JP3592512B2 - High frequency signal detector - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-frequency signal detection device suitable for detecting an unspecified high-frequency signal.
[0002]
[Prior art]
In general, in wireless communication between devices, it is often the case that a so-called communication system and a communication time are known in advance, such as a frequency band used and a modulation system. Therefore, in a normal wireless communication, a transmission / reception device having a communication method which is the same as that of the transmission / reception device is provided, and communication is performed in a common time zone.
[0003]
However, there is a case where it is desired to catch an emergency communication radio wave or to communicate with the transmission partner in a state where the partner is not specified and the presence of the partner is not clear, such as emergency communication in the case of distress. In such a case, for the receiving side, the transmission time as well as the communication method of the other party are completely unknown. Further, only in such a case, the transmission radio wave of the other party is often weak, and there is much noise, and the reception environment is not always good.
[0004]
Recent wireless communication devices have made remarkable progress in both hardware and software as seen in mobile terminal devices. Also, like satellite communication, the communication area has expanded to outer space, and many various communication systems have become complicated.
[0005]
For example, in the satellite communication system, a digital modulation system has recently become mainstream, and a multiple access has been adopted in order to efficiently use the on-board equipment. The multiple access is a communication in which a large number of earth stations and terminals access and communicate with a vacant radio line. The multiple access includes frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access. (CDMA).
[0006]
In the TDMA system, a signal in the same frequency band is divided on the time axis to form a plurality of channels, and the transmitting side transmits a burst signal in a time band of an empty channel. There is also a so-called time random multiple access (TRMA) system in which the timing of signal appearance is not defined, such as a slot-type Aloha system.
[0007]
The TRMA system transmits a burst signal obtained by compressing a digital signal in a short time. However, since the transmission timing itself is unknown to the receiving side, the transmitting side needs to transmit and detect the burst signal with high accuracy. The condition is that the frequency stability of the carrier frequency is good.
[0008]
FIG. 5 is a configuration diagram showing a conventional high-frequency signal detection device configured as a part of a receiver. For example, when an amplitude modulation (AM) wave whose transmission carrier frequency is unknown is to be received, the signal is received by an antenna 1. The transmitted radio wave, that is, the high-frequency signal is amplified by the high-frequency amplifier 2 and then supplied to the frequency converter (MIX) 3 where it is mixed with the local oscillation signal from the variable local oscillator (LO) 4 to generate the intermediate frequency ( IF) signal. The IF signal is subjected to AM detection in a demodulation circuit 6 after noise is suppressed by a band-pass filter (BPF) 5, and an audio signal is output from a speaker 7. Here, if the transmission carrier frequency of the other party is unknown, the local oscillation frequency of the variable local oscillator 3 is adjusted, and transmission radio waves from a specific other party can be caught by so-called channel selection.
[0009]
[Problems to be solved by the invention]
As described above, even in an unspecified transmission partner, the transmission time, transmission frequency, modulation method, and the like from the partner are often known on the reception side in many cases. Signals from the other party can be selected and received easily. However, it is not easy to efficiently and promptly catch a transmission radio wave whose communication method is unknown as well as a transmission time zone, such as emergency communication in the case of distress.
[0010]
Also, if the transmission destination side unspecified is not only the communication system or the like is unknown, the then since the transmission power is very weak and often, often a child distracted to many noise reception environment is not always good . Moreover, in a state where the transmission frequency is also unknown, it is not easy to search a wide frequency range and catch it instantaneously, and some solution has been demanded.
[0011]
[Means for Solving the Problems]
According to the present invention, in a high-frequency signal detection device, A / D conversion means for performing A / D conversion by sampling a reception high-frequency region on a time axis to obtain a discrete digital signal of the reception high-frequency signal, and this A / D conversion means Fast Fourier transform means for dividing the frequency bandwidth of the discrete digital signal into a plurality of discrete digital signals, and the time axis of the discrete digital signal appearing in each divided region of the frequency bandwidth divided into a plurality by the fast Fourier transform means Signal processing means for calculating the correlation between the amplitude levels of the received high-frequency signal and the modulation method of the received high-frequency signal .
[0012]
As described above, according to the present invention, the received high-frequency region is converted into a discrete digital signal by A / D conversion on the time axis, and the bandwidth is divided in the received high-frequency region by the fast Fourier transform of the discrete digital signal. Is
[0013]
Although the noise power at the time of reception is proportional to the reception bandwidth, in the present invention, the reception high-frequency region is subdivided by the fast Fourier transform, and the subdivision realizes low noise in each divided region. . In addition, depending on the setting of the number of divisions, it is possible to simultaneously increase the bandwidth of the reception area. Further, digitization of the received high-frequency signal by A / D conversion enables high-speed operation in the signal processing means, and the signal processing means determines the correlation of the amplitude level on the time axis between the discrete digital signals. Since the arithmetic processing is performed, the bandwidth of the received high-frequency signal can be estimated.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a high-frequency signal detecting device according to the present invention will be described in detail with reference to FIGS. Note that the same components as those of the conventional configuration shown in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0015]
FIG. 1 is a circuit diagram showing a first embodiment of a high-frequency signal detection device according to the present invention. As in FIG. 5, the description will be made assuming that the high-frequency signal detection device is applied to a receiver.
