CN112714091A - Method and device for determining symbol synchronization position in digital signal - Google Patents
Method and device for determining symbol synchronization position in digital signal Download PDFInfo
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- CN112714091A CN112714091A CN202110323008.1A CN202110323008A CN112714091A CN 112714091 A CN112714091 A CN 112714091A CN 202110323008 A CN202110323008 A CN 202110323008A CN 112714091 A CN112714091 A CN 112714091A
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- H04L27/26—Systems using multi-frequency codes
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- H—ELECTRICITY
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- H04L2027/0026—Correction of carrier offset
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Abstract
The application provides a method and a device for determining a symbol synchronization position in a digital signal, wherein a rough synchronization position of a symbol in the digital signal is determined by calculating a cross-correlation value between a signal long code field and a local long code field in the received digital signal; determining a range to be compensated from the cached digital signals based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through a carrier frequency offset estimation value obtained through calculation to obtain compensated symbol baseband data points; and determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points. Therefore, the carrier frequency offset compensation is carried out on the symbol baseband data points in the digital signal, and then the accurate synchronization position of the symbol in the digital signal is determined on the basis of the rough synchronization position of the symbol, which is beneficial to improving the accuracy of the determination result of the symbol synchronization position.
Description
Technical Field
The present application relates to the field of digital signal transmission technologies, and in particular, to a method and an apparatus for determining a symbol synchronization position in a digital signal.
Background
In a digital signal broadcasting system or an interactive digital information transmission system, a digital signal frame transmitted by a transmitter usually includes a frame header (preamble) portion for frame detection, frame synchronization, carrier synchronization or symbol synchronization of a received signal. In various frame formats defined by various wireless transport standard protocols, the first two fields of the header part, i.e., the Short Tracking Field (STF) of 8us and the Long Tracking Field (LTF) of 8us, are identical in format. In the first field (STF of 8 us) functions such as signal detection, dc offset detection and cancellation, signal power adjustment, etc. are performed. And the LTF field of 8us is used to implement functions such as carrier fine frequency offset estimation and elimination, precise synchronization of OFDM symbols, and channel estimation.
According to the 802.11 series standard, when a plurality of transmitting antennas are used to transmit different digital signals, in order to avoid the potential beamforming problem, the signals transmitted by the respective transmitting antennas need to be subjected to time domain cyclic shift, which results in the occurrence of "pseudo multipath" phenomenon when a receiver performs symbol timing synchronization. These "pseudo multipath" phenomena are inherent properties caused by cyclic shift between transmitted signals, and a receiving end cannot eliminate a digital signal after receiving the digital signal, which causes inaccurate symbol timing synchronization in a complex channel environment, and further introduces inter-symbol interference (ISI), so that a receiving result has a deviation.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a method and an apparatus for determining a symbol synchronization position in a digital signal, in which a carrier frequency offset compensation is performed on a symbol baseband data point in the digital signal, so as to determine a precise symbol synchronization position in the digital signal based on a coarse symbol synchronization position, which is helpful to improve the accuracy of a determination result of the symbol synchronization position.
The embodiment of the application provides a method for determining a symbol synchronization position in a digital signal, which comprises the following steps:
identifying a signal long code field from a received digital signal and acquiring a local long code field;
determining a coarse synchronization position of a symbol in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field;
calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determining a carrier frequency offset estimation value of the digital signal;
determining a range to be compensated from the cached digital signal based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data point in the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point;
and determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points.
Further, the determining the coarse symbol synchronization position in the digital signal by calculating the cross-correlation value between the signal long code field and the local long code field includes:
determining a cross-correlation value between each symbol baseband data point in the signal long code field and a corresponding symbol local data point in the local long code field;
and determining the rough symbol synchronization position in the digital signal based on the determined cross-correlation values and a preset energy gathering window.
Further, the determining a coarse symbol synchronization position in the digital signal based on the determined cross-correlation values and a preset energy gathering window includes:
determining channel path energy of each symbol baseband data point in an energy collection range in the digital signal based on the determined cross-correlation values and a preset energy collection window;
and determining the position of the symbol baseband data point with the maximum channel path energy in the energy collection range as the symbol rough synchronization position.
Further, the calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determining an estimated carrier frequency offset value of the digital signal includes:
calculating an autocorrelation value between each symbol baseband data point in the first subfield and a corresponding symbol baseband data point in the second subfield in the signal long code field;
and determining the carrier frequency offset estimation value of the digital signal based on each autocorrelation value obtained by calculation.
Further, the determining a to-be-compensated range from the cached digital signal based on the coarse symbol synchronization position, and performing carrier frequency offset compensation on the symbol baseband data point within the to-be-compensated range through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point includes:
determining a compensation initial position point from the buffered digital signal based on the coarse synchronization position and the number of symbol baseband data points in each subfield of each field;
determining the range between the compensation initial position point and the rough synchronization position as a range to be compensated;
and carrying out carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through the carrier frequency offset estimation value to obtain compensated symbol baseband data points.
