CN112666579B - OQPSK-based satellite bidirectional time comparison data signal demodulation method - Google Patents
OQPSK-based satellite bidirectional time comparison data signal demodulation method Download PDFInfo
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Abstract
The embodiment of the invention discloses a satellite bidirectional time alignment data signal demodulation method based on OQPSK, which comprises the following steps: s100, a carrier synchronization loop receives an OQPSK intermediate frequency data transmission signal and generates a local coherent carrier and a dynamic auxiliary signal; the local coherent carrier carries out digital down-conversion and matched filtering on the OQPSK intermediate frequency data transmission signal to output two baseband digital signals; s102, the bit synchronization loop receives the two baseband digital signals and generates a pulse signal and an integration time auxiliary signal, the pulse signal completes sampling judgment on the received signal at the optimal moment, and data information is demodulated. The invention can complete the accurate synchronization and information demodulation of the high data rate satellite bidirectional time comparison OQPSK data signal carrier and data bit phase. And further, the frequency band utilization efficiency is improved, real-time interaction of a large amount of data information is completed, and real-time high-precision time transmission among multiple stations is realized.
Description
Technical Field
The invention relates to the technical field of satellite bidirectional time-frequency transmission. And more particularly, to an OQPSK based satellite two-way time alignment data signal demodulation method.
Background
High-precision time synchronization is the basis of time-frequency quantity transmission and tracing. Along with the popularization of the rapid UTC by the International metering office (BIPM), each timekeeping laboratory also puts forward higher requirements on the real-time performance of remote comparison results. The satellite bidirectional time comparison technology is a high-precision time transmission mode which is widely applied. The two ground stations transmit modulation time signals to the satellite at the same time, the two stations respectively receive signals from the opposite station after the signals are forwarded by the satellite, and the two ground stations subtract the received signal data after the received signal data are exchanged, so that the high-precision time clock difference between the two stations is obtained.
At present, a pseudo code spread spectrum signal is mostly selected as a satellite bidirectional time comparison signal in the satellite bidirectional time transmission technology, and a BPSK-DS modulation system is adopted.
Disclosure of Invention
The invention aims to provide a satellite bidirectional time alignment data signal demodulation method based on OQPSK. To solve at least one of the problems with the prior art.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the invention provides a satellite bidirectional time comparison signal demodulation method based on OQPSK, which comprises the following steps:
s100, a carrier synchronization loop receives an OQPSK intermediate frequency data transmission signal and generates a local coherent carrier and a dynamic auxiliary signal; the local coherent carrier carries out digital down-conversion and matched filtering on the OQPSK intermediate frequency data transmission signal to output two baseband digital signals;
s102, the bit synchronization loop receives the two baseband digital signals and generates a pulse signal and an integration time auxiliary signal, the pulse signal completes sampling judgment on the received signal at the optimal moment, and data information is demodulated.
In a specific embodiment, the method further comprises:
the carrier synchronization loop receives the integration time auxiliary signal output by the bit synchronization loop to prevent the carrier synchronization loop from jumping data bits in the coherent integration time.
In a specific embodiment, the method further comprises:
and the bit synchronization loop receives the dynamic auxiliary signal output by the carrier synchronization loop, completes the accurate tracking of the data bit phase of the OQPSK baseband data signal under the assistance of frequency, and demodulates real-time comparison data information.
In a specific embodiment, the method adopts an OQPSK carrier synchronization loop algorithm based on MAP criterion to realize carrier synchronization;
the method adopts a bit synchronization loop algorithm based on a Gardner algorithm to realize bit synchronization.
In one embodiment of the present invention, in one embodiment,
the OQPSK intermediate frequency data transmission signal received by the carrier synchronization loop is expressed as:
in the formula (1), T s Representing clock sampling period, f c Represents the carrier frequency of the received signal, θ represents the initial phase of the carrier, m I (n)、m Q (n) is an OQPSK baseband signal, expressed as:
in the formula (2), a i 、b i The value of +1, -1 represents two paths of orthogonal data information, T s Representing the clock sampling period, T representing the data period, g (·) representing the baseband symbol waveform function.
