Cross-subcarrier frequency offset estimation method and device suitable for OFDM (Orthogonal Frequency Division Multiplexing) system, medium and program product

Abstract

The invention provides a cross-subcarrier frequency offset estimation method and device suitable for an OFDM (Orthogonal Frequency Division Multiplexing) system, a medium and a program product, in the method, a mode of combining a time domain and a frequency domain is adopted, channel estimation is firstly carried out by pilot frequency data in the frequency domain, integral multiple carrier frequency offset is estimated through a search method, then part of pilot frequency data is converted to the time domain, and the time domain is converted to the frequency domain. And correlation is carried out on pilot frequency data in a time domain, and decimal carrier frequency offset is estimated. Therefore, by adopting a mode of combining the time domain and the frequency domain, the frequency offset estimation range can be effectively improved, (M + 0.9) fsc can be realized according to actual requirements, and M is integral multiple carrier frequency offset.

Description

Technical Field

[0001] The present invention relates to the field of wireless communications, and in particular to a method, device, medium and program product for estimating cross-subcarrier frequency offsets in an OFDM system. Background Art

[0002] Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier technology, and the current mainstream 4G and 5G both use this technology. OFDM uses multiple orthogonal subcarriers to transmit high-speed information bits. It is particularly sensitive to frequency deviation. The offset of the carrier will destroy the orthogonality between subcarriers and cause inter-carrier interference, thereby reducing system performance. Especially for high-speed motion scenarios, such as aviation communication user terminals on high-speed flying aircraft platforms, civil airliners generally fly at a speed of 800km / h, while military aircraft have a maximum flight speed of more than Mach 4. In the above scenario, it will bring greater Doppler frequency deviation, and even cross-subcarrier situations.

[0003] In the existing frequency offset estimation scheme, the characteristic of frequency offset in time domain being converted into phase offset in frequency domain is usually used. After cross-correlation of pilot sequences in frequency domain and accumulation and summation, the frequency offset is calculated by phase offset. However, this algorithm has a serious flaw. Because of the limited range and periodicity of phase variation, it can only estimate the fractional frequency offset within the carrier. For example, if two pilots are separated by 1 symbol, the estimated frequency offset range is 0.5f. sc , f sc is the subcarrier frequency interval. For cross-carrier scenarios, the frequency offset estimated by this method is difficult to meet system requirements, affecting system demodulation. Summary of the invention

[0004] The present invention aims to provide a cross-subcarrier frequency offset estimation method, device, medium and program product applicable to an OFDM system, so as to solve the problem that the frequency offset estimation algorithm currently has a small frequency offset resistance range.

[0005] The present invention provides a method for estimating frequency offset across subcarriers applicable to an OFDM system, comprising the following steps:

[0006] Step 1: Parameter setting, including the number of cross-subcarriers N and the pilot length L for frequency domain processing f And the time domain processing pilot length L t ;

[0007] Step 2: Process the pilot length L according to the number of cross-subcarriers N and the frequency domain f , perform channel estimation in the frequency domain according to the sliding window method, and then calculate the reference signal received power Rsrp;

[0008] Step 3: Find the maximum value of the reference signal received power Rsrp to determine the integer multiple carrier frequency offset f int ;

[0009] Step 4: Process the pilot length L according to the time domain t , convert the selected frequency domain pilot data to the time domain to obtain the time domain pilot data Pilot t ;

[0010] Step 5: Follow L t / 2 length, the time domain pilot data Pilot t Divide into two parts, then perform correlation processing, and then accumulate and sum to obtain the relevant data CorrVal;

[0011] Step 6, average the relevant data CorrVal, and then perform alpha filtering to obtain the filtering result filterVal;

[0012] Step 7: Take the phase of the filtering result filterVal and calculate the fractional carrier frequency deviation f dec ;

[0013] Step 8: Set the integer multiple carrier frequency to f int and fractional multiples of the carrier frequency deviation f dec Add together to get the final frequency deviation estimate f o .

[0014] In some embodiments, in step 2, a sliding window is performed in the frequency domain with a step of N, and a data is slid each time, and a total of 2N+1 sliding windows are required. The initial sliding window length is defined as -N, and the last sliding window length is N; after each sliding window, L is selected. f The frequency domain pilot data of length is used to perform channel estimation, and then the reference signal received power Rsrp is calculated.

