CN116961817A - AIS signal frame synchronization method, AIS signal frame synchronization device, AIS signal frame synchronization equipment and storage medium - Google Patents
AIS signal frame synchronization method, AIS signal frame synchronization device, AIS signal frame synchronization equipment and storage medium Download PDFInfo
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Abstract
The invention discloses an AIS signal frame synchronization method, an AIS signal frame synchronization device, AIS signal frame synchronization equipment and a storage medium, wherein the AIS signal frame synchronization method comprises the following steps: receiving a complex baseband signal, and performing differential conversion processing on the complex baseband signal to obtain a first differential conversion result; sending the first differential transformation result into a set time window, carrying out differential energy detection on the first differential transformation result, and determining the detected maximum window energy as a decision reference threshold; modulating and performing differential transformation on the local training sequence to obtain a second differential transformation result; and performing cross-correlation calculation processing on the first differential transformation result and the second differential transformation result, and determining a frame synchronization identification point of the complex baseband signal according to the decision reference threshold and the cross-correlation calculation result. According to the AIS signal frame synchronization method disclosed by the invention, the decision reference threshold is determined according to the differential energy detection result after differential transformation of the received signal, and a self-adaptive decision threshold is provided for peak value determination of the subsequent cross-correlation calculation result, so that the sensitivity of frame synchronization is improved.
Description
Technical Field
The present invention relates to the field of digital communications technologies, and in particular, to an AIS signal frame synchronization method, apparatus, device, and storage medium.
Background
Synchronization techniques are very important in digital communication systems, and in general, digital communication systems need to implement multiple synchronization functions to achieve correct data communication tasks. Synchronization in communication systems can be divided into carrier synchronization, bit synchronization, frame synchronization, and network synchronization. Wherein frame synchronization is to find the arrival of a frame, or the beginning of a frame, for separating different frames. For time division multiplexing signals, to correctly distinguish each signal at the receiving end, as the transmitting end should first add some special codes to the head or tail of the information stream to make distinguishing marks so that the receiving end can correctly distinguish the information, then the process of acquiring and distinguishing the information streams at the receiving end is called frame synchronization.
The automatic identification system (Automatic Identification System, AIS) is a novel navigation aid system integrating marine vessel identification, safety monitoring and communication navigation functions between vessels and base stations. Because the AIS receiving and transmitting system has the characteristics of larger channel time variation, larger Doppler frequency offset, large-range time delay and the like, the received AIS signal demodulation judgment error is caused, and the error rate is high, so that high-sensitivity synchronous timing and signal-to-noise ratio estimation is required.
The traditional AIS signal synchronization timing method comprises an energy detection method, a correlation detection method, a maximum likelihood method and the like, but the energy detection method has poor noise resistance, the correlation detection method needs to finish carrier synchronization before frame synchronization, and the maximum likelihood method has high algorithm complexity, strict requirement on channel estimation and difficult engineering realization. In engineering implementation, the method generally needs to set a decision threshold of a correlation peak value in advance, and if the power of a transmitter changes, a channel fades, a frequency offset changes greatly and the like, the decision condition also changes accordingly, and the fixed decision threshold value can cause the problems of inaccurate synchronization timing, high false alarm rate and the like.
Disclosure of Invention
The invention provides an AIS signal frame synchronization method, an AIS signal frame synchronization device, AIS signal frame synchronization equipment and a storage medium, so as to accurately synchronize and time AIS signals.
According to an aspect of the present invention, there is provided an AIS signal frame synchronization method, including:
receiving a complex baseband signal, and performing differential conversion processing on the complex baseband signal to obtain a first differential conversion result;
sending the first differential transformation result into a set time window, carrying out differential energy detection on the first differential transformation result, and determining the detected maximum window energy as a decision reference threshold;
Modulating and performing differential transformation on the local training sequence to obtain a second differential transformation result;
and performing cross-correlation calculation processing on the first differential transformation result and the second differential transformation result, and determining a frame synchronization identification point of the complex baseband signal according to the decision reference threshold and the cross-correlation calculation result.
Further, the time window comprises a first time window and a second time window, the first time window and the second time window are connected in front and back, and the number of window symbols is consistent with the number of symbols of the initial buffer zone of the complex baseband signal.
Further, performing differential energy detection on the first differential transformation result, including:
at each sampling instant, determining a first window energy of the first time window and a second window energy of the second time window respectively;
if the continuous set times of the energy of the first window are larger than the energy of the second window, determining the last sampling time as a signal energy stabilizing time; wherein the set times are equal to the number of window symbols of each time window;
and taking the first window energy of the signal energy stabilizing moment as the maximum window energy.
Further, after determining the signal energy stabilization moment, the method further comprises:
and determining the ratio of the first window energy and the second window energy at the moment of stabilizing the signal energy as the signal-to-noise ratio estimated value of the complex baseband signal.
Further, determining a frame synchronization identification point of the complex baseband signal according to the decision reference threshold and a cross-correlation calculation result comprises:
performing peak detection on the cross-correlation calculation result according to the decision reference threshold value to obtain a target peak value;
and determining the signal position corresponding to the target peak value as a frame synchronization identification point of the complex baseband signal.
