Wireless communication method and system for phase noise mitigation

Abstract

The present disclosure relates to a wireless communication method (50) implemented by a terminal (20) of a wireless communication system (10) for exchanging data with a radio access network (11) of said wireless communication system, said method comprising: - determining (S50) a phase noise time coherence index representative of the time coherence of the phase noise affecting the baseband signal obtained from the radio frequency signal received by the terminal; - transmitting (S51) said phase noise time coherence indicator to said radio access network (11) of a wireless communication system; Includes.

Description

[Technical Field]

[0001] The present disclosure relates to wireless communication systems, and more particularly to a wireless communication method that enables improved phase noise mitigation. Priority is claimed to European Patent Application No. 23305597.9, filed April 18, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Phase noise is a physical phenomenon that occurs due to instabilities in the local oscillators of any wireless communication equipment, for example base stations and terminals (also known as user equipment) of a wireless communication system.

[0003] In wireless communications between a transmitter (e.g., a base station) and a receiver (e.g., a terminal), phase noise is introduced both at the transmitter side (e.g., when one or more local oscillators frequency-convert a baseband signal from a baseband frequency to a carrier frequency) and at the receiver side (e.g., when one or more local oscillators frequency-convert a radio frequency signal from a carrier frequency to a baseband frequency). The characteristics of the introduced phase noise depend on the respective characteristics of each local oscillator involved, and therefore, for the same base station, the phase noise characteristics may change when communicating with different terminals because each terminal uses its own local oscillator with its own characteristics. Also, the amount of phase noise introduced at the terminal is usually more important than the amount of phase noise introduced at the base station because the base station may usually be equipped with a more efficient local oscillator than the terminal.

[0004] Typically, the phase noise affecting the data signal can be estimated at the receiver side by inserting a pilot signal at the transmitter side. Since the pilot signal is known to both the transmitter and the receiver, the receiver can estimate the phase noise affecting the received pilot signal and use the estimated phase noise for the pilot signal to predict and compensate for the phase noise affecting the data signal.

[0005] Phase noise increases as the carrier frequency used to exchange radio frequency signals increases. Next-generation wireless communication systems are targeting sub-terahertz (e.g., less than 300 gigahertz) and terahertz (THz) carrier frequencies (approximately 1000 gigahertz), which are greater than the carrier frequencies used in current wireless communication systems. This increase in carrier frequency opens up the possibility of considering higher data rates. However, this also entails an increased impact of phase noise on wireless communication performance, which may require an increased number of pilot signals required for phase noise estimation, thereby limiting the achievable data rate of data signals. Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure aims to improve the situation, in particular by proposing a solution that allows a base station to take into account the phase noise peculiarities of each terminal with which it exchanges data, thereby addressing at least some or all of the limitations of the prior art mentioned above, and in some cases at least reducing the amount of pilot signals required for phase estimation. [Means for solving the problem]

[0007] To this end, according to a first aspect, the present disclosure relates to a wireless communication method, implemented by a terminal of a wireless communication system, for exchanging data with a radio access network of the wireless communication system, the method comprising: determining a phase noise time coherence index representative of the time coherence of phase noise affecting a baseband signal obtained from a radio frequency signal received by the terminal; transmitting the phase noise time coherence indicator to a radio access network of a wireless communication system; Includes.

[0008] Thus, the terminal evaluates the time coherence of the phase noise affecting the received baseband signal, which is mostly introduced by the terminal's local oscillator (at least when communicating with a base station). The time coherence of the phase noise is typically a measure of the average correlation between the phase noise introduced at times separated by a given delay, evaluated for different delays (also known as the phase noise autocorrelation function). Thus, the time coherence measures, on average, how quickly the introduced phase noise is expected to change over time. The terminal determines a phase noise time coherence index that represents the time coherence and thus indicates how quickly the introduced phase noise is expected to change over time. Depending on the embodiment, the phase noise time coherence index may correspond, for example, to an estimated phase noise autocorrelation function (or information derived therefrom, e.g., its initial slope, lower bound, its mean value, etc.), a binary value indicating whether the phase noise is fluctuating quickly or slowly, etc.

[0009] The phase noise time coherence indicator is then transmitted to the radio access network. For example, the phase noise time coherence indicator may be transmitted directly or indirectly to a base station with which the terminal needs to exchange data. The phase noise time coherence indicator may also be stored in a database that can be retrieved, as needed, by a base station with which the terminal needs to exchange data.

