Methods for radio transmission and radio transmission systems

Abstract

A method for the radio transmission of AIS telegrams on the one hand and radio signals that do not conform to the AIS procedure on the other hand via a single antenna, characterized by the following steps: - Connecting an AIS transceiver to the antenna; - Reserving an AIS timeslot using the SOTDMA procedure; - Transmitting an AIS telegram in the reserved timeslot using the SOTDMA procedure; - Connecting a radio module that operates according to a procedure other than the AIS procedure to the antenna; - Transmitting radio signals from and / or for the radio module via the antenna; - Interrupting the transmission of radio signals from and / or for the radio module and connecting the AIS transceiver to the antenna; - Transmitting an AIS telegram in a free AIS timeslot using the CSTDMA procedure;- Connecting the radio module to the antenna and continuing the transmission of radio signals from and / or for the radio module via the antenna, whereby, in the event that an AIS timeslot reserved according to the SOTDMA procedure is still available while radio signals from and / or for the radio module are being transmitted via the antenna, the transmission of these radio signals is interrupted, the AIS transceiver is connected to the antenna and an AIS telegram is sent in the reserved timeslot according to the SOTDMA procedure.

Description

The invention relates to a method for radio transmission according to the preamble of claim 1 and a radio transmission system for carrying out this method according to claim 7. Nowadays, commercial shipping uses a special system called AIS (Automatic Identification System) to exchange data via VHF radio. AIS allows ships to identify themselves and transmit relevant static, voyage-related, and dynamic data, including their own position, clearly to others. Static data provides information such as the ship's name, international radio call sign, ship type, and dimensions. This data is characteristic of the vessel and enables its identification. Voyage-related data includes the current draft, the port of destination, the estimated time of arrival (ETA), and, where applicable, information on the cargo category. This data is fixed for at least one voyage and provides information about the ship's current mission. Dynamic data is of particular importance for collision avoidance with other ships. This data includes precise information about the ship's position, speed and course over ground, exact heading, and current turning behavior. These data are automatically exchanged between AIS transmitting and / or receiving devices at short intervals using special VHF transmitters and receivers. The VHF transmitter sends the data telegrams alternately on one of two internationally defined AIS radio frequencies (161.975 MHz and 162.025 MHz). One of the special features of AIS technology compared to other radio services is the automatic organization of the interaction of several AIS devices on one radio frequency without mutual interference. This is achieved through the SOTDMA (Self-Organizing Time Division Multiple Access) transmission method. The data is transmitted within one or more time slots reserved for the AIS device on the two radio channels. Each AIS transmitter creates its own transmission schedule based on its observed past data traffic and knowledge of future actions by other AIS devices within range. The time slots required for its own transmission are then reserved accordingly. Alternatively, the CSTDMA (Carrier Sense Time Division Multiple Access) transmission method can be used. In this method, data is transmitted during free time slots on the respective radio channel. To do this, the AIS transmitter checks whether the respective radio channel is free during the current time slot before transmitting the data telegram. There are two AIS classes: "Class A" transceivers must be used in commercial shipping subject to reporting requirements and operate according to the SOTDMA method. "Class B" transceivers can be implemented using SOTDMA or CSTDMA technology. They are mostly used in the recreational craft sector, but are not mandatory. There is now another radio system used on commercial and recreational vessels. This system is called DSC (Digital Selective Calling). It is used to send short telegrams (data-based messages) via radio to other ships or coastal stations. A key function is the transmission of a distress call. This includes, among other things, the current position of the vessel that made the call. This allows help to be requested. DSC also operates in the VHF marine frequency band (VHF = ultra-high frequency: 156.000 MHz to 162.050 MHz) and is tuned worldwide to the frequency 156.525 MHz (channel 2070). Unlike AIS, DSC uses two-tone modulation with a data rate of 1200 baud. One tone represents the information "0" and the other the information "1". Groups of 10 such bits constitute a character. These characters are used to form DSC messages or data telegrams. VHF transceivers on ships are usually also equipped with a two-way radio system, which allows the skipper – in addition to DSC transmission and reception – to establish and maintain a two-way radio connection with another user in the VHF marine frequency band. In the following, we will refer to