JP2989884B2 - Satellite communication method and satellite communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a channel selection system in a case where a ground station performs random access time division multiplex packet communication using a plurality of channels in satellite communication.

[Conventional technology]

Conventionally, as a packet collision resolution algorithm when a ground station performs random access time division multiplex packet communication in satellite communication, if a collision occurs at a central control station receiving packets from each ground station, the collision is resolved. A block access type collision resolution algorithm that disables transmission of a new packet from all ground stations and a free access type collision resolution algorithm that allows a new packet to be transmitted at any time even when a collision occurs have been proposed. In addition, a multi-channel block access type collision resolution algorithm and a free access type collision resolution algorithm for performing collision resolution using a plurality of channels for each scheme have been proposed. For details, refer to the literature (HHYan “A new
free acsess collision resolution algolithm ", Pr
oc IEEE INFOCM 89 'pp 1057-1062).

[Problems to be solved by the invention]

In the above-described conventional block access type collision resolution algorithm, a new packet is not accessed during the collision resolution period, and a relatively high throughput can be obtained because the normal collision state is resolved earlier. When the number is large, a new collision is caused, and in such a case, there is a disadvantage that the delay characteristic is deteriorated.

In the free access method, a new packet can be transmitted at any time, so that a new packet generated later may resolve the collision earlier than a station that has already started retransmission, and the collision may increase. There was a risk of developing into a burst collision.

In addition, the multi-channel block access collision resolution algorithm and the multi-channel free access collision resolution algorithm can perform collision resolution faster than in the case of a single channel. A similar problem occurred with the single channel case.

[Means for solving the problem]

The present invention relates to a satellite communication method in which a plurality of ground stations perform time-division multiplexed packet communication of random access using a plurality of channels with a central control station via a satellite, wherein the central control station transmits packets transmitted from the plurality of ground stations. Is received for each channel, a collision in each channel in the same reception time slot is detected for each channel, and a retransmission request cannot be made due to a shortage of retransmission channels in the collision channel group and the previous transmission time slot. WA stored in advance
A retransmission waiting channel group composed of an IT channel group, and a plurality of transmission channels determined by leaving at least one new packet transmission channel from a first algorithm predetermined based on the number of channels in the retransmission waiting channel group. The retransmission channel group group in units of channels, the retransmission waiting channel group and the retransmission channel group group are made to correspond to each other from a predetermined second algorithm, and only the corresponding portions are linked to each other to form the plurality of earths. And the earth station receives the retransmission waiting channel group and the retransmission channel group group in which a portion corresponding to the retransmission waiting channel group is linked. An earth station that requires retransmission, if the channel group for retransmission is linked to a channel that requires retransmission, One of the retransmission channel groups is randomly selected and retransmitted to the central control station.If the retransmission channel group does not link to the channel requiring retransmission, the central control station sends the next WAIT retransmission to the central control station until receiving a retransmission waiting channel group and the retransmission channel group group,
An earth station that does not require retransmission of the channels in the received retransmission channel group, randomly selects one of the remaining channels from the received retransmission channel group, and transmits a new packet to the selected channel. It is characterized in that it is transmitted to a central control station.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing one embodiment of a satellite communication network configuration including the present invention. In FIG. 1, a plurality of ground stations
30 communicates with the central control station 20 via one satellite 10,
The ground stations cannot communicate with each other without passing through the central control station 20.

FIG. 2 is a configuration diagram of the central control station 20. The reception data is received by the reception unit 21 for each channel, and is sent to the collision detection unit 22. The collision detection unit 22 performs collision detection for each channel, and sends the result to the retransmission waiting group detection unit 23. The retransmission waiting group detection unit 23 retransmits due to lack of retransmission channels in the group of collision resolution channels detected by the collision detection unit 22 due to the success / failure of retransmission packet transmission and the transmission / failure of new packet, and the previous transmission time slot. At least one new packet transmission channel from a predetermined first algorithm described later based on the number of channels in the retransmission waiting channel group composed of the WAIT channel group stored in advance because the request could not be made A retransmission channel group group is determined in units of a plurality of channels determined by leaving the above, and the retransmission waiting channel group and the retransmission channel group group are linked to each other only in corresponding portions from a predetermined second algorithm described later. And send the result
Send to 24. The transmitting unit 24 transmits to the remote earth stations as information the retransmission channel group and the retransmission channel group group in which the portions corresponding to the retransmission channel group are linked.

 FIG. 3 is a configuration diagram of the remote earth station 30.

