CN117279087B - Synchronous position determining method, synchronous position determining device, electronic equipment and storage medium - Google Patents
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Abstract
The application provides a synchronous position determining method, a synchronous position determining device, electronic equipment and a storage medium, and relates to the technical field of communication, wherein the method comprises the following steps: comparing the cross-correlation value of the local sequence and the received signal with a preset threshold, and determining a correlation peak value of which the first cross-correlation value is larger than the preset threshold; wherein the preset threshold is determined based on the autocorrelation value of the local sequence; searching a first peak value of the cross-correlation value in the first search window by taking the position corresponding to the correlation peak value as the starting point of the first search window, and determining the position corresponding to the first peak value as the position of a first synchronous point; and searching a second peak value with the cross-correlation value larger than a preset threshold in a second search window based on the positions of 10 frames and/or 11 frames spaced from the current synchronization point, and determining the position corresponding to the second peak value as the position of the next synchronization point until the positions of all the synchronization points are determined. The method and the device realize effectiveness judgment of the cross correlation peak and search of a plurality of cross correlation peaks, and improve the synchronization efficiency of the GSM system.
Description
Technical Field
The present disclosure relates to the field of communications technologies, and in particular, to a method and apparatus for determining a synchronization position, an electronic device, and a storage medium.
Background
The global system for mobile communications (Global System for Mobile Communications, GSM) is a digital mobile communications standard and is widely used in the communications of mobile terminals.
The most common method for signal synchronization of GSM is to perform cross-correlation between local data and air interface data, search cross-correlation peaks and judge synchronization points for synchronization. However, in the current cross-correlation peak searching process, judgment on the effectiveness of the cross-correlation peak is generally lacking, so that frequent error synchronization is caused, and the synchronization efficiency of the GSM system is reduced. Meanwhile, multipath causes multiple cross correlation peaks, and general cross correlation peak search only supports search for the first peak, resulting in timing error.
Disclosure of Invention
Aiming at the problems in the prior art, the embodiment of the application provides a synchronous position determining method, a synchronous position determining device, electronic equipment and a storage medium.
In a first aspect, an embodiment of the present application provides a method for determining a synchronization position, including:
comparing the cross-correlation value of the local sequence and the received signal with a preset threshold, and determining a correlation peak value of which the first cross-correlation value is larger than the preset threshold; wherein the preset threshold is determined based on an autocorrelation value of the local sequence;
Searching a first peak value of the cross-correlation value in a first search window by taking the position corresponding to the correlation peak value as a starting point of the first search window, and determining the position corresponding to the first peak value as a position of a first synchronization point;
searching a second peak value with the cross correlation value larger than the preset threshold in a second search window based on the position of 10 frames and/or 11 frames spaced from the current synchronization point, and determining the position corresponding to the second peak value as the position of the next synchronization point until the positions of all the synchronization points are determined; wherein the current synchronization point is any synchronization point including the first synchronization point.
In some embodiments, the searching for the second peak with the cross-correlation value greater than the preset threshold in the second search window based on the position spaced 10 frames and/or 11 frames from the current synchronization point includes:
determining a first signal segment based on a position spaced 10 frames from the current synchronization point;
searching for the second peak within the first signal segment based on the second search window;
if the second peak value is not searched in the first signal segment, determining a second signal segment based on a position which is 11 frames away from the current synchronous point;
Searching for the second peak within the second signal segment based on the second search window;
and if the second peak value is not searched in the first signal segment and the second signal segment, searching the first peak value again.
In some embodiments, the searching for the second peak value with the cross-correlation value greater than the preset threshold in the second search window based on the position separated from the current synchronization point by 10 frames and/or 11 frames further comprises:
and if the second peak value is searched in the first signal segment for 4 times continuously, directly determining the second signal segment for the 5 th time, and searching the second peak value in the second signal segment.
In some embodiments, further comprising:
and performing fast Fourier transform FFT segmentation cross-correlation operation on the local sequence and the received signal, and performing normalization processing on the result to obtain the cross-correlation value.
In some embodiments, the FFT point number is 2 times the length of the local sequence.
In some embodiments, the determining the first signal segment includes:
taking forward 1/2 of the length of the local sequence at a position 10 frames apart from the current synchronization point as a starting point of the first signal segment, wherein the length of the first signal segment is equal to the FFT point number;
The determining the second signal segment includes:
and taking forward 1/2 of the length of the local sequence at a position 11 frames apart from the current synchronous point as the starting point of the second signal segment, wherein the length of the second signal segment is equal to the FFT point number.
In some embodiments, the searching for the second peak comprises:
determining a cross-correlation result of the first signal segment and/or the second signal segment;
and searching the second peak value by taking the center of the cross-correlation result of the first signal segment and/or the second signal segment as the center of the second search window.
In a second aspect, embodiments of the present application further provide a synchronization position determining apparatus, including:
the first determining module is used for comparing the cross-correlation value of the local sequence and the received signal with a preset threshold and determining a first correlation peak value of which the cross-correlation value is larger than the preset threshold; wherein the preset threshold is determined based on an autocorrelation value of the local sequence;
the second determining module is used for searching a first peak value of the cross-correlation value in a first search window by taking the position corresponding to the correlation peak value as a starting point of the first search window, and determining the position corresponding to the first peak value as a position of a first synchronization point;
The third determining module is used for searching a second peak value with the cross correlation value larger than the preset threshold in a second searching window based on the position of 10 frames and/or 11 frames which are spaced from the current synchronizing point, and determining the position corresponding to the second peak value as the position of the next synchronizing point until the positions of all the synchronizing points are determined; wherein the current synchronization point is any synchronization point including the first synchronization point.
In a third aspect, an embodiment of the present application further provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor, where the processor implements a method for determining a synchronization position according to any one of the above methods when executing the program.