[0015] In some embodiments, the calculation formula of the reference signal received power Rsrp is as follows:

[0016]

[0017] Among them, Pilot f Pilot is the received frequency domain pilot data. local It is the local pilot data.

[0018] In some embodiments, in step 3, 2N+1 reference signal received powers Rsrp are calculated according to step 2, and the arrangement sequence of these 2N+1 reference signal received powers is (-N:N), and the sequence N corresponding to the maximum value is found in these 2N+1 reference signal received powers. int , and then calculate the integer multiple carrier frequency deviation fint , calculated as follows:

[0019] f int =N int ·f sc

[0020] Among them, f sc is the subcarrier frequency spacing.

[0021] In some embodiments, in step 4, the selected frequency domain pilot data is converted to the time domain through an IFFT operation.

[0022] In some embodiments, in step 6, the filtering result filterVal is calculated as follows:

[0023] filterVal=McorrVal*(1-aFactor)+hisVal*aFactor

[0024] Among them, McorrVal is the average value of the relevant data corrVal, aFactor is the alpha factor, and hisVal is the relevant data corrVal calculated last time.

[0025] In some embodiments, in step 7, the fractional carrier frequency offset f dec The calculation of is as follows:

[0026]

[0027] Among them, arctan() is the inverse tangent function.

[0028] The present invention also provides an electronic device, comprising:

[0029] at least one processor; and a memory communicatively coupled to the at least one processor;

[0030] The memory stores instructions that can be executed by the at least one processor, and the at least one processor executes the instructions stored in the memory, so that the at least one processor performs the method.

[0031] The present invention also provides a computer-readable storage medium, wherein the computer-readable storage medium is used to store instructions, and when the instructions are executed, the above method is implemented.

[0032] The present invention also provides a computer program product, which, when called by a computer, enables the computer to execute the above method.

[0033] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0034] 1. The present invention adopts a combination of time and frequency domains. In the frequency domain, the pilot data is first used for channel estimation. Through the search method, the integer multiple carrier frequency offset is estimated. Then, part of the pilot data is converted to the time domain. The pilot data is correlated in the time domain to estimate the fractional multiple carrier frequency offset. The combination of time and frequency domains can effectively increase the frequency offset estimation range. According to actual needs, (M+0.9)f can be achieved. sc , where M is an integer multiple of the carrier frequency deviation.

[0035] 2. The present invention can flexibly configure the number of subcarrier searches and the pilot length of time-frequency domain processing according to actual application scenarios, and control algorithm processing overhead. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A flowchart of a method for estimating cross-subcarrier frequency offset applicable to an OFDM system is provided in an embodiment of the present invention.

[0037] Figure 2 Schematic diagram of a sliding window in an embodiment of the present invention.

[0038] Figure 3 A schematic diagram of the structure of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] like Figure 1 As shown, an embodiment of the present invention provides a method for estimating frequency offset across subcarriers applicable to an OFDM system, which specifically includes the following steps:

[0042] Step 1: Parameter setting, including the number of cross-subcarriers N and the pilot length L for frequency domain processing f And the time domain processing pilot length L t ;

[0043] Step 2: Process the pilot length L according to the number of cross-subcarriers N and the frequency domain f , perform channel estimation in the frequency domain according to the sliding window method, and then calculate the reference signal received power Rsrp;

[0044] Step 3: Find the maximum value of the reference signal received power Rsrp to determine the integer multiple carrier frequency offset f int ;

[0045] Step 4: Process the pilot length L according to the time domain t , convert the selected frequency domain pilot data to the time domain to obtain the time domain pilot data Pilot t ;

[0046] Step 5: Follow L t / 2 length, the time domain pilot data Pilot t Divide into two parts, then perform correlation processing, and then accumulate and sum to obtain the relevant data CorrVal;

[0047] Step 6, average the relevant data CorrVal, and then perform alpha filtering to obtain the filtering result filterVal;

[0048] Step 7: Take the phase of the filtering result filterVal and calculate the fractional carrier frequency deviation f dec ;

[0049] Step 8: Set the integer multiple carrier frequency to f int and fractional multiples of the carrier frequency deviation f dec Add together to get the final frequency deviation estimate f o .

