KR20050023701A - Method for controlling back-off of random access and its program recording record medium - Google Patents

Abstract

PURPOSE: A backoff control method in a random access method and a recording medium for recording a program thereof are provided to largely set contention windows of non-priority user groups, and to separate contention windows of priority user groups from the windows of the non-priority user groups, thereby resolving contentions with the non-priority groups while reducing an access delay. CONSTITUTION: A system assigns priority to plural users(S1). If a random access transmission is requested from the users(S2), the system decides whether the users are assigned with the priority(S3). The system sets sizes of contention windows by setting contention window parameters according to each priority user group and non-priority user group(S4,S5). The system performs a backoff method(S6), and decides whether the frequency of random access retransmission exceeds the frequency of maximum retransmission(S7). If not, the system updates the contention windows, and determines a backoff time(S8). The system transmits data(S9), and monitors whether the second collision occurs(S10). If not, the system completes the procedure.

Description

TECHNICAL FIELD OF CONTROLLING BACK-OFF OF RANDOM ACCESS AND ITS PROGRAM RECORDING RECORD MEDIUM}

The present invention relates to a backoff control method in a random access method.

The random access method is used to request an initial radio access network or a user who has not been allocated a radio band to make a band request. Also, the random access method is used as a multiple access method for transmitting data traffic itself, such as a WLAN network.

Slot Aloha (Slotted Aloha) is typically used for the random access method is for the network initial access attempt, radio band allocation request, and data transmission on the common channel.

In the slot Aloha method according to the prior art embodiment, since users who attempt to access the network randomly access the radio band, a collision occurs when multiple users access simultaneously.

After a conflict between multiple users, if all of the conflicting users attempt to retransmit to the next slot, the collision continues, and the system can no longer operate properly.

In order to prevent such a phenomenon, when a collision occurs, all users perform a retransmission mechanism to resolve the collision.

1 illustrates a backoff control method in a random access scheme according to the prior art.

As shown in Fig. 1, if the amount of users attempting to access (transmit) the wireless channel is G, G is the case of users B attempting to retransmit due to a collision with a new packet occurring (N). It is sum.

Since new packets occur unexpectedly, we usually control the number of users who attempt to access by controlling the users who try to retransmit.

FIG. 2 illustrates a slot Aloha system throughput curve, in which the horizontal axis represents G and the vertical axis represents throughput.

As shown in Figure 2, the performance of the system depends on the number of users attempting to transmit to the system. The collision avoidance algorithm is superior as the yield remains closest to G (G = 1), which yields the highest yield.

A widely used collision resolution algorithm is exponential backoff. The exponential backoff method attempts to access a randomly selected slot within a contention window for retransmission, and the contention window size increases exponentially with the number of collisions.

Figure 3 shows an example of a binary channel exponential radio channel approach.

As shown in FIG. 3, the binary-index backoff method determines a transmission point randomly within a contention window by increasing a contention window exponentially 2 according to the number of collisions when a user who detects a collision occurs. do.

For example, if the contention window of the first collision user is 8, the second transmission attempt is determined within the 8th slot at the current slot time.

As shown in Fig. 3, if 5 is selected, the user attempts to transmit to the fifth slot. If a collision occurs again, the collision count is 2 and the contention window is 16. The third transmission attempt is then randomly determined within 16 slots from the time of the collision.

That is, if a collision continues to occur, the system recognizes that the load has increased and increases the contention window to reduce the system load due to retransmission at the present time and resolve the collision.

Methods for increasing the contention window according to the number of collisions include linear backoff, truncated exponential backoff, step backoff, and the like.

However, a user having multiple collisions has a problem in that a contention window is rapidly increased even when no user occupies the radio band, and thus a transmission delay is rapidly increased.

In order to solve the above problem, if the contention window size is set small and the same application is applied every time without increasing the contention window according to the number of collisions, there is a problem that it is impossible to control the collision frequency according to the system load variation.

The method of controlling the backoff in the random access method according to the prior art has a problem in that it may cause a long-term access delay in the case of a user requiring a fast access attempt because the user cannot control priority.

SUMMARY OF THE INVENTION The present invention provides a method for controlling a backoff in a random access method to reduce an average access delay to a wireless access network by giving priority to users attempting to transmit in a random access method in a wireless access network. It is to provide a recording medium recording the program.

In order to solve this problem, the present invention reduces the average transmission delay of priority users by giving priority to users with priority and non-priority users by giving priority to users and controlling contention window size and position in slot Aloha method.

