Direct conversion radio receiver and control method thereof

Abstract

To stably receive a signal by a direct conversion type radio receiver.SOLUTION: A radio receiver (10) includes a local oscillator (4) for generating a local oscillation signal (So), a direct conversion part (1) for performing frequency conversion by mixing a radio frequency signal (RF) in which a tone signal is superposed and the local oscillation signal (So), an FM detector part (2) for detecting a center frequency of the radio frequency signal (RF), and an AFC control part (73) for controlling the frequency of the local oscillation signal (So). The AFC control part (73) controls the local oscillator (4) so that the frequency of the local oscillation signal (So) matches the center frequency detected by the FM detector part (2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a direct conversion radio receiver and the like. [Background technology]

[0002] In a direct conversion radio receiver, demodulation is performed by mixing the received signal with a signal generated by a local oscillator inside the receiver, which has a frequency (received frequency) very close to the frequency of the received signal. However, if the frequency of the received signal and the frequency of the local oscillator completely match, demodulation becomes impossible. For this reason, it is known that the frequency of the signal generated by the local oscillator inside the receiver is usually set to be different from the frequency of the received signal, as described in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5292061 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a direct conversion receiver receives a signal that includes (superimposes) a low-frequency binary FSK signal, such as a tone signal used in DCS (Digital Coded Squelch), the following problem occurs.

[0005] When receiving a signal containing a binary FSK signal using a direct conversion system, the receiving frequency is controlled by AFC (Automatic Frequency Control) to target a frequency shifted by several tens to 200 Hz from the center frequency (carrier frequency) of the received signal. If the FSK signal contained in the received signal has a low frequency, such as a tone signal, and contains successive "1s" or "0s," the center frequency of the binary FSK signal cannot be accurately detected by AFC. Therefore, the receiving frequency may be shifted higher or lower than the target frequency. In such a case, if a portion of the frequency of the modulated wave of the received FSK signal (e.g., the modulation frequency of "1") coincides with the frequency of the local oscillator and falls within a region that cannot be decoded, the portion of the modulated wave cannot be properly received.

[0006] An object of one aspect of the present invention is to provide a direct conversion wireless receiver that stably receives signals. [Means for solving the problem]

[0007] In order to solve the above problems, a direct conversion radio receiver according to one embodiment of the present invention includes a local oscillator that generates a local oscillation signal, a frequency conversion unit that mixes a radio frequency signal having a tone signal superimposed thereon with the local oscillation signal to perform frequency conversion, a frequency detection unit that detects the center frequency of the radio frequency signal, and a control unit that controls the frequency of the local oscillation signal, wherein the control unit controls the local oscillator to match the frequency of the local oscillator to the center frequency detected by the frequency detection unit.

[0008] In order to solve the above-mentioned problems, one aspect of the present invention provides a control method for a direct conversion radio receiver including a local oscillator that generates a local oscillation signal, a frequency conversion unit that mixes a radio frequency signal on which a tone signal is superimposed with the local oscillation signal to perform frequency conversion, and a frequency detection unit that detects the center frequency of the radio frequency signal, and includes controlling the local oscillator to match the frequency of the local oscillation signal to the center frequency detected by the frequency detection unit.

[0009] According to the above configuration, when a radio frequency signal on which a tone signal is superimposed is received, the local oscillation signal is tuned to the center frequency of the detected radio frequency signal, thereby enabling stable reception of the radio frequency signal.

[0010] In order to solve the above problems, a direct conversion radio receiver according to one aspect of the present invention includes a local oscillator that generates a local oscillation signal, a frequency conversion unit that mixes a radio frequency signal with the local oscillation signal to perform frequency conversion, a frequency detection unit that detects the center frequency of the radio frequency signal, a control unit that controls the frequency of the local oscillation signal, and a memory unit that stores received signal information that indicates whether a tone signal is superimposed on the received radio frequency signal, and the control unit controls the local oscillator to match the frequency of the local oscillation signal to the center frequency of the radio frequency signal based on the received signal information if the tone signal is superimposed on the radio frequency signal, and controls the local oscillator to shift the frequency of the local oscillation signal from the center frequency of the radio frequency signal if the tone signal is not superimposed on the radio frequency signal.

