SYMMETRICAL DATA TRANSFER METHOD AND DEVICES FOR IMPLEMENTING IT

Description

[0001] The invention relates to a data transmission method defined in independent claim 1, in which data transmission between a first transceiver and a second transceiver is carried out via cable in both directions at a data rate of the same order of magnitude. The invention further relates to a modem comprising a transceiver with a first interface for data transmission and a computer connected to the transceiver via a second interface. The invention further relates to a railway system comprising a first subsystem with a first modem and a second subsystem with a second modem, wherein the first modem and the second modem are connected to each other via a first interface. Finally, the invention relates to a computer program product and a deployment device for this computer program product, wherein the computer program product is equipped with program instructions for carrying out this method.

[0002] In railway technology, there are applications where signal transmission between railway components in both directions is required. For example, signal transmission may be necessary between an indoor installation in a signal box and an outdoor installation, represented, for instance, by a light signal or a balise. For this purpose, the railway components are connected by cables.

[0003] ISDN signal transmission is widely used. However, this is an outdated technology, and it is foreseeable that the necessary hardware components will become increasingly difficult to obtain. Therefore, for signal transmission applications such as railway technology, there is a need for alternative transmission technologies.

[0004] Document EP 1 855 413 A1 describes a method for providing frames and providing predefined bit lengths in each frame for transmitting data from a sender to a receiver and vice versa. Each frame comprises a time slot during which no information is transmitted from the sender to the receiver and vice versa, and the pulse is transmitted from the sender to the receiver.

[0005] Document US 2008 / 247367 A1 describes embodiments of systems and methods for the coexistence of Bluetooth and WiMAX. A temporal reference associated with one frame is determined, and then another wireless frame is aligned with this temporal reference.

[0006] Document US 2004 / 117076 A1 describes a system for the remote control of one or more locomotives. The system comprises a remote control unit into which a human operator inputs commands and a locomotive control unit mounted in the locomotive. The remote control unit communicates with the locomotive control unit via a radio frequency (RF) communication link.

[0007] The object of the invention is to provide a data transmission method or a device for carrying out this data transmission method for signals in both directions, which ensures high reliability during transmission and is particularly suitable for safety-critical applications such as railway engineering applications. Furthermore, the object of the invention is to provide a computer program product and a delivery device for this computer program product with which the aforementioned method can be carried out.

[0008] This problem is solved according to the invention with the subject matter of the claim specified at the outset (data transmission method) in that A Time Division Duplex (TDDuplex) method is used to transmit the data-representing signals in both directions, in which time slots for sending and time slots for receiving the signals are assigned to the first and second transceivers respectively, the assignment of the time slots for the first and second transceivers is synchronized in such a way that one time slot for sending and one time slot for receiving always run synchronously, and an OFDM method is used for modulating the signals. in which all available carrier frequencies are used for both directions of transmission, with each time slot being assigned a modulation rule for each carrier frequency used.

[0009] For transmitting signals in both directions (duplex operation), a Time Division Duplex (TDD) method is used. In this method, defined time slots are allocated for the transceiver's operation for both sending and receiving data, ensuring that the transceiver is always either transmitting or receiving exclusively. A distinction is made between time slots for transmitting signals and time slots for receiving signals. When the term "time slots" is used generally, the statements associated with it apply equally to both transmitting and receiving time slots.

[0010] To ensure the transmission quality as described above, the invention provides that each time slot for each carrier frequency used is assigned a modulation scheme, and that this modulation scheme can be redefined by means of control signals also transmitted, if the modulation scheme for the respective carrier frequency is to be changed. This makes it possible to react specifically to a deterioration in transmission quality at each carrier frequency used, with changes being made by modifying the modulation scheme.

[0011] Each channel used for transmission is assigned a carrier frequency. The carrier frequency is linked to a modulation scheme. This creates an array of modulation schemes assigned to the carrier frequencies, which, in connection with this invention, shall also be referred to as a modulation table. Part of the modulation scheme is also a data rate to be transmitted for the signals to be transmitted, the level of which influences a reserve for transmission losses (for example, due to transmission errors) in the respective carrier frequency.

[0012] According to the invention, OFDM (Orthogonal Frequency-Division Multiplexing) is an implementation of multicarrier modulation. It is a modulation method that uses multiple orthogonal carriers for digital data transmission (i.e., the maximum of a carrier lies at a zero crossing of each of its neighboring carriers, thereby reducing interference between signals modulated onto adjacent carriers).

