JPS6340054B2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to an initial connection method performed by a reference station in a satellite communication method using a satellite switch time division multiple access method (hereinafter abbreviated as SS/TDMA method). .

(Background technology) What is SS/TDMA? Satellite Switching/Time
It is an abbreviation for Division Multiple Access, and is one of the most anticipated future forms of satellite communications. First, SS/TDMA will be briefly explained using a diagram.

Figure 1 is a diagram of the principle of the SS/TDMA system, showing the structure of the repeater inside the communication satellite and the relationship between the corresponding earth station. In the figure, reference numeral 1 indicates a spot beam antenna mounted on a satellite, and as an example, there is shown a case where four antennas are used for transmitting and receiving. Each antenna produces a narrow spot beam 2 which illuminates a limited spot area 3 (A, B, C and D) on the ground. Conversely, each antenna receives radio waves radiated from the earth stations 4 in areas A, B, C, and D, respectively.

The SS/TDMA method uses spot beams in this way to increase the gain of the satellite antenna, significantly increasing the effective radiated power, and to use the same frequency for well-separated spot areas. A major feature is that it allows the construction of an ideal communication system in terms of frequency reuse.

The route from the earth station to the satellite is called the up link, and the reverse is called the down link.Antenna 1 is separated into up link and down link, and one has a narrow spot beam and the other has a wide beam. A combination of beams is also possible.

For the sake of simplicity, the explanation will be continued using the configuration shown in FIG. 1 as an example.

In the figure, only one earth station 4 is shown in each region, but in reality each region can include a plurality of earth stations. Area A, B, C,
The radio waves emitted from the earth station in D are received by the corresponding antennas 1, RA, RB,
It is amplified by a receiver 5 shown as RC and RD. On the other hand, the power to be irradiated from antenna 1 to each area is indicated by transmitter 6 as TA, TB, TC, and TD.
They are each supplied by:

A matrix switch 7 is provided to connect the up link and the down link, and is controlled by a matrix switch control circuit 8.
The function of a matrix switch is determined by the connection mode that indicates the combination of which uplink and which downlink are to be connected, and by switching between several connection modes according to a predetermined time schedule, any uplink can be connected. - The link and down link will be coupled periodically. Among these connection modes there is also a broadcast mode in which generally one uplink signal is connected to all downlinks. An example of a combination of connection modes is shown in FIG.

The figure shows a case in which five connection modes, . . . , are periodically repeated. b) indicates which area the signals from each area are connected to the corresponding down link from the perspective of uplink receivers RA, RB, RC, and RD; b)
From a different perspective, is the down link transmitter TA,
Viewed from TB, TC, and TD, it shows which area the signal to be radiated to each area is supplied from the corresponding up link.

Therefore, each region is connected periodically and intermittently. The communication method performed via such communication satellites is limited to TDMA, that is, the time division multiple access method, and the repetition period of the above-mentioned connection mode corresponds to the frame period of TDMA.

Generally, in the TDMA communication system, one of the participating earth stations
serves as a reference station, and the reference station sends a signal called a reference burst according to its own timing standard.
It is transmitted at TDMA frame intervals and received by each participating station to establish a timing standard for the communication system.

However, in the case of SS/TDMA, the connection mode switching described above is performed according to the timing standard built into the matrix switch control circuit 8 shown in Figure 1, so the reference station first sets its own timing standard on the satellite. must be synchronized to the timing reference of Of course, the distance between the satellite and the reference station will sometimes vary even when using geostationary satellites, so the above meaning of "synchronization" means that the reference station will be able to synchronize the transmitted signal according to its own timing standards. , on the satellite, means that it controls its own timing reference so that it is synchronized with the satellite's timing reference.

As explained above at length, the present invention
This relates to a device used as a reference station in a satellite communication system using the SS/TDMA method.

