CN105656820A - Satellite AIS (Automatic Identification System) signal detecting and processing device and method for use under high conflict - Google Patents

Abstract

The invention relates to a satellite AIS signal detection and processing device and method thereof in the case of signal conflict, which solves the problems of Doppler frequency deviation and signal conflict existing in the satellite AIS system. Since the Doppler frequency offset presents a certain distance distribution characteristic, the Doppler frequency offset can be used to further refine the area, and the difference in the Doppler frequency offset is used to simulate multi-channel reception in the baseband, and interference cancellation technology is added to each channel. Two methods improve the signal detection probability at the satellite receiving end.

Description

Device and method for detecting and processing satellite AIS signal under high conflict

technical field

The invention relates to a detection and processing device and method for satellite receiving AIS (Automatic Identification System, automatic identification system) signals, and the method can effectively deal with Doppler frequency deviation and signal conflict.

Background technique

For the terrestrial AIS system, the communication between different terminals or with the base station is carried out in a SOTDMA (self-organized time division multiple access, that is, self-organized time division multiple access) frame coverage area (about 200 nautical miles), and a SOTDMA frame has 2250 time slots. Before communication, the terminal will pre-apply for one or two consecutive TDMA time slots, and the terminals in the same SOTDMA frame are allocated to different time slots by self-organization, thus effectively preventing different terminals in the coverage area of the SOTDMA frame from sending information to the ground Information conflict at station time. For the satellite AIS system, it continues to use the ground AIS protocol (SOTDMA protocol), but the effective coverage of a single satellite is usually much larger than the coverage area of a SOTDMA frame. At this time, the satellite AIS receiver will receive signals from different SOTDMA frame coverage areas. The information sent by the terminal in the network increases the probability of information collision at the receiver.

Referring to Figure 1 and Figure 2, it can be seen that there are two situations for the conflict mechanism. (1) There are multiple self-organizing areas (SOTDMA areas) within the satellite receiving range, and terminals in different organization areas may be in the same time slot AIS information is sent and arrives at the satellite receiver at the same time, resulting in AIS signal conflict; (2) For the satellite AIS system, the transmission distance between "terminal-satellite" is far greater than 200 nautical miles, resulting in a relative transmission delay between different terminals that is much greater than 2ms, This will cause mutual interference of information between different time slots, that is to say, even if the terminals in the monitoring area send AIS information in different time slots, AIS signal collisions will be caused due to the influence of signal transmission delay. Both of these conflict phenomena will lead to errors in receiving AIS information, and then reduce the probability of terminal detection. Solving the problem of satellite AIS multi-network signal conflict is one of the key technologies of satellite AIS.

Obviously, the information collision probability of each time slot is related to the number of terminals within the effective satellite coverage and the information reporting rate of the ship's equipment. The problem of information conflict in satellite AIS system is directly related to the reliability of satellite AIS system for terminal information monitoring and the capacity of the whole system, so it is necessary to propose a reasonable solution to the problem of information conflict.

Moreover, LEO satellites (Low Earth Orbit, Low Earth Orbit) introduce a large Doppler frequency offset, which is related to the position of the terminal, and the existence of the frequency offset may also affect the carrier synchronization of the receiver. For a full-beam AIS antenna, since the AIS communication rate is 9.6kbps, the Doppler frequency deviation close to ±4kHz will have a great impact on the reliability of terminal information monitoring.

For the multi-signal separation of the same frequency and simultaneous conflict, the method of high-precision direction finding and beam synthesis or the blind separation method is mainly used at present. However, due to the influence of multi-beam antenna design, antenna mutual coupling, direction finding accuracy, and channel conditions, it is difficult to popularize and apply it in actual engineering. The present invention adopts a simple single-channel receiving and processing method, divides the baseband into multiple channels through the difference of Doppler frequency deviation, and filters and processes the signals respectively, so as to improve the reliability of terminal information monitoring.

Contents of the invention

In order to solve at least one of the above-mentioned problems and/or deficiencies, and provide at least one of the following advantages, the present invention accordingly provides a satellite AIS signal detection and processing device and method under high conflict, which can improve the reliability of terminal information monitoring .

