METHOD FOR IMPROVING ANTENNA MATCHING AND NODE

Abstract

A method improves antenna matching for a node, in particular a sensor apparatus and/or actuator apparatus, of a communications network. The node is capable of radio communication and has a radio module equipped with an antenna and a transmit path and/or receive path for radio signals to be emitted and/or received. The node has a power supply apparatus, which is preferably energy self-sufficient, in particular a battery. The antenna has an impedance and in the receive situation and/or in the transmit situation in the case of adjustable matchings, preferably by use of adjustable matching networks, the signal to noise ratio associated with each matching is estimated, and a matching is selected from the different matchings for the receive mode and/or the transmit mode.

Claims

1. A method for improving antenna matching for a node of a communications network, the node being capable of radio communication and having a radio module equipped with an antenna and a transmit path and/or receive path for radio signals to be emitted and/or received, the antenna having an impedance and the node further having a power supply apparatus, which comprises the steps of: estimating, in a receive situation and/or in a transmit situation in a case of adjustable matchings, a signal-to-noise ratio associated with each of the adjustable matchings; and selecting a matching from different ones of the adjustable matchings for a receive mode and/or a transmit mode.

2. The method according to claim 1, which further comprises: comparing estimated SNR ratios, or data derived therefrom, with each other; and selecting impedance matching on a basis of a comparison.

3. The method according to claim 1, which further comprises selecting an impedance matching for which the estimated SNR ratio and/or a value derived therefrom is most favorable or most suitable for the receive mode and/or the transmit mode.

4. The method according to claim 1, which further comprises estimating the SNR ratio of a receive signal being a digital receive signal or of an analog receive signal.

5. The method according to claim 1, wherein the SNR ratio is a signal-to-noise ratio S/N, a carrier-to-noise ratio C/N or a noise figure RZ.

6. The method according to claim 1, wherein the SNR ratio is a negative SNR ratio.

7. The method according to claim 1, wherein a bandwidth is included in an estimate of the SNR ratio.

8. The method according to claim 1, which further comprises making a power measurement in the receive path after, or at, an output of an input amplifier or a low noise amplifier.

9. The method according to claim 1, wherein in a case of estimating respective SNR ratios for at least one bit, ascertaining a power per bit with respect to a noise power, or for at least one symbol, ascertaining a power per symbol with respect to the noise power.

10. The method according to claim 1, which further comprises partitioning a receive bandwidth into individual frequency channels, and a power measurement is made in each of the individual frequency channels.

11. The method according to claim 8, which further comprises filtering received radio signals by analog and/or digital filters before the power measurement.

12. The method according to claim 1, which further comprises ascertaining for a plurality of symbols, power components S and N, and results are averaged or related to one another.

13. The method according to claim 1, which further comprises detecting identical symbols in an input signal.

14. The method according to claim 13, which further comprises: establishing on a basis of a correlation with a pre-known symbol sequence in the input signal whether or not the input signal is present; and comparing a symbol sequence with the pre-known symbol sequence for assisting in estimating the SNR ratio for individual symbols of the symbol sequence.

15. The method according to claim 14, wherein the symbol sequence is a synchronization sequence, a pilot sequence or a preamble sequence.

16. The method according to claim 1, which further comprising digitizing an input signal by means of an analog-to-digital converter into I/O data, and the SNR ratio is estimated on a basis of I/O data.

17. The method according to claim 1, which further comprises cycling the different ones of the adjustable matchings within a data packet.

18. The method according to claim 1, which further comprises incorporating a delay in order to take account of a group delay until a power measurement is performed.

19. The method according to claim 4, which further comprises using a downlink signal, an uplink signal or an external wanted signal as the receive signal for estimating the SNR ratio.

20. A method for improving antenna matching for a node of a communications network, the node being capable of radio communication and having a radio module equipped with an antenna and a transmit path and/or a receive path, and the node further having a power supply apparatus, wherein the antenna having an impedance, which further comprises: determining empirically a dependency of a gain on matchings and storing the dependency of the gain in the node; determining empirically a dependency of a noise power on the matchings and storing the dependency of the noise power in the node; and estimating the impedance of the antenna from a change in the gain and in the noise power caused by the matchings, or selecting the antenna matching for operating the node on a basis of considering an approximation or best fit.

