CN113452406A - Signal demodulation method, device, equipment and medium with variable transmission rate - Google Patents
Signal demodulation method, device, equipment and medium with variable transmission rate Download PDFInfo
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- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04B1/69—Spread spectrum techniques
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Abstract
The invention provides a signal demodulation method, a device, equipment and a medium with variable transmission rate. The method comprises the following steps: capturing a spread spectrum signal transmitted by a user; dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; after the demodulation of the service section of the spread spectrum signal is finished, dividing the data section of the spread spectrum signal into a plurality of sub-data sections for sequential buffering according to the data transmission rate of the data section of the spread spectrum signal, and demodulating the data of the sub-data sections which are buffered. The invention can carry out real-time iterative demodulation on the spread spectrum signals with inconstant data transmission rate and has lower complexity.
Description
Technical Field
The present invention relates to the field of satellite communications technologies, and in particular, to a method, an apparatus, a device, and a medium for demodulating a signal with a variable transmission rate.
Background
In recent years, with the rapid development of aerospace technologies, satellite communication is becoming an important direction for the development of the communication field. The low-earth-orbit satellite has a large global coverage area, can realize global dead-angle-free full coverage, has a short transmission distance and is an important component of satellite communication. However, low-orbit satellites have a fast moving speed, are influenced by a strong doppler phenomenon when communicating with the ground, and are influenced by factors such as distance, terrain, weather, and the like, so that the low-orbit satellites have a low signal-to-noise ratio when communicating. Due to the limited transmission power of satellites, communication systems with lower bit error rates using lower signal-to-noise ratios are necessary. Meanwhile, the system must have the function of completing real-time and accurate demodulation of data under an extremely low signal-to-noise ratio.
For a conventional low-earth orbit satellite demodulation module, coherent demodulation or noncoherent demodulation is often used. For a binary Phase Shift keying (bpsk) modulation system with frequency offset, demodulation is performed by using a non-coherent demodulation mode, although the implementation complexity is low, the frequency offset and the Phase search accuracy are poor; for full coherent demodulation, due to the fact that the transmission signal rate is constantly changed and the low-earth orbit satellite moves more violently around the earth, frequency deviation change rate is often generated while frequency deviation is generated, and accurate frequency deviation and phase estimation cannot be achieved.
Disclosure of Invention
The invention provides a signal demodulation method, a signal demodulation device, a signal demodulation equipment and a signal demodulation medium with variable transmission rate, which are used for solving the defect that the prior art cannot perform accurate search and compensation on frequency deviation according to the frequency deviation change rate and realizing accurate search and compensation on frequency deviation generated by Doppler phenomenon caused by low-orbit satellite motion.
The invention provides a signal demodulation method with variable transmission rate, which comprises the following steps:
capturing a spread spectrum signal sent by a user, and performing coarse compensation on frequency offset and phase of the spread spectrum signal according to a pilot frequency band of the spread spectrum signal;
dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; when the cached sub-service segment data is demodulated, searching frequency offset and phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments;
after the demodulation of the service segment of the spread spectrum signal is finished, dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for caching in sequence according to the transmission rate of the data segment data of the spread spectrum signal, and demodulating the cached sub-data segment data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated.
The invention provides a signal demodulation method with variable transmission rate, which comprises the following steps:
when demodulating the cached sub-service segment data, searching the frequency offset and the phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments, comprising:
based on a service segment local template, carrying out square de-modulation on the sub-service segment data, and determining the frequency offset and phase estimation values of the sub-service segment data;
after determining the frequency offset and the phase estimation value of the first sub-service segment data, correcting the phase estimation value of the first sub-service segment data according to the frame header data and the local frame header data of the spread spectrum signal to obtain a corrected phase estimation value;
and compensating the first sub-service segment data according to the frequency offset estimation value of the first sub-service segment data and the corrected phase estimation value, calculating the phase of the last bit data of the first sub-service segment data according to the corrected phase estimation value, and using the phase as the reference phase of the next sub-service segment data, so that after the phase estimation value of the next sub-service segment data is determined, the phase estimation value of the next sub-service segment data is corrected according to the reference phase, and the phase continuity of the adjacent sub-service segment data is ensured.
The invention provides a signal demodulation method with variable transmission rate, which comprises the following steps:
when demodulating the cached sub-data segment data, searching the frequency offset and the phase of the sub-data segment data, and generating a reference phase of the next sub-data segment data for ensuring the phase continuity of the adjacent sub-data segments, including:
based on a data segment local template, carrying out square demodulation on the data of the sub data segment, and determining the frequency offset and the estimated value of the phase of the data of the sub data segment;
after determining the frequency offset and the phase estimation value of the first-segment sub-data segment data, correcting the phase estimation value of the first-segment sub-data segment data according to the frame header data and the local frame header data of the spread spectrum signal to obtain a corrected phase estimation value;
and compensating the first sub-data segment data according to the frequency offset estimation value of the first sub-data segment data and the corrected phase estimation value, calculating the phase of the last bit data of the first sub-data segment data according to the corrected phase estimation value, and using the phase as the reference phase of the next sub-data segment data, so that after the phase estimation value of the next sub-data segment data is determined, the phase estimation value of the next sub-data segment data is corrected according to the reference phase, and the phase continuity of the adjacent sub-data segment data is ensured.