[0050] The present invention adopts a combination of time and frequency domains. In the frequency domain, the pilot data is first used for channel estimation. Through the search method, the integer multiple carrier frequency offset is estimated. Then, part of the pilot data is converted to the time domain. The pilot data is correlated in the time domain to estimate the fractional multiple carrier frequency offset. The combination of time and frequency domains can effectively increase the frequency offset estimation range. According to actual needs, (M+0.9)f can be achieved. sc , where M is an integer multiple of the carrier frequency deviation.

[0051] In some embodiments, in step 2, according to the number of cross-subcarriers N and the pilot length L in the frequency domain processing f , in the frequency domain according to Figure 2 In this way, the sliding window is performed with a step of N. Each time a data is slid, a total of 2N+1 sliding windows are required. The initial sliding window length is defined as -N, and the last sliding window length is N. After each sliding window, select L fThe frequency domain pilot data of length is used to perform channel estimation, and then the reference signal received power Rsrp is calculated. The specific calculation formula of the reference signal received power Rsrp is as follows:

[0052]

[0053] Among them, Pilot f Pilot is the received frequency domain pilot data. local It is the local pilot data.

[0054] In some embodiments, in step 3, 2N+1 reference signal received powers Rsrp can be calculated from step 2, and the arrangement sequence of these 2N+1 reference signal received powers is (-N:N), and the sequence N corresponding to the maximum value is found in these 2N+1 reference signal received powers. int , and then calculate the integer multiple carrier frequency deviation f int , the specific calculation method is as follows:

[0055] f int =N int ·f sc

[0056] Among them, f sc is the subcarrier frequency spacing.

[0057] In some embodiments, in step 4, the pilot length L is processed according to the time domain T , the selected frequency domain pilot data is converted to the time domain through the IFFT (Inverse Fast Fourier Transform) operation to obtain the time domain pilot data Pilot t , the specific formula is as follows:

[0058]

[0059] Among them, n is the time domain data index, and k is the frequency domain data index.

[0060] In some embodiments, in step 5, the time domain pilot data Pilot is obtained from step 4. t , the time domain pilot data Pilot t Divide into two segments, each of length Then, the correlation processing is performed, and the relevant data corrVal is obtained by accumulating and summing. The specific formula is as follows:

[0061]

[0062] In some embodiments, in step 6, the correlation data corrVal calculated from multiple pilot symbols is averaged. In order to reduce the interference caused by the burst error, it is also necessary to perform alpha filtering on the average value to obtain the filtering result filterVal. The specific calculation of the filtering result filterVal is as follows:

[0063] filterVal=McorrVal*(1-aFactor)+hisVal*aFactor

[0064] Among them, McorrVal is the average value of the correlation data corrVal, aFactor is the alpha factor, the default value is 0.75, hisVal is the correlation data corrVal calculated last time, and the initial value is 0.

[0065] In some embodiments, in step 7, after the filtering result filterVal is obtained in step 6, a phase operation is performed, and then the fractional carrier frequency deviation f is calculated. dec , the specific calculation is as follows:

[0066]

[0067] Among them, arctan() is the inverse tangent function.

[0068] In some embodiments, in step 8, the integer multiple carrier frequency offset f obtained in step 3 is int And the fractional multiple carrier frequency deviation f obtained in step 7 dec Add together to get the final frequency offset estimation result f o , the specific calculation is as follows:

[0069] f o =f int +f dec

[0070] The effect of the present invention is further described below in conjunction with simulation experiments.

[0071] The simulation parameter settings are shown in Table 1.

[0072] Table 1, simulation parameter settings:

[0073]

[0074] In the AWGN (Additive White Gaussian Noise) channel, when the SNR (Signal to Interference plus Noise Ratio) is 0dB, the subcarrier spacing f scThe frequency deviation is 30Khz, and the frequency deviation is set to 70KHz. The frequency deviation estimated by the method of the present invention is 69.4Khz.

