CN109856615B - Distance measurement method and system based on CSS technology - Google Patents
Distance measurement method and system based on CSS technology Download PDFInfo
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Abstract
The invention provides a distance measurement method and a system based on a CSS technology, comprising the following steps: calculating a time synchronization start index in a received signal; preliminarily calculating a frequency synchronization initial index in a received signal; calculating a coarse frequency offset value of a received signal and a service signal starting point index according to the time synchronization starting index and the frequency synchronization starting index; calculating an accurate frequency synchronization initial index by adopting an interpolation fitting method; performing ID judgment according to a service signal in the transmitting signal; calculating to obtain an accurate service signal initial point index according to the time synchronization initial index and the accurate frequency synchronization initial index; and calculating to obtain an accurate TOA measurement value according to the accurate service signal starting point index. By adopting the technical scheme provided by the application, the high-precision distance measurement can be realized in the distance measurement process based on the CSS technology by greatly improving the precision of frequency synchronization.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a ranging method and a ranging system based on a CSS (cascading Style sheets) technology.
Background
Chirp Spread spectrum css (chirp Spread spectrum) is a linear spreading technique applied in communication systems, and its characteristics can be summarized as: the anti-interference and anti-multipath capability is strong, the power consumption and the delay are lower, the transmission distance is long and the distance measuring capability is strong. CSS technology can be applied in most complex environments to achieve wireless positioning, for example, indoor wireless positioning such as intelligent garages, industrial monitoring and control, and outdoor wireless positioning such as outdoor personnel and network equipment positioning, accident management, and remote patient positioning.
Various ranging schemes based on the CSS technique are proposed in the industry, and the most widely used scheme is time of arrival (toa) (time of arrival), and the principle thereof is shown in fig. 1: a transmitting terminal transmits a ranging request signal; the receiving end receives the request signal and carries out synchronous demodulation processing; the receiving end immediately transmits a ranging response signal after synchronous demodulation is finished; and the transmitting terminal receives the response signal and carries out synchronous demodulation processing.
The TOA is calculated as shown in equation 1, where T1 represents the time required for the transmitting end to complete from the transmitting signal to the final synchronous demodulation response signal, T2 represents the time taken for synchronous demodulation from the receiving end, time statistics are usually performed by using clk, and 1 clk represents the duration of 1 sampling point.
Due to the offset of the frequency point of the carrier wave of the transmitting end and the receiving end and the Doppler effect, the frequency of the carrier wave of the receiving end and the frequency of the carrier wave of the transmitting end cannot reach 0 frequency after demodulation down-conversion, namely the central frequency band of the carrier wave of the receiving end is inconsistent with that of the carrier wave of the transmitting end, namely the frequency offset. The calculation accuracy of the frequency offset affects the calculation accuracy of T2, and thus the final ranging accuracy. The precision of the existing frequency offset calculation scheme can only reach 1 or-1 sampling points, and the precision is not enough in a scene with higher requirement on the distance measurement precision. For example, the duration of a single sampling point is set to 80ns, i.e. the distance corresponding to the single sampling point is set to 24 m. If the required distance measurement accuracy is not more than 5m, the accuracy is far from sufficient. Reducing the duration of a single sampling point can improve accuracy, but this means an increase in the sampling rate, which can greatly increase the required resources and power consumption. The method has important research significance and practical value for realizing high-precision ranging under the condition of limited resources and power consumption.
Disclosure of Invention
In view of this, the invention provides a ranging method and system based on the CSS technology, which can greatly improve the precision of frequency synchronization in the ranging process based on the CSS technology, thereby significantly improving the calculation precision of T2 and realizing high-precision ranging.
The invention provides a distance measurement method based on a CSS technology, which comprises the following steps:
calculating a time synchronization start index in a received signal;
the calculating of the time synchronization start index in the received signal includes: the receiving end generates a local down chirp signal with a modulation value of 0.
Preliminarily calculating a frequency synchronization initial index in a received signal;
the preliminary calculation of the frequency synchronization start index in the received signal includes: a receiving end generates a local up chirp signal up chirp with a modulation value of 0;
calculating a coarse frequency offset value of a received signal and a service signal starting point index according to the time synchronization starting index and the frequency synchronization starting index;
calculating an accurate frequency synchronization initial index by adopting an interpolation fitting method;
the method for calculating the accurate frequency synchronization initial index by adopting the interpolation fitting method comprises the following steps:
adjusting the central frequency point of the local down chirp signal down chirp to be the coarse frequency offset value;
removing noise before the initial point index of the service signal in the received transmitting signal according to the initial point index of the service signal, namely removing a signal before the initial point index of the service signal in the received transmitting signal;
mapping the up chirp signal up chirp in the leading signal after the noise is removed to obtain three signals up _ advance, up and up _ delay; specifically, the method comprises the following steps:
performing forward cyclic shift on the up chirp signal up chirp in the preamble signal by N sampling points to obtain an up _ advance signal;
and carrying out backward cyclic shift on the up chirp signal up chirp in the preamble signal by N sampling points to obtain an up _ delay signal.
Performing correlation calculation on the three signals up _ advance, up and up _ delay after mapping processing to obtain three correlation peak values and three correlation peak value position indexes;
the correlation calculation specifically includes:
k rising chirp signals up chirp in the leading signals are selected to carry out correlation calculation;
calculating the correlation values of three mappings up _ advance, up and up _ delay of one rising chirp signal up chirp;
respectively obtaining the maximum value of the three mapping correlation values and the position index corresponding to the maximum value, wherein the maximum value of the correlation values is the correlation peak value of the mapping to which the correlation value belongs, and the position index corresponding to the maximum value is the position index corresponding to the mapping correlation peak value to which the correlation peak value belongs.
