JPH0637710A - Mobile body satellite communication system - Google Patents

Abstract

PURPOSE:To realize a mobile a mobile body satellite communication system without the need of a branching filter used for a conventional system in which two-way digital communication is served among lots of mobile stations and a few base stations by means of the FDM system. CONSTITUTION:In the case of two-way digital communication from a base station to plural mobile stations by using different transmission reception frequencies, the system is featured such that a first half time slot field in one frame synchronously with a unique word of a digital signal sent from the base station to the mobile stations is used for a time slot field of a reception signal of the mobile stations and a latter half time slot field in the one frame of the digital signal is used for a time slot field of a transmission signal of the mobile stations, and is provided with a changeover control circuit 14 which uses a frame synchronizing separator circuit 10 provided to a reception section of each mobile station detecting a frame synchronizing signal from the unique word, sets the first half time slot field and the latter half time slot field based on the frame synchronizing signal to output control signal, with a 1st RF switch 2 turning on/off a high power transmission signal of a transmission section with the control signal of the changeover control circuit 14 and with a 2nd RF switch 3 turning on/off a reception signal of a low noise amplifier of the reception section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile satellite communication system for communicating between a large number of mobile stations and a small number of base stations using a communication satellite.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional mobile station for mobile satellite communication has an antenna 1 and a demultiplexer (DPX) 2.
1, HPA4, transmission channel frequency synthesizer (TX
CFS) 5, modulation circuit (MOD) 6, frame generation circuit (FR / GEN) 7, code decoding circuit 8, user terminal 9, frame separation circuit (FR DIV) 10, reception channel frequency synthesizer 11, low noise amplifier ( LNA)
It consists of 13. FIG. 6 shows the frequency band assigned to mobile satellite communication and the frequency characteristics required of the demultiplexer 21. That is, the transmission / reception signal is separated by the frequency filter of the DPX2 by utilizing the fact that the transmission / reception frequency bands are different, and the transmission / reception operation is performed completely independently. In the base station as well, transmission and reception are independent, so the conventional method is characterized in that full bidirectional communication is possible. The operation of the apparatus will be described with reference to FIG. Reference numeral 9 is a user terminal, which is a handset in the case of voice communication. The encoding / decoding circuit 8 encodes an analog signal from the user's terminal 9 into a digital signal and vice versa. For example, a voice encoder / decoder. The frame generation circuit 7 periodically inserts a unique word (UW) pattern as shown in FIG. 5 to form a frame. The transmission channel frequency synthesizer 5 generates a carrier wave having a frequency of a channel designated by an external designation and supplies it to the modulation circuit 6 to generate a modulated wave. This modulated signal is HPA
The power is amplified at 4, supplied to the antenna via the DPX 21, and radiated toward the satellite. On the contrary, the receiving part is antenna 1
The received signal from is passed through the DPX 21 and low-noise amplified by the LNA 13. The RXCFS 11 generates a local oscillation signal having a reception channel frequency designated from the outside to generate a DEM.
Demodulation is carried out after converting the received signal supplied to 12 into an IF signal. Demodulated signal is UW in FR DIV10
First, frame synchronization is established using the pattern, the information data is separated, the audio signal is input to the encoding / decoding circuit 8 and reproduced, and supplied to the terminal 9.

[0003]

In the conventional mobile satellite communication system described above, the attenuation amount at (dB) in the reception band of the transmission side filter of the DPX is the spread of the signal spectrum of the HPA output and the wide band thermal noise. Is to suppress. Further, the attenuation ar (dB) in the transmission band of the reception side filter is to prevent the reception unit from being saturated due to the sneak of the transmission power. In the case of mobile satellite communication, there is a very large difference of about 150 db between the power level of the transmission signal and the power level of the reception signal, and a large attenuation amount at, ar is required. Therefore, it is necessary to increase the pass loss of the filter, increase the transmission power loss, increase the receiver noise temperature, and increase the size of the antenna.

