CN111786920B - Multi-system CSS signal demodulation method and device - Google Patents

Multi-system CSS signal demodulation method and device Download PDF

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CN111786920B
CN111786920B CN201910265013.4A CN201910265013A CN111786920B CN 111786920 B CN111786920 B CN 111786920B CN 201910265013 A CN201910265013 A CN 201910265013A CN 111786920 B CN111786920 B CN 111786920B
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cfo
data
value
synchronization
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CN111786920A (en
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周海然
杨利
鲍东山
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Shanghai Nufront Electronic Technology Co ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2669—Details of algorithms characterised by the domain of operation
    • H04L27/2671—Time domain
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H04L27/2659—Coarse or integer frequency offset determination and synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H04L27/266—Fine or fractional frequency offset determination and synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/38—Demodulator circuits; Receiver circuits
    • H04L27/3845—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier
    • H04L27/3854—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier using a non - coherent carrier, including systems with baseband correction for phase or frequency offset
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset

Abstract

The application provides a method and a device for demodulating a multilevel CSS signal, comprising the following steps: performing analog-to-digital conversion on the multilevel CSS modulation signal to obtain a digital baseband signal; performing downsampling processing on the digital baseband signal; detecting the downsampled signal, and detecting whether the data arrives; when the data arrives, time domain synchronization is carried out on the input data, and a synchronized signal is output; searching the position of the frame separator SFD for the synchronized signal; judging and obtaining an integer value CFO_Int of the carrier frequency offset CFO according to the output signal after time domain synchronization and the position of the frame separator SFD; estimating a decimal value CFO_Frac of the carrier frequency offset CFO; and demodulating the effective data, and carrying out carrier frequency offset compensation on the demodulated data to obtain final demodulated data.

Description

Multi-system CSS signal demodulation method and device
Technical Field
The application belongs to the technical field of wireless communication, and particularly relates to a method and a device for demodulating a multilevel CSS signal.
Background
In modern communication systems, the communication technology applied to the internet of things is various, and the multilevel chirp spread spectrum CSS (Chirp Spread Spectrum) modulation transmitter has the characteristic of ultra-low power consumption, so that the transmitter is outstanding in the internet of things communication technology. However, the multi-system CSS receiver has not been realized by explicit and better technology, and it is difficult for the existing receiver to achieve both power consumption and performance. The current schemes for implementing a multi-system CSS receiver in the industry are: the method of coherent and matched filtering is adopted for receiving, but the power consumption and the surface are large; the method of solving the frequency by difference is adopted for receiving, but the performance is poor, and the SNR of the required channel is high; the direct FFT method is adopted for synchronization and reception, the power consumption and the surface are large, and the characteristics of low power consumption, small area and high performance of the Internet of things are not met by the scheme.
Disclosure of Invention
In view of this, the application provides a method and a device for demodulating a multilevel CSS signal, which are characterized in that after cascade integral comb filtering CIC downsampling, a related method is used for synchronizing time domain and frequency domain, and an FFT method is used for demodulation, so that the method and the device have lower power consumption and area under the premise of high performance.
The application provides a multi-system CSS signal demodulation method, which comprises the following steps:
performing analog-to-digital conversion on the multi-system CSS modulation signal to obtain a digital baseband signal;
performing downsampling processing on the digital baseband signal to obtain a downsampled signal;
further, the down-sampling the digital baseband signal includes:
the digital baseband signal is subjected to preliminary downsampling through a cascade integral comb filter, and high-frequency noise is filtered, so that a preliminary downsampled signal for filtering the high-frequency noise is obtained;
and the preliminary downsampling signal is subjected to further downsampling after passing through a compensation filter, and in-band attenuation of the cascade integral comb filter is compensated to output a downsampling signal.
Detecting data of the downsampled signal, detecting whether the data arrives, setting an energy detection threshold value, calculating a correlation energy value of a current input data frame, and indicating that the data arrives when the correlation energy value is larger than the threshold value;
when the data arrives, time domain synchronization is carried out on the input data, and a synchronized signal is output;
further, the time domain synchronization of the data comprises coarse synchronization and fine synchronization;
the time domain coarse synchronization performs time domain shift on the received data according to the frame marks and the sampling point marks;
and the time domain fine synchronization further synchronizes the data after coarse synchronization, searches for a position index corresponding to the maximum value of the correlation energy value, and performs time domain shift on the data according to the position index corresponding to the maximum value of the correlation energy value.
Searching the position of the frame separator SFD in the synchronized signal; specifically, the location of the search frame separator SFD includes:
searching the position of the frame separator SFD by adopting a correlation method, and calculating the correlation energy value p '(n, k) of the output x' (n, k) after the fine synchronization;
the position index fine_idx ' corresponding to the maximum value of the correlation energy value p ' (n, k) is found, and fine_idx ' is the position of the frame separation symbol SFD.
