Wireless station and frequency error correction method

Abstract

To provide a wireless station and a method for correcting frequency errors with which it is possible to suppress a variation in the frequency accuracy of each oscillator in a wireless station equipped with a plurality of oscillators.SOLUTION: A wireless station 1 comprises: a first oscillator 11 for outputting a first reference signal whose first target value is a target frequency; at least one second oscillator 12 for outputting a second reference signal whose second target value, consisting of the first target value with a target deviation added, is a target frequency; and a signal generation unit 26 for generating an object signal whose first intermediate frequency is a target frequency, on the basis of the second reference signal. The wireless station 1 further includes: a demodulation unit 33 for demodulating a second intermediate frequency signal generated for the object signal so as to generate a demodulated signal; a deviation detection unit 34 for detecting a frequency deviation between the first and the second reference signals on the basis of the demodulated signal; and an error correction unit 35 for correcting a frequency error of the second reference signal with respect to the second target frequency in accordance with a discrepancy of the frequency deviation from the target deviation.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a radio station and a frequency error correction method.

Background Art

[0002] A local oscillator is composed of an oscillation circuit composed of discrete components and a PLL (Phase-Locked Loop)-VCO (Voltage Controlled Oscillator) having one reference frequency oscillator. An example of a radio station equipped with this type of local oscillator is disclosed in Patent Document 1.

[0003] The PLL-VCO may be realized by a PLL IC (Integrated Circuit) incorporating a VCO. The PLL IC enables FM (Frequency Modulation), specifically FSK (Frequency Shift Keying), in a wide frequency band of 10 MHz or more and 1400 MHz or less.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the above-described PLL IC is used near an integer multiple of the oscillation frequency of the reference frequency oscillator constituting the PLL-VCO, integer boundary spurs may occur. When integer boundary spurs occur, the radio station on the transmission side may not be able to satisfy the spur standard defined by the Radio Law, and spur reception of receiving radio waves other than the desired radio waves may occur at the radio station on the receiving side.

[0006] In order to suppress the influence of integer value boundary spurs on transmission and reception, there is a radio station equipped with a plurality of reference frequency oscillators and switching between and using the plurality of reference frequency oscillators. Frequency errors due to aging occur in the reference frequency oscillators. The magnitude of the frequency error due to aging may vary for each reference frequency oscillator.

[0007] For example, in a radio station communicating with a base station, regarding the reference frequency oscillator used when frequency-converting a received signal received from the base station, based on the received signal, the radio station can correct the frequency error of the reference frequency oscillator provided in the radio station according to 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, regarding the reference frequency oscillator used when generating a transmission signal transmitted to the base station, since the frequency error cannot be corrected as described above, the frequency accuracy may decrease.

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to provide a radio station and a frequency error correction method capable of suppressing variations in the frequency accuracy of each oscillator in a radio station equipped with a plurality of oscillators.

Means for Solving the Problem

[0009] To achieve the above object, a radio station according to a first aspect of the present invention A first oscillator that outputs a first reference signal whose first target value is the target frequency is used for reception processing And at least one second oscillator that outputs a second reference signal whose second target value obtained by adding a target deviation to the first target value is the target frequency And a signal generation unit that generates a target signal whose first intermediate frequency is the target frequency based on the second reference signal is used for transmission processing And Based on the target signal, frequency-convert using the first reference signal and generates a conversion signal, which is an unmodulated signal, based on the first reference signal And A receiving unit that receives a signal generated by performing modulation based on a target signal whose frequency matches the first target value, and performs frequency conversion using the conversion signal based on the received signal to generate a first intermediate frequency signal whose first intermediate frequency is the target frequency In the reception mode, frequency conversion is performed using the first reference signal based on the first intermediate frequency signal to generate a second intermediate frequency signal whose frequency is lower than the first intermediate frequency. In the error correction mode Based on the target signal, frequency-convert using the first reference signal theGenerate a second intermediate frequency signal, generated a demodulation unit that generates a demodulated signal by demodulating the second intermediate frequency signal, When the demodulation unit generates the demodulation signal based on the first intermediate frequency signal, the frequency deviation between the first reference signal and the target signal is detected based on the demodulation signal. When the demodulation unit generates the demodulation signal based on the target signal a deviation detection unit that detects a frequency deviation between the first reference signal and the second reference signal based on the demodulated signal, corrects the frequency error of the first reference signal with respect to the target signal according to the frequency deviation between the first reference signal and the target signal an error correction unit that corrects a frequency error of the second reference signal with respect to the second target value according to a deviation of the frequency deviation between the first reference signal and the second reference signal from a target deviation, and is provided with.

