CN114726696A - Frequency offset estimation method based on narrow band system, terminal and storage medium - Google Patents
Frequency offset estimation method based on narrow band system, terminal and storage medium Download PDFInfo
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Abstract
The embodiment of the application relates to the technical field of communication of the Internet of things, and discloses a frequency offset estimation method based on a narrow-band system, a terminal and a storage medium. The method comprises the following steps: acquiring a pilot frequency symbol and a time-frequency position of the pilot frequency symbol in a received OFDM symbol, and generating a local pilot frequency symbol corresponding to the pilot frequency symbol; acquiring a first channel estimation value based on the pilot frequency symbol and the local pilot frequency symbol; acquiring a second channel estimation value based on the first channel estimation value; acquiring a third channel estimation value based on different differential distances; acquiring a first frequency offset estimation value based on the third channel estimation value; and performing first-order loop filtering on the first frequency offset estimation value to obtain a second frequency offset estimation value. The frequency offset estimation method based on the narrow-band system solves the problems that the frequency offset of the existing narrow-band system is greatly influenced by noise and the reliability of frequency offset estimation cannot be guaranteed in a weak coverage scene, and improves the accuracy of the frequency offset estimation of the narrow-band system.
Description
Technical Field
The embodiment of the application relates to the technical field of communication of the internet of things, in particular to a frequency offset estimation method based on a narrow-band system, a terminal and a storage medium.
Background
With the increasing demand of the internet of things, a plurality of internet of things communication solutions and standards are presented. The narrowband Internet Of Things (NB-IoT) is a cellular-based narrowband Internet Of Things wireless communication standard and has the characteristics Of wide coverage, large connection, low power consumption and low cost. In a communication system, due to the influence of factors such as frequency difference between a transmitting end and a receiving end, doppler shift introduced by movement of the receiving end, and the like, frequency deviation (frequency offset) exists between a carrier frequency and the frequency of a local crystal oscillator. Due to the influence of the factors of introducing the frequency deviation, deviation occurs between the center frequency of the signal sent by the sending end and the center frequency of the received signal, namely, the frequency deviation occurs on the signal of the receiving end. Therefore, the frequency offset needs to be correctly estimated and compensated at the receiving end, so that the communication system can stably operate.
Disclosure of Invention
An object of the embodiment of the application is to provide a frequency offset estimation method, a terminal and a storage medium based on a narrowband system, which solve the problems that the frequency offset of the existing narrowband internet of things system is greatly influenced by noise and the reliability of frequency offset estimation cannot be guaranteed in a weak coverage scene.
In order to solve the above technical problem, an embodiment of the present application provides a frequency offset estimation method based on a narrowband system, including the following steps: acquiring a pilot frequency symbol and a time-frequency position of the pilot frequency symbol in a received OFDM symbol; generating a local pilot symbol corresponding to the pilot symbol based on the pilot symbol and the time-frequency position of the pilot symbol; acquiring a first channel estimation value based on the pilot frequency symbol and the local pilot frequency symbol; the first channel estimation value is a channel estimation value of the pilot frequency symbol at the time-frequency position of the pilot frequency symbol; acquiring a second channel estimation value based on first channel estimation values corresponding to a plurality of pilot symbols on an OFDM symbol; the second channel estimation value is a channel estimation value of the pilot frequency symbol in a time period; acquiring a third channel estimation value based on different differential distances; the differential distance is the distance of two pilot symbols in time, and the third channel estimation value is the channel estimation value of the pilot symbols in different differential distances; acquiring a first frequency offset estimation value based on the third channel estimation value; and performing first-order loop filtering on the first frequency offset estimation value to obtain a second frequency offset estimation value.
In addition, the performing first-order loop filtering on the first frequency offset estimation value to obtain a second frequency offset estimation value includes: performing first-order loop filtering on the first frequency offset estimation value through a loop filter, and calculating a second frequency offset estimation value through a formula (1) and a formula (2):
yn＝yn-1+kif (2)
wherein the content of the first and second substances,
the central frequency of the output signal of the loop filter is the second frequency offset estimation value; f is the central frequency of the input signal of the loop filter, namely a first frequency offset estimation value; y isnIs kiCenter frequency, y, of the output signal at the present moment of the branchn-1Is kiCenter frequency, k, of the output signal at a moment in time on a branchp、kiAre the coefficients of the loop filter.
