JP2743826B2 - Wireless communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication system, and more particularly to a digital radio communication system in which a master station and a number of slave stations perform multidirectional multiplex communication via a radio line.

[0002]

2. Description of the Related Art There are a time division multiplex system and a frequency division multiplex system as signal transmission systems of a digital radio communication system in which a master station and a number of slave stations perform multidirectional multiplex communication via a radio line. In the time division multiplexing method, a signal from the master station to each slave station is time multiplexed and transmitted to all slave stations in a continuous wave,
The slave station is a system that performs time division multiplex transmission between slave stations using transmission information as an intermittent burst signal. On the other hand, the frequency multiplexing method is a method in which a carrier wave having a different frequency is used for each channel, and multiplex communication is performed by dividing the frequency axis.

In any of the systems, communication must be performed at a stable frequency in order to effectively utilize limited frequency resources, while a large number of slave stations are required to be reduced in size and cost. .

For this reason, transmission from a master station to a slave station in a time-division multiplexing broadcast mode and transmission from a slave station to a master station by a frequency multiplexing method have been conventionally performed, so that the master station has high stability. A wireless communication system that reproduces a reference clock at a slave station and performs stabilization control using the reference clock as a reference signal (Japanese Patent Laid-Open No. 62-188440: title of invention: "Multidirectional multiplex communication system"), or a slave station Regenerate the clock frequency of the digital signal from the received carrier signal from the master station,
A wireless communication system that generates a carrier wave for highly stable transmission by using a relatively low-stability oscillator by forming a phase synchronization circuit or a frequency synchronization circuit of a slave station based on a clock signal (Japanese Unexamined Patent Application Publication No. 248137: The title of the invention "wireless communication device") is known.

[0005]

However, in any of the above-mentioned conventional wireless communication systems, there is a possibility that the control of the carrier wave oscillating means is performed even when the slave station is transmitting. In this case, since the transmission frequency of the slave station changes during transmission, the communication quality is degraded, and transmission information may not be transmitted correctly. In particular, when a digital system is used as the carrier control means, the transmission frequency changes discontinuously, which has a large effect.

Further, in the above-mentioned conventional radio communication system, since the loop bandwidth is reduced in order to stabilize the oscillation frequency during synchronization, the amount of feedback is small, the reference clock is reproduced, and the reception is synchronized. Therefore, there is a problem that it takes time until the carrier oscillation means is stabilized and the slave station starts transmission.

[0007] The present invention has been made in view of the above points,
By synchronizing the transmission carrier of the slave station with the transmission timing clock of the stable master station in frequency, the frequency difference between slave stations is eliminated, the system is stabilized, and the communication quality is deteriorated during the transmission of the slave station. It is an object of the present invention to provide a wireless communication system capable of preventing the problem.

It is another object of the present invention to provide a radio communication system capable of shortening the time from when the slave station synchronizes the reception to when the slave station starts transmission.

[0009]

According to the present invention, in order to achieve the above object, data is time-division multiplexed from a master station to all of a plurality of slave stations based on the timing of a reference clock, and is transmitted as a continuous wave. In a wireless communication system that performs time-division transmission of transmission information as an intermittent burst signal from each of a plurality of slave stations to a master station, each of the plurality of slave stations receives a transmission signal from the master station, Reference clock reproducing means for reproducing a reference clock from the received signal; variable frequency generating means for generating a carrier reference signal of a burst signal to be transmitted and varying a carrier reference signal frequency by a control signal; Detects the frequency difference of the signal, controls the variable frequency generation means so that the frequency difference is less than a certain value, and permits transmission when the frequency difference becomes less than a certain value. Frequency control means, a transmission means for modulating a carrier reference signal with transmission information after receiving a transmission permission by the frequency control means, and transmitting a modulated wave as a burst signal, and frequency control during transmission of the burst signal by the transmission means. Control means for forcibly stopping the control of the variable frequency generating means by the means and outputting a constant frequency from the variable frequency generating means.

