JP2850589B2 - Satellite communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a time-division multiple access satellite communication system for performing communication between a station (central station) and a plurality of stations (peripheral stations), and particularly to an improvement in a slot access method in which peripheral stations access time slots.

[0002]

2. Description of the Related Art As is well known, in a time division multiple access (TDMA) satellite communication system in which a plurality of peripheral stations access a central station using a common channel via one satellite in a time division manner. A so-called random access method in which a peripheral station always selects an arbitrary time slot and transmits packet data at any time as a method for accessing a central station from a peripheral station, and a combined method in which a random access method and a reservation method are used in combination. Is often adopted.

The random access method includes a slotted Aloha method. This method has the advantage of enabling low-latency transmission when the message occurrence rate is low, but when the message occurrence rate is high, packet data transmitted on the same time slot collide with each other, and the channel utilization efficiency and propagation There is a problem that the delay is worsened.

[0004] In the composite system, reservation of a time slot and transmission of a short message (a message length of one time slot or less) are performed by a slotted Aloha system, and a long message (a message length of several time slots) is reserved. This is a method of transmitting in a time slot. This method is
This is an access method that can flexibly cope with a case where the message occurrence rate is low to high. However, since the slotted Aloha method is adopted, when the message occurrence rate (especially the short message occurrence rate) increases to some extent, the above-mentioned random access method becomes As in the case of only the above, there is a problem that many collisions occur and the propagation delay increases.

Therefore, in the conventional satellite communication system employing the slotted Aloha system, as shown in FIG. 10, each peripheral station having detected a collision waits for a random time interval for retransmission of the colliding packet data. I'm trying to do it. That is, in FIG. 10, the peripheral stations T ₁ and T ₂ use the same time slot 1 to transmit packet data A ₁ ,
Sends the B ₁ respectively, the collision occurs. Peripheral station T ₁
And T ₂ detect the collision at the end of time slot 3, respectively. Then, the peripheral stations T ₁ and T ₂ generate random numbers to determine the time slot interval until retransmission. The generated random number is, as shown in FIG. 10, the peripheral station T ₁ is 2, the peripheral station T ₂ is 5, the peripheral station T ₁ and the T ₂ are, after the collision detecting two time slots and 5 The retransmission is performed after waiting only for the time slot.

[0006]

The conventional retransmission method described above is a method which is generally adopted as one of means for minimizing the deterioration of the system performance due to an increase in collisions. It is necessary that retransmission of the colliding packet data can be completed efficiently and in a short time.
However, when the message occurrence rate increases, the frequency of transmitting new data increases, so that collision between new data and retransmitted data also occurs.

[0007] For example, in FIG. 10, the peripheral station T ₂ are,
As described above, retransmission of the packet data B ₁ ′ is attempted using the time slot 9, but if another peripheral station T ₃ transmits new packet data C ₁ using the same time slot 9, a collision similarly occurs. I do. This is because each peripheral station in the satellite communication system cannot monitor the line state of the channel that accesses the central station, so that even if a packet data of one peripheral station has collided, the other peripheral stations may have a new packet data. It is based on the fact that it is difficult to perform control that suppresses transmission of data.

[0008] In short, in the above-mentioned conventional retransmission method in which the retransmission interval is determined by random number generation, when the message occurrence rate becomes high, collision between new data and retransmission data also occurs. There is a problem that deterioration is inevitable.

An object of the present invention is to provide a satellite communication system having a slot access system capable of effectively suppressing repetition of collision between packet data and deteriorating system performance.

[0010]

To achieve the above object, the satellite communication system of the present invention has the following configuration. That is, the satellite communication system according to the first aspect of the present invention comprises a central station and a plurality of peripheral stations, and when a plurality of peripheral stations access the central station using a common channel via a satellite in a time division manner. ,
In a time-division multiple access satellite communication system that employs at least a random access method in which all peripheral stations randomly access a time slot, which is a unit obtained by time-sharing a common channel; The central station is means for allocating time slots in units of peripheral station groups; and the time slot is assigned at the beginning of each time slot.
Set to recognize the use status of the mobile station between the central station and peripheral stations.
Monitor mini-slots as multiple mini-time sharing areas ,
Means for allocating as many retransmission time slots as necessary and allocating random access time slots when a signal is present in two or more mini-slots. Means for transmitting a signal to a fixedly assigned mini-slot among a plurality of mini-slots provided in a part of a time slot when transmitting a time slot; and a time slot assigned for retransmission or random. Means for determining whether the access is for access.

