A large frequency offset estimation method for an OFDM communication system using reference signals

Abstract

The present disclosure describes a method for carrier frequency offset (CFO) estimation of a physical channel in a mobile communication system. The method includes the following steps: performing channel estimation on a received signal on a physical channel based on a plurality of orthogonal frequency division multiplexing (OFDM) symbols in one or more reference signals (RS). The method includes: determining a plurality of phase rotation values Φ and corresponding time differences s between different OFDM symbols in one or more RS within a base phase rotation range including + / −π to obtain a first CFO estimation candidate value f0. Expanding the base phase rotation range to provide an extended phase rotation range greater than + / −π to obtain additional CFO estimation candidate values f1, f2... f n .

Description

Technical Field

[0001] The present invention relates to a method for large frequency offset estimation in a mobile wireless communication system using a reference signal (RS), particularly for an orthogonal frequency division multiplexing (OFDM) communication system, such as, but not limited to, a fifth-generation (5G) new radio (NR) communication system. Background Art

[0002] In a 5G NR communication system, a high carrier frequency orthogonal frequency division multiplexing (OFDM) system is sensitive to frequency errors caused by the following reasons: (i) high Doppler frequency shift in the communication system, such as those that may be encountered in a high-speed environment, e.g., a high-speed train or a vehicle-to-everything (V2X) sidelink communication system; and / or (ii) frequency mismatch between the local oscillators of the communication device transmitter and receiver. This frequency mismatch is labeled as carrier frequency offset (CFO). Since demodulation highly depends on signal phase information, the signal phase rotation caused by CFO reduces the accuracy of demodulation. CFO also causes inter-carrier interference (ICI), degrading the performance of the OFDM system. To improve the performance of the OFDM system, CFO should be accurately estimated and compensated. However, the CFO estimation range is limited by the RS structure in the NR communication system, such as the separation interval of the RS in the time domain.

[0003] In a 5G NR communication system, the four main RSs are Demodulation Reference Signal (DMRS), Phase-Tracking RS (PTRS), Sounding RS (SRS), and Channel State Information RS (CSI-RS), etc.

[0004] CN11146447A1 discloses a frequency offset calculation method for a New Radio (NR) Physical Uplink Shared Channel (PUSCH). The frequency offset calculation method includes a first step: receiving multiple segments of reference signals and respectively sampling the received multiple segments of reference signals. The method includes: calculating the phase differences between the multiple segments of reference signals according to the distribution of the sampled multiple segments of reference signals in the corresponding time domain to obtain a plurality of phase difference values. The method further includes: processing the signals in the corresponding frequency domain according to the obtained phase difference values to obtain a first frequency offset group, where the first frequency offset group includes a plurality of frequency offset values. Then, the first frequency offset group is processed through a preset first value-taking rule algorithm to obtain a first frequency offset value. This method has many drawbacks. For example, this method cannot distinguish whether the phase difference exceeds the range, thus limiting the measurement range. This method also requires calculating and combining the first and second groups of frequency offsets, which is computationally complex. This method is only applicable to NR PUSCH.

[0005] CN112398764B discloses a frequency offset estimation method for the combination of Demodulation Reference Signal (DMRS) and Phase Tracking Reference Signal (PTRS). The method includes: performing channel estimation on the resource units carrying PTRS and DMRS corresponding to the subcarriers where PTRS is located to obtain the channel estimation values of each reference signal. The method includes: calculating the correlation values between adjacent reference signal symbols according to the channel estimation values of each reference signal, and then obtaining the distance between adjacent reference signal symbols, where the distance between adjacent reference signal symbols is the number of OFDM symbols separated by adjacent reference signal symbols. The method estimates the frequency offset based on the correlation values between all adjacent reference signal symbols and the distance between adjacent reference signal symbols to obtain a frequency offset estimation result. This method has some drawbacks. For example, this method is only applicable to DMRS and PTRS, which makes it difficult to use in other channels. Not all DMRS subcarriers are used, only those on the PTRS subcarriers are used, so the signal-to-noise ratio (SNR) is lower than when using all DMRS subcarriers. In addition, due to the lack of a noise suppression method, the noise in the channel response estimation will be severe. This method cannot distinguish whether the phase difference exceeds the range, which limits the measurement range.

[0006] There is a need for a method that provides a more accurate Carrier Frequency Offset (CFO) estimate for radio devices in a mobile communication system, especially for 5G NR radio devices.

[0007] Objective of the Invention

[0008] An object of the present invention is to alleviate or avoid, to a certain extent, one or more problems related to the known CFO estimation methods in a 5G NR communication system.

[0009] The above object is achieved by the combination of the features of the main claim; the dependent claims disclose further advantageous embodiments of the present invention.

