CN116506004B - Collaborative communication PCMA system signal searching method and device - Google Patents
Collaborative communication PCMA system signal searching method and device Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04B7/00—Radio transmission systems, i.e. using radiation field
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- H04B7/185—Space-based or airborne stations; Stations for satellite systems
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The application discloses a collaborative communication PCMA system signal searching method and device, which specifically comprises the following steps: starting a searching device, initializing parameters of the searching device, selecting a signal interval, collecting data in the signal interval, performing fast Fourier transform on the data in the signal interval, converting the data into frequency domain representation, searching a peak value in the frequency domain representation, judging whether the peak value is larger than a set threshold value, if the peak value is larger than the set threshold value, searching successfully, recording the signal interval when searching successfully, and calculating a frequency offset value; and if the peak value is smaller than the set threshold value, reselecting the signal interval near the signal interval, collecting the data in the reselected signal interval, and repeating the steps. The application improves the searching efficiency through the collaborative communication PCMA system signal searching method, and reduces the influence caused by satellite Doppler.
Description
Technical Field
The application relates to the field of signal searching and discloses a method and a device for searching signals of a cooperative communication PCMA system.
Background
The paired carrier multiple access (PCMA: paired Carrier Multiple Access) multiplexing technology was proposed by the usa via sat company in 1998. The PCMA technology is widely adopted in satellite communication because of the characteristics of bandwidth resource saving, strong confidentiality and little influence on the error code performance of the system.
In satellite communication, station type 1 and station type 2 transmit signals y1 (t) and y2 (t), respectively, and receive signals y1 (t) +y2 (t). y1 (t), y2 (t) are signals transmitted in the same space, time and frequency, and the receiver cannot communicate if conventional demodulation methods are used. Since the transmission sequence of the own station is known, the communication problem under such conditions can be solved by adopting the PCMA multiplexing technology. In engineering application, PCMA multiplexing technology of an asymmetric cooperative communication mode is often adopted for products; during communication, the transmit-side sequence is known, while the delay, attenuation, and noise of the entire satellite link are unknown, and during engineering, PCMA satellite equipment needs to cancel out the components of the local signal from the satellite received signal.
The application focuses on the delay estimation module in PCMA satellite communication system signal demodulation, delay tau estimation is the first step of signal processing of the receiving end, and whether the subsequent demodulation can be normal or not is determined. Meanwhile, because the satellite link condition is unknown, the estimation of tau has the characteristics of wide search range, large calculated amount and long processing time, and the experience of a user is very influenced. The estimation of the delay tau often needs to estimate an approximate delay value through the parameters of the satellite and the longitude and latitude of the place where the satellite equipment is located, and then accurately obtain the satellite-to-earth delay through a signal processing method. The more accurate the external parameters are, the simpler the signal processing method is, but in the practical use process, the larger the error of the estimated value is usually given due to the restriction of the external conditions, so the estimation of the signal delay τ is often complicated.
Disclosure of Invention
The application aims to: a method and apparatus for searching a signal of a cooperative communication PCMA system are provided to solve the above-mentioned problems.
The technical scheme is as follows: according to one aspect of the present application, there is provided a collaborative communication PCMA system signal searching method, including the steps of:
s1, starting a searching device and initializing parameters of the searching device;
s2, dividing the time window into a preset number of time slots, selecting the median value of the preset number of time slots as a signal interval, and collecting data in the signal interval;
s3, performing fast Fourier transform on the data in the signal interval to convert the data into a frequency domain representation;
s4, searching a peak value in the frequency domain representation, judging whether the peak value is larger than a set threshold value, if so, searching is successful, and turning to the step S5, and if so, turning to the step S6;
s5, recording a signal interval when the search is successful, and calculating a frequency offset value through a frequency estimation algorithm;
s6, judging whether the signal interval is the last interval, if so, turning to the step S1, and if not, reselecting the signal interval near the signal interval, collecting data in the reselected signal interval, and turning to the step S3.
