JPS58151132A - Automatic frequency controlling system - Google Patents

Abstract

PURPOSE:To attain an AFC (automatic frequency control) resistant to noise and having narrow band, by using a modulation wave with a PN code series for a reference pilot signal and controlling a local oscillating frequency with a difference between the carrier component of the pilot and a nominal carrier frequency. CONSTITUTION:In a reference pilot forming circuit 6, a carrier is modulated with the PN code series from a PN code generator 3 with a ring-balanced modulator 2 and outputted to an output terminal 5. Only the reference pilot of a reception signal (intermediate frequency) is inputted to a correlation device 9, where the PN code series and the pilot of the two-phase PSK wave are multiplied and correlation is taken for both. A phase locked circuit 11 controls the phase of the code series of a PN code generator 10 so as to maximize the correlation output. Thus, the carrier component of the original reference pilot are inputted to a carrier extracting circuit 12 and outputted to a PLL13 only when the input level is a prescribed threshold or over. The PLL13 outputs the frequency difference between the input signal and the nominal frequency signal as a control signal to control the local oscillating frequency so as to make the frequency difference to zero.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on an automatic station wave number control method using reference/arm pilot signals, for example, SCPC (Single Channel).
This book is suitable for use in the FDMA (Frequency Division Multiple Access) system, which allocates one voice line to one carrier wave, which is called the FDMA (Frequency Division Multiple Access) system.

SC in maritime satellite communication systems and domestic satellite communication systems
The PC method is widely used, but in the SCPC method, the occupied frequency bandwidth of each 1i carrier wave is narrow, and the frequency interval between carrier waves is narrow, so it is inevitable that the number of transmitting waves and the receiving frequency are well distributed. be. Therefore, frequency deviations of communication carrier waves caused by frequency fluctuations of the local oscillator of the satellite repeater (transponder), frequency fluctuations of various local oscillators in the m-sphere station equipment, and dotsora deviation due to satellite motion, etc. To compensate, automatic frequency control (AFC) using a reference/mother plot is performed.

Then, each earth station transmits a standard pilot pilot to the satellite, either in common or individually, and after it is relayed dynamically, AFC is performed using the received pilot of the own station. This makes it possible to correct most of the frequency deviations caused by the various frequency fluctuation factors mentioned above. In addition, since frequency fluctuations of transponders play a large role in satellite communication systems, even when a common reference pilot is used, it is possible to correct the small portion of the frequency deviation.

AFC using individual reference pilots is called the individual pilot method, and high-precision AFC can be achieved in practice, but in this method, it was common to use an unmodulated carrier wave for the reference pilot.

However, unmodulated pilots have some drawbacks as described below. That is, (1) It is easy to suffer from noise such as cross-modulation noise where energy is concentrated within a narrow band, and there is a risk of synchronization being lost due to this. Since the satellite's transponder has strong nonlinearity, when many narrowband carrier waves of the 5CPC system are commonly amplified by the transponder, many narrowband cross-modulation products are generated, which can be mistaken for an unchangeable I11 pilot. To eliminate cross-modulation noise, it is good to have a sufficient S/N margin after demodulating the mother pilot, but this is not appropriate because it means an increase in the satellite power consumed for pilot amplification.

(21) The frequency band for eel conservation, which is required to uniformly classify the source of the reference pilot sent by each earth station, is large, and the efficiency of using the koji wave number of the satellite optimization system is significantly reduced. Since a station cannot maintain control by capturing the reference pilots of other stations, it is often necessary for each reference pilot to have a dedicated band that is at least twice the expected maximum frequency deviation and to provide sufficient frequency spacing. A typical satellite communication system requires an interval of 100 KHz to 200 Kfh.Incidentally, a system such as the Inmarsat (International Maritime Satellite Organization) system, where the maximum frequency deviation is expected to be ±55 KHz, is accessed by 20 earth stations. Assuming the case, the frequency band dedicated to the 2° standard/sairot is:

55 x 2 x 20 = 2,200 K output (=
2.2 degrees b). In Inmarsat/Stem, where the frequency band of the transformer 4nd is 7.5 MHz, this value reaches as much as 30- in total, resulting in extremely poor frequency utilization efficiency.

