JP4000999B2 - Automatic frequency control circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic frequency control circuit used when receiving a frame in which an ASK-modulated slot and a PSK-modulated slot are mixed.
[0002]
[Prior art]
In a dedicated short-range communication (DSRC) system, a frame control message slot (FCMS) for transmitting control information and a message data slot for transmitting data when data is transmitted from a roadside wireless device to an in-vehicle terminal. A frame that has been subjected to ASK modulation or QPSK modulation including (MDS) is used (see, for example, Non-Patent Document 1).
[0003]
[Non-Patent Document 1]
“Narrow area communication (DSRC) system standard”, ARIB STD-T75 1.0, Radio Industry Association, September 6, 2001, p50, p65
[0004]
[Problems to be solved by the invention]
As a narrow-area communication system, an automatic toll collection (ETC) system has already been put into practical use, and the current automatic toll collection system uses an ASK-modulated frame control message slot and a message data slot from a roadside radio. Data is transmitted to the in-vehicle terminal. In a system where the amount of transmission data is not so large, such as an ETC system, there is no problem even if an ASK-modulated slot is used, but a large amount of data is transmitted from the roadside radio to an in-vehicle terminal that is traveling at high speed. When constructing a new system, it is desirable to use QPSK-modulated slots that can increase the amount of data transfer per unit time.
[0005]
By the way, when a new system for transmitting data using a slot subjected to QPSK modulation is constructed, it is desirable for the user that both the new system and the existing ETC system can be used with one in-vehicle terminal. In order to do this, for example, the following method can be considered.
[0006]
The roadside radio of the new system transmits a frame in which ASK-modulated frame control message slots and QPSK-modulated message data slots are mixed. The frame control message slot for ASK modulation includes information indicating that the slot is for the new system.
[0007]
On the other hand, the roadside radio of the ETC system transmits a frame including an ASK-modulated frame control message slot and a message data slot as it is. The frame control message slot for ASK modulation includes information indicating that the slot is an ETC system.
[0008]
The in-vehicle terminal is provided with two demodulation units, an ASK demodulation unit and a QPSK demodulation unit. Then, based on the output of the ASK demodulator, when it is detected that the frame control message slot of the new system has been received, the output of the QPSK demodulator is validated and the reception of the frame control message slot of the ETC system is detected. In such a case, the output of the ASK demodulator is validated.
[0009]
As described above, it is possible to use a new system and an existing ETC system with a single in-vehicle terminal.
[0010]
However, if a new system uses a frame in which an ASK-modulated frame control message slot and a QPSK-modulated message data slot are mixed, the following problem occurs. That is, reception of a frame in which ASK-modulated slots and QPSK-modulated slots are mixed results in reception of intermittent (burst) modulated waves when viewed with respect to QPSK-modulated slots. When receiving an intermittently modulated wave, it depends on the frequency deviation between the input modulated wave frequency and the local oscillator in the feedback loop controlled by the demodulator until the clock recovery and carrier recovery are performed after the modulation wave is input. There is a problem that it takes time to do.
[0011]
Therefore, an object of the present invention is to shorten the time required for carrier reproduction and clock reproduction as much as possible by utilizing the fact that slots subjected to ASK modulation and slots subjected to PSK modulation coexist.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the first automatic frequency control circuit according to the present invention provides:
A first local oscillator for outputting a first local oscillation signal;
The first local oscillation signal output from the first local oscillating unit and the received frame, which is a received frame and includes a frame in which an ASK-modulated slot and a PSK-modulated slot are mixed, A first mixer that outputs one intermediate frequency signal;
A first correction signal is output based on the frequency of the signal corresponding to the unmodulated wave portion in the ASK-modulated slot in the first intermediate frequency signal output from the first mixer. 1 control unit;
A second local oscillator for outputting a second local oscillation signal having a frequency corresponding to the control signal;
The first intermediate frequency signal output from the first mixer and the second local oscillation signal output from the second local oscillation unit are used to perform frequency conversion, and a second intermediate frequency signal is output. 2 mixers,
A second correction signal is output based on the frequency of the signal corresponding to the unmodulated wave portion in the ASK-modulated slot in the second intermediate frequency signal output from the second mixer. Two control units;
An addition unit that generates a control signal for the second local oscillation unit by adding the first correction signal and the second correction signal is provided.
