KR101710711B1 - Green Small Cell Operation Using Belief Propagation in Wireless Networks - Google Patents

Abstract

The present invention relates to a green small cell operation method which comprises the steps of: transmitting an initial belief message to a user terminal; receiving a first belief message from the user terminal; transmitting, to the user terminal, a second belief message generated from the first belief messages of the user terminal except a corresponding user terminal; measuring reliability of an access point by using a lastly received first belief message after repeating a step of receiving the first belief message and a step of transmitting the second belief message, a predetermined number of times; and transmitting the reliability of the access point to the user terminal. Therefore, by realizing belief propagation for measuring surrounding distribution of a user terminal which is not observed yet based on a state of a user terminal which is already observed, the energy efficiency of the whole network can be increased.

Description

[0001] The present invention relates to a method of operating a small-sized cell using a reliable propagation in a wireless network,

The present invention relates to a method for operating a small cell and an access point and a user terminal. More particularly, the present invention relates to a method for efficiently operating an access point using a trust message for access point and user terminal information.

A small cell is a low-power wireless access point with a range of operation of several hundred meters (m), and it places the terminal close to the base station and reduces the operating range (cell size) Can be solved. In addition, since the terminal is positioned close to the base station, power consumption of the terminal can be reduced, and the installation cost and the maintenance cost are less than that of the existing base station. It is classified into metro cell, micro cell, pico cell, and femto cell depending on the use range and usage. It can be divided into home, enterprise, and hotspot depending on the installation area and service purpose.

Cell search method (Korean Patent Laid-Open No. 10-2014-0132686)

A first problem to be solved by the present invention is to provide a small cell operating method for efficiently operating an access point using a trust message for access point and user terminal information.

A second object of the present invention is to provide an access point for efficiently operating an access point using a trust message for an access point and user terminal information.

A third problem to be solved by the present invention is to provide a user terminal that efficiently operates an access point using a trust message for an access point and user terminal information.

According to another aspect of the present invention, there is provided a method for transmitting an initial trust message, the method comprising: transmitting an initial trust message to a user terminal; Receiving a first trust message from a user terminal; Transmitting to the user terminal a second trust message generated from first trust messages of other user terminals except for the user terminal; Receiving the first trust message and the second trust message repeatedly for a predetermined number of times, and calculating the reliability of the access point using the last received first trust message; And transmitting the reliability of the access point to the user terminal. The user terminal determines an access point to be connected using the reliability of the access point and the intensity of the received signal, and the access point, to which the user terminal is not connected, The value included in the first trust message is defined as an expected value of the local energy efficiency and the expected value has a meaning of a probability that the corresponding user terminal is connected to the corresponding access point, The second trust message is generated from the first trust messages of the other user terminals except for the corresponding user terminal, and the second trust message is generated from the second trust messages of the other access points except for the local energy efficiency and the corresponding access point, Based on the state of the user terminal And implementing a propagation propagation (Belief propagation) for calculating a cell.

According to another aspect of the present invention, there is provided a method for transmitting an initial trust message, the method comprising: receiving an initial trust message from an access point; Transmitting to the access point a first trust message generated from initial trust messages of other access points excluding the access point; Receiving a second trust message from an access point; Receiving the reliability of the access point from the access point after repeating the step of transmitting the first trust message and receiving the second trust message a predetermined number of times; And determining the access point to be connected using the reliability of the received access point and the strength of the received signal and connecting the determined access point to the access point, wherein the access point to which the user terminal is not connected turns off the power, The value included in the message is defined as an expected value of the local energy efficiency, and the expected value has a meaning of a probability that the user terminal is connected to the access point. The first trust message indicates a local energy efficiency of the corresponding user terminal, And the second trust message is generated from the first trust messages of the other user terminals except for the corresponding user terminal so that the unacknowledged user terminal is not yet observed based on the state of the already observed user terminal (Belief prop) that calculates the ambient distribution of user terminals and a small cell operating method is implemented.

According to an embodiment of the present invention, the first trust message and the second trust message are updated while repeating transmission / reception of the first trust message and transmission / reception of the second trust message. Lt; / RTI >

delete

In order to achieve the second object of the present invention, there is provided an access point of a wireless network including a small cell, the access point comprising: an initial trust message to a user terminal; a first trust message from a user terminal; To the user terminal and transmits the reliability of the access point to the user terminal; And generating a second trust message from the first trust messages of the other user terminals except for the user terminal, repeating the reception of the first trust message and the transmission of the second trust message a predetermined number of times, Wherein the user terminal determines an access point to be connected based on the reliability of the access point and the strength of the received signal, and the access point to which the user terminal is not connected The value included in the first trust message is defined as an expected value of the local energy efficiency and the expected value has a meaning of a probability that the corresponding user terminal is connected to the corresponding access point, The local energy efficiency of the terminal and the second energy efficiency of the other access points except for the corresponding access point And the second trust message is generated from the first trust messages of the other user terminal except for the corresponding user terminal so as to calculate the surrounding distribution of the user terminal not yet observed based on the state of the already observed user terminal Wherein the access point is characterized in that it implements the belief propagation that the access point transmits.

