Calibration of atomic clocks

Abstract

There are provided methods and systems comprising one or more processing circuitries configured to obtain data informative of a time bias associated with a receiver, wherein said time bias is caused at least by a frequency drift of an atomic clock, and use the data to determine data informative of the frequency drift of the atomic clock. There are also provided methods and systems comprising one or more processing circuitries configured to obtain data informative of a frequency drift associated with a receiver, wherein at least part of the receiver is connected to a frequency source comprising an atomic clock, and use the data to estimate a frequency drift of the atomic clock.

Description

[0001] CALIBRATION OF ATOMIC CLOCKS

[0002] TECHNICAL FIELD

[0003] The presently disclosed subject matter is in the field of calibration of atomic clocks.

[0004] BACKGROUND

[0005] References considered to be relevant as background to the presently disclosed subject matter are listed below (acknowledgement of the references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter):

[0006] US 8,674,778;

[0007] US 8,125,279;

[0008] US 8,884,706;

[0009] US 7,015,762;

[0010] US 10,466,363; and

[0011] US 1,031,0091.

[0012] GENERAL DESCRIPTION

[0013] In accordance with certain aspects of the presently disclosed subject matter, there is provided a system comprising one or more processing circuitries configured to obtain data informative of a time bias associated with a receiver, wherein said time bias is caused at least by a frequency drift of an atomic clock, and use the data to determine data informative of the frequency drift of the atomic clock.

[0014] In addition to the above features, the system according to this aspect of the presently disclosed subject matter can comprise one or more of features (i) to (xliv) listed below, in any desired combination or permutation which is technically possible: i. the frequency drift of the atomic clock corresponds to a frequency drift of an oscillatory signal generated by the atomic clock; ii. the data informative of the time bias have been calculated based on signals received by the receiver from a GNSS network; iii. the receiver, or a processing circuitry of the receiver, is configured to measure time based on an oscillatory signal provided by the atomic clock; iv. the atomic clock serves as frequency source for the receiver; v. the system is configured to use the data informative of the frequency drift of the atomic clock to trigger correction of the frequency drift of the atomic clock; vi. the system is configured to use the data informative of the frequency drift of the atomic clock to generate a command for correcting the frequency drift of the atomic clock; vii. the system is configured to transmit the command to the atomic clock, or to at least one or more components of the atomic clock; viii. the data informative of the time bias have been calculated based on signals received by the receiver from a GNSS network, and equations comprising position and time bias of the receiver; ix. the system is configured to obtain the data informative of a time bias, from the receiver; x. the one or more processing circuitries are configured to determine the data informative of a time bias associated with the receiver; xi. the system is configured, for each of a plurality of instants of time Tt. to obtain data Bl informative of a time bias associated with the receiver at the time 7). and use at least part of the data B7 to determine data informative of the frequency drift of the atomic clock at some of the plurality of instants of time , xii. the receiver comprises a global navigation satellite system (GNSS) receiver; xiii. the receiver is connected to a frequency source comprising the atomic clock; xiv. a processing circuitry controlling the receiver, or being part of the receiver, is connected to a frequency source comprising the atomic clock; xv. the one or more processing circuitries are configured to control at least one of one or more components of the receiver or one or more components of the atomic clock; xvi . the one or more processing circuitries are part of at least one of the receiver or of the atomic clock; xvii . the receiver comprises one or more internal processing circuitries, different from the one or more processing circuitries; xviii. the system is configured to use the data informative of the frequency drift of the atomic clock to enable correction of the frequency drift of the atomic clock, without requiring usage of a 1PPS signal of the receiver; xix. the one or more processing circuitries are configured to obtain data informative of a time bias associated with the receiver, at different instants of time; xx. the system further comprises the receiver and the atomic clock; xxi. the system is configured to provide an oscillatory signal, and a pulsed signal; xxii. the atomic clock is operative to provide the oscillatory signal, and the receiver is operative to provide the pulsed signal; xxiii. the atomic clock is operative to provide the oscillatory signal, and the receiver is operative to provide the pulsed signal, wherein the pulsed signal is a 1PPS signal; xxiv. the receiver, the atomic clock, and the one or more processing circuitries, are located in a same package; xxv. the one or more processing circuitries are located remotely from the receiver and the atomic clock; xxvi. the receiver comprises an internal frequency source, and is also connected to a frequency source comprising the atomic clock; xxvii. the time bias associated with the receiver has been measured during a period of time in which the internal frequency source is turned off; xxviii. the time bias associated with the receiver has been measured during a period of time in which the receiver does not use the internal frequency source to measure time; xxix. the one or more processing circuitries are operative to send a command to the internal frequency source, to turn off said internal frequency source; xxx. the system is configured to determine data informative of the frequency drift of the atomic clock based on a first time bias associated with the receiver, determined at a first time before a signal interruption, and a second time bias associated with the receiver, determined at a second time after the signal interruption; xxxi. during the signal interruption, the receiver is not operative to receive signals from a global navigation satellite network; xxxii. during the signal interruption, the receiver is not operative to generate a 1PPS signal; xxxiii. during the signal interruption, the receiver undergoes a spoofing attack; xxxiv. the system is configured to obtain first data BT1informative of a time bias associated with the receiver at a first time 7^, and obtain second data BT2informative of a time bias associated with the receiver at a second time T2. and use the first data BT1and the second data BT2to determine the data informative of a frequency drift of the atomic clock; xxxv. using the first data BT1and the second data B^to determine the data informative of a frequency drift of the atomic clock, which comprises using a difference between BT2and BT1and a difference between T2and Ti, xxxvi. using the first data BT1and the second data BT2to determine the data FD informative of a frequency drift of the atomic clock comprises using FD_ BT2-BT

[0015] T2-T-L ’ xxxvii. in most or all of the period of time ]Tt; T2[, the receiver is not operative to receive signals from a GNSS network; xxxviii. in most or all of the period of time ]?i; T2[, the receiver is not operative to generate a 1PPS signal; xxxix. in most or all of the period of time ]T1; T2L the receiver undergoes a spoofing attack; xl. the system is configured to store, in a memory, data informative of a time bias of the receiver determined at a plurality of instants of time; xli. the system is operative to switch between a first mode and a second mode, wherein in the first mode, the one or more processing circuitries are configured to obtain data informative of a time bias associated with the receiver, wherein the receiver is connected to a frequency source comprising an atomic clock, and use the data to determine data informative of a frequency drift of the atomic clock; in the second mode, the atomic clock is operative to receive a pulsed signal from the receiver, and to use it to calibrate its frequency drift; xlii. the pulsed signal is a 1PPS signal; xliii. the one or more processing circuitries are operative to communicate with the receiver and the atomic clock using wireless communication; and xliv. at least part of the receiver is connected to a frequency source comprising the atomic clock.

[0016] In accordance with other aspects of the presently disclosed subject matter, there is provided a method comprising, by one or more processing circuitries, obtaining data informative of a time bias associated with a receiver, wherein said time bias is caused at least by a frequency drift of an atomic clock, and using the data to determine data informative of the frequency drift of the atomic clock.

[0017] In addition to the above features, the method according to this aspect of the presently disclosed subject matter can comprise one or more of features (i) to (xliv) listed above with respect to the system, in any desired combination or permutation which is technically possible.

[0018] In accordance with other aspects of the presently disclosed subject matter, there is provided a non-transitory computer readable medium comprising instructions that, when executed by one or more processing circuitries, cause the one or more processing circuitries to perform: obtaining data informative of a time bias associated with a receiver, wherein said time bias is caused at least by a frequency drift of an atomic clock, and using the data to determine data informative of the frequency drift of the atomic clock.

[0019] In addition to the above features, the non-transitory computer readable medium comprises instructions that, when executed by the one or more processing circuitries, cause the one or more processing circuitries to perform one or more of features (i) to (xliv) listed above with respect to the system, in any desired combination or permutation which is technically possible.