21. A method for improving antenna matching for a node of a communications network, the node being capable of radio communication and having a radio module equipped with an antenna and a transmit path and/or receive path, the node further having a power supply apparatus, wherein the antenna having an impedance, which comprises the steps of: sending, via the node, a plurality of packets or portions of the packets for different matchings; performing, via a receiver, signal to noise ratio estimates on a basis of the packets or the portions of the packets; and notifying, via a recipient, the node of a matching from the different matchings, or information based thereon.

22. The method according to claim 21, wherein the different matchings are known to the recipient or a base station.

23. The method according to claim 21, wherein matching-associated SNR ratios for a plurality of nodes or for the node and a base station are taken into account.

24. The method according to claim 23, wherein: account is taken in a transmit situation for one node and in a receive situation for another node; or account is taken in a transmit situation for one node and in a receive situation for the base station, or account is taken in a transmit situation for the base station and in a receive situation for the node.

25. A node capable of radio communication, the node comprising: a radio equipped with an antenna and a transmit path and/or receive path; a power supply apparatus; an impedance matching element; and the node being operated in accordance with the method claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0051] FIG. 1 is a highly simplified schematic diagram of an arrangement of a plurality of nodes capable of bidirectional radio communication, and of a base station and a data center or Cloud in a communications network;

[0052] FIG. 2 is a highly simplified schematic diagram of an example of a node in the communications network of FIG. 1, for instance in the form of a sensor apparatus;

[0053] FIG. 3 is a highly simplified schematic diagram of a first example of a transmit and receive path of the node in the communications network of FIG. 1;

[0054] FIG. 4 is a highly simplified schematic diagram of a second example of a receive path of the node in the communications network of FIG. 1;

[0055] FIG. 5 is a graph showing an example of an added noise power R of the receiver of the node at a temperature of 20° C., and partitioning into two bands;

[0056] FIG. 6A is a graph showing a power variation of an MSK-modulated signal;

[0057] FIG. 6B is a graph showing frequency-channel partitioning in a frequency band of a symbol or bit;

[0058] FIG. 6C is a graph showing power measured in each frequency channel in the frequency band of a symbol or bit;

[0059] FIG. 7 is a graph showing another frequency-channel partitioning in the frequency band of a symbol or bit;

[0060] FIG. 8 is a graph showing a signal train in the time domain;

[0061] FIG. 9 is a graph showing in Cartesian coordinates a symbol or bit sequence over time;

[0062] FIG. 10A is a highly simplified schematic diagram of the relationships in a Smith chart for an estimate based on the best-fit approach;

[0063] FIG. 10B is a highly simplified schematic diagram of further relationships in the Smith chart for an estimate based on the best-fit approach; and

[0064] FIG. 11 is a highly simplified schematic diagram of an arrangement for ascertaining the SNR ratio from I/O data.

DETAILED DESCRIPTION OF THE INVENTION

[0065] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown an arrangement of a plurality of nodes 1, for instance in the form of sensor apparatuses, capable of unidirectional or bidirectional radio communication. These transmit, in the uplink, data SD, for instance consumption data and/or other operating data, by radio to a base station 10. This may be a data collector, for example. In the base station 10, data is conditioned and forwarded, for instance via the Internet, to a data center 28 or Cloud for further use. In the case of a node 1 capable of bidirectional radio communication, this node can receive data in the downlink from the base station 10. In addition, according to an embodiment variant, a design in which nodes 1 can also communicate with one another is also possible if required.

[0066] A node in the form of a sensor apparatus can measure, for instance, a physical or chemical property E, for example the temperature of an object, the flow rate of a fluid as part of a flow meter, or the electrical conductivity (for instance to measure a salt content). Alternatively, for instance, a sensor apparatus can determine by means of the reaction with reagents, the constituent materials B or, for example, a water quality. A color change indicates whether the water quality is good enough. Finally, a sensor apparatus may also produce measured variables relating to situational information I. Such sensor apparatuses can generally be used in implementing the “Internet of Things” (IoT).