According to a first aspect of the present invention, there is provided a method of controlling a backoff in a random access method, the method comprising: a) selecting a plurality of users attempting to access a wireless access network and giving access priority; b) when a first collision occurs after a random access transmission from a plurality of users to the wireless access network is requested, setting a parameter for increasing the contention window for retransmission differently for each priority / non-priority user; And c) performing a backoff control within a range not to exceed the maximum number of retransmissions set by the system when the size of the competition window for each user is set in the step b).

In step a), it is preferable to use a truncated contention window to give priority to the users.

In step b), the plurality of users may be divided into a priority user group and a non-priority user group to determine a contention window size of each group.

The contention window size of the priority user group and the non-priority user group may be determined by Equation 1 below.

In the determining of the contention window size of the priority user group, it is preferable to set the contention window growth rate alpha of the high priority users to be smaller than the contention window growth rate of the low priority users.

Preferably, the contention window increase rate alpha of the priority user group is set smaller than the contention window increase rate beta of the non-priority user group.

The step c) may include: a) updating the contention window according to the number of collisions and determining a backoff time if the number of random access retransmissions of an unspecified user does not exceed the maximum number of retransmissions; B) transmitting data when step a) is completed and monitoring whether a secondary collision occurs; C) If the secondary collision occurs in step b), check whether the number of random access retransmissions exceeds the maximum number of retransmissions, and repeat steps a) and b) within a range not exceeding the maximum number of retransmissions. Performing; And d) if the secondary collision does not occur in step b), notifying the user of the transmission success and terminating the system.

In step c), when the number of random access retransmissions of the unspecified user exceeds the maximum number of retransmissions, it is preferable to inform the user of the transmission failure and terminate the system.

According to a second aspect of the present invention, a recording medium recording a program of a method for controlling a backoff in a random access method includes: a first function of selecting a plurality of users attempting access to a wireless access network and giving priority to the access; When the first function is completed, when a first collision occurs after a random access transmission from a plurality of users is requested to the wireless access network, a parameter for increasing a contention window for retransmission is set differently for each priority / non-priority user. 2 functions; And a third function of performing a backoff control within a range not to exceed the maximum number of retransmissions set by the system when the size of the competition window for each user is set through the second function.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

First, a backoff control method in a random access method according to an embodiment of the present invention will be described in detail with reference to FIG. 4.

4 is a flowchart illustrating a backoff control method in a random access method according to an embodiment of the present invention.

As shown in FIG. 4, the method for controlling a backoff in a random access method according to an embodiment of the present invention gives priority to a plurality of users who attempt to access a wireless access network first (S1).

At this time, the users to which priority is given are users whose transmissions are delayed due to collisions, for example. In the random access scheme, a truncated contention window is used to give priority to each user.

When a random access transmission is requested from the unspecified users to the wireless access network (S2), the system determines whether the user has been given priority (S3).

Competitive window parameters are set for each priority user group to which priority is given and a non-priority user group to which priority is not given, thereby setting a contention window size as shown in Equation 1 below (S4 and S5).

Where CW _{with p} is the contention window size of the priority user group, CW _{without p} is the contention window size of the non-priority user group, r is the number of retransmissions, alpha is the growth rate of the contention window of the priority user group, and beta (alpha <beta) The competitive window growth rate, rand [min, max], of the priority user group represents a function of randomly selecting one number between min and max, respectively.

In this case, alpha and beta are p-exponentials representing the exponential growth rate of the contention window size according to the number of collisions. The high priority users are set small and the low priority users are set high.

This indicates that, in the same trial, users of a high priority group set the contention window size small, and users of a low priority group set the contention window size large.

In other words, users with low priority spread widely and attempt to access the wireless access network, reducing the probability of collision among users with high priority, and also because of the low contention window size of users with low priority, and waiting time due to backoff. This reduces the overall latency

As described above, the competition between the priority user group and the non-priority user group is eliminated by changing the contention window size between the priority user group and the non-priority user group and separating the competition section by the time difference.

When the contention window parameter for each user group is determined, the backoff scheme is implemented (S6).

The system determines whether the number of random access retransmissions of the user exceeds the maximum number of retransmissions. If the number of random access retransmissions exceeds the maximum number of retransmissions, the system notifies the user of transmission failure and terminates the system.

When the number of random access retransmissions does not exceed the maximum number of retransmissions, the contention window is updated according to the number of collisions, and the backoff time is determined (S8).

