CN110311878B - Synchronous detection method for locking state of 16QAM carrier demodulation loop - Google Patents
Synchronous detection method for locking state of 16QAM carrier demodulation loop Download PDFInfo
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- CN110311878B CN110311878B CN201910453865.6A CN201910453865A CN110311878B CN 110311878 B CN110311878 B CN 110311878B CN 201910453865 A CN201910453865 A CN 201910453865A CN 110311878 B CN110311878 B CN 110311878B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/38—Demodulator circuits; Receiver circuits
- H04L27/3818—Demodulator circuits; Receiver circuits using coherent demodulation, i.e. using one or more nominally phase synchronous carriers
Abstract
The invention provides a synchronous detection method for the locking state of a 16QAM carrier demodulation loop, which can obviously improve the accuracy of 16QAM carrier locking indication. The invention is realized by the following technical scheme: the locking state detection module takes a section of data of the 16QAM signals after bit synchronization and carrier synchronization to respectively send the data into the I, Q data storage module, and then respectively sends the data into the self-adaptive threshold adjustment module and the normalized signal high-order moment calculation module; the self-adaptive threshold value adjusting module counts the data distribution number of each constellation point and performs threshold value adjustment in a self-adaptive mode according to the distribution condition; the normalized signal high-order moment calculation module calculates I, Q the normalized high-order moment of I, Q signal output by the data storage module, sends the output measurement value to the comparator to compare with the self-adaptive adjustment threshold value, judges the locking state of the 16QAM carrier loop and outputs the carrier locking indication state.
Description
Technical Field
The invention relates to a method for synchronously detecting the locking state of a 16QAM carrier demodulation loop based on a self-adaptive threshold in the field of wireless communication, in particular to a method for synchronously locking the locking state of the carrier demodulation loop in a 16QAM digital demodulator.
Technical Field
With the continuous development of aviation and aerospace technologies, the exploration and development process of human beings on the outer space is accelerated, the types of satellite effective loads and the types of services carried by the satellite effective loads are more and more, and the amount of information to be transmitted is larger and larger. In order to transmit the information to the ground command center, the data transmission rate is required to be higher and higher. In order to effectively transmit more data in a limited bandwidth channel, various modulation schemes have been developed to solve the contradiction between limited bandwidth and transmission of a large amount of data. The quadrature amplitude modulation QAM is a digital modulation mode combining amplitude and phase, and the QAM modulation mode effectively relieves the bandwidth contradiction of a transmission satellite: in a general digital modulation mode, one code element usually carries lbit information, and amplitude and phase of a modulation signal modulated by QAM both carry information, and as for M-ary QAM, with an increase of M value, the amount of information carried is also increased, for example, one code element in 16QAM carries 4 bits of information, which greatly improves the utilization rate of a channel, so that the QAM modulation mode is widely applied in the fields of satellite communication, deep space communication and mobile communication. Although the number of QAM modulation levels increases and the spectrum has a higher utilization rate, the decrease of the minimum euclidean distance brings about a loss of signal error rate performance, so that the spectrum utilization rate and the signal transmission reliability need to be balanced when the number of QAM modulation levels is selected. Therefore, in order to meet the requirement of high-speed data transmission, the 16QAM modulation mode has a very wide application prospect in future satellite data transmission systems and communication repeater systems.
In a communication system, due to the reasons of the frequency inconsistency of local oscillators at the transmitting end and the receiving end, doppler shift, time-varying characteristics of a channel, and the like, carrier frequency offset and phase offset exist at the transmitting end and the receiving end, which are reflected on a QAM constellation diagram, namely a rotated constellation, and thus the performance of a receiver can be greatly reduced. With the increase of QAM order and the increase of modulation signal constellation points and the increase of signal amplitude, the constellation points become denser and denser, the gain of the phase discriminator becomes larger and larger, the loop bandwidth is reduced, and a small phase error can cause wrong judgment. And the loop bandwidth is reduced, the symbol synchronization convergence time is prolonged, and the loop steady-state error is reduced. Generally, the larger the loop bandwidth, the faster the loop converges, but the larger the range of detected value jitter. In carrier synchronization, two stages of carrier acquisition and carrier tracking are generally required. In the carrier capture stage, a wider bandwidth is expected, and signals with larger frequency deviation can be rapidly captured; the carrier tracking phase is expected to have a narrower bandwidth to reduce the variance of the carrier phase estimate. The carrier locking indication is an important index for judging whether the carrier synchronization loop is in an acquisition stage or a tracking stage, and is one of key technologies of a receiver. The 16QAM receiver is to complete demodulation of the 16QAM signal, and first to complete symbol synchronization, and then complete demodulation of the signal through subsequent modules of equalization, carrier recovery, and the like. The implementation of the symbol synchronization algorithm is therefore a crucial part. The Gardner symbol synchronization algorithm is an asynchronous clock recovery method, a symbol clock is locally generated, a sampling time symbol value is obtained by adopting an interpolation method, and if the Gardner algorithm is directly applied to a 16QAM demodulation system, the timing error detection result is correct in some points and is wrong in some points. For large amounts of data, the average of these errors is zero, since without timing error, the intermediate points may be 0, -1, 1, -2, 2, with an average of zero. These errors can result in jitter in the timing clock.