Further, the determining the precise synchronization position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data point includes:
extracting a preset number of baseband data points to be calculated from each field of the compensated symbol baseband data points;
for each baseband data point to be calculated in each field, calculating the noise power of the baseband data point to be calculated, and the noise weighted sum of the noise power of the corresponding baseband data point to be calculated in other fields except the field to which the baseband data point to be calculated belongs in each field of the digital signal;
and determining the accurate synchronous position of the symbols in the digital signal according to the determined weighted sum of the plurality of noises.
Further, the determining a symbol fine synchronization position in the digital signal according to the determined weighted sum of the plurality of noises includes:
determining a minimum noise weighted sum from the plurality of noise weighted sums;
and determining a fine synchronization position of a symbol in the digital signal based on the position of the minimum noise weighted sum and the coarse synchronization position.
The embodiment of the present application further provides a device for determining a symbol synchronization position in a digital signal, where the device for determining includes:
the receiving module is used for identifying a signal long code field from a received digital signal and acquiring a local long code field;
a first position determination module, configured to determine a coarse synchronization position of a symbol in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field;
the frequency offset estimation module is used for calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field and determining a carrier frequency offset estimation value of the digital signal;
the compensation module is used for determining a range to be compensated from the cached digital signals based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through the carrier frequency offset estimation value to obtain compensated symbol baseband data points;
and the second position determining module is used for determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points.
Further, when the first position determination module is configured to determine the coarse symbol synchronization position in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field, the first position determination module is configured to:
determining a cross-correlation value between each symbol baseband data point in the signal long code field and a corresponding symbol local data point in the local long code field;
and determining the rough symbol synchronization position in the digital signal based on the determined cross-correlation values and a preset energy gathering window.
Further, when the first position determination module is configured to determine the coarse symbol synchronization position in the digital signal based on the determined cross-correlation values and a preset energy gathering window, the first position determination module is configured to:
determining channel path energy of each symbol baseband data point in an energy collection range in the digital signal based on the determined cross-correlation values and a preset energy collection window;
and determining the position of the symbol baseband data point with the maximum channel path energy in the energy collection range as the symbol rough synchronization position.
Further, when the frequency offset estimation module is configured to calculate an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determine a carrier frequency offset estimation value of the digital signal, the frequency offset estimation module is configured to:
calculating an autocorrelation value between each symbol baseband data point in the first subfield and a corresponding symbol baseband data point in the second subfield in the signal long code field;
and determining the carrier frequency offset estimation value of the digital signal based on each autocorrelation value obtained by calculation.
Further, when the compensation module is configured to determine a range to be compensated from the cached digital signal based on the coarse synchronization position, and perform carrier frequency offset compensation on the symbol baseband data point within the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point, the compensation module is configured to:
determining a compensation initial position point from the buffered digital signal based on the coarse synchronization position and the number of symbol baseband data points in each subfield of each field;
determining the range between the compensation initial position point and the rough synchronization position as a range to be compensated;
and carrying out carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through the carrier frequency offset estimation value to obtain compensated symbol baseband data points.
Further, when the second position determining module is configured to determine the precise synchronization position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points, the second position determining module is configured to:
extracting a preset number of baseband data points to be calculated from each field of the compensated symbol baseband data points;
for each baseband data point to be calculated in each field, calculating the noise power of the baseband data point to be calculated, and the noise weighted sum of the noise power of the corresponding baseband data point to be calculated in other fields except the field to which the baseband data point to be calculated belongs in each field of the digital signal;
and determining the accurate synchronous position of the symbols in the digital signal according to the determined weighted sum of the plurality of noises.
Further, when the second position determining module is configured to determine the symbol fine synchronization position in the digital signal according to the determined weighted sum of the plurality of noises, the second position determining module is configured to:
determining a minimum noise weighted sum from the plurality of noise weighted sums;
and determining a fine synchronization position of a symbol in the digital signal based on the position of the minimum noise weighted sum and the coarse synchronization position.
An embodiment of the present application further provides an electronic device, including: a processor, a memory and a bus, the memory storing machine-readable instructions executable by the processor, the processor and the memory communicating via the bus when the electronic device is operating, the machine-readable instructions being executable by the processor to perform the steps of the method for determining a symbol synchronization position in a digital signal as described above.
Embodiments of the present application further provide a computer-readable storage medium, which stores a computer program, and when the computer program is executed by a processor, the computer program performs the steps of the method for determining a symbol synchronization position in a digital signal as described above.
The method and the device for determining the symbol synchronization position in the digital signal provided by the embodiment of the application identify a signal long code field from a received digital signal and acquire a local long code field; determining a coarse synchronization position of a symbol in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field; calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determining a carrier frequency offset estimation value of the digital signal; determining a range to be compensated from the cached digital signal based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data point in the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point; and determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points. Therefore, the carrier frequency offset compensation is carried out on the symbol baseband data points in the digital signal, and then the accurate synchronization position of the symbol in the digital signal is determined on the basis of the rough synchronization position of the symbol, which is beneficial to improving the accuracy of the determination result of the symbol synchronization position.
In order to make the aforementioned objects, features and advantages of the present application more comprehensible, preferred embodiments accompanied with figures are described in detail below.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.
