JPH01206760A - Sweep control circuit - Google Patents

Abstract

PURPOSE:To securely and stably obtain synchronization and to shorten time to be needed for leading-in by executing sweep, which further adds prescribed quantity, from a time point when the synchronization can be obtained at first. CONSTITUTION:Synchronism decision is executed in a synchronism deciding circuit 7 based on the bit error rate of demodulating data. From the point of time when the synchronism decision is executed in this synchronism deciding circuit 7, a sweep control part 20 further executes the additional sweep in a step shape by the prescribed quantity and a signal to cause the frequency of a local oscillator 3 to close to a carrier frequency is supplied to the local oscillator 3. The output oscillating frequency of the local oscillator 3 is multiplied to a receiving signal and the demodulating data are outputted.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a sweep control circuit in an AFC (automatic frequency control) circuit for pulling in the carrier frequency of a signal sent from a transmitting circuit in a receiving circuit, and synchronizing it reliably and stably. In order to reduce the time required for the subsequent pull-in by carrier recovery (CR), additional sweeps are performed in steps of a predetermined amount from the time when synchronization is determined, and the frequency of the local oscillator is changed to the carrier wave. The configuration includes a sweep control section that supplies a signal to the local oscillator to approximate the frequency.

[Industrial application field]

The present invention relates to a sweep control circuit in an AFC (Automatic Frequency Control 1) circuit for pulling in the carrier frequency of a signal sent from a transmitting circuit in a receiving circuit.

In the field of digital wireless communications, especially digital satellite communications, it is necessary for the receiving circuit to repopulate the carrier frequency of the signal sent from the transmitting circuit in order to receive the signal sent from the transmitting circuit. It is being done. When the receiving frequency changes and synchronization is lost, the receiving circuit sweeps the output oscillation frequency of the voltage controlled oscillator (VCXO) to bring it to the correct carrier frequency.

[Conventional technology]

Conventionally, the above sweep control has been performed in accordance with synchronization determination by unique word detection based on the bit error rate (BER) of received demodulated data. For example, the third
As shown in the figure, the frequency f1 of the voltage controlled oscillator (local oscillator) is stepped from high to low to approach the true carrier frequency fo, but before it enters the stable synchronization region F1 where synchronization is sufficiently stable. , the frequency [1 is the true carrier frequency f. An unstable synchronous region E that approaches to some extent
If synchronization happens to be achieved in step 2, the sweep is stopped at that point, and the carrier wave is then regenerated.4: (In CI) The circuit changes frequency 11 continuously (in an analog manner) to obtain carrier wave frequency f. Let me draw you in! , :.

In FIG. 3, Po is the frequency f1 and [. The theoretical value of the bit error rate determined by the CN ratio (ratio of carrier wave power to noise power) obtained for a poem that is ideally demodulated by matching, Pl is the result of synchronization judgment by unique word detection, The upper limit value of the bit error rate at which synchronization can be stably achieved, P2, is the upper limit value of the bit error rate at which synchronization can be achieved even intermittently. fs, f
s' is the frequency at which the error rate is 21, 1'i.

fi' is the frequency at which the bit error rate is P2.

Here, the areas (fi', fs'), (Ti, fs)
is an unstable periodic region (a region in which synchronization may or may not be achieved) [2, E3, and the region (fs', fs) will be referred to as a stable synchronization region E+.

[Problem to be solved by the invention]

As in the above conventional example, the stepwise sweep is stopped in the unstable synchronization region E2, and then the carrier wave frequency f is continuously set by the CR circuit. This caused an unstable phenomenon in which synchronization would be lost after a while, and there was a problem that stable synchronization could not be achieved. carrier frequency f by the circuit. There was a problem in that it took a long time to retract.

SUMMARY OF THE INVENTION An object of the present invention is to provide a sweep control circuit that can reliably and stably synchronize and shorten the time required for subsequent pull-in by the CR circuit.

[Means to solve the problem]

FIG. 1 shows a block diagram of the principle of the present invention. In the figure, 7 is a synchronization determination circuit that performs synchronization determination based on the bit error rate (BER) of demodulated data, and 3 is a local oscillator that obtains demodulated data by multiplying the received signal by its output oscillation frequency f1. be. Further, 20 causes the synchronization determination circuit 7 to further perform an additional sweep in steps of a predetermined amount from the time when the synchronization is determined, so that the frequency f1 of the local oscillator 3 is changed to the carrier frequency 1-o.
This is a sweep control section 20 that supplies a signal to the local oscillator 3 to bring it closer to .