In addition, the central frequency of the output signal on the loop filter branch of the first frequency offset estimation value is delayed through a delay unit.
In addition, the obtaining a first frequency offset estimation value based on the third channel estimation value includes:
calculating an average value of the third frequency offset estimation values, and calculating a phase difference to obtain the first frequency offset estimation value, as shown in formula (3):
wherein the content of the first and second substances,
is a first frequency offset estimate, TsubIs the time difference of the pilot symbols, L is the number of pilot symbols,
for the second channel estimate on OFDM symbol l,
is the conjugate of the channel estimate at a differential distance D over OFDM symbol l.
In addition, the obtaining a second channel estimation value based on first channel estimation values corresponding to a plurality of pilot symbols on an OFDM symbol includes:
combining the first channel estimation values of different pilot symbols on the same OFDM symbol, and acquiring a second channel estimation value as shown in formula (4);
wherein the content of the first and second substances,
for the second channel estimate on the OFDM symbol/,
k is a frequency domain resource index of the pilot frequency symbol on the OFDM symbol, and l is a time domain resource index of the pilot frequency symbol on the OFDM symbol.
In addition, the obtaining a first channel estimation value based on the pilot symbol and the local pilot symbol includes:
calculating a first channel estimation value by a least square algorithm, as shown in equation (5);
wherein the content of the first and second substances,
the first channel estimation value of the pilot frequency symbol is shown, k is the frequency domain resource index of the pilot frequency symbol on the OFDM symbol, l is the time domain resource index of the pilot frequency symbol on the OFDM symbol, X is the local pilot frequency signal, and Y is the receiving end signal.
In addition, the pilot symbols include a narrowband reference signal and a narrowband synchronization signal, wherein the narrowband synchronization signal includes a primary synchronization signal and a secondary synchronization signal;
the pilot symbols include one or more of a narrowband reference signal, a primary synchronization signal, and a secondary synchronization signal.
An embodiment of the present application further provides a terminal, including: a loop filter and at least one processor connected to the loop filter; and a memory communicatively coupled to the at least one processor; wherein the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method for estimating frequency offset based on a narrowband system described above.
In addition, the terminal also comprises a delay unit, and the delay unit is in communication connection with the loop filter.
Embodiments of the present application further provide a computer-readable storage medium storing a computer program, which when executed by a processor implements the above-mentioned frequency offset estimation method based on a narrowband system.
Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:
the embodiment of the application provides a frequency offset estimation method, a terminal and a storage medium based on a narrow band system, firstly, pilot frequency symbols and time-frequency positions of the pilot frequency symbols are obtained from received OFDM symbols, and local pilot frequency symbols corresponding to the pilot frequency symbols are generated; then, based on the pilot frequency symbols and the local pilot frequency symbols, first channel estimation values corresponding to various types of pilot frequency symbols are calculated, then the first channel estimation values are combined to obtain a second channel estimation value, a third channel estimation value is calculated by selecting different differential distances, the third channel estimation value is averaged, a phase difference is calculated to obtain a first frequency offset estimation value, and finally, first-order loop filtering is performed on the first frequency offset estimation value to obtain a second frequency offset estimation value, namely an accurate frequency offset estimation value, so that the accuracy of the frequency offset estimation value of the narrowband system is improved.
On one hand, according to the frequency offset estimation method based on the narrowband system provided by the embodiment of the application, the time-frequency position of the pilot symbol corresponding to each pilot symbol is obtained in the OFDM symbol through a plurality of different pilot symbols, a local pilot symbol is generated, and a first channel estimation value is calculated according to the pilot symbol and the local pilot symbol; the pilot frequency symbol not only adopts a narrowband reference signal NRS, but also flexibly utilizes a narrowband primary synchronization signal NPSS and a narrowband secondary synchronization signal NSSS as pilot frequency symbols to carry out frequency offset estimation; and a plurality of different types of pilot symbols are adopted, so that a more accurate frequency offset estimation result can be obtained. On the other hand, the embodiment of the application obtains a third channel estimation value by selecting a proper differential distance; the third channel estimation values under different differential distances are averaged, and then the first frequency offset estimation value is calculated, so that the influence of noise on the first frequency offset estimation value can be effectively reduced, the accuracy of the first frequency offset estimation value is improved, and the accuracy of the second frequency offset estimation value is improved. In addition, the first-order loop filtering is performed on the first frequency offset estimation value by adopting a loop filter, the loop filter filters a rapidly-changed phase error caused by input signal noise and a high-frequency component leaked by a phase detector, and the second frequency offset estimation value is more accurate by selecting a proper loop filtering coefficient, so that the accuracy and the reliability of the frequency offset estimation of the narrowband internet of things system are ensured.