Fig. 1 is a flowchart of a method for determining a symbol synchronization position in a digital signal according to an embodiment of the present application;
FIG. 2 is a diagram of a digital signal frame structure;
fig. 3 is a flowchart of another method for determining a symbol synchronization position in a digital signal according to an embodiment of the present application;
FIG. 4 is a schematic diagram of a precise synchronization position determination;
FIG. 5 is a second schematic diagram illustrating a precise synchronization position determination method;
fig. 6 is a schematic structural diagram of an apparatus for determining a symbol synchronization position in a digital signal according to an embodiment of the present application;
fig. 7 is a schematic structural diagram of an electronic device according to an embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present application, presented in the accompanying drawings, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. Every other embodiment that can be obtained by a person skilled in the art without making creative efforts based on the embodiments of the present application falls within the protection scope of the present application.
Research shows that when a plurality of transmitting antennas are used for transmitting different digital signals, in order to avoid the potential problem of beam forming, the signals transmitted by the transmitting antennas need to be subjected to time domain cyclic shift, which causes the phenomenon of 'pseudo multipath' in the process of symbol timing synchronization of a receiver. These "pseudo multipath" phenomena are inherent properties caused by cyclic shift between transmitted signals, and a receiving end cannot eliminate a digital signal after receiving the digital signal, which causes inaccurate symbol timing synchronization in a complex channel environment, and further introduces inter-symbol interference (ISI), so that a receiving result has a deviation.
Based on this, the embodiment of the present application provides a method for determining a symbol synchronization position in a digital signal, which can accurately determine an accurate synchronization position of a symbol in the digital signal, so that a signal receiving result is not affected by the number of transmitting antennas.
Referring to fig. 1, fig. 1 is a flowchart illustrating a method for determining a symbol synchronization position in a digital signal according to an embodiment of the present disclosure. As shown in fig. 1, a method for determining a symbol synchronization position in a digital signal provided in an embodiment of the present application includes:
s101, identifying a signal long code field from the received digital signal, and acquiring a local long code field.
Here, in an Orthogonal Frequency Division Multiplexing (OFDM) digital information system, a frame structure of a digital signal is as shown in fig. 2, and fig. 2 is a schematic diagram of the frame structure of the digital signal. The frame structure of digital signal includes a frame header (preamble) containing two parts of Short Tracking Field (STF) and Long Tracking Field (LTF), the STF Field is composed of 10 identical subfields (STF 1-STF 10) in 802.11n, 802.11ac and 802.11ax systems, and the LTF Field contains two identical OFDM symbols, i.e. LTF1 and LTF2, and the two subfields of LTF contain a common cyclic prefix LTF GI. Illustratively, for a baseband signal of 20MHz bandwidth, the STF field has 160 baseband data points and 16 baseband data points per subfield. LTF1 and LTF2 each have 64 baseband data points, both sharing an LTF GI of 32 baseband data points, and the GI length of the subsequent SIG field is 16 baseband data points; for the 40MHz bandwidth signal mode, the number of baseband data points corresponding to these fields is doubled, and the 20MHz bandwidth is taken as an example in the embodiment of the present application for description.
In a multipath channel environment, if the delay spread of the STF field is located in the shaded area shown in fig. 2, the optimal symbol synchronization position for the LTF1 symbol is located in an area with length L, so that no inter-symbol interference (ISI) is introduced into the OFDM symbols in the subsequent SIG symbol and payload. If the synchronization position of LTF1 is shifted to the left beyond the range of L, the subsequent OFDM symbol may introduce multipath spreading of the previous symbol. If the synchronization position of LTF1 is shifted to the right beyond L, the subsequent OFDM symbol will introduce the energy of its next adjacent symbol.
In this step, a signal long code field of the digital signal is identified from the received digital signal, and at the same time, a local long code field is obtained.
Here, the local long code field is a preset field including 64 baseband data points.
And S102, determining a rough synchronization position of a symbol in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field.
In this step, a cross-correlation value between the received signal long code field and the local long code field is calculated, and a coarse synchronization position of the symbol is determined from the received digital signal according to the calculated cross-correlation value.
S103, calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determining a carrier frequency offset estimation value of the digital signal.
In the step, a first subfield and a second subfield are determined from a received signal long code field, an autocorrelation value between the first subfield and the second subfield is calculated, and a carrier frequency offset estimation value when a symbol baseband data point in a digital signal is compensated is determined according to the autocorrelation value obtained by calculation.
S104, determining a range to be compensated from the cached digital signals based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through the carrier frequency offset estimation value to obtain compensated symbol baseband data points.
In the step, based on the rough synchronization position determined from the digital signal, determining a to-be-compensated range of the symbol baseband data point to be compensated from the buffered digital signal according to the number of the symbol baseband data points contained in each field; and then carrying out carrier frequency offset compensation on the symbol baseband data points in the range to be compensated of the digital signal through the carrier frequency offset estimation value obtained by calculation to obtain the compensated symbol baseband data points.
And S105, determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points.
In this step, the noise power of each baseband data point to be calculated in the compensated baseband data points of the symbol is calculated, and then the accurate synchronization position of the symbol is determined from the digital signal according to the noise power of each baseband data point to be calculated.