this combination device as a DSC / VHF two-way radio. The invention is based on the idea of ​​using only one antenna for both radio systems (AIS and DSC / VHF radio) commonly used in the marine market, as well as other transmit / receive signals such as S-AIS, IoT, DVB-T, DAB, GSM, LTE, and other future transmit / receive systems, and of splitting the antenna signal path into multiple signal paths (e.g., coaxial cables). This idea is not new and is often referred to as an "antenna splitter" or "antenna switch." German patent DE 10 2009 018 057 A1 describes an antenna switch that allows AIS and DSC transmission via a single antenna. This is achieved using a switching function that prioritizes AIS over DSC at certain times and DSC at other times. A disadvantage of the antenna switch known from DE 10 2009 018 057 A1 is that only one of the two radio systems (e.g., AIS and DSC / VHF radio) can transmit at a time, and that the switch assigns a higher priority to one of the two systems. Depending on the switch's design, it alternates between the two systems. This means that when transmitting simultaneously, one system is connected to the antenna, and the other system is left "idle" (i.e., terminated with an impedance of typically 50 ohms). This prevents both simultaneous transmission by multiple systems and a continuous connection via the antenna from the transmitter to a receiver on board. The question always arises as to which system takes precedence over the other. According to the current state of technology, the following cases exist: (A) The AIS has higher priority than the DSC radio system. If the AIS transceiver transmits, a DSC / VHF radio currently transmitting will be interrupted for the duration of the AIS telegram. (B) The DSC / VHF radio has higher priority than the AIS transceiver. If the DSC / VHF radio is transmitting, the AIS transceiver cannot interrupt this transmission. In case (A), the advantage is that an AIS position message is transmitted via the antenna to other vessels or coastal stations, even if a relatively long radio communication is currently underway using the DSC / VHF radio. The radio communication is only interrupted for the duration of the AIS telegram (26.7 ms), which will only be audible as a very brief "click" in the participants' speakers. This does not interfere with the radio communication. It is more problematic if the AIS telegram interrupts a DSC telegram. A DSC distress call might then not be received. This is much more critical compared to voice radio, as a distress call is considered vital. However, a DSC telegram has built-in redundancy. This redundancy consists of repeating each transmitted character in the telegram after every four characters (i.e., after 33 1 / 3 ms). The receiver is therefore able to utilize this redundancy to detect and, if necessary, correct erroneous characters. This works because the characters are 10 bits long, meaning they have a set of 1024 bit patterns. Only 128 of these patterns are used, allowing for 128 different characters. This system thus has a so-called Hamming interval, which enables the detection of erroneous characters. If an AIS telegram, which is 26.7 ms long, interrupts the DSC telegram, this can be detected due to the Hamming interval, and the receiver uses the repetition to correct these erroneous characters. However, there is a crucial disadvantage: correction is not guaranteed, as it is always possible that the receiver might demodulate one or more valid characters from the noise during the interruption caused by an AIS telegram. Thus, the DSC receiver may still receive valid characters during the interruption, which could be different from the repeated characters. Since the DSC receiving station does not know which character (the first or the repeated one) occurred during the interruption interval of the transmitting station, it may choose the wrong one, and the DSC telegram will not be evaluated. This results in a vital distress call being missed. Similar signal failures can also occur with other transmission systems. In case (B), all DSC telegrams (or VHF radio transmissions) are always transmitted via the antenna. The disadvantage of this is that during prolonged radio communication with the DSC / VHF radio, no AIS messages are transmitted via the antenna. As a result, the vessel in question may disappear from the electronic chart displays (ECDIS) of other vessels or become stationary. The safety that AIS is intended to provide for collision avoidance is no longer guaranteed. This disadvantage is particularly noticeable with Class B SOTDMA transceivers. Should the AIS device be unable to reserve a next transmission slot due to prioritized DSC / VHF transmission, the time until a new AIS telegram can be sent will be extended by the time until the end of the VHF radio conversation plus the time to re-establish the SOTDMA procedure (reservation time plus time until the AIS telegram is sent). From CN 101917205 A, a CSTDMA / SOTDMA dual-system AIS transceiver is known which operates in either the CSTDMA or SOTDMA mode depending on the preset configuration. Upon receiving a corresponding message from a base station or if a specific switching condition occurs, the AIS transceiver switches to the other mode, thus allowing the advantages of both methods to be utilized. US