Note that the drawback (1) above also applies to AFC using a common reference pilot.

SUMMARY OF THE INVENTION In view of the above prior art, it is an object of the present invention to provide an automatic frequency control force formula that is resistant to noise in which energy is concentrated in a narrow band and that has a narrow frequency band occupied for AFC.

The above purpose is to use a carrier wave modulated with a PN code sequence as the reference pilot, and to regenerate it by finding the correlation between the carrier wave component of the received reference pilot and a PNe code sequence with the same pattern as that used for modulation. , the oscillation frequency of the frequency conversion local oscillator in at least one of the receiving system and the transmitting system is suppressed so as to correct the frequency deviation of the overconfident carrier wave from the difference between the frequency of the reproduced carrier wave component and a predetermined nominal frequency. Especially achievable. The present invention will be described below with reference to the drawings.

Figure 1 (a) to (c) iim shows a typical example of a communication system to which the present invention can be applied. Figure 3(c) shows a satellite communication system with mobile station M, and Figure (c) shows a satellite communication system between land stations 8 via communication satellite ST. shows an overconfidence system. In addition, it can be applied to various overconfidence systems.

In the present invention, the carrier wave is modulated with a PN code sequence, that is, a Grus pattern with an extremely long repetition period of /4 turns, which is also called a pseudo-Randander pattern, and is used as a reference pilot.
At the time of reception, by taking the phase with the same PN code sequence used for modulation, it can be distinguished from other reference pilots having the same carrier frequency but different PN code sequences as 8Ai1. Of course, if the carrier frequencies are different, the distinction will become clearer. On the other hand, when the carrier wave is modulated with a PN code sequence, the spectrum is spread out, and when the next phase is calculated, the spread spectrum is concentrated, but energy is concentrated within a narrow band due to cross-modulation noise. By finding the phase of noise, the energy is diffused.

Therefore, even if a large number of strong intermodulation noises are received, the energy is spread by determining the phase, so that only the carrier wave of the reference pilot can be captured, and loss of synchronization will not occur.

The present invention applies frequency control in the transmitting system so that the frequency of the communication carrier wave for the other station is constant during reception, and in other cases in which frequency control is performed on the receiving side so that the frequency of the communication carrier wave for the other station changes. However, in the satellite communication system between mobile station M and land station 8 in Figure 1-), it is difficult to provide frequency control equipment to mobile station L due to space limitations. Alternatively, since it is economically inconvenient, the land station E may be equipped with a MuFC equipment that controls the frequency of the communication carrier waves transmitted by the elevated station E, and an AFC equipment that follows and receives the uncontrolled communication carrier waves from the mobile station M. It's good to be prepared. In addition, in systems such as satellite communication systems where one station can receive the nine-standard pilot modulated with a PN code sequence, there is no need for each station to transmit it individually, and it can be received in the area where it can be received. If one station transmits the reference pilot on behalf of the other stations (common pilot method), other stations can use this to send AF to the receiving or transmitting system.
Can manage C. Note that when using the common pilot method to modify the transmission system by using MuFC, it is important to control only the frequency of the communication carrier wave and not to control the frequency of the reference pilot. Of course, when AFC is applied to the overconfidence system using the individual pilot method, frequency control may be performed in conjunction with the communication carrier wave and the reference pilot.

FIG. 2 shows an example of a circuit for creating a standard No. 9 pilot. In the PI diagram, 1 is a reference parameter, a pilot carrier wave oscillator (REFO8C), 2 is a balanced modulator (MOD), 3 is a PN code generator, 4 is a bandpass filter, and 5 is an output terminal. The operation of the reference/9-lot creation circuit 6 shown in the figure is as follows. A balanced modulator 2 such as a carrier line ring modulator from a carrier wave oscillator l performs balanced modulation using a PN code sequence from a 9PN code generator 3, and the modulated output is filtered to remove cine frequency components by a bandpass filter 4. After that, it is output to the output terminal 5. In other words, the signal at the output terminal 5 becomes a two-phase PSKa whose transmission rate is the bit rate of the PN code sequence used for modulation, that is, the clock.
The spectrum is spread within a frequency band equal to the clock of the PN code sequence.