The method for determining the symbol synchronization position in the digital signal provided by the embodiment of the application identifies a signal long code field from a received digital signal and acquires a local long code field; determining a coarse synchronization position of a symbol in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field; calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determining a carrier frequency offset estimation value of the digital signal; determining a range to be compensated from the cached digital signal based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data point in the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point; and determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points. Therefore, the carrier frequency offset compensation is carried out on the symbol baseband data points in the digital signal, and then the accurate synchronization position of the symbol in the digital signal is determined on the basis of the rough synchronization position of the symbol, which is beneficial to improving the accuracy of the determination result of the symbol synchronization position.
Referring to fig. 3, fig. 3 is a flowchart illustrating another method for determining a symbol synchronization position in a digital signal according to an embodiment of the present disclosure. As shown in fig. 3, a method for determining a symbol synchronization position in a digital signal according to an embodiment of the present application includes:
s301, identifying a signal long code field from the received digital signal, and acquiring a local long code field.
S302, determining a cross-correlation value between each symbol baseband data point in the signal long code field and a corresponding symbol local data point in the local long code field.
In the step, a symbol local data point corresponding to each symbol baseband data point in a signal long code field of a received digital signal is determined from the local long code field; for each symbol baseband data point, a cross-correlation value is calculated between the symbol baseband data point and its corresponding symbol local data point.
Specifically, the cross-correlation value between the signal long code field and the local long code field is calculated by the following formula:
wherein, γ cross_corr (n) For signals in the long code fieldnThe cross-correlation value between the symbol baseband data point and the local long code field,Nis as followsnThe number of symbol baseband data points in the field to which each symbol baseband data point belongs,
is as followsiThe conjugate of the local data point of the individual local symbol,
is as followsiA symbol baseband data point corresponding to each local symbol local data point,absrepresenting an absolute value.
And S303, determining a rough synchronization position of the symbol in the digital signal based on the determined cross correlation values and a preset energy gathering window.
In the step, firstly, an energy collecting window for collecting the energy of each symbol baseband data point in the digital signal is set according to the number of the symbol baseband data points in the SIG field in the digital signal; then, based on the cross-correlation value of each symbol baseband data point in the signal long code field in the determined digital signal and the energy collection window, the symbol rough synchronization position in the digital signal is determined by sliding the form of the energy collection window on the digital signal.
Here, in the normal GI mode, since the number of symbol baseband data points in the SIG field and the number of symbol baseband data points in the GI part in the other subsequent fields are both 16, a 17-point window long energy collection window can be used to collect the channel path energy of each symbol baseband data point. When a signal is received using a single transmit antenna, this position is the symbol synchronization position of the first sub-field due to the maximum value position found at the rear of the first sub-field and the front of the second sub-field in the signal long code field; when a plurality of transmitting antennas are used for receiving signals, in order to avoid the potential beam forming problem, different values of cyclic shift exist among the transmitting signals of each transmitting antenna, so that when cross-correlation value calculation is carried out in a signal long code field, a pseudo multipath phenomenon generated by the cyclic shifted signals appears on the left side of a channel path without the cyclic shifted signals. These pseudo multi-paths are also covered by the energy collecting window of 17 points, when the multi-path channel delay is long, the energy collecting window of 17 points is not enough to cover all path energy, and the receiving end cannot predict the number of transmitting antennas at the signal transmitting end, so that the synchronization position at this time is not necessarily correct.
S304, calculating an autocorrelation value between a first sub-field and a second sub-field in the signal long code field, and determining a carrier frequency offset estimation value of the digital signal.
S305, determining a range to be compensated from the cached digital signal based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data point in the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point.
S306, determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points.
The descriptions of S301, S304 to S306 may refer to the descriptions of S101, S103 to S105, and the same technical effects can be achieved, which is not described in detail herein.
Further, step S303 includes: determining channel path energy of each symbol baseband data point in an energy collection range in the digital signal based on the determined cross-correlation values and a preset energy collection window; and determining the position of the symbol baseband data point with the maximum channel path energy in the energy collection range as the symbol rough synchronization position.
In the step, for each symbol baseband data point, an energy calculation range of the symbol baseband data point within the energy collection range is determined based on a preset energy collection window, and channel path energy of the symbol baseband data point is calculated according to a cross-correlation value of each symbol baseband data point in the energy calculation range.
Specifically, the channel path energy of the symbol baseband data point is calculated by the following formula:
wherein the content of the first and second substances,p path (n) Is as followsnThe channel path energy of the individual symbol baseband data points,Kfor the number of symbol baseband data points in the energy gathering window,kfor the second position in the current energy collection windowkOne symbol baseband data point, gamma cross_corr (n-k) Is the signal of the first (in the long code field)n-k) One symbol baseband data point.
And comparing the channel path energy of each corresponding baseband data point in the energy collection range, determining a symbol baseband data point with the maximum channel path energy in the energy collection range, and determining the position of the symbol baseband data point with the maximum channel path energy as a symbol rough synchronization position.
Further, step S304 includes: calculating an autocorrelation value between each symbol baseband data point in the first subfield and a corresponding symbol baseband data point in the second subfield in the signal long code field; and determining the carrier frequency offset estimation value of the digital signal based on each autocorrelation value obtained by calculation.
