CN108712190B - Multi-carrier tracking method and tracking device - Google Patents
Multi-carrier tracking method and tracking device Download PDFInfo
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- CN108712190B CN108712190B CN201810377837.6A CN201810377837A CN108712190B CN 108712190 B CN108712190 B CN 108712190B CN 201810377837 A CN201810377837 A CN 201810377837A CN 108712190 B CN108712190 B CN 108712190B
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- H04B1/707—Spread spectrum techniques using direct sequence modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
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Abstract
The present invention relates to the field of multi-carrier communication technologies, and in particular, to a multi-carrier tracking method and a tracking apparatus. The method comprises the following steps: receiving a direct spread signal sent by a transmitting end, demodulating the direct spread signal, and converting the frequency of the direct spread signal to zero frequency to obtain a zero frequency direct spread signal; extracting intermediate frequency points in the direct sequence spread spectrum signals as intermediate frequency control words; obtaining the residual frequency offset of the direct sequence spread spectrum signal according to the zero-frequency direct sequence spread spectrum signal, and using the residual frequency offset as a residual frequency offset control word; obtaining carrier control words according to the intermediate frequency control words and the residual frequency offset control words; the carrier control word is used for adjusting the carrier loop to eliminate the error and synchronize the adjusted direct-sequence spread-spectrum signal with the carrier of the direct-sequence spread-spectrum signal sent by the transmitting end; and outputting the direct-sequence spread spectrum signal synchronized with the transmitting terminal. The invention greatly simplifies the complexity of loop filtering processing, can stably complete frequency offset measurement, and has good anti-multipath and anti-noise functions.
Description
Technical Field
The present invention relates to the field of multi-carrier communication technologies, and in particular, to a multi-carrier tracking method and a tracking apparatus.
Background
A phase-locked loop is a frequency and phase synchronous control system whose performance is closely linked to the function of the synchronous system. Its operation can be illustrated by the schematic block diagram of the phase locked loop shown in fig. 1, in which fig. 1 the loop input signal is the signal vi(t)＝Visin[w0t+θ(t)]And additive noise n (t). It is connected to the output of a Voltage Controlled Oscillator (VCO)
Are applied together to a multiplier, here a Phase Detector (PD), the phase detection action of which produces an error voltage vd(t) the magnitude and waveform of the voltage varies depending on vi(t) and v0(t) the difference in frequency and phase between (t) and additive noise n (t). Error signal vd(t) after processing by the Loop Filter (LF), the frequency and phase of the VCO output signal can be changed to track the frequency and phase of the upper loop input signal. At the VCO output signal v0In the expression of (t), in the expression,
a tracking estimate representing the frequency and phase of the input signal. Thus in the absence of noise, when
When the value is in accordance with θ (t), complete synchronization can be obtained.
With the development of digital circuit technology, especially the wide application of large scale integrated circuits and microprocessors, all the components of the phase-locked loop are implemented by digital circuits, which are called digital phase-locked loops (DPLLs). All-digital phase-locked loops generally fall into four categories:
(1) a trigger-type digital phase-locked loop (FF-DPLL) features that a bistable trigger is used as digital phase detector, which is triggered by the positive zero crossing point of input signal and local controlled clock signal to generate a set pulse and a reset pulse whose interval between pulses reflects the phase error.
(2) A nyquist rate digital phase locked loop (NR-DPLL) samples the input signal at the nyquist rate (fixed rate pulses) before entering a digital phase detector, and digitally multiplies it with a locally controlled clock to produce a digital phase error.
(3) A zero crossing detection digital phase locked loop (CZ-DPLL) in which a loop samples the zero crossing point of an input signal with a local controlled clock pulse, and if the loop cannot sample at the zero crossing point exactly, the magnitude of the actual sample value reflects a phase error and can be used to adjust the phase of the local clock signal.
(4) A loop phase detector compares the phase of an input signal with the phase of a local clock signal cycle by cycle, and outputs a corresponding leading or lagging pulse in response to the leading or lagging phase for adjusting the local clock phase accordingly.