According to the present invention, in order to achieve the above-mentioned other object, each of the slave stations has the above-mentioned reference clock reproducing means, variable frequency generating means, transmitting means and control stopping means , respectively. instead of the control hand stage, an error detection circuit for detecting a frequency difference between the reference clock and the carrier reference signal, said amplified output signal of the error detecting circuit in a controlled gain with gain controlled by the gain control signal Output as a frequency control signal to the variable frequency generating means, a frequency control signal generating means to make the frequency difference less than a certain value, and detect whether the frequency difference is less than a certain value,
When at least the frequency difference is greater than a certain value, while outputting a gain control signal for controlling the gain of the frequency control signal generating means more than when the frequency difference is less than or equal to a certain value,
Gain control means for outputting a transmission permission signal when the frequency difference becomes equal to or less than a predetermined value.

[0011]

In the present invention, each of the slave stations reproduces the reference clock of the master station by the reference clock reproducing means, and the carrier frequency reference signal synchronized with the reference clock is outputted from the variable frequency generating means by the frequency control means. Therefore, an oscillator with low stability can be used for the variable frequency generating means, and during transmission of the burst signal by the transmitting means, the control of the variable frequency generating means by the frequency control means is forcibly stopped to generate the variable frequency. Since the means outputs a constant frequency, the transmission frequency can be kept constant during burst signal transmission.

Further, according to the present invention, when the frequency difference between the reproduced reference clock and the carrier reference signal detected by the error detection circuit is larger than a certain value, the frequency control signal is at least higher than when the frequency difference is smaller than the certain value. Since the gain of the generating means is controlled to a large value, control is performed such that the carrier reference signal is quickly brought closer to the target reference clock frequency in the early stage of the control in which the frequency difference is large. The carrier reference signal can be prevented from changing significantly.

[0013]

Next, an embodiment of the present invention will be described. FIG. 1 shows a configuration diagram of an embodiment of a wireless communication system according to the present invention. As shown in the figure, a master station 10 is bidirectionally connected to a slave station 30 via a wireless line 20. The master station 10 has a transmitter 11 and a receiver 12. Also, the transmitter 1
1 is a frame conversion circuit 111, a reference clock generation circuit 1
12, a modulation circuit 113 and a local oscillator 114.

On the other hand, the slave station 30 is one of a plurality of slave stations having the same configuration in this wireless communication system, and includes a receiver 31, a transmitter 32, a logic circuit 33, and the like. The receiver 31 includes a mixer 311, a local oscillator 312, a demodulation circuit 313, and a clock recovery circuit 31.
4 and a frame conversion circuit 315. The transmitter 32 includes a frame conversion circuit 321 and a clock generation circuit 32.
2, a frequency control circuit 323, a local oscillator 324, a modulation circuit 325, and the like.

This embodiment is, for example, a VSAT system,
The master station 10 is called a hub (HUB) station and transmits a continuous wave time division multiplexed signal (TDM signal). The plurality of slave stations 30 are micro satellite communication earth stations (VSAT stations) which receive the TDM signal transmitted from the master station 10 via the radio line 20 including satellites, and obtain the clock of the master station 10 from the received signal. On the other hand, while reproducing, a time-division burst signal (TDMA signal) is transmitted to the master station 10 via the radio line 20 including a satellite.

Next, the operation of this embodiment will be described.
First, the operation of the downlink will be described. In the master station 10, transmission data is supplied to a frame conversion circuit 111, where a reference clock generation circuit 11 having extremely high frequency stability is provided.
2 is converted to a frame format for wireless communication synchronized with the reference clock generated. Frame conversion circuit 111
The frame signal extracted from the plurality of slave stations 3
A continuous digital signal time-divided for zero,
The carrier wave supplied to the modulation circuit 113 and input from the local oscillator 114 is modulated into a modulated wave in the transmission frequency band,
Time division multiplexing of continuous waves (TDM: Time Division)
on Multiplex) signal.

The slave station 30 transmits the above TD transmitted by the master station 10.
The M signal is received via the radio line 20, and the received signal is input to the mixer 311 in the receiver 31, where the local oscillator 3
The frequency is converted to a baseband signal by multiplying by the local oscillation frequency signal from T.12. This baseband signal is input to the demodulation circuit 313 and the clock recovery circuit 314, respectively.

