.

8. The method according to any one of claims 3 to 7, wherein: At least one of the orbit determination and the time synchronization is based on one or more of: an SBAS message received together with the GNSS signal; Ranging authentication and / or message authentication of the GNSS signal; a HAS message received together with the GNSS signal; and / or An ISM message received together with the GNSS signal.

9. The method according to any one of claims 3 to 8, further comprising: Based on a result of at least one of the orbit determination and the time synchronization, signal tracking of the GNSS signal is maintained during a time slot in which the navigation signal is transmitted to avoid loss of lock and / or reacquisition.

10. The method according to any one of the preceding claims, further comprising: demodulating the GNSS signal to obtain GNSS content transmitted together with the GNSS signal; and At least a portion of the GNSS content is included in a navigation message that is transmitted with the navigation signal toward the earth in a GNSS frequency band.

11. The method according to claim 10, wherein: The GNSS content may relate to one or more of the following: SBAS messages; SAR returns link message; Integrity Support Message, ISM; High Accuracy Service, HAS, Message; Emergency warning messages; and / or Authentication message.

12. The method according to any one of the preceding claims, further comprising: In frequency division duplex, FDD, mode, a second navigation signal is transmitted towards the earth in a second GNSS frequency band different from the GNSS frequency band or a non-GNSS frequency band.

13. The method according to any one of the preceding claims, further comprising: Radio occultation is performed based on the received GNSS signal in the time slot in which the GNSS signal of the TDD mode is received.

14. The method according to any one of the preceding claims, further comprising: Reflection measurements are performed based on the received GNSS signals in the time slots in which the GNSS signals in the TDD mode are received.

15. The method according to any one of the preceding claims, further comprising: Operations for detecting and / or locating unwanted emissions in the GNSS frequency band are performed in time slots in which the GNSS signal in the TDD mode is received.

16. The method according to any one of the preceding claims, further comprising: Radio interference estimation is performed in time slots in which the GNSS signals in the TDD mode are received.

17. A method according to any one of the preceding claims, wherein: The navigation signal is a navigation signal used for one or more of code-based ranging measurements, carrier-based measurements, and Doppler measurements at a receiver and / or low-complexity acquisition at a receiver.

18. The method according to any one of the preceding claims, further comprising: Receiving an uplink signal from a user equipment for a two-way navigation service, wherein the two-way navigation service involves one or more of: time transmission between the user equipment and the payload; time transmission between the user equipment and another user equipment; The time limit of the user equipment; The location limits of the user equipment; and / or The payload verifies the location of the user equipment.

19. A method according to any one of the preceding claims, wherein: The payload is a satellite payload on a low earth orbit, LEO, satellite.

20. A method according to any one of the preceding claims, wherein: A plurality of payloads are provided on respective spacecraft in one or more layers of a multi-layered satellite navigation system.

21. The method according to claim 20, when claim 20 refers to claim 18, wherein: The composition of the uplink signal depends on the previous reception of a downlink navigation message by one or more of: a signal from said payload; a signal from another payload; and / or GNSS signal.

22. A method according to any one of the preceding claims, wherein: The GNSS frequency band is one of the frequency bands E1, E6, E5, E5a and E5b defined by Galileo or one of the frequency bands L1, L2 and L5 defined by GPS.

23. A satellite payload having receiving and transmitting capabilities, wherein: The satellite payload is configured to perform a method according to any of the preceding claims.

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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