Among the connection modes shown in Figure 2, the initial connection for the reference station to synchronize its own timing reference with the satellite timing reference uses connection mode V, in which the reference burst transmitted from the reference station can be received over the entire area. I will do it. (In the example in Figure 2, it is assumed that the reference station is located in area B.) This connection mode V
We will call this period the reference window.

Generally, the length of the reference window is shorter than the other windows so that the position of the reference window within the TDMA frame cycle can be identified.

Conventionally, the following methods have been used as initial connection methods at the reference station. The reference station has a length longer than the reference window, that is, about twice the length, in order to find the reference window, and the first half has a frequency _{of 1} ,
The second half transmits a burst carrier wave with a different frequency, ₂ . This burst wave signal returned from the satellite is detected using a frequency discrimination circuit, etc.
Measure the length of the first half of the frequency ₁ part and the second half of the frequency ₂ part. If the center of the reference window and the center of the burst wave match, the lengths of each will be 1/2 of the length of the reference window and will also match. By adjusting the burst wave transmission timing to achieve this condition,
You can know the timing of the reference window.

With the above, it is possible to establish general synchronization as the first step in the initial connection.

Next, as a second step, synchronization based on detailed timing at the bit rate of the communication signal is required, but since this is outside the scope of the present invention, a description thereof will be omitted.

However, in order to implement this traditional method,
This requires modulation/demodulation circuits and control circuits that are not normally needed in the communication system, such as a burst wave generator circuit for frequencies ₁ and ₂ in the transmitter circuit system and a frequency discriminator in the receiver circuit system.
This has the disadvantage that the device becomes complicated and expensive.

(Problems to be solved by the invention) The present invention aims to eliminate these drawbacks, and shortens the time required for timing detection by using the same hardware as the communication signal and some control circuits. Link and down
One or both of the links contain multiple spot beams, and the connection between the up and down links is sequentially switched according to a predetermined connection mode by a satellite switch, which is based on a timing reference on the satellite. Therefore, it is a satellite communication system consisting of a communication satellite that has a function of repeating at a fixed frame period, and a plurality of earth stations that communicate by time division multiple access using this communication satellite, and one of the earth stations is a reference station. In the connection mode, the reference window that is provided for synchronization and provides loopback connection to the area where the reference station is located is detected, and based on this, the timing reference of the own station is synchronized with the timing reference on the satellite. In connection control,
The reference station continuously communicates a burst initial connection signal including a synchronization word with a series of transmission numbers that repeat in the frame period at intervals that are an integer fraction of the frame period and shorter than the time width of the reference window. By transmitting to the satellite, the initial connection signal is received via the satellite switch, the synchronization word is detected from the received initial connection signal, a detection pulse indicating the detection result is generated, and the satellite switch returns to connection mode. A reference point is a position at which a number of detection pulses consecutively appear as many as the number of initial connection signals that can be effectively included in the reference window width from among the patterns of the detection pulses that are intermittently generated corresponding to the arrangement within the frame. The satellite communication initial connection method is such that the corresponding transmission timing is determined by identifying the reception timing of the window and reading the early transmission number included in the initial connection signal corresponding to the detection pulse of the position.

(Structure and operation of the invention) FIG. 3 shows an embodiment of a reference station TDMA device according to the present invention, in which 301 is a demodulator, 302 is a modulator, 303 is a synchronization signal detection circuit, 304 is an initial connection control circuit, and 305 is a 306 is a synchronization word generation circuit, 307 is a data word generation circuit, 308 is a clock generation circuit, and 309 is a transmission/reception timing generation circuit.
In the TDMA communication control unit, 310 is a reception IF signal input terminal, 311 is a transmission IF signal output terminal, 312 is a baseband communication signal output terminal, and 313 is a baseband communication signal input terminal. To operate this in normal communication, a received IF signal input from 310 is demodulated by 301 and input to 303 and 309 as a baseband signal. 3
At 03, a synchronization word is detected, and the detection signal is input to 304 and 305. 305 is now 30
Generates the reception and transmission timing necessary for normal communication based on the clock pulses 306 and 8.
307 and 309. 306 outputs a demodulator synchronization establishment word and synchronization word to be added to the head of the burst TDMA signal, and 307 similarly outputs a data word including control information such as a transmission number, which will be described later. 309 converts the burst TDMA signal into a baseband communication signal based on the timing information of 305 and outputs it to 312, and vice versa.
The baseband communication signal inputted from 302 is converted into a burst TDMA signal and outputted to 302.
302 time-division multiplexes the signals of 306, 307, and 309, and then modulates the signals to generate a transmission IF signal.