Further, performing peak detection on the cross-correlation calculation result according to the decision reference threshold to obtain a target peak value, including:
determining a final decision threshold according to the decision reference threshold;
comparing the cross-correlation calculation result of each sampling time with the cross-correlation calculation results of the front and rear adjacent times;
and taking the cross-correlation calculation result which is larger than the cross-correlation calculation result of the adjacent time and the final judgment threshold value as the target peak value.
Further, determining a final decision threshold from the decision reference threshold includes:
Acquiring a judgment threshold coefficient;
and determining the product of the decision reference threshold and the decision threshold coefficient as the final decision threshold.
According to another aspect of the present invention, there is provided an AIS signal frame synchronization apparatus comprising:
the first differential conversion module is used for receiving the complex baseband signal, and carrying out differential conversion processing on the complex baseband signal to obtain a first differential conversion result;
the decision reference threshold determining module is used for sending the first differential transformation result into a set time window, detecting differential energy of the first differential transformation result, and determining the detected maximum window energy as a decision reference threshold;
the second differential transformation module is used for modulating and carrying out differential transformation processing on the local training sequence to obtain a second differential transformation result;
and the frame synchronization identification point determining module is used for performing cross-correlation calculation processing on the first differential transformation result and the second differential transformation result, and determining the frame synchronization identification point of the complex baseband signal according to the decision reference threshold and the cross-correlation calculation result.
Optionally, the time window includes a first time window and a second time window, where the first time window and the second time window are connected front and back, and the number of window symbols is consistent with the number of symbols in the initial buffer of the complex baseband signal.
Optionally, the decision reference threshold determining module is further configured to:
at each sampling instant, determining a first window energy of the first time window and a second window energy of the second time window respectively;
if the continuous set times of the energy of the first window are larger than the energy of the second window, determining the last sampling time as a signal energy stabilizing time; wherein the set times are equal to the number of window symbols of each time window;
and taking the first window energy of the signal energy stabilizing moment as the maximum window energy.
Optionally, the apparatus further includes a signal-to-noise ratio determining module, configured to determine a ratio of the first window energy and the second window energy at the time of the signal energy stabilization as a signal-to-noise ratio estimated value of the complex baseband signal.
Optionally, the frame synchronization identification point determining module is further configured to:
performing peak detection on the cross-correlation calculation result according to the decision reference threshold value to obtain a target peak value;
and determining the signal position corresponding to the target peak value as a frame synchronization identification point of the complex baseband signal.
Optionally, the frame synchronization identification point determining module is further configured to:
determining a final decision threshold according to the decision reference threshold;
Comparing the cross-correlation calculation result of each sampling time with the cross-correlation calculation results of the front and rear adjacent times;
and taking the cross-correlation calculation result which is larger than the cross-correlation calculation result of the adjacent time and the final judgment threshold value as the target peak value.
Optionally, the frame synchronization identification point determining module is further configured to:
acquiring a judgment threshold coefficient;
and determining the product of the decision reference threshold and the decision threshold coefficient as the final decision threshold.
According to another aspect of the present invention, there is provided an electronic apparatus including:
at least one processor; and
a memory communicatively coupled to the at least one processor; wherein, the liquid crystal display device comprises a liquid crystal display device,
the memory stores a computer program executable by the at least one processor to enable the at least one processor to perform the AIS signal frame synchronization method according to any one of the embodiments of the invention.
According to another aspect of the present invention, there is provided a computer readable storage medium storing computer instructions for causing a processor to implement the AIS signal frame synchronization method according to any one of the embodiments of the present invention when executed.
The invention discloses an AIS signal frame synchronization method, which comprises the steps of firstly receiving a complex baseband signal, and performing differential modulation conversion processing on the complex baseband signal to obtain a first differential conversion result; then sending the first differential transformation result into a set time window, carrying out differential energy detection on the first differential transformation result, and determining the detected maximum window energy as a decision reference threshold; modulating and performing differential transformation on the local training sequence to obtain a second differential transformation result; and finally, carrying out cross-correlation calculation processing on the first differential transformation result and the second differential transformation result, and determining the frame synchronization identification point of the complex baseband signal according to the decision reference threshold and the cross-correlation calculation result. According to the AIS signal frame synchronization method disclosed by the invention, the decision reference threshold is determined according to the differential energy detection result after differential transformation of the received signal, and the self-adaptive decision threshold is provided for peak value determination of the subsequent cross-correlation calculation result, so that the sensitivity of frame synchronization is improved, and the influence of external channel variation is avoided. And the synchronization method for carrying out cross-correlation calculation on the received signal and the local training sequence modulation signal and then searching the peak value is simple to realize, low in operand and small in influence of frequency offset.