According to one aspect of the application, the predetermined time window of step S2 is specifically:
s21, collecting sample data of a signal to be searched;
s22, establishing a probability model based on sample data, wherein the probability model is used for describing probability distribution of the occurrence of the signal to be searched in different time windows;
s23, selecting a time window with the maximum occurrence probability as a preferential searching object based on the probability model.
According to one aspect of the application, the re-selecting of the signal interval in the vicinity of the signal interval in step S6 is specifically: a time slot is shifted from the signal interval as a reselected signal interval.
According to one aspect of the application, the predetermined number of time slots in step S2 is 32 time slots.
According to another aspect of the present application, there is provided a cooperative communication PCMA system signal search device, including:
the interval dividing module is used for describing probability distribution of the occurrence of the signal to be searched in different time windows through the constructed probability model, dividing the time windows into a preset number of time slots equally based on the probability model, and selecting the time window with the maximum occurrence probability as a preferential searching object;
the fast Fourier transform module is used for performing fast Fourier transform on the data in the signal interval to convert the data into a frequency domain representation;
the frequency domain searching module searches a peak value in the frequency domain representation, judges whether the peak value is larger than a set threshold value, and if the peak value is larger than the set threshold value, the searching is successful;
and the frequency offset calculation module calculates a frequency offset value through a frequency estimation algorithm in a signal interval when the search is successful.
The beneficial effects are that: the application provides the method that the searching is preferentially carried out in the time window with the maximum probability, and then the searching is gradually carried out nearby the time window in sequence, so that the searching efficiency is improved, the influence caused by satellite Doppler is reduced, and the error caused by signal delay is reduced through the segmented searching of the time window.
Drawings
Fig. 1 is a schematic diagram of PCMA signaling.
Fig. 2 is a schematic diagram of a PCMA satellite signal processing flow.
Fig. 3 is a segmentation process diagram of a time window.
Fig. 4 is a flow chart of collaborative communication PCMA system signal search.
Detailed Description
The paired carrier multiple access (PCMA: paired Carrier Multiple Access) multiplexing technology was proposed by the usa via sat company in 1998. The PCMA technology is widely adopted in satellite communication because of the characteristics of bandwidth resource saving, strong confidentiality and little influence on the error code performance of the system.
As shown in fig. 1, in the satellite communication process, station type 1 and station type 12 transmit signals y1 (t) and y2 (t), respectively, and receive signals y1 (t) +y2 (t). y1 (t), y2 (t) are signals transmitted in the same space, time and frequency, and the receiver cannot communicate if conventional demodulation methods are used. Since the transmission sequence of the own station is known, the communication problem under such conditions can be solved by adopting the PCMA multiplexing technology. In engineering application, PCMA multiplexing technology of an asymmetric cooperative communication mode is often adopted for products.
During communication, the transmit-side sequence is known, while the delay, attenuation, and noise of the entire satellite link are unknown, and during engineering, PCMA satellite equipment needs to cancel out the components of the local signal from the satellite received signal.
The application focuses on a delay estimation module in PCMA satellite communication system signal demodulation, where the position of the signal demodulation process is shown in fig. 2. The estimation of the delay τ is the first step in the signal processing at the receiving end, and determines whether the subsequent demodulation can be normal. Meanwhile, because the satellite link condition is unknown, the estimation of tau has the characteristics of wide search range, large calculated amount and long processing time, and the experience of a user is very influenced. The estimation of the delay tau often needs to estimate an approximate delay value through the parameters of the satellite and the longitude and latitude of the place where the satellite equipment is located, and then accurately obtain the satellite-to-earth delay through a signal processing method. The more accurate the external parameters are, the simpler the signal processing method is, but in the practical use process, the larger the error of the estimated value is usually given due to the restriction of the external conditions, so the estimation of the signal delay τ is often complicated.