[0013] The data signals to be transmitted are first split into several low-rate substreams. Each of these substreams is modulated individually using a conventional modulation technique such as narrow-bandwidth quadrature amplitude modulation, and the modulated RF signals are then transmitted together. To distinguish the individual signals during demodulation at the receiver, it is necessary that the carriers in the function space are orthogonal. This ensures that the substreams interfere with each other as little as possible.

[0014] The OFDM transmission technology described above is typically used for transmitting data at relatively high rates, for example, in wireless LAN networks. However, the transmission reliability achievable with this technology would not be sufficient for railway applications. This is the basis for the invention's approach: to implement only the data modulation using OFDM technology, but to select a TDD method, as known from ISDN, to ensure bidirectional communication. This makes it possible to use all available carrier frequencies for both directions of transmission. Therefore, the choice of frequency can be based on achieving the highest possible transmission quality, rather than on whether the carrier frequency is intended for upload or download.

[0015] The application of a TDD method is further facilitated by the fact that data transmission in both directions occurs at a data rate of the same order of magnitude. This means that the data transmission rates for one direction and the other differ by no more than a factor of 10 on average over time, and preferably by no more than a factor of 2. In terms of the design of the data transmission in both directions, the data transmission method can therefore be described as symmetrical.

[0016] For example, in railway applications, the applications that exchange data are largely equivalent with regard to the amount of data to be exchanged. This also means that, advantageously, the available reserves for eliminating transmission errors can be distributed equally between both transmission directions to improve transmission quality. This makes the transmission method according to the invention equally reliable in both directions (more on this below).

[0017] "Useful signals" within the meaning of the invention are those signals for which the data transmission method is carried out, i.e., those signals that are to be exchanged. In other words, they are signals that are required for the operation of applications that communicate with each other using the data transmission method.

[0018] In contrast, "control signals" are those signals required to carry out the data transmission process. Specifically, it is necessary to exchange control signals for changing modulation rules so that the first transceiver and the second transfer can communicate continuously. It is also necessary to synchronize the communication between the first and second transceivers. For this purpose, synchronization signals, which also function as control signals, can be sent at regular intervals.

[0019] In the context of the invention, "computer-aided" or "computer-implemented" can be understood as an implementation of the method in which at least one computer performs at least one process step of the method.

[0020] The term "computer" covers all electronic devices with data processing capabilities. Computers can include, for example, personal computers, servers, handheld computers, mobile phones and other communication devices, processors, and other electronic devices for data processing, which may preferably also be connected to a network.

[0021] In the context of the invention, a "processor" can be understood to mean, for example, a converter, a sensor for generating measurement signals, or an electronic circuit. In particular, a processor can be a central processing unit (CPU), a microprocessor, a microcontroller, or a digital signal processor, possibly in combination with a memory unit for storing program instructions, etc. A virtualized processor or a soft CPU can also be understood as a processor.

[0022] In the context of the invention, a "storage unit" can be understood to mean, for example, a computer-readable memory in the form of a working memory (Random-Access Memory, RAM) or data storage device (hard drive or data carrier).

[0023] "Interfaces" can be implemented in hardware, for example as a wired or wireless connection, or in software, for example as an interaction between individual program modules of one or more computer programs.

[0024] The term "program modules" refers to individual functional sequences that enable a program sequence of computer-aided process steps according to the invention. These functional sequences can be implemented in a single computer program or in several communicating computer programs. The interfaces implemented here can be implemented in software within a single processor or in hardware if multiple processors are used.

[0025] According to one embodiment of the invention, it is provided that, for synchronization in a synchronization process, a synchronization signal is transmitted from the first transceiver or the second transceiver to the other transceiver.

[0026] Synchronization is necessary so that the timeslots for transmitting and receiving are complementary and perfectly aligned. This means that a transmitting timeslot in the first transceiver is synchronized with a receiving timeslot in the second transceiver, and vice versa.

[0027] Synchronization by sending a synchronization signal has the advantage of compensating for time drift between the first and second transceivers. This particularly allows the use of COTS (commercial-off-the-shelf) components, resulting in cost advantages.

[0028] According to one embodiment of the invention, it is provided that several time slots lie between successive synchronization processes, wherein the successive synchronization processes form a frame.

[0029] For example, eight time slots can be contained within a frame. Other frame sizes are also conceivable. The synchronization process itself also requires a certain amount of time. By combining multiple time slots between synchronization processes, the transmission capacity available for exchanging useful signals increases.