The signal demodulation method with variable transmission rate provided by the invention also comprises the following steps:
and pre-compensating the spread spectrum signal according to the frequency offset estimation value of the first sub-data segment data, and selecting a data segment local template with higher frequency offset precision to perform square demodulation on the next sub-data segment data based on the pre-compensated spread spectrum signal, thereby determining the frequency offset and phase estimation values of the next sub-data segment data.
The invention provides a signal demodulation method with variable transmission rate, which comprises the following steps:
dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for sequentially caching according to the transmission rate of the data segment data of the spread spectrum signal, and the method comprises the following steps:
and dividing the data segment of the spread spectrum signal into sub-data segments with different lengths for sequentially caching according to the difference of the transmission rates of the data segment data.
The present invention also provides a signal demodulation apparatus with a variable transmission rate, comprising:
the first processing module is used for capturing a spread spectrum signal sent by a user and carrying out coarse compensation on frequency offset and phase of the spread spectrum signal according to a pilot frequency band of the spread spectrum signal;
the second processing module is used for dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching, and demodulating the cached sub-service segment data in sequence; when the cached sub-service segment data is demodulated, searching frequency offset and phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments;
the third processing module is used for dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for caching according to the transmission rate of the data segment data of the spread spectrum signal after the demodulation of the service segment of the spread spectrum signal is finished, and demodulating the cached sub-data segment data in sequence; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated.
According to the signal demodulation apparatus with a variable transmission rate provided by the present invention, the second processing module is specifically configured to:
based on a service segment local template, carrying out square de-modulation on the sub-service segment data, and determining the frequency offset and phase estimation values of the sub-service segment data;
after determining the frequency offset and the phase estimation value of the first sub-service segment data, correcting the phase estimation value of the first sub-service segment data according to the frame header data and the local frame header data of the spread spectrum signal to obtain a corrected phase estimation value;
and compensating the first sub-service segment data according to the frequency offset estimation value of the first sub-service segment data and the corrected phase estimation value, calculating the phase of the last bit data of the first sub-service segment data according to the corrected phase estimation value, and using the phase as the reference phase of the next sub-service segment data, so that after the phase estimation value of the next sub-service segment data is determined, the phase estimation value of the next sub-service segment data is corrected according to the reference phase, and the phase continuity of the adjacent sub-service segment data is ensured.
The present invention also provides an electronic device, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the signal demodulation method with variable transmission rate as described in any of the above when executing the program.
The present invention also provides a non-transitory computer readable storage medium having stored thereon a computer program which, when executed by a processor, performs the steps of the method for variable transmission rate signal demodulation as described in any of the above.
The invention also provides a computer program product comprising a computer program which, when executed by a processor, carries out the steps of the method for demodulating a signal with a variable transmission rate as described in any one of the above.
The signal demodulation method, the device, the equipment and the medium with variable transmission rate, provided by the invention, carry out coarse compensation on frequency deviation and phase of a spread spectrum signal by capturing the spread spectrum signal sent by a user and according to a pilot frequency band of the spread spectrum signal. Then dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; when the cached sub-service segment data is demodulated, frequency offset and phase search is carried out on the sub-service segment data, and a reference phase of the next sub-service segment data used for ensuring the phase continuity of the adjacent sub-service segments is generated. After the demodulation of the service section of the spread spectrum signal is finished, dividing the data section of the spread spectrum signal into a plurality of sub-data sections for sequential caching according to the transmission rate of the data section data of the spread spectrum signal, and demodulating the cached sub-data section data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated. Therefore, the method is suitable for variable-rate transmission of the same-section signal, and compared with constant-rate demodulation of the traditional algorithm, the method can carry out frequency offset phase estimation with different precision on different rates of different positions of the same-section signal, and greatly reduces the influence of the frequency offset change rate on the frequency offset estimation value of the section in a mode of segmented cache demodulation, so that the frequency offset change rate can be ignored, and accurate search and compensation of the frequency offset generated by the Doppler phenomenon caused by the low-orbit satellite motion are realized.