Performing interpolation fitting operation by using the three correlation peak values and the three correlation peak value position indexes to obtain a position index corresponding to the maximum value in fitting calculation;
selecting K rising chirp signals up chirp in the preamble signal to perform interpolation fitting calculation to obtain a position index corresponding to a maximum value in the K fitting calculations;
the interpolation fitting method includes any calculation method capable of realizing an interpolation fitting function, such as polynomial fitting, dichotomy, interpolation filtering method, window function method, and the like.
Further, the polynomial fitting includes:
calculating polynomial coefficients;
subdividing the position index;
fitting calculation is carried out, and a position index corresponding to the maximum value is determined;
and averaging the position indexes corresponding to the maximum values in the K fitting calculations to obtain accurate frequency synchronization initial indexes.
Performing ID judgment according to a service signal in the transmitting signal;
calculating to obtain an accurate service signal initial point index according to the time synchronization initial index and the accurate frequency synchronization initial index; and calculating to obtain an accurate TOA measurement value according to the accurate service signal starting point index.
Further, the method also comprises the steps of carrying out reverse measurement, exchanging the transmitting party and the receiving party, namely, transmitting data by the receiving end, receiving data by the transmitting end, repeating the TOA calculation process, and averaging the two corresponding TOA values to obtain an accurate TOA measured value.
The application also provides a ranging system based on CSS technique, includes:
the first calculation module is used for calculating a time synchronization starting index in a received signal;
the first calculating module is further configured to generate a local down chirp signal down chirp with a modulation value of 0 at the receiving end.
The second calculation module is used for preliminarily calculating a frequency synchronization initial index in the received signal; calculating a coarse frequency offset value of a received signal and a service signal starting point index according to the time synchronization starting index and the frequency synchronization starting index; the second calculation module is further configured to generate a local up chirp signal with a modulation value of 0 at the receiving end;
the second calculation module is further configured to calculate an accurate frequency synchronization start index by using an interpolation fitting method;
further, the second calculation module includes:
an adjusting unit, configured to adjust a center frequency point of the local down chirp signal to the coarse frequency offset value;
a first processing unit, configured to remove, according to the start point index of the service signal, noise in the received transmission signal before the start point index of the service signal, that is, remove a signal in the received transmission signal before the start point index of the service signal;
the second processing unit is used for mapping the up chirp signal up chirp in the leading signal after the noise is removed to obtain three signals up _ advance, up and up _ delay;
the second processing unit is specifically configured to:
performing forward cyclic shift on the up chirp signal up chirp in the preamble signal by N sampling points to obtain an up _ advance signal;
and carrying out backward cyclic shift on the up chirp signal up chirp in the preamble signal by N sampling points to obtain an up _ delay signal.
The first calculation unit is used for carrying out correlation calculation on the three signals up _ advance, up and up _ delay after mapping processing to obtain three correlation peak values and three correlation peak value position indexes;
the first computing unit is configured to:
k rising chirp signals up chirp in the leading signals are selected to carry out correlation calculation;
calculating the correlation values of three mappings up _ advance, up and up _ delay of one rising chirp signal up chirp; respectively obtaining the maximum value of the three mapping correlation values and the position index corresponding to the maximum value, wherein the maximum value of the correlation values is the correlation peak value of the mapping to which the correlation value belongs, and the position index corresponding to the maximum value is the position index corresponding to the mapping correlation peak value to which the correlation peak value belongs.
The second calculation unit is used for carrying out interpolation fitting operation by utilizing the three correlation peak values and the three correlation peak value position indexes to obtain a position index corresponding to the maximum value in the fitting calculation;
selecting K rising chirp signals up chirp in the preamble signal to perform interpolation fitting calculation to obtain a position index corresponding to a maximum value in the K fitting calculations;
the second calculating unit adopts any calculating method capable of realizing the interpolation fitting function, such as polynomial fitting, dichotomy, interpolation filtering method, window function method and the like, to realize the interpolation fitting calculation.
And the third calculation unit is used for averaging the position indexes corresponding to the maximum values in the K fitting calculations to obtain accurate frequency synchronization initial indexes.
The judging module is used for judging the ID according to the service signal in the transmitting signal;
the third calculation module is used for calculating to obtain an accurate service signal initial point index according to the time synchronization initial index and the accurate frequency synchronization initial index; and calculating to obtain an accurate TOA measurement value according to the accurate service signal starting point index.
Furthermore, the ranging system based on the CSS technique further includes reverse measurement, where the transmitter and the receiver exchange, that is, the receiver transmits data, the transmitter receives data, and repeats the TOA calculation process, and averages the two corresponding TOA values to obtain an accurate TOA measurement value.
The application provides a distance measurement method and a distance measurement system based on a CSS technology, wherein an interpolation fitting method is adopted to calculate an accurate frequency synchronization initial index; and then calculating to obtain an accurate service signal initial point index, and obtaining an accurate TOA measured value. By greatly improving the precision of frequency synchronization, high-precision distance measurement can be realized in the distance measurement process based on the CSS technology.
For the purposes of the foregoing and related ends, the one or more embodiments include the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects and are indicative of but a few of the various ways in which the principles of the various embodiments may be employed. Other benefits and novel features will become apparent from the following detailed description when considered in conjunction with the drawings and the disclosed embodiments are intended to include all such aspects and their equivalents.
Drawings
FIG. 1 is a schematic diagram of a ranging method based on CSS technology according to the present invention;
fig. 2 is a signal processing flowchart of a ranging method based on CSS technology provided in the present invention;
FIG. 3 is a flow chart of a ranging method based on CSS technology provided by the present invention;
FIG. 4 is a flow chart of a method for calculating a precise frequency synchronization index according to the present invention;
fig. 5 is a structural block diagram of a ranging system based on CSS technology according to the present invention.
Detailed Description
The following description and the drawings sufficiently illustrate specific embodiments of the invention to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. The examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The scope of embodiments of the invention encompasses the full ambit of the claims, as well as all available equivalents of the claims. Embodiments of the invention may be referred to herein, individually or collectively, by the term "invention" merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed.