[0010] As mentioned above, the phase noise depends on the carrier frequency used, and as a result, the phase noise temporal coherence index represents the temporal coherence of the phase noise introduced for the considered carrier frequency through which the base station and the terminal exchange data. Therefore, the phase noise temporal coherence index depends on the considered carrier frequency and may be different if data is to be exchanged via a millimeter-wave carrier frequency or if data is to be exchanged via a (sub)THz carrier frequency, etc.

[0011] Reporting the phase noise time coherence indicator determined by the terminal to the radio access network is advantageous in that it allows the base station to adjust its behavior to characteristics of the phase noise affecting communications between the base station and the terminal, ultimately improving wireless communication performance. For example, in an uplink from the terminal to the base station, the base station may adjust parameters of phase noise estimation and correction based on whether the introduced phase noise is expected to vary slowly or quickly, e.g., to ensure that the average phase noise estimation error remains below a predetermined threshold regardless of the time coherence of the phase noise. In a downlink from the base station to the terminal, the base station may use the received phase noise time coherence indicator to adjust the design of pilot signals inserted for phase noise estimation, e.g., by adjusting the time spacing between pilot signals based on whether the introduced phase noise is expected to vary slowly or quickly (e.g., by considering a larger time spacing when the phase noise is expected to vary slowly than when the phase noise is expected to vary quickly).

[0012] In certain embodiments, the wireless communication method according to the first aspect may further include one or more of the following optional features, considered alone or in any technically possible combination:

[0013] In a particular embodiment, determining the phase noise time coherence index includes estimating a phase noise autocorrelation function of the phase noise based on signals received from at least one base station of the radio access network, and the phase noise time coherence index corresponds to or is determined based on the estimated phase noise autocorrelation function. In a particular embodiment, the phase noise temporal coherence index is given by: - the initial gradient of the estimated phase noise autocorrelation function, - a binary value indicating the rate of change of the phase noise, - the period before the phase noise coherence falls below the threshold, the value of the estimated phase noise autocorrelation function for a given delay, the lower limit to which the estimated phase noise autocorrelation function tends, -Average value of estimated phase noise autocorrelation function represents at least one of the following:

[0014] In a particular embodiment, determining the phase noise temporal coherence index includes retrieving calibration data stored in a non-volatile memory of the terminal, and the phase noise temporal coherence index corresponds to or is determined based on the calibration data.

[0015] According to a second aspect, the present disclosure relates to a computer program product including instructions that, when executed by at least one processor, configure the at least one processor to perform a wireless communication method according to any one of the embodiments of the first aspect.

[0016] According to a third aspect, the present disclosure relates to a terminal in a wireless communication system, the terminal comprising a processing circuit and a wireless communication unit configured to perform the wireless communication method according to any one of the embodiments of the first aspect.

[0017] According to a fourth aspect, the present disclosure relates to a wireless communication method, implemented by a base station of a wireless communication system, for exchanging data with a terminal of the wireless communication system, the method comprising: determining a phase noise time coherence index of the terminal, the time coherence index representing the time coherence of the phase noise affecting a baseband signal obtained from a radio frequency signal received by the terminal; - determining, for a terminal, a time interval of a pilot signal transmitted by a base station to the terminal based on the determined phase noise time coherence index; transmitting signals to a terminal, the signals including data signals and pilot signals, the pilot signals spaced apart in time based on a time interval determined for the terminal; Includes.

[0018] In certain embodiments, the wireless communication method according to the fourth aspect may further include one or more of the following optional features, considered alone or in any technically possible combination:

[0019] In a particular embodiment, determining the phase noise temporal coherence index of the terminal comprises: receiving from a terminal a phase noise temporal coherence indicator transmitted according to any one of the embodiments of the first aspect; - estimating a phase noise temporal coherence index of the terminal based on a signal received from the terminal; - retrieving a phase noise time coherence index of the terminal from a database; Contains one of the following:

[0020] In certain embodiments, the time interval is adjusted to the temporal coherence of the terminal's phase noise by selecting a lower time interval in response to a determined phase noise temporal coherence indicator indicating a shorter coherence time than in response to a determined phase noise temporal coherence indicator indicating a larger coherence time. Essentially, "large" and "short" should be understood relative to each other; thus, phase noise with a shorter coherence time is expected to change faster than phase noise with a larger coherence time, i.e., the time interval increases (strictly or non-strictly monotonically) with the coherence time of the phase noise. The coherence time corresponds, for example, to the delay before the average correlation between the introduced phase noises falls below a predetermined threshold.

