JPH07288497A - Satellite communication method/device - Google Patents

Abstract

PURPOSE:To provide a satellite communication system which has the high circuit efficiency and can perform the transmission with preference to an important circuit. CONSTITUTION:This satellite communication system comprises a center station 101 which performs the time division multiplex connection communication via a communication satellite and the slave station groups 104-106 which contain plural slave stations and also have the priority that is previously set. The station 101 measures the traffic value to each slave station group and scures a random slot that is available to all slave station groups on a communication from when the traffic value exceeds a fixed level. At the same time, the station 101 assigns successively the preferential slots that are available to each corresponding slave station group in order of higher priority ranks. Then each slave station performs the communication by means of its assigned preferential slot.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to satellite communication systems, and more particularly to time division multiple access (TDM) via communication satellites.
A) The present invention relates to a communication method in a satellite communication system that is composed of a central station that performs communication and at least one slave station.

[0002]

2. Description of the Related Art A satellite communication system communicates between a central station and a slave station via a communication satellite. Transmissions from two or more slave stations collide with each other on the same carrier at the same time on the communication satellite. When a so-called congestion state occurs, the central station cannot correctly receive any transmission. When such a situation occurs, each slave station has to perform transmission again and the line efficiency decreases.
In particular, if the traffic volume on the satellite line increases, the probability of collision of transmission increases and congestion easily occurs. Therefore, conventionally, various satellite communication systems have been studied in which congestion is suppressed to a low level even if the traffic volume increases and the line efficiency is high.

As an example thereof, for example, a RA-TDMA system in which a transmission message is randomly packetized and transmitted in a slotted unit, or a line allocation request is first made when a transmission message is requested, and a line is reserved in advance. Reservation-TD to prevent transmission collision by doing
MA method etc. are mentioned. In addition, a method of monitoring the line and selecting the RA-TDMA method when the traffic volume is small, and switching to the Reservation-TDMA method or the like to prevent a decrease in line efficiency due to collision when the traffic volume increases is also used. ing.

[0004]

Among the above-mentioned conventional communication methods, the RA-TDMA method has an advantage that transmission can be started immediately at the time when a transmission request is generated, but a plurality of slave stations are required. If they are transmitted at the same time, a so-called transmission collision causes the message to be lost, and retransmission is required. As described above, when the amount of transmission increases, collisions frequently occur, and there is a problem that the line efficiency is extremely reduced due to retransmission. In addition, when the traffic volume increases, transmission collisions occur uniformly regardless of the importance of each line, and there is a drawback that important messages and urgent messages cannot be preferentially transmitted.

On the other hand, in the Reservation-TDMA system, a reserved telegram is transmitted at the time when a transmission request is made to secure a line, so that it is possible to prevent a telegram collision. However, if the traffic volume increases, reservation messages will be sent frequently, so R
Similar to the case of the A-TDMA system, transmission collision occurs and the line efficiency becomes low. Furthermore, since a line is assigned and fixed to one slave station, other stations are locked out for that line. Therefore, while one line is congested and transmission is regulated, other lines may have a sufficient margin, and in such a case the line efficiency is rather lowered. there were.

In the present invention, as described above, in any method, in view of the problem that the throughput decreases in the entire system as the traffic volume increases, the transmission timing and transmission method of the telegram generated from the slave station. It is an object of the present invention to provide a satellite communication method which has high line efficiency and can preferentially perform transmission to an important line by controlling, and a system which realizes this method.

[0007]

A satellite communication method provided by the present invention has a central station for performing TDMA communication via a communication satellite, and at least one slave station for each, and slave stations with priorities set in advance. A satellite communication method performed with a group, in which the central station first measures the traffic volume between each slave station group, and if the traffic volume exceeds a certain value, all the slave station groups on the communication frame. Reserve a random slot that can be used by. After that, priority slots that can be used only by the slave station group are assigned in order from the slave station group with the highest priority. In this case, it is preferable to assign priority slots so that the traffic amount per slot decreases as the priority increases and the line becomes stable. As a slot allocation method, for example, when the traffic volume is the lowest, priority slots are allocated only to the highest priority group, and the rest are allocated as random slots. Then, priority slots are sequentially assigned as the traffic volume increases, and the rest are random slots. At this time, a fixed number of random slots are secured, and if the remaining random slots to which the priority slots are allocated become less than the fixed amount, the allocation of priority slots is terminated.