Regulation 2017 / 0256169 A1 describes a system and procedure for reporting and monitoring vessel positions. Regarding AIS, it states that Class A transceivers have a transmit power of up to 12.5 watts, while Class B transceivers are limited to a transmit power of 2 watts. The object of the invention is now to avoid the disadvantages of the above-mentioned cases (A) and (B) and thus to intelligently solve the transmission of DSC messages and AIS messages (as well as other - including future - methods) via a common antenna. This problem is solved by a method for radio transmission with the features of claim 1 and a radio transmission system according to claim 7. Advantageous embodiments and further developments of the invention will become apparent from the dependent claims, the following explanations, and the description of the exemplary embodiment. The invention describes a fundamental improvement of the antenna switching device described in DE 10 2009 018 057 A1 with regard to the use of only one antenna for transmitting AIS and DSC signals, particularly when using SOTDMA Class B transceivers. A significant increase in the overall system's performance is achieved through communication between the connected devices and switching the transmission method in the AIS transceiver depending on the expected transmission success. The invention is based on the following considerations: With an antenna switch according to the prior art as described in DE 10 2009 018 057 A1, it is possible to transmit an AIS message during a prolonged VHF radiotelephony operation without interfering with the radiotelephony participants. The vessel remains visible on the Electronic Navigation Displays (ECDIS) within the transmitter's reception range with a sufficiently good update rate, which is ensured by the interval between successive AIS messages. However, this is not possible if the AIS transceiver in use operates with the SOTDMA method. The SOTDMA method in the AIS network works as follows: The data to be transmitted is transferred within one or more time slots reserved for the AIS device. Each AIS device creates its own transmission schedule based on the past data traffic it has observed and its knowledge of future actions by other AIS devices within range. The time slots required for its own transmission are then reserved. The transmitted data packets are received by all other vessels equipped with such a device within range, thus enabling the transmission of all the aforementioned data. If the antenna used jointly for AIS and VHF radio is occupied by the VHF radio, then from the moment the antenna is occupied by the VHF radio, only the telegram already reserved in the reserved timeslot via the SOTDMA procedure can be transmitted. To do this, the antenna switch interrupts the transmission of the VHF radio system in order to transmit its own telegram. Should the VHF radio link remain active after the reserved telegram has been transmitted (continuous signal), the necessary SOTDMA procedures cannot be followed. The SOTDMA transceiver cannot "listen" to the AIS network to register reservations because the antenna is occupied by the continuous signal from the VHF transmitter. Therefore, the transmitter would be unable to send an AIS message for the duration that the VHF radio occupies the antenna while transmitting. This problem is solved by the invention in that the SOTDMA transceiver checks whether the antenna line is occupied by the VHF radio. If so, the already reserved transmission can be carried out by briefly interrupting the VHF transmission. Thus, the already reserved AIS telegram transmission is executed by interrupting the VHF transmission for the brief duration of one or two slots. A subsequent cyclic transmission cannot then take place using the SOTDMA method because the timeslot reservation is no longer valid and collision-free transmission slots are not guaranteed. One way to still transmit a signal is to change the AIS transmission method used. Transmission using the CSTDMA method, interrupting VHF radio traffic for the length of an AIS slot, is possible. In the CSTDMA method, before transmitting a telegram in a slot, a check is performed to see if a carrier signal is present. If not, the AIS telegram is transmitted within that slot. According to the invention, the system checks whether the VHF radio is occupying the antenna during the scheduled and reserved AIS transmission using SOTDMA technology. If so, the next scheduled and reserved transmission is still sent. Immediately afterward, it is checked whether the VHF radio is still occupying the antenna. If so, no future reservation is created for the next transmission; instead, the Carrier Sense (CSTDMA) method is applied for the time of the scheduled transmission. Within the time slot, it is checked whether a carrier is present, and if not, the transmission is sent. The switch from the SOTDMA to the CSTDMA method is seamless. As soon as the VHF radio is no longer occupying the antenna, the time slot table of reservations made by other AIS stations is updated in the following time period (1 frame = 1 minute) and forwarded using the CSTDMA method.After that, the system switches to the original SOTDMA procedure (with reservations for future transmissions). The radio transmission system according to the