In this step, the signal length code field includes a first sub-field (LFT 1) and a second sub-field (LFT 2), the LTFs 1 and 2 have 64 baseband data points, respectively, and the LTFs 1 and 2 have a common cyclic prefix LTF GI (as shown in fig. 2).
For each symbol baseband data point in the first sub-field, an autocorrelation value is calculated between that symbol baseband data point and its corresponding symbol baseband data point in the second sub-field.
Specifically, the autocorrelation value is calculated by the following formula:
wherein, γ auto_corr (n) For signals in the long code fieldnThe autocorrelation values of the individual symbol baseband data points,
is a symbol baseband data point in the first sub-field,
the conjugate of the symbol baseband data point in the second subfield.
And determining a carrier frequency offset estimation value required for compensating the symbol baseband data point in the range to be compensated in the digital signal based on each autocorrelation value obtained by calculation.
Specifically, the carrier frequency offset estimation value is calculated by the following formula:
wherein, DeltafIs an estimate of the carrier frequency offset, gamma auto_corr (n) For signals in the long code fieldnThe autocorrelation values of the individual symbol baseband data points,Nis the number of symbol baseband data points in the field.
Further, step S305 includes: determining a compensation initial position point from the buffered digital signal based on the coarse synchronization position and the number of symbol baseband data points in each subfield of each field; determining the range between the compensation initial position point and the symbol rough synchronization position as a range to be compensated; and carrying out carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through the carrier frequency offset estimation value to obtain compensated symbol baseband data points.
In this step, a compensation initial position point for compensating the symbol baseband data points in the buffered digital signal is determined based on the determined coarse synchronization position and the number of symbol baseband data points in each subfield of the individual field in the digital signal.
Determining the range between the compensation initial position point and the rough synchronization position in the digital signal as a range to be compensated; and carrying out carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through the carrier frequency offset estimation value obtained through calculation to obtain compensated symbol baseband data points.
Wherein the fields of the digital signal include a signal long code field and a signal short code field, the signal long code field including a first subfield and a second subfield.
Further, step S306 includes: extracting a preset number of baseband data points to be calculated from each field of the compensated symbol baseband data points; for each baseband data point to be calculated in each field, calculating the noise power of the baseband data point to be calculated, and the noise weighted sum of the noise power of the corresponding baseband data point to be calculated in other fields except the field to which the baseband data point to be calculated belongs in each field of the digital signal; and determining the accurate synchronous position of the symbols in the digital signal according to the determined weighted sum of the plurality of noises.
In this step, a preset number of baseband data points to be calculated are extracted from each field of the compensated symbol baseband data points, for example, a preset number of baseband data points to be calculated are extracted from a first sub-field of the long signal code field, a preset number of baseband data points to be calculated are extracted from a second sub-field of the long signal code field, and a preset number of baseband data points to be calculated are extracted from the short signal code field.
And for each baseband data point to be calculated extracted from the first sub-field of the signal long code field, calculating the noise weighted sum between the noise power of the baseband data point to be calculated and the noise power of the corresponding baseband data point to be calculated in other fields except the field to which the baseband data point to be calculated belongs in each field of the digital signal.
Calculating the noise power of each baseband data point to be calculated by the following formula:
when the extracted baseband data point to be calculated is located in the signal short code field:
wherein the content of the first and second substances,
is as followskThe noise power of each baseband data point to be calculated,r cfo the compensated symbol baseband data points.
When the extracted baseband data point to be calculated is located in the first subfield:
wherein the content of the first and second substances,
is as followskThe noise power of each baseband data point to be calculated,r cfo the compensated symbol baseband data points.
When the extracted baseband data point to be calculated is located in the second subfield:
wherein the content of the first and second substances,
is as followskThe noise power of each baseband data point to be calculated,r cfo the compensated symbol baseband data points.
And determining the precise synchronous position of the symbol from the digital signal according to the calculated weighted sum of the plurality of noises.
Further, the determining a symbol fine synchronization position in the digital signal according to the determined weighted sum of the plurality of noises includes: determining a minimum noise weighted sum from the plurality of noise weighted sums; and determining a fine synchronization position of a symbol in the digital signal based on the position of the minimum noise weighted sum and the coarse synchronization position.
Comparing the determined noise weighted sums, and determining a minimum noise weighted sum from the noise weighted sums; determining the position of the symbol baseband data point after the minimum noise weighting and the corresponding compensation as the position of the minimum noise weighting sum; and determining the precise synchronization position of the symbol in the digital signal based on the position of the minimum noise weighted sum and the determined rough synchronization position.
Here, when there is no multipath delay spread of the STF field or GI energy of the SIG field in the two truncated fields, the calculated noise power is necessarily the average noise power of the current digital signal, and if the two fields contain multipath delay spread or energy of other fields, the calculated noise power is necessarily greater than the average noise power of the current digital signal. Therefore, by utilizing the characteristics of the frame head of the transmitted signal, the compensated symbol baseband data point obtained by carrier frequency offset compensation is selected in a certain range, the average noise power at the corresponding moment can be obtained according to the formula of calculating the noise power, the position with the minimum noise power is found, and the precise synchronization position of the symbol is further obtained.