[0010] Another object of the present invention is to provide a more accurate CFO estimate for radio devices in a mobile communication system, especially 5G NR radio devices.

[0011] Those skilled in the art will derive other objects of the present invention from the following description. Therefore, the above statement of objects is not exhaustive and is only used to illustrate some of the multiple objects of the present invention. Summary of the Invention

[0012] In a first main aspect, the present invention provides a method for estimating the carrier frequency offset (CFO) of a physical channel in a mobile communication system. The method includes the following steps: performing channel estimation on the received signal on the physical channel based on a plurality of orthogonal frequency division multiplexing (OFDM) symbols in one or more reference signals (RS). The method includes: determining a plurality of phase rotation values Φ and corresponding time differences s between different OFDM symbols in the one or more RS within a basic phase rotation range including + / -π to obtain a first CFO estimation candidate value f0. Extending the basic phase rotation range to provide an extended phase rotation range greater than + / -π, and obtaining additional CFO estimation candidate values f1, f2... f within the extended phase rotation range n 。

[0013] Preferably, the additional CFO estimation candidate values f1, f2... f within the extended phase rotation range n are determined, selected or calculated according to the correlation result between the received RS after CFO compensation and the ideal RS.

[0014] Preferably, the CFO estimation candidate value is obtained from the slope of a univariate linear regression function that describes the relationship between the phase rotation and time difference between different OFDM signals.

[0015] In a second main aspect, the present invention provides a method for estimating the carrier frequency offset (CFO) of a physical channel in a mobile communication system, the method including: performing channel estimation on the received signal on the physical channel based on a plurality of orthogonal frequency division multiplexing (OFDM) symbols in one or more reference signals (RS), and determining the phase rotation Φ and corresponding time difference s between different OFDM symbols in one or more RS within an extended phase rotation range greater than + / -π to obtain a plurality of CFO estimation candidate values f0, f1, f2... f within the extended phase rotation range n 。

[0016] In a third main aspect, the present invention provides a radio device in a mobile communication system, the radio device comprising a memory storing machine-readable instructions and a processor for executing the machine-readable instructions, such that when the processor executes the machine-readable instructions, it configures the radio device to implement the method of the first main aspect or the second main aspect of the present invention.

[0017] In a fourth main aspect, the present invention provides a non-transitory computer-readable medium storing machine-readable instructions, wherein when the machine-readable instructions are executed by a processor, they configure the processor to implement the method of the first main aspect or the second main aspect of the present invention.

[0018] The present invention content does not necessarily disclose all features necessary to define the present invention; the present invention may exist in a sub-combination of the disclosed features.

[0019] The features of the present invention have been broadly outlined above so that the following detailed description of the present invention can be better understood. Other features and advantages of the present invention will be described below, which form the subject matter of the claims of the present invention. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be easily used as a basis for modifying or designing other structures to achieve the same purpose of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and further features of the present invention will be apparent from the following description of the preferred embodiments, which are provided by way of example only in conjunction with the accompanying drawings, wherein:

[0021] Figure 1 is a block schematic diagram of an improved radio device or network node of the present invention;

[0022] Figure 2 is a flowchart of a method of the present invention;

[0023] Figure 3 shows the resource mapping of resource blocks (RB) in an OFDM system, illustrating the limitation of the CFO estimation range;

[0024] Figure 4 shows the sounding reference signal (SRS) resource mapping of an OFDM system, indicating that the method of the present invention is applicable to SRS;

[0025] Figure 5 shows the extension of the CFO estimation range of the present invention;

[0026] Figure 6 shows the possible phase rotation values within the extended CFO estimation range;

[0027] Figure 7Shows Figure 2 the stages of some steps of the method;

[0028] Figure 8 Shows Figure 2 the stage of one of the steps of the method;

[0029] Figure 9 Shows the linear regression method that forms Figure 2 part of the method. Detailed implementation manner

[0030] The following description only describes the preferred embodiments by way of example and does not limit the combination of essential features for implementing the present invention.

[0031] The phrase "one embodiment" or "an embodiment" mentioned in this specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present invention. The phrase "in one embodiment" that appears throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. In addition, the various features described may be shown by some embodiments but not by other embodiments. Similarly, various requirements are described, and these requirements may be the requirements of some embodiments but not of other embodiments.

[0032] It should be understood that the elements shown in the figures can be implemented in various forms of hardware, software or a combination thereof. These elements can be implemented in a combination of hardware and software on one or more appropriately programmed general-purpose devices, which can include a processor, a memory, and an input / output interface.

[0033] This specification illustrates the principles of the present invention. Therefore, it should be understood that those skilled in the art will be able to design various arrangements that, although not explicitly described or shown herein, embody the principles of the present invention and are included within its spirit and scope.

