JPH0693643B2 - Communication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is a broadcast type in which a master station and a plurality of slave stations are connected via the same transmission medium, and communication from the master station to all slave stations is possible. The present invention relates to a multi-point type communication system configured by using the channel and multiple access type channels capable of communicating from all child stations to the parent station.

(Problems of Prior Art) In a multipoint type communication method, a polling method in which a master station sequentially sends a transmission command to a slave station and the slave station sends information according to the command is well known. However, in this method, the master station sends polling to the slave station and cannot poll other slave stations until the reply from the slave station that received it arrives, so it was applied to systems with large transmission delay such as satellite communication. In this case, there arises a problem that the use efficiency of the transmission line is significantly reduced.

On the other hand, when the slave station receives a transmission command from the master station, the reservation information is sent at the same time as the data. If there is no data, only the reservation information is notified in advance so that the slave station can send a reply to the transmission command. If transmission is possible before receiving, it is possible to improve the above-mentioned problems and realize a communication system in which the transmission path is highly used.

However, when a normal packet to be transmitted is a single packet, a reservation is made to send this as well, and the packet is sent with a transmission command from the master station, which is extremely inefficient.
Also, when trying to improve this, when receiving a transmission command,
If only a single packet can be sent without making a reservation in advance, the cycle of the transmission command becomes very long and the efficiency of use of the transmission path decreases.

(Object of the Invention) An object of the present invention is to enable a single plurality of packets to be transmitted by a certain plurality of slave stations without making a reservation in advance for a transmission command from a master station, thereby enabling a single packet to be transmitted. It is to reduce the waiting time for sending.

(Structure of the Invention) According to the present invention, a master station and a plurality of slave stations are connected via the same transmission medium, and each slave station multiplexes an information frame including reservation information and transmission information in synchronization with an instruction from the master station. In the communication method of transmitting to the access channel, the master station transmits information to the broadcast channel to instruct each slave station to transmit based on the reservation information obtained from the frame received from each slave station,
If multiple slave stations are divided into certain groups and there is no reservation, the master station issues a transmission instruction to each group in sequence at a single packet length interval, and two or more stations within the group simultaneously transmit a single packet length information frame. When a master station detects a collision, the communication system is characterized by sequentially instructing each slave station in the group to transmit a single packet length information frame.

(Embodiment) FIG. 4 is an example of a communication form to which the communication system of the present invention is applied. In the figure, one master station and a plurality of slave stations can communicate with each other via one satellite. Usually, the master station uses a larger antenna than the slave station to transmit a high power signal and receive a low power signal so that the slave station can transmit and receive with a small antenna. Therefore, the slave stations cannot communicate with each other, and there are multiple access channels from the slave stations to the master station (hereinafter referred to as uplink) and broadcast channels from the master station to the slave stations (hereinafter referred to as downlink). . In this example, both lines have a line speed of 56 Kbps.

FIG. 5 is a diagram showing an uplink frame format in this embodiment. The frame is an information frame only. In the figure, the guard time is a non-transmission time for adjusting the transmissions from the respective slave stations so that they do not overlap due to timing deviation and the like, and consists of 4 bits. The preamble is a section for transmitting a signal for synchronizing timing etc. on the receiving side and consists of 44 bits, and the address is a section for transmitting the address of the own station and consists of 16 bits,
The control is a section that shows control information such as whether or not there is a reservation, the length of the reservation, etc., and consists of 16 bits.The FCS is a redundant bit string for detecting errors on the receiving side, consisting of 16 bits. A section of data is added. The packet length is fixed.

FIG. 6 is a diagram showing how to use the downlink. In the downlink, the channel is divided into an access control channel and an information transmission channel by time division multiplexing. Specifically, as shown in the figure, a channel for access control is cut out at a rate of 1 bit per 8 bits. 49Kb for the remaining 7 bits
Used as a channel for sending ps information. On the other hand, the access channels are further grouped into 12-bit units to form one confirmation frame. The confirmation frame includes a 1-bit synchronization bit, an 8-bit address part, a 2-bit control part, and a 1-bit parity bit. The synchronization bit is used to extract 1 bit from 8 bits in TDM and to secure the frame synchronization of the access channel. Since this sync bit is added once every 12 bits in the access channel, the sync bit appears once every 96 bits in the original 56 Kbps line. This is the same as the frame length when there is no transmission information on the uplink, and the information frame is also an integral multiple of this. Therefore, if each slave station transmits a frame at an appropriate timing in synchronization with the downlink synchronization bit, the frames can be transmitted without collision. The address part indicates a destination address and a group address. Each slave station receives the frame when the address is its own address or the group address to which the own station belongs, and the frame is decoded by the control part. Do. Reservation information of a frame to be transmitted next from the slave station is shown in the control section.