The most widely used ranging scheme based on the CSS technique is time Of arrival (toa) (time Of arrival), and the principle thereof is shown in fig. 1: a transmitting terminal transmits a ranging request signal; the receiving end receives the request signal and carries out synchronous demodulation processing; the receiving end immediately transmits a ranging response signal after synchronous demodulation is finished; and the transmitting terminal receives the response signal and carries out synchronous demodulation processing.
The TOA is calculated as shown in equation 1, where T1 represents the time required for the transmitting end to complete from the transmitting signal to the final synchronous demodulation response signal, T2 represents the time taken for synchronous demodulation from the receiving end, time statistics are usually performed by using clk, and 1 clk represents the duration of 1 sampling point.
The receiving end receives a transmitting signal transmitted by the transmitting end through a wireless communication system, wherein the transmitting signal comprises noise and a service signal, and part of the noise is positioned in front of the service signal. The noise before the service signal may affect the subsequent frequency offset calculation, resulting in an increase in error of the ranging calculation result, and therefore, synchronization is required to determine the starting point of the service signal in the received signal and remove the noise before the index of the starting point of the service signal. It should be noted that the synchronization according to the present invention includes two parts, time synchronization and frequency synchronization.
Wherein, the frame structure of the transmission signal is: the method comprises the steps that a leading signal and a service signal are adopted, the frame structure of the leading signal is 'up chirp + down chirp', the up chirp signal is a rising chirp signal, and the frequency of the signal rises linearly; the down-chirp signal is a down-chirp signal, i.e., a signal whose frequency is linearly decreased, and hereinafter referred to as an up-chirp signal and a down-chirp signal for short.
Further, the preamble signal includes a plurality of up-chirp signals and a plurality of down-chirp signals, and both modulation values of the up-chirp signals and the down-chirp signals are 0;
the service signal is composed of a plurality of up chirp signals with specific modulation values, and the modulation values of the up chirp signals can be the same or different. The modulation values of the individual up chirp signals are typically selected to be different modulation values in view of communication reliability.
Example one
The invention provides a ranging method and a ranging system based on a CSS technology, wherein a signal processing flow chart is shown in figure 2;
the specific steps, as shown in fig. 3, include:
s101, calculating a time synchronization starting index in a received signal.
The method adopts a cross-correlation scheme as a time synchronization scheme, and specifically comprises the following steps:
1) generating a local signal, the local signal comprising two parts: a receiving end generates a local down chirp signal with a modulation value of 0; the receiving end generates a local up chirp signal with a modulation value of 0.
Unlike the up-chip and down-chip signals in the transmitted signals, the up-chip and down-chip signals in the transmitted signals include noise effects, and the local up-chip and local down-chip signals do not include noise, i.e., ideal up-chip and down-chip signals. Since the chirp signal is widely applied, the specific generation mode can refer to a linear modulation principle or radar application, and the generation mode is not detailed in the invention.
2) Multiplying the local down chirp signal by the up chirp signal in the preamble signal, and then performing fft operation;
3) setting a time synchronization threshold, wherein the time synchronization threshold is related to the signal-to-noise ratio of a signal and can be obtained according to simulation result statistics; searching and storing a position index loca _ time corresponding to the fft amplitude value higher than the time synchronization threshold;
since the preamble signal comprises a plurality of symbols (one up-chip signal or one down-chip signal is one symbol), each symbol can determine a position index loca _ time value corresponding to a magnitude higher than a time synchronization threshold;
4) in the index range of [ loca _ time loca _ time + symbol _ len/2] of each symbol (symbol _ len is the number of sample points contained in a single symbol, and symbol _ len of each symbol is the same), searching and storing a position index loca _ time _ max corresponding to the maximum value of the fft amplitude of each symbol;
5) calculating the difference value delta _ time between loca _ time _ max and loca _ time of each symbol for all symbols contained in the preamble signal, namely, the delta _ time is loca _ time _ max-loca _ time, and storing the delta _ time value of each symbol;
all symbols included in the preamble signal are averaged Δ _ time, which is a time synchronization start index sync _ start _ idx, i.e., sync _ start _ idx is mean (Δ _ time), where mean () represents the averaging.
S102, preliminarily calculating a frequency synchronization initial index in a received signal;
after the time synchronization is completed, the frequency synchronization processing is performed, which specifically includes:
1) multiplying the local up chirp signal by a down chirp signal in the preamble signal, and then performing fft operation;
2) setting a frequency synchronization threshold, searching and storing a position index loca _ freq corresponding to the fft amplitude value which is higher than the frequency synchronization threshold, wherein the frequency synchronization threshold is the same as the time synchronization threshold;
3) determining a position index loca _ freq value corresponding to the amplitude value of each symbol higher than the time synchronization threshold because the preamble signal comprises a plurality of symbols;
4) in the index range of [ loca _ freq loca _ freq + symbol _ len/2] of each symbol, searching and storing a position index loca _ freq _ max corresponding to the maximum value of the fft amplitude;
calculating the difference value delta _ freq between loca _ freq _ max and loca _ freq of each symbol, namely delta _ freq equals to loca _ freq _ max-loca _ freq, for all symbols contained in the preamble signal, and storing the delta _ freq value of each symbol;
5) calculating a coarse frequency offset value of a received signal and a service signal starting point index according to the time synchronization starting index and the frequency synchronization starting index;
specifically, all symbols Δ _ freq included in the preamble signal are averaged, and the Δ _ freq average value is a frequency synchronization start index freq _ start _ idx that is preliminarily calculated, that is, freq _ start _ idx is mean (Δ _ freq), where mean () represents averaging.