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One or more embodiments are illustrated by the corresponding figures in the drawings, which are not meant to be limiting.
Fig. 1 is a flowchart of a frequency offset estimation method based on a narrowband system according to an embodiment of the present application;
fig. 2 is a flowchart of a loop filter process provided in an embodiment of the present application;
fig. 3 is a schematic diagram of a terminal according to an embodiment of the present application.
Detailed Description
To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, it will be appreciated by those of ordinary skill in the art that in the examples of the present application, numerous technical details are set forth in order to provide a better understanding of the present application. However, the technical solution claimed in the present application can be implemented without these technical details and various changes and modifications based on the following embodiments. The following embodiments are divided for convenience of description, and should not constitute any limitation to the specific implementation manner of the present application, and the embodiments may be mutually incorporated and referred to without contradiction.
With the increase of the demand for interconnection between people and things and communication between things and things, communication technology is continuously developing to meet new demand in addition to meeting the traditional demand for interconnection between people and things. In this context, according to the service features and application scenarios of the internet of things, the 3rd Generation Partnership Project (3 GPP) has formulated the standards of the narrowband internet of things NB-IoT to meet the continuously developing service requirements of the internet of things.
The third generation partnership project 3GPP has been collaborated by the global standards organization with the goal of developing 3G specifications. The 3GPP defines a third-generation Mobile communication standard, i.e., Universal Mobile Telephone System (UMTS), for a wireless interface based on a gsm mac core network and using Wideband Code Division Multiple Access (WCDMA), and is responsible for defining a protocol compatible with an ANSl-41 core network on the wireless interface. In order to ensure compatibility between 3G systems designed by various manufacturers and to share design resources, a 3GPP standard is established to standardize wideband code division multiple access WCDMA.
The narrowband Internet of things NB-IoT is a cellular-based narrowband Internet of things wireless communication standard and has the characteristics of wide coverage, large connection, low power consumption and low cost. Based on a narrowband and flexible network deployment mode, the NB-IoT can be directly deployed to the existing network and coexists with the existing network. The narrow-band Internet of things NB-IoT is inherited from LTE (Long Term evolution), and on the basis of LTE, the narrow-band Internet of things NB-IoT greatly simplifies channels and signaling interaction, and meets the characteristics of low power consumption and low cost of the narrow-band Internet of things NB-IoT.
As known from the background art, frequency deviation (frequency offset) exists between a carrier frequency and a frequency of a local crystal oscillator, and the frequency offset of a receiving end needs to be correctly estimated and compensated, so that a communication system can stably operate. Setting the center frequency of a signal transmitted by a transmitting end to be fcDue to the influence of the frequency deviation, the center frequency of the received signal is fc' if the frequency offset between the transmitting end and the receiving end is fcAnd fc' Difference, set frequency offset to
Then
In addition, in order to maintain the low-cost characteristics of the narrowband internet of things NB-IoT chip and the module, when the ambient temperature changes rapidly, the crystal oscillator may have a large frequency drift, and at this time, the receiving end needs to be able to track the frequency drift. In particular, the narrowband internet of things NB-IoT system employs Orthogonal Frequency Division Multiplexing (OFDM), and a communication system based on OFDM is more sensitive to Frequency offset because the Frequency offset may destroy orthogonality between subcarriers. The Orthogonal Frequency Division Multiplexing (OFDM) system has strict requirements on orthogonality among subcarriers, and any small carrier frequency offset destroys the orthogonality among the subcarriers, thereby causing mutual interference (ISI) among the subchannels.
In order to solve the problem that the existing narrowband internet of things NB-IoT frequency offset is greatly affected by noise and the reliability of frequency offset estimation cannot be guaranteed in a weak coverage scenario, referring to fig. 1, an embodiment of the present application provides a frequency offset estimation method based on a narrowband system, including the following steps:
step S1, obtaining the pilot symbols and their time-frequency positions in the received OFDM symbols.
Step S2, based on the pilot symbol and the time-frequency position of the pilot symbol, generates a local pilot symbol corresponding to the pilot symbol.
