JPS5910096B2 - Initial connection device in time division multiple access - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes TDMA (Time Division Mult
This invention relates to an initial access device used in satellite communications (ipleaccess (time division multiple access)).

TDMA satellite communication system is a system in which multiple satellite communication earth stations are connected to one
This is a communication method in which two satellite repeaters are shared in a time-division manner to communicate with each other. In this communication system, even if the satellite used is a geostationary satellite, the influence of slight relative positional fluctuations with each earth station cannot be avoided. FIG. 1 is a conceptual diagram of a frame format of TDMA satellite communication, and the horizontal axis shows time and shows the temporal arrangement when signals transmitted from each station pass through a satellite repeater. This arrangement is repeated with each TDMA frame as one cycle. The signals transmitted from each station are transmitted in the form of intermittent signals called bursts, and the burst signals arriving from each earth station must be controlled so that they do not overlap each other at the input of the satellite repeater. In FIG. 1, A is called a reference burst and includes a synchronization signal that serves as a reference for a TDMA frame. This reference burst is transmitted from a reference station selected from among many stations participating in the communication system. B, B', B''... indicate burst signals transmitted from each station, and C indicates time slots assigned to other stations that are not currently transmitting. Relative position fluctuations with each earth station appear as fluctuations in the radio wave propagation time between each station and the satellite.Therefore, to compensate for this, once synchronization is established, each earth station receives signals through the satellite repeater. By comparing the local station synchronization signal and the allocated time position for the local station 5 synchronization signal in the received frame and adjusting the transmission timing from time to time to eliminate the error, it always reaches the satellite repeater input at the correct timing. Frame synchronization and burst synchronization techniques are required to control the frame synchronization and burst synchronization.Also, when a station that has stopped transmitting starts transmitting for the first time, at what timing should it transmit, and at what position in the received frame should it receive data? Since the link information for controlling the ability is lost,
There is a need for a so-called initial connection technique in which such stations acquire transmission timing by some method without interfering with stations with which they are already communicating.

Japanese Patent Publication No. 41-22102 and Japanese Patent Publication No. 42-6417 use a frame synchronization method, a burst synchronization method, and an initial connection method in which the time slot assigned to the own station is predicted at the start of transmission from satellite orbit prediction data. T.D.
Basic synchronization techniques for MA satellite communications are disclosed.

Various methods are now being used for initial connection, but they can be broadly classified into prediction methods, out-of-band measurement methods, and low-power methods.

Among these methods, the low power method, which is efficient in terms of band utilization efficiency and requires small equipment for initial connection, has been widely used as an excellent method. FIG. 2 is an explanatory diagram of the initial connection method classified as this low power method.

The symbols A, B, and C are all the same as in FIG. Second
In Figure A, a special initial connection signal D that is approximately 20 dB lower than the normal signal level is continuously transmitted, and the initial connection signal is PN (PsendOrandOmNOise).
PSK (P series) and other special digital series
haseShiftKeying) modulated signal is used, . The transmission timing information is obtained by checking the relative positional relationship between the phase of the received and demodulated sequence and the synchronization signal. Figure 2 shows the unmodulated carrier wave E.
is transmitted in a pulsed manner with low power, and its position within the TDMA frame is manually or automatically swept to detect when it falls within a designated time slot.

These methods provide the timing information needed for the initial connection,
It is efficient because it can be obtained using the same communication band 4 of the same relay device as regular communication, but because the initial connection signal is transmitted with low power, the reception S/N is extremely poor.

In order to solve this problem, the width of one bit of the PN sequence or the pulse width of the unmodulated carrier wave is reduced to one bit of the regular signal.
The signal width is chosen to be much larger than the bit width, that is, the S/N ratio during demodulation is improved as a narrowband signal.

. In conventional satellite communications using the 6GHZ/4GHZ band, by using the above-mentioned countermeasures against the reduction in received power, that is, the deterioration of S/N, it was possible to perform initial connection using the low power method.