The traditional lock indication detection method of the MPSK demodulation loop needs to eliminate modulation information first and then carry out lock detection. Similar to the processing method of MPSK, it is also possible to detect whether the carrier loop is locked by removing the modulation information of the 16QAM signal and then comparing with a preset locking indication threshold. However, the biggest disadvantage of this method is that 16QAM is different from QPSK, 8PSK, etc. modulation methods, and the locking threshold of 16QAM signal will be affected by the distribution of signal constellation points. When the constellation points of the input signal do not obey uniform distribution, the locking threshold of the 16QAM carrier synchronization locking detection method is greatly different from the locking threshold when the constellation points obey uniform distribution, and the decision failure may occur. In engineering applications such as aerospace measurement and control, satellite application, high-speed data transmission and the like, both a user and a receiver loop need to accurately know the current carrier synchronization locking state of the receiver so as to perform accurate operation.
Disclosure of Invention
The invention aims to overcome the defect that the traditional 16QAM carrier synchronization locking detection method possibly generates judgment failure when constellation points of input signals are not uniformly distributed, and provides a 16QAM carrier demodulation loop locking state synchronization detection method which has a simpler circuit structure, high carrier locking indication accuracy and is easy to realize on a digital domain and based on an adaptive threshold.
The above object of the present invention can be achieved by the following measures, wherein the method for synchronously detecting the locked state of the 16QAM carrier demodulation loop has the following technical characteristics: a locking state detection module of a carrier loop is constructed in a 16QAM demodulation module, the input of the locking state detection module is a 16QAM signal after carrier synchronization and bit synchronization are completed, a section of data of the 16QAM signal after bit synchronization and carrier synchronization is respectively sent into an I, Q data storage module, and then the data is respectively sent into an adaptive threshold value adjustment module and a normalized signal high-order moment calculation module; the self-adaptive threshold adjusting module counts the data distribution number of each constellation point and dynamically adjusts the threshold according to the distribution condition of each constellation point; the carrier synchronization locking detection loop compares the calculated value of the normalized high-order moment with the threshold value output by the threshold value adjusting module at each moment, the normalized signal high-order moment calculating module calculates I, Q the normalized high-order moment of the I, Q signal output by the data storage module, averages the normalized high-order moment, sends the output measurement value into the comparator, compares the output measurement value with the locking threshold value output by the adaptive threshold value adjuster, judges that the carrier loop is locked when the calculated high-order moment value is smaller than the detection threshold value, otherwise judges that the carrier loop is unlocked, and outputs the carrier locking state indication; and resetting the phase-locked loop when the carrier loop synchronous locking indication judges that the lock is lost.
Compared with the prior art, the invention has the following beneficial effects:
the circuit structure is simpler. The invention constructs a locking state detection module of a carrier loop locking detector in a 16QAM demodulation module, the locking state detection module takes a section of data of a 16QAM signal after bit synchronization and carrier synchronization and respectively sends the data to an I, Q data storage module, and then respectively sends the data to an adaptive threshold value adjusting module and a normalized signal high-order moment calculating module; by calculating the normalized high-order moment of the input signal, the influence of the change of the input amplitude of the traditional algorithm signal on the judgment is eliminated. The method utilizes the statistical characteristic of the 16QAM signal to dynamically adjust the locking decision threshold value, thereby carrying out the synchronous locking of the 16QAM carrier loop, compared with the prior art that the digital synchronous loop is used for adjusting the AD sampling clock in a feedback mode, the circuit structure is simpler. By calculating the normalized high-order moment of the input signal and the dynamic calculation judgment threshold, the calculation is simple and reliable, the locking threshold can be adaptively adjusted according to the statistical characteristics of the input data, and the condition that the judgment of different input data is invalid by the traditional threshold selection method is avoided. And is convenient for the realization of FPGA and DSP engineering.
