JP3003406B2 - Packet 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 packet communication system, and more particularly to an idle signal (IS) indicating an idle communication channel when three or more terminals share one communication channel for data communication. ISMA (I
dle Signal Multiple Acces
and s) a packet communication system.

[0002]

2. Description of the Related Art In general, in packet communication, control information such as a destination, an attribute of data, a data length, and a serial number is added to data to be transmitted, and transmitted as a set of burst data. In addition, when there is a communication request, each terminal station accesses a communication channel in order to transmit data on a time slot or a frame using an arbitrary time or a synchronized system clock as a minimum unit.

On the other hand, in non-packet communication, a plurality of communication channels are provided, and only when a communication request is made from a terminal station is allocated to a terminal station requesting an empty channel under control of, for example, a central station of the system. Therefore, the terminal station occupies the communication channel from the time when the communication request of the terminal station is accepted until the communication disconnection request is issued by the terminal station.

[0004] In addition, many wireless systems using the packet communication system are applied to satellite communications, and the first to be put into practical use is a computer network called the Aloha System of the University of Hawaii, USA. The access protocol used for packet communication has been well studied in the last 15 years and many schemes have been proposed. Basically, Aloha system and CSMA (Carrier Sen)
se Multiple Access) system. The maximum throughput of the Aloha method is 0.184 for the pure Aloha method, and the maximum throughput is 0.18 for the slotted Aloha method.
363, which is a low value. The CSMA system has been proposed to improve the throughput of the Aloha system, in which the transmission distance between the farthest terminal pair is a packet length (transmission time).
Can significantly improve the throughput when it is sufficiently small. There are many types of CSMA systems. Among them, the non-pe
In the resistive CSMA system, the signal propagation time between the farthest terminal pair is 0.001 which is a value a standardized by the packet length.
In this case, it is 0.938. The CSMA system generally has a large throughput, but the problem is that the assumption that all terminal pairs can observe each other's transmission becomes a problem. When this condition is not satisfied, the characteristics deteriorate rapidly. This problem is called a hidden terminal problem, and is particularly problematic in land mobile communications. One way to solve this problem is to use I
There is an SMA method.

Next, the conventional ISMA system will be described with reference to a time chart shown in FIG. In the ISMA system,
A central station capable of communicating with all terminals 1 to M is provided. The central station always monitors the communication channel, and when the communication channel is free, the short IS signal IS1-I
Send S1N. The terminal desiring transmission transmits packet data immediately after the IS is observed. On the other hand, after transmitting one IS, the central station transmits the next IS if no packet transmission from any terminal is observed even if the round trip time a to the farthest terminal elapses. On the other hand, when a packet (for example, packet 1) is observed, the transmission of the next IS
Send The throughput of this system is given by equation (1).

S = ge− ^g / (1 + a + be− ^g ) (1) where b is the length of IS and g is the traffic per IS. This equation shows that when b = 0, slott
It matches the throughput of ed non-persistent CSMA. From this equation, it can be seen that if the length b of the IS is about the same as a, the CSMA throughput does not significantly deteriorate.

Next, FIG. 5 shows a configuration diagram of a conventional system using the ISMA system. FIG. 6A shows an example of the configuration of a packet and an idle signal of the conventional system. 6 (b) shows a signal format of an idle signal transmitted from the central office. FIG.
In (a), the preamble is a signal used for reproducing the clock on the receiving side, and usually an alternating signal of "1" and "0" is sent. The data attribute is a signal for discriminating whether the signal included in the user data section is information of the connected terminal or control information such as an ACK signal returned from the receiving terminal to the transmitting terminal when data is correctly received. The transmission address and the reception address are numbers assigned to each terminal station in the system. The transmission terminal station multiplexes its own number into the transmission address, and multiplexes the destination number into the reception address. The error control is control information for checking whether packet transmission has been performed correctly. The preamble of FIG. 6B is a signal for satisfying the same function as the preamble of FIG. 6A, and the header is a signal indicating the end of the preamble and indicating that a packet may be transmitted thereafter.