Judging and obtaining an integer value CFO_Int of the carrier frequency offset CFO according to the output signal after time domain synchronization and the position of the frame separator SFD;
estimating a decimal value CFO_Frac of the carrier frequency offset CFO;
the estimating the decimal value of the carrier frequency offset CFO includes:
calculating a correlation value cor (n, k) of a preamble sequence x' (n, k);
performing Fourier transform on the correlation value cor (n, k), solving the amplitude value, and finding out the maximum three points in the amplitude value and the label of the three points;
calculating an approximate signal-to-noise ratio (SNR) of the preamble sequence correlation value cor (n, k);
delaying the preamble sequence x '(n, k) by one sampling point, and calculating an approximate signal-to-noise ratio SNR' of the delayed preamble sequence;
the fractional value cfo_frac of CFO is derived from the integer value cfo_ Int, SNR, SNR' of CFO.
Demodulating the effective data to obtain demodulated data; and carrying out carrier frequency offset CFO compensation on the demodulated data, and adjusting the demodulated data according to the carrier frequency offset integer value CFO_Int and the carrier frequency offset decimal value CFO_Frac to obtain final demodulated data.
The application also provides a multi-system CSS signal demodulation device, which comprises:
the analog-to-digital conversion module is used for carrying out analog-to-digital conversion on the multi-system CSS modulation signal to obtain a digital baseband signal;
the downsampling module is used for performing downsampling processing on the digital baseband signal to obtain a downsampled signal;
the downsampling module comprises:
the first downsampling unit is used for performing preliminary downsampling on the digital baseband signal through a cascade integral comb filter and filtering high-frequency noise to obtain a preliminary downsampled signal for filtering the high-frequency noise;
and the second downsampling unit is used for further downsampling the preliminary downsampling signal after passing through the compensation filter, compensating in-band attenuation of the cascade integral comb filter and outputting the downsampling signal.
The detection module is used for detecting data by adopting a related method and detecting whether the data arrives or not;
the detection module comprises:
a determining unit for setting a threshold value of the energy detection,
a calculation unit calculating a correlation energy value of a current input data frame,
and the comparison unit is used for comparing the correlation energy value of the current input data frame with the threshold value of energy detection, and when the correlation energy value is larger than the threshold value, the data arrival is indicated.
The synchronous processing module is used for carrying out time domain synchronization on input data when the data arrives and outputting a synchronized signal;
the synchronous processing module comprises:
the first synchronization unit is used for performing time domain coarse synchronization and performing time domain shift on the received data according to the frame marks and the sampling point marks;
and the second synchronization unit is used for performing time domain fine synchronization on the data after coarse synchronization, searching a position index corresponding to the maximum value of the correlation energy value, and performing time domain shift on the data according to the position index corresponding to the maximum value of the correlation energy value.
The searching module is used for searching the position of the frame separator SFD in the synchronized signal;
the searching module is further used for searching the position of the frame separator SFD by adopting a correlation method and calculating the correlation energy value of the output after the fine synchronization;
and searching a position index corresponding to the maximum value of the correlation energy value, wherein the position index corresponding to the maximum value is the position of the frame separation symbol.
The computing module is used for computing carrier frequency offset CFO;
the computing module comprises:
an integer calculation unit, configured to determine, according to the output signal after time domain synchronization and the position where the frame separator SFD is located, an integer value cfo_int of the carrier frequency offset CFO;
a decimal computing unit for estimating a decimal value CFO_Frac of the carrier frequency offset CFO;
further, the decimal computing unit is configured to:
performing Fourier transform on the correlation value cor (n, k), solving the amplitude value, and finding out the maximum three points in the amplitude value and the label of the three points;
calculating an approximate signal-to-noise ratio (SNR) of the preamble sequence correlation value cor (n, k);
delaying the preamble sequence by one sampling point, and calculating the approximate signal-to-noise ratio SNR' of the delayed preamble sequence;
the fractional value CFO_Frac of the CFO is calculated from the integer values CFO_Int, SNR, and CFO.
The system also comprises an adjusting module, a data processing module and a data processing module, wherein the adjusting module is used for demodulating effective data; and carrying out carrier frequency offset CFO compensation on the demodulated data, and adjusting the demodulated data according to the carrier frequency offset integer value CFO_Int and the carrier frequency offset decimal value CFO_Frac.
Compared with the scheme in the prior art, the scheme provided by the application has the following advantages:
1. the application reduces the synchronous and demodulation area and reduces the power consumption by adopting the cascade integral comb filter and the compensation filter to carry out downsampling on the signals after analog-to-digital conversion.