FIG. 1 is a sequence diagram showing a transmission state of each frame in the present invention. In the figure, the flow of time is shown on the right side. The arrows indicate the transmission status of each frame. Di (k) is an information frame sent from the slave station at address i containing reservation information for reserving k slots, and A (i) is It is a confirmation frame sent to the slave station of address i.

PF (Y) is a command for accelerating transmission, and when the slave station whose address or group address is Y receives PF (Y), it can transmit a single packet. If there are no packets to send, nothing is sent.

Here, as an example, the number of slave stations is 8 and the address is 1
Group addresses G1, G2, G3, G4 with integers from 1 to 8
On the other hand, the first station and the second station, the third station and the fourth station, the fifth station and the sixth station, and the seventh station and the eighth station correspond to each other.

In the initial state, there is no reservation at all, so first, a promotion frame that promotes the transmission of a single packet at the packet length interval from the master station.
PF is sent. Each slave station transmits one packet when the destination address of the reservation promotion frame is a packet to be transmitted at its own address or a group address to which its own station belongs. If the number of packets to be transmitted is several, the number of remaining packets is written in the reservation information field of the packet to be transmitted.

In the example of FIG. 1, when the promotion frame PF (G3) is received, the fifth station belonging to the group address G2 transmits the packet,
And reserved 1 packet. If the master station has completed the transmission of the previous confirmation frame at that point, it immediately transmits the confirmation frame with the end before the transmission. In this example, since the reservation was the first time, the confirmation frame A (5) is immediately transmitted. After transmitting the confirmation frame, the master station transmits the next confirmation frame or the prompting frame, which is transmitted at intervals of the number of reserved packets. As a result, the reserved packet does not collide. This is because the prompt frame arrives at each station when the packet transmission is completed.

By the way, as shown in the example, packets may collide. It has packets to be transmitted to the third and fourth stations that have received the acceleration frame PF (G2), and simultaneously transmits them to cause a collision. When the master station detects a collision, it transmits a prompt frame to each of the predictive stations. In the example, first, the promotion frame PF (3) is transmitted to the third station, and then the promotion frame PF (4) is transmitted to prevent collision again. The same is performed thereafter.

As can be seen from this example, in the present invention, when there is only a single packet, it can be sent without reservation, the polling cycle is short, and the transmission waiting time is greatly shortened.

Next, the operations of the prediction station and the master station in the present invention will be described. Second
The figure is an example of a preliminary station. In the figure, a downlink signal is input from terminal 1. The signal input from the terminal 1 is received by the receiver 5 to obtain a received signal. The received signal is input to the sync detection circuit 7 and the sync bit generated once every 96 bits is detected. A clock that is seven times that of the synchronization information is generated and supplied to the demultiplexing circuit 6. The demultiplexing circuit 6 demultiplexes the received signal into a 49 Kbps information sequence and a 7 Kbps control frame sequence based on the synchronous clock, the information sequence is output from the terminal 2, and the control frame is supplied to the address detection circuit 9. . The control frames are the prompt frame and the confirmation frame. Address detection circuit 9
Then, the address portion is detected based on the synchronization information supplied from the circuit 7, and it is judged whether the contents including the group address are addressed to the own station, and those other than those addressed to the own station are discarded. When the frame addressed to the own station is received, the control signal decoding circuit 10 decodes the control unit and determines whether the frame is the promotion frame or the confirmation frame. The amount of information input from the terminal 3 to the buffer circuit 12 is written in the reservation information storage circuit 11. When the signal from the circuit 10 indicates the promotion frame, the entire amount -1 stored in the buffer is used as the reservation information,
When the confirmation frame is designated, the remaining amount of the previously reserved amount is used as the reservation information. The frame creating circuit 13 creates an information frame based on the output of the control signal decoding circuit 10 as follows. When the output of the control signal decoding circuit 10 indicates the promotion frame, one packet is taken out from the buffer circuit 12 and the reservation information from the reservation information storage circuit 11 is added to this packet to form an information frame. When the output of the control signal decoding circuit 10 indicates a confirmation frame, the previously reserved amount and reservation information are obtained from the reservation information storage circuit 11, and the packet of the previously reserved amount is taken out from the buffer circuit 12, and the reservation information is stored in this. To add an information frame. If the buffer circuit 12
If there are no packets, nothing is sent. The reservation frame is created using the reservation information input from the reservation information storage circuit 11, and the information frame is created using the reservation information and the information stored in the buffer. The created frame is converted by the transmitter 14 into a transmission waveform and transmitted. The timing at this time is determined as follows. Based on the synchronization signal output from the synchronization detection circuit 7, the delay circuit 8 outputs the transmission timing information after a predetermined delay if the synchronization signal is to be received by the preliminarily station. The frame is transmitted based on this timing information.