[Effect]

When the synchronization determination circuit 7 first establishes synchronization, it is in an unstable synchronization region, and if this continues, the synchronization will be lost after a while. Therefore, by performing an additional sweep by a predetermined amount from the time when synchronization is first achieved, the stable synchronization region is brought into being. As a result, compared to the conventional example in which the step-like sweep was stopped in the unstable synchronization region, synchronization can be achieved reliably and stably, and the carrier wave frequency f applied to the subsequent carrier recovery (CR) circuit can be achieved. . It is possible to shorten the amount of poetry required to draw in the poem.

〔Example〕

FIG. 2 shows a block diagram of a first embodiment of the invention.

The modulation method in the present invention is BPSK, the carrier frequency f, )=56.175tyl-1z, and the transmission speed is 133 kbps.

In the figure, 1 is a received signal input terminal, 2 is a multiplier that multiplies the received signal by the carrier frequency to obtain demodulated data, 3 is a voltage controlled oscillator (VCXO), and 4 is a phase comparison that compares the phase with a reference signal. 5 is a 4-channel recovery (CR) circuit that controls the oscillation frequency of the VCXO 3 by the phase error signal from the phase comparator 4, and 6 is a DA converter. (locked loop) is configured.

7 is a synchronization determination circuit, which determines the bit error rate (BE) of demodulated data.
Synchronization judgment is performed by unique word detection based on R). Reference numeral 8 designates a sweep circuit drive control circuit, which includes a pulse generator 9 that generates a trigger pulse, a timer 10 that is set with a time to continue outputting trigger pulses after synchronization is determined by the synchronization determination circuit 7, and a pulse generator 9. It is composed of a gate circuit 11 that gates the empty pulse.

12 is a sweep circuit, which is driven by a trigger pulse taken out from the sweep circuit drive control circuit 8, and generates frequency data for sweeping stepwise from a higher side to a lower side each time a trigger pulse arrives. Generator 1
It consists of 3.

In FIG. 2, while the synchronization determination circuit 7 detects that the synchronization is not achieved (the "synchronization loss" period shown in FIG. 4), the pulse generator 9 of the sweep circuit drive control circuit 8 generates a pulse. is supplied to the sweep circuit 12 via the gate circuit 11 as a trigger pulse. This results in
The frequency data generator 13 outputs frequency data for sweeping stepwise from high to low every time a trigger pulse arrives, and is supplied to the DA converter 6 via the CR circuit 5 and converted into an analog voltage. The output oscillation frequency of the VCXO3 is controlled. That is, in FIG.
Frequency 11 of XO3 is...■,■.

■... is swept in a step-like manner.Here, if the synchronization determination circuit 7 detects that synchronization has been established (the fourth
In the figure, the timer 1o is activated by the control signal from the synchronization determination circuit 7, and as described later, the gate circuit 11 is opened for the time set here, and the pulse generator The pulses from 9 are further supplied to the sweep circuit 12 as N (for example, 5) trigger pulses. As a result, after synchronization is achieved in the unstable synchronization region E2, a stepwise sweep is performed for five trigger pulses (■, ■, ■, ■, ■ in Fig. 3), and then a stepwise sweep is performed. will be stopped. Thereafter, the frequency is continuously changed by the operation of the CR circuit 5 to bring the frequency to the carrier wave frequency fo.

In this case, the additional sweep amount S after the synchronization determination is set as follows. It is shown in Figure 3. Unstable synchronization region E2
, the limit where synchronization can be achieved corresponding to the outside of F3 (marked with a circle in Figure 5), and the CR circuit within the stable synchronization region E1.
Limit to pull in the carrier frequency fo within seconds (x mark in Figure 5)
The results are shown in FIG. In FIG. 5, if it is in the range surrounded by the broken line (diagonal line), it can be pulled into the carrier frequency fo within 10 seconds by the CR circuit.

From FIG. 5, in order to apply the circuit of the present invention when the CN ratio is O(E or more), the additional sweep f141s must be 1.5 kHz.
It can be seen that it is about 2.

Next, if the width of one step of the additional sweep is w1 and the number of steps of the additional sweep is N, then -WN. Here, if the step width W is too small, the number of steps required to sweep the range (for example, IQOkHz section) becomes large, which is shown by the solid line in Figure 5. It takes a long time to reach the vicinity of the carrier frequency (upper kHz), and even in such a vicinity, the number of additional sweep steps N increases, and the time it takes to reach the stable synchronization region E1 becomes longer. Therefore, the step width W is S/
If it is limited to the range from 2 to S15, the range of the number of steps N will be from 2 to 5. The optimum values of the step width W and the number of steps N were determined while confirming the operation through experiments within these ranges. The results are W = 0.4 kHz, N = 3°,',3 = 1.2 kl-17.

