JPH07235957A - Frequency correcting system - Google Patents

Abstract

PURPOSE:To perform frequency correction in a frequency wider than ever by using a conventional digital demodulator without depending on digital transmission speed. CONSTITUTION:The reliability of the frequency of a detected reception signal is checked by checking whether or not synchronism with a signal sent from a transmitter is established by a synchronism establishment detector 15. When it is Judged that deviation occurs by the synchronism establishment detector 15, an operation processor 11 adjusts a reference signal so as to detect the frequency of the reception signal by adjusting a reference signal generator 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the reception frequency of a radio device having automatic frequency control, for example, a demodulation device in a mobile communication device, detects the transmission frequency of a base, and determines the frequency accuracy of a reference oscillator of a mobile station. The present invention relates to a system that follows the accuracy of a base station transmission frequency.

[0002]

2. Description of the Related Art FIG. 12 is a block diagram showing a conventional frequency correction system. In the figure, 1 is a reception signal input terminal, 2 is a band pass filter for extracting a predetermined band from the input signal, 3 is an amplifier for amplifying the output signal of the pass filter 2, 4 is an output from the amplifier 3 and the first local portion. A first mixer 5 for mixing with the oscillation frequency, 5 is a first intermediate frequency filter for extracting a first intermediate frequency from the output of the first mixer 4, and 6 is a first amplifier for amplifying the output of the first intermediate frequency waver 5. 1 intermediate amplifier, 7 is a second mixer for mixing the output of the amplifier 6 and the second local oscillation frequency, 8
Is a second intermediate frequency extracted from the output of the second mixer
Intermediate frequency filter, 9 is a demodulator for extracting necessary data and a signal necessary for frequency correction from the second intermediate frequency output from the second intermediate frequency filter 8, and 10 is for measuring the frequency of the second intermediate frequency Frequency measuring circuit, 12 is a reference signal generator of its own station, 11 is an arithmetic processing unit that calculates the reference frequency correction amount of the time station based on the measured frequency, 13 is a second local oscillator, and 14 is a reference signal. It is a first local oscillator that creates a first local oscillation frequency from a generator 12.

Next, the operation will be described. During continuous reception,
The transmission frequency of the base station is measured by the frequency measuring circuit 10, the amount of error is calculated by the arithmetic processing unit 11, and the reference signal generator 12 is corrected.

[0004]

In the case of the digital mobile communication system in FIG. 12, the frequency measuring circuit measures the error amount of the frequency oscillated by the reference signal generator 12 based on the frequency of the second intermediate frequency in the demodulator 9. Measure at 10. The measurement limit depends on the transmission rate of the digital signal and the modulation method. For those exceeding the above limits, the frequency cannot be corrected using the conventional frequency correction method. The main reason for this is considered as follows. The first local oscillator 14 is influenced by the reference signal generator 12 because it is controlled by the synthesizer method. In particular, the higher the frequency of the first local oscillator 14, the greater its influence. Therefore, the change amount of the first local oscillator with respect to the error of the reference signal generator 12 becomes larger than the range in which the frequency error can be detected by the demodulator 9, and the range in which the base station transmission frequency can be followed becomes narrow.

The present invention enables frequency correction in a wider range of frequencies by utilizing a conventional digital demodulator regardless of the digital transmission rate.

[0006]

A frequency correction system according to the present invention has the following elements. (A) Reference signal generating means for generating a reference signal, (b) Frequency of the signal from the digital transmitter which receives the signal from the digital transmitter and is received based on the reference signal generated from the reference signal generating means. Frequency detection means for detecting, (c) synchronization establishment detection means for detecting establishment of synchronization with the signal received from the digital transmitter, and (d) detection by the frequency detection means based on the detection result by the synchronization establishment detection means. Arithmetic processing means for obtaining a difference from the transmission frequency of the digital transmitter from the determined frequency and correcting the reference signal generated by the reference signal generating means.