[0067] The node 1 could also be an actuator apparatus. An actuator receives electrical signals and acts on an external object. Apart from the classical case of a mechanical effect (for instance by means of a rod operated by the actuator), there is also the option of an electromagnetic effect (when the actuator produces an electric or magnetic field that holds a ferromagnetic object in a certain position). Finally, the actuator may also cause a secondary reaction in the object by means of control signals, and act in a certain sense as a translator of signals, which it receives itself via radio, into electrical signals, which it forwards over a line.

[0068] Finally, a node 1 could combine properties both of a sensor apparatus of the type described above and also of an actuator apparatus of the type described above.

[0069] FIG. 2 is used to explain in greater detail an example of a design of a node 1 in the form of a sensor apparatus, although in principle this may also be identical or similar in the case of an actuator apparatus.

[0070] The node 1 contains a power supply apparatus 4, in particular a battery, which is energy self-sufficient over a long period. This is configured in particular to supply the node 1 with electrical power for years (long-life battery). The power supply apparatus preferably has a capacity of no more than 10 Ah in view of an energy-saving mode of operation.

[0071] In addition, a radio module 2 is provided, on which is formed an antenna 3. The antenna 3 can be housed in the radio module 2, preferably on its circuit board. However, it can also be preferably detachably connected to the radio module 2. The node 1 also contains a microprocessor 11, which can be provided as part of the radio module 2 or else separately therefrom. The microprocessor 11 is connected to a memory 16. In addition, at least one sensor element 17 can be provided, for instance a temperature sensor, piezoelectric transducer or the like, which is used to detect a physical or chemical property E, material constituents B or situational information I, and to output a corresponding measurement variable E, B, I.

[0072] FIG. 2 also shows, purely by way of example for illustrative purposes, an object 18 in the vicinity of the antenna 3 of the radio module 2 at a distance A from the node 1. The object 18 may be, for instance, a temporary perturbation source or else a permanently present perturbation source, which causes detuning of the antenna 3 and hence of the reception.

[0073] FIG. 3 shows in a highly simplified schematic form an example variant of the transmit path 5 and receive path 6 of the radio module 2 of the node 1 capable of bidirectional communication. The transmit path 5 contains a TX modulation element 9 for modulating, for instance, the signals originating from the sensor (not shown in FIG. 3), a PA or power amplifier 7, and a matching element 12, which achieves a match to 50 Ohms, for example. The receive path 6 likewise contains a corresponding matching element 13, and an amplifier, for instance an LNA 8 (low noise amplifier) and/or an RF front-end 19 for amplifying the signals received via the antenna 3.

[0074] The receive path 6 also contains a SNR estimator 32, whose operating principle is explained in detail later. Arranged after the antenna 3 is a matching element 15 for selective setting of different matchings Z0, Z1, Zn, i.e. different antenna matchings M0, M1, Mn or transformation paths for the receive mode and/or the transmit mode of the node 1. In this way, multi-stage antenna matching can be performed that is different in each case. For example, the matchings described in DE 10 2016 010 045 A1 can be provided as the selectively switchable matchings. Alternatively or additionally, other controllable elements that adjust the antenna matching, for instance voltage-controlled variable capacitances (e.g. varactor diodes), can also be used for this purpose. The matching element 15 can preferably be controlled by the microprocessor 11 (not shown in FIG. 3). The source impedance of the LNA 8 is composed of the unknown antenna impedance Z_Ant and the transformation path given by the associated antenna matching M0, M1, Mn. A power measurement (signal or noise) is preferably made at, or after, the output of the LNA 8.

