Carrier regenerating device correctly operable in mobile satellite communication

2029~7~ This invention relates to a carrier regenerating - or recovery device for use in a mobile station of a mobile satellite communication network.

In mobile satellite communications, a modulated signal is transmitted from a master station to mobile stations and ~rom each mobile station to the master station. The modulated signal is derived by modulating a carrier signal at a frame period by a data signal representative of a message and by unique words which are periodically interspersed in the data signal. The modulated signal therefore comprises a modulated data signal and modulated unique words and will hereafter be referred to as a modulated overall signal. The unique ` words are preliminarily known at the mobile stations.

Such a unique word will herein be called a locally known unique word.

; In order to get primarily the message, each , mobile station comprises a carrier regenerating device for ; regenerating the carrier signal as a regenerated carrier signal from the modulated overall signal received at the , mobile station under consideration as an input modulated ,l signal having the frame period and comprising the modulated data signal and the modulated unique words which are periodically scattered in the modulated data signal. The carrier regenerating device comprises a demodulating circuit for using the regenerated carrier signal in quadrature demodulating the input modulated signal to -l produce a demodulated overall signal which comprises a demodulated data signal representative of the message and demodulated unique words. A conventional carrier regenerating or recovery circuit is for regenerating or producing the regenerated carrier signal from the demodulated overall signal. A carrier regenerating loop is therefore formed by the demodulating circuit and the carrier regenerating circuit.

The carrier regenerating loop is well operable insofar as the input modulated signal is supplied thereto steadily above a predetermined signal to noise (S/N) ratio.

It should, however, be noted that the carrier regenerating 202g~7~ - 2 loop may not always be supplied with the input modulated signal above the predetermined siqnal to noise ratio.

For example, the mobile station moves from a location to another location and may be subjected to shadowing by buildings and trees depending on the location.

In a worst case, the carrier regenerating loop will not receive the input modulated signal at all.

In such an event, the carrier regenerating circuit is put into a free running state.

The regenerated carrier signal steps out from frame synchronism, namely, out of synchronism with the frame period.

As a result, a phase shift occurs in the regenerated carrier signal.

In addition, a frequency shift may appear in the regenerated carrier signal.

The mobile station may move in due course to a location where the carrier regenerating loop can receive the input modulated signal above the predetermined signal to noise ratio.

It takes, however, a long recovery time for the carrier regenerating circuit to regenerate the regenerated carrier signal again in synchronism with the frame period.

This results in a long-continued and disagreeable click noise when the message is an audible one.

It is an object of the present invention to provide a carrier regenerating device for use in a mobile j 25 station of mobile satellite communication, which device is always correctly operable even when the mobile station is in a location susceptible to shadowing.

It is another object of this invention to provide a carrier regenerating device of the type described, which can recover frame synchronism of a recovered carrier signal as soon as possible when the mobile station moves away from the location subjected to the shadowing.

It is still another object of this invention to provide a carrier regenerating device of the type described, which comprises, besides a conventional carrier regenerating loop, a carrier regenerating subloop for correcting a phase error of the recovered carrier signal.

.. .- . . . ~ 202967~ -- 3 - It is a subordinate object of this invention to provide a carrier regenerating device of the type described, in which the carrier regenerating subloop is for additionally correcting a frequency error of the recovered carrier signal.

Other objects of this invention will become clear as the description proceeds.

Accordingly, one aspect of the present invention provides a carrier regenerating device for regenerating a regenerated carrier signal from a modulated overall signal having a frame period and comprising a modulated data signal and modulated unique words which are periodically interspersed in said modulated data signal, said carrier regenerating device comprising: a demodulating circuit for quadrature demodulating said modulated overall signal using said regenerated carrier signal to produce a demodulated overall signal comprising a demodulated data signal and demodulated unique words; a carrier regenerating circuit for recovering a recovered carrier signal from said demodulated overall signal; a cross-correlating circuit for calculating a cross-correlation coefficient between said demodulated overall signal and a locally known unique word from said demodulated overall signal; a frame synchronizing j circuit for producing an aperture signal which defines aperture intervals at said frame period, using said crosscorxelation coefficient when said cross-correlation coefficient is below a predetermined threshold value; a phase error calculating circuit for calculating a phase error between the phase of said recovered carrier signal and said regenerated carrier signal using said crosscorrelation coefficient; and correction setting means for setting said phase error at said aperture intervals in said carrier regenerating circuit to conform said recovered carrier signal with said regenerated carrier signal.