Further, when a telegram is transmitted from the slave station group to the central station, the central station cannot detect a telegram collision of the slave station. Therefore, the slave station transmits a telegram containing the group name to which the slave station belongs. The station should detect the number of messages and the group name and judge whether the traffic volume should increase or decrease. When the slave station is assigned a priority slot, the slave station may use the assigned priority slot for communication, or may use the random slot for communication. However, communication using a slot assigned to another slave station is prohibited. In this case, whether to use the priority slot or the random slot is determined by the type of message, the degree of importance, the degree of urgency, and the availability of the random slot. For example, when transmitting a message of high importance, , One of the random slots and the priority slot with high line stability is selected, and communication is performed using the selected slot.

Further, the satellite communication system provided by the present invention includes a central station for performing TDMA communication via a communication satellite, and a slave station group having at least one slave station and having a priority set. Constitute. In this configuration, the central station, traffic measuring means for measuring the traffic volume between each slave station group, and a data comparison means for comparing the measured traffic volume with a predetermined threshold value,
As a result of the comparison, when the traffic volume exceeds a certain value, secure a random slot that can be used by all slave stations on the communication frame, and assign a priority slot that can be used only by the slave station group in descending order of priority. It has slot allocation means and transmission means for transmitting the allocation result to each slave station. On the other hand, each slave station has a slot selecting means for determining a slot to be used for transmitting a message according to the result of the slot allocation transmitted from the transmitting means and the importance of the transmitted message.

[0010]

In the present invention, the traffic measuring means of the central station measures the traffic volume between the slave station groups and guides the measured value to the comparing means. As a result of the comparison, when recognizing that the traffic volume exceeds a certain value, the slot allocation means secures a random slot that can be used by all slave station groups on the communication frame, and the slave station group with a higher priority order in order. Assign a priority slot that can be used only by the slave group. After the allocation, the allocation result is transmitted to each slave station group by the transmission means. As a result, a certain number or more of slots are always secured for the slave station group to which the priority slot is assigned. The slave station group to which the priority slot is assigned can communicate using a random slot and a priority slot dedicated to the slave station group. Which slot is used for message transmission is determined by the slot selection means according to the importance of the message, for example.

Also, by securing random slots in advance as described above, it is possible to avoid a situation in which all slots become priority slots. When all slots are priority slots, for example, when there are groups A to E,
When the slots for the groups A to C are secured, the remaining slots are exhausted, and the groups D and E are not assigned slots and cannot communicate at all.
According to the present invention, the slot allocation on the communication frame can be easily changed. Therefore, regardless of the group configuration of the slave stations, the slot allocation is always changed to ensure the stability of the slave station group having a high priority. You can

Since all slots are random slots when the traffic volume is low, a certain line is congested and transmission is restricted, while there is no sufficient margin in other lines. Also, in each slave station, when transmitting a telegram with a high degree of importance, one of the random slots and the priority slot, which has high line stability, is selected, and transmission is performed using the selected slot. Telegrams with high importance are less likely to collide with other telegrams. Furthermore, as the priority increases, 1
By allocating priority slots so that the traffic volume per slot decreases, the line is protected according to the priority order even when the traffic volume increases.

[0013]

The present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram of an embodiment of the present invention.
Is a central station, 102 is a communication satellite, 103 is a slave station, and 104-
Reference numeral 106 is a slave station group. As shown, each slave group 104-106 includes at least one slave 1
03 is assigned, and these slave stations are communication satellites 102
Information is communicated with the central station 101 via the. Each of the slave station groups 104 to 106 is independent of each other, and the priority order is determined in advance for each slave station group. The slave stations are group A, group B, group C ... In descending order of priority. The communication from the central station 101 to the slave stations is performed by a time division multiplexing (TDM) communication system or a TDMA communication system.

