JPS5877339A - Connecting system between central station and plurality of peripheral stations applied to satellite communication system for data communication - Google Patents

Abstract

PURPOSE:To surely keep synchronism, by detecting a deviation of a burst signal received at a central station from a peripheral station from a time position on a substantial frame and transmitting a control signal minimizing the error to the peripheral station, in the time devision multiple access of the central station and each peripheral station with satellite relay. CONSTITUTION:A central station 20 drives a reference frame timing generator 22 with an output of a reference frequency source 21 in synchronizing with the land communication network and transmits signals in a frequency f1 with the reference frame timing. The reception time of each data burst is forecast based on the reference timing signal from the generator 22, the error between the actual reception time and the forecast time is detected and a timing control signal to minimize this error is transmitted. A peripheral station 30 picks up a reception reference frame timing signal, interpretes a timing control signal at a control signal decoder 33, controls a delay circuit 34 and superimposes the data burst of itself on the assigned location of the reference frame timing and transmits 35 signals in a frequency f2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a satellite communication system for data communications, and particularly to a connection system between a central station and a plurality of peripheral stations applied to a domestic satellite communication system having a synchronized data communication network.

In data communication systems using digital communication technology, each piece of data is transmitted in a periodic format called a frame.

The issue of “synchronization” becomes very important. Therefore, when constructing a large communication network using such communication systems, it is necessary to synchronize the entire communication network with a single reference clock. It is also possible to create a data communication network based on the above, but in this case it is necessary to consider the effects of Dossiler based on changes in the orbital position of communication satellites. When it is desired to implement a data communication network connecting a large number of earth stations using satellite communication, it is known that TDMA (time division multiple access) communication systems are advantageous due to their great flexibility. However, this TDMA
Communication systems typically have their own reference clocks, which creates various problems in connecting such digital satellite communication systems to terrestrial data communication networks. For example, in order to absorb the effects of Doppler on the satellite, a Doppler buffer memory circuit is installed to smooth out fluctuations in the 24-hour cycle and to absorb the effects of the difference in the reference clock frequency between the two communication systems. A special mechanism called a pre/ochronous connection must be used to compensate for the difference in incoming frame phase. This is a complex means of allowing data loss to resolve the accumulated frame phase difference without losing frame synchronization.

An object of the present invention is to solve the above problems and to provide a single central station connected to a terrestrial data communication network with a simpler configuration.
Both were connected to the same terrestrial data communications network. Alternatively, it is an object of the present invention to provide a connection method between a central station and a plurality of peripheral stations that can apply a satellite communication system between a large number of peripheral stations connected to an independent regional communication network.

The features of the invention are, firstly, that one central office (another central office);

In a satellite communication system consisting of a number of peripheral stations (generally smaller stations that are simpler than the central station) and a number of peripheral stations (there may be an equivalent station to back up the central station).

The central station occupies one frequency and transmits information for the peripheral stations using any modulation scheme, while the nine peripheral stations share one or more other frequencies with each other, providing time division multiple access. The 2nd & C central station has a frequency source synchronized to the frame timing of the terrestrial data communication network, and the frame reference timing of the time division multiple access for the satellite communication system. This is because the central station maintains synchronization of the time division multiple access by creating and transmitting the burst reception timing from each peripheral station that is generated and received by the central station.

As will be explained in detail later, in the former case, the effective transmission power of the central station and peripheral stations can be freely selected, so if the central station is equipped with a large antenna, the peripheral stations can be equipped with small antennas. The advantage is that the station structure can be realized easily and at low cost. In addition, the latter allows one peripheral station to completely rely on the central station to control the transmission and transmission of time division multiple access, which is important for system maintenance. Connectivity to the network is most easily achieved at the central station with the highest traffic, and furthermore, peripheral stations connected to the same data communications network can be connected simply via a Doppler buffer, eliminating the need for complex plesiochronous connection functions. The effect of improving the performance and economical efficiency of the satellite communication system 4 is significant.