In a fourth aspect, embodiments of the present application also provide a non-transitory computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements a method of synchronous position determination as described in any of the above.
In a fifth aspect, embodiments of the present application also provide a computer program product comprising a computer program which, when executed by a processor, implements a method of determining a synchronization position as described in any of the above.
According to the synchronization position determining method, the synchronization position determining device, the electronic equipment and the storage medium, the self-correlation value of the local sequence is used for setting the preset threshold, the effectiveness of the cross-correlation peak value is judged, meanwhile, the time slot structure of the GSM system is combined, the next synchronization point is searched at the position of 10 frames and/or 11 frames of the current synchronization point interval, the search of a plurality of cross-correlation peak values generated by multipath is supported, point-by-point comparison of a large amount of data is not needed, the operation efficiency is greatly improved, the operation complexity is reduced, and meanwhile, the timing precision of system synchronization can be increased due to the arrangement of the search window.
Drawings
For a clearer description of the present application or of the prior art, the drawings that are used in the description of the embodiments or of the prior art will be briefly described, it being apparent that the drawings in the description below are some embodiments of the present application, and that other drawings may be obtained from these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of a TDMA frame provided by the prior art;
fig. 2 is a schematic diagram of a 51-multiframe structure provided in the prior art;
Fig. 3 is a flowchart of a method for determining a synchronization position according to an embodiment of the present application;
fig. 4 is a schematic flow chart of sliding cross-correlation between a local sequence and a received signal according to an embodiment of the present application;
fig. 5 is a schematic flow chart of FFT cross correlation between a local sequence and a received signal provided in an embodiment of the present application;
fig. 6 is a schematic structural diagram of a synchronous position determining device 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
The global system for mobile communications (Global System for Mobile Communications, GSM) is a digital mobile communications standard and is widely used in the communications of mobile terminals. The modulation mode adopted by the GSM system is Gaussian minimum shift keying (Gaussian Filtered Minimum Shift Keying, GMSK).
GMSK modulation is based on minimum shift keying (Minimum Shift Keying, MSK) modulation, which is inserted with a gaussian low pass pre-modulation filter before the MSK modulator, filtering the modulated signal. GMSK modulation has the following advantages: compared with other phase shift keying modes, the spectrum efficiency is obviously improved; can be amplified by a nonlinear amplifier and remain undistorted; is not affected by amplitude variation, and has more elasticity to noise.
The multiple access techniques currently applied mainly include: frequency division multiple access (Frequency Division Multiple Access, FDMA) for different earth stations to communicate using channels of different frequencies; time division multiple access (Time Division Multiple Access, TDMA) allows several earth stations to share a channel, but slices a carrier at different times, dividing it into multiple time slots for different users, and accommodating more users than frequency division multiple access; code division multiple access (Code Division Multiple Access, CDMA), also commonly uses a channel for multiple earth stations, but each earth station is assigned a unique "code sequence" that is orthogonal to each other.
In the GSM system, the wireless interface adopts a combination of TDMA and FDMA. Fig. 1 is a schematic diagram of a TDMA frame provided in the prior art, and as shown in fig. 1, each TDMA frame includes 8 time slots, each time slot being a channel, and the entire frame duration being approximately 4.616 milliseconds (ms). The 26 consecutive TDMA frames constitute 1 service multiframe with a period of 120ms for the traffic channel and the associated control channel. The 51 consecutive TDMA frames constitute a control multiframe with a period of 235.385ms for the broadcast control channel and the common control channel. A plurality of consecutive TDMA multiframes constitute a superframe, including consecutive 51×26=1326 TDMA frames, one superframe having a duration of 6.12 seconds(s). 2048 consecutive superframes constitute 1 super-frame, each period comprising 2715648 TDMA frames, with a time period of 3 hours 28 minutes 53 seconds 760 milliseconds.
Wherein, one TDMA frame is 4.616ms, and total 8 time slots are TS0 to TS7, each time slot is 0.577ms, each time slot corresponds to 156.25 bits (bit), and the code rate is 156.25/(120/26/8) =270.8333 kilo-baud (KBaud). Without over-sampling, one TDMA frame is 156.25×8=1250 bits.
Fig. 2 is a schematic diagram of a 51-multiframe structure provided in the prior art, as shown in fig. 2, a base station and a mobile terminal in a GSM system synchronize and communicate under the multiframe structure, where:
f denotes a frequency correction channel (Frequency Correction Channel, FCCH) frame, the pulses are frequency correction burst (Frequency Correction Burst, FB) pulse sequences for synchronizing the frequency.
S denotes a synchronization channel (Synchronization Channel, SCH) frame, the burst is a working synchronization burst (Synchronization Burst, SB) burst sequence for resolving TDMA frame numbers and base station identification (Basic Service Identification Code, BSIC) codes for distinguishing between different cells having the same channel frequency.
B denotes a broadcast control channel (Broadcast Control Channel, BCCH) frame, and the Burst is a Normal Burst (NB) Burst sequence for solving general information about the cell.
C denotes a common control channel (Common Control Channel, CCCH) frame, the pulses are a sequence of normal bursts for receiving paging and access.
I denotes an Idle (Idle) frame, and the pulse is an Idle Burst (DB) pulse sequence, which does not contain any useful information.
The format of information in one time slot on a TDMA channel is called a burst sequence, and in fig. 2, the following four types are involved:
frequency correction burst (FB) for frequency synchronization correction of a mobile station. FB contains 142 bits fixed to "0", i.e. a pure carrier wave without modulation (which can be understood as a frequency stable sine wave).
A working synchronization burst Sequence (SB), abbreviated as synchronization sequence, is used for time synchronization of the mobile station. The SB includes a 64bit fixed synchronization training sequence: b962 040F 2d45 7610 b (only one training sequence different from NB, SB), and 39 bits of encrypted data on either side.
