Radio station and frequency error compensation method

Abstract

To provide a radio station and a frequency error compensation method that are capable of compensating for a variation in frequency accuracy between a plurality of oscillators in a radio station having the oscillators.SOLUTION: A radio station 1 comprises a first oscillator 11 that outputs a first reference signal in which a first target value is a target frequency, at least one second oscillator 12 that outputs a second reference signal in which a second target value obtained by adding a target deviation to the first target value is the target frequency, a demodulation unit 33 that generates a demodulation signal, and a deviation detection unit 34 that detects a frequency deviation between the first reference signal and the second reference signal based on the demodulation signal. The radio station 1 comprises an error compensation unit 35 that compensates for a frequency error of the first reference signal with respect to the first target value according to a deviation of the frequency deviation from the target deviation.SELECTED DRAWING: Figure 1

Description

Technical Field

[0006] , ,

[0005] ,

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

Background Art

[0002] A local oscillator is composed of an oscillation circuit constituted by discrete components and a PLL (Phase-Locked Loop) - VCO (Voltage Controlled Oscillator) having one reference frequency oscillator. An example of a radio station provided 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 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 integral 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 in the radio station on the receiving side.

[0006] To suppress the impact of integer-value boundary spurious signals 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 these age-related frequency errors may vary from one reference frequency oscillator to another.

[0007] For example, in a radio station communicating with a base station, the reference frequency oscillator used to frequency-convert the received signal from the base station can be corrected to match the reference frequency oscillator of the radio station based on the received signal. By correcting the frequency error as described above, the frequency accuracy of the reference frequency oscillator used during reception can be maintained. However, the reference frequency oscillator used when generating the transmission signal sent to the base station cannot have its frequency error corrected as described above, resulting in a decrease in frequency accuracy. As a result, in a radio station equipped with multiple oscillators, variations in the frequency accuracy of each oscillator may occur.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a radio station and a frequency error compensation method that can compensate for variations in the frequency accuracy of each oscillator in a radio station equipped with multiple oscillators. [Means for solving the problem]

[0009] To achieve the above objective, a radio station according to the first aspect of the present invention is: A first oscillator that outputs a first reference signal whose first target value is the target frequency, A 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, A signal generation unit that generates a target signal whose first intermediate frequency is the target frequency based on the second reference signal, A demodulation unit generates a demodulated signal by frequency-converting the target signal using the first reference signal to generate a second intermediate frequency signal whose frequency is lower than the first intermediate frequency, and demodulating the second intermediate frequency signal. A deviation detection unit detects the frequency deviation between the first reference signal and the second reference signal based on the demodulated signal, An error compensation unit that compensates for the frequency error of the first reference signal with respect to the first target value, in accordance with the deviation of the frequency deviation of the first reference signal and the second reference signal from the target deviation, It is equipped with.

[0010] Preferably, the error compensation unit repeatedly compensates the frequency error of the first reference signal with respect to the first target value by a predetermined amount, according to the deviation of the frequency deviation of the first reference signal and the second reference signal from the target deviation.

[0011] Preferably, in a receiving mode in which signals from other radio stations are received, a receiving period in which the signals are received and a non-receiving period in which the reception of the signals is stopped are repeated. The error compensation unit compensates for the frequency error of the first reference signal with respect to the first target value in accordance with the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation during the non-reception period.

[0012] Preferably, after the reception adjustment period immediately following the start of the reception mode has elapsed, the reception period and the non-reception period are repeated. The error compensation unit compensates for the frequency error of the second reference signal with respect to the second target value during the reception adjustment period, in accordance with the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

[0013] Preferably, the signal generation unit generates the target signal during the reception adjustment period and the non-reception period, and generates a conversion signal which is an unmodulated signal based on the first reference signal or the second reference signal during the reception period. The device further includes a receiving unit that receives a signal generated by modulating a target signal whose frequency matches the first target value or the second target value, and generates a first intermediate frequency signal whose first intermediate frequency is the target frequency by performing frequency conversion based on the received signal using the first reference signal or the conversion signal based on the second reference signal whose frequency is the target frequency, wherein the receiving unit further includes a receiving unit. The demodulation unit generates the second intermediate frequency signal based on the target signal or the first intermediate frequency signal, and generates the demodulated signal by demodulating the second intermediate frequency signal. The deviation detection unit detects the 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, and detects the frequency deviation between the first reference signal or the second reference signal used in the frequency conversion for generating the first intermediate frequency signal used in generating the demodulated signal and the target signal based on the demodulated signal. When the first reference signal is used in the frequency conversion for generating the first intermediate frequency signal, the error compensation unit compensates for the 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 during the reception period. When the second reference signal is used in the frequency conversion for generating the first intermediate frequency signal, the error compensation unit compensates for the frequency error of the second reference signal with respect to the target signal in accordance with the frequency deviation between the second reference signal and the target signal during the reception period.

[0014] Preferably, when the first reference signal is used in the frequency conversion for generating the first intermediate frequency signal, the error compensation unit repeatedly compensates for the frequency error of the first reference signal with respect to the target signal by a predetermined amount in accordance with the frequency deviation between the first reference signal and the target signal during the reception period, and when the second reference signal is used in the frequency conversion for generating the first intermediate frequency signal, the unit repeatedly compensates for the frequency error of the second reference signal with respect to the target signal by a predetermined amount in accordance with the frequency deviation between the second reference signal and the target signal during the reception period.

[0015] Preferably, the error compensation unit compensates for the frequency error of the second reference signal with respect to the target signal during the reception period, in accordance with the frequency deviation between the second reference signal and the target signal, and then compensates for the frequency error of the first reference signal with respect to the first target value during the non-reception period immediately following the reception period, in accordance with the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

[0016] Preferably, after the frequency error of the first reference signal with respect to the target signal has been compensated during the reception period of the reception mode, a transmission mode is started for transmitting a signal based on the second reference signal to another radio station, and during the transmission adjustment period immediately following the start of the transmission mode, The demodulation unit generates the demodulated signal based on the target signal, The deviation detection unit detects the frequency deviation between the first reference signal and the second reference signal based on the demodulated signal. The error compensation unit compensates for 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.

[0017] Preferably, the system comprises a plurality of second oscillators that output second reference signals with second target values ​​that are different from each other. In the reception period of the reception mode, after the frequency error of the second reference signal output by any of the second oscillators with respect to the target signal is compensated, when a transmission mode for transmitting a signal based on the second reference signal output by the other second oscillator to another radio station is started, in the transmission time adjustment period immediately after the start of the transmission mode, The demodulation unit generates the demodulated signal based on the target signal based on the second reference signal output by the other second oscillator. The error compensation unit compensates for the frequency error of the second reference signal output by the other second oscillator 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 output by the other second oscillator from the target deviation.

[0018] Preferably, it further includes a frequency adjustment unit that adjusts the frequency of the first reference signal output by the first oscillator. The error compensation unit controls the frequency adjustment unit to adjust the frequency of the first reference signal according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation, thereby compensating for the frequency error of the first reference signal with respect to the first target value.

[0019] Preferably, the frequency adjustment unit includes a voltage-controlled oscillator that oscillates at an oscillation frequency according to a control voltage, a frequency divider that divides the output of the voltage-controlled oscillator by a division ratio, a phase comparator that outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider and the first reference signal output by the first oscillator, and a loop filter that converts the phase difference signal into a voltage and outputs the voltage to the voltage-controlled oscillator. The error compensation unit compensates for the frequency error of the first reference signal with respect to the first target value by adjusting the division ratio of the frequency divider included in the frequency adjustment unit according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

[0020] Preferably, it further includes a frequency adjustment unit that adjusts the frequency of the first reference signal output by the first oscillator. The error compensation unit compensates for the frequency error of the first reference signal with respect to the target signal by controlling the frequency adjustment unit to adjust the frequency of the first reference signal according to the frequency deviation between the first reference signal and the target signal.

[0021] Preferably, the frequency adjustment unit includes a voltage-controlled oscillator that oscillates at an oscillation frequency corresponding to a control voltage, a frequency divider that divides the output of the voltage-controlled oscillator by a frequency division ratio, a phase comparator that outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider and the first reference signal output by the first oscillator, and a loop filter that converts the phase difference signal into a voltage and outputs the voltage to the voltage-controlled oscillator. The error compensation unit compensates for the frequency error of the first reference signal with respect to the target signal by adjusting the frequency division ratio of the frequency divider in the frequency adjustment unit according to the frequency deviation between the first reference signal and the target signal.

[0022] Preferably, the signal generation unit includes a voltage-controlled oscillator that oscillates at an oscillation frequency corresponding to a control voltage, a frequency divider that divides the output of the voltage-controlled oscillator by a frequency division ratio, a phase comparator that outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider and the first reference signal or the second reference signal, and a loop filter that converts the phase difference signal into a voltage and outputs the voltage to the voltage-controlled oscillator. The error compensation unit compensates for the frequency error of the second reference signal with respect to the second target value by adjusting the division ratio of the frequency divider when the phase comparator outputs the phase difference signal based on the phase difference between the signal divided by the frequency divider and the second reference signal, in accordance with the deviation of the frequency deviation of the first reference signal and the second reference signal from the target deviation.

[0023] Preferably, the signal generation unit includes a voltage-controlled oscillator that oscillates at an oscillation frequency corresponding to a control voltage, a frequency divider that divides the output of the voltage-controlled oscillator by a frequency division ratio, a phase comparator that outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider and the first reference signal or the second reference signal, and a loop filter that converts the phase difference signal into a voltage and outputs the voltage to the voltage-controlled oscillator. The error compensation unit compensates for the frequency error of the second reference signal with respect to the target signal by adjusting the division ratio of the frequency divider when the phase comparator outputs the phase difference signal based on the phase difference between the signal divided by the frequency divider and the second reference signal, according to the frequency deviation between the second reference signal and the target signal.

[0024] Preferably, the signal generation unit generates the target signal, which is a modulated signal, by modulating it based on the input target data and the second reference signal.

[0025] Preferably, the signal generation unit generates the target signal, which is an unmodulated signal based on the second reference signal.