2. Before explaining the present invention in detail, the basic conditions that the system should have will be explained.

FIG. 1 is an explanatory diagram of a communication system that uses different transmission frequencies between a central station and peripheral stations.

In (4) K in the figure, it is assumed that l has the ability to output an output Pi at the transmitting/receiving equipment of the central office. 2 is the antenna of the central office and has a gain of G1. No. 3 has the ability to output an output P2 with the transmitting/receiving equipment of one of the plurality of peripheral stations. 4 is the antenna of the peripheral station 3 and has a gain of 02. Communication between the two stations is carried out via a satellite 5, but here, for the sake of simplicity, it is assumed that the satellite 5 is completely transparent and of the IR type.

As a result, the power tiA of the central station 1 received by the peripheral station 3
G Gn Pt (where A is a coefficient), and the power of the peripheral station 3 received by the central station 1 is nQIG2 Pt (where B is a coefficient). Since the loss in propagation between both stations is equal in both directions, A=B. If the modulation method used for communication at the other end is the same 9, for example PSK modulation, and the receiving noise temperature of both stations is the same, then 07M (received power to noise ratio) corresponding to the threshold of the receiving equipment of both stations will also be Because they are equal.

It must be p1=p,'. In reality, the central station must have sufficient margin for transmission power in order to improve system reliability, and it may be possible to install a low-noise amplifier with better performance than the peripheral stations. P1)
It will be P2. However, the influence of the antenna is
Since we can think of it as a product of This can be achieved using a small station equipped with a small antenna. 1 of the antenna size of the surrounding station
The two limits are given by the combination with the characteristics of the low noise amplifier (G/T characteristics).

Between such unbalanced stations, each frequency fx
When transmission is performed using f2 and f2, the level on the satellite becomes as shown in Fig. 1←), resulting in a large level difference. In other words, if such a communication system were to be realized by time division multiple access using a single frequency, the U level would have to be matched on the satellite, so the nine peripheral stations would have antennas with the same gain as the central station. However, as is the first requirement of the present invention, by using different frequencies for communication from the central station to the peripheral station and communication from the peripheral station to the central station, the scale of the peripheral stations can be greatly reduced.

Here, it is assumed that most of the traffic of the plurality of peripheral stations is directed to the central station.

Therefore, it is unique that communications between one peripheral station are received once by the central station and then retransmitted to the other peripheral station. It is assumed that the peripheral stations share the same frequency, mutually access the satellite through time division multiple access, and send data destined for the central station.9 The size of the peripheral stations (transmission power, etc.) depends on the transmission bit rate for transmission. Determined by Therefore, by assigning n frequencies to one surrounding lunar eclipse, it is possible to reduce the transmission pit rate transmitted by one surrounding station to 1/n.
In an extreme case, n matches the number of peripheral stations, and communication from one peripheral station to the central station requires 5 CPCs (Single Channel).
It is conceivable that this method may be the same as the P@wCarrier, ) method.

Also in this case, as shown in the second feature of the present invention, the purpose of the present invention is achieved by controlling the transmission timing of burst-compressed data from the central station. I can do it. In other words, the time division multiple access in the present invention includes the case where there is only one burst in a frame.

Next, a TDMA (time division multiple access) system to which the connection method according to the present invention is applied will be described with reference to the TDMA frame configuration diagram shown in FIG. In the figures, (a) shows a conventional example, and (b) shows an example of the present invention. First, in (a),
Reference numerals 11 and 11' indicate reference bursts transmitted from the earth station (corresponding to the central station in the present invention) selected as the reference station among the participants, and are transmitted at nine periodic intervals. This period and the position of the reference burst define a TDMA frame. 1
2,13. ..., ■Good is the data sent from each station.
Shows burst.

The reference station also often transmits data in the form of data bursts separately from the reference burst. Each station is shown on the satellite (A)
Receive all bursts arranged as follows.

The reference frame timing for reception is established depending on the reception position of the reference burst. Stations other than the reference station 9 define the reference frame timing for transmission, for example by placing a delay consisting of the reference timing for reception, and transmit their own data burst at the assigned position on the reference frame timing for transmission. do. The local data burst sent to the satellite.