Step S3, acquiring a first channel estimation value based on the pilot frequency symbol and the local pilot frequency symbol; the first channel estimation value is a channel estimation value of the pilot frequency symbol at the time frequency position of the pilot frequency symbol.
Step S4, acquiring a second channel estimation value based on the first channel estimation values corresponding to the plurality of pilot symbols on the OFDM symbol; the second channel estimate is a channel estimate of the pilot symbols over the time period.
Step S5, acquiring a third channel estimation value based on different differential distances; the differential distance is the distance of two pilot symbols in time, and the third channel estimation value is the channel estimation value of the pilot symbols at different differential distances.
And step S6, acquiring a first frequency offset estimation value based on the third channel estimation value.
And step S7, performing first-order loop filtering on the first frequency offset estimation value to obtain a second frequency offset estimation value.
In a communication system, the bandwidth that a channel can provide is usually much wider than the bandwidth required for transmitting one signal, and if one channel only transmits one signal, it is very wasteful, and in order to make full use of the bandwidth of the channel, a frequency division multiplexing method is usually adopted. Orthogonal frequency division multiplexing OFDM is one of multi-Carrier modulation MCM (Multi Carrier modulation), realizes parallel transmission of high-speed serial data through frequency division multiplexing, has better anti-multipath fading capability, can support multi-user access, and has the basic principle that a signal is divided into N sub-signals, and then N sub-signals are used for respectively modulating N sub-carriers which are orthogonal to each other; the channel is divided into a plurality of orthogonal sub-channels, the high-speed data signal is converted into parallel low-speed sub-data streams, and the parallel low-speed sub-data streams are modulated to be transmitted on each sub-channel. The orthogonal sub-carriers can be modulated and demodulated by fast fourier transform (FFT/IFFT). Since the frequency spectrums of the sub-carriers overlap with each other, higher frequency spectrum efficiency can be obtained.
The carriers in OFDM are orthogonal, each carrier has an integral number of carrier periods in a symbol time, and the frequency spectrum zero of each carrier is overlapped with the zero of the adjacent carrier, so that the interference between the carriers is reduced. Because of the partial overlap between the carriers, the OFDM improves the band utilization ratio compared to the conventional Frequency Division Multiple Access (FDMA).
In general, pilot symbols are inserted into OFDM to meet different requirements, for example, the pilot insertion method includes Time Division Multiplexing (TDM) insertion, Frequency Division Multiplexing (FDM) insertion, and discrete insertion (a combination of FDM and TDM). Different pilot insertion modes are suitable for different purposes (such as synchronization, phase noise compensation, channel estimation and the like), for example, a dedicated pilot symbol (i.e. TDM insertion mode) is suitable for channel estimation and coarse synchronization of time domain/frequency domain; the dedicated pilot subcarriers (i.e. FDM insertion mode) are adopted to be suitable for phase compensation and fine adjustment of carrier frequency; while the scattered pilot insertion can be used for channel estimation and fine adjustment of carrier frequency offset, thereby effectively reducing the overhead of the pilot.
The time division multiplexing TDM is characterized in that time slots are planned and allocated in advance and are fixed, so the time division multiplexing TDM is also called synchronous time division multiplexing. Its advantages are fixed time slot distribution, easy regulation and control, and suitability for digital information transmission. Specifically, in OFDM, a time division multiplexing TDM is used to insert pilot symbols, that is, the time provided for the whole channel to transmit information is divided into a plurality of time slices (time slots for short), and different pulse signals are inserted into different time slots, so as to sequentially realize multiplexing of multiple signals in the time domain; and allocating the time slots to each signal source for use, and each signal monopolizes a channel in the own time slot for data transmission. The pilot is sent on all sub-carriers, the minimum unit of the time domain is an OFDM symbol containing pilot information, and the system transmits one pilot symbol every several data symbols.
In some embodiments, the pilot symbols include a Narrowband Reference Signal (NRS) and a Narrowband Primary Synchronization Signal (NPSS), a Narrowband Secondary Synchronization Signal (NSSS), and multiple types of pilot symbols are used for frequency offset estimation, which can provide a more accurate frequency offset estimation result.
