CN107508647B - Detection probability calculation method of satellite-borne AIS system based on power difference - Google Patents
Detection probability calculation method of satellite-borne AIS system based on power difference Download PDFInfo
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Abstract
The invention relates to the field of satellite communication, in particular to a power difference-based detection probability calculation method for a satellite-borne AIS system, which includes the steps of superposing signals with different power difference values, calculating the total signal power of different signals reaching a satellite receiving end to form collision signals, demodulating and calculating the collision signals, and counting the demodulation probability of each part of signals; and finally, calculating the overall detection probability of the satellite-borne AIS system according to the counted demodulation probability, thereby more effectively evaluating the performance of the satellite-borne AIS system and better reflecting the actual performance of the satellite-borne AIS system.
Description
Technical Field
The invention relates to the field of satellite communication, in particular to a power difference-based detection probability calculation method for a satellite-borne AIS system.
Background
In recent years, marine economy has become more important, marine transportation activities have become more frequent, and it has become important to enhance marine vessel management. An Automatic Identification System (AIS) for ships is widely used for monitoring and maintaining the safety of ships during marine navigation as a marine ship navigation aid and approach tool.
The ship detection probability is used as an important technical index of the satellite-borne AIS system and is an important certificate for measuring the performance of the satellite-borne AIS system. Compared with a shore-based AIS system, the satellite-borne AIS system is wider in coverage range, and the collision condition of AIS signals received by satellites is more serious, so that the demodulation performance of the satellite-borne AIS is seriously influenced. At present, a theoretical detection probability model used in a satellite-borne AIS system can only roughly describe the overall performance of the system, and under the condition of multiple signal conflicts, the detection probability of the systems is only calculated simply by taking the number of the signal conflicts as a standard, and the realization of the actual AIS system engineering cannot be well guided.
Disclosure of Invention
The invention provides a power difference-based detection probability calculation method for a satellite-borne AIS system, which is used for optimizing a ship detection probability model of the satellite-borne AIS system.
In order to solve the technical problems, the invention adopts the following technical scheme:
a power difference-based detection probability calculation method for a satellite-borne AIS system is disclosed, and the calculation method specifically comprises the following steps:
a. superposing the signals with different power difference values, and calculating the total signal power of different signals reaching a satellite receiving terminal to form a collision signal;
b. demodulating and calculating the collision signals according to different power compositions of the collision signals, and counting the demodulation probability of each part of signals;
c. and calculating the integral detection probability of the satellite-borne AIS system according to the counted demodulation probability.
Further, in step a, the calculation formula of the total signal power reaching the satellite receiving end is:
Preceive＝Psend+PsendAntGain+PfreeSpaceLoss+PreceiveAntGain
wherein, PreceiveIndicating the AIS signal power, P, received by the satellitesendRepresenting the transmitted power, P, of the AIS berthsendAntGainShows the gain, P, of the AIS slipway antennafreeSpaceLossRepresenting the spatial path loss, P, between the ship's platform and the satellitereceiveAntGainThe gain of the space-borne AIS antenna is shown.
Further, in step b, the specific calculation method is as follows:
for n-time collision signals, the formula for counting and solving the demodulation probability of m signals is as follows:
wherein m isiRepresenting the composition of m colliding signals, njThis indicates that n signals can be resolved, and Q is an influence factor based on a specific demodulation algorithm.
Further, when the collision signals are demodulated and calculated, different collision signals are demodulated by using a JMLSE demodulation algorithm.
Further, in step c, the calculation formula of the overall detection probability of the satellite-borne AIS system is as follows:
＝πAmνm
wherein, pi is a row vector vmIs a vector of (1,2,3, …, m), and Am represents the probability of demodulating m signals from the received k signals.