However, as the frequency band in use expands to 10 GHz or more in the future, the attenuation of received power due to rain will greatly increase compared to the past. Therefore, the initial connection signal power must be further lowered so as not to interfere with the reduced normal signal, and the problem arises that the initial connection may not be performed successfully using the low power method. In order to solve this problem, it has been considered to use a prediction method in which the approximate transmission timing is estimated by some kind of predictive calculation and the burst is transmitted with regular signal power from the beginning.

However, the previously used prediction methods include the celestial position estimation ephemeris (Special Publication No. 41-22102 and Special Publication No. 42-64).
17) and the method disclosed in the IEICE, Communication Method Study Group materials (Mr. Watanabe et al.'s "Study of TDMA system using multiple transponder operation" No. CS-74-165), but the former method is A large-scale satellite tracking device is required to create an ephemeris, and the latter stores several days of distance data between the station and the satellite and calculates the distance at the time of initial connection. Therefore, a large amount of memory is required, and if distance data is not stored in the memory in advance, this method cannot be used for the first initial connection, so it must be used in conjunction with other methods. There is a problem.

A common problem with both methods is that when the orbit is corrected to maintain the position of the satellite, initial connection cannot be established until sufficient data regarding the new orbit is obtained. The object of the present invention is to provide an initial connection device which eliminates the above-mentioned disadvantages. According to the present invention, in a time division multiple access communication system in which a plurality of stations share one satellite repeater in a time division manner and communicate with each other, a station that attempts to start new communication is assigned to the own station. In an initial connection device that generates a transmission timing for inserting a signal from its own station within a specified time, a first means for determining reception of a reference synchronization signal transmitted from a specific station and using this as a reception time reference. Then, the own station synchronization signal transmitted from the own station is received again via the satellite repeater, and is compared with the allocated time position for the own station signal determined based on the reception time standard to generate an error signal. a second means for maintaining the transmission time reference of the own station signal by correcting the transmission timing of the own station according to the signal; and information representing a relative time difference between the reception time reference and the transmission time reference at other stations in operation. a third means for receiving the first time difference information and generating the first time difference information; a fourth means for calculating the first time difference information and generating the second time difference information; and the own station participates in the communication system. According to the present invention, there is provided an initial j-period access device in time division multiple access, including fifth means for controlling the transmission timing of the second means in response to the second time difference information when starting transmission.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 3 is a block diagram showing one embodiment of the present invention. First, we will explain the operation when the initial connection has already been completed and the synchronization state has already been established. We will then explain how the initial connection device of the invention operates to enter such a synchronized state. The receiver 1 receives, demodulates and decodes radio waves from a communication satellite into a digital signal, and supplies a part of it to a reference synchronization signal selection circuit 2.

The reference synchronization signal selection circuit 2 includes a detector (not shown) that detects a unique pattern of the reference synchronization signal, and a detector having a certain time width that includes the time position (time slot) where the reference synchronization signal exists. An aperture generator (not shown) that generates an aperture correctly selects and receives a synchronization signal from a reference station, and generates a narrow and sharp reception frame pulse at its output when the reference synchronization signal is received. This is added to the received frame counter 3. The reception frame counter 3 is a counter that counts the system clock output from the system clock oscillator 4. The reception frame pulse is applied to the reset terminal and reset to 0 at each frame break to maintain reception frame synchronization. Assuming that the standard length of one frame is N in the unit of the system clock, in a steady synchronization state, each time the value of the frame counter reaches N, it is set to O in the received frame panores, but the counter itself is also set to N. The decoder is equipped with a decoder, and even if the received frame pulse is accidentally dropped, when it becomes N, it is automatically reset to O, acting as a flywheel to maintain a high degree of stability in receiving frame synchronization. .

