JPH05300067A - Transmission system for small aperture antenna - Google Patents

Abstract

PURPOSE:To remarkably reduce the cost for the installation of the antenna with a small aperture and less interference with adjacent satellites. CONSTITUTION:A center station 10 sends frequency hopping information for frequency hopping to each satellite communication use small sized earth station VSAT 40 while multiplexing the information onto TDM data, and each VSAT 40 applies spread processing to a slotted ALOHA signal of its own station based on the sent frequency hopping information and returns the result. The center station 10 implements inverse spread processing based on the returned frequency hopping.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a transmission system for a small diameter antenna of an earth station. In particular, it relates to a transmission method for using a small antenna of a small earth station for satellite communication (hereinafter referred to as VSAT) connected to a central station via a star network.

[0002]

2. Description of the Related Art The VSAT system is a satellite communication system using an antenna with a diameter of about 1.2 m, and has recently been rapidly developed because its system cost is lower than that of a conventional satellite communication system.

However, in general, in the VSAT system forming a star network, the cost borne by the user is equal to the cost of the central station and the satellite line usage fee, and the burden per station is equal. Generally small,
The equipment cost and the installation cost of the VSAT installed in each station dominates the cost per station because it becomes the burden of one station as it is.

Of the above installation costs, the installation cost of the antenna is dominant for the following reasons. Even if the antenna is of the 1.2 m aperture class, for example, its opening area is considerably large and must be installed so that it can withstand the wind pressure applied by a typhoon or the like. For this reason, it is necessary to sufficiently perform the foundation work for installing the antenna.

Further, when the antenna diameter is large, an installation space corresponding to that is required, which may be a hindrance when installing it in a general company or a construction shop like VSAT.

[0006] Conventionally, in the transmission system for a small-diameter antenna, the signal-to-noise ratio obtained on the line during communication must be kept above a predetermined value in relation to the characteristics guaranteed by the communication equipment. Since the diameter is proportional to the antenna gain, when the antenna diameter is reduced, the power supplied to the antenna is increased according to the degree to which the antenna gain is reduced.

[0007]

However, in such a conventional transmission system for a small-diameter antenna, it is possible to prevent the reduction of the antenna gain due to the reduction of the antenna diameter by this operation as the quality of the communication line. However, the following problems occur.

With the recent development of satellite communication, the number of satellites for communication has increased dramatically. Moreover, most of the communication satellites are located on the equator because of geostationary satellites. As a result, the space between satellites has become extremely small. For example, in Japan, private satellites are arranged at intervals of 4 °, and in the United States, they are arranged at intervals of 2 °.

Under such an environment, there is a problem in that a signal transmitted by VSAT may interfere with other satellites. In the 1.2 m aperture class antenna, the gain in the off-axis direction of the antenna drops rapidly, so the amount of interference with adjacent satellites is not so large, but in the 75 cm aperture class antenna, the off-axis gain does not decrease so much. For this reason, since the antenna feeding power is correspondingly increased even if the antenna aperture is made small, the effective radiation power (EIRP) in the main beam direction of the antenna does not change, so that it is radiated toward the adjacent satellite. The interference signal power increases. For this reason, there is a problem in that it is difficult to adopt a small-diameter antenna even though it is clear that the cost of the device can be reduced.

The present invention solves the above problems,
It is an object of the present invention to provide a transmission system for a small-diameter antenna, which has less interference with adjacent satellites, can use a small-diameter antenna, and can significantly reduce the cost of antenna installation.

[0011]

SUMMARY OF THE INVENTION The present invention is directed to a central station for transmitting data of its own station via a time division multiplex line, and transmission of data of its own station based on timing information of the time division multiplex signal of this central station. In a transmission system for a small diameter antenna equipped with a small earth station for a plurality of satellite communications for controlling timing and data length and transmitting to this central station via a slotted aloha line, the central station comprises The small earth station includes a generation unit that generates frequency hopping information for performing frequency hopping, and a multiplexing unit that multiplexes and transmits the generated frequency hopping information to a time division multiplexed signal of its own station. Each small earth station
Separation means for separating the frequency hopping information multiplexed in the transmitted time division multiplexed signal, and return means for subjecting the slotted aloha signal of its own station to frequency hopping based on the separated frequency hopping information and returning it. The central station includes a delay circuit for delaying the time required to return the slotted aloha signals returned from the plurality of small earth stations, and the returned slots based on the delayed frequency hopping information. Despreading processing means for performing despreading processing on the rotated arrow signal.