In a specific embodiment, the S100 includes
S1000, stripping the carrier wave of the input OQPSK intermediate frequency data transmission signal through quadrature down-conversion processing;
s1002, transmitting a baseband signal obtained after down-conversion to a MAP phase discriminator for phase discrimination to obtain a phase error discrimination signal;
s1004, outputting the phase error identification signal to a loop filter, and processing the received phase error identification signal to filter noise and high-frequency components by the loop filter to obtain a phase-locked loop frequency word;
s1006, the phase-locked loop frequency word controls the phase-locked loop NCO to generate two paths of orthogonal local coherent carriers, carrier stripping of the OQPSK intermediate frequency data transmission signals is completed, and the OQPSK baseband data transmission signals are output.
In a specific embodiment, the step S1002 includes:
setting the coherent integration time as a data bit period for eliminating the influence of data bit jump on carrier phase discrimination, receiving an integration time auxiliary signal input by a bit synchronous loop at the same time to avoid the occurrence of data bit jump in the coherent integration time of a phase-locked loop, adding the results obtained by multiplying the coherent accumulation of K inputs through a multiplier and an accumulator by a signal output by a coherent accumulation module, averaging to obtain a discrimination result, carrying out incoherent accumulation on the discrimination result, and finally obtaining a phase error discrimination signal.
In a specific embodiment, the output result of the coherent accumulation is shown in formula (3):
in the formula (3), the amino acid sequence of the compound,for receiving the phase difference of the OQPSK signal carrier and the local carrier, N represents the number of data accumulated in the coherent accumulation time, k=0, 1,.. c (n)，m s (n) is a baseband signal outputted after down-conversion;
the phase error discrimination signal is shown in formula (4):
in a specific embodiment, the update period of the carrier synchronization loop is T renew ＝KT。
The beneficial effects of the invention are as follows:
the invention provides a satellite bidirectional time comparison data signal demodulation method based on OQPSK. The method can finish the accurate synchronization and information demodulation of the high data rate satellite bidirectional time comparison OQPSK data signal carrier and data bit phase. And further, the frequency band utilization efficiency is improved, real-time interaction of a large amount of data information is completed, and real-time high-precision time transmission among multiple stations is realized.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 shows a schematic block diagram of high data rate satellite bi-directional time alignment OQPSK data signal demodulation according to one embodiment of the invention.
Fig. 2 shows a block diagram of a phase-locked loop module for high data rate satellite bi-directional time alignment OQPSK data signal demodulation, according to one embodiment of the invention.
Fig. 3 shows a schematic block diagram of a MAP-based phase detector in a high data rate satellite two-way time alignment OQPSK data signal demodulation phase-locked loop, according to one embodiment of the invention.
Fig. 4 shows a flow chart of a method for demodulating a high data rate satellite bi-directional time alignment OQPSK data signal according to an embodiment of the invention.
Detailed Description
In order to make the technical scheme and advantages of the present invention more apparent, embodiments of the present invention will be described in further detail with reference to the accompanying drawings. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and that this invention is not limited to the details given herein.
The invention provides a satellite bidirectional time comparison data signal demodulation method based on OQPSK, which is shown in figure 4, according to the high data rate satellite bidirectional time comparison OQPSK data signal demodulation schematic block diagram shown in figure 1, and comprises the following steps:
s100, a carrier synchronization loop receives an OQPSK intermediate frequency data transmission signal and generates a local coherent carrier and a dynamic auxiliary signal; the local coherent carrier carries out digital down-conversion and matched filtering on the OQPSK intermediate frequency data transmission signal to output two baseband digital signals;
s102, the bit synchronization loop receives the two baseband digital signals and generates a pulse signal and an integration time auxiliary signal, the pulse signal completes sampling judgment on the received signal at the optimal moment, and data information is demodulated. The optimal time refers to the time when the signal to noise ratio of the received signal is maximum.
In a specific embodiment, the method further comprises:
the carrier synchronization loop receives the integration time auxiliary signal output by the bit synchronization loop to prevent the carrier synchronization loop from jumping data bits in the coherent integration time.
In a specific embodiment, the method further comprises:
and the bit synchronization loop receives the dynamic auxiliary signal output by the carrier synchronization loop, completes the accurate tracking of the data bit phase of the OQPSK baseband data signal under the assistance of frequency, and demodulates real-time comparison data information. The carrier synchronization loop provides Doppler frequency for the bit synchronization loop to assist bit timing, reduces dynamic stress required to bear, further reduces noise quantity of the bit synchronization loop and improves tracking precision of code phase. The carrier synchronization loop and the bit synchronization loop mutually assist and mutually support, and synchronization and demodulation of signals are completed together.