A reception time slot decoder 5 is connected to the reception frame counter 3. Reception time slot decoder 5
is the reference position of the self-station synchronization signal on the received frame (assuming that this is delayed by L units from the position of the reference synchronization signal in the unit of the system clock).
) is stored and held, and the received frame counter 3
When the value of becomes L, a self-station reference position pulse is generated and given to the time difference measuring circuit 6. The output of the local station synchronization signal selection circuit 7 is added to the other input of the time difference measurement circuit 6, and this selection circuit 7 is a detector (not shown) that detects the unique pattern of the local station synchronization signal. In the synchronized state, an aperture generator (not shown) that opens a predetermined time width that includes the time slot of the local station synchronization signal at the time position where the local station synchronization signal exists is used to extract the local station from the received signal. A synchronization signal is correctly selected, and upon receiving it, a narrow, sharp G-width station synchronization signal reception pulse is generated at its output. In this way, the time difference measuring circuit 6 measures the absolute value and polarity of the time difference between the two input pulses, the own station reference position pulse and the own station synchronization signal reception pulse, for each arbitrary received frame, and uses the absolute value as the time difference counter. 8, and depending on its polarity, one of the two outputs F and S of the time difference counter 8 can be enabled. Further, the time difference measurement circuit 6 is controlled by a measurement frame selection circuit 9. This measurement frame selection circuit 9 takes timing by counting the set pulses of the reception frame counter 3, etc., selects one reception frame at a rate of about once every 0.3 seconds, and in that frame, the time difference measurement circuit 6 enable. The enabled time difference measuring circuit 6 measures the absolute value of the time difference between the own station reference position pulse and the own station synchronization signal reception pulse in the selected frame as described above, sets it in the time difference counter 8, If the counter value is not 0, and if the local station synchronization signal reception pulse is ahead of the local station reference position pulse, the logic level of the time difference counter output F is set to 1, and the logic level of the other same counter output S is set to O. shall be.
If, on the other hand, the local station synchronization signal reception pulse lags behind the phase station reference position pulse, control is performed so that the logic level of the time difference counter output S is set to 1 and F is set to O. Both outputs of said time difference counter 8 are connected to two reset inputs N+1 and N-1 of a transmitted frame counter 10.

Similarly to 3, the transmission frame counter 10 is a counter that counts the system clock output from the system clock oscillator 4, and is normally set to the value N.
When a unit-length transmission frame is generated, if the logic level of input N+1 becomes 1, the counter value is controlled to be reset to N+1, and if the logic level of input N-1 becomes 1, the counter value is reset. is controlled to be reset to N-1. A transmission time slot decoder 11 is connected to the transmission frame counter.

Like the reception time slot decoder, this holds the value L, and when the content of the transmission frame counter reaches L, it generates the own station synchronization signal transmission position pulse. This own-station synchronization signal transmission position pulse is applied to the synchronization signal generation circuit 12, which generates a local-station synchronization signal according to its timing, and this is sent to the satellite through the transmitter 13. By adopting such a configuration, the above-described system including a satellite (not shown) constitutes one servo loop as described below.

That is, assume that the measurement frame selection circuit 9 has enabled the time difference measurement circuit 6 in the current received frame. Then, the time relationship between the local station synchronization signal reception pulse and the local station reference position pulse in that frame is measured, and it is assumed that the former is ahead of the latter by X clocks. This value X is immediately set in the time difference counter 8, and at the same time, the logic level of the output F of the time difference counter 8 becomes 1.

