JP2003298668A - Burst signal receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a burst signal receiver wherein high speed pulling of a carrier frequency is enabled when C/N ratio of a received burst signal is deteriorated. <P>SOLUTION: In a control circuit 200, when a reception detecting circuit 70 detects reception of a burst signal, frequency of a local signal used for down conversion is changed by every 400 Hz by controlling a PLL circuit 30 every time when 128 symbols in a carrier regeneration code CR are received, and the above process is performed as far as a carrier regeneration detecting circuit 120 detects regeneration of a carrier. In a loop filter 102 of a carrier regenerating circuit 100, a time constant is set to be small in accordance with the above variable control of local signal frequency, and setting is so performed that a frequency is pulled in a range of about ±200 Hz. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, TDMA.
The present invention relates to a burst signal receiving device used for communication using burst signals, such as a (Time Division Multiple Access) method.

[0002]

2. Description of the Related Art In many satellite communication systems, a TDMA system is adopted as a connection system between an earth station and a satellite station.

In a satellite communication system adopting the TDMA system, as shown in FIG. 4, a satellite station S and earth stations A and B communicating with the satellite station S transmit at the same radio frequency by each station on the time axis. Communication is performed by dividing the time that should be used.

As shown in FIG. 5, the earth station A burst-transmits the transmission data during the time slots A1 and A2 assigned to the earth station A, and the earth station B similarly transmits the time to the time assigned to itself. The transmission data is burst-transmitted during the periods of slots B1 and B2.

In this way, the burst signals transmitted from the earth stations A and B are temporally arranged on the satellite station S,
It is transmitted to the earth stations A and B.

Then, the earth stations A and B receive the burst signal sent from the satellite station S, and extract only the burst signal inserted in the time slot addressed to the own station from the burst signal.

In the earth stations A and B, the position of the time slot of the own station is specified based on the reference bursts R1 and R2 which the satellite station S inserts in the burst signal.
The reference bursts R1 and R2 are transmitted from the reference station R on the ground to the satellite station S.

By the way, in order for the earth stations A and B to receive and demodulate the burst data addressed to itself in the burst signal, it is necessary to establish burst synchronization with the burst signal.

Therefore, the earth stations A and B, in the burst demodulation circuit provided in the receiving device, carry out the carrier recovery code CR (all "1") inserted in the received burst signal.
Code) and a clock recovery code BTR (alternating code of "1" and "0"), the carrier wave and the clock are recovered.

Then, the earth stations A and B demodulate the burst data addressed to themselves in a state where these carrier waves and clocks can be correctly reproduced, that is, in a synchronized state.

However, between the satellite station S and the earth stations A and B, there is a possibility that a carrier signal has a frequency difference of about ± 1 kHz.

For this reason, in the conventional burst signal demodulation circuit, the time constant of the loop filter is set to a small value so that this frequency difference can be pulled in during the reception period of the carrier recovery code CR.

However, when the time constant of the loop filter is set to a small value, when the C / N ratio of the received burst signal deteriorates (deterioration of about 15 dB) due to the influence of rain attenuation, the noise causes the pull-in. It was sometimes gone.

On the other hand, if the time constant of the loop filter is set to a large value in order to reduce the influence of the deterioration of the C / N ratio, it takes a long time to pull in, and the carrier recovery code CR is pulled in during the reception period. There was a problem that I could not do it.

[0015]

Conventionally, when the C / N ratio of a received burst signal deteriorates due to the influence of rain attenuation or the like, there is a problem in that the noise makes it impossible to perform pull-in.

The present invention has been made to solve the above problem, and provides a burst signal receiving apparatus capable of pulling a carrier frequency at high speed even when the C / N ratio of the received burst signal is deteriorated. The purpose is to do.

[0017]

To achieve the above object, the present invention is a burst signal receiving apparatus used for communication using burst signals, in which a local signal is oscillated by changing the frequency according to a control signal. And a control for selectively switching the frequency of the local signal oscillated by the oscillating means to a plurality of preset values within the burst signal carrier pull-in period. And a demodulation means for demodulating the received burst signal using the local signal oscillated by the oscillating means, and a carrier component is regenerated from the received signal demodulated by the demodulation means, and the carrier component is removed for modulation. It is configured such that it is provided with a regenerating means for taking out the components.

In the burst signal receiving device having the above configuration, the frequency of the local signal oscillated by the oscillating means is selectively switched to a plurality of preset values during the carrier wave pull-in period of the burst signal to receive the received burst signal. I am trying to demodulate.