[0034] In addition, the principles, aspects and embodiments of the present invention and their specific examples are described herein, aiming to cover their structural and functional equivalents. In addition, such equivalents also include currently known equivalents and equivalents developed in the future, that is, any developed element that performs the same function, regardless of its structure.

[0035] Therefore, for example, those skilled in the art will understand that the block diagrams presented here represent the conceptual diagrams of systems and devices that embody the principles of the present invention.

[0036] The functions of the various elements shown in the figures can be provided by using dedicated hardware as well as hardware capable of executing software in conjunction with appropriate software. When provided by a processor, these functions can be provided by a single dedicated processor, a single shared processor, or multiple individual processors, some of which may be shared. In addition, the explicit use of the term "processor" or "controller" should not be construed to refer only to hardware capable of executing software and can implicitly include, but is not limited to, digital signal processor ("DSP") hardware, read-only memory ("ROM") for storing software, random access memory ("RAM"), and non-volatile memory.

[0037] In a claim, any element expressed as a means for performing a particular function is intended to cover any means for performing that function, including, for example, a) a combination of circuit elements that perform that function or b) any form of software, and thus, including firmware, microcode, etc., in combination with appropriate circuitry for executing the software to perform the function. The invention defined by these claims resides in the functions provided by the various recited means being combined and brought together in the manner claimed. It is thus contemplated that any means that provides these functions is equivalent to the means shown herein.

[0038] The mention of 5G radio equipment in the following description does not exclude the application of the methods described herein to radio equipment of compatible mobile communication systems.

[0039] 5G NR is a new mobile communication standard proposed by the 3rd Generation Partnership Project (3GPP), which makes significant improvements based on the 4G LTE-advanced (LTE-A) standard. Its main focuses are enhanced mobile broadband, ultra-reliable and low-latency communication, and massive machine-type communication. To achieve these goals, 3GPP has introduced a unified network architecture, adopted a new physical layer design, and supported new technologies such as extremely high carrier frequencies, large frequency bandwidths, and massive multiple-input multiple-output (MIMO) and beamforming. These significant modifications have increased the challenges of the synchronization process. In fact, very high defined carrier frequencies result in large CFO values, and usually, an accurate and expensive oscillator is required to adjust the transmitter and radio equipment to achieve interference-free communication. The interference sources are mainly related to the imperfections of the OFDM system, which is affected by the CFO, resulting in inter-carrier interference (ICI) and inter-symbol interference (ISI). Errors in the transmitter and radio equipment oscillators cause CFO, which is a linear phase on the time-domain samples and causes ICI on the subcarriers. The impact of the CFO increases over time because it is proportional to the discrete-time exponent. The CFO in OFDM is usually normalized by the subcarrier spacing and thus expressed as the ratio between the frequency error and the subcarrier spacing.

[0040] In addition, 3GPP has introduced a new high-dimensional phased array-based mechanism to establish a highly directional transmission link between the gNodeB and the user UE. This mechanism requires precise alignment of the transmitter and radio device beams, which is achieved through a set of operations called beam management. Beam management requires complex algorithms and advanced processing at the gNodeB and UE to perform various control tasks, including initial access and beam tracking, which increases the challenges of the synchronization process.

[0041] Compared with known methods for determining CFO estimation, the present invention relates to a method for CFO estimation for a mobile communication system, especially a 5G NR radio device, wherein the basic phase rotation range is extended to provide an extended phase rotation range greater than + / -π to obtain additional CFO estimation candidates, which will support a larger CFO estimation range and obtain a more accurate CFO estimation value.

[0042] Figure 1 An exemplary embodiment of an improved radio device apparatus 100 according to the concept of the present invention is shown. In the illustrated embodiment, the radio device apparatus 100 may include a communication device, such as a UE (represented by the Figure 1 dashed box in), which is communicatively connected to a gNodeB (base station (BS) 103) operating in a 5G NR communication system environment 115. However, the improved radio device apparatus 100 of the present invention is not limited to operating in an NR 5G communication system, but may include a radio device apparatus for a 4G cellular network or any suitable cellular network. In another embodiment, the radio device apparatus 100 may include a network sniffer device, which is communicatively connected to the gNodeB (BS) 103 or forms a part of the gNodeB (BS) 103.

[0043] The radio device apparatus 100 may include a plurality of functional blocks for performing its various functions. For example, the radio device apparatus 100 includes a receiver module 110, which provides received signal processing and is configured to provide a received signal and / or information extracted therefrom to a functional block module 120, which may include various data sinks, control elements, user interfaces, etc. Although the receiver module 110 is described as providing received signal processing, it should be understood that this functional block may be implemented as a transceiver that provides both transmit and receive signal processing. Regardless of the specific configuration of the receiver 110, the embodiment includes a signal detection module 130 arranged in association with the receiver module 110 to facilitate accurate processing and / or decoding of the received information and channel signals in accordance with the present invention. The information and channel signals may be received via the antenna module 105.

