JP2001053589A - Method and system for automatic frequency control of radio system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute time-division transmission and reception of a digital phase modulation signal and an FM signal by stopping automatic frequency control for correcting deviation of frequency obtained, based on the sample of the digital phase modulation signal through the use of a relation between a previously set frequency controlled variable and a controlled voltage in an FM signal section. SOLUTION: A transmission side repeatedly and consecutively transmits a no- modulation carrier signal and a digital phase modulation signal in order of a QPSK signal and an FM signal, e.g. from a no-signal state. In a no-modulation carrier signal period, a demodulator 30 detects plural phase rotating quantity at fixed sampling intervals to calculate the frequency deviation from this. Based on the relation between a previously set frequency controlled variable and a controlled voltage, a control part 40 sends the controlled voltage to a voltage-control crystal oscillator 50. When a frequency deviation is made sufficiently small by successively correcting the controlled voltage in a direction making the frequency deviation zero, a fixed sampling timing is switched to a symbol timing to shift to AFC operation to receive the QPSK signal and the FM signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic frequency control method for a radio system for transmitting / receiving a digital phase modulation signal and an FM signal at one carrier frequency in a time division manner, and a technique relating to the automatic frequency control system.

[0002]

2. Description of the Related Art In a wireless system in which an FM system is conventionally used, when a digital phase modulation system (for example, π / 4 QPSK, etc.) is considered for the purpose of enhancing the functions in the future, the transition period is considered. In both cases, both of the above-mentioned methods may be mixed, and thereafter, all of the methods shift to the digital phase modulation method. Therefore, in order to correspond to both the above-mentioned systems, the transmission / reception function of both the systems is necessary in the radio system in the transition period, and in this case, when each carrier frequency is not given to each system, This wireless system requires time division transmission. FIG. 8 shows the relationship between the transition period and the future wireless system.
Old FM transmitter 510, old FM receiver 520, new digital FM transmitter 530, and new digital FM receiver 54
0 is shown.

[0003]

However, the prior art has the following problems. When the carrier frequency change due to environmental temperature, aging, etc. is relatively large compared to the digital signal transmission speed, or when the carrier frequency is high and the digital signal transmission speed is small, that is, the ratio (transmission speed / transmission speed) In a system with a small carrier frequency, the conventional automatic frequency control (hereinafter, referred to as AFC) method does not function properly due to an insufficient tracking frequency range or an influence of a modulation sideband. Also, the AFC circuit for digital demodulation does not function properly with FM signals. When the receiving frequency cannot be accurately tracked, the error rate (BER) of the received digital signal deteriorates.

[0004] The present invention has been made in view of the above problems, and has as its object to detect a frequency shift by adding an unmodulated carrier signal without providing a special circuit, and to detect the frequency shift. It is an object of the present invention to provide an automatic frequency control method of a wireless system for transmitting / receiving a digital phase modulation signal and an FM signal at one carrier frequency in a time-division manner, and a technique relating to the automatic frequency control system.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic frequency control method for a radio system for transmitting and receiving a digital phase modulation signal and an FM signal on one carrier frequency in a time division manner. Detecting a non-modulated carrier signal placed before the digital phase modulation signal in step (a), measuring the amount of phase rotation of each of the unmodulated carrier signals at a plurality of sample intervals having a predetermined sample time, And the sample interval, and calculates the frequency shift amount to 0H based on a preset relationship between the frequency control amount and the control voltage.
calculating the control voltage to be adjusted to z, performing automatic frequency control in the section of the digital phase modulation signal based on the frequency control amount, and stopping the automatic frequency control in the section of the FM signal. An automatic frequency control method for a wireless system. The gist of the present invention according to claim 2 is that, when the variation of each of the phase rotation amounts with respect to a predetermined number of the sample intervals is within / less than a predetermined value, the non-modulated carrier signal is determined and the calculated The frequency shift amount is set to a first frequency shift amount, the control voltage is set to a first control voltage, and the first frequency shift amount is adjusted to be 0 Hz. The second phase rotation amount is measured at the sample interval, and the second frequency shift amount is calculated based on the ratio between the second phase rotation amount and the next sample interval.
A difference between the frequency shift amount and the second frequency shift amount,
Adjusting the second frequency shift amount with a second control voltage based on a ratio to the control voltage, repeating the calculation of the frequency shift amount until the n-th n-th frequency shift amount becomes equal to or less than or less than a predetermined value; 2. The method according to claim 1, wherein when the n-th frequency shift amount becomes equal to or less than a predetermined value, the calculation of the frequency shift amount is stopped, and the automatic frequency control is performed in a section of the digital phase modulation signal. The present invention resides in an automatic frequency control method for a wireless system described above. The gist of the present invention according to claim 3 is to output from the first control voltage to the (n-1) th control voltage for adjusting the first frequency shift amount to the (n-1) th frequency shift amount to a voltage controlled crystal oscillator. 3. The automatic frequency control method for a wireless system according to claim 1, wherein the automatic frequency control is performed with high accuracy by suppressing the influence of sensitivity variation of the voltage controlled crystal oscillator. Claim 4
The gist of the present invention resides in a storage medium in which a program capable of executing the automatic frequency control method for a wireless system according to any one of claims 1 to 3 is recorded. The gist of the present invention described in claim 5 is an automatic frequency control system of a wireless system for transmitting and receiving a digital phase modulation signal and an FM signal in a time-division manner at one carrier frequency. A demodulator that detects a modulated carrier signal and outputs a phase rotation amount; a control unit that outputs a control voltage for correcting a frequency deviation amount calculated from the phase rotation amount; and a control unit that inputs the control voltage and outputs the frequency deviation amount. And a voltage-controlled crystal oscillator for generating a frequency control amount corresponding to the amount. The gist of the present invention according to claim 6 is that the demodulator comprises: a quasi-synchronous quadrature demodulator for outputting an I signal and a Q signal corresponding to the digital modulation signal; A phase delay detector for detecting the amount of rotation, wherein the phase delay detector switches the sample timing from a fixed timing to an output of a symbol timing generation circuit in order to receive the digital phase modulation signal. An automatic frequency control system for a wireless system according to claim 5.