[0026] A frequency error compensation method according to a second aspect of the present invention is: A frequency error compensation method performed by a radio station comprising: 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, obtained by adding a target deviation to the first target value, is a target frequency; Based on the second reference signal, a target signal is generated whose first intermediate frequency is the target frequency. Based on the target signal, a second intermediate frequency signal is generated by frequency conversion using the first reference signal, the second intermediate frequency signal having a frequency lower than the first intermediate frequency, and a demodulated signal is generated by demodulating the second intermediate frequency signal. Based on the demodulated signal, the frequency difference between the first reference signal and the second reference signal is detected. The frequency error of the first reference signal with respect to the first target value is compensated according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation. [Effects of the Invention]

[0027] The radio station according to the present invention compensates for the frequency error of the first reference signal with respect to the first target value, in accordance with the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation. This makes it possible to compensate for variations in the frequency accuracy of each oscillator in a radio station equipped with multiple oscillators. [Brief explanation of the drawing]

[0028] [Figure 1] Block diagram showing the configuration of a radio station according to Embodiment 1 of the present invention. [Figure 2] This figure shows the timing at which the radio station according to Embodiment 1 performs frequency error compensation processing in receiving mode. [Figure 3] A flowchart illustrating an example of the operation of the frequency error compensation processing of the first reference signal during the reception period performed by the radio station according to Embodiment 1. [Figure 4] A flowchart illustrating an example of the operation of the frequency error compensation processing of the second reference signal during the reception adjustment period performed by the radio station according to Embodiment 1. [Figure 5] A flowchart illustrating an example of the operation of the frequency error compensation processing of the second reference signal during the reception period performed by the radio station according to Embodiment 1. [Figure 6] A flowchart illustrating an example of the operation of the frequency error compensation processing of the first reference signal during the non-reception period performed by the radio station according to Embodiment 1. [Figure 7] This figure shows the timing at which the radio station according to Embodiment 1 performs frequency error compensation processing in transmission mode. [Figure 8] Block diagram showing the configuration of a radio station according to Embodiment 2 of the present invention. [Figure 9] A flowchart illustrating an example of the operation of the frequency error compensation processing of the second reference signal during the reception adjustment period performed by the radio station according to Embodiment 2. [Figure 10] A flowchart illustrating an example of the operation of the frequency error compensation processing of the first reference signal during the non-reception period performed by the radio station according to Embodiment 2. [Figure 11] Block diagram showing the configuration of a radio station according to Embodiment 3 of the present invention. [Figure 12] This figure shows the timing at which the radio station according to Embodiment 3 performs frequency error compensation processing in receiving mode. [Figure 13] This figure shows the timing at which the radio station according to Embodiment 3 performs frequency error compensation processing in transmission mode. [Figure 14] Block diagram showing the configuration of the frequency adjustment unit included in a modified example of the radio station according to the embodiment. [Modes for carrying out the invention]

[0029] The following describes in detail, with reference to the drawings, a radio station and a frequency error compensation method according to embodiments of the present invention. In the drawings, the same or equivalent parts are denoted by the same reference numerals.

[0030] (Embodiment 1) The radio station 1 shown in Figure 1 is, for example, a double superheterodyne radio station. The radio station 1 shown in Figure 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, obtained by adding a target deviation to the first target value, is the target frequency. In Embodiment 1, the radio station 1 includes one first oscillator 11 and one second oscillator 12.

[0031] Radio station 1 uses frequency modulation, specifically FSK (Frequency Shift Keying), as its modulation method. Radio station 1 includes an input unit 21 that receives input data for transmission to other radio stations, 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 compensation data to compensate for frequency errors or conversion data to generate an unmodulated signal used for frequency conversion, and a symbol mapper 24 that maps the transmission data or compensation data to multi-level FSK symbols. Radio station 1 also includes an oscillator switch 25 connected to a first oscillator 11 and a second oscillator 12, which switches between the first oscillator 11 and the second oscillator 12 to output a first reference signal or a second reference signal.

[0032] The radio station 1 includes a signal generation unit 26 that generates a conversion signal S1, which is an unmodulated signal based on a first or second reference signal output by an oscillator switch 25; a transmission modulated signal S2, which is based on a first or second reference signal output by an oscillator switch 25; and a target signal S3, which corresponds to a second reference signal output by an oscillator switch 25. The signal generation unit 26 includes a phase comparator 38 that outputs a phase difference signal based on the first or second reference signal and a signal divided by a frequency divider 41; 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 corresponding to a control voltage; and a frequency divider 41 that divides the output of the VCO 40 according to the division ratio.

[0033] Radio station 1 includes a signal switch 27 that outputs the conversion signal S1, the transmission modulation signal S2, or the target signal S3 acquired from the signal generation unit 26, switching the output destination, and a transmission unit 28 that generates a transmission signal from the transmission modulation signal S2 output by the signal switch 27. The transmission signal generated by the transmission unit 28 is transmitted to any other radio station via the transmit / receive switch 29 and the antenna 30.

[0034] Radio station 1 includes a receiving unit 31 that generates a first intermediate frequency signal from a received signal received by an antenna 30 and supplied via a transmit / receive switching unit 29. The receiving unit 31 includes an amplifier 42 that amplifies the received signal received by the antenna 30 and supplied via the transmit / receive switching unit 29, and a mixer 43 that generates a first intermediate frequency signal from the received signal output by the amplifier 42 and a conversion signal S1 output by a signal switch 27.

[0035] Radio station 1 includes a signal switch 32 that switches and outputs either the target signal S3 output by the signal switch 27 or the first intermediate frequency signal generated by the receiving unit 31.

[0036] The radio station 1 includes a demodulation unit 33 that generates a demodulated signal by frequency conversion using a first reference signal based on the target signal S3 or first intermediate frequency signal output by the signal switch 32, and demodulating the second intermediate frequency signal. 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, which is a second intermediate frequency with a frequency lower than the first intermediate frequency; an AD converter 45 that generates digital data from the second intermediate frequency signal; and an FM (Frequency Modulation) detection unit 46 that performs demodulation processing on the digital data generated by the AD converter 45 to generate a demodulated signal.

[0037] Radio station 1 includes a deviation detection unit 34 that detects the frequency deviation between a first reference signal or a second reference signal and a target signal, or the frequency deviation between the first reference signal and the second reference signal, based on the 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 a first reference signal or a second reference signal and a target signal, or the frequency deviation between the first reference signal and the second reference signal, based on the synchronization word.

[0038] The radio station 1 includes an error compensation unit 35 that compensates for the frequency error of the first oscillator 11 or the second oscillator 12 based on the frequency deviation, an output signal processing unit 36 ​​that extracts output data from the demodulated signal, and an output unit 37 that outputs the output data.

[0039] To control the above-mentioned components, the radio station 1 is equipped with a controller 50. The controller 50 comprises a CPU (Central Processing Unit) 51, I / O (Input / Output) 52, RAM (Random Access Memory) 53, and ROM (Read-Only Memory) 54. To avoid complexity and facilitate understanding, signal lines from the controller 50 to each component of the radio station 1 are omitted. The controller 50 is connected to each component of the radio station 1 via the I / O 52 and controls the start, end, and processing content of each component. The CPU 51 controls the radio station 1 by executing control programs stored in the ROM 54. Commands, data, etc., input via the I / O 52 are processed and temporarily stored in the RAM 53. The CPU 51 reads the commands, data, etc., stored in the RAM 53 as needed and controls the radio station 1.

[0040] The first oscillator 11 has a crystal oscillator and an oscillation circuit, and outputs a first reference signal to the oscillator switch 25 and the demodulation unit 33. In Embodiment 1, the first reference signal is a sinusoidal 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 oscillator and an oscillation circuit, and outputs a second reference signal to the oscillator switch 25. In Embodiment 1, the second reference signal is a sinusoidal clock signal. The second target value f2, which is the target frequency of the second reference signal, is, for example, 51.33 MHz.

[0041] The first oscillator 11 is formed by an oscillator whose output frequency can be adjusted by applying an external frequency control voltage, such as a VCXO (Voltage Controlled Crystal Oscillator) or VTCCXO (Voltage Controlled Temperature Compensated Crystal Oscillator). The second oscillator 12 may be formed by a VCXO, VTCCXO, etc., similar to the first oscillator 11, or it may be formed by an oscillator that does not have the function of adjusting the output frequency by a frequency control voltage, such as an SPXO (Simple Packaged Crystal Oscillator).

[0042] Radio station 1 enters a receive mode when it is activated, when a receiving channel is determined by scanning, etc., to receive signals from other radio stations. The receive mode and transmit mode, which transmits signals to other radio stations, are switched according to the operation of the control panel of radio station 1. The receive channel in receive mode and the transmit channel in transmit mode are determined according to the operation of the control panel.

[0043] In receiving mode, radio station 1 performs receiving processing to receive signals from other radio stations based on a first reference signal output by a first oscillator 11 or a second reference signal output by a second oscillator 12 corresponding to a determined receiving channel. Radio station 1 communicates using a communication method that allows intermittent reception, such as a communication method that includes redundant data in the downlink frame or a TDMA (Time Division Multiple Access) method. Including redundant data in the downlink frame means that the same data is transmitted repeatedly, or that a blank channel signal is transmitted. When radio station 1 enters receiving mode, periods of receiving signals and periods of not receiving signals alternate.

[0044] When the reference signal corresponding to the receiving channel in the receiving mode is the first reference signal output by the first oscillator 11, the oscillator switch 25 outputs the first reference signal obtained from the first oscillator 11 to the signal generation unit 26. The data output unit 23 outputs conversion data used to generate an unmodulated signal used for frequency conversion to the signal generation unit 26. The conversion data is, for example, data consisting of consecutive zeros.

[0045] 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. Specifically, in the receiving mode, the signal generation unit 26 generates a conversion signal S1, which is an unmodulated signal with a frequency lower than the receiving frequency by a first intermediate frequency, based on the first reference signal, and outputs it to the signal switch 27. For example, the signal generation unit 26 generates a conversion signal S1, which is a signal in which conversion data output from the data output unit 23, indicating that the frequency deviation is 0, is superimposed on a carrier wave signal with a frequency lower than the receiving frequency by a first intermediate frequency. The receiving frequency is, for example, a frequency that falls within the range of 360 MHz or higher and 400 MHz or lower. The first intermediate frequency is, for example, 49.95 MHz.