Therefore, the outgoing frame counter 10 is controlled so that it is reset every N+1, so if the timing of the local station synchronization signal transmission position pulse is set to 4 based on the value of the received frame counter, then the timing of the local station synchronization signal transmission position pulse is relatively 1 unit clock per frame. You will be delayed at a certain rate. The value X set in the enabled time difference counter 8 is the value X set in the enabled time difference counter 8.
Each time it is set, it is decremented by 1, and it is controlled so that it becomes O just after the X frame. When the value of the time difference counter 8 becomes O, the time difference counter 8 disables itself and sets the logic level of both F and S outputs to O. Therefore, the timing of transmitting the local synchronization signal will be delayed by the measured error amount X after the X frame, so it will be corrected on the transmitting side by the measured error amount. become. Since the local station synchronization signal with the corrected transmission timing is received through the satellite within 0.3 seconds, the measurement frame selection circuit 9 enables the time measurement circuit 6 next time to receive the received local station synchronization signal reception pulse. When measuring the mutual time relationship between the current station reference position pulse and the local station reference position pulse, the measurement is performed on a signal that already includes the results of the previous correction. In this way, if there is a certain error in the measurement results, it operates as a servo system that automatically corrects it, so once a synchronized state is established, the rest is automatically determined by the design. It becomes possible to maintain stable synchronization within the error range. Furthermore, once a synchronized state is established, even if the distance to the satellite changes from moment to moment, stable synchronization can be maintained regardless of the distance to the satellite, as long as the rate of change is within a certain range that can be tracked by this servo system. is also clear. In this case, what can be determined by the distance between your own station and the satellite is the time it takes from sending out your own station's synchronization signal until it is relayed through the satellite and detected again by your own station. This determines the relative time relationship between the received frame counter 3 and the transmitted frame counter 10. More specifically, it is determined what value (assumed to be P) the transmit frame counter has at the moment the receive frame counter is reset to O. In other words, this P is a value uniquely determined by the distance to the satellite. Even if the distance to the satellite is not known, as long as the corresponding value of P can be obtained within the required error range, the value of P can be determined. is set in the transmitting frame counter 10 at the timing of the pulse that resets the receiving frame counter 3, and continues counting from then on, and using this transmitting timing to send out the synchronization signal of the own station as described above. When it is received, the local station synchronization signal reception pulse is determined by an error of P from the local station reference position pulse. It is clear that this is within a certain error range. For example, if a station whose distance to the satellite is the same as your own station has already established synchronization, you can immediately initialize by setting the value of P of that station to your own station's transmit frame counter as described above. You will now be able to connect and establish synchronization. The present invention provides an apparatus for making an initial connection using the principles described above.

To accomplish this, as shown in FIG. 3, a time difference receiving circuit 14, an arithmetic circuit 15, a time difference register 16, an initial connection control circuit 17, etc. are further provided. The time difference receiving circuit 14 corresponds to the above-mentioned P of the T station transmitted from a reference station or a station suitable for the own station (this station will be called a T station) from among the stations that have already established synchronization in the system. This is a circuit that receives the value of the TDMA system, and the common control channel of the TDMA system can be used for this purpose. The received value of P of the T station (this is written as PB), that is, the first time difference information, is applied to the calculation circuit 15, and necessary correction calculations are performed based on the difference in geographical position between the T station and the own station. The resulting value becomes the value PLl, that is, the second time difference information, and is stored in the time difference register 16. When the PR of the T station is updated according to the movement of the satellite, the PL is also updated accordingly. Now,
The initial connection of the own station is performed as follows.

First, the reception frame synchronization of the own station has already been established, and as described above, the latest PL value necessary for the own station is stored in the time difference register 16. Of course, the transmitter 13 is still disabled and the local station is not transmitting anything. Therefore, when the initial connection control circuit 17 commands the start of the initial connection, the control circuit 17 transfers the contents (PL) of the time difference register 16 to the transmission frame counter 10 at the timing of the reset pulse of the first reception frame counter 3 that appears next.
The system clock count continues from that value. Next, the initial connection control circuit 17
enables the transmitter 13 and transmits only the synchronization signal portion thus generated. The first synchronization signal sent out is relayed by the satellite and received again at this station, but as mentioned above, it is received within the error range determined by the PL error from the correct position where the local station synchronization signal should be. . If this is within the error range necessary for operating the servo system, the servo system starts operating, and after a certain period of time, transmission frame synchronization is established. Establishment of transmission frame synchronization means that the local station synchronization signal reception pulse has the necessary narrow width aperture (1) created based on the local station reference position pulse.
(not shown), and if the local station synchronization signal reception pulse passes through that aperture, it can be determined that transmission frame synchronization has been established. When transmission frame synchronization is established, the data burst of the own station is transmitted, and if necessary, the reception frame counter is reset under the control of the control circuit 17.The transmission frame counter 1 is reset at the timing of the set pulse.
It is also possible to read the contents of 0 into the read time difference register 18 and send it to the outside through the time difference transmission circuit 19, thereby using it as the value of P for initial connection of other stations in the system. As described above, by using the initial connection device of the present invention, it is possible to perform the initial connection without emitting any signals for initial connection. It is necessary to obtain