[0004]

According to the mobile satellite communication system of the present invention, when two-way digital communication is performed from a base station to a plurality of mobile stations using different transmission and reception frequencies,
The first half time slot area in one frame synchronized with the unique word of the digital signal transmitted from the base station to the mobile station is used as the time slot area of the received signal of the mobile station, and the latter half of one frame of the digital signal is included. The time slot area is used as the time slot area of the transmission signal of the mobile station, the frame synchronization signal is detected from the unique word by the frame synchronization separation circuit provided in the receiving section of the mobile station, and the frame synchronization signal is detected. A switching control circuit for setting the first half time slot region and the latter half time slot region to output a control signal, and a first control circuit for turning on / off a high power transmission signal of a transmission unit by the control signal of the switching control circuit. Second RF switch for turning on / off the received signal to the RF switch of the receiver and the low noise amplifier of the receiver. And a pitch.

[0005]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the first embodiment of the present invention, and FIG. 3 is a signal format diagram of the present embodiment. In FIG.
The same reference numerals as those in the conventional example of FIG. 4 have the same configurations. The RF switches (RF SW) 2 and 3 added in this embodiment are
Reference numeral 14 is a switching control circuit, and 15A and 15B are power supply circuits (PS). Further, the conventional duplexer is deleted.

Next, the operation of this embodiment will be described with reference to FIG. FIG. 3A shows a format of a reception signal of a mobile station received from a base station, which has the same radio frequency but is time-divided into two in one frame to obtain a signal for own station and a signal for other station. Use separately. Therefore, the data transmission speed is doubled, and the data is transmitted in half the conventional time slot. The in-frame structure of the signal for the own station includes a unique word (UW) for synchronization, a mobile ID (MID) that is the ID of the own station, and data. The same applies to the case of a signal for other stations. This MID is provided to distinguish the time slot of the own station from the time slot of another station. A reception frame pulse is generated based on W (FIG. 3b), and a transmission / reception control signal including data is transmitted / received in this one frame as shown in FIG. 3 (c). Therefore, focusing on the signal applied to the own station,
After the reception burst signal is received in the first time slot of one frame, the transmission burst signal of the own station is transmitted from the mobile station shown in FIG. 3 (d) to the base station in the latter half time slot. This transmission burst signal has a preamble (PR) in order to avoid overlap with the reception burst signal, and mobile ID data of its own station is arranged after PR. Also in this case, the MID that distinguishes the own station from other stations is inserted. Next, how the above-mentioned signal operation is realized by the configuration of FIG. 1 will be described. RF switch 3 now
When is on and is in the receiving state, the frame synchronization signal is detected in the reception frame synchronization separation circuit 10 via the demodulator 12, and the frame synchronization is established. The switching control circuit 14 operates based on this frame synchronization signal, and the RF switch 3
Is turned on and the RF switch 2 is turned off. On the other hand, this reception frame synchronization signal is also supplied to the transmission frame generation circuit 7 to generate a transmission frame in synchronization with reception. In the latter half of one frame, the switching control circuit 14 turns on the RF switch 2 and turns off the RF switch 3 at a substantially intermediate position in one frame for the encoded signal to be transmitted, and shifts to the transmission operation. In order to surely demodulate the burst signal, the mobile station attaches a preamble (PR) at the beginning, and subsequently shows the transmission source, so that the mobile station's MID
Is added and sent. The base station side can use the MID not only to know the source but also to establish reception frame synchronization. Moreover, since the transmission and reception frequencies are separated, the base station can simultaneously perform the transmission and reception operation, and the communication operation similar to the conventional one may be performed. Further, in the system of the present invention, the band is expanded in order to increase the transmission data transmission speed as compared with the reception channel, so the RF frequency of the reception channel is doubled, but as shown by the shaded area in FIG. In addition, more frequencies are assigned to transmission than to reception, so that frequencies can be effectively used. Further, in the system of the present invention, the signal from the base station is doubly time-multiplexed by doubling the data transmission rate of the baseband, so that the number of carrier signals can be theoretically halved as compared with the conventional method. . Therefore, cross-modulation noise between carrier waves is reduced, so that the amplifier on the satellite can be operated at higher output.

