LT6402B - METHOD OF SEGMENTING RADIO FREQUENCY SIGNALS - Google Patents

Abstract

The method according to the invention is implemented using a conventional automatic identification system with satellite tracking, which includes shipping signal transmitters and receivers, orbiting satellite capable of receiving signals from ship transmitters. In the digital map, the surface of the earth is divided into zones with an approximate width 2/3 the width of the satellite viewing field (the width of the zone must be such that two identical lines do not enter the satellite viewport), and the zones are divided into sub-widths equal to the maximum distance between vessels. In this way, a recurring number of nodes is formed in each of the zones in the split map. Such a structure of zones and senses is formed as a digital map of the earth's surface, which is introduced into the automatic recognition system. In such a division, the set of packet time intervals is divided into sub-domains of each zone equally or in different proportions. The part of the vessel of the automatic identification system of each ship located in one of the idlers assigns a time interval from that tag, or another closest idle, to a set of time intervals. This avoids overlapping of the automatic recognition system signals on the receiving satellite.

Description

The present invention relates to a method for distributing radio signals in a multiple time access (TDMA) system, and more particularly in a TDMA Automatic Identification System (AIS), a non-overlapping satellite transmission.

State of the art

Recently, various systems have been widely used to ensure the safety of transport movements. Waterborne transport uses AIS (Automatic Identification System), which operates on the principle of SOTDMA (Self-Organizing Multiple Access using Time). This is a variant of TDMA (Multiple Access Using Time). The principle behind this system is that many communication devices operating at the same frequency to transmit their messages at different times of the day, so as not to interfere with each other.

Vessels exchange location, speed and other information using AIS. Vessels communicate with each other and their messages do not overlap. Naturally, the messages do not overlap only within the vessel's communication area. Outside the communication area of such a vessel, another vessel may already use the same time slot (TS - Time Slot) to send a message, thus preventing vessels from each other to interfere. The SOTDMA AIS system is organized so that data packets in the ship communication area (diameter about 80 km) do not overlap in time and do not require external infrastructure for time slot allocation. The time intervals are synchronized in time, and each transmitter on board sets a free time interval for sending the message and uses it to communicate with the vessels in the area. When a vessel changes the reserved message transmission time interval, the entire time interval in the data transmission range is re-synchronized by notifying the other vessels of the vacant time interval and occupying a new time interval from the available free time intervals in the communication area. Using the SOTDMA AIS principle, each minute is divided into 2250 equal time intervals of 26.67 ms each. This avoids signal overlapping between vessels using the AIS radio frequency.

While the AIS system is primarily designed to assist ship navigation and enhance navigation safety, it is also used to track the movement of vessels in the water. AIS signals can be detected by terrestrial means, but their range is quite limited.

AIS systems can also be used in combination with earth-orbit satellites, which are used to track vessels that are far from the shore. The satellite field of view is about 5000 km in diameter, i.e. it is many times more than the diameter of the ship's communication area, so the data packets received by the satellite can overlap. The signal with overlapping data packets is impossible to decode and determine the ship's position. The aforementioned lack of communication system results from the fundamental problem of multiple transmitters operating simultaneously. If a plurality of transmitters are operating at the same frequency at the same time, the receivers normally cannot receive such a signal. In order to receive signals from transmitters operating simultaneously on the same frequency, it is necessary that such transmitters operate on different frequencies (channels).

If the satellite field of view is narrow, for example 80km in diameter, the problem of overlap is not relevant. In such an area, the messages do not overlap, as its diameter is equal to the communication distance within which the vessels can agree on the TS to be used. However, implementing such a narrow operating angle on a satellite, for example by installing large directional antennas, is technically difficult.

The closest analogue is disclosed in U.S. Patent Application Ser. US 08 / 170,167. It describes the system and the way to distribute the incoming signals to the satellite so that they do not overlap. This is done by processing all incoming satellite signals using mathematical combinations of satellite-receiving (antenna) signals. In this way, the satellite field of view is segmented to form several signal zones with areas. The object of the present invention is to minimize the field of view of the satellite. Unfortunately, the narrow field of view, due to the very large dimensions of the antenna system, is very difficult to implement.

In the method of the present invention, the reception of signals transmitted by the AIS system by a satellite having a field of view wider than the communication distance between the ships is accomplished with a reduced likelihood of signal overlap. The proposed method does not require any hardware replacement of the AIS system used, as everything is done at the computer program level on board the AIS system equipment.

Brief Description of the Invention

Within the ship communication distance (40-90 km), the SOTDMA AIS system ensures that data packets do not overlap in time. When a satellite receives AIS signals from ships, its field of view is wide (~ 5000 km) and wider than the communication distance between ships. From a wider space perspective, data packets overlap and decoding becomes impossible. In high-traffic areas, data packets can overlap even if the satellite viewing field is several hundred kilometers wide.

In a digital map, the Earth's surface is divided into areas approximately 2/3 of the width of the satellite viewing field (the width of the area must be such that two identical faces do not enter the satellite viewfinder) and the areas are divided into sub-areas equal to maximum communication distance between ships. In this way, a repeated map is formed in each of the zones in a divided map. Such a structure of zones and subdivisions is formed as a digital map of the earth, which is entered into the AIS system. In this division, the TS packet of the packets is distributed to the subdivisions of each zone in equal or different proportions.

For each ship in one of the sub-areas, the AIS part of the ship shall assign a TS from that sub-set, or the next-most sub-set, to the TS set. This avoids overlapping of AIS signals in the receiving satellite.

