WO1996002995A2 - Data transmission by frequency shift - Google Patents

Abstract

The invention concerns a method and layout for transmitting data between several subscribers (1, 3, 4, 5). The data are modulated by frequency shift keying to produce a transmission signal (14... 19), the carrier frequencies allocated to particular values being exact multiples of half the data transmission rate and the carrier frequency signals being coupled to the data signal in such a way as to be locked in phase, so that the phase of the carrier frequency signals matches whenever the data value changes. A central subscriber (1) sends out a transmission signal (14, 15, 19) which the other subscribers (3, 4, 5) receive, demodulate and use for synchronisation, even in breaks between communications in which there are no data to be transmitted. The invention has the advantage that there is no data loss at the start of a transmission and transmission systems can be used whose cutoff frequency is of the same order as the data transmission rate. The invention can be used in data transmission in general.

Description

description

Method and arrangement for the transmission of data

The invention relates to a method for the transmission of data between a plurality of subscribers, in which the data is modulated by frequency shift keying to generate a transmission signal, and to a suitable arrangement.

Frequency shift keying is also generally known under the term frequency shift keying (FSK). In this modulation method, different carrier frequencies are assigned to the individual data values. To generate a transmission signal, for example, a voltage-controlled oscillator can be used, on the voltage input of which a data signal is carried. If the data signal has two discrete voltage levels, an alternating signal with two carrier frequencies is generated as the transmission signal, which, however, do not suddenly change into one another. When modulating and demodulating digital data, difficulties can arise due to transients if the carrier frequencies are not many times higher than the data rate. By selecting the carrier frequencies at a sufficient distance from the data rate, the transmission capacity in narrow-band transmission channels is thus subject to narrow limits.

The object of the invention is to find a method for transmitting data in which an increase in the data rate up to the order of magnitude of the carrier frequencies is possible, and to provide a suitable arrangement.

To achieve this object, the new method of the type mentioned at the outset has the features of claim 1. Advantageous further developments of the method are specified in claims 2 to 9. A new arrangement to carry out the The method is described in claim 10, an advantageous embodiment of this arrangement in claim 11.

The invention has the advantage that the carrier frequencies and the data rate can be of the same order of magnitude. Since the central subscriber also sends a carrier frequency signal to the other subscribers during the message breaks, a reference signal is constantly available to all subscribers for synchronizing their own oscillator via a phase locked loop. A synchronization character preceding the message, a so-called preamble, which would otherwise be required to synchronize the participants, is not required. Since the scanning frequency of the receivers is constantly locked onto the carrier frequency, errors in the demodulator are avoided and correct data are determined immediately from the start of a message. This is particularly advantageous if several participants communicate with a central participant via a wireless transmission medium or with a bus via a repeater. In this case, inexpensive means of transmission can be used to achieve the data rate prevailing in the bus. For example, inexpensive infrared light-emitting diodes, which can be operated at a maximum of 10 MHz, are sufficient for the optical transmission of data at a data rate of 1 MB / s.

Based on the drawings, in which an embodiment of the invention is shown, the invention and embodiments and advantages are explained in more detail below.

Show it:

Figure 1 shows an arrangement for the transmission of

Data and FIG. 2 a block diagram of the devices of two subscribers required for the transmission.

