METHOD AND DEVICE FOR BIDIRECTIONAL COMMUNICATION BETWEEN MEASURING INSTRUMENTS AND DATA COLLECTORS

Description

[0001] The technical field of the invention is the communication between measuring devices and data collectors.

[0002] A method for bidirectional communication according to the preamble of claim 1 is known from US 2010 / 0060479. This publication describes a display device that can communicate with a smart meter via a bidirectional radio communication link.

[0003] US 2013 / 0215806 A1 discloses a bidirectional radio communication system in the field of mobile communications for bidirectional data exchange of video data or computer graphics. The method comprises two devices, one of which, according to one variant, is equipped with a frequency offset detection block. However, this variant is considered disadvantageous due to the circuit complexity required in both devices.

[0004] US 2004 / 0116981 A1 relates to bidirectional communication between an implantable medical device and an external unit, wherein the implantable medical device has a transmit and receive frequency that are to have a specified difference from each other. For communication, the external unit transmits an "all-call" signal over a plurality of frequency channels with a bandwidth that is narrower than the normal bandwidth compared to the respective bandwidth of the frequency channel. However, for normal communication between the external unit and the implantable device, the full bandwidth of the bidirectional communication is used.

[0005] In the context of this description of the invention, a measuring device is generally understood to be one that not only transmits digitized measured values ​​as individualized data telegrams to a data collector via short-range radio, but can also receive control telegrams from the collector via radio. Reference is made to the publications DE 10 2004 061 742 B4 and DE 10 2010 005 587 A1. Each of the measuring devices uses its sensors to record, for example, the consumption of cold and hot water, household gas, or heat quantities from radiators, and in particular, electrical power, at predetermined intervals, optionally with subsequent analog-to-digital conversion of sensor values. By adding a time stamp and a measuring device identification, a sequence of device-specific data telegrams is created.These are transmitted from the respective meter to the receiver of the remotely installed data collector, also known as a concentrator, which is assigned to several meters. In the data collector, the data telegrams from as many meters as possible are temporarily stored and, if necessary, preprocessed before being read out wirelessly and then transmitted directly or via a mobile storage device to a central location for evaluation, for example, for the creation and distribution of annual consumption statements.

[0006] The measuring devices and the data collector are equipped for bidirectional radio communication via license-free short-range frequency bands. Therefore, control telegrams can also be transmitted from the data collector's transmitter to individual measuring devices, particularly those for recording electrical power consumption. These serve primarily to optimize consumption costs on the one hand and to stabilize the grid on the other; for example, during periods of low load from the supply grid, large electric motor or electrothermal household appliances can be temporarily switched on via the data collector, which is designed as a smart meter, especially under reduced tariff conditions during certain night hours.The circuit design of the receiver and transmitter in the data collector, as well as their equipment with comparatively large, tuned antennas, is not critical, since there is usually sufficient space in the housing of the data collector and also electrical operating power from batteries or even a mains connection.

[0007] However, the meter at the consumer device should be as unobtrusive as possible, meaning it should be as compact as possible. Since a power connection is regularly unavailable for their operation, each meter must operate autonomously using batteries, which are typically expected to last for ten years. Therefore, due to a lack of resources, meter communication here must be operated with comparatively minimal radio transmission and reception equipment and circuitry. This makes interference-free narrowband downlink transmission of decodable control telegrams from the data collector to individual metering devices particularly difficult.

[0008] In recognition of such circumstances, the present invention is based on the technical problem of achieving, even under such adverse boundary conditions, in particular, a reception of the control telegrams from the data collector in the measuring devices that can still be demodulated without any problems.

[0009] GB691865 A discloses a unidirectional radio relay.

[0010] US 4,490,722 A discloses the use of a superheterodyne receiver for monitoring the distance between a stationary transmitting station and a mobile receiving station. A change in distance is detected as a phase shift between an unmodulated carrier frequency received by the transmitter and a different superheterodyne frequency generated in the receiver. To compensate for drift, the mobile station periodically initiates a frequency comparison between its superheterodyne frequency and the frequency received by the stationary station, in order to adjust the latter to the specified frequency offset for the subsequent phase measurement.