The common burst sequence (NB) mainly carries the information of the control channels except the traffic channel and the associated control channel. In NB, first, the frame flag of 3 bits is followed by the user encrypted data divided into two 57 bits and the 26bit training sequence sandwiched between them (the training sequence in NB is totally divided into 8 kinds, and the training sequences of different cells, even different channels of the same cell, may be different).
An idle burst sequence (DB) which is sent out by the base station in some special cases, without useful information contained therein; DB is in substantially the same format as NB except that two 57bit encrypted data bits therein become two fixed values.
Except that the FSCCI where there is an Idle frame is 11 TDMA frames different from the next FSBC, the remaining adjacent synchronization positions differ by 10 TDMA frames.
Network synchronization is a major problem of mobile communication systems, and it is necessary to maintain the clock quality of the mobile communication system at a specific level in order to reduce transmission and reception errors, to improve network efficiency, to improve network quality, to improve user satisfaction, and the like. The clock synchronization of the GSM system is mainly used to determine the transmission time slots.
The most common method for signal synchronization of the GSM system is to perform cross-correlation between local data and air interface data, search correlation peaks and judge synchronization points for synchronization.
On the one hand, for cross-correlation in GSM synchronization, there are two ways of sliding cross-correlation and fast fourier transform (Fast Fourier Transform, FFT), and the calculation results of both ways are equivalent. When the number of calculated points is large, the operation amount of sliding cross-correlation is far higher than that of FFT cross-correlation. In practical implementation, the data are continuous, and if the length of each cross-correlation is too long, high operation amount is necessarily caused. Therefore, it is necessary to select an appropriate cross-correlation method, and the amount of computation and the amount of memory of data can be reduced.
On the other hand, in the process of searching the cross correlation peak, the effectiveness of the cross correlation peak is not judged in the prior art, so that frequent error synchronization is caused, and the synchronization efficiency of the system is reduced. Meanwhile, multipath causes multiple cross correlation peaks, and the related scheme in the prior art often only supports judgment of the first cross correlation peak, so that advanced timing errors are caused.
Aiming at the problems in the prior art, the embodiment of the application provides a synchronization position determining method, a synchronization position determining device, an electronic device and a storage medium, wherein a preset threshold is set by utilizing an autocorrelation value of a local sequence, validity of a cross-correlation peak value is judged, meanwhile, a time slot structure of a GSM system is combined, search of a next synchronization point is carried out near a position of 10 frames and/or 11 frames of a current synchronization point interval, search of a plurality of cross-correlation peak values generated by multipath is supported, point-by-point comparison of a large amount of data is not needed, operation efficiency is greatly improved, operation complexity is reduced, and meanwhile, setting of a search window can also increase timing precision of system synchronization.
For the purposes of making the objects, technical solutions and advantages of the present application more apparent, the technical solutions in the present application will be clearly and completely described below with reference to the drawings in the present application, and it is apparent that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.
Fig. 3 is a flowchart of a method for determining a synchronization position according to an embodiment of the present application, as shown in fig. 3, an execution body of the method may be a state machine, and at least includes the following steps:
step 301, comparing a cross-correlation value of a local sequence and a received signal with a preset threshold, and determining a correlation peak value of which a first cross-correlation value is larger than the preset threshold; wherein the preset threshold is determined based on an autocorrelation value of the local sequence.
Specifically, an Autocorrelation (autocorrection) value of the local sequence is obtained, denoted as Acorr, and a preset threshold is determined as follows: x Acorr. Alternatively, X may be set to 70% or other percentages. The preset threshold is used as a judging condition for the effectiveness of the cross-correlation peak value.
And performing cross-correlation calculation on the received signal by using the local sequence, comparing the cross-correlation value with a preset threshold, determining the position of a first correlation peak value larger than the preset threshold, and determining that the peak position of the first cross-correlation value is close to the correlation peak value.
And 302, searching a first peak value of the cross-correlation value in a first search window by taking the position corresponding to the correlation peak value as a starting point of the first search window, and determining the position corresponding to the first peak value as a position of a first synchronization point.
Specifically, the position corresponding to the correlation peak value is used as the starting point of the first search window, the maximum value of the cross correlation value, namely the first peak value, is searched, and the position of the first synchronization point can be determined based on the position corresponding to the first peak value. It is easy to think that the first peak value searched out at this time is necessarily larger than the preset threshold, so that it is not necessary to separately judge the validity of the first peak value. Meanwhile, by setting the first search window, the timing accuracy of synchronization can be increased.
Step 303, searching a second peak value with the cross correlation value larger than the preset threshold in a second search window based on the position of 10 frames and/or 11 frames spaced from the current synchronization point, and determining the position corresponding to the second peak value as the position of the next synchronization point until the positions of all the synchronization points are determined; wherein the current synchronization point is any synchronization point including the first synchronization point.
Specifically, since multipath produces a plurality of cross-correlation peaks, it is not sufficient to determine only one cross-correlation peak, and further searching is required.
According to the analysis described above: except that the FSCCI where there is an Idle frame is 11 TDMA frames different from the next FSBC, the remaining adjacent synchronization positions differ by 10 TDMA frames. Thus, it can be determined that the interval between synchronization points should be 10 frames or 11 frames.
After determining the position of the first synchronization point, a second search window is set, and for each subsequent synchronization point search, the next cross-correlation peak, i.e. the second peak, can be searched for in the vicinity of the position of the current synchronization point, which is spaced 10 frames and/or 11 frames apart, and the position of the next synchronization point is determined based on the position of the second peak. The current synchronization point may be any synchronization point including the first synchronization point.
The step of searching for the next synchronization point based on the current synchronization point is repeated until all synchronization points are searched.