The reference pilot created in this way is converted into a desired radio frequency by an AGG converter in the communication equipment, and then sent to the communication satellite or directly to the partner station.

Standard A in Figure 3? An example of a circuit that regenerates a carrier wave and creates a color code based on the frequency is shown below. In the same figure, 7
Welfare down control t<- Input terminal for received signal from evening, 8F
9 is a correlator, 101 is a variable phase PN code generator, 11 is a PN code phase synchronization circuit,
12 is a carrier wave mall path, 13 is a phase-locked loop (PLL), 14 is a nominal frequency signal input terminal, 15
and 15& are output terminals for control signals having opposite polarities, and 16 is an inverting amplifier. Note that a balanced modulator is used as the correlator 9. The carrier extraction circuit 12 only passes force signals above a certain level, and limits the amplitude of excessive signals.

The signal entering input terminal 14 is the nominal intermediate frequency signal of the carrier of the reference number to be acquired. Below, the carrier wave regeneration and control signal production shown in Figure 3 will be explained. i1. The operation of the circuit 17 will be explained. The received signal, which has been converted to an intermediate frequency by a down converter in the communication equipment, is separated from the received signal by a bandpass filter 8, and only the received reference pilot is input to a correlator 9. In the correlator 9, P from the PN code generator lO
The N code sequence is multiplied by the reception reference pilot of the two-phase PSK wave, and the reception reference pilot is modulated with the PN code sequence to find the correlation between the two. As mentioned above (if the patterns of the PN code sequences do not match, the phase output will be low, but even if they match, if the phases are out of alignment, the correlation output will be low).

Therefore, the output signal of the phase shifter 9 is PN code phase synchronization 1 path 1.
1, and this phase synchronization circuit 11 controls the phase of the PN code sequence generated by the phase-variable PN code generator IO so that the correlation output is maximized.

Tsumushi, correlator 91 phase synchronization circuit 11 and phase variable P
A feedback loop constituted by the N code generator 10 reproduces the carrier wave component of the original reference number 4 from the received reference number 9 which has been spread spectrum, and outputs it from the correlator 9. The output signal of the correlator 9 is input to the carrier extraction circuit 12, and if the input level exceeds a predetermined threshold, it is determined that the desired reference pilot is being received, and the input carrier wave component is directly input to the PLL.
Output to I3. If it is below the threshold, it may be due to other reference pilots or noise, and these will not be adopted. The PLL 13 detects the frequency difference between the input signal from the carrier extraction circuit 12 and the nominal frequency signal from the reference input terminal 14, and outputs a signal indicating the frequency difference as a control signal to the output terminal 15.15m. When AFC is applied to this control signal line communication carrier wave, it is applied to the local oscillator of the up converter of the transmission system from one output terminal, e.g. The local oscillator frequency is applied to the local oscillator of the system down converter, and the local oscillation frequency is tilJil such that the frequency difference becomes zero in both cases. In addition, as the signal input to the reference input terminal 14, if the transmission and reception of the reference mother pilot are performed at the same station, the signal from the carrier wave oscillator l in the reference/arm pilot generation i path 6 can also be used. However, if the transmitting and receiving stations are different, a separate oscillator with the same oscillation frequency is installed.

FIG. 4 shows an example of the application of the present invention to a maritime satellite communication system. In this example, a land station is provided with an automatic frequency control OIk function for both transmission and reception, thereby eliminating the burden on the ship station's equipment. Figure 4 (~Fi) shows the transmission system automatic frequency control system of the land station, and Figure 4 (b) also shows the reception system automatic frequency control system of the land station. First, to explain the circuit of ai4@(-, %101 is Telephone line, 102 is a voice signal modulator, 103 is a reference pilot and modulation signal synthesizer, the output of the synthesizer is 1.27th! converter 104゜10
5 to 6 The frequency is converted to the GHz band, and the antenna 10
It will be sent to 6 multi-communication satellites. Communication # Hoshi's transponder converts U6GH Atsushi to 1-5 GH+c+ and transfers it to the ship station, so the land station also receives this 1.5G output, and the first and second down converters 107 and 108 convert the intermediate wave control number. carrier wave regeneration and control signal generation circuit 17
Enter.

