EP1525729A1 - Reception arrangement for a radio signal - Google Patents

Abstract

The invention relates to a reception arrangement for a radio signal, comprising a downlink mixer (3) with a downstream signal processing chain and a demodulator (6). An RSSI signal is obtained between the downlink mixer (3) and the demodulator (6), for example in a limiter (5). Said signal is filtered by a high-pass filter, averaged and supplied to a comparator (15). According to the level of the RSSI signal thus processed, the recognition unit (8) can easily detect whether there are any useful signals, amplitude-modulated signals or frequency-modulated signals. The demodulator (6) is correspondingly controlled by a control unit (9). According to the cited principle, a recognition process can be especially easily and precisely carried out and the demodulator can be correspondingly adjusted, according to whether an amplitude-modulated signal or a frequency-modulated signal is received.

Description

description

Receiving arrangement for a radio signal

The present invention relates to a receiving arrangement for a radio signal.

In modern mobile radio, which works with digital modulation methods, both phase or frequency modulation methods as well as amplitude modulation methods and combinations of the two are common.

It is therefore desirable to build universally usable radio receivers that can handle different types of modulation. A problem with such multi-system receivers, however, is that the demodulator must know the type of modulation in order to be able to demodulate correctly. For this purpose, it is desirable to carry out as early as possible in the signal processing chain with which modulation method a received high-frequency signal is modulated.

The object of the present invention is to provide a receiving arrangement for a radio signal which is designed for at least two different types of modulation and which enables a relatively quick recognition of the modulation method by which a radio signal is modulated with little effort.

According to the invention, the object is achieved by a receiving arrangement for a radio signal, comprising:

- a downward frequency converter with a first input for coupling the radio signal, with a second input for supplying a local oscillator signal and with an output, - an amplifier with an amplifier input, which is coupled to the output of the downward frequency converter, with an amplifier output and with an output for deriving a received field strength signal, a demodulator for demodulating a down-mixed, amplified signal, with a signal input which is connected to the amplifier output, with a signal output for deriving a demodulated signal and with a control input for preselecting a demodulation method a set of predetermined demodulation methods and - a detection unit, comprising a high-pass filter with an input connected to the output of the amplifier for deriving a received field strength signal, and a threshold comparator connected at its input to the output of the high-pass filter and at its output is coupled to the control input of the demodulator, designed to emit a value representing the modulation method of the radio signal.

The amplifier can be designed with a gain factor of 1.

According to the present principle, an analysis of the received field strength signal is carried out in order to detect which modulation method is used to modulate a received radio signal.

The received field strength signal is normally also referred to as a receive signal strength indicator (RSSI) signal. On the basis of the RSSI signal normally provided anyway by the received signal chain, amplitude-modulated signals can be easily distinguished from frequency-modulated and / or phase-modulated signals according to the principle presented.

For example, signals modulated in an amplitude shift keying (ASK) can be distinguished from frequency-shifted signals (FSK). In addition to the exemplary distinction between ASK and FSK, any other modulation method developed based on phase or amplitude modulation can also be detected with the present principle.

According to the present principle, the DC component of the RSSI signal is initially suppressed and only the AC component of the RSSI signal is evaluated.

The direct component of an RSSI signal is normally used to measure the current field strength. Depending on the measured field strength, depending on the mobile radio standard used, the transmission power of the respective mobile radio device is set, for example. The measurement signal can alternatively or additionally be transmitted to the base station in order to determine the transmission power of the base station in an adaptive control.

If no radio signal is received at all, the alternating component of the RSSI signal has a certain size, which is determined by the reception architecture, the radio channel and the noise characteristics. The processed RSSI signal at the input of the threshold value comparator increases when an amplitude-modulated signal is received, since the signal energy increases due to the amplitude fluctuations. On the other hand, when a signal with a constant amplitude is received, as is the case with frequency-modulated or phase-modulated signals, the filtered RSSI signal value becomes smaller and tends towards zero for larger field strengths.

