JP7698205B2 - Radio station and frequency error correction method - Google Patents

Description

The present invention relates to a radio station and a frequency error correction method.

The local oscillator is composed of an oscillation circuit made up of discrete components and a PLL (Phase-Locked Loop)-VCO (Voltage Controlled Oscillator) with one reference frequency oscillator. An example of a wireless station equipped with this type of local oscillator is disclosed in Patent Document 1.

A PLL-VCO can be realized by a PLL IC (Integrated Circuit) with a built-in VCO. A PLL IC enables FM (Frequency Modulation), specifically FSK (Frequency Shift Keying), over a wide band from 10 MHz to 1400 MHz.

Japanese Patent Application Publication No. 9-326752

When the above-mentioned PLL IC is used near an integer multiple of the oscillation frequency of the reference frequency oscillator that constitutes the PLL-VCO, integer boundary spurious emissions may occur. When integer boundary spurious emissions occur, the transmitting radio station may not be able to meet the spurious emission standards set forth in the Radio Law, and the receiving radio station may experience spurious reception in which it receives radio waves other than the desired radio waves.

To suppress the effects of integer boundary spurious on transmission and reception, some radio stations are equipped with multiple reference frequency oscillators and switch between them. Reference frequency oscillators develop frequency errors over time. The magnitude of frequency error over time can differ for each reference frequency oscillator.

For example, in a wireless station that communicates with a base station, the frequency error of the reference frequency oscillator used when converting the frequency of a signal received from the base station can be corrected based on the received signal to match the reference frequency oscillator of the base station. By correcting the frequency error as described above, the frequency accuracy of the reference frequency oscillator used during reception can be maintained. However, the frequency accuracy of the reference frequency oscillator used when generating a transmission signal to be sent to the base station can be reduced because the frequency error cannot be corrected as described above.

The present invention has been made in consideration of the above circumstances, and aims to provide a radio station and a frequency error correction method that can suppress the variation in frequency accuracy of each oscillator in a radio station equipped with multiple oscillators.

In order to achieve the above object, a radio station according to a first aspect of the present invention comprises:
a first oscillator that outputs a first reference signal, the first target value of which is a target frequency and is used in reception processing ;
at least one second oscillator that outputs a second reference signal used in a transmission process, the second target value being a target frequency obtained by adding a target deviation to the first target value;
a signal generating unit that generates a target signal having a first intermediate frequency as a target frequency based on the second reference signal, and generates a conversion signal that is an unmodulated signal based on the first reference signal ;
a receiving section that receives a signal generated by performing modulation based on a target signal having a frequency that coincides with the first target value, and performs frequency conversion using the conversion signal based on the received signal to generate a first intermediate frequency signal having the first intermediate frequency as a target frequency;
a demodulation unit that, in a reception mode, performs frequency conversion based on the first intermediate frequency signal using the first reference signal to generate a second intermediate frequency signal having a second intermediate frequency lower than the first intermediate frequency, and in an error correction mode, performs frequency conversion based on the target signal using the first reference signal to generate the second intermediate frequency signal, and demodulates the generated second intermediate frequency signal to generate a demodulated signal;
a deviation detection unit that detects a frequency deviation between the first reference signal and the target signal based on the demodulation signal when the demodulation unit generates the demodulated signal based on the first intermediate frequency signal, and detects a frequency deviation between the first reference signal and the second reference signal based on the demodulation signal when the demodulation unit generates the demodulated signal based on the target signal;
an error correction unit that corrects a frequency error of the first reference signal with respect to the target signal in accordance with the frequency deviation between the first reference signal and the target signal, and corrects a frequency error of the second reference signal with respect to the second target value in accordance with a deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation;
Equipped with.

Preferably, the signal generating unit generates the target signal, which is a modulated signal, by performing modulation based on the input target data and the second reference signal.

Preferably, the signal generating unit generates the target signal, which is an unmodulated signal based on the second reference signal.

Preferably, the error correction unit corrects the frequency error of the first reference signal relative to the target signal according to a frequency compensation amount that reduces the frequency deviation between the first reference signal and the target signal.

Preferably, the error correction unit corrects a frequency error of the first reference signal relative to the target signal in accordance with the frequency compensation amount, corrects the frequency error of the second reference signal relative to the second target value in accordance with a deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation, and then corrects the frequency error of the first reference signal relative to the target signal and the frequency error of the second reference signal relative to the second target value in accordance with the frequency compensation amount.

A frequency error correction method according to a second aspect of the present invention comprises:
A frequency error correction method performed by a wireless station including: a first oscillator that outputs a first reference signal used in a reception process , the first target value being a target frequency; and at least one second oscillator that outputs a second reference signal used in a transmission process, the second target value being a target frequency obtained by adding a target deviation to the first target value, the method comprising:
generating a target signal having a first intermediate frequency as a target frequency based on the second reference signal, and generating a conversion signal which is an unmodulated signal based on the first reference signal;
receiving a signal generated by performing modulation based on a target signal having a frequency that coincides with the first target value, and performing frequency conversion using the conversion signal based on the received signal to generate a first intermediate frequency signal having the first intermediate frequency as a target frequency;
In a reception mode, a second intermediate frequency signal is generated, which is a second intermediate frequency signal having a frequency lower than the first intermediate frequency, by performing frequency conversion using the first reference signal based on the first intermediate frequency signal; in an error correction mode, a second intermediate frequency signal is generated by performing frequency conversion using the first reference signal based on the target signal, and a demodulated signal is generated by demodulating the generated second intermediate frequency signal;
detects a frequency deviation between the first reference signal and the target signal based on the demodulated signal when the demodulated signal is generated based on the first intermediate frequency signal, and detects a frequency deviation between the first reference signal and the second reference signal based on the demodulated signal when the demodulated signal is generated based on the target signal,
A frequency error of the first reference signal relative to the target signal is corrected in accordance with the frequency deviation between the first reference signal and the target signal, and a frequency error of the second reference signal relative to the second target value is corrected in accordance with a deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