[0010] Preferably, 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.

[0011] Preferably, the signal generation unit generates the target signal, which is an unmodulated signal based on the second reference signal.

[0013] Preferably, the error correction unit corrects a frequency error of the first reference signal with respect to the target signal according to a frequency compensation amount that reduces the frequency deviation between the first reference signal and the target signal.

[0014] Preferably, the error correction unit corrects the frequency error of the first reference signal with respect to the target signal according to the frequency compensation amount after correcting the frequency error of the second reference signal with respect to the second target value according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation, according to the frequency compensation amount the frequency error of the first reference signal with respect to the target signal and corrects the frequency error of the second reference signal with respect to the second target value.

[0015] The frequency error correction method according to the second aspect of the present invention is a first oscillator that outputs a first reference signal whose first target value is a target frequency is used for reception processing and at least one second oscillator that outputs a second reference signal whose second target value obtained by adding a target deviation to the first target value is a target frequency, and is a frequency error correction method performed by a radio station provided with is used for transmission processing and, Generate a target signal whose first intermediate frequency is the target frequency based on the second reference signal, generates a conversion signal, which is an unmodulated signal, based on the first reference signal receives a signal generated by performing modulation based on a target signal whose frequency matches the first target value, and performs frequency conversion using the conversion signal based on the received signal to generate a first intermediate frequency signal whose first intermediate frequency is the target frequency In the reception mode, frequency conversion is performed using the first reference signal based on the first intermediate frequency signal to generate a second intermediate frequency signal whose frequency is lower than the first intermediate frequency. In the error correction mode Based on the target signal, perform frequency conversion using the first reference signal to the generate a second intermediate frequency signal, generated generate a demodulated signal by demodulating the second intermediate frequency signal, When the demodulation signal is generated based on the first intermediate frequency signal, the frequency deviation between the first reference signal and the target signal is detected based on the demodulation signal. When the demodulation signal is generated based on the target signal detect the frequency deviation between the first reference signal and the second reference signal based on the demodulated signal, corrects the frequency error of the first reference signal with respect to the target signal according to the frequency deviation between the first reference signal and the target signal correct the frequency error of the second reference signal with respect to the second target value according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

Advantages of the Invention

[0016] The wireless station according to the present invention includes a first oscillator that outputs a first reference signal whose first target value is the target frequency, and at least one second oscillator that outputs a second reference signal whose second target value obtained by adding a target deviation to the first target value is the target frequency. The wireless station corrects the frequency error of the second reference signal with respect to the second target value according to the deviation of the frequency deviation between the first reference signal and the second reference signal detected based on the demodulated signal generated from the target signal based on the second reference signal from the target deviation. Thereby, in a wireless station including a plurality of oscillators, it is possible to suppress variations in the frequency accuracy of each oscillator.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the radio station and the frequency error correction method according to the embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent parts are denoted by the same reference numerals.

[0019] (Embodiment 1) The radio station 1 according to Embodiment 1 will be described by taking a radio station using the double superheterodyne method as an example. The radio station 1 shown in FIG. 1 includes a first oscillator 11 that outputs a first reference signal whose first target value is the target frequency, and at least one second oscillator 12 that outputs a second reference signal whose second target value is the target frequency obtained by adding a target deviation to the first target value. In Embodiment 1, the radio station 1 includes one first oscillator 11 and one second oscillator 12.

[0020] In the reception mode, the radio station 1 performs reception processing for receiving a signal from another radio station using the first reference signal. Further, in the transmission mode, the radio station 1 performs transmission processing for transmitting a signal to another radio station using the second reference signal. In the error correction mode, the radio station 1 corrects the frequency error of the second oscillator 12 in accordance with the first oscillator 11. Specifically, in the error correction mode, the radio station 1 generates a second intermediate frequency signal by frequency-converting the first reference signal based on a target signal that is generated using the second reference signal and whose first intermediate frequency is the target frequency, demodulates the second intermediate frequency signal, and detects the frequency deviation between the first reference signal and the second reference signal from the demodulated signal obtained. Then, the radio station 1 corrects the frequency error of the second reference signal with respect to the second target value according to the frequency deviation and the target deviation.