From a different point of view, the aboveunderstood carrier regenerating device is characterised according to this invention by: a cross-correlating circuit ~.r . ~ 202967~ -- 4 for calculating a cross-correlation coefficient between the demodulated overall signal and a locally known unique word;

a frame synchronizing circuit for using the crosscorrelation coefficient in producing an aperture signal which defines aperture intervals at the frame period; a phase error calculating circuit for using the crosscorrelation coefficient and the aperture signal in calculating phase errors which the recovered carrier signal has relative to the regenerated carrier signal at the aperture intervals, respectively; and correction setting means for successively setting the phase errors in the carrier regenerating circuit at the aperture intervals to make the recovered carrier signal become the regenerated carrier signal.

The invention will be more readily understood from the following description of a preferred embodiment thereof given, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a block diagram of a carrier regenerating device according to a first embodiment of the present invention;

Figure 2 shows a result of computer simulation of a cross-correlation coefficient used in the carrier regenerating device depicted in Figure 1;

Figure 3 shows on a phase plane the result illustrated in Figure 2;

;i Figure 4 shows an aperture interval for defining a frame period in the carrier regenerating device depicted in Figure 1;

Figure 5 shows on a phase plane a crosscorrelation coefficient which is computer simulated in connection with a case where an input modulated signal i5 supplied with a severe attenuation to the carrier regenerating device depicted in Figure 1;

Figure 6 is a block diagram of a carrier regenerating device according to a second embodiment of ` this invention, . _ ! '',:

' .

~' . .

_ 5 - 2 ~296 7~ Figure 7 is a block diagram of a carrier regenerating circuit for use in the carrier regenerating device illustrated in Figure 6; and Figure 8 is a block diagram of a digital VCO for use in the carrier regenerating circuit illustrated in Figure 7.

Referring to Figure 1, attention will he directed to a carrier regenerating device according to a first embodiment of the present invention. The carrier regenerating device is for use in a mobile station of a mobile satellite communication network which comprises a master station for such mobile stations. It will be assumed that a carrier signal is subjected to modulation at the master station and with a frame period into a modulated signal by a data signal representative of a message and that unique words are periodically interspersed at the frame period throughout the data signal. The unique words are known at the mobile station. A unique word is therefore referred to herein as a locally known unique word.

Inasmuch as the carrier signal is modulated at the master station by the data signal or by the locally known unique word, the modulated signal comprises a modulated data signal and modulated unique words and is herein called a modulated overall signal. The mobile station has demodulator input and output terminals 11 and 12. Through a receiving unit which is typical of mobile stations and is therefore not shown, the demodulator input terminal 11 is supplied with the modulated overall signal as an input modulated signal.

The carrier regenerating device is for regenerating the carrier signal from the input modulated signal as a regenerated carrier signal in the manner which will become clear as the description proceeds. An ordinary coherent demodulator unit 16 is supplied with the input modulated signal through the demodulator input terminal 11 and is for demodulating the input modulated signal into an ,; . .

.~ - 6 ~ 202967~ output demodulated signal which comprises a demodulated data signal and demodulated unique words. The output demodulated signal may alternatively be called either a demodulated data sequence or a demodulated overall signal and is delivered to the demodulator output terminal 12.