Substituting the obtained sync _ start _ idx and freq _ start _ idx values into formula 2 can preliminarily calculate the start point index and the coarse frequency offset value of the traffic signal in the received signal. Wherein coarse _ real _ start _ idx represents a start point index of a traffic signal in a received signal, and coarse _ freq _ shift represents a coarse frequency offset value.
S103, accurate frequency synchronization, and calculating an accurate frequency synchronization initial index by adopting an interpolation fitting method;
the scheme can obviously improve the precision of the frequency synchronization starting index freq _ start _ idx, so that the precision of the frequency offset calculation is improved to-0.1 or 0.1 sample points.
Specifically, as shown in fig. 4, the method includes:
103a, adjusting the central frequency point of the local down chirp signal to the coarse frequency offset value; according to a coarse frequency offset value coarse _ freq _ shift obtained in the frequency synchronization operation, a locally generated down chirp signal is adjusted, and the adjusting method comprises the following steps: the bandwidth is kept unchanged, the central frequency point is adjusted from the previous 0 value to the coarse frequency offset value coarse _ freq _ shift, and the adjusted local down chirp signal is dn _ chirp.
103b, removing noise before the initial point index of the service signal in the received transmitting signal according to the initial point index of the service signal;
specifically, S102 calculates a start point index coarse _ real _ start _ idx value of a service signal in the received signal, and removes a signal before coarse _ real _ start _ idx, that is, removes noise before the start point index of the service signal.
103c, mapping the up chirp signal in the leading signal in the transmitting signal after the noise is removed, and outputting three signals up _ advance, up and up _ delay;
wherein, the up signal is the up chirp signal in the preamble signal; performing forward cyclic shift on the up chirp signal in the preamble signal by N (N generally takes 1 or 2) sampling points to obtain an up _ advance signal; and performing backward cyclic shift on the up chirp signal in the preamble signal by N sampling points to obtain an up _ delay signal.
For example, assuming that the number of samples in the up signal is M, up _ advance ═ up (N +1: M) up (1: N), and up _ delay ═ up (M-N +1: M) up (1: M-N) ]. The mapping operation is embodied in the transmitted signal, that is, the adjacent three symbols in the preamble signal can be mapped according to the above rule.
103d, performing correlation calculation on the three signals up _ advance, up and up _ delay after mapping processing to obtain three correlation peak values and three correlation peak value position indexes;
and selecting K up chirp signals in the pilot signals to carry out correlation calculation, wherein the number of the symbols contained in the pilot signals is L, and K is less than or equal to L.
The single symbol correlating operation comprises:
1) the correlation values of three mappings up _ advance, up and up _ delay of one up chirp signal are calculated according to equation 3: up _ advance _ cor, up _ cor, and up _ delay _ cor
Wherein abs () represents a modulo operation, fft () represents fast fourier transform, up _ advance, up, and up _ delay are the three mappings obtained in step S103c, and dn _ chirp is the adjusted local down chirp signal;
2) respectively obtaining the maximum value of the three mapping correlation values and the position index corresponding to the maximum value, wherein the maximum value of the correlation values is the correlation peak value of the mapping to which the correlation value belongs, and the position index corresponding to the maximum value is the position index corresponding to the mapping correlation peak value to which the correlation peak value belongs;
further, the maximum value of up _ advance _ cor, up _ cor, and up _ delay _ cor and its corresponding position index are obtained according to formula 4,
wherein max (up _ advance _ cor), max (up _ cor), andmax (up _ delay _ cor) represents the correlation peak values to which up _ advance, up, and up _ delay are mapped, respectively, and n-1、n0And n1Respectively representing the position indexes corresponding to the three mapping correlation peaks.
103e, performing interpolation fitting operation by using the three correlation peak values and the three correlation peak value position indexes to obtain a position index corresponding to the maximum value in the fitting calculation;
optionally, the interpolation fitting method includes: polynomial fitting, dichotomy, interpolation filtering method, window function method and other calculation methods capable of realizing the interpolation fitting function.
The present application is illustrated with only a 2 nd order polynomial fit:
1) first, polynomial coefficients a, b, c are calculated according to equation 5.
In the formula [ a b c]Three coefficients representing a polynomial of order 2, n-1Position index, n, representing the corresponding correlation peak of the up _ advance map0Position index, n, representing the corresponding correlation peak of the up map1Position index, y, representing the correlation peak corresponding to the up _ delay mapping-1Represents the correlation peak value corresponding to the mapping up _ advance mapping, namely max (up _ advance _ cor), y0Represents the correlation peak value corresponding to the up mapping, namely max (up _ cor), y1Represents the correlation peak value corresponding to the up _ delay mapping, namely max (up _ delay _ cor);
2) and subdividing the position index according to a formula 6, performing fitting calculation, and determining a maximum value y and a position index n corresponding to the maximum value.
Where step represents the subdivided step value of the position index, n-1And n1Lower and upper limits for ni, respectively.
103f, selecting K symbols in the preamble signal to perform interpolation fitting calculation, wherein each symbol is subjected to the 103d-103e calculation to respectively obtain a position index n corresponding to the maximum value in the fitting calculation of each symbol of the K symbols;
and 103g, averaging the position indexes corresponding to the maximum values in the K fitting calculations to obtain accurate frequency synchronization initial indexes.
Averaging the n values of a sequence obtained in S103f, the result is the accurate frequency synchronization start index accurate _ freq _ start _ idx.
S104, judging the ID according to the service signal in the transmitting signal;
and judging the ID according to the service signal in the transmitted signal, wherein the service signal is an up chirp signal containing a specific modulation value.
Specifically, a cross-correlation scheme is used to calculate a modulation value of the service signal to be measured. That is, the up chirp signal in the service signal to be measured is multiplied by the local down chirp signal, then fft is solved, and the position index corresponding to the maximum value of the amplitude of fft in each symbol is searched, and the position index is the modulation value. If the modulation value of each symbol is equal to the specific modulation value, continuing the next operation; and on the contrary, the ID is not considered as a service signal, and the subsequent operation is stopped and is not carried out any more.