[0011] In order to solve the above-mentioned problems, one aspect of the present invention provides a control method for a direct conversion radio receiver including a local oscillator that generates a local oscillation signal, a frequency conversion unit that mixes a radio frequency signal with the local oscillation signal to perform frequency conversion, and a frequency detection unit that detects the center frequency of the radio frequency signal, the control method including: based on received signal information indicating whether the tone signal is superimposed on the received radio frequency signal, controlling the local oscillator to match the frequency of the local oscillation signal to the center frequency of the radio frequency signal if the tone signal is superimposed on the radio frequency signal, and controlling the local oscillator to shift the frequency of the local oscillation signal from the center frequency of the radio frequency signal if the tone signal is not superimposed on the radio frequency signal.

[0012] According to the above configuration, when a radio frequency signal having a tone signal superimposed thereon is received, the local oscillator signal is tuned to the center frequency of the radio frequency signal. On the other hand, when a radio frequency signal having no tone signal superimposed thereon is received, the local oscillator signal is shifted from the center frequency of the radio frequency signal. Therefore, the radio frequency signal can be received stably regardless of whether a tone signal is superimposed thereon or not. [Effects of the Invention]

[0013] According to one aspect of the present invention, a direct conversion wireless receiver can stably receive signals. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing the configuration of a main part of a wireless receiver according to an embodiment of the present invention; [Figure 2] 5 is a flowchart showing a procedure for setting a reception frequency by the wireless receiver. [Figure 3] FIG. 2 is a diagram illustrating an example of setting a reception frequency for a DCS modulated signal by the wireless receiver. [Figure 4]10 is a diagram illustrating another example of setting of a receiving frequency for a DCS modulated signal by the wireless receiver. FIG. [Figure 5] FIG. 10 is a diagram illustrating an example of setting a reception frequency for a DCS modulated signal by a wireless receiver of a comparative example. [Figure 6] 10 is a diagram illustrating another example of setting of a reception frequency for a DCS modulated signal by the wireless receiver of the comparative example. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Embodiment] Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS.

[0016] <Wireless receiver configuration> FIG. 1 is a block diagram showing the configuration of the main parts of a wireless receiver 10 according to one embodiment of the present invention.

[0017] 1, the wireless receiver 10 is a direct conversion type wireless receiver. The wireless receiver 10 includes a direct conversion unit 1 (frequency conversion unit), an FM detection unit 2 (frequency detection unit), a noise detection unit 3, a local oscillator 4, a storage device 5 (storage unit), an operation unit 6, and a control device 7.

[0018] The direct conversion unit 1 mixes (multiplies) the received radio frequency signal RF with the local oscillation signal So to convert the intermediate frequency signal to an intermediate frequency signal IF (converted signal) with a frequency of 0 Hz. To this end, the direct conversion unit 1 includes a 90-degree phase shifter, a first mixer, a second mixer, two low-pass filters, and two AD converters (not shown). The radio frequency signal RF may or may not have a tone signal superimposed thereon.

[0019] The 90-degree phase shifter outputs a 0-degree oscillation signal with a phase difference of 0 degrees and a 90-degree oscillation signal with a phase difference of 90 degrees based on the local oscillation signal So. The first mixer frequency-converts the radio frequency signal RF to an I signal by mixing it with the 0-degree oscillation signal. The second mixer frequency-converts the radio frequency signal RF to a Q signal by mixing it with the 90-degree oscillation signal. Two low-pass filters remove unnecessary frequency components from the I signal and Q signal, respectively, and output the signals. Two AD converters digitally convert the signals output from the two low-pass filters, outputting an I-channel intermediate frequency signal IF and a Q-channel intermediate frequency signal IF.