The arrangement in FIG. 1 consists of a central subscriber 1, which is connected to a bus network 2 as a repeater is, as well as three further participants 3, 4 and 5. In this exemplary embodiment, the transmission takes place optically by infrared light. For this purpose, participants 1, 3, 4 and 5 are each provided with transmission devices 6, 7, 8, 9, which have inexpensive infrared light-emitting diodes, and with receiving devices 10, 11, 12, 13 with photodiodes. Depending on the direction, the transmitters 6 ... 9 are modulated via two different carrier frequency pairs in order to avoid mutual interference and to ensure a clear selection by means of bandpasses in the receiving devices 10 ... 13. A first signal direction is shown in FIG. 1 by arrows 14, 15 and 16, a second signal direction by arrows 17, 18 and 19. To transmit data at a data rate of 1 MB / s, the carrier frequencies f _l0 = 2 MHz and f _lu = 1 MHz are used in the first direction, which corresponds to the arrows 14, 15 and 16, for the second signal direction in accordance with the arrows 17 , 18 and 19 uses the carrier frequencies f2o = ³ MHz ^unci - ^ 2u = -L _" ^{5 KΑz} . They are in integer ratios to half the data rate and are derived from a single frequency via integer dividers. The center or repeater 1 continuously sends a signal of a frequency of the carrier frequency pair fι ₀ , fτ_ _u to the further participants 3, 4 and 5. A transmission signal with a carrier frequency which is assigned to the signal position of the stop state is also transmitted during the message breaks a reference signal for synchronization is constantly available to all participants 1, 3, 4 and 5. In participants 3, 4 and 5 the synchronization takes place via a phase locked loop with a voltage controlled oscillator. The result is a simplex transmission with a data rate that is in the range of the carrier frequency. For duplex transmission, the other participants 3, 4 and 5 send one after the other in time when they are requested to submit a message by the participant 1. They all use the carrier frequencies f2 ₀ and f2u »which are only switched through with a transmission enable to the transmission devices 7, 8 and 9 to generate a transmission signal. In the zen central subscriber or repeater 1, the reception and the synchronous demodulation of the carrier frequencies f2 ₀ ^and d f2 _U is thus possible without additional synchronization at the start of transmission, since a rigid coupling with respect to the carrier frequencies is already achieved by the direction of the arrows 14, 15 and 16 transmitted transmission signal exists. If the subscribers 3, 4 and 5 are located at a variable location, only phase-related phase shifts can occur, but these do not lead to sampling errors on the demodulated signal. Due to the type of data transmission between subscribers 1, 3, 4 and 5 according to the invention, in the case of a repeater as subscriber 1, it is possible to address subscribers 3, 4 and 5 on bus 2 directly as subscriber 20. Similar to repeaters that connect two identical segments of a bus system to one another, repeater 1 also establishes a bus connection between subscribers 3, 4 and 5 and subscriber 20 located in another segment. If the data rate on bus 2 is also 1 MB / s, no special features need to be taken into account when transferring data via repeater 1. Participants 3, 4 and 5 on the wireless transmission medium can have master and slave functions, so that master-slave operation and multimaster operation as well as mixed operation are possible.

FIG. 2 shows the block diagram of a central participant 21 and a further participant 22. A central clock 24 of 12 MHz is generated in the subscriber 21 by an oscillator 23. This central clock 24 is performed on two dividers 25 and 26. The divider 25, which divides the central clock 24 by 6, forms a carrier frequency signal of the frequency f _l0 = 2 MHz, the divider 26 with the quotient 12 forms a carrier frequency signal of the frequency f _lu = 1 MHz. A switch 27 is controlled by the data 28 to be sent, which are provided by further devices of the central subscriber 21, not shown in FIG. 2. The transmission data 28 are synchronized with the central clock 24 so that the switching points of the switch 27, which Dulator of the transmission data 28 acts to always come to the times when the carrier frequency signals supplied by the dividers 25 and 26 are in phase. The zero crossing of the carrier frequency signals is preferably selected as the switchover point. A light-emitting diode with a suitable connection 29 generates an optical transmission signal 30 from the modulated transmission signal. The further subscriber 22 has a photodiode with a signal amplifier 31 for receiving the optical transmission signal 30 for generating a digital reception signal 32. The signal 32 is fed both to a phase locked loop and to a synchronous demodulator 33. The phase-locked loop, which consists of a phase comparator 34 and a voltage-controlled oscillator 35, is used to synchronize the subscriber 22 so that it is clocked at the same frequency as the central subscriber 21. For this purpose, a clock signal 36 is generated by the phase control loop, which corresponds to the central clock 24. Controlled by this clock signal 36, the synchronous demodulator 33 delivers received data 37 from the digital received signal 32. Since an optical transmission signal 30 is also transmitted by the central subscriber 21 during message breaks, the clock signal 36 is always at the central clock 24 synchronized, and receive errors at the start of messages are avoided. Similar to the sending device of the central subscriber 21, the sending device of the other subscriber 22 is also constructed. Two carrier frequency signals of the frequencies f2 ₀ = 3 MHz and ^f 2u ^{= 1} < ⁵ W * ¹² are generated from the clock signal 36 by a divider 38, which divides it by 4, or with a divider 39 by division by 8. Synchronized with the clock signal 36, transmission data 40 for modulation and a control signal 41 for transmission release are routed to a switching device 42 in the further subscriber 22. A light-emitting diode with a suitable connection 43 in turn supplies an optical transmission signal 44. This is received in the central subscriber 21 by a photodiode with a signal amplifier 45 and in a synchronous demodulator 46 which is controlled by the central clock 24. clocks is converted into received data 47. The internal connection of the central subscriber 21, for example for the simultaneous transmission of the received data 47 as transmitted data 28 in a repeater function, is not shown in FIG. 2 for reasons of clarity.