[0020] In accordance with certain aspects of the presently disclosed subject matter, there is provided a system comprising one or more processing circuitries configured to obtain data informative of a frequency drift associated with a receiver, wherein at least part of the receiver is connected to a frequency source comprising an atomic clock, and use the data to estimate a frequency drift of the atomic clock. In addition to the above features, the system according to this aspect of the presently disclosed subject matter can comprise one or more of features (xlv) to (xlvii) listed below, in any desired combination or permutation which is technically possible: xlv. the data informative of a frequency drift associated with the receiver have been determined based on signals received by the receiver from a GNSS network; xlvi. the data informative of a frequency drift associated with the receiver have been determined based on signals received by the receiver from a GNSS network and equations comprising velocity of the receiver and frequency drift associated with the receiver; and xlvii. using the data informative of a frequency drift associated with the receiver comprises performing a filtering operation of the data informative of a frequency drift associated with the receiver obtained a plurality of instants of time.

[0021] In addition to the above features, the system according to this aspect of the presently disclosed subject matter can comprise one or more of features (i) to (xliv) listed above, in any desired combination or permutation which is technically possible.

[0022] In accordance with other aspects of the presently disclosed subject matter, there is provided a method comprising, by one or more processing circuitries, obtaining data informative of a frequency drift associated with a receiver, wherein at least part of the receiver is connected to a frequency source comprising an atomic clock, and using the data to estimate a frequency drift of the atomic clock.

[0023] In addition to the above features, the system according to this aspect of the presently disclosed subject matter can comprise one or more of features (i) to (xlvii) listed above, in any desired combination or permutation which is technically possible.

[0024] In accordance with other aspects of the presently disclosed subject matter, there is provided a non-transitory computer readable medium comprising instructions that, when executed by one or more processing circuitries, cause the one or more processing circuitries to perform: obtaining data informative of a frequency drift associated with a receiver, wherein at least part of the receiver is connected to a frequency source comprising an atomic clock, and using the data to estimate a frequency drift of the atomic clock.

[0025] In addition to the above features, the non-transitory computer readable medium comprises instructions that, when executed by the one or more processing circuitries, cause the one or more processing circuitries to perform one or more of features (i) to (xlvii) listed above with respect to the system, in any desired combination or permutation which is technically possible.

[0026] According to some examples, an efficient solution for calibrating an atomic clock is provided.

[0027] According to some examples, a solution enabling quick calibration of an atomic clock is provided.

[0028] According to some examples, there is provided a solution which enables calibration of an atomic clock, even when a timing signal (e.g., 1PPS signal), provided by a receiver, is not available.

[0029] According to some examples, there is provided a solution for calibrating an atomic clock, which is robust to the absence of communication between a GNSS receiver and a GNSS network. In particular, even if this interruption of communication between the GNSS receiver and the GNSS network has a long duration (e.g., a few hours), the system is operative to determine the frequency drift of the atomic clock immediately after this communication has resumed.

[0030] According to some examples, the proposed solution is able to efficiently calibrate an atomic clock, even in the presence of jamming (in which the receiver cannot receive signals from the GNSS network).

[0031] According to some examples, the proposed solution is able to efficiently calibrate an atomic clock, even in the presence of spoofing (in which the receiver receives an erroneous signal from another source, which does not correspond to the true signal provided by the GNSS network).

[0032] According to some examples, the proposed solution is able to efficiently calibrate an atomic clock, even if the receiver does not receive, continuously, signals from the GNSS network.

[0033] According to some examples, the proposed solution is able to efficiently calibrate an atomic clock, even if the receiver can receive signals from the GNSS network only a few seconds or a few minutes over a few hours.

[0034] According to some examples, the proposed solution increases the availability of an atomic clock over time.

[0035] According to some examples, the proposed solution provides a system which generates an accurate oscillatory signal. According to some examples, the proposed solution provides a system which generates both an accurate oscillatory signal and an accurate timing signal.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to understand the invention and to see how it can be carried out in practice, embodiments will be described, by way of non-limiting examples, with reference to the accompanying drawings, in which:

[0038] Fig. 1A illustrates an architecture of a system usable to calibrate an atomic clock, according to some examples of the invention;

[0039] - Fig. IB illustrates another architecture of a system usable to calibrate an atomic clock, according to some examples of the invention;

[0040] Fig. 1C illustrates a variant of the architecture of Fig. 1A;

[0041] Fig. ID illustrates a variant of the architecture of Fig. IB;

[0042] Fig. IE illustrates another architecture of a system usable to calibrate an atomic clock, according to some examples of the invention;

[0043] - Fig- 2 illustrates a generalized flow-chart of a method of determining the frequency drift of an atomic clock, according to some examples of the invention;

[0044] - Fig. 3 illustrates a generalized flow-chart of a method of determining the frequency drift of an atomic clock, usable in the method of Fig. 2, according to some examples of the invention;

[0045] - Fig. 4 illustrates a generalized flow-chart of a method of determining the frequency drift of an atomic clock at different instants of time, according to some examples of the invention;

[0046] - Fig. 5 illustrates a graph depicting the availability over time of a pulsed signal generated by the receiver;

[0047] - Fig. 6 illustrates a generalized flow-chart of a method of correcting the frequency drift of an atomic clock, according to some examples of the invention, according to some examples of the invention;

[0048] Fig. 7 illustrates a generalized flow-chart of a method of obtaining an oscillatory signal (informative of a frequency) and a timing signal (pulsed signal), according to some examples of the invention; - Fig. 8 illustrates a system operative to provide an oscillatory signal (informative of a frequency) and a timing signal (pulsed signal), according to some examples of the invention;

[0049] - Fig- 9 illustrates a generalized flow-chart of a method enabling switching between two modes of calibration, according to some examples of the invention; and

[0050] - Fig. 10 illustrates a generalized flow-chart of another method enabling determining the frequency drift of an atomic clock, according to some examples of the invention.

[0051] DETAILED DESCRIPTION

[0052] Attention is now drawn to Figs. 1A to IE, which each depicts a system (see references 1000, 1001, 1003, 1004, and 1005) usable to calibrate an atomic clock, as explained with reference to the various methods described hereinafter. In particular, each system is usable to execute one or more of the methods described with reference to Figs. 2, 3, 4, 6, 7, 9, and 10. Note that the various methods and systems described herein can be used also to calibrate a clock which is not necessarily an atomic clock, such as a clock which is more accurate than an atomic clock.

[0053] Elements of the system(s) depicted in Fig. 1 A to IE can be made up of any combination of software and hardware and / or firmware. One or more elements of the system(s) depicted in Figs. 1A to IE may be centralized in one location or dispersed over more than one location.

[0054] In other examples of the presently disclosed subject matter, the system(s) of Figs. 1A to IE may comprise fewer, more, and / or different elements than those shown in Figs. 1A to IE. Likewise, the specific division of the functionality’ of the disclosed system to specific parts, as described below, is provided by way of example, and other various alternatives are also construed within the scope of the presently disclosed subject matter.

[0055] Fig. 1A depicts a system 1000 including a receiver 100. The receiver 100 is, for example, a GNSS (Global navigation satellite system) receiver. A GNSS receiver is operative to receive signals from a GNSS network. Examples of GNSS networks include GPS, GLONASS, Galileo, BeiDou, QZSS, and IRNSS. This list is not limitative. The receiver 100 can include a component (not represented), such as an antenna enabling radio and / or RF reception, with a localization network, such as a GNSS network.

[0056] In some examples, the receiver 100 can also transmit data or signals. It can include a component (not represented), such as an antenna enabling radio and / or RF transmission.

[0057] The receiver 100 includes at least one processing circuitry 101, which includes one or more processors, and one or more memories.