[0075] The node 1 is normally in sleep mode in order to save energy. In order to receive a receive signal, the node 1 opens a receive window, this being done by the microprocessor 11 enabling the receive path 6, i.e. switching the receive path “to receive”. As soon as a receive signal is received via the antenna 3, the matching element 15 varies successively a matching Z0, Z1, Zn of the receive path 6, which includes the antenna 3, and the associated SNR ratio SNR, SNR1, SNRn, or the change therein, is evaluated in each case in the SNR estimator 32. In the SNR estimator 32, that SNR ratio that is favorable, i.e. preferably the highest, is then selected from the set of determined SNR ratios SNR, SNR1, SNRn. The matching selected from the plurality of matchings Z0, Z1, Zn that have been cycled through can then be used for the transmit mode and/or receive mode. For the example configuration shown in FIG. 3, the adaptive matching of the impedance is the same. Thus, in this case the impedance matching also applies simultaneously to the transmit path 5. This need not necessarily be the case, however.

[0076] The matching element 15 can be implemented, for example, by means of fixed matching networks on a printed circuit board.

[0077] In the configuration of the receive path 6 shown in FIG. 4, the impedance matching element 15 is part of the receive path 6.

[0078] In the case of a node that is capable of unidirectional radio communication, the matching element 15 is part of the receive path 6 or the transmit path 5, depending on whether the node can only transmit or only receive.

[0079] The bandwidth can be included in the estimate of the matching-dependent SNR ratio. The SNR ratio SNR1-SNRn can be estimated from a digital receive signal or an analog receive signal.

[0080] According to a further exemplary embodiment of the invention, the SNR ratio, which is dependent on the given antenna matching, can also be estimated in the uplink by a receiver (e.g., of an additional node, a base station 10 or in the data center 28 or Cloud), and the appropriate antenna matching, or information based thereon, confirmed to the node 1 in the downlink. In this case, however, it may be sufficient to send only one message or a few messages in the uplink.

[0081] The SNR ratio can preferably be determined or estimated in relation to a symbol and/or frequency channel.

[0082] For example, the node 1 transmits on a first frequency for symbol 1 and on a second frequency for symbol 2. The receiver concentrates on symbol 1, for instance, by partitioning the receive bandwidth of the first frequency into a plurality of receive channels. This is preferably done by a frequency-domain separation e.g. by means of a Fourier transform (DFT or FFT) or by adjusting the phase locked loop (PLL). The number of expected occupied channels is known from the data rate of the uplink waveform. For example, symbol 1 has a bandwidth of 25 kHz. The receiver checks the power in each frequency channel. If a signal were present, a large amount of power would be detected in the frequency channel concerned, whereas little or no power would be detected in the other frequency channels. The spectrum depends on the modulation and pulse-shaping. These must be known to the receiver.

[0083] FIG. 6A shows by way of example the frequency spectrum of a known modulation (e.g., MSK with Gaussian filter with BT=1.0). A definite power gap is evident between the main lobe and side lobes.

[0084] FIG. 6B shows the frequency band (dashed line) for the symbol 31 by way of example. The frequency band or frequency spectrum of the symbol 31 depends on the modulation and what is known as the pulse-shaping. The frequency spectrum contains, for instance for MSK modulation with a Gaussian filter, as shown in FIG. 6A, a main lobe and a plurality of side lobes. In order to find a signal, the frequency band of interest can be partitioned into the individual receive channels 14, as shown in FIGS. 6B and 6C. The receiver checks the power in each frequency channel 14. If a signal has been detected then, as shown in FIG. 6B, a far greater power is measured in one channel 14 than in the other channels. The type of modulation and the pulse-shaping of the input signal should be known in the receiver. Thus, if a power is identified in a channel 14, and has the correct spacing as regards the frequency, then a signal for a symbol has been detected.

[0085] If, on the other hand, no appreciable differences were identified by the receiver in the individual frequency channels 14, then no usable signal was present, and therefore the receiver is disabled again or the receive window is closed again. The receive window can be re-opened at a later point in time.

[0086] On the basis of detecting the signal and the noise, then for each signal received from the receiver in the uplink for different antenna matchings, an associated SNR estimate can be performed.

[0087] Preferably, for the SNR estimate, the detection of a signal, for instance that for a specific symbol, can be performed repeatedly successively in time, and a comparison of the relevant measured values can be performed for a plurality of successively received symbols, preferably of the same type, or an averaging carried out.