[0021] In certain embodiments, the time interval is determined by using a predetermined performance function that represents the phase noise estimation performance at the terminal as a function of the time interval between pilot signals. In certain embodiments, determining the time interval is performed by determining the maximum time interval for which the phase noise estimation performance meets a minimum phase noise performance requirement.

[0022] In certain embodiments, the determination of the time spacing is performed by considering the minimum time spacing allowed for spacing the pilot signals and / or the maximum time spacing allowed for spacing the pilot signals.

[0023] In a particular embodiment, the performance function represents phase noise estimation performance when performing finite impulse response, FIR, minimum mean square error, MMSE phase noise estimation at the terminal.

[0024] In a particular embodiment, a lookup table LUT is stored in a non-volatile memory of the base station, the LUT including different time intervals associated with respective different phase noise temporal coherence indexes, and determining the time interval for the terminal includes retrieving the time interval associated with the phase noise temporal coherence index determined for the terminal from the LUT.

[0025] According to a fifth aspect, the present disclosure relates to a computer program product including instructions that, when executed by at least one processor, configure the at least one processor to perform a wireless communication method according to any one of the embodiments of the fourth aspect.

[0026] According to a sixth aspect, the present disclosure relates to a base station of a wireless communication system, the base station comprising a processing circuit and a wireless communication unit configured to perform a wireless communication method according to any one of the embodiments of the fourth aspect.

[0027] According to a seventh aspect, the present disclosure relates to a wireless communication system, comprising at least one terminal according to any one of the embodiments of the present disclosure and at least one base station according to any one of the embodiments of the present disclosure.

[0028] In a particular embodiment, the wireless communication system uses Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing DFT-s-OFDM. The invention will be better understood on reading the following description, given as a non-limiting example and made with reference to the figures in which: [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic diagram of a wireless communication system; [Figure 2] 1 is a schematic diagram of an exemplary embodiment of a terminal of a wireless communication system; [Figure 3] 1 is a schematic diagram of an exemplary embodiment of a base station of a wireless communication system; [Figure 4] 10 is a plot illustrating an example of a phase noise autocorrelation function for a terminal and a base station. [Figure 5] 1 is a diagram illustrating the main steps of an exemplary embodiment of a wireless communication method implemented, for example, by a terminal. [Figure 6] 2 is a diagram illustrating the main steps of an exemplary embodiment of a wireless communication method implemented, for example, by a base station. [Figure 7] 7 is a plot illustrating an example of a performance function that can be used to adjust the time spacing between pilot signals in the wireless communication method of FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0030] In these figures, the same reference numerals from one figure to another indicate the same or similar elements. For clarity, elements shown are not drawn to scale unless otherwise noted.

[0031] Additionally, the order of steps depicted in these figures is provided for illustrative purposes only and is not meant to limit the present disclosure, which may be applied to the same steps performed in different orders.

[0032] Figure 1 schematically illustrates an exemplary embodiment of a wireless communication system 10. As illustrated in Figure 1, the wireless communication system 10 comprises one or more terminals 20 (also known as user equipment) and a radio access network RAN ​​11. The RAN 11 comprises one or more base stations 30. The terminals 20 are adapted to exchange data with the base stations 30 of the RAN 11 via wireless links established with the base stations 30. The RAN 11 is adapted to exchange data with a core network CN 12 to forward data received from the terminals 20 to the CN 12 and to receive data from the CN 12 to be forwarded to the terminals 20.

[0033] 2 schematically illustrates an exemplary embodiment of terminal 20. In this exemplary embodiment, terminal 20 includes processing circuitry 21. For example, processing circuitry 21 includes one or more processors and one or more memories. The one or more processors may include, for example, a central processing unit (CPU), a digital signal processor (DSP), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), etc. The one or more memories may include any type of computer-readable volatile and non-volatile memory (such as a magnetic hard disk, a solid-state disk, an optical disk, an electronic memory, etc.). The one or more memories may store a computer program product in the form of a set of program code instructions that are executed by the one or more processors to perform all or a portion of the steps of wireless communication method 50.

[0034] The terminal 20 also comprises a radio communication unit 22 coupled to the processing circuitry 21, enabling the terminal 20 to exchange data in the form of radio frequency signals over a radio link with the RAN 11. The radio communication unit 22 includes, for example, radio frequency circuitry comprising components that would be known to those skilled in the art (antennas, amplifiers, local oscillators, mixers, analog and / or digital filters, etc.).