[0046] In detail, the phase comparator 38 of the signal generation unit 26 outputs a phase difference signal to the loop filter 39, which is a signal corresponding to the phase difference between the first 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, integrates and smooths the current to convert it into a voltage, and outputs this voltage as a control voltage to the VCO 40. The oscillation frequency of the VCO 40 changes according to the output of the loop filter 39. The frequency divider 41 divides the output of the VCO 40 according to a division ratio determined according to the reception mode, and outputs the divided signal to the phase comparator 38. Through the above processing, the signal generation unit 26 generates a conversion signal S1.

[0047] The signal switch 27 sends the conversion signal S1, which is an unmodulated signal output from the signal generation unit 26, to the receiving unit 31.

[0048] The amplifier 42 in the receiving unit 31 is, for example, an LNA (Low Noise Amplifier) ​​and amplifies the received signal that is received by the antenna 30 and supplied via the transmit / receive switching unit 29. The amplifier 42 sends the amplified received signal to the mixer 43. The mixer 43 multiplies the conversion signal S1 output by the signal switch 27 and the received signal amplified by the amplifier 42 to generate a first intermediate frequency signal with a frequency of the first intermediate frequency, and outputs it to the signal switch 32.

[0049] 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.

[0050] The mixer 44 of the demodulation unit 33 outputs a second intermediate frequency signal to the AD converter 45, the second intermediate frequency signal having a frequency equal to the difference between the frequency of the first reference signal and the first intermediate frequency. If 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 to the AD converter 45, which is the value obtained by subtracting 49.95 MHz from 50.40 MHz.

[0051] The AD converter 45 performs AD conversion on the second intermediate frequency signal to generate digital data, which is then sent to the FM detection unit 46. The FM detection unit 46 determines which of the four predetermined amplitude levels corresponds to each data value acquired from the AD converter 45, and outputs a 2-bit data corresponding to the determined amplitude level, specifically one of 00, 01, 10, or 11, as a demodulated signal to the synchronization word detection unit 47.

[0052] The synchronization word detection unit 47 performs a correlation calculation between the demodulated signal and the synchronization word, shifting it one symbol at a time, or in other words, two bits at a time. If the correlation value is greater than or equal to a threshold, the synchronization word can be considered detected. The synchronization word is a known sequence of bit data. The synchronization word detection unit 47 sends the synchronized demodulated signal to the output signal processing unit 36 ​​and the deviation calculation unit 48.

[0053] The output signal processing unit 36 ​​extracts audio data from the demodulated signal that has been synchronized after a synchronization word has been detected by the synchronization word detection unit 47, performs a DA (Digital-to-Analog) conversion to generate an analog audio signal, and sends it to the output unit 37. The output unit 37 includes 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.

[0054] As described above, radio station 1 receives signals from other radio stations and outputs audio signals based on the first reference signal output by the first oscillator 11.

[0055] When the reference signal corresponding to the receiving channel in the receiving mode is the second reference signal output by the second oscillator 12, the receiving process of the radio station 1 is the same as the receiving process based on the first reference signal described above. However, the oscillator switch 25 outputs the second reference signal obtained from the second oscillator 12 to the signal generation unit 26, and the signal generation unit 26 generates a conversion signal S1, which is an unmodulated signal, based on the second reference signal output by the oscillator switch 25.

[0056] If a frequency error occurs in the first oscillator 11, causing the frequency of the first reference signal to deviate from the first target value, the frequency of the first intermediate frequency signal output by the mixer 43 will deviate from the target value, the first intermediate frequency. Similarly, if a frequency error occurs in the second oscillator 12, causing the frequency of the second reference signal to deviate from the second target value, the frequency of the first intermediate frequency signal output by the mixer 43 will deviate from the target value, the first intermediate frequency. As a result, the frequency of the second intermediate frequency signal output by the mixer 44 will deviate from the target value, the second intermediate frequency. Therefore, in reception mode, the radio station 1 performs frequency error compensation processing to compensate for the frequency error of at least one of the first reference signal and the second reference signal while performing the above-described reception processing.

[0057] Figure 2 shows the timing at which radio station 1 performs frequency error compensation processing in receive mode. The received signal indicates the reference signal corresponding to the received channel. In Figure 2, the first reference signal is represented by REF1 and the second reference signal by REF2. The same applies to subsequent figures.

[0058] Radio station 1 compensates for frequency errors during the reception adjustment period, which is a predetermined length of time immediately after the start of the receiving mode, the receiving period, which is when it receives signals from other radio stations, and the non-receiving period, during which it does not receive signals from other radio stations. If the receiving channel is changed during the receiving mode, a new receiving mode is started on the changed receiving channel, and radio station 1 compensates for frequency errors during the reception adjustment period, the receiving period, and the non-receiving period of the new receiving mode. In the receiving mode, radio station 1 performs compensation processing 1-4 to compensate for frequency errors at the timings shown in Figure 2.

[0059] [Compensation Processing 1] As shown in Figure 2, when the reference signal corresponding to the receiving channel is the first reference signal, and the receiving period begins, radio station 1 starts compensation processing 1, specifically the frequency error compensation processing shown in Figure 3. When the reference signal corresponding to the receiving channel is the first reference signal, radio station 1 does not perform frequency error compensation processing during the receiving adjustment period and the non-receiving period.

[0060] Steps S11 to S14 in Figure 3 are the same as the reception processing based on the first reference signal described above. The oscillator switch 25 outputs the first reference signal acquired from the first oscillator 11 to the signal generation unit 26. The signal generation unit 26 generates a conversion signal S1, which is an unmodulated signal whose frequency is lower than the reception frequency by a first intermediate frequency, based on the first reference signal acquired from the first oscillator 11 via the oscillator switch 25 (step S11). The signal generation unit 26 sends the generated conversion signal S1 to the signal switch 27. The signal switch 27 acquires the conversion signal S1 generated in step S11 and sends it to the mixer 43 provided in the receiver 31.

[0061] Mixer 43 receives the signal from the base station, which is received by antenna 30, supplied via transmit / receive switching unit 29, and amplified by amplifier 42, and multiplies it with the conversion signal S1 to generate a first intermediate frequency signal (step S12). Mixer 43 sends the generated first intermediate frequency signal to signal switch 32. Signal switch 32 sends the first intermediate frequency signal acquired from mixer 43 to demodulation unit 33.

[0062] The mixer 44 in the demodulation unit 33 multiplies the first reference signal supplied from the first oscillator 11 and the first intermediate frequency signal generated in step S12, which is supplied via the signal switch 32, to generate a second intermediate frequency signal (step S13). The mixer 44 sends the generated second intermediate frequency signal to the AD converter 45.

[0063] The FM detection unit 46 of the demodulation unit 33 performs demodulation processing on the digital data generated by AD conversion of the second intermediate frequency signal generated in step S13 using the AD converter 45, thereby generating a demodulated signal (step S14). The FM detection unit 46 sends the generated demodulated signal to the deviation detection unit 34.

[0064] 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 (step S15).

[0065] In detail, the deviation calculation unit 48 of the deviation detection unit 34 shown in Figure 1 calculates the frequency deviation from the DC (Direct Current) offset included in the symbol corresponding to the synchronization word detected by the synchronization word detection unit 47. Preferably, the deviation calculation unit 48 outputs the moving average value of the frequency deviation as the frequency deviation.

[0066] The deviation calculation unit 48 sends the detected frequency deviation to the error compensation unit 35. The detected frequency deviation indicates the difference in frequency between the first reference signal and the frequency of the target signal. For example, if the frequency of the first reference signal is higher than the frequency of the target signal, the frequency deviation is a positive number, and if the frequency of the first reference signal is lower than the frequency of the target signal, the frequency deviation is a negative number.

[0067] As shown in Figure 3, the error compensation unit 35 controls the first oscillator 11 according to the frequency deviation detected in step S15, specifically by adjusting the frequency control voltage applied to the first oscillator 11 to correct the frequency error of the first reference signal (step S16). For example, the error compensation unit 35 changes the frequency control voltage by increasing or decreasing the input value to the DAC (Digital-Analog Converter) that applies the frequency control voltage to the control input terminal of the first oscillator 11.

[0068] The DAC outputs an analog voltage signal corresponding to the input value to the control input terminal of the first oscillator 11. In other words, the analog voltage signal output by the DAC is a frequency control voltage. The error compensation unit 35 adjusts the input value of the DAC, thereby adjusting the frequency control voltage applied to the control input terminal of the first oscillator 11, and thus adjusting the frequency of the first reference signal output by the first oscillator 11.

[0069] In step S16, the error compensation unit 35 compensates for the frequency error of the first reference signal with respect to the frequency of the target signal by a predetermined amount, according to the frequency deviation detected in step S15. Specifically, if the frequency deviation detected in step S15 is a positive number, the error compensation unit 35 decreases the input value of the DAC by 1 in step S16. If the frequency deviation detected in step S15 is a negative number, the error compensation unit 35 increases the input value of the DAC by 1 in step S16. As a result, the frequency control voltage changes, and the first reference signal output by the first oscillator 11 is adjusted.

[0070] Once step S16 is completed, the radio station 1 finishes the process of compensating for the frequency error of the first reference signal. Thereafter, the radio station 1 repeats the process of compensating for the frequency error of the first reference signal shown in Figure 3 at predetermined time intervals, for example, every second. As a result, the error compensation unit 35 repeatedly compensates for the frequency error of the first reference signal with respect to the frequency of the target signal by a predetermined amount. As a result, it becomes possible to make the frequency of the first reference signal output by the first oscillator 11 of the radio station 1 follow that of the reference oscillator installed at the base station that outputs the target signal. As described above, by gradually changing the frequency control voltage, it becomes possible to gradually compensate for the frequency error of the first reference signal output by the first oscillator 11.