[0020] The FM detector 2 performs demodulation based on the two intermediate frequency signals IF, and outputs a low-frequency demodulated signal AF. The FM detector 2 also detects the center frequencies of the two intermediate frequency signals IF, and outputs center frequency information Fc to the AFC control unit 73 of the control device 7. The FM detector 2 performs signal processing digitally, and is therefore configured, for example, by a DSP (Digital Signal Processor).

[0021] The noise detector 3 detects noise components present in the demodulated signal AF and outputs the detected noise components as noise pulses Pn.

[0022] The local oscillator 4 has a VCO (Voltage Controlled Oscillator) and generates a local oscillation signal So. The local oscillator 4 generates a reference signal having a frequency represented by reception frequency setting information Sc output from the control device 7, and adjusts the frequency of the local oscillation signal So output by the VCO to a frequency synchronized with the reference signal. For this reason, the local oscillator 4 is configured with a PLL (Phase Lock Loop) circuit.

[0023] The storage device 5 is composed of a semiconductor memory or the like, and stores reception frequency information and reception tone setting information. The reception frequency information is information about the reception frequency set for each channel, and also includes tone signal information indicating whether a tone signal is superimposed on the radio frequency signal RF received at that reception frequency. The reception tone setting information is information that specifies whether a DCS signal or a CTCSS (Continuous Tone-Coded Squelch System) signal is set as the tone signal to be received when the tone squelch is turned on.

[0024] The operation unit 6 accepts various operations for the wireless receiver 10. The operation unit 6 has keys, a dial, a touch panel display, etc. The operation unit 6 outputs a dial operation signal Sd in response to a channel selection operation using the dial. Note that the on / off state of the tone squelch is determined for each channel by pre-set reception tone setting information.

[0025] The control device 7 is configured with a processor such as a CPU (Central Processing Unit), and controls the operation of the local oscillator 4. To realize its control function, the control device 7 has a noise squelch control section 71, an information output control section 72, and an AFC (Automatic Frequency Control) control section 73 (control section).

[0026] When the noise squelch control unit 71 recognizes from the noise pulse Pn from the noise detection unit 3 that noise at a level at which output should be blocked has been detected, it closes the noise squelch by not outputting the noise squelch state signal SQL. The noise squelch control unit 71 also provides the noise squelch state signal SQL to the AFC control unit 73.

[0027] When a dial operation signal Sd is input from the operation unit 6, the information output control unit 72 reads out reception frequency information for the channel selected by the dial operation signal Sd from the storage device 5 and outputs it to the AFC control unit 73. When a tone operation signal St is input from the operation unit 6, the information output control unit 72 reads out reception tone setting information from the storage device 5 and outputs it to the AFC control unit 73.

[0028] When receiving frequency information is input from the information output control unit 72, if the receiving frequency information includes receiving tone setting information, the AFC control unit 73 generates receiving frequency setting information Sc for matching the frequency of the local oscillation signal So to the center frequency of the intermediate frequency signal IF based on the center frequency information Fc from the FM detection unit 2, and outputs the generated information to the local oscillator 4.

[0029] When receiving frequency information is input from the information output control unit 72, if the receiving frequency information does not include tone signal information, or if receiving tone setting information is not input from the information output control unit 72, the AFC control unit 73 generates receiving frequency setting information Sc for shifting the frequency of the local oscillation signal So from the center frequency of the intermediate frequency signal IF based on the center frequency information Fc from the FM detection unit 2, and outputs the generated information to the local oscillator 4.

[0030] The AFC control unit 73 performs the above control to align the frequency of the local oscillation signal So with the center frequency of the intermediate frequency signal IF when the noise squelch is open due to the noise squelch state signal SQL being output from the noise squelch control unit 71. On the other hand, when the noise squelch is closed due to the noise squelch state signal SQL not being output, the AFC control unit 73 does not perform the above control to align the frequency of the local oscillation signal So with the center frequency of the intermediate frequency signal IF.

[0031] In the radio receiver 10, the direct conversion section 1, the FM detection section 2, the AFC control section 73, and the local oscillator 4 constitute an AFC section.

[0032] <Radio receiver operation> FIG. 2 is a flowchart showing the procedure (control method) for setting the reception frequency by the wireless receiver 10.