In order to achieve the third object, the present invention provides a user terminal of a wireless network configured with a small cell, comprising: an initial trust message from an access point; a first trust message to an access point; 2 communication unit receiving the trust message and receiving the reliability of the access point from the access point; And generating a first trust message from the initial trust message or the second trust messages of the other access point except for the access point, repeating the transmission of the first trust message and the reception of the second trust message for a predetermined number of times, And a processor for determining an access point to be connected using the reliability of the received access point and the intensity of the received signal and connecting the access point to the access point, wherein the access point to which the user terminal is not connected turns off the power, Is defined as an expected value of the local energy efficiency and the expectation value has a meaning of a probability that the corresponding user terminal is connected to the access point and the first trust message includes the local energy efficiency of the user terminal and the corresponding access point Lt; RTI ID = 0.0 > of the < / RTI > other access points, 2 trust message is generated from the first trust messages of the other user terminals except for the corresponding user terminal, thereby generating a belief propagation that calculates an ambient distribution of the user terminal that has not yet been observed based on the state of the user terminal already observed The present invention provides a user terminal,

According to the present invention, unnecessary power of the access point can be turned off to increase the energy efficiency of the entire network.

1 is a block diagram of an access point and a user terminal according to an embodiment of the present invention.
2 shows a small cell network.
3 shows a factor graph of an access point and a user terminal.
Figure 4 compares the results of small cell operation according to an embodiment of the present invention.
5 to 6 are flowcharts of a method of operating a small cell according to an embodiment of the present invention.

Prior to the description of the concrete contents of the present invention, for the sake of understanding, the outline of the solution of the problem to be solved by the present invention or the core of the technical idea is first given.

A method of operating a small cell according to an exemplary embodiment of the present invention includes transmitting an initial trust message to a user terminal, receiving a first trust message from the user terminal, receiving first trust messages Transmitting the second trust message to the user terminal, repeating the step of receiving the first trust message and transmitting the second trust message a predetermined number of times, And transmitting the reliability of the access point to the user terminal. The user terminal determines an access point to be connected using the reliability of the access point and the strength of the received signal, , And the access point to which the user terminal is not connected is powered off And a gong.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art, however, that these examples are provided to further illustrate the present invention, and the scope of the present invention is not limited thereto.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, in which: It is to be noted that components are denoted by the same reference numerals even though they are shown in different drawings, and components of different drawings can be cited when necessary in describing the drawings. In the following detailed description of the principles of operation of the preferred embodiments of the present invention, it is to be understood that the present invention is not limited to the details of the known functions and configurations, and other matters may be unnecessarily obscured, A detailed description thereof will be omitted.

1 is a block diagram of an access point and a user terminal according to an embodiment of the present invention.

A wireless network composed of small cells according to an embodiment of the present invention has an environment as shown in FIG. A plurality of access points (APs) are randomly distributed in the coverage of a macro cell base station covering a wide range. (The access point is installed at a random location by the user within the range of the macro cell.) Each access point broadcasts a signal called a beacon signal to neighboring user equipments (UEs) at regular intervals. Since each access point transmits a unique Beacon signal, when a user terminal receives a signal transmitted from a specific access point, it can know which signal is transmitted from which access point. The user terminal receives the beacon signal from neighboring access points, measures the intensity of each signal, and estimates the channel from the information.

The access point and the user terminal exchange information with each other, and each access point and the user terminal performs a Belief Propagation (BP) method. The trust propagation method consists of message transfer between access points and user terminals and operates in a distributed manner. After the execution of the algorithm, each user terminal can determine which access point should be connected to. Each access point is turned on when there is a user terminal connected thereto, but turned off when there is no connected user terminal.

The access point 110 and the user terminal 120 of the wireless network configured by small cells are composed of the communication units 111 and 121 and the processing units 112 and 122.

Each of the communication units 111 and 121 exchanges information with each other, and the processing units 112 and 122 process the information and derive a result according to the information.

The communication unit 111 of the access point 110 transmits an initial trust message to the user terminal, receives the first trust message from the user terminal, transmits the second trust message to the user terminal, .

