JPH05130001A - Synchronization control system - Google Patents

Abstract

PURPOSE:To simplify facilities of a communication satellite and an earth station with respect to the synchronization control system absorbing a difference from a transmission speed between a ground line and a satellite line. CONSTITUTION:In the synchronization control system absorbing a difference from a transmission speed between a satellite line whose transmission speed depends on a communication satellite 11 and set between earth stations 13 via a satellite and a ground line asynchronous with the satellite line, the transmission speed of the satellite line in the communication satellite 11 is set higher than the transmission speed of the ground line, and the earth station 13 is provided with a frame phase comparison means 15 sending a slip detection notice in response to a phase difference of frames on both the lines, a stuffing means 17 inserting a pseudo frame to a transmission frame from the ground line and sending the resulting frame to the satellite line, and a destuffing means 19 eliminating a pseudo frame from a reception burst received from the satellite line, smoothing the fluctuation of the frame phase and sending the result to the ground line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous control system which absorbs a difference in transmission speed between these lines in a satellite communication system which forms a communication path through a terrestrial line and a satellite line which is asynchronous with the terrestrial line.

[0002]

2. Description of the Related Art A multi-beam antenna having a plurality of sharp beams and a dynamic matrix switch (hereinafter referred to as "intra-satellite switch") capable of time-division switching between the beams or between the repeaters. SS-TDMA that provides communication services between multiple zones according to the TDMA method via an onboard communication satellite
The (Satellite Switched-TDMA) method can allocate the same radio channel to a plurality of geographically separated service zones, so that the frequency utilization efficiency is high and a single service zone is divided into a plurality of beams for irradiation. Therefore, in the earth station, the received electric field level is increased and the antenna can be downsized, so that it is being actively put to practical use.

FIG. 4 is a diagram showing a configuration example of an SS-TDMA system. In the figure, a reference station 41 and a transmitting / receiving station 42
_A , 42 _B , and 42 _C are connected to the communication satellite 43 via a satellite line accessible by the TDMA system, and are also connected to a TDMA system ground line synchronized with a DCS clock which is a master clock on the ground side.

SS-TDMA system having such a configuration
Then, the communication satellite 43 has a small service zone described above.
Communication service in each zone by dividing into zones A, B, C
Provide the service. Furthermore, the communication satellite 43 is mounted on this.
The master clock generated by the oscillator (hereinafter referred to as "satellite
Master clock ”. ) Satellite TDMA
Each time via the switch in the satellite
A communication path corresponding to a zone is formed, and for example, in FIG.
In the time slot of the satellite TDMA frame,
Trust 42_A, 42_C, 42_BThe burst received from
Each transmitting / receiving station 42_A, 42_B, 42_CSent to
In the time slot, the transceiver station 42_BFour
Two_A, 42_C, The transceiver station 42 in the time slot_C,
42_A, 42 _BSend and receive bursts respectively received from
Trust 42_A, 42_B, 42_CSend to.

On the other hand, the reference station 41 detects satellite TDMA frames from the burst pattern (hereinafter referred to as "zone switching pattern") transmitted from the communication satellite 43 in this manner, and at a predetermined timing for each frame. Send a reference burst (Fig. 4). Transceiver station 42 _A ,
Since 42 _B and 42 _C recognize the reference burst by correlation detection from each satellite TDMA frame to establish frame synchronization and transmit and receive the burst at the timing of the time slot adapted to the zone switching pattern, different zones are connected to each other. Communication services are provided.

Further, the reference station 41 reproduces the satellite master clock from the zone switching pattern to constantly monitor the frequency difference from the DCS clock, and sends a control signal according to the monitoring result to the communication satellite 43. Since the communication satellite 43 finely adjusts the frequency of the satellite master clock according to the control signal, the occurrence of bit slip caused by the asynchronousness of the satellite master clock and the DCS clock is avoided.