[0011] The object is achieved according to the invention by the method according to claim 1 and by the system according to claim 5. In the subject matter according to claim 5, for bidirectional radio communication, the data collector's receiver and transmitter are each equipped with an oscillator; whereas, for reasons of complexity, only one common oscillator is provided for each measuring device's transceiver. Advantageous embodiments of the method and the system are claimed in the dependent claims.

[0012] The center or reference frequency, which is to be subjected to amplitude, phase, or frequency modulation, especially binary modulation, before transmission, is derived from a usually quartz-stabilized oscillator frequency. This reference frequency is also generated on the receiving side for demodulating the modulated telegrams. However, even quartz-stabilized oscillator frequencies are not constant over the long term; they drift, particularly depending on the operating time and operating temperature of the respective quartz crystal, as well as due to other influences on the circuit. Optimal reception gain, however, is only achieved when the transmitter and receiver operate with the same reference frequency; at the very least, the receiver must still be able to recognize the transmitter's reference frequency.If the deviation is too great, the modulated reception frequencies are so far off-center, or even outside the passband curves of reception filters, that eventually no more telegrams can be demodulated.

[0013] In practice, such a frequency drift is not critical in the case of broadband uplink radio connections from the respective measuring device to the common data collector, since, as already mentioned, considerable resources are available for reception at the data collector, meaning that almost any effort can be made in antenna and filter design in order to be able to reconstruct demodulable data telegrams despite the migrated reference frequency.

[0014] However, as mentioned above, the very limited resources available to the respective meter for receiving control telegrams via its transceiver are critical. If there is a center frequency offset between the data collector transmitter and the meter receiver, the latter quickly becomes unable to demodulate usable control telegrams for the current smart meter function, i.e., for configuring the so-called intelligent meter to influence consumption.

[0015] To remedy this, according to the invention, frequency difference measurements are performed at the data collector; and based on these results, the transmit reference frequency derived from the quartz oscillator circuit is detuned until sufficient center frequency agreement is achieved for the narrowband downlink connection from the data collector to the corresponding measuring device.

[0016] This inventive solution and its implementation in terms of apparatus are explained in more detail below using the schematic diagram of a preferred implementation example, simplified to the essential functional principles, as shown in the single figure of the drawing. Further developments of the inventive solution also result from this and the dependent claims.

[0017] Each of the numerous measuring devices 11, also referred to as smart meters (only one of which is shown here), communicates bidirectionally with at least one common data collector 12, also referred to as a concentrator. Each measuring device 11 is equipped with a transceiver 13 for broadband transmission of data telegrams 14 (uplink) and narrowband reception of control telegrams 15 (downlink). The data collector 12, on the other hand, has separate receivers 16 and transmitters 17.

[0018] The transceiver 13, the receiver 16, and the transmitter 17 each contain an oscillator 18, in particular a quartz oscillator. From their respective oscillator frequencies F, the center or carrier frequency to be encoded on the transmit side, referred to here as the reference frequency f, is derived for a modulator 23 by frequency division or multiplication in downstream conditioners 19. Within the scope of the present invention, the modulator 23 can be designed equally for frequency, phase, or amplitude modulation. Furthermore, the telegram coding does not necessarily have to be binary (e.g., 2FSK); other codings, such as 4FSK, can also be advantageously used. The correspondingly designed receive-side demodulator 24 operates on the same reference frequency f with filters tuned to it (not shown).

[0019] However, due to aging and temperature influences, particularly on oscillators 18, the respective specified oscillator frequencies F13, F16, and F17 drift, which is why the carrier or reference frequencies f13, f16, and f17 derived from them on-site no longer match. In extreme cases, if the receiving side cannot determine which reference frequency f (f13 or f17) was modulated on the transmitter side, no demodulation on the receiving side is possible at all. The optimal transmission conditions in this regard, however, are achieved when the reference frequencies f are identical on the transmit and receive sides.