Further, a large helical antenna is used at the receiving end of the satellite as a receiving antenna of the satellite-borne AIS signal.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects:
according to the invention, the detection probability calculation is carried out on the signals by utilizing different power differences of the AIS signals, compared with the traditional theoretical detection probability model and the actual detection probability model, the performance evaluation of the satellite-borne AIS system can be carried out more effectively, and compared with the theoretical detection probability model, the actual performance of the system can be better reflected, and the calculation value of the actual detection probability model of the system is closer.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a schematic diagram of signal collision;
FIG. 3a is a graph illustrating the impact of a double collision signal power difference on the overall detection probability during simulation according to the present invention;
FIG. 3b is a graph illustrating the effect of a double collision signal power difference on the detection probability of a higher power signal in simulation according to the present invention;
FIG. 3c is a graph illustrating the effect of dual collision signal power difference on the detection probability of lower power signals in simulation according to the present invention;
FIG. 4a is a diagram illustrating the effect of the power difference of the triple collision signals on the overall detection probability in the simulation according to the present invention;
FIG. 4b is a graph illustrating the effect of triple collision signal power difference on the detection probability of higher power signals in simulation according to the present invention;
FIG. 4c is a graph illustrating the effect of triple collision signal power difference on the detection probability of an intermediate power signal during simulation according to the present invention;
FIG. 4d is a graph illustrating the effect of triple collision signal power difference on the detection probability of lower power signals in a simulation according to the present invention;
FIG. 5 is a comparison of the detection probability calculation method of the present invention with actual and theoretical detection probabilities.
Detailed Description
The technical solution proposed by the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. Advantages and features of the present invention will become apparent from the following description and from the claims. It is noted that the drawings are in greatly simplified form and that non-precision ratios are used for convenience and clarity only to aid in the description of the embodiments of the invention.
At present, due to the fact that satellite-borne AIS signals have serious time slot conflict, the signals are subjected to serious time delay and frequency offset interference, the complexity of a related satellite-borne AIS signal demodulation technology is high, and the performance evaluation difficulty of a satellite-borne AIS system is high. Aiming at various problems in the design of the satellite-borne AIS system, the invention provides the power difference-based detection probability calculation method for the satellite-borne AIS system, and the model is adopted to carry out simulation evaluation on the ship detection probability of the satellite-borne AIS system, so that the performance of the power difference-based detection probability model is greatly improved compared with that of the traditional theoretical detection probability model.
Now, referring to fig. 1, a method for calculating a detection probability based on a signal power difference according to the present invention will be described in detail.
Firstly, signals with different power difference values are superposed, the total signal power of different signals reaching a satellite receiving terminal is calculated to form a collision signal, and the calculation formula of the total signal power reaching the satellite receiving terminal is as follows:
Preceive＝Psend+PsendAntGain+PfreeSpaceLoss+PreceiveAntGain
wherein, PreceiveIndicating the AIS signal power, P, received by the satellitesendRepresenting the transmitted power, P, of the AIS berthsendAntGainShows the gain, P, of the AIS slipway antennafreeSpaceLossRepresenting the spatial path loss, P, between the ship's platform and the satellitereceiveAntGainThe gain of the space-borne AIS antenna is shown.
Then, according to different power compositions of the collision signals, demodulating and calculating the collision signals, and counting the demodulation probability of each part of signals, wherein, as the AIS signals are transmitted in different time slots to form multilayer collision signals, the invention counts and calculates the demodulation probability of m signals in the n-fold collision signals, and the calculation formula is as follows:
in this formula, miRepresenting the composition of m colliding signals, njThis indicates that n signals can be resolved, and Q is an influence factor based on a specific demodulation algorithm.
In the preferred embodiment of the present invention, when performing demodulation calculation on collision signals, it is preferable to separately demodulate different collision signals by using a JMLSE demodulation algorithm.
And finally, calculating the overall detection probability of the satellite-borne AIS system according to the counted demodulation probability, wherein the calculation formula is as follows:
＝πAmνm
wherein, pi is a row vector vmIs a vector of (1,2,3, …, m), Am denotes k received from
Probability of demodulating m signals from among the signals.
Generally, the present invention uses a large helical antenna at the satellite receiving end as the receiving antenna for the on-board AIS signals.
The invention will now be described with reference to a specific application example 1.