S105, TOA calculation, comprising:
calculating to obtain an accurate service signal starting point index (accrate _ real _ start _ idx) according to the time synchronization starting index (sync _ start _ idx) and the accurate frequency synchronization starting index (accrate _ freq _ start _ idx); and calculating to obtain an accurate TOA measurement value according to the accurate service signal starting point index actual _ real _ start _ idx.
1) Adjusting the CLK count, and calculating and acquiring an accurate initial point index of a service signal in a received signal through the accurate frequency synchronization initial index;
substituting the value of access _ freq _ start _ idx obtained in S103 into equation 2 again can obtain the value of access _ real _ start _ idx, and then substituting into equation 7 can obtain the accurate time T2 for receiving end synchronous demodulation.
T2＝(end_idx-accurate_real_start_idx)*clk (equation 7)
Where end _ idx represents the index of the last sample of the received signal, accept _ real _ start _ idx represents the index of the first valid sample of the received signal, and clk represents the duration of one sample.
2) In the reverse measurement, the difference between the clocks at the transmitting end and the receiving end may cause the difference between the calculated T2 values, and in order to minimize the influence caused by the difference between the clocks, the average value is obtained after the two T2 values obtained after the forward and reverse measurements are performed.
The transmitting end and the receiving end are interchanged, that is, the receiving end transmits data, the transmitting end receives data, and the above calculation steps are repeated, it should be noted that the transmitted signal in the reverse measurement process is completely consistent with the forward direction. The reverse measurement ultimately outputs a T2 value, here T2 is referred to as T2' for distinguishing from T2 in the forward measurement.
3) TOA calculation, substituting T2, T2' obtained in S104-S105 into formula 1:
the corresponding two TOA values can be obtained separately.
Further, averaging the two TOA values obtained in S105 yields the final TOA measurement TOA _ measure. Therefore, the measured distance is TOA _ measure light speed.
Further, the above steps S101 to S105 only describe the process in the single ranging mode, and in practical applications, the TOA is affected by the multipath delay, resulting in a large ranging error. In order to reduce the effect of multipath delay, multiple ranging operations are performed, and then the results of the multiple ranging operations are averaged, typically, the number of ranging operations is at least greater than 10. The number of ranging measurements needs to be determined by the actual test results and performance requirements.
Example two
The present application further provides a ranging system 200 based on the CSS technique, as shown in fig. 5, including:
210. a first calculating module, configured to calculate a time synchronization start index in a received signal, and specifically configured to:
1) generating a local signal, the local signal comprising two parts: a receiving end generates a local down chirp signal with a modulation value of 0; the receiving end generates a local up chirp signal with a modulation value of 0.
Unlike the up-chip and down-chip signals in the transmitted signals, the up-chip and down-chip signals in the transmitted signals include noise effects, and the local up-chip and local down-chip signals do not include noise, i.e., ideal up-chip and down-chip signals. Since the chirp signal is widely applied, the specific generation mode can refer to a linear modulation principle or radar application, and the generation mode is not detailed in the invention.
2) Multiplying the local down chirp signal by the up chirp signal in the preamble signal, and then performing fft operation;
3) setting a time synchronization threshold, wherein the time synchronization threshold is related to the signal-to-noise ratio of a signal and can be obtained according to simulation result statistics; searching and storing a position index loca _ time corresponding to the fft amplitude value higher than the time synchronization threshold;
since the preamble signal comprises a plurality of symbols (one up-chip signal or one down-chip signal is one symbol), each symbol can determine a position index loca _ time value corresponding to a magnitude higher than a time synchronization threshold;
4) in the index range of [ loca _ time loca _ time + symbol _ len/2] of each symbol (symbol _ len is the number of sample points contained in a single symbol, and symbol _ len of each symbol is the same), searching and storing a position index loca _ time _ max corresponding to the maximum value of the fft amplitude of each symbol;
5) calculating the difference value delta _ time between loca _ time _ max and loca _ time of each symbol for all symbols contained in the preamble signal, namely, the delta _ time is loca _ time _ max-loca _ time, and storing the delta _ time value of each symbol;
all symbols included in the preamble signal are averaged Δ _ time, which is a time synchronization start index sync _ start _ idx, i.e., sync _ start _ idx is mean (Δ _ time), where mean () represents the averaging.
220. The second calculation module is used for preliminarily calculating a frequency synchronization initial index in the received signal;
after the time synchronization is completed, the frequency synchronization processing is performed, which specifically includes:
1) multiplying the local up chirp signal by a down chirp signal in the preamble signal, and then performing fft operation;
2) setting a frequency synchronization threshold, searching and storing a position index loca _ freq corresponding to the fft amplitude value which is higher than the frequency synchronization threshold, wherein the frequency synchronization threshold is the same as the time synchronization threshold;
3) determining a position index loca _ freq value corresponding to the amplitude value of each symbol higher than the time synchronization threshold because the preamble signal comprises a plurality of symbols;
4) in the index range of [ loca _ freq loca _ freq + symbol _ len/2] of each symbol, searching and storing a position index loca _ freq _ max corresponding to the maximum value of the fft amplitude;
calculating the difference value delta _ freq between loca _ freq _ max and loca _ freq of each symbol, namely delta _ freq equals to loca _ freq _ max-loca _ freq, for all symbols contained in the preamble signal, and storing the delta _ freq value of each symbol;
5) the second calculation module is further configured to calculate a coarse frequency offset value of the received signal and a service signal starting point index according to the time synchronization starting index and the frequency synchronization starting index;
specifically, all symbols Δ _ freq included in the preamble signal are averaged, and the Δ _ freq average value is a frequency synchronization start index freq _ start _ idx that is preliminarily calculated, that is, freq _ start _ idx is mean (Δ _ freq), where mean () represents averaging.