[0044] Although the signal detection module 130 is shown as being deployed as part of the receiver module 110 (e.g., as part of the radio device module control and logic circuitry), the deployment configuration is not limited to this according to the inventive concept. For example, the signal detection module 130 can be deployed as a functional block of the radio device 100, which is different from the receiver module 110 but connected to the receiver module 110. For example, the signal detection module 130 can be implemented using logic circuitry and / or executable code / machine-readable instructions stored in the memory 140 of the radio device 100 for execution by the processor 150 to perform the functions described herein. For example, the executable code / machine-readable instructions can be stored in one or more memories 140 (such as random access memory (RAM), read-only memory (ROM), flash memory, magnetic memory, optical memory, etc.), suitable for storing one or more instruction sets (such as application software, firmware, operating system, applets, etc.), data (such as configuration parameters, operating parameters and / or thresholds, collected data, processed data, etc.), etc. One or more memories 140 can include processor-readable memories for use by one or more processors 150, which are operable to execute code segments of the signal detection module 130 and / or utilize the data provided thereby to perform the functions of the detection module 130 described herein. Additionally or alternatively, the signal detection module 130 can include one or more dedicated processors (e.g., application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), graphics processing unit (GPU), etc.) to perform the functions of the signal detection module 130 as described herein.

[0045] In one embodiment of the invention, the signal detection module 130 performs a method for CFO estimation. The signal detection module 130 performs channel estimation on the received signal on the physical channel based on OFDM symbols in one or more RSs. The signal detection module 130 determines a plurality of phase rotation values and corresponding time differences between different OFDM symbols in one or more RSs within a base phase rotation range including + / -π to obtain a first CFO estimation candidate value. Then, the signal detection module 130 extends the base phase rotation range to provide an extended phase rotation range greater than + / -π to obtain additional CFO estimation candidate values within the extended phase rotation range. One of the first CFO estimation candidate value and the additional CFO estimation candidate values is used for the received signal processing of the radio device 100.

[0046] Although Figure 1 the radio device 100 is described for a UE, it can include any node in a mobile wireless communication system configured to implement the method of the present invention.

[0047] Figure 2Shows a preferred method 200 according to the present invention for determining CFO estimation candidates and subsequently determining a final CFO estimation candidate for received signal processing.

[0048] Reference Figure 2 , in a first step 205 of method 200, a signal detection module 130 performs channel estimation of a received signal based on a plurality of OFDM symbols in one or more RSs. The RSs can include any one or more of the following: Physical Downlink Shared Channel (PDSCH) DMRS and PTRS; Physical Downlink Control Channel (PDCCH) DMRS; Physical Broadcast Channel (PBCH) DMRS; CSI-RS; Physical Uplink Shared Channel (PUSCH) DMRS and PTRS; Physical Uplink Control Channel (PUCCH) format 1 / 2 / 3 / 4 DMRS; SRS; DMRS of Physical Sidelink Shared Channel (PSSCH); PTRS of PSSCH; DMRS of Physical Sidelink Control Channel (PSCCH); and DMRS of Physical Sidelink Broadcast Channel (PSBCH).

[0049] In some embodiments, the step 205 of performing channel estimation includes a least squares method based on a plurality of OFDM symbols in one or more RSs, but any other channel estimation method can also be employed. The least squares method can include:

[0050]

[0051] where k is the RS subcarrier index within the resources allocated to the received signal;

[0052] l n is the symbol index of the nth RS symbol, n = 0, 1, 2, 3, …, N - 1;

[0053] R(k, l n ) is the received signal on subcarrier k of symbol l n ;

[0054] P(k, l n ) is the ideal RS signal on subcarrier k of symbol l n , |P(k, l n )| = 1; and

[0055] P*(k, l n ) is the complex conjugate of P(k, l n ).

[0056] In the second step 210 of method 200, the signal detection module 130 determines a plurality of phase rotation values Φ and corresponding time differences s between different OFDM symbols in one or more RSs within a basic phase rotation range to obtain a first CFO estimation candidate value f0. The basic phase rotation range in an OFDM system includes + / -π.