On the other hand, the shorter the period of the sweep trigger pulse, the faster the sweep can be performed. However, a synchronization determination must be made during this period, and this synchronization determination requires approximately 01
Since a time of seconds is required, in the present invention, the period is set to 0.25 seconds with a margin.

As mentioned above, step width W-0.4kHz, step T
Number of times N = 3, Sue (-jms = 1.2 kl
−(z.

When conducting an experiment with a sweep trigger pulse period of 0.25 seconds, at CN Jt Od8 or higher, the stable synchronization state is within the stable synchronization region El at the end of the step sweep, and then the carrier wave is recovered within 10 seconds in the CR circuit. Frequency T
It was recognized that the o was drawn in.

In this way, in the present invention, when the synchronization determination circuit 7 first performs synchronization determination in the unstable synchronization region E2, an additional sweep is performed from that point, so that the frequency f+ of the local oscillator is changed to the carrier frequency fo. Get even closer to ↓
However, the carrier wave frequency F due to the subsequent continuous sweep of the CR circuit can be synchronized more reliably and stably than in the conventional example. Retraction can be performed in a shorter time than in the conventional example.

By the way, as shown in Fig. 6, when the signal transmission speeds are different (transmission speed A+ (bps) <transmission speed A2 (b
1) 8)), the sensitivity of the stable synchronization region and the unstable synchronization region differs depending on the transmission speed. In a system where the transmission speed varies greatly, the magnitude of these regions varies greatly. The additional sweep amount after the above-mentioned synchronization determination is the carrier wave frequency f from the synchronized frequency. The decision was made from the requirement to recover the difference up to lc. Therefore, in a system where the amount of additional sweep is constant, if the transmission speed changes, there are cases in which the signal cannot pass through the unstable synchronization region or passes through the stable synchronization region.

In order to prevent this J: from happening, as shown in Figure 6,
Change the additional sweep amount appropriately according to the transmission speed (S+
, S2) is necessary. In the same figure, it is A+.

Although there are two systems, A2, the same applies to the J:Una communication system, which has a higher transmission speed.

As mentioned above 1. Since there is a relationship Z,5=W-N, in order to change the sweep amount S, it is necessary to change the step width W, the number of steps N, or both. Specifically, the size of the unstable synchronization region and stable synchronization region at each transmission speed is known, and the additional sweep amount S+ is calculated to deal with each transmission speed.

Determine S2. The step width and the number of steps are determined so as to satisfy 52=W2/N2 when the transmission speed is A+: S+-.WI-NI when the transmission speed is Δ2. In a system that can have k transmission speeds A+ to Ak, S+ - WI .Nl 5k = Wk - Nk.

= 12 − From the above, by appropriately changing the step widths W+, W2, . . . or the number of steps N+, N2, . . . or both in accordance with the transmission speeds Δ+, A2, . After the sweep is completed, the local oscillator frequency 1 can be brought to the stable synchronization region, and the carrier frequency f can be brought to the stable synchronous region by the CR circuit. It can be shortened to old news until it is drawn into.

In FIG. 7, the sweep amount is varied depending on the transmission speed as described above. FIG. 6 shows a block diagram of a second embodiment of the present invention.

In FIG. 7, the same components as those in FIG. 2 are designated by the same numbers and their explanations will be omitted.

First, a case where only the step width W of the sweep is changed will be described. In FIG. 7, reference numeral 15 denotes a sweep circuit which selects one of the step width information VV+ and W2 by a switching signal, and supplies a step width control signal to the frequency data generator 17. The frequency data generator 17 generates frequency data that sweeps in a stepwise manner with either a sweep width WI or W2 in response to a step width control signal.

Note that when changing the step width W, the step number switching signal of the timer 19 in the sweep circuit drive control circuit 18 is not used (that is, N+ = N2 = N).
.

Now, when the transmission speed is A1, the sweep circuit 15 selects the step width information W+ by the step width switching signal, and the frequency data generator 17 selects the step width information W+.
Generate sweeping frequency data. Note that the number of steps N of the additional sweep is constant, for example, 5. As shown in FIG. 8(A), the frequency f! After synchronization is achieved with ■, the number of steps N set by timer 19
= 5 times of additional time trigger pulses (Fig. 8(C)) are subsequently supplied to the sweep circuit 15, and the frequency f1 is
, ■, ■, ■ and the step width W+ is the carrier frequency f. get closer to Thereafter, the signal is continuously swept by the CR circuit and pulled into the carrier frequency fo.

