JP2817166B2 - TDMA channel allocation method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a TDMA channel allocation control system using a multiple access system in which one satellite communication channel is time-shared and shared by a plurality of stations. Message type is
Improve channel utilization efficiency in a wide variety of cases, such as short messages sent randomly, messages sent randomly and in bursts, and messages sent periodically, and management, maintenance, and maintenance in actual application of the system. Regarding facilitation of operation.

[Conventional technology]

Conventional TDMA channel allocation techniques include the following schemes.

As shown in FIG. 9, a slotted Aloha system that allows all stations to access all slots.

As shown in FIG. 10, a pure TDMA system in which accessible slots are assigned to all stations one by one.

As shown in FIG. 11, a reservation aloha system in which a station that wants to transmit performs a random access for reservation to a reservation channel to allocate a dedicated transmission slot.

As shown in Fig. 12, the slotted Aloha method and the reserved Aloha method are combined, and a short message is transmitted by the slotted Aloha method, and a long message is transmitted by the reserved Haloha method.

[Problems to be solved by the invention]

The slotted Aloha method enables transmission with a small delay when the message occurrence rate is low. However, when the occurrence rate is large, there is a problem that both the channel use efficiency and the propagation delay are deteriorated.

In contrast, the pure TDMA method performs efficient and stable operation when the message occurrence rate of all ground stations is high, but the occurrence rate of one ground station is high, but that of another station is low. As described above, it is not an efficient transmission method when the message occurrence rate of the ground station is biased, and when the occurrence rate of the whole station is low, the efficiency problem and the delay characteristic are worse than the slotted Aloha method There is a problem.

The reservation Aloha method is an efficient transmission method when the distribution of the message length shows a large variation. In addition, the system can flexibly cope with uneven message occurrence rates of ground stations. However, when the overall occurrence rate is low, there is a problem that the delay characteristic is worse than that of the slotted Aloha system.

The combined random / reservation method is a method in which the slotted Aloha method and the reservation Aloha method are combined. A message having a short message length (hereinafter referred to as a short message) is a slotted Aloha method, and a message having a long message length is a reservation Aloha method. It is transmitted in a system. Since the features of the two methods are combined, it is possible to flexibly cope with various message length distributions, even when the message occurrence rate is low to relatively high, even when the occurrence rate of the ground station is biased. System. However, even in this method, the message reservation is performed by the slotted Aloha method, so that if the message occurrence rate of the ground station (especially that of short messages) becomes larger than a certain limit, the performance of the system deteriorates. There's a problem.

It can be seen that an excellent system can be obtained by solving the problems in the combined random / reservation system. For this purpose, when the message occurrence rate is high (referred to as high load), a pure TDMA element may be introduced for reservation or transmission of a short message. However, if pure TDMA is introduced as it is under heavy load, the disadvantage of pure TDMA, that is, inefficiency when the message occurrence rate of the ground station is biased, is also introduced. Therefore, a user model showing the message occurrence status of each ground station created from the previous records and conditions was constructed in the process inside the control station, and the slot to be assigned according to the model was added. It becomes an efficient system that can cope with such a bias.

However, in this method, it is difficult to appropriately determine how many slots should be allocated to the dedicated access part of the station selected from the model. In order to solve this problem, first, the channel assignment will be reconsidered from the viewpoint of permission of individual ground stations to access slots.

Reviewing the conventional method from this viewpoint, the slotted Aloha method is a method in which all stations are granted access permission to all slots, and the pure TDMA method always accesses one station in one slot. It is understood that a scheme in which a slot is granted and slots exist fairly to all stations, and a reservation Aloha scheme is a scheme in which one station allocates access-permitted slots by making a reservation. . In the slotted Aloha system, all stations are given access permission to the slot. Apart from this, not all the stations, but a slot in which a plurality of stations are given access permission can be considered. Such a slot will be called a station group slot (including the case of all stations). A slot to which only one station is permitted to access without reservation as in the pure TDMA scheme is called a single station slot. Further, a slot to which access permission is given to only one station by reservation is called a reserved slot.