[0013]
Moreover, the second automatic frequency control circuit according to the present invention includes:
In the first automatic frequency control circuit,
A difference between a frequency of a signal corresponding to an unmodulated wave portion in the ASK-modulated slot in the first intermediate frequency signal and an ideal first intermediate frequency in the first intermediate frequency signal. It has the structure which outputs the 1st correction signal according to this.
[0014]
The third automatic frequency control circuit according to the present invention is
In the first or second automatic frequency control circuit,
A difference between a frequency of a signal corresponding to a non-modulated wave portion in the ASK-modulated slot in the second intermediate frequency signal and an ideal second intermediate frequency in the second control unit. The second correction signal according to the above is output.
[0015]
The fourth automatic frequency control circuit according to the present invention is
In the first, second or third automatic frequency control circuit,
An ASK demodulator that performs ASK demodulation on a frame in which the ASK modulated slot and the PSK modulated slot are mixed;
A first frequency counter unit that measures the frequency of the first intermediate frequency signal output from the first mixer when the demodulated data output from the ASK demodulator is "1", and
The first control unit is configured to output the first correction signal based on a measurement result of the first frequency counter unit at the time of receiving the ASK modulated slot.
[0016]
The fifth automatic frequency control circuit according to the present invention is
In the fourth automatic frequency control circuit,
A second frequency counter for measuring the frequency of the second intermediate frequency signal output from the second mixer when the demodulated data output from the ASK demodulator is "1"; and
The second control unit is configured to output the second correction signal based on a measurement result of the second frequency counter unit at the time of receiving the ASK modulated slot.
[0017]
The sixth automatic frequency control circuit according to the present invention is
In any one of the first to fifth automatic frequency control circuits,
The ASK modulated slot is a frame control message slot in a narrow area communication system,
The PSK modulated slot is a message data slot in a narrow area communication system.
[0018]
The seventh automatic frequency control circuit according to the present invention is
In any one of the first to sixth automatic frequency control circuits,
A PSK demodulator that performs PSK demodulation on the second intermediate frequency signal output from the second mixer is provided.
[0019]
[Action]
Based on the frequency of the signal corresponding to the unmodulated wave portion in the ASK modulated slot in the first intermediate frequency signal output from the first mixer, the first control unit A first correction signal for correcting the frequency deviation Δf1 (frequency deviation caused by the radio device and the first local oscillation unit) included in the frequency signal is output. The first correction signal is applied to the second local oscillation unit through the addition unit, and the frequency of the second local oscillation signal output from the second local oscillation unit is corrected so as to eliminate the frequency deviation Δf1. To do. Therefore, when receiving the slot subjected to PSK modulation, the frequency deviation Δf2 included in the second intermediate frequency signal output from the second mixer does not include the frequency deviation Δf1, and thus the second intermediate frequency signal The frequency deviation Δf2 included in can be made small. As a result, the time required for carrier reproduction and clock reproduction can be shortened as much as possible, and the number of preamble bits can be minimized.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0021]
FIG. 1 is a block diagram of an embodiment of the present invention, showing a configuration of an in-vehicle terminal 1 to which an automatic frequency control circuit according to the present invention is applied.
[0022]
Referring to FIG. 1, the in-vehicle terminal 1 includes an antenna 11, an ASK demodulator 12, a first mixer 13, a first local oscillator 14, a first frequency counter unit 15, and a first control. 16, second mixer 17, second local oscillator 18, second frequency counter 19, second controller 20, adder 21, QPSK demodulator 22, data recovery A unit 23 and a processing unit 24 are included.
[0023]
FIG. 2 is a diagram showing an example of a frame received by the in-vehicle terminal 1 (a frame transmitted by the roadside radio), and an ASK-modulated frame control message slot FCMS and QPSK-modulated first and second frames The message data slots MDS1 and MDS2 are configured. Note that the in-vehicle terminal 1 according to the present embodiment can also receive a frame in which both the frame control message slot FCMS and the first and second message data slots MDS1 and MDS2 are ASK modulated.