Thus, while the frequency of the local signal oscillated by the oscillating means is variably controlled, the carrier frequency error with the communication partner at any frequency can be reduced. For this reason, it is possible to set the range of the carrier wave pull-in frequency of the reproducing means to be narrow and to set the time constant to be small in accordance with this.

Therefore, according to the burst signal receiving device having the above configuration, the local signal frequency is variably controlled,
Since the carrier frequency error with the communication partner can be reduced to some extent, the carrier can be pulled in at a high speed even if the C / N ratio of the received burst signal is deteriorated due to rain attenuation or the like.

[0021]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a burst signal receiving apparatus according to an embodiment of the present invention.

The burst signal receiving apparatus shown in this figure is provided in the receiving section of the earth station shown in FIG. 4, for example, and an RF signal received from a satellite station is downconverted to an IF signal by a frequency converter (not shown). It is converted and input.

The burst signal receiving device comprises a distributor 10, multipliers 21 and 22, and a PLL (Phase Locked Loop) circuit 3.
0, variable frequency oscillator 40, phase shifters 51 and 52, band limiting filters 61 and 62, reception detection circuit 70, A / D converters 81 and 82, digital filters 91 and 92, carrier recovery circuit 100, clock recovery circuit 110. A carrier wave reproduction detection circuit 120 and a control circuit 200 are provided.

The divider 10 receives the IF signal down-converted by the frequency converter in the preceding stage, divides it into two, and outputs it to the multipliers 21 and 22.

The variable frequency oscillator 40 generates a local signal having a frequency within a predetermined range. The generated local signal is supplied to a PLL circuit 30 and phase shifters 51 and 5 which will be described later.
Output to 2.

In the PLL circuit (PLL) 30, the frequency of the local signal generated by the variable frequency oscillator 40 is set by the control circuit 200 described later based on the local signal generated by the variable frequency oscillator 40. The variable frequency oscillator 40 is controlled so that the frequency becomes the frequency Lo.

The phase shifter (-π / 4) 51 advances the phase of the input local signal by -π / 4, and multiplies it by 2
1 while the phase shifter (+ π / 4) 52 advances the phase of the local signal by π / 4 and multiplies this by 22.
Output to.

The multiplier 21 adds a phase shifter 5 to the IF signal.
The local signal input from 1 is multiplied to down-convert the IF signal into a baseband signal. As a result, of the quadrature-modulated signals, the I signal is demodulated,
This signal is output to the band limiting filter 61.

Similarly, the multiplier 22 adds the IF signal to
The IF signal is down-converted into a baseband signal by multiplying the local signal input from the phase shifter 52. As a result, of the quadrature-modulated signal, the Q signal is demodulated, and this signal is output to the band limiting filter 62.

The band limiting filter 61 removes noise and harmonic components contained in the I signal input from the multiplier 21, and only the baseband signal of the target frequency is received and detected by the detection circuit 70 and the A / D converter (A). / D) 81 to output.

Similarly, the band limiting filter 62 removes noise and harmonic components contained in the Q signal input from the multiplier 22, and only the baseband signal of the target frequency is received and detected by the detection circuit 70 and the A / D converter. It outputs to the device (A / D) 82.

The reception detection circuit 70 includes a band limiting filter 6
By inputting the baseband signal from 1 and 62, it is detected that the reception of the burst signal is started, and when the reception is detected, the control circuit 200 is notified of this fact. .

The A / D converter 81 samples the baseband signal that has passed through the band limiting filter 61 based on the clock signal from the clock reproduction circuit 110 described later and converts it into a digital signal.

This digital signal is filtered by the digital filter 91 and then the carrier recovery circuit 1
Is output to 00. The digital filter 91 is
Filtering is performed based on the clock signal from the clock recovery circuit 110.

Similarly, the A / D converter 82 samples the baseband signal passed through the band limiting filter 62 based on the clock signal from the clock reproduction circuit 110 and converts it into a digital signal.

This digital signal is filtered by the digital filter 92 and then the carrier recovery circuit 1
Is output to 00. The digital filter 92 is
Filtering is performed based on the clock signal from the clock recovery circuit 110.

The carrier wave regenerating circuit 100 is provided with an oscillator 101 and a loop filter 102, and the frequency of the signal generated by the oscillator 101 is converted into digital filters 91 and 9.
Based on the carrier reproduction code CR in the digital signal that has passed through 2, the loop filter 102 reproduces the carrier by pulling it into the frequency of the carrier. The reproduced carrier wave is output to the carrier wave reproduction detection circuit 120.

The loop filter 102 is set to have a small time constant so that the frequency difference of the carrier signal can be quickly drawn.