The control output of this circuit 17 is transmitted from the terminal 15 to the variable frequency local oscillator 104 of the first up converter 104 in the transmission system.
&, and the local oscillation frequency is controlled to match the carrier component of the regenerated reference pilot or the nominal frequency. The local oscillation frequency changes by the amount of deviation in the opposite direction to the frequency deviation. This corrects the frequency deviation caused by the transponders, and the 1 and 5G signals received by the ship station are corrected.
The communication carrier wave in the Hz band is kept constant.

Therefore, the ship station does not need to apply AFC to reception.

To explain the circuit No. 41), the communication carrier wave sent out by the ship station is T,5CTZ, which is converted to 4 GHz IF K by a satellite transformer and transferred to the land station. Therefore, at the land station, L 1.2 up converter 1
On 09,110, the standard motherboard was converted to 1.6G output and sent out. The land station receives the reference signal transmitted by its own station, which is relayed by satellite and set to 4 GHz, converts it to an intermediate frequency (by the 1st and 2nd down converters 111 and 112), and then regenerates the carrier wave. and is input to the control signal generation circuit 17. The control output of this circuit 170 is given from a terminal 15m to a variable frequency local oscillator 112m of the second downconverter 112, and the local oscillator jldfIt is generated so that the carrier wave component of the regenerated reference pilot matches the nominal frequency.

The number is controlled. Then, the local oscillation frequency changes by the deviation amount in the same direction as the frequency deviation. As a result, the frequency deviation caused by the transponder is corrected, and the land station can follow and receive the communication carrier wave whose frequency has deviated even if the ship station does not apply AFC to the transmission. Therefore, the received signal obtained from the @2 down converter 112 to the output terminal 113 is a frequency-corrected signal, and the demodulator 114 obtains the desired ship station audio signal.

In Fig. 4 (&), AFC is applied to the reference pilot sent out together with the communication carrier wave, and the frequency of the reference/'e pilot changes, so other stations use this reference pilot to control the transmission system or reception of the station concerned. L inconvenience occurs when AFC is applied to the thread. In other words, it can be said that AF C is suitable for the h>u individual pilot system shown in FIG. On the other hand, No. 41￥r (b)
In this case, since AFC is not applied to the reference pilot itself to be sent out, one other station can apply AFC to its reception system using this reference pilot. In this case, the other station in question is set up to send out the reference pilot*.
From the antenna 106 and the first down converter 111 shown in FIG. 4 to the carrier wave regeneration and control signal generation path 17, the oscillator of the nominal frequency signal is well biased. In other words, #4 knowledge can be applied to both the individual pilot method and the common non-pilot method.

A specific example of applying A k' C to the 1N carrier wave in the common pilot system is shown in j151N. The major difference between Fig. 5 and Fig. 4-) is that no AFC is applied to the up-converter system of the reference pilot;
This means that converter 4 is applied with MiAFC.

Tsumashi, reference/(output of plot creation circuit 6 and modulator 1)
The outputs of 02 are passed through separate a1111/converters 104'04 and then combined in the combiner 103, and the carrier wave regeneration and control signal generation circuit 170 @signal is sent to terminal 1.
5 to only the variable frequency local oscillator 104m of the ARA/converter 104 for communication carrier waves. With this, AFC is not applied to the transmitted reference pilot, so it is possible to receive the reference pilot from another station and compare the frequency of its carrier wave component with the nominal mg number from a separately prepared oscillator. , the communication carrier wave can be sent out after being subjected to AFC.

In the example of FIG. 5, the control signal from the output terminal 15m of the carrier wave regeneration and control signal generation circuit 17 is applied to the frequency variable local oscillator 108a of the second down converter 108, and the reference pilot receiving system KAFC is applied. This is to take into consideration that since AFC is not applied to the quasi-pilot that is sent out, there is a possibility that it may fall out of the receivable frequency band due to frequency deviation caused by the satellite's transponder, etc. . In other words, even if a large frequency deviation occurs, the reference signal can always be received within the receivable frequency band.