A clock recovery circuit 314 extracts a timing signal component from the baseband signal and recovers a reference clock of the master station 10. The clock recovery circuit 314 converts the recovered clock a into a demodulation circuit 313, a frame conversion circuit 315, and a frequency control circuit 323. Respectively. The demodulation circuit 313 converts the baseband signal from the mixer 311 into the reproduced clock a
To obtain a demodulated signal. The demodulated signal is supplied to the frame conversion circuit 315, where the received data for the slave station 30 is separated based on the reproduced clock a. The received data is output via the logic circuit 33.

Next, the operation of the uplink will be described.
The transmission data of the slave station 30 is supplied to the logic circuit 33. On the other hand, the reproduced clock a is supplied to the frequency control circuit 323 in the transmitter 32, where the local oscillator 3
24 is converted into a control voltage for controlling the oscillation frequency. The reproduction clock a is obtained by reproducing the reference clock of the master station 10, and the oscillation frequency (carrier signal) of the local oscillator 324 controlled by the control voltage generated based on the reproduction clock a is set to all the slave stations. Is the same.

As will be described later, the frequency control circuit 323 recognizes the synchronization of the reproduced clock a by the clock synchronization signal c from the logic circuit 33 and starts frequency control. Also,
The frequency control circuit 323 activates the frequency synchronization signal e when the frequency error between the recovered clock a and the carrier reference signal d becomes equal to or less than a predetermined value. When the frequency synchronizing signal e is activated and the frequency synchronizing signal e becomes active, the logic circuit 33 determines that transmission is permitted and passes the input transmission data to supply it to the frame conversion circuit 321.

The frame conversion circuit 321 is a logic circuit 3
When the control stop signal b input from 3 is set to a predetermined level by the above-mentioned transmission permission, the operation is enabled,
The input transmission data is converted into a wireless communication frame format synchronized with the transmission clock generated by the clock generation circuit 322.

The signal converted into the frame format is a digital signal having a finite length, and is supplied to a modulation circuit 325, where the carrier reference signal d input as a carrier from the local oscillator 324 is modulated and transmitted in the transmission frequency band. It is converted into a modulated wave. An output modulated wave of the modulation circuit 325 is a time division multiple access (TDMA: Time Division M).
The signal is transmitted to the wireless line 20 as a burst signal of a multiple access (multiple access) communication.

As described above, according to the present embodiment, the slave station 30
Is generated in synchronization with the reference clock of the master station 10, so that each slave station conventionally has a 5 × 1
A short-term stability of 5 × 10 ⁻⁶ (1 × 10 ⁻⁶⁾ has been required, which requires a highly stable oscillator of about 0 ⁻⁸ / year.
/ Year) of the local oscillator 324
In addition, the frequency control circuit 323 can be constituted by a logic circuit having several k gates, thereby realizing communication with high frequency stability and downsizing and cost reduction of the device.

The frequency control circuit 323 is connected to the transmitter 32
Is transmitting the burst signal, the control of the local oscillator 324 is temporarily stopped by the control stop signal b input from the logic circuit 33, thereby preventing the transmission frequency from changing during the transmission.

Next, the configuration and operation of the frequency control circuit 323 constituting the main part of the present embodiment will be described in more detail. FIG. 2 shows a block diagram of the frequency control circuit 323 of FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals. 2, a frequency control circuit 323 includes an error detection circuit 41 that detects a frequency error with respect to a carrier reference signal d based on a recovered clock a, a gain adjustment circuit 42,
A control stop circuit 43, a gain control circuit 44 for controlling the gain of the gain adjustment circuit 42, an integrator 45 for integrating the output signal of the gain adjustment circuit 42, and a D / D converter for converting the output signal of the integrator 45 into an analog signal. An A converter 46 is provided.

The gain control circuit 44 compares the level of a predetermined threshold value with the output signal of the error detection circuit 41, and selects an input gain control signal according to the output signal of the comparator 441. And a selector 442. Further, the integrator 45 includes an adding circuit 451 and a delay circuit 452.