Further, the frequency difference of the carrier signal with the communication partner is expected to be approximately ± 1 kHz, whereas the loop filter 102 is set so as to pull in the frequency in the range of approximately ± 200 Hz. .

Then, the carrier wave regenerating circuit 100 uses the carrier wave regenerated in this way to extract I data and Q data as modulation components from the digital signals that have passed through the digital filters 91 and 92, respectively, and to the clock regenerating circuit 110. Output.

The clock reproduction circuit 110 reproduces the clock based on the clock reproduction code BTR among the I data and the Q data input from the carrier wave reproduction circuit 100. The reproduced clock, I data, and Q data are output to a data reproduction circuit (not shown) in the subsequent stage.

Further, the clock is supplied to the A / D converter 8
1, 82, and digital filters 91, 92.

The carrier wave reproduction detection circuit 120 detects that the carrier wave input from the carrier wave reproduction circuit 100 is in a locked state in which the carrier wave is pulled in to a desired frequency, and detects this in the data reproduction circuit or control circuit 200 at the subsequent stage. To notify.

The control circuit 200 centrally controls each unit of the burst signal receiving apparatus to realize reception of the burst signal sent from the transmitting side.

In addition, the control circuit 200 reproduces the carrier wave by P during the reception period of the carrier wave reproduction code CR.
The frequency Lo set for the LL circuit 30 is ± 1 kH
The range of z is 400 Hz, f0, f1, f2, f3
The variable control is performed in 5 steps of f4.

Next, with reference to FIG. 2 and FIG. 3, the receiving operation of the burst signal receiving apparatus having the above configuration will be described.
Here, in particular, the operation until the carrier wave is reproduced will be described.

FIG. 2 is a flow chart for explaining the carrier wave reproduction control by the control circuit 200, and the carrier wave is reproduced by this control.

FIG. 3 shows the received burst signal and the PLL.
Circuit 30, reception detection circuit 70, and carrier recovery circuit 10
The operation state of 0 will be described.

As shown in this figure, one received burst signal is a carrier recovery code CR and a clock recovery code BT.
R, unique word UW, user data DATA and preamble PA, and carrier reproduction code CR is 64.
0 symbol, clock recovery code BTR is 128 symbols, unique word UW is 32 symbols, user data DATA is 496 symbols, and preamble PA is 8 symbols.

First, in step 2a, "1" is set to the parameter x, and the process proceeds to step 2b.

In step 2b, it is determined whether the reception detection circuit 70 has notified that the reception of the burst signal has started.

If there is a notification that the reception of the burst signal has been started, the process proceeds to step 2c. On the other hand, if there is no notification, the notification generation is awaited.

In step 2c, fx is set as the frequency Lo in the PLL circuit 30, and the process proceeds to step 2d.

As a result, the PLL circuit 30 controls the variable frequency oscillator 40 so as to generate the local signal of the frequency fx.

Then, the received burst signals are multiplied by the local signals by the multipliers 21 and 22 to be down-converted into the base band signals, and the band limiting filters 61 and 62 and the A / D converters 81 and 82. Then, the signal is input to the carrier recovery circuit 100 via the digital filters 91 and 92.

On the other hand, the carrier recovery circuit 100 is
The loop filter 102 attempts to reproduce the carrier by pulling the frequency of the signal generated by the oscillator 101 into the frequency of the carrier based on the carrier reproduction code CR.

In step 2d, the PL in step 2c
From the frequency setting for the L circuit 30, the carrier recovery code C
It is determined whether or not the carrier recovery detection circuit 120 has detected that the carrier pull-in is completed until R of 128 symbols is received.

Here, if the carrier has been completely pulled in by the time the carrier recovery code CR is received by 128 symbols, the process proceeds to step 2f. On the other hand, if the pulling is not completed, the step is carried out. Move to 2e.

In step 2e, the parameter x is "1".
Is added (incremented), and the process proceeds to step 2c.

As a result, in step 2c, after the carrier recovery code CR has been received by 128 symbols from the previous frequency setting, the variable frequency oscillator 40 newly sets the frequency f.
The PLL circuit 30 controls so as to generate the x local signal.

On the other hand, in step 2f, since the pulling of the carrier wave is completed, fx is fixedly set as the frequency Lo in the PLL circuit 30, and the processing ends.

As a result, in the carrier wave reproducing circuit 100,
Using the regenerated carrier, digital filters 91, 9
I data and Q data are extracted as modulation components from the digital signal passing through 2, and BTR, UW, DATA and PA are obtained as reception data, and these are output to the clock recovery circuit 110.

The clock reproduction circuit 110 reproduces the clock based on the clock reproduction code BTR of the I data and Q data input from the carrier wave reproduction circuit 100.