Substituting the obtained sync _ start _ idx and freq _ start _ idx values into formula 2 can preliminarily calculate the start point index and the coarse frequency offset value of the traffic signal in the received signal. Wherein coarse _ real _ start _ idx represents a start point index of a traffic signal in a received signal, and coarse _ freq _ shift represents a coarse frequency offset value. The second calculation module is further configured to calculate an accurate frequency synchronization start index by using an interpolation fitting method;
the second calculation module is further configured to calculate an accurate frequency synchronization start index by using an interpolation fitting method; further, the second calculation module includes:
220a, adjusting the central frequency point of the local down chirp signal to the coarse frequency offset value; according to a coarse frequency offset value coarse _ freq _ shift obtained in the frequency synchronization operation, a locally generated down chirp signal is adjusted, and the adjusting method comprises the following steps: the bandwidth is kept unchanged, the central frequency point is adjusted from the previous 0 value to the coarse frequency offset value coarse _ freq _ shift, and the adjusted local down chirp signal is dn _ chirp.
220b, a first processing unit, configured to remove, according to the start point index of the service signal, noise in the received transmission signal before the start point index of the service signal, that is, remove, in the received transmission signal, a signal before the start point index of the service signal; removing noise before the initial point index of the service signal in the received transmitting signal according to the initial point index of the service signal; specifically, the second calculating module 220 calculates a start point index coarse _ real _ start _ idx value of the service signal in the received signal, and removes a signal before the coarse _ real _ start _ idx value, that is, removes noise before the start point index of the service signal.
220c, a second processing unit, configured to perform mapping processing on the up chirp signal in the noise-removed preamble signal to obtain three signals up _ advance, up, and up _ delay;
the second processing unit is specifically configured to:
performing forward cyclic shift on the up chirp signal in the preamble signal by N sampling points to obtain an up _ advance signal;
performing backward cyclic shift on the up chirp signal in the preamble signal by N sampling points to obtain an up _ delay signal;
wherein, the up signal is the up chirp signal in the preamble signal; n is generally 1 or 2;
for example, assuming that the number of samples in the up signal is M, up _ advance ═ up (N +1: M) up (1: N), and up _ delay ═ up (M-N +1: M) up (1: M-N) ]. The mapping operation is embodied in the transmitted signal, that is, the adjacent three symbols in the preamble signal can be mapped according to the above rule.
220d. a first calculation unit for:
k up chirp signals in the preamble signals are selected to carry out correlation calculation;
calculating the correlation values of three mappings up _ advance, up and up _ delay of one up chirp signal; respectively obtaining the maximum value of the three mapping correlation values and the position index corresponding to the maximum value, wherein the maximum value of the correlation values is the correlation peak value of the mapping to which the correlation value belongs, and the position index corresponding to the maximum value is the position index corresponding to the mapping correlation peak value to which the correlation peak value belongs.
And selecting K up chirp signals in the pilot signals to carry out correlation calculation, wherein the number of the symbols contained in the pilot signals is L, and K is less than or equal to L.
The single symbol correlating operation comprises:
1) calculating the correlation values of three mappings up _ advance, up _ chirp and up _ delay of one up _ chirp signal according to formula 3: up _ advance _ cor, up _ cor, and up _ delay _ cor
Wherein abs () represents a modulo operation, fft () represents fast fourier transform, up _ advance, up, and up _ delay are the three mappings obtained in step S103c, and dn _ chirp is the adjusted local down chirp signal;
2) respectively obtaining the maximum value of the three mapping correlation values and the position index corresponding to the maximum value, wherein the maximum value of the correlation values is the correlation peak value of the mapping to which the correlation value belongs, and the position index corresponding to the maximum value is the position index corresponding to the mapping correlation peak value to which the correlation peak value belongs;
further, the maximum value of up _ advance _ cor, up _ cor, and up _ delay _ cor and its corresponding position index are obtained according to formula 4,
where max (up _ advance _ cor), max (up _ cor), and max (up _ delay _ cor) represent correlation peak values mapping up _ advance, up, and up _ delay, respectively, and n is-1、n0And n1Respectively representing the position indexes corresponding to the three mapping correlation peaks.
220e, a second calculating unit, configured to perform interpolation fitting operation by using the three correlation peak values and the three correlation peak value position indexes, to obtain a position index corresponding to a maximum value in fitting calculation;
selecting K up chirp signals in the preamble signals to perform interpolation fitting calculation to obtain a position index corresponding to a maximum value in the K fitting calculations;
the second calculating unit adopts any calculating method capable of realizing the interpolation fitting function, such as polynomial fitting, dichotomy, interpolation filtering method, window function method and the like, to realize the interpolation fitting calculation.
The present application is illustrated with only a 2 nd order polynomial fit:
1) first, polynomial coefficients a, b, c are calculated according to equation 5.
In the formula [ a b c]Three coefficients representing a polynomial of order 2, n-1Position index, n, representing the corresponding correlation peak of the up _ advance map0Position index, n, representing the corresponding correlation peak of the up map1Position index, y, representing the correlation peak corresponding to the up _ delay mapping-1Represents the correlation peak value corresponding to the mapping up _ advance mapping, namely max (up _ advance _ cor), y0Represents the correlation peak value corresponding to the up mapping, namely max (up _ cor), y1Represents the correlation peak value corresponding to the up _ delay mapping, namely max (up _ delay _ cor);
2) and subdividing the position index according to a formula 6, performing fitting calculation, and determining a maximum value y and a position index n corresponding to the maximum value.
Where step represents the subdivided step value of the position index, n-1And n1Lower and upper limits for ni, respectively.