A radio station according to the present invention includes a first oscillator that outputs a first reference signal whose first target value is a target frequency, and at least one second oscillator that outputs a second reference signal whose second target value, which is the first target value plus a target deviation, is the target frequency. The radio station corrects the frequency error of the second reference signal relative to the second target value in accordance with the deviation from the target deviation of the frequency deviation between the first and second reference signals detected based on a demodulated signal generated from a target signal based on the second reference signal. This makes it possible to suppress variation in frequency accuracy of each oscillator in a radio station that includes multiple oscillators.

FIG. 1 is a block diagram showing a configuration of a radio station according to a first embodiment of the present invention; A flowchart showing an example of an operation of a frequency error correction method performed by a wireless station according to the first embodiment. A flowchart showing an example of an operation of a frequency error correction method performed by a wireless station according to the first embodiment. FIG. 11 is a block diagram showing a configuration of a radio station according to a second embodiment of the present invention; A flowchart showing an example of an operation of a frequency error correction method performed by a radio station according to a second embodiment. FIG. 1 is a block diagram showing a configuration of a modified example of a wireless station according to an embodiment of the present invention. A flowchart showing a modified example of the operation of the frequency error correction method performed by the wireless station according to the embodiment.

The following describes in detail the wireless station and frequency error correction method according to an embodiment of the present invention with reference to the drawings. Note that in the drawings, the same or equivalent parts are given the same reference numerals.

(Embodiment 1)
A wireless station 1 according to a first embodiment will be described below by taking a double superheterodyne wireless station as an example. The wireless station 1 shown in Fig. 1 includes a first oscillator 11 that outputs a first reference signal whose first target value is a target frequency, and at least one second oscillator 12 that outputs a second reference signal whose second target value, which is the first target value plus a target deviation, is the target frequency. In the first embodiment, the wireless station 1 includes one first oscillator 11 and one second oscillator 12.

In the reception mode, the wireless station 1 performs a reception process to receive signals from other wireless stations using a first reference signal. In the transmission mode, the wireless station 1 performs a transmission process to transmit signals to other wireless stations using a second reference signal. In the error correction mode, the wireless station 1 corrects the frequency error of the second oscillator 12 in accordance with the first oscillator 11. In detail, in the error correction mode, the wireless station 1 generates a second intermediate frequency signal by frequency conversion using the first reference signal based on a target signal that is generated using the second reference signal and has a first intermediate frequency as a target frequency, and detects the frequency deviation between the first and second reference signals from the demodulated signal obtained by demodulating the second intermediate frequency signal. Then, the wireless station 1 corrects the frequency error of the second reference signal relative to the second target value according to the frequency deviation and the target deviation.

In order to suppress deterioration of the frequency accuracy of each oscillator of the wireless station 1, specifically, the frequency accuracy of the first oscillator 11 and the second oscillator 12, it is preferable to correct the frequency error of the first reference signal that serves as a reference when correcting the frequency error of the second reference signal. As an example of a process for correcting the frequency error of the first reference signal, the wireless station 1 may receive a signal generated by performing modulation based on a target signal whose frequency is a first target value in a reception mode, and correct the frequency error of the first reference signal relative to the first target value based on the received signal. In the first embodiment, the wireless station 1 receives a signal generated by performing modulation based on the target signal from a base station, which is an example of another wireless station having a reference oscillator that outputs a target signal, and corrects the frequency error of the first reference signal relative to the first target value based on the received signal.

The components of the wireless station 1 will be described below using an example in which frequency modulation, specifically FSK (Frequency Shift Keying), is used as the modulation method. The wireless station 1 includes an input unit 21 that accepts data input, an input signal processing unit 22 that performs signal processing on the data input by the input unit 21 to generate data for transmission, a data output unit 23 that outputs correction data for correcting frequency errors and conversion data for generating an unmodulated signal used in frequency conversion, and a symbol mapper 24 that maps the data for transmission or the correction data to multilevel FSK symbols.

The wireless station 1 further includes an oscillator switch 25 connected to the first oscillator 11 and the second oscillator 12, which outputs a first reference signal or a second reference signal, and a signal generator 26 which generates a conversion signal that is a target signal or a transmission modulation signal corresponding to the second reference signal output by the oscillator switch 25, or an unmodulated signal corresponding to the first reference signal output by the oscillator switch 25. The wireless station 1 further includes a signal switch 27 which outputs the target signal, the transmission modulation signal, or the conversion signal acquired from the signal generator 26, and a transmitter 28 which generates a transmission signal from the transmission modulation signal output by the signal switch 27. The transmission signal generated by the transmitter 28 is transmitted to any other wireless station via the transmission/reception switch 29 and the antenna 30.