FIG. 5 shows a packet communication system in which one central station 500 and M terminal stations 510 to 520 are connected by a radio frequency signal. The central office 500 includes an antenna 501, a receiver 502, and a packet detection device 50.
3. IS generator 505, multiplexer 506, transmitter 5
07. The terminal stations 1 to M are an antenna 511, a receiver 512, an IS control device 513, a retransmission control device 514,
It comprises an input / output controller 515, a packet controller 516, and a transmitter 517. The central station receiver 502 receives radio waves from the terminal stations, converts the radio frequency signals from the antennas into baseband signals by frequency conversion and demodulation operations, and performs packet control from the terminal stations by the packet detection device 503. Devices 516 and 526, IS controller 51
It has a function of receiving 3,523 data. Therefore, the packet detection device 503 of the central office 500 monitors the received data, detects whether or not the speech channel is currently used, and sends the result to the IS generation device 505. Based on this information, the IS generator 505 generates an IS signal and sends it to the multiplexer 506 when the communication channel is not used. The multiplexing device 506 multiplexes the IS signal and the header to generate an IS signal and sends it to the transmitter 507.

On the other hand, the input / output device 515 of the terminal station 510
A device that interfaces with a data terminal device (not shown), converts a signal from the terminal into a signal suitable for signal processing in the terminal station, and sends the signal to the packet control device 516.
The reverse operation is also performed. That is, the packet control device 51
6, in the up direction, receiving terminal data from the input / output device 515, assembling a packet according to the format shown in FIG.
In accordance with the information from, the operation of sending the packet to the transmitter 517 with the probability p only when the channel is free is performed, and in the case where the packet is not correctly received by the opposite terminal due to the collision, the retransmission control of the assembled packet is performed. Instruct device 514 to store the send packet. The same operation is performed when a packet whose transmission has failed in the past is sent from the retransmission control device 514. In the downlink direction, it is determined from the data attribute signal of the baseband signal from the receiver 512 whether the received data is user data or ACK information. If the data is user data, it is checked whether or not the packet has been correctly received by the error control information. When it is correct, this is separated and the input / output device 5
Pass to 15. If the data attribute signal is ACK information, it is determined that the previously transmitted packet has been correctly received, and the fact is transmitted to the retransmission control device 514 to erase the stored previous packet information. Command. I
The S control device 513 decodes the baseband signal from the receiver 512 and, if it is an IS signal from the central office, separates the IS signal of the head information in FIG. The transmission timing is generated, and the packet controller 516 is notified that the communication channel is currently idle. The retransmission control device 514 is the packet control device 51
6 receives the same information as the packet sent to the transmitter 517 from the packet control device 516, and stores it until ACK information for the packet from the partner terminal station is received. Also, when the packet is transmitted by the packet control device 516 and the other terminal receives the packet correctly, the ACK information to be returned is returned even if a sufficient time has passed to return the ACK information. Determines that the packet transmission has failed, and starts a retransmission procedure. The above is the function of each component of the conventional system employing the ISMA system. M terminal stations (520 and the like) having the same function as the terminal station 510 are wirelessly connected to the central station 500.