[0007]

By the way, in such a conventional synchronous control system, a highly stable variable frequency oscillator is mounted on the communication satellite in order to remotely control the frequency of the satellite master clock at a predetermined interval from the ground. However, in addition to the above-mentioned characteristics, the oscillator must have the reliability to withstand the space environment.
There were many technical difficulties and it could not be realized easily.

Further, in the reference station, in order to transmit a control signal for varying the frequency of the satellite master clock to the communication satellite, in addition to the facility provided for the original communication service, for example, a transmitting terminal station device, a transmitting device, A transmitting antenna and other facilities were required, and the cost was high.

Further, the reference station reproduces the satellite master clock from the zone switching pattern to detect the frequency difference from the DCS clock. The frequency of the clock thus reproduced is Doppler associated with the attitude control of the communication satellite. Since the shift amount is included, it is necessary to have an arithmetic processing function of predicting and removing the shift amount from the movement of the communication satellite.

It is an object of the present invention to provide a synchronous control system capable of simplifying the equipment of communication satellites and earth stations.

[0011]

FIG. 1 is a block diagram showing the principle of the present invention. In the present invention, the transmission rate is determined by the communication satellite 11, and the earth stations 131 to ₁ are transmitted via the communication satellite.
A satellite line set up as a relay transmission line between the 3 _Ns ,
In the synchronous control system that absorbs the difference in transmission speed between the satellite line and the asynchronous terrestrial line, the communication satellite 11 sets the satellite line transmission rate higher than the terrestrial line transmission rate, and the earth stations 13 _{1 to} 13 _N The frame phase comparing means 15 which monitors the phase difference between the frames of the satellite line and the terrestrial line and sends a slip detection notice according to the result of the monitoring, and the frame phase comparing means 15 which responds to the detection notice of the transmission frame given from the terrestrial line. Stuffing means 17 for inserting a pseudo frame including specific identification information and transmitting the pseudo frame to the satellite line, and removing the pseudo frame from the reception burst received from the satellite line based on the correlation with the identification information, and removing and slipping the pseudo frame. And a destuffing means 19 for smoothing the fluctuation of the frame phase caused by the above and sending it to the terrestrial line.

[0012]

In the present invention, the transmission speed of the satellite line is set higher than that of the terrestrial line, and the earth stations 13 _{1 to} 13 _N
The frame phase comparison means 15 detects a slip in frame units that occurs according to such a difference in transmission rate and sends a detection notification. The stuffing means 17 inserts a pseudo frame into the transmission frame in response to such a notification and sends it to the satellite line. In the earth station which has received the received burst including the pseudo frame from the satellite line, the destuffing means 19 removes the pseudo frame from the burst and smooths the removal process and the fluctuation of the frame phase due to the slip as described above. To send to.

That is, the difference in transmission speed between the satellite line and the ground line can be absorbed without remote control of the oscillator mounted on the communication satellite 11 from the ground. There is no need to install a reliable oscillator or to provide the earth station with the facilities required for the remote control described above.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a diagram showing an embodiment of the present invention.

In the figure, the transmission frame to be transmitted from the terrestrial line to the satellite line is a random access memory (RA
M) given to the data inputs of 21 _Ta , 21 _Tb , 21 _Tc ,
The data outputs of these memories are wired or connected to one input of the OR gate 22. OR gate 2
At the output of 2, the transmission burst to be transmitted on the satellite line is obtained. The received bursts received from the satellite line and demodulated are satellite plane selection signal generating circuit 23 _R and random access memories (RAM) 21 _Ra , 21 _Rb , 2
Received frames to be sent to the terrestrial line are obtained at the data outputs of these random access memories given to the data inputs of 1 _Rc and 21 _Rd .