[0057] Figure 3 It shows the basic phase rotation range Φ∈[-π,π] of the OFDM system. It can be seen that the CFO estimation range is inversely proportional to the time difference between two RSs. For example, based on the maximum CFO estimation range is twice that of and three times that of The phase rotation value represented as and the time difference represented as

[0058] are in one-to-one correspondence. Figure 4 Referring to and the gist of the method of the present invention is to perform channel estimation from different OFDM symbols in the frequency domain, from which the phase rotation value

[0059] In some embodiments, for step 210 of method 200, the plurality of phase rotation values and their corresponding time differences are determined by:

[0060]

[0061]

[0062] where k is the RS subcarrier index within the resources allocated to the received signal;

[0063] l n is the symbol index of the nth RS symbol, n = 0, 1, 2, 3,..., N-1;

[0064] is the channel estimation on subcarrier k of symbol l n ;

[0065] is the complex conjugate of;

[0066] Tl n is the start time of symbol l n ; and

[0067] The operation of arg f(x) provides the parameter x from the objective function f(x).

[0068] Determine multiple phase rotation values in the above manner and their corresponding time differences An unexpected benefit is that the signal-to-noise ratio SNR is improved by reducing noise.

[0069] It should be understood that any suitable method can be used to determine multiple phase rotation values and their corresponding time differences

[0070] Now refer to Figure 5 and 6 to illustrate and describe the next stage of Method 200 for expanding the CFO estimation range.

[0071] In Figure 5 , the central region 300 between the outwardly extending arrows 301, 302 includes the basic phase rotation range Φ ∈ [-π, π], which limits the CFO estimation range in the OFDM system. To estimate the CFO in a larger range, Method 200 expands the phase rotation range Φ to be greater than [-π, π]. In Figure 5 's example, the phase rotation range Φ is increased to [-3π, 3π], that is, increased by + / -2π, providing the extended phase rotation regions 303, 304, corresponding to the arrows 301, 302.

[0072] Given the original phase rotation value Φ ori 305, further phase rotation values Φ1, Φ2 306, 307 are obtained from the extended phase rotation regions 303, 304 respectively, where the first of the further phase rotation values Φ1, Φ2 306, 307, Φ1 306, is derived from Φ1 = Φ ori +2π, and the second of the further phase rotation values Φ1, Φ2 306, 307, Φ2 307, is derived from Φ2 = Φ ori -2π. This is shown in Figure 6 , where the inner arrow line 401 includes Φ ori , the middle inner arrow line 402 includes Φ1 = Φ ori +2π, and the outer arrow line 403 includes Φ2 = Φ ori -2π.

[0073] Refer to Figure 5 again, for the original phase rotation value Φ oriDetermine the first CFO estimation candidate value f0 308, determine the first additional CFO estimation candidate value f1 309 for the first additional phase rotation value Φ1 306, and determine the second additional CFO estimation candidate value f2 310 for the second additional phase rotation value Φ2 307. The first and additional phase rotation values Φ ori , Φ1, Φ2 correspond to Δf = f0, f1, f2.

[0074] In Figure 5 , where ΔT is the time difference between two RSs For example, if the time difference between two DMRS symbols is 0.25 ms, then in this case,

[0075] In Figure 5 's example, the CFO estimation range has been extended to three times the normal range.

[0076] Although it has been found that extending the basic phase rotation range Φ ∈ [-π, π] by + / - 2π is sufficient to achieve the objectives of the present invention, in a more general case, the basic phase rotation range Φ ∈ [-π, π] can be extended by + / - 2mπ to obtain additional CFO estimation candidate values f1, f2, f, f4... f within a larger extended phase rotation range n， corresponding to the phase rotation values Φ1, Φ2, Φ3, Φ4,... Φ n = [Φ ori + / - 2mπ], where m is a positive integer and m is greater than or equal to 1.

[0077] The subsequent steps 215, 220 of method 200 involve extending the CFO estimation range as described above and using the first and additional CFO estimation candidate values f0, f1, f2... f n ; to compensate the received signal, and then after the received signal has been compensated with the first and additional CFO estimation candidate values f0, f1, f2... f n compensation, determine the cross-correlation value between the ideal RS and the received RS, and then based on this correlation result, determine all phase rotation values within the extended range.

[0078] Steps 215, 220 of method 200 are shown more completely in Figure 7 . In Figure 7 's example and in the following description, the phase rotation range Φ is considered to have been extended to [-3π, 3π], and the reference DMRS is used as one or more RSs.

[0079] Steps 215, 220 of method 200 include Figure 7 the first stage 505 in ori, Φ1, Φ2 (Φ ori now denoted as Φ0) corresponding to the inter-carrier interference (ICI) for the first and two additional CFO estimation candidates Δf = f0, f1, f2 is compensated. This involves calculating using Δf and compensating it to the received DMRS.

[0080] In some embodiments, the first stage 505 is derived from:

[0081]

[0082]

[0083]

[0084] where

[0085] m is the subcarrier index within the allocated resources;

[0086] i is the CFO candidate index;

[0087] R is the frequency-domain sequence of the received RS; and

[0088] is the circular convolution operator.