Next, the operation of the frequency control circuit 323 will be described. The recovered clock a extracted from the clock recovery circuit 314 in FIG. 1 is supplied to the error detection circuit 41 in FIG. 2, where it is converted into an error signal corresponding to a frequency error with respect to the output carrier reference signal d of the local oscillator 324. rear,
Comparator 44 in gain adjustment circuit 42 and gain control circuit 44
1 respectively.

The comparator 441 compares the error signal with a predetermined threshold and outputs a signal corresponding to the magnitude of the error.
This is input to the selector 442 as a select signal and is output to the outside as a frequency synchronization signal e. As a result of comparison by the comparator 441, the frequency synchronizing signal e becomes active when the error signal is equal to or less than the threshold value, and gives the logic circuit 33 transmission permission.

On the other hand, the selector 442 selects a value according to the comparison result of the comparator 441, supplies it to the gain adjustment circuit 42 as the gain control signal f, and variably controls the gain. That is, when the initial frequency error is large, the selector 442 sets the gain control signal f that increases the gain of the gain adjustment circuit 42.
Is output, and when the frequency error is reduced, a gain control signal f for reducing the gain of the gain adjustment circuit 42 is output.

The error signal taken out by level control by the gain adjustment circuit 42 is supplied to an addition circuit 451,
Here, after being added to the signal from the delay circuit 452, the signal is delayed by one sample period by the delay circuit 452. The feedback circuit including the adding circuit 451 and the delay circuit 452 constitutes an integrator 45, and a value obtained by integrating the error signal is extracted from the delay circuit 452.

The output value of the integrator 45 is the D / A converter 4
6, where it is converted to an analog control voltage and then supplied to a local oscillator 324. Local oscillator 324
Is a variable frequency oscillator, for example, having a short-term stability of 5 × 10 ^-6
It is composed of a voltage controlled crystal oscillator (VCXO) having a relatively low stability of about (1 × 10 ⁻⁶ / year). This allows
The output oscillation frequency (carrier reference signal d) of the local oscillator 324 is variably controlled according to the analog control voltage from the D / A converter 46.

Here, when the initial frequency error is large, the gain of the gain adjustment circuit 42 is greatly controlled.
The oscillation frequency of the local oscillator 324 (that is, the carrier reference signal d) is controlled so as to approach the target frequency quickly, and when the frequency error becomes small, the gain adjustment circuit 42
Is controlled so that the output carrier reference signal d of the local oscillator 324 does not suddenly change in frequency due to noise or the like. As a result, the time from when the synchronization of the reproduction clock a is established to when the slave station 30 starts transmission can be shortened as compared with the related art.

Since the delay circuit 452 is reset by the clock synchronizing signal c, the integrator 45 uses the clock synchronizing signal c until the synchronization of the reproduced clock a is established. An integrated value is output so that the signal d has the center frequency of the variable range.

The above is the operation during the period other than the transmission period of the slave station 30, but in the present embodiment, the gain adjustment circuit 42 during the transmission period.
Is configured such that the gain is controlled to zero by the output signal of the control stop circuit 43. That is, when the control halt signal b is active (during the transmission period), the control halt circuit 43 outputs a gain control signal for setting the gain to zero to the gain adjustment circuit 42, thereby outputting the output signal of the gain adjustment circuit 42. Set to zero.

As a result, the output integrated value of the integrator 45 is fixed at a predetermined value, and the output carrier reference signal d of the local oscillator 324 is forcibly held at a constant value (predetermined transmission carrier frequency). Thus, according to the present embodiment, the transmission frequency is always kept at a constant value during the transmission period of the slave station 30, and it is possible to prevent the deterioration of the communication quality.

The present invention is not limited to the above-described embodiment. For example, the frequency control circuit 323 may be configured to include only one of the gain control circuit 44 and the control stop circuit 43. . In this case, since one of the gain control circuit 44 and the control stop circuit 43 is deleted,
The size of the device can be further reduced.