In one possible embodiment, as shown in fig. 4, fig. 4 is a schematic diagram of a precise synchronization position determination method. The STF and LTF fields are used to determine the exact synchronization position of the symbol. When receiving digital signal
Then, calculating to obtain a cross-correlation value between a signal long code field and a local long code field of the digital signal through a cross-correlation value calculation formula; determining a coarse synchronization position (Search _ point 17) of the digital signal; determining a compensation initial position point from the buffered digital signal according to the coarse synchronization position (Search _ point 17) and the number of symbol baseband data points in each subfield of each field in the digital signal, as shown in fig. 4, after determining Search _ point17, determining the compensation initial position point as a position backed by 64+32+48=144 points from the Search _ point17 position according to the number of baseband data points of each subfield, and further determining a to-be-compensated range for carrier frequency offset compensation; calculating to obtain an autocorrelation value between a first subfield and a second subfield in a signal long code field through an autocorrelation value calculation formula, and further calculating to obtain a carrier frequency offset estimation value through a carrier frequency offset estimation value calculation formula; carrying out carrier frequency offset compensation on the symbol baseband data point in the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data pointr cfo (n) (ii) a If the Search _ point17 position is used as the base pointnThen, the noise power of the compensated symbol baseband data point in each field can be calculated by the following formula:
here, if the coarse synchronization position of Search _ point17 is within the multipath spread delay range of LTF1, then
It will appear as a "downhill" with a high left side and a low right side. While
When the sliding range enters the LTF-GI, the sliding range appears to be an upward slope with a lower left side and a higher right side. Therefore, the temperature of the molten metal is controlled,
and
the weighted sum of (a) then appears as a "pot" at the bottom of which the exact symbol synchronization position can be found. Assuming the bottom position of the' basink’，
And
the weighted sum of the symbol synchronization positions is minimized, the symbol synchronization position is accuraten+k'. If the coarse synchronization position of Search _ point17 is outside the multipath spread delay range of LTF1, then
And
the combination of (A) and (B) is in an 'upslope' shape with a lower left side and a higher right side, and can still be found
And
the merged minimum position of (c).
In this possible embodiment, the average noise power or the signal-to-noise ratio of the digital signal can also be usedSNRThe estimation of (2) is changed, namely when the average noise power or the signal-to-noise ratio meets a certain threshold, only the symbol rough synchronization position is needed; and when the average noise power or the signal-to-noise ratio does not meet a certain threshold, determining the accurate synchronization position of the symbol on the basis of the rough synchronization position.
In one possible embodiment, as shown in fig. 5, fig. 5 is a second schematic diagram of the precise synchronization position determination method. The LTF1 and LTF2 fields are used to determine the exact synchronization position of the symbol. After the coarse synchronization position (Search _ point 17) of the digital signal is determined, according to the number of the symbol baseband data points of each subfield, a compensation initial position point is determined to be a position which is back from the Search _ point17 position by 64+32=96 points; and (3) carrying out carrier frequency offset compensation on the symbol baseband data point in the range to be compensated, and calculating the noise power of the compensated symbol baseband data point in each field by using the following formula if the Search _ point17 position is used as a base point n:
here, if the coarse synchronization position of Search _ point17 is within the multipath spread delay range of LTF1, then
Will appear as a "downhill" with a high left side and a low right side, and
the sliding range appears as an "up-slope" with the lower left side and the higher right side when entering the SIG-GI field. Thus, it is possible to provide
And
the merging of (a) appears as a "pot" where the exact synchronization position of the symbol can be found at the bottom of the "pot". Assuming the bottom position of the' basink’，
And
when the combined value is minimum, the precise synchronous position of the symbol isn+k'. If the coarse synchronization position of Search _ point17 is outside the multipath spread delay range of LTF1, then
And
the combination of (A) and (B) is in an 'upslope' shape with a lower left side and a higher right side, and can still be found
And
the merged minimum position of (c).
In this possible implementation, some changes may also be made according to the estimation of the average noise power or the signal-to-noise ratio within the digital signal, i.e. when the average noise power or the signal-to-noise ratio satisfies a certain threshold, only the symbol coarse synchronization position is performed; and when the average noise power or the signal-to-noise ratio does not meet a certain threshold, determining the accurate synchronization position of the symbol on the basis of the rough synchronization position.
The method for determining the symbol synchronization position in the digital signal provided by the embodiment of the application identifies a signal long code field from a received digital signal and acquires a local long code field; determining a cross-correlation value between each symbol baseband data point in the signal long code field and a corresponding symbol local data point in the local long code field; determining a symbol rough synchronization position in the digital signal based on each determined cross-correlation value and a preset energy collection window; calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determining a carrier frequency offset estimation value of the digital signal; determining a range to be compensated from the cached digital signal based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data point in the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point; and determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points. Therefore, the carrier frequency offset compensation is carried out on the symbol baseband data points in the digital signal, and then the accurate synchronization position of the symbol in the digital signal is determined on the basis of the rough synchronization position of the symbol, which is beneficial to improving the accuracy of the determination result of the symbol synchronization position.