A Costas carrier tracking loop is typically used in a direct-spread receiver because the data-modulated signal remains after the receiver has stripped the carrier and code signals from the received spread-spectrum signal. The Costas loop is insensitive to 180 degree phase flip of the I and Q signals if the pre-detection integration time of the I and Q signals does not span the bit transitions of the data. The particular nature of the Costas loop is the Costas discriminator and phase adjustment capability relative to the receiver's natural clock phase in the receiver pre-detection integration zone. In order to prevent integration from crossing the transition boundaries of the data, a phase adjustment feature of the integration and accumulation function is required.
The output Phase error and characteristics of the Costas Phase Locked Loop discriminator are substantially similar to those of a pure PLL (Phase Locked Loop), and the first 3 discriminators are identical to those used in the pure PLL. The fourth discriminator, the pure phase locked loop, uses four quadrant arctangent, while the Cosats loop discriminator uses two quadrant arctangent. The four-quadrant ATAN functional phase-locked loop discriminator remains linear over the entire ± 180 ° input error range, while the two-quadrant Cosats discriminator remains linear over half the input error range (± 90 °).
The GPS system adopts a spread spectrum communication system, uses two carrier frequencies of L wave band as carrier waves (two carrier waves L1 and L2 are 1575.42MHz and 1227.6MHz respectively), and carries out spread spectrum modulation on pseudo-random codes (C/A codes and P codes) and navigation messages. Carrier synchronization is a key technology in spread spectrum communication, and is easy to implement in low dynamics, while in high dynamics environment, because of carrier frequency offset and C/a code offset caused by satellite motion, the carrier extraction after code capture is greatly affected by multipath effect and doppler frequency shift, so that the lock losing phenomenon may occur, and it is difficult to accurately extract the carrier. Therefore, carrier recovery is a difficult point in spread spectrum communication under high dynamic conditions.
Disclosure of Invention
In view of the above, the present invention is proposed to provide a multi-carrier tracking method and a tracking apparatus that overcome or at least partially solve the above problems.
In one aspect of the present invention, a multi-carrier tracking method is provided, which includes the following steps:
receiving a direct spread signal sent by a transmitting end, demodulating the direct spread signal, and converting the frequency of the direct spread signal to zero frequency to obtain a zero frequency direct spread signal;
extracting intermediate frequency points in the direct sequence spread spectrum signals as intermediate frequency control words;
obtaining the residual frequency offset of the direct sequence spread spectrum signal according to the zero-frequency direct sequence spread spectrum signal, and using the residual frequency offset as a residual frequency offset control word;
obtaining carrier control words according to the intermediate frequency control words and the residual frequency offset control words;
the carrier control word is used for adjusting the carrier loop to eliminate the error and synchronize the adjusted direct-sequence spread-spectrum signal with the carrier of the direct-sequence spread-spectrum signal sent by the transmitting end;
and outputting the direct-sequence spread spectrum signal synchronized with the transmitting terminal.
Further, the residual frequency offset is obtained according to the following formula: and removing the zero-frequency direct spread signal in the direct spread signal to obtain the residual frequency offset of the direct spread signal.
Further, the carrier control word is obtained according to the following formula: and adding the intermediate frequency control word and the residual frequency offset control word to obtain a carrier control word.
Further, the received direct sequence spread spectrum signal is a baseband signal output after mixing a preset intermediate frequency point and an original signal sent by a transmitting end.
Further, the calculation of the residual frequency offset is performed at a low signal rate of 31.3725 Ksps.
In a second aspect of the present invention, a multi-carrier tracking apparatus is provided, including:
the direct sequence spread spectrum signal receiving module is used for receiving the direct sequence spread spectrum signal sent by the transmitting terminal and respectively sending the direct sequence spread spectrum signal to the direct sequence spread spectrum signal demodulating module and the intermediate frequency point extracting module;
the direct spread spectrum signal demodulation module is used for demodulating the received direct spread spectrum signal, converting the frequency of the direct spread spectrum signal into zero frequency to obtain a zero frequency direct spread spectrum signal and sending the zero frequency direct spread spectrum signal to the residual frequency offset control word calculation module;
the intermediate frequency point extraction module is used for extracting intermediate frequency points in the received direct sequence spread spectrum signals, using the extracted intermediate frequency points as intermediate frequency control words and sending the intermediate frequency control words to the carrier control word calculation module;
the residual frequency offset control word calculation module is used for obtaining the residual frequency offset of the direct sequence spread spectrum signal according to the received zero frequency direct sequence spread spectrum signal, and sending the residual frequency offset of the direct sequence spread spectrum signal as a residual frequency offset control word to the carrier control word calculation module;
the carrier control word calculation module is used for obtaining carrier control words according to the received intermediate frequency control words and residual frequency offset control words and sending the carrier control words to the carrier loop adjustment module;
the carrier loop adjusting module is used for adjusting the carrier loop by utilizing the received carrier control words, eliminating errors, synchronizing the adjusted direct spread signal with the direct spread signal carrier sent by the transmitting end and sending the synchronized direct spread signal to the synchronous direct spread signal output module;
and the synchronous direct sequence spread spectrum signal output module is used for outputting the received synchronous direct sequence spread spectrum signal.