[0058] The processing circuitry 101 can perform various processing operations. For example, the processing circuitry 101 is configured to determine, based on signals received by the receiver 100 from a GNSS network, position of the receiver 100, and time bias (also called time error, or time shift) associated with the receiver 100. Additional operations which can be performed by the processing circuitry 101, are described hereinafter.

[0059] The receiver 100 can include additional components of a standard GNSS receiver, which are not described for the sake of simplicity.

[0060] In some examples, the receiver 100 is operative to generate a signal informative of time (also called timing signal). This signal informative of time is generally a pulse per second signal (designated in the art as a PSS signal or 1PPS signal). This is not limitative.

[0061] The receiver 100 is connected to a frequency source. Note that this does not require that all components of the receiver 100 be connected with the frequency source. In some examples, the processing circuitry 101 is connected (directly or indirectly) to the frequency source.

[0062] As visible in Fig. 1A, the frequency source comprises an atomic clock 120. In particular, the frequency source can be the atomic clock 120. Therefore, the receiver 100 (and in particular, its processing circuitry 101) is connected to the atomic clock 120 (serving as a frequency source for the receiver 100).

[0063] An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. Different types of atomic clocks are present in the market, such as caesium-based atomic clocks, rubidium-based atomic clocks, hydrogen-based atomic clocks, etc. The various systems and methods described hereinafter can be used to calibrate different types of atomic clocks, and are not limited to a specific type of atomic clock. An atomic clock generally provides at least two outputs: an oscillatory signal (a typical frequency of this oscillatory signal is 10 MHz - this is not limitative), and a signal informative of time. The signal informative of time is generally a pulse per second signal (designated in the art as a PSS signal or 1PPS signal). This is not limitative.

[0064] The atomic clock 120 can include various components, such as a processing circuitry 121. The atomic clock 120 can further include other additional components present in standard atomic clocks. These additional components are therefore not described.

[0065] The term “connected to” (the receiver 100 is “connected to” the frequency source corresponding to the atomic clock 120) covers any connection (direct or indirect) enabling the receiver 100 (or any component thereof) to receive data from the atomic clock 120, and, in particular, the oscillatory signal 160 generated by the atomic clock 120. In some examples, the receiver 100 (or any component thereof) receives from the atomic clock 120 only the oscillatory signal 160.

[0066] If necessary, the receiver 100 can send data to the atomic clock 120, through the connection between the receiver 100 and the atomic clock 120.

[0067] In some examples, the connection between the receiver 100 and the atomic clock 120 can be performed using one or more hardware connections. Non-limitative examples of hardware connections include one or more BNC (Bayonet Neill- Concelman) connectors, coaxial connectors, etc. Depending on the length of this hardware connection, the receiver 100 and the atomic clock 120 may be spaced apart. Alternatively, the length of the hardware connection can be selected to enable the receiver 100 and the atomic clock 120 to be located at a similar location, e.g., in the same package. This is not limitative.

[0068] The atomic clock 120 provides to the receiver 100 an oscillatory signal 160 at a known frequency. The receiver 100 (and in particular its processing circuitry 101) can use the oscillatory signal 160 for measuring time. As a consequence, a time bias is present in the time measured by the receiver 100 (and in particular by its processing circuitry 101), which is caused at least by a frequency drift of the atomic clock 120 (corresponding to the frequency drift of the oscillatory signal 160). This will be discussed further hereinafter.

[0069] In addition, the receiver 100 can use the oscillatory signal 160 to process signals received from the GNSS network. In particular, the receiver 100 can use the oscillatory signal 160 to perform a down-conversion of the RF signals received by the receiver 100 from the GNSS network. This is however not limitative.

[0070] As visible in Fig. 1A, a processing circuitry 110 is operatively coupled to the receiver 100 and to the atomic clock 120. The term “operatively coupled” includes at least the fact that the processing circuitry 110 can exchange data with the receiver 100 and with the atomic clock 120. As explained hereinafter, the processing circuitry 110 can receive from the processing circuitry 101 data informative of the frequency drift of the atomic clock 120 and can use this data to generate a command for the atomic clock 120, which instructs the atomic clock 120 to correct its frequency drift accordingly.

[0071] In some examples, the processing circuitry 110 is located in the same location as the receiver 100 and / or the atomic clock 120.

[0072] In some examples, the processing circuitry 110 is located remote from the receiver 100 and / or the atomic clock 120 and communicates with the receiver 100 and / or with the atomic clock 120 using wireless communication (e.g., Wi-Fi, or any other adapted wireless communication channel, etc.).

[0073] In some examples, the processing circuitry 110 communicates with the receiver 100 and / or with the atomic clock 120 using hardware connection(s), such as, but not limited to, an Ethernet connection.

[0074] In some examples, the receiver 100, the processing circuitry 110, and the atomic clock 120 are located in a common package 149. This is not limitative.

[0075] Fig. IB depicts a variant of the architecture of Fig. 1A. In Fig. 1A, the internal processing circuitry 101 of the receiver 100 performs some or all of the tasks performed by the processing circuitry 110 in the architecture depicted in Fig. 1A. In some examples of this architecture, the processing circuitry 101 can determine the time bias of the receiver 100 and deduce from the time bias the frequency drift of the atomic clock 120. The processing circuitry 101 can also generate a command for the atomic clock 120, instructing the atomic clock 120 to correct its frequency drift accordingly. Therefore, it is not necessary to use the processing circuitry 110 as an interface between the receiver 100 and the atomic clock 120.

[0076] In some examples, the receiver 100, the processing circuitry 110, and the atomic clock 120 are located in a common package 151. This is not limitative.

[0077] In some examples, the processing circuitry 101 is located remote from the receiver 100 and / or the atomic clock 120 and communicates with the receiver 100 and / or with the atomic clock 120 using wireless communication. Fig. 1C depicts a variant of the architecture of Fig. 1A. In Fig. 1C, the receiver 100 further includes an internal frequency source 102. The internal frequency source 102 can include an oscillator, which provides a frequency signal (oscillator signal) to the receiver 100, and, in particular, to the processing circuitry 101 of the receiver 100. An oscillator is a device that produces a periodic signal. A non -limitative example of this oscillator is a quartz oscillator. In this architecture, the receiver 100 can receive an oscillatory signal from its internal frequency source 102 and from the external frequency source (atomic clock 120). The processing circuitry 101 can be operative to turn off the internal frequency source 102 (by sending a turn off command to the internal frequency source 102), or to use, exclusively, the oscillatory signal 160 provided by the external frequency source (atomic clock 120) in order to measure time (without necessarily turning off the internal frequency source 102).

[0078] Fig. ID depicts a variant of the architecture of Fig. IB. The architecture of Fig. ID is similar to the architecture of Fig. IB in that the processing circuitry 101 can determine the time bias associated with the receiver 100, deduce from the time bias the frequency drift of the atomic clock 120, and generate a command for the atomic clock 120 to correct its frequency drift accordingly. In addition, in the architecture of Fig. ID, the receiver 100 further includes an internal frequency source 102. In this architecture, the receiver 100 can receive an oscillatory signal, both from its internal frequency source 102 and from the external frequency source (atomic clock 120). In some examples, the processing circuitry 101 can be operative to turn off the internal frequency source 102 (by sending a turn off command to the internal frequency source 102), or to use, exclusively, the oscillatory signal provided by the external frequency source (atomic clock 120) in order to measure time (without necessarily turning off the internal frequency source 102).

[0079] In some examples, the receiver 100 and the atomic clock 120 are located in a common package 157. This is not limitative.

[0080] Fig. IE describes another variant. In the system 1005, one or more processing circuitries 150 are coupled with both at least some of the components 170 of a receiver, and at least some of the components 180 of an atomic clock. In particular, the one or more processing circuitries 150 are connected to one or more components 170 of a receiver, and to one or more components 180 of an atomic clock. The one or more processing circuitries 150 can control at least some of the components 170 of the receiver, and at least some of the components 180 of the atomic clock.