As described above, since the mobile station of the present invention transmits / receives in a time division manner, it is not necessary to have a high degree of isolation between the transmitter and the receiver, and both transmission power loss and receiver system noise temperature can be minimized. .

Next, a second embodiment of the present invention will be described with reference to FIG. Also in the case of the second embodiment, as shown in FIG. 3, the data transmission rate is doubled and the first half of one frame is used as the reception burst signal of the own station and the latter half is used as the transmission burst signal of the own station. The transmission method is adopted. As can be seen by comparing the second embodiment with the first embodiment of FIG.
The RF switches 2 and 3 of the first embodiment are stopped, and the HPA4
Power supply (PS) 15A and power supply (PS) for LNA 13
15B is provided. In the case of the receiving operation in the second embodiment, the switching control circuit 14 turns on the PS 15B to activate the LNA 13, and turns off the PS 15A to deactivate the HPA 4. In the case of the transmission operation, the opposite control operation is naturally performed. In the second embodiment, since the power of the HPA 4 is turned off especially at the time of reception, it has a great effect on the reduction of power consumption. Further, since the transmission power is cut off, it is sufficient to protect the LNA 13 from the transmission power with a configuration of at most the circulator 2A, without the need for the RF switch 3 having a large amount of shield attenuation as in the first embodiment.

[0009]

As described above, the present invention has the following effects by providing an RF switch for transmission / reception and a switching control circuit, or by providing a power source for turning on / off each of HPA and LNA.

(1) While providing a bidirectional communication service, the conventional duplexer is not required, and the power feeding loss is minimized. Therefore, it is possible to realize a device in which the HPA power is reduced and the receiver noise temperature is lowered.

(2) Since the number of carriers in the communication channel from the base station to the mobile station can be reduced by half, cross modulation noise in the satellite relay amplifier can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment of the present invention.

FIG. 3 is a signal format and a time chart for explaining the operation of the present embodiment.

FIG. 4 is a block diagram of a conventional mobile satellite communication device.

FIG. 5 is a signal format diagram of a conventional example.

FIG. 6 is a characteristic diagram of a conventional duplexer.

[Explanation of Codes] 1 Antenna 2, 3 RF Switch 4 High Power Amplifier (HPA) 5 Transmission Channel Frequency Synthesizer (TX / FS)
YNTH 6 Modulation circuit (MOD) 7 Transmission frame generation circuit (FR GEN) 10 Frame synchronization separation circuit (FR DIV) 11 Reception channel frequency synthesizer (RX ・ F ・
SYNTH) 12 Demodulation circuit (DEM) 13 Low noise amplifier (LNA) 14 Switching control circuit (SW CONT) 15A, 15B Power supply (PS)

Claims (3)

[Claims] 1. A unique word of a digital signal transmitted from the base station to the mobile station when bidirectional digital communication is performed from the base station to a plurality of mobile stations using different transmission and reception frequencies. The first half time slot area in one synchronized frame is set as the time slot area of the reception signal of the mobile station, and the second half time slot area in one frame of the digital signal is set as the time slot area of the transmission signal of the mobile station. Characteristic mobile satellite communication system. 2. A frame synchronization separation circuit provided in a receiver of the mobile station detects a frame synchronization signal from the unique word, and based on the frame synchronization signal, the first half time slot region and the second half time slot. A switching control circuit that sets a region and outputs a control signal,
A first RF switch for turning on / off the high power transmission signal of the transmission section and a second R for turning on / off the reception signal to the low noise amplifier of the reception section by the control signal of the switching control circuit.
The mobile satellite communication system according to claim 1, further comprising an F switch. 3. A transmission power supply for a high power amplifier for transmission instead of the first and second RF switches, and a reception power supply for a low noise amplifier for reception, wherein the control signal of the switching control circuit is used for the above 3. The mobile satellite communication system according to claim 2, wherein the transmission power supply and the reception power supply are turned on and off or off and on, respectively.