[0071] [Compensation Processing 2] As shown in Figure 2, if the reference signal corresponding to the receiving channel of the receiving mode is the second reference signal, the radio station 1 performs compensation processing 2, specifically the frequency error compensation processing shown in Figure 4, during the reception adjustment period immediately after the start of the receiving mode.

[0072] The oscillator switch 25 outputs a second reference signal obtained from the second oscillator 12 to the signal generation unit 26. Based on the second reference signal obtained from the second oscillator 12 via the oscillator switch 25, the signal generation unit 26 generates a target signal S3, which is a modulated signal in which modulation data based on compensation data is superimposed on a carrier signal whose frequency is the first intermediate frequency (step S21).

[0073] In detail, the data output unit 23 shown in Figure 1 outputs compensation data used to compensate for frequency errors to the symbol mapper 24. In Embodiment 1, the compensation data is fixed data including a synchronization word.

[0074] The symbol mapper 24 maps the compensation data generated by the data output unit 23 to symbols and outputs the modulation data indicating the mapped symbols as target data to the signal generation unit 26. For example, when radio station 1 performs 4-level FSK, the symbol mapper 24 assigns the symbol +1 to the 2-bit data 00, the symbol -1 to the 2-bit data 01, the symbol +3 to the 2-bit data 10, and the symbol -3 to the 2-bit data 11. A frequency deviation amount is defined for each symbol.

[0075] The signal generation unit 26 generates a modulated signal, the target signal S3, by performing frequency modulation based on the input target data and the second reference signal output by the oscillator switch 25. The target data used to generate the target signal S3 is the modulation data input from the symbol mapper 24.

[0076] In detail, the phase comparator 38 of the signal generation unit 26 outputs a phase difference signal to the loop filter 39, which 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, integrates and smooths the current to convert it into a voltage, and outputs this voltage as a control voltage to the VCO 40. The oscillation frequency of the VCO 40 fluctuates up and down according to the modulation data output from the symbol mapper 24, centered around a center frequency that changes according to the output of the loop filter 39. FM (Frequency Modulation) modulation is performed by the fluctuation of the oscillation frequency as described above. The frequency divider 41 divides the output of the VCO 40 according to a division ratio determined according to the transmission mode, and outputs the divided signal to the phase comparator 38. Through the above process, the signal generation unit 26 generates the target signal S3 and outputs the target signal S3 to the signal switch 27.

[0077] The signal switch 27 sends the target signal S3 generated as described above to the signal switch 32. The signal switch 32 receives the target signal S3 from the signal switch 27 and sends the target signal S3 to the demodulation unit 33.

[0078] As shown in Figure 4, the mixer 44 in the demodulation unit 33 multiplies the first reference signal supplied from the first oscillator 11 and the target signal S3 generated in step S21, which is supplied via the signal switches 27 and 32, to generate a second intermediate frequency signal (step S22). Specifically, the mixer 44 generates 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, and outputs the generated second intermediate frequency signal to the AD converter 45.

[0079] The FM detection unit 46 of the demodulation unit 33 performs demodulation processing on the digital data generated by AD conversion of the second intermediate frequency signal generated in step S22 using the AD converter 45, thereby generating a demodulated signal (step S23). The demodulation unit 33 sends the generated demodulated signal to the deviation detection unit 34.

[0080] 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 (step S24). The deviation detection unit 34 sends the detected frequency deviation to the error compensation unit 35. The detected frequency deviation represents the frequency deviation between the first reference signal and the second reference signal.

[0081] The error compensation unit 35 adjusts the frequency division ratio 41 of the signal generation unit 26 according to the deviation of the frequency deviation detected in step S24 from the target deviation (step S25). In step S25, the error compensation unit 35 compensates for the frequency error of the second reference signal by controlling the signal generation unit 26 to adjust the frequency of the target signal S3 according to the frequency deviation between the first reference signal output by the first oscillator 11 and the second reference signal output by the second oscillator 12.

[0082] For example, the error compensation unit 35 determines a division ratio adjustment amount to bring the frequency deviation between the first reference signal and the second reference signal closer to the target deviation, and adjusts the division ratio of the frequency divider 41 according to the division ratio adjustment amount. More specifically, the error compensation unit 35 adjusts the division ratio of the frequency divider 41 according to the division ratio adjustment amount when the phase comparator 38 outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider 41 and the second reference signal. For example, the error compensation unit 35 adjusts the division ratio of the frequency divider 41 when the reference signal corresponding to the receiving channel in the receiving mode is the second reference signal.

[0083] When the frequency of the first reference signal matches the first target value f1 and the frequency of the second reference signal matches the second target value f2, the division ratio of the frequency divider 41 in transmission mode is defined as N0. When the frequency of the second reference signal becomes higher than the second target value f2 while the frequency of the first reference signal matches the first target value f1, the frequency deviation f2-f1 between the first reference signal and the second reference signal becomes larger than the target deviation. At this time, the error compensation unit 35 adjusts the division ratio of the frequency divider 41 to a value greater than N0 when the reference signal corresponding to the receiving channel in reception mode is the second reference signal.

[0084] By setting the frequency division ratio to a value greater than N0, the frequencies of the conversion signal S1 and target signal S3 output by the signal generation unit 26 become lower compared to when the frequency division ratio is N0. In other words, when the frequency of the second reference signal becomes higher than the second target value f2, the frequencies of the conversion signal S1 and target signal S3 are adjusted to become lower. By adjusting the frequencies of the signals output by the signal generation unit 26, specifically the conversion signal S1 and target signal S3, the frequency error of the second reference signal output by the second oscillator 12 with respect to the second target value is compensated.

[0085] When the frequency of the first reference signal matches the first target value f1, and the frequency of the second reference signal becomes lower than the second target value f2, the frequency deviation f2-f1 between the first and second reference signals becomes smaller than the target deviation. At this time, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 of the signal generation unit 26 in transmission mode to a value smaller than N0.

[0086] By setting the frequency division ratio to a value smaller than N0, the frequencies of the conversion signal S1 and target signal S3 output by the signal generation unit 26 become higher compared to when the frequency division ratio is N0. In other words, when the frequency of the second reference signal becomes lower than the second target value f2, the frequencies of the conversion signal S1 and target signal S3 are adjusted to become higher. By adjusting the frequencies of the signals output by the signal generation unit 26, specifically the conversion signal S1 and target signal S3, the error in the frequency of the second reference signal output by the second oscillator 12 relative to the second target value is compensated.

[0087] The frequency division ratio adjustment amount is determined according to the frequency deviation f2-f1 between the first reference signal and the second reference signal, and the specifications of the PLL (Phase-Locked Loop) IC (Integrated Circuit) used to realize the signal generation unit 26. In other words, the frequency division ratio adjustment amount is determined according to the specifications of the PLL IC to compensate for the deviation of the frequency deviation f2-f1 between the first reference signal and the second reference signal from the target deviation.

[0088] Once the process in step S25 of Figure 4 is completed, radio station 1 terminates the process of compensating for the frequency error of the second reference signal.

[0089] As a result of the above processing, even if the frequency of the second reference signal output by the second oscillator 12 deviates from the second target value, the frequency deviation of the signal output by the signal generation unit 26 based on the second reference signal is suppressed. Specifically, the frequency division ratio of the frequency divider 41 is adjusted when the reference signal corresponding to the receiving channel of the receiving mode is the second reference signal, thereby suppressing the frequency deviation of the conversion signal S1 and the target signal S3 based on the second reference signal. As a result, the center frequency of the conversion signal S1 is maintained at a frequency lower than the receiving frequency by the first intermediate frequency, and the center frequency of the target signal S3 is maintained at the first intermediate frequency.

[0090] [Compensation Processing 3] As shown in Figure 2, if the signal corresponding to the receiving channel in the receiving mode is the second reference signal, the radio station 1 performs compensation processing 3, specifically the frequency error compensation processing shown in Figure 5, during the receiving period of the receiving mode.

[0091] Step S31 in Figure 5 is the same as the reception process based on the second reference signal described above. The oscillator switch 25 outputs the second reference signal obtained from the second oscillator 12 to the signal generation unit 26. The signal generation unit 26 generates a conversion signal S1, which is an unmodulated signal whose frequency is lower than the reception frequency by a first intermediate frequency, based on the second reference signal obtained from the second oscillator 12 via the oscillator switch 25 (step S31). The signal generation unit 26 sends the generated conversion signal S1 to the signal switch 27. The signal switch 27 obtains the conversion signal S1 generated in step S31 and sends it to the mixer 43 provided in the reception unit 31. The processing from steps S12 to S14 is the same as the processing from S12 to S14 shown in Figure 3.

[0092] The deviation detection unit 34 detects the frequency deviation of the second intermediate frequency signal, in other words, the frequency deviation between the second reference signal and the target signal, based on the synchronization word included in the demodulated signal generated in step S14 (step S32).

[0093] In detail, the deviation calculation unit 48 of the deviation detection unit 34 shown in Figure 1 calculates the frequency deviation from the DC offset included in the symbol corresponding to the synchronization word detected by the synchronization word detection unit 47. Preferably, the deviation calculation unit 48 outputs the moving average value of the frequency deviation as the frequency deviation.

[0094] The deviation calculation unit 48 sends the detected frequency deviation to the error compensation unit 35. The detected frequency deviation indicates the difference in frequency between the second reference signal and the target signal frequency. For example, if the frequency of the second reference signal is higher than the frequency of the target signal, the frequency deviation is a positive number, and if the frequency of the second reference signal is lower than the frequency of the target signal, the frequency deviation is a negative number.

[0095] As shown in Figure 5, the error compensation unit 35 adjusts the frequency division ratio of the signal generation unit 26 according to the frequency deviation detected in step S32 (step S33). For example, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 to compensate for the frequency deviation between the second reference signal and the target signal. More specifically, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 when the phase comparator 38 outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider 41 and the second reference signal to compensate for the frequency deviation between the second reference signal and the target signal.