220f, averaging the position indexes corresponding to the maximum values in the K fitting calculations to obtain accurate frequency synchronization initial indexes;
selecting K symbols in the preamble signal to perform interpolation fitting calculation, wherein each symbol is subjected to the 103d-103e calculation to respectively obtain a position index n corresponding to the maximum value in the fitting calculation of each symbol of the K symbols;
230. the judging module is used for judging the ID according to the service signal in the transmitting signal;
performing ID judgment according to a service signal in a transmitting signal, wherein the service signal is an up chirp signal containing a specific modulation value;
specifically, a cross-correlation scheme is used to calculate a modulation value of the service signal to be measured. That is, the up chirp signal and the local down chirp signal in the service signal to be measured are multiplied, then fft is solved, and the position index corresponding to the maximum value of the amplitude of fft in each symbol is searched, and the position index is the modulation value. If the modulation value of each symbol is equal to the specific modulation value, continuing the next operation; and on the contrary, the ID is not considered as a service signal, and the subsequent operation is stopped and is not carried out any more.
240. A third calculating module, configured to calculate an accurate service signal starting point index, accept _ real _ start _ idx, according to the time synchronization starting index sync _ start _ idx and the accurate frequency synchronization starting index, accept _ freq _ start _ idx; calculating to obtain an accurate TOA measurement value according to the accurate service signal starting point index actual _ real _ start _ idx, specifically:
1) adjusting the CLK count, and calculating and acquiring an accurate initial point index of a service signal in a received signal through the accurate frequency synchronization initial index;
averaging the position indexes corresponding to the maximum values in the K fitting calculations to obtain accurate frequency synchronization initial indexes; averaging the n values of a sequence obtained in S220f, wherein the result is the accurate frequency synchronization start index accurate _ freq _ start _ idx;
the value of accept _ real _ start _ idx can be obtained by substituting the accept _ freq _ start _ idx into equation 2, and then the value of accept _ real _ start _ idx can be substituted into equation 7 to obtain the time T2 for accurate synchronous demodulation at the receiving end.
T2(end _ idx-accurate _ real _ start _ idx) clk (equation 7)
Where end _ idx represents the index of the last sample of the received signal, accept _ real _ start _ idx represents the index of the first valid sample of the received signal, and clk represents the duration of one sample.
2) Furthermore, the ranging system based on the CSS technique further includes reverse measurement, where the transmitter and the receiver exchange, that is, the receiver transmits data, the transmitter receives data, and repeats the TOA calculation process, and averages the two corresponding TOA values to obtain an accurate TOA measurement value.
The transmitting end and the receiving end are interchanged, that is, the receiving end transmits data, the transmitting end receives data, and the above calculation steps are repeated, it should be noted that the transmitted signal in the reverse measurement process is completely consistent with the forward direction. The reverse measurement ultimately outputs a T2 value, here T2 is referred to as T2' for distinguishing from T2 in the forward measurement.
3) TOA calculation, substituting the obtained T2 and T2' into formula 1:
the corresponding two TOA values can be obtained separately.
Further, averaging the two TOA values yields the final TOA measurement TOA _ measure. Therefore, the measured distance is TOA _ measure light speed.
Compared with the scheme in the prior art, the invention has the following advantages:
1. by utilizing the precise frequency synchronization scheme provided by the invention, the precision of frequency synchronization can be improved to (-0.10.1) sample points, and the precision is improved by 10 times, so that the measurement precision of the TOA of the T2 is greatly improved, and the high-precision ranging is realized under the condition of limited resources and power consumption.
2. The deterioration of TOA caused by inconsistent clocks of the transmitting end and the receiving end can be weakened by using a reverse measurement scheme.
Those of skill in the art will understand that the various exemplary method steps and apparatus elements described in connection with the embodiments disclosed herein can be implemented as electronic hardware, software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative steps and elements have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The steps of a method described in connection with the embodiments disclosed above may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a subscriber station. In the alternative, the processor and the storage medium may reside as discrete components in a subscriber station.
The disclosed embodiments are provided to enable those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope or spirit of the invention. The above-described embodiments are merely preferred embodiments of the present invention, which should not be construed as limiting the invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (16)
1. A ranging method based on CSS technology comprises the following steps:
calculating a time synchronization start index in a received signal;
preliminarily calculating a frequency synchronization initial index in a received signal;
calculating a coarse frequency offset value of a received signal and a service signal starting point index according to the time synchronization starting index and the frequency synchronization starting index;
and (3) calculating an accurate frequency synchronization initial index by adopting an interpolation fitting method: removing noise before a starting point index of a service signal in a transmitting signal, performing mapping processing and correlation calculation to obtain three correlation peak values and three correlation peak value position indexes, and performing interpolation fitting calculation according to the three correlation peak values and the three correlation peak value position indexes;
performing ID judgment according to a service signal in the transmitting signal;
calculating to obtain an accurate service signal initial point index according to the time synchronization initial index and the accurate frequency synchronization initial index; and calculating to obtain an accurate TOA measurement value according to the accurate service signal starting point index.
2. The CSS-based ranging method of claim 1, further comprising performing reverse measurement, wherein the transmitter and the receiver exchange data, i.e., the receiver transmits data and the transmitter receives data, and repeating TOA calculation procedure, and averaging two corresponding TOA values to obtain an accurate TOA measurement value.
3. The CSS-technology-based ranging method of claim 1, wherein the calculating a time synchronization start index in the received signal comprises: the receiving end generates a local down chirp signal down chirp with a modulation value of 0.
4. The CSS-technology-based ranging method of claim 1, wherein the preliminary calculating of the frequency synchronization start index in the received signal comprises: the receiving end generates a local up chirp signal up chirp with a modulation value of 0.