The radio station 1 further includes a receiver 31 that generates a first intermediate frequency signal from a received signal received by the antenna 30 and supplied via the transmission/reception switch 29, and a signal switch 32 that outputs the target signal output by the signal switch 27 or the first intermediate frequency signal generated by the receiver 31. The radio station 1 further includes a demodulator 33 that generates a second intermediate frequency signal by frequency conversion using a first reference signal based on the target signal or the first intermediate frequency signal output by the signal switch 32, and demodulates the second intermediate frequency signal to generate a demodulated signal. The radio station 1 further includes a deviation detector 34 that detects the frequency deviation between the first reference signal and the target signal and the frequency deviation between the first reference signal and the second reference signal based on the demodulated signal, and an error corrector 35 that corrects the frequency error of the first oscillator 11 and the second oscillator 12 based on the frequency deviation.

The radio station 1 further includes an output signal processing unit 36 that extracts output data from the demodulated signal, and an output unit 37 that outputs the output data.

To control the above-mentioned components, the wireless station 1 includes a controller 50. The controller 50 includes a CPU (Central Processing Unit) 51, an I/O (Input/Output) 52, a RAM (Random Access Memory) 53, and a ROM (Read-Only Memory) 54. To avoid complication and to facilitate understanding, the signal lines from the controller 50 to each component of the wireless station 1 are omitted. The controller 50 is connected to each component of the wireless station 1 via the I/O 52, and controls the start, end, and content of processing of each component. The CPU 51 executes a control program stored in the ROM 54 to control the wireless station 1. In addition, commands, data, etc. input via the I/O 52 are processed and temporarily stored in the RAM 53. The CPU 51 reads commands, data, etc. stored in the RAM 53 as necessary and controls the wireless station 1.

Details of each part of the wireless station 1 having the above configuration are described below. The first oscillator 11 has a crystal resonator and an oscillation circuit, and outputs a first reference signal. In the first embodiment, the first reference signal is a sine wave clock signal. The first target value f1, which is the target frequency of the first reference signal, is, for example, 50.40 MHz. The second oscillator 12 has a crystal resonator and an oscillation circuit, and outputs a second reference signal. In the first embodiment, the second reference signal is a sine wave clock signal.

The input unit 21 includes a microphone that captures audio and generates an analog audio signal, a low-frequency amplifier that amplifies the amplitude of the analog audio signal, and the like.

The input signal processing unit 22 performs A-D (Analog-to-Digital) conversion on the amplified analog audio signal, compresses and encodes it, and adds a synchronization word, a header, etc. to generate data for transmission. The synchronization word is a known bit data sequence.

The data output unit 23 outputs correction data used to correct the frequency error to the symbol mapper 24. In the first embodiment, the correction data is fixed data including a synchronization word. The synchronization word included in the correction data is the same as the synchronization word included in the transmission data. The data output unit 23 outputs conversion data used to generate an unmodulated signal used in frequency conversion to the signal generation unit 26. The conversion data is, for example, data consisting of successive 0s.

The symbol mapper 24 maps the transmission data generated by the input signal processing unit 22 or the correction data generated by the data output unit 23 to symbols, and outputs modulation data indicating the mapped symbols. For example, when the wireless station 1 performs 4-level FSK, the symbol mapper 24 assigns a +1 symbol to the 2-bit data 00, a -1 symbol to the 2-bit data 01, a +3 symbol to the 2-bit data 10, and a -3 symbol to the 2-bit data 11. The amount of frequency shift is determined for each symbol.

In the receiving mode, the oscillator switch 25 outputs a first reference signal obtained from the first oscillator 11, and in the transmitting mode or error correction mode, it outputs a second reference signal obtained from the second oscillator 12.

The signal generating unit 26 generates a modulated target signal by performing frequency modulation based on the input target data and the second reference signal output by the oscillator switch 25, or generates a conversion signal that is an unmodulated signal based on the first reference signal output by the oscillator switch 25. The target data used to generate the target signal is the modulation data input from the symbol mapper 24.

In detail, the signal generating unit 26 includes a phase comparator 38 that outputs a phase difference signal based on a first reference signal and a signal divided by a frequency divider 41 described below, a loop filter 39 that converts the phase difference signal into a voltage and outputs it, a VCO (Voltage Controlled Oscillator) 40 that oscillates at an oscillation frequency according to a control voltage, and a frequency divider 41 that divides the output of the VCO 40 according to a frequency division ratio output by a ΔΣ modulator (not shown).

The phase comparator 38 outputs a phase difference signal that is a signal corresponding to the phase difference between the first or second reference signal output by the oscillator switch 25 and the signal output from the VCO 40 and divided by the frequency divider 41.

The loop filter 39 converts the phase difference signal output by the phase comparator 38 into a current, converts the current into a voltage by integrating and smoothing it, and outputs this voltage to the VCO 40 as a control voltage.

In reception mode, the VCO 40 generates and outputs a conversion signal S1, which is an unmodulated signal whose frequency is a first intermediate frequency lower than the reception frequency based on a first reference signal. For example, in reception mode, the VCO 40 generates a conversion signal S1, which is a signal obtained by superimposing conversion data, which is output from the data output unit 23 and indicates that the frequency deviation is zero, on a carrier signal whose frequency is a first intermediate frequency lower than the reception frequency. The reception frequency is, for example, a frequency in the range of 360 MHz or more and 400 MHz or less. The first intermediate frequency is, for example, 49.95 MHz.

In the transmission mode, the VCO 40 generates and outputs a transmission modulation signal S2, which is a modulated signal in which modulation data based on the transmission data is superimposed on a carrier signal whose frequency is the transmission frequency based on the second reference signal. The transmission frequency is, for example, a frequency in the range of 360 MHz or more and 400 MHz or less.