Further, the residual frequency offset control word calculation module calculates the residual frequency offset by using the following formula: and removing the zero-frequency direct spread signal in the direct spread signal to obtain the residual frequency offset of the direct spread signal.
Further, the carrier control word calculation module calculates the carrier control word by using the following formula: and adding the intermediate frequency control word and the residual frequency offset control word to obtain a carrier control word.
Further, the received direct sequence spread spectrum signal is a baseband signal output after mixing a preset intermediate frequency point and an original signal sent by a transmitting end.
Further, the calculation of the residual frequency offset is performed at a low signal rate of 31.3725 Ksps.
Compared with the prior art, the multi-carrier tracking method and the multi-carrier tracking device provided by the invention have the following progress: the carrier control word is obtained by utilizing the intermediate frequency control word and the residual frequency offset control word, and the carrier loop is adjusted by utilizing the obtained carrier control word, so that the complexity of loop filtering processing is greatly simplified, the frequency offset measurement can be stably completed, the loop is simple, and the anti-multipath and anti-noise functions are good.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a schematic block diagram of a phase locked loop in the prior art;
fig. 2 is a flowchart illustrating a multi-carrier tracking method according to an embodiment of the present invention;
fig. 3 is a block diagram illustrating device connections of a multi-carrier tracking apparatus according to an embodiment of the present invention;
fig. 4 is a flowchart of a multi-carrier tracking method according to an embodiment of the present invention;
fig. 5 is a carrier tracking diagram (frequency offset setting FOE-3.13 KHZ) for a multipath channel signal-to-noise ratio of-5 Db;
fig. 6 is a diagram of a parallel processing architecture for a multi-carrier loop (different parallel branches input different frequency offsets);
FIG. 7 is a diagram of frequency offset estimated under a pre-frequency offset 6.9KHZ branch with a frequency offset set at 9 KHZ;
fig. 8 is an amplitude contrast plot integrated at a frequency offset setting of 9KHZ at different frequency offset settings.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The embodiment of the invention provides a multi-carrier tracking method and a multi-carrier tracking device.
Fig. 2 schematically shows a step diagram of a multi-carrier tracking method in the present embodiment. Referring to fig. 2, the present embodiment provides a multi-carrier tracking method, including the following steps:
receiving a direct spread signal sent by a transmitting end, demodulating the direct spread signal, and converting the frequency of the direct spread signal to zero frequency to obtain a zero frequency direct spread signal;
extracting intermediate frequency points in the direct sequence spread spectrum signals as intermediate frequency control words;
obtaining the residual frequency offset of the direct sequence spread spectrum signal according to the zero-frequency direct sequence spread spectrum signal, and using the residual frequency offset as a residual frequency offset control word;
obtaining carrier control words according to the intermediate frequency control words and the residual frequency offset control words;
the carrier control word is used for adjusting the carrier loop to eliminate the error and synchronize the adjusted direct-sequence spread-spectrum signal with the carrier of the direct-sequence spread-spectrum signal sent by the transmitting end;
and outputting the direct-sequence spread spectrum signal synchronized with the transmitting terminal.
According to the multi-carrier tracking method, the carrier control words are obtained by the intermediate frequency control words and the residual frequency offset control words, and the carrier loop is adjusted by the obtained carrier control words, so that the complexity of loop filtering processing is greatly simplified, frequency offset measurement can be stably completed, the loop is simple, and the multi-carrier tracking method has good anti-multipath and anti-noise functions.
In this embodiment, the carrier loop is a costas carrier tracking loop. The costas carrier tracking loop is used as a carrier loop, so that the loop filtering processing is simplified and practical.