[0081] In other words, the receiver and the atomic clock share one or common processing circuitries 150.

[0082] The components 170 of the receiver can include, for example, components present e.g. in a GNSS receiver, such as a component enabling receiving RF signals, components enabling sampling the received signal into a digital signal, etc. This list is not limitative.

[0083] The components 180 of the atomic clock include (inter alia) a laser component, and additional components of an atomic clock. This list is not limitative.

[0084] The atomic clock serves as a frequency source for the receiver. In some examples, the one or common processing circuitries 150 are operative to measure time based on the oscillatory signal 160 provided by the components 180 of the atomic clock (acting as a frequency source). Time measured by the one or common processing circuitries 150 is biased, due at least to the presence of a frequency drift in the oscillatory signal 160 generated by the components 180 of the atomic clock.

[0085] As explained hereinafter, the time bias can be measured (e.g., by the one or more processing circuitries 150) based on signals received by the components 180 of the receiver, from a network (e.g., GNSS network). Therefore, the time bias is designated as “associated with the receiver”.

[0086] The architecture of Fig. IE provides an integrated solution in which the system 1005 includes a receiver 100 (corresponding to the components 170, associated with the processing circuitry 150) and an atomic clock 120 (corresponding to the components 180, associated with the processing circuitry 150). Processing circuitries are shared between the receiver and the atomic clock.

[0087] The processing circuitry 160, the components 170 of the receiver, and the components 180 of the atomic clock, may be located in the same package 152. At least some of them may be located on a common chip.

[0088] Note that one or more other architectures, different from the architectures described with reference to Figs. 1A to IE, can be used.

[0089] Attention is now drawn to Fig. 2.

[0090] There is a need to calibrate the frequency of an atomic clock, since there is a small drift in the frequency of the atomic clock overtime. In particular, the oscillatory signal (with a typical frequency of 10 MHz - this value being non-limitative) provided by the atomic clock encounters a frequency drift overtime.

[0091] An existing solution uses a GNSS-disciplined clock, which consists of an atomic clock that is continuously being corrected using the coordinated universal timing signal (UTC), or standard second, in the form of 1PPS pulses recovered from the GNSS signal. This technique is known as “disciplining”. This technique suffers from several drawbacks. This calibration is a lengthy process (typically 12 to 24 hours). In addition, if the GNSS signal is not available during a certain period of time (which induces, in turn, unavailability of the 1PPS signal), performing the calibration is heavily compromised. Unavailability of the GNSS signal can be due to various factors: unavailability of the satellites, scrambling of the GNSS signal (by the operator, or by a third party), or other factors.

[0092] Fig. 2 proposes a solution for calibrating an atomic clock. The method of Fig. 2 can use an architecture as described with respect to any of Figs. 1A to IE. This is however not limitative, and any suitable architecture enabling the implementation of the method of Fig. 2 can be used.

[0093] The method of Fig. 2 includes obtaining (operation 200) data informative of time bias (also called time error) associated with the receiver 100. This time bias is designated as “associated with the receiver 100” since it is measured based on signals received by the receiver 100 (and is informative of a time error with respect to one or more reference clocks of a network generating the signals received by the receiver 100).

[0094] Operation 200 can include obtaining data informative of a time bias associated with the receiver 100 at a plurality of instants of time.

[0095] As explained hereinafter, time is measured by the receiver 100 based on the oscillatory signal 160 provided by the frequency source, which corresponds to the atomic clock 120. Note that when referring to operations performed by a receiver, such as measuring time, or other operations (determining position, time bias, etc.), this can include performing these actions by one processing circuitries associated with a receiver, or at least with some components of a receiver, such as the processing circuitry 101 or the processing circuitry 150.

[0096] When referring to a processing circuitry of the receiver, or associated with the receiver, this can correspond to a processing circuitry which performs operations informative of parameters of the receiver, such as estimating position and time bias of the receiver. The time bias associated with the receiver is informative of the bias in the time as measured by one or more processing circuitries associated with the receiver (based on one or more signals provided by a frequency source - corresponding, in Figs. 1A to IE to the atomic clock).

[0097] The time bias (also called time error, clock bias, or clock error) associated with the receiver 100 can correspond (in at least some examples) to the difference between the time measured by the receiver 100 (and in particular by a processing circuitry, such as processing circuitry 101 or 150), and a reference time. The reference time can correspond to the time measured by a localization network, such as a GNSS network, which is assumed to be accurate.

[0098] The time bias of the receiver 100 is caused at least by the frequency drift of the frequency source (which is, in this case, the atomic clock 120). This is due to the fact that the receiver 100 (and in particular a processing circuitry associated with the receiver 100, such as processing circuitry 101 or 150) uses the oscillatory signal 160 provided by the atomic clock 120 in order to measure time. This can be illustrated in a simple non- limitative example. Assume that at time “12:00” (as measured by the receiver 100), the receiver 100 attempts to measure its position, using the signals transmitted by the transmitters (e.g., satellites) of the GNSS network. Assume that at time “12:01” (as measured by the receiver 100), the receiver 100 attempts to once again measure its position, using the signals transmitted by the transmitters (e.g., satellites) of the GNSS network. In order to measure the time “12:01”, the receiver 100 uses the oscillatory signal 160 provided by the atomic clock 120. Indeed, assuming that the oscillatory signal 160 provided by the atomic clock 120 has a (theoretical) frequency of 10 MHz (this value is not limitative), one second corresponds to 10 million periods of this oscillatory signal. This correspondence can be used by the receiver 100 to measure one second (or any other relevant unit of time).

[0099] However, in reality, the actual frequency of the oscillatory signal 160 provided by the atomic clock 120 is slightly different from its (theoretical) frequency of 10 MHz. This difference is called frequency drift. The frequency drift of the atomic clock 120 causes a time bias in the time measured by the receiver 100.

[0100] In light of the foregoing, the frequency drift of the atomic clock 120 corresponds to the frequency drift of a signal (e.g., oscillatory signal 160) provided by the atomic clock 120 (or by at least some components thereof). The receiver 100 (via a processing circuitry of the receiver 100, or coupled with the receiver 100, as depicted in Figs. 1A to IE) repeatedly estimates its own time bias, at different instants of time. The estimate of the time bias is performed by using signals received by the receiver from a localization network, such as a GNSS network.

[0101] The receiver 100 generally solves several equations in which the unknown variables are its position (three unknown coordinates X, Y and Z of its 3D position) and the time bias. A non-limitative example of computing the position and the time bias associated with the receiver 100 is described in https: / 7en.wikipedia.org / wiki / SateIIite navigation soIution#Note, incorporated herein by reference. The operation of measuring the position and the time bias (by determining the pseudo-range of the receiver 100 to four satellites) is generally designated as pseudo-range measurements and time estimation.

[0102] In some examples, at operation 200, data informative of a time bias associated with the receiver 100 is computed by the processing circuitry 101 of the receiver 100 and communicated to the processing circuitry 110 (for example in the architectures of Figs. 1A and 1C).

[0103] In some examples, at operation 200, data informative of a time bias associated with the receiver 100 is computed by the processing circuitry 101 of the receiver 100 (for example in the architectures of Figs. IB and ID).

[0104] In some examples, at operation 200, data informative of a time bias associated with the receiver 100 is computed by the processing circuitry 150 controlling component(s) 170 of the receiver 100 (for example in the architecture of Fig. IE).

[0105] The method of Fig. 2 further includes using (operation 210) the data informative of the time bias associated with the receiver 100 to determine data informative of a frequency drift of the atomic clock 120.

