JP2007166208A - Fsk signal detection apparatus, receiver, and fsk signal detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio receiver 10 capable of discriminating whether or not a received signal includes an FSK signal without using the RSSI and noise squelch or the like. <P>SOLUTION: An inflection point extraction unit 13 generates a signal whereby an inflection point can be derived as a changing point between symbols on the basis of a baseband signal 11, and a BPF 17 detects a symbol rate of the baseband signal on the basis of an input signal from the inflection point extraction unit 13. On the other hand, a power spectrum arithmetic unit 25 calculates an FFT value of the input signal from the inflection point extraction unit 13 and calculates a power spectrum at a plurality of frequency points on the basis of the FFT value. A symbol discrimination unit 26 discriminates that the baseband signal is the FSK signal when a frequency fm at a maximum power spectrum is 1/symbol rate on the basis of input data from the power spectrum arithmetic unit 25. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an FSK signal detection device that detects the presence or absence of an FSK (Frequency Shift Keying) signal, a receiver equipped with the FSK signal detection device, and an FSK signal detection method.

  Some digital radios employ FSK as a digital modulation signal. In such an FSK receiver, channel scanning is appropriately performed to find a channel including the FSK signal and decode the FSK signal of the channel.

  The channel scan in the conventional FSK receiver is performed, for example, by the following procedure.

S1: When FM or SSB is performed as the secondary modulation, analog demodulation is performed on the received signal.

S2: Sense signal level at the receiver is detected based on RSSI (Received Signal Strength Indicator) and noise squelch.

S3: If the sensation signal level is equal to or higher than a preset level, the sensation signal is assumed to be a desired FSK signal, and FSK demodulation is performed on the sensation signal.

S4: After receiving a symbol clock synchronization preamble of a digital modulation signal, a frame synchronization word is detected.

S5: If a frame synchronization word is detected, data reception is continued.

S6: If a frame synchronization word cannot be detected, and if channel scanning is in progress, the process proceeds to the next channel after a predetermined time has elapsed. If the channel scan is not being performed and reception is being continued, mute control is performed.

Patent Document 1 discloses that an FSK signal detection apparatus capable of receiving both an analog modulation signal and a digital modulation signal receives a reception mode as an analog signal depending on whether the reception signal to be unmuted is analog modulation or digital modulation. The mode is automatically switched to the mode or the digital reception mode, and then the mute is released so that the correct demodulation is performed when the mute is released.
JP 2005-26871 A

  The problems of channel scanning in the conventional FSK receiver are as follows.

(A) Predetermined hardware is required to determine the input signal level. For example, in the case of an FM receiver, generally, an FM detection IC generates an RSSI signal. The noise squelch signal is generated from a circuit that rectifies and integrates the detection signal. In addition, an SSB receiver or the like for a received radio wave in which amplitude modulation is used as secondary modulation can replace the AGC voltage of the IF signal with the RSSI signal, but the AGC voltage changes due to noise or the like. In some cases, it is not possible to accurately determine the presence or absence of an input feeling signal from the AGC voltage.

(B) In order to determine whether the FSK signal is included in the received signal, it is necessary to receive the received signal of each channel for a long time, and when waiting for a plurality of channels, the time required for the entire channel scan It becomes long. That is, it is necessary to detect a preamble and a frame synchronization word in order to determine that the received signal includes the FSK signal. If data communication has already been started, the receiver must wait until the transmission side retransmits the frame synchronization word in order to determine the presence or absence of the FSK signal in the received signal.

  An object of the present invention is to provide an FSK signal detection device capable of determining whether or not a received signal includes an FSK signal without using RSSI or noise squelch, a receiving device equipped with the same, and an FSK signal detection method Is to provide.

  Another object of the present invention is to provide an FSK signal detecting device, a receiving device equipped with the same, and an FSK signal detecting method capable of speeding up the determination as to whether or not the received signal includes an FSK signal.