[0033] 2, the AFC control unit 73 determines whether or not the noise squelch state has been acquired based on the noise squelch state signal SQL from the noise squelch control unit 71 (step S1). Next, the AFC control unit 73 determines whether or not the noise squelch is open based on the acquired noise squelch state (step S2). If the AFC control unit 73 determines in step S2 that the noise squelch is closed (NO), the process returns to step S1.

[0034] If the AFC control unit 73 determines in step S2 that the noise squelch is open (YES), it acquires center frequency information Fc from the FM detection unit 2 (step S3) and determines whether a certain time (for example, 200 milliseconds) has elapsed since acquiring the center frequency information Fc (step S4). If the AFC control unit 73 does not determine in step S4 that the certain time has elapsed (NO), it returns the process to step S3.

[0035] The AFC control unit 73 performs a control operation of the local oscillator 4 based on the result of analyzing the latest center frequency information Fc acquired within a certain period of time.

[0036] If the AFC control unit 73 determines in step S4 that a certain period of time has elapsed (YES), it acquires reception frequency information and reception tone setting information from the information output control unit 72 (step S5).The AFC control unit 73 determines whether a tone signal is included (superimposed) in the received signal based on the tone reception information (step S6).

[0037] If the AFC control unit 73 determines in step S6 that the received signal contains a tone signal (YES), it controls the local oscillator 4 so that the target reception frequency, i.e., the frequency of the locally oscillated signal So of the local oscillator 4, is centered on the frequency of the received signal (step S7). As a result, the local oscillator 4 sets the frequency of the locally oscillated signal So (step S8), and the process ends.

[0038] If the AFC control unit 73 determines in step S6 that the received signal does not contain a tone signal (NO), it controls the local oscillator 4 to tune the received frequency to a frequency near the center of the received signal, but shifts the frequency from the center (step S9), and proceeds to step S8.

[0039] <Setting the receiving frequency of the radio receiver> An example of setting the reception frequency when the wireless receiver 10 receives a signal containing a DCS signal as a tone signal will be described below. Fig. 3 is a diagram showing an example of setting the reception frequency for a DCS modulated signal by the wireless receiver 10. Fig. 4 is a diagram showing another example of setting the reception frequency for a DCS modulated signal by the wireless receiver 10.

[0040] In Figure 3, the right end of the DCS signal modulated wave (binary FSK modulated wave) corresponds to "1" of the DCS signal, and the left end corresponds to "0" of the DCS signal. The sweep that occurs when the frequency transitions between the right-end waveform and the left-end waveform appears as noise and looks like a band (the gray part in Figure 3).

[0041] As shown in Figure 3, the AFC control unit 73 sets the frequency of the local oscillation signal So so that the receiving frequency fc1, i.e., the center frequency of the passband of the wireless receiver 10, matches the center frequency fc2 of the received signal containing the DCS signal modulated wave. In this state, the center frequency of the passband falls within a range where the DCS signal modulated wave cannot be received, but the DCS signal modulated wave (spectrum) exists across that range. In this state, the DCS signal modulated wave can be received without any problems. Furthermore, in the example shown in Figure 3, there is a frequency margin at both high and low frequencies for the above spectrum.

[0042] Figure 4 shows a case where the frequency control accuracy of the AFC unit is low, resulting in a deviation D in the receiving frequency fc1 in the higher direction compared to the receiving state in Figure 3. Even in this case, the center frequency range that cannot be received by the wireless receiver 10 is located inside the spectrum. As a result, even in this state, the DCS signal modulated wave can be received without any problems.

[0043] 4, the example is explained as an example where the received frequency has shifted upward, but even if the received frequency has shifted downward, the DCS signal modulated wave can be received without any problems. In other words, as long as the AFC unit has enough frequency accuracy to keep the received frequency fc1 within the spectrum, the DCS signal modulated wave can be received without any problems.