Now, the distance from earth station T to the satellite at a certain point in time is
Assume that the distance from the own station to the satellite at the same point in time is plotted on the Y-axis.

In general, even if the relative positional relationship between the earth station T and the own station is given, and the value of X is given, the value of Y cannot be determined in principle from this alone. Now, if a geostationary communication satellite periodically moves around a certain range around its reference stationary point,
The trajectory becomes a closed curve as shown in Figure 4, and generally, for the same X value X1, the corresponding Y value is Yl, Y,
' will take on two different values. This Yl,
The difference in Y,' varies depending on the magnitude of the satellite's movement and the relative relationship between the earth station T and the own station, so in general, even if the distance from the T station to the satellite is known, only that is used. It is difficult to accurately determine the distance from your station to the satellite. However, in cases where the distance between earth stations is relatively small compared to the distance to the satellite, such as in Japan's domestic satellite system, as shown in Figure 5, the distance Y( In many cases, the necessary approximation of t) can be obtained simply by adding the distance X(t) from the T station to the satellite at that time and a certain value KT determined by the partner station T.

In this case, the calculation performed by the calculation circuit 15 may be PL-PR+KT, and the present invention can be used most effectively.

As an application example, if we consider a TDMA communication system whose service area is Obe City in Japan, the location of Obe City is within the range of 136A ± 6.0 degrees east longitude and 38.5 degrees north latitude ± 5.5 degrees. enter.

Using the values of the geostationary communication satellite [Sakura], 0 in the north, south, east, and west
．． It is maintained within the range of 1 signal and the orbital eccentricity is maximum 0.000
It is 1. The reference station is located at 136 east longitude in the center of the service area.
This reference station, which is located at 38.5 degrees north latitude and does not require any special initial connection, first emits a reference synchronization signal and receives it at its own station to establish reception frame synchronization. As a result, in the case of a reference station, it is possible to obtain its own P value independently from the beginning without the help of other stations, so that P value can be broadcast within the system and used by each station. Make it.

Each station is KE, which is the value obtained by converting the difference between the distance from the reference station to the satellite and the distance from each earth station to the satellite when the satellite is in the center of the orbit maintenance range to the difference in P (KE takes a different value depending on the earth station) is a constant in terms of time), and the arithmetic circuit 15
P from the reference station when making the initial connection.
An initial connection is made using R and this KE as PL=PR+KE.

The value of this KE was determined from the orbital parameters of the satellite and the relative positional relationship between the reference station and each station, as it can be easily approximated by calculations in advance, independent of this initial connection device. may be set in the arithmetic circuit 15. As a result, if the initial connection is successful, it is also possible to update the degree of approximation of the KE value based on actual operational data, if necessary.

When initial connection is made in this way, the point where the error in transmission timing is greatest is 130 E longitude and 33 N latitude.
The transmission timing error is maximum ±6.8 μSe.
c. Therefore, it is sufficient to allocate a time slot with a time width of about 15 μSec as an error in the transmission synchronization signal at the time of initial connection, which is a value that can be used in a practical TDMA system. As another example of application, the following configuration can also be adopted. That is, the stations that transmit the value of P are not limited to the reference station as described above, but some of the stations are equipped with the readout time difference register 18 and the time difference transmission circuit 19, and these stations transmit the transmission frame. When synchronization is established, the value of P measured by the own station is sent together with the own station identification code.