[0106] Operation 210 can be performed e.g., by at least one of processing circuitry 110, 101, or 150. This is not limitative.

[0107] There is a direct relationship between the time bias of the receiver 100 and the frequency drift of the atomic clock 120. Indeed, as mentioned above, the frequency drift of the atomic clock 120 (used as frequency source by the receiver 100, or by a processing circuitry associated with the receiver, to measure time) causes a time bias in the time measured by the receiver 100. In light of the foregoing, it is possible to use the time bias determined at operation 200 to determine the frequency drift of the atomic clock 120. In some examples (see Figs. IB and ID), the receiver 100 can include an internal frequency source 102. In this case, it is possible to measure the time bias of the receiver 100 during a period of time in which the internal frequency source 102 is turned off.

[0108] In some examples, a processing circuitry (such as processing circuitry 101 or 110) sends a command to the internal frequency source 102, enabling turning off the internal frequency source 102. In some other examples, a hardware connection is disabled, preventing the receiver 100 from using the internal frequency source 102 for measuring time.

[0109] Alternatively, the time bias of the receiver 100 has been measured during a period of time in which the receiver 100 does not use the internal frequency source 102 to measure time.

[0110] Indeed, the time bias of the receiver 100 is used to determine the frequency drift of the atomic clock 120. If the receiver 100 uses its internal frequency source 102 for measuring time, then the frequency drift that is computed corresponds to the frequency drift of its internal frequency source, and not of the atomic clock 120.

[0111] As can be understood from the method of Fig. 2, since the receiver 100 uses the oscillatory signal 160 provided by the atomic clock 102 to measure time, the time bias (time error) of the receiver 100 is informative of the frequency drift of the atomic clock 102. It is therefore possible to compute the frequency drift of the atomic clock 102 based on the time bias of the receiver 100. Once the frequency drift of the atomic clock 102 has been computed, it is possible to send a command to the atomic clock 102 for correcting its frequency drift accordingly. Calibration of the frequency drift of the atomic clock 102 is therefore ensured.

[0112] Attention is now drawn to Fig. 3, which illustrates a non-limitative example of a method of determining the frequency drift of the atomic clock 120, based on the time bias of the receiver 100.

[0113] The method of Fig. 3 includes obtaining (operation 300) first data BT1informative of a time bias associated with the receiver 100 at a first time 7^ .

[0114] The method of Fig. 3 further includes obtaining (operation 310) second data BT2informative of a time bias associated with the receiver 100 at a second time T2.

[0115] In some examples, the difference between T±and T2is above a few minutes, such as any value equal to or larger than 5 or 10 minutes. This is not limitative. The method of Fig. 3 further includes using (operation 320) the first data BT1and the second data BT2to determine the data informative of a frequency drift of the atomic clock 120.

[0116] The frequency drift FD of the atomic clock 120 at time T2is a function of the time bias BTZof the receiver 100 at time T2and of the time bias BT1of the receiver 100 at time Ti (FD(T2~) = f BT2, BT1-)).

[0117] In some examples, the following non-limitative equation can be used:

[0118] Equation 1

[0119] Note that the method of Fig. 3 can be generalized to a plurality of instants of time, as depicted in Fig. 4. Assume that the time bias BT. of the receiver 100 is obtained at each of a plurality of instants of time Tt. with i from 1 to N, and N greater than two (operation 400). It is possible to determine (operation 410) the frequency drift FD(Tj) of the atomic clock 120 at the plurality of instants of time Tt. In particular, the following non-limitative equation can be used (with i from 2 to N):

[0120] Equation 2

[0121] It is also possible to perform an aggregation of the estimate of the frequency drift obtained at a plurality of instants of time. For example, an average of different estimates of the frequency drift can be determined.

[0122] Attention is now drawn to Fig. 5, which depicts the availability of the signal informative of time (e.g., 1PPS signal) provided by the receiver 100.

[0123] From time To to time Ti, the signal informative of time provided by the receiver 100 is available. After time Ti, the signal informative oftime provided by the receiver 100 is not available (or with a low accuracy preventing its usage for calibrating the atomic clock 120) . At time Ti, the signal informative of time provided by the receiver 100 is again available.

[0124] In the period of time ]TI:T2[ (this notation corresponds to the interval of time between Ti and Ti, excluding Ti and Ti), the receiver 100 is not operative to receive signals from a GNSS network, which, in turn, prevents the receiver 100 from generating a 1PPS signal. In the conventional approach, in which the 1PPS signal is used to calibrate an atomic clock, the lack of availability of the 1PPS signal between Ti and T2 prevents the calibration of the atomic clock. In particular, in the conventional approach, it is necessary to start the process of calibration from scratch, each time the 1PPS signal is not available.

[0125] Alternatively, between Ti and Ti (noted ]TI:T2[), the receiver 100 receives signal(s) from the GNSS network with a signal to noise ratio which is below a threshold, such that the 1PPS signal generated by the receiver 100 is inaccurate and cannot be used for calibrating an atomic clock using the conventional approach.

[0126] Alternatively, between Ti and T2 (noted ]TI:T2[), the receiver 100 undergoes a spoofing attack. This refers to the practice of manipulating or tricking a GNSS receiver by broadcasting false GNSS signals. Essentially, it misleads the GNSS receiver into believing it is located somewhere it is not, resulting in the device providing inaccurate location data. As a consequence, the GNSS receiver generates a 1PPS signal which is erroneous. In the conventional approach, in which the 1PPS signal is used to calibrate the atomic clock, not only is the frequency drift of the atomic clock not corrected, but this will also generate additional errors in the frequency of the atomic clock.

[0127] In the approach proposed herein, even though the 1PPS signal is not available between Ti and T2 (or, in case of spoofing, the 1PPS signal is available but is erroneous), it is possible to determine the frequency drift at time T2. This is due to the fact that the calibration of the atomic clock 120 as described in Figs. 2 to 4 does not require the usage of a 1PPS signal.

[0128] Therefore, in the scenario depicted in Fig. 5, although the receiver 100 is not operative to receive signals from a GNSS network between Ti and T2 (which in turn, prevents the receiver 100 from generating a 1PPS signal), or receives signals from the GNSS network with a small signal to noise ratio, the frequency drift at time T2 can be determined. In particular, the time bias at time Ti, which is the last time at which the receiver 100 was able to receive signals from the GNSS network before the interruption 500 (signal interruption), and the time bias at time T2, which is the first time at which the receiver is operative again to receive signals from the GNSS network after the interruption 500, can be computed and used to determine the frequency drift of the atomic clock 120 at time T2. Equation 1 can be used to determine the frequency drift of the atomic clock 120 at time T2 (this is however not limitative).

[0129] Note that it is also possible to determine the time bias at any time Tz before time Ti, at which the receiver 100 is operative to receive signals from the GNSS network, and at any time Ty after time T2, at which the receiver 100 is operative to receive signals from the GNSS network. The frequency drift FD (TY) at time TYof the atomic clock 120 can be computed based on the time bias of the atomic clock 120 at time TYand the time bias of the atomic clock 120 at another time Tz before the interruption 500.

[0130] In other words, the method of calibration described in Figs. 2 to 4 is much less sensitive to the interruption 500 of the signal informative of time (1PPS signal) generated by the receiver 100. As mentioned above, the signal interruption can include e.g. a scenario in which the 1PPS signal is not available at all, or a scenario in which the 1PPS signal is erroneous (for example, during a spoofing attack). This provides a much robust solution and increases the availability rate of the atomic clock 120 overtime.

[0131] Attention is now drawn to Fig. 6.

[0132] Once the frequency drift of the atomic clock 120 has been determined (see operation 600, using e.g., the method(s) of Figs. 2 to 4), it is possible to use this data to trigger correction of the frequency drift of the atomic clock 120 (operation 610).

