JPH0771037B2 - Packet transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used for satellite packet communication based on a multiple access system called slotted Aloha system, and indirectly for increasing the transmission amount of each earth station. The present invention relates to a packet transmission device that automatically changes the packet transmission procedure according to the above to prevent deterioration of service quality of packet transmission and enables efficient use of satellite lines.

[Prior Art] FIG. 2 shows a conventional configuration example of a packet transmission device of an earth station which constitutes a satellite packet communication network operated by a multiple access system called an Aloha system with a slot. In the figure, (1) is a packet input terminal for inputting data as a packet, (2) is a packet buffer for temporarily storing packets input from the packet input terminal (1),
(3) is a logical switch for explaining this configuration,
(4) is a first transmission packet input terminal provided in a burst transmitter (5) described later, (5) is a burst transmitter that forms packets into bursts, and transmits the bursts, and (6) is a transmission bucket buffer , (7) is a random delay generator,
(8) is a second transmission packet input terminal provided in the burst transmitter (5), and (9) is a reception confirmation signal (ACK / ▲).
▼) Input terminal.

FIG. 3 shows an example of a satellite packet communication network operated by an earth station having the packet transmitting device of FIG.
This communication network is composed of n slave stations, 1 master station and communication satellites. In the figure, (10), (11) and (12) are slave stations S1, S2 and Sn, respectively. Although not shown in the figure, it is assumed that there are n such slave stations, and these are collectively called a slave station group. Further, (13) is a master station M, and (14) is a communication satellite.

Now, for ease of explanation, it is assumed that the frequencies transmitted by the slave stations to the transponders on the satellite are different from the frequencies transmitted by the master station. That is, the slave stations share one frequency region on the transponder (multiple access to the transponder). The conventional example shown in FIG. 2 will be described assuming that the slotted Aloha system is used as the multiple access system. The description of the transmission of the master station in this case will be omitted because it is not related to the gist of the present invention when the present invention is described.

The slotted Aloha system is a type of time division multiple access system that divides transponders on the time axis and relays radio waves from slave stations that use the same transmission frequency. Therefore, a fixed time segment is set on the commonly used transponders. This one section is called a slot. The conceptual diagram is shown in FIG. In the figure, for the sake of explanation, the slots on the transponder are shown with numbers, but in reality, there is no setting of such numbers for distinguishing individual slots. Each slave station can confirm only the slot delimiter.

Next, a signal transmitted from each slave station to this transponder will be described. A signal (data string) to be transmitted is generated in blocks at each slave station. This one block is called a packet. This packet may be sent from other parts of each slave station, for example, another device on the ground side to which the slave stations are connected, or may be considered to be generated by the slave stations themselves. In addition to the data to be originally transmitted (hereinafter referred to as a message), this packet includes address data indicating the source and destination of this packet, control data for correctly transmitting the packet, and the like.
The bit string forming such a packet is, for example, shift-shift modulated and transmitted from the slave station. At this time, a preamble is further added to the leading edge of the packet in order to accurately demodulate and reproduce the bit string at the receiving station. A so-called auxiliary bit string is added. Thus, one unit of the radio wave finally transmitted from the transmitter by the slave station is called a burst. FIG. 5 shows an example of the bit configuration of burst.

Now, a conventional packet transmission device that executes a burst transmission procedure by the slotted Aloha method will be described in order with reference to FIG. First, the transmission packet is input to the packet buffer (2) through the packet input terminal (1). The packet buffer (2) is a part for temporarily storing a packet input from the packet input terminal (1) when it cannot be immediately sent to the burst transmitter (5). The packet input to the packet buffer (2) is the first one of the burst transmitter (5) when the packet buffer (2) is empty (no packets are accumulated) and the switch (3) is closed. Send packet input terminal (4) and send packet buffer (6)
Entered in. On the other hand, when the switch (3) is open, or when the packet is already stored in the buffer, the packet is also stored. The burst transmitter (5) is composed of a modulation section, an RF section, an antenna, etc. The packet input to the first transmission packet input terminal (4) is shown in FIG. 5, and a preamble is added to this packet. Then, it is immediately transmitted to the communication satellite (14). However, the burst transmitter (5) has a function of finely adjusting the transmission timing of the burst (for a maximum of one slot time), and the burst transmission timing is adjusted so that the burst will fit exactly in the slot on the satellite transponder shown in FIG. Control and send. For example, as shown in FIG. 4, the burst a transmitted from the slave station S1 (10) is just stored in the slot 6 on the transponder. In the figure, the time from the start time of the transmission of the burst a to the leading edge of the slot 6 is the propagation delay time required for the radio wave to reach the transponder from the slave station S1 (10). This carrier delay time is slightly different for each slave station (about 130 msec) to correspond to the distance between the earth station and the satellite, and each station fine-tunes the burst transmission timing according to its propagation delay time. I will send this, but
Description of such a burst synchronization technique is not necessary for explaining the present invention, so that it is omitted and each earth station has a function of arranging a burst at a predetermined position on the transponder. And