A demodulating circuit 16 i5 supplied with the input modulated signal from the demodulator input terminal 11 and with the regenerated carrier signal. The demodulating circuit 16 is ~or producing the demodulated data sequence in the manner known in the art. The demodulated data sequence is delivered not only to the demodulator output terminal 12 but also to a carrier regenerating or recovery circuit 17 and to a clock regenerating circuit 18. The carrier regenerating circuit 17 is for supplying a recovered carrier signal to the demodulating circuit 16. The clock regenerating circuit 18 is for delivering a regenerated clock signal to a clock , regenerator output connection 19.

Inasmuch as the ; regenerated clock signal is used in other parts of the mobile station in the known manner, the clock regenerator i', output connection 19 is only partly illustrated.

Insofar as the level of the input modulated signal supplied to the demodulator input terminal 11 is above a predetermined signal to noise (S/N) ratiol the 25 recovered carrier signal is correctly coincident with the regenerated carrier signal.

When the input modulated signal is delivered to the terminal 11 with a severely attenuated level, the carrier regenerating circuit 17 is put into a free running state.

In this event, the 30 recovered carrier signal may step out of frame synchronism, ;~ namely, out of synchrony with the frame period.

As a result, the recovered carrier signal will presant an j undesirable phase error relative to the regenerated carrier signal.

In order to make the carrier regenerating circuit 17 correctly produce the regenerated carrier signal, quadrature demodulation is used in the demodulating circuit ., ~ ~.

i.

:, ..

!;

~ ' .' , ' ~ .

: 2029675 - 7 17. The demodulated data sequence therefore becomes a quadrature demodulated signal which is a complex-valued signal and can be represented by real and imaginary signal components. In any event, a carrier regenerating loop is formed by a combination of the demodulating circuit 16 and the carrier regenerating circuit 17.

The carrier regenerating circuit 17 comprises an adjusting element which will later be illustrated and has first and second control terminals 21 and 26 which are depicted separately from the carrier regenerating circuit ~7 merely for convenience of illustration~ A crosscorrelating circuit 23 is supplied with the demodulated data signal from the demodulating circuit 16. The crosscorrelating circuit 23 is for locating or detecting the demodulated unique words in the demodulated data sequence by calculating a cross-correlation coefficient between the demodulated data sequence and the locally known unique word. The cross-correlating circuit 23 thereby produces a cross-correlation signal which typically represents the cross-correlation coefficient and may alternatively be related to the cross-correlation coefficient.

A frame synchronizing circuit 24 is supplied with the cross-correlation signal and compares the level of the cross-correlation signal with a predetermined threshold value. The frame synchronizing circuit 24 outputs an aperture signal that is synchronized with the unique word, if the level of the cross-correlation signal is lower than the threshold value, i.~., if the frame synchronism is not established. The frame synchronizing circuit 24 does not output the aperture signal, if the level of the crosscorrelation signal is equal to or higher than the theshold value, i.e., if the frame synchroism is established.

A phase error calculating circuit 25 is supplied with the cross-correlation signal and the aperture signal and calculates the phase error in the manner which will shortly be described. The phase error calculating circuit 25 thereby produces a phase error signal which represents . .

. ' .

202967~ -- 8 -the phase error and is delivered to the first control terminal 21 when the circuit 25 is supplied with the aperture.

The phase error calculating circuit 25 delivers a O level as the phase error signal to a first control terminal 21 when the circuit 25 is not supplied with the aperture.

This means that the aperture signal may define the timing of adjustment of the adjusting element in the carrier regenerating circuit 17 by aperture interval.

Supplied to the first control terminal 21, the phase error signal is used to adjust the adjusting element at the aperture interval.

The adjusting element may thereby correct the phase error of the recovered carrier signal to cause the recovered carrier signal to become identical with the regenerated carrier signal.

It may be mentioned here that the carrier regenerating circuit 17 produces the recovered carrier signal with a carrier signal phase angle which may or may not be identical with a correct phase angle of the regenerated carrier signal.

Using the cross-correlation signal and the aperture signal, the phase error calculating circuit 25 calculates the correct phase angle and may alternatively be called a phase calculating circuit. A combination of the cross-correlating, the frame synchronizing, and the phase error calculating circuits 23 to 25 is supplied with the demodulated data sequence and serves as a carrier regenerating subloop for correcting the phase error of the recovered carrier signal in the carrier regenerating circuit 17.

