JPH01109933A - Data transmission method - Google Patents

Abstract

PURPOSE:To improve the line utilizing efficiency selecting a data sending zone again if a sent data and other sent data collide with each other and sending the data in the selected data sending zone. CONSTITUTION:Time slots T1-T10 are used as a frame and frames are divided into an area A of time slots T1-T5 and an area B of time slots T6-T10. Radio waves 21-23 sent at first from earth stations 2-4 are sent to the area A, subject to frequency conversion by a satellite and the result reaches the earth. In such a case, if a radio wave like the time slot T4 is in the state of collision, the result is an error signal and reaches each earth station, where the error is detected. An earth station recognizing the occurrence of collision sends this time the data toward the area B. That is, the radio wave 24 from the earth station 3 is transmitted to the time slot T7 and the radio wave 25 from the earth station 4 is transmitted to the time slot T9.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a data transmission method that can be used in a communication system using a satellite.

BACKGROUND OF THE INVENTION In recent years, data packet communications using satellites have been actively researched and are being put into practical use. FIG. 8 is a conceptual diagram of data packet communication using a satellite. In the figure, 1 is a satellite,
2.3.4 is a transmitting/receiving device on earth (hereinafter referred to as earth station)
, 5 is the earth.

fl is a radio wave heading from the earth station 2.3.4 to the satellite, and f2 is a radio wave heading from the satellite to the earth station 2.3.4. The radio wave fl emitted from the earth station 2.3.4 is frequency-converted by the satellite l and becomes a radio wave f2. Each earth station, for example, earth station 1, earth station 2, or earth station 3, can communicate with each other using satellite l.

At this time, a propagation delay of approximately 260 m5 occurs. In communications using satellites, the slotted Aloha method is being considered as a data transmission method, taking into consideration the large propagation delay time due to the distance between the satellite and the earth.

An example of the slotted Aloha method, which is the conventional data transmission method described above, will be described below with reference to the drawings. FIG. 9 is a conceptual diagram of the slotted Aloha method, which is a conventional data transmission method.

In the figure, 2.3.4 is the earth station, and 6 is the satellite
1 shows the state of radio waves received on the time axis, and T1, T2, T3, . . . are time slots. 7, 8, and 9 respectively indicate radio waves transmitted from earth station 2.3.4, and 10.11 indicate radio waves retransmitted from earth station 3.4.

FIG. 10 is a flowchart illustrating a slotted Aloha data transmission method, which is a conventional data transmission method. The Slofted Aloha data transmission method, which is a conventional data transmission method, will be described with reference to FIGS. 9 and 10. Each earth station transmits data using the method shown in FIG. 1O. That is, initial settings are made and the memory is cleared (Fig. 10-12). Monitor whether transmission data is generated (Figure 1θ-13), and if transmission data is generated, add additional information such as the destination to the transmission data and packetize it (Figure 10-14). Store data in memory (Figure 10-
15). The transmission data stored in the memory is sent out on radio waves towards the time slot shown in Figure 9-6 (Figure 10-16 and 17), where the packet length of the transmission data stored in the memory is It is shorter than the above time slot length. Then, the radio wave is transmitted from the beginning of the time slot. In the example of FIG. 9, the radio waves transmitted from earth station 2 are sent to time slot 1-T2, and the radio waves transmitted from earth stations 3 and 4 are sent to time slot T5. Therefore, the information of time slot T2 is frequency-converted by satellite l as shown in FIG. 8 and reaches other earth stations.

On the other hand, at time slot T5, radio waves from earth stations 3 and 4 collide. Therefore, the information of time slot T5, which is frequency-converted by the satellite 1 and sent back to each earth station, becomes an error signal containing an error in data, and when it reaches each earth station, an error is detected. Earth stations 3 and 4 can recognize that their emitted radio waves have caused a collision due to an error in the position of time slot T5 (
Figure 10-18). The earth station recognizes that a collision has occurred, generates a random number internally, and after the time determined by the random number has elapsed (
(Fig. 10-19), the transmission data stored in the memory is transmitted again on radio waves toward the time slot of Fig. 9-6 (Fig. 1.theta.-16 and 17). In the case of Fig. 9, the radio wave IO from earth station 3 is in time slot T7, and the radio wave 11 from earth station 4 is in time slot TI.
Sent to O. Through the above procedure, information from each earth station is sent to the destination earth station.

FIG. 11 is a conceptual diagram showing the relationship between throughput and traffic of the slotted Aloha method, which is a conventional data transmission method shown in FIG. In the figure, the average number of packets S per unit time generated from all earth stations is input to a terminal 101. 103 is a system that employs the Surosotedo Aloha method. The average traffic G is input to the input terminal 102 of the system 103. An average number S of successfully transmitted packets per unit time without data packet collisions occurs at the output 105 of the system 103.

In the system 103, data packet collision occurs and the number of packets required to be retransmitted is on average R per unit time, which is generated at the terminal 104. Therefore, the average traffic G applied to the terminal 102 can be expressed as G=S+R (1).

In a stable state, the number S of packets applied to the input terminal 101 is output to the output terminal 105.

The number S of packets is equal. Here, as a unit time, Fig. 9 6
If the slot length of the time slot Tn is selected, S is the throughput. Hereafter, the slot length of time slot Tn in FIG. 9 will be selected as the unit time. It is assumed that the generation distribution of traffic G and S follows Poisson distribution. The probability QL that a transmission request for L packets is generated at the terminal 102 within a unit time is determined by Poisson's law as follows: QL = OL-EXP(G) /L! ”” (
2) In order for one packet to be successfully transmitted, it is necessary that no packet collision occurs. For this purpose, it is necessary that no other packet transmission requests occur. That is, when L=O.

The average number of packets generated at the terminal 102 within a unit time is G
Therefore, S ``G-Qo = G-EXP(G) '' (3)
Multiply.

Now, when actually operating the system, the problem is how much delay time it takes for information to reach the other party.

The question then becomes how many collisions should we be prepared for before reaching the other party? Then, the probability PK of success in a transmission attempt under collection is determined.

The probability q that a particular packet is successfully transmitted is q=Gl
O=EXP (G)... (4) Therefore,
The probability y that the packet will fail in transmission is )'=1-Q=1-EXP (-G)... (
5) Probability U of success for the first time in the Kth transmission. is UK=q
')' =lliXP(-G) ・(1-EXP(-G))"
-...-(6) Therefore, the probability PK of success in K or fewer transmission attempts is . In order for 99.9% of the transmitted packets to be successfully transmitted in 3 attempts or less, the above equations (3) and (
According to 7), when the throughput S is calculated by setting =3, S =0.0 9 , which means that the system must be operated with poor line utilization efficiency.

Problems to be Solved by the Invention In the method described above, in order to successfully transmit most of the transmitted packets within a certain amount of time, the system must be operated in a state with poor line usage efficiency as explained above. (For example, when S=3, throughput S=0.09). In view of the above-mentioned problems, the present invention provides a data transmission method that can improve line utilization efficiency.

Means for Solving the Problems In order to solve the above-mentioned problems, the data transmission method of the present invention provides control for controlling to which region of the data transmission region divided into a plurality of time regions data should be transmitted. a data sending area is selected by the means, and data is sent from the data packet sending means in the selected data sending area;
When a collision is detected by the detection means for detecting a collision between the transmission data and other transmission data, a data transmission area is selected again by the control means, and the data packet transmission means sends data to the selected data transmission area. It has a method in which the data is sent out.

Effects: Due to the above-described configuration, the present invention can improve line utilization efficiency compared to conventional data transmission methods.

Embodiment Hereinafter, a data transmission method which is an embodiment of the present invention will be explained with reference to the drawings. A conceptual diagram of data packet communication using a satellite in the present invention is shown in FIG. 8, as in the conventional example.