[0035] In other words, the processing circuit 21 and the wireless communication unit 22 of the terminal 20 form a set of means constituted by software (a specific computer program product) and / or hardware (CPU, DSP, FPGA, ASIC, discrete electronic components, radio frequency circuits, etc.) for performing all or part of the steps of the wireless communication method 50 described below. Of course, the terminal 20 may optionally comprise other components not shown in the figures or described in detail herein.

[0036] 3 schematically illustrates an exemplary embodiment of a base station 30. In this exemplary embodiment, the base station 30 includes a processing circuit 31. For example, the processing circuit 31 includes one or more processors and one or more memories. The one or more processors may include, for example, a CPU, a DSP, an FPGA, an ASIC, etc. The one or more memories may include any type of computer-readable volatile and non-volatile memory (such as a magnetic hard disk, a solid-state disk, an optical disk, an electronic memory, etc.). The one or more memories may store a computer program product in the form of a set of program code instructions that are executed by the one or more processors to perform all or a portion of the steps of the wireless communication method 60.

[0037] The base station 30 also comprises a wireless communication unit 32 coupled to the processing circuitry 31, enabling the base station 30 to exchange data in the form of radio frequency signals over a wireless link with the terminal 20. The wireless communication unit 32 includes, for example, radio frequency circuitry comprising components that would be known to those skilled in the art.

[0038] In other words, the processing circuit 31 and the wireless communication unit 32 of the base station 30 form a set of means configured by software (a specific computer program product) and / or hardware (CPU, DSP, FPGA, ASIC, discrete electronic components, radio frequency circuits, etc.) for performing all or part of the steps of the wireless communication method 60 described below. Of course, the base station 30 may optionally comprise other components not shown in the figures or described in detail herein. In particular, the base station 30 may include a communication unit for exchanging data with the CN 12.

[0039] The wireless communication units 22, 32 of the terminal 20 and the base station 30, respectively, implement one or more wireless communication protocols, e.g., Wi-Fi and / or Bluetooth wireless communication protocols, and / or cellular communication protocols such as 3G, 4G, 5G, etc. Depending on the embodiment, the wireless communication system 10 may correspond to a wireless local area network, WLAN, or a wireless wide area network, WWAN, etc. In some embodiments, the wireless communication system 10 relies at least in part on orthogonal frequency division multiplexing (OFDM) and / or discrete Fourier transform spread OFDM, DFT-s-OFDM.

[0040] As described above, in wireless communication between a transmitter (e.g., a base station 30) and a receiver (e.g., a terminal 20), phase noise is introduced both at the transmitter side (e.g., when one or more local oscillators frequency-convert a baseband signal from a baseband frequency to a carrier frequency) and at the receiver side (e.g., when one or more local oscillators frequency-convert a radio frequency signal from a carrier frequency to a baseband frequency). The characteristics of the introduced phase noise depend on the respective characteristics of each local oscillator involved, and therefore, for the same base station 30, the phase noise characteristics may change when communicating with different terminals 20 because each terminal 20 uses its own local oscillator with its own characteristics. Also, the amount of phase noise introduced at the terminal 20 is usually more important than the amount of phase noise introduced at the base station 30 because the base station 30 is usually equipped with a more efficient local oscillator.

[0041] In the following, the case of phase noise mitigation in the downlink, DL, wireless communication, i.e., from the base station 30 to the terminal 20, is considered non-limitingly. However, the present disclosure may also be applied to phase noise mitigation in the uplink, UL, wireless communication, i.e., from the terminal 20 to the base station 30.

[0042] In the terminal 20, the baseband signal obtained after frequency conversion of the received radio frequency signal can be represented in the time domain as a continuous signal / sample.

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[0043] For example, phase noise can be expressed by its second-order statistics as follows:

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[0044] FIG. 4 illustrates the phase noise simulation model for a base station 30 (referred to as "BS") and a terminal 20 (referred to as "UE") at different carrier frequencies by considering the phase noise simulation model defined by the 3rd Generation Partnership Project (3GPP) in Technical Recommendation TR 38.803 V 14.3.0.

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[0045] Figure 5 illustrates in schematic form the main steps of an exemplary embodiment of a wireless communication method 50 implemented by terminal 20. Wireless communication method 50 of Figure 5 introduces supporting tools that enable phase noise mitigation and generally improving wireless communication performance between RAN 11 and terminal 20.