[0089] The first stage 505 can be implemented using an ICI compensation filter with a small number of taps, performing convolution in the frequency domain to reduce ICI.

[0090] Steps 215, 220 of method 200 include Figure 7 the second stage 510 in, i.e., calculating the cross-correlation value between the ideal DMRS sequence and the received DMRS sequence compensated by the first stage 505. The cross-correlation value between the ideal DMRS sequence and the received DMRS sequence can be derived from the following:

[0091]

[0092] Steps 215, 220 of method 200 include Figure 7 the third stage 515 in, i.e., selecting the CFO estimation candidate with the optimal or maximum correlation result.

[0093] In some embodiments, the third stage 515 includes: comparing the compensated cross-correlation values (compensating the received DMRS signal using the first and additional CFO estimation candidates f0, f1, f2) using the following:

[0094]

[0095] where is the received RS sequence after frequency-domain compensation, Δf = f i ;

[0096] P * is the complex conjugate in the frequency domain of the ideal RS sequence, |P(k)| = 1; and

[0097] is the operation of finding the parameter x that gives the maximum value from the objective function f(x).

[0098] where C1 is the maximum cross-correlation value, then otherwise if C2 is the maximum C, then otherwise

[0099] Steps 215 and 220 of method 200 include Figure 7 the fourth stage 520 in i.e., based on the corrected phase rotation ref and the corresponding time difference s

[0100] In some embodiments, the fourth stage 520 may include: correcting or compensating the remaining signal phase rotation value by:

[0101]

[0102]

[0103]

[0104] where is the time difference corresponding to all phase rotations ; and

[0105] if A ≥ 0.

[0106] Compared with other methods, it is better to use an ICI compensation filter with a small number of taps for convolution in the frequency domain to compensate for the ICI caused by CFO, because in a 5G NR communication system, the input signal of the baseband unit (BBU) of the eNodeB includes resource elements (REs) in the frequency domain. Generally, more computational effort is required to convert back to the time domain. An alternative is to use a look-up table stored in memory to obtain values according to the candidate phase rotation values, and the length of can be smaller to reduce the computational complexity. A downsampling method can also be used to further reduce the computational complexity.

[0107] Although method 200 obtains more than one phase rotation value, only one phase rotation value can be selected to extend the CFO estimation range. Any remaining phase rotation values can be correspondingly corrected without performing convolution and correlation for each phase rotation value.

[0108] The next step 225 of method 200 involves determining a final CFO estimation candidate based on all phase rotation values from different RS OFDM symbols. Step 225 of method 200 is better illustrated by FIGS. Figure 8 and Figure 9 and involves calculating a final CFO value based on the updated phase rotation values and the corresponding time differences. Calculating the final CFO value.

[0109] In some embodiments, step 225 includes: using linear regression to obtain The slope of s with respect to. This involves a first stage 605 of sorting in ascending order and labeling it as s j , and the corresponding phase rotation values are labeled as as Figure 9 shown.

[0110] The second stage 610 includes: performing linear regression to obtain The slope of s with respect to:

[0111]

[0112] N is typically less than 10, so the computational complexity is relatively small compared to other methods and steps such as channel estimation steps.

[0113] The third stage 615 includes: calculating the final CFO estimation candidate:

[0114]

[0115] It should be understood that using the linear regression method in step 225 is preferred but not mandatory. Other methods can be employed to combine all phase rotation values within the extended range to obtain the final CFO estimation candidate from the following:

[0116]

[0117] In some embodiments, the final CFO estimation candidate is obtained from the following:

[0118]

[0119] where s ref is the time difference corresponding to the first extended phase rotation .

[0120] Method 200 uses the final CFO estimation candidate values to compensate the received signal in the radio device 100.

[0121] The present invention also provides a method for physical channel carrier frequency offset (CFO) estimation in a mobile communication system. The method includes: performing channel estimation on the received signal on the physical channel based on a plurality of orthogonal frequency division multiplexing (OFDM) symbols in one or more reference signals (RS); determining the phase rotation Φ and the corresponding time difference s between different OFDM symbols in one or more RS within an extended phase rotation range greater than + / -π to obtain a plurality of CFO estimation candidate values f0, f1, f2... f n 。

[0122] The present invention also provides a radio device having a processor and a memory storing machine-readable instructions, wherein when the machine-readable instructions are executed by the processor, they configure the radio device to implement the method of any one of the appended method claims.

[0123] The radio device may include a UE.

[0124] The radio device may include a mobile communication system network node, such as a BS or including a part of a BS.

[0125] The present invention also provides a non-transitory computer-readable medium storing machine-readable instructions, wherein when the machine-readable instructions are executed by the processor, they configure the processor to implement the method of any one of the appended method claims.