[0037]

As described above, according to the present invention,
During the transmission of the burst signal by the transmission means, the control of the variable frequency generation means by the frequency control means is forcibly stopped, and a constant frequency is output from the variable frequency generation means, and the transmission frequency is kept constant during the transmission of the burst signal. , The transmission frequency changes during the transmission of the slave station, the communication quality deteriorates,
Inconvenience that transmission information cannot be transmitted correctly can be prevented beforehand.

Further, according to the present invention, control is performed such that the carrier reference signal approaches the target reference clock frequency quickly in the initial stage of the control in which the frequency difference is large. Since it does not change much, the time required for frequency synchronization can be reduced compared to the conventional method, which shortens the time until the start of transmission of the slave station, and responds to noise etc. after synchronization. Thus, the phenomenon that the frequency of the carrier reference signal changes rapidly can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a frequency control circuit in FIG.

[Explanation of symbols]

 Reference Signs List 10 master station 11, 32 transmitter 12, 31 receiver 20 radio line 30 slave station 33 logic circuit 41 error detection circuit 42 gain adjustment circuit 43 control stop circuit 44 gain control circuit 45 integrator 111, 315, 321 frame conversion circuit 112 Reference clock generation circuit 113, 325 Modulation circuit 314 Clock recovery circuit 323 Frequency control circuit 324 Local oscillator for carrier reference signal generation

Claims (2)

(57) [Claims] 1. A master station transmits time-division multiplexed data to a plurality of slave stations based on the timing of a reference clock and transmits the data in a continuous wave. Is a wireless communication system for transmitting transmission information in a time-division manner as an intermittent burst signal, wherein each of the plurality of slave stations receives a transmission signal from the master station and reproduces the reference clock from the received signal. Clock recovery means, a variable frequency generation means for generating a carrier reference signal of the burst signal to be transmitted, and varying the carrier reference signal frequency by a control signal; a reference clock recovered by the reference clock recovery means; Detecting a frequency difference of the carrier reference signal from the variable frequency generating means, and controlling the variable frequency generating means so that the frequency difference is equal to or less than a fixed value; Frequency control means for permitting transmission when the frequency difference becomes equal to or less than the predetermined value; and a modulated wave obtained by modulating the carrier reference signal with transmission information after receiving the transmission permission by the frequency control means. As the burst signal, and during the transmission of the burst signal by the transmitter, the control of the variable frequency generating means by the frequency control means is forcibly stopped, and a constant frequency is output from the variable frequency generating means. A wireless communication system comprising: 2. The data is time-division multiplexed from the master station to all of the plurality of slave stations based on the timing of the reference clock and transmitted as a continuous wave, and each of the plurality of slave stations transmits the data to the master station. Is a wireless communication system for transmitting transmission information in a time-division manner as an intermittent burst signal, wherein each of the plurality of slave stations receives a transmission signal from the master station and reproduces the reference clock from the received signal. Clock recovery means, a variable frequency generation means for generating a carrier reference signal of the burst signal to be transmitted, and varying the carrier reference signal frequency by a control signal; a reference clock recovered by the reference clock recovery means; An error detection circuit for detecting a frequency difference of the carrier reference signal from the variable frequency generating means; and a gain controlled and controlled by the gain control signal. A frequency control signal generating means for amplifying the output signal of the error detection circuit and outputting the amplified signal as a frequency control signal to the variable frequency generating means, so that the frequency difference becomes a fixed value or less; Detecting whether or not the frequency difference is equal to or less than a certain value, and controlling the gain of the frequency control signal generating means to be larger than when the frequency difference is equal to or less than the certain value at least when the frequency difference is larger than the certain value. Gain control means for outputting the gain control signal and outputting a transmission permission signal when the frequency difference becomes equal to or less than the predetermined value; and receiving the transmission permission signal from the gain control means and transmitting the carrier wave with transmission information. Transmitting means for transmitting a modulated wave obtained by modulating a reference signal as the burst signal; and transmitting the burst signal during transmission of the burst signal by the transmitting means.
Control of the variable frequency generating means by the number control signal generating means.
Control is forcibly stopped, and the variable frequency
A wireless communication system comprising: a control stop unit that outputs a wave number .