[0088] In the example diagram shown in FIG. 5, the receive band of bandwidth 20 kHz, for example, is partitioned by filters into two bands (wanted signal and noise). The band region on the left in FIG. 5 also contains the wanted signal; the right-hand band region contains only the base noise (noise floor). In the left-hand band region, according to the invention the gain or change in gain is ascertained for each of respective different antenna matchings Z0, Z1, Zn of the matching networks of the impedance matching element 15. In the right-hand band region, a measurement is made only of the increase in the base noise caused thereby. Thus from the available measured values, different SNR ratios SNR1-SNRn can be determined depending on the different impedances, and that antenna matching can be selected that corresponds to the highest SNR ratio, for instance.

[0089] An input signal that can form the basis for ascertaining the different SNR ratios SNR1-SNRn may also be an uplink signal from another node in the network rather than, for instance, a downlink signal from a base station 10.

[0090] In the diagram shown in FIG. 7, the receive band is partitioned by two filters into two frequency channels 14a, 14b about the carrier frequency F (carrier), with the one frequency channel 14a on the left in FIG. 7 containing only the noise, and the other frequency channel 14a on the right in FIG. 7 containing a power caused by the signal for the symbol 31. This makes it possible to search, for instance, only in the frequency channel 14b, and hence to find more easily the input signal, for example for a symbol 31, in order to ascertain the associated SNR ratio.

[0091] It is also possible to analyze the receive signal in terms of its time domain. Since the symbol duration or symbol sequence (pilot sequence or synchronization sequence or training sequence) is known, it is possible to observe according to the given symbol train an input/output signal, which switches with the symbol duration; cf. FIG. 8. When the symbol 31 is transmitted at 8T, a power is present, otherwise not. In this case, detecting the power within the preamble of a data packet is particularly advantageous because alternating symbols are transmitted there. The detection of the power should preferably comprise a plurality of preferably identical symbols in order to be able to perform the estimate of the associated SNR ratio over a plurality of symbols preferably of the same type. Again in this case, the power (signal or noise) is measured for each of a plurality of antenna matchings Z0, Z1, Zn.

[0092] An estimate of the SNR ratio on the basis of digital signals or I/O signals for different matchings is shown by way of example in FIG. 11. The analog input signals (data packets 22 or segments of data packets) are processed after the input in the receive apparatus or the radio chip 20 into digital signals or I/O signals for instance by means of an I/O technique (in-phase/quadrature technique). This can be done, for example, by splitting the analog input signal into two signal components, where one signal component is generated with the original phase (I data), and the other signal component is generated at a reference frequency shifted through 90°, for instance, (Q data). In this case, these signals or data 23 can be diverted out of the radio chip 20, for instance by means of a switch 34, and fed via an interface 27 to a microcontroller 24, wherein a power measurement can be performed on the digital data 23 or digitized data, for instance in the microcontroller 24. The diverted digital data 23 or digitized signals are thus not decoded in the radio chip 20 or a downstream decoder 29 but are used for ascertaining the associated SNR ratio. The radio chip has a clock generator (quartz) 21 and a digital filter 26.

[0093] The filter 26, which may be arranged on the radio chip 20 or on the microprocessor 24, can be used, for instance, to filter the data and feed the data to a decimator 33. Here, a portion of the data is selected by means of an integer decimation factor, and finally used for ascertaining the SNR ratio. In addition, the microcontroller can have a memory 25. The measured or estimated data, or data or information derived therefrom, can be fed back, for instance via a feedback channel 35, to the radio chip 20 or otherwise conditioned in order to be able to establish the appropriate matching. The individual functionalities can obviously also be combined in the radio chip 20.

[0094] The receiver can thereby measure from the digital data (I/O data), for instance within a data packet, the signal level and the noise floor for each of the different matchings, and compare the measured values, or values derived therefrom, with one another. The matching having the most favorable or highest SNR ratio can be selected. This way of estimating the SNR ratio is significantly faster and also considerably more flexible in how it is ascertained. The data that is not diverted is decoded in the decoder 29.

[0095] The symbols are preferably symbols based on frequency modulation and/or amplitude modulation, for instance MSK, FSK or QPSK modulation.