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In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
Fig. 1 is a schematic flow chart of a signal demodulation method with variable transmission rate according to the present invention;
FIG. 2 is a schematic diagram of a frame structure provided by the present invention;
FIG. 3 is a second flowchart of a method for demodulating a signal with a variable transmission rate according to the present invention;
FIG. 4 is a third schematic flow chart of a signal demodulation method with variable transmission rate according to the present invention;
fig. 5 is a schematic structural diagram of a signal demodulation apparatus with variable transmission rate provided by the present invention;
fig. 6 is a schematic structural diagram of an electronic device provided in the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the signal demodulation method with variable transmission rate provided by the present invention is mainly applied to short frame burst communication, and is suitable for a communication system in which the communication rate changes with the service change and needs real-time demodulation in the communication process. At this time, the communication process is considered to occur under a lower signal-to-noise ratio, and an initial frequency offset exists in the system
Initial phase of
And a constant rate of change of frequency offset
. In a highly dynamic environment, the instantaneous phase of the residual modulation of the baseband received signal is a time-varying function through quadrature mixing by the receiver. For example, assuming that only frequency offset is present, the function is a slope (the slope represents the frequency offset). The specific waveform of this function may be complex depending on the law of motion of the carrier. If short frame burst communication is considered, this corresponds to a short time-domain truncation of the time function to be studied. Expanding the function waveform in the time domain truncation according to power series, and if only a constant term and a first-order component are reserved, only considering an initial phase and a frequency offset; when the change in the speed of the carrier (i.e. the acceleration) cannot be neglected within the burst frame duration, the constant term, the first order component and the second order component have to be preserved. Then, at this point, if the first of the communication systemFrequency offset of a symbol is noted
Then the frequency offset of the Nth symbol can be considered as
。
Since the data transmission rate and the data length of the communication system are not constant, a special frame structure is required to describe the frame information. The invention needs to divide the burst frame into three parts: pilot segment, service segment and data segment. The pilot frequency band is a full 1 sequence and is used for capturing and coarse compensation of frequency offset; the service segment is used for providing information of the frame, such as a frame header, a frame length, a data segment rate and the like; the data segment is used to transmit data. The signal symbol rate of pilot band and service band is kept constant, and the length and transmission rate of data band can be changed according to different services. The service segment indicates that bytes of the data segment rate change when the data segment rate changes. The receiving end firstly demodulates and decodes the service segment in real time after capturing a frame, and initializes the demodulation module of the data segment according to the data segment information given by the service segment. Thus, real-time and accurate demodulation of the data segment can be ensured. In addition, the receiving end determines the polarity according to the frame header part of the received signal service segment, and the polarity is used for solving the absolute ambiguity.
Fig. 1 is a schematic flow chart of a method for demodulating a signal with a variable transmission rate according to the present invention, fig. 2 is a schematic flow chart of a frame structure according to the present invention, fig. 3 is a schematic flow chart of a method for demodulating a signal with a variable transmission rate according to the present invention, and fig. 4 is a schematic flow chart of a method for demodulating a signal with a variable transmission rate according to the present invention. The transmission rate variable signal demodulation method of the present invention is described below with reference to fig. 1 to 4, and includes:
step 101: capturing a spread spectrum signal sent by a user, and performing coarse compensation on frequency offset and phase of the spread spectrum signal according to a pilot frequency band of the spread spectrum signal;
in this step, the spread spectrum signal sent by the user is captured first, and according to the pilot frequency band of the spread spectrum signal, the coarse compensation of the frequency offset and the phase is performed on the spread spectrum signal.
Step 102: dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; when the cached sub-service segment data is demodulated, searching frequency offset and phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments;
in the step, in order to resist the influence caused by the frequency deviation change rate and ensure the real-time demodulation of the signal so as to solve the signal of the service segment in a short time and further adjust the receiving of the data segment signal according to the information of the service segment, the service segment of the spread spectrum signal after being unframed is subjected to segmented cache processing, and at the moment, because the frequency deviation change rate of each segment of data is changed, the frequency deviation change rate of each segment of the spread spectrum signal is subjected to segmented cache processing
The smaller value may be considered acceptable for the error that occurs when the frequency offset is a constant value within the segment, or when the mathematical expectation of the frequency offset is used to describe the linearly varying frequency offset within the segment.
In this step, for each piece of cached sub-service segment data, a local template or fast Fourier transform (fft) is used to search for frequency offset and phase, and a reference phase of the next piece of sub-service segment data is generated. It should be noted that, since the search frequency offset needs to use square demodulation, phase ambiguity is easily caused in the process, and therefore, the continuity of the phase needs to be ensured. Namely: for the first service segment data after segmentation, the invention uses the polarity of the frame head part after demodulation to judge the absolute phase thereof and generates the reference phase of the next service segment data, and then the phase solved according to each service segment data keeps continuous with the phase generated by the previous segment, thus ensuring the phase of each segment data to be correct.
In the step, according to the frequency offset estimation value of the sub-service segment data, the service segment local template is pre-compensated to obtain a thinned service segment local template, and based on the thinned service segment local template, the next sub-service segment data is subjected to square demodulation to determine the frequency offset and phase estimation value of the next sub-service segment data. Therefore, the frequency offset searched for each service segment data is used for removing the residual frequency offset of the service segment data on one hand; and on the other hand, the data is fed back to a front-stage module of the system to pre-compensate the next-stage data. Therefore, the absolute value of the frequency offset can be gradually reduced, and further, a refined template is gradually used for carrying out finer searching on the frequency offset.