The first control terminal 21 collectively serves as a correction setting arrangement for using the aperture signal in setting the correct phase angle in the carrier regenerating ~ircuit 17 at the aperture intervals to keep ; the carrier signal phase angle at the correct phase angle, namely, in setting the phase error in the adjusting element of the carrier regenerating circuit 17 to adjust the carrier signal phase angle at the aperture interval if the ' - . , :. .

~,1 . : .

~............. .

.

202967~ g recovered carrier signal is not identical with the regenerated carrier signal.

The recovered carrier signal is thereby rendered identical with the regenerated carrier signal.

~he cross-correlation coefficient will now be called a main cross-correlation coefficient and be demoted ~i, by ~ as a function of a parameter ~ which has a dimension of time.

Being a complex-value signal, the demodulated data sequence can be represented by r(t) which is a complex-value function of time t.

Likewise, the locally known unique word is represented by y~t) as another complex-value function.

The main cross-correlation coefficient is given by an equation:

., (1) [r r ( t) y~ ( t . ~) dt~ / (2NT), where y*(t) represents a conjugate function of the locally known unique word, 2N represents the length of a unique word in bits, and T represents a time slot.

If attention is directed to the demodulated unique words, it is possible ~ to represent the demodulated data sequence by `` r(t) = y(t~ + n(t), (2) i where n(t) represents a noise signal.

When Equation (2) is used, Equation ~1) can be rewritten into a sum of first and second terms, where the first term represents an autocorrelation coefficient related to the demodulated unique words and has a maximum value at each time instant when each demodulated unique word appears in the demodulated data sequence. The second term represents a subordinate cross-correlation coefficient between the noise signal and the locally known unique word and is identical with a filter output signal of a filter ....

` 2029~75 -- 10 -y(-t) which is supplied with the noise signal.

In general, the second term is smaller than the first term.

Referring to Figure 2, the main cross-correlation coefficient is computer simulated as a simulated 5 coefficient.

On carrying out computer simulation, it is surmised that the carrier signal is subjected at the master station to quadrature phase shift keying (QPSK) modulation at the frame period of 256 bits by the data signal and the unique words of 64 bits long, and that input modulated 10 signal is supplied to the carrier regenerating device with a carrier to noise (C/N) ratio of 3 dB, namely, with an Eb/No ratio (a ratio of signal energy per bit to noise power per 1 Hz) of 0 dB.

In Figure 2, the abscissa represents the 15 parameter ~ on a scale which may be different from the time unit used for the time t.

The correlation signal has a signal level plot~ed along the ordinate on an arbitrary scale.

It is, however, evident in connection with the simulated coefficient that vertical lines are drawn ~ 20 perpendicularly of the abscissa at a spacing of five time j units where each time unit is equal to the frame period divided by 1~.

Horizontal lines are drawn perpendicularly of the ordinate to represent plus 1.0 at the top, 0.0 at the middle, and minus 1.0 at the bottom.

Turning to Figure 3, the simulated coefficient is illustrated in a phase plane.

It should be noted that the cross-correlation signal is a complex-valued signal.

Radius vectors represent signal levels of the crosscorrelation signal and have arguments ~ which represent 30 correlation signal phase angles and are given by:

= arctan [I(~ )]/[R(~(~))]~ (3) i where R and I are used to represent real and imaginary signal components of the complex-value cross-correlation signal.

.A !

.. . . .

- . . ~ .

`: , . . . .

-~ 202g~7~ Further turning to Figure 4, the main crosscorrelation signal has signal levels above the predetermined threshold value for the simulated coefficient in each time interval which is herein called an aperture interval. It is therefore evident that Figure 4 illustrates an aperture signal which successively represents aperture intervals at the frame period. The predetermined threshold value can be optimally determined with reference to Figure 2.