Overall, the evaluation of the RSSI signal corresponding to the present principle enables a particularly simple and quick determination of how a received radio signal is modulated and / or whether a useful signal is received at all. A particular advantage results from the fact that the direct component of the RSSI signal is usually evaluated anyway in radio receivers in order to determine the reception field strength.

According to the present method, it is possible to determine at all whether a signal is present in the receiving channel and, instead or in addition, to make a decision as to whether a received radio signal is phase or frequency modulated or amplitude modulated.

The received field strength signal is preferably provided at an output of a limiting amplifier, a so-called limiter, which is connected downstream of the downward frequency converter.

The AC component of the RSSI signal, which is obtained with the high-pass filter, is preferably processed in the detection unit by forming the mean value, the effective value or the mean value.

The spectrum of the RSSI signal must not be cut too far beforehand.

The threshold value comparator evaluates the prepared RSSI

Signal prefers one or two threshold values and, by comparing the processed RSSI signal with the threshold values, determines whether there is no signal at all, an amplitude-modulated signal or only a phase- or frequency-modulated signal.

In the case of a frequency-modulated signal, it is detected according to the present principle whether the signal has a constant envelope.

Further details and advantageous refinements of the present invention result from the subclaims. The invention is explained in more detail using an exemplary embodiment with reference to the drawings.

Show it:

FIG. 1 shows a block diagram of an exemplary reception arrangement with RSSI signal evaluation according to the present principle,

FIG. 2 shows the comparison of an RSSI signal in the case of amplitude modulation with one in the case of frequency modulation,

3 shows an exemplary embodiment of the detection unit of FIG. 1 evaluating the RSSI signal,

Figure 4 exemplary waveforms of selected signals with frequency modulation and

Figure 5 exemplary signal waveforms of selected signals with amplitude modulation.

Figure 1 shows a radio receiver arrangement using a block diagram. A low-noise preamplifier 2 is coupled to a receiving antenna 1 and is connected to a first input of a downward frequency mixer 3. The second connection of the downward frequency mixer 3 is connected to a frequency generator (not shown), which provides a local oscillator signal with the carrier frequency of the received signal. At the output of the frequency mixer 3 there is an intermediate frequency signal on an intermediate frequency level IF, which is filtered in a downstream bandpass filter 4. A limiting amplifier 5, a so-called limiter, which is constructed in several stages, is connected to the output of the intermediate frequency filter 4. Its output is connected to the input of a demodulator 6, for amplitude shift keying and for frequency shift keying is designed to be selectable. Another filter 7 is connected to the demodulator output of demodulator 6.

Limiter 5 has another output at which a reception field strength signal is available, a so-called RSSI signal (Receive Signal Strength Indicator). The RSSI output of the limiter 5 is connected to a detection unit 8, which controls a control unit 9 as a function of high-frequency signal components of the RSSI signal, which is connected at its output to a control input for preselecting a demodulation method on the demodulator 6.

The detection unit 8 comprises on the input side a high-pass filter 10, 11 with a series capacitance 10 and a resistor 11 connected to ground. The high-pass filter 10, 11 is followed by an effective value determination circuit 12, 13, 14, which has a diode 12 polarized in the flow direction and one connected in series connected resistor 13 with a downstream capacitor 14 to ground. A high-pass filtered and averaged RSSI signal is accordingly available at the output of the effective value generator, which is fed in at an input of a threshold value comparator 15 to which the effective value generator is connected. The threshold value comparator 15 comprises two further inputs, to each of which an upper and lower threshold value signal can be fed.