In this embodiment, the residual frequency offset is obtained according to the following formula: and removing the zero-frequency direct spread signal in the direct spread signal to obtain the residual frequency offset of the direct spread signal. The carrier control word is obtained according to the following formula: and adding the intermediate frequency control word and the residual frequency offset control word to obtain a carrier control word. The received direct sequence spread spectrum signal is a baseband signal which is output after the preset intermediate frequency point and an original signal sent by a transmitting terminal are mixed. In this embodiment, the calculation of the residual frequency offset is performed at a low signal rate of 31.3725 Ksps. In this embodiment, the identified frequency range of the carrier loop is-3.9 KHZ to 3.9 KHZ.
Fig. 3 schematically shows a device connection block diagram of a multi-carrier tracking apparatus in this embodiment. Referring to fig. 3, the present embodiment provides a multi-carrier tracking apparatus, including:
the direct sequence spread spectrum signal receiving module is used for receiving the direct sequence spread spectrum signal sent by the transmitting terminal and respectively sending the direct sequence spread spectrum signal to the direct sequence spread spectrum signal demodulating module and the intermediate frequency point extracting module;
the direct spread spectrum signal demodulation module is used for demodulating the received direct spread spectrum signal, converting the frequency of the direct spread spectrum signal into zero frequency to obtain a zero frequency direct spread spectrum signal and sending the zero frequency direct spread spectrum signal to the residual frequency offset control word calculation module;
the intermediate frequency point extraction module is used for extracting intermediate frequency points in the received direct sequence spread spectrum signals, using the extracted intermediate frequency points as intermediate frequency control words and sending the intermediate frequency control words to the carrier control word calculation module;
the residual frequency offset control word calculation module is used for obtaining the residual frequency offset of the direct sequence spread spectrum signal according to the received zero frequency direct sequence spread spectrum signal, and sending the residual frequency offset of the direct sequence spread spectrum signal as a residual frequency offset control word to the carrier control word calculation module;
the carrier control word calculation module is used for obtaining carrier control words according to the received intermediate frequency control words and residual frequency offset control words and sending the carrier control words to the carrier loop adjustment module;
the carrier loop adjusting module is used for adjusting the carrier loop by utilizing the received carrier control words, eliminating errors, synchronizing the adjusted direct spread signal with the direct spread signal carrier sent by the transmitting end and sending the synchronized direct spread signal to the synchronous direct spread signal output module;
and the synchronous direct sequence spread spectrum signal output module is used for outputting the received synchronous direct sequence spread spectrum signal.
The direct sequence spread spectrum signal receiving module is respectively connected with the direct sequence spread spectrum signal demodulating module and the intermediate frequency point extracting module, the direct sequence spread spectrum signal demodulating module is connected with the residual frequency deviation control word calculating module, the carrier wave control word calculating module is respectively connected with the intermediate frequency point extracting module and the residual frequency deviation control word calculating module, and the carrier wave loop adjusting module is respectively connected with the carrier wave control word calculating module and the synchronous direct sequence spread spectrum signal outputting module.
According to the multi-carrier tracking device, the carrier control words are obtained by the intermediate frequency control words and the residual frequency offset control words, and the carrier loop is adjusted by the obtained carrier control words, so that the complexity of loop filtering processing is greatly simplified, frequency offset measurement can be stably completed, the loop is simple, and the multi-carrier tracking device has good anti-multipath and anti-noise functions.
In this embodiment, the carrier loop is a costas carrier tracking loop. The costas carrier tracking loop is used as a carrier loop, so that the loop filtering processing is simplified and practical.
In this embodiment, the residual frequency offset control word calculation module calculates the residual frequency offset by using the following formula: and removing the zero-frequency direct spread signal in the direct spread signal to obtain the residual frequency offset of the direct spread signal. The carrier control word calculation module calculates the carrier control word by using the following formula: and adding the intermediate frequency control word and the residual frequency offset control word to obtain a carrier control word. The received direct sequence spread spectrum signal is a baseband signal which is output after the preset intermediate frequency point and an original signal sent by a transmitting terminal are mixed. In this embodiment, the calculation of the residual frequency offset is performed at a low signal rate of 31.3725 Ksps. In this embodiment, the identified frequency range of the carrier loop is-3.9 KHZ to 3.9 KHZ.