2. The related energy detection method provided by the application can effectively detect the arrival of data, and compared with the traditional Schmidl-Cox detection method, the related energy detection method provided by the application has the advantages of small required resources and high precision.
3. The carrier frequency offset detection and compensation method provided by the application can effectively compensate carrier frequency offset, and has the advantages of high speed and high resource utilization rate compared with the traditional signal frequency solving method.
To the accomplishment of the foregoing and related ends, the one or more embodiments comprise 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, the disclosed embodiments are intended to include all such aspects and their equivalents.
Drawings
FIG. 1 is a flow chart of the generation of a multi-system CSS modulation signal provided by the present application;
fig. 2 is a flowchart of a method for demodulating a multi-system CSS modulation signal according to a first embodiment of the present application;
FIG. 2a is a flow chart of a downsampling process according to a first embodiment of the application;
FIG. 2b is a flow chart of a time domain synchronization process according to a first embodiment of the present application;
fig. 2c is a flowchart of a decimal method for estimating carrier frequency offset CFO according to a first embodiment of the present application;
fig. 3 is a system block diagram of a multi-system CSS modulation signal demodulation apparatus according to a second embodiment of the present application.
Detailed Description
The following description and the drawings sufficiently illustrate specific embodiments of the application to enable those skilled in the art to practice them. Other embodiments may involve structural, logical, electrical, process, and other changes. The embodiments represent only 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 application encompasses the full ambit of the claims, as well as all available equivalents of the claims. These embodiments of the application may be referred to herein, individually or collectively, by the term "application" merely for convenience and without intending to voluntarily limit the scope of this application to any single application or inventive concept if more than one is in fact disclosed.
Example 1
The chirp spread spectrum CSS (Chirp Spread Spectrum) is a way of spreading transmission, and is accomplished by the chirp signal itself, without the need for a pseudo-random sequence for frequency spreading, as compared to the direct sequence spread spectrum DSSS (Direct Sequence Spread Spectrum). The Chirp signal can be expressed generally as:wherein A is amplitude; />Is the phase; μ is the slope of its frequency curve.
The signal waveform under CSS modulation can be defined as
The multi-system CSS signal in the application is obtained by a modification of the CSS signal, in particular the instantaneous frequency of the multi-system CSS signal is expressed as:
f i the starting frequencies for different chirp symbols are related to the data to be transmitted as follows: />d (k) is the data to be transmitted, and k is the index of the data. A single Chirp symbol under basic CSS modulation can only transmit 1 bit of data (+1 or-1), while a single Chirp symbol under multilevel CSS modulation can transmit s bits of data.
The multi-system CSS modulation transmitter has the characteristics of low power consumption and high performance, however, the multi-system CSS receiver has not been realized by a clear and better technology, and the application provides a demodulation method and device for a multi-system CSS modulation signal aiming at the multi-system CSS receiver.
As shown in fig. 1, a multi-system CSS modulation signal is first acquired: the antenna receives the radio frequency signal, after being amplified by the Low noise amplifier LNA (Low noise amplifier), the carrier wave is generated by the phase-locked loop PLL (Phase locked loops), the gain of the signal is adjusted by the gain variable amplifier VGA (Variable gain amplifiers), and then the high frequency signal is filtered out by the Low pass filter LP (Low pass), so that the multilevel CSS modulation signals Din_I and Din_Q can be obtained.
The application provides a multi-system CSS signal demodulation method, as shown in figure 2, comprising the following steps:
s101, carrying out analog-to-digital conversion on a multi-system CSS modulation signal to obtain a digital baseband signal;
s102, carrying out downsampling treatment on the digital baseband signal to obtain a downsampled signal;
further, as shown in fig. 2a, the downsampling the digital baseband signal includes:
s102a, performing preliminary downsampling on the digital baseband signal through a cascade integral comb filter CIC (Cascade Integral Comb), and filtering high-frequency noise to obtain a preliminary downsampled signal for filtering the high-frequency noise;
s102b, the preliminary downsampling signal is subjected to further downsampling after passing through a compensation filter Comp (Compensatory filter), in-band attenuation of a cascade integral comb filter CIC is compensated, and a downsampling signal x (n, k) is output.
S103, carrying out data detection on the downsampled signal x (n, k), detecting whether data arrives,
specifically, a correlation method is adopted for detection, and the correlation energy value p (n, k) of the downsampled signal is calculated:wherein k is the label of the input data frame, M is the length of a frame, n is the label of a sampling point in a frame, up_c (n) is a reference signal generated by a lookup Table (Loop Up Table) Chirp_LUT;
setting a threshold value TH for energy detection 1 The correlation energy value p (n, k) of the current input data frame is compared with the threshold value TH 1 Comparing when p (n, k) > TH 1 Indicating that data is coming.