The satellite communication system according to the second invention is the satellite communication system according to the first invention; wherein the means for allocating a time slot in the central station in units of peripheral station groups is provided for each peripheral station group. Traffic as an indication of the data transmission frequency of each peripheral station to which it belongs
Day from information sending frequency coefficients of the group of each peripheral station
Means for determining the sum of data transmission frequencies; and means for allocating slots to each group based on the transmission frequency coefficient.

[0012]

Next, the operation of the satellite communication system of the present invention configured as described above will be described. In the present invention, a mini-slot portion is provided for each time slot, peripheral stations are divided into groups, the central station allocates slots in units of the groups, and the peripheral stations transmit packet data using the allocated slots. When transmitting, a signal is transmitted to a fixed minislot. Then, the central station recognizes the occurrence of data collision by using a plurality of minislots, and allocates a retransmission slot and a random access slot to the group. As a result, retransmission data does not collide with each other, and retransmission data does not collide with newly transmitted data.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the satellite communication system according to the present invention includes a central station C and a plurality of peripheral stations (T ₁ , T ₂ , T ₃ ,...), And the central station C transmits in a broadcast mode. However, a plurality of peripheral stations (T ₁ , T ₂ , T ₃ ,...) Access a central station C using time slots set in a time division manner on a common channel via a satellite S. This is a connection type satellite communication network. A host terminal is connected to the central station C, and a plurality of peripheral stations (T ₁ , T ₂ , T ₃ ,...)
..) Connects a user data terminal to realize a star network.

Here, the present invention employs only a random access method (eg, a slotted Aloha method) or a combination of a random access method and a reservation method as a method for a plurality of peripheral stations to access a central station. In a satellite communication system employing a combined system, a slot access system for accessing a time slot by a slotted Aloha system is intended to be improved, and the following description will focus on a portion relating to the present invention.

First, the signal format will be described. FIG.
Indicates a signal format from the central station to the peripheral station. In FIG. 2, the central station transmits in a broadcast mode, but transmits a frame timing signal at regular time intervals. This is a control signal that is a reference of a frame used when transmitting by the peripheral station. Then, between the frame timing signals, control information (reception response signal, slot assignment information, etc.) is transmitted following the frame timing signal, and a predetermined number of control information is transmitted after the control information until the next frame timing signal. Packet data is transmitted. The control information is information in units of one frame.

FIG. 3 shows a signal format from the peripheral station to the central station. In FIG. 3, this signal format is generated by each peripheral station based on the frame timing signal. That is, a channel common to each peripheral station is divided into frames of a fixed time length, and each frame is divided into a predetermined number of time slots (three in the illustrated example). As shown in the figure, one time slot is set at the beginning with a mini-slot portion composed of a plurality of mini-slots, followed by a data slot portion that stores actual transmission data (packet data). Is done. That is, each peripheral station transmits data using the data slot unit, and at that time, transmits a signal to one of the plurality of mini slots. The minislot to which a signal is to be transmitted is fixedly assigned as described later.

Next, the configuration will be described. FIG. 4 shows the configuration of the central station. In FIG. 4, the transmission / reception device 1 performs transmission / reception with the satellite S and performs frequency conversion between a high frequency band and an intermediate frequency band. The signal received by the transmitting / receiving device 1 is transmitted to the receiving unit 2
Are demodulated and error corrected and input to the demultiplexing unit 3.

The separating unit 3 outputs the demodulated and error-corrected 1
A signal for a frame is received from the receiving unit 2 and separated into user data and a control signal to be passed to a host terminal connected to the central station, and the user data is passed to a host terminal (not shown) via a reception data buffer 4. . On the other hand, the control signal is output to the channel monitoring unit 5. The control signal includes the minislot portion transmitted by the peripheral station, slot reservation request information, the address of the peripheral station that transmitted the data, and the like.

Based on the control signal from the demultiplexing unit 3, the channel monitoring unit 5 determines traffic information indicating the data transmission frequency of each peripheral station and which time slot has been used to normally receive the transmitted data. Indicating data reception information;
And minislot information indicating which minislot of the minislot section the signal has been sent to. The traffic information is output to the peripheral station model forming unit 6, the minislot information is output to the slot assignment determining unit 7, and the data reception information is output to the reception response signal generation unit 9, respectively.