[0046] As shown in FIG. 5, a wireless communication method 50 includes: a step S50 of determining, by the processing circuit 21 of the terminal 20, a phase noise temporal coherence index representative of the temporal coherence of the phase noise affecting the baseband signal obtained from the radio frequency signal received by the wireless communication unit 22 of the terminal 20; a step S51 of transmitting, by the wireless communication unit 22 of the terminal 20, a phase noise time coherence indicator to the RAN 11 of the wireless communication system 10; Includes.

[0047] Thus, the terminal 20 evaluates the time coherence of the phase noise affecting the received baseband signal and transmits a phase noise time coherence indicator to the RAN 11. Since the statistical properties of the phase noise depend on the carrier frequency, the phase noise time coherence indicator is determined for a considered carrier frequency at which the terminal 20 will exchange data with a base station 30 of the RAN 11, by evaluating the phase noise time coherence at one or more frequencies related to the considered carrier frequency, e.g., directly at the considered carrier frequency and / or at one or more frequencies close to the considered carrier frequency and / or at a bounded frequency band including the considered carrier frequency.

[0048] The phase noise temporal coherence may be evaluated by any method known to those skilled in the art. For example, the statistical characteristics of the phase noise introduced by the terminal 20 may be determined in advance (e.g., during the manufacturing process of the terminal 20), for example, by calibration. Such calibration data may be stored in a non-volatile memory of the terminal 20 and may correspond to or be used to determine a phase noise temporal coherence index. In some cases, such calibration data may be available for multiple different possible frequencies or bounded frequency bands to enable the terminal 20 to determine a phase noise temporal coherence index for different possible carrier frequencies. In such cases, the terminal 20 may use calibration data associated with the considered carrier frequency to determine the associated phase noise temporal coherence index. In some cases, the terminal 20 may determine multiple phase noise temporal coherence indexes to be transmitted to the RAN 11, associated with different possible carrier frequencies at which the terminal 20 may exchange data with the RAN 11. Such calibration data may be used in particular when it can be assumed that the phase noise experienced by the terminal 20 is mainly introduced by components (e.g., local oscillators) of the terminal 20 itself. Indeed, in such cases, the phase noise introduced by the base station 30 may be considered negligible, and a phase noise time coherence indicator determined based on such calibration data may be used to exchange data with any base station 30 of the RAN 11.

[0049] In some embodiments, the phase noise experienced by the terminal 20 may be estimated by using radio frequency signals received from the RAN 11, for example, based on pilot signals inserted by the RAN 11 in radio frequency signals transmitted in the DL. The time coherence of the phase noise for a given carrier frequency may be evaluated based on multiple successive phase noise estimations performed by the terminal 20 based on radio frequency signals received from the RAN 11 at one or more frequencies related to the considered carrier frequency (e.g., directly on the considered carrier frequency and / or at one or more frequencies close to the considered carrier frequency and / or at a bounded frequency band including the considered carrier frequency). If the phase noise experienced by the terminal 20 can be considered to be mainly introduced by the terminal 20 itself, it is possible to use radio frequency signals received from any base station 30 of the RAN 11 (over frequencies related to the considered carrier frequency). Then, if the phase noise introduced by the base station 30 is not negligible, such that the statistical characteristics of the phase noise experienced by the terminal 20 depend on the particular base station with which the terminal 20 is communicating, it is better to rely on radio frequency signals transmitted only by the particular base station 30 with which the terminal 20 exchanges data. In other words, if the phase noise introduced by the base station 30 is not negligible, the time coherence of the phase noise is evaluated for a particular pair including the terminal 20 and the base station 30 of the RAN 11 with which the terminal 20 will exchange data on the DL.

[0050] As mentioned above, the phase noise temporal coherence index represents the temporal coherence of the phase noise experienced by terminal 20 for the considered carrier frequency. Depending on the embodiment, the phase noise temporal coherence index may correspond, for example, to an estimated phase noise autocorrelation function (or information derived therefrom, such as its initial slope, lower bound, its mean value, the period before it falls below a predefined threshold, its value for a predefined delay, etc.), a binary value indicating whether the phase noise is fast or slow varying, etc.

[0051] For example, in some embodiments, determining the phase noise time coherence index for a given carrier frequency may include estimating a phase noise autocorrelation function based on signals received at one or more frequencies related to the carrier frequency from at least one base station 30 of the RAN 11 (e.g., only base stations 30 with which the terminal 20 should exchange data, if the phase noise introduced by the base station 30 is not negligible compared to the phase noise introduced by the terminal 20 itself). Generally speaking, estimating the phase noise autocorrelation function may use any pilot-aided (i.e., relying on a pilot signal that may be different from the pilot signal inserted for short-term phase noise estimation) and / or blind (i.e., not relying on a pilot signal) estimation method known to those skilled in the art, with the selection of a particular estimation method corresponding to specific, but non-limiting, embodiments of the present disclosure.