Thus, the above problem can be regarded as a problem of optimal distribution of the station group slot, the single station slot, and the reserved slot. To solve this optimal distribution problem, the concept of instance competition was introduced. That is, in this method, an instance requesting a station group slot, an instance requesting a single station slot, and an instance requesting a reserved slot are respectively generated in the control station process according to the user model, and those instances are generated based on the contents of the rule base. It has a mechanism for optimally distributing station group slots, single station slots, and reserved slots depending on the result of contention.

[Means for solving the problem]

The TDMA channel allocation system of the present invention is composed of one control station and a plurality of ground stations, and a TDMA channel using a multiple access system in which a common channel via a satellite is time-shared and shared by a plurality of ground stations. In the allocation method, the control station includes: a user who configures a user model indicating a state of occurrence of a message of the plurality of ground stations based on past records and conditions;
A model component, a first instance requesting a station group slot to which a plurality of ground stations, including all stations, are granted access, according to the user model, and a single ground station not based on a reservation. Generating a second instance requesting a single station slot to which access permission is given only by the first and a third instance requesting a reservation slot to which access permission is given to only one ground station based on the reservation; To a slot allocation determining unit that performs slot allocation to the plurality of ground stations according to a result of the contention of the third instance, and a rule base that defines a contention rule for the instance of the slot allocation determining unit. I do.

〔Example〕

 This method will be described with reference to the drawings.

FIG. 1 is a configuration example of a satellite communication network to which the present system is applied. A plurality of ground stations T communicate with the satellite S via the control station C. Since the antenna of each ground station T is very small, the antenna is once transmitted via the satellite S to the control station C having a large antenna, and the control station C transmits the transmission again via the satellite S with a large output. . Each ground station T constantly monitors signals from the control station C via a satellite.
It is assumed that communication cannot be performed without passing through a satellite / control station. Further, the control station C monitors traffic at the same time as mediation of transmission, and sends out slot assignment / control information.

FIG. 2 shows the configuration of the control station C shown in FIG. The received transmission from the ground station T is sent to the slot identification unit 4 via the reception unit 2 and the channel monitoring unit 3. The slot identification unit 4 determines whether the transmission of the information is currently permitted, and when an appropriate time is reached, the communication is transmitted to each ground station via the transmission unit 5.

The channel monitoring unit 3 monitors the received traffic, and further receives a flot reservation request from each ground station. These pieces of information are transferred to the user / model configuration unit 6, the slot assignment determination unit 7, and the history base update unit 8.

In the slot assignment determining unit 7, based on the user model, an instance for requesting a single station slot therein,
An instance requesting a station group slot, an instance requesting a reserved slot (a single station instance,
Station instance and reservation instance). Each of these instances has a conflicting term therein, and changes the conflicting term of each instance according to the rules in the rule base 9 and information from the channel monitoring unit 3. The simplest general term is represented by one change number (competitive variable). Allocate a slot to the instance having the largest value of the conflict variable. However, various variations are possible for the competitive term, for example, there are types such as diamonds and spades in addition to numbers in playing cards. In any case, in this way, the instances are contended and the slots are allocated. The slot allocation information determined here is transmitted to each ground station via the slot allocation information transmission unit 10, the slot identification unit 4, and the transmission unit 5.

Based on information from the channel monitoring unit 3, information from the history base 11 (recording of past message transmissions at specific times of each ground station), and the rules in the rule base 12, Constructs an Eisa model showing the state of the message transmission of each ground station.

The history-based updating unit 8 updates the history based on the information from the channel monitoring unit 3.

FIG. 3 shows a configuration of a general ground station. The generated data is first packetized by the packetizing unit 13 and further put into the transmission buffer 14. Then, the data in the buffer is copied to the slot identification unit 15. The slot control unit 15 sends the packet to the transmission unit 16 in an appropriate slot by combining the allocation information from the channel monitoring unit 19 and the information from the retransmission control unit 20. See FIG. 4 for the mechanism for determining the slot to be transmitted in this part. This figure shows a flow chart in which data transmitted from a certain ground station is focused on until the data is successfully transmitted.