[0044] Next, an example of setting the reception frequency when a wireless receiver of a comparative example receives a signal containing a DCS signal as a tone signal will be described. Fig. 5 is a diagram showing an example of setting the reception frequency for a DCS modulated signal by the wireless receiver of the comparative example. Fig. 6 is a diagram showing another example of setting the reception frequency for a DCS modulated signal by the wireless receiver of the comparative example.

[0045] The wireless receiver of the comparative example is a receiver with a general AFC function, which does not have an AFC control unit 73 like wireless receiver 10. Figure 5 shows a case in which the wireless receiver uses a general AFC function to shift the reception frequency fc1 upward from the center frequency fc2 of the reception signal containing the DCS signal modulated wave by an amount D, as in Figure 3. In this case, as in the case shown in Figure 4, the DCS signal modulated wave can be received without any problems.

[0046] Figure 6 shows a case where the frequency control accuracy of the AFC function is low, causing the receiving frequency fc1 to deviate further in the higher direction compared to the receiving state in Figure 5. In this case, we can see that the right edge of the spectrum of the DCS signal's modulated wave overlaps with the area that the wireless receiver cannot receive. As a result, the "1" level of the DCS signal cannot be received correctly.

[0047] Effects of the embodiment The wireless receiver 10 according to this embodiment includes a local oscillator 4, a direct conversion unit 1, an FM detection unit 2, and an AFC control unit 73. The direct conversion unit 1 mixes a radio frequency signal RF on which a tone signal is superimposed with a local oscillation signal So from the local oscillator 4, thereby converting the radio frequency signal RF into two intermediate frequency signals IF whose phases are orthogonal to each other. The FM detection unit 2 detects the center frequencies of the two intermediate frequency signals IF. The AFC control unit 73 controls the local oscillator 4 to match the frequency of the local oscillation signal So to the detected center frequency.

[0048] As a result, when receiving a radio frequency signal RF on which a tone signal is superimposed, the local oscillation signal So is tuned to the center frequency of the tone signal, thereby enabling stable reception of the radio frequency signal RF.

[0049] Furthermore, as mentioned above, even if the frequency control accuracy of the AFC unit is low, the receiver can still be used practically. Therefore, there is no need to secure a long period of time for frequency analysis or for averaging the received frequency, which are the time required to improve the frequency control accuracy of the AFC unit, and the local oscillator 4 can be controlled in a short period of time.

[0050] Furthermore, storage device 5 stores received signal information (received frequency information and received tone setting information) indicating whether or not a tone signal is superimposed on radio frequency signal RF. If a tone signal is superimposed on radio frequency signal RF, AFC control unit 73 controls local oscillator 4 to tune the frequency of locally generated signal So to the detected center frequency. If a tone signal is not superimposed on radio frequency signal RF, AFC control unit 73 controls local oscillator 4 to shift the frequency of locally generated signal So from the detected center frequency.

[0051] As a result, when receiving a radio frequency signal RF on which a tone signal is superimposed, the local oscillation signal So is tuned to the center frequency of the radio frequency signal RF. On the other hand, when receiving a radio frequency signal RF on which no tone signal is superimposed, the local oscillation signal So is shifted from the center frequency of the radio frequency signal RF. Therefore, the radio frequency signal RF can be received stably regardless of whether a tone signal is superimposed or not.

[0052] The tone signal may be a DCS signal. This aligns the frequency of the local oscillation signal with the center frequency of the received signal based on frequency information, making it possible to control the frequency of the local oscillation signal in a short time for DCS signals whose center frequency is difficult to detect.

[0053] When receiving a low-speed binary FSK signal such as a DSC signal, the binary FSK signal is received as a modulated wave that moves back and forth between two frequencies: one shifted to a higher frequency and one shifted to a lower frequency. In this case, because the DCS signal is modulated at a low speed, when divided into unit time periods, the frequency shifts to either the higher or lower side for a certain period of time. In addition, because the DCS signal is modulated with logical data of "1" or "0," the duty ratios of "1" and "0" also differ.