The FSK signal detection apparatus of the present invention includes the following.
Baseband signal extraction means for extracting a baseband signal from the received signal;
Power spectrum calculation means for calculating the power spectrum of the baseband signal,
Symbol rate detection means for detecting the symbol rate of the baseband signal, and determination means for determining the presence or absence of the FSK signal in the received signal based on the power spectrum and the frequency corresponding to the symbol rate.

  The receiver of the present invention is equipped with the aforementioned FSK signal detection device, and further, channel switching means for switching to the next channel when the FSK signal detection device determines that there is no FSK signal for the received signal of each channel during the channel scan period. It has.

The FSK signal detection method of the present invention includes the following steps.
Extracting a baseband signal from the received signal;
Calculating the power spectrum of the baseband signal;
Detecting a symbol rate of the baseband signal, and determining the presence or absence of an FSK signal in the received signal based on a power spectrum and a frequency corresponding to the symbol rate.

  According to the present invention, it is possible to detect the presence or absence of an FSK signal in a baseband signal based on the power spectrum and symbol rate of the baseband signal.

  FIG. 1 is a block diagram of the main part of a portable or in-vehicle wireless receiver 10. FIG. 1 shows a portion of the radio receiver 10 that is involved in processing from FSK demodulation to symbol output and FSK signal determination.

  Among reception signals received by the wireless receiver 10, a reception signal of a predetermined channel is selected by an IF converter (not shown), and an IF signal related to the selected reception signal is an FSK demodulator (not shown). The baseband signal 11 is generated as a signal after FSK demodulation.

  When FSK is used for primary modulation and FM or SSB is used for secondary modulation (RF modulation), an IF signal after IF demodulation is detected by FM demodulation or SSB demodulation, and then baseband signal 11 is generated by FSK demodulation. . On the other hand, when only FSK modulation is used, the baseband signal 11 is generated only by FSK demodulation of the IF signal after IF demodulation.

  FIG. 2 is a diagram illustrating an example of the baseband signal 11. 2 to 6, the horizontal axis represents time, and the vertical axis represents amplitude level. The baseband signal 11 is an 8-level FSK signal in the illustrated example, but may be a binary or other value. The baseband signal 11 is supplied to an LPF (Low Pass Filter) 12.

  FIG. 3 is a diagram showing the output of the LPF 12. The LPF 12 is, for example, a Gaussian filter, and the processing in the LPF 12 prevents intersymbol symbol interference due to noise or the like. The output of the LPF 12 is sent to the inflection point extractor 13.

  FIG. 4 is a diagram showing the output of the inflection point extractor 13. The inflection point refers to a turning point between symbols, and the input X (n) and the output Y (n) in the inflection point extractor 13 have the relationship of the following equation (1).

Y (n) = | X (n−a) −X (n−b) | − | X (n−c) −X (n−d) |

However, 0 ≦ a <b <c <d, d <fs / fsym, and ba−dc = dc. Note that fs is a sampling frequency of the baseband signal, and fsym is a symbol rate frequency desired to be received. Further, | ˜ | means an absolute value.

  Y (n) is an example of the inflection point derivation signal. When n is the time of the inflection point, Y (n) = 0. For example, Y (n) becomes 0 when the slopes between two points (between a and b and between c and d) in two consecutive symbols are equal. In Y (n), when Y (n) = 0 except at the inflection point, it is when going down a mountain of symbols. Thus, Y (n) is an ideal inflection point derivation signal and passes through the origin 0 at a predetermined timing when the FSK signal is felt. Since the predetermined timing is a cycle of 2 / fsym, it can be said that Y (n) includes the frequency component of fsym.

  A BPF (Band-Pass Filter) 17 receives Y (n) from the inflection point extractor 13 and extracts a symbol rate. The output of the BPF 17 is sent to the binarizer 18.

  FIG. 5 shows the output of the binarizer 18. The binarizer 18 outputs positive and negative values of a predetermined level when the input from the BPF 17 is positive and negative, respectively. In this example, +300 and −300 are set as positive and negative predetermined levels of the binarizer 18, respectively.