[0096] In step S33, the error compensation unit 35 compensates for the frequency error of the second reference signal with respect to the frequency of the target signal by a predetermined amount, according to the frequency deviation detected in step S32. Specifically, if the frequency deviation detected in step S32 is a positive number, the error compensation unit 35 increases the division ratio of the frequency divider 41 by 1 in step S33 when the reference signal corresponding to the receiving channel of the receiving mode is the second reference signal. If the frequency deviation detected in step S32 is a negative number, the error compensation unit 35 decreases the division ratio of the frequency divider 41 by 1 in step S33 when the reference signal corresponding to the receiving channel of the receiving mode is the second reference signal.

[0097] Once step S33 is completed, radio station 1 finishes the process of compensating for the frequency error of the second reference signal. Thereafter, radio station 1 repeats the process of compensating for the frequency error of the second reference signal shown in Figure 5 at predetermined time intervals, for example, every second. As a result, the error compensation unit 35 repeatedly compensates for the frequency error of the second reference signal with respect to the frequency of the target signal by a predetermined amount. This makes it possible to gradually compensate for the frequency error of the second reference signal output by the second oscillator 12.

[0098] As a result of the above processing, even if the frequency of the second reference signal output by the second oscillator 12 deviates from the second target value, the frequency deviation of the signal output by the signal generation unit 26 based on the second reference signal is suppressed. Specifically, the frequency division ratio of the frequency divider 41 is adjusted when the reference signal corresponding to the receiving channel of the receiving mode is the second reference signal, thereby suppressing the frequency deviation of the conversion signal S1 and the target signal S3 based on the second reference signal. As a result, the center frequency of the conversion signal S1 is maintained at a frequency lower than the receiving frequency by the first intermediate frequency, and the center frequency of the target signal S3 is maintained at the first intermediate frequency.

[0099] [Compensation Processing 4] As shown in Figure 2, when the signal corresponding to the receiving channel in receiving mode is the second reference signal, radio station 1 performs compensation processing 4, specifically the frequency error compensation processing shown in Figure 6, during the non-receiving period of receiving mode.

[0100] The processing in steps S21 to S24 is the same as the processing in steps S21 to S24 shown in Figure 4. The error compensation unit 35 controls the first oscillator 11 according to the deviation of the frequency deviation detected in step S24 from the target deviation, specifically by adjusting the frequency control voltage applied to the first oscillator 11 to correct the frequency error of the first reference signal (step S41). For example, the error compensation unit 35 changes the frequency control voltage by increasing or decreasing the input value to the DAC that applies the frequency control voltage to the control input terminal of the first oscillator 11.

[0101] In step S41, the error compensation unit 35 compensates for the frequency error of the first reference signal relative to the first target value by a predetermined amount, according to the deviation of the frequency deviation detected in step S24 from the target deviation. Specifically, if the frequency deviation detected in step S24 is greater than the target deviation, the error compensation unit 35 decreases the input value of the DAC by 1 in step S41. If the frequency deviation detected in step S24 is less than the target deviation, the error compensation unit 35 increases the input value of the DAC by 1 in step S41. As a result, the frequency control voltage changes, and the first reference signal output by the first oscillator 11 is adjusted.

[0102] Once step S41 is completed, the radio station 1 finishes the process of compensating for the frequency error of the first reference signal. Thereafter, the radio station 1 repeats the process of compensating for the frequency error of the first reference signal shown in Figure 6 at predetermined time intervals, for example, every second. As a result, the error compensation unit 35 repeatedly compensates for the frequency error of the first reference signal relative to the first target value by a predetermined amount. As a result, it becomes possible to correct the frequency error of the first reference signal output by the first oscillator 11 of the radio station 1 to match the second reference signal.

[0103] In transmission mode, radio station 1 performs a transmission process to transmit a signal to another radio station based on a first reference signal output by a first oscillator 11 or a second reference signal output by a second oscillator 12, which corresponds to the determined transmission channel.

[0104] When the reference signal corresponding to the transmission channel in transmission mode is the first reference signal output by the first oscillator 11, the oscillator switch 25 outputs the first reference signal obtained from the first oscillator 11 to the signal generation unit 26. The signal generation unit 26 generates a transmission modulation signal S2 based on the first reference signal, where the first target value is the target frequency. More specifically, based on the first reference signal, the signal generation unit 26 generates a transmission modulation signal S2, which is a modulation signal in which modulation data generated by mapping the transmission data generated by the input signal processing unit 22 to symbols using the symbol mapper 24 is superimposed on a carrier wave signal whose frequency is the transmission frequency.

[0105] Similarly, when the reference signal corresponding to the transmission channel in transmission mode is the second reference signal output by the second oscillator 12, the oscillator switch 25 outputs the second reference signal obtained from the second oscillator 12 to the signal generation unit 26. The signal generation unit 26 generates a transmission modulation signal S2 based on the second reference signal, where the second target value is the target frequency. More specifically, based on the first reference signal, the signal generation unit 26 generates a transmission modulation signal S2, which is a modulation signal in which modulation data generated by mapping the transmission data generated by the input signal processing unit 22 to symbols using the symbol mapper 24 is superimposed on a carrier wave signal whose frequency is the transmission frequency.

[0106] The target center frequency of the modulated transmission signal S2 is a transmission frequency higher than the first intermediate frequency. The transmission frequency is, for example, a frequency within the range of 360 MHz or higher and 400 MHz or lower. When the reference signal corresponding to the transmission channel is the first reference signal, if the frequency of the first reference signal deviates from the first target value, the center frequency of the modulated transmission signal S2 generated by the signal generation unit 26 will deviate from the target center frequency. Similarly, when the reference signal corresponding to the transmission channel is the second reference signal, if the frequency of the second reference signal deviates from the second target value, the center frequency of the modulated transmission signal S2 generated by the signal generation unit 26 will deviate from the target center frequency.

[0107] Therefore, radio station 1 performs frequency error compensation processing during the transmission adjustment period, which is a predetermined period immediately following the start of the transmission mode. Figure 7 shows the timing at which radio station 1 performs frequency error compensation processing in transmission mode. The transmission signal indicates the reference signal corresponding to the transmission channel. The received-compensated signal is the reference signal corresponding to the previous receiving mode, and indicates the reference signal whose frequency error has been compensated during the receiving period.

[0108] As shown in Figure 7, if the reference signal corresponding to the transmission mode is the same as the reference signal corresponding to the immediately preceding reception mode, the frequency error is compensated during the reception period, and therefore, radio station 1 does not perform frequency error compensation processing during the transmission adjustment period. If the reference signal corresponding to the transmission mode is the first reference signal and the reference signal corresponding to the immediately preceding reception mode is the second reference signal, the frequency error of the first reference signal is compensated during the non-reception period, and therefore, radio station 1 does not perform frequency error compensation processing during the transmission adjustment period.

[0109] If the reference signal corresponding to the transmission channel is the second reference signal, and the reference signal corresponding to the immediately preceding reception mode is the first reference signal, then radio station 1 performs frequency error compensation processing for the second reference signal during the transmission adjustment period. In other words, if a transmission mode in which the reference signal corresponding to the transmission channel is the second reference signal is started after the frequency error of the first reference signal has been compensated in the reception mode, then radio station 1 performs compensation processing 5 to compensate for the frequency error of the second reference signal during the transmission adjustment period.

[0110] [Compensation Processing 5] The compensation process 5 is the same as the compensation process 2 shown in Figure 4. However, in step S25, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 according to the frequency division ratio adjustment amount, when the reference signal corresponding to the transmission channel of the transmission mode is the second reference signal.

[0111] As a result of the above processing, even if the frequency of the second reference signal output by the second oscillator 12 deviates from the second target value, the frequency deviation of the signal output by the signal generation unit 26 based on the second reference signal is suppressed. Specifically, the frequency division ratio of the frequency divider 41 is adjusted when the reference signal corresponding to the transmission channel of the transmission mode is the second reference signal, thereby suppressing the frequency deviation of the transmission modulation signal S2 and the target signal S3. As a result, the center frequency of the transmission modulation signal S2 is maintained at the transmission frequency, and the center frequency of the target signal S3 is maintained at the first intermediate frequency.

[0112] After the above-mentioned transmission adjustment period has elapsed, radio station 1 performs transmission processing based on the first reference signal or the second reference signal.

[0113] The input unit 21 shown in Figure 1 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. The input unit 21 sends the amplified analog audio signal to the input signal processing unit 22.

[0114] The input signal processing unit 22 performs an analog-to-digital (AD) conversion on the amplified analog audio signal, compresses and encodes it, and adds a synchronization word, header, etc., to generate data for transmission. The synchronization word included in the data for transmission is the same as the synchronization data included in the compensation data. The input signal processing unit 22 sends the generated data for transmission to the symbol mapper 24.

[0115] The symbol mapper 24 maps the transmission data generated by the input signal processing unit 22 to symbols and outputs modulation data indicating the mapped symbols to the signal generation unit 26.

[0116] If the reference signal corresponding to the transmission channel in the transmission mode is the first reference signal, the oscillator switch 25 outputs the first reference signal acquired from the first oscillator 11 to the signal generation unit 26.

[0117] The signal generation unit 26 generates a transmission modulated signal S2, which is a modulated signal in which modulation data based on transmission data is superimposed on a carrier wave signal whose frequency is the transmission frequency, based on a first reference signal acquired from the oscillator switch 25, and outputs it to the signal switch 27. Since the frequency error of the first reference signal is compensated during the reception or non-reception period of the immediately preceding reception mode, the center frequency of the transmission modulated signal S2 is maintained at the transmission frequency.

[0118] The signal switch 27 sends the modulated signal S2 for transmission, output from the signal generation unit 26, to the transmission unit 28.

[0119] The transmitting unit 28 amplifies the modulated signal S2 for transmission to a desired level suitable for transmission, reduces unwanted signals such as harmonics to generate a transmission signal, and transmits the transmission signal to other radio stations via the transmit / receive switching unit 29 and the antenna 30.