It should be understood that the description in this section is not intended to identify key or critical features of the embodiments of the invention or to delineate the scope of the invention. Other features of the present invention will become apparent from the description that follows.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flowchart of an AIS signal frame synchronization method according to a first embodiment of the invention;
FIG. 2 is a schematic diagram of a burst slot structure of an AIS standard protocol according to a first embodiment of the present invention;
fig. 3 is a schematic diagram of a differential conversion process of a complex baseband signal according to a first embodiment of the present invention;
fig. 4 is a schematic diagram of a modulation procedure of a local training sequence according to a first embodiment of the present invention;
FIG. 5 is a schematic diagram of a cross-correlation process according to a first embodiment of the present invention;
Fig. 6 is a flowchart of an AIS signal frame synchronization method according to a second embodiment of the invention;
FIG. 7 is a diagram of a window energy variation provided in accordance with a second embodiment of the present invention;
FIG. 8 is a schematic diagram of a frame synchronization simulation result according to a second embodiment of the present invention;
fig. 9 is a schematic structural diagram of an AIS signal frame synchronization device according to a third embodiment of the invention;
fig. 10 is a schematic structural diagram of an electronic device implementing the AIS signal frame synchronization method according to the fourth embodiment of the invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Example 1
Fig. 1 is a flowchart of an AIS signal frame synchronization method according to an embodiment of the present invention, where the embodiment is applicable to a case of performing synchronization timing in digital communication, and the method may be applied to an AIS signal frame synchronization device, where the device may be implemented in a form of hardware and/or software, and where the device may be configured in an electronic device. As shown in fig. 1, the method includes:
s110, receiving the complex baseband signal, and performing differential conversion processing on the complex baseband signal to obtain a first differential conversion result.
The complex baseband signal is obtained by sampling a GMSK (Gaussian minimum shift keying, gaussian Filtered Minimum Shift Keying) signal received by an AIS (Automatic Identification System, automatic ship identification system) receiver from an antenna through an ADC (analog to digital converter) after passing through a radio frequency channel, and performing DDC down-conversion and filtering.
In this embodiment, the AIS is a novel navigation aid system integrating functions of marine vessel identification, safety monitoring and communication navigation between a vessel and a base station, and is composed of a shore-based receiving facility, a satellite-based receiving facility and shipborne equipment, and a slipway provided with the AIS equipment can automatically broadcast relevant information such as dynamic information, static information, voyage information and the like of the vessel to other vessels and base stations, so that the navigation condition of the vessels in the nearby sea area is mastered. According to the standard protocol of the AIS, the burst slot structure is shown in fig. 2, and is composed of a start buffer, a training sequence, a start flag, information bits, a frame detection sequence, an end flag and an end buffer.
Optionally, the AIS receiver receives GMSK signals from the antenna, performs ADC sampling on the GMSK signals after passing through the radio frequency channel, performs DDC down-conversion and filtering processing to obtain complex baseband signals, and then performs differential conversion on the complex baseband signals. Differential transformation is a commonly used method of signal processing, by which signals can be converted into another form for better analysis and processing. For the complex baseband signal obtained in this step, differential transformation can be completed by a method of shifting left and right by half symbol periods, respectively, and then performing conjugate multiplication. Where symbol period (i.e., symbol width) refers to the time width occupied by the transmission symbol.
Wherein, the expression of the complex baseband signal is as follows:
wherein n is the sampling time, T s For sampling time interval, Φ 0 For the initial phase, the range of values is [ -pi, pi]，Φ s Delta as instantaneous phase f For carrier frequency offset, r (n) is the obtained complex baseband signal, and z (n) is noise.
Fig. 3 is a schematic diagram of a differential conversion process of a complex baseband signal according to an embodiment of the present invention, where as shown in the drawing, a complex baseband signal r (n) is shifted left and right by half a symbol period, and then conjugate multiplication is performed to obtain a first differential conversion result as follows:
Wherein T is the code element period, n is the sampling time, T s For sampling time interval r * Is the conjugate of r.
And S120, sending the first differential transformation result into a set time window, carrying out differential energy detection on the first differential transformation result, and determining the detected maximum window energy as a decision reference threshold.
The time window is a set time period, the differential energy detection is to detect the signal energy in the time window, and the maximum window energy is the signal energy maximum value corresponding to the time window.
In this embodiment, for a standard protocol signal in AIS communication, in the differential energy detection process, from the start buffer of the signal, as the signal gradually enters a time window, the window energy gradually becomes larger until the signal energy stabilizes, the signal completely enters, and the window energy reaches a maximum value.
Optionally, the signal after differential transformation, that is, the first differential transformation result is sent to a set time window, differential energy detection is performed on the time window, and the detected maximum window energy is determined as a decision reference threshold value, so that the method can be used for judging the frame synchronization identification point in the subsequent step. In order to avoid the influence of burst noise, a sliding window moving recursion summation method can be used for window difference energy detection, and the basic principle is that at each sampling time n, a new value is added in the summation, and an old value is discarded. The following is the calculation of this moving recursive summation:
Wherein l is the number of window symbols in the time window, e n For decision variables, the cumulative sum of the received signal energy at the number of window symbols, i, is expressed as:
when n is the stable moment of signal energy, E n+1 I.e. the maximum window energy required in this step.
S130, modulating and differential converting the local training sequence to obtain a second differential conversion result.
Where the local training sequence is a known symbol (at the head of a frame) preceding the transmitted data frame, and may be used for time and frequency synchronization and channel estimation at the receiving end, the processing acts in the time domain, typically in the form of one or more consecutive symbols.
In this embodiment, the local training sequence may be a constant 0,1 alternating sequence, and may be subjected to NRZI (No Return to Zero Inverted-reverse non-return-to-zero) encoding first and then GMSK modulation mapping, where the signal expression of the modulation signal of the local training sequence is as follows:
wherein T is time, n is sampling time, h is modulation index, GMSK takes 1/2, L is symbol correlation length, q (T) represents phase shaping function of Gaussian filter, T is symbol period, a i Represents the sequence of 0,1 alternating sequence after NRZI coding.
Fig. 4 is a schematic diagram of a modulation process of a local training sequence according to an embodiment of the present invention, where the local training sequence is subjected to NRZI coding and GMSK modulation to obtain a corresponding modulation signal as shown in the figure. The GMSK modulation step comprises Gaussian filtering and phase integration, and an in-phase component and a quadrature component obtained after the phase integration are added to obtain a modulation signal pream (t) of a local training sequence.
Then, the pream (t) is shifted left and right by half a code element period respectively, and conjugate multiplication is carried out to obtain a second differential transformation result as follows:
wherein T is symbol period, T s For sampling time intervals, pream * Is the conjugation of pream.
And S140, performing cross-correlation calculation processing on the first differential transformation result and the second differential transformation result, and determining a frame synchronization identification point of the complex baseband signal according to the decision reference threshold and the cross-correlation calculation result.
The meaning of the cross-correlation of the two functions is: the complex conjugate and inverse translation are integrated infinitely by multiplying the two functions, respectively. Physically, the result of the cross-correlation operation reflects a measure of similarity between the two signals. The frame synchronization mark point is the position where the frame synchronization mark is located, and the frame synchronization mark is a mark for starting the useful signal, and is used for indicating that the position is followed by a bit containing useful information in the signal.
In this embodiment, after the first differential conversion result and the second differential conversion result after differential conversion of the received complex baseband signal and the local training sequence are obtained, a calculated value of each sampling moment can be obtained through cross-correlation operation, then, peak values in the calculated values of the cross-correlations are compared, and auxiliary judgment is performed according to a decision reference threshold value, so that a target peak value in the calculated values is obtained, and a signal position corresponding to the target peak value, namely, a frame synchronization identification point.
Fig. 5 is a schematic diagram of a cross-correlation process provided in the embodiment of the present invention, where, as shown in the drawing, after differential transformation is performed on a modulation signal of a local training sequence and a received complex baseband signal, the cross-correlation calculation is performed on the results of the two differential transformations, and then a target peak value in each cross-correlation calculation value is found.
Optionally, the first differential transformation result Δ obtained according to equation (2) rr (n) and a second differential transformation result delta obtained according to formula (6) pream (n) performing cross-correlation calculation and writing into a convolution form as follows:
in the method, in the process of the invention,the cross-correlation calculation result at the sampling time n is shown.
Preferably, the calculation result value may be calculatedAs a reference point, if->Is greater than->And is also greater than- >At the same time->And is also greater than the decision reference threshold, so that the starting point of the signal is n-1, namely, the signal position corresponding to the n-1 sampling moment is determined as the frame synchronization identification point of the complex baseband signal.
The invention discloses an AIS signal frame synchronization method, which comprises the steps of firstly receiving a complex baseband signal, and performing differential conversion processing on the complex baseband signal to obtain a first differential conversion result; then sending the first differential transformation result into a set time window, carrying out differential energy detection on the first differential transformation result, and determining the detected maximum window energy as a decision reference threshold; modulating and performing differential transformation on the local training sequence to obtain a second differential transformation result; and finally, carrying out cross-correlation calculation processing on the first differential transformation result and the second differential transformation result, and determining the frame synchronization identification point of the complex baseband signal according to the decision reference threshold and the cross-correlation calculation result. According to the AIS signal frame synchronization method disclosed by the invention, the decision reference threshold is determined according to the differential energy detection result after differential transformation of the received signal, and the self-adaptive decision threshold is provided for peak value determination of the subsequent cross-correlation calculation result, so that the sensitivity of frame synchronization is improved, and the influence of external channel variation is avoided. And the synchronization method for carrying out cross-correlation calculation on the received signal and the local training sequence and then searching the peak value is simple to realize, low in operand and less affected by frequency offset.
Example two
Fig. 6 is a flowchart of an AIS signal frame synchronization method according to a second embodiment of the present invention, where the method may be applied to an AIS signal frame synchronization device, and this embodiment is a refinement of the foregoing embodiment. As shown in fig. 6, the method includes:
s210, receiving the complex baseband signal, and performing differential conversion processing on the complex baseband signal to obtain a first differential conversion result.
In this embodiment, the AIS system receives GMSK signals through a receiver antenna, performs ADC sampling on the GMSK signals after passing through a radio frequency channel, performs DDC down-conversion and filtering processing to obtain complex baseband signals, and then performs differential conversion on the complex baseband signals. Differential transformation is a commonly used method of signal processing, by which signals can be converted into another form for better analysis and processing. For the complex baseband signal obtained in this step, differential transformation can be completed by a method of shifting left and right by half symbol periods, respectively, and then performing conjugate multiplication. Where symbol period (i.e., symbol width) refers to the time width occupied by the transmission symbol. The signal expression of the first differential transformation result may be as shown in formula (2) in the above-described embodiment.
S220, sending the first differential transformation result into a set time window, and respectively determining the first window energy of the first time window and the second window energy of the second time window at each sampling moment.
The time window comprises a first time window and a second time window, the first time window and the second time window are connected in front of and behind, and the number of window symbols is consistent with the number of symbols of a starting buffer zone of the complex baseband signal.
In this embodiment, in order to obtain more accurate maximum window energy, a manner of performing packet differential energy detection by using a dual sliding window may be adopted, that is, two consecutive time windows, i.e., a first time window and a second time window, are set, the lengths of the two time windows are equal, the number of signal symbols included in the windows, i.e., the number of window symbols, is also equal, and the number of symbols in the initial buffer of the complex baseband signal is set. For example, if the starting buffer length is 8 bits, the oversampling multiple is 4, and the number of symbols in the starting buffer is 32, the number of window symbols in each window is 32.
Alternatively, packet detection is an approximate estimate of the start of a data packet, i.e. whether new data arrives on the channel in burst mode, and when no data packet arrives, the signal r is received n Of only noise, i.e. r n ＝z n The method comprises the steps of carrying out a first treatment on the surface of the And when a data packet arrives, the signal r is received n Adding the component s of the data signal n I.e. r n ＝s n +z n . Thus, the first window energy and the second window energy can be determined separately, and packet detection can be performed based on the change in the received signal energy value.
And S230, if the continuous set times of the energy of the first window are larger than the energy of the second window, determining the last sampling time as the signal energy stabilizing time.
Wherein, the set times is equal to the number of window symbols of each time window.
In this embodiment, since the first time window and the second time window are in a front-to-back adjacent relationship, the signal will first enter the first time window and then enter the second time window, and the number of symbols in the window is consistent with the number of symbols in the initial buffer zone of the complex baseband signal, so that the energy of the first window gradually increases before the signal energy stabilizes at a moment, and the energy of the second window remains unchanged; at the moment of signal energy stabilization, the energy of the first window reaches the maximum value, and the energy of the second window is still the minimum value; after the moment of signal energy stabilization, the first window energy remains unchanged and the second window energy starts to increase gradually. Taking the initial buffer area length as 8 bits and the oversampling multiple as 4 as an example, the number of window symbols of each window is 32, and if the first window energy is continuously 32 times greater than the second window energy, determining the 32 th sampling time as the signal energy stabilizing time.
Alternatively, a detection variable M may be defined n ＝A n /B n The energy of the first window is continuously set for times larger than that of the second window, namely M n The continuous setting times is more than 1, and the time when the maximum value occurs is the signal energy stabilizing time n p 。
FIG. 7 is a schematic diagram of a window energy variation according to an embodiment of the present invention, in which A and B represent a first time window and a second time window, respectively, A n And B n The first window energy and the second window energy are respectively represented, each window contains the same number of symbols, and according to the frame structure of AIS, the number of window symbols is set as the number of symbols of a starting buffer (Ramp-Up), and A is before the stable moment of signal energy n Gradually increase, B n Maintaining unchanged; after the moment of signal energy stabilization, A n Almost remain unchanged, B n And starts to increase again; and at the moment of signal energy stabilization, A n Reach maximum value, B n Still at a minimum. Detecting variable M n At the signal energy stabilization time n p Reaching a maximum.
S240, taking the first window energy at the moment of signal energy stabilization as the maximum window energy, and determining the detected maximum window energy as a decision reference threshold.
In the present embodiment, the signal energy stabilization moment n is determined p Thereafter, a first window energy A may be present at this time peak As the maximum window energy and as a decision reference threshold. A is that peak The value can be used asThe reference threshold for the decision is searched for subsequent sync peaks.
Further, after determining the signal energy stabilization moment, it is also possible to: and determining the ratio of the first window energy and the second window energy at the moment of stabilizing the signal energy as the signal-to-noise ratio estimated value of the complex baseband signal.
In this embodiment, at the time of signal energy stabilization, the first window energy includes the sum of signal energy and noise energy, and the second window energy includes only noise energy, so that the following signal-to-noise ratio estimation value can be obtained:
wherein M is peak For the signal-to-noise ratio estimation value, A peak For at signal energy stabilization moment n p Is the first window energy of B np For at signal energy stabilization moment n p Is set to the second window energy of (2).
S250, modulating and performing differential transformation processing on the local training sequence to obtain a second differential transformation result.
In this embodiment, the local training sequence may be a constant 0,1 alternating sequence, and may be first coded by NRZI (No Return to Zero Inverted —reverse non-return to zero), then mapped by GMSK modulation, then shifted left and right by half a symbol period, and finally conjugate multiplied, where the signal expression for obtaining the second differential transformation result may be as shown in equation (6) in the above embodiment.
S260, performing cross-correlation calculation processing on the first differential transformation result and the second differential transformation result, and performing peak detection on the cross-correlation calculation result according to the decision reference threshold value to obtain a target peak value.
In this embodiment, after the first differential conversion result and the second differential conversion result after differential conversion of the received complex baseband signal and the local training sequence are obtained, a calculated value of each sampling moment can be obtained through cross-correlation operation, then, peak values in the calculated values of the cross-correlations are compared, and auxiliary judgment is performed according to a decision reference threshold value, so that a target peak value in the calculated values is obtained, and a signal position corresponding to the target peak value, namely, a frame synchronization identification point. Wherein the expression of the cross-correlation calculation may be as shown in the formula (7) in the above embodiment.
Optionally, the method for performing peak detection on the cross-correlation calculation result according to the decision reference threshold value to obtain the target peak value may be: determining a final decision threshold according to the decision reference threshold; comparing the cross-correlation calculation result of each sampling time with the cross-correlation calculation results of the front and rear adjacent times; and taking the cross-correlation calculation result which is larger than the cross-correlation calculation result of the adjacent time and larger than the final judgment threshold value as a target peak value.
In particular, the calculation result value can be calculatedAs a reference point, if->Is greater than->And is also greater than->At the same time->Also greater than the final decision threshold, the target peak is +.>
The method for determining the final decision threshold according to the decision reference threshold may be: acquiring a judgment threshold coefficient; the product of the decision reference threshold and the decision threshold coefficient is determined as the final decision threshold. I.e. the value of the final decision threshold can be alpha x A peak Wherein alpha is a decision threshold coefficient, which can be determined by simulation experiments.
S270, determining the signal position corresponding to the target peak value as a frame synchronization identification point of the complex baseband signal.
In this embodiment, after determining the target peak value, if the target peak value isAnd the starting point of the signal is n-1, namely, the signal position corresponding to the n-1 sampling moment is determined as the frame synchronization identification point of the complex baseband signal, and the synchronization timing identification is output.
Fig. 8 is a schematic diagram of a frame synchronization simulation result provided by the embodiment of the present invention, where as shown in the drawing, the decision threshold is a final decision threshold, according to the above frame synchronization method, it may be searched that the cross correlation calculation result of the sampling moment 268 is greater than the adjacent value and greater than the final decision threshold, and then the position of the sampling moment 268 is determined as the synchronization identification point.
According to the AIS signal frame synchronization method disclosed by the embodiment of the invention, the decision reference threshold is determined according to the differential energy detection result after differential transformation of the received signal, the self-adaptive decision threshold is provided for peak value determination of the subsequent cross-correlation calculation result, the sensitivity of frame synchronization is improved, the influence of external channel variation is avoided, the energy stability moment of the received signal can be conveniently found by adopting a double sliding window mode during differential energy detection, and complex multiplication operation is simplified. And the synchronization method for carrying out cross-correlation calculation on the received signal and the local training sequence and then searching the peak value is simple to realize, low in operand and less affected by frequency offset.
Example III
Fig. 9 is a schematic structural diagram of an AIS signal frame synchronization device according to a third embodiment of the present invention. As shown in fig. 9, the apparatus includes: a first differential transformation module 310, a decision reference threshold determination module 320, a second differential transformation module 330 and a frame synchronization identification point determination module 340.
A first differential conversion module 310, configured to receive a complex baseband signal, and perform differential conversion processing on the complex baseband signal to obtain a first differential conversion result;
the decision reference threshold determining module 320 is configured to send the first differential transformation result into a set time window, perform differential energy detection on the first differential transformation result, and determine the detected maximum window energy as a decision reference threshold.
The second differential transformation module 330 is configured to perform modulation and differential transformation on the local training sequence, so as to obtain a second differential transformation result.
The frame synchronization identification point determining module 340 is configured to perform cross-correlation computation on the first differential transformation result and the second differential transformation result, and determine a frame synchronization identification point of the complex baseband signal according to the decision reference threshold and the cross-correlation computation result.
Optionally, the time window includes a first time window and a second time window, the first time window and the second time window are connected in front of and behind, and the number of symbols of the window is consistent with the number of symbols of the initial buffer zone of the complex baseband signal.
Optionally, the decision reference threshold determining module 320 is further configured to:
at each sampling moment, determining the first window energy of a first time window and the second window energy of a second time window respectively; if the continuous set times of the energy of the first window is larger than that of the energy of the second window, determining the last sampling time as a signal energy stabilizing time; setting the number of times equal to the number of window symbols of each time window; the first window energy at the moment of signal energy stabilization is taken as the maximum window energy.
Optionally, the apparatus further comprises a signal-to-noise ratio determining module 350, configured to determine a ratio of the first window energy and the second window energy at the moment of signal energy stabilization as a signal-to-noise ratio estimated value of the complex baseband signal.