In a specific embodiment, the method adopts an OQPSK carrier synchronization loop algorithm based on MAP criterion to realize carrier synchronization;
the method adopts a bit synchronization loop algorithm based on a Gardner algorithm to realize bit synchronization.
In one embodiment of the present invention, in one embodiment,
the OQPSK intermediate frequency data transmission signal received by the carrier synchronization loop is expressed as:
in the formula (1), T s Representing clock sampling period, f c Represents the carrier frequency of the received signal, θ represents the initial phase of the carrier, m I (n)、m Q (n) is an OQPSK baseband signal, expressed as:
in the formula (2), a i 、b i The value of +1, -1 represents two paths of orthogonal data information, T s Representing the clock sampling period, T representing the data period, g (·) representing the baseband symbol waveform function.
In a specific embodiment, in the process of phase tracking on the carrier of the OQPSK data transmission, a phase-locked loop is adopted, and a schematic block diagram thereof is shown in fig. 2. In a specific embodiment, the S100 includes:
s1000, stripping the carrier wave of the input OQPSK intermediate frequency data transmission signal through quadrature down-conversion processing;
s1002, transmitting a baseband signal obtained after down-conversion to a MAP phase discriminator for phase discrimination to obtain a phase error discrimination signal;
s1004, outputting the phase error identification signal to a loop filter, and processing the received phase error identification signal to filter noise and high-frequency components by the loop filter to obtain a phase-locked loop frequency word; wherein the high frequency components are mainly due to mixing and are related to a specific carrier frequency.
S1006, the phase-locked loop frequency word controls the phase-locked loop NCO to generate two paths of orthogonal local coherent carriers, carrier stripping of the OQPSK intermediate frequency data transmission signals is completed, and the OQPSK baseband data transmission signals are output.
Digitally controlled oscillators (NCO, numerically controlled oscillator).
In a specific embodiment, the step S1002 includes:
setting the coherent integration time as a data bit period for eliminating the influence of data bit jump on carrier phase discrimination, receiving an integration time auxiliary signal input by a bit synchronous loop at the same time to avoid the occurrence of data bit jump in the coherent integration time of a phase-locked loop, adding the results obtained by multiplying the coherent accumulation of K inputs through a multiplier and an accumulator by a signal output by a coherent accumulation module, averaging to obtain a discrimination result, carrying out incoherent accumulation on the discrimination result, and finally obtaining a phase error discrimination signal.
Phase discrimination selection for carriers is based on maximumThe phase discrimination method of the posterior probability (MAP) criterion has high discrimination precision and simple realization, and the schematic block diagram is shown in figure 3. The phase-locked loop firstly down-converts the baseband signal m output after down-conversion c (n)，m s (n) performing coherent accumulation to improve the signal-to-noise ratio of the signal. In a specific embodiment, the output result of the coherent accumulation is shown in formula (3):
in the formula (3), the amino acid sequence of the compound,for receiving the phase difference of the OQPSK signal carrier and the local carrier, N represents the number of data accumulated in the coherent accumulation time, k=0, 1.
The phase error discrimination signal is shown in formula (4):
in a specific embodiment, the phase error discrimination signal is obtained by averaging the summation of the K coherent integration products, and therefore, the update period of the carrier synchronization loop is T renew =kt. T denotes a data period.
The invention provides a satellite bidirectional time comparison data signal demodulation method based on OQPSK. The method can finish the accurate synchronization and information demodulation of the high data rate satellite bidirectional time comparison OQPSK data signal carrier and data bit phase. And further, the frequency band utilization efficiency is improved, real-time interaction of a large amount of data information is completed, and real-time high-precision time transmission among multiple stations is realized.
The invention uses high data rate OQPSK data signal to carry out bidirectional time transfer, and obtains data phase delay information by demodulating the data signal at the receiving end. The demodulation performance of the high data rate OQPSK data transmission signal directly determines the time transfer accuracy, and affects the data transmission quality of the communication system to a great extent. The existing satellite bidirectional time comparison signal demodulation algorithm is improved, and a phase-locked loop and bit loop combined mode is adopted, so that the high-data-rate satellite bidirectional time comparison OQPSK data transmission signal can be demodulated, and the high-data-rate multi-station satellite bidirectional real-time comparison is realized.
It should be understood that the foregoing examples of the present invention are provided merely for clearly illustrating the present invention and are not intended to limit the embodiments of the present invention, and that various other changes and modifications may be made therein by one skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.
Claims (6)
1. A method for demodulating satellite bidirectional time alignment data signals based on OQPSK, comprising:
s100, a carrier synchronization loop receives an OQPSK intermediate frequency data transmission signal and generates a local coherent carrier and a dynamic auxiliary signal; the local coherent carrier carries out digital down-conversion and matched filtering on the OQPSK intermediate frequency data transmission signal to output two baseband digital signals;
s102, a bit synchronization loop receives the two baseband digital signals and generates a pulse signal and an integration time auxiliary signal, wherein the pulse signal completes sampling judgment on a received signal at the optimal moment, and data information is demodulated;
the method further comprises the steps of:
the carrier synchronization loop receives an integration time auxiliary signal output by the bit synchronization loop to prevent the carrier synchronization loop from jumping data bits in the coherent integration time;
the method further comprises the steps of:
the bit synchronization loop receives the dynamic auxiliary signal output by the carrier synchronization loop, completes the accurate tracking of the data bit phase of the OQPSK baseband data signal under the assistance of frequency, and demodulates real-time comparison data information;
the S100 comprises
S1000, stripping the carrier wave of the input OQPSK intermediate frequency data transmission signal through quadrature down-conversion processing;
s1002, transmitting a baseband signal obtained after down-conversion to a MAP phase discriminator for phase discrimination to obtain a phase error discrimination signal;
s1004, outputting the phase error identification signal to a loop filter, and processing the received phase error identification signal to filter noise and high-frequency components by the loop filter to obtain a phase-locked loop frequency word;
s1006, the phase-locked loop frequency word controls the phase-locked loop NCO to generate two paths of orthogonal local coherent carriers, carrier stripping of the OQPSK intermediate frequency data transmission signals is completed, and the OQPSK baseband data transmission signals are output.
2. The demodulation method as claimed in claim 1, wherein,
the method adopts an OQPSK carrier synchronization loop algorithm based on MAP criterion to realize carrier synchronization;
the method adopts a bit synchronization loop algorithm based on a Gardner algorithm to realize bit synchronization.
3. The demodulation method as claimed in claim 1, wherein,
the OQPSK intermediate frequency data transmission signal received by the carrier synchronization loop is expressed as:
in the formula (1), T s Representing clock sampling period, f c Represents the carrier frequency of the received signal, θ represents the initial phase of the carrier, m I (n)、m Q (n) is an OQPSK baseband signal, expressed as:
in the formula (2), a i 、b i The value of +1, -1 represents two paths of orthogonal data information, T s Representing the clock sampling period, T representing the data period, g (·) representing the baseband symbol waveform function.
4. The demodulation method according to claim 1, wherein S1002 comprises:
setting the coherent integration time as a data bit period for eliminating the influence of data bit jump on carrier phase discrimination, receiving an integration time auxiliary signal input by a bit synchronous loop at the same time to avoid the occurrence of data bit jump in the coherent integration time of a phase-locked loop, adding the results obtained by multiplying the coherent accumulation of K inputs through a multiplier and an accumulator by a signal output by a coherent accumulation module, averaging to obtain a discrimination result, carrying out incoherent accumulation on the discrimination result, and finally obtaining a phase error discrimination signal.
5. The demodulation method as claimed in claim 4, wherein,
the output result of the coherent accumulation is shown in formula (3):
in the formula (3), the amino acid sequence of the compound,for receiving the phase difference of the OQPSK signal carrier and the local carrier, N represents the number of data accumulated in the coherent accumulation time, k=0, 1,.. c (n)，m s (n) is a baseband signal outputted after down-conversion;
the phase error discrimination signal is shown in formula (4):
6. the demodulation method as claimed in claim 5, wherein,
the update period of the carrier synchronization loop is T renew ＝KT。
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| CN110927752A (en) * | 2019-12-13 | 2020-03-27 | 北京无线电计量测试研究所 | High-rate satellite bidirectional time comparison signal demodulation method and system |
| CN110932720A (en) * | 2019-12-13 | 2020-03-27 | 北京无线电计量测试研究所 | Frequency discrimination method and system for satellite two-way time comparison signal |
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