[0020] In order to achieve the best possible demodulation ratios for control telegrams 15 received at each measuring device 11 with the least possible circuit complexity, despite the drift of the reference frequencies f, the receiver 16 of the data collector 12 is equipped with at least one comparator 20 for a reference frequency f13 currently received by a measuring device 11 and for its own current, actual reference frequency f16. What is explained here in serial block circuitry to simplify the explanation is, in circuit practice, a frequency meter, usually implemented in software, which determines and stores or outputs the desired frequency values ​​and the frequency differences simultaneously or sequentially.

[0021] The frequency comparator 20 is connected in parallel to the demodulator 24, so to speak; as outlined, it is connected on the one hand to the input for the receiver-side reference frequency f16 and on the other hand to the input for received reference frequencies f13 or f17. At the data collector 12, a calibration telegram 21.17 is transmitted from the transmitter 17 to the receiver 16 in order for the comparator 20 to determine the received instantaneous transmitter-side reference frequency f17 as such with respect to the reference frequency f16 currently generated at the receiver end, namely the frequency difference f17 - f16. Furthermore, the receiver 16 of the data collector 12 receives a data telegram 14 just received from the transceiver 13, or a calibration telegram 21.13 triggered as an alternative, with its current reference frequency f13; and the frequency difference f13 - f16 is determined from this in the comparator 20.These two frequency differences, in turn, are connected to a subtractor 22, which delivers their difference (f17 - f16) - (f13 - f16) as the frequency difference f17 - f13 = Δf; into which the receiver reference frequency f16 is consequently no longer included. The reference frequency f17, formed a priori for the downlink, is shifted by this difference frequency Δf, fed, for example, into the conditioner 19.17 of the transmitter 17; so that the reference frequencies f17 = f13 for the modulator 23 in the transmitter 17 and for the receiving-side demodulator in the transceiver 13 now match.

[0022] As explained above, this correspondence between the modulation and demodulation reference frequencies f results in optimal conditions for demodulation of the control telegram 15 received downlink by the measuring device 11, without requiring the measuring device 11 and its transceiver 13 to incur additional circuitry for determining and, if necessary, correcting the current transceiver-side reference frequency f13. Rather, the downlink frequency correction is performed in the data collector 12; and this is not based on an internal frequency measurement, but rather by means of a real (calibration) telegram 21 exchanged between the transmitter 17 and the receiver 16, thus capturing all radio-related conditions.

[0023] In order to achieve optimal reception of the smart meter control telegrams 15 transmitted by a concentrator, a data collector 12, in a measuring device 11 with a transceiver 13 for bidirectional, for example, binary frequency modulated, data exchange, despite its minimal resources, the current drift-prone modulation reference frequency f17 at the data collector 12 is shifted according to the invention by the instantaneous frequency difference Δf between the current transmitter-side reference frequency f17 and the current transceiver-side reference frequency f13. As a result, the current reference frequencies f17 = f13 match during downlink reception without having to intervene in the measuring device 11.This frequency difference Δf at the data collector 12 is obtained from a comparison of the current receiver-side demodulation reference frequency f16 with, on the one hand, the current transmitter-side reference frequency f17 and, on the other hand, the current transceiver-side reference frequency f13 from telegrams 14, 21 from the transmitter 17 of the data collector 12 and from the transceiver 13 of the measuring device 11, which are received by the receiver 16 of the data collector 12. Without utilizing the resources of the measuring device 11, this transmit-receive frequency adjustment only requires a frequency-measuring comparator 20 to be connected upstream and downstream of the demodulator 24 at the data collector 12, followed by a difference frequency subtractor 22 connected to the transmitter-side conditioner 19, 17, for deriving the reference frequency f from a quartz-stabilized oscillator frequency F. List of reference symbols

[0024] 11Measuring device 12Data collector 13Transceiver 14Data telegram 15(Control) telegram 16Receiver 17Transmitter 18Oscillator; F = oscillator frequency 19Conditioner; f = reference frequency; Δf = frequency difference f17 - f13 20Comparator 21Calibration telegram 22Subtractor 23Modulator 24Demodulator