Further, the frequency correction system according to the present invention has the following elements. (A) Reference signal generating means for generating a reference signal; (b) Frequency detection for receiving a signal from a digital transmitter and detecting the frequency of the received signal based on the reference signal generated by the reference signal generating means. Means, (c) synchronization establishment detecting means for detecting establishment of synchronization with a signal received from the digital transmitter, and (d) synchronization signal input means for inputting a synchronization signal indicating synchronization timing of a signal received from the digital transmitter. (E) When the synchronizing signal is inputted by the synchronizing signal input means, the difference between the frequency detected by the frequency detecting means and the transmission frequency of the digital transmitter is obtained based on the detection result by the synchronization establishment detecting means. Arithmetic processing means for correcting the reference signal generated by the reference signal generating means.

Further, the frequency correction system according to the present invention has the following elements. (A) reference signal generating means for generating a reference signal, (b) local transmitting means for generating a local oscillation frequency based on the reference signal generated by the reference signal generating means, and (c) a signal from a digital transmitter. Frequency detecting means for detecting the frequency of the received signal based on the reference signal generated by the reference signal generating means and the local transmitting frequency generated by the local transmitting means, and (d) the local transmitting means. Local oscillation frequency measuring means for measuring the local oscillation frequency generated by
(E) Arithmetic processing means for correcting the local oscillation frequency generated by the local oscillation means based on the frequency measured by the local oscillation frequency measuring means.

The frequency correction system according to the present invention has the following elements. (A) Reference signal generating means for generating a reference signal; (b) Frequency detection for receiving a signal from a digital transmitter and detecting the frequency of the received signal based on the reference signal generated by the reference signal generating means. Means (c) in the frequency detection of the frequency detection means,
Electric field level determination means for detecting the electric field level, (d) based on the detection result by the electric field level determination means, a difference from the transmission frequency of the digital transmitter is obtained from the frequency detected by the frequency detection means, and the reference signal is obtained. Arithmetic processing means for correcting the reference signal generated by the generating means.

[0010]

In the frequency correction system according to the present invention, the reception signal detected by the frequency detecting means is checked by checking whether or not the synchronization with the signal sent from the transmitter is established by the synchronization establishment detecting means. Check frequency reliability. When the synchronization establishment detecting means determines that the synchronization is lost, the arithmetic processing means adjusts the reference signal generating means to adjust the reference signal. That is, the reference signal is adjusted so that the frequency detecting means can detect the frequency of the received signal.

Further, in the frequency correction system according to the present invention, the arithmetic signal processing means causes the arithmetic signal processing means to input the synchronizing signal indicating the synchronizing timing of the received signal.
The reference signal generated by the reference signal generating means is corrected by using the time when the synchronization signal is input. Therefore, it is possible to perform frequency correction over a wide range even during a burst reception operation during continuous communication.

Further, the frequency correction system according to the present invention measures the local oscillation frequency generated by the local oscillation means by the local oscillation frequency measuring means, and based on the frequency measured by the local oscillation frequency measuring means by the arithmetic processing means. The local oscillation frequency generated by the local oscillation means is corrected. This correction cancels the error amount between the frequency generated by the local oscillation means and the true frequency, and the error amount generated by the local oscillation means is removed from the local oscillation frequency used by the frequency detection means.

In the frequency correction system according to the fourth aspect of the present invention, the electric field level determination means detects the electric field level when the frequency detection means detects the frequency. The arithmetic processing means invalidates the frequency detected by the frequency detecting means when the detected electric field level is equal to or lower than a predetermined reference.
On the other hand, when the detected electric field level is equal to or higher than the predetermined reference, the frequency detected by the frequency detecting means is regarded as valid and is used as a basis for correcting the reference signal generating means.