The frame synchronized with the TDMA frame of the land line
The lame pulse and DCS clock are ground level selection signals.
Generation circuit 24_T, 24_RGiven to. Ground selection signal
Generation circuit 24_T3 bit output of each is random
Access memory 21_Ta~ 21 _TcWrite enable end of
Frame phase comparison circuit 25 connected to the child_TOne side
Connected to the input of. Ground plane selection signal generation circuit 24_Rof
The 4-bit output is the random access memory 2
1_Ra~ 21_RdConnected to the read enable pin of
Two frame phase comparison circuit 25_RConnected to one input
It

The satellite master clock regenerated from the zone switching pattern and the satellite TDMA frame pulse synchronized with the clock are the satellite plane selection signal generation circuit 2.
Given to 3 _T and 23 _R. Satellite plane selection signal generation circuit 2
3-bit output of 3 _T is connected to the read enable terminal of the random access memory 21 _Ta through 21 _Tc respectively, and are connected to the other input of the frame phase comparator circuit 25 _T. The output of the frame phase comparison circuit 25 _T is connected to the stuff control input of the satellite plane selection signal generation circuit 23 _T and the other input of the OR gate 22.

The 4-bit output of the satellite plane selection signal generating circuit 23 _R is the random access memories 21 _Ra to 2 _Ra , respectively.
It is connected to the write enable terminal of 1 _Rd and is also connected to the other input of the frame phase comparison circuit 25 _R. The output of the frame phase comparison circuit 25 _R is connected to the frame slip input of the satellite plane selection signal generation circuit 23 _R.

The circuit of this embodiment is arranged at the interface between the satellite line and the terrestrial line in the reference station and the transmitting / receiving station, and as shown by the chain line in FIG. 2, synchronizes the transmission to the satellite line. Since the transmission synchronization control unit and the reception synchronization control unit that synchronizes the reception are oppositely configured, the components that perform the same operation corresponding to each of these units have the first reference numeral as described above. It is shown by adding " _T " indicating the transmission synchronization control unit or " _R " indicating the reception synchronization control unit as a subscript of.

Further, since the random access memory 21 is composed of a plurality of surfaces, the reference numbers thereof are the second subscripts " _a " to " _a " indicating the identifiers a to d of the respective surfaces.
" _d " is given to indicate each surface.

Further, in this embodiment, the SS-
Since the structure of the TDMA system is the same as that shown in FIG. 4, its description is omitted here. Regarding the correspondence between the present embodiment and the block diagram shown in FIG. 1, the communication satellite 43 corresponds to the communication satellite 11, and the reference station 41 and the transmitting / receiving stations 42 _{A to} 42 _C correspond to the earth stations 13 _{1 to} 13 _N. Then
The frame phase comparison circuits 25 _T and 25 _R correspond to the frame phase comparison means 15, and the random access memories 21 _Ta to
21 _Tc , OR gate 22, satellite plane selection signal generating circuit 23
_T and the ground plane selection signal generating circuit 24 _T correspond to the stuffing means 17 and are connected to the random access memory 21 _Ra .
21 _Rd , the satellite plane selection signal generation circuit 23 _R and the ground plane selection signal generation circuit 24 _R correspond to the destuffing means 19.

FIG. 3 is a diagram for explaining the operation of this embodiment. The operation of this embodiment will be described below with reference to FIGS. In the communication satellite, the frequency of the satellite master clock is fixedly set in advance to a value higher than the frequency of the DCS clock.

Ground level selection signal generation circuit of transmission synchronization control section
24_TThen, a PCM frame synchronized with the DCS clock
The specified number of times (= 16) is counted and the ground TDMA
Generate a clock that indicates the
To the ring counter. Each of this ring counter
Output is random access memory 21_Ta~ 21 _Tc
As a write enable signal to
The active (low level) bit of
It can be switched to re-cyclic according to the lock. did
Therefore, the transmission frame given from the land line is
Random access memory 21 for each game_TSurface a, surface b,
Regularly and regularly written on surface c, surface a, ...
Be imbued.

[0024] The satellite surface selection signal generating circuit 23 _T is, satellite T
The DMA frame pulse is applied to the 3-bit ring counter. Each output of the ring counter is given to the random access memories 21 _{Ta to} 21 _Tc as a read enable signal, and the active (low level) bit of these is switched cyclically in response to the satellite TDMA frame pulse. Therefore, the transmission frame held in advance in the random access memories 21 _{Ta to} 21 _Tc is read in synchronization with the satellite master clock and transmitted to the satellite line as a transmission burst via the OR gate 22.