According to the synchronous position determining method provided by the embodiment of the application, the autocorrelation value of the local sequence is used for setting the preset threshold, the effectiveness of the cross-correlation peak value is judged, meanwhile, the time slot structure of the GSM system is combined, the next synchronization point is searched near the 10 frames and/or 11 frames of the current synchronization point interval, the search of a plurality of cross-correlation peak values generated by multipath is supported, point-by-point comparison is not needed for a large amount of data, the operation efficiency is greatly improved, the operation complexity is reduced, and the setting of the search window can also increase the timing precision of system synchronization.
In some embodiments, the searching in step 303 for the second peak value with the cross-correlation value greater than the preset threshold in the second search window based on the position spaced 10 frames and/or 11 frames from the current synchronization point specifically includes:
Determining a first signal segment based on a position spaced 10 frames from the current synchronization point;
searching for the second peak within the first signal segment based on the second search window;
if the second peak value is not searched in the first signal segment, determining a second signal segment based on a position which is 11 frames away from the current synchronous point;
searching for the second peak within the second signal segment based on the second search window;
and if the second peak value is not searched in the first signal segment and the second signal segment, searching the first peak value again.
Specifically, since the FSCCI of the Idle frame is different from the next FSBC by 11 TDMA frames in the GSM system, the remaining adjacent synchronization positions are different by 10 TDMA frames.
Thus, if there is a correlation peak, it should be near the position 10 frames or 11 frames from the current synchronization point. A first signal segment may be determined at a position spaced 10 frames behind the current synchronization point; the second signal segment may be determined at a position spaced 11 frames behind the current synchronization point. The length of the signal section can be flexibly set. Wherein, the first signal segment corresponds to the case without Idle frame, and the second signal segment corresponds to the case with Idle frame.
In the process of searching the cross-correlation peak value, the interval between adjacent synchronous points is 10 frames or more than that of Idle frames, so that the search of the cross-correlation peak value in the first signal segment is preferentially considered.
First, a second peak value larger than a preset threshold is searched in a first signal section, and if the second peak value is searched, the position corresponding to the second peak value is used as the position of the next synchronization point. If the second peak value is not searched in the first signal section, searching the second peak value larger than the preset threshold in the second signal section, and if the second peak value is searched, taking the position corresponding to the second peak value as the position of the next synchronization point.
If no second peak is found in both the first signal segment and the second signal segment, then it is assumed that no synchronization point exists in both segments and the search for the first peak needs to be re-performed, i.e. the execution of step 301 and step 302 is re-performed.
Optionally, a second search window is set, the length of the second search window being 2 times the length of the first search window.
Specifically, a second search window is set, the length of which is 2 times the length of the first search window. For example, assuming that the oversampling multiple (Sample Per Symbol) is sps, the lengths of the first and second search windows are 8×sps and 16×sps, respectively; the lengths of the first search window and the second search window may be a minimum of 1×sps and 2×sps, respectively; the lengths of the first search window and the second search window may be a maximum of 32×sps and 64×sps, respectively. The search strategy can be flexibly adjusted in actual implementation.
According to the synchronous position determining method provided by the embodiment of the application, in the cross-correlation peak value searching process, according to the time slot structure in the GSM system, the condition of 10 frames of intervals between the synchronous points is preferentially considered, the next synchronous point is searched based on the current synchronous point, the searching of a plurality of cross-correlation peaks generated by multipath is supported, and a great amount of data does not need to be compared point by point, so that the operation efficiency is greatly improved, and the operation complexity is reduced.
In some embodiments, the searching in step 303 for the second peak value with the cross-correlation value greater than the preset threshold in the second search window based on the position spaced 10 frames and/or 11 frames from the current synchronization point further includes:
and if the second peak value is searched in the first signal segment for 4 times continuously, directly determining the second signal segment for the 5 th time, and searching the second peak value in the second signal segment.
Specifically, further considering the characteristics of the time slot structure in the GSM system, if the second peak is searched in the first signal segment for 4 consecutive times, that is, if the FSBC or FSCC without the Idle frame is searched for 4 consecutive times, the search of the second peak is directly performed at 11 frames intervals, that is, in the second signal segment, at the 5 th time, without performing the search of the second peak at 10 frames intervals.
According to the synchronous position determining method provided by the embodiment of the application, the characteristics of a time slot structure in a GSM system are considered, if the second peak value is searched in the first signal section for 4 times continuously, the second signal section is directly determined for the 5 th time, and the second peak value is searched in the second signal section, so that the operation efficiency is further improved, and the operation complexity is reduced.
In some embodiments, further comprising:
and performing fast Fourier transform FFT segmentation cross-correlation operation on the local sequence and the received signal, and performing normalization processing on the result to obtain the cross-correlation value.
Specifically, assume that the received signal isxThe local sequence of M points issThen receive the signalxAnd local sequencesThe complex cross-correlation result r of (2) is:
wherein,representing the cross-correlation function,nrepresent the firstnThe index value of the time instant of the sample,mrepresent the firstmIndex value of each sampling time, M is window length, i.e. training sequence period, marked +.>Representing the conjugate.
When n=0, the received signal and the local sequence are exactly aligned.
Fig. 4 is a schematic flow chart of sliding cross-correlation between a local sequence and a received signal, which is provided in an embodiment of the present application, and as shown in fig. 4, the sliding cross-correlation is intuitively described.
Assume that ，/>，/>，/>For receiving signals +.>Is a local sequence. From the relation of the linear correlation and the fourier transformation, it is possible to obtain +.>Inverse fast fourier transform result +.>：
Then receive the signalxAnd local sequencesThe complex cross-correlation result of (2) can be expressed as:
wherein the IFFT represents an inverse fast fourier transform (Inverse Fast Fourier Transform).
The equivalent expression of cross-correlation is in the form of FFT and IFFT. Fig. 5 is a schematic flow chart of cross-correlation between a local sequence and a received signal FFT provided in the embodiment of the present application, and as shown in fig. 5, the result of post-FFT conjugation of the local sequence complementary to 0 may be calculated in advance. And the length of 0 to the integer power of 2 is added for convenience of practical implementation.