[0075] Based on the same technical concept, an embodiment of the present invention further provides an electronic device, which can implement the cross-subcarrier frequency offset estimation method process applicable to OFDM system provided by the above embodiment of the present invention. In one embodiment, the electronic device can be a server, or a terminal device or other electronic device. Figure 3 As shown, the electronic device may include:

[0076] At least one processor, and a memory connected to the at least one processor. The specific connection medium between the processor and the memory is not limited in the embodiment of the present invention. Figure 3 The example in this article is that the processor and memory are connected through a bus. Figure 3 The connections between other components are shown in bold lines, which are only for illustration and are not intended to be limiting. The bus can be divided into address bus, data bus, control bus, etc. Figure 3 In the diagram, only one thick line is used, but this does not mean that there is only one bus or only one type of bus. Alternatively, a processor can also be called a controller, and there is no limitation on the name.

[0077] In an embodiment of the present invention, the memory stores instructions that can be executed by at least one processor, and the at least one processor can execute a cross-subcarrier frequency offset estimation method applicable to an OFDM system discussed above by executing the instructions stored in the memory. The processor can implement Figure 3 The functions of each module in the device shown.

[0078] Among them, the processor is the control center of the device, which can use various interfaces and lines to connect the various parts of the entire control device, and monitor the device as a whole by running or executing instructions stored in the memory and calling data stored in the memory, various functions of the device and processing data.

[0079] In an optional design, the processor may include one or more processing units, and the processor may integrate an application processor and a modem processor, wherein the application processor mainly processes an operating system, a user interface, and application programs, and the modem processor mainly processes wireless communications. It is understandable that the modem processor may not be integrated into the processor. In some embodiments, the processor and the memory may be implemented on the same chip, and in some embodiments, they may also be implemented separately on separate chips.

[0080] The processor may be a general-purpose processor, such as a CPU, a digital signal processor, an application-specific integrated circuit, a field programmable gate array or other programmable logic device, a discrete gate or transistor logic device, or a discrete hardware component, and may implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of the present invention. A general-purpose processor may be a microprocessor or any conventional processor, etc. In combination with the steps of a method for estimating cross-subcarrier frequency offsets applicable to an OFDM system disclosed in an embodiment of the present invention, the steps may be directly embodied as being executed by a hardware processor, or may be executed by a combination of hardware and software modules in the processor.

[0081] As a non-volatile computer-readable storage medium, the memory can be used to store non-volatile software programs, non-volatile computer executable programs and modules. The memory may include at least one type of storage medium, such as flash memory, hard disk, multimedia card, card-type memory, random access memory (Random Access Memory, RAM), static random access memory (Static Random Access Memory, SRAM), programmable read-only memory (Programmable Read Only Memory, PROM), read-only memory (Read Only Memory, ROM), electrically erasable programmable read-only memory (Electrically Erasable Programmable Read-Only Memory, EEPROM), magnetic memory, disk, optical disk, etc. The memory is any other medium that can be used to carry or store the desired program code in the form of instructions or data structures and can be accessed by a computer, but is not limited thereto. The memory in the embodiment of the present invention can also be a circuit or any other device that can realize a storage function, used to store program instructions and / or data.

[0082] By designing and programming the processor, the code corresponding to the cross-subcarrier frequency offset estimation method applicable to the OFDM system introduced in the above embodiment can be fixed into the chip, so that the chip can execute the code when running. Figure 1 The steps of the method of the embodiment shown. How to design and program a processor is a technique known to those skilled in the art and will not be described in detail here.

[0083] Based on the same inventive concept, an embodiment of the present invention further provides a storage medium storing computer instructions. When the computer instructions are executed on a computer, the computer executes a cross-subcarrier frequency offset estimation method applicable to an OFDM system discussed above.

[0084] In some optional embodiments, the present invention also provides various aspects of a method for estimating cross-subcarrier frequency offsets applicable to an OFDM system, which can also be implemented in the form of a program product, which includes program code. When the program product is run on an apparatus, the program code is used to enable the control device to execute the steps of a method for estimating cross-subcarrier frequency offsets applicable to an OFDM system according to various exemplary embodiments of the present invention described above in this specification.

[0085] It should be noted that, although several units or subunits of the device are mentioned in the above detailed description, this division is merely exemplary and not mandatory. In fact, according to an embodiment of the present invention, the features and functions of two or more units described above can be embodied in one unit. Conversely, the features and functions of a unit described above can be further divided into multiple units to be embodied. In addition, although the operation of the method of the present invention is described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. Additionally or alternatively, some steps can be omitted, multiple steps can be combined into one step for execution, and / or one step can be decomposed into multiple steps for execution.