In the error correction mode, the VCO 40 generates and outputs a target signal S3 in which modulation data based on the correction data is superimposed on a carrier signal having a frequency of the first intermediate frequency based on the second reference signal.

In the reception mode, the signal switch 27 sends the conversion signal S1, which is an unmodulated signal output from the VCO 40, to the reception unit 31. In the transmission mode, the signal switch 27 sends the transmission modulation signal S2 output from the VCO 40 to the transmission unit 28. In the error correction mode, the signal switch 27 sends the target signal S3 output from the VCO 40 to the signal switch 32.

The transmitter 28 amplifies the modulated signal for transmission to a desired level suitable for transmission, reduces unnecessary signals, such as harmonics, to generate a transmission signal, and transmits the transmission signal to other radio stations via the transmission/reception switching unit 29 and antenna 30.

The receiving unit 31 includes an amplifier 42 that amplifies the received signal received by the antenna 30 and supplied via the transmission/reception switching unit 29, and a mixer 43 that generates a first intermediate frequency signal from the received signal output by the amplifier 42.

The amplifier 42 has, for example, an LNA (Low Noise Amplifier) and amplifies the received signal. The mixer 43 multiplies the conversion signal S1 output by the signal switcher 27 with the received signal amplified by the amplifier 42 to generate and output a first intermediate frequency signal having a frequency of the first intermediate frequency.

In the reception mode, the signal switch 32 sends the first intermediate frequency signal acquired from the mixer 43 of the receiving unit 31 to the demodulation unit 33. In the error correction mode, the signal switch 32 sends the target signal S3 acquired from the VCO 40 via the signal switch 27 to the demodulation unit 33.

The demodulation unit 33 includes a mixer 44 that multiplies the first reference signal by the output of the signal switcher 32 to generate a second intermediate frequency signal having a second intermediate frequency lower than the first intermediate frequency, an A-D converter 45 that generates digital data from the second intermediate frequency signal, and an FM (Frequency Modulation) detection unit 46 that performs a demodulation process on the digital data generated by the A-D converter 45 to generate a demodulated signal.

In the reception mode, the mixer 44 outputs a second intermediate frequency signal whose frequency is the difference between the frequency of the first reference signal and the frequency of the first intermediate frequency signal. When the first target value f1, which is the target frequency of the first reference signal, is 50.40 MHz and the first intermediate frequency is 49.95 MHz, the mixer 44 outputs a second intermediate frequency signal of 0.45 MHz, which is the value obtained by subtracting 49.95 MHz from 50.40 MHz.

In the error correction mode, the mixer 44 outputs a second intermediate frequency signal whose frequency is the difference between the frequency of the first reference signal and the frequency of the target signal S3.

The A-D converter 45 A-D converts the second intermediate frequency signal to generate digital data, which it then sends to the FM detection unit 46.

The FM detection unit 46 determines which of four predetermined amplitude levels each data value obtained from the A-D converter 45 corresponds to, and outputs the two-bit data corresponding to the determined amplitude level, specifically, one of 00, 01, 10, or 11, as a demodulated signal.

The deviation detection unit 34 includes a synchronization word detection unit 47 that detects a synchronization word included in the demodulated signal, and a deviation calculation unit 48 that detects the frequency deviation between the first reference signal and the target signal and the frequency deviation between the first reference signal and the second reference signal based on the synchronization word.

The synchronization word detection unit 47 repeats the correlation calculation between the demodulated signal and the synchronization word, shifting it by one symbol at a time, in other words, by two bits at a time. If the correlation value is equal to or greater than a threshold as a result of the correlation calculation, it can be considered that the synchronization word has been detected.

The deviation calculation unit 48 calculates the frequency deviation from a DC (Direct Current) offset contained in the symbol corresponding to the detected synchronization word. It is preferable that the deviation calculation unit 48 outputs the moving average value of the frequency deviation as the frequency deviation.

When the radio station 1 is in reception mode and a frequency error occurs in the first oscillator 11, specifically when the frequency of the first reference signal deviates from the first target value, the frequency of the first intermediate frequency signal output by the mixer 43 deviates from the target value, the first intermediate frequency. As a result, the frequency of the second intermediate frequency signal output by the mixer 44 deviates from the target value, the second intermediate frequency. The deviation calculation unit 48 calculates the frequency deviation of the second intermediate frequency signal from the demodulated signal based on the second intermediate frequency signal, in other words, the frequency deviation between the first reference signal and the target signal, and sends the calculated frequency deviation to the error correction unit 35.

When the wireless station 1 is in the error correction mode and a frequency error occurs in the second oscillator 12, specifically when the difference between the frequency of the first reference signal and the frequency of the second reference signal differs from the target deviation, the center frequency of the target signal S3 deviates from the first intermediate frequency, which is the target value. As a result, the center frequency of the frequency of the second intermediate frequency signal, which is the output of the mixer 44, deviates from the second intermediate frequency, which is the target value. The deviation calculation unit 48 calculates the deviation of the center frequency of the second intermediate frequency signal from the demodulated signal based on the second intermediate frequency signal, in other words, the frequency deviation between the frequency of the first reference signal and the frequency of the second reference signal, and sends the calculated frequency deviation to the error correction unit 35.