The carrier locking indication accuracy is high. The invention adopts a self-adaptive threshold value adjusting module to count the data distribution number of each constellation point, and dynamically adjusts the threshold value according to the distribution condition of each constellation point. The method has the advantages that the 16QAM signal constellation points are counted, the threshold value of the locking judgment is adjusted in real time, and the influence of non-uniform distribution of input signals on the judgment threshold value is eliminated by calculating the statistical characteristics of the input signals. The self-adaptive threshold adjusting module dynamically adjusts the locking decision comparison threshold in real time, realizes the locking synchronization of the 16QAM carrier, can eliminate the influence of the non-uniform distribution of the input signal on the decision threshold, and improves the robustness of the locking indication decision. The constellation diagram has small jitter and quick synchronization time, and improves the accuracy of the 16QAM carrier locking indication.
The invention judges whether the 16QAM carrier loop is locked or not by comparing the normalized high-order moment of the output signal of the carrier loop with the threshold value of dynamic calculation, and is suitable for the carrier locking detection of 16QAM demodulation under various environments.
Drawings
For a more clear understanding of the present invention, the invention will now be described by reference to the accompanying drawings, in which:
fig. 1 is a schematic diagram of the circuit principle of the adaptive threshold based 16QAM carrier lock detection of the present invention.
Fig. 2 is a schematic diagram of mapping points and decision of a 16QAM constellation according to the present invention.
FIG. 3 is different in the case of no noise
Scale the lock detector of the present invention outputs the desired plot.
The following will describe the present invention in further detail with reference to the accompanying drawings.
Detailed Description
See fig. 1. According to the invention, a locking state detection module of a carrier loop locking detector is constructed in a 16QAM demodulation module, the input of the locking state detection module is a 16QAM signal after carrier synchronization and bit synchronization are completed, a section of data of the 16QAM signal after bit synchronization and carrier synchronization is respectively sent into an I, Q data storage module, and then the data is respectively sent into an adaptive threshold value adjustment module and a normalized signal high-order moment calculation module; the self-adaptive threshold adjusting module counts the data distribution number of each constellation point and dynamically adjusts the threshold according to the distribution condition of each constellation point; the carrier synchronization locking detection loop compares the calculated value of the normalized high-order moment with the threshold value output by the threshold value adjusting module at each moment, the normalized signal high-order moment calculating module calculates I, Q the normalized high-order moment of the I, Q signal output by the data storage module, averages the normalized high-order moment, sends the output measurement value into the comparator, compares the output measurement value with the locking threshold value output by the adaptive threshold value adjuster, judges that the carrier loop is locked when the calculated high-order moment value is smaller than the detection threshold value, otherwise judges that the carrier loop is unlocked, and outputs the carrier locking state indication; and resetting the phase-locked loop when the carrier loop synchronous locking indication judges that the lock is lost.
In an optional embodiment, the carrier loop locking detector includes an I-path data storage module and a Q-path data storage module connected to the adaptive threshold adjustment module, and an I-path data and Q-path data normalized signal high-order moment calculation module, where the I-path data and Q-path data normalized signal high-order moment calculation module is connected to the adaptive threshold adjustment module, and the adaptive threshold adjustment module includes a 16QAM decision device module and a data statistical characteristic calculation module and a threshold adjustment module, where the 16QAM decision device module and the 16QAM decision device module are sequentially connected in series, and a comparator for comparing an output of the adaptive threshold adjustment module with an output of the normalized signal high-order moment calculation module. Wherein the I, Q data storage module stores 16QAM demodulated signals for a period of time, typically 16384 demodulation points can be taken. The decision device module carries out constellation point decision on the 16QAM signal of the input module, then the constellation point decision is sent to the back-end data statistical characteristic calculation module to count the data distribution number of each constellation point, and the threshold value is dynamically adjusted according to the distribution condition of each constellation point. The normalized signal high-order moment calculation module calculates I, Q the normalized high-order moment of I, Q signal output by the data storage module, firstly calculates 4 power of signal, eliminates the modulation information of 16QAM signal, then calculates the average value after normalizing,then the calculation formula of the normalized signal high order moment can be obtained:
where N represents the total number of points, IkIs the real part of the kth input point, QkIs the imaginary part of the kth input point, ykRepresenting the kth group of inputs Ik、QkRe represents the operation of taking the real part of the complex signal.