[0096] An alternative variant of estimating the SNR ratio can also be based on correlation. The base station 10 transmits a known symbol sequence, pilot sequence or bit sequence, for instance 10111, and once it has been found (cf. e.g. FIG. 9) an SNR estimate is performed. It is possible, for example, to average over the measured powers associated with the individual pilots. In addition, the proportion of noise is known (cf. FIG. 9, dashed circle), and therefore the SNR ratio can be determined therefrom.

[0097] Alternatively, if there is no known symbol present, the symbol 31 of interest can be detected using a frequency threshold, with the detected symbols of the same type then being analyzed in terms of their power. This variant requires slightly more computing power.

[0098] According to a further embodiment according to the invention, a change in noise figure and change in gain are ascertained from at least two SNR values, and the impedance Z_Ant of the antenna derived therefrom. The following model is used to ascertain the change in gain and the change in noise figure from the SNR ratio, Gain refers to the total gain, i.e. the total input amplification in the receive path 6. Likewise, the noise figure refers to the total noise figure of the input path 6, regardless of whether the noise figure is caused by the LNA 8 or by a mismatch. The gain G1 and the noise power N1 added thereto vary for a receive signal according to the impedance. For a fixed matching circuit, G1 and N are unchanged. The SNR estimate is then obtained as follows:

[00001]${\mathrm{SNR}}_1=\frac{S{G}_1}{N_1}$

[0099] The sum of both powers is also known:

P.sub.tot1=SG.sub.1+N.sub.1

[0100] If now the impedance matching Z, Z+1, Z+n of the input path is changed, the gain G.sub.2 and the noise power N.sub.2 also change. The SNR ratio and the total power are obtained as follows:

[00002]${\mathrm{SNR}}_2=\frac{{\mathrm{SG}}_2}{N_2}{P}_{\mathrm{tot}2}={\mathrm{SG}}_2+N_2$

[0101] Comparing both total powers gives:

[00003]$\frac{P_{\mathrm{tot}1}}{P_{\mathrm{tot}2}}=\frac{{\mathrm{SG}}_1+N_1}{{\mathrm{SG}}_2+N_2}=\frac{N_1\left(\frac{{\mathrm{SG}}_1}{N_1}+1\right)}{N_2\left(\frac{{\mathrm{SG}}_2}{N_2}+1\right)}=\frac{N_1\left({\mathrm{SNR}}_1+1\right)}{N_2\left({\mathrm{SNR}}_2+1\right)}$

[0102] Since

[00004]$\frac{P_{\mathrm{tot}1}}{P_{\mathrm{tot}2}}$

and also SNR.sub.1 and SNR.sub.2 can be estimated, the ratio between N.sub.1 and N.sub.2 is known, which is also the case if the noise powers are estimated separately:

[00005]$\frac{N_1}{N_2}=C_1$

[0103] Comparing the ratio of SNR.sub.1 and SNR.sub.2 gives:

[00006]$\frac{{\mathrm{SNR}}_1}{{\mathrm{SNR}}_2}=\frac{\frac{{\mathrm{SG}}_1}{N_1}}{\frac{{\mathrm{SG}}_2}{N_2}}=\frac{G_1{N}_2}{G_2{N}_1}=C_2$

[0104] Alternatively, C2 can also be found directly by dividing the signal power for matching 1 and the signal power for matching 2:

[00007]$\frac{G_1}{G_2}=\frac{S_1}{S_2}=\frac{G_{1}S}{G_{2}S}=C_3$

[0105] The ratio of the two gains can be found therefrom:

[00008]$\frac{G_1}{G_2}=C_2\frac{N_1}{N_2}=C_2{C}_1=C_3$

[0106] Thus the change in the noise figure F and the change in the gain can be determined definitively from the two SNR values and the total power; see the points on the set of lines in the Smith chart of FIG. 10A.

[0107] The impedance can be determined definitively from the two ratios:

[00009]$\frac{G\left(Z_2\right)}{G\left(Z_1\right)}=C_3\frac{N\left(Z_2\right)}{N\left(Z_1\right)}=C_1$

[0108] Since the dependency of the gain on the impedance Z is known, and the noise power N is a known function for obtaining the noise figure from the impedance, there are 2 equations and 2 unknowns Z.sub.1 and Z.sub.2. It is therefore possible to find the unknowns.