The configuration and operation of FIG. 2 are common to the slave stations. now,
Just as a packet was input to the packet input terminal (1) of the slave station S1 (10) and a burst corresponding to this was transmitted to the slot 6, the same applies to the packet input terminal (1) of the slave station S2 (11). The packet is input at the time, and as a result, the slave station S2
If (11) also transmits burst b so that the burst fits in slot 6, these bursts collide on the transponder. In other words, in the slotted Aloha system, when each station transmits a burst,
Since there is only a restriction that the burst can be stored in any of the slots on the transponder and the slot to be used is not specified, when only one burst happens to reach the slot, the burst is normally relayed and the master station M ( However, if two or more bursts arrive in the same slot and a collision occurs, the transmission of those bursts has failed. Then, those bursts that failed to be transmitted are retried. This is called burst retransmission. Next, the procedure of retransmission will be described.

First, in order to perform retransmission, it is necessary to know whether the transmitted burst has succeeded or failed in transmission. In the satellite communication network as shown in FIG. 3, normally, when the master station M (13) confirms the normal reception of the burst, the master station M (13)
From the slave station group S1 (10) to Sn (12). That is, the normally received burst can specify the slave station or the like of the transmission source by examining the address data and control data of the packet included in the burst. Based on this, the master station M (13) sends back the reception confirmation information (hereinafter referred to as ACK) of the burst to the slave station. Each slave station can know from the ACK signal whether the previously transmitted burst has been successfully transmitted. On the contrary, if the transmission fails, it is possible to know the transmission failure by not receiving the expected ACK signal within the predetermined time. This will be expressed here as ▲ ▼. ACK / ▲ ▼ signal is the reception confirmation signal terminal (9)
Through the transmission packet buffer (6).

Now, in FIG. 2, the slave station which has input the packets to the burst transmitter (5) and the transmission packet buffer (6) through the switch (3) according to the command from the transmission packet buffer (6) opens the switch (3), The input of the packet to the burst transmitter (5) and the transmission packet buffer (6) is cut off. Of course, as described above, the packet input from the packet input terminal (1) during this period is accumulated in the packeter buffer (2). The reason for opening the switch (3) is to stop the transmission of the next burst until it is confirmed that the burst transmitted by the burst transmitter (5) has been transmitted correctly. When an ACK signal for the burst is received after the burst is transmitted, the switch (3) is closed and a new packet can be transmitted again. On the other hand, when the ACK signal cannot be received within the predetermined time, that is, in the case of ▼, the same packet as the packet that has failed to be transmitted is retransmitted. Since this packet is stored in the transmission packet buffer (6), the packet is input to the second input terminal (8) of the burst transmitter (5). At this time, the retransmission packet accumulated in the transmission packet buffer (6) is input to the second input terminal (8) after an appropriate delay generated by a random number from the time of confirmation. The reason for adding delay is
This is to reduce the possibility of re-collision caused by bursts that collided being retransmitted from the respective slave stations again at the same time. This random delay is added by the random delay generator (7), and the random numbers generated by each slave station are independent. Of course, ▲ ▼ is AC even for resending
Retransmission is repeated until K is confirmed and an ACK signal is received. The packets in the transmission packet buffer (6) are the same as the packets transmitted by the burst transmitter (5) until the ACK signal is received.