[0014]

【Example】

Example 1. FIG. 1 is a block diagram of the first embodiment. TDM
In the case of A system digital transmission communication, communication cannot be performed unless synchronization is established between the base station and the mobile device side in the system sequence. Therefore, the base station and the mobile station perform an operation of "synchronization establishment" before starting communication.
In FIG. 1, reference numeral 15 is a synchronization establishment detecting device, and whether the data output of the demodulator 9 is valid or invalid is determined by the synchronization establishment detecting result from the synchronization establishment detecting device 15. That is, the arithmetic processing unit 11 determines whether or not the count data from the frequency measuring circuit 10 is reliable based on a signal from the synchronization establishment detecting unit 15.

FIG. 2 shows a data reproducible range of a typical detector which is based on the synchronous detection. The phase error correctable range of the demodulator 9 depends on the transmission rate and the modulation method. Now, assuming that the transmission rate is 42 kbps and the modulation method is π / 4DQPSK, the phase error correctable range in the demodulator 9 is 42 at maximum.
k / 16 = ± 2.625 kHz.

While the synchronization establishment detecting device 15 continues to detect the synchronization and the establishment of the synchronization is established by using the definite data, the synchronization word, etc. included in the digital communication data, the frequency measurement is performed. The reference signal generator 12 is adjusted based on the frequency output from the circuit 10.
If the first local oscillator 14 deviates from the target frequency due to an error in the reference signal generator 12, the input frequency of the demodulator 9 is out of the range of 2.625 kHz as shown by f1 in FIG. Then, the synchronization establishment detecting device 15 judges that the synchronization cannot be detected, and the arithmetic processing device 11 sets the reference signal generator 12 to a small fixed amount higher or lower, and the synchronization establishment detecting device 15 again sets the data currently demodulated. Check if is within the range of synchronous detection. This series of operations is repeated a fixed number of times, and when it enters the synchronous detectable range as indicated by f0 in FIG. 2 within a fixed number of times, the arithmetic processing unit is based on the frequency data measured by the frequency measuring circuit 10 next. The frequency of the reference signal generated by the reference signal generator 12 is corrected by 11 so that it becomes the target frequency. Specifically, based on the data obtained from the demodulator 9 and the synchronization establishment detecting device 15, the reference signal generator 12 is set so that the reproduction reference signal necessary for digital demodulation by the demodulator 9 becomes effective. to correct. As a result, it is possible to correct the frequency by exceeding the reproducible reference frequency range of the demodulator 9.

FIG. 3 is a flow chart showing the frequency correction operation by the synchronization establishment detecting device 15. When the input frequency of the demodulator 9 is deviated from the synchronization detectable range as shown in FIG. 2, the synchronization establishment detection device 15 detects the synchronization loss. When the synchronization establishment detecting device 15 determines that the synchronization cannot be achieved, the frequency of the reference signal of the reference signal generator 12 is adjusted using the arithmetic processing device 11 in S20. After that, again in S10, it is determined whether or not the synchronization establishment detecting device 15 can detect the synchronization. When it is determined that the synchronization cannot be detected, the frequency of the reference signal is adjusted again by the arithmetic processing unit 11 in S20.

When it is determined that the synchronization establishment detecting device 15 can detect the synchronization by repeating the steps S10 and S20, the frequency is measured by the frequency measuring circuit 10 in S30, and the frequency is measured based on the measured frequency data. In S40, the arithmetic processing unit 11 causes the reference signal generator 1 to operate.
The frequency generated from 2 is corrected to be the target frequency. The synchronization establishment detecting device 15 that has executed the step of S40 returns to S10 again, and returns to the process of determining whether or not the input frequency of the demodulator is deviated. Thereafter, by repeating this step, it is possible to correct the frequency in a wide range of frequencies.

In this way, the reference signal generator 12 for generating the reference signal and changing the frequency of the reference signal according to the correction amount, and the local oscillator 14 for generating the local oscillation frequency based on the reference signal are provided. In the digital transceiver having the transmission frequency of the base station detected from the received signal, the synchronization establishment detection device 15 includes the reliability of the detected transmission frequency from the base station in the digital communication data. Judgment is made by using fixed data, synchronization word, etc., and the deviation of the reception frequency of the own station from the transmission frequency from the base station is recognized, and the frequency accuracy of the reference signal oscillator of the own station follows the accuracy of the base station transmission frequency Can be made.