Next, when the transmission speed is A2, d3 is applied to the sweep circuit 15.
Then, the step width information W2 is selected by the step width switching signal, and the frequency data generator 17 selects the step width information W2.
2 generates sweeping frequency data. As shown in FIG. 8(B), after the frequency f1 has a cycle of ■, the frequency f1 is changed to the carrier wave frequency f with a step width W2 by an additional trigger pulse shown in FIG. 8(C). get closer to

On the other hand, a case will be described in which only the number of sweep steps N is changed. In FIG. 7, the timer 19 is switched and set to times corresponding to the number of steps N+ and N2, respectively, in response to a step number switching signal. This sets the gate open time of the gate circuit 11. Note that when changing the number of steps N, the selector 16 of the sweep circuit 15 is not used (that is, Wl...W2...W
).

Now, when the transmission speed is A1, the timer 19 of the sweep circuit drive control circuit 18 is switched and set to a time such that the number of additional sweep steps becomes N1. Figure 9 (
As shown in A), after the frequency 11 is synchronized at ■, the additional time for the number of steps N1-5 set by the timer 19 = 15 - trigger pulse (Figure 9 (C)) continues. is supplied to the sweep circuit 15, and the frequency f+ is changed to ■, ■, ■.

(2) and the step width W to approach the carrier frequency fO.

Next, when the transmission speed is A2, the timer 19 is switched and set to set a time such that the number of additional sweep steps becomes N2. As shown in FIG. 9(B), the frequency f+ is [
After synchronization is achieved at the timer 19, an additional trigger pulse (
9(C)) is subsequently supplied to the sweep circuit 15, and the frequency f1 is set to 0. ■,■,...,■ and step width W
and the carrier frequency f. get closer to 1. Note that both the number of steps N and the step width may be varied.

In this way, in the second embodiment of the present invention, since the sweep amount is varied depending on the transmission speed, it is possible to reliably and stably synchronize at the end of the sweep at any transmission speed.

[Effects of the Invention] As explained above, according to the present invention, the stable synchronization region is pulled into the stable synchronization region by further performing an additional sweep by a predetermined amount from the time when synchronization is first achieved, so that the unstable synchronization region is not affected. Compared to the conventional example in which the stepwise sweep was stopped, synchronization can be achieved reliably, stably, and the carrier wave frequency f is achieved by the subsequent 4-Year Recovery (CR) circuit. The time required for retraction can be shortened.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram of the first embodiment of the invention, Fig. 3 is a diagram showing the relationship between stable and unstable synchronization regions and frequency sweep, and Fig. 4 is a diagram showing the relationship between stable and unstable synchronization regions and frequency sweep. A diagram explaining the trigger pulse for additional sweep after synchronization judgment, Figure 5 shows the limit frequency that can be synchronized and the CR circuit.
Figure 6 is a diagram showing the size of stable and unstable synchronization regions corresponding to different transmission speeds. Figure 7 is a block diagram of the second embodiment of the present invention. Figure 8 shows the case where the step width is changed according to the transmission speed in the second embodiment of the present invention, and Fig. 9 shows the case where the number of steps is changed according to the transmission speed in the second embodiment of the present invention. It is a diagram. In the figure, 1 is a received signal input terminal, 2 is a multiplier, 3 is a voltage controlled oscillator (local oscillator), 4 is a phase comparator, 5 is a main relay recovery (CR) circuit, 6 is a D/A converter, 7 8.18 is a synchronization judgment circuit, 8.18 is a sweep circuit drive control circuit, 9 is a pulse generator, 10.19 is a timer, 11 is a gate circuit, 12.15 is a sweep circuit, 13.17 is a frequency data generator, 14 is a PLL. 16 is a selector, and 20 is a sweep control section. Patent applicant Fujitsu Co., Ltd. Agent Patent attorney Tadahiko Ito

Claims (2)

[Claims] (1) In a sweep control circuit configured to control step-like frequency sweep by the local oscillator (3) based on synchronization determination from demodulated data in the synchronization determination circuit (7), a predetermined step further from the time when the synchronization determination is made. a sweep control unit (20) for supplying a signal to the local oscillator (3) for causing the frequency (f_1) of the local oscillator (3) to approach the carrier frequency (f_0) by performing an additional sweep of the type; A sweep control circuit characterized by: (2) The sweep control unit (20) has means (16, 19).The sweep control circuit according to claim 1, further comprising: 19).