Of course, the transmission method according to the invention is also applicable to other physical transmission types, e.g. B. wired or with radio, applicable.

Claims

claims l. Method for the transmission of data between several participants (1, 3, 4, 5), in which - the data is modulated by frequency shift keying to generate a transmission signal (14 ... 19), the carrier frequencies assigned to the individual values being an integer ¬ multiple of half the data rate and the carrier frequency signals are phase locked to the data signal, such that the phase of the carrier frequency signals coincides with each change of the data value, - A central subscriber (1) also transmits a transmission signal with a carrier frequency of a data value during the message breaks in which no data are to be transmitted - Other participants (3, 4, 5) receive the transmission signal (14, 15, 16), demodulate and use it for synchronization. 2. The method according to claim 1, characterized gekennzeich¬ net, - That each change of the data value takes place in an in-phase zero crossing of the carrier frequency signals. 3. The method according to claim 1 or 2, characterized gekenn¬, - That the other participants (3, 4, 5) only transmit a transmission signal (17, 18, 19) with a carrier frequency when data is to be transmitted, and - that the carrier frequencies assigned to the individual values, which the central participant (l) sends differ from those sent by the other participants (3, 4, 5). 4. The method according to claim 2 or 3, characterized gekenn¬, - That the other participants (3, 4, 5) use the same carrier frequencies for sending data. 5. The method according to any one of the preceding claims, characterized by - That the central participant (1) modulates all received data by frequency shift keying with its carrier frequencies to produce a transmission signal (14, 15, 16) and sends it to the other participants (3, 4, 5). 6. The method according to any one of claims 4 or 5, characterized in that - That in the participants (1, 3, 4, 5) each use synchronous demodulators (33, 46) for demodulating the transmission signal (30, 44), the synchronous demodulator (46) of the central participant (1) for demodulating the transmission signals sent by the further participants (3, 4, 5) and the synchronous demodulators (33) of the further participants (3, 4, 5) for demodulating the transmission signal sent by the central subscriber (1) are set. 7. The method according to any one of the preceding claims, da¬ characterized in that the transmission takes place wirelessly. 8. The method according to claim 7, characterized gekennzeich¬ net, - That the transmission takes place optically by infrared light. 9. The method according to claim 8, characterized gekennzeich¬ net, - That the central participant (1) is a repeater, which feeds all optically received data into a wire-bound transmission network (2) and vice versa. 10. Arrangement for the transmission of data - With a central participant (1) and at least one further participant (3, 4, 5) with whom data can be modulated by frequency shift keying to generate a transmission signal (14 ... 19), the carrier frequencies assigned to the individual values being a integer multiple of half the data rate and the carrier frequency signals are phase-locked to the data signal, such that the phase of the carrier frequency signals coincides with each change of the data value, and which are designed in such a way - That the central participant (1) sends a transmission signal (14, 15, 16) with a carrier frequency of a data value even during the pauses in which no data is to be transmitted, and - that the further participants (3, 4, 5 ) receive, demodulate and use the transmission signal (14, 15, 16) for synchronization. 11. Arrangement according to claim 10, characterized in - That the other participants (3, 4, 5) only send a transmission signal (17, 18, 19) with a carrier frequency when data is to be transmitted, and - That the carrier frequencies assigned to the individual values, which the central subscriber (1) sends, differ from those which are transmitted by the other subscribers (3, 4, 5).