[0030] The number of time slots that can elapse between two successive synchronization processes depends on the accuracy of the clocks used. It must be ensured that any time drift between successive synchronization processes does not compromise the transmission method with regard to the reliable transmission of signals.

[0031] According to one embodiment of the invention, the synchronization signal is used to determine the signal propagation time between the first transceiver and the second transceiver.

[0032] The synchronization signal can be advantageously used to determine a previously unknown signal propagation delay in the connection between the first and second transceivers. This can be done, for example, by sending the signal from the first transceiver to the second and then back again from the second to the first. The time difference between sending the synchronization signal and receiving it by the first transceiver allows the signal propagation delay to be determined (more on this below).

[0033] According to one embodiment of the invention, it is provided that during the synchronization process, after sending and receiving the synchronization signal, a grace period is traversed before the next transmit time slot and receive time slot are reached in the first transceiver and in the second transceiver, respectively.

[0034] Including a grace period has the advantage of allowing the synchronization signal to decay after transmission before a useful signal is sent and received in the following timeslot. This ensures uninterrupted transmission and avoids an increase in the correction rate caused by the synchronization signal.

[0035] According to one embodiment of the invention, it is provided that the same carrier frequency range is used for sending and receiving the signals in the first transceiver and in the second transceiver.

[0036] The advantage of using the same carrier frequency range for both directions has already been explained. By applying the TDD method, the carrier frequency range can be used for both transmitting and receiving signals. This means that the carrier frequencies defining the carrier frequency range can be selected solely based on transmission quality. The advantage is that the transmission quality is equally high for both transmission and transmission directions.

[0037] The possibility of selecting suitable carrier frequencies, i.e., carrier frequencies that offer good transmission quality, presupposes that more carrier frequencies are available for transmission than are required by the data rates to be transmitted. In other words, a reserve for modifying the transmission method can also consist of the availability of unused carrier frequencies, which, if necessary, can preferably be selected equally for both transmission directions.

[0038] According to one embodiment of the invention, it is provided that signals received in the first transceiver and second transceiver are amplified depending on the transmission-related attenuation of the signal.

[0039] This embodiment of the invention takes into account the fact that the transceivers for receiving signals have a dynamic range within which the receiver is optimally controlled. However, the transmission method should be usable with the same hardware for transmission lines of different lengths. Since the transmission attenuation increases with the line length, the transceivers cannot be controlled equally well with respect to the dynamic range for different transmission distances.

[0040] This problem can be addressed by amplifying the signals. The amplification is then adjusted in operation so that the signal received by the transceiver is optimally modulated. Greater attenuation during transmission requires greater amplification, and conversely, lower attenuation requires less amplification. Attenuation typically increases over longer transmission distances.

[0041] According to one embodiment of the invention, it is provided that the degree of amplification is determined during the initialization of the data transmission process.

[0042] Initialization of the data transmission process takes place when the data transmission process is started. At this point, the attenuation of the transmission path can be checked to create optimized transmission conditions from the outset, ensuring that the signal amplification is optimally set. Initialization is particularly necessary during initial commissioning. However, it is also advisable during recommissioning, for example, after the data transmission process is restarted following a period of inactivity, because transmission conditions, especially the transmission attenuation, may have changed in the meantime.

[0043] The aforementioned problem is alternatively solved according to the invention with the subject matter of the claim (modem) specified at the outset by the modem being configured to carry out a method for data transmission according to one of the preceding claims.

[0044] The aforementioned problem is also alternatively solved according to the invention with the subject matter of the claim specified at the outset (railway system) by the fact that the first modem (M1) and the second modem (M2) are each designed in accordance with the preceding claim.

[0045] The devices offer the advantages already explained in connection with the method described in more detail above. The statements made regarding the method according to the invention also apply accordingly to the devices according to the invention.

[0046] Furthermore, a computer program product with program commands for carrying out the said inventive method and / or its embodiments is claimed, wherein the inventive method and / or its embodiments can be carried out by means of the computer program product.

[0047] Furthermore, a provisioning device for storing and / or providing the computer program product is required.

[0048] The delivery device is, for example, a storage unit that stores and / or provides the computer program product. Alternatively and / or additionally, the delivery device is, for example, a network service, a computer system, a server system, in particular a distributed, for example cloud-based, computer system and / or virtual computer system, which preferably stores and / or provides the computer program product in the form of a data stream.