In this step, after the service segment is demodulated, the length and rate of the data segment are initialized. And switching the local template according to the speed gear, and generating the initial phase of the data segment signal.
Step 103: after the demodulation of the service segment of the spread spectrum signal is finished, dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for caching in sequence according to the transmission rate of the data segment data of the spread spectrum signal, and demodulating the cached sub-data segment data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated.
In this step, after the demodulation of the service segment of the spread spectrum signal is finished, the data segment of the spread spectrum signal is divided into sub-data segments with different lengths for sequentially caching according to the difference of the transmission rates of the data segment. And then, searching the frequency offset and the phase of each section of cached sub-data section data by adopting a local template or FFT (fast Fourier transform algorithm), and generating the reference phase of the next section of sub-data section data. It should be noted that, since the search frequency offset needs to use square demodulation, phase ambiguity is easily caused in the process, and therefore, the continuity of the phase needs to be ensured. Namely: for the segmented first segment data, the invention uses the polarity of the frame head part after demodulation to judge the absolute phase and generates the reference phase of the next segment data, and then the phase solved according to each segment data keeps continuous with the phase generated by the previous segment, thus ensuring the correct phase of each segment data.
In this step, according to the frequency offset estimation value of the sub-data segment data, the data segment local template is pre-compensated to obtain a refined data segment local template, and based on the refined data segment local template, the next sub-data segment data is subjected to square de-modulation to determine the frequency offset and phase estimation value of the next sub-data segment data. Therefore, the frequency offset searched for each data segment is used for removing the residual frequency offset of the data segment on one hand; and on the other hand, the data is fed back to a front-stage module of the system to pre-compensate the next-stage data. Therefore, the absolute value of the frequency offset can be gradually reduced, and further, a refined template is gradually used for carrying out finer searching on the frequency offset.
The signal demodulation method with variable transmission rate provided by the invention captures the spread spectrum signal sent by the user and carries out coarse compensation of frequency deviation and phase on the spread spectrum signal according to the pilot frequency band of the spread spectrum signal. Then dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; when the cached sub-service segment data is demodulated, frequency offset and phase search is carried out on the sub-service segment data, and a reference phase of the next sub-service segment data used for ensuring the phase continuity of the adjacent sub-service segments is generated. After the demodulation of the service section of the spread spectrum signal is finished, dividing the data section of the spread spectrum signal into a plurality of sub-data sections for sequential caching according to the transmission rate of the data section data of the spread spectrum signal, and demodulating the cached sub-data section data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated. Therefore, the method is suitable for variable-rate transmission of the same-section signal, and compared with constant-rate demodulation of the traditional algorithm, the method can carry out frequency offset phase estimation with different precision on different rates of different positions of the same-section signal, and greatly reduces the influence of the frequency offset change rate on the frequency offset estimation value of the section in a mode of segmented cache demodulation, so that the frequency offset change rate can be ignored, and accurate search and compensation of the frequency offset generated by the Doppler phenomenon caused by the low-orbit satellite motion are realized.
Based on the content of the foregoing embodiment, in this embodiment, when demodulating the cached sub service segment data, performing frequency offset and phase search on the sub service segment data, and generating a reference phase of the next sub service segment data for ensuring that the phases of adjacent sub service segments are continuous includes:
based on a service segment local template, carrying out square de-modulation on the sub-service segment data, and determining the frequency offset and phase estimation values of the sub-service segment data;
after determining the frequency offset and the phase estimation value of the first sub-service segment data, correcting the phase estimation value of the first sub-service segment data according to the frame header data and the local frame header data of the spread spectrum signal to obtain a corrected phase estimation value;
and compensating the first sub-service segment data according to the frequency offset estimation value of the first sub-service segment data and the corrected phase estimation value, calculating the phase of the last bit data of the first sub-service segment data according to the corrected phase estimation value, and using the phase as the reference phase of the next sub-service segment data, so that after the phase estimation value of the next sub-service segment data is determined, the phase estimation value of the next sub-service segment data is corrected according to the reference phase, and the phase continuity of the adjacent sub-service segment data is ensured.