However, this is performed when the received signal is short, and in fact, the received signal is continuous, so in the embodiment of the present application, FFT piecewise cross-correlation is used, that is, two 0 values of the received signal are complemented by the received signal.
Based on this, one comparison is made of the calculation amounts of the sliding cross-correlation and the FFT cross-correlation: the number of signal points is N, the length of the local sequence is M, the number of FFT points is 2M each time, and the number of FFT points is:
the sliding cross-correlation complex multiplier is approximately nxm.
The FFT cross correlation includes an FFT and IFFT, a complex multiplication of N points (the local sequence portion may be calculated in advance), and the complex multiplier is 2n×log2 ((2N)/(N/M)) +4n=2n×log2 (M) +4n.
The ratio of the complex operation amounts of the two is: m/(2×log2 (M) +4).
With the increase of the local sequence length, the operation amount of the FFT cross-correlation is obviously smaller than that of the sliding cross-correlation. When M is equal to 64, 128, 256 and 512, the ratio of the complex multiplication operation amounts is 4, 7.1, 12.8 and 23.3.
Furthermore, in the embodiment of the application, FFT segmentation cross-correlation is adopted, cross-correlation is not required all the time, point-by-point comparison is not required for a large amount of data, calculation of FFT cross-correlation values and search of cross-correlation peaks are only required to be carried out when the calculation is carried out to proper positions, and therefore operation complexity and data storage requirements can be reduced.
Further, when judging the cross correlation peak value, the value of the cross correlation peak value needs to be compared with the value of the self correlation of the local sequence. However, the amplitude of the synchronization sequence in the signal must be scaled with respect to the local sequence, so that the values of the cross-correlation and the autocorrelation need to be compared at the same level, i.e. the amplitude level of the cross-correlation needs to be identical to the local autocorrelation level, in the following way:
assuming that the local sequence is S1, the received signal corresponding to the synchronization position is S2, the amplitude relationship is s2=a·s1, and the local autocorrelation result is: sa=sum [ s1·conj (S1) ], where sum represents a summation operation and conj represents a conjugation operation. The cross correlation result Sc of the received signal and the local sequence at the synchronization position is: sc=sum [ s2·conj (S1) ]=a·sum [ s1·conj (S1) ]=a·sa.
The energy Sp of the received signal at the synchronization position is:
。
a as a to-be-evaluated value, can be obtained:the resulting converted cross-correlation value Scx is:
the above results are only derived at the synchronous position and are generalized to all the cross-correlation results, the calculated scaling value A of the cross-correlation at each point is different, but the normalized cross-correlation result is not larger than the autocorrelation value, and 70% or other percentages of the autocorrelation value can be defined as a preset threshold. Note that the normalized result is also set to 0 when the denominator Sp is 0.
According to the synchronous position determining method, FFT sectional cross correlation is adopted to calculate the cross correlation value of the local sequence and the received signal, compared with sliding cross correlation, the calculated result is equivalent, but the calculation complexity is obviously reduced, the storage requirement of data is reduced, and meanwhile, the calculation complexity is further reduced through normalization processing.
In some embodiments, the FFT point number is 2 times the length of the local sequence.
Specifically, when the cross-correlation result outputted each time coincides with the local sequence length, the number of FFT points is twice that of the local sequence, and the number of segments of the segmentation is the largest at this time, but the overall operation amount is the smallest.
And setting an oversampling multiple sps, and generating a GMSK modulated local sequence of 64sps points, which is oversampled by the sps, based on a 64-bit fixed synchronous training sequence SB.
And carrying out FFT sectional cross correlation on the received signal by using the local sequence, wherein the number of FFT points in each time is 64sps multiplied by 2=128 sps, namely, a 128sps point signal is input, a cross correlation result of the 64sps points is output, and the signal slides by the 64sps points each time.
In the synchronization position determining method provided by the embodiment of the application, the number of FFT points is set to be 2 times the length of the local sequence, and at the moment, the number of segmented segments is the largest, but the whole operation amount is the smallest.
In some embodiments, the determining the first signal segment includes:
taking forward 1/2 of the length of the local sequence at a position 10 frames apart from the current synchronization point as a starting point of the first signal segment, wherein the length of the first signal segment is equal to the FFT point number;
the determining the second signal segment includes:
and taking forward 1/2 of the length of the local sequence at a position 11 frames apart from the current synchronous point as the starting point of the second signal segment, wherein the length of the second signal segment is equal to the FFT point number.
Specifically, when the FFT piecewise cross correlation is adopted, 1/2 of the length of the local sequence is taken forward at the position of the current synchronization point at a position spaced by 10 frames backward, and the length of the first signal segment is the same as the number of FFT points, i.e., 2 times the length of the local sequence, as the start point of the first signal segment.
And taking 1/2 of the length of the local sequence forward at the position of the current synchronous point at the position of 11 frames later, and taking the length of the second signal segment as the starting point of the second signal segment, wherein the length of the second signal segment is the same as the number of FFT points, namely 2 times the length of the local sequence.
Taking the length of the local sequence as 64sps point and the FFT point as 128sps point as an example, the starting point of the first signal segment is the position of the current synchronization point, which is 10 frames after the position of 1250×10×sps=12500 sps point and then advanced by 64 sps/2=32 sps point, and the length of the first signal segment is 128sps point. The start of the second signal segment is the position of the current synchronization point which is spaced 11 frames back, i.e. 1250 x 11 x sps=13750 sps points then advanced by 64 sps/2=32 sps points, the length of the second signal segment being 128sps points.
According to the synchronous position determining method, the FFT point number is set based on the length of the local sequence, and the positions and the lengths of the first signal section and the second signal section are set, so that data in a specific position are buffered and reprocessed when the number reaches a proper position, the searched cross-correlation peak can be guaranteed to be near an expected position, the operation efficiency is greatly improved, and the operation complexity and the data storage requirement are reduced.