Optionally, the frame synchronization identification point determining module 340 is further configured to:
performing peak detection on the cross-correlation calculation result according to the decision reference threshold value to obtain a target peak value; and determining the signal position corresponding to the target peak value as a frame synchronization identification point of the complex baseband signal.
Optionally, the frame synchronization identification point determining module 340 is further configured to:
determining a final decision threshold according to the decision reference threshold; comparing the cross-correlation calculation result of each sampling time with the cross-correlation calculation results of the front and rear adjacent times; and taking the cross-correlation calculation result which is larger than the cross-correlation calculation result of the adjacent time and larger than the final judgment threshold value as a target peak value.
Optionally, the frame synchronization identification point determining module 340 is further configured to:
acquiring a judgment threshold coefficient; the product of the decision reference threshold and the decision threshold coefficient is determined as the final decision threshold.
The AIS signal frame synchronization device provided by the embodiment of the invention can execute the AIS signal frame synchronization method provided by any embodiment of the invention, and has the corresponding functional modules and beneficial effects of the execution method.
Example IV
Fig. 10 shows a schematic diagram of the structure of an electronic device 10 that may be used to implement an embodiment of the invention. Electronic devices are intended to represent various forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers. Electronic equipment may also represent various forms of mobile devices, such as personal digital processing, cellular telephones, smartphones, wearable devices (e.g., helmets, glasses, watches, etc.), and other similar computing devices. The components shown herein, their connections and relationships, and their functions, are meant to be exemplary only, and are not meant to limit implementations of the inventions described and/or claimed herein.
As shown in fig. 10, the electronic device 10 includes at least one processor 11, and a memory, such as a Read Only Memory (ROM) 12, a Random Access Memory (RAM) 13, etc., communicatively connected to the at least one processor 11, in which the memory stores a computer program executable by the at least one processor, and the processor 11 may perform various appropriate actions and processes according to the computer program stored in the Read Only Memory (ROM) 12 or the computer program loaded from the storage unit 18 into the Random Access Memory (RAM) 13. In the RAM 13, various programs and data required for the operation of the electronic device 10 may also be stored. The processor 11, the ROM 12 and the RAM 13 are connected to each other via a bus 14. An input/output (I/O) interface 15 is also connected to bus 14.
Various components in the electronic device 10 are connected to the I/O interface 15, including: an input unit 16 such as a keyboard, a mouse, etc.; an output unit 17 such as various types of displays, speakers, and the like; a storage unit 18 such as a magnetic disk, an optical disk, or the like; and a communication unit 19 such as a network card, modem, wireless communication transceiver, etc. The communication unit 19 allows the electronic device 10 to exchange information/data with other devices via a computer network, such as the internet, and/or various telecommunication networks.
The processor 11 may be a variety of general and/or special purpose processing components having processing and computing capabilities. Some examples of processor 11 include, but are not limited to, a Central Processing Unit (CPU), a Graphics Processing Unit (GPU), various specialized Artificial Intelligence (AI) computing chips, various processors running machine learning model algorithms, AIS signal processors (DSPs), and any suitable processor, controller, microcontroller, etc. The processor 11 performs the various methods and processes described above, such as the AIS signal frame synchronization method.
In some embodiments, the AIS signal frame synchronization method may be implemented as a computer program tangibly embodied on a computer-readable storage medium, such as storage unit 18. In some embodiments, part or all of the computer program may be loaded and/or installed onto the electronic device 10 via the ROM 12 and/or the communication unit 19. When the computer program is loaded into RAM 13 and executed by processor 11, one or more of the steps of AIS signal frame synchronization described above may be performed. Alternatively, in other embodiments, processor 11 may be configured to perform the AIS signal frame synchronization method in any other suitable manner (e.g., by means of firmware).
Various implementations of the systems and techniques described here above may be implemented in digital electronic circuitry, integrated circuit systems, field Programmable Gate Arrays (FPGAs), application Specific Integrated Circuits (ASICs), application Specific Standard Products (ASSPs), systems On Chip (SOCs), load programmable logic devices (CPLDs), computer hardware, firmware, software, and/or combinations thereof. These various embodiments may include: implemented in one or more computer programs, the one or more computer programs may be executed and/or interpreted on a programmable system including at least one programmable processor, which may be a special purpose or general-purpose programmable processor, that may receive data and instructions from, and transmit data and instructions to, a storage system, at least one input device, and at least one output device.
A computer program for carrying out methods of the present invention may be written in any combination of one or more programming languages. These computer programs may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the computer programs, when executed by the processor, cause the functions/acts specified in the flowchart and/or block diagram block or blocks to be implemented. The computer program may execute entirely on the machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.
In the context of the present invention, a computer-readable storage medium may be a tangible medium that can contain, or store a computer program for use by or in connection with an instruction execution system, apparatus, or device. The computer readable storage medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. Alternatively, the computer readable storage medium may be a machine readable signal medium. More specific examples of a machine-readable storage medium would include an electrical connection based on one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.