In the first stage of the initial connection according to the present invention, the initial connection control circuit 304 controls 306 and 307 to send a burst initial connection signal at an interval of an integer fraction of the frame period of the satellite switch as shown in FIG. 4b. are generated continuously and transmitted to the satellite via an RF transmitter. FIG. 4a shows one initial connection signal, 41 is a synchronization establishment word for quickly establishing synchronization with the carrier wave and clock in order to demodulate the burst signal received by the demodulator, and 42 is a synchronization establishment word with a specific 1. A synchronization word consisting of a combination of zeros and detected separately from other parts, 43 is a different number for each initial connection signal, that is, a transmission number is attached to distinguish between many initial connection signals that exist within one frame period. The data word 44 is a supplementary part for arranging this burst-like initial connection signal at intervals of an integer fraction of the frame period of the satellite switch.

FIG. 4c shows the arrangement within a frame 45 in a connected mode in which a signal transmitted from a certain area of the reference station is returned to the same area via a satellite. These connection modes are also called "windows" because signals pass through them. In the example shown in FIG. 2, it is assumed that the reference station is in area B, so the connection mode having a "B→B" connection is the return connection window. Of these,
Connection mode V, which is the reference window, is shorter than the other windows, so by checking the width of the window, the fourth
46 in Figure c can be identified as the reference window.

The initial connection signal, which is continuously transmitted from the reference station as shown in Figure 4b, passes through the satellite switch that turns on and off as shown in Figure 4c, and is then retransmitted to the earth station, where it is transmitted by the RF receiver of the reference station. The received IF signal is applied to the terminal 310 in FIG. 3, and demodulated by the demodulator 301. Since the synchronization word included in the initial connection signal is a specific combination pattern of 1 and 0 as described above, it is easily detected by the synchronization signal detection circuit 303. Success or failure of detection is communicated to the initial connection control circuit 304 in the form of presence or absence of a detection pulse. Since the initial connection signal, ie, the synchronization word, is detected at the position where the folding window exists within the frame, as a result, the arrangement of the synchronization word detection pulses 303 generated is as shown in FIG. 3D. Since the number of consecutive synchronization word detection pulses corresponds to the width of the window, it is possible to easily identify the reference window whose width is known as the shortest window. This judgment is 3
04 and outputs a frame pulse to the position corresponding to the received reference window as shown in the figure e,
It is output to the transmission/reception timing generation circuit 305 as a reception reference timing signal in initial connection control.

The example in Figure 4 is an example in which the time width of the reference window is selected to be twice the initial connection signal interval, and since it is possible to pass up to two complete initial connection signals, these are included. Synchronous words are also detected,
As a result, two consecutive synchronization word detection pulses are obtained. However, this is a special case, and in many cases, only one complete initial connection signal is passed through, and the initial connection signals before and after it are passed in partially cut-off forms. In this case, in the deleted initial connection signal, for example, even if the synchronization word 42 can pass,
If the preceding synchronization establishment word 41 does not pass, the demodulator will not be able to correctly demodulate the synchronization word, and therefore the synchronization word will not be detected and no synchronization word detection pulse will appear. Therefore, the initial connection control circuit 304 identifies the position where two consecutive synchronization word detection pulses or only one synchronization word detection pulse is detected in the frame period, determines this as the reception position of the reference window, and sets the position at that position. A frame pulse is generated as a reception reference timing.