In some embodiments, the searching for the second peak comprises:
Determining a cross-correlation result of the first signal segment and/or the second signal segment;
and searching the second peak value by taking the center of the cross-correlation result of the first signal segment and/or the second signal segment as the center of the second search window.
Specifically, after the first signal segment and/or the second signal segment are determined, peak searching is not required to be performed on each point on the first signal segment and/or the second signal segment, so that the searching range can be further narrowed.
The first signal segment and the second signal segment are collectively called a target signal segment, taking the length of the target signal segment as 128sps point as an example, and performing FFT cross-correlation on the first signal segment and the second signal segment by using a local sequence to obtain a cross-correlation result of 64sps points. If there is a cross-correlation peak, it must be within the + -32 sps point of the two 64sps points and located near the center of the + -32 sps point. The transformation was a mathematical result, i.e. near the center of the 64sps point in the two sections.
The center of the cross-correlation result of the first signal segment and/or the second signal segment is used as the center of the second search window, and the second peak value is searched, so that the cross-correlation peak value can be ensured to be near the expected position. Wherein the length of the second search window can be flexibly set.
According to the synchronous position determining method, the range of searching the first signal segment and/or the second signal segment in the synchronous point searching process is further defined and reduced, the operation efficiency is improved, and the operation complexity and the data storage requirement are reduced.
The method for determining a synchronization position provided in the present application is further described in a specific embodiment.
The code rate of the GSM system is 270.8333KBaud, and assuming that the oversampling multiple is sps, the sampling rate (Sampling Frequency) is: fs=code rate×oversampling multiple, and by combining with the frame structure characteristics of GSM, the following method is adopted to perform correlation peak search:
step a, generating GMSK modulated local sequence of 64×sps=64 sps points with 64bit synchronization Sequence (SB), and finding the autocorrelation value of the local sequence to be Acorr, and setting the threshold to be x×acorr=xacorr, where X may be set to be 70% or other percentages.
And B, carrying out FFT sectional cross-correlation and normalization on the received signal by using a local sequence, wherein the number of FFT points in each time is 64×sps×2=128 sps points, namely, 128sps point signals are input, the cross-correlation result of the 64sps points is output, and the signals slide by 64sps points each time.
And C, outputting a normalized cross-correlation result to 64sps points each time, comparing the normalized cross-correlation result with a threshold Xacorr point by point, searching a maximum value in a first search window in the 64×sps×1/8=8 sps points after the point when a first correlation peak value larger than the threshold is found, taking the position of the maximum value as the position of a first synchronization point, and stopping the cross-correlation operation.
And D, counting the number of input signal points, namely, performing FFT cross-correlation normalization on signals of 128sps points from the position of the synchronization point in the last step, namely, the position of the synchronization point is backward spaced by 10 frames, namely, 1250×10×sps=12500 sps points, and 11 frames, namely, 1250×11×sps=13750 sps points, and starting to take the position of the 64×sps/2=32 sps points in advance, so that the cross-correlation normalization results of two sections of 64sps points can be obtained, and respectively correspond to the possible case without/with an Idle frame, if a correlation peak exists, the correlation peak is necessarily within +/-32 sps points of the two sections of 64sps points and is positioned near the center of the +/-32 sps points.
And E, setting a second search window of 64×sps×1/4=16 sps points, and carrying out peak search at a position of + -8 sps points near the center of the + -32 sps points of the two sections in the step D to find out the maximum peak value meeting the requirement of being larger than the threshold Xacorr.
Step F, if a maximum value exceeding a threshold is searched in the first 64sps point, considering that an Idle frame does not exist, recording the position of the maximum value as a synchronous point position, and continuously searching the position of the next 10 frames at intervals; if the maximum value exceeding the threshold is not found in the first section, searching in the second section 64sps point, if the maximum value exceeding the threshold is found, considering that an Idle frame exists, and recording the position of the maximum value as the position of the synchronization point; if the maximum value exceeding the threshold is not found in the second section, the two sections are considered to have no synchronization point, and the step B is skipped to search again; if the FSBC/FSCC without the Idle frame is searched for 4 times continuously, the peak value of the FSCCI is directly searched for under the condition of 11 frames at intervals at the 5 th time, and the operation is circulated until all synchronous positions are recorded.
The synchronous position search of the GSM system is carried out through the operation, the cross-correlation operation is not required all the time, the point-by-point comparison is not required to be carried out on a large amount of data, the data of a specific position is only required to be cached and reprocessed when counted to the proper position, the determined peak value can be ensured to be near the expected position, the operation efficiency is greatly improved, the data storage requirement in the operation process is greatly reduced, and meanwhile, the setting of a search window can increase the synchronous timing precision.
Based on the synchronization position determining method provided by the embodiment, with the oversampling multiple sps=4 and the sampling rate fs=1.0833 MHz, the number of FFT points is 512 points, that is, the input 512-point signal outputs the cross-correlation result of 256 points, and simulation experiments are performed on the case that the signal slides 256 points each time, and the result shows that the cross-correlation peak value is more than 94.14% of the autocorrelation value when no frequency offset exists, and the frequency offset is ±1k to ±2k, the threshold is set to be 70% of the autocorrelation value and can be synchronized to the correlation peak (sometimes slightly higher), and the correlation peak is relatively stable in ±1k (83.59% of the autocorrelation value to 90.23% of the autocorrelation value). When no frequency offset exists and the frequency offset exists, the number of points obtained at intervals of 10/11 frames is 50000 or 55000, and the time slot structure of the GSM is completely met.
The synchronous position determining device provided in the present application is described below, and the synchronous position determining device described below and the synchronous position determining method described above can be referred to correspondingly to each other.