[0049] The provision of the computer program product takes the form of a program data block as a file, in particular as a download file, or as a data stream, in particular as a download data stream. This provision can also, for example, take the form of a partial download consisting of several parts. Such a computer program product is, for example, read into a system using the provisioning device, so that the method according to the invention is executed on a computer.

[0050] Further details of the invention are described below with reference to the drawing. Identical or corresponding drawing elements are each provided with the same reference numerals and are only explained more than once to the extent that differences arise between the individual figures.

[0051] The exemplary embodiments described below are preferred embodiments of the invention. In these embodiments, the described components each represent individual features of the invention that can be considered independently of one another. Each of these features further develops the invention independently and can therefore be considered part of the invention individually or in a combination other than that shown. Furthermore, the described components can also be combined with the features of the invention described above.

[0052] They show: Figure 1 An exemplary embodiment of the devices according to the invention (modem and railway system) with their interactions shown schematically, Figure 2 the signal amplitude s as a function of time t in a diagram, in which an exemplary frame with 8 time slots for the transmission of signals is shown, Figure 3an embodiment of the inventive method for transmitting signals in a frame according to Figure 2 as a flowchart, whereby the individual process steps can be implemented individually or in groups by program modules, and whereby the functional units and interfaces are defined according to Figure 1 are indicated by example, Figure 4 An embodiment of the method according to the invention with the program modules of a direct channel estimation and an indirect channel estimation, wherein the method according to Figure 3 in the procedure according to Figure 4 is embedded several times.

[0053] In Figure 1This diagram schematically depicts a railway system. It is represented by a signal box (SW) and a track (GL). Track GL also includes a light signal (LSG) and a train protection system (ZSE). The train protection system (ZSE) could, for example, be a balise. This diagram is highly simplified. The railway system could contain additional functional elements beyond those shown, which, due to a common functional relationship, define the railway system.

[0054] The illustrated elements can, however, serve to explain the functioning of a signal transmission according to the invention. The signal transmission takes place via a wired first interface S1. It connects a first sub-system of the railway system, which is located in Figure 1 as an indoor system IA in the SW signal box, with a second sub-system of the railway system, which is in Figure 1as an external installation AA on track GL, for example in a switch box not shown in detail.

[0055] In the indoor unit IA, a first modem M1 and in the outdoor unit AA, a second modem M2 are used for transmitting signals via the first interface S1. The first modem M1 includes a first transceiver TC1, a first computer CP1, and a first storage device SE1. The computer CP1 is connected to the transceiver TC1 via a second interface S2.1 and to the first storage device SE1 via a third interface S3.1.

[0056] The second modem M2 is configured accordingly. A second computer CP2 is connected via a second interface S2.2 to a second transceiver TC2 and via a third interface S3.2 to a second storage device SE2. The first transceiver TC1 and the second transceiver TC2 communicate with each other via the aforementioned first interface S1, a wired interface designed to bridge greater distances, for example, up to 20 km. In addition to signal transmission via the first interface S1, a power line PL is also provided between the first modem M1 in the indoor installation IA and the second modem M2 in the outdoor installation AA, supplying power to the second modem M2.

[0057] The first modem, M1, is configured to transmit control commands from the SW interlocking system to the AA external control unit. This unit is configured to transmit the control commands to the LSG light signal via a fourth interface, S4, and to the ZSE train protection system via a fifth interface, S5. Conversely, feedback signals from the ZSE train protection system or the LSG light signal can be transmitted to the SW interlocking system in the same way via the first interface, S1.

[0058] As mentioned, the railway facility is according to Figure 1 This is a highly simplified representation. In particular, additional computers, not shown, may be used to control the light signal LSG or the train protection device ZSE in the external system AA, as well as to generate control commands in the internal system IA.

[0059] In Figure 2The signal waveform of the transmitted signal s over time t of one of the two transceivers is shown. In this exemplary embodiment, it is assumed that this is the first transceiver, TC1. The signal waveform will be explained using a frame FRM, where Figure 2 This can be deduced from the fact that this frame FRM represents a section of the temporal progression of the signal s, and in this way an unrepresented sequence of frames is created.

[0060] As in Figure 2 As depicted, the frame is bounded (and defined) by synchronization signals SCS, which are sent at regular intervals by the first transceiver TC1. Time slots ZSS are available within the FRM frame for sending both the synchronization signal SCS and the data signals NTS and control signals STS. As shown in Figure 2As indicated, a transmission signal is sent via the first interface S1. This is represented by a signal waveform in the form of oscillations (fluctuations in signal amplitude) in Figure 2 As indicated. Furthermore, there are time slots ZSE for receiving, in which the first transceiver TC1 does not transmit, but receives. The received signal is in Figure 2 Not shown. The transmit signal is not present in the time slots for receiving ZSE, as it cannot be transmitted (due to the operating principle of the time-division duplex method).