[0021] In order to suppress the decrease in the frequency accuracy of each oscillator of the radio 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 the process of correcting the frequency error of the first reference signal, in the reception mode, the radio station 1 receives a signal generated by performing modulation based on a target signal whose frequency is the first target value, and corrects the frequency error of the first reference signal with respect to the first target value based on the received signal. In Embodiment 1, the radio station 1 receives a signal generated by performing modulation based on a target signal from a base station, which is an example of another radio station having a reference oscillator that outputs the target signal, and corrects the frequency error of the first reference signal with respect to the first target value based on the received signal.

[0022] Taking the case where frequency modulation, specifically, FSK (Frequency Shift Keying), is used as the modulation method as an example, each part of the radio station 1 will be described below. The radio station 1 includes an input unit 21 that receives the input of data, an input signal processing unit 22 that performs signal processing on the data input by the input unit 21 to generate transmission data, a data output unit 23 that outputs correction data for correcting the frequency error and conversion data for generating an unmodulated signal used for frequency conversion, and a symbol mapper 24 that maps the transmission data or the correction data to multi-value FSK symbols.

[0023] The wireless station 1 further includes an oscillator switch 25 connected to the first oscillator 11 and the second oscillator 12 for outputting a first reference signal or a second reference signal, and a signal generation unit 26 for generating a target signal, a modulation signal for transmission, or a conversion signal which is 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 for outputting the target signal, the modulation signal for transmission, or the conversion signal acquired from the signal generation unit 26, and a transmission unit 28 for generating a transmission signal from the modulation signal for transmission output by the signal switch 27. The transmission signal generated by the transmission unit 28 is transmitted to any other wireless station via the transmission / reception switch unit 29 and the antenna 30.

[0024] The wireless station 1 further includes a reception unit 31 for generating a first intermediate frequency signal from the reception signal received by the antenna 30 and supplied via the transmission / reception switch unit 29, and a signal switch 32 for outputting the target signal output by the signal switch 27 or the first intermediate frequency signal generated by the reception unit 31. The wireless station 1 further includes a demodulation unit 33 for generating a demodulated signal by frequency-converting using the first reference signal based on the target signal or the first intermediate frequency signal output by the signal switch 32 and demodulating the second intermediate frequency signal. The wireless station 1 further includes a deviation detection unit 34 for detecting 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 correction unit 35 for correcting the frequency errors of the first oscillator 11 and the second oscillator 12 based on the frequency deviation.

[0025] The wireless station 1 further includes an output signal processing unit 36 for extracting output data from the demodulated signal, and an output unit 37 for outputting the output data.

[0026] To control each of the above 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 complexity and 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 processing content of each component. The CPU 51 executes the control program stored in the ROM 54 to control the wireless station 1. Also, commands, data, etc. input via the I / O 52 are processed and temporarily stored in the RAM 53. The CPU 51 reads out the commands, data, etc. stored in the RAM 53 as needed to control the wireless station 1.

[0027] Details of each component of the wireless station 1 having the above configuration will be described below. The first oscillator 11 includes a crystal oscillator and an oscillation circuit and outputs a first reference signal. In Embodiment 1, 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 includes a crystal oscillator and an oscillation circuit and outputs a second reference signal. In Embodiment 1, the second reference signal is a sine-wave clock signal.

[0028] The input unit 21 includes a microphone that captures sound and generates an analog audio signal, a low-frequency amplifier that amplifies the amplitude of the analog audio signal, and the like.

[0029] 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 transmission data. The synchronization word is a known bit data sequence.

[0030] The data output unit 23 outputs correction data used when correcting the frequency error to the symbol mapper 24. In Embodiment 1, 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 for generating an unmodulated signal used for frequency conversion to the signal generation unit 26. The conversion data is, for example, data in which 0s are consecutive.

[0031] 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 radio station 1 performs 4 - value FSK, the symbol mapper 24 assigns a symbol of +1 to 2 - bit data 00, a symbol of -1 to 2 - bit data 01, a symbol of +3 to 2 - bit data 10, and a symbol of -3 to 2 - bit data 11. A frequency offset amount is determined for each symbol.

[0032] The oscillator switch 25 outputs the first reference signal acquired from the first oscillator 11 in the reception mode, and outputs the second reference signal acquired from the second oscillator 12 in the transmission mode or the error correction mode.

[0033] The signal generation unit 26 generates a target signal, which is a modulated 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, which is an unmodulated signal, based on the first reference signal output by the oscillator switch 25. The target data used for generating the target signal is the modulation data input from the symbol mapper 24.