Returning to FIG. 3 again, the data received by the ground station is passed to the channel monitor 19 via the receiver 18. If this data is channel assignment information from the control station, the information is passed to the slot identification unit 15, and if the data is a reception response from the control station to data transmitted from the own station to the station group slot, , And confirms the success / failure of the transmission, and sends the information to the transmission buffer unit 14. If unsuccessful, the transmission buffer unit 14 performs a retransmission operation.
If the received data is data from another station addressed to the own station, the received data is transferred to the reception buffer unit 21 and output therefrom as reception data.

Next, an example of channel access will be described with reference to FIGS. In this system, the following assumptions are made.

A. It is assumed that there are four ground stations in addition to the control station, and the propagation delay between the ground station and the control station is two slots.

B. Up to two messages can be entered in the ground station buffer.

C. It is assumed that there are two types of short messages consisting of one bucket and two types of long messages consisting of three packets.

D. Once a ground station has made a reservation, it does not transmit it in the station group slot until it has transmitted the message for the reservation.

E.1 Define a frame as a 5-slot break.

The following simple rules are provided as simple rules for explaining the operation of the engagement coefficient.

For the single station instance, the model transmission coefficient (No. 7, 8
The same value as that shown in FIG.

In the station group instance, stations that add up to the transmission coefficient of the model and total 10 or more are regarded as one station group.

The reservation instance has an engagement coefficient of (reservation slot + 1) × 3.

When a slot is assigned to an instance,
Three is subtracted from the competition factor for that instance.

For each frame, 2 is added to the contention coefficients of the single station instance and the station group instance.

If there is no actual packet transmission in the slot to which the single station instance is assigned, the contention coefficient of the station group instance including the station is increased by three.

If multiple instances have the same competition coefficient,
In the order of reservation → station group → single station instance, if it is equal to the competition coefficient of an instance of the same class (such as multiple single station instances with the same competition coefficient), the instance is assigned before Give priority to the one that has passed the most time.

First, FIG. 5 will be described. In this case, the message occurrence rate of each ground station is low. As shown in FIG. 7, the transmission coefficient of the model is low. Therefore, first, as shown in the upper left of FIG. 5, a single station instance having the same competition coefficient as the transmission coefficient of the model and two station group instances according to the rules are generated. The engagement coefficient of the station group instance is
According to the rules, the sum of the transmission coefficients of the A and B stations in the model (10) for the station group instance representing the A and B stations, and the transmission coefficient of the C and D stations for the station group instance representing the C and D stations (12).

Slot allocation is determined by the contention of these instances. In the first frame, first, the station group instance CD having the highest contention coefficient is allocated. Assignments apply rules,
The competition coefficient is 9. Then, the station group instance AB having the highest competition coefficient is assigned this time, and its competition coefficient becomes 7. Next, the station group instance CD is allocated again, and the contention coefficient becomes 6. Next, the single station instance B is assigned, and its contention coefficient becomes 5. In this way, slot allocation is determined according to the contention coefficient. Such a situation is shown in the allocation slot part of the figure.

Since the rule is applied at the beginning of the frame, the contention coefficient of the instance in the next frame is two times the contention coefficient at the end of the previous frame as shown. (Excluding reservation instances) When slot assignment is determined in the control station, the information is immediately transmitted to each ground station. For example, the allocation information to the first C and D stations in the figure arrives at each ground station in the fourth slot in the total slots after a two-slot propagation delay time. Upon obtaining this information, the stations C and D having the short message in the transmission buffer immediately transmit the message. The messages of the two stations reach the control station at the sixth slot in total after the propagation delay time of two slots. The state of this part is shown in the part of the control station channel in the figure. The control station sends the colliding message back to the ground station. The stations C and D detect that the transmission has failed at the ninth slot after the propagation delay time of two slots again.

At the B station, a short message and a long message are present in the transmission buffer in the fifth slot in total. Although a message can be transmitted in the seventh slot of the control station channel, no message is transmitted here as a result of retransmission control. Then, the message is transmitted at the seventh slot in total toward the ninth slot of the control station channel. At this time, three slots are reserved at the same time in order to transmit the remainder of the long message remaining in the transmission buffer and the short message. With this reservation, a reservation instance for station B is generated at the end of the ninth slot in total. The competition coefficient at this time is calculated by a rule. As a result, the reserved instance is assigned to the tenth slot among the assigned slots.