[0109] The impedance Z_Ant of the antenna can then be obtained definitively from Z.sub.1 and Z.sub.2. The G function and the N function are measured in advance in the laboratory over the entire receiver and stored in the μC.

[0110] Preferably a plurality of gain ratios and a plurality of noise-figure ratios can be obtained. This means that a plurality of distances are known in the Smith chart of FIG. 10B, allowing the impedance to be obtained more definitively.

[0111] First, all the points that satisfy the equations are found on the Smith chart. If there are a plurality of points that give sensible antenna impedances by back-transformation, further matchings are set in order to have even more equations, or a closer point (a more likely point) is selected.

[0112] In addition, the unknown (sought) antenna impedance range can be determined by minimizing the difference between measured and modulated gain/noise figure.

[0113] Noise figure F and gain G are thus deterministic functions of the source impedance Z of the receiver (receive path 6). This functional relationship can be measured a priori in the laboratory for the existing LNA, and stored in a suitable form in the radio module (e.g. in a table).

[0114] The source impedance of the LNA Z_Q is composed of the unknown antenna impedance Z_Ant and the transformation path T_Match (M1, M2, M3) given by the variable antenna matching. The circuit has N different selectable transformation paths known a priori.

[0115] For an unknown impedance Z_Ant and a transformation path T_Match selected from the N possible paths, it is thus possible to calculate from the laboratory data stored in the device:

[0116] Noise figure according to model: F_model (Z_Q)=F_model (Z_Ant, T_Match)

[0117] Gain according to model: G_model (Z_Q)=G_model (Z_Ant, T_Match)

[0118] Now the device can measure the gain ratios and the noise-figure ratios for all N possible transformation paths. This yields two vectors of N elements.

[0119] For these N transformation paths, it is also possible to calculate in the device from the above model data an expected noise floor that depends on the unknown antenna impedance.

[0120] Hence the unknown, sought antenna impedance can be obtained mathematically by minimizing the difference between measured and modelled gain/noise figure:

[00010]$Z_{\mathrm{Ant},\mathrm{sought}}=\underset{Z_{\mathrm{Ant}}}{\min }\mathrm{differenceModelToMeasurement}$$Z_{\mathrm{Ant},\mathrm{sought}}=\underset{Z_{\mathrm{Ant}}}{\min }\left(.Math.\mathrm{MeasuredGain}\left(T_{\mathrm{Match}}\right)-\mathrm{GainModel}\left(Z_{\mathrm{Ant}},T_{\mathrm{Match}}\right).Math.+.Math.\mathrm{MeasuredNoiseFigure}\left(T_{\mathrm{Match}}\right)\mathrm{NoiseFigureModel}\left(Z_{\mathrm{Ant}},T_{\mathrm{Match}}\right).Math..Math.\right)$

[0121] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0122] 1 node [0123] 2 radio module [0124] 3 antenna [0125] 4 power source [0126] 5 transmit path [0127] 6 receive path [0128] 7 PA (power amplifier) [0129] 8 LNA (low noise amplifier) [0130] 9 TX modulation element [0131] 10 node [0132] 11 microprocessor [0133] 12 noise matching element [0134] 13 noise matching element [0135] 14a frequency channel [0136] 14b frequency channel [0137] 15 impedance matching element [0138] 16 memory [0139] 17 sensor element [0140] 18 object [0141] 19 RF front-end [0142] 20 radio chip [0143] 21 clock generator (quartz) [0144] 22 data packet [0145] 23 I/O data [0146] 24 microprocessor [0147] 25 memory [0148] 26 filter [0149] 27 interface [0150] 28 data center [0151] 29 receive window [0152] 30 data packet [0153] 31 bit [0154] 32 SNR estimator [0155] 33 decimator [0156] 34 switch [0157] 35 feedback channel [0158] G gain [0159] F noise figure [0160] M transformation path [0161] N noise power [0162] Z impedance point