Example 1
Generally, the observation range of the satellite-borne AIS system is wide, and in a water area with dense ships, the satellite-borne AIS system receives a plurality of AIS signals from different cells at the same time, and the signals form collision signals at a satellite receiving end, so that the demodulation performance of a satellite receiver is seriously influenced. Since different AIS signals may arrive at different times at the satellite receiver, signal collision conditions at the satellite receiver are generally classified into two categories:
multiple ships select the same time slot to send signals and reach a satellite receiving end in the same time slot to form a first-type signal collision, as shown in fig. 2;
different ships select different time slots to transmit AIS signals, and the AIS signals reach a satellite receiving end in the same time slot due to space propagation delay, so that signals transmitted by the previous time slot and signals transmitted by the next time slot are overlapped to form second-type signal collision, as shown in the second-type collision in fig. 2.
The collision signal received by the satellite-borne AIS system usually consists of a plurality of signals with different powers, and when the collision signal is demodulated, the different power components have a large influence on the demodulation of the signal.
In the invention, the signal power reaching the satellite receiving end is calculated as:
Preceive＝Psend+PsendAntGain+PfreeSpaceLoss+PreceiveAntGain
the range of radius 20 nautical miles is an AIS (automatic identification system) cell, and self-organizing time division multiple access protocols are used among ships in the cell for time slot division, so that time slot conflict in the cell is avoided. In order to simplify the model, it can be considered that the AIS signals transmitted by the ships within one cell are the same in the time slot of the satellite receiving end through the spatial transmission.
The JMLSE algorithm is used in the invention for signal demodulation.
Generating signals with different power difference values, superposing the signals to form collision signals, respectively demodulating by using a demodulation algorithm, and counting the detection probability of the algorithm under different power difference values.
In this embodiment, the double collision signal generated by the computer is used to simulate the double collision signal received by the satellite-borne AIS receiver. In the case of double collision, the JMLSE demodulation algorithm is used to demodulate the double collision signals, and statistics are made on the demodulation probability conditions of the partial signals therein, as shown in fig. 3a-3 c.
In the invention, a triple collision signal generated by a computer is used for simulating a triple collision signal received by a satellite-borne AIS receiver. In the case of triple collision, the triple collision signals are demodulated by using a JMLSE demodulation algorithm, and the demodulation probability conditions of the signals of each part are counted, as shown in fig. 4a-4 d.
As can be seen from FIG. 3a, the demodulation algorithm used in the present invention is more sensitive to the power difference parameter under the condition of double collision, and the overall detection probability of the double collision signal with the power difference of 2-16 dB is higher; as can be seen from fig. 3b, for the higher power signal, when the power difference is 2dB or more, the detection probability performance of the demodulation algorithm used in the present invention is higher; as can be seen from fig. 3c, for lower power signals, the detection probability performance of the demodulation algorithm used in the present invention decreases rapidly when the power difference is above 16 dB.
As can be seen from fig. 4a, the demodulation algorithm used in the present invention is sensitive to the power difference of each signal in the triple collision case. For two signals with higher power, when the power difference value of the two signals is within the range of 2-16 dB and the power difference values of the two signals and the signal with the lowest power are both greater than 2dB, the overall detection probability is higher. As can be seen from fig. 4b, when the power difference between the signal with the highest power and the other two signals is above 2dB, the detection probability of the signal with the highest power value is also higher; as can be seen from fig. 4c, when the power difference between two signals with relatively high power is 2-16 dB, and the power difference between two signals with relatively low power is more than 2dB, the detection probability of the signal with the intermediate power value is high; as can be seen from fig. 4d, the signal with the lowest power value is not decoded, which is related to the specific selected demodulation method.
The invention carries out calculation according to different power compositions of collision signals, and for a signal with n-times collision, the calculation mode of the probability of m signals can be solved:
wherein m isiRepresenting the composition of m colliding signals, njRepresenting the case where n signals can be resolved, Q is the influence factor based on a particular demodulation algorithm.
For the overall detection probability of the satellite-borne AIS system, the calculation formula is as follows:
＝πAmνm
where π is a row vector, vmIs a vector of (1,2,3, …, m), Am represents the probability of demodulating m signals from k received signals, and k represents the probability of receiving k signals at the satellite receiving end at the same time.