Referring to fig. 6, fig. 6 is a schematic structural diagram of an apparatus for determining a symbol synchronization position in a digital signal according to an embodiment of the present disclosure. As shown in fig. 6, the determining means 600 includes:
a receiving module 610, configured to identify a signal long code field from a received digital signal, and obtain a local long code field;
a first position determining module 620, configured to determine a coarse synchronization position of a symbol in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field;
a frequency offset estimation module 630, configured to calculate an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determine a carrier frequency offset estimation value of the digital signal;
a compensation module 640, configured to determine a range to be compensated from the cached digital signal based on the coarse synchronization position, and perform carrier frequency offset compensation on a symbol baseband data point within the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point;
a second position determining module 650, configured to determine an accurate synchronization position of a symbol in the digital signal by calculating a noise power of each baseband data point to be calculated in the compensated symbol baseband data point.
Further, when the first position determining module 620 is configured to determine the coarse symbol synchronization position in the digital signal by calculating the cross-correlation value between the signal long code field and the local long code field, the first position determining module 620 is configured to:
determining a cross-correlation value between each symbol baseband data point in the signal long code field and a corresponding symbol local data point in the local long code field;
and determining the rough symbol synchronization position in the digital signal based on the determined cross-correlation values and a preset energy gathering window.
Further, when the first position determination module 620 is configured to determine the coarse synchronization position of the symbol in the digital signal based on the determined cross-correlation values and a preset energy gathering window, the first position determination module 620 is configured to:
determining channel path energy of each symbol baseband data point in an energy collection range in the digital signal based on the determined cross-correlation values and a preset energy collection window;
and determining the position of the symbol baseband data point with the maximum channel path energy in the energy collection range as the symbol rough synchronization position.
Further, when the frequency offset estimation module 630 is configured to calculate an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determine a carrier frequency offset estimation value of the digital signal, the frequency offset estimation module 630 is configured to:
calculating an autocorrelation value between each symbol baseband data point in the first subfield and a corresponding symbol baseband data point in the second subfield in the signal long code field;
and determining the carrier frequency offset estimation value of the digital signal based on each autocorrelation value obtained by calculation.
Further, when the compensation module 640 is configured to determine a range to be compensated from the cached digital signal based on the coarse synchronization position, and perform carrier frequency offset compensation on a symbol baseband data point within the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point, the compensation module 640 is configured to:
determining a compensation initial position point from the buffered digital signal based on the coarse synchronization position and the number of symbol baseband data points in each subfield of each field;
determining the range between the compensation initial position point and the rough synchronization position as a range to be compensated;
and carrying out carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through the carrier frequency offset estimation value to obtain compensated symbol baseband data points.
Further, when the second position determining module 650 is configured to determine the precise synchronization position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data point, the second position determining module 650 is configured to:
extracting a preset number of baseband data points to be calculated from each field of the compensated symbol baseband data points;
for each baseband data point to be calculated in each field, calculating the noise power of the baseband data point to be calculated, and the noise weighted sum of the noise power of the corresponding baseband data point to be calculated in other fields except the field to which the baseband data point to be calculated belongs in each field of the digital signal;
and determining the accurate synchronous position of the symbols in the digital signal according to the determined weighted sum of the plurality of noises.
Further, when the second position determining module 650 is configured to determine the symbol fine synchronization position in the digital signal according to the determined weighted sum of the plurality of noises, the second position determining module 650 is configured to:
determining a minimum noise weighted sum from the plurality of noise weighted sums;
and determining a fine synchronization position of a symbol in the digital signal based on the position of the minimum noise weighted sum and the coarse synchronization position.
The device for determining the symbol synchronization position in the digital signal provided by the embodiment of the application identifies the signal long code field from the received digital signal and acquires the local long code field; determining a coarse synchronization position of a symbol in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field; calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determining a carrier frequency offset estimation value of the digital signal; determining a range to be compensated from the cached digital signal based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data point in the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point; and determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points. Therefore, the carrier frequency offset compensation is carried out on the symbol baseband data points in the digital signal, and then the accurate synchronization position of the symbol in the digital signal is determined on the basis of the rough synchronization position of the symbol, which is beneficial to improving the accuracy of the determination result of the symbol synchronization position.
Referring to fig. 7, fig. 7 is a schematic structural diagram of an electronic device according to an embodiment of the present disclosure. As shown in fig. 7, the electronic device 700 includes a processor 710, a memory 720, and a bus 730.
The memory 720 stores machine-readable instructions executable by the processor 710, when the electronic device 700 runs, the processor 710 communicates with the memory 720 through the bus 730, and when the machine-readable instructions are executed by the processor 710, the steps of the method for determining a symbol synchronization position in a digital signal in the method embodiment shown in fig. 1 and fig. 3 may be performed.
An embodiment of the present application further provides a computer-readable storage medium, where a computer program is stored on the computer-readable storage medium, and when the computer program is executed by a processor, the step of the method for determining a symbol synchronization position in a digital signal in the method embodiments shown in fig. 1 and fig. 3 may be executed.
It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other ways. The above-described embodiments of the apparatus are merely illustrative, and for example, the division of the units is only one logical division, and there may be other divisions when actually implemented, and for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection of devices or units through some communication interfaces, and may be in an electrical, mechanical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.