Other embodiments of the present invention are shown in FIGS. 6 and 7. The purpose of this embodiment is to reduce the synchronization acquisition time required for initial acquisition of the reference pilot as much as possible, and each of the embodiments shown in FIGS. 2 and 3 always uses the spread spectrum reference pilot. However, unmodulated pilots are used only during initial acquisition. In other words, if only the spread spectrum reference arm pilot is used, it takes time to synchronize the phases of the PN code generator 100, which have the same frequency and variable phase, when correlating for carrier wave recovery. Therefore, if the unmodulated pilot is used only during initial acquisition, phase synchronization of the PN code will be possible! It doesn't take much time because there is no In this case, the same drawbacks as in the past, such as the widening of the occupied frequency band, will be avoided, but the probability that multiple pilots will become unmodulated pilots at the same time is extremely low, and the spread spectrum pylon ) 4C and unchanged lIi pilot) OM
Even if the number of Im is 1, it will not cause interference.Conversely, for @Okikomanoya Pilot, the spread spectrum standard looks like noise, and the frequency change in the initial acquisition time is extremely small, so the spectrum after extraction is When spreading is performed, the disadvantages of the conventional method do not arise because 8-wave number synchronization is rarely lost during the establishment of phase synchronization of the PN code.

In the tk6 diagram, mode switching is performed by adding changeover switches 18 and 19 to the standard pilot lot creation (b), the road, and the tortoise 2. The reference number 4 pilots have already been captured.
During times when FC Rogue is in a synchronous state, switches 18 and 19 are connected to the diffusion mode side contacts 18m and 19 respectively.
The circuit 11Lh2 performs the same operation as the example shown in the diagram. AF'C Loose Synchronization or Loss During the time period when attempting to capture the reference/pilot, the switch or the initial acquisition mode false contacts 18b and 19b are applied, and the carrier waves of the reference and -9 pilot are not subjected to spectrum spread and are ignored. The modulated signal is output to the output terminal 5 as it is. In addition, if the AFC Rogue is out of synchronization,
For example, the state in which the output of the carrier wave extraction circuit 12 is considered to be zero, that is, the AFC cycle is out of alignment, is determined in advance by the phase synchronization circuit 11.
It can be detected if the failure continues for a certain period of time or more, which is determined by taking into account operating characteristics, etc.

Figure 7 shows the carrier wave regeneration and control signal generation circuit;
Changeover switches 20 and 21 are added to the circuit shown in the figure, as well as a narrowband bandpass filter 22 and an envelope detector 23. In the synchronized state of AFC loose, switch 20
．． 21 is inserted into the diffusion mode side contacts 20m and 21m,
The circuit is manufactured in the same way as the circuit shown in Figure 3. When the AF'C loop becomes out of synchronization, the switch closes the initial acquisition mode side contact 20b.
.

When the AFCO period is established in either of FIGS. 6 and 7, the switch is returned to the spread mode contact, the spread spectrum PN code synchronization is established, and the spread mode enters the AF C1 state. When entering spread spectrum PN code synchronization, the frequencies have already matched, so the phases of the PN codes match in a short time.

Table 1 shows the system specifications for an embodiment of the present invention, assuming a satellite communication system with 20 stations that transmit reference pilots with an expected maximum frequency deviation of ±55 kHz. For reference, Table 1 shows the specifications of the conventional non-modulated pilot system. Furthermore, FIG. 8 shows an example of the arrangement of the transmission chest wave number of the reference pilot of the Eastern method shown in Table 1. In Fig. 8, Ps = Pte company's nominal cage pilot, Pl, Pte, FiPt, and P. 7e diagram is shown when the 7e is subjected to the maximum frequency deviation.