[0034] Specifically, the signal generation unit 26 includes a phase comparator 38 that outputs a phase difference signal based on the first reference signal and the signal divided by a frequency divider 41 described later, 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 the control voltage, and a frequency divider 41 that divides the output of the VCO 40 according to the division ratio output by a ΔΣ modulator (not shown).

[0035] The phase comparator 38 outputs a phase difference signal, which is a signal corresponding to the phase difference between the first reference signal or the second reference signal output by the oscillator switch 25 and the signal output from the VCO 40 and divided by the frequency divider 41.

[0036] The loop filter 39 converts the phase difference signal output by the phase comparator 38 into a current, integrates and smoothes the current to convert it into a voltage, and outputs this voltage as a control voltage to the VCO 40.

[0037] In the reception mode, the VCO 40 generates and outputs a conversion signal S1, which is an unmodulated signal with a frequency lower than the reception frequency by the first intermediate frequency based on the first reference signal. For example, in the reception mode, the VCO 40 generates a conversion signal S1, which is a signal obtained by superimposing conversion data output from the data output unit 23 and indicating that the frequency offset amount is 0 on a carrier signal with a frequency lower than the reception frequency by the first intermediate frequency. The reception frequency is, for example, a frequency included in the range of 360 MHz or more and 400 MHz or less. The first intermediate frequency is, for example, 49.95 MHz.

[0038] In the transmission mode, the VCO 40 generates and outputs a transmission modulation signal S2, which is a modulation signal obtained by superimposing modulation data based on the transmission data on a carrier signal with a frequency equal to the transmission frequency based on the second reference signal. The transmission frequency is, for example, a frequency included in the range of 360 MHz or more and 400 MHz or less.

[0039] In the error correction mode, the VCO 40 generates and outputs a target signal S3 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.

[0040] In the reception mode, the signal switch 27 sends a conversion signal S1, which is an unmodulated signal output from the VCO 40, to the receiving unit 31. In the transmission mode, the signal switch 27 sends a transmission modulation signal S2 output from the VCO 40 to the transmission unit 28. In the error correction mode, the signal switch 27 sends a target signal S3 output from the VCO 40 to the signal switch 32.

[0041] The transmission unit 28 amplifies the transmission modulation signal to a desired level suitable for transmission, reduces unnecessary signals such as harmonics to generate a transmission signal, and transmits the transmission signal to another radio station via the transmit / receive switch unit 29 and the antenna 30.

[0042] The receiving unit 31 includes an amplifier 42 that amplifies a received signal received by the antenna 30 and supplied via the transmit / receive switch unit 29, and a mixer 43 that generates a first intermediate frequency signal having a frequency of the first intermediate frequency from the received signal output by the amplifier 42.

[0043] 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 from the signal switch 27 and 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.

[0044] In the reception mode, the signal switch 32 sends the first intermediate frequency signal obtained from the mixer 43 included in the receiving unit 31 to the demodulation unit 33. In the error correction mode, the signal switch 32 sends the target signal S3 obtained from the VCO 40 via the signal switch 27 to the demodulation unit 33.

[0045] The demodulation unit 33 includes a mixer 44 that multiplies the first reference signal and the output of the signal switch 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) detector 46 that performs demodulation processing on the digital data generated by the A-D converter 45 to generate a demodulated signal.

[0046] In the reception mode, the mixer 44 outputs a second intermediate frequency signal having a frequency that is the difference between the frequency of the first reference signal and 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.

[0047] In the error correction mode, the mixer 44 outputs a second intermediate frequency signal having a frequency that is the difference between the frequency of the first reference signal and the frequency of the target signal S3.

[0048] The A-D converter 45 performs A-D conversion on the second intermediate frequency signal to generate digital data and sends it to the FM detector 46.

[0049] The FM detector 46 determines which of the four predetermined amplitude levels each data value acquired from the A-D converter 45 corresponds to, and outputs 2-bit data associated with the determined amplitude level, specifically, any one of 00, 01, 10, and 11, as the demodulated signal.

[0050] 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.

[0051] The synchronous word detection unit 47 performs a correlation operation between the demodulated signal and the synchronous word one symbol at a time, or in other words, shifts it by two bits at a time and repeats. As a result of the correlation operation, if the correlation value is equal to or greater than the threshold value, it can be considered that the synchronous word has been detected.

[0052] The deviation calculation unit 48 calculates the frequency offset from the DC (Direct Current) offset included in the symbol corresponding to the detected synchronous word. The deviation calculation unit 48 preferably outputs the moving average value of the frequency offset as the frequency deviation.

