JPH0563621A - Subminiature satellite communication system - Google Patents

Abstract

PURPOSE:To provide a subminiature satellite communication system capable of controlling the transmission level of a VSAT station. CONSTITUTION:An HUB station forms a transmission instruction, a slot number in use and slot utilization information in the order of younger station numbers, for example, based on station number information of all participating VSAT stations for which a transmission level control section 4 is registered and a modulator 2 sends an in-bound signal. The demodulator 5 of the VSAT station detects the transmission instruction and the slot utilization information and a modulator 6 forms and outputs an in-bound signal corresponding to the transmission instruction. Moreover, the modulator 6 references the slot operating information in the transmission of general data to select a slot. Then the demodulator 1 of the HUB station measures a reception level DELTAL of the reception in-bound signal, the transmission level control section 4 forms the DELTAL information with a station number added thereto and the modulator 2 sends the in-bound signal. The demodulator 5 of the VSAT station detects the DELTAL information and the modulator 6 corrects the transmission level by DELTAL.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a micro satellite communication system composed of a central station and a large number of micro earth stations,
In particular, it relates to a transmission level control system for a micro earth station.

[0002]

2. Description of the Related Art A micro-satellite communication system to which the present invention is applied has an extremely small antenna aperture (1.2
VSAT (Very Small Ap), which is composed of a large number of ultra-small earth stations (up to 1.8 meters) and a central station that has a relatively large antenna and controls the entire system.
erture Terminal) system is generally called, is a system that is usually applied to the communication system with a relatively small amount of communication per station.

In the VSAT system, the micro earth station is V
The SAT station and the central station are called HUB stations, and the VSAT station is H
The satellite line that carries the signal transmitted to the UB station is called the inbound line, and the satellite line that carries the signal that the HUB station transmits to the VSAT station in broadcast mode is called the outbound line. Therefore, the signal transmitted from the VSAT station to the HUB station is called. Is called an inbound signal, and a signal transmitted from the HUB station to the VSAT station is called an outbound signal.

And, the inbound line is all the participating VSA
Although it is a satellite line (one line) shared by T stations, the system in which all participating VSAT stations share this inbound line is
Participate in one frame set on the time axis in a time-sharing manner V
TDMA (Time Division Multipl) assigned to SAT stations
e Access) method and slotted Aloha method, which is a type of random access method. In the VSAT system, since the number of participating stations is very large, the TDMA method reduces the line utilization efficiency, and problems such as a decrease in throughput and an increase in the line connection time become prominent. Therefore, the slotted Aloha method is often used. ing.

In the VSAT system, a satellite transponder is shared by a large number of participating stations, so that only one V
Even in the SAT station, if the transmission signal is bad, there is a risk of adversely affecting the communication of other stations. That is, as the transmission signal failure, for example, if the transmission frequency fluctuates, other signals are disturbed, and if the transmission level fluctuates, excessive level transmission occurs, which affects the satellite transponder operating point and causes non-linearity. As a result, the line quality of all other signals is deteriorated.

Further, in the VSAT system, Ku is generally used.
Frequency called band, ie uplink 14GH
Although frequencies in the z band and the downlink 12 GHz band are used, since the Ku band has a large amount of rainfall attenuation, there is a problem in that the signal level is lowered due to rainfall in addition to the fluctuation of the transmission level.

Therefore, in the VSAT system, each VSA is
The T station prevents fluctuations in frequency by adopting a highly stable oscillator, prevents fluctuations in the transmission level by automatic level control (ALC) for temperature compensation of gain, and has a high utilization rate in the transmission level. In order to provide a communication line of good quality, the line is designed to be higher by the amount of rain attenuation assumed, that is, the transmission is always set to an extra high level.

[0008]

DISCLOSURE OF THE INVENTION The conventional VSA described above
The T system employs a high level fixed system that constantly transmits at a high level in order to compensate for rain attenuation and ensure good line quality even in rainy weather. This is one of the causes for lowering satellite transponder utilization efficiency. There is a problem that is becoming.

An object of the present invention is to provide a micro satellite communication system in which each micro earth station can variably control the transmission level.