Based on the content of the foregoing embodiment, in this embodiment, when demodulating the cached sub-data segment data, performing frequency offset and phase search on the sub-data segment data, and generating a reference phase of the next sub-data segment data for ensuring phase continuity of adjacent sub-data segments, includes:
based on a data segment local template, carrying out square demodulation on the data of the sub data segment, and determining the frequency offset and the estimated value of the phase of the data of the sub data segment;
after determining the frequency offset and the phase estimation value of the first-segment sub-data segment data, correcting the phase estimation value of the first-segment sub-data segment data according to the frame header data and the local frame header data of the spread spectrum signal to obtain a corrected phase estimation value;
and compensating the first sub-data segment data according to the frequency offset estimation value of the first sub-data segment data and the corrected phase estimation value, calculating the phase of the last bit data of the first sub-data segment data according to the corrected phase estimation value, and using the phase as the reference phase of the next sub-data segment data, so that after the phase estimation value of the next sub-data segment data is determined, the phase estimation value of the next sub-data segment data is corrected according to the reference phase, and the phase continuity of the adjacent sub-data segment data is ensured.
Based on the content of the foregoing embodiment, in this embodiment, the method further includes:
and pre-compensating the spread spectrum signal according to the frequency offset estimation value of the first sub-data segment data, and selecting a data segment local template with higher frequency offset precision to perform square demodulation on the next sub-data segment data based on the pre-compensated spread spectrum signal, thereby determining the frequency offset and phase estimation values of the next sub-data segment data.
In this embodiment, it should be noted that, for each piece of sub-service segment data, the sub-service segment data is debugged based on the service segment local template, and for each piece of sub-service segment data, other sub-service segments except the first sub-service segment data are modulated by using the data segment local template with higher frequency offset precision determined by the spread spectrum signal pre-compensated by the frequency offset estimation value of the first sub-service segment data.
Based on the content of the foregoing embodiment, in this embodiment, dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for sequentially buffering according to the transmission rate of the data segment data of the spread spectrum signal includes:
and dividing the data segment of the spread spectrum signal into sub-data segments with different lengths for sequentially caching according to the difference of the transmission rates of the data segment data.
The following is illustrated by specific examples:
the first embodiment is as follows:
in the present embodiment, the service segment includes 384 symbols, the rate 2Ksps is taken as an example, wherein the first 32 symbols are synchronization headers; the data segment contains 10240 symbols, rate 250sps, 500sps, 2ksps, 4ksps, 8ksp, 32ksps, 256ksps for example; firstly, the received data is segmented and buffered, wherein 64 symbols of the service segment are segmented into 6 segments, the data segment is segmented according to 256 symbols of rate steps with the service rate being different below 2k, and the segments with the service rate being 2k and above 2k are segmented according to 128 symbols. And then generating a template required by the service section and the data section for searching the frequency offset change rate. Because the dynamic range of the service segment residual frequency offset is large, a coarse template is used for searching, and 64 sine waves with the frequency range of minus 64Hz to plus 64Hz and the interval of 2Hz can be generated by taking +/-64 Hz residual frequency offset as an example in the scheme. For the data segment, sine waves ranging from-16 Hz to +16Hz and having an interval of 0.5Hz can be generated. The segmented data is then square de-modulated (assuming BPSK). And for the first-end data, multiplying and accumulating the service segment templates, taking an absolute value of an obtained result, finding out the frequency of the template corresponding to the maximum absolute value as a frequency deviation estimation value of the first-segment data, and estimating the phase of the first-segment data.
In this embodiment, the first segment of data is subjected to frequency offset and phase compensation, the polarity of the frame header is compared with that of the local frame header, if the frame header is in phase, the result of phase estimation is kept, otherwise, pi is added to the result of phase estimation.
In this embodiment, the phase of the last bit of data of this segment of data is calculated as the reference phase of the next segment of data based on the estimated phase. Since the second and subsequent data cannot be phase corrected by comparing the frame headers, the ambiguity can only be resolved by comparing the reference phase generated by the previous segment. As long as the calculated phase of each segment of data is ensured to be continuous with the phase of the previous segment, the phases of all subsequent segments of data can be ensured to be correct as long as the phase of the first segment of data is solved.
The invention has the following beneficial effects:
the invention can carry out real-time iterative demodulation on frame data with unknown frame length and can adapt to variable rate. Compared with the common algorithm for demodulating the whole frame after buffering, the method has better real-time performance, not only can feed back the frequency offset value to the receiving end in real time, but also can guide the subsequent data to change the frame length or the data symbol rate.
The invention can accurately search and compensate the frequency offset generated by Doppler phenomenon caused by low-orbit satellite motion. Compared with the traditional FFT frequency offset searching method, the method has higher precision and smaller computation amount, can save time delay by a parallel computation method and is used for ensuring the real-time property of signal transmission;
the invention can be adapted to the variable transmission rate of the same segment of signals at the same time. Compared with the constant rate demodulation of the traditional algorithm, the method can carry out frequency offset phase estimation with different precision on different rates of different positions of the same frame signal, and selects the optimal template suitable for the rate to carry out frequency offset search, thereby saving time, and saving storage and operation resources.
The invention is insensitive to the frequency deviation change rate. Because the segment length and the segment number are controllable, the influence of the frequency offset change rate on the frequency offset estimation module of the segment is extremely small by changing the segment length, so that the frequency offset change rate can be ignored.