[0053] When the radio station 1 is in the 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 first intermediate frequency which is the target value. As a result, 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 frequency deviation of the second intermediate frequency signal, in other words, the frequency deviation between the first reference signal and the target signal, from the demodulated signal based on the second intermediate frequency signal, and sends the calculated frequency deviation to the error correction unit 35.

[0054] When the radio 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 is different 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, in other words, the frequency deviation between the frequency of the first reference signal and the frequency of the second reference signal, from the demodulated signal based on the second intermediate frequency signal, and sends the calculated frequency deviation to the error correction unit 35.

[0055] The error correction unit 35 corrects the frequency errors of the first reference signal and the second reference signal according to the frequency deviation detected by the deviation detection unit 34. Specifically, the error correction unit 35 controls the first oscillator 11 so as to reduce the frequency deviation between the first reference signal and the target signal, and adjusts the frequency of the first reference signal. Further, the error correction unit 35 controls the second oscillator 12 so as to make the frequency deviation between the first reference signal output from the first oscillator 11 with the frequency error corrected and the second reference signal approach the target deviation, and adjusts the frequency of the second reference signal.

[0056] The output signal processing unit 36 extracts voice data from the demodulated signal in which the synchronization word is detected by the synchronization word detection unit 47 included in the deviation detection unit 34 and synchronization is achieved, performs D-A (Digital-to-Analog) conversion to generate an analog voice signal, and sends it to the output unit 37.

[0057] The output unit 37 includes a low-frequency amplifier that amplifies the analog voice signal, and a speaker that outputs the analog voice signal amplified by the low-frequency amplifier.

[0058] The frequency error correction process performed by the wireless station 1 having the above configuration will be described below. When activated, the wireless station 1 enters the reception mode and starts the frequency error correction process of the first reference signal shown in FIG. 2.

[0059] Based on the first reference signal acquired from the first oscillator 11 via the oscillator switcher 25, the signal generation unit 26 generates and outputs a conversion signal S1, which is an unmodulated signal whose frequency is lower than the reception frequency by the first intermediate frequency (step S11). The signal switcher 27 sends the conversion signal S1 generated in step S11 to the mixer 43 included in the receiving unit 31.

[0060] The mixer 43 multiplies the reception signal from the base station received by the antenna 30, supplied via the transmit / receive switch unit 29, and amplified by the amplifier 42 and the conversion signal S1 to generate and output a first intermediate frequency signal (step S12).

[0061] The mixer 44 included in the demodulation unit 33 multiplies the first reference signal and the first intermediate frequency signal generated in step S12 supplied via the signal switch 32 to generate and output a second intermediate frequency signal (step S13).

[0062] The FM detection unit 46 included in 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 by the A-D converter 45 to generate a demodulated signal (step S14).

[0063] 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).

[0064] The error correction unit 35 corrects the frequency error of the first reference signal output by the first oscillator 11 according to 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 with respect to the target signal according to 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 radio station 1 ends the process of correcting the frequency error of the first reference signal. After that, the radio station 1 repeats the process of correcting the frequency error of the first reference signal shown in FIG. 2 at regular intervals. As a result, it becomes possible to make the frequency of the first reference signal output by the first oscillator 11 included in the radio station 1 follow the reference oscillator provided in the base station and outputting the target signal.

[0065] After the frequency error of the first reference signal is corrected by the above-described process, for example, when the radio station 1 enters the error correction mode by operating an operation unit (not shown) of the radio station 1, the radio station 1 starts the frequency error correction process of the second reference signal shown in FIG. 3.

[0066] In the error correction mode, the signal generation unit 26 generates and outputs a target signal S3, which is a modulation signal in which modulation data based on correction data is superimposed on a carrier signal having a first intermediate frequency, based on a 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 supply of the target signal S3 generated in step S21 from the signal switch 27 and sends the target signal S3 to the demodulation unit 33.

[0067] The mixer 44 included in the demodulation unit 33 multiplies the first reference signal and the target signal S3 generated in step S21 supplied via the signal switches 27 and 32 to generate and output a second intermediate frequency signal (step S22).

[0068] The FM detection unit 46 included in the demodulation unit 33 performs demodulation processing on digital data generated by A-D converting the second intermediate frequency signal generated in step S22 by the A-D converter 45 to generate a demodulated signal (step S23).

[0069] Based on the synchronization word included in the demodulated signal, 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, and sends the detected frequency deviation to the error correction unit 35 (step S24).