As shown in fig. 4, the application provides a method and a device for searching a signal of a cooperative communication PCMA system, which specifically comprise the following steps:
s1, starting a searching device and initializing parameters of the searching device;
s2, dividing the time window into a preset number of time slots, selecting the median value of the preset number of time slots as a signal interval, and collecting data in the signal interval;
s3, performing fast Fourier transform on the data in the signal interval to convert the data into a frequency domain representation;
s4, searching a peak value in the frequency domain representation, judging whether the peak value is larger than a set threshold value, if so, searching is successful, and turning to the step S5, and if so, turning to the step S6;
s5, recording a signal interval when the search is successful, and calculating a frequency offset value through a frequency estimation algorithm;
s6, judging whether the signal interval is the last interval, if so, turning to the step S1, and if not, reselecting the signal interval near the signal interval, collecting data in the reselected signal interval, and turning to the step S3.
In one embodiment, the satellite-to-ground delay value is estimated by searching the signal, the sampling rate of the signal is 160MHz, the symbol rate of the signal is 40Msps, the satellite-to-ground delay error is input externally for + -15 ms, the time window is segmented, all sampling points of 30ms in the time window are related to the local sequence, and the optimal position is estimated. The method comprises the following steps: when the device starts to start searching, the receiving end performs 32 equal divisions on a total time window of 30ms, and the time window is sequentially: tstart-T1, T1-T2, … …, T31-Tend.
A. B, receiving signals of T15-T16 time slots, performing correlation operation, and converting to the step B;
B. c, judging whether a correlation peak exists or not by taking FFT (fast Fourier transform) of correlation operation, and if the correlation peak is larger than a set threshold, searching successfully and turning to the step C; otherwise, turning to the step D;
C. the searching is successful, and the current position information and the frequency offset value are given;
D. searching the next time slot forward/backward, performing correlation operation, and turning to the step B.
The estimated range of the design device is + -15 ms, and the probability that the true value of the satellite-to-ground delay is at or near the 0ms moment is large, so that the searching is started from the median value, and the searching time can be reduced statistically.
The satellite communication adopted in the application is communication based on synchronous orbit satellites, the current satellite state is that the satellite earth speed is less than +/-5 m/s, and the bit timing deviation caused by satellite Doppler is not more than 0.67 symbol/s. The higher the sampling rate, the higher the complexity of the search and the longer the time required for computation. This results in the search obtaining a delay value that is not the actual delay value of the current satellite.
Therefore, the application adopts the strategy of time window segment search, and the processing delay is reduced to 1/32 as the window of each search is only 30/32ms, and the timing deviation caused by satellite Doppler is very small and can be ignored in the processing time of the data segment.
The specific time window is as follows:
s21, collecting sample data of a signal to be searched;
s22, establishing a probability model based on sample data, wherein the probability model is used for describing probability distribution of the occurrence of the signal to be searched in different time windows;
s23, selecting a time window with the maximum occurrence probability as a preferential searching object based on the probability model.
The searching is preferentially carried out in the time window with the highest probability, and then the searching is gradually carried out in the vicinity of the time window, so that the searching efficiency is improved.
In a further embodiment, T is defined m To estimate the satellite-to-ground delay, T w For an indefinite window duration, the actual satellite-to-ground delay is therefore at T m ±T w Within the range. Definition T p To process T w Time, t, required for data within a window w For the window segment post-duration, t p To process t w Time, T, required for data within window 0 For the starting time, T s Is one symbol width. Correlation length l=4096, time T corresponding to correlation length c =4096×40m. The method comprises the following specific steps:
step 1, when the device designed by the application starts to work, initializing T w Divided into 32 sections, numbered N from-16 to 15, respectively. The correlation sliding window is 0.5 x T s For stepping, each section sliding window is numbered 1-75000.
Step 2, starting searching from n=0 and p=1, and obtaining T from the transmitting end by the input port 0 To T 0 +T c Time of day transmitting modulation symbols and obtaining T from receiving ADC 0 +T m To T 0 +T m +T c Signal received at moment:
according to the application, the sending modulation symbols and the receiving data can be sequentially written into the external DDR memory according to the sampling time, and only the data of the corresponding address of the DDR is required to be read when the data at the corresponding moment is obtained.
And step 3, correlating the two paths of complex signals, and taking DFT, wherein the operation expression is as follows:
S（k）=∑ n=0 N-1 StSr * exp（-j（2π/N）kn）；
wherein, the liquid crystal display device comprises a liquid crystal display device,Stfor transmitting signed complex signals, sr * For conjugation of the received signal, n= 4096,0.ltoreq.k.ltoreq.n-1.