The locking state detection module sends the 16QAM signal which completes carrier synchronization and bit synchronization to the 16QAM carrier locking detection module based on the adaptive threshold, and the input signal firstly takes 16384 data through the I, Q data storage module and respectively sends the data to the normalization signal high-order moment calculation module and the adaptive threshold adjustment module at the rear end. In a normalized signal high-order moment calculation module, the normalized high-order moment of the input signal is defined and calculated through the normalized high-order moment; meanwhile, the input signal sent to the self-adaptive threshold adjusting module is firstly subjected to constellation point judgment through a 16QAM (Quadrature amplitude modulation) judgment device, then sent to a data statistical characteristic calculating module for constellation point statistics, and the number N of the 16QAM data on 45 DEG, 135 DEG, 225 DEG and 315 DEG phase constellation points is respectively counted1Number N of 16QAM data on phase constellation points of non-45 DEG, 135 DEG, 225 DEG and 315 DEG2Then sending the statistical result into a threshold value adjusting module, in the adaptive threshold value adjusting module, the 16QAM signal sent into the adaptive threshold value adjusting module firstly carries out constellation point judgment, judges which constellation position each data point is at, and then respectively counts the data number N on the 45 DEG, 135 DEG, 225 DEG and 315 DEG phase constellation points1Number N of 16QAM data on phase constellation points of non-45 DEG, 135 DEG, 225 DEG and 315 DEG2Dynamically calculating a lock threshold value according to
By passing
Calculating the threshold value, and using the value and self-adaptation calculated by the normalized signal high-order moment calculation moduleComparing the threshold values output by the threshold value adjusting module, and judging that the carrier loop is locked when the calculated high-order moment value is smaller than the detection threshold value; otherwise, the carrier loop is judged to be out of lock.
See fig. 2. In an optional embodiment, the 16QAM signal uses a real part I and an imaginary part Q as a rectangular coordinate system, divides k input 16QAM constellation mapping points into constellation maps equally distributed as four quadrants of the rectangular coordinate system, sends the input 16QAM signal to a 16QAM decision module for constellation point decision, calculates the euclidean distance between the input signal and each corresponding constellation point, and determines which constellation point the data is located at if the euclidean distance is the minimum with which constellation point.
See fig. 3. Under the condition that constellation points are distributed in different conditions and noise interference does not exist, the constellation points are different under the noise-free condition
When the 16QAM is locked, the locking measurement value calculated by using the signal normalized high-order moment is shown in the figure, and when the 16QAM signals are all distributed at the phases of 45 degrees, 135 degrees, 225 degrees and 315 degrees, the locking value is-1; when the 16QAM signals are all distributed at phases other than 45 °, 135 °, 225 °, 315 °, the lock value is 0.28. Therefore, the method for synchronously detecting the locking state of the 16QAM carrier demodulation loop based on the self-adaptive threshold can eliminate the influence of non-uniform distribution of input signals on the decision threshold and improve the robustness of the locking indication decision.
What has been described above is merely a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, variations and modifications can be made without departing from the principle of the present invention, for example, by adjusting the actual structure and by extending to other application platforms in other system fields, and such changes and modifications should be construed as falling within the protection scope of the present invention.