The error correction unit 35 corrects the frequency error of the first reference signal and the second reference signal according to the frequency deviation detected by the deviation detection unit 34. In detail, the error correction unit 35 controls the first oscillator 11 to adjust the frequency of the first reference signal so as to reduce the frequency deviation between the first reference signal and the target signal. Furthermore, the error correction unit 35 controls the second oscillator 12 to adjust the frequency of the second reference signal so as to bring the frequency deviation between the first reference signal and the second reference signal output by the first oscillator 11, in which the frequency error has been corrected, closer to the target deviation.

The output signal processing unit 36 extracts audio data from the demodulated signal in which the synchronization word has been detected by the synchronization word detection unit 47 of the deviation detection unit 34 and synchronization has been achieved, performs D-A (Digital-to-Analog) conversion to generate an analog audio signal, and sends it to the output unit 37.

The output unit 37 has a low-frequency amplifier that amplifies the analog audio signal, and a speaker that outputs the analog audio signal amplified by the low-frequency amplifier.

The frequency error correction process performed by the wireless station 1 having the above configuration is described below. When the wireless station 1 is started, it goes into the reception mode and starts the frequency error correction process of the first reference signal shown in FIG. 2.

The signal generating unit 26 generates and outputs a conversion signal S1, which is an unmodulated signal whose frequency is lower than the receiving frequency by the first intermediate frequency, based on the first reference signal acquired from the first oscillator 11 via the oscillator switch 25 (step S11). The signal switch 27 sends the conversion signal S1 generated in step S11 to the mixer 43 provided in the receiving unit 31.

The mixer 43 multiplies the received signal from the base station, which is received by the antenna 30, supplied via the transmission/reception switching unit 29, and amplified by the amplifier 42, with the conversion signal S1 to generate and output a first intermediate frequency signal (step S12).

The mixer 44 included in the demodulation unit 33 multiplies the first reference signal by the first intermediate frequency signal generated in step S12 and supplied via the signal switcher 32 to generate and output a second intermediate frequency signal (step S13).

The FM detection unit 46 of the demodulation unit 33 performs demodulation processing on the digital data generated by A-D converting the second intermediate frequency signal generated in step S13 using the A-D converter 45, thereby generating a demodulated signal (step S14).

The deviation detection unit 34 detects the frequency deviation of the second intermediate frequency signal, in other words, the frequency deviation between the first reference signal and the target signal, based on the synchronization word included in the demodulated signal generated in step S14, and sends the detected frequency deviation to the error correction unit 35 (step S15).

The error correction unit 35 corrects the frequency error of the first reference signal output by the first oscillator 11 in accordance with the frequency deviation detected in step S15 (step S16). For example, the error correction unit 35 corrects the frequency error of the first reference signal relative to the target signal in accordance with the frequency compensation amount that reduces the frequency deviation between the first reference signal and the target signal. When the process of step S16 is completed, the wireless station 1 ends the process of correcting the frequency error of the first reference signal. Thereafter, the wireless station 1 repeats the process of correcting the frequency error of the first reference signal shown in FIG. 2 at predetermined time intervals. As a result, it becomes possible to make the frequency of the first reference signal output by the first oscillator 11 provided in the wireless station 1 track the reference oscillator provided in the base station and outputting the target signal.

After the frequency error of the first reference signal is corrected by the above-mentioned process, if the wireless station 1 is put into error correction mode, for example, by operating an operation unit (not shown) of the wireless station 1, the wireless station 1 starts the frequency error correction process of the second reference signal shown in FIG. 3.

In the error correction mode, the signal generating unit 26 generates and outputs a target signal S3, which is a modulated signal in which modulation data based on correction data is superimposed on a carrier signal having a frequency of the first intermediate frequency, based on the second reference signal acquired from the second oscillator 12 via the oscillator switch 25 (step S21). The signal switch 27 sends the target signal S3 generated in step S21 to the signal switch 32. The signal switch 32 receives the target signal S3 generated in step S21 from the signal switch 27 and sends the target signal S3 to the demodulation unit 33.

The mixer 44 included in the demodulation unit 33 multiplies the first reference signal by the target signal S3 generated in step S21 and supplied via the signal switches 27 and 32 to generate and output a second intermediate frequency signal (step S22).

The FM detection unit 46 of the demodulation unit 33 performs demodulation processing on the digital data generated by A-D converting the second intermediate frequency signal generated in step S22 using the A-D converter 45, thereby generating a demodulated signal (step S23).

The deviation detection unit 34 detects the frequency deviation of the second intermediate frequency signal, in other words, the frequency deviation between the first reference signal and the second reference signal, based on the synchronization word included in the demodulated signal, and sends the detected frequency deviation to the error correction unit 35 (step S24).

The error correction unit 35 corrects the frequency error of the second reference signal output by the second oscillator 12 in accordance with the deviation of the frequency deviation detected in step S24 from the target deviation (step S25). For example, the error correction unit 35 corrects the frequency error of the second reference signal relative to the second target value so that the frequency deviation between the first and second reference signals approaches the target deviation. When the process of step S25 is completed, the wireless station 1 ends the process of correcting the frequency error of the second reference signal. Thereafter, the wireless station 1 repeats the process of correcting the frequency error of the second reference signal shown in FIG. 3 at predetermined time intervals. As a result, it becomes possible to make the frequency of the second reference signal output by the second oscillator 12 included in the wireless station 1 follow the frequency of the first reference signal output by the first oscillator 11.