[0016]
That is, it is assumed that a transmission radio wave whose frequency and modulation method are unknown is received by the antenna 1, and the transmission radio wave (received high-frequency signal) is amplified by the high-frequency amplifier 2 and then supplied to the frequency converter 3. The received high-frequency signal supplied to the frequency converter 3 is mixed with a local oscillation signal from the variable local oscillator 4 and converted into an intermediate frequency (IF) signal having a bandwidth of 10 KHz in this embodiment.
[0017]
The received high-frequency signal converted into an IF signal having a bandwidth of 10 KHz is supplied to an analog / digital (A / D) converter 8 after noise is removed through a band-pass filter 5, where the 12.8 KHz signal is transmitted. A digital signal sampled on the time axis by the sampling (sampling) frequency fs, that is, a discrete time digital signal is generated.
[0018]
That is, the IF signal having a bandwidth of 10 KHz is converted into a digital data string composed of discrete digital signals by A / D conversion, and is supplied to the fast Fourier transform (FFT) circuit 9.
[0019]
The FFT circuit 9 performs a 128-point FFT process on the time axis so that the IF band of 10 KHz is subdivided into 100 divided regions (bins) as shown in FIGS. 2A and 2B. Configured. That is, the IF signal of a high frequency is divided into 100 divided regions each having a bandwidth of 100 Hz by the subdivision in the FFT circuit 9, and the output of each digital data (91, 92,... 9100) in the divided region is output to the next stage. Are supplied in parallel to the signal processing circuit 10.
[0020]
As shown in FIG. 3, the signal processing circuit 10 is provided with memories (10a1, 10a2,... 10a100) for storing input digital data in time series, and provided for comparing data in each memory in time series. Each of the first and second combining circuits (10b11, 10b12, 10b21, 10b22,..., 10b1001, 10b1002) and each of the first and second combining circuits (10b11, 10b12, 10b21, 10b22,..., 10b1001, 10b1002) And a central processing unit (CPU) 10c that processes and computes the output signal of FIG.
[0021]
Therefore, the digital data in each of the divided areas supplied from the FFT circuit 9 to the corresponding memories 10a1, 10a2,... 10a100 respectively correspond to the first and second combining circuits (10b11, 10b12, 10b21, 10b22,. , 10b1002), a composite signal is generated in two frames each of which is time-series. The memory (10a1, 10a2,..., 10a100) in this embodiment is configured to form one frame with five digits, as shown in FIG. The power comparators 10ca1, 10ca2,..., 10ca100 are configured to be supplied.
[0022]
Each of these combined signals is supplied to a corresponding one of the power comparators 10ca1, 10ca2,..., 10ca100 of the CPU 10c, so that each of the power comparators 10ca1, 10ca2,. Is output.
[0023]
That is, when a change is output to a corresponding power comparator (10ca1, 10ca2,..., 10ca100) for a certain divided region among the frequency divided regions by the FFT circuit 9, the reception frequency signal corresponding to the divided region is output. Presence can be detected.
[0024]
The output of each of the power comparators 10ca1, 10ca2,..., 10ca100 is supplied to an arithmetic circuit 10cb, where the calculation of the correlation on the frequency axis in each reception frequency band, the frequency domain of the existing reception signal, that is, The presence or absence of continuity in the frequency band, the occupied frequency bandwidth, the center frequency, and the like are detected, and the detection signal 101 is sent from the signal processing circuit 10 to the digital filter 11 and the demodulation circuit 6 as shown in FIG. Is supplied to the speaker 7 and output.
[0025]
In this manner, the signal processing circuit 10 calculates the center position of the bandwidth of the received high-frequency signal and the like, so that the center frequency of the received IF signal, that is, the transmission carrier frequency of the transmission radio wave can be estimated.
[0026]
However, in the case of an unknown received radio wave, a change in the center frequency (transmission carrier frequency) value and the bandwidth is also expected, so that the arithmetic circuit 10cb of the signal processing circuit 10 performs noise averaging or noise processing by the threshold processing. By removing the signal, the estimation probability of the center frequency and the occupied frequency bandwidth of the transmission radio wave can be increased, and highly sensitive and highly reliable detection can be performed. The above-described processing operation in the signal processing circuit 10c can be easily performed by an algorithm using software.