[0024]
The frame control message slot FCMS includes a preamble (PR), a unique word (UW1), control information, and a CRC, and a guard time is set before and after the preamble (PR).
[0025]
The first and second message data slots MDS1 and MDS2 include a ramp bit (R), a preamble (PR), a unique word (UW2), data, and a CRC.
[0026]
The antenna 11 includes the frame shown in FIG. 2 transmitted as a 5.8 GHz band modulated wave from a roadside radio (not shown), or the frame control message slot FCMS and the first and second message data slots MDS1 and MDS2. Receive an ASK modulated frame.
[0027]
The ASK demodulator 12 performs ASK demodulation on the frame received by the antenna 11 and outputs demodulated data.
[0028]
The first mixer 13 performs frequency conversion based on the frame (5.8 MHz band modulated wave) received by the antenna 11 and the local oscillation signal of the frequency f1 output from the first local oscillation unit 14. The intermediate frequency signal IF1 is output.
[0029]
The first frequency counter unit 15 measures the frequency of the signal corresponding to the unmodulated wave portion in the frame control message slot FCMS in the first intermediate frequency signal IF1 output from the first mixer 13.
[0030]
The first control unit 16 determines the first intermediate frequency signal IF1 based on the difference between the frequency of the first intermediate frequency signal IF1 measured by the first frequency counter unit 15 and the ideal first intermediate frequency. The first correction signal a for correcting the frequency deviation Δf1 (frequency deviation by the roadside radio or the first local oscillation unit 14) included in is output. Various methods can be adopted as a method of outputting the correction signal a corresponding to the difference. For example, a method of using a table in which the difference and the value of the correction signal a are associated and registered is used. Can be adopted. That is, when the difference is obtained, a method of referring to the table and outputting the correction signal a having a value registered corresponding to the difference can be employed.
[0031]
The second local oscillation unit 18 outputs a second local oscillation signal having a frequency f2 corresponding to the control signal c output from the addition unit 21.
[0032]
The second mixer 17 performs frequency conversion using the first intermediate frequency signal IF1 output from the first mixer 13 and the local oscillation signal of the frequency f2 output from the second local oscillation unit 18, 2 intermediate frequency signal IF2 is output.
[0033]
The second frequency counter unit 19 measures the frequency of the signal corresponding to the unmodulated wave portion of the frame control message slot FCMS in the second intermediate frequency signal IF2 output from the second mixer 17.
[0034]
The second control unit 20 determines the second intermediate frequency signal IF2 based on the difference between the frequency of the second intermediate frequency signal IF2 measured by the second frequency counter unit 19 and the ideal second intermediate frequency. The second correction signal b for correcting the frequency deviation Δf2 included in the signal is output.
[0035]
The adder 21 adds the first correction signal a and the second correction signal b, and outputs a control signal c for the second local oscillator 18.
[0036]
The QPSK demodulator 22 performs QPSK demodulation on the second intermediate frequency signal IF2.
[0037]
When receiving the frame control message slot FCMS, the data reproducing unit 23 outputs the control information and CRC in the demodulated data output from the ASK demodulating unit 12 to the processing unit 24, and immediately after outputting the CRC, A frequency acquisition instruction d is output to the first and second controllers 16 and 20. When the message data slots MDS1 and MDS2 are received, if they are QPSK modulated, the data and CRC in the modulated data output from the QPSK demodulator 22 are output to the processor 24, and the ASK If it is modulated, the data and CRC in the demodulated data output from the ASK demodulator 12 are output to the processing unit 24.
[0038]
[Description of operation of embodiment]
Next, the operation of this embodiment will be described in detail.
[0039]
Now, for example, the frame control message slot FCMS is ASK modulated and the first and second message data slots MDS1 and MDS2 are QPSK modulated as shown in FIG. It is assumed that the signal is received by the antenna 11.
[0040]
The 5.8 GHz band modulated wave received by the antenna 11 is supplied to the ASK demodulator 12 and the first mixer 13.
[0041]
The first mixer 13 performs frequency conversion using the 5.8 GHz band modulated wave supplied from the antenna 11 and the first local oscillation signal input from the first local oscillation unit 14, and performs the first intermediate frequency signal. Output IF1. The first intermediate frequency signal IF1 is supplied to the first frequency counter unit 15 and the second mixer 17.