[0120] When the reference signal corresponding to the transmission channel in transmission mode is the second reference signal, the operation of radio station 1 is the same as the transmission process based on the first reference signal described above. However, the oscillator switch 25 outputs the second reference signal obtained from the second oscillator 12 to the signal generation unit 26, and the signal generation unit 26 generates a transmission modulated signal S2 by superimposing modulation data on the carrier signal based on the second reference signal and outputs it to the signal switch 27. Since the frequency error of the second reference signal is compensated during the reception period of the immediately preceding reception mode or the transmission adjustment period of the transmission mode, the center frequency of the transmission modulated signal S2 is maintained at the transmission frequency.

[0121] As described above, the error compensation unit 35 in the radio station 1 according to Embodiment 1 compensates for the frequency error of the first reference signal or the second reference signal with respect to the target signal, according to the frequency deviation between the first reference signal or the second reference signal detected based on the demodulated signal generated from the received signal and the target signal. This compensates for the frequency error of the reference signal used in the reception processing.

[0122] With the frequency error of the first reference signal used for reception processing compensated, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 of the signal generation unit 26 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, even if the frequency of the second reference signal deviates from the second target value, the frequency error of the second reference signal is compensated by adjusting the frequency division ratio of the frequency divider 41 of the signal generation unit 26 according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

[0123] With the frequency error of the second reference signal used for reception processing compensated, the error compensation unit 35 corrects the frequency error of the first reference signal 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, even if the frequency of the first reference signal deviates from the first target value, the frequency error of the first reference signal is compensated according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

[0124] As described above, radio station 1 compensates for the frequency error of the first reference signal relative to the first target value or the frequency error of the second reference signal relative 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. Therefore, even if signals cannot be received from other radio stations, it is possible to compensate for variations in the frequency accuracy of each oscillator in radio station 1.

[0125] According to the radio station 1, in both the process of compensating for the frequency error of the first reference signal and the process of compensating for 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 to detect the frequency deviation in order to compensate for the frequency errors of the first reference signal and the second reference signal, and the complexity of the structure of the radio station 1 is suppressed.

[0126] (Embodiment 2) The method for compensating for the frequency error of the first reference signal with respect to the first target value and the frequency error of the second reference signal with respect to the second target value is not limited to the examples described above. The radio station 2 according to Embodiment 2 differs from the radio station 1 according to Embodiment 1 in that it compensates for the frequency error of the first reference signal or the second reference signal using a target signal which is an unmodulated signal.

[0127] The radio station 2 according to Embodiment 2 shown in Figure 8 has the same configuration as radio station 1, but differs from radio station 1 in that the data output unit 23 outputs only conversion data, the signal generation unit 26 generates a target signal S4 which is an unmodulated signal in place of the target signal S3, the signal switch 27 outputs the conversion signal S1, the transmission modulated signal S2, or the target signal S4 acquired from the signal generation unit 26 by switching the output destination, the FM detection unit 46 outputs the demodulated signal to the synchronization word detection unit 47 and the deviation calculation unit 48, and the deviation calculation unit 48 calculates the frequency deviation from the demodulated signal. The conversion data is data used to generate an unmodulated signal used for frequency conversion, and is, for example, data consisting of consecutive zeros.

[0128] The timing at which radio station 2 performs frequency error compensation processing in reception mode is the same as in Embodiment 1. The operation of radio station 2 during the reception period is the same as the operation of radio station 1 in Embodiment 1 shown in Figures 3 and 5. However, in steps S15 and S32, the deviation calculation unit 48 calculates the frequency deviation from the DC offset of the demodulated signal acquired from the FM detection unit 46. It is preferable that the deviation calculation unit 48 outputs the moving average value of the frequency deviation as the frequency deviation.

[0129] When the reference signal corresponding to the receiving channel of the receiving mode is the second reference signal, during the receiving adjustment period, the radio station 2 performs compensation processing 2, specifically, the frequency error compensation processing of the second reference signal shown in Figure 9. The oscillator switch 25 outputs the second reference signal acquired from the second oscillator 12 to the signal generation unit 26. Based on the second reference signal acquired from the second oscillator 12 via the oscillator switch 25, the signal generation unit 26 generates a target signal S4, which is an unmodulated signal on which conversion data output from the data output unit 23 indicating that the frequency deviation is 0 is superimposed on a carrier signal whose frequency is the first intermediate frequency (step S51). The signal generation unit 26 outputs the generated target signal S4 to the signal switch 27.

[0130] The signal switch 27 sends the target signal S4 generated in step S51 to the signal switch 32. The signal switch 32 receives the target signal S4 generated in step S51 from the signal switch 27 and sends the target signal S4 to the demodulation unit 33.

[0131] The mixer 44 in the demodulation unit 33 multiplies the first reference signal and the target signal S4 generated in step S51, which is supplied via the signal switches 27 and 32, to generate a second intermediate frequency signal (step S52). Specifically, the mixer 44 generates 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, and outputs the generated second intermediate frequency signal to the AD converter 45.

[0132] The processes from steps S23 to S25, which are performed after the completion of step S52, are the same as the processes from steps S23 to S25 shown in Figure 4. Once the process of step S25 is completed, radio station 2 finishes the process of compensating for the frequency error of the second reference signal.

[0133] As a result of the above processing, even if the frequency of the second reference signal output by the second oscillator 12 deviates from the second target value, the frequency deviation of the signal output by the signal generation unit 26 based on the second reference signal is suppressed. Specifically, the frequency division ratio of the frequency divider 41 is adjusted when the reference signal corresponding to the receiving channel of the receiving mode is the second reference signal, thereby suppressing the frequency deviation of the conversion signal S1 and the target signal S4 based on the second reference signal. As a result, the center frequency of the conversion signal S1 is maintained at a frequency lower than the receiving frequency by the first intermediate frequency, and the center frequency of the target signal S4 is maintained at the first intermediate frequency.

[0134] When the reference signal corresponding to the receiving channel in the receiving mode is the second reference signal, during the non-receiving period, the radio station 2 performs compensation processing 4, specifically, the frequency error compensation processing of the first reference signal shown in Figure 10. The processing in steps S51 and S52 is the same as the processing in steps S51 and S52 shown in Figure 9. The processing in steps S23 and S24 is the same as the processing in steps S23 and S24 shown in Figure 4. The processing in step S41 is the same as the processing in step S41 shown in Figure 6. Once the processing in step S41 is completed, the radio station 2 terminates the processing of compensating for the frequency error of the first reference signal. After that, the radio station 2 repeats the processing of compensating for the frequency error of the first reference signal shown in Figure 10 at predetermined time intervals, for example, every second. As a result, it becomes possible to correct the frequency error of the first reference signal output by the first oscillator 11 of the radio station 2 to match the second reference signal.

[0135] The timing at which radio station 2 performs frequency error compensation processing in transmission mode is the same as in Embodiment 1. If the reference signal corresponding to the transmission channel in transmission mode is the second reference signal, and the reference signal corresponding to the immediately preceding reception mode is the first reference signal, then radio station 2 performs compensation processing 5, specifically, compensation processing for the frequency error of the second reference signal, during the transmission adjustment period.

[0136] The compensation process 5 is the same as the compensation process 2 shown in Figure 9. However, in step S25, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 when the reference signal corresponding to the transmission channel of the transmission mode is the second reference signal, according to the frequency division ratio adjustment amount.

[0137] As described above, the error compensation unit 35 in the radio station 2 according to Embodiment 2 compensates for the frequency error of the first reference signal or the second reference signal with respect to the target signal, according to the frequency deviation between the first reference signal or the second reference signal detected based on the demodulated signal generated from the received signal and the target signal. This compensates for the frequency error of the reference signal used in the reception processing.

[0138] With the frequency error of the first reference signal used for reception processing compensated, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 of the signal generation unit 26 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 S4 based on the second reference signal from the target deviation. As a result, even if the frequency of the second reference signal deviates from the second target value, the frequency error of the second reference signal is compensated by adjusting the frequency division ratio of the frequency divider 41 of the signal generation unit 26 according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

[0139] With the frequency error of the second reference signal used for reception processing compensated, the error compensation unit 35 corrects the frequency error of the first reference signal 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 S4 based on the second reference signal, from the target deviation. As a result, even if the frequency of the first reference signal deviates from the first target value, the frequency error of the first reference signal is compensated according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

[0140] As described above, radio station 2 compensates for the frequency error of the first reference signal relative to the first target value or the frequency error of the second reference signal relative 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. Therefore, even if signals cannot be received from other radio stations, it is possible to compensate for variations in the frequency accuracy of each oscillator in radio station 2.

[0141] Since radio station 2 calculates the frequency deviation between the first reference signal and the second reference signal based on the demodulated signal output by the FM detection unit 46, it does not need to wait for the synchronization word detection process to be completed. Therefore, radio station 2 can perform the frequency deviation calculation process quickly.

[0142] (Embodiment 3) The number of second oscillators in radio stations 1 and 2 is arbitrary. As an example, radio station 3, which has a second oscillator 49 in addition to the configuration of radio station 1, is shown in Figure 11. Radio station 3 has one first oscillator 11 and two second oscillators 12 and 49.

[0143] The oscillator switch 25 is connected to the first oscillator 11 and the second oscillators 12 and 49, and switches between the first oscillator 11 and the second oscillators 12 and 49 to output the first reference signal obtained from the first oscillator 11, the second reference signal obtained from the second oscillator 12, or the second reference signal obtained from the second oscillator 49 to the signal generation unit 26.

[0144] In receiving mode, radio station 3 performs reception processing to receive signals from other radio stations using the first reference signal output by the first oscillator 11, the second reference signal output by the second oscillator 12, or the second reference signal output by the second oscillator 49.

[0145] The operation of the radio station 3's reception processing when the reference signal corresponding to the receiving channel is the first reference signal output by the first oscillator 11 or the second reference signal output by the second oscillator 12 is the same as the operation of the radio station 1 according to Embodiment 1. The operation of the radio station 3's reception processing when the reference signal corresponding to the receiving channel is the second reference signal output by the second oscillator 49 is the same as the operation of the radio station 1's reception processing when the reference signal corresponding to the receiving channel is the second reference signal output by the second oscillator 12. However, the signal generation unit 26 generates a conversion signal S1 based on the second reference signal output by the second oscillator 49 and outputs it to the signal switch 27.