As described above, according to this embodiment, whether or not the synchronization with the received signal is established even if there is an intermediate frequency error that exceeds the phase error correctable range originally possessed by the digital demodulator. By checking, it is judged whether the reproduction reference signal from the demodulator is true or false, the intermediate frequency data is driven into the phase error correctable range of the demodulator, and the effective reproduction frequency is counted to determine a wide range. It is possible to correct the frequency over the range.

Example 2. FIG. 4 shows a block diagram of a frequency correction system during burst reception. The synchronizing signal input terminal 17 inputs a control signal for enabling / disabling the frequency measuring operation of the frequency measuring circuit 10. During burst communication, the received signal is received discontinuously on the time axis as shown in FIG. Where S1, S2, S
3. ． ． Is a reception slot, and data necessary for demodulation is sent from the base station. Therefore, the synchronization timing as shown in FIG. 5 is created by a CPU (not shown) or a dedicated device for generating the synchronization timing, and is input from the synchronization signal input terminal 17. This synchronization timing is input from the synchronization signal input terminal 17, and the output location is not constant. For example, CP not shown
There is a circuit dedicated to U or to output the timing depending on the system. By inputting this synchronization timing, the frequency measuring circuit 10a measures the frequency of the second intermediate frequency during the reception slot, and the measured effective frequency data is calculated by the arithmetic processing unit 11 so that the same as in the continuous reception is obtained. It is possible to create correction data. This correction data is used by the arithmetic processing unit 1 during burst communication.
1 is created by working on the output data of the frequency measuring circuit 10 in synchronization with the slot of its own station and cumulatively calculating the data output from the frequency measuring circuit 10 for a certain period of time.

In this way, even when the receiver operates during a burst during continuous communication, the intermediate frequency count operation is synchronized with the receiving slot, and the intermediate data is detected by accumulating the divided data later. Enables and enables correction of the oscillation frequency of the reference signal generator of the local station.
Therefore, the base station transmission frequency can be detected and the frequency accuracy of the reference oscillator of the mobile station can be made to follow the accuracy of the base station transmission frequency even during burst communication by time division (TDMA) digital communication.

Example 3. FIG. 6 shows an example in which the configuration based on the above-described first embodiment is used to further improve the tracking accuracy. In the double superheterodyne system as shown in FIG. 6, the intermediate frequency input to the demodulator 9 is different from the originally desired frequency due to the error in the reference signals generated by the first local oscillator 14 and the second local oscillator 13a. There is a risk. That is, in the conventional configuration, the intermediate frequency input to the demodulator 9 includes the error of the second local oscillator 13, and this error amount cannot be removed. In the present embodiment, the second local oscillation frequency is measured by the second local oscillation frequency measuring circuit 16 with the reference signal generator 12 as a reference,
The arithmetic processing unit 11 calculates the correction amount so as to cancel the error amount from the true frequency of the second local oscillator 13a, and corrects the signal generated by the second local oscillator 13a. Therefore, the intermediate frequency input to the demodulator 9 does not include the error amount of the second local oscillator 13a.

As described above, by correcting not only the first local oscillator but also the second local oscillator, the reception frequency on the mobile unit side can be made even closer to the base station transmission frequency.

In this way, the frequency of the local oscillator of the mobile station can be measured during communication, and the frequency accuracy of the reference oscillator of the mobile station can be made to follow the accuracy of the base station transmission frequency even during long-time communication.