In the present invention, "n" means a natural number.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, the automatic frequency control system of the wireless system according to the present embodiment includes a frequency mixer 10, a bandpass filter 20, a demodulator 30, a control unit 40, a voltage controlled crystal oscillator 50, a synthesizer type oscillation circuit. The demodulator 30 includes a quasi-synchronous quadrature demodulator 32 and a phase delay detector 34.

[0008] Quasi-synchronous quadrature demodulator 32 and phase delay detector 3
The demodulator 30 provided with 4 is in a state of waiting for reception.
An operation of detecting an unmodulated carrier signal at a fixed timing is performed.

FIG. 2 is a block diagram of the quasi-synchronous quadrature demodulator 32 included in the demodulator 3 shown in FIG. 1, and corresponds to a digital phase modulation signal. In FIG. 2, a multiplier 110, a low-pass filter 120, a quasi-synchronous carrier frequency 130, and a 90 ° phase shifter 14 are shown.
0 and an analog-to-digital converter ADC, and output an I signal and a Q signal. Other components are generally known, and thus description thereof is omitted.

FIG. 3 is a block diagram of the phase delay detector 34 of the automatic frequency control system. Phase delay detector 34
Detects the amount of phase rotation using the I signal and the Q signal output from the quasi-synchronous quadrature demodulation unit 32 shown in FIG. FIG. 3 shows an instantaneous angle conversion circuit 210, a subtractor 220, a delay circuit 230, and a symbol timing generation circuit 240. Other components are generally known, and thus description thereof is omitted.

Next, the operation of the automatic frequency control system of the radio system according to the present embodiment will be described. FIG.
Indicates the transmission format of the automatic frequency control system.
On the transmitting side of the wireless system, the non-modulated carrier signal A, the digital phase modulation signal B, and the FM signal C are transmitted in this order from the non-signal state, and the unmodulated carrier signal A,
After transmitting the transmission formats of the digital phase modulation signal B and the FM signal C continuously, the transmission is terminated. The receiving side in the automatic frequency control system of the wireless system needs to perform high-speed AFC operation.

In a reception waiting state, the demodulator 30 including the quasi-synchronous quadrature demodulator 32 shown in FIG. 2 and the phase delay detector 34 shown in FIG. 3 performs an operation of detecting the unmodulated carrier signal A at a fixed timing.

FIG. 5 is a diagram showing a frequency shift amount of the unmodulated carrier signal A. From the unmodulated carrier signal A, the phase rotation amount (Δθ) at a predetermined sample interval (τ) within the sample time T is measured a plurality of times. The phase gradients S1, S2, S3... Meaning these ratios are almost equal to the gradient K.