The station that will make the initial connection from now on will select a station that can use the above approximation formula from among the reference station or the stations that have already established transmission frame synchronization and are sending out the value of P. A preset K for that station specified by the PR value from the station and its station identification code.
The arithmetic circuit 15 calculates PL from the value of T and performs initial connection. In this application example, if a station that transmits the value of P every 51st to 10th in latitude and longitude is provided in the coverage of one geostationary satellite, any station in the entire coverage of that satellite can use the initial connection of the present invention. You can use the device to make the initial connection. Alternatively, as another example of application, a small station within the system may perform the initial connection of the present invention using PR from a large station where the geographical conditions allow the above simple approximation formula, and the large station itself may use the conventional It is also conceivable to configure a TDMA system with equipment that can perform the initial connection independently using the method described above, thereby reducing the burden on small stations and streamlining the entire system.

Alternatively, the own station receives the value of P from two or more stations that have already established synchronization, and uses the arithmetic circuit 15 to perform a more advanced calculation than that described above based on the value of P, It is also possible to obtain the value of P with the accuracy without being restricted by geographic conditions.

This method can also be applied to the overall application example described above. As detailed above, according to the present invention, it is possible to provide an initial connection device that performs initial connection in a theoretically simple and highly reliable manner without emitting any signal for initial connection, and moreover, it can meet the requirements as described above. By applying this device to the TDMA system in various different ways depending on the situation, the various drawbacks of the conventional initial connection device as described above can be eliminated, and the effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a frame format of time division multiple access communication, FIG. 2 is an explanatory diagram of a conventional initial connection method, FIG. 3 is a block diagram showing an embodiment of the initial connection device of the present invention, and FIG. The figure is an explanatory diagram showing the correlation between the distances from two earth stations to a satellite, and FIG. 5 is an explanatory diagram showing the correlation between the distances from two earth stations to a satellite in a case particularly suitable for applying the present invention. It is. In the figure, 1 is a receiver, 2 is a reference station synchronization signal selection circuit, 3 is a reception frame counter, 4 is a system clock generator, 5 is a reception time slot decoder, 6 is a time difference measurement circuit, and 7 is a local station synchronization signal selection circuit. 8 is a time difference counter, 9 is a measurement frame selection circuit, 10 is a transmission frame counter, 11 is a transmission time slot decoder, 12 is a synchronization signal generation circuit, 13 is a transmitter, 14 is a time difference reception circuit, 15 is an arithmetic circuit, 16 is a time difference register, 17 is an initial connection control circuit, 18 is a read time difference register, and 19 is a time difference transmission circuit.

Claims (1)

[Claims] 1 In a time-division multiple access communication system in which multiple stations use one satellite repeater in a time-division manner to communicate with each other, a station attempting to start a new communication must do so within the time allotted to it. In the initial connection device that generates the transmission timing for inserting the signal from the station, the first connection device determines the reception of the reference synchronization signal transmitted from the specific station and uses this as the reception time reference.
means, the self-station synchronization signal transmitted from the own station is received again via the satellite repeater, and an error signal is generated by comparing it with the allocated time position for the own-station signal determined based on the reception time standard. a second means for correcting the transmission timing of the own station using an error signal to maintain the transmission time reference of the own station signal, and representing a relative time difference between the reception time reference and the transmission time reference at other stations in operation; a third means for receiving information and generating first time difference information; a fourth means for calculating the first time difference information and generating second time difference information; and a local station participating in the communication system. Initial connection in time division multiple access, characterized in that it includes a fifth means for controlling the transmission timing of the second means in response to the second time difference information during the process of starting transmission in order to Device.