S104, when the data arrives, carrying out time domain synchronization on the input data and outputting a synchronized signal;
in particular, the time domain synchronization of the data, as shown in figure 2b, includes coarse synchronization and fine synchronization,
s104a, performing time domain coarse synchronization, and performing time domain shift on the received data according to the frame marks and the sampling point marks;
when the arrival of data is detected in S103, that is, the correlation energy value p (n, k) of the current input data frame is detected to be greater than the threshold TH 1 And at the moment, the frame index k 'and the sampling point index n' shift the time domain of the received data, and shift k 'frames and n' sampling point periods to obtain the data after coarse synchronization.
S104b, carrying out time domain fine synchronization, carrying out further synchronization on the data after coarse synchronization,
specifically, a position index [ -, fine_idx ] =max (p (n, k)) corresponding to the maximum value of the correlation energy value is found, and the data is subjected to time domain shift according to the index, namely, the data after coarse synchronization is shifted by (fine_idx-1) sampling point periods, wherein fine_idx is a sampling point label of fine synchronization, and fine synchronization is performed according to the label, so that a synchronized output signal x' (n, k) is obtained.
S105, searching the position of the frame separator SFD (StartFrame Delimiter) in the signal x' (n, k) after synchronization;
searching the position of the frame separator SFD by adopting a correlation method, and calculating the correlation energy value p' (n, k) of the output after the fine synchronization;
further, the method comprises the steps of,x' (n, k) is output after time domain fine synchronization, k is the label of an input data frame, M is the length of one frame, n is the label of a sampling point in one frame, and dn_c (n) is a reference signal generated by a Chirp_LUT;
the position index corresponding to the maximum value of the correlation energy value p '(n, k) is found [ -, fine_idx' ] =max (p (n, k) '), and the position index fine_idx' is the position of the frame separation symbol SFD.
S106, judging to obtain an integer value CFO_int of the carrier frequency offset CFO (CarrierFrequencyOffset) according to a fine_idx of a sampling point label and a fine_idx' of a frame separator SFD in time domain synchronization;
specifically, according to the time domain synchronization and the position fine_idx' where the frame separator SFD is located, an integer value of the carrier frequency offset CFO may be calculated:
s107, estimating a decimal value CFO_Frac of a carrier frequency offset CFO;
estimating that the data to be transmitted by the transmitter comprises a Preamble sequence (Preamble), wherein symbols in the Preamble sequence are up_c (n); as shown in fig. 2c, comprising:
s107a, calculating a correlation value cor '(n, k) of a preamble sequence of data x' (n, k) after time domain fine synchronization; and carrying out point multiplication on the data x' (n, k) preamble sequence after time domain fine synchronization and a reference signal up_c (n): cor (n, k) =x' (n, k) ×up_c (n), obtaining a correlation value cor (n, k) of the preamble sequence;
s107b, carrying out Fourier transform on the correlation value COR (N, K), solving amplitude values, and finding out the largest three points in the amplitude values and the label [ m ] where the largest three points are located by COR (N, K) = |FFT { COR (N, K) } | 1 ,m 2 ,m 3 ,p 1 ,p 2 ,p 3 ]=max3 (COR (N, K)), where m 1 ～m 3 At maximum three values, p 1 ～p 3 The label corresponding to the largest three values;
s107c. calculating an approximate signal-to-noise ratio SNR of the preamble correlation value cor (n, k):
s107d, delaying the preamble sequence of the data after the time domain fine synchronization by one sampling point, and calculating the approximate signal-to-noise ratio of the delayed preamble sequence;
illustratively, the time-domain fine synchronized data is delayed by 1 sampling point and is multiplied by cor '(n, k) =x' (n+1, k) ×up_c (n) with reference signal up_c (n), fourier transformed and amplitude calculated: COR '(N, K) = |fft { COR' (N, K) }I, find the largest three points in the amplitude and the label where they are: [ m ]' 1 ,m' 2 ,m' 3 ,p' 1 ,p' 2 ,p' 3 ]=max3 (COR ' (N, K)), the approximate signal-to-noise ratio SNR ' after the delay is calculated '
Wherein m is 1 ～m 3 Three values at maximum; p1', p2', p3' are the labels where the three maxima are located;
it should be noted that if there is no CFO fraction and other non-ideal factors, the value of SNR' will be higher than the threshold TH 2 . The demodulation result do p_real The reference sign p where the largest value of the amplitude is 1 ’。
S107e, obtaining the decimal value of the CFO according to the integer value, SNR and SNR' of the CFO;
in particular, the method comprises the steps of,
1) When the value of cfo_int is an integer, the SNR is judged:
SNR is greater than threshold TH 2 The CFO no fraction is represented, where the CFO value cfo_int '=round (cfo_int), cfo_frac' =0, round is a rounding function;
SNR is less than threshold TH 2 Then it indicates that there is a CFO fraction, at which time the CFO value cfo_int' =round (cfo_int);
further, when the CFO fraction exists, it is necessary to determine whether the polarity is positive or negative: the result of demodulation in step S107b of the up-chirp signal in the preamble is do p_real Because there is a fractional part, the correct result may be p 1 Or p 2 ；
The ideal demodulation result should be do p_ideal ＝round(CFO_Int)；
Will do p_real Comparing with ideal demodulation result, taking p 1 And p 2 Is closest to do p_ideal One number of (2) is the result of correct demodulation of the up-chirp signal in the preamble, denoted p 0 The method comprises the steps of carrying out a first treatment on the surface of the If p is 0 Is less than p 1 The polarity of the CFO decimal is positive, noted as: CF (compact flash)O_frac '=1, if the value of p0 is greater than p1', the polarity representing the CFO fraction is negative, noted as: cfo_frac' = -1.
