WO1995034823A1

WO1995034823A1 - Method and device for the measurement of field strength in a radio channel and the neighbouring channels using zero if

Info

Publication number: WO1995034823A1
Application number: PCT/EP1995/000436
Authority: WO
Inventors: Rainer Perthold; Heinz GERHÄUSER
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 1994-06-10
Filing date: 1995-02-07
Publication date: 1995-12-21
Also published as: DE4420448C1

Abstract

Described is a method of measuring the field strength in a radio channel and the neighbouring channels using zero IF, the method calling for the generation of an HF signal with a first frequency range and the preparation of a frequency-modulated local-oscillator signal with a frequency range essentially the same as that of the HF signal and which has an essentially constant spectral power density over its frequency range. The HF signal and the frequency-modulated local-oscillator signal are mixed and a frequency range selected in the baseband. A value characteristic of the power is determined in the frequency range selected and the value determined is analysed in order to determine the field strength in the frequency range selected.

Description

Method and device for measuring the field strength in a radio channel and its neighboring channels by means of zero IF

description

The present invention relates to a method and a device for measuring the field strength in a radio channel and its adjacent channels by means of zero IF.

The main area of application of the method and the device according to the invention is in the field of industrial remote controls. In systems for radio remote control in the industrial area, it may be necessary, because of the dense occupancy of the frequency bands used, to check whether the set channel is already being used by other users before the transmitter is started up. In this case, the transmitter must change to another frequency and check the assignment there again. This search process before the connection is established is compulsory in some countries, but in principle makes sense in any case in order to avoid collisions.

Due to the limited large signal strength and adjacent channel selection of the receiver, it is possible that radio links operating in the adjacent channels interfere with the transmission. Therefore, the measurement of the field strength should always also extend to the adjacent channels, whereby they correspond to their distance from frequency used should be weighted.

Known systems for checking the occupancy of a frequency use conventional superheterodyne receivers with one or more intermediate frequencies, which are independent of the used transmitter work.

The receiver is set to the frequency to be examined and the RSSI signal (RSSI - Received Signal Strength Indication = display of the strength of the received signal) output by the receiver is measured three times within 3 milliseconds. As soon as a measured value exceeds the prescribed limit value, the transmitter and the receiver assigned to it change to a different channel and the field strength is determined again.

To simplify this known system, one possibility is to use the unmodulated signal of the transmitter as a local oscillator signal. This eliminates the need for a separate frequency synthesis in the receiver. In this case, however, it is necessary to increase the tuning range of the transmitter by the amount of the intermediate frequency.

However, these known systems have various disadvantages.

An almost complete receiver is required to measure the field strength, which means that in the case of a transmission link operating in simplex mode, the effort for the receiver to measure the signal strength generally exceeds the effort for the transmitter.

Furthermore, it is difficult, especially with transmitters with a large tuning range, to expand this accordingly.

Another disadvantage is that after the field strength has been measured, the transmitter must first be switched back to the transmission frequency, as a result of which the settling time to be observed effectively increases the time required for measuring the field strength.

Furthermore, for a recipient who has a large A complex concurrent preselector is to be provided in the frequency range.

A known method for measuring the field strength in a radio channel is field strength measurement using zero IF.

The field strength measurement by means of zero IF takes place in such a way that a high-frequency signal, the power of which has to be determined, is converted directly into the baseband via a mixer. An existing transmitter serves as the local oscillator. The channel is selected by low-pass filtering in the LF range (LF = low frequency). This principle is referred to as zero IF. The LF signal is amplified logarithmically and the peak value of this amplified LF signal serves as a measurement variable. This can be determined using an appropriate rectifier and is proportional to the peak value of the RF signal within the selected channel. An optional low-pass filter enables the measured value to be averaged. The measured peak value is then either digitized via an A / D converter (A / D converter = analog / digital converter) or compared with a set limit value by a comparator.

The principle of zero-IF described above has some fundamental disadvantages as soon as no complex IQ demodulator is used for frequency conversion. In this case, the amplitude of the RF signal, the frequency of which is close to that of the local oscillator, can no longer be clearly determined within the specified measurement time.

Furthermore, very low frequencies in the baseband cannot be evaluated, since the mixer generates an equal component at the output due to asymmetries, which significantly exceeds the useful signal and thereby drives the LF amplifier into the limit. It is therefore necessary to carry out the selection in the baseband by means of band passes.

Both effects can lead to considerable measurement errors. Learn as soon as a monofrequency signal is used as the local oscillator.