  The output of the binarizer 18 is sent to a PLL (Phase Locked Loop) 19. The PLL 19 has a well-known configuration and includes a phase comparator 191, an internal clock generator 192, and a timing adjuster 193. The phase comparator 191 performs phase comparison between the input from the binarizer 18 and the internal clock from the internal clock generator 192. The timing adjuster 193 adjusts the generation timing of the internal clock (symbol clock) of the internal clock generator 192 based on the output of the phase comparator 191.

  FIG. 6 is a signal waveform diagram for explaining the operation of the PLL 19. In FIG. 6, the baseband signal 11 (indicated by a solid line) is overwritten with a symbol clock (indicated by a dotted line) as an output of the PLL 19. Initially, the symbol clock is not synchronized with the baseband signal 11. However, as a result of the phase comparison in the phase comparator 191 and the adjustment in the internal clock generator 192, the symbol clock is quickly synchronized with the baseband signal 11. .

  The symbol capture unit 20 receives the baseband signal 11 and the symbol clock generation timing signal from the internal clock generator 192 of the PLL 19 and performs symbol determination on the baseband signal 11 at the falling timing of the symbol clock. The symbol output 21 corresponds to the determination result of the symbol capturing device 20 and is sent to the host CPU (not shown) as a demodulated signal of the baseband signal 11.

On the other hand, Y (n) output from the inflection point extractor 13 is also sent to the power spectrum calculator 25. The power spectrum calculator 25 has a known configuration and includes an N-point FFT unit 251 and a power calculator 252. The N-point FFT unit 251 is a high-speed Fourier transformer that divides a frequency range from DC to 1/2 of the sampling frequency of the baseband signal into N / 2 equal frequency intervals. If the imaginary number is 0, N-point real number (real) and imaginary number (imag) Fourier transform results are output. The power calculator 252 uses the data of 1 to N / 2 converted by the N-point FFT unit 251 and squares the absolute value for each frequency division (power = 1 / N (sqrt (real ² + image ² )) ² ) Perform the calculation as a power spectrum. 1 / N in the arithmetic expression can be omitted.

  The symbol determiner 26 examines N / 2 points of power spectrum data from the power spectrum calculator 25, and detects the frequency fm that is the maximum power spectrum among them. When fm is 1 / symbol rate, it is determined that the selected received signal has the target FSK signal, and in other cases, it is determined that the selected received signal does not have the target FSK signal. The symbol determiner 26 can obtain information on the symbol rate from the BPF 17.

  For example, if the wireless receiver 10 is designed to receive an FSK signal with a symbol rate of 1000 Hz (1000 sps), and if fm is 1000 Hz (1000 sps), the received signal being selected has a target FSK signal. However, when fm is 500 Hz (500 sps), it is determined that there is no target FSK signal in the selected received signal, assuming that an FSK signal other than the specification is received.

  The determination output 27 corresponds to the determination result of the symbol determiner 26 and is sent to the host CPU (not shown) as a demodulated signal of the baseband signal 11.

  A host CPU (not shown) performs corresponding processing based on the determination output 27. For example, in the channel scan period, when it is determined that there is no target FSK signal in the channel currently selected for reception, switching to the next channel is performed, and it is determined that the target FSK signal is present. If it is, the subsequent channel scan is stopped, and data processing or audio processing is performed based on the symbol output 21. If it is determined that the target FSK signal is present during the non-channel scan period, mute is executed.

  If the functions of the power spectrum calculator 25 as well as the functions of the PLL 19 and the symbol capturing unit 20 are incorporated in a single digital signal processor (DSP: not shown), the hardware elements used in the radio receiver 10 will be described. The score can be greatly reduced.

  FIG. 7 is a configuration diagram of the FSK signal detection device 40. The portion illustrated in FIG. 1 in the wireless receiver 10 is an example of the FSK signal detection device 40. The FSK signal detection device 40 includes a baseband signal extraction unit 41, a power spectrum calculation unit 42, a symbol rate detection unit 43, and a determination unit 44.