As described above, the wireless station 1 according to the first embodiment corrects the frequency error of the second reference signal relative to the second target value in accordance with the deviation from the target deviation of the frequency deviation between the first and second reference signals detected based on the demodulated signal generated from the target signal S3 based on the second reference signal. As a result, the frequency of the second reference signal output by the second oscillator 12 can be made to follow the frequency of the first reference signal output by the first oscillator 11, and the variation in frequency accuracy of each oscillator in the wireless station 1 is suppressed.

In the wireless station 1, the frequency error of the second reference signal output by the second oscillator 12 is corrected in accordance with the first reference signal output by the first oscillator 11, so that even when signals cannot be received from other wireless stations, it is possible to suppress the variation in frequency accuracy of each oscillator in the wireless station 1.

Furthermore, by correcting the frequency error of the first reference signal according to the frequency deviation between the first reference signal and the target signal detected based on the demodulated signal generated from the received signal, the frequency of the first reference signal output by the first oscillator 11 can be made to follow the frequency of the target signal output by a reference oscillator provided in another wireless station. As a result, it is possible to suppress deterioration in the frequency accuracy of each oscillator in the wireless station 1. By performing the frequency error correction process as described above, it is possible to correct the frequency error of each oscillator in a wireless station 1 that has multiple oscillators, specifically, the first oscillator 11 and the second oscillator 12.

According to the wireless station 1, in both the process of correcting the frequency error of the first reference signal and the process of correcting the frequency error of the second reference signal, the frequency deviation calculated by the deviation calculation unit 48 based on the synchronization word detected by the synchronization word detection unit 47 is used. Therefore, there is no need to provide separate circuits for detecting the frequency deviation in order to correct the frequency errors of the first reference signal and the second reference signal, and the structure of the wireless station 1 is prevented from becoming complicated.

(Embodiment 2)
The method of correcting the frequency error of the second reference signal with respect to the second target value is not limited to the above example. A wireless station 2 that corrects the frequency error of the second reference signal by using a target signal that is an unmodulated signal will be described in a second embodiment, focusing on differences from the wireless station 1 according to the first embodiment.

The wireless station 2 according to the second embodiment shown in FIG. 4 has a similar configuration to the wireless station 1, but differs from the wireless station 1 in that the data output unit 23 outputs only conversion data and the signal generation unit 26 generates the target signal S4, which is an unmodulated signal.

The data output unit 23 outputs conversion data used to generate an unmodulated signal for frequency conversion to the signal generation unit 26. The conversion data is, for example, data consisting of successive 0s.

The signal generating unit 26 generates a conversion signal S1, which is an unmodulated signal, based on the first reference signal output by the oscillator switch 25, and generates a target signal S4, which is an unmodulated signal, based on the second reference signal output by the oscillator switch 25.

In detail, in the reception mode, the VCO 40 generates and outputs the conversion signal S1 based on the first reference signal, as in the first embodiment. In the transmission mode, the VCO 40 generates and outputs the transmission modulation signal S2 based on the second reference signal, as in the first embodiment. In the error correction mode, the VCO 40 generates and outputs the target signal S4, which is an unmodulated signal having a frequency of the first intermediate frequency, based on the second reference signal. Specifically, in the error correction mode, the VCO 40 generates the target signal S4, which is a signal obtained by superimposing conversion data, which is output from the data output unit 23 and indicates that the frequency deviation is zero, on a carrier signal having a frequency of the first intermediate frequency.

In the reception mode, the signal switch 27 sends the conversion signal S1 output from the VCO 40 to the reception unit 31. In the transmission mode, the signal switch 27 sends the transmission modulation signal S2 output from the VCO 40 to the transmission unit 28. In the error correction mode, the signal switch 27 sends the target signal S4 output from the VCO 40 to the signal switch 32.

In the reception mode, the signal switch 32 sends the first intermediate frequency signal acquired from the mixer 43 of the receiving unit 31 to the demodulation unit 33. In the error correction mode, the signal switch 32 sends the target signal S4 acquired from the VCO 40 to the demodulation unit 33 via the signal switch 27.

In the reception mode, the mixer 44 outputs a second intermediate frequency signal whose frequency is the difference between the frequency of the first reference signal and the frequency of the first intermediate frequency signal. In the error correction mode, the mixer 44 outputs a second intermediate frequency signal whose frequency is the difference between the frequency of the first reference signal and the frequency of the target signal S4.

The FM detection unit 46 outputs the demodulated signal to the synchronization word detection unit 47 and the deviation calculation unit 48. In the error correction mode, the deviation calculation unit 48 calculates the frequency deviation from the DC offset of the demodulated signal. It is preferable that the deviation calculation unit 48 outputs the moving average value of the frequency deviation as the frequency deviation.

When the radio station 2 is in the error correction mode and a frequency error occurs in the second oscillator 12, specifically when the difference between the frequency of the first reference signal and the frequency of the second reference signal differs from the target deviation, the center frequency of the target signal S4 deviates from the first intermediate frequency, which is the target value. As a result, the center frequency of the frequency of the second intermediate frequency signal, which is the output of the mixer 44, deviates from the second intermediate frequency, which is the target value. The deviation calculation unit 48 calculates the deviation of the center frequency of the second intermediate frequency signal from the demodulated signal based on the second intermediate frequency signal, in other words, the frequency deviation between the frequency of the first reference signal and the frequency of the second reference signal, and sends the calculated frequency deviation to the error correction unit 35.