[0061] Furthermore, in Figure 2 It can be seen that a frame FRM provides four timeslots for transmitting (ZSS) and four timeslots for receiving (ZSE). In addition, there is a timeslot for transmitting (ZSS) in which the synchronization signal (SCS) is transmitted. The remaining timeslots are available for transmitting a data signal (NTS) and / or a control signal (STS), as described in Figure 2This is also indicated. Signals relating to the ongoing application of the railway system are to be understood as utility signals. These could, for example, be the control of a light signal. Signals necessary for the operation of the transmission method according to the invention are to be understood as control signals (STS). These could, for example, be adjustments to the process flow of the transmission method that are required to ensure the transmission quality in the long term (more on this below).

[0062] It should be noted that the time slots for receiving ZSE can also contain both received user signals NTS and received control signals STS, even if this is in Figure 2not shown. A frame FRM of the second transceiver TC2 would look similar to that of the first transceiver TC1; except that the transmit timeslots ZSS and the receive timeslots ZSE, at least of those timeslots transmitting the data signals NTS and the control signals STS, would be complementary to those shown. Figure 2 They would be arranged as shown. This ensures that the second transceiver, TC2, receives while the first transceiver, TC1, transmits, and vice versa.

[0063] For receiving the SCS synchronization signal through the timeslot for transmitting ZSS of the first transceiver TC1 (in Figure 2(as shown) a time slot for receiving ZSE (not shown) is simultaneously available in the second transceiver TC2. If the signal propagation time in the cable implemented via the first interface S1 is known, the process can be synchronized by receiving the synchronization signal SCS in the second transceiver TC2, thereby correcting any clock drift for synchronizing the time windows.

[0064] The synchronization signal SCS can also be used, in a manner not shown, to determine the signal propagation time in the cable forming the first interface S1. For this purpose, the synchronization signal SCS, transmitted by the first transceiver TC1, is received by the second transceiver TC2, received back, and then received again by the first transceiver TC1. If the response time of the second transceiver TC2 is known, the signal propagation time can be determined by subtracting the response time of the second transceiver TC2 from the time it is received and the transmission time of the synchronization signal SCS by the first transceiver TC1. The result is then divided by 2. Naturally, the roles of transceivers TC1 and TC2 can be reversed in this propagation time measurement procedure.

[0065] Furthermore, in Figure 1Grace periods KT are shown. These are provided in the transmission time slot ZSS of the synchronization signal SCS so that the synchronization signal can decay and does not interfere with the transmission of control signals STS and user signals NTS in subsequent transmission time slots ZSS. These grace periods also apply in the transmission time slots and / or in the reception time slots (the latter in Figure 2 (Not shown) Grace periods KT can be provided to account for signal propagation times. This ensures that transmitted signals STS, NTS can be fully received within the available receive time window ZSE, even considering their propagation time. Therefore, signal transmission ends in the transmit time window ZSS by the amount of the grace period KT before the actual end of the transmit time window ZSS.

[0066] In Figure 2It is further shown that the signals sent in the transmission time windows ZSS do not necessarily always contain control signals STS and user signals NTS. Control signals STS only need to be transmitted if changes are to be made to the transmission procedure currently in progress. User signals NTS only need to be transmitted if communication is required between the indoor unit IA and the outdoor unit AA. In contrast, synchronization signals SCS are transmitted every time there is a transition from one frame FRM to the next.

[0067] In Figure 3 is shown in a flowchart how the process flow within a framework FRM according to Figure 2 The first transceiver, TC1, can be configured as such. The second transceiver, TC2, is also indicated, although the procedure has been simplified here.

[0068] After starting at the beginning of the FRM framework (see Figure 2 ) First, a synchronization step, SYNC, takes place, in which a synchronization signal is sent or exchanged between the first transceiver TC1 and the second transceiver TC2 via the first interface S1 (as described above). This occurs in the first Figure 2 The timeslot shown is used for transmitting ZSS, while at the same time a timeslot ZSE is available in the second transceiver TC2.