Claims (5)
1. A synchronous detection method for 16QAM carrier demodulation loop locking state has the following technical characteristics: establishing a carrier loop lock state in a 16QAM demodulation moduleThe detection module inputs 16QAM signals after carrier synchronization and bit synchronization, the 16QAM signals after the bit synchronization and the carrier synchronization are respectively sent to the I, Q data storage module by taking a section of data, the 16QAM signals after the carrier synchronization and the bit synchronization are sent to the 16QAM carrier locking detection module based on the adaptive threshold value by the locking state detection module, 16384 data of the input signals are respectively sent to the normalization signal high-order moment calculation module and the adaptive threshold value adjustment module at the rear end by the I, Q data storage module, the normalization signal high-order moment calculation module defines the normalization high-order moment of the input signals by the normalization high-order moment, calculates the normalization high-order moment of the I, Q signals output by the I, Q data storage module, calculates the 4 power of the I, Q signals, eliminates the modulation information of the 16QAM signals, averages the 16QAM signals after normalization, obtaining a calculation formula of the high-order moment of the normalized signal:
meanwhile, the input signal is subjected to constellation point judgment through a 16QAM (Quadrature amplitude modulation) judgment device, then the input signal is sent to a data statistical characteristic calculation module to be subjected to constellation point statistics, and the number N of the 16QAM data on 45 DEG, 135 DEG, 225 DEG and 315 DEG phase constellation points is respectively counted1Number N of 16QAM data on phase constellation points of non-45 DEG, 135 DEG, 225 DEG and 315 DEG2The self-adaptive threshold adjusting module counts the data distribution number of each constellation point and dynamically adjusts the threshold according to the distribution condition of each constellation point; the 16QAM signal carries out constellation point judgment through an adaptive threshold value adjusting module, judges the constellation position of each data point, and respectively counts the data number N on 45 DEG, 135 DEG, 225 DEG and 315 DEG phase constellation points1Number N of 16QAM data on phase constellation points of non-45 DEG, 135 DEG, 225 DEG and 315 DEG2Dynamically calculating a lock threshold according to:
by passing
Calculating the size of a threshold, comparing the value calculated by the normalized signal high-order moment calculation module with the threshold output by the self-adaptive threshold adjustment module, and judging that the carrier loop is locked when the calculated high-order moment value is smaller than the detection threshold, otherwise, judging that the carrier loop is lost; the carrier-locked synchronous locking detection loop compares the calculated normalized high-order moment value with the threshold value output by the threshold value adjusting module at each moment, the normalized signal high-order moment calculating module calculates I, Q the normalized high-order moment of the I, Q signal output by the data storage module, the output measurement value is sent to the comparator, the output measurement value is compared with the locking threshold value output by the self-adaptive threshold value adjuster, when the calculated high-order moment value is smaller than the detection threshold value, the carrier loop is judged to be locked, otherwise, the carrier loop is judged to be unlocked, when the carrier loop synchronous locking indication judges to be unlocked, the phase-locked loop is reset, wherein N represents the total number of points, I represents the total number of points, andkis the real part of the kth input point, QkIs the imaginary part of the kth input point, ykRepresenting the kth group of inputs Ik、QkRe represents the operation of taking the real part of the complex signal.
2. The method of claim 1, wherein the method comprises: the carrier loop locking detector comprises an I-path data storage module, a Q-path data storage module, an I-path data and Q-path data normalization signal high-order moment calculation module and a comparator, wherein the I-path data storage module and the Q-path data storage module are connected with the adaptive threshold adjusting module, and the comparator compares the output of the adaptive threshold adjusting module with the output of the normalization signal high-order moment calculation module.
3. The method of claim 2, wherein the method comprises: the connection self-adaptive threshold adjusting module comprises a 16QAM decision device module and a data statistical characteristic calculating module and a threshold adjusting module, wherein the 16QAM decision device module is connected with the output ends of the I-path data storage module and the Q-path data storage module, and the 16QAM decision device module and the threshold adjusting module are sequentially connected in series.
4. The method of claim 1, wherein the method comprises: the 16QAM signal takes a real part I and an imaginary part Q as a rectangular coordinate system, k input 16QAM constellation mapping points are divided into constellation diagrams which are equally distributed according to four quadrants of the rectangular coordinate system, the input 16QAM signal is sent to a 16QAM decision module to carry out constellation point decision, the Euclidean distance between the input signal and each corresponding constellation point is calculated, and the Euclidean distance between the input signal and which constellation point is the minimum, and the data is judged to be located at which constellation point.
5. The method of claim 4, wherein the method for detecting the synchronization of the locked state of the 16QAM carrier demodulation loop comprises: under the condition that constellation points are distributed in different conditions and noise interference does not exist, the constellation points are different under the noise-free condition
When the 16QAM is locked, a locking metric value calculated by using the signal normalized high-order moment is used, and when the 16QAM signals are all distributed at the phases of 45 degrees, 135 degrees, 225 degrees and 315 degrees, the locking value is-1; when the 16QAM signals are all distributed at phases other than 45 °, 135 °, 225 °, 315 °, the lock value is 0.28.
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