  Baseband signal extraction means 41 extracts a baseband signal from the received signal. The power spectrum calculation means 42 calculates the power spectrum of the baseband signal. The symbol rate detection means 43 detects the symbol rate of the baseband signal. The determination unit 44 determines the presence or absence of the FSK signal in the received signal based on the power spectrum and the frequency corresponding to the symbol rate.

  In the FSK signal detection device 40, an example of the baseband signal is that shown in FIG. Examples of the power spectrum calculation unit 42, the symbol rate detection unit 43, and the determination unit 44 are the power spectrum calculator 25, the BPF 17, and the symbol determiner 26 of the wireless receiver 10, respectively.

  Since the FSK signal detection device 40 detects the presence or absence of the FSK signal in the baseband signal based on the power spectrum and the symbol rate, hardware for detecting RSSI and noise squelch can be omitted. Further, the FSK signal detection device 40 can detect the presence or absence of the FSK signal without waiting for the reception of the symbol clock synchronization preamble and the frame synchronization word, thereby reducing the time required for detection.

  The advantage of the method of detecting the presence or absence of the FSK signal in the baseband signal based on the power spectrum and the symbol rate is that the reception period is shortened, and the presence or absence of the FSK signal in the baseband signal can be detected without difficulty when receiving a small number of symbols. Is what you can do. Also, when FM and SSB are subjected to secondary modulation, the presence or absence of an FSK signal can be detected. Furthermore, only the presence or absence of the FSK signal can be checked ignoring digital modulation other than the FSK specification. In order to check the presence or absence of the FSK signal, the detected symbol rate can be used for a symbol determination by switching the communication speed for each received signal in a multi-rate modem or the like that handles a plurality of symbol rates. .

  FIG. 8 is a configuration diagram of an FSK signal detection device 50 that embodies the FSK signal detection device 40. Regarding the elements of the FSK signal detection device 50, the same elements as those of the FSK signal detection device 40 are designated by the same reference numerals, and description thereof will be omitted.

  Inflection point extraction means 51 can be added to the FSK signal detection device 50. The inflection point extraction means 51 generates an inflection point derivation signal for deriving an inflection point of the baseband signal. And the power spectrum calculation means 42 calculates the power spectrum of the baseband signal based on the inflection point derivation signal. Further, the symbol rate detection means 43 detects the symbol rate of the baseband signal based on the inflection point derivation signal.

  An example of the inflection point extraction means 51 is the inflection point extractor 13, and the inflection point derivation signal is generated based on the above-described equation (1) in the wireless receiver 10, for example. Based on the inflection point derivation signal, the power spectrum and symbol rate of the baseband signal can be generated smoothly.

  In the FSK signal detection device 50, the power spectrum calculation means 42 may generate a power spectrum of the baseband signal by performing Fourier transform on the inflection point derivation signal. An example of a Fourier transform portion in the power spectrum calculation means 42 is an N-point FFT unit 251 (FIG. 1).

  In the FSK signal detection device 50, the determination means 44 receives the received signal based on whether or not the frequency corresponding to the maximum power spectrum among the plurality of power spectra related to the plurality of frequency points is a frequency corresponding to the symbol rate. The presence or absence of the FSK signal can be determined.

  FIG. 9 is a configuration diagram of the receiver 55. The receiver 55 includes the FSK signal detection device 40 or the FSK signal detection device 50, and also includes a channel switching unit 56 and a mute unit 57.

  When the FSK signal detection device 40 or the FSK signal detection device 50 determines that there is no FSK signal in the channel scan period, the channel switching means 56 switches to the next channel. When the FSK signal detection device 40 or the FSK signal detection device 50 determines that there is no FSK signal for a predetermined channel in the non-channel scan period, the mute means 57 performs mute.

  FIG. 10 is a flowchart of the FSK signal detection method 65.

  In S66, a baseband signal is extracted from the received signal. In S67, the power spectrum of the baseband signal is calculated. In S68, the symbol rate of the baseband signal is detected. In S69, the presence or absence of the FSK signal in the received signal is determined based on the power spectrum and the frequency corresponding to the symbol rate.