The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a non-volatile computer-readable storage medium executable by a processor. Based on such understanding, the technical solution of the present application or portions thereof that substantially contribute to the prior art may be embodied in the form of a software product stored in a storage medium and including instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.
Finally, it should be noted that: the above-mentioned embodiments are only specific embodiments of the present application, and are used for illustrating the technical solutions of the present application, but not limiting the same, and the scope of the present application is not limited thereto, and although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope disclosed in the present application; such modifications, changes or substitutions do not depart from the spirit and scope of the exemplary embodiments of the present application, and are intended to be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (10)
1. A method for determining a symbol synchronization position in a digital signal, the method comprising:
identifying a signal long code field from a received digital signal and acquiring a local long code field;
determining a coarse synchronization position of a symbol in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field;
calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field, and determining a carrier frequency offset estimation value of the digital signal;
determining a range to be compensated from the cached digital signal based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data point in the range to be compensated through the carrier frequency offset estimation value to obtain a compensated symbol baseband data point;
and determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points.
2. The method of claim 1, wherein the determining the coarse symbol synchronization position in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field comprises:
determining a cross-correlation value between each symbol baseband data point in the signal long code field and a corresponding symbol local data point in the local long code field;
and determining the rough symbol synchronization position in the digital signal based on the determined cross-correlation values and a preset energy gathering window.
3. The method of claim 2, wherein the determining the coarse symbol synchronization position in the digital signal based on the determined cross-correlation values and a preset energy gathering window comprises:
determining channel path energy of each symbol baseband data point in an energy collection range in the digital signal based on the determined cross-correlation values and a preset energy collection window;
and determining the position of the symbol baseband data point with the maximum channel path energy in the energy collection range as the symbol rough synchronization position.
4. The method of determining according to claim 1, wherein said calculating an autocorrelation value between a first sub-field and a second sub-field of the long code field of the signal, and determining an estimated carrier frequency offset of the digital signal comprises:
calculating an autocorrelation value between each symbol baseband data point in the first subfield and a corresponding symbol baseband data point in the second subfield in the signal long code field;
and determining the carrier frequency offset estimation value of the digital signal based on each autocorrelation value obtained by calculation.
5. The method according to claim 1, wherein the determining a range to be compensated from the buffered digital signal based on the coarse symbol synchronization position, and performing carrier frequency offset compensation on a symbol baseband data point in the range to be compensated through the estimated carrier frequency offset value to obtain a compensated symbol baseband data point includes:
determining a compensation initial position point from the buffered digital signal based on the coarse synchronization position and the number of symbol baseband data points in each subfield of each field;
determining the range between the compensation initial position point and the rough synchronization position as a range to be compensated;
and carrying out carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through the carrier frequency offset estimation value to obtain compensated symbol baseband data points.
6. The method of claim 1, wherein said determining the exact synchronization position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points comprises:
extracting a preset number of baseband data points to be calculated from each field of the compensated symbol baseband data points;
for each baseband data point to be calculated in each field, calculating the noise power of the baseband data point to be calculated, and the noise weighted sum of the noise power of the corresponding baseband data point to be calculated in other fields except the field to which the baseband data point to be calculated belongs in each field of the digital signal;
and determining the accurate synchronous position of the symbols in the digital signal according to the determined weighted sum of the plurality of noises.
7. The method of claim 6, wherein said determining a symbol-accurate synchronization position in said digital signal based on said determined weighted sum of the plurality of noise comprises:
determining a minimum noise weighted sum from the plurality of noise weighted sums;
and determining a fine synchronization position of a symbol in the digital signal based on the position of the minimum noise weighted sum and the coarse synchronization position.
8. An apparatus for determining a symbol synchronization position in a digital signal, the apparatus comprising:
the receiving module is used for identifying a signal long code field from a received digital signal and acquiring a local long code field;
a first position determination module, configured to determine a coarse synchronization position of a symbol in the digital signal by calculating a cross-correlation value between the signal long code field and the local long code field;
the frequency offset estimation module is used for calculating an autocorrelation value between a first subfield and a second subfield in the signal long code field and determining a carrier frequency offset estimation value of the digital signal;
the compensation module is used for determining a range to be compensated from the cached digital signals based on the rough synchronization position, and performing carrier frequency offset compensation on the symbol baseband data points in the range to be compensated through the carrier frequency offset estimation value to obtain compensated symbol baseband data points;
and the second position determining module is used for determining the accurate synchronous position of the symbol in the digital signal by calculating the noise power of each baseband data point to be calculated in the compensated symbol baseband data points.
9. An electronic device, comprising: a processor, a memory and a bus, the memory storing machine-readable instructions executable by the processor, the processor and the memory communicating via the bus when the electronic device is operating, the machine-readable instructions being executed by the processor to perform the steps of the method for determining a symbol synchronization position in a digital signal according to any one of claims 1 to 7.
10. A computer-readable storage medium, characterized in that the computer-readable storage medium has stored thereon a computer program which, when being executed by a processor, carries out the steps of the method for determining a symbol synchronization position in a digital signal according to any one of claims 1 to 7.
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