As described above, in the burst signal receiving apparatus having the above configuration, within the carrier wave pull-in period (640 symbols).
In each of the above, every time 128 symbols of the carrier recovery code CR are received, the frequency of the local signal used for the down conversion is variably controlled by 400 Hz to perform the orthogonal demodulation.

As a result, the frequency of the local signal is set to 40
While variably controlling by 0 Hz, it is possible to reduce the carrier frequency error with the communication partner to ± 200 Hz or less at any frequency.

Therefore, the pull-in frequency range of the loop filter 102 can be set to a narrow range of about ± 200 Hz, and the time constant of the loop filter 102 can be set to a small value accordingly.

Therefore, according to the burst signal receiving apparatus having the above structure, even if the C / N ratio of the received burst signal is deteriorated due to rain attenuation or the like, the carrier wave can be pulled in at high speed.

The present invention is not limited to the above embodiment.

In the above embodiment, the satellite communication system adopting the TDMA system has been described as an example, but other communication can be applied as long as the communication is performed by a burst signal. .

Needless to say, the present invention can be similarly implemented even if various modifications are made without departing from the scope of the present invention.

[0072]

As described above, according to the present invention, the frequency of the local signal oscillated by the oscillating means is selectively switched to a plurality of preset values during the carrier wave pull-in period of the burst signal to be received. The burst signal is demodulated.

This makes it possible to reduce the carrier frequency error with the communication partner at any frequency while variably controlling the frequency of the local signal. For this reason, it is possible to set the range of the carrier wave pull-in frequency of the reproducing means to be narrow and to set the time constant to be small in accordance with this.

Therefore, according to the present invention, the carrier frequency error with the communication partner can be reduced to some extent by the variable control of the local signal frequency, so that the C / N of the received burst signal is affected by rain attenuation or the like.
It is possible to provide a burst signal receiving device capable of pulling a carrier wave at high speed even when the ratio deteriorates.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of an embodiment of a burst signal receiving apparatus according to the present invention.

2 is a flowchart for explaining carrier wave reproduction control of the burst signal receiving device shown in FIG.

FIG. 3 is a diagram for explaining a received burst signal and operating states of the PLL circuit, the reception detection circuit, and the carrier recovery circuit shown in FIG.

FIG. 4 is a diagram schematically showing a system configuration of a satellite communication system adopting a TDMA system.

FIG. 5 is a diagram for explaining communication performed in a satellite communication system adopting the TDMA system.

[Explanation of symbols]

10 ... Distributor 21, 22 ... Multiplier 30 ... PLL circuit (PLL) 40 ... Variable frequency oscillator 51, 52 ... Phase shifter 61, 62 ... Band limiting filter 70 ... Reception detection circuit 81, 82 ... Converter 91, 92 ... Digital filter 100 ... Carrier recovery circuit 101 ... Oscillator 102 ... Loop filter 110 ... Clock recovery circuit 120 ... Carrier recovery detection circuit 200 ... Control circuit

Claims (4)

[Claims] 1. A burst signal receiving device used for communication using a burst signal, comprising: oscillating means capable of oscillating a local signal by changing a frequency in accordance with a control signal, and within a carrier wave pull-in period of the burst signal. In which the control signal is given to the oscillating means to selectively switch the frequency of the local signal oscillated by the oscillating means to a plurality of preset values, and the local signal oscillated by the oscillating means is used. And demodulating means for demodulating the received burst signal, and reproducing means for reproducing a carrier component from the received signal demodulated by the demodulating means and removing the carrier component to extract a modulated component. Burst signal receiver. 2. The input detection means for detecting the input of the burst signal is further provided, and the control means is within the carrier wave pull-in period of the burst signal when the input detection means detects the input of the burst signal. 2. The burst signal receiving apparatus according to claim 1, wherein the frequency of the local signal oscillated by the oscillating means is selectively switched to a plurality of preset values. 3. The reproducing means further comprises reproduction detecting means for detecting that the carrier wave component has been reproduced by the reproducing means, and the control means oscillates when the reproduction detecting means detects reproduction of the carrier wave component. The burst signal receiving apparatus according to claim 1, wherein the frequency of the local signal generated by the means is fixed. 4. The reproducing means includes an oscillator for reproducing the carrier wave component, and a frequency oscillated by the oscillator until the control means switches the frequency of the local signal to the next frequency. By varying in the frequency range based on the interval of the frequency represented by a plurality of values, by synchronizing with the frequency of the carrier component included in the received signal demodulated by the demodulation means,
The burst signal receiving device according to claim 1, further comprising: a loop filter that causes the oscillator to generate the carrier component.