The processing unit 112 of the access point 110 generates a second trust message from the first trust messages of the other user terminals except for the user terminal and transmits the first trust message and the second trust message to a predetermined The reliability of the access point is calculated using the last received first trust message. Then, the access point to which the user terminal is not connected turns off the power.

The communication unit 121 of the user terminal 120 receives the initial trust message from the access point, transmits the first trust message to the access point, receives the second trust message from the access point, .

The processing unit 122 of the user terminal 120 generates a first trust message from the initial trust message or the second trust messages of another access point except for the corresponding access point and transmits the first trust message and the second trust message After the reception is repeated a predetermined number of times, the access point to be connected is determined based on the reliability of the received access point and the strength of the received signal, and the access point is connected to the access point. The access point to be connected is determined based on the reliability of the access point and the strength of the received signal.

During the transmission and reception of the first trust message and the transmission and reception of the second trust message, the first trust message and the second trust message are updated.

The first trust message may be generated from second trust messages of other access points except the local energy efficiency of the corresponding user terminal and the corresponding access point, and the second trust message may be generated from other user terminals 1 trust messages and the first trust message and the second trust message may be derived using a trust propagation method.

Hereinafter, a process of exchanging trust messages between the access point and the user terminal and determining an access point to be turned off with respect to the access point to which the user terminal is connected will be described in detail.

The information of the user terminal is used so that the ON / OFF operation of the access point can be implemented in a distributed manner in a wireless network composed of randomly distributed access points. The small cell can be efficiently operated by using the reliability propagation method in using the information of the user terminal. The information used to turn the access point on and off is energy efficient and uses a trust message to derive it.

First, the trust message used here will be described.

The on-off status of the access point is expressed as follows.

로 정의하고, 사용자단말 UE는

로 정의한다. x_j는 엑세스 포인트가 켜져있으면 1 꺼져있으면 0이다. 엑세스포인트가 켜져있을때 동작전력 P_j,Op과 송신전력 P_j,Tx을 소비하는데 이는 다음과 같다.Here, the access point AP

, And the user terminal UE defines

. x _j is 0 if the access point is on and 0 if it is off. When the access point is turned on, the operating power P _{j, Op} and the transmission power P _{j, Tx} are consumed as follows.

에서 s_i,j는 다음과 같다.A user association matrix between the access point and the user terminal,

S _{i, j} is as follows.

The strength SINR _{i, j} of the signal received by the user terminal UE i from the access point AP j is expressed as follows.

Where g _{i, j} is the channel gain and N _o is the noise power. The maximum data rate of the user terminal UE i is as follows.

The transmission rate of the user terminal UE i calculated from Equation (4) is as follows.

이다.here

to be.

By using the above equations, the on-off state of the access point that can maximize the energy efficiency can be obtained, so that the small cell can be efficiently operated. The energy efficiency F (x), which is an objective function, is defined as a sum of the transmission rates of all user terminals (total network transmission rate) divided by the sum of the operating power consumed by the on-going access points, we can derive f _i (x).

That is, the on-off state x of each access point for maximizing the objective function F (x) is obtained. This can be expressed by the following equation.

로 정의하고, 온오프 상태는

로 정의하고, 단축된 표기는

로 정의한다. 그리고, 여기서, 각 엑세스 포인트의 온오프 상태 x에 따른 결합확률분포(joint probability distribution) p(x)는 볼츠만의 법칙(Boltzmann's law)를 이용하여 다음과 같이 나타낼 수 있다.The objective function F (x) can be transformed into a form suitable for the optimization framework using the following propagation method. First, to use the on-off state x of each access point, the set of discrete random variables

And the on-off state is defined as

, And the abbreviated notation

. Here, the joint probability distribution p (x) according to the ON / OFF state x of each access point can be expressed as follows using Boltzmann's law.

로 표현한다. Equation (9) can be applied to a factor graph of an access point and a user terminal as shown in FIG. As shown in FIG. 3, a variable node is expressed as an on-off state xj as an access point, and a factor node is represented as a user terminal

.

In order to derive the on-off state (x) for optimizing the objective function and the cell connection matrix (s) according to the state, a message transmission method in the reliable propagation is used.