The peripheral station model forming section 6 forms a user model indicating the transmission frequency of each peripheral station based on the traffic information from the channel monitoring section 5. Then, a transmission frequency coefficient is set for each peripheral station group in which the peripheral stations are grouped, and is output to the slot allocation determining unit 7. FIG.
Shows an example of a peripheral station model.

The number of groups in which the peripheral stations are divided is determined based on the data generation rate of the entire system. For example, as shown in FIG. 7, the peripheral stations (a, b, c) are divided into the peripheral stations. Group 1 is set, and peripheral stations (d, e, f) are set as peripheral station group 2. In FIG. 7, a numeral written in a square below the peripheral station name is a transmission frequency indicating a data transmission rate of the peripheral station. This is the user model. Since the transmission frequency coefficient of the peripheral station group is the sum of the transmission frequencies of the peripheral stations in the group, the transmission frequency coefficient of group 1 is 24, and the transmission frequency coefficient of group 1 is 23. Become.

The slot assignment determining unit 7 assigns a time slot to a peripheral station group with reference to the transmission frequency coefficient for each peripheral station group input from the peripheral station model construction unit 6. This time slot assignment follows, for example, the following rules: Time slot assignment is performed with priority given to the peripheral station group having the higher transmission frequency coefficient. The transmission frequency coefficient of the peripheral station group to which the time slot is assigned is the number set in advance corresponding to the number of each peripheral station.
In the embodiment, three are subtracted. When a peripheral station requiring a retransmission slot is included in a peripheral station group to which a time slot is allocated, the time slot is individually allocated to the peripheral station. Since the transmission frequency of each peripheral station is updated for each frame based on the latest traffic information, the transmission frequency coefficient of the peripheral station group is updated accordingly.

Specifically, the procedure is as shown in FIG. In FIG.
The numbers in the circles are the transmission frequency coefficients of each peripheral station group updated at the beginning of each frame. Each slot has a group name and a number to which the slot is assigned, and the number is a transmission frequency coefficient obtained by subtracting three from each other. For example, in the first slot of the n-th frame, the transmission frequency coefficient of the same as that of the group 1 is 24 and 23,
The first slot is assigned to group 1 according to the rule, and the transmission frequency coefficient of group 1 is reduced by three to 21 according to the rule. Similarly, in the second slot, since the transmission frequency coefficient of group 2 is large (21 <23), the second slot is allocated to group 2, and the transmission frequency coefficient is 20. Hereinafter, similarly, in the illustrated example, slots are assigned alternately to groups 1 and 2.

The slot allocation determining unit 7 determines whether or not a packet collision has occurred based on the mini-slot information from the channel monitoring unit 5. If a collision has occurred, the slot allocation determining unit 7 determines the collision packet according to the rule. 2 sent
A slot for retransmission is allocated to one or more peripheral stations.

For example, in FIG. 8, since the fifth slot of the n-th frame is assigned to group 1,
The three peripheral stations a, b, and c attempt data transmission by the random access method using the fifth slot. At this time, each of the three peripheral stations transmits a signal to a mini-slot that is fixedly assigned to itself. Accordingly, since the central station uses three mini-slots when receiving the fifth slot, it knows that the transmission packets of the three peripheral stations a, b, and c have collided. The station is assigned a retransmission slot.

The slot allocation information transmitting section 8 outputs the information on the slot allocation determined by the slot allocation determining section 7 to the multiplexing section 12 in units of one frame. Further, the reception response signal generation unit 9 generates a reception response signal for the data received from the peripheral station based on the data reception information from the channel monitoring unit 5, and outputs it to the multiplexing unit 12. The frame timing signal generator 11 outputs the generated frame timing signal to the multiplexer 12. On the other hand, user data from a host terminal (not shown) is input to the multiplexing unit 12 via the transmission data buffer 10.

Thus, the output of the slot allocation information transmitting section 8 (slot allocation information), the output of the reception response signal generation section 9 (reception response signal), the output of the transmission data buffer 10 (user data), and the generation of the frame timing signal The output (frame timing signal) of the unit 11 is time-division multiplexed by the multiplexing unit 12 and is coded and modulated by the transmitting unit 13.
It is transmitted from the transmitting / receiving device 1 to the satellite S.