On the one hand, a satellite AIS signal detection and processing device under high conflict is provided. The signal first passes through the radio frequency filter module and the baseband filter module in the device successively. For further demodulation, the module re-modulates the successfully demodulated signal and makes a difference with the original signal, and re-passes the baseband filter to achieve small signal demodulation; using the difference in Doppler frequency offset of different terminals, the baseband filter There are multiple narrow-band filters in the module; the interference elimination module separates collision signals with the same frequency offset but different power.

On the other hand, a method for detecting and processing satellite AIS signals under high conflict conditions is provided. Firstly, the AIS signal is subjected to radio frequency filtering; then the radio frequency filtered signal enters the baseband, and the difference in Doppler frequency deviation of different terminals is used to design the Multiple narrow-band filters are used to filter signals with different frequency offsets; finally, preliminary separation of AIS signals with different frequency offsets after narrow-band filtering is achieved.

When the signal contains large and small signals, if the large signal can be successfully demodulated (at this time, the small signal is regarded as interference), the interference elimination technology mainly includes remodulating the large signal and making a difference with the original signal, and the signal difference Demodulate again.

Through the difference of Doppler frequency offset, multi-channel reception is simulated in the baseband, and interference cancellation technology is added to each channel, and the two methods are combined to improve the signal detection probability of the satellite receiving end.

Description of drawings

Figure 1 is the cause of satellite AIS signal conflict;

Fig. 2 is the conflict type of satellite AIS signal;

Figure 3 shows the relationship between the satellite AIS signal Doppler frequency offset and the terminal position;

Figure 4 is a flow chart of satellite AIS signal processing.

detailed description

Embodiments of the invention are described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. Embodiments of the invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure is thorough and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Detailed descriptions of known functions and structures will be omitted to avoid obscuring the subject matter of the embodiments. The same reference numerals are used to designate the same elements in the drawings.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should be further understood that, unless expressly defined herein, terms (as defined in commonly used dictionaries) should be construed to have a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an idealized or overly formal manner. to explain their meaning.

The present invention will be described in detail below with reference to the accompanying drawings.

Referring to Figure 3, the Doppler frequency offset of the terminal shows obvious regional distribution characteristics, so even if terminals in different areas transmit AIS signals in the same time slot, the signals collide at the satellite receiving end, but due to the Doppler frequency offset The difference between the received signals can be achieved by designing different narrowband filters in the baseband.

When the difference in Doppler frequency deviation between terminal A and terminal B is large, the energy difference between the two signals can be increased after baseband filtering. For example, channel 1 is for the signal of terminal A, and the interference of terminal B can be suppressed so that the signal-to-interference ratio meets the demodulation threshold; channel 2 is for the signal of terminal B, and the interference of terminal A can be suppressed similarly. Through this method, it can be ensured that both signals are successfully demodulated, which increases the detection probability of the terminal.

When the two signals have the same frequency offset but a large difference in power, such as a Class A terminal signal (transmitting power 12.5W) and a Class B terminal signal (transmitting power 1W), even if the two signals conflict, but because they respectively meet the demodulation threshold , the interference cancellation technology can be used to demodulate the A signal first, and after the CRC check confirms that the signal analysis is correct, the signal is re-modulated by GMSK, and the re-modulated Class A terminal signal is subtracted from the original signal to further realize the signal difference Demodulation of Class B terminal signals.

Refer to Figure 4 to further illustrate the AIS signal processing flow. Its key modules include radio frequency filtering, baseband filtering, and interference cancellation. Through these three parts, the demodulation probability of AIS signals will be greatly improved.

First, the AIS signal is subjected to radio frequency filtering; AIS is designed as two radio frequency channels, the center frequency points are AIS1 (161.975MHz) and AIS2 (162.025MHz), and the bandwidth of the radio frequency filter is designed to be 25kHz.