The commonly used method for estimating the frequency offset of the narrowband internet of things NB-IoT receiver is based on a pilot frequency assisted frequency offset estimation algorithm proposed by Classen, the frequency offset is jointly estimated by the received frequency domain pilot frequency and the local frequency domain pilot frequency, and the frequency offset estimation value can be expressed as formula (a):
wherein the content of the first and second substances,
for the frequency offset estimation, TsubIs the time difference of the pilot frequency, L is the number of the pilot frequency, D is the differential distance, p (j) is the frequency domain position of the jth pilot frequency, Yk+D[p(j)，ε]Denotes the pilot frequency at p (j) on the k + D symbol period received, Xk[p(j)]Indicating the pilot at p (j) on the k + D symbol period.
In practice, the above equation (a) can be expressed in the form of Least Squares (LS) channel estimates over different OFDM symbols, the basic principle of the Least squares algorithm being to minimize the sum of the squares of the differences between the received signal and the noise-free data. The received signal may be represented as Y ═ HX + n, where X is the transmitted pilot signal, i.e., the local pilot signal, H is the channel transfer function, and n is noise. For pilot signals of NB-IoT of narrowband Internet of things, XX is satisfied*1, then
According to the least squares algorithm, the Classen frequency offset estimation algorithm can be represented by equation (b):
wherein, the first and the second end of the pipe are connected with each other,
for the frequency offset estimation, TsubIs the time difference of the pilot frequency, L is the number of the pilot frequency, D is the differential distance, p (j) is the frequency domain position of the jth pilot frequency,
for the channel estimate for the pilot located at p (j) over the k + D symbol period received,
the conjugate of the channel estimate for the pilot at p (j) on the k-th received symbol period.
It should be noted that, since the received signal not only carries the frequency offset but also is affected by noise, the frequency offset estimation value
May also be affected by noise. In particular, the wide coverage property of the narrowband internet of things NB-IoT determines that the cell edge terminal is usually in a worse channel condition, which may cause the frequency offset estimation value to be affected by noise more, so that the reliability of the frequency offset estimation cannot be guaranteed.
Since the least square algorithm is calculated by neglecting the noise, the accuracy of the obtained channel estimation value is greatly reduced when the noise is large. Therefore, an embodiment of the present application provides a frequency offset estimation method based on a narrowband system, which includes first obtaining a pilot symbol and a time-frequency position of the pilot symbol in a received OFDM symbol, and generating a local pilot symbol corresponding to the pilot symbol; and then calculating first channel estimation values corresponding to various different types of pilot symbols, combining the first channel estimation values to obtain second channel estimation values, calculating third channel estimation values by selecting different differential distances, averaging the third channel estimation values, calculating phase difference to obtain first frequency offset estimation values, and finally performing first-order loop filtering on the first frequency offset estimation values to obtain second frequency offset estimation values, namely accurate frequency offset estimation values, so as to improve the accuracy of the frequency offset estimation values of the narrowband internet of things system.
In some embodiments, the step S7 of performing first-order loop filtering on the first frequency offset estimation value to obtain a second frequency offset estimation value includes: performing first-order loop filtering on the first frequency offset estimation value through a loop filter, and calculating a second frequency offset estimation value through a formula (1) and a formula (2):
yn＝yn-1+kif (2)
wherein the content of the first and second substances,
the central frequency of the output signal of the loop filter is the second frequency offset estimation value; f is the central frequency of the input signal of the loop filter, namely a first frequency offset estimation value; y isnIs kiCenter frequency, y, of the output signal at the present moment of the branchn-1Is kiCenter frequency, k, of the output signal at a time on a branchp、kiAre the coefficients of the loop filter.
Referring to fig. 2, loop filtering may be performed on the first frequency offset estimation value obtained in step S6 by using a first-order loop filter, and the difference equation of the first-order loop filtering process is shown in the above formula (1) and formula (2), where k isp、kiAll coefficients of the loop filter are determined by the loop bandwidth and the input sampling rate, and k is adjusted similarlyp、kiLoop bandwidth is also affected. Typically, large bandwidth ringsThe loop filter can track the change of the input data quickly, the loop filter with small bandwidth can filter out the noise of the larger part, and the input data can be tracked more accurately, namely, the loop filter coefficient is increased, the loop bandwidth is increased, and the filtering effect of the noise is reduced. Considering convergence time and steady-state performance compromise, through a large number of simulation experiments, loop filtering parameters of the embodiment of the application adopt the following selection and configuration modes: k is a radical ofp＝0.1，ki0.02. According to actual requirements and scenes, loop filtering parameter selection different from the above can be adopted, for example, in a scene needing to quickly track the change of the upper frequency offset; larger loop coefficients may be selected and smaller loop coefficients may be selected when more stable loop output is desired.