However, if the satellite plane selection signal generating circuit 23 _T continues such an operation autonomously, a bit slip occurs because the DCS clock and the satellite master clock are asynchronous. The frame phase comparison circuit 25 _T compares the phases of the TDMA frame on the ground side and the TDMA frame on the satellite side in accordance with the write enable signal and the read enable signal given to the random access memories 21 _{Ta to} 21 _Tc , and When a crossing of frame timings (hereinafter referred to as "frame slip") is detected as a result of the comparison (FIG. 3), the stuff instruction information is transmitted for one frame period from the beginning of the subsequent frame (FIG. 3). Depending on such staff instruction information,
The satellite plane selection signal generating circuit 23 _T stops the stepping of the built-in ring counter, and the OR gate 22 transmits all the bits as a transmission burst (FIG. 3).
) Is output.

On the other hand, in the reception synchronization control section, the satellite plane selection signal generating circuit 23 _R sends the satellite TDMA frame pulse to 2
Give to four 4-bit ring counters. These ring counters always operate in parallel, and as shown in FIG. 3 (b), the first ring counter sends an output advanced by one frame period to the second ring counter. Note that in FIG. 3, for simplicity, the outputs of these ring counters are shown by the surfaces a to d of the random access memory 21 _R that can be selected by the outputs. The satellite plane selection signal generating circuit 23 _R selects one of the outputs of the two ring counters in this way and respectively selects the random access memory 21 _Ra.
It is given as a write enable signal of ~ 21 _Rd . Therefore, the burst (reception burst) relayed by the communication satellite in accordance with the above-mentioned inter-zone switching pattern is cyclically written to the surface a, the surface b, the surface c, the surface d, the surface a, ... Of the random access memory 21 _R. Be done.

The ground plane selection signal generation circuit 24 _R is similar to the ground plane selection signal generation circuit 24 _T described above in that the ground TDMA is used.
A clock indicating a frame is generated, and the clock is supplied to a 4-bit ring counter. The ring counter outputs a plane selection signal (read enable signal) delayed by one frame or more from either of the two ring counters provided in the satellite plane selection signal generation circuit 23 _R. Therefore, the surface a of the random access memory 21 _R is
From (d) to (d), the contents that are surely held in advance are read out in synchronization with the terrestrial TDMA frame for each frame and sent to the terrestrial line as a reception frame.

However, when the satellite plane selection signal generating circuit 23 _R continues the above-mentioned operation autonomously, the stuff frame transmitted from the transmitting / receiving transmitting / receiving station is directly output as the receiving frame.

The satellite plane selection signal generating circuit 23 _R constantly monitors the contents of the received burst to check the stuff frame (see FIG. 3).
) Is detected, the output of the second ring counter is given as a write enable signal for the random access memories 21 _{Ra to} 21 _Rd after the start timing (FIG. 3) of the subsequent frame.

Further, the frame phase comparison circuit 25_RIs la
NDAM access memory 21_Ra~ 21 _RdWriting given to
Depending on the enable signal and the read enable signal
When a frame slip is detected, the satellite plane selection signal is generated.
Road 23_RIs notified of the detection timing (FIG. 3).
In response to such notification, the satellite plane selection signal generation circuit 23
_RIs above until the final timing of the subsequent frame (Fig. 3)
Stop the stepping of the two ring counters
Random output of the first ring counter from the frame
Access memory 21_Ra~ 21_RdWrite enable signal
Give as.

That is, the received stuff frame
Is given by the first ring counter which is advanced in phase
Random access memo by write enable signal
21 _Ra~ 21_RdOn the surface (plane c in the example shown in FIG. 3).
The data is retained, but the write enable signal described above is then retained.
No. is given from the second ring counter which is out of phase
Therefore, the subsequent frame should be on the same plane as the stuff frame.
Be written down. Also, when a frame slip occurs
Since the two ring counters stop running,
The ring counter has a frame slip followed by
Random access memory 21 for holding the memory_RFace selection
Information (= b) is retained. Therefore, random access
Set memory 21_Ra~ 21_RdOn each side of the received burst
Received frames excluding included stuff frames are sequentially
It is stored without omission.