는 상기 목적함수를 최대화하며 다음과 같이 나타낼 수 있다.When 1 / τ is ∞, p (x) and F (x) are close to their maximum values. At this time, the expected value of the on-

Maximizes the objective function and can be expressed as:

이고,

는 랜던 변수 X_j의 국부 기대값이다. 여기서 신뢰전파 방법을 이용하여 엑세스 포인트 온오프를 의미하는 랜덤변수 Xj에 따른 p(x)의 주변확률분포(marginal probability distribution)를 구할 수 있고, 주변확률분포를 추정함으로써 문제의 근사화된 답을 구할 수 있다. 추정된 주변확률분포를 이하 신뢰 Belief b_j(x_j)로 정의한다.here,

ego,

Is the local expected value of the random variable X _j . Here, we can obtain the marginal probability distribution of p (x) according to the random variable Xj, which means the access point on-off, using the confidence propagation method, and obtain the approximate answer of the problem by estimating the neighborhood probability distribution . The estimated belief distribution is defined as Belief b _j (x _j ).

The access point and the user terminal transmit and receive the trust message including b _j (x _j ) defined as above, and determine on / off of the access point using the derived result.

First, each access point AP j generates an initial trust message including an initial value according to a uniform distribution using Equation (11) and transmits it to each user terminal UE i.

Next, each user terminal UE i receiving the initial trust message generates a first trust message using Equation (12) and transmits the first trust message to each access point AP j. The value included in the first trust message is defined as the expected value of the local energy efficiency, which has a similar meaning to the probability that the user terminal UE i is connected to the access point AP j. The first trust message is generated from the second trust messages of other access points except for the local energy efficiency of the user terminal and the corresponding access point.

Then, each access point AP j receiving the first trust message generates a second trust message, which is a new trust message, using the information included in the first trust message, using Equation (13) UE i. This message has a similar meaning to the probability that it should be turned on according to the results observed by other user terminals. The second trust message is generated from the first trust messages of the other user terminals except for the corresponding user terminal.

Thereafter, the steps of Equation (12) for sending and receiving the first trust message and (13) for sending and receiving the second trust message are repeated a predetermined number of times. The number of iterations may be predetermined or may vary depending on the number of access points or user terminals, the target network energy efficiency, and the network environment.

The access point repeats the step of receiving the first trust message and the step of transmitting the second trust message a predetermined number of times and then transmits the first trust message to the access point < RTI ID = 0.0 > The reliability b _j (x _j ) is calculated.

The reliability of the calculated access point is transmitted to all user terminals.

The user terminal having received the reliability of the finally calculated access point determines an access point to be connected by using the reliability of the received access point and the strength of the received signal and connects to the access point as shown in the following Equation (15).

? J is an integer valued function, and? Is a weighting factor. If the weighting factor η = 0, it is connected to the access point providing the highest received signal strength, and if η → ∞, it is connected to the highest-reliability access point.

If the access point to which the user terminal is to be connected is determined through the above process, the access point to which the user terminal is not connected can turn off the power to optimize the energy efficiency of the entire network.

Figure 4 compares the results of small cell operation according to an embodiment of the present invention and shows that the energy efficiency of the small cell operation according to the embodiment of the present invention using the reliable propagation method is higher than the standard by 129% Which is more efficient.

FIG. 5 is a flowchart illustrating a process performed by an access point in a small cell operating method according to an exemplary embodiment of the present invention. FIG. 6 is a flowchart illustrating a process performed by a user terminal in a small cell operating method according to an exemplary embodiment of the present invention. to be.

5 and 6 correspond to the detailed description of the access point and the user terminal in FIGS. 1 to 4, and a duplicate description will be omitted.

The access point transmits an initial trust message to the user terminal in step 510, receives the first trust message from the user terminal in step 520, and generates the first trust message from the first trust messages of other user terminals except for the corresponding user terminal in step 530 Transmits the second trust message to the user terminal, repeats the step of receiving the first trust message and transmitting the second trust message for a predetermined number of times in step 540, and then transmits the finally received first trust message And the reliability of the access point is transmitted to the user terminal in step 550. In step 550, The access point to which the user terminal is not connected turns off the power.

The user terminal receives the initial trust message from the access point in step 610 and transmits to the access point a first trust message generated from initial trust messages of other access points excluding the access point in step 620. In step 630, Receives the second trust message from the access point, transmits the first trust message and receives the second trust message in step 640 for a predetermined number of times, receives the reliability of the access point from the access point, An access point to be connected is determined based on the reliability of the received access point and the intensity of the received signal, and the access point is connected to the corresponding access point.

During the transmission and reception of the first trust message and the transmission and reception of the second trust message, the first trust message and the second trust message are updated. Wherein the first trust message is generated from second trust messages of another access point excluding the local energy efficiency of the corresponding user terminal and the corresponding access point and the second trust message is generated from the first trust message of the other user terminal except for the corresponding user terminal, Messages, and the first trust message and the second trust message are derived using a belief propagation method.