[0069] In the next step, a generated signal is retrieved from a PROC process step of the railway application, which is simplified according to Figure 3The signal has the bit sequence 110001. This signal is now to be transmitted using the OFDM method. In a subsequent splitting step for the SER-PAR signal, the bit sequence is distributed across three carrier frequencies (channels). As indicated, this results in the sub-signals 11, 00, and 01. These sub-signals are then distributed across several orthogonal carrier frequencies, symbolized by the splitting into a real component RE and an imaginary component IM.

[0070] The resulting OFDM signal is then subjected to an inverse discrete Fourier transform (IDFT) so that a single signal with a real component (RE) and an imaginary component (IM) can subsequently be subjected to a digital-to-analog conversion (DAC) step. The analog signal thus obtained is transmitted via the first interface S1 to the second transceiver TC2. For this purpose, as shown in Figure 3As indicated, the first transceiver TC1 is in a timeslot for transmitting ZSS and the second transceiver TC2 is in a timeslot for receiving ZSE.

[0071] In the second transceiver TC2, an analog-to-digital conversion (ADC) takes place in the next step, followed by a reception procedure that is analogous to the reception procedure that will be described below for the transceiver TC1.

[0072] In the second transceiver, TC2, a transmit timeslot ZSS occurs, coinciding with a receive timeslot ZSE in transceiver TC1. A new signal from an unspecified process, containing the bit sequence 001001, is subjected to an OFDM process via a transmit procedure (not shown in detail), analogous to the one described above for the first transceiver, TC1, and concludes with a digital-to-analog conversion (DAC) step.

[0073] The signal is then transmitted via the first interface S1 to the first transceiver TC1, where the reception procedure begins. This starts with an analog-to-digital conversion (ADC) step followed by a Fourier transform (FFT) of the digitized signal. This splits the signal into its carrier frequencies, represented by the respective real (RE) and imaginary (IM) components, resulting in the partial signals 00, 10, and 01. In a subsequent aggregation step for the PAR-SER signal, the resulting signal 001001 is combined and can then be fed into a further PROC process step of the railway application.

[0074] A counter variable n is then incremented by 1 in a step n=n+1. Subsequently, in a query step to determine if the frame end has been reached, it is checked whether the counter variable n has already reached the number of time slots m for a frame (query step n=m). If so, the transmission in the respective frame is terminated (procedure step STOP). If not, the transmission is repeated for two further time slots: one for sending (ZSS) and one for receiving (ZSE) in transceivers TC1 and TC2.

[0075] The Figure 4 can be seen as the in Figure 3The described method, which outlines the procedure between two synchronization signals, can be embedded in a transmission method. This method employs both a direct channel estimation (DCE) and an indirect channel estimation (ICE) method in different stages to improve or maintain transmission quality. The method according to Figure 3 will be in Figure 4 represented by the transmit steps SEND S and Send 0, where these transmit steps can represent one time slot for sending ZSS or several time slots for sending ZSS, preferably the time slots belonging to a frame FRM.

[0076] When the connection between the two transceivers, i.e., the first and second transceivers (not shown), is initiated (procedure step START), a query is performed to determine whether the procedure should be initialized. This is particularly necessary during initial setup, when the first and second transceivers are still equipped by default with a modulation table containing modulation rules for various carrier frequencies. While communication between the first and second transceivers is therefore possible, it is highly unlikely to occur under optimal transmission conditions.

[0077] For this purpose, a channel estimation method is performed. This is referred to as direct channel estimation (DCE) because it can employ known channel estimation methods, as well as the one described below. According to Figure 4 For channel estimation, it is provided that during a transmission step for a signal SEND S in a timeslot ZSS on a selected transmission frequency, also referred to as a channel, the signal S is transmitted. In another timeslot ZSS, a transmission step without a signal SEND 0 is carried out, in which a transmission takes place, but no signal is modulated onto the respective carrier frequency. In both of the aforementioned transmission steps, a recording step for a receive parameter REC PAR is performed as a receive parameter according to Figure 4 The signal amplitude s was recorded. It should be noted that even in the case of a transmission step without a signal (SEND 0), a signal is received which represents noise during signal transmission. Therefore, in a subsequent determination step (CALC QNOISE), the signal-to-noise ratio for a transmission on the relevant channel can be determined.

[0078] In a subsequent query step, NEXT CH, it is checked whether another channel is present. If so, the direct channel estimation (DCE) method is also performed for this channel, i.e., this carrier frequency.