[0042]
The ASK demodulator 12 performs ASK demodulation on the 5.8 GHz band modulated wave supplied from the antenna 11 and supplies demodulated data to the first and second counter units 15 and 19 and the data reproducing unit 23.
[0043]
Assuming that the ASK-modulated frame control message slot FCMS is input to the ASK demodulator 12, the output of the ASK demodulator 12 is “0” and “1” serial data. In ASK modulation, an unmodulated wave is transmitted when transmission data is “1”, and is stopped when transmission data is “0”. Therefore, when the output of the ASK demodulator 12 is “1”, a 5.8 GHz band unmodulated wave is input to the first mixer 13, so when the output of the ASK demodulator 12 is “1”. If the first frequency counter unit 15 is operated, the frequency of the first intermediate frequency signal IF1 can be measured. Even when the QPSK-modulated first and second message data slots MDS1 and MDS2 are input, the output of the ASK demodulator 12 becomes “1”, and the first frequency counter unit 15 Although the frequency of the intermediate frequency signal IF1 is measured, the frequency measured at this time is not used by the first control unit 16.
[0044]
The first frequency counter unit 15 measures the frequency of the first intermediate frequency signal IF1 every time the output of the ASK demodulator 12 becomes “1”, and holds the latest measurement result.
[0045]
The first control unit 16 uses the frequency acquisition instruction d from the data reproduction unit 23 as a trigger, and the latest measurement result (frequency of the first intermediate frequency signal IF1) held by the first frequency counter unit 15 To get. Here, since the frequency acquisition instruction d is output from the data reproduction unit 23 immediately after receiving the CRC in the frame control message slot FCMS, the first control unit 16 sends 5 to the first mixer 13. It is possible to obtain a frequency when an 8 GHz band unmodulated wave is input.
[0046]
When the frequency of the first intermediate frequency signal IF1 is acquired, the first control unit 16 calculates the difference between the acquired frequency and the ideal frequency of the first intermediate frequency signal output from the first mixer 13. Based on the above, the first correction signal a is output. The first correction signal a is a signal for correcting the frequency deviation Δf1 included in the first intermediate frequency signal IF1.
[0047]
The first correction signal a output from the first control unit 16 is added to the second correction signal b in the adding unit 21 and supplied to the second local oscillating unit 18 as a control signal c.
[0048]
The second local oscillation unit 18 outputs a second local oscillation signal having a frequency f2 corresponding to the level of the control signal c.
[0049]
The second mixer 17 performs frequency conversion using the first intermediate frequency signal IF1 and the second local oscillation signal, and outputs a second intermediate frequency signal IF2. The second intermediate frequency signal IF2 is supplied to the second frequency counter unit 19 and the QPSK demodulator 22.
[0050]
The second frequency counter unit 19 measures the frequency of the second intermediate frequency signal IF2 every time the output of the ASK demodulator 12 becomes “1”, and holds the latest measurement result.
[0051]
The second control unit 20 uses the frequency acquisition instruction d from the data reproduction unit 23 as a trigger, and the latest measurement result (frequency of the second intermediate frequency signal IF2) held by the second frequency counter unit 19 To get. Thereafter, the second control unit 20 obtains the ideal frequency of the second intermediate frequency signal IF2 output from the second mixer 17 and the frequency of the second intermediate frequency signal IF2 acquired from the second frequency counter unit 19. The second correction signal b corresponding to the difference with the correct frequency is output.
[0052]
The second correction signal “b” output from the second control unit 20 is added to the first correction signal “a” in the addition unit 21 and supplied to the second local oscillation unit 18 as the control signal “c”.
[0053]
Here, when receiving the QPSK-modulated first and second message data slots MDS1 and MDS2, the frequency deviation Δf1 included in the first intermediate frequency signal IF1 has already been corrected by the first correction signal a. Therefore, the second intermediate frequency signal IF2 output from the second mixer 17 does not include the frequency deviation Δf1 due to the roadside radio and the first local oscillation unit 14. Therefore, at the time of receiving the first and second message data slots MDS1 and MDS2 subjected to QPSK modulation, it is only necessary to correct the frequency deviation Δf2 generated in the feedback loop, thereby improving the acquisition performance for the QPSK modulated wave. it can.