When a packet is generated from the host device and receives a retransmission buffer start signal from the receiving unit 32, the packet is accumulated in the retransmission buffer 31. The receiving unit 32 receives from the central control station 20 a retransmission channel group group in which portions corresponding to the transmission channel group and the retransmission channel group are linked as information and determines transmission success / failure. If there is a channel in the received retransmission channel group that requires retransmission, and the retransmission channel group is linked to the channel that requires retransmission, that is, if retransmission can be performed immediately, retransmission is performed. The channel group in the dedicated channel group is stored in a temporary storage area (not shown) and a stack start signal is output. If the retransmission channel group is not linked to the channel requiring retransmission, that is, if there is no available channel for immediate retransmission, the next retransmission waiting channel group and retransmission channel group group are received from the central control station. Until you
WAIT. If it is not necessary to retransmit a channel in the received retransmission channel group, that is, if a new packet may be transmitted, a retransmission buffer activation signal is transmitted and the remaining retransmission channel group group is reduced. Is stored in a temporary storage area (not shown), and the receiving unit 32 outputs a stack start signal to the retransmission stack unit 34. The retransmission stack unit 34 is activated by the above-mentioned stack activation signal, reads out the channel group from the temporary storage area of the reception unit 32, accumulates it in the stack, and activates the channel selection unit 33. The channel selection unit 33 randomly selects one channel from the group of channels stored in the retransmission stack unit 34 and sends it to the transmission unit 35. The transmission unit 35 retransmits the data stored in the retransmission buffer 31 to the central control station 20 using the selected channel.

FIG. 4 shows a specific example of channel selection.
Here, the total number of channels is 8, and the group size of the retransmission channel group is 3. Assuming that the number of retransmission waiting channels is G according to the first algorithm, when G = 0, since there is no retransmission group, access to a new packet is permitted in all channels. When G = 1, there is one retransmission group, so that access to a new packet is allowed on five channels.

Figure 5 shows the central control station when a packet is actually transmitted.
10 is a time chart showing the state of the channel at 20 and the state of the retransmission stack when the earth station 30 receives the data. (In the figure, NC; Non Collision, C;
Collision, N; New Packet, W; Wait channel, number; Indicates channel number. ) Propagation delay time is neglected to simplify the description of the algorithm. First, it is assumed that a collision has occurred in channels 2 and 6 in slot 1. Channels 2 and 6 as retransmission waiting channel groups, and G (1), G (1) shown in FIG.
When G (2) shown in FIG. 4 is sent to the earth station for channel 6, the station that transmitted the packet on channels 2 and 6 determines from the received information that the packet that collided on channel 2 in the next transmission slot. G (1), that is, any one of channels 1 to 3 is selected and transmitted. For the packet colliding on channel 6, G (2), that is, any one of channels 4 to 6, is selected and the packet is retransmitted. In this transmission slot, a new packet can be transmitted to channel 7 and channel 8. Assuming that packets collide in slots 4, 7, and 8 in slot 2, channels 4 and 7 are processed in the same manner as in the first slot, but packets that collide in channel 8 are in the retransmission channel group due to lack of retransmission channels. Is not linked and cannot be processed by the earth station, so one slot WAIT is performed.
In the third slot, a collision occurs in the channel 8, and the channel 8 and the second slot WAIT channel 8 are resolved in the next slot in the same manner as in the first slot.

Next, an example of the first algorithm and the second algorithm will be described.

★ First algorithm Now, Q: the number of all channels, R: the maximum number of groups that can retransmit at the same timing, P: the number of channels that can retransmit new packets, S: the channel used to resolve one collision channel Number.

The quotient of R = [(Q-1) / S) If the number of retransmission waiting channels is G, if G ≧ R ... the number of channels that can be retransmitted simultaneously is R
In this case, the number of channels that can be accessed by a new packet is P = Q−R × SG <R ... The number of channels that can be retransmitted at the same time is G
In this case, the number P of channels that can be accessed by the new packet is P = Q−G × S ★ Second algorithm For example, the order of the smallest channel number of the retransmission waiting channel group and the smallest of the channel group numbers of the retransmission channel group group There is a method of associating with the order.

〔The invention's effect〕

As described above, according to the present invention, it is possible to resolve a collision state by allocating, as necessary, a group of channels that can access a new packet and a group of channels that exclusively transmit an accessible retransmission packet of a retransmission packet. High-speed operation is possible, and there is an effect that a satellite communication system that can realize a high utilization rate and a short waiting time can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a satellite communication network configuration including the present invention, FIG. 2 is a configuration diagram of a central control station 20, FIG. 3 is a configuration diagram of a remote earth station 30, and FIG. FIG. 5 is a time chart showing the state of the channel in the central control station 20 when a packet is actually transmitted and the state of the retransmission stack when the earth station 30 receives the data. It is. 10 ... satellite, 20 ... central control station, 21 ... receiving unit, 22 ...
Collision detection unit, 23: retransmission waiting group detection unit, 24: transmission unit, 30: ground station, 31: retransmission buffer, 32: reception unit, 33: channel selection unit, 34: retransmission Stack unit, 35 ... Transmission unit.