Next, the operation of the master station will be described with reference to FIG. The uplink signal is input from the terminal 101 and received by the receiver 105. The receiver 105 performs timing detection using the preamble, detection of the demodulation carrier phase, etc., and outputs the frame from which the preamble has been removed. The output frame is checked by the frame decoding circuit 106 for FCS, the transmission address detection reservation information is detected, and the original information is output through the terminal 102. As a result of FCS check,
The decrypted transmission address and reservation information are the address storage circuit
111 and the transmission timing detection circuit 107 are input. The transmission timing detection circuit 107 calculates the timing of transmitting the confirmation frame based on the reservation information. The frame creation circuit 108 creates a control frame using the reservation information and the output address of the address storage circuit 111 at the designated timing. The address storage circuit 111 stores the address of the slave station and the group address. When the output of the frame decoding circuit 106 indicates that there is no reservation, the group addresses are sequentially output to the frame creating circuit 108, and if there is a reservation, Output address of received frame, if
If the FCS check shows that it is wrong, it is determined that a collision has occurred, and the addresses of the slave stations belonging to the group address output at the time before the propagation delay time from the present are sequentially output. In the multiplexing circuit 109, the transmission information input from the terminal 103 is multiplexed at a rate of 1 bit per 8 bits. The multiplexed bit string is converted into a transmission waveform by the transmitter 110 and transmitted to the downlink via the terminal 104.

(Effect of the Invention) As described above, according to the present invention, when a slave station has only a single packet, it can be sent without reservation, the polling cycle is short, and the transmission waiting time is greatly shortened. I will provide a.

[Brief description of drawings]

FIG. 1 is a sequence diagram showing a frame transmission state in the communication system of the present invention, FIG. 2 is a diagram showing an embodiment of a communication device of a slave station of the present invention, and FIG. 3 is a communication of a master station of the present invention. FIG. 4 is a diagram showing an embodiment of an apparatus, FIG. 4 is a diagram showing an example of a communication form to which the present invention is applied, FIG. 5 is a diagram showing a frame format of a multiple access channel, and FIG. 6 is a transmission form of a broadcast type channel. FIG. In the figure, 5 and 105 are receivers, 14 and 110 are transmitters, 6 is a demultiplexing circuit, 7 is a synchronization detection circuit, 8 is a delay circuit, 9 is an address detection circuit, and 10 is a control signal code. Reference numeral 11 is a reservation information storage circuit, 12 is a buffer circuit, 13 and 108 are frame creating circuits, 106 is a frame decoding circuit, 107 is a frame timing detection circuit, and 109 is a multiplexing circuit. And 111 is an address storage circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumio Akashi 5-33-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (56) References JP-A-52-60516 (JP, A) JP-A-SHO 57-139898 (JP, A)

Claims (1)

[Claims] 1. A master station and a plurality of slave stations are connected through the same transmission medium, and each slave station synchronizes an information frame containing reservation information and transmission information to a multiple access channel in synchronization with an instruction from the master station. In a communication system in which the master station transmits information to the broadcast channel to instruct each slave station to transmit based on the reservation information obtained from the frame received from each slave station, a plurality of slave stations are grouped into a certain group. If there is no reservation, the master station sequentially sends a transmission instruction to each group at single packet length intervals, and two or more stations in the group simultaneously transmit single packet length information frames, and the master station When a collision is detected, a communication method characterized by sequentially instructing each slave station in the group to transmit a single packet length information frame.