[0070] The error correction unit 35 corrects the frequency error of the second reference signal output by the second oscillator 12 according to 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 with respect to the second target value so that the frequency deviation between the first reference signal and the second reference signal approaches the target deviation. When the process of step S25 is completed, the radio station 1 ends the process of correcting the frequency error of the second reference signal. Thereafter, the radio 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 provided in the radio station 1 follow the frequency of the first reference signal output by the first oscillator 11.

[0071] As described above, the radio station 1 according to the first embodiment corrects the frequency error of the second reference signal with respect to the second target value according to the deviation of the frequency deviation between the first reference signal and the second reference signal detected based on the demodulated signal generated from the target signal S3 based on the second reference signal from the target deviation. 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 variations in the frequency accuracy of each oscillator in the radio station 1 are suppressed.

[0072] According to the radio station 1, in order to correct the frequency error of the second reference signal output by the second oscillator 12 in accordance with the first reference signal output by the first oscillator 11, even when signals cannot be received from other radio stations, it is possible to suppress variations in the frequency accuracy of each oscillator in the radio station 1.

[0073] Furthermore, by correcting the frequency error of the first reference signal according to the frequency deviation between the first reference signal detected based on the demodulated signal generated from the received signal and the target 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 the reference oscillator provided in another radio station. As a result, it becomes possible to suppress a decrease in the frequency accuracy of each oscillator in the radio station 1. By performing the frequency error correction process as described above, it is possible to correct the frequency errors of the respective oscillators in the radio station 1 including a plurality of oscillators, specifically, the first oscillator 11 and the second oscillator 12.

[0074] According to the radio 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. For this reason, there is no need to provide a circuit for individually detecting the frequency deviation in order to correct the frequency errors of the first reference signal and the second reference signal, and the complication of the structure of the radio station 1 is suppressed.

[0075] (Embodiment 2) The method for correcting the frequency error of the second reference signal with respect to the second target value is not limited to the above example. The radio station 2 that corrects the frequency error of the second reference signal using the target signal that is an unmodulated signal will be described in Embodiment 2 focusing on the differences from the radio station 1 according to Embodiment 1.

[0076] The radio station 2 according to Embodiment 2 shown in FIG. 4 has the same configuration as the radio station 1, but is different from the radio station 1 in that the data output unit 23 outputs only the conversion data, and the signal generation unit 26 generates the target signal S4 that is an unmodulated signal.

[0077] The data output unit 23 outputs the conversion data used for generating the unmodulated signal used for frequency conversion to the signal generation unit 26. The conversion data is, for example, data in which 0s are continuous.

[0078] The signal generation 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.

[0079] Specifically, in the reception mode, similar to the first embodiment, the VCO 40 generates and outputs a conversion signal S1 based on the first reference signal. In the transmission mode, similar to the first embodiment, the VCO 40 generates and outputs a modulation signal S2 for transmission based on the second reference signal. In the error correction mode, the VCO 40 generates and outputs a target signal S4, which is an unmodulated signal with a frequency of the first intermediate frequency, based on the second reference signal. Specifically, in the error correction mode, the VCO 40 generates a target signal S4, which is a signal obtained by superimposing conversion data output from the data output unit 23 and indicating that the frequency offset amount is 0, on a carrier signal with a frequency of the first intermediate frequency.

[0080] The signal switch 27 sends the conversion signal S1 output from the VCO 40 to the receiving unit 31 in the reception mode. The signal switch 27 sends the modulation signal S2 for transmission output from the VCO 40 to the transmitting unit 28 in the transmission mode. The signal switch 27 sends the target signal S4 output from the VCO 40 to the signal switch 32 in the error correction mode.

[0081] In the reception mode, the signal switch 32 sends the first intermediate frequency signal obtained 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 obtained from the VCO 40 via the signal switch 27 to the demodulation unit 33.

[0082] In the reception mode, the mixer 44 outputs a second intermediate frequency signal with a frequency that is the difference between the frequency of the first reference signal and the first intermediate frequency signal. In the error correction mode, the mixer 44 outputs a second intermediate frequency signal with a frequency that is the difference between the frequency of the first reference signal and the frequency of the target signal S4.

[0083] The FM demodulation 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 offset 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 offset as the frequency deviation.

[0084] 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 is different from the target deviation, the center frequency of the target signal S4 deviates from the first intermediate frequency that 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 that 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.