[0027]
Further, according to this embodiment, the noise power (N) at the time of reception is proportional to the reception bandwidth, so that the noise immunity is further improved. That is, as described above, the reception high-frequency (IF) region is subdivided into a plurality of bandwidths by the FFT circuit 9, so that noise reduction in each of the divided regions is realized, and the signal (S) -to-noise ratio is reduced. (N) It is possible to obtain a high-frequency signal detection device having a good ratio (S / N).
[0028]
That is, in general, when the signal power (C) to noise power (N) ratio, that is, the value of C / N is small on the receiving side, the detection probability of the transmission high-frequency signal decreases and the erroneous detection probability increases. Since the noise power (N) is proportional to the size of the reception bandwidth, a sufficient C / N is secured and the transmission radio wave is increased by narrowing the reception bandwidth by the FFT circuit 9 as in this embodiment. It can be accurately detected with probability.
[0029]
Explaining the principle of the improvement of the anti-noise characteristic by showing specific numerical values, for example, it is assumed that the occupied frequency bandwidth of the transmission radio wave is 1 KHz, and the transmission carrier frequency is unstable and changes. Therefore, assuming that the transmission carrier frequency (IF) having a bandwidth of 1 KHz changes to ± 5 KHz, the reception side requires a reception bandwidth of about 10 KHz.
[0030]
The C / N needed to accurately detect the transmission radio wave, if assumed to be 10 dB, obtains the noise power (noise power density _{N O)} ratio of per signal power (C) versus 1Hz in bandwidth 10 KHz.
[0031]
Since the noise power is proportional to the reception bandwidth as described above, when demodulating an IF signal having a bandwidth of 10 KHz in the conventional configuration shown in FIG. 6, C / N _{O at} 10 KHz is 40 dBHz because 10 KHz is 40 dBHz. , 50 dBHz (= 40 dBHz + 10 dB).
[0032]
On the other hand, as in this embodiment, the reception bandwidth is subdivided by the FFT circuit 9, and each output bandwidth is 100 Hz as described above. Therefore, if the condition of C / N required for accurately detecting and demodulating a transmission radio wave in this reception bandwidth is the same 10 dB, the C / N in each reception bandwidth (100 Hz) of the FFT circuit 9 is assumed. When seeking _O, as shown in FIG. 2 (b) and (c), 100 Hz is because it is 20dBHz, C / _{N O} would be a 30dBHz (= 20dBHz + 10dB).
[0033]
That is, in this embodiment, the frequency division of the IF signal by the FFT circuit 9 improves the C / N by 20 dB (= 50 dB−30 dBHz) under the same condition as that of the related art, that is, 10 dB. Can be detected accurately.
[0034]
In other words, as in this embodiment, the IF signal is A / D-converted, the discrete digital signal is band-divided by the FFT circuit 9, and 10 KHz is divided into 100 parallel outputs of 100 Hz. by 20dB improvement than C / N _O in the conventional IF signal, if the original of the same detection probability, an effect that the demodulation of the comparison with the conventional receiving radio waves 20dB also requires only a small received power is obtained.
[0035]
As described above, in the high-frequency signal detection device according to this embodiment, even if the received power is weak, the transmitted radio wave is instantaneously and accurately detected with a high probability, and the detection signal 101 is subjected to signal processing as shown in FIG. The signal can be supplied from the circuit 10 to the speaker 7 via the digital filter 11 and the demodulation circuit 6.
[0036]
In the above embodiment, although the frequency of the received radio wave is completely described as an unknown, the frequency of the transmission radio wave is known in advance that the modulation scheme and carrier frequency (channel) 及 beauty occupied bandwidth and the like If the receiving side is known in advance, in the above-described configuration, the variable local oscillator 4 is controlled and adjusted, a standby state is set on a predetermined channel, and the reception frequency bandwidth is optimized, so that a good anti-noise characteristic is obtained. It goes without saying that the presence or absence of the transmission radio wave can be efficiently determined.
[0037]
Therefore, as described above, the arithmetic circuit 10cb of the signal processing circuit 10 can detect the transmission carrier frequency and the bandwidth of the transmission radio wave from the output of each of the power comparators 10ca1, 10ca2,. The signal 102 is supplied to the digital filter 11 at the next stage, and the filter characteristic is adjusted and controlled so as to match the reception IF band, so that the noise characteristic can be further improved and demodulation can be performed with high sensitivity.
[0038]
Next, in the first embodiment, the frequency mixer 3 is configured so that the bandwidth of the IF signal is 10 KHz. However, while ensuring the condition that unknown radio waves are detected with a high probability, a wider band is used. An unknown signal can be received.
