KR20180088223A - Method of Controlling Congestion for Reducing Acess Delay time of Terminal in Wireless Mobile Network - Google Patents

Abstract

Disclosed is a congestion control method for reducing an access delay time of a terminal in a wireless mobile communication network. The disclosed congestion control method determines the number of retransmissions of a terminal in a specific service and applies different access probabilities for each terminal based on the determined access number. According to the present invention, access delay can be reduced through congestion control in a random access channel (RACH) of the wireless mobile communication network.

Description

TECHNICAL FIELD The present invention relates to a congestion control method for reducing a connection delay time of a terminal in a wireless mobile communication network,

Embodiments of the present invention relate to a congestion control method for shortening a connection delay time of a terminal in a wireless mobile communication network.

As the demand for machine-type communication (MTC) grows, it becomes important to support it in the wireless mobile communication network. MTC has different characteristics from existing human-to-human communication. In particular, the congestion problem on the random access channel (RACH) has become an urgent problem to solve because it has a lot of small data, the number of MTC terminals is much larger than that of smart phones, and that there are many uplink-oriented communications.

 Random access is initiated when the UEs accessing the eNB send a preamble to the specified RACH. At this time, the preamble has a predetermined number (V), and the terminal randomly selects one to transmit. At this time, only the UE that selected the unique preamble is allocated the uplink resource by the eNB. When a plurality of UEs select one preamble, a collision occurs, random access fails in the corresponding RACH, and the random access process is performed again after the random back-off. Therefore, if too many terminals perform random access at the same time, preamble collision occurs, the efficiency of random access decreases, and the connection time increases rapidly.

An access class barring (ACB) (or p-persistent method) technique has been proposed as an effective way to solve this problem. Predicts the number of terminals that the eNB intends to access in advance, and controls the connection probability when the number is larger than the allowed number of connections. A terminal that transmits a system information block (SIB) message including a barging factor and transmits randomly is selected before the preamble transmission. If the random number is less than the barring factor, random access is performed. In the opposite case, it becomes barring for a certain time. However, this technique has a disadvantage that the access delay time of the terminal increases rapidly. Therefore, in ACB, MTC terminal is divided into several access classes (AC), and when congestion occurs, ACs with low priority conrtol. (AC based control)

 1 is a diagram illustrating a random access procedure in LTE-A.

Disclosure of Invention Technical Problem [8] The present invention is directed to a congestion control method capable of shortening a delay time according to connection of a terminal.

According to an aspect of the present invention, there is provided a congestion control method for determining a number of retransmissions of a terminal in a specific service and applying different access probabilities for each terminal based on the determined number of accesses do.

According to the present invention, there is an advantage that connection delay can be shortened through congestion control in the RACH (Random Access Channel) of the wireless mobile communication network.

1 shows a random access procedure in LTE-A;
Figure 2 is an analysis of causes of connection delays;
3 illustrates a framework of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" .

Also, when an element is referred to as " comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

,

) =(MTC 단말의 최대 허용 지연시간, 서비스가 허락하는 access dealy 초과 비율)로 정의된다고 가정한다. 예를 들어 (800ms, 5%)이면 목표 access delay는 800ms이고 5% 미만의 access delay 초과를 요구하는 것이다. 두 조건간에는 다음과 같은 수식이 정의된다.An object of the present invention is to propose a method of controlling RACH congestion while satisfying an access delay condition required by a delay-constrained MTC terminal. The access delay conditions of the MTC terminal assumed in this study are as follows. (

,

) = (Maximum allowed delay time of the MTC terminal, access allowy excess rate allowed by the service). For example (800ms, 5%), the target access delay is 800ms and requires an access delay of less than 5%. The following equations are defined between the two conditions.

(1)

(One)

2 is an analysis of the cause of the connection delay.

FIG. 2 is summarized as follows.

(2)

(2)

(3)

(3)

(4)

(4)

은 재전송 횟수가 r인 단말들의 access delay이다. 수식 (4)는 네트워크에 재전송 횟수에 대한 분포를 eNB가 안다고 가정하였을 때의 네트워크의 예상 access delay를 정의한 것이며,

이 재전송 횟수가 r인 단말의 비율이다. 이 값은 random access의 결과로부터 통계적 추측을 통하여 구할 수 있다. 본 발명에서는 이를 normal distribution으로 approximation 하여 재전송 횟수 분포와, 접속확률에 따른 access delay model을 제시한다.

Is the access delay of the terminals with the number r of retransmissions. Equation (4) defines the expected access delay of the network when the eNB knows the distribution of the number of retransmissions to the network,

Is the ratio of the terminal having the number of retransmissions r. This value can be obtained by statistical guessing from the result of random access. In the present invention, this is approximated by a normal distribution, and a retransmission frequency distribution and an access delay model according to a connection probability are presented.

(5)

(5)

In the case of the existing ACB, when the number of UEs performing random access to one random access channel is estimated to be N, the connection probability is determined as follows to maximize random access throughput.

However, if N is very large, a small p is set, which results in a spike in access delay. Therefore, in this study, we operate the existing ACB first and then operate the enhanced ACB to meet the access delay condition when a lot of connections are expected.

3 is a diagram showing a framework of the present invention.

From Equation (3), it can be said that the access delay of a terminal with a large r (retransmitted) is high. In order to reduce access delay, access delay can be satisfied if it is possible to give access priority to the terminals that stay on the network for a long time, that is, the number of retransmissions.

을 재전송 횟수가 r인 단말들에게 적용되는 접속확률이라고 정의하자. Access delay를 감소시키는

을 구하기 위하여 utility function을 정의한다.

은 재전송 횟수가 r인 단말들의 utility function이며 r이 클수록 (즉, 오랜 시간 패킷을 못보낸 단말일수록) 접속권한을 줬을 때 큰 값을 나타낸다. 이를 간단한 모델로 정의하여

로 정의한다.

은 가중치 값으로

for

를 만족하는 상수이다. 결과적으로 본 발명에서 제안하는 방식을 수식화하면 다음과 같다.Therefore, the present invention proposes a method of applying different access probabilities according to the number of connections.

Is defined as a connection probability applied to terminals having a retransmission count r. Reducing Access Delays

The utility function is defined to obtain

Is the utility function of the terminals with the number of retransmissions r, and it shows a large value when the r is larger (that is, the terminal that has not sent the packet for a long time) gives the access right. We define this as a simple model

.

Is the weight value

for

. As a result, the method suggested by the present invention can be expressed as follows.

(6)(P1)

(6)

st (c1)

(c4)

(c2)

(c4)

(C.1) is the access delay condition (ie, the ratio exceeding access delay), and (C.2) RACH throughput condition.

집합을 구하게 된다. By using this optimization problem, it is possible to guarantee a certain amount of RACH throughput while satisfying the access delay condition

And a set is obtained.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims (1)

Determining a number of retransmissions of a terminal in a specific service and applying a different connection probability for each terminal based on the determined connection count.

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