DE19509141C2 - Method and arrangement for exchanging data - Google Patents

Description

The invention relates to a method and an arrangement for the contactless exchange of Data between two devices, one of which is preferably mobile. For the increasing control of modes of transport and with the increasing bidirectional transfer Information on road users is becoming increasingly powerful wireless Transmission techniques needed.

Depending on the requirements, radio-microwave and light transmission technologies are already in use Commitment. For transmission at close range with a geometrically defined coupling area have transmission systems with light, preferably in the infrared, as a carrier proven. As long as possible when the vehicle drives past the fixed station Coupling time should be achieved, the opening angle of both the transmitter and the Receiver relatively large. For this reason, LEDs have become light sources (light-emitting diodes) because they are easy to use and low price have a large radiation range. The controlling transmitter output stage usually consists of a switching transistor which is either fully activated or completely blocks. These simple circuits ensure the least heating of the Power amplifiers and are easy to set up.

With the increasing use of such systems, however, the problems of each other decrease Disturbance, especially in systems in which the vehicle transmits continuously, causing the geometric delimitation of the coupling area is removed.

When receiving, the selection of the desired light carrier is analogous to the frequency selection with RF receivers, for example through optical filters, not possible because of physical Reasons only LED's can be produced with certain light wavelengths. Generate the LED's Light in a wide range, which also changes with the ambient temperature.  

For this reason, the actual information becomes a so-called subcarrier modulated. The signal thus formed then modulates the actual carrier, that is Infrared light. After the conversion of the light signals into electrical signals, the Subcarrier recipient selected. This reduces interference by others Transmitter with a subcarrier of different frequencies.

Such a transmission method is used for control systems in local public transport standardized. This process is described in improved form in the patent specification 39 15 137.

Compared to transmission methods without subcarrier, with the so-called baseband modulation, this transmission method is already significantly less prone to interference.

The increasing amount of information requires ever higher data rates. But there Switching speed of the LED’s is limited, higher data rates can only be achieved by one reduced frequency ratio of subcarrier frequency to data transmission frequency achieved will. The receiver must then be designed to be very broadband and thus lose its Ability to select interference signals. Another disadvantage of the above subcarrier modulation is that large harmonic range of the subcarrier signal caused by the pulse shape.

This makes the selection of the interference signal even with narrowband receivers worsened.

The invention has for its object the above-described disadvantages of the prior art Avoid technology.

The solution to this can be seen in the features of claims 1 and 3, respectively.

The respective subordinate claims relate to further developments of the subject matter of these Expectations.

Figure 1 shows the most important components of a unidirectional transmission. However, bidirectional use will often be used in practical operation. The control STG1 ( 11 ) uses the generator G1 ( 12 ) to promptly request the data D1 with the signal DAN and to modulate the data in the modulator MOD ( 13 ). The modulated data D2 are converted by the transmitter S ( 14 ) into light signals D3, which reach the receiver E ( 24 ). In the receiver, the light signals are converted into corresponding electrical signals D4 which, after being converted into a digital signal 41 by the stage AD ( 26 ), are fed to the demodulator DEM ( 23 ) and, in the case of receivers with a continuous data output signal DAB, to the PLL stage ( 25 ). In the demodulator DEM ( 23 ), the signal D41 is returned by the receiver to the original binary signal D5. The demodulation is supported by the control STG2 ( 2 ), which supplies the necessary clock signals which are derived from the generator G2 ( 22 ). The control STG2 ( 2 ) also generates the message DAB, which signals the presence of binary data.

Figure 2 shows the time course of the most important signals. The binary data D1 are provided with the data request signal DAN by the data generator (not shown). The clock rate of the clock T corresponding to the subcarrier frequency fs is here twice as high as the data transmission rate 1 / fD.

The modulation method according to the invention is that two pulse packets consisting of any number of pulses are generated synchronously in the modulated signal D2 per bit of the data signal D1, which lead in time by + Δp or -Δp compared to the unmodulated subcarrier T (f _S ), or hurry. In the case of a binary 1 in the signal D1, the two associated pulse packets of the pair of pulse packets have the same offset direction + Δp or -Δp, whereas with a binary 0 the offset direction changes. Figure 2 shows the solution with pulse packages that consist of only one pulse. The direction of offset also changes after each pulse packet pair, i.e. between the second pulse packet of a pulse packet pair (end of the bit) and the first pulse packet of the subsequent pulse packet pair (beginning of the next bits), so that the pulse sequence for the binary sequence of the signal D1 shown in Figure 2 D2 after the modulator MOD ( 13 ) results. This type of modulation has no frequency deviation from the subcarrier signal f _S , since the time offsets compensate for one another, provided that the sum of the transmitted bits of value 1 is an even number. The evaluation or implementation of the signal D4 in the receiver is based on the evaluation of the time intervals of the pulse packets of a pair of pulse packets. The amplitude of the light signal D3 essentially corresponds to D2. The signal D4 generated by the receiver E shows the typical behavior that arises due to frequency limitation. Figure 3 shows the most important signals for signal evaluation. After the signal D4 has been converted into a binary signal D41 (Schmit trigger), the distance between the pulse packets of a pair of pulse packets is checked by the fixed time 1 / f _{S of} the signal D41. If the pulse packet distance corresponds to 1 / f _S , it is a binary 1, if the distance is too large or too small it is a binary 0. The signal T = 1 / f _S is derived from the received signal D41; for example with the help of the PLL circuit PLL ( 25 ).