Brief description of the drawings

Other features and advantages of the invention are described in the detailed description of the invention with reference to the following drawings:

Fig. 1 shows the distribution of time intervals between subzones in the zones;

Fig. 2 shows a hexagonal arrangement of characters;

Fig. Figure 3 shows the arrangement of characters in quadrangular forms;

Fig. Figure 4 shows an array of ships in (a) one subdivision and (b) four subdivisions.

Before referring to the detailed description of the invention, with reference to the drawings of exemplary embodiments of the invention, it is to be noted that identical elements are denoted by the same numerals throughout the drawings.

Detailed Description of the Invention

It should be understood that many specific details are set forth to provide a full and comprehensible description of an exemplary embodiment of the invention. However, it will be apparent to one skilled in the art that the details of the embodiments of the invention do not limit the scope of the invention, which may be practiced without such specific guidance. The well-known techniques, procedures, and ingredients have not been described in detail to avoid the confusion of exemplifying embodiments of the invention. Furthermore, this description is not to be construed as limiting the examples provided, but merely as an implementation thereof.

The method according to the invention is implemented using a conventional AIS satellite tracking system, which comprises signal transmitters and receivers for shipping vessels, a satellite orbiting satellite capable of receiving signals transmitted by ship transmitters.

The method of ensuring the reception of signals from all ships in the orbit satellite involves providing the TDMA system, for example AIS, with special transmission order parameter values (4), such as TS (4), and assigning such equipment to the Earth. assigning the surface software to zones (1) and subdivisions (2), and assigning TS (4) to each ship from the subdivision set (4) or the subdivision (4) of the subdivision.

Special software for assigning TS (4) to the entire Earth's surface, or navigable area into zones (1) and sub-areas (2), involves the use of various geometric shapes suitable for covering the entire Earth's surface or navigable area. The dimensions of each zone (1) are larger than the dimensions of the satellite field of view (3) for example 1.5 times, i.e. the area width is 3/2 of the radius width. Depending on the area of zone (1), each map zone (1) is divided into a number of sub-zones (2). Numbers (2) are assigned numbers based on their location in the area (1) so that they do not overlap in the satellite view field (3). The width of the flags (2) is approximately equal to the communication distance between the vessels. For example, if each area comprises nine sub-areas (2), then at any given time the satellite may only see one set of sub-areas (2) from 1 to 9. Each sub-area (2) is assigned a number of TS (4) available to the vessel. with other ships. For example, if there are nine facets (2), then the 2250 TS (4), which divides the minute, is divided by 250 TS (4) for each facet (2).

Since the distribution of vessels (5, 5 ') will be uneven in any part of the map, for optimal utilization of TS (4), the boundaries of the embankments should pass through the areas (5, 5') with the highest density of vessels, zones (1) and embankments (2). ) need not be of regular shape, for example, the shape of adjacent areas (1) and footings (2) may differ. The amount of TS (4) may also vary between different brands (2).

According to the invention, the AIS equipment on each ship determines the ship's position coordinates and thereby identifies itself in which area (2) on the said segmented digital map the ship is located. A free TS (4) is located in the footer (2), allowing the ship to send data to other vessels and to the satellite. If there is 250 TS (4) in the footprint, i.e. radio channels, then approximately 250 vessels can use the channels in that area (2). If there are more ships in subnet (2) than in assigned TS (4), then the AIS system looks for a free TS in the next closest subnet (2), or executes an algorithm that is typically AIS. The AIS system thus modified according to the invention is downward compatible with the conventional AIS system.

Although many features and advantages have been enumerated in the description of the invention, together with the structural details and features of the invention, the description is exemplary of the invention. Changes may be made to the details, in particular the shape, size and layout of the materials, without departing from the principles of the invention, in accordance with the most widely understood meanings of the terms used herein.

Claims (7)

1. A method for segmenting radio frequency signals comprising selecting and assigning values (4) of a parameter indicative of radio frequency signal transmission in a TDMA system, and receiving such signals from a TDMA system, wherein the TDMA system groups possible radio frequency signal transmission sequences. assigning parameter values (4) to each vehicle using a TDMA system for assigning to each satellite in its field of view each RF signal associated with a corresponding RF signal order indicative parameter value (4), wherein said grouping of the indicative parameter values (4) of the radio frequency signal transmission order is performed according to geographical coordinates. 2. A method according to claim 1, characterized in that in the TDMA system the values (4) of the parameter indicating the order of transmission of the radio frequency signals are grouped into sets (2) forming zones (1) defined by geographical coordinates. 3. A method according to claim 2, characterized in that the areas (1) and sub-areas (2) used in the TDMA system are defined by geographical coordinates, dividing the areas of the world map into a network of regular and / or irregular geometric shapes. 4. A method as claimed in claim 2 or 3, wherein the width of the edge (2) of each zone (1) is approximately equal to the distance between the vehicles using the TDMA system. 5. A method as claimed in any one of claims 2 to 4, wherein in the TDMA system, the size of the division area (1) of the parameter (4) indicating the order of transmission of the radio frequency signals is larger than the satellite field of view (3). 6. A method according to any one of the preceding claims, characterized in that the selection and assignment of the values of the parameter (4) indicating the order of transmission of the radio frequency signals is carried out by a TDMA system, which is an AIS system. 7. A method according to any one of claims 1, 4 to 6, characterized in that the values of the parameter indicating the order of transmission of the radio frequency signals are time interval values (4).