As described above, according to this embodiment, unlike the conventional example, it is not necessary to remotely variably control the frequency of the satellite master clock from the reference station, so that the transmission equipment and other facilities required for the variable control are It is not necessary, and the configuration of the oscillator mounted on the communication satellite can be simplified.

In this embodiment, an example of application of the satellite communication system adopting the SS-TDMA system to the reference station and the transmitting / receiving station is shown, but the present invention is not limited to such a communication system, and a communication satellite Any satellite communication system can be applied as long as it is a satellite communication system that forms a communication path through a satellite line whose transmission rate is determined according to a clock generated therein and an asynchronous terrestrial line.

In the present embodiment, the number of faces of the random access memory 21 is set to 3 in the transmission synchronization control unit and 4 in the reception synchronization control unit.
The number of planes is not limited to this. For example, if the transmission delay time to the satellite line due to the synchronization control is allowed, set four or more planes in the transmission synchronization control unit and five or more planes in the reception synchronization control unit. May be.

Further, in the present embodiment, the random access memory 21 is used as an elastic memory indispensable for the synchronous control, but the present invention is not limited to such a storage element, and, for example, a dual port RAM or FIFO. ,
As long as the register file can be written and read alternately at a predetermined timing, any file can be used.

[0036]

As described above, the present invention sets the transmission rate of the satellite line higher than the transmission rate of the terrestrial line, and at the earth station, the number of frame slips generated depending on the difference in the transmission rates is set. As a subsequent transmission frame, a pseudo frame is sent to the satellite line, and the pseudo frame contained in the pseudo burst is removed from the reception burst received from the satellite line to smooth the fluctuation of the frame phase and send it to the terrestrial line.

That is, since the difference in the transmission speed between the satellite line and the ground line can be absorbed without remotely controlling the internal oscillator of the communication satellite from the ground, the configuration of the above-mentioned oscillator is simplified in the communication satellite and the earth station Then, since the facility which was conventionally required to perform the remote control described above and the arithmetic processing function which is indispensable to eliminate the Doppler effect associated with the attitude control of the communication satellite are not required, The size of the satellite communication system can be reduced, and the satellite communication system can be made highly reliable and inexpensive.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of this embodiment.

FIG. 4 is a diagram showing a configuration example of an SS-TDMA system.

[Explanation of symbols]

 11 communication satellite 13 earth station 15 frame phase comparison means 17 stuffing means 19 destuffing means 21 random access memory 22 OR gate 23 satellite plane selection signal generation circuit 24 ground plane selection signal generation circuit 25 frame phase comparison circuit 41 reference station 42 transceiver station 43 communication satellite

Claims (1)

[Claims] 1. A transmission rate is determined by the communication satellite (11), and earth station (13 ₁ to 1 via the communication satellite
3 _N ) In a synchronous control system that absorbs a difference in transmission speed between a satellite line set as a relay transmission line between them and an asynchronous terrestrial line, the communication satellite (11) uses the satellite line. Is set higher than the transmission speed of the terrestrial line, and the earth station (13 _{1 to} 13 _N ) monitors the phase difference between the frames of the satellite line and the terrestrial line, and depending on the monitoring result. And a frame phase comparison means (15) for transmitting a slip detection notification, and a pseudo frame including specific identification information according to the detection notification is inserted into a transmission frame given from the terrestrial circuit and transmitted to the satellite circuit. Staffing means (17)
A pseudo frame is removed from the reception burst received from the satellite line based on the correlation with the identification information, and the fluctuation of the frame phase due to the removal and the slip is smoothed and sent to the terrestrial line. A synchronous control system comprising stuffing means (19).