FIG. 1 is a conceptual diagram of a data sending method in a first embodiment of the present invention. In Fig. 1, 2.3.4 is the earth station, 20 is the state of the radio waves received by the satellite l in Fig. 8, shown on the time axis, Tl, T2, T3,...
・ is a time slot.

21, 22.23 respectively indicate radio waves transmitted from earth station 2.3.4, and 24.25 indicate radio waves retransmitted from earth station 3.4. Time slot T1 to TlO
is a frame, and the frame is divided into time slots T1 to T
It is divided into an A area from time slot T6 to TIO and a B area from time slot T6 to TIO. FIG. 3 is a flowchart illustrating the data sending method of the present invention. The data transmission method of the present invention will be explained with reference to FIGS. 1 and 3.

Each earth station transmits data using the method shown in FIG.

That is, initial settings are made and the memory and M value are cleared (Fig. 3-32). It is necessary to monitor whether or not transmission data is generated (Figure 3-33), and if transmission data is generated, it is packetized by adding additional information such as the destination to the transmission data (Fig. 3-33).
Figure 3-34). The packetized transmission data is stored in memory (Fig. 3-35). Determine whether it is the beginning of the time slot in Figure 1 20 (Fig. 3-36), and if it is the beginning of the time slot, then determine the M value (Fig.
37). If the M value is 0, then it is determined whether the area is A (FIG. 3-38). If the M value is 1 or more, then it is determined whether it is in the B area (FIG. 3-39). After that, the transmission data stored in the memory is sent out (Figure 3-4).
0). Here, the packet length of the transmission data stored in the memory 〒 is shorter than the time slot length. Then, the data is sent out from the beginning of the time slot.

The data transmitted for the first time (hereinafter referred to as first transmission data) is A.
Transmitted in the g range. In the example shown in FIG. 1, the radio waves transmitted from earth station 2 are sent out in time slot T1, and the radio waves transmitted from earth stations 3 and 4 are sent out in time slot T4.

Therefore, the information of time slot T1 is frequency-converted by satellite 1 as shown in FIG. 8 and reaches other earth stations. On the other hand, in time slot T4, radio waves from earth stations 3 and 4 collide. Therefore, the information of time slot T4, which is frequency-converted by the satellite 1 and sent back to each earth station, becomes an error signal containing an error in the data, and reaches each earth station where the error is detected. Earth stations 3 and 4 can recognize that their emitted radio waves have caused a collision because there is an error in the position of time slot T4 (Figure 3-41). The earth station that recognizes that a collision has occurred increments the M value by one (Figure 3-42). A random number is generated internally, and after the time determined by the random number has elapsed (Figure 3-
43), the transmission data stored in the memory is transmitted again on radio waves, aiming at the time slot shown in FIG. 120. At this time, the M value is 1 or more, so the data for retransmission (hereinafter referred to as retransmission data) is B
It is sent to the time slot of the area. In the case of Figure 1, the radio wave 24 from earth station 3 is time slot T.
7, the radio wave 25 from earth station 4 is time slot I-T9.
sent to. Through the above procedure, information from each earth station is sent to the destination earth station. - In FIG. 3, 301 indicates the operation method of the control means for controlling which area of the data sending head area divided into a plurality of time areas should be sent, 40 indicates the operation of the data packet sending means, and 41 This affects the operation of the detection means for detecting data collisions.

FIG. 4 is a conceptual diagram showing the relationship between throughput and traffic in the data transmission method of the present invention shown in FIG. In the figure, the average number of packets S per unit time generated from all earth stations is input to a terminal 106. The average number of packets S is transmitted in area A in FIG. Therefore, if the ratio of the A area to the frame is a, the average number of packets input to the A area is S/a per unit time. 107 is a block that converts frame traffic into AM area traffic, and a terminal 108 shows the average number of packets S/a per unit time input to the A area. Reference numeral 109 denotes a block showing an operational model of area A. An average number of packets successfully transmitted per unit time through the A2B area without data packet collisions, 81, occurs at the output 110 of block 109. In block 109, data packet collision occurs and the number of packets requiring retransmission is on average R1 per unit time, which is generated at terminal 111. The number R1 of retransmitted packets per unit time is transmitted in the BeJf area. A block 113 converts the number R1 of retransmitted packets per unit time in the Afil area into traffic in the BjI area.