The above situation is shown in FIG. For example, in slot 6
Burst a from S1 (10) and burst b from slave station S2 (11) collide, and as a result, S1 is
Suppose that ▼ a and S2 confirmed ▲ ▼ b. Slave stations S1, S2
In (10) and (11), bursts a ′ and b ′ are retransmitted after the delay of R _a and R _b by the generation of random numbers, respectively, and this succeeds. This success is confirmed by ACKa 'and ACKb', respectively.

The above is the description of the method of the burst transmission procedure by the Aloha method with slot and the operation of the conventional example of the packet transmission device of the earth station which achieves this.

[Problems to be Solved by the Invention]

Since the conventional packet transmission device is configured as described above, if the number of packet transmissions per unit slot of the slave stations in the slotted Aloha system is small, the probability of collision between bursts is low, so most packets are transmitted. Succeeds in the first transmission, but the possibility of collision increases as the number of packet transmissions per unit slot increases. When this collision occurs, the transmission of new packets is stopped until the retransmission is successful, so the packets input during this time are accumulated in the packet buffer one after another, and if there are accumulated packets in the packet buffer, the retransmission is successful. Then, the next packet will be transmitted at the same time. That is, there is a problem in that the collision of bursts promotes an increase in the transmission solubility of packets including retransmissions, which may make it more difficult for the slave stations to successfully transmit bursts.

The present invention has been made to solve the above problems, and is to be used in a satellite communication network operated by a multiple access system based on the Aloha system with slots to perform packet transmission more smoothly. Therefore, it is an object of the present invention to provide a packet transmission device capable of constantly shortening the normal arrival time of packets on average in a line in which the amount of packet transmission per slot fluctuates.

[Means for Solving the Problems]

A packet transmitting apparatus according to the present invention comprises a packet buffer for temporarily accumulating packets input from a packet input terminal, a burst transmitter for forming packets accumulated in the packet buffer into bursts, and transmitting the packets. When a packet is input to the burst transmitter, a transmission packet buffer that temporarily stores the packet, and a packet that is stored in the transmission packet buffer is delayed by a randomly generated time and is retransmitted to the burst transmitter as a retransmission packet. The burst transmitter is provided with a random delay generator for sending, and at the time of packet retransmission due to collision of transmission packets, a transmission reservation request signal corresponding to the packet storage amount of the packet buffer is added to the retransmission packet and retransmitted. The reservation switch assigned to the transmission reservation request signal A signal of packet information and sequentially transmits the packets accumulated in the packet buffer based on the reserved slot information, and the random delay generator generates a packet based on the transmission slot of the retransmission packet and the reserved slot information. A feature is that the transmission slot of the retransmission packet is changed when the throttle already reserved for another station matches.

[Action]

The packet transmission device in the present invention reserves a slot for transmitting bursts corresponding to these packets through a retransmission burst when a packet arrives during a retransmission operation of a collision packet, so that successful retransmission is confirmed,
When the reserved slots are contacted, the packets accumulated in the meantime use the reserved slots and can be efficiently transmitted without collision, preventing long-term packet retention and enabling effective operation of the slots.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, (1) is a packet input terminal for inputting data as a packet, (2) is a packet buffer for temporarily storing the packet input at the packet input terminal (1) as necessary, (3) Is provided for transmitting the packets accumulated in the packet buffer (2), and is a logical switch for explaining this configuration,
(4) is a first transmission packet input terminal provided in the burst transmitter (5), (5) is a burst transmitter for forming packets from the packet buffer (2) into bursts and transmitting the burst packets, (6) Is a transmission packet buffer for accumulating packets for burst retransmission of the burst transmitter (5), (7) is a random delay generator for generating a random delay time for burst retransmission, and (8) is the burst transmission Second transmission packet input terminal provided on the machine (5) for inputting a packet for burst retransmission, (9)
Is the input terminal of the reception confirmation signal (ACK / ▲ ▼ signal),
(18) is a reservation slot information input terminal for inputting a signal of reservation slot information assigned to the transmission reservation request added to the burst retransmission from the burst transmitter (5),
Reference numeral (19) is a signal for notifying the burst transmitter (5) of the packet storage amount provided in the packet buffer (2).

Next, the operation of the apparatus of this embodiment based on the above configuration will be described. The operation upon successful transmission of the burst is the same as in the case of the conventional example of FIG. 2 and is as follows.