[0126] The above device may be implemented at least partially in software. Those skilled in the art will understand that the above device may be implemented at least partially using a general-purpose computer device or using a customized device.

[0127] Here, various aspects of the methods and apparatuses described herein can be implemented on any device including a communication system. The program aspects of the technology can be considered a "product" or "article of manufacture", typically in the form of executable code and / or associated data, carried or embodied on a machine-readable medium. "Storage" media include any or all of the memories of a mobile station, computer, processor, or similar device, or their associated modules, such as various semiconductor memories, tape drives, disk drives, etc., which can provide storage for software programming at any time. All or part of the software can sometimes be communicated via the Internet or various other telecommunications networks. For example, such communication can cause the software to be loaded from one computer or processor to another. Thus, another type of media that can carry software elements includes light waves, radio waves, and electromagnetic waves, such as used over a physical interface between local devices, via wired and optical landline networks, and via various air links. Physical elements that carry such waves, such as wired or wireless links, optical links, etc., can also be considered media that carry software. As used herein, unless restricted to tangible non-transitory "storage" media, terms such as computer or machine "readable medium" refer to any medium that participates in providing instructions to a processor for execution.

[0128] Although the invention has been illustrated and described in detail in the accompanying drawings and the foregoing description, it should be regarded as illustrative rather than restrictive. It should be understood that only exemplary embodiments have been shown and described and that the scope of the invention is in no way limited thereby. It is understood that any feature described herein can be used in any embodiment. The exemplary embodiments do not exclude each other or other embodiments not described herein. Thus, the invention also provides embodiments that include combinations of one or more of the above-described exemplary embodiments. Modifications and variations can be made to the invention without departing from the spirit and scope thereof, and thus, only the limitations as set forth in the appended claims should be imposed.

[0129] In the foregoing description of the appended claims and the invention, unless the context requires otherwise due to express language or necessary implication, the word "comprising" or variations such as "includes" or "including" are used in an inclusive sense, i.e., specifying the presence of the stated features, but not excluding the presence or addition of further features in various embodiments of the invention.

[0130] It should be understood that if any prior art publication is mentioned herein, such reference does not constitute an admission that the publication forms part of the common general knowledge in the art.

Claims

1. A method for estimating carrier frequency offset (CFO) of a physical channel in a mobile communication system, the method comprising: Performing channel estimation on a received signal on a physical channel based on a plurality of orthogonal frequency division multiplexing (OFDM) symbols in one or more reference signals (RS); Determining a plurality of phase rotation values Φ and corresponding time differences s between different OFDM symbols in the one or more RS within a base phase rotation range including + / -π to obtain a first CFO estimation candidate value f0; And Expand the base phase rotation range to provide an extended phase rotation range greater than + / -π, and obtain additional CFO estimation candidates f1, f2... f within the extended phase rotation range n ; Use the first and additional CFO estimation candidate values f0, f1, f2…f n Compensate the received signal; After compensating the received signal with the first and additional CFO estimation candidate values f0, f1, f2... f n the cross-correlation value between the ideal RS and the received RS is determined; And Based on the determined cross-correlation values, one of the first and additional CFO estimation candidates f0, f1, f2…f n is determined as the final CFO estimate.

2. The method according to claim 1, wherein the first CFO estimation candidate value f0 corresponds to a base phase rotation value Φ0 = Φ ori , where Φ ori is the original phase rotation value, and the additional CFO estimation candidate values f1, f2... f n in the extended phase rotation range respectively correspond to phase rotation values Φ1, Φ2,... Φ n = [Φ ori + / - 2mπ], where m is a positive integer.

3. The method according to claim 1, wherein the extended phase rotation range extends the base phase rotation range of + / -π to + / -2mπ, where m is greater than or equal to 1.

4. The method according to claim 1, wherein compensating the received signal is obtained by using the first and additional CFO estimation candidate values f0, f1, f2... f n as follows: Among them m is a subcarrier index within the allocated resources; i is an index of the CFO candidate value; R is the frequency domain sequence of the received RS; and is a circular convolution operator.

5. The method according to claim 4, wherein after compensating the received signal with the first and additional CFO estimation candidate values f0, f1, f2... f n the cross-correlation values are compared and obtained by the following means: and Among them is the received RS sequence after frequency domain compensation, Δf = f i ; P * is the complex conjugate of the ideal RS sequence in the frequency domain, |P(k)| = 1; and is an operation to find the parameter x that gives the maximum value from the objective function f(x); is the first extended phase rotation.

6. The method according to claim 1, wherein the method uses the final CFO estimation to compensate the received signal.

7. The method according to claim 6, wherein the method uses the final CFO estimation to compensate the received signal by using the final CFO estimation to correct the phase rotation Φ of other signals.