[0010]

In order to achieve the above object, the micro-satellite communication system of the present invention has the following configuration. That is, in the micro-satellite communication system of the present invention, a central station and a large number of micro-earth stations are connected via a satellite line, and each micro-earth station participates in a burst-like inbound signal to be transmitted to the central station. Broadcast to the satellite line (inbound line) shared by all micro earth stations, and the central station broadcasts outbound signals to all micro earth stations to a satellite line (outbound line) other than the inbound line. In the microsatellite communication system adapted to transmit by the above; the central station means for transmitting inbound signals to all the participating microearth stations one by one in a fixed order; detecting the reception level of the received inbound signal Means for transmitting the detected reception level value to the micro earth station which has transmitted the inbound signal, and the micro earth station. , Means for correcting the transmission level based on the detected reception level value received; is characterized in that comprises a.

[0011]

Next, the operation of the microsatellite communication system of the present invention configured as described above will be described. In the present invention, the transmission level of the micro earth station is variable, and the central station issues an instruction to all participating micro earth stations to transmit one station at a time, detects the reception level of the received inbound signal, and detects and receives it. Send the level value to the corresponding micro earth station. As a result, each micro earth station automatically adjusts the transmission level. Since the control from the central station is closed loop,
The transmission level of the micro earth station can be controlled accurately.

As a result, the transmission level of each micro earth station can be suppressed to the necessary minimum, and the utilization efficiency of the satellite transponder can be improved. Also, the transmission level control is performed using the satellite line, but this uses a small part of the working line and does not require a new separate line,
The band of the satellite transponder can be effectively used.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In the micro satellite communication system (VSAT system) of the present invention, a micro earth station (VSAT station) is a central station (HU).
The transmission level is automatically controlled under the control of the (B station).
The station B is provided with a demodulator 1, a modulator 2, a timing control circuit 3, and a transmission level control unit 4 as shown in FIG. 1A, and the VSAT station is shown as shown in FIG. 1B, for example. Further, a demodulator 5, a modulator 6 and a timing control circuit 7 are provided.

In the HUB station, the station number information of all the participating VSAT stations is registered in the transmission level control section 4, and the transmission level control section 4 instructs all the VSAT stations to transmit inbound signals, for example, in ascending order of station number. The transmission instruction to perform and the slot number to be used are output to the modulator 2.

In addition to the output of the transmission level control section 4, the modulator 2 is supplied with a timing signal from the timing control circuit 3 and transmission data from outside the drawing, and the outbound signal of the format shown in FIG. A transmission IF signal) is formed and output to a transmission stage (not shown). Outbound signals are sent in broadcast mode.

In FIG. 2 (a), the outbound signal is a signal of a fixed length frame, a pattern called a unique word having a strong autocorrelation is inserted at the beginning of the signal, and the frame according to the present invention is provided in the middle of the frame. A transmission instruction and slot usage information are inserted. That is, if the transmission instruction is not a multi-frame, for example, it is inserted in every frame and all the VSAT stations receive the instruction in order. Note that the transmission instruction is for one specific VSAT station, but the slot use information is transmitted using the all-station-designated dedicated station number so that all VSAT stations can capture it. V
This is because the SAT station transmits the inbound signal by the slotted Aloha method, but it is for preventing the general data from colliding with the signal for level control.

In the VSAT station, an inbound signal (reception IF signal) is input to the demodulator 5 via the reception system, and the reception data demodulated here is output to the outside of the drawing, and
Input to the timing control circuit 7. The demodulator 5 is given its own station number from outside the drawing.

The timing control circuit 7 detects the unique word from the received data, establishes the synchronization of the received frame, and adds the fixed delay determined by the own station to generate the transmission frame timing. The timing of occurrence is the demodulator 5
Is sent to the modulator 6 and used as a real-time timing.

The transmission frame timing is shown in FIG.
As shown in the format shown in (b), one frame is divided into several slots, and each VSAT station transmits an inbound signal (burst signal) in units of this one slot. The burst signal, which is formed by the modulator 6, is composed of a carrier wave reproduction signal, a station number and data as shown in FIG.