The method has high real-time performance and accuracy and low implementation complexity.
The following describes the transmission rate variable signal demodulation apparatus provided by the present invention, and the transmission rate variable signal demodulation apparatus described below and the transmission rate variable signal demodulation method described above can be referred to correspondingly.
As shown in fig. 5, the present invention provides a signal demodulation apparatus with variable transmission rate, which includes:
the system comprises a first processing module 1, a second processing module and a third processing module, wherein the first processing module is used for capturing a spread spectrum signal sent by a user and carrying out coarse compensation on frequency offset and phase of the spread spectrum signal according to a pilot frequency band of the spread spectrum signal;
the second processing module 2 is configured to divide the service segment of the spread spectrum signal into a plurality of sub-service segments for caching, and sequentially demodulate the cached sub-service segment data; when the cached sub-service segment data is demodulated, searching frequency offset and phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments;
the third processing module 3 is configured to, after the demodulation of the service segment of the spread spectrum signal is finished, divide the data segment of the spread spectrum signal into a plurality of sub-data segments for caching according to the transmission rate of the data segment data of the spread spectrum signal, and sequentially demodulate the cached sub-data segment data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated.
In this embodiment, a spread spectrum signal transmitted by a user is captured first, and according to a pilot band of the spread spectrum signal, coarse compensation of frequency offset and phase is performed on the spread spectrum signal.
In this embodiment, in order to counter the influence of the frequency offset change rate and ensure the real-time demodulation of the signal, so as to solve the signal of the service segment in a short time and further adjust the reception of the data segment signal according to the information of the service segment, the service segment of the spread spectrum signal after being deframed is buffered in segments, and at this time, because each segment of the data has the frequency offset change rate
The smaller value may be considered acceptable for the error that occurs when the frequency offset is a constant value within the segment, or when the mathematical expectation of the frequency offset is used to describe the linearly varying frequency offset within the segment.
In this embodiment, for each piece of cached sub-service segment data, a local template or FFT is used to search for the frequency offset and phase, and a reference phase of the next piece of sub-service segment data is generated. It should be noted that, since the search frequency offset needs to use square demodulation, phase ambiguity is easily caused in the process, and therefore, the continuity of the phase needs to be ensured. Namely: for the first service segment data after segmentation, the invention uses the polarity of the frame head part after demodulation to judge the absolute phase thereof and generates the reference phase of the next service segment data, and then the phase solved according to each service segment data keeps continuous with the phase generated by the previous segment, thus ensuring the phase of each segment data to be correct.
In the embodiment, the local template of the service segment is pre-compensated according to the frequency offset estimation value of the sub-service segment data to obtain a thinned local template of the service segment, and the next sub-service segment data is subjected to square demodulation based on the thinned local template of the service segment to determine the frequency offset and phase estimation value of the next sub-service segment data. Therefore, the frequency offset searched for each service segment data is used for removing the residual frequency offset of the service segment data on one hand; and on the other hand, the data is fed back to a front-stage module of the system to pre-compensate the next-stage data. Therefore, the absolute value of the frequency offset can be gradually reduced, and further, a refined template is gradually used for carrying out finer searching on the frequency offset.
In this embodiment, after the demodulation of the service segment is completed, the length and rate of the data segment are initialized. And switching the local template according to the speed gear, and generating the initial phase of the data segment signal.
In this embodiment, after the end of the demodulation of the service segment of the spread spectrum signal, the data segment of the spread spectrum signal is divided into sub-data segments with different lengths for sequentially buffering according to the difference of the transmission rates of the data segment data. And then, searching the frequency offset and the phase of each section of cached sub-data section data by adopting a local template or FFT (fast Fourier transform algorithm), and generating the reference phase of the next section of sub-data section data. It should be noted that, since the search frequency offset needs to use square demodulation, phase ambiguity is easily caused in the process, and therefore, the continuity of the phase needs to be ensured. Namely: for the segmented first segment data, the invention uses the polarity of the frame head part after demodulation to judge the absolute phase and generates the reference phase of the next segment data, and then the phase solved according to each segment data keeps continuous with the phase generated by the previous segment, thus ensuring the correct phase of each segment data.
In this embodiment, according to the frequency offset estimation value of the sub-data segment data, the data segment local template is pre-compensated to obtain a refined data segment local template, and based on the refined data segment local template, the next sub-data segment data is square-unmodulated to determine the frequency offset and phase estimation value of the next sub-data segment data. Therefore, the frequency offset searched for each data segment is used for removing the residual frequency offset of the data segment on one hand; and on the other hand, the data is fed back to a front-stage module of the system to pre-compensate the next-stage data. Therefore, the absolute value of the frequency offset can be gradually reduced, and further, a refined template is gradually used for carrying out finer searching on the frequency offset.