Depending on whether the filtered and averaged RSSI signal lies between the upper and lower threshold, above the upper threshold or below the lower threshold, the comparator 15 adjusts at respective outputs

ASK indicator signal, an FSK indicator signal or a noise indicator signal ready. Depending on whether an amplitude-modulated, a frequency-modulated or no useful signal is detected, the control logic 9 controls the demodulator 6. According to the present principle, the effective value of the RSSI signal without a DC component is used to distinguish whether an amplitude-modulated or a non-amplitude-modulated signal is present. Thus, only the alternating component of the received field strength signal is used to evaluate whether an amplitude-modulated or a frequency / phase-modulated signal is received.

In the first case, that no modulated useful signal is received at the antenna 1, the signal component used for the determination has a value that is determined by the system and the noise properties. If an amplitude-modulated signal is received, the rectified alternating component of the RSSI signal increases since the signal energy increases due to the amplitude fluctuation. In the case of a signal with a constant amplitude, that is to say a signal with a constant envelope, such as with pure frequency or phase modulation, the effective value or mean value becomes smaller and tends towards zero for larger field strengths. This decrease in the noise level progresses very rapidly as the received signal level increases, since the noise is quickly displaced by the limiter effect. It is thus possible to evaluate the signal with regard to its type of modulation near the sensitivity threshold of the receiver.

A total of three cases can be distinguished by corresponding threshold values on the comparator 15: if the rms value measured lies between the upper and lower threshold, no useful signal is received. If the effective value is above the upper threshold, it is an amplitude-modulated signal, for example an amplitude shift keying. If, on the other hand, the effective value is less than the lower threshold, a signal with a constant envelope, such as a frequency-shift-keyed signal, is coupled in to the antenna. Accordingly, the present principle not only allows a statement to be made as to whether there is an amplitude-modulated or a frequency-modulated signal, but also whether a signal is detected in the reception channel at all.

FIG. 2 shows a graph in a semi-logarithmic representation, in which the effective value of the alternating component of the RSSI signal is plotted in millivolts over the reception field strength of the high-frequency signal, measured in dBmW. Frequencies between 0 and 100 kHz were taken into account. It can be clearly seen that a distinction is possible even from low reception field strengths of approximately -115 dBm, whether an amplitude-shift keyed or a frequency shift keyed signal, referred to here as ASK or FSK, is present. With increasing reception field strength or input power, the distinction becomes easier and easier.

FIG. 3 shows, using a circuit diagram, an exemplary structure of the detection unit 8 with a high-pass filter 10, 11 connected to the RSSI output of the limiter 5, an RMS generator 12, 13, 14 connected downstream, comprising a diode 12, a series resistor 13 and a capacitance 14 to ground and with a comparator 15 designed as a transimpedance amplifier with two threshold value inputs.

The comparator comprises an ASK threshold value input and an FSK threshold value input, which are connected to a resistance divider comprising three series resistors 16, 17, 18, which is connected between a supply potential of plus 3 V and reference potential. The resistance values of resistors 16 to 18 are selected so that a potential of 800 mV is available at the ASK threshold input, while a potential of 400 mV is available at the FSK input. The transimpedance amplifier 15 comprises a controlled current source which outputs a current depending on whether the averaged RSSI signal is above or below the lower threshold with regard to the alternating components. Based on the output signal on Output of the comparator 15 can therefore be determined whether a useful signal is detected at all. The fact whether it is an amplitude-modulated or a frequency-modulated signal can also be read from the output signal of the transimpedance amplifier 15.

In the example of FIG. 3, in addition to the control of the control unit 9, which in turn controls the demodulator 6, in the present case a so-called data slicer is also controlled depending on whether an amplitude-modulated or a frequency-modulated signal is detected. This data slicer 19 is connected to the output of the data filter 7 in the signal processing chain of FIG. 1, but is not shown there.

FIG. 4 shows the simulation results using an exemplary embodiment of the present principle in the presence of a frequency shift keyed signal in accordance with the circuit diagram of FIG. 3. The signal voltage is plotted over time in milliseconds. You can see that in the upper part of the diagram

Course of the RSSI signal RSSI, the relatively constant course of the corresponding lower threshold SU of the comparator 15 and the signal course of the output signal S of the comparator. If the output signal S of the comparator is above the threshold SU, the output of the received signal processing chain is released and a corresponding demodulated output signal A, see lower half of the figure, is output.