The packet input to the packet input terminal (1) is sent to the burst transmitter (5) through the first transmission packet input terminal (4) if the packet buffer (2) is empty and the switch (3) is closed. ), And also to the transmission packet buffer (6) where it is stored. At the same time, the switch (3) is opened. If the packet buffer (2) has already accumulated a packet, or if the switch (3) is open, the packet is also accumulated in the packet buffer (2). The packet input from the first transmission packet input terminal (4) of the burst transmitter (5) is formed into a burst as shown in FIG. 5 in the burst transmitter (5) and is stored in the slot on the transponder earliest. It is sent at the timing. When the transmission is successful, an ACK signal which is a reception confirmation signal is obtained from the receiving station (for example, the master station M (13) in FIG. 3. When the ACK signal is obtained, the transmission packet buffer (6) transmits first. The switch (3) is closed at the same time that the accumulated packets are stopped, and if one is already accumulated in the packet buffer (2), one of the accumulated packets (normally It is input again to the burst transmitter (5) and the transmission packet buffer (6) through the switch (3) in the order in which they are transmitted and transmitted.

Now, if the transmitted burst collides with the burst from another station on the transponder and transmission fails, after a predetermined time passes through the input terminal (9), ▼ is determined. When ▲ ▼ is determined, the same packet stored in the transmission packet buffer (6) that failed to be transmitted is delayed by the time given by the random delay generator (7), and then the burst transmitter (5) stores the same packet. It is input to the second transmission packet input terminal (8). The burst transmitter (5) adds the preamplifier shown in FIG. 5 to the retransmitted packet and immediately transmits it at the timing synchronized with the slot. At this time, it is obtained and accumulated from the output terminal (19) of the packet buffer (2). The number of packets stored in the packet buffer (2) is notified by the packet number information signal, and reservation request information for requesting slots for transmitting the number of packets is written as data in a predetermined bit portion in the preamble. . This information is updated with new information from the output terminal (19) at each retransmission. When the burst including the reservation request information is successfully retransmitted and received by the master station, the master station M (13) allocates a specific slot on the transponder to the reservation by the reservation request information and assigns the reserved slot information to the slave station group. Contact S1 (10) ~ Sn (12). This allocation information is communicated to the packet transmission device through the reserved slot information terminal (18). Then, the packet transmission device allocated with the reserved slots transmits the packets requested at the time of the reservation request from the burst transmitter (5) one after another through the switch (3) and the burst transmitter (4) so as to fit in the slot. . Then, when the transmission of the predetermined packet requested at the time of the reservation request is completed, the state returns to the initial state of transmitting the packet in the packet buffer (2) to an arbitrary slot.

Next, an example of a reserved slot allocation method and the like related to the execution of this apparatus will be described.

Since this method allocates reserved slots, it is necessary to be able to specify the slot unlike the conventional method. The concept of normal frames is used to identify slots. A frame is composed of a set of slots and repeats at regular intervals. FIG. 6 shows the relationship between frames and slots.
In the example shown in the figure, a frame is composed of 64 slots, and numbers are sequentially assigned to the slots from the beginning of the frame. On the other hand, in the figure, the frames are also named as frame 1 and frame 2, but this is for explanation,
Actually, it is not necessary to specify individual frames. next,
An example of reservation request and allocation method will be shown.

Now, the horizontal axis of the slot / frame diagram of FIG. 6 is the time axis of the transponder converted to the earth station,
That is, it is assumed that when the earth station transmits a radio wave in slot 1 of frame 1 in the figure, the radio wave is stored in frame 1 and slot 1 on the transponder.