Example 4. FIG. 7 shows a system block diagram in which the reliability of the frequency correction system is improved in a weak electric field. Reference numeral 18 is a reception electric field level judgment device for judging the electric field level from the demodulator 9a. In FIG. 8, assume that the electric field level from the demodulator 9a is on the line indicated by L2. L3 is a judgment criterion in the reception electric field level judging device 18, and it is considered that the frequency of the second intermediate frequency is correctly measured by the frequency measuring circuit 10 when L2 is above this line. However, the judgment reference line L
3 can be adjusted from the outside. L1 is the minimum section in which the frequency measuring circuit 10 measures the frequency, and is preferably shorter than the fading cycle. In the case of the example in FIG. 8, a1, a2, and a5 are regarded as the frequencies measured by the frequency measuring circuit 10 being correct, and are treated as data necessary for frequency correction in the arithmetic processing unit 11. On the other hand, a
Since 3 and a4 do not reach the judgment reference line, the frequency measured by the frequency measuring circuit 10 during this period is invalid.

In this way, when the reliability of the reproduced signal from the demodulator 9 becomes extremely low due to fading on the mobile unit side in a weak electric field, the frequency data in that section is invalidated and a certain constant electric field is applied. When the level is reached, the data from the demodulator 9 is validated, and the frequency measuring circuit 10 measures the frequency of the second intermediate frequency.

By excluding the frequency measurement in the weak electric field, the reliability of the frequency of the second intermediate frequency is improved, and the correction error in the arithmetic processing unit 11 can be reduced. That is, by combining the frequency correction operation with the electric field measurement even in the weak electric field, the accuracy of the frequency measurement of the second intermediate frequency in the weak electric field can be increased and the reliability of the frequency correction can be improved.

Example 5. FIG. 9 is a block diagram of a system that incorporates the elements of both the second embodiment and the fourth embodiment. That is, FIG. 9 shows a system for improving the reliability of the frequency correction system during burst reception in a weak electric field. In this embodiment, as shown in FIG. 10, slots S1, S2, S3. ． ． At, the received electric field level determination device 18 determines the electric field level from the demodulator 9a. In the case of the example in FIG. 10, since the electric field level L2 determined by the reception electric field level determination device 18 is above the determination reference line L3 in the section a1 corresponding to the slot S1, the data obtained from the slot S1 is calculated. It is handled as data necessary for frequency correction in the device 11. On the other hand, in the section a2 corresponding to the slot S2, the electric field level is below the determination reference line L3, and thus the data obtained from the slot S2 is used as data that cannot be used for frequency correction. In the case of the section a3 corresponding to the slot S3, the electric field level is above the determination reference line L3, so the data obtained from the slot S3 is treated as the data necessary for frequency correction. In this way, during fading, electric field detection is performed in slot units during burst communication so that errors do not occur in the frequency correction system on the mobile unit side during weak electric fields,
The mobile station side detects the base station transmission frequency more accurately.

Example 6. FIG. 11 shows a block diagram of a system incorporating the elements of both the third embodiment and the fourth embodiment. This improves the frequency correction accuracy as a whole, and improves the reliability of frequency correction in a weak electric field.

[0031]

As described above, according to the present invention, whether the frequency detected by the frequency detecting means is reliable or not can be checked by checking whether the synchronization is established by the synchronization establishing detecting means. Since the judgment is made and the arithmetic processing means adjusts the reference signal generated from the reference signal generating means, frequency correction in a wide range becomes possible.

Further, since the intermediate frequency counting operation is synchronized with the receiving slot even during the burst receiving operation during continuous communication, the frequency can be corrected even during the burst receiving operation. That is, it is possible to correct the frequency even during burst communication, that is, even in a call state of discontinuous reception.

Further, the error can be removed from the local oscillation frequency output from the local oscillation means by measuring and correcting the local oscillation frequency generated from the local oscillation means.

Further, the frequency can be correctly corrected even in the weak electric field, and the reliability of the frequency correction in the weak electric field is improved.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a frequency correction system according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a frequency correction system according to a first embodiment of the present invention.