[0054] When receiving a modulated wave of the DCS signal described above, it is difficult to find its center frequency, and it tends to be detected as being either too high or too low. If one were to try to improve the frequency accuracy of the AFC unit, one could expect improvement by lengthening the frequency analysis time or the frequency averaging processing time. However, this ultimately requires a long time for frequency control by the AFC control unit 73, making it impractical.

[0055] This embodiment is also effective in the case of digital wireless communication in which the reception passband is narrow.

[0056] Furthermore, as described above, the ON / OFF state of the tone squelch does not have to be a preset setting, but may be switched by the user's operation on the operation unit 6. In such a configuration, for example, the touch panel display of the operation unit 6 is provided with operation keys as tone keys for turning the tone squelch ON / OFF. The operation unit 6 outputs tone key operation as a tone operation signal. Each time a tone key is pressed, the tone squelch setting is switched in turn between DCS signal selection, CTCSS signal selection, and tone squelch OFF.

[0057] When the tone squelch is turned on by operating the tone key, the AFC control unit 73 controls the local oscillator 4 to match the frequency of the local oscillation signal So with the detected center frequency. When the tone squelch is turned off, the AFC control unit 73 controls the local oscillator 4 to shift the frequency of the local oscillation signal So from the detected center frequency.

[0058] [Software implementation example] The functions of the control device 7 of the wireless receiver 10 are realized by a program for causing a computer to function as the control device 7, and by a program for causing a computer to function as each part of the control device 7.

[0059] In this case, the control device 7 includes, as hardware for executing the program, a computer having, for example, at least one processor and at least one storage device 5. By executing the program using the control device 7 and the storage device 5, the functions described in each of the above embodiments are realized.

[0060] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0061] In addition, some or all of the functions of each of the control units can be realized by logic circuits. For example, an integrated circuit in which a logic circuit that functions as each of the control blocks is formed is also included in the scope of the present invention. In addition, the functions of each of the control blocks can also be realized by, for example, a quantum computer.

[0062] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Furthermore, embodiments obtained by appropriately combining the technical means disclosed in the embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0063] 1 Direct conversion section (frequency conversion section) 2 FM detector (frequency detector) 4 Local Oscillator 5 Storage device (storage unit) 10. Radio receiver 73 AFC control unit (control unit) IF intermediate frequency signal (conversion signal) RF radio frequency signal So local oscillator signal

Claims

1. a local oscillator that generates a local oscillation signal; a frequency conversion unit that mixes a radio frequency signal with the local oscillation signal to convert the frequency; a frequency detection unit that detects a center frequency of the radio frequency signal; a control unit that controls the frequency of the local oscillation signal; a storage unit that stores received signal information including tone signal information indicating whether a tone signal is superimposed on the received radio frequency signal and tone setting information indicating the type of the superimposed tone signal, a control unit that controls the local oscillator to match the frequency of the local oscillation signal with the center frequency of the radio frequency signal when a binary FSK modulated tone signal is superimposed on the radio frequency signal as the tone signal based on the received signal information, and controls the local oscillator to shift the frequency of the local oscillation signal from the center frequency of the radio frequency signal when the tone signal is not superimposed on the radio frequency signal, based on the received signal information.

2. 2. The direct conversion radio receiver according to claim 1, wherein the binary FSK modulated tone signal is a DCS (Digitally Coded Squelch) signal.

3. A control method for a direct conversion radio receiver including a local oscillator that generates a local oscillation signal, a frequency conversion unit that mixes a radio frequency signal with the local oscillation signal to convert the frequency, and a frequency detection unit that detects a center frequency of the radio frequency signal, 1. A control method for a direct conversion radio receiver, comprising: controlling the local oscillator to match the frequency of the local oscillation signal to a center frequency of the radio frequency signal when a binary FSK modulated tone signal is superimposed on the radio frequency signal as the tone signal, based on received signal information including tone signal information indicating whether a tone signal is superimposed on the received radio frequency signal and tone setting information indicating a type of the superimposed tone signal; and controlling the local oscillator to shift the frequency of the local oscillation signal from the center frequency of the radio frequency signal when the tone signal is not superimposed on the radio frequency signal.

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