It is received again and its position on the reference frame timing of reception is checked. As a result, if there is an error, the TDMA frame configuration on the satellite is maintained within the error by modifying the transmit reference frame timing.

In the system of the present invention, since the central station and the peripheral stations use different frequencies, the central station uses the reference burst in the TDMA frame in which the data burst of one station and the peripheral station are transmitted, as shown in Figure 9 (b). I can't send it again.

Even if one of the peripheral stations becomes a reference station, other peripheral stations cannot receive the low power level signal using small antennas. For this reason, in the present invention, the transmission timing of data bursts of one peripheral station is controlled by the central station. That is, one peripheral station is informed of the time difference between its received reference frame timing and its transmitted reference frame timing in the form of a control signal from the central station, thereby modifying the transmission timing of the data burst.

Moreover, the results are monitored only by the central office. From this, in the present invention, the TDMA system is controlled based on the reference frame timing at a central station on the ground, whereas in the prior art the TDMA system is controlled based on the reference burst position on the satellite. As you can see, it is characterized by the following points. As a result, the timing of the data included in the data burst from each peripheral station received by the central station can be automatically synchronized with this reference timing, simplifying the interface with the terrestrial line. , it is possible to eliminate complex Doppler buffers and solatiochronous connection functions.

On the other hand, on the side of one peripheral station, if the input/output of one station is connected to a small-scale regional communication network, the station only needs to provide a reference clock. Furthermore, even if one peripheral station happens to need to connect to the same terrestrial data communication network as the central station, that is, a communication network synchronized to the same reference clock, all that is required is a Doppler buffer; There is no need for a dead connection, so there is no loss of data.

FIG. 3 is a block diagram showing the configuration of a satellite communication system as an embodiment of the present invention. In this figure, a central station 2o is provided with a highly stable oscillator or a reference frequency source 21' synchronized with a terrestrial communication network, and a reference frame timing generator 22 is driven depending on the output of the reference frequency source 21'. Any modulation method may be used for the data transmitted from the central station using the frequency f,1, but the frame timing of data transmission is determined by this generator 2.
Two reference frame timings are used. Transmitting device 2
The output data of No. 3 is transmitted from the antenna 24 to the satellite 40, relayed to the satellite 40 multiple times, and captured by the antenna 31 of the peripheral station 30. .

A received signal received by the Acitena 31 is demodulated by a receiving device 32 having a receiving reference frame timing extraction circuit,
Distributed where needed. One part is the control signal decoder 33
and decodes the timing control signals sent from the central station to this peripheral station. The decoded timing control signal controls the delay control circuit 34 to align the time relationship between the reference frame timing generated by the transmission reference frame timing generation circuit in the transmitter 35 and the above-mentioned reception reference frame timing. Control. The transmitter 35 places the data burst of its own station on the assigned position on the reference frame timing generated as described above, and transmits it from the antenna 31 using the frequency f2.

This transmitted signal is captured by the antenna 24 of the central station via the satellite 40, demodulated by the receiving device 25 including a timing comparison circuit, and distributed to necessary locations. The receiving device 25 further has information on the position assigned to each peripheral station on the TDMA frame, and predicts the reception time of each data burst based on the reference timing signal from the reference frame timing generator 22. When a data burst from a peripheral station is actually received, a comparison is made with the predicted time position to detect an error. The transmission timing control signal generation circuit 26 corrects the content of the signal previously sent to the corresponding peripheral station based on the measured timing error, and transmits it again to the peripheral station by the transmitter 23.

Since such control is performed for each peripheral station, each peripheral station is cyclically sent multiple control signals from the central station.

The cycle period needs to be longer than 0.6 seconds, which is required for the round trip of the signal between the central station and the peripheral stations, and can be made longer as the satellite's position is more stable, but generally it is 1. It will take about 3 seconds.