Table 1 As explained above, in the present invention, the spectrum of the reference p41 pilot is spread by direct spreading using a PN code sequence, so even if the occupied frequency bands of the reference pilots of 2fIL or more overlap, each station can still reach the desired station. For example, you can separate your station's reference pilot from others. Therefore, the frequency spacing between reference pilots can be made considerably smaller than twice the expected maximum frequency deviation, and furthermore, if the number of reference pilots is not so large, all the reference pilots can be reduced to x-am numbers. It can also be sent. That is, since the chest frequency bandwidth occupied by the reference pilot is much narrower than in the conventional system, the frequency band utilization efficiency of the entire system is increased.

Furthermore, since the present invention performs spectrum spreading, even if noise such as cross-modulation noise where energy is concentrated or concentrated in the west of the wave frequency range is received, these noises will be converted into energy or diffused during demodulation. This greatly reduces the amount of noise.

Note that if the carrier frequency tIL of the reference pilot is sufficiently different from the carrier frequency tIL, the same number of PN code sequences for spectrum spreading or the same reference pilot can be used in the same communication system. However, if the PN code sequences are different, it is possible to identify that the pilot acquired by PN code synchronization is the desired pilot to be transmitted from the own station.

[Brief explanation of the drawing]

Fig. m1 is an explanatory diagram showing an example of a communication system to which the present invention can be applied, Figs. 2 and 3 are block diagrams showing an embodiment of the present invention, and Fig. 4 is an explanatory diagram showing an example of a communication system to which the present invention can be applied. A block diagram showing a specific example applied to the system, FIG. 5 is a block diagram showing another specific example, and FIGS. 61 and 7 are block diagrams showing other embodiments of the present invention. It is an explanatory diagram showing an example. 1 is a reference pilot carrier wave oscillator, 2L balanced chest transformer, 3 is a PN code generator, 4 is a pantone noise filter, sFi output terminal, 6 is a spectrum-sim spread reference pilot creation circuit, 7 is a receiver 8Fi bandpass filter, 9 is a correlator, 10 is a variable phase PN code generator, 11 is a phase synchronization circuit, 12 is a carrier extraction circuit, 13#i phase lock rroug, 14 is a nominal frequency signal input terminal. Input terminals, 15 and 15m are output terminals for frequency control signals, 16Fi inverting amplifier, 17 are carrier wave regeneration and control HI number generation circuits, 18 to 21
1 mode switching switch, 22 #i narrow IF range pantone filter, 23 is envelope line detector, 101 company turtle Fj! J! , 102 is a modulator, 103 is a combiner, 104, 104', 105, 109 and 11° are up converters, 106 is an antenna, 107, 10.8, 11 and 112 are Dakun converters, 104m, 108m and 112& is a variable frequency local oscillator, 113 is a reception signal output terminal, and 114tJ is a repeater. Patent noodle person Kokusai Telegraph Kimewa Co., Ltd. Patent attorney Mitsuishi Shibe (and 1 other person) Procedural amendment April 74, 1975 Dear Commissioner of the Japan Patent Office 1, Indication of matter e+ 1982 Patent Application No. 33087 Showa era
Judgment No. 2, Title of Invention: Automatic Frequency Control System 3, Jllll, Relationship with 11 Cases Patent Applicant: No. 3-2 Nishi-Shinjuku 2-chome WA, Shinjuku-ku, Tokyo (121) International Telegraph and Telephone Corporation 4 Agent 7: Contents of the amendment In the drawings, Figure 7 is amended to the attached supplementary amended drawing @ Figure 7, line 9. & Attached 1 or more copies of IIF catalog correction drawings Figure 7

Claims (1)

[Claims] In the transmitter, the carrier wave serving as the reference pilot signal is
It is modulated and transmitted using an N code sequence. , on the receiving side, the received signal is received by calculating the correlation with a signal of a code sequence equal to the PN code sequence, and the carrier wave component of 9 standard/+Ilot is reproduced, and the reproduced f
c, gM Controlling the oscillation frequency of the frequency conversion local oscillator of at least one of the receiving system and the transmitting line so as to correct the frequency deviation of the communication carrier wave from the difference between the frequency of the M transmission wave component and a predetermined nominal carrier wave frequency. Automatic frequency control method with % image.