The signal demodulation device with the variable transmission rate provided by the invention carries out coarse compensation on frequency deviation and phase of the spread spectrum signal by capturing the spread spectrum signal sent by a user and according to the pilot frequency band of the spread spectrum signal. Then dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; when the cached sub-service segment data is demodulated, frequency offset and phase search is carried out on the sub-service segment data, and a reference phase of the next sub-service segment data used for ensuring the phase continuity of the adjacent sub-service segments is generated. After the demodulation of the service section of the spread spectrum signal is finished, dividing the data section of the spread spectrum signal into a plurality of sub-data sections for sequential caching according to the transmission rate of the data section data of the spread spectrum signal, and demodulating the cached sub-data section data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated. Therefore, the method is suitable for variable-rate transmission of the same-section signal, and compared with constant-rate demodulation of the traditional algorithm, the method can carry out frequency offset phase estimation with different precision on different rates of different positions of the same-section signal, and greatly reduces the influence of the frequency offset change rate on the frequency offset estimation value of the section in a mode of segmented cache demodulation, so that the frequency offset change rate can be ignored, and accurate search and compensation of the frequency offset generated by the Doppler phenomenon caused by the low-orbit satellite motion are realized.
Fig. 6 illustrates a physical structure diagram of an electronic device, which may include, as shown in fig. 6: a processor (processor)601, a communication Interface (Communications Interface)603, a memory (memory)602 and a communication bus 604, wherein the processor 601, the communication Interface 603 and the memory 602 communicate with each other through the communication bus 604. The processor 601 may invoke logic instructions in the memory 602 to perform a variable transmission rate signal demodulation method comprising: capturing a spread spectrum signal sent by a user, and performing coarse compensation on frequency offset and phase of the spread spectrum signal according to a pilot frequency band of the spread spectrum signal; dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; when the cached sub-service segment data is demodulated, searching frequency offset and phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments; after the demodulation of the service segment of the spread spectrum signal is finished, dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for caching in sequence according to the transmission rate of the data segment data of the spread spectrum signal, and demodulating the cached sub-data segment data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated.
Furthermore, the logic instructions in the memory 602 may be implemented in software functional units and stored in a computer readable storage medium when the logic instructions are sold or used as independent products. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
In another aspect, the present invention also provides a computer program product, the computer program product including a computer program, the computer program being stored on a non-transitory computer-readable storage medium, wherein when the computer program is executed by a processor, the computer is capable of executing the method for demodulating a signal with a variable transmission rate provided by the methods, the method including: capturing a spread spectrum signal sent by a user, and performing coarse compensation on frequency offset and phase of the spread spectrum signal according to a pilot frequency band of the spread spectrum signal; dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; when the cached sub-service segment data is demodulated, searching frequency offset and phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments; after the demodulation of the service segment of the spread spectrum signal is finished, dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for caching in sequence according to the transmission rate of the data segment data of the spread spectrum signal, and demodulating the cached sub-data segment data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated.
In yet another aspect, the present invention further provides a non-transitory computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements a method for demodulating a signal with a variable transmission rate provided by the methods above, captures a spread spectrum signal transmitted by a user, and performs coarse compensation of frequency offset and phase on the spread spectrum signal according to a pilot band of the spread spectrum signal; dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; when the cached sub-service segment data is demodulated, searching frequency offset and phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments; after the demodulation of the service segment of the spread spectrum signal is finished, dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for caching in sequence according to the transmission rate of the data segment data of the spread spectrum signal, and demodulating the cached sub-data segment data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated.
The above-described embodiments of the apparatus are merely illustrative, and the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware. With this understanding in mind, the above-described technical solutions may be embodied in the form of a software product, which can be stored in a computer-readable storage medium such as ROM/RAM, magnetic disk, optical disk, etc., and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the methods described in the embodiments or some parts of the embodiments.
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 method for demodulating a signal having a variable transmission rate, comprising:
capturing a spread spectrum signal sent by a user, and performing coarse compensation on frequency offset and phase of the spread spectrum signal according to a pilot frequency band of the spread spectrum signal;
dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching in sequence, and demodulating the cached data of the sub-service segments; when the cached sub-service segment data is demodulated, searching frequency offset and phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments;
after the demodulation of the service segment of the spread spectrum signal is finished, dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for caching in sequence according to the transmission rate of the data segment data of the spread spectrum signal, and demodulating the cached sub-data segment data; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated.