FIG. 3 is a flowchart illustrating the operation of the frequency correction system according to the first exemplary embodiment of the present invention.

FIG. 4 is a diagram illustrating a frequency correction system according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a synchronization timing according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a frequency correction system according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating a frequency correction system according to a fourth embodiment of the present invention.

FIG. 8 is a diagram for explaining the operation of the frequency correction system according to the fourth embodiment of the present invention.

FIG. 9 is a diagram illustrating a frequency correction system according to a fifth embodiment of the present invention.

FIG. 10 is a diagram for explaining the operation of the frequency correction system according to the fourth embodiment of the present invention.

FIG. 11 is a diagram illustrating a frequency correction system according to a sixth embodiment of the present invention.

FIG. 12 is a diagram illustrating a conventional frequency correction system.

[Explanation of symbols]

 1 Received Signal Input Terminal 2 Bandpass Filter 3 Amplifier 4 First Mixer 5 First Intermediate Frequency Filter 6 First Intermediate Amplifier 7 Second Mixer 8 Second Intermediate Frequency Filter 9 Demodulator 10, 10a Frequency Measurement circuit 11, 11a Arithmetic processing device 12 Reference signal generator 13, 13a Second local oscillator 14 First local oscillator 15 Synchronization establishment detection device 16 Second local oscillation frequency measurement circuit 17 Synchronization signal input terminal 18 Reception electric field level determination device

Claims (4)

[Claims] 1. A frequency correction system having: (a) a reference signal generating means for generating a reference signal; (b) a reference signal generated by the reference signal generating means for receiving a signal from a digital transmitter. Frequency detecting means for detecting the frequency of a signal from the digital transmitter received based on (c) synchronization establishment detecting means for detecting establishment of synchronization with the signal received from the digital transmitter, and (d) synchronization establishment detecting means. Arithmetic processing means for obtaining the difference from the frequency detected by the frequency detecting means and the transmission frequency of the digital transmitter on the basis of the detection result of the above, and correcting the reference signal generated by the reference signal generating means. 2. A frequency correction system having: (a) a reference signal generating means for generating a reference signal; (b) a reference signal generated by the reference signal generating means for receiving a signal from a digital transmitter. Frequency detection means for detecting the frequency of the signal received based on (c) synchronization establishment detection means for detecting the establishment of synchronization with the signal received from the digital transmitter, and (d) the signal received from the digital transmitter. Sync signal input means for inputting a sync signal indicating a sync timing, and (e) when the sync signal is input by the sync signal input means, the sync signal is detected by the frequency detection means based on the detection result by the synchronization establishment detection means. Arithmetic processing means for obtaining the difference from the transmission frequency of the digital transmitter from the frequency and correcting the reference signal generated by the reference signal generating means. 3. A frequency correction system having the following elements: (a) reference signal generating means for generating a reference signal; (b) local portion for generating a local oscillation frequency based on the reference signal generated by the reference signal generating means. (C) a signal from a digital transmitter is received, and the frequency of the received signal is determined based on the reference signal generated by the reference signal generation means and the local transmission frequency generated by the local transmission means. Frequency detecting means for detecting, (d) local oscillation frequency measuring means for measuring the local oscillation frequency generated by the local oscillation means, (e) local oscillation based on the frequency measured by the local oscillation frequency measuring means Arithmetic processing means for correcting the local oscillation frequency generated by the means. 4. A frequency correction system having the following elements: (a) reference signal generating means for generating a reference signal, (b) receiving a signal from a digital transmitter, and generating a reference signal from the reference signal generating means. Frequency detection means for detecting the frequency of the signal received based on (c) electric field level determination means for detecting the electric field level when the frequency is detected by the frequency detection means, (d) detection result by the electric field level determination means Based on the above, arithmetic processing means for obtaining the difference from the transmission frequency of the digital transmitter from the frequency detected by the frequency detecting means and correcting the reference signal generated by the reference signal generating means.