[0052] When the phase noise autocorrelation function is estimated, the phase noise time coherence index may correspond to the estimated phase noise autocorrelation function (which is then transmitted to the RAN 11) or may be determined based on the estimated phase noise autocorrelation function. In the latter case, the phase noise time coherence index may represent, for example, an initial slope of the estimated phase noise autocorrelation function. "Initial slope" means

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[0053] Phase noise coherence

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[0054] According to another non-limiting example, the phase noise temporal coherence index may be, for example,

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[0055] The one or more phase noise time coherence indicators determined by the terminal 20 are then transmitted to the RAN 11 during step S61. For example, the one or more phase noise time coherence indicators can be transmitted directly to a base station 30 with which the terminal 20 will exchange data on the DL, or indirectly, i.e., via another base station 30 of the RAN 11. Alternatively, or in a combination thereof, the one or more phase noise time coherence indicators can be stored in a database that can be retrieved by any base station 30 with which they wish to exchange data with the terminal 20, etc.

[0056] Figure 6 schematically illustrates the main steps of an exemplary embodiment of a wireless communication method 60 implemented by a base station 30 of the RAN 11. The wireless communication method 60 of Figure 6 illustrates a non-limiting example of how a phase noise time coherence measure of a terminal 20 may be used at a base station 30 to improve phase noise mitigation at the terminal 20, thereby improving wireless communication performance between the base station 30 and the terminal 20.

[0057] As illustrated in FIG. 6, the wireless communication method 60 includes a step S60 of determining one or more phase noise temporal coherence measures for the terminal 20.

[0058] For example, determining one or more phase noise time coherence indicators by the base station 30 for the terminal 20 may consist of receiving (directly or indirectly) the phase noise time coherence indicators from the terminal 20 (transmitted by the terminal 20 during step S51 of the wireless communication method 50 of FIG. 5 ). In such a case, the phase noise time coherence indicators are received by the wireless communication unit 32 of the base station 30 during step S60.

[0059] In another example, determining one or more phase noise time coherence indicators by the base station 30 for the terminal 20 may consist of retrieving the phase noise time coherence indicators from a database in which they have been previously stored by the RAN 11.

[0060] In yet another example, one or more phase noise time coherence indicators for terminal 20 may be estimated by base station 30 based on UL (pilot and / or data) signals transmitted by terminal 20 to RAN 11.

[0061] 6, the wireless communication method 60 includes a step S61 of determining, by the processing circuitry 31 of the base station 30, the time spacing of pilot signals transmitted by the base station 30 to the terminal 20 in DL. The time spacing of the pilot signals is determined based on a phase noise time coherence index determined for the terminal 20 of a carrier frequency with which the base station 30 will exchange data with the terminal 20. The pilot signals should be used by the terminal 20 to estimate the phase noise affecting the received signal, and step S61 aims to adjust the time spacing between the pilot signals to the phase noise time coherence of the phase noise experienced in DL.

[0062] 6, the wireless communication method 60 then includes a step S62 of transmitting a signal by the wireless communication unit 32 of the base station 30 to the terminal 20. The transmitted signal includes a data signal and a phase noise estimation pilot signal. The phase noise estimation pilot signal is spaced in time based on the time interval determined for the terminal 20.

[0063] For example, the time interval determined during step S61 may directly correspond to the time interval used between phase noise estimation pilot signals, which are, for example, inserted periodically into the signal transmitted during step S62. In another example, the time interval determined during step S61 may correspond to the maximum time interval allowed for separating the phase noise estimation pilot signals in time, which are, for example, inserted such that the time interval between two consecutive phase noise estimation pilot signals is equal to or less than the time interval determined during step S62.

[0064] It is emphasized that the time interval determined during step S61 depends on the carrier frequency at which the signal is transmitted to the terminal 20 during step S62 and on the terminal 20 itself, since the phase noise autocorrelation function may differ for each terminal 20. Thus, the base station 30 may end up using different time intervals for the phase noise estimation pilot signal when exchanging data with different terminals 20 at the same carrier frequency.