According to the present invention, the generating means includes a random number generating circuit for generating a random code, and a frequency for outputting a frequency hopping frequency to each of the plurality of small earth stations based on the output of the random number generating circuit. A mapping circuit, wherein the multiplexing means multiplexes an output of the frequency mapping circuit into a time division multiplexed signal of the central station, and a first modulator which modulates and outputs the output of the multiplexing circuit. The separating means includes a first demodulator for demodulating a time division multiplexed signal from the central station, and a separating circuit for separating frequency hopping information from the central station from an output of the first demodulator. And a spread frequency data generation circuit for generating spread data based on the output of the separation circuit, a first frequency synthesizer, and an output of the first frequency synthesizer. A second modulator for frequency-hopping and transmitting the slotted aloha signal of its own small earth station, wherein the despreading processing means outputs despreading data based on the frequency hopping information from the delay circuit. A despreading data generating circuit and a second frequency synthesizer, and a second demodulator for demodulating the slotted Aloha signal from the corresponding small earth station based on the output of the second frequency synthesizer. You can

[0013]

In the central station, the generating means generates the frequency hopping information for each of the small earth stations to perform the frequency hopping, and the frequency hopping information generated by the multiplexing means is multiplexed on the time division multiplexed signal of its own station. To send. Each of the plurality of small earth stations separates the frequency hopping information multiplexed in the transmitted time division multiplexed signal by the separating means, and returns the slotted aloha signal of its own station based on the separated frequency hopping information by the returning means. Frequency hopping and return. The central station delays the time required for each of the slotted aloha signals returned from the plurality of small earth stations by the delay circuit to be returned, and the despreading processing means returns the above based on the delayed frequency hopping information. Performs despreading of slotted Aloha signals.

As described above, there is little interference with adjacent satellites and a small-diameter antenna can be used, so that the cost for installing the antenna can be greatly reduced.

[0015]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a transmission system for a small diameter antenna according to an embodiment of the present invention. FIG. 2 is a block diagram of a transmitter of a central station of a transmission system for a small diameter antenna according to an embodiment of the present invention. FIG. 3 is a block diagram of the receiving section of the central station of the transmission system for a small diameter antenna of the present invention. FIG. 4 is a block diagram of the VSAT of the transmission system for a small diameter antenna of the present invention.

1 to 4, in the transmission system for a small-diameter antenna, a central station 10 which transmits data of its own station as a time division multiplex line of an outbound line via a TDM line 50, and a time division of the central station 10. Controls the data transmission timing and data length of its own station on the basis of the timing information of the multiplexed signal, and controls the inbound line slotted aloha line 6
VSAT 40 ₁ to 40 _n as a plurality of small earth stations for satellite communication for transmitting to the central station 10 via 0. Here, the feature of the present invention is that the transmitting unit 20 of the central station 10 is the VSAT 40 Generating means for respectively generating frequency hopping information for performing frequency hopping,
The VSAT4 includes a multiplexing unit that multiplexes and transmits the generated frequency hopping information to the time division multiplexed signal of the local station.
0 is a separating means for separating frequency hopping information multiplexed in the transmitted time division multiplexed signal, and frequency hopping is applied to the slotted aloha signal of its own station based on the separated frequency hopping information and returned. The receiving unit 30 of the central station 10 including the returning means is a VSAT.
A delay circuit 32 for delaying the time required to return the slotted aloha signals returned from the despreading processing for despreading the returned slotted aloha signals based on the delayed frequency hopping information. And processing means.

