JPS6359032A - Inter-burst carrier frequency deviation compensating circuit - Google Patents

Abstract

PURPOSE:To correct the deviation of a carrier frequency from a normal value at every burst by utilizing a preamble part signal inserted to the loading part of each burst and applying an automatic closed loop frequency control for only the period of the preamble part in a multiphase PSK modulation wave. CONSTITUTION:The output of a voltage comparator 11 goes to logic '1' for periods t1-t2 corresponding to the sequence and the CR/BTR of a preamble. A frequency discriminator 5 generates a voltage proportional to a deviation F from a F3+B/2 to reduce a noise by a low pass filter 6. A sample/hold amplifier 7 acts like a conventional amplifier singly when the output of the voltage comparator 11 is logic '1'. Thus, the output of the low pass filter 6 is amplified and fed back to a variable voltage control oscillator 8, thereby resulting that the F2 is controlled so as to cancel the deviation F of the carrier frequency of burst from the normal value F1.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for correcting carrier frequency differences between burst modulated waves transmitted from each station in the system at a receiving station in a time division multiple access communication system. The present invention relates to a frequency control circuit.

[Conventional technology]

Figure 9 is, for example, @Satellite Communication Technology 1222 page diagram'
1.22 [edited by the Institute of Electronics and Communication Engineers, supervised by the authorities, published by Corona Publishing] is a configuration diagram of a carrier wave regeneration circuit for burst four-phase PSX modulated waves. In the figure, h is the input terminal of the 4 psx modulated wave, 0 is the multiplier, @ is the bandpass filter,
En.

- is a frequency converter, the first narrow band filter, armor is 4
The divider, the trowel is an output terminal for the reproduced carrier wave component, and the decoy is a phase detector, which in combination with a narrowband filter operates as a frequency discriminator.

The punishment is a low-pass filter, and (c) is a voltage-controlled OT variable total oscillator.

Next, the operation will be explained. In Figure 9, input terminal Q
If the signal f input to the camphor is a 4-phase PSK modulated wave,
By multiplying by 4, an unmodulated component consisting of 4 times the frequency can be obtained. This multiplied signal has the original signal P
Since it is SK modulated, it is accompanied by broadband modulation noise.

After this is suppressed by a band M and a filter 4, a frequency discriminator circle is used to suppress the frequency f, which is usually a low frequency.

The frequency is converted to C example is fI-140MHz.

The output signal f of the frequency converter eυ (f = 180 MHz, fI = 40 MH2), the noise (thermal noise and modulation noise) is sufficiently suppressed by the acid component narrow band filter (2), and its output is the O/N ratio. Good unmodulated components can be obtained. When this is divided into 4 minutes by the divider and the frequency is converted again by the frequency converter (to), an unmodulated component (regenerated carrier wave) with the same frequency as the center frequency of the input signal fl is obtained at the output terminal (c). It will be done.

Here, considering the case where the center frequency f is generally different for each burst, in the frequency band fI, for each burst, the frequency deviation is proportional to the deviation from the nominal value at the point of the input terminal a barrel. arise.

On the other hand, a narrowband filter has a characteristic of causing phase rotation with respect to the input frequency, as shown in FIG.

This fact is because the phase rotation is maintained up to the point on the output terminal side, so although the carrier wave is regenerated, it has undergone phase rotation according to the frequency deviation at the input terminal (point I81). When used to demodulate a PSK modulated wave, it will cause deterioration to the demodulated signal.

Therefore, in general, the variation tl of frequency deviation for each burst is
In addition to stipulating the specifications of the sending side to keep it within a certain range,! The frequency deviation caused in the satellite transponder (this gives equal frequency deviation to all bursts)
An automatic frequency control circuit is installed on the receiver side to cancel the
is required. The example phase detector and low-pass filter circuit shown in FIG. 9 are for performing these functions.

The operation of this circuit is shown in FIG. Now, assume that eight bursts a, b, and c are being received repeatedly.

The output of the example phase detector has positive or negative values (Va, V'b, Vc) depending on the deviation of the carrier frequency of each burst from the nominal value, as shown at 0η in Figure 10 β). can get. Assuming that the low band width of the low pass filter 271 is sufficiently longer (for example, 100 times) than the burst repetition period, the output voltage between each burst has an averaged DC component of 6υ, as shown by -.

That is, this DC component corresponds to the average deviation of the carrier frequency of all bursts from the nominal value, which controls the voltage-controlled variable oscillator.
Frequency deviations common to all bursts are canceled out.

FIG. 11 is a diagram showing the resulting phase rotation experienced by the recovered carrier wave extracted from each burst in the f3 frequency band.