[0133] This can include sending (operation 610) a command to the atomic clock 120 (and / or to at least one or more components of the atomic clock 120, used to generate the oscillatory signal 160 of the atomic clock 120, such as a laser of the atomic clock 120), for correcting the frequency drift of the atomic clock 120. This command can include the value of the frequency drift, which is used by the atomic clock 120 to correct its frequency drift. In some examples, the command can include an instruction instructing the atomic clock 120 to perform a correction of its frequency drift. The correction can be performed by the atomic clock 120 itself. The ability of an atomic clock to correct its frequency drift based on an input correction value is present in standard atomic clocks.

[0134] Assume that the frequency drift of the atomic clock 120 is determined at time TK and includes the value of the frequency drift (e.g. “P”). The command can be transmitted immediately (or shortly after) time TK to the atomic clock 120, which then triggers a selfcalibration of its frequency drift, by applying a correction of its oscillatory signal by a value equal to -P.

[0135] In the architecture of Figs. 1A and 1C, the command can be generated by the processing circuitry 110 and transmitted from the processing circuitry 110 to the atomic clock 120.

[0136] In the architecture of Figs. IB and ID, the command can be generated by the processing circuitry 101 and transmitted from the processing circuitry 101 to the atomic clock 120. In the architecture of Fig. IE, the processing circuitry 150 can directly control one or more components 180 (such as the laser component) of the atomic clock 120 in order to correct the frequency drift.

[0137] Attention is now drawn to Fig. 7.

[0138] In some examples, the system described in Figs. 1A to IE (see references 1000, 1001, 1003, 1004 and 1005), or any equivalent system, can be used as follows.

[0139] Assume that an (accurate) oscillatory signal is required for a certain application. The oscillatory signal can be used to provide a certain reference frequency.

[0140] As explained in the various methods described above, the frequency drift of the atomic clock 120 is calibrated overtime. According to the method of Fig. 7, it is proposed to obtain (operation 700) an (accurate) oscillatory signal from the atomic clock 120, whose frequency drift is corrected using the various methods described above. A non-limitative example of this oscillatory signal 800 is depicted in Fig. 8. This oscillatory signal 800 has a known frequency (which is corrected using the various methods described herein) and can therefore be used as a reference frequency by one or more external system(s) 820 in communication with the system 1000, 1001, 1003, 1004, or 1005. The external system 820 is, for example, another receiver, a transmitter, a radar, a measurement system, etc. This list is not limitative.

[0141] This oscillatory signal 800 can be obtained by the external system(s) 820 using any adapted connection. In some examples, a hardware connection can be used, such as (but not limited to) a coaxial connection or a BNC connection between the external system 820 and the atomic clock 120.

[0142] In some examples, it can be required to obtain an (accurate) pulsed signal (signal informative of time) for a certain application.

[0143] In some examples, the receiver 100 is operative to generate a pulsed signal, informative of time. The method of Fig. 7 can include obtaining (operation 710) the pulsed signal generated by the receiver 100. In some examples, the pulsed signal is a 1PPS signal, which is generally considered as an accurate timing signal. A non-limitative example of the pulsed signal 810 is illustrated in Fig. 8.

[0144] The pulsed signal 810 can be transmitted by the receiver 100 to one or more external system(s) 820 using any adapted connection(s) (e.g., hardware connection).

[0145] Note that the oscillatory signal 800 (generated by the atomic clock 120, and corrected using the various methods described herein), and the pulsed signal 810, can be transmitted to the same external system 820, or to different external systems 820. It turns out that the system (see e.g., 1000, 1001, 1003, 1004, or 1005) is able to both provide an accurate oscillatory signal (informative of a reference frequency, by the atomic clock 120), corrected using the various methods described herein, and an accurate pulsed signal (informative of time, by the receiver 100).

[0146] A versatile system is obtained, which provides both accurate frequency information and accurate timing information.

[0147] Attention is now drawn to Fig. 9, which describes another method of calibrating the atomic clock 120.

[0148] This method enables switching (operation 900) between a first mode 901 of calibration of the atomic clock 120, and a second mode 902 of calibration of the atomic clock 120.

[0149] In the first mode 900 (first mode of calibration), the method of Fig. 2 is used. In particular, in the first mode 900, data informative of a time bias associated with a receiver connected to an atomic clock 120, is obtained (operation 200). The data is used (operation 210) to determine data informative of the frequency drift of the atomic clock 120. A command can be sent to the atomic clock 120, instructing the atomic clock 120 to perform a calibration of its frequency drift (correction of its frequency drift) based on the data informative of the frequency drift of the atomic clock 120.

[0150] In the second mode 901 (second mode of calibration), the method includes transmitting a pulsed signal from the receiver 100 to the atomic clock 120. The pulsed signal is informative of time. In particular, the pulsed signal can be a 1PPS signal provided by the receiver 100. The atomic clock 120 then uses the pulsed signal to correct its frequency drift. Non-limitative examples of performing the second mode can be found e.g. in l tp : / / epw i ipgdia;p g / wiki ('.-PS .disciplined, ..oscillator '■

[0151] The switch between the first mode and the second mode can be controlled by a processing circuitry, such as (but not limited to) the processing circuitry 110, 101, or 150.

[0152] In some examples, the switch between the first mode 901 and the second mode 902 can be performed in response to an event. In particular, in some examples, the event can correspond to the unavailability of the 1PPS signal generated by the receiver 100, and / or to a number of satellites which are available for communicating with the receiver 100, which is below a threshold.

[0153] When the event is detected, a switch can be performed from the second mode 902 (which requires the 1PPS signal) to the first mode 901 (which does not require the 1PPS signal). When the 1PPS signal generated by the receiver 100 is again available, or when the number of satellites which are available for communicating with the receiver 100, is above a threshold, a switch can be performed from the first mode 901 to the second mode 902.

[0154] Even when the system operates in the second mode 902, it is possible to store in a memory the time bias determined by the receiver 100 at each instant of time. The memory can be part of the receiver 100 or can be an external memory accessible by the processing circuitry of the receiver 100. When the system is switched to the first mode 901, it can use data informative of the time bias stored in the memory to determine the frequency drift.

[0155] For example, assume that the system operates in the second mode 902 in the period of time between To and Ti. During this period of time, although the time bias of the receiver 100 is not used to calibrate the atomic clock 120, it can be measured by the receiver 100 at each instant of time and stored in a memory. Assume that immediately after time Ti, the 1PPS signal is not available. A switch of the system to the first mode 901 can be operated. Assume that at time Ti, the signals provided by the GNSS network are available again for the receiver 100. It is now possible to determine the frequency drift at time Ti, by using the time bias at time T and the time bias at time Ti (see e.g., Equation 1).

[0156] Attention is now drawn to Fig. 10, which describes another method of calibrating the frequency drift of an atomic clock.

[0157] The method of Fig. 10 can rely on the usage of an architecture described with reference to Figs. 1A to IE. This is however not limitative.

[0158] The method of Fig. 10 includes obtaining (operation 1050) data informative of a frequency drift associated with the receiver 100. In particular, operation 200 can include obtaining data informative of a frequency drift associated with the receiver 100 at a plurality of instants of time.

[0159] As explained above, the receiver 100 uses a frequency source which provides a signal at a reference frequency. In the architecture of Figs. 1A to IE, the frequency source used by the receiver 100 is the atomic clock 120. As a consequence, the frequency drift associated with the receiver 100 corresponds to the frequency drift of the atomic clock 120.

[0160] Determination of the frequency drift of the receiver 100 relies on the usage of signals received by the receiver 100 from a localization network, such as a GNSS network.

[0161] When the receiver 100 (and in particular, its processing circuitry 101, or another processing circuitry communicating with the receiver 100, such as the processing circuitry 110) atempts to determine its velocity, it can determine the frequency of the signals received from the GNSS network. The perceived frequency is affected by the Doppler shift, due to the relative motion between the receiver 100 and the constellation of transmiters (satellites) of the GNSS network.