Referring to Figure 5, the main cross-correlation coefficient is computer-simulated in connection with a case where fading occurs in the input modulated signal such that the carrier regenerating circuit 17 is put into the free running state.

The recovered carrier signal steps out of 15 the frame synchronism.

Reviewing Figures 1 through 5, the frame synchronizing circuit 24 produces the aperture signal which cyclically defines the aperture interval exemplified in Figure 4.

In this manner, the frame synchronizing circuit 20 24 establishes and keeps the frame synchronism even when the input modulated signal is supplied to the carrier regenerating device below the predetermined signal to noise ratio so that the main cross-correlation signal is undesiredly kept in a state illustrated in Figure 5.

; 25 The phase error calculating circuit 25 uses the real and the imaginary cross-correlation signal components in calculating the correlation signal phase angle in i compliance with Equation (3).

The correlation signal phase angle gives the correct phase angle.

The correlation 30 signal phase angle therefore gives the phase error at each frame period or frame bit interval.

In Figure 4, the phase error is equal to zero.

The phase error calculating circuit 25 can therefore be implemented by a read-only memory (ROM).

When 35 each of the real and the imaginary cross-correlation signal components and the phase error signal is an eight-bit ' . .

~' . , t 2029~7~ - 12 signal, the read-only memory should have a memory capacity of 512 kilobits.

It will now be presumed that the recovered carrier signal went out of frame synchronism in the manner illustrated in Figure 5 and that the input modulated signal afterwards reached the predetermined signal to noise ratio at a certain time instant.

Under the circumstances, the carrier signal phase angle is adjusted in the carrier regenerating circuit 17 to become equal to the correct phase angle at the aperture interval that is defined by the aperture signal at the time instant in question.

It is thereby possible to rapidly recover from asynchrony which the frame synchrony of the recovered carrier signal is unavoidably subjected to.

It should be noted in connection with Figures 2 and 3 that the noise signal n(t) comprises the demodulated ~, data signal.

Depending on noise and on bit patterns of the demodulated data signal, the second term may have a considerably greater signal level.

The cross-correlation signal may become as exemplified in Figure 5.

Even in such an event, the carrier regenerating device operates ~ correctly because the aperture interval is specified at the ; frame period.

Referring now to Figure 6, the description will proceed to a carrier regenerating device according to a , second embodiment of this invention.

Similar parts are designated by like reference numerals and are similarly operable with likewise named signals. It should be noted that the adjusting element of the carrier regenerating circuit 17 has a second control terminal 26 which is again depicted separately ~rom the carrier regenerating circuit 17.

In the manner pointed out heretobefore, the recovered carrier signal may have a frequency error relative to the regenerated carrier signal. In other words, the recovered carrier signal may have a carrier signal frequency different from the regenerated carrier ~.

'~ ' ' . ~ .. ' - . , .

~' , ' , .

, 202~67~ - 13 signal. A frequency error ralculating circuit 29 is supplied with the phase error signal from the phase error calculating circuit 25 and is controlled by the aperture signal delivered from the frame synchronizing circuit 24.

The frequency error calculating circuit 29 is alternatively called a frequency calculating circuit and i5 for calculating such frequency errors at the aperture interval, respectively, to produce a frequency error signal which represents the frequency errors and is delivered to the second control terminal 26.

The frequency error calculating circuit 29 is operable as follows. The phase error signal is used at first in calculating a phase angle sequence of the correlation signal phase angles ~ (2), ..., ~(m), ....

and ~(M) according to Equation (3) at first through M-th frame periods or frame bit instants, where M represents the duration of the message in frame periods and where m is variable between 1 and M, both inclusive~ An error function E(t~ will be used in connection with angular frequency to represent the frequency error which is variable with time t. At the m-th frame period, the error function has an m-th error function phase given by an equation:

13 (mKT) =J E ( t) dt + ~ ( O ), where K represents the frame period in bits and ~(0) represents an initial phase. At the aperture intervals which successively specify the first through the M-th frame periods, the error function phases are compared with the correlation signal phase angles of the phase angle sequence. For example, (e(2KT) - e(KT)) is compared with (~(2) - ~(1)).