FIG. 2 is a block diagram of the central station 101 in the satellite communication system of the present embodiment. 201 is an antenna section, 202 is a high frequency section, 203 is a transmission buffer,
Reference numeral 204 is a modulation unit, 205 is a demodulation unit, 206 is a received message monitoring unit, 207 is a reception buffer, and 208 is a slot allocation unit.

A telegram obtained by a baseband signal from a host computer (not shown) is transmitted by the transmission buffer 2.
It is temporarily stored in 03. The accumulated telegram is transmitted to the modulation section 204 under the control of the slot allocation section 208. The control content will be described later. Modulator 20
Reference numeral 4 modulates the baseband signal, converts it into an intermediate frequency band signal, and sends it to the high frequency unit 202. High frequency section 202
Is an intermediate frequency band signal sent from the modulator 204,
The signal is converted into a high frequency band signal for transmission to the communication satellite 102 and amplified. This high frequency band signal is transmitted to the communication satellite 102 through the antenna unit 201.

On the other hand, a weak high frequency band signal received from the communication satellite 201 by the antenna unit 201 is amplified by the high frequency unit 202 and converted into an intermediate frequency band signal. The converted signal is demodulated by the demodulation unit 205 and converted into a baseband signal. The reception telegram monitoring unit 206 extracts the telegram from the baseband signal demodulated by the demodulation unit 205, and classifies the telegram into the above-mentioned telegram addressed to the host computer and the control telegram. The reception buffer 207 temporarily stores a message received from the received message monitoring unit 206 to the host computer or the like. The slot allocation unit 208 analyzes the control message received from the received message monitoring unit 206 and determines the traffic status on the line. It also generates a priority slot allocation message and a random slot notification message for the slave station group, and sends both baseband signals to the modulator 204. Further, the transmission timing of the electronic message from the host computer or the like is controlled by the notification from the transmission buffer 203.

FIG. 3 is a block diagram of the slave station 103 in the satellite communication system of this embodiment. 301 is an antenna section, 302 is a high frequency section, 303 is a transmission buffer, and 3 is a transmission buffer.
Reference numeral 04 is a modulation unit, 305 is a demodulation unit, 306 is a received message monitoring unit, 307 is a reception buffer, and 308 is a slot selection unit.

A telegram obtained by a baseband signal from a terminal device (not shown) or the like is temporarily stored in the transmission buffer 303. The accumulated messages are stored in the slot selection unit 308.
It is sent to the modulation unit 304 under the control of. Modulator 3
04 modulates this baseband signal, converts it into an intermediate frequency band, and transmits it to the high frequency unit 302. High frequency section 302
Then, the transmitted intermediate frequency band signal is transmitted to the communication satellite 102.
The signal is converted to a high frequency band signal for transmission to and amplified. This high frequency band signal is transmitted to the communication satellite 102 through the antenna unit 301.

On the other hand, the weak high frequency band signal received from the communication satellite 102 by the antenna section 301 is amplified by the high frequency section 302 and converted into an intermediate frequency band signal. The converted signal is demodulated by the demodulation unit 305 and converted into a baseband signal. The reception message monitoring unit 306 extracts a message from the baseband signal demodulated by the demodulation unit 305 and classifies the message into a message addressed to the terminal device and a control message. The reception buffer 307 temporarily stores a message received from the received message monitoring unit 306 to the host computer or the like.

The slot selecting unit 308 analyzes the control message received from the received message monitoring unit 306, and stores information on priority slots and random slots assigned by the central station. Further, a slot for transmitting a message is determined from the notification from the transmission buffer 303, the importance of the message, the urgency, and the availability of random slots, and the message is transmitted using the determined slot.