Fig. 6 is a schematic structural diagram of a synchronous position determining apparatus according to an embodiment of the present application, and as shown in fig. 6, the apparatus at least includes:
a first determining module 601, configured to compare a cross-correlation value of a local sequence and a received signal with a preset threshold, and determine a correlation peak value of which a first cross-correlation value is greater than the preset threshold; wherein the preset threshold is determined based on an autocorrelation value of the local sequence;
a second determining module 602, configured to search for a first peak value of the cross-correlation value in a first search window with a position corresponding to the correlation peak value as a start point of the first search window, and determine that the position corresponding to the first peak value is a position of a first synchronization point;
a third determining module 603, configured to search, in a second search window, for a second peak value with the cross-correlation value greater than the preset threshold based on the positions spaced by 10 frames and/or 11 frames from the current synchronization point, and determine the position corresponding to the second peak value as the position of the next synchronization point until the positions of all synchronization points are determined; wherein the current synchronization point is any synchronization point including the first synchronization point.
In some embodiments, the searching for the second peak with the cross-correlation value greater than the preset threshold in the second search window based on the position spaced 10 frames and/or 11 frames from the current synchronization point includes:
determining a first signal segment based on a position spaced 10 frames from the current synchronization point;
searching for the second peak within the first signal segment based on the second search window;
if the second peak value is not searched in the first signal segment, determining a second signal segment based on a position which is 11 frames away from the current synchronous point;
searching for the second peak within the second signal segment based on the second search window;
and if the second peak value is not searched in the first signal segment and the second signal segment, searching the first peak value again.
In some embodiments, the searching for the second peak value with the cross-correlation value greater than the preset threshold in the second search window based on the position separated from the current synchronization point by 10 frames and/or 11 frames further comprises:
and if the second peak value is searched in the first signal segment for 4 times continuously, directly determining the second signal segment for the 5 th time, and searching the second peak value in the second signal segment.
In some embodiments, further comprising:
and the fourth determining module is used for carrying out fast Fourier transform FFT segmentation cross-correlation operation on the local sequence and the received signal, and carrying out normalization processing on the result to obtain the cross-correlation value.
In some embodiments, the FFT point number is 2 times the length of the local sequence.
In some embodiments, the determining the first signal segment includes:
taking forward 1/2 of the length of the local sequence at a position 10 frames apart from the current synchronization point as a starting point of the first signal segment, wherein the length of the first signal segment is equal to the FFT point number;
the determining the second signal segment includes:
and taking forward 1/2 of the length of the local sequence at a position 11 frames apart from the current synchronous point as the starting point of the second signal segment, wherein the length of the second signal segment is equal to the FFT point number.
In some embodiments, the searching for the second peak comprises:
determining a cross-correlation result of the first signal segment and/or the second signal segment;
and searching the second peak value by taking the center of the cross-correlation result of the first signal segment and/or the second signal segment as the center of the second search window.
Fig. 7 is a schematic structural diagram of an electronic device provided in an embodiment of the present application, and as shown in fig. 7, the electronic device may include: a processor (processor) 701, a communication interface (Communications Interface) 702, a memory (memory) 703 and a communication bus 704, wherein the processor 701, the communication interface 702 and the memory 703 communicate with each other through the communication bus 704. The processor 701 may invoke logic instructions in the memory 703 to perform a synchronous position determination method comprising:
comparing the cross-correlation value of the local sequence and the received signal with a preset threshold, and determining a correlation peak value of which the first cross-correlation value is larger than the preset threshold; wherein the preset threshold is determined based on an autocorrelation value of the local sequence;
searching a first peak value of the cross-correlation value in a first search window by taking the position corresponding to the correlation peak value as a starting point of the first search window, and determining the position corresponding to the first peak value as a position of a first synchronization point;
searching a second peak value with the cross correlation value larger than the preset threshold in a second search window based on the position of 10 frames and/or 11 frames spaced from the current synchronization point, and determining the position corresponding to the second peak value as the position of the next synchronization point until the positions of all the synchronization points are determined; wherein the current synchronization point is any synchronization point including the first synchronization point.
Further, the logic instructions in the memory 703 may be implemented in the form of software functional units and may be stored in a computer readable storage medium when sold or used as a stand alone product. Based on such understanding, the technical solution of the present application may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution, in the form of a software product stored in a storage medium, including several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), a magnetic disk, or an optical disk, or other various media capable of storing program codes.
In another aspect, the present application also provides a computer program product comprising a computer program, the computer program being storable on a non-transitory computer readable storage medium, the computer program, when executed by a processor, being capable of performing the method of determining a synchronization position provided by the methods described above, the method comprising:
Comparing the cross-correlation value of the local sequence and the received signal with a preset threshold, and determining a correlation peak value of which the first cross-correlation value is larger than the preset threshold; wherein the preset threshold is determined based on an autocorrelation value of the local sequence;
searching a first peak value of the cross-correlation value in a first search window by taking the position corresponding to the correlation peak value as a starting point of the first search window, and determining the position corresponding to the first peak value as a position of a first synchronization point;
searching a second peak value with the cross correlation value larger than the preset threshold in a second search window based on the position of 10 frames and/or 11 frames spaced from the current synchronization point, and determining the position corresponding to the second peak value as the position of the next synchronization point until the positions of all the synchronization points are determined; wherein the current synchronization point is any synchronization point including the first synchronization point.