[0079] Once all available channels have been checked and their signal-to-noise ratio is known, a signal gain adjustment (SET AMP) can be performed to improve transmission quality. This ensures that the signal amplitude of the signal received by the first or second transceiver is optimally adjusted. Additionally, after the transmission quality for all channels has been estimated, the modulation table can be updated in a modulation adjustment (SET MOD). This update prioritizes channels with comparatively good transmission quality. Furthermore, the data rate can be adjusted so that it is higher for channels with better transmission quality than for channels with poorer transmission quality.These modifications assume that the total nominally available transmission volume of the transmission method in question is not fully utilized. This is particularly relevant in railway applications, as the (preferably wired) data connection is primarily used for transmitting messages and control commands that require a small data volume.

[0080] With the updated modulation table, it is now possible to perform SEND S transmission steps in which useful signals NTS (see below). Figure 2 ) are transferred to initiate a PROC process (see below). Figure 3to support the transmission process. For the purpose of monitoring the transmission process, the correction rate resulting from the transmission of the signals is recorded at regular intervals, preferably for each frame, for a defined number of time slots, or over a defined period, in a recording step REC CR. Correction of the transmitted data can be carried out in a manner known per se by determining bit errors in coded signals. The recording of the correction rate is performed according to... Figure 4 Specifically, over a defined period T, where in a query step t=T it is checked whether the end of the defined period has been reached (alternatively, not shown, the monitored time slots can also be counted and compared with a defined number for the time slots).

[0081] Once this is the case, the indirect channel estimation method (ICE) is initiated. This channel estimation method is called indirect because it does not use a received parameter that would allow a direct conclusion about the transmission quality. Instead, it uses the correction rate for transmitted data, from which conclusions about transmission quality can only be drawn indirectly. Therefore, the indirect channel estimation method (ICE) described below depends on whether changes to the transmission method actually contribute to an improvement in the error rate—and thus indirectly in the transmission quality.

[0082] For this purpose, a query step CR>MAX checks whether the correction rate is greater than an upper limit MAX. If so, a data rate reduction step RED DR is performed to provide more redundancy for reliable transmission of the user data. Subsequently, another signal is sent in a transmit step SEND S, and a recording step for the correction rate REC CR is performed. In a subsequent query step CR <CROLD wird abgefragt, ob sich durch die Reduktion der Datenrate auch die Fehlerrate verkleinert hat. Ist dies der Fall, so wird die Reduktion der Datenrate beibehalten und es wird der nächste Sendeschritt für Signale SEND S durchgeführt. Ist dies nicht der Fall, so wird in einem Zurücksetzungsschritt für die Datenrate DR=DROLD wieder die alte Datenrate gesetzt, da sich die Maßnahme nicht bewährt hat.Alternatively, the carrier frequency can also be changed in a CHANGE TF step, provided a carrier frequency is available that has not yet been used. With these changes, the next transmission step for a signal SEND S is performed.

[0083] However, if the CR>MAX query step returns a negative result, CR will be used in the next query step. <MIN geprüft, ob die Korrekturrate kleiner als ein unterer Grenzwert ist (der untere Grenzwert liegt betragsmäßig unterhalb des oberen Grenzwertes oder ist mit diesem gleich, d. h. MAX ≥ MIN). Ist dies der Fall, wird in einem Steigerungsschritt RISE DR die Datenrate gesteigert, damit "gute" Trägerfrequenzen besser ausgelastet werden. In einem nachfolgenden Abfrageschritt CR> CROLD checks whether the correction rate has increased. If so, a reset step DR=DROLD resets the data rate, as an increase in error correction indicates that the carrier frequency was already optimally utilized. However, if the correction rate does not change, the next transmission step for a signal SEND S is performed at the new data rate.

[0084] After both query steps for the correction rate have been completed, a further query step, NEW INI, is executed, asking whether a re-initialization should be performed. This is also possible during the process, although this requires interrupting the data transmission for user data (NTS). This must be ensured through appropriate process control of PROC, such that interrupting data transmission does not pose any security risks. This is of paramount importance, especially in railway technology; the initialization step can, for example, be carried out during operational breaks.