Continuation of the front page (72) Inventor Yoshikuni Onosato RC-1 1-1-1 Kojimacho, Chofu-shi, Tokyo (56) References JP-A-59-198037 (JP, A) JP-A-2-132933 (JP) , A) (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 7/14

Claims (2)

(57) [Claims] 1. A satellite communication method in which a plurality of ground stations perform time-division multiplexed packet communication for random access using a plurality of channels with a central control station via a satellite, wherein the central control station transmits data from the plurality of ground stations. A packet is received for each channel, a collision in each channel in the same reception time slot is detected for each channel, and a retransmission request can be made due to a shortage of retransmission channels in the collision channel group and the previous transmission time slot. There was no pre-stored WA
A retransmission waiting channel group composed of an IT channel group, and a plurality of channels determined by leaving at least one new packet transmission channel from a first algorithm predetermined based on the number of channels in the retransmission waiting channel group. A retransmission channel group group in units of, the retransmission channel group group and the retransmission channel group group are made to correspond to each other from a predetermined second algorithm, and only the corresponding portions are linked to each other, so that the plurality of earth stations Send to
Each of the earth stations receives the retransmission waiting channel group and the retransmission channel group group in which a portion corresponding to the retransmission waiting channel group is linked, and needs to retransmit the received retransmission channel group channel. When the channel group for retransmission is linked to the channel requiring retransmission, one channel in the channel group for retransmission is randomly selected and retransmitted to the central control station, and the retransmission is required. When the channel group for retransmission is not linked to a channel, the retransmission to the central control station is waited until the next channel group for retransmission and the channel group group for retransmission are received from the central control station, and the received retransmission is performed. An earth station that does not require retransmission of a channel in the group of channels for retransmission, A satellite communication method characterized by randomly selecting one channel from among the channels and transmitting a new packet to the central control station. 2. A satellite communication system in which a plurality of ground stations perform time-division multiplexed packet communication of random access using a plurality of channels with a central control station via a satellite, wherein the central control station transmits signals from the plurality of ground stations. A receiving unit that receives a packet for each channel, and a collision detecting unit that detects a collision in each channel in the same reception time slot of a packet transmitted from the ground station received by the receiving unit for each channel. , A previously stored WA that could not request retransmission due to lack of retransmission channels in the previous transmission time slot and the collision channel group detected by the collision detection unit.
For retransmission in units of a plurality of channels determined by leaving at least one new packet transmission channel from the first algorithm predetermined based on the number of channels in the retransmission waiting channel group composed of the IT channel group A channel group group is determined, a channel group group for retransmission and the channel group group for retransmission are associated with each other from a predetermined second algorithm, and a retransmission group detection unit that links only the corresponding portions to each other; A transmitting unit that receives from the detecting unit, and transmits the retransmission waiting channel group and the retransmission channel group group in which a portion corresponding to the retransmission waiting channel group is linked to the plurality of earth stations; A retransmission buffer for receiving and accumulating a new packet from a higher-level device upon receipt of a buffer start signal, Receiving, from a station, the retransmission waiting channel group and the retransmission channel group group in which a portion corresponding to the retransmission waiting channel group is linked, and requires retransmission of a channel in the received retransmission channel group and requires the retransmission. If the retransmission channel group is linked to the channel to be re-transmitted, the channel group in the retransmission channel group is accumulated in a temporary storage area and a stack activation signal is output, and the retransmission channel group is connected to the channel requiring retransmission. When not linking, wait until the next retransmission waiting channel group and the retransmission channel group group are received from the central control station, and when the retransmission of the channel in the received retransmission channel group is not necessary, A retransmission buffer start signal is transmitted, and the remaining channels obtained by reducing the received retransmission channel groups are reduced. A receiving unit that accumulates in a temporary storage area and outputs the stack activation signal, a retransmission stack unit that is activated by the stack activation signal, receives a channel group in the temporary storage area from the reception unit, and accumulates the stack in a stack. A channel selection unit that randomly selects one channel from the channel group that is activated by the retransmission stack unit and stored in the stack; and that selects the data that is activated by the channel selection unit and stored in the retransmission buffer. And a transmission unit for retransmitting to the central control station by using a selected channel.