In the invention, a large helical antenna is used for carrying out receiving antenna simulation, a detection probability model based on power difference is used for carrying out calculation, under the condition that the satellite height is 600Km, data of 1 minute is observed, the signal-to-noise ratio in a channel is assumed to be 10dB, ships are uniformly distributed in a satellite observation range, and the simulation result is shown in figure 5.
In the case of a satellite height of 600Km, the satellite covers 68 × 68 cells;
in the simulation model, the number of ships is respectively 500, 1000, 1500, 2000, 2500, 3000, 3500 and 4000;
three simulation models, namely a theoretical detection probability model, a detection probability calculation model based on a power difference value and an actual detection probability model, are used for carrying out detection probability comparison:
(1) within the same observation time range, along with the increase of the number of ships, the detection probabilities calculated by the three detection probability models are all rapidly reduced;
(2) the difference value of the detection probability calculated by the theoretical detection probability model compared with the actual detection probability model is larger, the actual performance of the satellite-borne AIS system cannot be reflected well, and only simple estimation can be carried out;
(3) compared with a theoretical detection probability model, the detection probability calculation model based on the power difference value can more effectively evaluate the performance of the satellite-borne AIS system and is closer to the value calculated by the actual detection probability model of the system.
Therefore, compared with a theoretical detection probability model, the power difference-based detection probability calculation method for the satellite-borne AIS system can better reflect the actual performance of the system.
It should be understood by those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention, and that the foregoing disclosure is only illustrative of the preferred embodiments of the invention. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents, and one skilled in the art can make variations and modifications within the spirit and scope of the invention as defined by the appended claims.
Claims (5)
1. A power difference-based detection probability calculation method for a satellite-borne AIS system is characterized by specifically comprising the following steps:
a. superposing the signals with different power difference values, and calculating the total signal power of different signals reaching a satellite receiving terminal to form a collision signal;
b. demodulating and calculating the collision signals according to different power compositions of the collision signals, and counting the demodulation probability of each part of signals;
c. calculating the overall detection probability of the satellite-borne AIS system according to the counted demodulation probability, wherein the calculation formula of the overall detection probability of the satellite-borne AIS system is as follows:
＝πAmνm
wherein, pi is a row vector vmIs a vector of (1,2,3, …, m), and Am represents the probability of demodulating m signals from the received k signals.
2. The power difference-based detection probability calculation method for the AIS system on the satellite according to claim 1, wherein in step a, the calculation formula of the total signal power reaching the receiving end of the satellite is:
Preceive＝Psend+PsendAntGain+PfreeSpaceLoss+PreceiveAntGain
wherein, PreceiveIndicating the AIS signal power, P, received by the satellitesendRepresenting the transmitted power, P, of the AIS berthsendAntGainShows the gain, P, of the AIS slipway antennafreeSpaceLossRepresenting the spatial path loss, P, between the ship's platform and the satellitereceiveAntGainThe gain of the space-borne AIS antenna is shown.
3. The power difference-based detection probability calculation method for the satellite-borne AIS system according to claim 1, wherein in step b, the specific calculation method is as follows:
for n-time collision signals, the formula for counting and solving the demodulation probability of m signals is as follows:
wherein m isiRepresenting the composition of m colliding signals, njThis means that n signals can be resolved, Q is an influence factor based on a specific demodulation algorithm, and P (n)j|mi) Probability of demodulating n signals from m-multiple-collision signals, P (m)i) The probability that m signals collide together in the signals received by the satellite-borne AIS system is obtained.
4. The power difference-based detection probability calculation method for the AIS system, according to claim 1 or 3, wherein in the step of performing demodulation calculation on the collision signals, different collision signals are demodulated by using a JMLSE demodulation algorithm.
5. The power difference-based detection probability calculation method for the satellite-borne AIS system according to claim 1, characterized in that a large helical antenna is used at a satellite receiving end as a receiving antenna of the satellite-borne AIS signal.
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| CN106230496A (en) * | 2016-08-03 | 2016-12-14 | 上海交通大学 | Spaceborne AIS receiver demodulation method based on soft output Viterbi demodulating algorithm |
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| CN106230496A (en) * | 2016-08-03 | 2016-12-14 | 上海交通大学 | Spaceborne AIS receiver demodulation method based on soft output Viterbi demodulating algorithm |
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