FIG. 6 is a diagram showing the correction of the frequency deviation amount of the unmodulated carrier signal A. When the amount of phase rotation Δθ at the phase gradient Sn1 is known, the amount of frequency deviation (Δf) is calculated from Δθ / τ. The phase rotation amount of the phase gradient Sn1 is Δθ1 radian, and the initial frequency deviation amount (first frequency deviation amount) is Δf1.
When the frequency is set to Hz, the relation of the equation (a) is established.

Initial frequency deviation amount: Δf1 Hz = Δθ1 radian / (2πτ) seconds... (A) The deviation amount is set to 0 Hz based on a preset frequency control amount / control voltage relationship. As described above, the control voltage (first control voltage) ΔV1 is outputted from the control unit 40 shown in FIG. By this operation, the second phase gradient S
At n2, as shown in FIG. 6, the residual phase rotation amount (second phase rotation amount) Δθ2, which is the deviation amount, becomes small. Assuming that the residual frequency deviation amount (second frequency deviation amount) is Δf2 Hz, the relationship of Expression (2) is established.

Residual frequency shift amount: Δf2 Hz = Δθ2 radian / (2πτ) seconds (b) Further, as shown in equation (c), frequency control based on the relationship of frequency control amount / control voltage The sensitivity (next control voltage) is calibrated, the next control voltage (second control voltage) ΔV2 is set,
The next residual frequency deviation generated from the control voltage ΔV2 has an extremely small value.

Frequency control sensitivity ΔV2 = (Δf1-Δf2) / ΔV1 (C) This operation is repeated as Sn3... Snn, and the nth residual frequency shift is performed. This operation is stopped when the amount (the amount of the n-th frequency shift) falls within or below a predetermined value. At this time,
Generate up to the (n-1) th control voltage.

Next, in order to receive the digital phase modulation signal B, the sample timing is switched from the fixed timing to the output of the symbol timing generation circuit 240, and the digital phase modulation signal B is received. In the amount of the (n-1) th frequency shift, the shift is sufficiently small, so that the conventional AFC method can be applied thereafter. In some cases, the section of the unmodulated carrier signal A cannot be received depending on the propagation condition of the radio channel. However, the digital phase modulated signal B and the FM signal C have several tens of symbol sections (symbol interval SY).
.DELTA..theta. Does not become substantially constant over M) as in S1, S2, S3... As shown in FIG. FIG. 7 shows a π / 4 QPSK signal as an example of the digital phase modulation signal B. This makes it clear that the unmodulated carrier signal A
Can be determined. In the figure, the horizontal axis represents the symbol interval SYM,
The vertical axis represents the amount of phase rotation (Δθ).

The automatic frequency control method and the automatic frequency control system for a wireless system according to the embodiment are configured as described above, and thus have the following effects. If the carrier frequency change due to environmental temperature, aging, etc. is relatively large compared to the digital signal transmission speed, or
When the carrier frequency is high and the transmission speed of the digital signal is low, that is, in a system where the ratio (transmission speed / carrier frequency) is small, the frequency control can function normally.

In the present embodiment, the present invention is not limited to this. The present invention can be applied to an automatic frequency control method and an automatic frequency control system suitable for a wireless system to which the present invention is applied.

Further, the number, position, shape, etc. of the above-mentioned constituent members are not limited to the above-mentioned embodiment, but can be set to a suitable number, position, shape, etc. for carrying out the present invention.

In each of the drawings, the same components are denoted by the same reference numerals.

[0023]

Since the present invention is configured as described above, the following effects can be obtained. The frequency shift can be detected using a digital demodulator and the large frequency shift can be controlled only by adding the unmodulated carrier signal without providing a special circuit. Also, since the signal to be added is a non-modulated carrier signal, there is an effect that the occupied band does not increase and there is no interference with other transmission systems.

[Brief description of the drawings]

FIG. 1 is a block diagram of an automatic frequency control system of a wireless system according to an embodiment of the present invention.

FIG. 2 is a block diagram of a quasi-synchronous quadrature demodulator of FIG. 1;

FIG. 3 is a block diagram of a phase delay detector of FIG. 1;

FIG. 4 is a diagram showing a transmission format of FIG. 1;

FIG. 5 is a diagram illustrating a frequency shift amount of the unmodulated carrier signal of FIG. 1;

FIG. 6 is a diagram illustrating correction of a frequency shift amount of the unmodulated carrier signal of FIG. 1;

FIG. 7 is a diagram illustrating an example of a digital phase modulation signal of FIG. 1;

FIG. 8 is a diagram illustrating a relationship between a transition period and a future wireless system.