[0065] During step S61, the time interval is adjusted to the phase noise time coherence experienced by terminal 20 in DL so that the base station 30 will generally transmit the phase noise estimation pilot signal more frequently when the phase noise coherence time is short (i.e., the phase noise is expected to vary rapidly) than when the phase noise coherence time is large (i.e., the phase noise is expected to vary slowly). Thus, during step S61, the base station 30 will typically select a smaller time interval in response to a received phase noise time coherence indicator indicating a short coherence time than in response to a received phase noise time coherence indicator indicating a large coherence time. For example, a lookup table (LUT) stored in the non-volatile memory of the base station 30 may be pre-established, the LUT including different time intervals associated with respective different phase noise time coherence indicators. The time interval to be used may then be determined for the considered terminal 20 by searching the LUT for the time interval associated with the phase noise time coherence indicator determined for (e.g., received from) the terminal 20. It is also possible to store several such LUTs, each associated with a different frequency or frequency band, and step S61 uses the LUT associated with the carrier frequency to be used during step S62 to transmit the signal to the terminal 20 (i.e. determined for the frequency closest to the carrier frequency considered or determined for the frequency band including the carrier frequency considered).

[0066] In some embodiments, the time interval is determined at the base station 30 by using a predetermined performance function that represents the phase noise estimation performance at the terminal 20 as a function of the time interval between the phase noise pilot signals. Such a performance function may, for example, assume that a particular phase noise estimation method is used at the terminal 20. Any phase noise estimation method that uses phase noise estimation pilot signals may be considered, and the selection of a particular method corresponds to a specific, but non-limiting, embodiment of the present disclosure. Finally, without limitation, the performance function assumes that a finite impulse response, FIR, minimum mean square error, or MMSE phase noise estimation is performed at the terminal 20 (e.g., a Wiener filter-based phase noise estimation).

[0067] We now present non-limiting examples of performance functions that can be used to determine the time interval used during step S61. For this purpose, the time interval

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[0068] According to the FIR-MMSE format, the goal is to

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[0069] These quantities can then be estimated for the terminal 20 as the phase noise autocorrelation function

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[0070] Assuming such FIR-MMSE filter-based phase noise estimation in the terminal 20, the performance of the short-term phase noise estimation depends on the pilot signal (i.e., the time interval used)

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[0071] In the base station 30, the phase noise autocorrelation function of the terminal 20 is

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[0072] In some embodiments, the base station 30 calculates the phase noise autocorrelation function of the terminal 20.

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[0073] However, minimizing the above equation in this way is difficult over the time interval

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[0074] In such cases, the time interval that minimizes the overhead represented by the insertion of the phase noise estimation pilot signal, i.e., maximizes the time interval

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[0075] In some embodiments, the minimum time interval allowed to separate the phase noise estimation pilot signals is

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[0076] FIG. 7 shows the performance functions determined for different carrier frequencies by considering the 3GPP phase noise simulation model.

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[0077] Next, the terminal 20 receives the signal transmitted by the base station 30 during step S62. The pilot signal is used by the terminal 20 to estimate the phase noise affecting the received data signal, and the estimated phase noise is compensated for on the received data signal to improve wireless communication performance. By adjusting the time interval of the pilot signal to the time coherence of the phase noise experienced by the terminal 20, a trade-off between phase noise mitigation performance and the overhead represented by the phase noise estimation pilot signal can be achieved, thereby improving wireless communication performance.

[0078] It is emphasized that the present disclosure is not limited to the exemplary embodiments described above, and variations of the exemplary embodiments described above are also within the scope of the present disclosure.

[0079] For example, in the example in which the base station 30 uses a performance function to determine the time interval of the phase noise estimation pilot signal, it has been mainly considered that an FIR-MMSE filter-based phase noise estimation is performed in the terminal 20. Of course, other (short-term) phase noise estimation methods may be considered in the terminal 20, and the corresponding performance functions may be determined in a similar manner by those skilled in the art. For example, least squares, LS, or linear regression phase noise estimation may also be performed in the terminal 20.

[0080] Also, this disclosure is primarily made with consideration given to the case of phase noise mitigation in DL from base station 30 to terminal 20. However, this disclosure may also be applied to phase noise mitigation in UL. In such a case, wireless communication method 50 of FIG. 5 is performed by base station 30, and wireless communication method 60 of FIG. 6 is performed by terminal 20.