[0162] In order to determine its velocity, the receiver 100 compares the frequency of the signals received from the GNSS network with the reference frequency signal of its frequency source (in this case, the reference frequency signal is the oscillatory signal 160 of the atomic clock 120).

[0163] Determination of the velocity of the receiver 100 (using the Doppler effect of the signals received from the GNSS network) includes also determining the frequency drift of the frequency source of the receiver 100.

[0164] Determination of the velocity and of the frequency drift can include solving pseudo-range rate equations, as described e.g., in htps: / / gnss-sdr.org / docs / sp- blocks / observables / , incorporated herein by reference in its entirety.

[0165] According to some examples, data informative of a frequency drift associated with the receiver 100 include a plurality of estimates of the frequency drift associated with the receiver 100, at a plurality of instants of time.

[0166] The frequency drift estimated by the receiver 100 should correspond to the actual frequency drift of the atomic clock 120. However, in practice, the estimate of the frequency drift performed by the receiver 100 based on the signals received from the GNSS network generally includes noise. In other words, the data obtained at operation 1050 includes information on the frequency drift of the atomic clock, together with noise.

[0167] In order to improve the accuracy of the estimate of the frequency drift of the atomic clock 120, the data informative of a frequency drift associated with the receiver 100, estimated at different instants of time, can be further processed (operation 1060) to estimate the frequency drift of the atomic clock 120.

[0168] In particular, the plurality of estimates of the frequency drift (estimated at different instants of time) can be fed to a filter, which atempts to isolate the actual frequency drift of the atomic clock 120 from the noise. In some examples, a Kalman filter can be used. Other adapted filters can be used.

[0169] The output of the filter corresponds to a more accurate estimate of the frequency drift of the atomic clock 120.

[0170] Once the frequency drift of the atomic clock 120 has been estimated, it is possible to trigger correction of the frequency drift of the atomic clock 120 (operation 1070). This can include sending a command to the atomic clock 120, for correcting the frequency drift of the atomic clock 120. This command can include the value of the frequency drift, which is used by the atomic clock 120 to correct its frequency drift. In some examples, the command can include an instruction instructing the atomic clock 120 to perform a correction of its frequency drift. The correction can be performed by the atomic clock 120 itself. The ability of an atomic clock to correct its frequency drift based on an input correction value is present in standard atomic clocks.

[0171] Assume that the frequency drift of the atomic clock 120 is determined at time TK and includes the value of the frequency drift (e.g. “P”). The command can be transmitted immediately (or shortly after) time TK to the atomic clock 120, which then triggers a selfcalibration of its frequency drift, by applying a correction of its oscillatory signal by a value equal to -P.

[0172] The various systems described herein can be used in various applications, such as (but not limited to): control systems (e.g., electrical control systems), telecommunication systems, cellular stations, radar systems, measurement systems, etc.

[0173] In the drawings and descriptions set forth, identical reference numerals indicate those components that are common to different embodiments or configurations. Elements in the drawings are not necessarily drawn to scale.

[0174] In the detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the presently disclosed subject matter may be practiced without these specific details. In other instances, well-known methods have not been described in detail so as not to obscure the presently disclosed subject matter.

[0175] Unless specifically stated otherwise, it is appreciated that throughout the specification, discussions utilizing terms such as “obtaining”, “using”, “switching”, “generating”, “calibrating”, “determining”, or the like, refer to the action(s) and / or process(es) of one or more processing circuitries that manipulate and / or transform data into other data, said data represented as physical, such as electronic, quantities and / or said data representing the physical objects.

[0176] The terms “computer” should be expansively construed to include any kind of hardware-based electronic device with a processing circuitry (e.g., digital signal processor (DSP), a GPU, a TPU, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), microcontroller, microprocessor etc.). The processing circuitry can comprise, for example, one or more processors operatively connected to one or more computer memories, loaded with executable instructions for executing operations, as described in the specification. The processing circuitry encompasses a single processor or multiple processors, which may be located in the same geographical zone, or may, at least partially, be located in different zones, and may be able to communicate together.

[0177] Operations in accordance with the teachings herein may be performed by a computer or computerized device specially constructed for the desired purposes, or by a general -purpose computer or computerized device specially configured for the desired purpose by a computer program stored in a computer readable storage medium.

[0178] As used herein, the phrase "for example", "such as", and variants thereof, describe non-limiting examples of the presently disclosed subject matter.

[0179] Fewer, more, and / or different stages than those shown in the methods of Figs. 2, 3, 4, 6, 7, 9, and 10 may be executed. In embodiments of the presently disclosed subject matter, one or more stages illustrated in the methods of Figs. 2, 3, 4, 6, 7, 9, and 1 may be executed in a different order, and / or one or more groups of stages may be executed simultaneously.

[0180] At least some of the one or more processors referred to herein can represent one or more general-purpose processing devices such as a microprocessor, a central processing unit, or the like. More particularly, a given processor may be one of a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor implementing other instruction sets, or a processor implementing a combination of instruction sets. The one or more processors may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a network processor, or the like. The one or more processors are configured to execute instructions for performing the operations and steps discussed herein.

[0181] The memories referred to herein can comprise one or more of the following: internal memory, such as, e.g., processor registers and cache, etc., main memory such as, e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.

[0182] The terms “non-transitory memory” and “non-transitory computer readable medium” used herein should be expansively construed to cover any computer memory suitable to the presently disclosed subject matter. The terms should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and / or associated caches and servers) that store the one or more sets of instructions. The terms shall also be taken to include any medium that is capable of storing or encoding a set of instructions for execution by the computer, or the processing circuitries, and that cause the computer, or the processing circuitries, to perform any one or more of the methodologies of the present disclosure.

[0183] The invention contemplates a computer program being readable by a computer for executing one or more methods of the invention. The invention further contemplates a machine -readable memory tangibly embodying a program of instructions executable by the machine for executing one or more methods of the invention.

[0184] It is to be noted that the various features described in the various embodiments may be combined according to all possible technical combinations.

[0185] It is to be understood that the invention is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Hence, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the presently disclosed subject matter.

[0186] Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope, defined in and by the appended claims.

Claims

CLAIMS1. A system comprising one or more processing circuitries configured to:- obtain data informative of a time bias associated with a receiver, wherein said time bias is caused at least by a frequency drift of an atomic clock, and- use the data to determine data informative of the frequency drift of the atomic clock.

2. The system of claim 1 , wherein the frequency drift of the atomic clock corresponds to a frequency drift of an oscillatory signal generated by the atomic clock.

3. The system of claim 1 or of claim 2, wherein the data informative of the time bias have been calculated based on signals received by the receiver from a GNSS network.

4. The system of any one of claims 1 to 3, wherein the receiver, or a processing circuitry of the receiver, is configured to measure time based on an oscillatory signal provided by the atomic clock.

5. The system of any one of claims 1 to 4, wherein the atomic clock serves as a frequency source for the receiver.

6. The system of any one of claims 1 to 5, configured to use the data informative of the frequency drift of the atomic clock to trigger correction of the frequency drift of the atomic clock.

7. The system of any one of claims 1 to 6, configured to use the data informative of the frequency drift of the atomic clock to generate a command for correcting the frequency drift of the atomic clock.

8. The system of claim 7, configured to transmit the command to the atomic clock, or to at least one or more components of the atomic clock.

9. The system of any one of claims 1 to 8, wherein the data informative of the time bias have been calculated based on: signals received by the receiver from a GNSS network, and- equations comprising position and time bias of the receiver.

10. The system of any one of claims 1 to 9, configured to obtain the data informative of a time bias from the receiver.

11. The system of any one of claims 1 to 10, wherein the one or more processing circuitries are configured to determine the data informative of a time bias associated with the receiver.

