A carrier-to-noise ratio estimation method

Abstract

The application belongs to the technical field of signal processing, and specifically discloses a carrier-to-noise ratio estimation method. Through the application, the power of the baseband signal is used as the pre-information for calculating the carrier-to-noise ratio, the mapping relationship between the signal power and the noise power between the wideband characteristics of the baseband signal and the narrowband characteristics of the integrated signal is explored, and then the estimation of the carrier-to-noise ratio is realized. This method can fully utilize the frequency band characteristics of the signal, and fully consider the statistical relationship between the baseband signal and the integrated signal. Compared with the traditional method, it has higher estimation accuracy and accuracy in medium and high signal-to-noise ratio. By flexibly selecting the signal length required for carrier-to-noise ratio estimation, the method can obtain higher carrier-to-noise ratio estimation accuracy in a short non-coherent integration period, thereby meeting the real-time requirements of some algorithm modules in the receiver, and then improving the carrier-to-noise ratio estimation accuracy in the high dynamic scene, so as to overcome the limitations of the classic method under high dynamic conditions.

Description

Technical Field

[0001] This application belongs to the field of signal processing technology, and more specifically, relates to a carrier-to-noise ratio estimation method. Background Technology

[0002] Carrier-to-noise ratio Carrier-to-noise ratio (CNR) is a normalized metric for signal-to-noise ratio (SNR), a key measurement output of receivers in spread spectrum systems (such as GNSS receivers), and a standard for measuring satellite signal quality. In GNSS receivers, the carrier-to-noise ratio is provided to the user along with PVT (Position, Velocity, Time) information for further utilization. Furthermore, CNR can be used in various application scenarios, such as setting signal acquisition thresholds, monitoring satellite signal quality, using carrier phase for multipath error correction, using power information for spoofing detection, positioning, and system status assessment. Therefore, research on CNR estimation has significant practical implications.

[0003] Currently, the most commonly used method for estimating the carrier-to-noise ratio (CNR) of received signals, both domestically and internationally, is the narrowband-wideband power ratio (NWPR) method. This method estimates the CNR by calculating the ratio of the narrowband power to the wideband power of the received signal. Specifically, the narrowband power is obtained by measuring the integrated signal power over a narrower bandwidth; the wideband power is obtained by measuring the integrated signal power over a wider bandwidth; the ratio of these two values ​​can be used to estimate the signal-to-noise ratio, thus yielding the CNR.

[0004] However, the method has the following problems: (1) The bandwidth difference between narrowband and wideband is small, which leads to a large estimation deviation when estimating the carrier-to-noise ratio; (2) Generally speaking, the longer the integration time when estimating the carrier-to-noise ratio, the higher the estimation accuracy. However, in high dynamic scenarios, the signal amplitude and phase exhibit rapid changes and a large range of changes, which contradicts the long integration time required for carrier-to-noise ratio estimation. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this application is to provide a carrier-to-noise ratio estimation method, which aims to solve the contradiction between the long integration time required by the existing carrier-to-noise ratio estimation methods and the rapid changes in signal amplitude.

[0006] The first aspect of this application relates to a carrier-to-noise ratio estimation method, comprising:

[0007] The summation of the squares of the integral signal within several coherent integration periods is performed to obtain the total power of the desired integral signal and noise.

[0008] The baseband signal samples in the same number of coherent integration periods are squared and summed to obtain the total power of the expected baseband signal and noise;

[0009] The carrier-to-noise ratio is calculated by using the wideband characteristic of the baseband signal, the narrowband characteristic of the integration signal, and the mapping relationship between the signal power and the noise power of the baseband signal and the integration signal.

[0010] The baseband signal is a signal obtained by stripping the intermediate frequency carrier and the Doppler shift in the intermediate frequency signal in the receiver, and includes an in-phase baseband signal and a quadrature baseband signal. The integration signal is a signal obtained by stripping the spreading code from the baseband signal and then coherent integration, and includes an in-phase integration signal and a quadrature integration signal.

[0011] Preferably, the calculation formula of the total power of the expected integration signal and noise is as follows:

[0012]

[0013] wherein, is the power of the integration signal, and are the in-phase integration signal and the quadrature integration signal of the current branch, respectively, is the number of coherent integration periods, and the subscript is the current branch, and the subscript is the coherent integration period.

[0014] Preferably, the calculation formula of the total power of the expected baseband signal and noise is as follows:

[0015]

[0016] wherein, is the power of the baseband signal, is the number of coherent integration periods, is the number of sampling points in the coherent integration period, and are the in-phase baseband signal and the quadrature baseband signal, respectively, indicates the sampling point.

[0017] Preferably, the carrier-to-noise ratio calculation formula is as follows:

[0018]

[0019] wherein, is the carrier-to-noise ratio, is the number of sampling points in the coherent integration period, is the power of the integration signal, is the power of the baseband signal. is a coherent integration period.

[0020] Preferably, the selected time length for the carrier-to-noise ratio estimation should take into account both the stability of the estimation result and the calculation real-time performance, the greater the time length, the better the stability of the estimation result, and the worse the calculation real-time performance.

[0021] Preferably, the stripping of the intermediate frequency carrier and the Doppler shift in the intermediate frequency signal comprises:

[0022] (1) down-converting the radio frequency signal received by the receiver antenna to obtain an intermediate frequency signal;

[0023] (2) multiplying the intermediate frequency signal with a cosine carrier in a first mixer to obtain an in-phase baseband signal, and multiplying the intermediate frequency signal with a sine carrier in a second mixer to obtain a quadrature baseband signal, wherein the cosine carrier and the sine carrier are both generated by a carrier NCO.

[0024] Preferably, the coherent integration after stripping the baseband signal of the spread spectrum code comprises:

[0025] (1) inputting the in-phase baseband signal and the quadrature baseband signal into a correlator to perform correlation operation with a local real-time branch spread spectrum code generated by a code NCO, so as to strip the spread spectrum code;

[0026] (2) inputting the output of the correlator into an integration cleaner to perform coherent integration, and the output of the integration cleaner is an in-phase integration signal and a quadrature integration signal.

[0027] Preferably, the carrier-to-noise ratio estimation method is applied to a receiver of a spread spectrum system.

[0028] The second aspect of the present application relates to a computer readable storage medium, which stores a computer program, when the computer program runs on a processor, so that the processor enters the carrier-to-noise ratio estimation method as described in the first aspect.

[0029] It can be understood that the beneficial effects of the above-mentioned second aspect can be referred to the related description in the first aspect, which will not be repeated here.

[0030] In general, the above technical solutions conceived by the present application have the following beneficial effects compared with the prior art:

[0031] The application provides a carrier-to-noise ratio estimation method, which takes the power of a baseband signal as the prior information for calculating the carrier-to-noise ratio, uses the wideband characteristics of the baseband signal and the narrowband characteristics of an integrated signal, explores the mapping relationship between the signal power and the noise power, and then realizes the estimation of the carrier-to-noise ratio. This method can fully utilize the frequency band characteristics of the signal, and fully considers the statistical relationship between the baseband signal and the integrated signal, and has higher accuracy than the traditional method at medium and high signal-to-noise ratios; the application can flexibly select the signal length required for carrier-to-noise ratio estimation, and can obtain higher carrier-to-noise ratio estimation accuracy in a shorter non-coherent integration period, thereby meeting the real-time requirements of some algorithm modules in the receiver, and then improving the carrier-to-noise ratio estimation accuracy in a high dynamic scene, so as to overcome the limitations of the classic method under high dynamic conditions. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a flowchart of a carrier-to-noise ratio estimation method provided by an embodiment of the application.

[0033] Figure 2 is a standard deviation result comparison chart of the application and the NWPR method provided by an embodiment of the application. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0035] In the application, the term "and / or" is used to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In the application, the symbol " / " represents the relationship of or, for example, A / B represents A or B.

[0036] In the application, the terms "first" and "second" in the specification and claims are used to distinguish different objects, and not to describe the specific order of the objects. For example, the first response message and the second response message are used to distinguish different response messages, and not to describe the specific order of the response messages.

[0037] In the embodiments of the application, the words such as "exemplary" or "for example" are used to mean by way of example, illustration or description. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of the application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the use of "exemplary" or "for example" is intended to present the relevant concept in a specific manner.

[0038] In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, for example, a plurality of processing units refers to two or more processing units, and the like; a plurality of elements refers to two or more elements, and the like, unless otherwise specified.

[0039] For the convenience of understanding, the English abbreviations and related technical terms involved in the embodiments of the present application are explained and described below.

[0040] GNSS receiver: the main components include antenna, radio frequency front end, baseband processing unit, data processing and control unit, user interface, power system, storage unit and communication interface. These components work together to realize the functions of satellite signal reception, processing and positioning calculation.

[0041] Radio frequency front end: usually includes low noise amplifier, band pass filter and mixer. The band pass filter is used to filter out interference signals, and the mixer converts the radio frequency satellite signal to intermediate frequency signal.

[0042] BCPR: baseband signal to integrated signal power ratio.

[0043] The embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0044] As shown in Figure 1 , the present application proposes a carrier-to-noise ratio estimation method, which includes the following steps:

[0045] First, the radio frequency signal received by the receiver antenna is converted to intermediate frequency signal after low noise amplification, filtering, down conversion and analog-to-digital conversion by the radio frequency front end. The cosine carrier and sine carrier generated by the carrier NCO are input into the mixer and multiplied by the intermediate frequency signal, and then the intermediate frequency carrier and Doppler shift are stripped to obtain the in-phase baseband signal and the quadrature baseband signal.

[0046] The radio frequency signal is converted to a digital intermediate frequency signal with a center frequency of after processing. Generally speaking, the center frequency of the intermediate frequency signal should be at least greater than the single sideband width of the main peak of the spread spectrum code spectrum, for example, the main peak width of GPS C / A code is about 2MHz, and the center frequency of the intermediate frequency signal should be at least 1MHz.

[0047] The intermediate frequency signal and the cosine carrier and sine carrier generated by the carrier NCO are input into the mixer, and in the mixer, the intermediate frequency signal is multiplied by the cosine carrier and the sine carrier respectively to strip the intermediate frequency carrier and the Doppler shift. At this time, the intermediate frequency signal multiplied by the cosine carrier is down-converted to the in-phase baseband signal , and the intermediate frequency signal multiplied by the sine carrier is down-converted to the quadrature baseband signal , and the center frequency of both is 0.

[0048] After the above processing, the radio frequency signal can be used to obtain the baseband signal. The baseband signal refers to the signal obtained by stripping the carrier and Doppler from the intermediate frequency signal. Its essence is a noisy direct-sequence spread spectrum (DSSS) signal.

[0049] The second step is to select a baseband signal within a certain time period and perform a square accumulation and summation operation to obtain the total power of the baseband signal within that time period.

[0050] right In-phase baseband signal for one integration period and orthogonal baseband signal Perform a square-sum operation to obtain the total power of the desired signal and broadband noise:

[0051]

[0052] in, For coherent integral period The number of sampling points within, The number of coherent integration cycles.

[0053] Baseband signals are based on sampling points as the basic unit, so the number of samples for the baseband signal can be flexibly selected (the total number of samples in the following text is a variable). (representation) to calculate a certain time period ( The number of coherent integral periods is The addition of noise power to the signal makes the selection of signal duration more flexible and can meet the real-time requirements of different modules.

[0054] In practical engineering applications, and The larger the value, the more stable the carrier-to-noise ratio estimation result, but... and The smaller the value, the better the real-time performance. and The selection of the algorithm should balance the stability of the estimation results and the real-time performance of the calculation. It should be rationally selected based on the magnitude and rate of change in the spread spectrum signal carrier-to-noise ratio in the actual signal environment and the real-time requirements of the task. and Assuming sampling rate Set to 5MHz, coherent integration period Setting it to 1ms, in a static scene, a 2s time interval can be chosen to estimate the carrier-to-noise ratio. The value is 2000. The value is 5000, and the total number of sampling points selected is [number missing]. One; in high dynamic scenes, to ensure the real-time of carrier-to-noise ratio calculation, carrier-to-noise ratio is estimated once every 5ms, so The value is 5, The value is 5000, and the number of selected sampling points is .

[0055] The third step is to input the baseband signal into the correlator to strip the spread spectrum code and obtain the despread signal, and the despread signal enters the integration cleaner with a coherent integration period of To obtain an integrated signal with higher signal-to-noise ratio.

[0056] The baseband signal And Is sent to the correlator for correlation operation with the local real-time branch spread spectrum code generated by the code NCO to strip the spread spectrum code, and then the correlator output is sent to the integration cleaner for coherent integration with a coherent integration period of To further improve the signal-to-noise ratio, the output of the integration cleaner is the in-phase integration signal And the quadrature integration signal .

[0057] The coherent integration period depends on the signal condition, and the integration time of GPS L1 C / A signal is usually 1ms under the condition of high carrier-to-noise ratio (40dB-Hz), and the integration time of GPS L1 C / A signal is up to 20ms under the condition of low carrier-to-noise ratio (25dB-Hz) without navigation bit assistance, subscript Indicates the real-time branch, subscript Indicates the Coherent integration period.

[0058] After the baseband signal enters the correlator and the integration cleaner, the integrated signal is obtained, and the signal bandwidths of the two signals are different, but the noise powers of the two signals are related, and the mathematical model of signal power and noise power can be established by using this correlation.

[0059] The fourth step is to perform square accumulation summation operation on the integrated signal to calculate the power of the integrated signal.

[0060] The in-phase integration signal And the quadrature integration signal Of the real-time branch are subjected to square accumulation summation operation, and the total power of the expected signal and narrowband noise is obtained:

[0061]

[0062] The fifth step is to send the calculated baseband signal power and integrated signal power into the carrier-to-noise ratio estimation algorithm module to realize real-time high-precision carrier-to-noise ratio estimation by using the time flexibility and wideband characteristics of the baseband signal.

[0063] Based on the baseband signal model, the baseband signal and the integral signal power ratio of the carrier-to-noise ratio are obtained by deducing the statistical characteristic relationship between the signal model and the carrier-to-noise ratio:

[0064]

[0065] Simulation experiment verification

[0066] Figure 2 The standard deviation of the carrier-to-noise ratio estimated by the method of the present application and the traditional NWPR method is compared. The larger the standard deviation, the worse the estimation accuracy. The parameter settings are: the carrier-to-noise ratio estimation time is 1s, and the coherent integration period is 1ms. Combined with Figure 2 It can be seen that the carrier-to-noise ratio estimation accuracy of the method of the present application is higher than that of the NWPR method at medium and high signal-to-noise ratios. Table 1 gives the specific values of the BCPR carrier-to-noise ratio estimation accuracy. And the method of the present application theoretically deduces the carrier-to-noise ratio estimation mean and accuracy The theoretical expression is as follows, and the simulation verifies the correctness of the theoretical derivation.

[0067]

[0068]

[0069] Table 1 BCPR carrier-to-noise ratio estimation mean square error

[0070]

[0071] It should be understood that the above device is used to execute the method in the above embodiment, and the corresponding program module in the device, the implementation principle and technical effect are similar to the description in the above method, and the working process of the device can refer to the corresponding process in the above method, which will not be repeated here.

[0072] Based on the method in the above embodiment, the present embodiment provides a receiver, which can include: a processor (Processor), a communication interface (Communications Interface), a memory (Memory) and a communication bus, wherein the processor, the communication interface and the memory complete mutual communication through the communication bus. The processor can call the logic instructions in the memory to execute the method in the above embodiment.

[0073] In addition, the logic instructions in the memory described above can be implemented in the form of a software function unit and sold or used as an independent product, and can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application essentially or say the part that contributes to the prior art or part of the technical solutions can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a plurality of instructions to make a computer device (which can be a personal computer, a server, or a network device, etc.) execute all or part of the steps of the method described in various embodiments of the present application.

[0074] Based on the method in the above embodiments, the embodiments of the present application provide a computer readable storage medium, which stores a computer program, and when the computer program runs on a processor, the processor executes the method in the above embodiments.

[0075] Based on the method in the above embodiments, the embodiments of the present application provide a computer program product, and when the computer program product runs on a processor, the processor executes the method in the above embodiments.

[0076] It can be understood that the processor in the embodiments of the present application can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. The general-purpose processor can be a microprocessor or any conventional processor.

[0077] The method steps in the embodiments of the present application can be implemented by means of hardware, or by means of a processor executing software instructions. The software instructions can be composed of corresponding software modules, which can be stored in a Random Access Memory (RAM), a flash memory, a Read-only Memory (ROM), a Programmable ROM (PROM), an Erasable PROM (EPROM), an Electrically EPROM (EEPROM), a register, a hard disk, a mobile hard disk, a CD-ROM, or any other form of storage medium well known in the art. An exemplary storage medium is coupled to a processor, such that the processor can read information from, and write information to, the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can be located in an ASIC.

[0078] In the above embodiments, all or some of the steps can be implemented by software, hardware, firmware or any combination thereof. When implemented by software, all or some of the steps can be implemented by one or more computer programs. When implemented by computer programs, the computer programs can be stored in a computer readable storage medium, and executed by a processor. The computer readable storage medium can be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Programmable ROM (PROM), an Erasable PROM (EPROM), an Electrically EPROM (EEPROM), a register, a hard disk, a mobile hard disk, a CD-ROM, or any other form of storage medium well known in the art. The computer readable storage medium can be coupled to the processor, such that the processor can read information from, and write information to, the computer readable storage medium. Of course, the computer readable storage medium can also be a component of the processor. The processor and the computer readable storage medium can be located in an ASIC.

[0079] It can be understood that various numerical numbers involved in the embodiments of the present application are only used for differentiation for convenience of description, and are not used to limit the scope of the embodiments of the present application.

[0080] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A carrier-to-noise ratio estimation method, characterized by, The method comprises: performing square summation operation on the integration signals in a plurality of coherent integration periods to obtain total power of expected integration signals and noise; performing square summation operation on baseband signal samples in the same number of coherent integration periods to obtain total power of expected baseband signals and noise; calculating the carrier-to-noise ratio by using the wideband characteristic of the baseband signals, the narrowband characteristic of the integration signals, and the mapping relationship between signal power and noise power between the baseband signals and the integration signals. The baseband signals are signals obtained by stripping the intermediate frequency carrier and Doppler shift from the intermediate frequency signals in the receiver, and comprise in-phase baseband signals and quadrature baseband signals; the integration signals are signals obtained by stripping the spreading code from the baseband signals and then performing coherent integration, and comprise in-phase integration signals and quadrature integration signals. The calculation formula of the total power of the expected integration signals and noise is as follows: wherein is the power of the integrated signal, and are the in-phase and quadrature integrated signals of the instantaneous branch, respectively, is the number of coherent integration periods, the subscript is the instantaneous branch, the subscript is the coherent integration period; The calculation formula of the total power of the expected baseband signals and noise is as follows: wherein, is the power of the baseband signal, is the number of sampling points within the coherent integration period, and are the in-phase baseband signal and the quadrature baseband signal, respectively, denotes the sampling point; The calculation formula of the carrier-to-noise ratio is as follows: wherein is the carrier-to-noise ratio, is the power of the integrated signal, is the coherence integration period.

2. The CNR estimation method of claim 1, wherein, When estimating the carrier-to-noise ratio, the selected time length should consider the stability of the estimation result and the calculation real-time performance. The greater the time length, the better the stability of the estimation result, and the worse the calculation real-time performance.

3. The CNR estimation method of claim 1, wherein, The signals obtained by stripping the intermediate frequency carrier and Doppler shift from the intermediate frequency signals in the receiver comprise: (1) down-converting the radio frequency signals received by the antenna of the receiver to obtain intermediate frequency signals; (2) multiplying the intermediate frequency signals and a cosine carrier in a first mixer to obtain in-phase baseband signals, and multiplying the intermediate frequency signals and a sine carrier in a second mixer to obtain quadrature baseband signals, wherein the cosine carrier and the sine carrier are both generated by a carrier NCO.

4. The CNR estimation method of claim 1, wherein, The coherent integration after stripping the spreading code from the baseband signals comprises: (1) inputting the in-phase baseband signals and the quadrature baseband signals into a correlator to perform correlation operation with a local real-time branch spreading code generated by a code NCO, so as to strip the spreading code; (2) inputting the output of the correlator into an integration canceller to perform coherent integration, and the output of the integration canceller is the in-phase integration signals and the quadrature integration signals.

5. The CNR estimation method according to any one of claims 1 to 4, characterized by, The carrier-to-noise ratio estimation method is applied to the receiver of a spread spectrum system.

6. A computer-readable storage medium, characterized in that, The computer readable storage medium stores a computer program, and when the computer program runs on the processor, the processor enters the carrier-to-noise ratio estimation method according to any one of claims 1 to 5.

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