In the example shown in the figure, the parse a has a center frequency fa that is squarely shifted from fI, and undergoes a phase rotation ψa. The concept of 4151 is applied to bursts b and c. The value If'b7cl is the maximum frequency deviation between each burst, and is often determined as a specification value for the transmitting side as described above so as not to cause any system problems.

[Problem that the invention seeks to solve]

The conventional automatic frequency control circuit is configured as described above.
Therefore, it was not effective when the difference in carrier frequency between bursts was too large to be ignored relative to the transmission speed, or when it had to become large.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an automatic frequency control circuit that responds quickly to each valley burst and has high accuracy.

[Means for solving problems]

The automatic frequency control circuit according to the present invention makes full use of the signal of the preamble part inserted at the head part of the valley burst in the multi-PSK modulated wave that is often used in time division multiple access communication systems. Closed-loop automatic frequency classification IIIk is performed only during this period.The means to fully identify this preamplifier portion is to install a relatively narrow bandpass filter and perform detection with a good carrier-to-noise ratio. It will be achieved.

[Effect]

The closed-loop automatic frequency control in this invention operates only in the preamble portion specified by the above-mentioned detection output, and operates at high speed so that the 1-minute loop responds during this period. At the same time, in the data section that follows, the frequency control state at the end of the preamble section is held until the end of the burst, thereby correcting the deviation of the carrier frequency from the normal value for each burst. .

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, the +II ri multiphase PSK modulated wave is received at the input terminal, and the multiphase PSK modulated wave inputted to this terminal has a carrier frequency that differs slightly from the normal frequency for each burst. Here, the normal frequency is assumed to be Fl as shown in the figure. (21 is the frequency converter (M engineering X)
For example, for input frequencies F, , F'2, a frequency (F2-F1) is output as an output. (
3) is an output terminal for the output signal output from the frequency converter (2), and its normal center frequency is F3.

(4) is a narrowband filter whose center frequency is (F
*10g). Here, it is the symbol rate of the BQP SK modulated wave. +51 is a frequency discriminator whose center frequency is ('' 4), which is the frequency F3 of the input signal.
It outputs a voltage proportional to the difference between and (Fs + s). (6) is a low-pass filter, (7) is a sample-and-hold amplifier, (8) is a voltage-controlled variable oscillator, (9)
is a wave detector, (1ω is a low-pass filter, and a voltage comparator). FIG. 8 explains the structure of the burst signal input to the input terminal Il+, and the IJ signal is provided for carrier wave and bit timing recovery in the preamble inserted at the beginning of the burst. This is a two-way PSK modulation part called the TR sequence, and is modulated with a fixed pattern 0101-. 0S is a data portion, which is, for example, 4K PSK modulated.

Now, as shown in Fig. 8, if we pay attention to the CR/BTR sequence part, its spectrum does not exist near the normal value F1 like Q4 and t+m (F,
-4) and (F, +8).

When this is frequency converted, it exists near (F, -, B) and (F, +8). Also, the curve Q in Fig.
4), and this bandwidth is the same as the data part [
13), and the output response speed of this bandpass filter is C
An appropriate value Vc is selected that is one minute faster compared to the length of the R/BTR sequence.

In this situation, the output of the voltage comparator (11) becomes logic 111 during the period t, .about.t corresponding to the CR/BTR sequence, as shown in line 1131 of FIG. 4. However, the time delay caused by the low-pass filter (lO) is not shown here for simplicity. On the other hand, frequency discriminator (5)
produces a voltage proportional to the deviation ΔPVC from (F8+ normal) and is noise reduced by the low-pass filter in (6).

Sample and hold amplifier (7) is a voltage comparison! (l1)
When the output of is logic Il'', it simply operates as a normal amplifier.

Therefore, the output of the low-pass filter 16) is amplified and fed back to the voltage-controlled variable oscillator (8), so that the deviation (, V) of the normal value Fl of the burst carrier frequency is canceled. F2 will be controlled and the center frequency at the output terminal (3) will be controlled to a value very close to its normal 1ilies. Figure 4 (Q indicates the input voltage of the voltage controlled variable oscillator (8).CR/
Input voltage Vsl of the voltage controlled variable oscillator (8) at the end of the BTR sequence (point t, FIG. 4 IB)
d, from this point on the output of the voltage comparator (11) is logic 10
', the sample-and-hold amplifier (7) enters a hold mode and is held in that state until the next burst is received.

In the above system, if the symbol rate B deviates from its normal value, this becomes a control error of one center frequency F3.

However, it is relatively easy to keep this symbol rate B at each transmitting station to a level that is not a problem; deviation, and the purpose of the invention is to compensate for this.

In addition, in the above embodiment, it is not used for frequency control (1
It goes without saying that the same thing can be achieved with 't8).