[0054]
FIG. 3 is a block diagram illustrating a configuration example of the data reproducing unit 23, which includes an ASK reproducing unit 231, a QPSK reproducing unit 232, and a switching unit 233.
[0055]
FIG. 4 is a flowchart showing a processing example of the ASK playback unit 231, and FIG. 5 is a flowchart showing a processing example of the QPSK playback unit 232.
[0056]
When the ASK reproducing unit 231 constantly monitors the demodulated data output from the ASK demodulating unit 12 and detects the unique word UW1 in the frame control message slot FCMS (FIG. 4, step S41 is YES), the switching signal to the switching unit 233 is displayed. e is set to “1” (step S43). The switching circuit 233 connects the ASK playback unit 231 and the processing unit 24 when the switching signal e is “1”, and connects the QPSK playback unit 232 and the processing unit 24 when the switching signal e is “0”.
[0057]
Thereafter, the ASK playback unit 231 outputs the control information and CRC input following the unique word UW1 to the switching circuit 233 (step S44). At this time, since the switching signal e is “1”, the switching circuit 233 outputs the control information and CRC from the ASK playback unit 231 to the processing unit 24. The control information of the frame control message slot FCMS stores information indicating whether the subsequent first and second message data slots MDS1 and MDS2 are ASK-modulated or QPSK-modulated. In step S44, the ASK playback unit 231 determines whether the subsequent first and second message data slots MDS1 and MDS2 are QPSK-modulated or ASK-modulated based on the control information. The process of recognizing is also performed.
[0058]
When the CRC output is completed, the ASK playback 231 outputs a frequency acquisition instruction d to the first and second control units 16 and 20 (step S45). After that, when the subsequent first and second message data slots MDS1 and MDS2 are QPSK modulated (step S46 is YES), the switching signal e is set to “0” (step S47), and the step Returning to the process of S41, when the subsequent first and second message data slots MDS1 and MDS2 are ASK modulated (NO in step S46), the process immediately returns to the process of step S41.
[0059]
If the subsequent first and second message data slots MDS1, MDS2 are QPSK modulated, the unique word UW2 cannot be detected (NO in step S42), and the process returns to step S41. On the other hand, when the subsequent first and second message data slots MDS1 and MDS2 are ASK modulated, the unique word UW2 is detected in step S42 and input following the unique word UW2. Data and CRC are output to the switching unit 233 (step S48).
[0060]
On the other hand, the QPSK reproducing unit 232 constantly monitors the demodulated data output from the QPSK demodulating unit 22 and detects the unique word UW2 in the first and second message data slots MDS1 and MDS2 (FIG. 5, step S51 is changed). YES), the data and CRC input following the unique word UW2 are output to the switching unit 233 (step S52). At this time, since the switching signal e output from the ASK playback unit 231 is “0”, the switching unit 233 outputs the data and CRC output from the QPSK playback unit 232 to the processing unit 24.
[0061]
Other Embodiments of the Invention
In the embodiment shown in FIG. 1, the first and second control units 16 and 20 receive the frequency from the first and second frequency counter units 15 and 19 only once during reception of the frame control message slot FCMS. The correction signals a and b are output based on the read values, but the first and second control units 16 and 20 perform first and second multiple times during reception of the frame control message slot FCMS. The frequency may be read from the frequency counter units 15 and 19 and the correction signals a and b may be output based on the average value.
[0062]
【The invention's effect】
The first effect of the present invention is to shorten carrier recovery time and clock recovery time in reception of a frame in which ASK modulated slots and PSK modulated slots are mixed, which is intermittent reception of PSK modulated waves. It is a point that can be done. The reason is that the frequency deviation (frequency deviation due to the roadside radio and the first local oscillator) included in the first intermediate frequency signal is removed when the ASK modulated slot is received, and the PSK modulated slot is removed. This is because it is sufficient to correct only the frequency deviation by the second local oscillation unit at the time of reception.