2. The method for demodulating a signal with a variable transmission rate according to claim 1, wherein, when demodulating the buffered sub service segment data, a frequency offset and phase search is performed on the sub service segment data, and a reference phase for the next sub service segment data for guaranteeing phase continuity of adjacent sub service segments is generated, comprising:
based on a service segment local template, carrying out square de-modulation on the sub-service segment data, and determining the frequency offset and phase estimation values of the sub-service segment data;
after determining the frequency offset and the phase estimation value of the first sub-service segment data, correcting the phase estimation value of the first sub-service segment data according to the frame header data and the local frame header data of the spread spectrum signal to obtain a corrected phase estimation value;
and compensating the first sub-service segment data according to the frequency offset estimation value of the first sub-service segment data and the corrected phase estimation value, calculating the phase of the last bit data of the first sub-service segment data according to the corrected phase estimation value, and using the phase as the reference phase of the next sub-service segment data, so that after the phase estimation value of the next sub-service segment data is determined, the phase estimation value of the next sub-service segment data is corrected according to the reference phase, and the phase continuity of the adjacent sub-service segment data is ensured.
3. The method of claim 1, wherein when demodulating the buffered sub-data, the method searches for a frequency offset and a phase of the sub-data and generates a reference phase of a next sub-data for guaranteeing phase continuity of adjacent sub-data, comprising:
based on a data segment local template, carrying out square demodulation on the data of the sub data segment, and determining the frequency offset and the estimated value of the phase of the data of the sub data segment;
after determining the frequency offset and the phase estimation value of the first-segment sub-data segment data, correcting the phase estimation value of the first-segment sub-data segment data according to the frame header data and the local frame header data of the spread spectrum signal to obtain a corrected phase estimation value;
and compensating the first sub-data segment data according to the frequency offset estimation value of the first sub-data segment data and the corrected phase estimation value, calculating the phase of the last bit data of the first sub-data segment data according to the corrected phase estimation value, and using the phase as the reference phase of the next sub-data segment data, so that after the phase estimation value of the next sub-data segment data is determined, the phase estimation value of the next sub-data segment data is corrected according to the reference phase, and the phase continuity of the adjacent sub-data segment data is ensured.
4. The method of demodulating a variable transmission rate signal according to claim 3, further comprising:
and pre-compensating the spread spectrum signal according to the frequency offset estimation value of the first sub-data segment data, and selecting a data segment local template with higher frequency offset precision to perform square demodulation on the next sub-data segment data based on the pre-compensated spread spectrum signal, thereby determining the frequency offset and phase estimation values of the next sub-data segment data.
5. The method of claim 1, wherein dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for sequentially buffering according to the transmission rate of the data segment of the spread spectrum signal comprises:
and dividing the data segment of the spread spectrum signal into sub-data segments with different lengths for sequentially caching according to the difference of the transmission rates of the data segment data.
6. A signal demodulation apparatus with variable transmission rate, comprising:
the first processing module is used for capturing a spread spectrum signal sent by a user and carrying out coarse compensation on frequency offset and phase of the spread spectrum signal according to a pilot frequency band of the spread spectrum signal;
the second processing module is used for dividing the service segment of the spread spectrum signal into a plurality of sub-service segments for caching, and demodulating the cached sub-service segment data in sequence; when the cached sub-service segment data is demodulated, searching frequency offset and phase of the sub-service segment data, and generating a reference phase of the next sub-service segment data for ensuring the phase continuity of the adjacent sub-service segments;
the third processing module is used for dividing the data segment of the spread spectrum signal into a plurality of sub-data segments for caching according to the transmission rate of the data segment data of the spread spectrum signal after the demodulation of the service segment of the spread spectrum signal is finished, and demodulating the cached sub-data segment data in sequence; when the cached sub-data segment data is demodulated, frequency offset and phase search is carried out on the sub-data segment data, and a reference phase of the next sub-data segment data used for ensuring the phase continuity of the adjacent sub-data segments is generated.
7. The apparatus according to claim 6, wherein the second processing module is specifically configured to:
based on a service segment local template, carrying out square de-modulation on the sub-service segment data, and determining the frequency offset and phase estimation values of the sub-service segment data;
after determining the frequency offset and the phase estimation value of the first sub-service segment data, correcting the phase estimation value of the first sub-service segment data according to the frame header data and the local frame header data of the spread spectrum signal to obtain a corrected phase estimation value;
and compensating the first sub-service segment data according to the frequency offset estimation value of the first sub-service segment data and the corrected phase estimation value, calculating the phase of the last bit data of the first sub-service segment data according to the corrected phase estimation value, and using the phase as the reference phase of the next sub-service segment data, so that after the phase estimation value of the next sub-service segment data is determined, the phase estimation value of the next sub-service segment data is corrected according to the reference phase, and the phase continuity of the adjacent sub-service segment data is ensured.
8. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor when executing the program performs the steps of the method for demodulating a signal with a variable transmission rate according to any one of claims 1 to 5.
9. A non-transitory computer-readable storage medium, on which a computer program is stored, wherein the computer program, when being executed by a processor, implements the steps of the transmission rate variable signal demodulation method according to any one of claims 1 to 5.
10. A computer program product comprising a computer program, characterized in that the computer program, when being executed by a processor, carries out the steps of the method for demodulating a signal with a variable transmission rate according to any one of claims 1 to 5.
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