[Explanation of symbols]

 A unmodulated carrier signal B digital phase modulation signal C FM signal ADC analog-to-digital converter K gradient S1, S2, S3, Sn1, Sn2, Sn3 phase gradient SYM symbol interval T sample time 10 frequency mixer 20 bandpass filter 30 demodulator 32 Quasi-synchronous quadrature demodulation unit 34 Phase delay detection unit 40 Control unit 50 Voltage-controlled crystal oscillator 60 Synthesizer oscillation circuit 110 Multiplier 120 Low-pass filter 130 Quasi-synchronous carrier frequency 140 90 ° phase shifter 210 Instantaneous angle conversion circuit 220 Subtraction Device 230 delay circuit 240 symbol timing generation circuit 510 old FM transmitter 520 old FM receiver 530 new digital FM transmitter 540 new digital FM receiver

Claims (6)

[Claims] 1. An automatic frequency control method for a radio system for transmitting and receiving a digital phase modulation signal and an FM signal at one carrier frequency in a time division manner, comprising: an unmodulated carrier wave arranged before the digital phase modulation signal in a reception signal. Detecting a signal, measuring a phase rotation amount of each of the unmodulated carrier signals at a plurality of sample intervals having a predetermined sample time, and calculating a frequency shift amount based on a ratio between the phase rotation amount and the sample interval. Calculating the control voltage for adjusting the frequency deviation amount to 0 Hz based on a relationship between a preset frequency control amount and a control voltage; and automatically calculating the control voltage in the section of the digital phase modulation signal based on the frequency control amount. Performing frequency control, and stopping the automatic frequency control in the section of the FM signal. Your way. 2. When the variation of each of the phase rotation amounts with respect to a predetermined number of the sample intervals is within / less than a predetermined value, the phase rotation amount is determined to be the unmodulated carrier signal, and the calculated frequency shift amount is set to a first value. The first voltage shift amount is adjusted to be 0 Hz using the control voltage as a first control voltage, and at the next sample interval of the sample time that is equal to the sample interval, A two-phase rotation amount is measured, and a second frequency shift amount is calculated based on a ratio between the second phase rotation amount and the next sample interval, and the first frequency shift amount and the second frequency shift amount are calculated. Difference and,
The second frequency shift amount is adjusted with a second control voltage based on the ratio to the first control voltage, and the calculation of the frequency shift amount is performed until the n-th frequency shift amount becomes equal to or less than a predetermined value. Repeating, when the n-th frequency shift amount becomes equal to or less than a predetermined value, the calculation of the frequency shift amount is stopped, and the automatic frequency control is performed in the section of the digital phase modulation signal. An automatic frequency control method for a wireless system according to claim 1. 3. The method according to claim 1, wherein the first control voltage for adjusting the first frequency shift amount to the (n-1) th frequency shift amount is equal to the (n-1) th frequency shift amount.
3. The automatic wireless system according to claim 1, wherein up to a control voltage is output to a voltage-controlled crystal oscillator, and the influence of sensitivity variation of the voltage-controlled crystal oscillator is suppressed to improve the automatic frequency control with accuracy. Frequency control method. 4. A storage medium on which is recorded a program capable of executing the automatic frequency control method for a wireless system according to claim 1. 5. An automatic frequency control system for a wireless system for transmitting and receiving a digital phase modulation signal and an FM signal in a time division manner at one carrier frequency, wherein an unmodulated carrier signal is detected at a fixed timing in a reception waiting state. A demodulator that outputs a phase rotation amount by using a control unit that outputs a control voltage that corrects a frequency deviation amount calculated from the phase rotation amount; and a frequency control that receives the control voltage and that corresponds to the frequency deviation amount. An automatic frequency control system for a wireless system, comprising: a voltage-controlled crystal oscillator that generates a quantity. 6. A demodulator for outputting an I signal and a Q signal in response to the digital modulation signal, and detecting the phase rotation amount based on the I signal and the Q signal. 6. A phase delay detection section, wherein the phase delay detection section switches a sample timing from a fixed timing to an output of a symbol timing generation circuit in order to receive the digital phase modulation signal. Automatic frequency control system for wireless systems.