[0039]
That is, FIG. 4 is a circuit showing only a main part of the high-frequency signal detecting device according to the second embodiment of the present invention, that is, a configuration of the FFT circuit 9 which is different from the device shown in FIG. Thus, the FFT circuit 9 is configured by a two-stage cascade connection including the first and second FFT circuits 91 and 92.
[0040]
In the embodiment shown in FIG. 4, the bandwidth of the IF signal is set to a wide band of 1 MHz, divided into 1/100 (= 10 KHz) by the first FFT circuit 91, and further divided by the second FFT circuit 92. Each 10 KHz band was configured to be further divided into 1/100 (= 100 Hz) bands. As a result, the divided output of the FFT circuit 9 is such that, similarly to the first embodiment, the signal processing circuit 10 can perform signal processing on the output digital signal under the condition that the bandwidth is 100 Hz. The difference from the first embodiment is that, although the number of parallel input digital data in the signal processing circuit 10 has increased from 100 to 10,000, the unknown high-frequency signal can be more sensitively processed by a faster signal processing operation. Can be detected more accurately.
[0041]
In this way, the cascade connection of the FFT circuits allows the output of the FFT circuit 9 to be subdivided into a sufficiently narrow band at the output of the FFT circuit 9 even when the frequency region of the received IF signal, that is, the received high-frequency signal is greatly expanded, and noise is reduced. A high-frequency signal detection device with improved characteristics can be obtained.
[0042]
In each of the above-described embodiments shown in FIGS. 1 to 4, it has been described that the arithmetic circuit 10cb of the signal processing circuit 10 detects the center carrier frequency of the received radio wave and its occupied frequency bandwidth by calculation. However, in the arithmetic circuit 10cb, a sliding window is formed, and for each output signal of each of the power comparators 10ca1, 10ca2,. For example, when signal detection is continuous, it can be estimated that the signal is a frequency modulation (FM) wave, and when the signal detection level changes on the time axis, it can be estimated that the signal is an AM wave.
[0043]
In addition, the arithmetic circuit 10cb analyzes the frequency spectrum on the time axis, so that it is possible to estimate the presence / absence of interference of a single modulated wave with a new modulated wave.
[0044]
Or as in the description, the high-frequency signal detector according to the invention, detection since C / N _O is improved by splitting the band of the received IF signal in which a frequency band is a digital signal by A / D converted by the FFT circuit The probability is increased, and unknown high-frequency signals can be detected with high sensitivity.
[0045]
【The invention's effect】
The high-frequency signal detection device according to the present invention has a simple configuration in which the A / D conversion means and the high-speed Fourier conversion means including one or more stages of high-speed Fourier conversion circuits are connected in cascade. Can be accurately detected with high sensitivity, and the modulation method of the received high-frequency signal can be estimated , which is a large practical effect.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a first embodiment of a high-frequency signal detection device according to the present invention.
2 (a) is a band characteristic diagram of an IF signal in the device shown in FIG. 1, FIG. 2 (b) is a band characteristic diagram of an FFT circuit output of the device shown in FIG. 1, and FIG. 2 (c) is a diagram. FIG. 3 is an explanatory diagram of a signal power to noise power density ratio per 1 Hz (C / N _O ) in the band shown in FIG.
FIG. 3 is a detailed circuit diagram of a signal processing circuit of the device shown in FIG.
FIG. 4 is a configuration diagram showing a main part (FFT circuit) of a high-frequency signal detection device according to a second embodiment of the present invention.
FIG. 5 is a configuration diagram showing a conventional high-frequency signal detection device.
6 is a band characteristic diagram of an IF signal of the device shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Antenna 2 High frequency amplifier circuit 3 Frequency converter 4 Variable local oscillator 5 Bandpass filter (BPF)
6 Demodulation circuit 7 Speaker 8 A / D converter 9 Fast Fourier transformer (FFT circuit)
10 signal processing circuit 10a memory 10b combining circuit 10c CPU
10ca Power comparator 10cb Operation circuit 11 Digital filter

Claims (2)

A / D conversion means for performing A / D conversion on the reception high-frequency region by sampling on a time axis to obtain a discrete digital signal of the reception high-frequency signal;
Fast Fourier transforming means for dividing the frequency bandwidth of the discrete digital signal by the A / D converting means into a plurality of parts,
Signal processing means for calculating the correlation of the amplitude level on the time axis of the discrete digital signal appearing in each divided region of the frequency bandwidth divided into a plurality by the fast Fourier transform means , A high-frequency signal detection device configured to estimate a modulation method of a received high-frequency signal . 2. The high-frequency signal detection device according to claim 1 , wherein the fast Fourier transform unit is constituted by a plurality of cascade-connected fast Fourier transform units, and is configured to subdivide the frequency bandwidth stepwise. apparatus.

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