Next, how the conventional central station and terminal station of the ISMA system operate will be described with reference to the flowchart of FIG. FIG. 8A is a flowchart showing the operation of the central office. The central station always detects whether the communication channel is free or busy, and if it is free, broadcasts the IS signal shown in FIG. 6 (b) to each terminal station, and if the communication channel is currently free. Notify that it is in a state. After sending the IS signal, the signal is again transmitted for a fixed time a determined by the sum of the round-trip propagation delay time to the farthest terminal and the signal processing time of the hardware and software at the central station transmitter and each terminal. The communication channel is monitored to determine whether a packet has been transmitted from the terminal station. If no packet is detected, an IS signal is sent again to repeat monitoring of the communication channel (see FIG. 7). When a packet is detected, the packet is received and the packet is relayed toward the terminal station in the down direction. After relaying the packet, an IS signal is immediately sent to continue monitoring the communication channel. FIG. 8B is a flowchart showing the operation of the terminal station. The terminal station constantly monitors whether there is a communication request from the terminal, and when there is a communication request, prepares to assemble a packet into a predetermined format and transmit it. (However, if the buffer storage device in the terminal station is full, a new communication request is rejected.) When the preparation for transmitting the packet is completed, the terminal station waits for an IS signal from the central station. When the IS signal is received, the packet transmission is performed with a probability p, and the transmission of the packet is postponed with a probability 1-p.
When a packet is transmitted, it is determined whether or not the packet has been correctly received by the other terminal. If the packet has not been correctly received, a retransmission procedure is started, and an IS signal is awaited for an opportunity to transmit the packet again. . If it is determined that the packet has been correctly received, the process returns to a state of waiting for a new communication request from the terminal. Here, there are various methods for determining whether or not a packet has been correctly received. A commonly used method is that when the receiving terminal described in FIG.
There is a method of returning ACK information to the transmitting terminal. As a method of returning an ACK, there is a method of assembling a packet so as to send ordinary user data and identifying it by data attribute information, a method of assigning a communication channel dedicated to ACK separately from a communication channel for information transmission, and the like.

Next, a time-series flow of signals when operated according to the above-described flow will be described with reference to a time chart of FIG. In a system in which M terminal stations communicate with each other via one central office, the central office may use IS signals IS1, IS2, and IS2 when the communication channel is idle.
I43 is sequentially transmitted. This IS signal has a length of b and arrives at the terminal station M, which is the farthest terminal station, after a lapse of time a / 2. Terminal station 1 receives IS2 and then IS3
A transmission request for a packet has been generated before the packet is received, and the packet 1 is transmitted to the central office immediately after receiving the IS3. The central station receives the packet 1 after a certain propagation delay time (smaller than a) and relays the packet 1 in the downstream direction. Also, the transmission of the IS signal is stopped at the central office while receiving and relaying the packet. Immediately after the relay is completed, the IS signals IS4 to IS7 are transmitted again. In terminal M, I
A packet transmission request occurs between the time when S6 is received and the time when IS7 is received, and immediately after IS7 is received, packet M is transmitted to the central office. The central office relays the packet M in the same manner as when receiving the packet 1, and transmits the IS signals IS8, IS9... Again immediately after the relay is completed.

The above is the operation of the conventional packet communication system using the ISMA system.

[0013]

SUMMARY OF THE INVENTION The above-mentioned conventional ISM
In the packet communication system using the A method, since the central station receives a packet from the first terminal station and does not transmit an IS signal while relaying the packet to the other terminal station, the terminal station having another packet transmission request waits. State and no data collision occurs. However, since the central station does not instruct the plurality of terminal stations in particular the control signals such as the order of data transmission right and priority processing to the plurality of terminal stations, data collision between the terminal stations and deterioration of throughput due to data retransmission are caused. There are drawbacks. That is, in the conventional ISMA system, when a packet transmission request occurs at a plurality of terminal stations during a continuous IS signal, each terminal station may transmit a packet at the same time. Inevitable. The method of transmitting with a probability p when having a transmission packet and suspending the transmission with a probability of 1-p is to reduce the above-mentioned probability of occurrence of collision, but it is basically possible to eliminate collision. Absent. Therefore, it is good if the traffic including retransmission packets is sufficiently smaller than the maximum throughput of the channel. However, if the communication requests from each terminal temporarily increase and as a result of frequent collisions, May increase rapidly, and eventually a new communication request may not be accepted. This means that the traffic g including retransmission in equation (1)
G = (1 + a + be− ^g ) / (1 + a + b) (2) The maximum throughput is obtained when g satisfies g in Expression (2). When g further increases, the traffic due to retransmission increases rapidly, This means that the throughput will eventually become zero. Therefore, the conventional ISMA method has a disadvantage that the system becomes unstable when the traffic temporarily exceeds the allowable value.

An object of the present invention is to provide a packet communication system in which the system does not become unstable even when the traffic temporarily exceeds the allowable value.