EP-0583027 discloses a circuit arrangement for determining the field strength of an FM transmitter with a demodulator, a comparator, an integrator stage and a microprocessor. This known arrangement relates to the fastest possible evaluation of a detected electrical field strength of an FM transmitter in order to determine whether a switchover to a new frequency of the same FM transmitter is to be carried out. This is not a matter of determining whether the new frequency is occupied, since it is assigned to the same FM transmitter and is therefore in any case occupied, but merely a determination of whether the electrical field strength provided is sufficient to justify changing the frequency of the FM transmitter.

EP-0236946 discloses a movable receiver unit with a function for providing information relating to the intensity of an electric field with a receiver unit, a level detector, a level memory and a level comparator for generating a gradient of the field strength to indicate a direction in which the Intensity of the electric field increases. This known device serves to indicate to a user of a mobile phone the direction in which he has to move in order, in the event that he has left the service area of the mobile phone network, to return to an area in which he has the mobile phone can use the phone. This known unit only detects the intensity of the electric field over a wide frequency range and determines whether the user is inside or outside the service area of the mobile phone network, i. H. whether it is possible to operate the mobile phone.

From GB 2191660 A a method for measuring the adjacent channel power in a transmission transmission is already known, in which a radio frequency useful signal with a frequency or phase-modulated local oscillator signal is mixed, a frequency range is selected in the baseband, the power is measured in the selected frequency range and the detected value is processed.

From US 5175880 and from US 4890332 methods for analyzing the spectrum of a radio signal and a device for assessing the quality of a mobile data communication are known, in which a high-frequency signal is converted into the baseband by means of a modulated local oscillator signal and then by means of filtering a band selection is carried out.

Starting from the prior art described above, the present invention is based on the object of measuring and evaluating the field strength within a radio channel with measuring times in the millisecond range by means of the zero-IF method, the power in neighboring channels being weakened into the measurement, it is irrelevant which type of modulation the user of the channel uses and what the exact carrier frequency is.

This invention is achieved by a method and a device for determining the field strength in a radio channel and its neighboring channels by means of zero IF according to claim 1 and claim 4.

Preferred developments of the present invention are defined in the subclaims.

The present invention provides a method for determining the field strength in a radio channel and its neighboring channels by means of zero IF, which comprises the following steps:

- Providing an HF useful signal with a first frequency range;

- Provision of a frequency-modulated local oscillator Signal whose frequency range essentially corresponds to the first frequency range and which has an essentially constant spectral power density over its frequency range;

- Mixing the HF useful signal and the frequency-modulated local oscillator signal;

- selecting a frequency range in the baseband;

- Detection of a value characteristic of the power in the selected frequency range; and

- Evaluation of the detected value characteristic of the power in order to determine the field strength in the selected frequency range.

The present invention provides a device for measuring the field strength in a radio channel and its neighboring channels by means of zero IF, which has the following features:

a device for mixing an HF useful signal and a frequency-modulated local oscillator signal, the frequency range of the local oscillator signal essentially corresponding to the frequency range of the HF useful signal and the local oscillator signal having an essentially constant spectral power density over its frequency range having;

a filter device for selecting a frequency range in the baseband;

a detection device for detecting a value characteristic of the power in the selected frequency range; and

a device for evaluating the detected value characteristic of the power in order to determine the field strength in the to determine the selected frequency range.

The present invention is based on the knowledge that the problems described in the field strength measurement by means of zero IF are solved by using a frequency-modulated local oscillator whose spectral power density is constant over the frequency range which essentially corresponds to the frequency range of the RF signal. This ensures that regardless of the position of the RF signal to be measured within the measurement bandwidth, a power proportional to the power of the RF signal is converted into the baseband. The value recorded, which is characteristic of the power, can be the effective or the peak value.

It is also achieved that adjacent channels weakened by recirculating mixing enter the power measurement.

The present invention makes it possible to use an existing transmitter as the local oscillator of a receiver for determining the field strength in a radio channel. The transmitter does not have to be modified for this, it only has to be frequency modulatable.

An advantage of the present invention is that the space requirement of the system according to the invention is less than that of a conventional super heterodyne receiver, since no bulky filters are required. Furthermore, the cost is lower.

Furthermore, it is not necessary to change the transmission frequency in order to carry out the measurement, as a result of which this can be carried out in a shorter time.

A preferred exemplary embodiment of the present invention is explained in more detail below with reference to the accompanying drawing. It shows: 1 shows an embodiment of the device according to the invention for determining the field strength in a radio channel and its neighboring channels by means of zero IF.

A preferred embodiment of the device according to the invention will now be described in more detail with reference to FIG. 1.

The circuit in FIG. 1 comprises an antenna 100 in order to receive the HF useful signal 102. In this exemplary embodiment, the HF useful signal 102 has a frequency range which extends from 407 MHz to 481 MHz.

A suitable frequency range is filtered out of the HF useful signal 102 by a suitable circuit, which in the preferred exemplary embodiment is formed by a series connection of a first HF bandpass 104, a preamplifier 106, a second HF bandpass 108 and a buffer amplifier 110 and fed to a mixer 112.