FIG. 4 shows an example of the structure of a communication frame used in this embodiment. FIG. 4A is a diagram for explaining the relationship between the frame structure and slots, and 401 is a superframe for communication using the TDMA communication method. The superframe 401 is slot-divided into # 1 to #n (natural number), and the transmitting station transmits on a slot basis.

FIG. 4B is a slot allocation situation diagram when the traffic volume is relatively low. In the figure, reference numeral 402 denotes a reference slot, which represents a slot start point in the superframe. Group 403 has the highest priority
, Which indicates that only slave stations belonging to the group A can preferentially use the priority slot 403 in this example. In this case, group A
The slots that can be used by the slave stations are not limited to the priority slot 403, but the remaining random slots 404 can be used when the traffic volume becomes high.
Random slot 4 for groups other than group A
Only 04 is used for transmission.

FIG. 4C is a slot allocation status diagram when priority slots are allocated to group B in addition to group A. 405 is a priority slot assigned to group B, and its assigned area is
It is determined by the traffic volume increase rate of the slave group B and the number of slave stations belonging to the group B. In this example,
Of the superframe 401, the reference slot 402,
A portion other than the priority slot 403 for group A and the priority slot 405 for group B becomes a random slot 406.

Next, the operation of the slot allocation unit 208 in the central station 101, that is, the above-mentioned control contents will be described based on the flowchart of FIG. 5 and the explanatory view of each communication frame configuration example shown in FIG. In FIG. 5, S indicates a processing step.

In the slot allocation unit 208, first, the traffic volume Q of the entire system is measured (S11: traffic measuring means), and the measured traffic volume Q is set to a predetermined threshold value T.
It is compared with H (S12: data comparison means). When the traffic amount Q is smaller than the threshold value TH (when the traffic amount is small), all slots on the superframe 401 are set as random slots (S13). On the other hand, S1
When it is recognized in 2 that the traffic volume Q is equal to or greater than the threshold value TH, it is determined according to the traffic volume Q whether or not priority slots are set in order from the slave station group having a higher priority. When the traffic volume Q is not so large, as shown in FIG. 4B, the priority slot is assigned only to the group A, and as the traffic volume Q increases, as shown in FIG. Group B, group C ... Are sequentially determined as groups to which priority slots are assigned (S14).

Next, the traffic volume in each slave station group for which priority slot allocation has been determined is measured (S1).
5). Then, from the measured traffic volume, the slot allocation area is determined according to the traffic increase rate and the number of slave stations belonging to the group (S16). in this case,
Since the size of the allocation area is determined by the traffic increase rate of the slave station group and the number of slave stations belonging to the group, as shown in FIG. It may be larger than the allocated area. Also, by assigning to the group with high priority so that the traffic volume per slot decreases, the occurrence rate of congestion decreases as the priority increases, and the line stability is almost proportional to the priority. This is preferable. Thereafter, similarly, priority slots are sequentially assigned to group C, group D, ... According to the traffic situation of the group, and the remaining slots are assigned as random slots. Also, in the group in which the traffic volume has decreased, the allocation of priority slots is completed (the above is the slot allocation means). In this case, the slot previously used as the priority slot is used as a random slot or a priority slot for another group.

In this way, traffic information indicating that all slots are random slots or that a slot area and a random slot area are assigned to a group to which each slave station belongs is transmitted to the slave station as a control message ( S17: Transmission means).

The slot selection unit 308 in each slave station analyzes the control message received from the received message monitor unit 306, and stores the priority slot, random slot, and traffic information on the line allocated by the central station.
Then, the electronic message information accumulated in the transmission buffer 303, its importance and urgency are detected, and the electronic message is transmitted from the information on the availability of priority slots and random slots and the traffic information on the line obtained from the central station. Determines a slot for (slot selection means). For example, for telegrams with high importance and urgency, transmission is performed using priority slots where congestion is unlikely to occur, and for other telegrams, transmission is performed using random slots and congestion occurs in priority slots. Try to suppress

As described above, in the present embodiment, the priority order is set for each slave station group and transmission is performed as described above, so that even if the total traffic volume increases, a slave station group with a high priority can be used. Congestion can be suppressed and the stability of the line increases as the priority increases, so the entire line becomes unstable regardless of the priority, and it is uniform regardless of the importance. The situation where congestion occurs will not occur. Further, since the size of the priority slot area is determined according to the traffic amount and the traffic amount is made uniform, the traffic amount can be easily made uniform at any time regardless of the configuration of the slave station group.