invention preferably includes a carrier frequency detection device (carrier sense) so that, when using a common antenna for VHF and AIS, the SOTDMA method used is automatically and seamlessly converted into a CSTDMA method when the antenna is occupied by a VHF radio signal or other signals. One or more existing reservations will still be sent out using the SOTDMA procedure. Once the antenna is no longer occupied by the VHF radio, the switching module can switch the AIS transceiver to the SOTDMA method after a period of one minute (one frame). Switching back to SOTDMA operation can be immediate or delayed. It is particularly advantageous if the switching between the two transmission methods is optimized according to the frequency of position reports. For example, CSTDMA is used if reserving a time slot for SOTDMA is not possible or is delayed for reasons other than the antenna being occupied by VHF radio. The maximum transmission power can be adjusted to the transmission power compliant with the respective transmission technology. The transmission power for CSTDMA must be reduced to 2 watts according to the regulations of the relevant authorities. The switching module can be integrated into the AIS transceiver or an AIS splitter, or into a separate housing. It may be provided that the use of a method (SOTDMA or CSTDMA) can be permanently set via a software command or by pressing a key. The AIS transceiver can transmit using both CSTDMA and SOTDMA technologies. It can be switched between these technologies via control lines and / or automatically. According to a particularly advantageous embodiment of the invention, the switching between CSTDMA and SOTDMA can be carried out in such a way that the probability and reliability of the position transmission is optimized and the occupancy situation of the antenna is taken into account in the best possible way. An embodiment of the invention will be explained in more detail below with reference to the drawing. The single drawing shows a block diagram of a radio transmission system according to the invention. An AIS transceiver (11) has a control output via which the priorities of the high-frequency signal lines (4, 5) of a radio module (9) and the AIS transceiver (11) are controlled via a control signal line (6) to a control unit (2) at an antenna switch (1). Additionally, the AIS transceiver (11) has an input to which information about the existence of a transmitted signal on the high-frequency signal line (4) to or from the radio module (9) (for example, a DSC / VHF radio) is supplied via a signal detection signal line (7) from a carrier frequency detection device (3) at the antenna switch (1). The antenna switch (1) is connected to the control unit (2), which performs the switching function according to the priority setting via the control signal line (6), and to the carrier frequency detection unit (3), which indicates the presence of a transmitted signal on the high-frequency signal line (4) via the signal detection signal line (7). The two units (2, 3) can also be integrated into the antenna switch (1). The existence of a transmitted signal can be detected in the antenna switch (1) by means of a high-frequency detector circuit at each of the inputs of the high-frequency signal lines (4, 5) - e.g. by means of a high-frequency rectifier diode. Alternatively or additionally, information about the activity of the radio module (9) can also be transmitted directly to the AIS transceiver (11) via a communication signal line (8). Furthermore, the radio module (9) can also be controlled directly by the AIS transceiver (11) via this communication signal line (8), e.g., to temporarily interrupt radio communication via the radio module (9). The antenna (10) is connected to the output of the antenna switch (1) - also via a high-frequency signal line. The AIS transceiver (11) can control the priority of the switching operation via the control signal line (6) when transmitting simultaneously on both high-frequency signal lines (4, 5) in the antenna switch (1). This means that if the priority for the high-frequency signal line (5) of the AIS transceiver (11) is set to high via the control signal line (6) and the control unit (2), the AIS transceiver (11) has priority over the radio module (9) (e.g., a DSC / VHF radio) if both are transmitting at the same time. The system now checks whether the radio module (9) is occupying the antenna (10) during an AIS transmission scheduled and reserved using SOTDMA technology. If so, the next scheduled and already reserved transmission will still be sent using SOTDMA technology. Immediately afterward, it is checked again whether the radio module (9) is still occupying the antenna (10). If so, no future reservation is created for the next transmission; instead, the Carrier Sense (CSTDMA) method is applied for the time of the scheduled transmission. Within the time slot, it is checked whether the AIS radio channel is free (i.e., whether a carrier signal is present in the airwaves), and if not, the transmission is sent. The switch from the SOTDMA to the CSTDMA method is seamless. As soon as the radio module (9) no longer occupies the antenna (10), the timeslot table of reservations made by other AIS stations is updated in the following time period (1 frame = 1 minute) and initially transmitted using the CSTDMA method (until the reserved timeslot is reached). Afterwards, the system switches to the original SOTDMA method (with reservations for future transmissions). REFERENCE MARK LIST: 1 Antenna switch 2 Control unit 3 Carrier frequency detection unit 4 Radio high-frequency signal line 5 AIS high-frequency signal line 6 Control signal line 7 Signal detection signal line 8 Communication signal line 9 Radio module 10 Antenna 11 AIS transceiver 12 Switching module