The HF useful signal is mixed in the mixer 112 with a frequency-modulated local oscillator signal 114.

The frequency-modulated local oscillator signal is generated by a transmitter 116 and a device 118 for modulating the local oscillator signal generated by the transmitter 116. The device 118 is connected to the transmitter 116.

The transmitter 116 comprises a series connection of a low pass 120, an oscillator 122 and an amplifier 124, which are connected between a first connection 126 and a second connection 128. The device 118 is connected to the first connection 126 of the transmitter 116.

The output signal 130 of the mixer 112 is fed to a circuit in order to select a frequency range in the baseband. len. This circuit comprises a series connection of a first LF bandpass 132, an LF amplifier 134, a second LF bandpass 136, a logarithmic amplifier 138, a peak value detector 140 and a video filter 142. This circuit is between the mixer 112 and the output 144 of the device switched.

At the output 144 follows the evaluation device (not shown), which carries out the evaluation of the detected peak value. B. includes an analog / digital converter or a comparator.

The device 118 for modulating the local oscillator signal is, for example, a device for generating a binary pseudo-random sequence.

In a further exemplary embodiment, device 118 provides a chirp signal in order to modulate the local oscillator signal generated by transmitter 116.

Claims

1. Method for determining the field strength in a radio channel and its neighboring channels by means of zero IF, with the following steps:

- Providing an HF useful signal (102) with a first frequency range;

- Providing a frequency-modulated local oscillator signal (114) whose frequency range essentially corresponds to the first frequency range and which has an essentially constant spectral power density over its frequency range;

- Mixing the HF useful signal (102) and the frequency-modulated local oscillator signal (114);

- selecting a frequency range in the baseband;

2. The method according to claim 1, characterized in that

that the characteristic value for the performance is the peak value.

3. The method according to claim 1, characterized in - ιi -

that the characteristic value for the performance is the effective value.

4. Device for determining the field strength in a radio channel and its neighboring channels, by means of zero IF, with the following features:

- A device (112) for mixing an HF useful signal (102) and a frequency-modulated local oscillator signal (114), the frequency range of the local oscillator signal (114) essentially being the frequency range of the HF Corresponds to the useful signal (102) and the local oscillator signal (114) has an essentially constant spectral power density over its frequency range;

- filter means (132-136) for selecting a frequency range in the baseband;

- A detection device (138-142) for detecting a value characteristic of the power in the selected frequency range; and

a device for evaluating the detected value characteristic of the power in order to determine the field strength in the selected frequency range.

5. The device according to claim 4, further characterized by the following features:

- an antenna (100) for receiving the HF useful signal (102);

- a first RF band pass (104);

- a preamplifier (106);

- a second RF band pass (108); - a buffer amplifier (110);

wherein the first RF bandpass (104), the preamplifier (106), the second RF bandpass (108) and the buffer amplifier (110) are connected in series between the antenna (100) and the mixer (112);

- a first NF band pass (132);

- an NF preamplifier (134);

- a second NF band pass (136);

- a logarithmic amplifier (138);

- a peak detector (140);

- a video filter (142);

the first NF bandpass (132), the NF preamplifier (134), the second NF bandpass (136), the logarithmic amplifier (138), the peak detector (140) and the video filter (142) serially between the mixer ( 112) and an output (144) are connected;

- a transmitter (116) for generating the local oscillator signal; and

- A device (118) for modulating the generated local oscillator signal, which is connected to the transmitter (116);

the transmitter (116) being connected to the mixer (112).

6. The device according to claim 5, characterized. that the transmitter (116) has the following features:

- a low pass (120);

- an oscillator (122); and

- an amplifier (124);

the low-pass filter (120), the oscillator (122) and the amplifier (124) being connected in series between a first connection (126) and a second connection (128) of the transmitter (116), the mixer (112) being connected to connected to the second port (128); and

that the device (118) for modulating the local oscillator signal is connected to the first connection (126).

7. The device according to claim 5 or 6, characterized gekennzeich¬ net,

that the device (118) for modulating the local oscillator signal is a device for generating a binary pseudo-random sequence.

8. The device according to claim 5 or 6, characterized gekenn¬ characterized

that the device (118) for modulating the local oscillator signal provides a chirp signal.

9. Device according to one of claims 4 to 8, characterized in

that the evaluation device is connected to the output (144).

10. The device according to claim 9, characterized in that the evaluation device includes an analog / digital converter.

11. The device according to claim 9, characterized in

that the evaluation device includes a comparator.

12. The apparatus according to claim 4, characterized in

that the characteristic value for the performance is the peak value.

13. The apparatus according to claim 4, characterized in that

that the characteristic value for the performance is the effective value.