8. The method according to claim 7, wherein the final CFO estimation is obtained from: where s ref is the time difference corresponding to the first extended phase rotation .

9. The method according to claim 8, wherein the final CFO estimation compensates the phase rotation Φ of other signals by: Among them is the time difference corresponding to all phase rotations ; and If A ≥ 0.

10. The method according to claim 1, wherein the final CFO estimate is determined to include one of the first and additional CFO estimate candidates f0, f1, f2... f having the best or maximum cross-correlation value. n among them.

11. The method according to claim 1, wherein the final CFO estimation is determined according to the determined cross-correlation value by using linear regression to obtain the slope of the phase rotation Φ with respect to time s.

12. The method according to claim 11, wherein the slope is obtained by: where s j is the time difference corresponding to all phase rotations Φ j , j = 1, 2... N 13. The method according to claim 12, wherein the final CFO estimation is obtained from:

14. The method according to claim 1, wherein the least squares method using the plurality of OFDM symbols in one or more RS is used for channel estimation.

15. The method according to claim 14, wherein the step of using the least squares method for channel estimation includes: where k is the RS subcarrier index within the resources allocated to the received signal; l n is the symbol index of the n-th RS symbol, where n = 0, 1, 2, 3, …, N-1; R(k, l n ) is the received signal on sub - carrier k of symbol l n ; P(k, l n ) is the ideal RS signal on subcarrier k of symbol l n , and |P(k, l n )| = 1; And P*(k,l n ) is the complex conjugate of P(k,l n ).

16. The method according to claim 3, wherein The plurality of phase rotation values Φ and their corresponding time differences s are determined by: and where k is the RS subcarrier index within the resources allocated to the received signal; l n is the symbol index of the n-th RS symbol, where n = 0, 1, 2, 3, …, N - 1; is the channel estimation on subcarrier k of symbol l n ; is the complex conjugate of; Tl n is the start time of symbol l n ; and argf(x) is an operation that provides parameter x from the objective function f(x).

17. The method according to claim 1, wherein the one or more RS include any one of the following: Physical downlink shared channel (PDSCH) demodulation reference signal (DMRS) and phase tracking reference signal (PTRS); Physical downlink control channel (PDCCH) DMRS; Physical broadcast channel (PBCH) DMRS; Channel state information reference signal (CSI-RS); Physical uplink shared channel (PUSCH) DMRS and PTRS; Physical uplink control channel (PUCCH) format 1 / 2 / 3 / 4 DMRS; Sounding reference signal (SRS); DMRS of the Physical Sidelink Shared Channel (PSSCH); PTRS of the PSSCH; DMRS of the Physical Sidelink Control Channel (PSCCH); and DMRS of the Physical Sidelink Broadcast Channel (PSBCH).

18. A method for estimating the carrier frequency offset (CFO) of a physical channel in a mobile communication system, the method comprising: Performing channel estimation on a received signal on a physical channel based on a plurality of orthogonal frequency division multiplexing (OFDM) symbols in one or more reference signals (RS); And Determine a phase rotation Φ and a corresponding time difference s between different OFDM symbols in one or more RSs within an extended phase rotation range greater than + / -π to obtain a plurality of CFO estimation candidates f0, f1, f2... f within the extended phase rotation range n ; Compensate the received signal using the plurality of CFO estimation candidate values f0, f1, f2... f n Compensate the received signal; After compensating the received signal with the plurality of candidate CFO estimates f0, f1, f2... f n the cross-correlation value between the ideal RS and the received RS is determined; And Based on the determined cross-correlation values, one of the multiple CFO estimation candidates f0, f1, f2... f n is determined as the final CFO estimate.

19. A radio device in a mobile communication system, the radio device comprising: A memory storing machine-readable instructions; And A processor that executes the machine-readable instructions such that when the processor executes the machine-readable instructions, the radio device is configured to: Perform channel estimation on a received signal on a physical channel based on a plurality of orthogonal frequency division multiplexing (OFDM) symbols in one or more reference signals (RS); Determine a plurality of phase rotations Φ and corresponding time differences s between different OFDM symbols in one or more RS within a base phase rotation range including + / -π to obtain a first CFO estimation candidate value f0; And Expand the basic phase rotation range to provide an extended phase rotation range greater than + / -π, so as to obtain additional CFO estimation candidates f1, f2... f within the extended phase rotation range n ; Use the first and additional CFO estimation candidate values f0, f1, f2…f n Compensate the received signal; After compensating the received signal with the first and additional CFO estimation candidate values f0, f1, f2... f n the cross-correlation value between the ideal RS and the received RS is determined; And Based on the determined cross-correlation values, one of the first and additional CFO estimation candidates f0, f1, f2... f n is determined as the final CFO estimate.

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