Also, since at least one complete initial connection signal passes through the reference window and is received as described above, the data word 43 contained therein is also properly received and demodulated. By reading the transmission number included in the data word in this way, it is possible to know the transmission number of the initial connection signal passing through the reference window, and therefore the reference transmission timing within the frame. These processes can be performed using a conventional correlation method or a simple arithmetic processing circuit using a microcomputer or the like.

In this way, as a first step in the initial connection,
The approximate reference timing of transmission and reception of the reference station corresponding to the frame timing of the satellite switch can be known in terms of the transmission interval of the initial connection signal.

In the second step, we set appropriate initial values based on the timing obtained in this way.
Full satellite switch frame synchronization can be established and the initial connection can be completed using known methods for maintaining constant synchronization, such as using metrics bits. Note that here we have explained the case where the transmission interval of the initial connection signal is 1/2 or less of the reference window time width, but when the transmission interval is an integer fraction of the frame period of the satellite switch and is shorter than the reference window time width, If it is short, the present invention can be applied.

(Effect of the invention) As explained above, since it is possible to use the circuits required for normal communication in common, it is possible to simplify the outline of the satellite switch required at the second stage of initial connection. It has the advantage that the timing can be easily obtained.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the principle of the SS/TDMA system, Fig. 2 is a diagram showing the connection mode of the satellite switch, Fig. 3 is an embodiment of the reference station TDMA device according to the present invention, and Fig. 4 is the initial connection signal, satellite Switch ON,
FIG. 3 is a diagram showing the relationship between OFF, the output of a synchronization word detector, and a frame pulse. 1...Spot beam antenna, 2...Spot beam, 3...Spot area, 4...Earth station,
5... Receiver, 6... Transmitter, 7... Matrix switch, 8... Matrix switch control, 301... Demodulator, 302... Modulator, 30
3...Synchronization signal detection circuit, 304...Initial connection control circuit, 305...Transmission/reception timing generation circuit,
306...Synchronization word generation circuit, 307...Data word generation circuit, 308...Clock generation circuit, 309
...TDMA communication control unit, 310...IF input terminal,
311...IF output terminal, 312...Baseband communication signal output terminal, 313...Baseband communication signal input terminal, 41...Synchronization establishment word, 42...
Synchronous word, 43...data word, 44...auxiliary word.

Claims (1)

[Claims] 1. One or both of the up link and the down link includes a plurality of spot beams, and the connection between the up link and the down link is established in a connection mode predetermined by the satellite switch. It consists of a communication satellite that has the function of switching sequentially according to the timing standards on the satellite and repeating this at a constant frame period according to the timing standard on the satellite, and a plurality of earth stations that communicate by time division multiple access using this communication satellite. In a satellite communication system, a reference station, which is one of the earth stations, detects a reference window that is provided for synchronization among the connection modes and provides loopback connection to the area where the reference station is located, and based on this, In initial connection control that synchronizes the timing reference of its own station with the timing reference on the satellite, the reference station sends a burst-like initial connection signal containing a synchronization word with a duration that is an integer fraction of the frame period and shorter than the time width of the reference window. The initial connection signal is received via the satellite switch by attaching a series of transmission numbers that repeat at intervals and frame cycles and continuously transmitting it to the communication satellite, and the synchronization word is extracted from the received initial connection signal. detect and generate a detection pulse indicating the detection result, and select a pattern of detection pulses that are effectively included in the reference window width from among the patterns of the detection pulses that are intermittently generated in accordance with the arrangement in the frame of the return mode of the satellite switch. By identifying the position where detection pulses appear consecutively as many times as the number of the initial connection signals to be obtained as the reception timing of the reference window, and by reading the transmission number included in the initial connection signal corresponding to the detection pulse at the position, A satellite communication initial connection method characterized by determining corresponding transmission timing.