[0015]

According to the packet communication system of the present invention, one central station and a plurality of terminal stations wirelessly connected share one communication channel and the central station has an idle communication channel. During a predetermined period, an idle signal is simultaneously transmitted to all of the plurality of terminal stations, and any one of the terminal stations obtains a packet data transmission right, relays the central station, and transmits a desired terminal station. In an ISMA-based packet communication system in which the central station stops sending idle signals until the central station stops transmitting idle data, when the central station terminates packet data relay by any one of the terminal stations, It has means for immediately transmitting a polling signal to all of the other terminal stations in order to give a packet data transmission right.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a system showing one embodiment of the present invention,
FIG. 2 is a signal format diagram of the present embodiment. FIG.
(B) shows a configuration example of a format in which a polling signal newly provided in the present embodiment and a conventional idle signal are transmitted from the central station to the terminal station in a procedure described later. Here, FIG.
In the information of each part in (a), the preamble is a signal used for clock recovery on the receiving side, and an alternating signal of "1" and "0" is normally sent. The data attribute indicates whether the signal included in the user data section is information on the connected terminal, or whether the AC is transmitted from the receiving terminal to the transmitting terminal when data is correctly received.
This signal is used to determine whether the information is control information such as a K signal. The transmission address and the reception address are numbers assigned to each terminal station in the system. The transmission terminal station multiplexes its own number into the transmission address, and multiplexes the destination number into the reception address. The error control is control information for checking whether packet transmission has been performed correctly. FIG.
The preamble of (b) is a signal for satisfying the same function as the preamble of FIG. The idle or polling signal is an IS signal similar to the conventional one in the ISMA mode and a specific pattern such as all "0" is multiplexed. In the polling mode, M terminal stations are sequentially assigned to each terminal. Station numbers are multiplexed. That is, a signal for giving a packet transmission right is transmitted for each terminal station. FIG. 1 illustrates a packet communication system in which one central station 100 and M terminal stations 110 to 120 are connected by a radio frequency signal. In FIG. 1, reference numeral 101 denotes antennas 111 and 121 at the central office, and antennas at terminal offices. Reference numeral 107 denotes a transmitter at the central station, and 117 and 127 denote transmitters at the terminal, which are a multiplexer 106 and packet controllers 116 and 12 respectively.
6 has a function of modulating the baseband signal from the base station 6, converting the baseband signal into a radio frequency signal, and transmitting the signal to the antenna. 102 is a receiver of the central office, 110 and 120 are receivers of the terminal stations, and converts a radio frequency signal from an antenna into a baseband signal by a frequency conversion and demodulation operation, respectively. 116 and 12
6. It has a function of sending to the IS / PL control devices 113 and 123. The packet detection device 103 of the central office 100 monitors the received data, detects whether the traffic channel is currently used, and compares the result with the collision detection device 104 and the IS.
/ PL generation device 105. The collision detection device 104 waits for ACK information from the receiving terminal after a certain packet has been transmitted.
If the ACK information is not detected even after a sufficient time has passed to return the CK information, it is determined that a packet collision has occurred, and the fact is notified to the IS / PL generation device 105.
In the IS / PL generation device 105, the packet detection device 103
When the system is in the ISMA mode and the communication channel is not used, a preamble signal is generated and transmitted to the multiplexer 106 based on the information from When the system is in the polling mode and the communication channel is not used, the multiplexing device 10
Send to 6. Further, based on the information from the collision detection device 104, when it is determined that a collision has occurred, the system is controlled so as to immediately shift to the polling mode, and a preamble signal and a terminal number are generated. , To the multiplexer 106. In the multiplexer 106, I
In the SMA mode, the IS signal from the IS / PL generation device 105 (specifically, the alternating signal of "0" and "1" in FIG. 6B) and the header in FIG. And sends it to the transmitter 107. In the polling mode, a PL signal, which is a polling signal obtained by multiplexing the terminal number with the preamble signal from the IS / PL generation device 105, is generated and transmitted to the transmitter 107.