Therefore, the terminal 114 has (a/(1-a)) ・
A traffic output of R1 results. Reference numeral 116 is a block showing an operation model of the 8M area. An average number of packets successfully transmitted per unit time through the B region without data packet collisions, 82, results at the output 118 of block 116. In block 116, data packet collision occurs and the number of packets requiring retransmission is on average R2 per unit time, which is generated at terminal 117. Therefore block 116
Let G be the traffic added to the input terminal 115 of 1' G=(abata)) °R! +, <R2°----°
(G of 81 is added to block 116.

The operation of block 116 indicating the operation in the s95 region is the slotted Aloha method itself.

Reference numeral 112 denotes a block for converting the throughput S1 of the A area to the throughput of the entire frame, and a throughput a-8l converted to the entire frame is generated at its output terminal 120.

Reference numeral 119 is a block for converting the throughput S2 in the B tri area to the throughput of the entire frame, and the throughput (1-a)·R2 converted to the entire frame is generated at its output terminal 121. Therefore, the total throughput S is the sum of the throughput a-31 in the A9i area and the throughput (1-a)·R2 in the B area. 122 is a block diagram showing addition; 123
is the throughput output terminal. Here S = a -31+ (1-a) ・S 2
= (9).

Now, the characteristics of the data transmission method of the present invention will be clarified using the same method as used in the conventional example. The throughput S1 in area A is calculated using S instead of G in equation (3).
/a is substituted. Therefore, S 1 = (S/a)4XP(-S/a)-"-"
・Similarly, the throughput S2 in the Q[IBR1 area is (3
) expression itself. That is, 52=G-EXP (-G) ...... α
It is υ. Substituting the 0ω formula and 00 formula into formula (9), S
= S -EXP(-3/a)+(1-a) HG-
IEXP(-G) then G-BXP(-G) = (1/(1-a)) ・S ・
(1-HXP(-3/a))・・・・・・・・・(2
) becomes.

Next, find the probability PK of success in sending letters less than or equal to the number of times.

The probability q that a particular packet will succeed in the first transmission is Q = Qo = E'XP (-3/a) +++++
Q3) Therefore, the probability y that the packet fails in transmission is y=t q=t-EXP (-3/a) ... α
0 Probability of success for the first Kth transmission after the 2nd time UK
From equation (6) and Cl41 equation, Uw □(1-EXP(-3/a)) ・EXP(-G
) ・(1-EXP(-G))"-"・・・・・・・・・
・・・・・・・・・ a9 Therefore, the probability P8 of success with less than 1 times t is the probability P8. In order for 99.9% of the transmitted packets to be successfully transmitted with three transmittals or less, throughput S is calculated by setting = 3 from the above formula (b) and 0[9, S = 0.135. becomes. Here, the ratio a of the ApJ region is set to 0.5.

If the data transmission method of the present invention is adopted, the throughput will be improved by about 50% compared to the throughput of the conventional example (0.09).

For reference, FIG. 5, FIG. 6, and FIG. 7 show data comparing the characteristics of the conventional Surosotedo Aloha method and the method of the present invention. 5 and 6 show the relationship between the ratio a of the A area and the throughput S. FIG. 5 shows the case when Δ=3, and FIG. 6 shows the case when Δ=2. FIG. 7 shows the relationship between the number of transmissions and the probability Pya of successful transmission with the number of transmittals less than 2 times. It can be confirmed that the present invention is superior to the conventional slotted Aloha method when K=2 or more.

A second embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a conceptual diagram of a data sending method showing a second embodiment of the present invention. In the same figure, 2.3.4 is the earth station, 26 is a time axis of the state of the radio waves received by the satellite l in Figure 8, and TIT2, T3, .
... is a time slot. 27, 28, and 29 are radio waves sent from earth station 2.3.4, and 30.31, respectively.
shows the radio waves retransmitted from earth station 3.4.