Referring to fig. 2, the delay unit F delays the center frequency of the output signal in the loop filter branch of the first frequency offset estimation value to filter the noise. Delay unit F will kiCenter frequency y of output signal at certain time of branchnIs delayed by one unit, and is delayed by kiCenter frequency y of output signal at a moment on the branchn-1After first-order loop filtering is performed on the first frequency offset estimation value, a second frequency offset estimation value is calculated through formula (1) and formula (2).
In some embodiments, obtaining the first frequency offset estimate based on the third channel estimate in step S6 includes:
calculating an average value of the third frequency offset estimation values, and calculating a phase difference to obtain a first frequency offset estimation value, as shown in formula (3):
wherein the content of the first and second substances,
is a first frequency offset estimate, TsubIs the time difference of the pilot symbols, L is the number of pilot symbols,
for the second channel estimate on OFDM symbol l,
is the conjugate of the channel estimate at a differential distance D over OFDM symbol l.
According to the method and the device, the first frequency offset estimation value is calculated according to a Classen algorithm, specifically, according to the types of different pilot symbols, different differential distances can be selected to calculate the average value of the third frequency offset estimation value, the phase difference is calculated to obtain the first frequency offset estimation value, and the influence of noise on the first frequency offset estimation value can be reduced.
In some embodiments, the obtaining a second channel estimation value based on the first channel estimation values corresponding to the plurality of pilot symbols on the OFDM symbol in step S4 includes: combining the first channel estimation values of different pilot symbols on the same OFDM symbol, and acquiring a second channel estimation value as shown in formula (4);
wherein the content of the first and second substances,
for the second channel estimate on the OFDM symbol/,
and k is a frequency domain resource index of the pilot symbol on the OFDM symbol, and l is a time domain resource index of the pilot symbol on the OFDM symbol.
According to the method and the device, the first channel estimation values of the pilot symbols of different frequency domain resources on the same OFDM symbol are combined, and more accurate frequency offset estimation results can be obtained through different types of pilot symbols.
In some embodiments, the obtaining the first channel estimation value based on the pilot symbols and the local pilot symbols in step S3 includes:
calculating a first channel estimation value by a least square algorithm, as shown in formula (5);
wherein the content of the first and second substances,
the first channel estimation value of the pilot frequency symbol is shown, k is the frequency domain resource index of the pilot frequency symbol on the OFDM symbol, l is the time domain resource index of the pilot frequency symbol on the OFDM symbol, X is the local pilot frequency signal, and Y is the receiving end signal.
Since the basic principle of the least squares algorithm is to minimize the sum of the squares of the differences between the received signal and the noise-free data, which is usually calculated by ignoring the noise, the accuracy of the obtained channel estimation value will be greatly reduced when the noise is large. Therefore, the embodiment of the present application provides a frequency offset estimation method based on a narrowband system, where a received signal is denoted as Y ═ HX + n, where X is a transmitted pilot signal, H is a channel transfer function, and n is noise. When ignoring noise, H ═ X-1Y, the first channel estimation value is thus calculated by equation (5).
In some embodiments, the pilot symbols in the above step include a narrowband reference signal and a narrowband synchronization signal, where the narrowband synchronization signal includes a primary synchronization signal and a secondary synchronization signal; the pilot symbols include one or more of a narrowband reference signal NRS, a primary synchronization signal NPSS, and a secondary synchronization signal NSSS.
In some embodiments, a narrowband reference signal NRS, a narrowband primary synchronization signal NPSS, and a narrowband secondary synchronization signal NSSS are used as pilot symbols, and different pilot symbols and time-frequency positions of corresponding pilot symbols are obtained from OFDM symbols, respectively, to generate corresponding local pilot symbols; then, based on the pilot frequency symbols and the local pilot frequency symbols, respectively calculating first channel estimation values of the pilot frequency symbols through a formula (5); then, pilot channel estimation values of different frequency domain resources on the same OFDM symbol are combined through a formula (4) to obtain a second channel estimation value; next, calculating a first frequency offset estimation value according to a Classen algorithm, specifically comprising the steps of: selecting different differential distances D to calculate the average value of correlation results of the least square estimation value according to different pilot frequency resource types, and calculating the phase difference through a formula (3) to obtain a first frequency offset estimation value; and finally, performing first-order loop filtering on the first frequency offset estimation value through a formula (1) and a formula (2), and selecting a proper loop filtering coefficient according to the pilot frequency resource type and the pilot frequency time period, so as to better filter noise and obtain a second frequency offset estimation value, namely an accurate frequency offset estimation value.