And step 4, searching the maximum value in the step S, and judging whether the maximum value meets the threshold requirement. If yes, go to step 6, otherwise go to step 5.
And 5, when n=0 and P is less than 75000, p=p+1, and continuing the operations of the step 2, the step 3 and the step 4.
In which Sr is T 0 +T m +0.5*T s *（P-1) to T 0 +T m +T c +0.5*T s * ADC acquisition data at time (P-1), st is T obtained from the sender 0 To T 0 +T c The modulation symbols are transmitted at time instants.
When n=0 and p=75000, n= -1 and p=0, the operations of step 2, step 3 and step 4 are continued.
In which Sr is T 0 +T m +0.5*T s * (P-1) +tp to T 0 +T m +T c +0.5*T s * ADC acquisition data at (P-1) +tp time, st is T obtained from a transmitting end 0 +t p To T 0 +T c +t p The modulation symbols are transmitted at time instants.
When N +.0, p = 75000, N is changed in the order of [0, -1, -2, -3,3 … …, -16] in turn, continuing the operations of step 2, step 3, step 4.
When N > 0, T 0 +T m +0.5×ts (P-1) +n×tw+2×tp to T 0 +T m +T c+ ADC acquisition data at time 0.5 (P-1) +Ntw+2 Ntp, where St is T obtained from the transmitting end 0 +2×tp to T 0 +T c Transmitting a modulation symbol at +2×n×tp;
when N is less than 0, sr is T 0 +T m +0.5×ts (P-1) +n×tw+ (1-2N) ×tp to T 0 +T m +T c+ ADC acquisition data at time 0.5 (P-1) +N+tw+ (1-2N), st is obtained from a transmitting end 0 +2×tp to T 0 +T c Transmitting a modulation symbol at +2×n×tp;
when n= -16 and p=75000, a signal indicating that all time windows cannot be searched currently returns to step 2, T0 is reselected with the current actual time, and a new search round is started.
And 6, recording the current N, P value, obtaining St and Sr values, and calculating the frequency offset through a frequency estimation algorithm.
And 7, outputting a final N, P value and a frequency offset parameter, and ending the search.
The experimental effect after improvement:
in the first experiment, the experimental parameter was that the number of modulation symbols was 1.2M within 30ms of the time window, and the sliding window was stepped by 0.5Ts, so the correlation times were 2.4M.
The data cannot be processed in real time, and the processing time of the 30ms window signal search signal is 1.92s through the interchange principle of the speed and the area of the FPGA. The satellite has a satellite earth velocity of < + -5 m/s with bit timing offset due to satellite Doppler at various processing delays.
In scenario 1, the search time window is 30ms, the signal processing delay is 1920ms, the time offset is 32ns, and the symbol offset is 1.28.
In scenario 2, the search time window is 15ms, the signal processing delay is 960ms, the time offset is 16ns, and the symbol offset is 0.64.
In scenario 3, the search time window is 7.5ms, the signal processing delay is 480ms, the time offset is 8ns, and the symbol offset is 0.32.
In the 4 th scene, the search time window is 30/32ms, the signal processing delay is 60ms, the time offset is 1ns, and the symbol offset is 0.04.
When the time window non-segmentation mode is used, the searched position is the satellite-to-ground delay amount 1.92s ago, and the current actual position and the searched position are maximally offset by 1.28 symbols due to satellite Doppler influence. In subsequent parameter estimation, the parameter may be unable to be estimated.
When time window segmentation is used, for example, taking 32 equal parts, the symbol offset brought by each search is not more than 0.04 symbol, and the offset does not influence the next search. And the next time point of continuous searching is added with t p And thus does not result in an offset accumulation. When the search is completed, the offset is not more than 0.04. Such calculations have little impact on subsequent parameter estimation. It can be seen that the satellite Doppler effect is reduced by a time window segment search.