To provide for interaction with a user, the systems and techniques described here can be implemented on an electronic device having: a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to a user; and a keyboard and a pointing device (e.g., a mouse or a trackball) through which a user can provide input to the electronic device. Other kinds of devices may also be used to provide for interaction with a user; for example, feedback provided to the user may be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user may be received in any form, including acoustic input, speech input, or tactile input.
The systems and techniques described here can be implemented in a computing system that includes a background component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front-end component (e.g., a user computer having a graphical user interface or a web browser through which a user can interact with an implementation of the systems and techniques described here), or any combination of such background, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include: local Area Networks (LANs), wide Area Networks (WANs), blockchain networks, and the internet.
The computing system may include clients and servers. The client and server are typically remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. The server can be a cloud server, also called a cloud computing server or a cloud host, and is a host product in a cloud computing service system, so that the defects of high management difficulty and weak service expansibility in the traditional physical hosts and VPS service are overcome.
It should be appreciated that various forms of the flows shown above may be used to reorder, add, or delete steps. For example, the steps described in the present invention may be performed in parallel, sequentially, or in a different order, so long as the desired results of the technical solution of the present invention are achieved, and the present invention is not limited herein.
The above embodiments do not limit the scope of the present invention. It will be apparent to those skilled in the art that various modifications, combinations, sub-combinations and alternatives are possible, depending on design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention.
Claims (10)
1. An AIS signal frame synchronization method, comprising:
receiving a complex baseband signal, and performing differential conversion processing on the complex baseband signal to obtain a first differential conversion result;
sending the first differential transformation result into a set time window, carrying out differential energy detection on the first differential transformation result, and determining the detected maximum window energy as a decision reference threshold;
modulating and performing differential transformation on the local training sequence to obtain a second differential transformation result;
And performing cross-correlation calculation processing on the first differential transformation result and the second differential transformation result, and determining a frame synchronization identification point of the complex baseband signal according to the decision reference threshold and the cross-correlation calculation result.
2. The method of claim 1, wherein the time window comprises a first time window and a second time window, the first time window and the second time window are connected in tandem and the number of window symbols is consistent with the number of symbols of the initial buffer of the complex baseband signal.
3. The method of claim 2, wherein performing differential energy detection on the first differential transformation result comprises:
at each sampling instant, determining a first window energy of the first time window and a second window energy of the second time window respectively;
if the continuous set times of the energy of the first window are larger than the energy of the second window, determining the last sampling time as a signal energy stabilizing time; wherein the set times are equal to the number of window symbols of each time window;
and taking the first window energy of the signal energy stabilizing moment as the maximum window energy.
4. A method according to claim 3, wherein after determining the moment of signal energy stabilization, further comprising:
and determining the ratio of the first window energy and the second window energy at the moment of stabilizing the signal energy as the signal-to-noise ratio estimated value of the complex baseband signal.
5. The method of claim 1, wherein determining the frame synchronization identification point of the complex baseband signal based on the decision reference threshold and the cross-correlation calculation result comprises:
performing peak detection on the cross-correlation calculation result according to the decision reference threshold value to obtain a target peak value;
and determining the signal position corresponding to the target peak value as a frame synchronization identification point of the complex baseband signal.
6. The method of claim 5, wherein peak detecting the cross-correlation calculation result according to the decision reference threshold value to obtain a target peak value comprises:
determining a final decision threshold according to the decision reference threshold;
comparing the cross-correlation calculation result of each sampling time with the cross-correlation calculation results of the front and rear adjacent times;
and taking the cross-correlation calculation result which is larger than the cross-correlation calculation result of the adjacent time and the final judgment threshold value as the target peak value.
7. The method of claim 6, wherein determining a final decision threshold from the decision reference threshold comprises:
acquiring a judgment threshold coefficient;
and determining the product of the decision reference threshold and the decision threshold coefficient as the final decision threshold.
8. An AIS signal frame synchronization apparatus, comprising:
the first differential conversion module is used for receiving the complex baseband signal, and carrying out differential conversion processing on the complex baseband signal to obtain a first differential conversion result;
the decision reference threshold determining module is used for sending the first differential transformation result into a set time window, detecting differential energy of the first differential transformation result, and determining the detected maximum window energy as a decision reference threshold;
the second differential transformation module is used for modulating and carrying out differential transformation processing on the local training sequence to obtain a second differential transformation result;
and the frame synchronization identification point determining module is used for performing cross-correlation calculation processing on the first differential transformation result and the second differential transformation result, and determining the frame synchronization identification point of the complex baseband signal according to the decision reference threshold and the cross-correlation calculation result.
9. An electronic device, the electronic device comprising:
at least one processor; and
a memory communicatively coupled to the at least one processor; wherein, the liquid crystal display device comprises a liquid crystal display device,
the memory stores a computer program executable by the at least one processor to enable the at least one processor to perform the AIS signal frame synchronization method of any one of claims 1-7.
10. A computer readable storage medium storing computer instructions for causing a processor to perform the AIS signal frame synchronization method of any one of claims 1-7.
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| CN117439850B (en) * | 2023-12-21 | 2024-02-23 | 中国电子科技集团公司第五十四研究所 | Self-adaptive OFDM symbol synchronization method |
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