In yet another aspect, the present application also provides a non-transitory computer readable storage medium having stored thereon a computer program which, when executed by a processor, is implemented to perform the method of determining a synchronization position provided by the methods described above, the method comprising:
comparing the cross-correlation value of the local sequence and the received signal with a preset threshold, and determining a correlation peak value of which the first cross-correlation value is larger than the preset threshold; wherein the preset threshold is determined based on an autocorrelation value of the local sequence;
Searching a first peak value of the cross-correlation value in a first search window by taking the position corresponding to the correlation peak value as a starting point of the first search window, and determining the position corresponding to the first peak value as a position of a first synchronization point;
searching a second peak value with the cross correlation value larger than the preset threshold in a second search window based on the position of 10 frames and/or 11 frames spaced from the current synchronization point, and determining the position corresponding to the second peak value as the position of the next synchronization point until the positions of all the synchronization points are determined; wherein the current synchronization point is any synchronization point including the first synchronization point.
The apparatus embodiments described above are merely illustrative, wherein the elements illustrated as separate elements may or may not be physically separate, and the elements shown as elements may or may not be physical elements, may be located in one place, or may be distributed over a plurality of network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art will understand and implement the present invention without undue burden.
From the above description of the embodiments, it will be apparent to those skilled in the art that the embodiments may be implemented by means of software plus necessary general hardware platforms, or of course may be implemented by means of hardware. Based on this understanding, the foregoing technical solution may be embodied essentially or in a part contributing to the prior art in the form of a software product, which may be stored in a computer readable storage medium, such as ROM/RAM, a magnetic disk, an optical disk, etc., including several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the method described in the respective embodiments or some parts of the embodiments.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting thereof; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the corresponding technical solutions.
Claims (9)
1. A method of synchronizing position determination, comprising:
comparing the cross-correlation value of the local sequence and the received signal with a preset threshold, and determining a correlation peak value of which the first cross-correlation value is larger than the preset threshold; wherein the preset threshold is determined based on an autocorrelation value of the local sequence;
searching a first peak value of the cross-correlation value in a first search window by taking the position corresponding to the correlation peak value as a starting point of the first search window, and determining the position corresponding to the first peak value as a position of a first synchronization point;
searching a second peak value with the cross correlation value larger than the preset threshold in a second search window based on the position of 10 frames and/or 11 frames spaced from the current synchronization point, and determining the position corresponding to the second peak value as the position of the next synchronization point until the positions of all the synchronization points are determined; wherein the current synchronization point is any synchronization point including the first synchronization point;
the searching for the second peak value with the cross-correlation value larger than the preset threshold in the second search window based on the position of 10 frames and/or 11 frames separated from the current synchronization point comprises the following steps:
determining a first signal segment based on a position spaced 10 frames from the current synchronization point;
Searching for the second peak within the first signal segment based on the second search window;
if the second peak value is not searched in the first signal segment, determining a second signal segment based on a position which is 11 frames away from the current synchronous point;
searching for the second peak within the second signal segment based on the second search window;
and if the second peak value is not searched in the first signal segment and the second signal segment, searching the first peak value again.
2. The synchronization position determining method according to claim 1, wherein searching for the second peak value, in which the cross-correlation value is greater than the preset threshold, in a second search window based on the position spaced 10 frames and/or 11 frames from the current synchronization point, further comprises:
and if the second peak value is searched in the first signal segment for 4 times continuously, directly determining the second signal segment for the 5 th time, and searching the second peak value in the second signal segment.
3. The synchronization position determining method according to claim 1 or 2, characterized by further comprising:
and carrying out FFT segmentation cross-correlation operation on the local sequence and the received signal, and carrying out normalization processing on the result to obtain the cross-correlation value.
4. A synchronization position determining method according to claim 3, characterized in that the number of FFT points is 2 times the length of the local sequence.
5. The method of synchronizing position determination according to claim 4, wherein the determining a first signal segment comprises:
taking forward 1/2 of the length of the local sequence at a position 10 frames apart from the current synchronization point as a starting point of the first signal segment, wherein the length of the first signal segment is equal to the FFT point number;
the determining the second signal segment includes:
and taking forward 1/2 of the length of the local sequence at a position 11 frames apart from the current synchronous point as the starting point of the second signal segment, wherein the length of the second signal segment is equal to the FFT point number.
6. The synchronization position determining method according to claim 5, wherein the searching for the second peak value includes:
determining a cross-correlation result of the first signal segment and/or the second signal segment;
and searching the second peak value by taking the center of the cross-correlation result of the first signal segment and/or the second signal segment as the center of the second search window.
7. A synchronous position determining apparatus, comprising:
The first determining module is used for comparing the cross-correlation value of the local sequence and the received signal with a preset threshold and determining a first correlation peak value of which the cross-correlation value is larger than the preset threshold; wherein the preset threshold is determined based on an autocorrelation value of the local sequence;
the second determining module is used for searching a first peak value of the cross-correlation value in a first search window by taking the position corresponding to the correlation peak value as a starting point of the first search window, and determining the position corresponding to the first peak value as a position of a first synchronization point;
the third determining module is used for searching a second peak value with the cross correlation value larger than the preset threshold in a second searching window based on the position of 10 frames and/or 11 frames which are spaced from the current synchronizing point, and determining the position corresponding to the second peak value as the position of the next synchronizing point until the positions of all the synchronizing points are determined; wherein the current synchronization point is any synchronization point including the first synchronization point;
the searching for the second peak value with the cross-correlation value larger than the preset threshold in the second search window based on the position of 10 frames and/or 11 frames separated from the current synchronization point comprises the following steps:
Determining a first signal segment based on a position spaced 10 frames from the current synchronization point;
searching for the second peak within the first signal segment based on the second search window;
if the second peak value is not searched in the first signal segment, determining a second signal segment based on a position which is 11 frames away from the current synchronous point;
searching for the second peak within the second signal segment based on the second search window;
and if the second peak value is not searched in the first signal segment and the second signal segment, searching the first peak value again.
8. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the method of synchronous position determination according to any one of claims 1 to 6 when the program is executed by the processor.
9. A non-transitory computer readable storage medium, on which a computer program is stored, characterized in that the computer program, when executed by a processor, implements the synchronization position determination method according to any one of claims 1 to 6.
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