For example, it is assumed that the slave station S1 (10) in FIG. 3 transmits a retransmission packet using slot 1 of the frame, requests a reservation slot for 2 slots accordingly, and assumes that the retransmission is successful. . In the figure, this burst reaches the master station M (13) after about 260 msec (twice the propagation delay time to the communication satellite is 130 msec) via the transponder.
On the other hand, the slave station S2 (11) uses the slot 64 of frame 1 to make a request for reserved slots for 3 slots, and it is assumed that this also succeeds in transmission. This burst indicated by b in the figure also reaches the master station after about 260 msec. That is, all of the reservation request information, which is transmitted in the slot of frame 1 and has been successfully transmitted, arrives by time ta of the master station M (13).
The master station M (13) allocates slots to these, based on the reservation request information generated in the frame 1 received from the time ta to the time tb. If Tp in the figure is the time required for the master station M (13) to perform this process, the master station M (13)
Transmits slot allocation information to the slave station group after time Tp from time tb. It is assumed that the frame period is set so that the frame arrives at least at the beginning of the frame 3. That is, the reservation requested in frame 1 is assigned by the beginning of frame 3 and the information is communicated to the slave station group. For example, in the figure, slots 3 and 4 of frame 3 and slots 60, 61 and 62 are reserved for the slave stations S1 (10) and S2 (11), respectively. Of course, these reservation slot information is input to the bucket transmitter from the reservation slot information input terminals (18) of all slave stations in FIG. The slave stations (here, the slave stations S1 (10) and S2 (11)) to which the reserved slots are allocated transmit the reservation target of the accumulated packet using these slots. The transmission of the generated burst is executed according to the above method after removing the reserved slot, and when the reserved slot is coincident with the result determined by the random delay generator (7) for the transmission slot of the retransmission packet in frame 2. Changes the transmission slot of the retransmission packet, so the reservation slot information is also input to the random delay generator (7).

The above is the description of the operation of FIG. 1 relating to an example of the present invention.

In the above embodiment, the length of the packet input to the packet input terminal (1) is set to a fixed length corresponding to one burst length, but if it is not a fixed length, that is, only the transmission time point is synchronized with any of the slots. However, the present invention can be similarly applied to the case of handling packets of various lengths that occupy several slots for long packets and transmit.
Of course, regarding the reservation of the storage packet in this case, it is necessary to use the occupied slot number as the reservation request information instead of the packet number.

〔The invention's effect〕

As described above, according to the present invention, in the packet transmitting device of the satellite communication earth station operated by the multiple access method called the slotted Aloha method, it is checked whether or not there is a stored packet when the burst is retransmitted, Sometimes the preamble part of the retransmission burst is used to receive the reserved allocation of the transmission slot for the accumulated packet, and if the retransmission packet is successfully transmitted, the accumulated packet during the retransmission procedure is smoothly transmitted using the reserved slot. Therefore, it is possible to switch to reservation mode at the time of packet retransmission due to collision of transmitted packets so that the normal arrival time of packets is always short on average for the line where the amount of packet transmission per slot fluctuates. , In the line condition where the packet transmission amount per slot is small, Packet same collision is also an effect that transmission of efficient packet can perform the packet transmission amount is large line status per slot that occurs frequently.

[Brief description of drawings]

FIG. 1 is a block diagram showing a packet transmitter according to an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional packet transmitter, and FIG. 3 is a satellite communication network for explaining the present invention. As an example, FIG. 4 is a diagram showing a state of slots for explaining the Aloha system with slots, FIG. 5 is a diagram showing a bit configuration example of a burst transmitted by a packet transmission device, and FIG. 6 is a slot reservation request, allocation, etc. It is a figure explaining the time relationship of. (1) is a packet input terminal, (2) is a packet buffer, (5) is a burst transmitter, (6) is a transmission packet buffer, (7) is a random delay generator, and (9) is a reception confirmation signal input terminal. , (18) is an input terminal for reserved slot information, and (19) is an output terminal for accumulated packet amount. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A packet buffer for temporarily storing packets input from a packet input terminal, a burst transmitter for forming packets stored in the packet buffer into bursts, and a burst transmitter for transmitting the packets from the packet buffer. When a packet is input to the transmission packet buffer, it temporarily stores the packet, and a random delay that delays the packet stored in the transmission packet buffer for a randomly generated time and sends it as a retransmission packet to the burst transmitter. A generator is provided, the burst transmitter adds a transmission reservation request signal corresponding to the packet storage amount of the packet buffer to a retransmission packet and retransmits the packet when the packet is retransmitted due to collision of transmission packets,
The signal of the reservation slot information assigned to this transmission reservation request signal is received, and the packets accumulated in the packet buffer are sequentially transmitted based on the reservation slot information. And a slot already reserved for another station based on the reserved slot information, the transmission slot of the retransmission packet is changed.