FIG. 5 shows the configuration of a peripheral station. FIG.
In, the transmission / reception device 14 performs transmission / reception with the satellite S and performs frequency conversion between a high frequency band and an intermediate frequency band.
The receiving unit 15 demodulates / receives a signal received by the transmitting / receiving device 14.
While performing error correction processing and outputting the detected frame timing signal to the frame synchronization section 16, error detection is performed on user data after demodulation and error correction and control information (reception response information, slot allocation information, etc.), and thereafter, Separation unit 1
8 is output.

The frame synchronizer 16 determines the frame timing to be used when the own station performs transmission, based on the detected and input frame timing signal. The slot timing generation unit 17 divides the frame determined by the frame synchronization unit 16 into several time slots, and outputs a signal indicating each slot timing to the slot identification unit 23.

The separation unit 18 receives the output of the reception unit 15 and separates the data into user data, a reception response signal, and slot allocation information. User data addressed to the own station is transmitted via a reception data buffer 19 to a user (not shown). Hand over to the data terminal,
It outputs the slot allocation information to the slot allocation table 20 and outputs a reception response signal to the transmission data buffer 22.

The slot allocation table 20 stores the
Then, a slot assigned to the peripheral station group to which the own station belongs and a slot assigned to the own station for retransmission are extracted from the slot assignment information input from, and recorded in the time table.

On the other hand, packetizing section 21 divides user data input from a user data terminal (not shown) into packets having a data length that can be accommodated in a data slot section of one time slot, and stores them in transmission data buffer 22. Let it.

The transmission data buffer 22 stores the transmission data from the packetizing section 21 in a transmission-only buffer, but obtains and stores from the slot identification section 23 the information of the time slot in which the station has actually attempted transmission. Then, the information is compared with the reception response signal from the separation unit 18, and a response to the time slot in which the own station has attempted data transmission is an acknowledgment ACK (Acknowledgement) or a negative response NAK (Not Acknowledge).
owledgement). Response is positive response AC
In the case of K, the transmitted data is deleted from the buffer, and if the response is a negative response NAK, the data whose transmission failed is stored again in the dedicated buffer for retransmission data in preparation for retransmission.

Then, as shown in FIG. 6, when the slot identification unit 23 receives the output of the slot timing generation unit 17 and detects the arrival of the slot timing, as shown in FIG.
(B) Referring to the slot assignment table 20, whether the time slot is a slot that the own station can transmit (a slot assigned to the group to which the own station belongs or a slot assigned to the own station for retransmission), It is determined whether the station cannot transmit (a slot allocated to another peripheral station group or another peripheral station), and
(E) Perform any of the processes. That is, (c) in the case of a time slot (random access slot) assigned to a peripheral station group to which the own station belongs, read new data from the transmission data buffer 22 and output it to the transmission unit 24. (D) In the case of a time slot assigned to the own station for retransmission, retransmission data is read from the transmission data buffer 22 and output to the transmission unit 24. on the other hand,
(E) Slots that cannot be transmitted by the own station (time slots allocated to other peripheral station groups or other peripheral stations)
Nothing is transmitted in that time slot. Note that when the slot identifying unit 23 performs the transmitting operation,
The time slot at that time is stored in the slot assignment table 20.
And the transmission data buffer 22.

Thus, the transmission data output from the slot identification unit 23 is encoded and modulated by the transmission unit 24 and transmitted from the transmission / reception device 14 to the satellite S.

Next, the slot access method of the present invention will be specifically described with reference to FIG. In FIG. 9, each frame is assumed to consist of five time slots, but as shown in FIG. 8, each slot of each frame is assigned to a peripheral station group. Peripheral stations a, b, and c belong to group 1, and in frame 1, first slot, third slot, and fifth slot are assigned.

Now, the peripheral stations a and b receive the packet A in the third slot (random access slot) of the frame 1.
_1, I was trying to send the same B _1. At this time, the mini-slot is fixedly determined and, for example, as shown in FIG.
Transmits a signal to minislot a, and peripheral station b transmits a signal to minislot b.

Then, since two mini-slots are used in the third slot of frame 1, central station C recognizes that a collision has occurred in the transmission packet of group 1 by monitoring the mini-slot portion. Then, a reception response signal having the content of the negative response NAK is created, and two peripheral stations involved in the collision are a and b, but the group 1
Since there is also a peripheral station c, two slots of the first and third slots of the frame 3 are allocated as retransmission slots, and a fifth slot of the frame 3 is allocated as a random access slot for the peripheral station c. Is created, and at the end of frame 1, a NAK for the third slot of frame 1 is created.
The response and the slot assignment information are transmitted in the broadcast mode.