The embodiment of the application provides a frequency offset estimation method based on a narrow-band system, on one hand, a pilot frequency symbol and a time-frequency position of the corresponding pilot frequency symbol are obtained in an OFDM symbol by aiming at a plurality of different pilot frequency symbols, and a corresponding local pilot frequency symbol is generated; then, based on the pilot frequency symbol and the local pilot frequency symbol, acquiring a first channel estimation value; the pilot frequency symbol not only adopts a narrowband reference signal NRS, but also flexibly utilizes a narrowband primary synchronization signal NPSS and a narrowband secondary synchronization signal NSSS as the pilot frequency symbol to carry out frequency offset estimation; and a plurality of different types of pilot symbols are adopted, so that a more accurate frequency offset estimation result can be obtained. On the other hand, in step S5 in the embodiment of the present application, a third channel estimation value is obtained by selecting an appropriate differential distance; the third channel estimation values under different differential distances are averaged, and then the first frequency offset estimation value is calculated, so that the influence of noise on the first frequency offset estimation value can be effectively reduced, the accuracy of the first frequency offset estimation value is improved, and the accuracy of the second frequency offset estimation value is improved. In addition, step S7 of the embodiment of the present application further employs a loop filter to perform first-order loop filtering on the first frequency offset estimation value, the loop filter filters a rapidly changing phase error caused by input signal noise and a high-frequency component leaked by the phase detector, and by selecting a suitable loop filter coefficient, the obtained second frequency offset estimation value is more accurate, thereby ensuring accuracy and reliability of the narrowband system frequency offset estimation.
Referring to fig. 3, another embodiment of the present application further provides a terminal, including: a loop filter 101 and at least one processor 102 connected to the loop filter 101; and a memory 103 communicatively coupled to the at least one processor 102; wherein, the memory 103 stores instructions executable by the at least one processor 102, and the instructions are executed by the at least one processor 102 to enable the at least one processor 102 to execute the narrowband system-based frequency offset estimation method provided by the above-mentioned embodiments.
In some embodiments, the terminal further comprises a delay unit 104, the delay unit 104 being communicatively coupled to the loop filter 101.
Where memory 103 and processor 102 are coupled by a bus, the bus may comprise any number of interconnected buses and bridges that couple one or more of the various circuits of processor 102 and memory 103 together. The bus may also connect various other circuits such as peripherals, voltage regulators, power management circuits, and the like, which are well known in the art, and therefore, will not be described any further herein. A bus interface provides an interface between the bus and the transceiver. The transceiver may be one element or a plurality of elements, such as a plurality of receivers and transmitters, providing a means for communicating with various other apparatus over a transmission medium. The data processed by the processor 102 is transmitted over a wireless medium through an antenna, which further receives the data and transmits the data to the processor 102.
The processor 102 is responsible for managing the bus and general processing and may also provide various functions including timing, peripheral interfaces, voltage regulation, power management, and other control functions. And memory 103 may be used to store data used by processor 102 in performing operations.
In addition, another embodiment of the present application provides a computer-readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the frequency offset estimation method based on the narrowband system provided by the foregoing embodiment.
That is, as can be understood by those skilled in the art, all or part of the steps in the method for implementing the embodiments described above may be implemented by a program instructing related hardware, where the program is stored in a storage medium and includes several instructions to enable a device (which may be a single chip, a chip, or the like) or a processor (processor) to execute all or part of the steps of the method described in the embodiments of the present application. And the aforementioned storage medium includes: various media capable of storing program codes, such as a U disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk.
It will be understood by those of ordinary skill in the art that the foregoing embodiments are specific examples for carrying out the present application, and that various changes in form and details may be made therein without departing from the spirit and scope of the present application in practice.