[0063]
The second effect of the present invention is that the throughput can be improved by reducing the number of bits of the preamble and increasing the data portion. This is because the clock reproduction time and carrier reproduction time can be shortened.
[Brief description of the drawings]
FIG. 1 is a block diagram of an embodiment of the present invention.
FIG. 2 is a diagram illustrating an example of a frame received by the in-vehicle terminal 1;
3 is a diagram illustrating a configuration example of a data reproducing unit 23. FIG.
FIG. 4 is a flowchart showing a processing example of an ASK playback unit 231.
FIG. 5 is a flowchart showing a processing example of a QPSK playback unit 232;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... In-vehicle terminal 11 ... Antenna 12 ... ASK demodulation part 13 ... 1st mixer 14 ... 1st local oscillation part 15 ... 1st frequency counter part 16 ... 1st control part 17 ... 2nd mixer 18 ... 2nd 2 local oscillation units 19 ... second frequency counter unit 20 ... second control unit 21 ... addition unit 22 ... QPSK demodulation unit 23 ... data reproduction unit 24 ... processing unit 231 ... ASK reproduction unit 232 ... QPSK reproduction unit 233 ... Switching part

Claims (7)

A first local oscillator for outputting a first local oscillation signal;
The first local oscillation signal output from the first local oscillating unit and the received frame, which is a received frame and includes a frame in which an ASK-modulated slot and a PSK-modulated slot are mixed, A first mixer that outputs one intermediate frequency signal;
A first correction signal is output based on the frequency of the signal corresponding to the unmodulated wave portion in the ASK-modulated slot in the first intermediate frequency signal output from the first mixer. 1 control unit;
A second local oscillator for outputting a second local oscillation signal having a frequency corresponding to the control signal;
The first intermediate frequency signal output from the first mixer and the second local oscillation signal output from the second local oscillation unit are used to perform frequency conversion, and a second intermediate frequency signal is output. 2 mixers,
A second correction signal is output based on the frequency of the signal corresponding to the unmodulated wave portion in the ASK-modulated slot in the second intermediate frequency signal output from the second mixer. Two control units;
An automatic frequency control circuit comprising: an adder that generates a control signal for the second local oscillator by adding the first correction signal and the second correction signal. The automatic frequency control circuit according to claim 1, wherein
A difference between a frequency of a signal corresponding to an unmodulated wave portion in the ASK-modulated slot in the first intermediate frequency signal and an ideal first intermediate frequency in the first intermediate frequency signal. An automatic frequency control circuit having a configuration for outputting a first correction signal according to the above. The automatic frequency control circuit according to claim 1 or 2,
A difference between a frequency of a signal corresponding to a non-modulated wave portion in the ASK-modulated slot in the second intermediate frequency signal and an ideal second intermediate frequency in the second control unit. An automatic frequency control circuit having a configuration for outputting a second correction signal corresponding to the frequency. The automatic frequency control circuit according to any one of claims 1 to 3,
An ASK demodulator that performs ASK demodulation on a frame in which the ASK modulated slot and the PSK modulated slot are mixed;
A first frequency counter unit that measures the frequency of the first intermediate frequency signal output from the first mixer when the demodulated data output from the ASK demodulator is "1", and
The first control unit is configured to output the first correction signal based on a measurement result of the first frequency counter unit at the time of reception of the ASK modulated slot. Frequency control circuit. The automatic frequency control circuit according to claim 4,
A second frequency counter for measuring the frequency of the second intermediate frequency signal output from the second mixer when the demodulated data output from the ASK demodulator is "1"; and
The second control unit is configured to output the second correction signal based on a measurement result of the second frequency counter unit at the time of reception of the ASK-modulated slot. Frequency control circuit. The automatic frequency control circuit according to any one of claims 1 to 5,
The ASK modulated slot is a frame control message slot in a narrow area communication system,
2. The automatic frequency control circuit according to claim 1, wherein the PSK modulated slot is a message data slot in a narrow area communication system. The automatic frequency control circuit according to any one of claims 1 to 6,
An automatic frequency control circuit comprising a PSK demodulator that performs PSK demodulation on the second intermediate frequency signal output from the second mixer.

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