The results of comparison are used in calculating an optimum error function ~(t) which minimizes an evaluation function:

., ~ -- . . .

: ' - - - . .

.~ . ' .

2029~7~ -- 14 - ., M ~ [(~(m) - ~(m-1)) (a(mKT) - ~((m-1))KT))] 2 `:

and which can be represented by a finite power series:

~ (f) = d[~(m) - ~(m-1)]/dt The frequency error is given by the zProth-order term of the finite power series and will be denoted by E(f).

Alternatively, the frequency error can approximately be given by a differential equation:

` E(~) = d[~(m) - ~(m-1)]/dt.

This approximation is effective in rapidly establishing frame synchronisation.

It will now be readily possible for one skilled in the art to implement the frequency error calculating circuit 29 by a microprocessor irrespective of minimization of the evaluation function or solution of the differential equation.

The above mentioned carrier regenerating subloop of this embodiment comprises the frequency error calculating circuit Z9 besides the cross-correlating, the frame synchronizing, and the phase error calculating circuits 23 to 25.

The subloop is supplied with the demodulated data sequence as before and corrects the phase ` 25 and the frequency errors of the recovered carrier signal in ' the carrier regenerating circuit 17.

a Figure 7 illustrates the carrier regenerating circuit 17 with reference to Figure 6 comprising a phase detector 33, a loop filter 34, and a digital voltage controlled oscillator (digital VC0) 35.

The phase detector 33 is supplied with the demodulated data sequence from the demodulating circuit 16, detects a phase error signal with a predetermined phase, and outputs a phase error signal.

` The loop filter 34 is supplied with the phase error signal .,: , ~ ; , - ' , . ~' 2~29675 - 15 from the phase detector 33, filters the phase error signal, and outputs a filtered phase error signal as a frequency signal. The digital VC0 35 as an integrator circuit is supplied with the filtered phase error signal as the frequency signal and delivers a recovered carrier signal to the demodulating circuit 16.

Figure 8 illustrates the digital VCO 35 which has oscillator input and output terminals 31 and 32. The oscillator input terminal 31 is for receiving the filtered phase error signal as the frequency signal from the loop filter 34. The oscillator output terminal 32 is for delivering the recovered carrier signal back to the demodulating circuit 16.

An input adder 36 is supplied with the filtered phase error signal as the frequency signal through the oscillator input terminal 31 and with the frequency error signal from the frequency error calculating circuit 29 through the second control terminal 26 when the aperture from the frame synchronizing circuit 24 is supplied to the frequency error calculating circuit 29, i.e., when nonsynchronization is established. However, the frequency error signal is not supplied to the carrier regenerating circuit 1? when the aperture is not supplied to the frequency error calculating circuit 29, i.e., when synchronization is established. The input adder 36 thereby produces an input sum signal. An output adder 37 is supplied with the phase error signal from the phase error calculating circuit 25 through the first control terminal 21 and with an intermediate sum signal which will be described later, when the aperture is supplied to the phase error calculating circuit 25, i.e., when nonsynchronization is established. However, the phase error signal from the phase error calculating circuit 25 is not supplied to the carrier regenerating circuit 17 when the 3S aperture is not supplied tn the phase error calculating circuit 25, i.e., when synchronization is established. The , , .

.. ' , ~ 202~675 - 16 output adder 37 thereby delivers the recovared carrier signal to the oscillator output terminal 32.

The input sum signal is supplied to an intermediate adder 38 for producing the intermediate sum signal, which has a current value renewed to a renewed value at each aperture interval and is delivered not only to the output adder 37 but also to a delay circuit 39 for producing a delayed signal by giving a delay z-l to the intermediate signal of the current value. The delayed signal is supplied to the intermediate adder 38 so that the intermediate signal represents the renewed value.