  Similar to the FSK signal detection device 40 and the FSK signal detection device 50, the FSK signal detection method 65 can be embodied in various ways. The following is an example.

  S66b (not shown in the drawing) can be added between S66 and S67. In S66b, an inflection point derivation signal for deriving an inflection point of the baseband signal is generated based on the baseband signal. In S67, the power spectrum of the baseband signal is generated based on the inflection point derivation signal, and in S68, the symbol rate of the baseband signal is detected based on the inflection point derivation signal.

  In S67, the power spectrum of the baseband signal may be generated by performing fast Fourier transform on the inflection point derivation signal.

  In S69, the presence / absence of an FSK signal in the received signal is determined based on whether or not the frequency corresponding to the maximum power spectrum among the plurality of power spectra related to the plurality of frequency points is a frequency corresponding to the symbol rate. May be.

  Although the present invention has been described with respect to the best mode, the present invention is not limited to this, and each constituent element in the best mode can be modified and embodied without departing from the gist of the invention. In addition, a plurality of constituent elements disclosed in the best mode are conveniently combined and added, or some constituent elements are deleted to form various inventions without departing from the gist of the invention. can do. Furthermore, various inventions can be formed by selecting predetermined components among a plurality of disclosed embodiments and combining them.

It is a principal part block diagram of the vehicle-mounted radio receiver. It is a figure which shows an example of a FSK signal. It is a figure which shows the output of LPF. It is a figure which shows the output of an inflection point extractor. It is a figure which shows the output of a binarizer.

It is a signal waveform diagram explaining the effect | action of PLL. It is a block diagram of a FSK signal detection apparatus. It is a block diagram of the FSK signal detection apparatus which actualized the FSK signal detection apparatus of FIG. It is a block diagram of a receiver. It is a flowchart of the FSK signal detection method.

Explanation of symbols

40: FSK signal detection device, 41: baseband signal extraction means, 42: power spectrum calculation means, 43: symbol rate detection means, 44: determination means, 50: FSK signal detection device, 51: inflection point extraction means, 55 : Receiver, 56: channel switching means, 57: mute means, 65: FSK signal detection method.

Claims (7)

Baseband signal extraction means for extracting a baseband signal from the received signal;
Power spectrum calculating means for calculating a power spectrum of the baseband signal;
Symbol rate detection means for detecting a symbol rate of the baseband signal, and determination means for determining the presence or absence of an FSK signal in the received signal based on the power spectrum and a frequency corresponding to the symbol rate;
An FSK signal detection device comprising: An inflection point generating means for generating an inflection point derivation signal for deriving an inflection point of the baseband signal based on the baseband signal;
The power spectrum calculating means for calculating a power spectrum of a baseband signal based on the inflection point derivation signal, and the symbol rate detection means for detecting a symbol rate of the baseband signal based on the inflection point derivation signal;
The FSK signal detection apparatus according to claim 1, further comprising: The power spectrum calculating means for calculating a power spectrum of a baseband signal by performing Fourier transform on the inflection point derivation signal;
The FSK signal detection apparatus according to claim 2, further comprising: The determination for determining the presence / absence of an FSK signal in the received signal based on whether or not a frequency corresponding to a maximum power spectrum among a plurality of power spectrums related to a plurality of frequency points is a frequency corresponding to a symbol rate. means,
The FSK signal detection device according to claim 1, comprising: A receiver equipped with the FSK signal detection device according to claim 1,
Channel switching means for switching to the next channel when the FSK signal detection device determines that there is no FSK signal for the received signal of each channel during the channel scan period,
The receiver according to claim 4, further comprising: A mute means for performing mute when the FSK signal detection device determines that there is no FSK signal for a predetermined channel in a non-channel scan period;
The receiver according to claim 5, further comprising: Extracting a baseband signal from the received signal;
Calculating a power spectrum of the baseband signal;
Detecting a symbol rate of the baseband signal; and determining the presence or absence of an FSK signal in the received signal based on the power spectrum and a frequency corresponding to the symbol rate;
An FSK signal detection method comprising:

Images