[0085] The frequency error correction process performed by the radio station 2 having the above configuration will be described below. The frequency error correction process of the first reference signal in the reception mode is the same as that in the first embodiment. After the frequency error of the first reference signal is corrected, for example, when the radio station 2 enters the error correction mode by operating an operation unit (not shown) of the radio station 2, the radio station 2 starts the frequency error correction process of the second reference signal shown in FIG. 5.

[0086] In the error correction mode, the VCO 40 generates a target signal S4, which is an unmodulated signal with a frequency of 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 supply of the target signal S4 generated in step S31 from the signal switch 27 and sends the target signal S4 to the demodulation unit 33.

[0087] The mixer 44 included in the demodulation unit 33 multiplies the first reference signal and the target signal S4 generated in step S31 supplied via the signal switches 27 and 32 to generate and output a second intermediate frequency signal (step S32). The processes from step S23 to step S25 performed after the completion of the process in step S32 are the same as the processes from step S23 to step S25 in FIG. 3.

[0088] When the process in step S25 is completed, the radio station 2 finishes the process of correcting the frequency error of the second reference signal. Thereafter, the radio station 2 repeats the process of correcting the frequency error of the second reference signal shown in FIG. 5 at regular intervals. As a result, it becomes possible to make the frequency of the second reference signal output from the second oscillator 12 provided in the radio station 2 follow the frequency of the first reference signal output from the first oscillator 11.

[0089] As described above, the radio station 2 according to the second embodiment corrects the frequency error of the second reference signal with respect to the second target value according to the deviation from the target deviation of the frequency deviation between the first reference signal and the second reference signal 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 from the second oscillator 12 can be made to follow the frequency of the first reference signal output from the first oscillator 11, and variations in the frequency accuracy of each oscillator in the radio station 2 are suppressed.

[0090] In the process of correcting the frequency error of the second reference signal, the radio station 2 calculates the frequency deviation between the first reference signal and the second reference signal based on the demodulated signal output from the FM detection unit 46, and thus does not need to wait for the completion of the detection process of the synchronization word. For this reason, the radio station 2 can perform the calculation process of the frequency deviation quickly.

[0091] The present invention is not limited to the examples of the above-described embodiments. The number of second oscillators provided in the radio stations 1 and 2 is arbitrary. As an example, the radio station 3 shown in FIG. 6 includes two second oscillators 12 and 49. When the radio 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 correction data is superimposed on a carrier signal having a first intermediate frequency based on the second reference signal output from the second oscillator 49.

[0092] The method for correcting the frequency error of the first reference signal is not limited to the above examples. As an example, the radio stations 1 to 3 may be other radio stations that communicate with the base station, and correct the frequency error of the first reference signal based on a received signal received from a radio station in which the frequency error of the oscillator has been corrected. As another example, the radio stations 1 to 3 may include a frequency counter that is calibrated according to a signal supplied from the outside, such as a PPS (Pulse Per Second) signal, and correct the frequency error of the first reference signal according to the actual frequency of the first reference signal obtained by the frequency counter.

[0093] For example, immediately after startup, the radio stations 1 to 3 correct the frequency error of the first reference signal as shown in FIG. 2, and after correcting the frequency error of the second reference signal as shown in FIG. 3, they may correct 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.

[0094] The processes from step S11 to S16 shown in FIG. 7 are the same as the processes 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 for correcting 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 is the same as the adjustment amount of the frequency of the second reference signal. As shown in FIG. 7, 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, it is possible to correct the frequency error in a shorter time.

[0095] In the above-described embodiment, the VCO 40 can oscillate over a frequency band including the transmission frequency and the reception frequency, for example, in the range of 360 MHz or more and 400 MHz or less, to a frequency band including an intermediate frequency band, for example, 49.95 MHz. However, the radio stations 1-3 may include a VCO that can oscillate in the use frequency band and a VCO that can oscillate in the intermediate frequency band.

[0096] 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 radio 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.

[0097] In radio stations 1-3, the input signal processing unit 22, the data output unit 23, the symbol mapper 24, the error correction unit 35, the output signal processing unit 36, the FM detection unit 46, the synchronization word detection unit 47, and the deviation calculation unit 48 may be implemented by a DSP (Digital Signal Processor), the signal generation unit 26 may be implemented by a PLL IC (Integrated Circuit) with a built-in VCO, and the mixer 44 and the A-D converter 45 may be implemented by an IF (Intermediate Frequency) detection IC.