If the COSTAS phase-locked receiver is adopted, the narrow-band tracking characteristic of a loop and the spread spectrum gain of the spread spectrum code integral are utilized, the output signal-to-noise ratio can be obviously improved, and a satisfactory receiving result is obtained.
The COSTAS phase demodulation receiver is actually a narrow-band tracking loop, an intermediate frequency point control digital and digital low-pass filter is added compared with a common phase-locked loop, and the loop filtering processing is simplified and practical.
The carrier loop filtering process comprises the following steps: if the intermediate frequency point is known in advance, it is mixed with the received signal, then the baseband signal is output, the baseband signal is input to the phase discriminator to carry out phase tracking after integral amplification, when the external input frequency changes, the intermediate frequency control word also changes, so that the intermediate frequency signal is down converted to near zero frequency. Therefore, the digital low-pass passband can be made narrower, so that the input end of the phase discriminator has enough signal-to-noise ratio, and the sensitivity of the receiver is improved.
The maximum frequency offset that a typical carrier loop can tolerate is the fsymbol/2 symbol rate, which is the rate at which the signal is modulated before being spread. For example, one symbol requires 255 spreading codes to spread, and each spreading code is 8 samples, and one symbol corresponds to 2040 samples of SP _ POINT ═ SP _ LEN ═ IPOINT, and the chip rate fcode is set to 8Msps, and the sampling rate is fs _ adc ═ 64 Msps. The symbol rate is fsymbol 8Msps/255 31.3725 Ksps. The maximum frequency offset that can be tolerated at this time is + -fsymbol/2 ═ 15.7 KSPS.
Referring to fig. 6, the signal collected by the ADC (Analog-to-Digital Converter) may be a real signal or a complex signal. If the real signal is the real signal, performing quadrature demodulation to zero frequency; if the signal is a complex signal, complex demodulation is performed to change to zero frequency. Only the frequency offset remains. If the signal acquired by the ADC has an intermediate frequency point, for example, f _ dif, this frequency point is used as an intermediate frequency control word (dif _ fcw): dif _ fcw ═ fix (f _ dif ^ 2^ 32/fs); this intermediate frequency control word and the following calculated residual frequency offset (foe _ fcw) are combined to a carrier control word (carry _ fcw). The center frequency point of the signal after frequency shifting is basically near zero frequency, the maximum deviation is about + -32KHZ, and the signal rate (fs _ adc) is very small compared with 64MSPS, so the residual frequency offset hardly influences the low-pass filter. After the signal is low-pass filtered, the signal rate is still kept in a high-speed state, the high-speed signal is subjected to carrier loop tracking, and is multiplied and added with the current local codes refp _ i and refp _ q to obtain a low-speed symbol signal (sigsymb), and the symbol rate fsymbol is 8Msps/255 is 31.3725 Ksps. The calculation of the residual frequency offset is performed at this low speed. The residual frequency and phase differences are compensated by means of a Costas-PLL loop.
A Costas carrier tracking loop is typically used in a direct-spread receiver because the data-modulated signal remains after stripping of the carrier and code signals in the received spread-spectrum signal. The Costas loop is insensitive to 180 degree phase flip of the I and Q signals if the pre-detection integration time of the I and Q signals does not span the bit transitions of the data.
For BPSK/QPSK (Quadrature Phase Shift keying) modulated signals, the most commonly used carrier synchronization method is the Costas loop. In the design, a modified Costas loop is adopted, and the modified Costas loop has a sawtooth-type phase discrimination characteristic, so that the influence of the "hanging" phenomenon of the loop is reduced, and as shown in fig. 4, the phase detector consists of a Sign function (Sign (#)) and a multiplier. The phase discrimination characteristic equation is as follows: theta (n) ═ sign [ I (n)]×Q(n)＝sign[cos(θe)]sin(θe)
Wherein the sign function is:
let the phase error thetaeIs theta.
For QPSK, only the phase detector equation needs to be replaced, as shown in the following equation:
θ(n)＝Sign(I(n))●Q(n)-Sign(Q(n))●I(n)
the code ring is in a capture state, the carrier loop is adjusted only according to the intermediate frequency point control word, the code ring is in a tracking state initial state, the carrier loop is adjusted according to the large frequency deviation word length, the code ring is in a tracking state stable state, and the carrier loop is adjusted according to the small frequency deviation word length.