Each VSAT station generates a transmission frame timing by adding a different fixed delay time to the frame timing with which synchronization is established. However, the delay time different for each station depends on the burst signal transmitted at that timing. On the satellite transponder, ie, to match the frame and slot timing received by the HUB station,
It is a value set for each VSAT station. Further, the outbound signal and the inbound signal have the same one frame length. Generally, this one frame length is set to be longer than the round trip propagation delay time to the satellite. A frame configuration may be used and one multiframe may be set long. However, in this case, it is necessary to transmit the slot number and the frame number.

Upon receipt of synchronization establishment, the demodulator 5 detects the inbound signal transmission instruction in the outbound signal based on the station number of its own station and transmits the slot number (in the case of one frame configuration), or the slot number. Number and frame number (in the case of multi-frame), the frame next to the frame which detected the transmission instruction to the modulator 6 (or,
It issues an instruction to transmit an inbound signal at a timing of a designated slot number of a predetermined frame in the next multiframe). On the other hand, when the demodulator 5 detects the slot use information that coincides with the all-station-designated dedicated station number, it outputs the slot use information to the modulator 6.

The modulator 6 forms an inbound signal (transmission IF signal) which is a burst signal to be transmitted to a predetermined slot in accordance with the transmission frame timing from the timing control circuit 7, and outputs it to a transmission stage (not shown). At this time, in response to the transmission instruction from the demodulator 5, the inbound signal is transmitted at the designated slot timing. On the other hand, for transmission data given from outside the figure, refer to the slot usage information, select a slot other than the slot designated by the other station for level control, and send an inbound signal at that slot timing. ..

Next, in the HUB station, the reception level (ΔL) of the inbound signals sequentially transmitted from all participating VSAT stations is sequentially measured by the level measuring circuit provided in the demodulator 1, and the transmission level control unit 4 The station number of the VSAT station corresponding to the detected reception level value is given to the modulator 2, and the modulator 2 sends the outbound signal.

Then, in each VSAT station, the demodulator 5 determines ΔL for its own station from the outbound signal from the HUB station.
Information is detected and sent to the modulator 6. The modulator 6 is provided with level changing means, and corrects the transmission level of the transmission IF signal by ΔL.

Since the level control from the HUB station described above is a closed loop, it is possible to accurately control the transmission level of the VSAT station. Thus, each VSAT station can automatically set the transmission level to an appropriate value according to the weather condition of the location where the VSAT station is located, and can perform communication.

[0026]

As described above, according to the micro-satellite communication system of the present invention, the transmission level of the micro-earth stations is variable, and the central station transmits one station to all participating micro-earth stations. , The reception level of the received inbound signal is detected, and the detected reception level value is transmitted to the corresponding micro earth station. As a result, each micro-earth station automatically adjusts the transmission level, so each micro-earth station can keep the transmission level to the minimum necessary level and improve the utilization efficiency of the satellite transponder. effective. Further, although the transmission level control is performed using the satellite line, since this uses only a part of the working line and does not require another new line, there is an effect that the band of the satellite transponder can be effectively used.

[Brief description of drawings]

FIG. 1A is a configuration block diagram of a central station (HUB station), and FIG. 1B is a configuration block diagram of a micro earth station (VSAT station).

2A is a frame format of an outbound signal transmitted by a HUB station, and FIG. 2B is a frame format of an inbound signal received by a HUB station.

FIG. 3 is a format of a burst signal transmitted by each VSAT station.

[Explanation of symbols]

 1 Demodulator 2 Modulator 3 Timing Control Circuit 4 Transmission Level Control Unit 5 Demodulator 6 Modulator 7 Timing Control Circuit

Claims (1)

[Claims] 1. A central station and a large number of micro earth stations are connected via a satellite line, and each micro earth station shares a burst-like inbound signal to be transmitted to the central station with all micro earth stations participating. The central station sends outbound signals to all participating micro-miniature earth stations to a satellite line (outbound line) other than the inbound line in broadcast mode. In a small satellite communication system; the central station transmits means for transmitting inbound signals one by one to all participating micro-earth stations in a fixed order; means for detecting a reception level of the received inbound signal; Means for transmitting a level value to the micro earth station that has transmitted the inbound signal; Nano-satellite communication system characterized in that it comprises: means for correcting the transmission level based on the Le value.