The system then transmits data (S8) and monitors whether a secondary collision occurs. (S9)

If the secondary collision occurs, the process returns to step S7 and repeats steps S8 to S10. However, if the secondary collision does not occur, the system notifies the user of the transmission success and terminates the system. (S10)

FIG. 5 illustrates a time slot flow according to a backoff control method in a random access method according to an embodiment of the present invention, in which (a) two users, a priority user group and a non-priority user group, have the same first attempt. Shows a backoff process when a collision occurs in (b), and (b) shows a backoff process when a collision occurs in a second attempt.

If two users in the priority group and two users in the non-priority group attempt random transmission simultaneously, it is assumed that alpha is 2 and beta is 3.

As shown in (a) of FIG. 5, since there is a possibility that a collision occurs between two groups because some of the contention windows overlap between the two groups, the contention window size of the priority user group may be small, thereby reducing the backoff delay.

As shown in (b) of FIG. 5, since the contention window is truncated in the priority user group, the contention window is isolated between the two groups, and the possibility of collision is greatly reduced.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited thereto, and various other changes and modifications are possible.

As described above, the method for controlling a backoff in the random access method according to the present invention adjusts the contention window size and position by appropriately setting parameters of the contention window without changing the structure or mechanism, and has a high frequency of collision due to the system overload. Even in situations, the size of the contention window can be differentially selected according to the priority, thereby reducing the average access delay by lowering the collision probability of high priority users.

1 illustrates a backoff control method in a random access scheme according to the prior art.

2 shows a system throughput curve of a slot Aloha scheme.

Figure 3 shows an example of a binary channel exponential radio channel approach.

4 is a flowchart illustrating a backoff control method in a random access method according to an embodiment of the present invention.

5 illustrates a time slot flow by a backoff control method in a random access method according to an embodiment of the present invention.

Claims (9)

a) screening a plurality of users attempting access to the wireless access network and assigning priority to access; b) After the step a) is completed, if a primary collision occurs after a random access transmission from a plurality of users is requested to a wireless access network, a parameter for increasing a contention window for retransmission is set differently for each priority / non-priority user. Doing; And c) performing a backoff control within a range not to exceed the maximum number of retransmissions set by the system when the size of the competition window for each user is set in the step b); Backoff control method in a random access method comprising a. The method of claim 1, Step a) is And using a truncated contention window to give priority to the users. The method of claim 1, B), And dividing the plurality of users into a priority user group and a non-priority user group to determine a contention window size of each group. The method of claim 3, The contention window size of the priority user group and the non-preferred user group is determined by the following equation; Where CW _{with p} is the competition window size of the priority user group, CW _{without p} is the competition window size of the non-priority user group, r is the number of retransmissions, alpha is the competition window growth rate of the priority user group, and beta is the competition of the non-priority user group. Window growth rate, rand [min, max], is a function that randomly selects a number between min and max; Backoff control method in a random access method characterized in that. The method according to claim 3 or 4, The determining of the contention window size of the priority user group may include: The competitive window growth rate (alpha) of high priority users is set to be smaller than the competition window growth rate of low priority users. The method of claim 4, wherein And a contention window increase rate (alpha) of the priority user group is set to be smaller than a contention window increase rate (beta) of the non-priority user group. The method of claim 1, C), A) if the number of random access retransmissions of an unspecified user does not exceed the maximum number of retransmissions, updating the contention window according to the number of collisions, and determining a backoff time; B) transmitting data when step a) is completed and monitoring whether a secondary collision occurs; C) If the secondary collision occurs in step b), check whether the number of random access retransmissions exceeds the maximum number of retransmissions, and repeat steps a) and b) within a range not exceeding the maximum number of retransmissions. Performing; And D) if the secondary collision does not occur in step b), notifying the user of the successful transmission and shutting down the system; Backoff control method in a random access method comprising a. The method of claim 1, C), If the number of random access retransmission of the unspecified user exceeds the maximum number of retransmissions, the method of notifying the user of the transmission failure and terminate the system. A recording medium on which a program of a backoff control method in a random access method is recorded, A first function of selecting a plurality of users attempting access to the wireless access network to give priority to the access; When the first function is completed, when a first collision occurs after a random access transmission from a plurality of users is requested to the wireless access network, a parameter for increasing a contention window for retransmission is set differently for each priority / non-priority user. 2 functions; And A third function of performing a backoff control within a range not to exceed the maximum number of retransmissions set by the system when the size of the competition window for each user is set through the second function; Recording medium recording a program comprising a.