Next, the input / output device 115 of the terminal station 110
A device that interfaces with a data terminal device (not shown), converts a signal from the terminal into a signal suitable for signal processing in the terminal station, and sends the signal to the packet control device 116.
The reverse operation is also performed. In the uplink direction, the packet control device 116 receives terminal data from the input / output device 115, assembles a packet according to the format shown in FIG. 2A, and, in accordance with information from the IS / PL control device 105, When the channel is free in the ISMA mode, the packet is sent to the transmitter 107 with a probability p. In the polling mode, if the terminal number of the PL signal sent from the central station is addressed to the own station, In the case where the packet is not correctly received by the partner terminal due to a collision or a transmission line error, the assembled packet is transmitted to the retransmission control device 114 and the packet is stored. Command. The same operation is performed when a packet whose transmission has failed in the past is sent from the retransmission control device 114. In the downlink direction, it is determined from the data attribute signal of the baseband signal from the receiver 112 whether the received data is user data or ACK information. If the received data is user data, it is checked whether or not the packet has been correctly received by the error control information. If it is correct, it is separated and passed to the input / output device 115. If the data attribute signal is ACK information, it is determined that the previously transmitted packet has been correctly received, and the fact is transmitted to the retransmission control device 114 to erase the stored previous packet information. Command. The IS / PL control device 113 decodes the baseband signal from the receiver 112, and if the baseband signal is an IS signal from the central office, separates the specific pattern shown in FIG. A timing is generated to inform the packet controller 116 that the communication channel is currently idle. When the baseband signal from the receiver 112 is a PL signal from the central office, FIG.
(B) It is determined whether or not the terminal number in the address is addressed to the own station. If the terminal number is addressed to the own station, a packet transmission timing is generated, and the packet control device 116 is permitted to transmit the packet. To inform. The retransmission control device 114 receives the same information as the packet transmitted from the packet control device 116 to the transmitter 117 from the packet control device 116, and stores it until ACK information for the packet from the partner terminal station is received. In the case where the ACK information to be returned has not been received even after a sufficient time has passed for the ACK information to be returned when the other terminal station correctly receives the packet after the packet is transmitted from the packet control device 116, ,
It determines that packet transmission has failed and starts the retransmission procedure. The M terminal stations including the terminal station 120 in FIG. 1 have the same function as the terminal station 110.

Next, the operation of the central station and the terminal stations of the system according to the present invention will be described with reference to the flowchart of FIG. In the ISMA mode, the central station always detects whether the channel is free or busy, and if free, broadcasts the IS signal shown in FIG. That is empty. After sending the IS signal, the signal is again transmitted for a fixed time a determined by the sum of the round-trip propagation delay time to the farthest terminal and the signal processing time of the hardware and software at the central station transmitter and each terminal. The communication channel is monitored to determine whether a packet has been transmitted from the terminal station. If no packet is detected, an IS signal is sent out again and the monitoring of the communication channel is repeated. When a packet is detected, the packet is received and the packet is relayed toward the terminal station in the down direction. After relaying the packet, immediately switch to polling mode and
After transmitting the L signal PL1, the communication channel is monitored in the same manner as in the ISMA mode. If no packet is transmitted from the polling terminal station during the time a, the polling signal PL2 of the next terminal station is started. If a packet transmitted by the terminal station being polled is detected during the monitoring time a, polling is restarted from the beginning. If no packet is detected from the terminal stations even after polling all M terminal stations in one round, it is determined that the traffic is small and the operation returns to the ISMA mode again.