FIG. 5 also shows the course of the characteristic signals from FIG. 3 on the basis of an example with an amplitude-shift keyed signal. The course of the RSSI signal, the signal threshold SO, the output signal S and the output signal A of the received signal chain is also clearly shown here. LIST OF REFERENCE NUMBERS

1 antenna

2 preamplifiers 3 down mixers

4 IF filters

5 limiters

6 demodulator

7 data filter 8 detection unit

9 control unit

10 capacity

11 resistance

12 diode 13 resistor

14 capacity

15 threshold comparator

16 resistance

17 resistance 18 resistance

19 Data slizer ASK amplitude shift key FSK frequency shift key S output signal SU threshold

RSSI reception field strength signal A output signal

Claims

claims 1. Receiving arrangement for a radio signal, comprising a downward frequency converter (3) with a first input for coupling in the radio signal, with a second input for supplying a local oscillator signal and with an output, an amplifier (5) with an amplifier input, which is coupled to the output of the down-frequency converter (3), with an amplifier output and with an output for deriving a received field strength signal (RSSI), - A demodulator (6) for demodulating a down-mixed, amplified signal, with a signal input which is connected to the output of the amplifier (5), with a signal output for deriving a demodulated signal and with a control input for preselecting a demodulation method from one Set of predetermined demodulation methods and - A detection unit (8) having a high-pass filter (10, 11) with an input which is connected to the output of the amplifier (5) for deriving the received field strength signal (RSSI), and a threshold value comparator (15) which its input is coupled to the output of the high-pass filter (10, 11) and its output is coupled to the control input of the demodulator (6), designed to output a value which represents the modulation method of the radio signal. 2. Receiving arrangement according to claim 1, d a d u r c h g e k e n n z e i c h n e t that in the detection unit (8) between the high-pass filter (10, 11) and the threshold value comparator (15) a means for averaging or effective value formation (12, 13, 14) is connected. 3. Receiving arrangement according to claim 1 or 2, characterized in that the threshold value comparator (15) has a threshold value input for supplying a signal threshold whose value lies between a value range characterizing an amplitude-modulated signal (ASK) and a value range characterizing a frequency-modulated signal (FSK) of the filtered reception field strength signal (RSSI). 4. Receiving arrangement according to claim 3, characterized in that the threshold value comparator (15) has a further threshold value input and that the value representing the modulation method of the radio signal can assume one of three predetermined states, of which no signal, amplitude-modulated signal (ASK) and frequency-modulated signal (FSK) are included. 5. Receiving arrangement according to one of claims 1 to 4, characterized in that for coupling the threshold comparator (15) to the control input of the demodulator (6) a control unit (9) is provided for preselecting a demodulation method from a set of predetermined demodulation methods depending on the value representing the modulation method of the radio signal. 6. Receiving arrangement according to one of claims 1 to 5, characterized in that a signal processing block (19) is coupled to the output of the demodulator (6) in the further signal processing chain, with a control input which is coupled to the output of the threshold value comparator (15) , 7. Receiving arrangement according to one of claims 1 to 6, characterized in that the down-frequency converter (3) with the amplifier (5) via an intermediate frequency filter (4) is coupled. 8. Receiving arrangement according to one of claims 1 to 7, d a d u r c h g e k e n n z e i c h n e t that the high-pass filter (10, 11) in the detection unit (8) comprises a series capacitance (10) with downstream resistance to ground (11). 9. Receiving arrangement according to one of claims 1 to 8, d a d u r c h g e k e n n z e i c h n e t that the amplifier (5) with the output for deriving the received field strength signal (RSSI) is a limiting amplifier.