The frequency error correction process performed by the wireless station 2 having the above configuration will be described below. The frequency error correction process for the first reference signal in the reception mode is the same as in embodiment 1. After the frequency error of the first reference signal is corrected, if the wireless station 2 is placed in the error correction mode, for example, by operating an operation unit (not shown) of the wireless station 2, the wireless station 2 starts the frequency error correction process for the second reference signal shown in FIG. 5.

In the error correction mode, the VCO 40 generates a target signal S4, which is an unmodulated signal whose frequency is the first intermediate frequency based on the second reference signal (step S31). The signal switch 27 sends the target signal S4 generated in step S31 to the signal switch 32. The signal switch 32 receives the target signal S4 generated in step S31 from the signal switch 27 and sends the target signal S4 to the demodulation unit 33.

The mixer 44 included in the demodulation unit 33 multiplies the first reference signal by the target signal S4 generated in step S31 and supplied via the signal switches 27 and 32 to generate and output a second intermediate frequency signal (step S32). The processes from steps S23 to S25 performed after the process of step S32 is completed are similar to the processes from steps S23 to S25 in FIG. 3.

When the processing of step S25 is completed, the wireless station 2 ends the processing of correcting the frequency error of the second reference signal. Thereafter, the wireless station 2 repeats the processing of correcting the frequency error of the second reference signal shown in FIG. 5 at predetermined time intervals. As a result, it becomes possible to make the frequency of the second reference signal output by the second oscillator 12 provided in the wireless station 2 follow the frequency of the first reference signal output by the first oscillator 11.

As described above, the wireless station 2 according to the second embodiment corrects the frequency error of the second reference signal relative to the second target value in accordance with the deviation from the target deviation of the frequency deviation between the first and second reference signals detected based on the demodulated signal generated from the target signal S4 based on the second reference signal. As a result, the frequency of the second reference signal output by the second oscillator 12 can be made to follow the frequency of the first reference signal output by the first oscillator 11, and the variation in frequency accuracy of each oscillator in the wireless station 2 is suppressed.

In the process of correcting the frequency error of the second reference signal, the wireless station 2 calculates the frequency deviation between the first and second reference signals based on the demodulated signal output by the FM detection unit 46, so there is no need to wait for the completion of the detection process of the synchronization word. This allows the wireless station 2 to quickly perform the process of calculating the frequency deviation.

The present invention is not limited to the above-described embodiment. The number of second oscillators provided in the wireless stations 1 and 2 is arbitrary. As an example, the wireless station 3 shown in FIG. 6 includes two second oscillators 12 and 49. When the wireless station 2 is in the error correction mode and corrects the frequency error of the second oscillator 49, the VCO 40 generates and outputs a target signal S3 in which modulation data based on the correction data is superimposed on a carrier signal having a frequency of the first intermediate frequency based on the second reference signal output by the second oscillator 49.

The method of correcting the frequency error of the first reference signal is not limited to the above example. As one example, the wireless station 1-3 may correct the frequency error of the first reference signal based on a signal received from another wireless station that communicates with the base station and in which the frequency error of the oscillator has been corrected. As another example, the wireless station 1-3 may include a frequency counter that is calibrated according to a signal supplied from outside, such as a PPS (Pulse Per Second) signal, and may correct the frequency error of the first reference signal according to the actual frequency of the first reference signal obtained by the frequency counter.

For example, immediately after startup, the wireless station 1-3 may correct the frequency error of the first reference signal as shown in FIG. 2, and then correct the frequency error of the second reference signal as shown in FIG. 3, and then correct the frequency error of the first reference signal and the frequency error of the second reference signal in accordance with the frequency deviation between the first reference signal and the target signal as shown in FIG. 7.

The processing from step S11 to S16 shown in FIG. 7 is the same as the processing shown in FIG. 2. After step S16, the error correction unit 35 corrects the frequency error of the second reference signal output by the second oscillator 12 according to the frequency deviation detected in step S15 (step S17). For example, the error correction unit 35 corrects the frequency error of the second reference signal output by the second oscillator 12 according to the frequency compensation amount that reduces the frequency deviation between the first reference signal and the target signal used to correct the frequency error of the first reference signal in step S16. In other words, the adjustment amount of the frequency of the first reference signal and the adjustment amount of the frequency of the second reference signal are the same. By correcting the frequency errors of the first reference signal and the second reference signal according to the frequency deviation between the first reference signal and the target signal as shown in FIG. 7, it is possible to correct the frequency error in a shorter time.

In the above embodiment, the VCO 40 can oscillate over a frequency band including the transmission and reception frequencies, for example, from 360 MHz or more to 400 MHz or less, to an intermediate frequency band including 49.95 MHz, but the wireless stations 1-3 may also be equipped with a VCO capable of oscillating in the frequency band being used and a VCO capable of oscillating in the intermediate frequency band.

The target deviation, which is the target value of the frequency deviation between the first reference signal and the second reference signal, is arbitrary. In the wireless station 2, the target deviation between the first reference signal and the second reference signal output by the second oscillator 12 and the target deviation between the first reference signal and the second reference signal output by the second oscillator 49 may be the same or different.

In the radio stations 1-3, the input signal processing unit 22, data output unit 23, symbol mapper 24, error correction unit 35, output signal processing unit 36, FM detection unit 46, synchronization word detection unit 47, and deviation calculation unit 48 may be realized by a DSP (Digital Signal Processor), the signal generation unit 26 may be realized by a PLL IC (Integrated circuit) with a built-in VCO, and the mixer 44 and A-D converter 45 may be realized by an IF (Intermediate Frequency) detection IC.