[0098] The modulation methods of wireless stations 1-3 are not limited to 4-value FSK, and any modulation method can be used as long as the frequency deviation can be detected from the demodulated signal. As an example, wireless stations 1-3 may perform binary FSK or multi-value FSK other than 4-value FSK. As another example, wireless stations 1-3 may perform PSK (Phase Shift Keying), for example, π / 4 DQPSK (Differential Quadrature Phase Shift Keying), or QAM (Quadrature Amplitude Modulation).

[0099] In addition, the above-mentioned hardware configurations and flowcharts are just examples and can be arbitrarily changed and modified.

Explanation of Signs

[0100] 1, 2, 3 Wireless stations 11 First oscillator 12 Second oscillator 21 Input section 22 Input signal processing section 23 Data output section 24 Symbol mapper 25 Oscillator switch 26 Signal generation section 27, 32 Signal switch 28 Transmitter 29 Transceiver switch section 30 Antenna 31 Receiver 33 Demodulation section 34 Deviation detection section 35 Error correction section 36 Output signal processing section 37 Output section 38 Phase comparator 39 Loop filter 40 VCO 41 Divider 42 Amplifier 43, 44 Mixer 45 A-D converter 46 FM Demodulation Unit 47 Synchronous Word Detection Unit 48 Deviation Calculation Unit 49 Second Oscillator 50 Controller 51 CPU 52 I / O 53 RAM 54 ROM S1 Conversion Signal S2 Transmission Modulation Signal S3, S4 Target Signals

Claims

1. A first oscillator in which a first target value is a target frequency and which outputs a first reference signal used for reception processing; At least one second oscillator in which a second target value obtained by adding a target deviation to the first target value is a target frequency and which outputs a second reference signal used for transmission processing; A signal generation unit that generates a target signal in which a first intermediate frequency is 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 unit that receives a signal generated by performing modulation based on a target signal whose frequency matches the first target value, and generates a first intermediate frequency signal in which the first intermediate frequency is a target frequency by performing frequency conversion using the conversion signal based on the received signal; In a reception mode, a second intermediate frequency signal having a second intermediate frequency lower than the first intermediate frequency is generated by performing frequency conversion using the first reference signal based on the first intermediate frequency signal, and in an error correction mode, the second intermediate frequency signal is generated by performing frequency conversion using the first reference signal based on the target signal, and a demodulation unit that generates a demodulated signal by demodulating the generated second intermediate frequency signal; A deviation detection unit that detects a frequency deviation between the first reference signal and the target signal based on the demodulated 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 demodulated 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 according to 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 according to a deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation; A radio station comprising the above.

2. 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.

3. 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.

4. The error correction unit corrects the frequency error of the first reference signal with respect to the target signal according to 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.

5. The error correction unit corrects the frequency error of the first reference signal with respect to the target signal according to the frequency compensation amount, and corrects the frequency error of the second reference signal with respect to the second target value according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation. After that, according to the frequency compensation amount, the frequency error of the first reference signal with respect to the target signal and the frequency error of the second reference signal with respect to the second target value are corrected. The radio station according to claim 4.

6. A frequency error correction method performed by a radio station including a first oscillator that outputs a first reference signal used for reception processing, where the first target value is a target frequency, and at least one second oscillator that outputs a second reference signal used for transmission processing, where the second target value obtained by adding a target deviation to the first target value is the target frequency. The method includes: Generating a target signal based on the second reference signal, where the first intermediate frequency is the target frequency, and generating a conversion signal that is an unmodulated signal based on the first reference signal. Receiving a signal generated by performing modulation based on a target signal whose frequency matches the first target value, and generating a first intermediate frequency signal whose first intermediate frequency is the target frequency by performing frequency conversion using the conversion signal based on the received signal. In the reception mode, based on the first intermediate frequency signal, frequency conversion is performed using the first reference signal to generate a second intermediate frequency signal whose frequency is lower than the first intermediate frequency. In the error correction mode, based on the target signal, frequency conversion is performed using the first reference signal to generate the second intermediate frequency signal, and a demodulated signal is generated by demodulating the generated second intermediate frequency signal. When the demodulated signal is generated based on the first intermediate frequency signal, the frequency deviation between the first reference signal and the target signal is detected based on the demodulated signal. When the demodulated signal is generated based on the target signal, the frequency deviation between the first reference signal and the second reference signal is detected based on the demodulated signal. According to the frequency deviation between the first reference signal and the target signal, correct the frequency error of the first reference signal with respect to the target signal, and according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation, correct the frequency error of the second reference signal with respect to the second target value. Frequency error correction method.

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