2) When the value of cfo_int is a fraction, the SNR' is judged:
SNR' is greater than threshold TH 2 Then it indicates that CFO has no fractional part, cfo_frac '=0, and the CFO value at this time cfo_int' =round (cfo_int+0.5);
SNR' is less than threshold TH 2 Then it indicates that there is a CFO decimal part, and the CFO real value cfo_int' =round (cfo_int+0.5) at this time;
when CFO decimal exists, it is necessary to determine the polarity: the demodulation result in step S107d is do p_real Because of the decimal presence, the correct result may be p 1 ' or p 2 ’；
The ideal demodulation result is do p_ideal ＝round(CFO_Int+0.5)
Will do p_real Comparing with ideal demodulation result, taking p' 1 Or p' 2 Closest do p_ideal One number of (2) is the result of correct demodulation of the up-chirp signal in the preamble, denoted p 0 The method comprises the steps of carrying out a first treatment on the surface of the If p is 0 Is less than p 1 ' the polarity of the CFO decimal is positive, noted: cfo_frac' =1, if p 0 The value of (2) is greater than p 1 ' the polarity of the CFO decimal is negative, noted as: cfo_frac' = -1.
S108, demodulating the effective data, and carrying out carrier frequency offset compensation on the data to obtain demodulated data;
carrying out correlation calculation on the effective data x "(N, K) to obtain a correlation value COR" (N, K);
COR”(N,K)＝|FFT{cor”(n,k)}|
finding the largest two points in the amplitude and the label where the largest two points are located: [ m ] " 1 ,m” 2 ,p” 1 ,p” 2 ]=max2 (COR "(N, K)); wherein m is 1 "and m 2 "is the maximum two values of amplitude, p 1 "and p 2 "is the label corresponding to the largest two magnitudes.
S109, carrying out carrier frequency offset CFO compensation on the demodulated data, and adjusting the demodulated data according to a carrier frequency offset integer value CFO_int and a carrier frequency offset decimal value CFO_Frac to obtain final output demodulated data Do;
when cfo_frac is 0, do=p' 1 -CFO_Int，
When cfo_frac is not 0:
1) Cfo_frac' =1: do=min (p' 1 ,p” 2 )-CFO_Int
2) Cfo_frac' = -1: do=max (p' 1 ,p” 2 )-CFO_Int
Example two
The present application provides a multi-system CSS signal demodulating apparatus 200, as shown in fig. 3, comprising:
an analog-to-digital conversion module 210, configured to perform analog-to-digital conversion on the multi-system CSS modulation signal to obtain a digital baseband signal;
a downsampling module 220, configured to perform downsampling processing on the digital baseband signal to obtain a downsampled signal;
further, the downsampling module 220 includes:
the first downsampling unit 220a is configured to perform preliminary downsampling on the digital baseband signal through a cascaded integrator-comb filter CIC, and filter out high-frequency noise, so as to obtain a preliminary downsampled signal that filters out the high-frequency noise;
the second downsampling unit 220b is configured to further downsample the preliminary downsampled signal after passing through the compensation filter Comp, compensate for the in-band attenuation of the cascaded integrator-comb filter CIC, and output a downsampled signal x (n, k).
The detecting module 230 is configured to detect whether data arrives by using a correlation method;
the detection module 230 includes:
a determining unit 230a for setting an energy detection threshold TH 1 ；
A calculating unit 230b calculating a correlation energy value of the current input data frame; calculating the correlated energy value p (n, k) of the downsampled signal:wherein k is the label of the input data frame, M is the length of a frame, n is the label of a sampling point in a frame, up_c (n) is a reference signal generated by a lookup Table (Loop Up Table) Chirp_LUT;
a comparison unit 230c for comparing the correlation energy value p (n, k) of the current input data frame with a threshold value TH 1 Comparing, when p (n, k)>TH 1 Indicating that data is coming.