Station C is assigned to the tenth slot of the control station channel, but station C is not transmitting here. Therefore, according to the rule, three are added to the competition coefficient of the station group instance CD including the station C.

Next, look at FIG. In this case, the message occurrence rate of each ground station is high. As shown in FIG. 8, the transmission coefficient of the model is high. All transmission coefficients of each station are 10
Therefore, the station group instance as shown in FIG. 5 is not generated. Slot assignment is performed by a single station instance and a reservation instance.

In the station C, the reservation of the third slot is made in the fourth slot in total, and thereby, the reservation instance of the station C is generated at the end of the sixth slot in the control station channel. Thereafter, the station C has transmitted all the reserved messages in the fifth, eighth and tenth slots. By the way, in the station C, a long message has occurred at the end of the tenth slot in total. Therefore, the reservation of two slots is again transmitted together with the message at the 14th slot in total. In the control station channel, this transmission reaches the 16th slot in total, but the reservation instance of the station C, whose contention coefficient was 9 so far, remains at the contention coefficient 9 based on the rule.

〔The invention's effect〕

As explained above, this method introduces the concept of instance contention, from when the message occurrence rate is high to low, regardless of the distribution of message length, and when the occurrence rate of the ground station is biased. This is a method that enables efficient message transmission with a minimum delay time.

In addition, slot allocation determination and user model configuration are performed according to rules, but by accumulating those rules in a rule base and separating them from the slot allocation determination unit and user model configuration unit, rules can be changed easily. The burden of maintenance and management is relatively reduced. In addition, a flexible system can be constructed, for example, by adding a rule that allows a user who pays a higher fee to assign priority to the competition coefficient operation rule.

In addition, by building a history base, performance predictions such as how the characteristics of the system will change if this number of ground stations are increased during a certain time period, and if certain stations are prioritized. This method is also possible based on this method.

[Brief description of the drawings]

1 is a configuration example of a satellite communication network to which the present invention is applied, FIG. 2 is a block configuration of a control station in FIG. 1, FIG. 3 is a block configuration of a ground station in FIG. 1, and FIG. FIG. 5 is a flow chart of a mechanism for determining a data transmission slot in a station, FIG. 5 is an example of channel access when the message occurrence rate at each ground station is low, and FIG. FIG. 7 shows an example of a transmission coefficient of the user model when the message occurrence rate at each ground station is low. FIG. 8 shows an example of a transmission coefficient of the user model when the message occurrence rate at each ground station is high. Fig. 9, Fig. 10
FIGS. 11 and 12 show examples of channel access by the slotted Aloha system, the pure TMDA system, the predicted Aloha system, and the combined random / reservation system, respectively. DESCRIPTION OF SYMBOLS 1 ... Transceiving apparatus, 2 ... Reception part, 3 ... Channel monitoring part, 4 ... Slot identification part, 5 ... Transmission part, 6 ... User model construction part, 7 ... Slot assignment determination part, 8 …
... History base updating section, 9... Rule base I, 10... Slot assignment information transmitting section, 11. 15 slot identification section, 16 transmission section, 17 transmission / reception apparatus, 18 reception section, 19 channel monitoring section, 20
... Retransmission control unit, 21 ... Reception buffer unit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 7/14-7/22 H04J 3/00-3/26 H04L 5/22-5/26

Claims (1)

(57) [Claims] 1. A TDMA channel assignment system using a multiple access system comprising a single control station and a plurality of ground stations, wherein a common channel via a satellite is time-shared and shared by a plurality of ground stations. The control station includes a user model configuration unit that indicates a user model configuration indicating a message occurrence state of the plurality of ground stations from past records and situations, and a plurality of user models according to the user model. A first instance requesting a station group slot to which a ground station is granted access, a second instance requesting a single station slot to which access is granted to only one ground station without reservation, and a reservation Generating a third instance requesting a reserved slot to which only one ground station is granted access permission based on the first
To a slot allocation determining unit that performs slot allocation to the plurality of ground stations according to a result of the contention of the third instance, and a rule base that defines a contention rule for the instance of the slot allocation determining unit. TDMA channel allocation scheme.