In a second experiment, the satellite-to-ground delay T was estimated m Is obtained by estimating the approximate position in the capture window T m ±T w In the more closely to T m The greater the probability, and therefore the search position, from T m Starting nearby, rather than from T m －T w Starting. The probability of the temporal distribution within the capture window is assumed to follow a normal distribution, the probability of the distribution of which is shown in the following table.
The distribution of time errors is bilaterally symmetrical, and the average time T from the upper edge to the lower edge is counted 1 And average time T of searching alternately from the middle left and right 2 。
T 1 =tp·∑ 32 n=1 （n*P（n））；
T 2 =tp·（∑ 16 n=1 （（2n-1）*P（17-n）））+∑ 16 n=1 （2n*P（16+n））；
Substituting and calculating to obtain T 1 ≈9.0*tp，T 2 =16.5×tp. It follows that with this search scheme, the search time can be statistically increased.
The preferred embodiments of the present application have been described in detail above, but the present application is not limited to the specific details of the above embodiments, and various equivalent changes can be made to the technical solution of the present application within the scope of the technical concept of the present application, and all the equivalent changes belong to the protection scope of the present application.
Claims (4)
1. A collaborative communication PCMA system signal searching method is characterized by comprising the following steps:
s1, starting a searching device and initializing parameters of the searching device;
s2, dividing the time window into a preset number of time slots, selecting the median value of the preset number of time slots as a signal interval, and collecting data in the signal interval;
s3, performing fast Fourier transform on the data in the signal interval to convert the data into a frequency domain representation;
s4, searching a peak value in the frequency domain representation, judging whether the peak value is larger than a set threshold value, if so, searching is successful, and turning to the step S5, and if so, turning to the step S6;
s5, recording a signal interval when the search is successful, and calculating a frequency offset value through a frequency estimation algorithm;
s6, judging whether the signal interval is the last interval, if so, turning to the step S1, and if not, reselecting the signal interval near the signal interval, collecting data in the reselected signal interval, and turning to the step S3;
the predetermined time window in step S2 is specifically:
s21, collecting sample data of a signal to be searched;
s22, establishing a probability model based on sample data, wherein the probability model is used for describing probability distribution of the occurrence of the signal to be searched in different time windows;
s23, selecting a time window with the maximum occurrence probability as a preferential searching object based on the probability model.
2. The method according to claim 1, wherein the re-selecting signal intervals in the vicinity of the signal interval in step S6 is specifically: a time slot is shifted from the signal interval as a reselected signal interval.
3. The method of claim 1, wherein the predetermined number of slots in step S2 is 32 slots.
4. A cooperative communication PCMA system signal search device, characterized by comprising:
the interval dividing module is used for describing probability distribution of the occurrence of the signal to be searched in different time windows through the constructed probability model, dividing the time windows into a preset number of time slots equally based on the probability model, and selecting the time window with the maximum occurrence probability as a preferential searching object;
the fast Fourier transform module is used for performing fast Fourier transform on the data in the signal interval to convert the data into a frequency domain representation;
the frequency domain searching module searches a peak value in the frequency domain representation, judges whether the peak value is larger than a set threshold value, and if the peak value is larger than the set threshold value, the searching is successful;
and the frequency offset calculation module calculates a frequency offset value through a frequency estimation algorithm in a signal interval when the search is successful.
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| WO2011003263A1 (en) * | 2009-07-06 | 2011-01-13 | 中兴通讯股份有限公司 | Detection method and apparatus based on random access process |
| CN110138698A (en) * | 2019-04-04 | 2019-08-16 | 中国人民解放军战略支援部队信息工程大学 | High order modulation linear hybrid signal frequency deviation first phase combined estimation method and device |
| CN111130683A (en) * | 2019-12-26 | 2020-05-08 | 江苏科大亨芯半导体技术有限公司 | Method and system for searching same-frequency adjacent cells of narrow-band Internet of things |
| CN112039613A (en) * | 2020-08-07 | 2020-12-04 | 中国卫通集团股份有限公司 | Processing method and device for asymmetric PCMA (pulse code division multiple Access) mixed signal |
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| WO2011003263A1 (en) * | 2009-07-06 | 2011-01-13 | 中兴通讯股份有限公司 | Detection method and apparatus based on random access process |
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