FIG. 4B is a flowchart showing the operation of the terminal station. The terminal station constantly monitors whether there is a communication request from the terminal, and when there is a communication request, prepares to assemble a packet into a predetermined format and transmit it. (However, if the storage device in the terminal station is full, a new communication request is rejected.) When the preparation for packet transmission is completed, the terminal station waits for an IS signal from the central station or a PL addressed to the own station. When the IS signal is received, the packet is transmitted with the probability p, the transmission of the packet is postponed with the probability 1-p, and when the PL signal addressed to the own station is received, the packet is transmitted with the probability 1. If a packet has been transmitted, it is then determined whether the packet has been correctly received by the other terminal. If the packet has not been correctly received, a retransmission procedure is started, and an IS signal or an automatic signal is sent to ask for an opportunity to transmit the packet again. Wait for a PL signal addressed to the station. If it is determined that the packet has been correctly received, the process returns to a state of waiting for a new communication request from the terminal. Next, a time-series flow of a signal when operated according to the above-described flow will be described with reference to a timing chart of FIG. In a system in which M terminal stations communicate with each other via one central office, the central office is initially in the ISMA mode and the communication channels are idle, so the IS signals IS1, IS2
Are sequentially transmitted. This IS signal has a length of b and arrives at the terminal station M which is the farthest terminal station after a lapse of time a / 2. In the terminal station 1, a packet transmission request has occurred between the time of receiving IS1 and the time of receiving IS2.
Immediately after receiving S2, the packet 1 is transmitted to the central station. The central station receives the packet 1 after a certain propagation delay time (smaller than a) and relays the packet 1 in the downstream direction. Immediately after the relay is over, the central office shifts to the polling mode and transmits the PL signals PL1 to PLM. In terminal M, I
A request to transmit a packet is made between the time when S2 is received and the time when the PLM is received, and the packet M is transmitted to the central office immediately after receiving the PLM. The central office relays the packet M in the same manner as when receiving the packet 1, and transmits the L signals PL1 to PLM again immediately after the relay is completed. Since no packet was transmitted from the terminal stations even when polling all the terminal stations, the central station again switches to the ISMA mode and transmits IS signals IS3, IS4,.

The above is the operation of the packet communication system according to the method of the present invention.

[0021]

As described above, according to the present invention, when traffic is temporarily increased by adding the transmission mode by the polling method at the end of transmission of a packet to the transmission mode by the ISMA method, As a result, transmission is performed in a polling mode without collision, and as a result, each terminal can sequentially process retransmitted packets that have been stuck before that, so that the system can be stably maintained. In the polling mode of the present invention, by performing the polling order and the number of times in accordance with a program, it is possible to perform polling with priority given to a terminal station having a particularly high packet occurrence rate. Further, by automatically switching between the ISMA mode and the polling mode according to the present invention based on the measurement result of the traffic amount for a certain period of time, it is possible to construct a system corresponding to various traffic situations. is there.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a signal format according to the present embodiment.

FIG. 3 is a time chart illustrating the operation of the present embodiment.

FIG. 4 is a flowchart showing the operation of the present invention.

FIG. 5 is a configuration diagram of a conventional packet communication system.

FIG. 6 is a configuration diagram of a conventional signal format.

FIG. 7 is a time chart showing the operation of the conventional example.

FIG. 8 is a flowchart showing the operation of the conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Central station 101, 111, 121 Antenna 102, 112, 122 Receiver 103 Packet detector 104 Collision detector 105 IS / PL generator 106 Multiplexer 107, 117, 127 Transmitter 113, 123 IS / PL controller 114 , 124 Retransmission control device 115, 125 Input / output control device 116, 126 Packet control device

Claims (3)

(57) [Claims] 1. A central station and a plurality of terminal stations wirelessly connected share one communication channel and transmit an idle signal from the central station at a predetermined cycle while the communication channel is idle. Information is simultaneously transmitted to all the terminal stations, and any one of the terminal stations obtains a packet data transmission right, relays the central station, transmits packet data to a desired terminal station, and transmits the packet data to the desired terminal station. In an ISMA-based packet communication system in which stations stop sending idle signals, when the central station finishes relaying packet data by one of the terminal stations, it immediately polls all of the other terminal stations. A packet communication system comprising means for transmitting a signal and giving packet data transmission right. 2. When the central station sends a polling signal to all of the plurality of terminal stations and there is no request to send packet data, the mode of the polling signal is changed to the idle signal mode of the ISMA system. The packet communication system according to claim 1, wherein the packet communication system is returned. 3. A predetermined time during which one of the terminal stations relays packet data to the other receiving terminal station by relaying the packet data to the central station and receives an acknowledgment (ACK) signal from the receiving terminal station. 2. The packet communication system according to claim 1, further comprising means for judging a packet collision when the central station does not receive an ACK signal after a lapse of time and shifting to a mode of the polling signal.