The generating means includes a random number generating circuit 21 for generating a random code, and a frequency mapping circuit 22 for outputting a frequency for frequency hopping to the VSAT 40 based on the output of the random number generating circuit 21, The multiplexing means includes a multiplexing circuit 23 that multiplexes the output of the frequency mapping circuit 22 into a time-division multiplexed signal of the central station 10, and a modulator 24 as a first modulator that modulates and outputs the output of the multiplexing circuit 23. The separation means includes a TDM demodulator 41 as a first demodulator for demodulating the time division multiplexed signal from the central station 10, and a separation for separating the frequency hopping information from the central station 10 from the output of the TDM demodulator 41. A circuit 42, a spread frequency data generation circuit 43 for generating spread data based on the output of the separation circuit 42, and a first frequency synthesizer. Frequency synthesizer as a seat 44
And VSAT based on the output of the frequency synthesizer 44.
And a modulator 45 as a second modulator for performing frequency hopping on the slotted ALO signal and transmitting the despreading data based on the frequency hopping information from the delay circuit 32. A despreading data generating circuit 33, a frequency synthesizer 34 as a second frequency synthesizer, and a demodulator 31 as a second demodulator for demodulating the slotted Aloha signal from the corresponding VSAT based on the output of the frequency synthesizer 34. including.

The operation of the transmission system for a small aperture antenna having such a configuration will be described. FIG. 5 shows a frame format of a satellite line of a transmission system for a small diameter antenna of the present invention. FIG. 1 shows a VSAT star network, which has a number of VSATs 40 centered around a central station 10.
₁ to 40 _n are connected, and the central station 10 is connected to the VSAT 40 via a TDM line 50 called outbound. The central station 10 time-multiplexes or packet-multiplexes data and transmits it to each VSAT 40 via the TDM line 50. Each VSAT 40 extracts only data for itself from a slot designated by time or packet-multiplexed data.

On the other hand, each VSAT 40 transmits data to the central station 10 via a slotted Aloha line which is one of the time division multiplexing systems. As shown in the frame format in Fig. 5, the slotted Aloha line is connected to each VSA.
The time interval and the transmittable slot timing that T may transmit are specified.

Therefore, in the system using the slotted ALOHA line, the transmission slot length and the transmission timing must be adjusted at all stations, so that the time base (frame) of the outband TDM signal transmitted from the central station 10 is generally used. Equivalent to timing).

In order to reduce the interference with the adjacent satellites when the small antenna of the inbound line (slotted aloha line) which is the object of this embodiment is adopted, the following method is performed.

The basic principle is realized by applying the frequency hopping method in the spread spectrum transmission method and reducing the spectrum density per unit band of the transmission power.

However, in the general spread spectrum system, in order to perform the demodulation operation on the receiving side (the central station side in this embodiment), the despreading synchronization process is necessary to despread the frequency spread signal. Is. In this embodiment, since the transmission timing and the transmission data length of VSAT are all controlled by the central station 10 by the TDM signal, the central station 1
Frequency spreading information is multiplexed with the TDM signal transmitted from 0 and transmitted, and the VSAT 40 receives this and spreads the frequency. As a result, since the central station 10 knows the spreading information of the spreading signal transmitted from the VSAT 40 in the corresponding slot, synchronization of the despreading operation for returning based on the spreading signal becomes very simple.

In FIG. 2, the transmitter 20 of the central station 10
Generates a random code in the random number generation circuit 21. The frequency mapping circuit 22 obtains the frequency to be frequency-hopping by the random number, the multiplexing circuit 23 multiplexes it with the TDM data, and sends it to the VSAT 40 via the modulator 24.

In FIG. 4, the TDM demodulator 41 has a TD
The modulation operation of the frequency hopping information multiplexed on the M line 50 is removed, and the demultiplexing circuit 42 and the spreading frequency data generating circuit 43 receive the frequency hopping information from which the modulation operation is removed, and generate spread data for each slot. .. The frequency synthesizer 44 changes the frequency based on the spread data and changes the output frequency of the modulator 45.

The output of the modulator 45 has a band equivalent to the band of the normal modulation speed when there is no frequency hopping. In particular, it is known that the maximum spectral density is equal to the value obtained by dividing the transmission power by the modulation rate when the half-cosine Nyquist filter is used. When frequency spreading is performed, the output of the modulator becomes wider than at least the modulation speed, so that the maximum spectrum power density decreases.
As the spread frequency is increased, the power density becomes smaller and the power density given to the adjacent satellite becomes smaller. Therefore, even when a small-diameter antenna is adopted, the influence on adjacent satellites can be reduced.