In the above embodiment, the loop automatic frequency control operation was performed using the CR/BTR sequence in the preamble part, but the same effect can be achieved by using the CR sequence in the preamble part. . FIG. 5 explains the structure of each burst signal in this case. (12a) is an unmodulated carrier component generally called CR sequence, and its nominal frequency is Fl.

(111b) is a two-phase PSK modulated wave for bit timing recovery called a BTR sequence.

The bet is the data part, for example, one that is 4-phase PSK modulated.

Next, to explain in detail when this CR sequence part is used, the spectrum is as shown in Fig. 6.
It exists only near the normal value IPI, such as 01fl. When this is frequency-converted by a frequency converter +21K, it exists only near the normal value F3.

This shows the characteristics of the allt-x bandpass filter (4),
At its center frequency F3, its bandwidth is sufficiently narrow for the spread of the spectrum 2 mmqη corresponding to the data portion +131, and the output zero velocity of this bandpass filter is equal to the CR frequency (xga). An appropriate value is selected so that the speed is sufficiently fast compared to the length. 1B'' in Figure 6
corresponds to the symbol rate in the case of 4K PSK waves. FIG. 7 shows the spectrum of the received signal in the BTR sequence part (Nib), and there is no center frequency (carrier frequency) component in this part.

In such a situation, the output of the voltage comparator (Ill) becomes logic 11@ during the interval tffltl.about.t2 corresponding to the CR sequence (12a), as shown in FIG. 8(B).

However, the time delay caused by the low-pass filter +IO+ is not shown here for simplicity. On the other hand, the frequency discriminator α
The wire generates a voltage proportional to the deviation ΔF of the carrier frequency from the normal value F3, and the noise is reduced by the low-pass filter (6). The sample and hold amplifier (7) simply operates as a normal amplifier when the output of the voltage comparator (11) is logic 111. Therefore, the output of the low@y filter (6) is amplified and fed back to the voltage controlled variable oscillator (8), resulting in the deviation (
Fg is controlled so that ΔF) is canceled out, and the center frequency of the output terminal (31) is controlled to a value very close to its normal value F3. This shows the input voltage of the oscillator (81.CR
At the end of the sequence (point t'Bt in Figure 8), the input voltage of the voltage controlled variable oscillator (8) is v2, and from this point onwards, the output of the voltage comparator (11) becomes logic ``01'', so sample hold is performed. The amplifier (7) goes into hold mode and remains there until the next burst is received.

In addition, in each of the above embodiments, explanation was given using a 4-phase PSK modulated wave as an example, but in this case, a polyphase P8 of 2 phases or 8 or more phases is used.
It can also be applied to K, and the same effects as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, it is not necessary to consider the addition of thermal noise caused by a quadrupler and modulation noise, as shown in the conventional example, and therefore the bandwidth of the bandpass filter is set to one automatic frequency. The control loop can be made wide enough to sufficiently converge within the CR/BTR sequence or the CR sequence, and the carrier frequency deviation for each burst can be compensated for in correspondence with the burst.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an inter-burst carrier frequency deviation compensation circuit according to an embodiment of the present invention, FIGS. 8 to 4 are operation explanatory diagrams for explaining the operation of FIG. 1, and FIGS. FIG. 8 is an operation explanatory diagram for explaining the operation of another embodiment of the present invention, FIG. 9 is a block diagram showing a conventional inter-burst carrier frequency deviation compensation circuit, FIG. 1θ and FIG.
The figure is an operation explanatory diagram for explaining the operation of FIG. 9. In the figure, (21 is a frequency converter, (4) is a bandpass filter, 16) is a frequency discriminator, and (6) is a low-pass filter 1.
7) is a sample-and-hold amplifier, (8) is a voltage-controlled variable oscillator, (9) is a detector, (lO) is a low-pass filter, (
II+ is a voltage comparator. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (3)

[Claims] (1) Convert the carrier wave (F1) of the received modulated signal to an intermediate frequency wave (F
3), in the intermediate frequency band, by detecting the difference from the nominal frequency (F3) and controlling the local oscillation frequency (F2) of the frequency converter, In an automatic frequency control loop that obtains an intermediate frequency close to the frequency (F3), the beginning of each burst is The automatic frequency control loop is operated only for the sequence signal of the preamble arranged in the preamble, and the local oscillation frequency (F2) is held at the final value in the sequence part other than the preamble sequence part. An inter-burst carrier frequency deviation compensation circuit. (2) The inter-burst carrier frequency deviation compensation circuit according to claim 1, wherein the preamble sequence signal is a CR/BTR sequence for carrier wave and bit timing recovery. (3) The inter-burst carrier frequency deviation compensation circuit according to claim 1, wherein the preamble sequence signal is a CR sequence for carrier wave regeneration.