[0146] To compensate for variations in the frequency accuracy of each oscillator in radio station 3, specifically the frequency accuracy of the first oscillator 11 and the second oscillators 12 and 49, radio station 3 compensates for the frequency error of at least one of the first reference signal output by the first oscillator 11, the second reference signal output by the second oscillator 12, and the second reference signal output by the second oscillator 49. The timing of when radio station 3 performs frequency error compensation processing in receive mode is shown in Figure 12. The way to read the figure is the same as in Figure 2. In Figure 12, the first reference signal output by the first oscillator 11 is represented by REF1, the second reference signal output by the second oscillator 12 is represented by REF2, and the second reference signal output by the second oscillator 49 is represented by REF3. The same applies to the following figures.

[0147] When the reference signal corresponding to the receiving channel is either the first reference signal output by the first oscillator 11 or the second reference signal output by the second oscillator 12, the operation of the frequency error compensation process performed by the radio station 3, specifically the operation of compensation process 1-4, is the same as the operation of the radio station 1 according to Embodiment 1.

[0148] The operation of the frequency error compensation processing performed by radio station 3 when the reference signal corresponding to the receiving channel is the second reference signal output by the second oscillator 49 is the same as the operation of radio station 1 when the reference signal corresponding to the receiving channel is the second reference signal output by the second oscillator 12. However, in step S21 shown in Figures 4 and 6 and step S31 shown in Figure 5, the signal generation unit 26 generates a signal based on the second reference signal output by the second oscillator 49. In step S25 shown in Figure 4 and step S33 shown in Figure 5, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 when the reference signal corresponding to the receiving channel of the receiving mode is the second reference signal output by the second oscillator 49.

[0149] In transmission mode, radio station 3 performs transmission processing to transmit a signal to another radio station using the first reference signal output by the first oscillator 11, the second reference signal output by the second oscillator 12, or the second reference signal output by the second oscillator 49. The timing of when radio station 3 performs frequency error compensation processing in transmission mode is shown in Figure 13. The interpretation of the figure is the same as in Figure 3. In transmission mode, radio station 3 performs frequency error compensation during the transmission adjustment period, which is the period immediately after the start of transmission mode.

[0150] When the reference signal corresponding to the transmission channel is the first reference signal output by the first oscillator 11, the operation of the radio station 3 is the same as the operation of the radio station 1 according to Embodiment 1.

[0151] When the reference signal corresponding to the transmission channel is the second reference signal output by the second oscillator 12, and the frequency error of the first reference signal or the second reference signal output by the second oscillator 12 is compensated in the immediately preceding reception mode, the operation of the radio station 3 is the same as the operation of the radio station 1 according to Embodiment 1.

[0152] When the reference signal corresponding to the transmission channel is the second reference signal output by the second oscillator 12, and the frequency error of the second reference signal output by the second oscillator 49 in the previous reception mode is compensated, the radio station 3 performs compensation processing 5, which is the same as the processing shown in Figure 4. However, in step S25, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 when the reference signal corresponding to the transmission channel is the second reference signal output by the second oscillator 12.

[0153] When the reference signal corresponding to the transmission channel is the second reference signal output by the second oscillator 49, and the frequency error of the first reference signal output by the first oscillator 11 or the second reference signal output by the second oscillator 12 in the previous receiving mode is compensated, the radio station 3 performs compensation processing 5, which is the same as the processing shown in Figure 4. However, in step S25, the error compensation unit 35 adjusts the division ratio of the frequency divider 41 when the reference signal corresponding to the transmission channel in the transmission mode is the second reference signal output by the second oscillator 49. When the reference signal corresponding to the transmission channel is the second reference signal output by the second oscillator 49, and the frequency error of the second reference signal output by the second oscillator 49 in the previous receiving mode is compensated, the radio station 3 does not perform frequency error compensation processing during the transmission adjustment period.

[0154] As described above, the error compensation unit 35 of the radio station 3 according to Embodiment 3 compensates for the frequency error of either the first reference signal output by the first oscillator 11 or the second reference signal output by the second oscillators 12, 49 with respect to the target signal, according to the frequency deviation between the target signal and either the first reference signal output by the first oscillator 11 or the second reference signal output by the second oscillators 12, 49, which are detected based on the demodulated signal generated from the received signal. This compensates for the frequency error of the reference signal used in the reception processing.

[0155] With the frequency error of the first reference signal used for reception processing compensated, the error compensation unit 35 adjusts the frequency division ratio of the frequency divider 41 of the signal generation unit 26 according to the deviation of the frequency deviation between the first reference signal and the second reference signal output by the second oscillator 12 or the second oscillator 49 from the target deviation. As a result, even if the frequency of the second reference signal output by the second oscillator 12 or the second oscillator 49 deviates from the second target value, the frequency error of the second reference signal is compensated by adjusting the frequency division ratio of the frequency divider 41 of the signal generation unit 26 according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

[0156] With the frequency error of the second reference signal output by the second oscillator 12 or second oscillator 49 used for reception processing compensated, the error compensation unit 35 corrects the frequency error of the first reference signal 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, even if the frequency of the first reference signal deviates from the first target value, the frequency error of the first reference signal is compensated according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation.

[0157] As described above, radio station 3 compensates for the frequency error of the first reference signal relative to the first target value or the frequency error of the second reference signal output by the second oscillator 12 or second oscillator 49 relative to the second target value, according to the deviation of the frequency deviation of the first reference signal and the second reference signal output by the second oscillator 12 or second oscillator 49 from the target deviation. Therefore, even if signals cannot be received from other radio stations, it is possible to compensate for variations in the frequency accuracy of each oscillator in radio station 3.

[0158] According to the radio station 3, in both the process of compensating for the frequency error of the first reference signal and the process of compensating for 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 to detect the frequency deviation in order to compensate for the frequency errors of the first reference signal and the second reference signal, and the complexity of the structure of the radio station 3 is suppressed.

[0159] The present invention is not limited to the embodiments described above. The method for correcting the frequency error of the first reference signal is not limited to the examples described above. For example, radio station 1-3 may compensate for the frequency error of the first reference signal or the second reference signal based on a received signal received from another radio station communicating with the base station, the radio station having its oscillator frequency error corrected. As another example, radio station 1-3 may be equipped with a frequency counter that is calibrated according to an externally supplied signal, such as a PPS (Pulse Per Second) signal, and compensate for the frequency error of the first reference signal or the second reference signal according to the actual frequency of the first reference signal or the second reference signal obtained by the frequency counter.

[0160] The method for compensating for the frequency error of the first reference signal is not limited to the example described above. Radio stations 1-3 may also include a frequency adjustment unit 60 as shown in Figure 14. The frequency adjustment unit 60 has the same configuration as the signal generation unit 26 and includes a phase comparator 61, a loop filter 62, a VCO 63, and a frequency divider 64.

[0161] The phase comparator 61 outputs a phase difference signal to the loop filter 62, which is a signal corresponding to the phase difference between the first reference signal output by the first oscillator 11 and the signal output from the VCO 63 and divided by the frequency divider 64. The loop filter 62 converts the phase difference signal output by the phase comparator 61 into a current, integrates and smooths the current to convert it into a voltage, and outputs this voltage as a control voltage to the VCO 63. The oscillation frequency of the VCO 63 changes according to the output of the loop filter 62. The signal output by the VCO 63 is supplied to the demodulation unit 33 and the oscillator switch 25. The frequency divider 64 divides the output of the VCO 63 according to a predetermined division ratio and outputs the divided signal to the phase comparator 61.

[0162] When radio stations 1-3 are equipped with a frequency adjustment unit 60, the error compensation unit 35 adjusts the division ratio of the frequency divider 64 to reduce the frequency deviation between the first reference signal and the target signal. The error compensation unit 35 adjusts the division ratio of the frequency divider 64 to reduce the deviation of the frequency deviations of the first reference signal and the second reference signal from the target deviation. This compensates for the frequency error of the first reference signal.

[0163] As described above, when the frequency error of the first reference signal is compensated by adjusting the frequency division ratio of the frequency divider 64, the first oscillator 11 may be formed as an oscillator that does not have a function to adjust the output frequency by a frequency control voltage, for example, an SPXO.

[0164] In the above-described embodiment, the VCO 40 is capable of oscillating across a frequency band including the range of 360 MHz or more and 400 MHz or less, which includes the transmission frequency, and the range of 310.05 MHz or more and 350.05 MHz or less, which includes a frequency that is only one intermediate frequency lower than the reception frequency, as well as a frequency band including the intermediate frequency band of 49.95 MHz. However, radio stations 1-3 may be equipped with a VCO capable of oscillating in the operating frequency band and a VCO capable of oscillating in the intermediate frequency band.

[0165] 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 3, 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.

[0166] In radio stations 1-3, the input signal processing unit 22, data output unit 23, symbol mapper 24, error compensation unit 35, output signal processing unit 36, FM detection unit 46, synchronization word detection unit 47, and deviation calculation unit 48 may be implemented using a DSP (Digital Signal Processor), the signal generation unit 26 may be implemented using a PLL IC (Integrated Circuit) with a built-in VCO, and the mixer 44 and AD converter 45 may be implemented using an IF (Intermediate Frequency) detection IC.

[0167] The modulation scheme of radio stations 1-3 is not limited to quadrigrade FSK; any scheme is acceptable as long as the frequency deviation can be detected from the demodulated signal. For example, radio stations 1-3 may use binary FSK or multi-level FSK other than quadrigrade FSK. As another example, radio stations 1-3 may use PSK (Phase Shift Keying), such as π / 4DQPSK (Differential Quadrature Phase Shift Keying), or QAM (Quadrature Amplitude Modulation).

[0168] Radio station 2 may be equipped with multiple second oscillators. In this case, the timing at which radio station 2 performs frequency error compensation processing is the same as that for radio station 3.