Claims

Method for the radio transmission of AIS telegrams on the one hand and of radio signals that do not conform to the AIS procedure on the other hand via a single antenna, characterized by the following steps: - Connecting an AIS transceiver to the antenna; - Reserving an AIS timeslot according to the SOTDMA procedure; - Transmitting an AIS telegram in the reserved timeslot according to the SOTDMA procedure; - Connecting a radio module that operates according to a procedure other than the AIS procedure to the antenna; - Transmitting radio signals from and / or for the radio module via the antenna; - Interrupting the transmission of radio signals from and / or for the radio module and connecting the AIS transceiver to the antenna; - Transmitting an AIS telegram in a free AIS timeslot according to the CSTDMA procedure;- Connecting the radio module to the antenna and continuing the transmission of radio signals from and / or for the radio module via the antenna, whereby, in the event that an AIS timeslot reserved according to the SOTDMA procedure is still available while radio signals from and / or for the radio module are being transmitted via the antenna, the transmission of these radio signals is interrupted, the AIS transceiver is connected to the antenna and an AIS telegram is sent in the reserved timeslot according to the SOTDMA procedure. Method for radio transmission according to claim 1, characterized in that after termination of the transmission of radio signals from and / or for the radio module via the antenna, the AIS transceiver is connected to the antenna and an AIS timeslot is reserved according to the SOTDMA method. Method for radio transmission according to claim 1 or 2, characterized in that, in the event that a reservation of an AIS timeslot cannot be successfully carried out according to the SOTDMA method, an AIS telegram is sent in a free AIS timeslot according to the CSTDMA method. Method for radio transmission according to one of the preceding claims, characterized in that the transmission power when sending an AIS telegram according to the SOTDMA method is 5 watts, when sending an AIS telegram according to the CSTDMA method is 2 watts. Method for radio transmission according to one of the preceding claims, characterized in that switching between an operating mode of the AIS transceiver according to the SOTDMA and the CSTDMA method is carried out via an electronic command and / or the actuation of a control element. Method for radio transmission according to one of the preceding claims, characterized in that, depending on the occupancy situation of the antenna and / or the probability of a secure transmission of AIS telegrams, the operating mode of the AIS transceiver according to the SOTDMA and the CSTDMA methods is switched. A radio transmission system for carrying out the method according to one of the preceding claims, characterized in that it comprises: - an AIS transceiver (11) configured and equipped to operate according to the SOTDMA and CSTDMA methods; - a radio module (9) configured and equipped to operate according to a method other than the AIS method; - an antenna (10) for transmitting and receiving radio signals; - an antenna switch (1) connected to the AIS transceiver (11), the radio module (9), and the antenna (10), and configured and equipped to switch either the AIS transceiver (11) or the radio module (9) to the antenna (10); - a control device (2) configured and equipped to control the antenna switch such that either the AIS transceiver or the radio module is connected to the antenna. is;- a switching module (12) designed and configured to switch the AIS transceiver (11) between operating modes according to the SOTDMA and CSTDMA procedures.; Radio transmission system according to claim 7, characterized in that it has a carrier frequency detection device (3) preferably operatively connected with the antenna switch (1), which is designed and configured to detect the occupancy of the antenna (10) by a radio signal from and / or for the radio module (9). Radio transmission system according to claim 7 or 8, characterized in that the switching module (12) is integrated into the AIS transceiver (11) or is housed in its own enclosure and is operatively connected to the AIS transceiver (11). Radio transmission system according to one of claims 7 to 9, characterized in that the AIS transceiver (11) and / or the switching module (12) has an electronic input and / or an operating element, in particular a push button, for switching between an operating mode of the AIS transceiver (11) according to the SOTDMA and the CSTDMA methods. Radio transmission system according to one of claims 7 to 10, characterized in that the transmit power of the AIS transceiver (11) is switchable between 5 W and 2 W.

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