The advantage of the transmission method described above lies in the very narrow-band receiver stage E, which is made possible by the low bandwidth of the type of modulation according to the application, although the ratio between subcarrier frequency and data frequency (factor 2 in the example shown) is small. The system can be adapted to different requirements by selecting the ratio n of subcarrier period 1 / f _S and time offset Δp. If the signal / noise ratio is unfavorable, a small factor n is selected. However, the bandwidth of the receiving circuit must be increased and interference signals can be filtered out more poorly.

Although the described modulation method ensures the low-interference operation of your own system, the steep edges of the transmitter pulses generate harmonics that can disturb other systems. For this reason, in a further development of the method, the transmission pulses are transformed into "bell pulses" with a low harmonic content, as shown in Figure 4.

Figure 5 shows the associated circuit, which consists of m transmitters, each individually via TA1. . . TAm can be controlled digitally by the modified logic level LOG1. The bell shape of the transmission signal is approximately achieved if a corresponding number of m transmission stages are activated simultaneously.

In Figure 4, nine stages are used. To generate the bell-shaped pulse shape, two transmission stages are activated at time a and four at time b. The maximum amount of light is reached at the apex d and e of the pulse with all nine transmitters. Which stage is controlled has no influence on the pulse shape of the transmission signal, since only the sum of the connected transmitters is decisive. However, in order to achieve a balanced load on the individual LEDs, which is desirable for reasons of aging, the following switching sequence is used, in which all 9 LEDs are switched on almost equally frequently. At the same time, the thermal load for all LEDs is balanced.

LED number

Claims (8)

1. A method for wireless transmission of digital data or information preferably in the mobile area with the aid of an electromagnetic modulated carrier, characterized in that the carrier is pulse-modulated and that in the modulation method per bit of the data D1 two pulse packets consisting of any number of pulses are generated , which lead or lag behind the unmodulated subcarrier T by the same constant amount Δp and that with a digital 1 of the signal D1 the two pulse packets of the pulse packet pair have the same offset polarity and that with a digital 0 the two associated pulse packets have a different offset polarity and also between the offset polarity is changed in two successive pairs of pulse packets, so that the individual time offsets compensate for one another over the entire duration of the transmission. 2. A method for evaluating the modulation signal described in claim 1, characterized in that in the receiver with the first pulse packet of the pulse packet pair a time step with the time f _{S is} started after its expiry it is checked whether the second pulse packet of the pulse packet pair coincides and that at Coincidence of the signal D5 receives the binary value 1 and if there is no coincidence D5 the binary value 0. 3. A method for generating pulses for wireless transmission of digital data or information, preferably in the mobile area with the aid of an optical carrier, in particular for implementing the modulation method according to claim 1 or 2, characterized in that the optical pulses ( Figure 2; Figure 4 ) are formed by adding the light quantities of several optical transmission stages, which are triggered in succession in a suitable combination ( Figure 5). 4. The method according to claim 3, characterized in that the individual Light emitting stages can be controlled in the time sequence in such a way that the Amplitude curve of the light signal D3 largely of the low harmonic bell shape (COS²) approximates. 5. The method according to claim 3 or 4, characterized in that the individual Light transmission stages can be controlled in the time sequence in such a way that the different Send stages almost the same number of times, resulting in an even and reduced aging of the LEDs and a favorable heat dissipation is achieved. 6. Arrangement for performing the method according to one of claims 1 to 5, characterized characterized in that a time step is provided which evaluates the time offsets.   7. Arrangement for performing the method according to one of claims 1 to 5, characterized by a pulse shaping device, in particular a Schmitt trigger for Reshaping the received impulses. 8. Order to carry out the procedure according to one of claims 3 to 5, characterized in that the transmission stages for the light pulses are light emitting diodes (LED).