[0085] Data transmission then continues, potentially using modified data rates (DR) or carrier frequencies (TF). During the next period (T), as previously explained, the correction rates are recorded and, if necessary, further modified. When an END TRANS query indicates that the end of the transmission (end of operation of the running PROC process) has been reached, the transmission process is terminated. Reference symbol list

[0086] SW Interlocking G Track IA Indoor system AA Outdoor system M1 ... M2 Modem TC1 ... TC2 Transceiver CP1 ... CP2 Computer SE1 ... SE2 Storage device PL Power line LSG Light signal ZSE Train protection system S1 ... S5 Interface s Signal strength t Time S Signal STS Control signal NT S User signal SCS Synchronization signal ZSE Time slot for receiving ZSS Time slot for sending FRM Frame SYNC Synchronization step SER-PAR Splitting step for the signal IDFT Inverse discrete Fourier transform DAC Digital-to-analog conversion ADC Analog-to-digital conversion FFT Fourier transform PAR-SER Combining step for the signal PROC Process step n=n+1 Incrementing the counter variable n=m Query step Frame end INI Query step Initialization SEND S Transmit step for a signal SEND 0 Transmit step without signal REC PAR Recording step for a receive parameter CALC QNOISE Determining step for Signal-to-noise ratio NEXT CH Query step: Is another channel available? SET AMP Setting step for signal gain SETMOD setting step for modulation REC CR recording step for correction rate t=T query step for the end of a defined period CR>MAX query step: correction rate greater than upper limit CR <MINAbfrageschritt: Korrekturrate kleiner als unterer Grenzwert RED DRReduzierungsschritt für Datenrate RISE DRSteigerungsschritt für Datenrate CR> CROLD query step: Increase in correction rate DR=DROLD reset step for data rate CHANGE TF carrier frequency change step NEW INI query step for re-initialization END TRANS query step end of transmission DCE direct channel estimation ICE indirect channel estimation

Claims

1. Data transmission method, in which a wired transmission of data between a first transceiver (TC1) and a second transceiver (TC2) takes place in both directions at a data rate in the same order of magnitude, wherein • a time division duplex method is used for the transmission of signals (S) representing data in both directions, in which method time slots for sending (ZSS) and time slots for receiving (ZSE) the signals are assigned to the first transceiver (TC1) and the second transceiver (TC2) in each case, such that each transceiver is always either only for sending or only for receiving, • the assignment of time slots for the first transceiver (TC1) and the second transceiver (TC2) is synchronised such that a time slot for sending (ZSS) and a time slot for receiving (ZSE) always run synchronously in each case, characterised in that • an OFDM method is used for modulating the signals (S), • in which method all available carrier frequencies are used both for the one transmission direction and for the other transmission direction, wherein a modulation specification is assigned to each time slot for each carrier frequency used.

2. Data transmission method according to claim 1, characterised in that in a synchronisation procedure (SYNC), for the purposes of synchronisation, a synchronisation signal (SCS) is transmitted from the first transceiver (TC1) or the second transceiver (TC2) to the respective other transceiver.

3. Data transmission method according to claim 2, characterised in that a number of time slots lie between successive synchronisation procedures (SYNC), wherein the successive synchronisation procedures form a frame (FRM).

4. Data transmission method according to claim 2, characterised in that the synchronisation signal (SCS) is used to determine the signal transit time between the first transceiver (TC1) and the second transceiver (TC2).

5. Data transmission method according to one of claims 2 to 4, characterised in that as part of the synchronisation procedure (SYNC) after sending and receiving the synchronisation signal (SCS), a waiting period is run through before the next time slot for sending (ZSS) and the time slot for receiving (ZSE) in the first transceiver (TC1) and in the second transceiver (TC2) in each case are reached.

6. Data transmission method according to one of the preceding claims, characterised in that the same carrier frequency range is used for sending and receiving the signals (S) in the first transceiver (TC1) and in the second transceiver (TC2).

7. Data transmission method according to one of the preceding claims, characterised in that signals (S) entering the first transceiver (TC1) and second transceiver (TC2) are amplified depending on the transmission-related damping of the signal (S).

8. Data transmission method according to claim 7, characterised in that the degree of amplification is specified as part of an initialisation of the data transmission method.

9. Modem (M1, M2), having • a transceiver with a first interface (S1) for data transmission and • a computer (CP1, CP2), which is connected to the transceiver via a second interface (S21, S22), characterised in that the modem (M1, M2) is configured to carry out a method for data transmission according to one of the preceding claims.

10. Railway system, having a first subsystem (IA) with a first modem (M1) and a second subsystem (AA) with a second modem (M2), wherein the first modem (M1) and the second modem (M2) are connected to one another via a first interface (S1), characterised in that the first modem (M1) and the second modem (M2) are designed in each case according to the preceding claim.

11. Computer program product with program commands for carrying out the method according to one of claims 1 - 8.

12. Provision apparatus for the computer program product according to the last preceding claim, wherein the provision apparatus stores and / or provides the computer program product.