Claims

1. Method for bidirectional communication between a data collector (12) having a transmitter (17) and a receiver (16), on the one hand, and meters (11) having transceivers (13), on the other hand, by means of a modulated reference frequency (f), wherein the transceiver (13), receiver (16) and transmitter (17) are provided with oscillators (18) having oscillator frequencies (F) which are subject to drift and from which the reference frequency (f) to be modulated or demodulated is derived, characterized in that, for the narrowband transmission of messages (15) from the data collector (12) to a meter (11), frequency difference measurements are carried out in the data collector (12) and, according to their results, the current transmitter-side reference frequency (f17) is shifted by the instantaneous frequency difference (Δf) between the current transmitter-side reference frequency (f17) and the current transceiver-side reference frequency (f13) until there is sufficient centre frequency correspondence for the narrowband downlink connection from the data collector (12) to the meter (11).

2. Method according to Claim 1, characterized in that the receiver-side reference frequency (f16) is compared both with the transmitter-side reference frequency (f17) and with the transceiver-side reference frequency (f13) in the data collector (12) and the frequency difference (Δf) is formed from the differences.

3. Method according to the preceding claim, characterized in that the transmitter-side reference frequency (f17) in a calibration message (21.17) emitted by the transmitter (17) of the data collector (12) and the transceiver-side reference frequency (f13) in a data message (14) emitted by the meter (11) are measured in the receiver (16) of said data collector (12).

4. Method according to the preceding claim, characterized in that the transmitter-side reference frequency (f17) in a calibration message (21.17) emitted by the transmitter (17) of the data collector (12) and the transceiver-side reference frequency (f13) in a calibration message (21.13) emitted by the meter (11) are measured in the receiver (16) of said data collector (12).

5. System designed to carry out the method according to at least one of the preceding method claims, having a data collector (12) with a transmitter (17) and a receiver (16) for the bidirectional interchange of modulated messages (15, 14) and having at least one meter (11) with a transceiver (13), wherein the data collector (12) comprises one oscillator (18) each for deriving a reference frequency (f17) which is subject to drift for the transmitter (17) and a reference frequency (f16) which is subject to drift for the receiver (16) of the data collector (12), and the meter (11) comprises an oscillator (18) for deriving a reference frequency (f13) which is subject to drift for the transceiver (13), wherein the messages (15) can be transmitted from the data collector (12) to a meter (11) in the narrowband, characterized by at least one comparator (20) in the data collector (12), to which the current receiver-side reference frequency (f16) and, on the one hand, the transmitter-side reference frequency (f17) currently transmitted by the transmitter (17) of the data collector (12) and received by the receiver (16) of the data collector (12) and, on the other hand, the currently received transceiver-side reference frequency (f13) are applied, having a subtractor (22), which is connected downstream of the comparator (20), for determining the frequency difference (Δf) between the two frequency differences (f17-f16 and f13-f16) between the reference frequency (f17) of the transmitter (17) and the reference frequency (f16) of the receiver (16) and between the reference frequency (f13) of the transceiver (13) and the reference frequency (f16) of the receiver (16), wherein the data collector is adapted to shift the transmitter-side reference frequency (f17) by the frequency difference (Δf) to the transceiver-side reference frequency (f13) until there is sufficient centre frequency correspondence for the narrowband downlink connection from the data collector (12) to the meter (11).

6. System according to the preceding claim, characterized in that conditioners (19) for deriving the reference frequencies (f) from the oscillator frequencies (F) are connected downstream of the oscillators (18), and in that the subtractor (22) is connected to the transmitter-side conditioner (19.17).

7. System according to one of the two preceding claims, characterized in that the frequency-measuring comparator (20) is connected to the inputs of the demodulator (24) for the receiver-side reference frequency (f16) and for the transceiver-side reference frequency (f13) to be demodulated.

8. System according to one of the three preceding claims, characterized in that the oscillators (18) are crystal-stabilized.