12. The system of any one of claims 1 to 11, configured to: for each of a plurality of instants of time Tt. obtain data BTtinformative of a time bias associated with the receiver at the timeand use at least part of the data BTtto determine data informative of the frequency drift of the atomic clock at some of the plurality of instants of time Tt.

13. The system of any one of claims 1 to 12, wherein the receiver comprises a global navigation satellite system (GNSS) receiver.

14. The system of any one of claims 1 to 13, wherein (i) or (ii) is met:(i) the receiver is connected to a frequency source comprising the atomic clock;(ii) a processing circuitry controlling the receiver, or being part of the receiver, is connected to a frequency source comprising the atomic clock.

15. The system of any one of claims 1 to 14, wherein (i) or (ii) is met:(i) the one or more processing circuitries are configured to control at least one of one or more components of the receiver or one or more components of the atomic clock;(ii) the one or more processing circuitries are part of at least one of the receiver or of the atomic clock.

16. The system of any one of claims 1 to 15, wherein the one or more processing circuitries correspond to one or more processing circuitries of the receiver itself.

17. The system of any one of claims 1 to 15, wherein the receiver comprises one or more internal processing circuitries, different from the one or more processing circuitries.

18. The system of any one of claims 1 to 17, configured to use the data informative of the frequency drift of the atomic clock to enable correction of the frequency drift of the atomic clock, without requiring usage of a 1PPS signal of the receiver.

19. The system of any one of claims 1 to 18, wherein the one or more processing circuitries are configured to obtain data informative of a time bias associated with the receiver, at different instants of time.

20. The system of any one of claims 1 to 19, further comprising the receiver and the atomic clock.

21. The system of claim 20, configured to provide :- an oscillatory signal, and- a pulsed signal.

22. The system of claim 21, wherein (i) or (ii) is met:(i) the atomic clock is operative to provide the oscillatory signal and the receiver is operative to provide the pulsed signal;(ii) the atomic clock is operative to provide the oscillatory signal and the receiver is operative to provide the pulsed signal, wherein the pulsed signal is a 1PPS signal.

23. The system of any one of claims 1 to 22, wherein the receiver, the atomic clock, and the one or more processing circuitries, are located in a same package.

24. The system of any one of claims 1 to 22, the one or more processing circuitries being located remotely from the receiver and the atomic clock.

25. The system of any one of claims 1 to 24, wherein the receiver:comprises an internal frequency source, and is also connected to a frequency source comprising the atomic clock.

26. The system of claim 25, wherein the time bias associated with the receiver has been measured during a period of time in which (i) or (ii) is met:(i) the internal frequency source is turned off; or(ii) the receiver does not use the internal frequency source to measure time.

27. The system of claim 25 or of claim 26, wherein the one or more processing circuitries are operative to send a command to the internal frequency source, to turn off said internal frequency source.

28. The system of any one of claims 1 to 27, configured to determine data informative of the frequency drift of the atomic clock based on: a first time bias associated with the receiver, determined at a first time before a signal interruption, and a second time bias associated with the receiver, determined at a second time after the signal interruption.

29. The system of claim 28, wherein during said signal interruption, (i), (ii) or (iii) is met:(i) the receiver is not operative to receive signals from a global navigation satellite network;(ii) the receiver is not operative to generate a 1PPS signal;(iii) the receiver undergoes a spoofing attack.

30. The system of any one of claims 1 to 29, configured to:- obtain first data BT1informative of a time bias associated with the receiver at a first time T , and- obtain second data BT2informative of a time bias associated with the receiver at a second time T2. and- use the first data BT1and the second data BT2to determine the data informative of a frequency drift of the atomic clock.

31. The system of claim 30, wherein (i) or (ii) is met:(i) said using the first data BT1and the second data BT2to determine the data informative of a frequency drift of the atomic clock comprises using a difference between BT2and BT1and a difference between(ii) said using the first data BT1and the second data BT2to determine the data FD informative of a frequency drift of the atomic clock comprises using:

32. The system of claim 30 or claim 31, wherein in most or all of the period of time ]7 ; T2[, the receiver is not operative to receive signals from a GNSS network.

33. The system of any one of claims 30 to 32, wherein in most or all of the period of time ] i; T2[, the receiver is not operative to generate a 1PPS signal.

34. The system of any one of claims 30 to 33, wherein in most or all of the period of time J x; T2[. the receiver undergoes a spoofing attack.

35. The system of any one of claims 1 to 34, configured to store, in a memory, data informative of a time bias of the receiver determined at a plurality of instants of time.

36. The system of any one of claims 1 to 35, operative to switch between a first mode and a second mode, wherein: in the first mode, the one or more processing circuitries are configured to obtain data informative of a time bias associated with the receiver, wherein the receiver is connected to a frequency source comprising an atomic clock, and to use the data to determine data informative of a frequency drift of the atomic clock; in the second mode, the atomic clock is operative to receive a pulsed signal from the receiver, and to use it to calibrate its frequency drift.

37. The system of claim 36, wherein the pulsed signal is a 1PPS signal.

38. The system of any one of claims 1 to 37, wherein the one or more processing circuitries are operative to communicate with the receiver and the atomic clock using wireless communication.

39. The system of any one of claims 1 to 38, wherein at least part of the receiver is connected to a frequency source comprising the atomic clock.

40. A system comprising one or more processing circuitries configured to:- obtain data informative of a frequency drift associated with a receiver, wherein at least part of the receiver is connected to a frequency source comprising an atomic clock, and- use the data to estimate a frequency drift of the atomic clock.

41. The system of claim 40, wherein the data informative of a frequency drift associated with the receiver have been determined based on signals received by the receiver from a GNSS network.

42. The system of claim 40 or of claim 41 , wherein the data informative of a frequency drift associated with the receiver have been determined based on: signals received by the receiver from a GNSS network;- equations comprising velocity of the receiver and frequency drift associated with the receiver.

43. The system of any one of claims 40 to 42, wherein using the data informative of a frequency drift associated with the receiver comprises performing a filtering operation of the data informative of a frequency drift associated with the receiver obtained a plurality of instants of time.

44. A method comprising, by one or more processing circuitries:- obtaining data informative of a time bias associated with a receiver, wherein said time bias is caused at least by a frequency drift of an atomic clock, and- using the data to determine data informative of the frequency drift of the atomic clock.

45. The system of claim 44, wherein the receiver, or a processing circuitry of the receiver, measures time based on an oscillatory signal provided by the atomic clock.

46. The method of claim 44 or of claim 45, wherein the data informative of the time bias have been calculated based on signals received by the receiver from a GNSS network.

47. The method of any one of claims 44 to 46, comprising determining data informative of the frequency drift of the atomic clock based on: a first time bias associated with the receiver, determined at a first time before a signal interruption, and a second time bias associated with the receiver, determined at a second time after the signal interruption.

48. The method of claim 47, wherein during said signal interruption, (i), (ii), or (iii) is met:(i) the receiver does not receive signals from a GNSS network;(ii) the receiver is not operative to generate a 1PPS signal;(iii) the receiver undergoes a spoofing attack.

49. A non-transitory computer readable medium comprising instructions that, when executed by one or more processing circuitries, cause the one or more processing circuitries to perform: obtaining data informative of a time bias associated with a receiver, wherein said time bias is caused at least by a frequency drift of an atomic clock, and using the data to determine data informative of the frequency drift of the atomic clock.

50. A non-transitory computer readable medium comprising instructions that, when executed by one or more processing circuitries, cause the one or more processing circuitries to perform: obtaining data informative of a frequency drift associated with a receiver, wherein at least part of the receiver is connected to a frequency source comprising an atomic clock, andusing the data to estimate a frequency drift of the atomic clock.

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