The carrier control word consists of two control words, an intermediate frequency point control word and a residual frequency offset control word. The intermediate frequency point is determined according to the central frequency point of the signal acquired by the ADC, and the residual frequency offset is determined by the result calculated by the carrier ring. The signal mixing may be quadrature demodulation down-conversion or complex down-conversion. The carrier control word is effectively the index of the COS/SIN table. The COS/SIN value is pre-stored, with a depth of 2^ N, and the word length of the COS/SIN index is N bits.
The input signal has modulation data bits, the carrier phase will generate 180-degree jump irregularly, PLL cannot be used for tracking at the moment, and a COSTAS phase discriminator is adopted, is insensitive to phase reversal, but has narrow linear range and large tracking noise. The invention adopts 2-level loop filtering, and multiplication coefficients are 1/2^ N, thereby avoiding multiplication operation, greatly simplifying the complexity of loop filtering processing, filtering noise by the loop filtering, stably finishing frequency deviation measurement, and having good multipath resistance and noise resistance although the loop is simple.
Two-stage filtering is adopted for loop filtering processing after the phase discriminator, and the processing of C1 and C2 both adopt truncation operation, so that the loop filtering delay is small, only 2 adders are needed for consuming resources, and the loop filtering processing is greatly simplified.
For the simplified loop filtering process, the performance is still stable, and through a multipath channel, the carrier loop can still be rapidly captured and stably tracked, as shown in fig. 5, the preset frequency offset FOE is 3.13KHZ, and the frequency offset error of the stable post-oscillation is controlled within + -50HZ, which can completely meet the system requirements. And the SNR set at this time is-5 Db, which indicates that the carrier loop has good multipath resistance and noise immunity.
The largest frequency range of the COSTAS phase discriminator is MaxDETF: (delta f)maxFsymbol/8, in which case fsymbol 8MHZ/255 31.37KHZ, so the identification frequency range is [ -3.9KHZ,3.9KHZ]It should be sufficient for a general system. However, in order to prevent the occurrence of large frequency offset, a parallel preset frequency offset design may be performed.
If for large frequency offsets, multiple parallel loops are required to operate simultaneously, e.g., 3 parallel loops are used. The set predicted frequency offset is FOE [ -2 Δ f [ ]max,0,2Δfmax]E.g., [ -6.97KHZ,0, 6.97KHZ]Setting the frequency error fre _ err to 9KHZ, the estimated range should be within when setting the frequency offset FOE (1) to 6.97KHZ, and the estimated error should be leefrre-fre-FOE (1) to 9KHZ-6.97HZ to 2.03KHZ, as illustrated in fig. 7 and 8. From a time statistic, it is certain that the power at the integral of the accurate frequency offset is estimated to be the maximum. In fig. 7, 1 symbol includes 2040 sample points.
For simplicity of explanation, the method embodiments are described as a series of acts or combinations, but those skilled in the art will appreciate that the embodiments are not limited by the order of acts described, as some steps may occur in other orders or concurrently with other steps in accordance with the embodiments of the invention. Further, those skilled in the art will appreciate that the embodiments described in the specification are presently preferred and that no particular act is required to implement the invention.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A multi-carrier tracking method, comprising the steps of:
receiving a direct spread signal sent by a transmitting end, demodulating the direct spread signal, and converting the frequency of the direct spread signal to zero frequency to obtain a zero frequency direct spread signal;
extracting intermediate frequency points in the direct sequence spread spectrum signals as intermediate frequency control words;
obtaining the residual frequency offset of the direct sequence spread spectrum signal according to the zero-frequency direct sequence spread spectrum signal, and using the residual frequency offset as a residual frequency offset control word;
obtaining carrier control words according to the intermediate frequency control words and the residual frequency offset control words;
the carrier control word is used for adjusting the carrier loop to eliminate the error and synchronize the adjusted direct-sequence spread-spectrum signal with the carrier of the direct-sequence spread-spectrum signal sent by the transmitting end;
and outputting the direct-sequence spread spectrum signal synchronized with the transmitting terminal.
2. The multi-carrier tracking method of claim 1, wherein the residual frequency offset is obtained according to the following formula: and removing the zero-frequency direct spread signal in the direct spread signal to obtain the residual frequency offset of the direct spread signal.