Odd numbered time slot of time slot Tn (n; 1
, 3.5, ...) in the All area, and an even numbered time slot (n; 2.4 in the time slot Tn).
．． 6,...) are allocated to time slots in the Bwi area. The following operation is exactly the same as that of the first embodiment shown in FIG. 1, so the explanation will be omitted. In the second embodiment shown in FIG. 2, the A95 area, which is an area for initial transmission, and the B area, which is an area for retransmission, are alternated. Therefore, when initial transmission data is generated, it takes at most one time slot to reach the Ag3 area, so there is an advantage that the waiting time for transmitting the initial transmission data is short.

In the first and second embodiments, the control method of the control means is to divide the data sending area into two time areas, the A area and the B area, and control which area the data should be sent to. However, the present invention is not limited to this, and for example, a method may be used in which the data is divided into three areas and controlled for initial transmission, first retransmission, and second and subsequent retransmission. Furthermore, a method may be used in which the usage area is controlled by dynamically varying the division ratio of the time area depending on the amount of input traffic. Further, although all retransmissions are sent in the B ffJI area, the retransmissions up to the nth time may be sent in the AifI area, and the (n+1)th and subsequent retransmissions may be sent in the bjl area. Furthermore, it is also possible to control probabilistically which time domain data should be sent.For example, retransmission data may be controlled such that it is sent to the A area with a probability of 20% and to the By area with a probability of 80%.

The initial transmission data may also be similarly controlled stochastically.

Furthermore, the probability value may be dynamically varied depending on the traffic state.

Effects of the Invention As described above, the present invention includes a means for packetizing data, a sending means for sending the data packet, a detecting means for detecting a data collision, and a data sending area in a plurality of time areas. By having a dividing means for dividing the data and a control means for controlling to which region of the time domain divided by the dividing means the data should be retransmitted depending on the degree of data collision, line usage efficiency is improved compared to conventional data transmission methods. can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the data transmission method in the first embodiment of the present invention, FIG. 2 is a conceptual diagram of the data transmission method in the second embodiment of the invention, and FIG. FIG. 4 is a flowchart showing the data transmission method in the embodiment; FIG. 4 is a conceptual diagram for explaining the relationship between traffic and throughput of the data transmission method in the first and second embodiments;
6 and 7 are characteristic diagrams showing the characteristics of the data transmission method in the first and second embodiments, FIG. 8 is a conceptual diagram of data packet communication using a satellite, and FIG. 9 is a conventional example. 10 is a flowchart showing the data transmission method of the conventional slotted Aloha method, and FIG. 11 is a conceptual diagram of the conventional slotted Aloha method.
FIG. 2 is a conceptual diagram for explaining the relationship between traffic and throughput of a data transmission method in the Aloha method. l...Satellite, 2.3.4...Earth station,
5...Earth, 6...Transmission data, 7.
8.9...First transmission wave from each earth station, 10.1
1...Retransmission wave from earth station 3.4, 20...
...Transmission data, 21.22.23...First transmission wave from each earth station, 24.25...Retransmission wave from earth station 3.4, 26... ...Sending data,
27.28.29...First transmission wave from each earth station, 30.31...Retransmission wave from earth station 3.4. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 1 Figure 2 Figure 2 → 2 Figure 4 Figure 6 a Figure 7-K (itfflEI) Figure 8 Figure 9? 3 4 Figure 10 Figure 11 Diagram G-30 shaku

Claims (1)

[Claims] A data transmission area is selected by a control means for controlling to which area of the data transmission area divided into a plurality of time areas the data should be sent, and the data is sent from the data packet transmission means in the selected data transmission area. When a collision is detected by the detection means for detecting a collision between the transmission data and other transmission data, the data transmission area is selected again by the control means, and the selected data is transmitted from the data packet transmission means. A data transmission method characterized in that the data is transmitted in a region.