5. The CSS-technology-based ranging method of claim 1, wherein the calculating the accurate frequency synchronization start index using an interpolation fitting method comprises:
adjusting the central frequency point of the local down chirp signal down chirp to be the coarse frequency offset value, wherein the modulation value of the local down chirp signal down chirp is 0;
removing noise before the initial point index of the service signal in the received transmitting signal according to the initial point index of the service signal, namely removing a signal before the initial point index of the service signal in the received transmitting signal;
mapping a rising chirp signal up chirp in a leading signal after noise removal, wherein the leading signal is positioned in the transmitting signal to obtain three signals up _ advance, up and up _ delay;
performing correlation calculation on the three signals up _ advance, up and up _ delay after mapping processing to obtain three correlation peak values and three correlation peak value position indexes;
performing interpolation fitting operation by using the three correlation peak values and the three correlation peak value position indexes to obtain a position index corresponding to the maximum value in fitting calculation;
selecting K rising chirp signals up chirp in the preamble signal to perform interpolation fitting calculation to obtain a position index corresponding to a maximum value in the K fitting calculations;
and averaging the position indexes corresponding to the maximum values in the K fitting calculations to obtain accurate frequency synchronization initial indexes.
6. The CSS-technology-based ranging method of claim 5, wherein the mapping the up chirp signal up chirp in the noise-removed preamble signal comprises:
performing forward cyclic shift on the up chirp signal up chirp in the preamble signal by N sampling points to obtain an up _ advance signal;
and carrying out backward cyclic shift on the up chirp signal up chirp in the preamble signal by N sampling points to obtain an up _ delay signal.
7. The CSS technology based ranging method of claim 5, wherein the correlating comprises:
k rising chirp signals up chirp in the leading signals are selected to carry out correlation calculation;
calculating the correlation values of three mappings up _ advance, up and up _ delay of one rising chirp signal up chirp;
respectively obtaining the maximum value of the three mapping correlation values and the position index corresponding to the maximum value, wherein the maximum value of the correlation values is the correlation peak value of the mapping to which the correlation value belongs, and the position index corresponding to the maximum value is the position index corresponding to the mapping correlation peak value to which the correlation peak value belongs.
8. The CSS technology based ranging method according to claim 5, wherein the interpolation fitting method comprises polynomial fitting, dichotomy, interpolation filtering method, and window function method.
9. The CSS technique-based ranging method of claim 8, wherein the polynomial fitting comprises:
calculating polynomial coefficients;
subdividing the position index;
and fitting calculation is carried out, and the position index corresponding to the maximum value is determined.
10. A ranging system based on CSS technology, comprising:
the first calculation module is used for calculating a time synchronization starting index in a received signal;
the second calculation module is used for preliminarily calculating a frequency synchronization initial index in the received signal; calculating a coarse frequency offset value of a received signal and a service signal starting point index according to the time synchronization starting index and the frequency synchronization starting index;
the second calculating module is further configured to calculate an accurate frequency synchronization start index by using an interpolation fitting method: removing noise before a starting point index of a service signal in a transmitting signal, performing mapping processing and correlation calculation to obtain three correlation peak values and three correlation peak value position indexes, and performing interpolation fitting calculation according to the three correlation peak values and the three correlation peak value position indexes;
the judging module is used for judging the ID according to the service signal in the transmitting signal;
the third calculation module is used for calculating to obtain an accurate service signal initial point index according to the time synchronization initial index and the accurate frequency synchronization initial index; and calculating to obtain an accurate TOA measurement value according to the accurate service signal starting point index.
11. The CSS-technology-based ranging system of claim 10, wherein the first calculating module is further configured to generate a local down chirp signal down chirp with a modulation value of 0 at a receiving end.
12. The CSS-technology-based ranging system of claim 10, wherein the second calculating module is further configured to generate a local up chirp signal up chirp with a modulation value of 0 at a receiving end.
13. The CSS-technology-based ranging system of claim 10, wherein the second calculation module comprises:
the adjusting unit is used for adjusting the central frequency point of the local down chirp signal to the coarse frequency offset value; the modulation value of the local down chirp signal down chirp is 0;
a first processing unit, configured to remove, according to the starting point index of the service signal, noise in the received transmission signal before the starting point index of the service signal, that is, remove, from the received transmission signal, a signal before the starting point index of the service signal;
the second processing unit is used for mapping the up chirp signal up chirp in the leading signal after the noise is removed to obtain three signals up _ advance, up and up _ delay;
the first calculation unit is used for carrying out correlation calculation on the three signals up _ advance, up and up _ delay after mapping processing to obtain three correlation peak values and three correlation peak value position indexes;
the second calculation unit is used for carrying out interpolation fitting operation by utilizing the three correlation peak values and the three correlation peak value position indexes to obtain a position index corresponding to the maximum value in the fitting calculation;
selecting K rising chirp signals up chirp in the preamble signal to perform interpolation fitting calculation to obtain a position index corresponding to a maximum value in the K fitting calculations;
and the third calculation unit is used for averaging the position indexes corresponding to the maximum values in the K fitting calculations to obtain accurate frequency synchronization initial indexes.
14. The CSS-technology-based ranging system of claim 13, wherein the second processing unit is configured to:
performing forward cyclic shift on the up chirp signal up chirp in the preamble signal by N sampling points to obtain an up _ advance signal;
and carrying out backward cyclic shift on the up chirp signal up chirp in the preamble signal by N sampling points to obtain an up _ delay signal.
15. The CSS-technology-based ranging system of claim 13, wherein the first computing unit is configured to:
k rising chirp signals up chirp in the leading signals are selected to carry out correlation calculation;
calculating the correlation values of three mappings up _ advance, up and up _ delay of one up chirp signal;
respectively obtaining the maximum value of the three mapping correlation values and the position index corresponding to the maximum value, wherein the maximum value of the correlation values is the correlation peak value of the mapping to which the correlation value belongs, and the position index corresponding to the maximum value is the position index corresponding to the mapping correlation peak value to which the correlation peak value belongs.
16. The CSS-technology-based ranging system of claim 13, wherein the second calculation unit performs interpolation fitting calculation using polynomial fitting, dichotomy, interpolation filtering, window function method.
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