The synchronization processing module 240 is configured to perform time domain synchronization on input data when the data arrives, and output a synchronized signal;
the synchronization processing module 240 includes:
a first synchronization unit 240a, configured to perform time domain coarse synchronization, and perform time domain shift on the received data according to the frame reference number and the sampling point reference number;
specifically, when the arrival of data is detected in S103, that is, the correlation energy value p (n, k) of the current input data frame is greater than the threshold TH 1 And (3) recording the frame mark k 'and the sampling point mark n', performing time domain shift on the received data, and moving k 'frames and n' sampling point periods to obtain the data after coarse synchronization.
A second synchronization unit 240b for performing time domain fine synchronization on the data after the coarse synchronization,
specifically, a position index [ -, fine_idx ] =max (p (n, k)) corresponding to the maximum value of the correlation energy value is found, and the data is subjected to time domain shift according to the index, namely, the data after coarse synchronization is shifted by (fine_idx-1) sampling point periods, wherein fine_idx is a sampling point label of fine synchronization, and fine synchronization is performed according to the label, so that a synchronized output signal x' (n, k) is obtained.
A searching module 250, configured to search the synchronized signal for a location where the frame separator SFD is located;
the searching module 250 is further configured to search the position of the frame separator SFD by using a correlation method, and calculate a correlation energy value p '(n, k) of the output x' (n, k) after the fine synchronization;
further, the method comprises the steps of,k is the label of an input data frame, M is the length of a frame, n is the label of a sampling point in a frame, dn_c (n) is a reference signal generated by a Chirp_LUT, x '(n, k) is output after time domain fine synchronization, and p' (n, k) is a correlation energy value;
the search module 250 is further configured to, in use,
searching a position index corresponding to the maximum value of the correlation energy value p' (n, k):
fine_idx ' ] =max (p (n, k) '), fine_idx ' being the position of the frame separation symbol.
A calculating module 260, configured to calculate a carrier frequency offset CFO;
the computing module 260 includes:
an integer calculation unit 260a, configured to determine, according to the output signal after time domain synchronization and the position where the frame separator SFD is located, an integer value cfo_int of the carrier frequency offset CFO;
specifically, according to the time domain synchronization and the position of the frame separator SFD, the integer value of the carrier frequency offset CFO can be obtained by calculation:
the decimal calculation unit 260b is configured to estimate a decimal value cfo_frac of the carrier frequency offset CFO.
The decimal computing unit 260b is specifically configured to:
the data transmitted by the transmitter comprises a Preamble sequence (Preamble), and symbols in the Preamble sequence are up_c (n);
calculating a correlation value cor (n, k) of a preamble sequence x' (n, k); the preamble sequence of the data x' (n, k) after the time domain fine synchronization is subjected to dot multiplication with a reference signal up_c (n) of the chirp_lut: cor (n, k) =x' (n, k) up_c (n);
obtaining a correlation value cor (n, k) of the preamble sequence; performing Fourier transform on the correlation value COR (N, K), and solving the amplitude COR (N, K) = |FFT { COR (N, K) } |, and finding out the largest three points in the amplitude and the label [ m ] where the three points are located 1 ,m 2 ,m 3 ,p 1 ,p 2 ,p 3 ]=max3 (COR (N, K)), where m 1 ～m 3 At maximum three values, p 1 ～p 3 The label corresponding to the largest three values;
calculating an approximate signal-to-noise ratio SNR of the preamble correlation value cor (n, k):
delaying the lead sequence of the data after the time domain fine synchronization by one sampling point, and calculating the approximate signal-to-noise ratio of the delayed lead sequence;
illustratively, the time-domain fine synchronized data is delayed by one sample point to be point multiplied with the reference signal: cor '(n, k) =x' (n+1, k) ×up_c (n) performs fourier transform and finds amplitude: COR '(N, K) = |fft { COR' (N, K) } | finds the largest three points in the magnitude and the label where they are located: [ m ]' 1 ,m' 2 ,m' 3 ,p' 1 ,p' 2 ,p' 3 ]=max3 (COR' (N, K)), and SNR:
obtaining the decimal value of the CFO according to the integer value, SNR and SNR' of the CFO;
in particular, the method comprises the steps of,
1) When the value of cfo_int is an integer, the SNR is judged:
SNR is greater than threshold TH 2 The CFO no fraction is represented, where the CFO value cfo_int '=round (cfo_int), cfo_frac' =0, round is a rounding function;
SNR is less than threshold TH 2 Then it indicates that there is a CFO fraction, at which time the CFO value cfo_int' =round (cfo_int);
further, when the CFO fraction exists, it is necessary to determine whether the polarity is positive or negative: the result of demodulation in step S107b of the up-chirp signal in the preamble is do p_real Because there is a fractional part, the correct result may be p 1 Or p 2 ；
The ideal demodulation result should be do p_ideal ＝round(CFO_Int); will do p_real And the ideal demodulation result do p_ideal Comparing, taking p 1 And p 2 Is closest to d p_ideal One number of (2) is the result of correct demodulation of the up-chirp signal in the preamble, denoted p 0 The method comprises the steps of carrying out a first treatment on the surface of the If p is 0 Is less than p 1 The polarity of the CFO decimal is positive, noted as: cfo_frac' =1, if p 0 The value of (2) is greater than p' 1 The polarity of the CFO decimal is negative, noted as: cfo_frac' = -1.