The modulation method of the wireless station 1-3 is not limited to 4-value FSK, and may be any method as long as it is possible to detect frequency deviation from the demodulated signal. As one example, the wireless station 1-3 may perform 2-value FSK, or may perform multi-value FSK other than 4-value FSK. As another example, the wireless station 1-3 may perform PSK (Phase Shift Keying), such as π/4DQPSK (Differential Quadrature Phase Shift Keying), or may perform QAM (Quadrature Amplitude Modulation).

The above hardware configuration and flowchart are merely examples and can be changed or modified as desired.

1, 2, 3 Radio Station
11 First oscillator
12 Second oscillator
21 Input section
22 Input signal processing unit
23 Data output unit
24 Symbol Mapper
25 Oscillator switch
26 Signal generating unit 27, 32 Signal switch
28 Transmission unit
29 Transmission/reception switching unit
30 Antenna
31 Receiving unit
33 Demodulation section
34 Deviation detection unit
35 Error correction section
36 Output signal processing unit
37 Output section
38 Phase comparator
39 Loop Filter
40 VCO
41 Frequency divider
42 Amplifier 43, 44 Mixer
45 A-D converter
46 FM detector
47 Sync word detector
48 Deviation calculation unit
49 Second oscillator
50 Controller
51 CPU
52 I/O
53 RAM
54 ROM
S1 Conversion signal
S2 Transmission modulated signal S3, S4 Target signal

Claims (6)

a first oscillator that outputs a first reference signal, the first target value of which is a target frequency and is used in reception processing ;
at least one second oscillator that outputs a second reference signal used in a transmission process, the second target value being a target frequency obtained by adding a target deviation to the first target value;
a signal generating unit that generates a target signal having a first intermediate frequency as a target frequency based on the second reference signal, and generates a conversion signal that is an unmodulated signal based on the first reference signal ;
a receiving section that receives a signal generated by performing modulation based on a target signal having a frequency that coincides with the first target value, and performs frequency conversion using the conversion signal based on the received signal to generate a first intermediate frequency signal having the first intermediate frequency as a target frequency;
a demodulation unit that, in a reception mode, performs frequency conversion based on the first intermediate frequency signal using the first reference signal to generate a second intermediate frequency signal having a second intermediate frequency lower than the first intermediate frequency, and in an error correction mode, performs frequency conversion based on the target signal using the first reference signal to generate the second intermediate frequency signal, and demodulates the generated second intermediate frequency signal to generate a demodulated signal;
a deviation detection unit that detects a frequency deviation between the first reference signal and the target signal based on the demodulation signal when the demodulation unit generates the demodulated signal based on the first intermediate frequency signal, and detects a frequency deviation between the first reference signal and the second reference signal based on the demodulation signal when the demodulation unit generates the demodulated signal based on the target signal;
an error correction unit that corrects a frequency error of the first reference signal with respect to the target signal in accordance with the frequency deviation between the first reference signal and the target signal, and corrects a frequency error of the second reference signal with respect to the second target value in accordance with a deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation;
A radio station equipped with The signal generation unit generates the target signal, which is a modulated signal, by performing modulation based on input target data and the second reference signal.
The radio station according to claim 1. The signal generation unit generates the target signal, which is an unmodulated signal based on the second reference signal.
The radio station according to claim 1. the error correction unit corrects a frequency error of the first reference signal with respect to the target signal in accordance with a frequency compensation amount that reduces the frequency deviation between the first reference signal and the target signal.
The radio station according to any one of claims 1 to 3 . the error correction unit corrects a frequency error of the first reference signal with respect to the target signal in accordance with the frequency compensation amount, and corrects a frequency error of the second reference signal with respect to the second target value in accordance with a deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation, and then corrects a frequency error of the first reference signal with respect to the target signal and a frequency error of the second reference signal with respect to the second target value in accordance with the frequency compensation amount.
The radio station according to claim 4 . A frequency error correction method performed by a wireless station including: a first oscillator that outputs a first reference signal used in a reception process , the first target value being a target frequency; and at least one second oscillator that outputs a second reference signal used in a transmission process, the second target value being a target frequency obtained by adding a target deviation to the first target value, the method comprising:
generating a target signal having a first intermediate frequency as a target frequency based on the second reference signal, and generating a conversion signal which is an unmodulated signal based on the first reference signal;
receiving a signal generated by performing modulation based on a target signal having a frequency that coincides with the first target value, and performing frequency conversion using the conversion signal based on the received signal to generate a first intermediate frequency signal having the first intermediate frequency as a target frequency;
In a reception mode, a second intermediate frequency signal is generated, which is a second intermediate frequency signal having a frequency lower than the first intermediate frequency, by performing frequency conversion using the first reference signal based on the first intermediate frequency signal; in an error correction mode, a second intermediate frequency signal is generated by performing frequency conversion using the first reference signal based on the target signal, and a demodulated signal is generated by demodulating the generated second intermediate frequency signal;
detects a frequency deviation between the first reference signal and the target signal based on the demodulated signal when the demodulated signal is generated based on the first intermediate frequency signal, and detects a frequency deviation between the first reference signal and the second reference signal based on the demodulated signal when the demodulated signal is generated based on the target signal,
correcting a frequency error of the first reference signal relative to the target signal in accordance with the frequency deviation between the first reference signal and the target signal, and correcting a frequency error of the second reference signal relative to the second target value in accordance with a deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.
Frequency error correction method.

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