Claims

1. A wireless communication method (50) implemented by a terminal (20) of a wireless communication system (10) for exchanging data with a radio access network (11) of said wireless communication system, said method comprising: - determining (S50) a phase noise temporal coherence index representative of the temporal coherence of the phase noise affecting the baseband signal obtained from the radio frequency signal received by said terminal; - transmitting (S51) said phase noise temporal coherence indicator to said radio access network of said wireless communication system; A method (50) comprising:

2. 2. The method (50) of claim 1, wherein determining the phase noise temporal coherence index comprises estimating a phase noise autocorrelation function of the phase noise based on a signal received from at least one base station (30) of the radio access network (11), and the phase noise temporal coherence index corresponds to the estimated phase noise autocorrelation function or is determined based on the estimated phase noise autocorrelation function.

3. The phase noise temporal coherence index is defined as follows: the initial gradient of the estimated phase noise autocorrelation function, a binary value indicating the rate of change of said phase noise, the period before the phase noise coherence falls below a threshold, the value of the estimated phase noise autocorrelation function for a given delay, a lower bound on the trend of the estimated phase noise autocorrelation function, the mean value of the estimated phase noise autocorrelation function The method (50) of claim 2, wherein the at least one of

4. 4. The method (50) of claim 1, wherein determining the phase noise temporal coherence index comprises retrieving calibration data stored in a non-volatile memory of the terminal (20), and the phase noise temporal coherence index corresponds to or is determined based on the calibration data.

5. 5. A computer program product comprising instructions that, when executed by at least one processor, configure the at least one processor to perform the method (50) of any one of claims 1 to 4.

6. A terminal (20) of a wireless communication system (10), the terminal (20) comprising a processing circuit (21) and a wireless communication unit (22) configured to perform the wireless communication method (50) according to any one of claims 1 to 4.

7. A wireless communication method (60) implemented by a base station (30) of a wireless communication system (10) for exchanging data with a terminal (20) of said wireless communication system, said method comprising: - determining (S60) a phase noise temporal coherence index of said terminal, which is representative of the temporal coherence of the phase noise affecting the baseband signal obtained from the radio frequency signal received by said terminal; - determining for said terminal the time interval of pilot signals transmitted by said base station to said terminal based on said determined phase noise temporal coherence index (S61); - transmitting a signal to said terminal (S62), the signals include data signals and pilot signals, the pilot signals being spaced apart in time based on the time interval determined for the terminal; Method (60).

8. Determining the phase noise temporal coherence index of the terminal comprises: receiving from the terminal the phase noise temporal coherence indicator transmitted according to any one of claims 1 to 4; - estimating the phase noise temporal coherence index of the terminal based on signals received from the terminal; - retrieving said phase noise temporal coherence index of said terminal from a database; The method (60) of claim 7, comprising one of:

9. 9. The method (60) of claim 7 or 8, wherein the time interval is adjusted to the temporal coherence of the phase noise of the terminal by selecting a lower time interval in response to the determined phase noise temporal coherence indicator indicating a shorter coherence time than in response to the determined phase noise temporal coherence indicator indicating a larger coherence time.

10. 10. The method (60) of any one of claims 7 to 9, wherein the time interval is determined by using a performance function that represents phase noise estimation performance at the terminal as a function of the time interval between the pilot signals.

11. 11. The method (60) of claim 10, wherein the determination of the time interval is made by determining a maximum time interval for which the phase noise estimation performance meets a minimum phase noise performance requirement.

12. 12. The method (60) of claim 10 or 11, wherein the determination of the time spacing is made by considering a minimum time spacing allowed to separate the pilot signals and / or a maximum time spacing allowed to separate the pilot signals.

13. 13. The method (60) of any one of claims 10 to 12, wherein the performance function represents a phase noise estimation performance when performing a finite impulse response, FIR, minimum mean square error, MMSE phase noise estimation at the terminal.

14. 9. The method (60) of claim 7 or 8, wherein a look-up table LUT is stored in a non-volatile memory of the base station, the LUT including different time intervals associated with respective different phase noise temporal coherence indexes, and determining the time interval for the terminal includes retrieving from the LUT the time interval associated with the phase noise temporal coherence index determined for the terminal.

15. 15. A computer program product comprising instructions that, when executed by at least one processor, configure the at least one processor to perform the method (60) of any one of claims 7 to 14.

16. A base station (30) of a wireless communication system (10), the base station comprising a processing circuit (31) and a wireless communication unit (32) configured to perform a wireless communication method (60) according to any one of claims 7 to 14.

17. A wireless communication system (10) comprising at least one terminal (20) according to claim 6 and at least one base station (30) according to claim 16.

18. A wireless communication system (10) according to claim 17, which uses Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing DFT-s-OFDM.

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