2) When the value of cfo_int is a fraction, the SNR' is judged:
SNR' is greater than threshold TH 2 Then it indicates that CFO has no fractional part, cfo_frac '=0, and the CFO value at this time cfo_int' =round (cfo_int+0.5);
SNR' is less than threshold TH 2 Then it indicates that there is a CFO decimal part, and the CFO real value cfo_int' =round (cfo_int+0.5) at this time;
when CFO decimal exists, it is necessary to determine the polarity: the demodulation result in step S107d is do p_real Because of the decimal presence, the correct result may be p 1 ' or p 2 ’；
The ideal demodulation result is do p_ideal =round (cfo_int+0.5), will d p_real And the ideal demodulation result do p_ideal Comparing, taking p' 1 Or p' 2 Closest do p_ideal One number of (2) is the result of correct demodulation of the up-chirp signal in the preamble, denoted p 0 The method comprises the steps of carrying out a first treatment on the surface of the If p is 0 Is less than p 1 ' the polarity of the CFO decimal is positive, noted: cfo_frac' =1, if p 0 The value of (2) is greater than p 1 ' the polarity of the CFO decimal is negative, noted as: cfo_frac' = -1.
The adjustment module 270 is configured to perform carrier frequency offset CFO compensation on the demodulated data, and adjust the demodulated data according to the carrier frequency offset integer value cfo_int and the carrier frequency offset decimal value cfo_frac.
The adjusting module is used for demodulating the effective data, and carrying out carrier frequency offset compensation on the data to obtain demodulated data;
carrying out correlation calculation on the effective data x "(N, K) to obtain a correlation value COR" (N, K);
COR”(N,K)＝|FFT{cor”(n,k)}|
finding the largest two points in the amplitude and the label where the largest two points are located: [ m ] " 1 ,m” 2 ,p” 1 ,p” 2 ]=max2 (COR "(N, K)); wherein m is 1 "and m 2 "is the maximum two values of amplitude, p 1 "and p 2 "is the label corresponding to the largest two magnitudes.
The adjusting module is used for carrying out carrier frequency offset CFO compensation on the demodulated data, and adjusting the demodulated data according to a carrier frequency offset integer value CFO_Int and a carrier frequency offset decimal value CFO_Frac to obtain final output demodulated data Do;
when cfo_frac is 0, do=p' 1 -CFO_Int，
When cfo_frac is not 0:
1) Cfo_frac' =1: do=min (p' 1 ,p” 2 )-CFO_Int
2) Cfo_frac' = -1: do=max (p' 1 ,p” 2 )-CFO_Int。
The application provides a method and a device for demodulating a multi-system CSS signal, which are characterized in that after cascade integral comb filtering CIC downsampling, a related method is used for synchronizing time domain and frequency domain, and an FFT method is used for demodulation, so that the method and the device have lower power consumption and area under the premise of high performance.
Those of skill in the art will appreciate that the various illustrative method steps and apparatus elements described herein in connection with the disclosed embodiments may 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 application.
The steps of a method described in connection with the above disclosed embodiments 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 an alternative embodiment, the processor and the storage medium may reside as discrete components in a subscriber station.
The embodiments disclosed may enable any person skilled in the art to make or use the application. 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 application. The above embodiments are only preferred embodiments of the present application, and are not intended to limit the present application, but any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present application should be included in the scope of the present application.