[0030]

As is apparent from the above description, according to the present invention, it is possible to effectively use the satellite line according to the traffic volume, and further, the line efficiency is lowered due to the retransmission due to the collision of the transmission or the congestion of the reserved telegram. Since this can be prevented, there is an effect that the throughput of satellite communication is increased. In particular, a slave station group with a high priority can perform communication by using a priority slot dedicated to the slave station group in addition to the random slot, so that the communication stability is higher than that of other groups. is there. Further, it is possible to protect the line in proportion to the priority order, and there is an effect that the usage pattern of the line can be flexibly changed according to the importance of the electronic message to be transmitted and received.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a satellite communication system according to an embodiment of the present invention.

FIG. 2 is a block configuration diagram of a central station according to an embodiment of the present invention.

FIG. 3 is a block configuration diagram of a slave station according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of a frame configuration example used in TDMA communication.

FIG. 5 is a flowchart showing the operation of the slot allocation unit of the central station.

[Explanation of symbols]

101 Central station 102 Communication satellite 103 Slave station 104, 105, 106 Slave station group 201, 301 Antenna section 202, 302 High frequency section 203, 303 Transmission buffer 204, 304 Modulation section 205, 305 Demodulation section 206, 306 Received message monitoring section 207, 307 Reception buffer 208 Slot allocation unit 308 Slot selection unit 401 Superframe 402 Reference slot 403 Priority slot assigned to group A 404, 406 Random slot 405 Priority slot assigned to group B

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michio Kikuta 3-3-3 Toyosu, Koto-ku, Tokyo NTT Data Communications Corp. (72) Inventor Shinsaku Okamura 3-chome, Toyosu, Koto-ku, Tokyo 3rd-3rd NTT Data Communications Co., Ltd.

Claims (4)

[Claims] 1. A satellite communication method performed between a central station which performs time division multiple access communication via a communication satellite and a slave station group including at least one slave station whose priority is set, The central station measures the traffic volume with the slave group, and if the traffic volume exceeds a certain value, secures a random slot that can be used by all slave groups on the communication frame, and gives priority to the priority slot. It is characterized in that a priority slot that can be used only by the slave station group is allocated in order from a slave station group having a higher order, and each slave station communicates with the central station using the random slot or the allocated priority slot. Satellite communication method. 2. The satellite communication method according to claim 1, wherein each of the slave stations selects one of the random slots or the assigned priority slots having a high communication line stability, and selects the selected slot. A satellite communication method characterized in that communication is performed with the central station by using the satellite communication method. 3. The satellite communication method according to claim 1, wherein the central station allocates the size of the priority slot so that the traffic volume per slot decreases as the priority increases. Characteristic satellite communication method. 4. A satellite communication system comprising a central station for performing time division multiple access communication via a communication satellite, and a slave station group having at least one slave station and having a priority set in advance, The central station is a traffic measuring means for measuring the traffic volume between each of the slave station groups, a data comparing means for comparing the measured traffic volume with a predetermined threshold value, and as a result of the comparison, the traffic volume has a threshold value. When exceeding, secures a random slot that can be used by all slave stations on the communication frame, and slot allocation means that allocates a priority slot that can be used only by the slave station group in order from the slave station group with a high priority, Transmission means for transmitting the allocation result in the slot allocation means to each slave station, wherein each slave station is Satellite communication system characterized by having a slot selection means for determining a slot to be used for transmission of the message based on the importance of the transmitted message and the slot allocation result transmitted from the transmitting means.