If each of the phase and the frequency errors is equal to zero, the digital VCO is operable as a digital integrator circuit. When the phase error signal is supplied to the output adder 37, the recovered carrier signal is rendered identical with the regenerated carrier signal as regards the carrier signal phase angle. When the ; phase and the frequency error signals are usad, the recovered carrier signal becomes correctly identical with the regenerated carrier signal not only as regards the carrier signal phase angle but also as regards the carrier ' signal frequency.

It is now understood that the carrier regenerating circuit 17 comprises the phase detector 33, the loop filter 34, and the input and the output adders 36 and 37 as first and second adjusting elements and a combination of the intermediate adder 38 and the delay circuit 39 as a carrier recovering unit for use in recovering the recovered carrier signal from the frequency signal with the carrier signal phase angle and with the carrier signal frequency. The first adjusting element (36) is supplied with the filtered phase error signal as the frequency signal for making the carrier recovering unit produce the intermediate sum signal as the recovered carrier signal, having an adjusted frequency which the carrier signal frequency is adjusted in compliance with a first amount of adjustment. The second adjusting element ~.

.. . .

: .

2029~7~ - 17 (37) is supplied with the recovered carrier signal having the adjusted frequency for adjusting the carrier signal phase angle to an adjusted phase angle in accordance with a second amount of adjustment.

The above-described correction setting arrangement (21, 26) is connected to the first and the second adjusting elements (36, 37).

The correction setting arrangement is for setting the frequency errors in the first adjusting element as the first amount of adjustment at the aperture interval and is for setting the phase errors in the second adjusting element as the second amount of adjustment at the aperture interval.

The correction setting arrangement thereby renders the recovered carrier signal having the adjusted frequency and the adjusted phase angle identical with the regenerated carrier signal not only as regards the carrier signal phase angle but also as regards the carrier signal frequency.

It is now understood that a combination of the ~irst and the second control terminals 21 and 26 serves as the correction setting arrangement in the carrier regenerating device illustrated with reference to Figures 6 and 8.

The correction setting arrangement is connected to the first and the second adjusting elements (36, 37) and is for setting the frequency errors in the first adjusting element as the first amount of adjustment at each of the aperture intervals and for setting the phase errors in the second adjusting element as the second amount of adjustment at each of the aperture intervals to make the recovered carrier signal with the adjusted phase angle and with the adjusted frequency become identical with the regenerated carrier signal not only as regards phase but also as regards frequency.

For use in the carrier regenerating devicP illustrated with reference to Figure 1, the digital voltage controlled oscillator need not comprise only the input adder 36 but also the output adder 37 as a single adjusting element.

The carrier recovering unit is for recovering the .

~, .

. " ' : .

202967~ - 18 recovered carrier signal from the filtered phase error signal with a carrier signal phase angle. The single adjusting element is supplied with the recovered carrier signal for adjusting the carrier signal phase angle in accordance with an amount of adjustment into an adjusted phase angle to produce the recovered carrier signal with the adjusted phase angle.

- The above-described correction setting arrangement 21 is connected to the single adjusting element. The correction setting arrangement is for setting the phase errors in the single adjusting element as the amount of adjustment at each of the aperture intervals to cause the recovered carrier signal to have the adjusted phase angle identical with that of the regenerated carrier signal.

While this invention has thus far been described in specific conjunction with only two preferred embodiments thereof, it will now be readily possible for one skilled in the art to carry this invention into effect in various other manners. For example, the input modulated signal may include the modulated unique words at the frame period partly among the modulated date signal and at one or a plurality of integral multiples of the frame period among a remaining part of the modulated data signal. The input modulated signal may be derived by subjecting the carrier ; signal to any manner of modulation, such as binary phase shift keying ~BPSK) modulation. The aperture signal from the ~rame synchronizing circuit may be supplied to only the carrier regenerating circuit. Then, the carrier regenerating circuit inputs the phase error signal and frequency error signal when the circuit is supplied with the aperture, but the phase calculating circuit and the frequency calculating circuit always deliver the phase error signal and the frequency error signal, respectively.

, ':

~' , ;, . . . ~ ' .