3. The multi-carrier tracking method of claim 2, wherein the carrier control word is derived according to the following formula: and adding the intermediate frequency control word and the residual frequency offset control word to obtain a carrier control word.
4. The multi-carrier tracking method according to claim 3, wherein the received direct sequence spread spectrum signal is a baseband signal output by mixing a preset intermediate frequency point with an original signal sent by the transmitting end.
5. The multi-carrier tracking method of claim 4, wherein the calculation of the residual frequency offset is performed at a low signal rate of 31.3725 Ksps.
6. A multi-carrier tracking apparatus for implementing the multi-carrier tracking method as claimed in claim 1, comprising:
the direct sequence spread spectrum signal receiving module is used for receiving the direct sequence spread spectrum signal sent by the transmitting terminal and respectively sending the direct sequence spread spectrum signal to the direct sequence spread spectrum signal demodulating module and the intermediate frequency point extracting module;
the direct spread spectrum signal demodulation module is used for demodulating the received direct spread spectrum signal, converting the frequency of the direct spread spectrum signal into zero frequency to obtain a zero frequency direct spread spectrum signal and sending the zero frequency direct spread spectrum signal to the residual frequency offset control word calculation module;
the intermediate frequency point extraction module is used for extracting intermediate frequency points in the received direct sequence spread spectrum signals, using the extracted intermediate frequency points as intermediate frequency control words and sending the intermediate frequency control words to the carrier control word calculation module;
the residual frequency offset control word calculation module is used for obtaining the residual frequency offset of the direct sequence spread spectrum signal according to the received zero frequency direct sequence spread spectrum signal, and sending the residual frequency offset of the direct sequence spread spectrum signal as a residual frequency offset control word to the carrier control word calculation module;
the carrier control word calculation module is used for obtaining carrier control words according to the received intermediate frequency control words and residual frequency offset control words and sending the carrier control words to the carrier loop adjustment module;
the carrier loop adjusting module is used for adjusting the carrier loop by utilizing the received carrier control words, eliminating errors, synchronizing the adjusted direct spread signal with the direct spread signal carrier sent by the transmitting end and sending the synchronized direct spread signal to the synchronous direct spread signal output module;
and the synchronous direct sequence spread spectrum signal output module is used for outputting the received synchronous direct sequence spread spectrum signal.
7. The multi-carrier tracking apparatus as claimed in claim 6, wherein the residual frequency offset control word calculation module calculates the residual frequency offset by using the following formula: and removing the zero-frequency direct spread signal in the direct spread signal to obtain the residual frequency offset of the direct spread signal.
8. The multi-carrier tracking device of claim 7, wherein the carrier control word calculation module calculates the carrier control word using the following equation: and adding the intermediate frequency control word and the residual frequency offset control word to obtain a carrier control word.
9. The multi-carrier tracking apparatus according to claim 8, wherein the received direct sequence spread spectrum signal is a baseband signal output by mixing a preset if frequency point with an original signal sent by the transmitting end.
10. The multi-carrier tracking apparatus of claim 9, wherein the calculation of the residual frequency offset is performed at a low signal rate of 31.3725 Ksps.
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| WO2004077692A1 (en) * | 2003-02-25 | 2004-09-10 | Roke Manor Research Limited | Spread spectrum baseband signal processor with decimation filtering |
| CN102801671A (en) * | 2012-07-20 | 2012-11-28 | 西安空间无线电技术研究所 | Carrier tracking device capable of adaptively adjusting parameters |
| CN106411807A (en) * | 2016-08-31 | 2017-02-15 | 北京钧威科技有限公司 | High-speed railway vehicle-ground communication system-based modulation and demodulation method and system |
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| WO2004077692A1 (en) * | 2003-02-25 | 2004-09-10 | Roke Manor Research Limited | Spread spectrum baseband signal processor with decimation filtering |
| CN102801671A (en) * | 2012-07-20 | 2012-11-28 | 西安空间无线电技术研究所 | Carrier tracking device capable of adaptively adjusting parameters |
| CN106411807A (en) * | 2016-08-31 | 2017-02-15 | 北京钧威科技有限公司 | High-speed railway vehicle-ground communication system-based modulation and demodulation method and system |
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