Claims (8)

1. A method for demodulating a multilevel CSS signal, comprising:
performing analog-to-digital conversion on the multi-system CSS modulation signal to obtain a digital baseband signal;
performing downsampling processing on the digital baseband signal to obtain a downsampled signal;
detecting data of the downsampled signal, detecting whether the data arrives, setting an energy detection threshold value, calculating a correlation energy value of a current input data frame, and indicating that the data arrives when the correlation energy value is larger than the threshold value;
when the data arrives, time domain synchronization is carried out on the input data, and a synchronized signal is output;
searching the position of the frame separator SFD in the synchronized signal;
judging and obtaining an integer value CFO_Int of the carrier frequency offset CFO according to the output signal after time domain synchronization and the position of the frame separator SFD;
estimating a decimal value CFO_Frac of the carrier frequency offset CFO;
demodulating the effective data to obtain demodulated data; carrying out carrier frequency offset CFO compensation on the demodulated data, adjusting the demodulated data according to the carrier frequency offset integer value CFO_Int and the carrier frequency offset decimal value CFO_Frac to obtain final demodulated data,
the down-sampling processing of the digital baseband signal includes:
the digital baseband signal is subjected to preliminary downsampling through a cascade integral comb filter, and high-frequency noise is filtered, so that a preliminary downsampled signal for filtering the high-frequency noise is obtained;
and the preliminary downsampling signal is subjected to further downsampling after passing through a compensation filter, and in-band attenuation of the cascade integral comb filter is compensated to output a downsampling signal.
2. The method of claim 1, wherein the time domain synchronization of the data comprises coarse synchronization and fine synchronization;
the time domain coarse synchronization performs time domain shift on the received data according to the frame marks and the sampling point marks;
and the time domain fine synchronization further synchronizes the data after coarse synchronization, searches for a position index corresponding to the maximum value of the correlation energy value, and performs time domain shift on the data according to the position index corresponding to the maximum value of the correlation energy value.
3. The method of claim 1, wherein searching for a location where a frame separator SFD is located comprises:
searching the position of the frame separator SFD by adopting a correlation method, and calculating the correlation energy value p '(n, k) of the output x' (n, k) after the fine synchronization;
the position index fine_idx ' corresponding to the maximum value of the correlation energy value p ' (n, k) is found, and fine_idx ' is the position of the frame separation symbol SFD.
4. A multi-system CSS signal demodulating apparatus, comprising:
the analog-to-digital conversion module is used for carrying out analog-to-digital conversion on the multi-system CSS modulation signal to obtain a digital baseband signal;
the downsampling module is used for performing downsampling processing on the digital baseband signal to obtain a downsampled signal;
a detection module for detecting whether the data arrives by adopting a correlation method,
the synchronous processing module is used for carrying out time domain synchronization on input data when the data arrives and outputting a synchronized signal;
the searching module is used for searching the position of the frame separator SFD in the synchronized signal;
the computing module is used for computing carrier frequency offset CFO;
the adjusting module is used for demodulating the effective data; carrying out carrier frequency offset CFO compensation on the demodulated data, and adjusting the demodulated data according to a carrier frequency offset integer value CFO_Int and a carrier frequency offset decimal value CFO_Frac, wherein the downsampling module comprises:
the first downsampling unit is used for performing preliminary downsampling on the digital baseband signal through a cascade integral comb filter and filtering high-frequency noise to obtain a preliminary downsampled signal for filtering the high-frequency noise;
and the second downsampling unit is used for further downsampling the preliminary downsampling signal after passing through the compensation filter, compensating in-band attenuation of the cascade integral comb filter and outputting the downsampling signal.
5. The multi-system CSS signal demodulation device as recited in claim 4 wherein,
the detection module comprises:
a determining unit for setting a threshold value of the energy detection,
a calculation unit calculating a correlation energy value of a current input data frame,
and the comparison unit is used for comparing the correlation energy value of the current input data frame with the threshold value of energy detection, and when the correlation energy value is larger than the threshold value, the data arrival is indicated.
6. The multi-system CSS signal demodulation device as recited in claim 4 wherein,
the synchronous processing module comprises:
the first synchronization unit is used for performing time domain coarse synchronization and performing time domain shift on the received data according to the frame marks and the sampling point marks;
and the second synchronization unit is used for performing time domain fine synchronization on the data after coarse synchronization, searching a position index corresponding to the maximum value of the correlation energy value, and performing time domain shift on the data according to the position index corresponding to the maximum value of the correlation energy value.
7. The multi-system CSS signal demodulation device as recited in claim 4 wherein,
the searching module is further used for searching the position of the frame separator SFD by adopting a correlation method and calculating the correlation energy value of the output after the fine synchronization;
and searching a position index corresponding to the maximum value of the correlation energy value, wherein the position index corresponding to the maximum value is the position of the frame separation symbol.
8. The multi-system CSS signal demodulation device as recited in claim 4 wherein,
the computing module comprises:
an integer calculation unit, configured to determine, according to the output signal after time domain synchronization and the position where the frame separator SFD is located, an integer value cfo_int of the carrier frequency offset CFO;
and the decimal computing unit is used for estimating a decimal value CFO_Frac of the carrier frequency offset CFO.
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