[0169] Furthermore, the hardware configuration and flowchart described above are examples only and can be changed and modified as needed. [Explanation of Symbols]

[0170] 1,2,3 Radio Stations 11. First Oscillator 12. Second Oscillator 21 Input section 22 Input Signal Processing Unit 23 Data Output Section 24 Symbol Mappa 25 Oscillator Switcher 26 Signal generation unit 27,32 Signal Switcher 28 Transmitter 29 Transmit / receive switching section 30 Antennas 31 Receiver 33 Demodulation Unit 34. Deviation detection unit 35 Error compensation section 36 Output signal processing unit 37 Output section 38,61 Phase comparator 39,62 Loop Filter 40,63 VCO 41,64 frequency divider 42 Amplifiers 43,44 Mixer 45 AD converters 46 FM detection section 47 Synchronized word detection unit 48. Deviation Calculation Section 49 Second Oscillator 50 Controllers 51 CPU 52 I / O 53 RAM 54 ROM 60 Frequency adjustment section S1 Conversion signal S2 Modulated signal for transmission S3, S4 Target Signals

Claims

1. A first oscillator that outputs a first reference signal whose first target value is the target frequency, A 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, A signal generation unit that generates a target signal whose first intermediate frequency is the target frequency based on the second reference signal, A demodulation unit generates a demodulated signal by frequency-converting the target signal using the first reference signal to produce a second intermediate frequency signal whose frequency is lower than the first intermediate frequency, and demodulating the second intermediate frequency signal. A deviation detection unit detects the frequency deviation between the first reference signal and the second reference signal based on the demodulated signal, An error compensation unit that compensates for the frequency error of the first reference signal with respect to the first target value in accordance with the deviation of the frequency deviation of the first reference signal and the second reference signal from the target deviation, A radio station equipped with the necessary equipment.

2. The error compensation unit repeatedly compensates the frequency error of the first reference signal with respect to the first target value by a predetermined amount, according to the deviation of the frequency deviation of the first reference signal and the second reference signal from the target deviation. The radio station according to claim 1.

3. In a receiving mode for receiving signals from other radio stations, a receiving period for receiving the signal and a non-receiving period for stopping the reception of the signal are repeated. The error compensation unit compensates for the frequency error of the first reference signal with respect to the first target value in accordance with the deviation of the frequency deviation of the first reference signal and the second reference signal from the target deviation during the non-reception period. A radio station according to claim 1 or 2.

4. After the reception adjustment period immediately following the start of the reception mode, the reception period and the non-reception period are repeated. The error compensation unit compensates for the frequency error of the second reference signal with respect to the second target value during the reception adjustment period, in accordance with the deviation of the frequency deviation of the first reference signal and the second reference signal from the target deviation. The radio station according to claim 3.

5. The signal generation unit generates the target signal during the reception adjustment period and the non-reception period, and generates a conversion signal which is an unmodulated signal based on the first reference signal or the second reference signal during the reception period. The device further includes a receiving unit that receives a signal generated by modulating a target signal whose frequency matches the first target value or the second target value, and generates a first intermediate frequency signal whose first intermediate frequency is the target frequency by performing frequency conversion based on the received signal using the first reference signal or the conversion signal based on the second reference signal whose frequency is the target frequency, wherein the first intermediate frequency is the target frequency. The demodulation unit generates the second intermediate frequency signal based on the target signal or the first intermediate frequency signal, and generates the demodulated signal by demodulating the second intermediate frequency signal. The deviation detection unit detects the 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, and detects the frequency deviation between the first reference signal or the second reference signal used in the frequency conversion for generating the first intermediate frequency signal used in generating the demodulated signal and the target signal based on the demodulated signal. The error compensation unit, when the first reference signal is used in the frequency conversion for generating the first intermediate frequency signal, compensates for the 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 during the reception period, and when the second reference signal is used in the frequency conversion for generating the first intermediate frequency signal, compensates for the frequency error of the second reference signal with respect to the target signal in accordance with the frequency deviation between the second reference signal and the target signal during the reception period. The radio station according to claim 4.

6. The error compensation unit, when the first reference signal is used in the frequency conversion for generating the first intermediate frequency signal, repeatedly compensates for the frequency error of the first reference signal with respect to the target signal by a predetermined amount in accordance with the frequency deviation between the first reference signal and the target signal during the reception period, and when the second reference signal is used in the frequency conversion for generating the first intermediate frequency signal, repeatedly compensates for the frequency error of the second reference signal with respect to the target signal by a predetermined amount in accordance with the frequency deviation between the second reference signal and the target signal during the reception period. The radio station according to claim 5.

7. The error compensation unit compensates for the frequency error of the second reference signal with respect to the target signal during the reception period, according to the frequency deviation between the second reference signal and the target signal, and then compensates for the frequency error of the first reference signal with respect to the first target value during the non-reception period immediately following the reception period, according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation. The radio station according to claim 5.

8. When, after the frequency error of the first reference signal with respect to the target signal has been compensated during the reception period of the reception mode, a transmission mode is started in which a signal based on the second reference signal is transmitted to another radio station, during the transmission adjustment period immediately following the start of the transmission mode, The demodulation unit generates the demodulated signal based on the target signal, The deviation detection unit detects the frequency deviation between the first reference signal and the second reference signal based on the demodulated signal. The error compensation unit compensates for 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. The radio station according to claim 5.

9. The system comprises a plurality of second oscillators that output second reference signals with second target values ​​that are different from each other, During the reception period of the reception mode, after the frequency error of the second reference signal output by one of the second oscillators with respect to the target signal has been compensated, a transmission mode is started in which a signal based on the second reference signal output by the other second oscillator is transmitted to another radio station, during the transmission adjustment period immediately following the start of the transmission mode, The demodulation unit generates the demodulated signal based on the target signal which is based on the second reference signal output by the other second oscillator. The error compensation unit compensates for the frequency error of the second reference signal output by the other second oscillator relative to the second target value, in accordance with the deviation of the frequency deviation between the first reference signal and the second reference signal output by the other second oscillator from the target deviation. The radio station according to claim 5.

10. The system further comprises a frequency adjustment unit that adjusts the frequency of the first reference signal output by the first oscillator, The error compensation unit compensates for the frequency error of the first reference signal with respect to the first target value by controlling the frequency adjustment unit to adjust the frequency of the first reference signal in accordance with the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation. A radio station according to claim 1 or 2.

11. The frequency adjustment unit includes a voltage-controlled oscillator that oscillates at an oscillation frequency corresponding to a control voltage, a frequency divider that divides the output of the voltage-controlled oscillator by a frequency division ratio, a phase comparator that outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider and the first reference signal output by the first oscillator, and a loop filter that converts the phase difference signal into a voltage and outputs the voltage to the voltage-controlled oscillator. The error compensation unit compensates for the frequency error of the first reference signal with respect to the first target value by adjusting the frequency division ratio of the frequency divider in the frequency adjustment unit in accordance with the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation. The radio station according to claim 10.

12. The system further comprises a frequency adjustment unit that adjusts the frequency of the first reference signal output by the first oscillator, The error compensation unit compensates for the frequency error of the first reference signal with respect to the target signal by controlling the frequency adjustment unit to adjust the frequency of the first reference signal according to the frequency deviation between the first reference signal and the target signal. The radio station according to claim 5.

13. The frequency adjustment unit includes a voltage-controlled oscillator that oscillates at an oscillation frequency corresponding to a control voltage, a frequency divider that divides the output of the voltage-controlled oscillator by a frequency division ratio, a phase comparator that outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider and the first reference signal output by the first oscillator, and a loop filter that converts the phase difference signal into a voltage and outputs the voltage to the voltage-controlled oscillator. The error compensation unit compensates for the frequency error of the first reference signal with respect to the target signal by adjusting the frequency division ratio of the frequency divider in the frequency adjustment unit according to the frequency deviation between the first reference signal and the target signal. The radio station according to claim 12.

14. The signal generation unit includes a voltage-controlled oscillator that oscillates at an oscillation frequency corresponding to a control voltage, a frequency divider that divides the output of the voltage-controlled oscillator by a frequency division ratio, a phase comparator that outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider and the first reference signal or the second reference signal, and a loop filter that converts the phase difference signal into a voltage and outputs the voltage to the voltage-controlled oscillator. The error compensation unit compensates for the frequency error of the second reference signal with respect to the second target value by adjusting the division ratio of the frequency divider when the phase comparator outputs the phase difference signal based on the phase difference between the signal divided by the frequency divider and the second reference signal, in accordance with the deviation of the frequency deviation of the first reference signal and the second reference signal from the target deviation. The radio station according to claim 4.

15. The signal generation unit includes a voltage-controlled oscillator that oscillates at an oscillation frequency corresponding to a control voltage, a frequency divider that divides the output of the voltage-controlled oscillator by a frequency division ratio, a phase comparator that outputs a phase difference signal based on the phase difference between the signal divided by the frequency divider and the first reference signal or the second reference signal, and a loop filter that converts the phase difference signal into a voltage and outputs the voltage to the voltage-controlled oscillator. The error compensation unit compensates for the frequency error of the second reference signal with respect to the target signal by adjusting the division ratio of the frequency divider when the phase comparator outputs the phase difference signal based on the phase difference between the signal divided by the frequency divider and the second reference signal, according to the frequency deviation between the second reference signal and the target signal. The radio station according to claim 5.

16. The signal generation unit generates the target signal, which is a modulated signal, by performing modulation based on the input target data and the second reference signal. A radio station according to claim 1 or 2.

17. The signal generation unit generates the target signal, which is an unmodulated signal based on the second reference signal. A radio station according to claim 1 or 2.

18. A frequency error compensation method performed by a radio station comprising: 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, obtained by adding a target deviation to the first target value, is a target frequency; Based on the second reference signal, a target signal is generated whose first intermediate frequency is the target frequency. Based on the target signal, a second intermediate frequency signal is generated by frequency conversion using the first reference signal, the second intermediate frequency signal having a frequency lower than the first intermediate frequency, and a demodulated signal is generated by demodulating the second intermediate frequency signal. Based on the demodulated signal, the frequency difference between the first reference signal and the second reference signal is detected. The frequency error of the first reference signal with respect to the first target value is compensated according to the deviation of the frequency deviation between the first reference signal and the second reference signal from the target deviation. Frequency error compensation method.

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