Then, the RF-filtered signal enters the baseband. Since the frequency offset of the AIS signal is different, multiple narrowband filters are designed in the baseband to filter signals with different frequency offsets; the effective bandwidth of the AIS signal corresponding to each frequency point is about 10KHz, but due to Introduce the Doppler frequency offset ±f, so the bandwidth is increased by 10+2f, and the bandwidth is divided into 5 parts on average, and the bandwidth of each channel is (10+2f)/5, and 5 narrowband filters are designed in the baseband for signal processing respectively . This is followed by Viterbi decoding, which is commonly used in the art.

Again, the AIS signals with different frequency offsets after narrowband filtering can be initially separated, and after the CRC check (cyclic redundancy check code CyclicRedundancyCheck), the signal is saved after being correct; if the CRC check in step 3 is correct, it can be further added The interference elimination technology further separates collision signals with the same frequency offset but different power, and the signal processing process ends when the CRC check error occurs. For example, when the A-band and B-band signals pass through the A filter, the B-band signal energy is suppressed, which can increase the power ratio of the A-band signal to the B-band signal and increase the demodulation probability. When the A1 and A2 signals pass through the A filter at the same time, and the A1 signal is 5dB higher than the A2 signal, the demodulation of the A1 signal can be realized, and then the demodulation of the A2 signal can be realized through the interference elimination method. First demodulate the A1 signal, if the CRC check is correct, then re-modulate the A1 signal, subtract the A1 modulation signal from the original signal, and then demodulate the A2 signal on the signal difference.

While the invention has been shown and described with reference to particular embodiments thereof, it will be understood by those skilled in the art that changes may be made in form and detail therein without departing from the spirit and scope of the invention as defined by the claims. various changes.

Claims (7)

1. The satellite AIS signal detection processing device under a kind of high conflict, it is characterized in that, signal passes through radio frequency filter module, baseband filter module in this device successively at first, for this group of signals of successful demodulation, utilize interference elimination module again to realize small For further demodulation of the signal, the module re-modulates the successfully demodulated signal and makes a difference with the original signal, and re-passes the baseband filter to realize small signal demodulation of the signal difference; using the difference in Doppler frequency offset of different terminals, the There are multiple narrowband filters in the baseband filter module; the interference elimination module separates collision signals with the same frequency offset but different power. 2. The satellite AIS signal detection processing device under the high conflict as claimed in claim 1, wherein said radio frequency filter comprises two radio frequency channels, and center frequency points are respectively AIS1161.975MHz and AIS2162.025MHz, and the radio frequency filter bandwidth is designed to be 25kHz . 3. The satellite AIS signal detection and processing device under high conflict conditions according to claim 2, wherein the effective bandwidth of the AIS signal corresponding to each frequency point is 10KHz. 4. The device for detecting and processing satellite AIS signals under high conflicts as claimed in any one of claims 1-3, wherein there are five narrowband filters. 5. A satellite AIS signal detection and processing method under a high conflict is characterized in that, at first the AIS signal is carried out radio frequency filtering; then the signal through the radio frequency filtering enters the baseband, utilizes the difference of different terminal Doppler frequency offsets, in the baseband Design a plurality of narrowband filters to realize the filtering of different frequency offset signals; finally realize preliminary separation of AIS signals with different frequency offsets after narrowband filtering, and when the CRC check of the signal after the preliminary separation is correct, increase the interference elimination step, so that the frequency Collision signals with the same partiality but different power are further separated until the CRC check error is complete; the interference elimination is to re-modulate the successfully demodulated signal and make a difference with the original signal, and re-pass the baseband filter to achieve the signal difference Small signal demodulation. 6. The satellite AIS signal detection and processing method under high conflict as claimed in claim 5, wherein the radio frequency filter comprises two radio frequency channels, the center frequency points are respectively AIS1161.975MHz and AIS2162.025MHz, and the radio frequency filter bandwidth is designed to be 25kHz. 7. The satellite AIS signal detection processing method under the high conflict as claimed in claim 5 or 6, wherein the effective bandwidth of the AIS signal corresponding to each frequency point is 10KHz, due to introducing Doppler frequency deviation ± f, so the bandwidth increases 10+2f, the bandwidth is divided into 5 parts on average, and the bandwidth of each channel is (10+2f)/5, and 5 narrowband filters are designed in the baseband for signal processing.