Claims (10)
1. A frequency offset estimation method based on a narrow band system is characterized by comprising the following steps:
acquiring a pilot frequency symbol and a time-frequency position of the pilot frequency symbol in a received OFDM symbol;
generating a local pilot symbol corresponding to the pilot symbol based on the pilot symbol and the time-frequency position of the pilot symbol;
acquiring a first channel estimation value based on the pilot frequency symbol and the local pilot frequency symbol; the first channel estimation value is a channel estimation value of the pilot frequency symbol at the time-frequency position of the pilot frequency symbol;
acquiring a second channel estimation value based on first channel estimation values corresponding to a plurality of pilot symbols on an OFDM symbol; the second channel estimation value is a channel estimation value of the pilot frequency symbol in a time period;
acquiring a third channel estimation value based on different differential distances; the differential distance is the distance of the two pilot symbols in time, and the third channel estimation value is the channel estimation value of the pilot symbols in different differential distances;
acquiring a first frequency offset estimation value based on the third channel estimation value;
and performing first-order loop filtering on the first frequency offset estimation value to obtain a second frequency offset estimation value.
2. The method of claim 1, wherein the performing a first-order loop filtering on the first frequency offset estimation value to obtain a second frequency offset estimation value comprises:
performing first-order loop filtering on the first frequency offset estimation value through a loop filter, and calculating a second frequency offset estimation value through a formula (1) and a formula (2):
yn＝yn-1+kif (2)
wherein the content of the first and second substances,
the central frequency of the output signal of the loop filter is the second frequency offset estimation value; f is the central frequency of the input signal of the loop filter, namely a first frequency offset estimation value; y isnIs kiCenter frequency, y, of the output signal at the present moment of the branchn-1Is kiCenter frequency, k, of the output signal at a time on a branchp、kiAre the coefficients of the loop filter.
3. The method of claim 2, wherein the center frequency of the output signal of the loop filter branch of the first frequency offset estimation value is delayed by a delay unit.
4. The method of claim 1, wherein obtaining the first frequency offset estimation value based on the third channel estimation value comprises:
calculating an average value of the third frequency offset estimation values, and calculating a phase difference to obtain the first frequency offset estimation value, as shown in formula (3):
wherein the content of the first and second substances,
is a first frequency offset estimate, TsubIs the time difference of the pilot symbols, L is the number of pilot symbols,
for the second channel estimate on OFDM symbol l,
is the conjugate of the channel estimate at a differential distance D over OFDM symbol l.
5. The method of claim 1, wherein the obtaining a second channel estimation value based on a first channel estimation value corresponding to a plurality of pilot symbols on an OFDM symbol comprises:
combining the first channel estimation values of different pilot symbols on the same OFDM symbol, and acquiring a second channel estimation value as shown in formula (4);
wherein the content of the first and second substances,
for the second channel estimate on the OFDM symbol/,
is the first channel estimation value of the pilot frequency symbol, k is the frequency domain resource index of the pilot frequency symbol on the OFDM symbol, l is the frequency domain resource index of the pilot frequency symbol on the OFDM symbolTime domain resource index on an OFDM symbol.
6. The method of claim 1, wherein the obtaining a first channel estimation value based on the pilot symbols and the local pilot symbols comprises:
calculating a first channel estimation value by a least square algorithm, as shown in formula (5);
wherein the content of the first and second substances,
the first channel estimation value of the pilot frequency symbol is shown, k is the frequency domain resource index of the pilot frequency symbol on the OFDM symbol, l is the time domain resource index of the pilot frequency symbol on the OFDM symbol, X is the local pilot frequency signal, and Y is the receiving end signal.
7. The method of claim 1, wherein the pilot symbols comprise a narrowband reference signal and a narrowband synchronization signal, wherein the narrowband synchronization signal comprises a primary synchronization signal and a secondary synchronization signal;
the pilot symbols include one or more of a narrowband reference signal, a primary synchronization signal, and a secondary synchronization signal.
8. A terminal, comprising:
a loop filter and at least one processor connected to the loop filter; and the number of the first and second groups,
a memory communicatively coupled to the at least one processor; wherein the content of the first and second substances,
the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method for narrowband system based frequency offset estimation according to any of claims 1-7.
9. The terminal of claim 8, further comprising:
and the delay unit is in communication connection with the loop filter.
10. A computer-readable storage medium, storing a computer program, wherein the computer program, when executed by a processor, implements the method for estimating frequency offset based on a narrowband system according to any one of claims 1 to 7.
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