In FIG. 3, the delay circuit 32 inputs the output frequency mapping information of the frequency mapping circuit 22 shown in FIG. 2, and the time from the central station 10 to the VSAT 40 until it is received by the central station 10 as an inbound line. Compensate for the delay time corresponding to. Since the despreading data generation circuit 33 is exactly the same as the spreading frequency data generation circuit 43 in the VSAT 10, the operations of the frequency synthesizer 44 and the demodulator 31 are exactly the same as the frequency hopping operation performed in the VSAT 40. That is, V
Corresponding to the transmission frequency popping performed by the SAT 40, the central station 10 also performs frequency hopping of the demodulator 31, and the same operation as a normal communication system is performed as a whole.

As described above, in this embodiment, the V
The frequency-hopping information that VSAT should perform is added to the outbound signal transmitted to SAT, and VSAT is transmitted.
Can perform frequency hopping based on this information to reduce the power density. Therefore, even when using a small-diameter antenna with a small decrease in the off-axis gain of the antenna, interference with adjacent satellites is reduced, and a small-diameter antenna can be adopted, greatly reducing the cost of antenna installation. be able to.

[0029]

As described above, the present invention has an excellent effect that interference with adjacent satellites is small, a small-diameter antenna can be used, and antenna installation cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a transmission system for a small diameter antenna according to an embodiment of the present invention.

FIG. 2 is a block configuration diagram of a transmitter of a central station of a transmission system for a small diameter antenna according to the present invention.

FIG. 3 is a block configuration diagram of a receiving unit of a central station of a transmission system for a small-diameter antenna of the present invention.

FIG. 4 is a transmission system VSAT for a small-diameter antenna of the present invention.
FIG.

FIG. 5 is a frame format of a satellite line of a transmission system for a small diameter antenna of the present invention.

[Explanation of symbols]

10 central station 20 transmitter 21 random number generating circuit 22 frequency mapping circuit 23 multiplexer 24 modulator 30 receiving unit 31 demodulator 32 delay circuit 33 despreads data generating circuit 34 the frequency synthesizer 40 ₁ ~40 _n VSAT 41 TDM demodulator 42 Separation circuit 43 Spreading frequency data generation circuit 44 Frequency synthesizer 45 Modulator 50 TDM line 60 Slotted Aloha line

Claims (2)

[Claims] 1. A central station for transmitting data of its own station via a time division multiplex line, and a transmission timing and data length of its own station are controlled based on timing information of the time division multiplex signal of this central station. In a transmission system for a small-diameter antenna equipped with a plurality of small earth stations for satellite communication that transmit to this central station via a lottery Aloha line, the central station performs frequency hopping for each of the plurality of small earth stations. The generating means for generating the frequency hopping information for performing, and the multiplexing means for transmitting the generated frequency hopping information by multiplexing the time-division multiplexed signal of its own station, and the plurality of small earth stations respectively Separating means for separating the frequency hopping information multiplexed in the separated time division multiplexed signal, and the slot station of the own station based on the separated frequency hopping information. The central station includes a delay circuit for delaying the time required to return the slotted aloha signals returned from the plurality of small earth stations, and A transmission system for a small-diameter antenna, comprising: despreading processing means for performing despreading processing for the returned slotted aloha signal based on the delayed frequency hopping information. 2. The generating means includes a random number generating circuit for generating a random code, and a frequency mapping circuit for outputting frequencies for frequency hopping to the plurality of small earth stations based on the output of the random number generating circuit. Including,
The multiplexing means includes a multiplexing circuit that multiplexes the output of the frequency mapping circuit into a time division multiplexed signal of the central station, and a first modulator that modulates and outputs the output of the multiplexing circuit. The means includes a first demodulator that demodulates the time division multiplexed signal from the central station, a separation circuit that separates the frequency hopping information from the central station from the output of the first demodulator, and a separation circuit of the separation circuit. A spread frequency data generation circuit that generates spread data based on the output and a first frequency synthesizer, and based on the output of the first frequency synthesizer, frequency-hopping the slotted aloha signal of the own small earth station and transmitting it. Including two modulators,
The despreading processing means corresponds to a despreading data generating circuit that generates despreading data based on the frequency hopping information from the delay circuit, a second frequency synthesizer, and an output of the second frequency synthesizer. The transmission system for a small diameter antenna according to claim 1, further comprising a second demodulator for demodulating a slotted ALO signal from a small earth station.