As is clear from the above explanation, according to the present invention, a satellite communication system is configured between a central station and peripheral stations having unbalanced equipment, and the flexibility of the TDMA communication system is utilized for data transmission. This not only makes it possible to connect to the terrestrial data communication network over a wide area and efficiently, but also has great effects in terms of improving the economic efficiency of the system.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a communication system that uses different transmission frequencies between the central station and peripheral stations, and Fig. 2 is a diagram illustrating a comparison with a conventional example of frame structure in a TDMA system to which the present invention is applied. , FIG. 3 is a block diagram showing the configuration of a satellite communication system as an embodiment of the present invention. In the figure, 20 is a central station, 21 is a reference frequency source, 22
2 is a reference frame timing generator, 23 is a transmission device of the central station, and 24 is an antenna of the central station. 25 is a receiving device of the central station, 26 is a transmission timing control signal generation circuit, 30 is a peripheral station, 31 is an antenna of the peripheral station,
32 is a peripheral station receiving device, 33 is a control signal decoder, 34
35 is a delay control circuit, 35 is a transmitting device of a peripheral station, and 40 is a satellite. Procedural Amendment (Spontaneous) Δ month, 1989 / Tomari Patent Office Commissioner Kazuo Wakasugi 1. Indication of the case 1982 Patent Application No. 176, 121 2. Name of the invention Applied to a satellite communication system for data communication. Connection method between a central station and multiple peripheral stations 3, and its relationship with the amended case Patent applicant address 5-33-1 Shiba, Minato-ku, Tokyo Name (423) NEC Corporation Representative Tadahiro Sekimoto 4. Agent 105 Address: 1-4-10 Nishi-Shinbashi, Minato-ku, Tokyo 6 Contents of amendment a) Attachment sheet] Next page (1) Lines 11 to 13 of page 4 of the specification ``Meanwhile, each of the nine peripheral stations uses one of the other frequencies...by time division multiple access...''. ...” is corrected. (2) On page 5, line 3 of the specification: "The former is the central office..."
``Due to the first feature mentioned above, the central station...''
Correct. (3) On page 5 of the specification, lines 7-8: “The latter...
'' and Aki's words are corrected to ``・Also, according to the second characteristic...''. (4) On page 6, line 14 of the specification, "A=B (1)" should be corrected to "A=n." (On page 7, line 19 of the specification) "According to the first feature of the present invention..." was replaced with "According to the first feature of the present invention..."
” is corrected. (6) In the 18th line of page 5 of the specification, it says [of data compressed in burst form...] What should be corrected to [of data formed in frame form...]? Claim 1. Applicable to a satellite communication system for data communication in which one central station and a plurality of peripheral stations are connected as a satellite kA, and the central station apparatus has nine reference frame timings for time division multiple access. means for transmitting data using one frequency in a frame configuration synchronized with the reference frame timing; means for comparing and detecting the deviation of the received burst signal from the time position on the frame where it should originally exist, using the reference timing; and a transmission timing control for minimizing the timing error detected by the comparing and detecting means. means for transmitting a signal to a corresponding peripheral station on all of the one frequency; between a central station and a plurality of peripheral stations, characterized by comprising means for transmitting a burst-like signal on one of the other one or more frequencies with well-controlled timing. Connection method.

Claims (1)

[Claims] 1.Applicable to a satellite communication system for data communication in which one central station and multiple peripheral stations are connected via a satellite, and generates reference frame timing for 9 time division multiple access in the central station equipment. means for transmitting data at one frequency under the control of a frame timing signal from the reference frame timing generating means; means for comparing and detecting the time position i of the burst signal on the frame where it should originally be based on the reference timing;
means for transmitting a transmission timing control signal for minimizing the timing error detected by the comparing and detecting means to a corresponding peripheral station using the one frequency; In response to the transmission timing control signal transmitted from the other one, the burst signal is transmitted to the other one at a timing controlled by the signal. Alternatively, a connection method between a central station and a plurality of peripheral stations, characterized by comprising means for transmitting on a plurality of shared frequencies.