The peripheral stations a, b, and c receive the NAK response and the slot allocation information at the timing of frame 2. Thereby, the peripheral stations a and b know that the transmission has failed.
Then, the peripheral station a retransmits the collision data A ₁ ′ on the first slot of the frame 3 allocated as the retransmission slot. In addition, the peripheral station b places collision data B on the third slot of frame 3 assigned as a retransmission slot.
Resend ₁ '.

On the other hand, in the peripheral station c, it is assumed that new data has arrived from the terminal by the end of the fifth slot of the frame 2. Then, the peripheral station c transmits the packet data C ₁ in the fifth slot of the frame 3 which is the random access slot assigned this time.

As described above, according to the slot access method of the present invention, retransmission is completed in a short time without causing data collision. In addition, retransmission data and new data do not collide.

[0042]

As described above, according to the satellite communication system of the present invention, mini-slots are provided in each time slot, peripheral stations are divided into groups, and the central station allocates slots for each group. When transmitting packet data using the allocated slot, the peripheral station transmits a signal to a fixedly set mini-slot. The central station recognizes the occurrence of data collision by using a plurality of mini-slots, and allocates a retransmission slot and a random access slot to the group. And there is no collision between the retransmitted data and the newly transmitted data. Therefore, according to the present invention, there is an effect that it is possible to provide a satellite communication system having a slot access system capable of avoiding deterioration of system performance due to repeated collision of data.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a satellite communication system embodying the present invention.

FIG. 2 is a signal format from a central station to a peripheral station.

FIG. 3 is a signal format from a peripheral station to a central station.

FIG. 4 is a configuration block diagram of a central station according to one embodiment of the present invention.

FIG. 5 is a configuration block diagram of a peripheral station according to an embodiment of the present invention.

FIG. 6 is a schematic processing diagram of a slot identification unit 23;

FIG. 7 is an explanatory diagram of grouping of peripheral stations.

FIG. 8 is an explanatory diagram of slot assignment to peripheral station groups and signal transmission to mini-slots.

FIG. 9 is a diagram illustrating a specific operation of the slot access method according to the present invention.

FIG. 10 is an explanatory diagram of data collision and retransmission control of the conventional Aloha system with slots.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmission / reception device 2 reception unit 3 separation unit 4 reception data buffer 5 channel monitoring unit 6 peripheral station model configuration unit 7 slot allocation determination unit 8 slot allocation information transmission unit 9 reception response signal generation unit 10 transmission data buffer 11 frame timing signal generation unit Reference Signs List 12 multiplexing unit 13 transmitting unit 14 transmitting / receiving device 15 receiving unit 16 frame synchronizing unit 17 slot timing generating unit 18 separating unit 19 receiving data buffer 20 slot allocation table 21 packetizing unit 22 transmitting data buffer 23 slot identifying unit 24 transmitting unit

Claims (2)

(57) [Claims] When a plurality of peripheral stations access a central station using a common channel via a satellite in a time-sharing manner, all the peripheral stations are connected to the central station. A time-division multiple access satellite communication method that employs at least a random access method for randomly accessing a time slot, which is a unit obtained by time-sharing a common channel;
The plurality of peripheral stations are divided into groups each consisting of a predetermined number of peripheral stations; the central station allocates time slots in units of peripheral station groups; and the use of the time slots at the beginning of each time slot Medium state
Multiple mini-time divisions set to recognize between heart and peripheral stations
Means for monitoring the minislot as an area and, when there is a signal in two or more minislots, allocating as many retransmission time slots as necessary and allocating a random access time slot. Means for transmitting a signal to a fixedly assigned mini-slot of a plurality of mini-slots provided in a part of the time slot when transmitting data on the time slot; Means for determining whether the time slot is for retransmission or for random access;
A satellite communication system comprising: 2. The satellite communication system according to claim 1, wherein the means for allocating a time slot in the central station on a per-peripheral-station group basis transmits, for each peripheral-station group, data transmission from each peripheral station belonging to the group. the frequency
Means for determining the transmission frequency coefficient of the group as the sum of the data transmission frequencies of the peripheral stations from the traffic information as information ; and means for allocating slots to each group based on the transmission frequency coefficient; A satellite communication system comprising: