Carrier-to-noise ratio estimation method

Abstract

The invention belongs to the technical field of signal processing, and particularly discloses a carrier-to-noise ratio estimation method. According to the carrier-to-noise ratio estimation method and device, the power of the baseband signal serves as the preposition information for calculating the carrier-to-noise ratio, the mapping relation between the signal power and the noise power between the baseband signal and the integral signal is explored by means of the broadband characteristic of the baseband signal and the narrowband characteristic of the integral signal, and then estimation of the carrier-to-noise ratio is achieved. According to the method, the frequency band characteristics of the signals can be fully utilized, the statistical relation between the baseband signals and the integral signals is fully considered, and compared with a traditional method, the method has higher estimation precision and accuracy in the middle and high signal-to-noise ratio; by flexibly selecting the signal duration required by carrier-to-noise ratio estimation, the method can obtain higher carrier-to-noise ratio estimation precision in a shorter incoherent integration period, thereby meeting the real-time requirements of some algorithm modules in a receiver, further improving the carrier-to-noise ratio estimation precision in a high-dynamic scene, and improving the performance of the receiver. And the limitation of a classical method under a high dynamic condition is overcome.

Description

Technical Field

[0001] The present application belongs to the technical field of signal processing, and more specifically, relates to a carrier-to-noise ratio estimation method. Background Art

[0002] Carrier-to-noise ratio ) is a normalized measure of the signal-to-noise ratio, a key measurement output of a receiver in a spread spectrum system (e.g., a GNSS receiver), and a measure of satellite signal quality. The carrier-to-noise ratio of the signal in a GNSS receiver is provided to the user along with PVT (Position, Velocity, Time) information for further use. Moreover, the carrier-to-noise ratio can be used in various application scenarios, such as signal capture threshold setting, satellite signal quality monitoring, multipath error correction using carrier phase, deception detection using power information, positioning, and system status evaluation. Therefore, studying the estimation of the carrier-to-noise ratio has important practical significance.

[0003] At present, the most commonly used method for estimating the carrier-to-noise ratio of received signals at home and abroad is the narrowband-wideband power ratio (NWPR). It estimates the carrier-to-noise ratio by calculating the ratio of the narrowband power to the broadband power of the received signal. Specifically: the narrowband power is obtained by measuring the integrated signal power in a narrow bandwidth; the broadband power is obtained by measuring the integrated signal power in a wider bandwidth; the ratio of the two can be used to estimate the ratio of the signal to noise, thereby obtaining the carrier-to-noise ratio.

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

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a method for estimating a carrier-to-noise ratio, aiming to solve the contradiction between the long integration time required in the existing carrier-to-noise ratio estimation method and the rapid change of signal amplitude.

[0006] A first aspect of the present application relates to a carrier-to-noise ratio estimation method, comprising: Performing a square accumulation and summing operation on the integrated signals within a number of coherent integration periods to obtain the total power of the desired integrated signal and the noise; The baseband signal samples within the same number of coherent integration periods are then subjected to a square accumulation and summation operation to obtain the total power of the desired baseband signal and noise; Calculate the carrier-to-noise ratio by using the broadband characteristics of the baseband signal, the narrowband characteristics of the integrated signal, and the mapping relationship between the signal power and the noise power between the baseband signal and the integrated signal; Among them, the baseband signal is the signal obtained by stripping the intermediate-frequency carrier and Doppler frequency shift from the intermediate-frequency signal of the receiver, including the in-phase baseband signal and the quadrature baseband signal; the integrated signal is the signal obtained by stripping the spreading code from the baseband signal and then performing coherent integration, including the in-phase integrated signal and the quadrature integrated signal.

[0007] Preferably, the calculation formula for the total power of the desired integrated signal and noise is as follows:

[0008] Among them, is the power of the integrated signal, and are the in-phase integrated signal and the quadrature integrated signal of the prompt branch respectively, is the number of coherent integration periods, the subscript is the prompt branch, and the subscript is the th coherent integration period.

[0009] Preferably, the calculation formula for the total power of the desired baseband signal and noise is as follows:

[0010] Among them, is the power of the baseband signal, is the number of coherent integration periods, is the number of sampling points within the coherent integration period, and are the in-phase baseband signal and the quadrature baseband signal respectively, represents the th sampling point.

[0011] Preferably, the calculation formula for the carrier-to-noise ratio is as follows:

[0012] Among them, is the carrier-to-noise ratio, is the number of sampling points within the coherent integration period, is the power of the integrated signal, is the power of the baseband signal, is the coherent integration period.

[0013] Preferably, the time length selected during carrier-to-noise ratio estimation should balance the stability of the estimation result and the real-time performance of the calculation. The larger the time length, the better the stability of the estimation result and the worse the real-time performance of the calculation.

[0014] Preferably, the stripping of the intermediate frequency carrier and Doppler frequency shift in the intermediate frequency signal includes: (1) Down-converting the radio frequency signal received by the receiver antenna to obtain an intermediate frequency signal; (2) Multiplying the intermediate frequency signal by a cosine carrier in a first mixer to obtain an in-phase baseband signal, and multiplying the intermediate frequency signal by a sine carrier in a second mixer to obtain a quadrature baseband signal, where both the cosine carrier and the sine carrier are generated by a carrier NCO.

[0015] Preferably, the stripping of the spreading code from the baseband signal and then coherent integration includes: (1) Feeding the in-phase baseband signal and the quadrature baseband signal into a correlator to perform a correlation operation with the local prompt branch spreading code generated by a code NCO to strip the spreading code; (2) The output of the correlator is fed into an integrator cleaner for coherent integration, and the output of the integrator cleaner is an in-phase integration signal and a quadrature integration signal.

[0016] Preferably, the carrier-to-noise ratio estimation method is applied to a receiver of a spread spectrum system.

[0017] The second aspect of the present application relates to a computer-readable storage medium storing a computer program, which, when running on a processor, causes the processor to enter the carrier-to-noise ratio estimation method as described in the first aspect.

[0018] It can be understood that the beneficial effects of the above second aspect can be referred to the relevant descriptions in the above first aspect and will not be elaborated here.

[0019] Generally speaking, compared with the prior art, the above technical solution conceived by the present application has the following beneficial effects: The present application proposes a carrier-to-noise ratio estimation method, which uses the power of the baseband signal as the pre-information for calculating the carrier-to-noise ratio, and explores the mapping relationship between the signal power and the noise power of the two by using the broadband characteristics of the baseband signal and the narrowband characteristics of the integration signal, thereby realizing the estimation of the carrier-to-noise ratio. This method can make full use of the frequency band characteristics of the signal and fully consider the statistical relationship between the baseband signal and the integration signal. Compared with the traditional method, it has higher accuracy at medium and high signal-to-noise ratios; the present application can flexibly select the signal duration required for carrier-to-noise ratio estimation, and can obtain a higher carrier-to-noise ratio estimation accuracy within a shorter non-coherent integration period, so as to meet the real-time requirements of some algorithm modules in the receiver, and further improve the carrier-to-noise ratio estimation accuracy in high-dynamic scenarios to overcome the limitations of the classical method under high-dynamic conditions. Description of the Drawings

[0020] Figure 1It is a schematic flowchart of a carrier-to-noise ratio estimation method provided by an embodiment of the present application.

[0021] Figure 2 It is a comparison chart of the standard deviation results between the present application and the NWPR method provided by an embodiment of the present application. Detailed implementation manners

[0022] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0023] The term "and / or" in the present application is a relational term describing associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. The symbol " / " in the present application represents an "or" relationship between associated objects. For example, A / B represents A or B.

[0024] The terms "first" and "second" etc. in the description and claims of the present application are used to distinguish different objects, rather than to describe a specific order of the objects. For example, the first response message and the second response message etc. are used to distinguish different response messages, rather than to describe the specific order of the response messages.

[0025] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner.

[0026] In the description of the embodiments of the present application, unless otherwise specified, the meaning of "a plurality of" refers to two or more. For example, a plurality of processing units refers to two or more processing units; a plurality of elements refers to two or more elements.

[0027] For ease of understanding, the following first explains and describes the English abbreviations and related technical terms involved in the embodiments of the present application.

[0028] GNSS receiver: Its main components include an antenna, a radio frequency front end, a baseband processing unit, a data processing and control unit, a user interface, a power supply system, a storage unit and a communication interface. These components work together to achieve the functions of receiving, processing satellite signals and performing positioning calculations.

[0029] RF front-end: Usually includes a low-noise amplifier, a band-pass filter, and a mixer. The band-pass filter is used to filter out interference signals, and the mixer down-converts the RF satellite signal to an intermediate-frequency signal.

[0030] BCPR: Baseband signal to integrated signal power ratio.

[0031] The embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application.

[0032] As Figure 1 shown, the present application proposes a method for estimating the carrier-to-noise ratio, including the following steps: First step, the RF signal received by the receiver antenna is processed by the RF front-end through low-noise amplification, filtering, down-conversion, and analog-to-digital conversion, etc., and then converted into an intermediate-frequency signal. The cosine carrier and sine carrier generated by the carrier NCO are respectively input into the mixer and multiplied by the intermediate-frequency signal, thereby stripping the intermediate-frequency carrier and Doppler frequency shift, and obtaining the in-phase baseband signal and the quadrature baseband signal.

[0033] The RF signal is converted into a digital intermediate-frequency signal with a center frequency of after being processed. Generally speaking, the center frequency of the intermediate-frequency signal should be at least greater than the one-sided bandwidth of the main peak of the spreading code spectrum. For example, the main peak width of the GPS C / A code is about 2 MHz, and the center frequency of the intermediate-frequency signal should be at least 1 MHz. At least 1 MHz.

[0034] The intermediate-frequency signal and the cosine carrier and sine carrier generated by the carrier NCO are input into the mixer. In the mixer, the intermediate-frequency signal is respectively multiplied by the cosine carrier and the sine carrier to strip the intermediate-frequency carrier and Doppler frequency shift. At this time, the intermediate-frequency signal multiplied by the cosine carrier is down-converted into an in-phase baseband signal and the intermediate-frequency signal multiplied by the sine carrier is down-converted into a quadrature baseband signal , and the center frequencies of both are 0.

[0035] The baseband signal can be obtained after the RF signal is processed as described above. The baseband signal refers to the signal obtained by stripping the carrier and Doppler in the intermediate-frequency signal, and its essence is a noisy direct-sequence spread-spectrum (DSSS) signal.

[0036] Second step, select the baseband signal within a certain period of time for square accumulation summation operation to obtain the total power of the baseband signal during this period.

[0037] For integral periods of the in-phase baseband signal and the quadrature baseband signal perform square accumulation summation operation to obtain the total power of the desired signal and broadband noise:

[0038] Among them, is the number of sampling points within the coherent integration period , and is the number of coherent integration periods.

[0039] The baseband signal takes the sampling point as the basic unit. Therefore, the number of samples of the baseband signal can be flexibly selected (the total number of samples is represented by the variable in the following text) to calculate the signal plus noise power within a certain period of time ( coherent integration periods are ), making the selection of the signal duration more flexible and meeting the real-time requirements of different modules.

[0040] In practical engineering applications, and the larger they are, the more stable the carrier-to-noise ratio estimation result is. However, and the smaller they are, the better the real-time performance is. Therefore, and should be selected considering both the stability of the estimation result and the real-time performance of the calculation. According to the magnitude and speed of the change in the carrier-to-noise ratio of the spread-spectrum signal in the actual signal environment and the real-time requirements of the task, and are reasonably selected. Assuming the sampling rate is set to 5 MHz and the coherent integration period is set to 1 ms, in a static scenario, a time interval of 2 s can be selected to estimate the carrier-to-noise ratio. Then takes the value of 2000, takes the value of 5000, and the total number of sampling points selected is ; in a high-dynamic scenario, to ensure the real-time performance of the carrier-to-noise ratio calculation, the carrier-to-noise ratio is estimated every 5 ms. Then takes the value of 5, takes the value of 5000, and the total number of sampling points selected is .

[0041] Step 3: Input the baseband signal into the correlator to strip the spreading code and obtain the despread signal. The despread signal enters the integrating and clearing device with a coherent integration period of to obtain an integrated signal with a higher signal-to-noise ratio.

[0042] The baseband signals and are sent into the correlator to perform a correlation operation with the local immediate-branch spreading code generated by the code NCO to strip the spreading code. Then the output of the correlator is sent into the integrating and clearing device for coherent integration with a period of The coherent integration is performed to further improve the signal-to-noise ratio. The output of the integrator cleaner is the in-phase integration signal and the quadrature integration signal .

[0043] The coherent integration period depends on the signal conditions. Under the condition of a relatively high carrier-to-noise ratio (40 dB-Hz), the integration time of the GPS L1 C / A signal is usually 1 ms. Under the condition of a relatively low carrier-to-noise ratio (25 dB-Hz) and without navigation bit assistance, the maximum integration time of the GPS L1 C / A signal is 20 ms. The subscript represents the prompt branch, and the subscript represents the th coherent integration period.

[0044] After the baseband signal enters the correlator and the integrator cleaner, the integration signal is obtained. The signal bandwidths of the two are different, but the noise powers of the two signals are correlated. This correlation can be used to establish a mathematical model of the signal power and the noise power.

[0045] Step 4: Perform a square accumulation summation operation on the integration signal to calculate the power of the integration signal.

[0046] Perform a square accumulation summation operation on the in-phase integration signal and the quadrature integration signal of the prompt branch to obtain the total power of the desired signal and the narrowband noise:

[0047] Step 5: Send the calculated baseband signal power and integration signal power into the carrier-to-noise ratio estimation algorithm module, and use the time flexibility and broadband characteristics of the baseband signal to achieve real-time and high-precision carrier-to-noise ratio estimation.

[0048] Starting from the baseband signal model, this application derives the relationship between the signal model and the statistical characteristics of the carrier-to-noise ratio, and obtains the carrier-to-noise ratio of the power ratio of the baseband signal to the integration signal:

[0049] The simulation experiment verifies Figure 2 Compare the standard deviations of the carrier-to-noise ratio estimations of the method of this application and the traditional NWPR method. The larger the standard deviation, the worse the estimation accuracy. The parameter settings are: the carrier-to-noise ratio estimation time is 1 s, and the coherent integration period is 1 ms. Combining Figure 2 it can be seen that at medium and high signal-to-noise ratios, the carrier-to-noise ratio estimation accuracy of the method of this application is higher than that of the NWPR method. Table 1 gives the specific values of the BCPR carrier-to-noise ratio estimation accuracy. And the method of this application theoretically derives the mean value of the carrier-to-noise ratio estimation , the theoretical expression is as follows, and the correctness of the theoretical derivation is verified by simulation.

[0050]

[0051]

[0052] Table 1 Mean Square Error of BCPR Carrier-to-Noise Ratio Estimation

[0053] It should be understood that the above device is used to execute the method in the above embodiment. For the corresponding program modules in the device, their implementation principles and technical effects are similar to those described in the above method. The working process of this device can refer to the corresponding process in the above method, and will not be elaborated here.

[0054] Based on the method in the above embodiment, an embodiment of the present application provides a receiver, which may include: a processor, a communications interface, a memory, and a communication bus. Among them, the processor, the communications interface, and the memory complete mutual communication through the communication bus. The processor can call the logical instructions in the memory to execute the method in the above embodiment.

[0055] In addition, when the logical instructions in the above memory are implemented in the form of a software functional unit and sold or used as an independent product, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application.

[0056] Based on the method in the above embodiment, an embodiment of the present application provides a computer-readable storage medium. The computer-readable storage medium stores a computer program. When the computer program runs on the processor, it enables the processor to execute the method in the above embodiment.

[0057] Based on the method in the above embodiment, an embodiment of the present application provides a computer program product. When the computer program product runs on the processor, it enables the processor to execute the method in the above embodiment.

[0058] It can be understood that the processor in the embodiments of the present application may be a central processing unit (CPU), or may also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The general-purpose processor may be a microprocessor or any conventional processor.

[0059] The method steps in the embodiments of the present application may be implemented in a hardware manner or by a processor executing software instructions. The software instructions may be composed of corresponding software modules, and the software modules may be stored in a random access memory (RAM), flash memory, read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), registers, hard disks, removable hard disks, CD-ROMs, or any other form of storage medium well known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium may also be a component of the processor. The processor and the storage medium may be located in an ASIC.

[0060] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the processes or functions described in the embodiments of the present application are generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium or transmitted through the computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center by wire (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wirelessly (such as infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that the computer can access or a data storage device such as a server or data center that includes one or more integrated available media. The available medium can be a magnetic medium (such as a floppy disk, hard disk, magnetic tape), an optical medium (such as a DVD), or a semiconductor medium (such as a solid state disk (SSD)), etc.

[0061] It can be understood that the various numerical numbers involved in the embodiments of the present application are only for the convenience of description and are not used to limit the scope of the embodiments of the present application.

[0062] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for estimating a carrier-to-noise ratio, characterized in that: include: Performing a square accumulation and summing operation on the integrated signals within a number of coherent integration periods to obtain the total power of the desired integrated signal and the noise; The baseband signal samples within the same number of coherent integration periods are then subjected to a square accumulation and summation operation to obtain the total power of the desired baseband signal and noise; The carrier-to-noise ratio is calculated by using the broadband characteristics of the baseband signal, the narrowband characteristics of the integrated signal, and the mapping relationship between the signal power and the noise power between the baseband signal and the integrated signal; The baseband signal is a signal obtained by stripping the intermediate frequency carrier and Doppler frequency shift from the intermediate frequency signal of the receiver, including an in-phase baseband signal and an orthogonal baseband signal; The integrated signal is a signal obtained by coherently integrating the baseband signal after stripping the spread spectrum code, including an in-phase integrated signal and an orthogonal integrated signal.

2. The method for estimating the carrier-to-noise ratio according to claim 1, wherein: The calculation formula for the total power of the expected integrated signal and noise is as follows: in, is the power of the integrated signal, and are the instantaneous branch in-phase integral signal and quadrature integral signal respectively, is the number of coherent integration cycles, subscript is an instant branch, subscript For the coherent integration period.

3. The method for estimating the carrier-to-noise ratio according to claim 1, wherein: The calculation formula for the total power of the desired baseband signal and noise is as follows: in, 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 sampling points.

4. The method for estimating the carrier-to-noise ratio according to claim 1, wherein: The carrier-to-noise ratio calculation formula is as follows: in, is the carrier-to-noise ratio, is the number of sampling points in the coherent integration period, is the power of the integrated signal, is the power of the baseband signal, is the coherent integration period.

5. The method for estimating the carrier-to-noise ratio according to claim 1, wherein: The time length selected for carrier-to-noise ratio estimation should take into account both the stability of the estimation result and the real-time performance of the calculation. The longer the time length, the better the stability of the estimation result and the worse the real-time performance of the calculation.

6. The method for estimating the carrier-to-noise ratio according to claim 1, wherein: The signal obtained by stripping the intermediate frequency carrier and Doppler frequency shift in the intermediate frequency signal of the receiver includes: (1) Down-convert the RF signal received by the receiver antenna to obtain an intermediate frequency signal; (2) The intermediate frequency signal is multiplied by the cosine carrier in the first mixer to obtain an in-phase baseband signal, and the intermediate frequency signal is multiplied by the sine carrier in the second mixer to obtain an orthogonal baseband signal. The cosine carrier and the sine carrier are both generated by the carrier NCO.

7. The method for estimating the carrier-to-noise ratio according to claim 1, wherein: The step of stripping the spread spectrum code from the baseband signal and then coherently integrating the signal comprises: (1) The in-phase baseband signal and the orthogonal baseband signal are sent to the correlator and correlated with the local instantaneous branch spreading code generated by the code NCO to strip off the spreading code; (2) The correlator output is sent to the integration cleaner for coherent integration. The output of the integration cleaner is an in-phase integration signal and an orthogonal integration signal.

8. The method for estimating the carrier-to-noise ratio according to any one of claims 1 to 7, characterized in that: The carrier-to-noise ratio estimation method is applied to a receiver of a spread spectrum system.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program runs on a processor, the processor is caused to enter the carrier-to-noise ratio estimation method according to any one of claims 1 to 8.

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