[0086] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0087] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a server, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0088] Program code for performing the operations of the present invention may be written using any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, C++, etc., and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user computing device, partially on the user equipment, as a stand-alone software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0089] Where a remote computing device is involved, the remote computing device may be connected to the user computing device through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0090] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0091] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for estimating frequency offset across subcarriers applicable to an OFDM system, characterized in that: The steps include: Step 1: Parameter setting, including the number of cross-subcarriers N and the pilot length L for frequency domain processing f And the time domain processing pilot length L t ; Step 2: Process the pilot length L according to the number of cross-subcarriers N and the frequency domain f , perform channel estimation in the frequency domain according to the sliding window method, and then calculate the reference signal received power Rsrp; Step 3: Find the maximum value of the reference signal received power Rsrp to determine the integer multiple carrier frequency offset f int ; Step 4: Process the pilot length L according to the time domain t , convert the selected frequency domain pilot data to the time domain to obtain the time domain pilot data Pilot t ; Step 5: Follow L t / 2 length, the time domain pilot data Pilot t Divide into two parts, then perform correlation processing, and then accumulate and sum to obtain the relevant data CorrVal; Step 6, average the relevant data CorrVal, and then perform alpha filtering to obtain the filtering result filterVal; Step 7: Take the phase of the filtering result filterVal and calculate the fractional carrier frequency deviation f dec ; Step 8: Set the integer multiple carrier frequency to f int and fractional multiples of the carrier frequency deviation f dec Add together to get the final frequency deviation estimate f o .

2. The method for estimating cross-subcarrier frequency offset applicable to OFDM system according to claim 1, characterized in that: In step 2, the window is slid in the frequency domain with a step of N. Each time a data is slid, a total of 2N+1 sliding windows are required. The initial sliding window length is defined as -N, and the last sliding window length is N. After each sliding window, select L f The frequency domain pilot data of length is used to perform channel estimation, and then the reference signal received power Rsrp is calculated.

3. The method for estimating cross-subcarrier frequency offset applicable to OFDM system according to claim 2, characterized in that: The calculation formula of the reference signal received power Rsrp is as follows: Among them, Pilot f Pilot is the received frequency domain pilot data. local It is the local pilot data.

4. The method for estimating cross-subcarrier frequency offset applicable to OFDM system according to claim 1, characterized in that: In step 3, 2N+1 reference signal received powers Rsrp are calculated according to step 2. The arrangement sequence of these 2N+1 reference signal received powers is (-N:N). The sequence N corresponding to the maximum value is found in these 2N+1 reference signal received powers. int , and then calculate the integer multiple carrier frequency offset f int , calculated as follows: f int =N int ·f sc Among them, f sc is the subcarrier frequency spacing.

5. The method for estimating cross-subcarrier frequency offset applicable to OFDM system according to claim 1, characterized in that: In step 4, the selected frequency domain pilot data is converted to the time domain through an IFFT operation.

6. The method for estimating cross-subcarrier frequency offset applicable to OFDM system according to claim 1, characterized in that: In step 6, the filter result filterVal is calculated as follows: filterVal=McorrVal*(1-aFactor)+hisVal*aFactor Among them, McorrVal is the average value of the relevant data corrVal, aFactor is the alpha factor, and hisVal is the relevant data corrVal calculated last time.

7. The method for estimating cross-subcarrier frequency offset applicable to OFDM system according to claim 1, characterized in that: In step 7, the fractional carrier frequency deviation f dec The calculation of is as follows: Among them, arctan() is the inverse tangent function.

8. An electronic device, characterized in that: include: at least one processor; and a memory communicatively coupled to the at least one processor; The memory stores instructions that can be executed by the at least one processor, and the at least one processor executes the method as described in any one of claims 1 to 7 by executing the instructions stored in the memory.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store instructions, and when the instructions are executed, the method according to any one of claims 1 to 7 is implemented.

10. A computer program product, characterized in that When the computer program product is called by a computer, the computer is caused to execute the method according to any one of claims 1 to 7.

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