Embodiments of the present invention may be implemented in the form of program instructions that can be executed on various computer means and recorded on a computer readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described with reference to particular embodiments, such as specific constituent elements, and limited embodiments and drawings. However, it should be understood that the present invention is not limited to the above- And various modifications and changes may be made thereto by those skilled in the art to which the present invention pertains.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

110: access point
120: User terminal
111, 121:
112, and 122:

Claims (11)

Transmitting an initial trust message to a user terminal;
Receiving a first trust message from a user terminal;
Transmitting to the user terminal a second trust message generated from first trust messages of other user terminals except for the user terminal;
Receiving the first trust message and the second trust message repeatedly for a predetermined number of times, and calculating the reliability of the access point using the last received first trust message; And
And transmitting the reliability of the access point to a user terminal,
The user terminal determines an access point to be connected using the reliability of the access point and the strength of the received signal,
The access point to which the user terminal is not connected turns off the power,
The value included in the first trust message is defined as an expected value of local energy efficiency, and the expected value has a meaning of a probability that the corresponding user terminal is connected to the access point,
Wherein the first trust message is generated from the second trust messages of another access point except for the local energy efficiency of the user terminal and the corresponding access point,
The second trust message is generated from the first trust messages of the other user terminals except for the corresponding user terminal, thereby generating a belief propagation message for calculating an ambient distribution of the user terminal that has not yet been observed based on the state of the already- ). ≪ / RTI > Receiving an initial trust message from an access point;
Transmitting to the access point a first trust message generated from initial trust messages of other access points excluding the access point;
Receiving a second trust message from an access point;
Receiving the reliability of the access point from the access point after repeating the step of transmitting the first trust message and receiving the second trust message a predetermined number of times; And
Determining an access point to be connected using the reliability of the received access point and the strength of the received signal, and connecting the determined access point to the access point,
The access point to which the user terminal is not connected turns off the power,
The value included in the first trust message is defined as an expected value of local energy efficiency, and the expected value has a meaning of a probability that the corresponding user terminal is connected to the access point,
Wherein the first trust message is generated from the second trust messages of another access point except for the local energy efficiency of the user terminal and the corresponding access point,
The second trust message is generated from the first trust messages of the other user terminals except for the corresponding user terminal, thereby generating a belief propagation message for calculating an ambient distribution of the user terminal that has not yet been observed based on the state of the already- ). ≪ / RTI > 3. The method according to claim 1 or 2,
Wherein the first trust message and the second trust message are updated while repeating transmission / reception of the first trust message and transmission / reception of the second trust message. delete delete An access point of a wireless network comprising small cells,
A communication unit for transmitting an initial trust message to the user terminal, receiving the first trust message from the user terminal, transmitting the second trust message to the user terminal, and transmitting the reliability of the access point to the user terminal; And
Generates a second trust message from the first trust messages of the other user terminals except the user terminal, repeats the reception of the first trust message and the transmission of the second trust message a predetermined number of times, 1 trust message to calculate the reliability of the access point,
The user terminal determines an access point to be connected using the reliability of the access point and the strength of the received signal,
The access point to which the user terminal is not connected turns off the power,
The value included in the first trust message is defined as an expected value of local energy efficiency, and the expected value has a meaning of a probability that the corresponding user terminal is connected to the access point,
Wherein the first trust message is generated from the second trust messages of another access point except for the local energy efficiency of the user terminal and the corresponding access point,
The second trust message is generated from the first trust messages of the other user terminals except for the corresponding user terminal, thereby generating a belief propagation message for calculating an ambient distribution of the user terminal that has not yet been observed based on the state of the already- ). ≪ / RTI > The method according to claim 6,
Wherein the first trust message and the second trust message are updated while repeating the reception of the first trust message and the transmission of the second trust message. delete 1. A user terminal of a wireless network comprising small cells,
A communication unit that receives an initial trust message from an access point, transmits a first trust message to the access point, receives a second trust message from the access point, and receives reliability of the access point from the access point; And
Generating a first trust message from an initial trust message or second trust messages of an access point other than the access point, repeating the transmission of the first trust message and the reception of the second trust message for a predetermined number of times, And a processing unit for determining an access point to be connected by using the reliability of the received access point and the intensity of the received signal and connecting the determined access point to the access point,
The access point to which the user terminal is not connected turns off the power,
The value included in the first trust message is defined as an expected value of local energy efficiency, and the expected value has a meaning of a probability that the corresponding user terminal is connected to the access point,
Wherein the first trust message is generated from the second trust messages of another access point except for the local energy efficiency of the user terminal and the corresponding access point,
The second trust message is generated from the first trust messages of the other user terminals except for the corresponding user terminal, thereby generating a belief propagation message for calculating an ambient distribution of the user terminal that has not yet been observed based on the state of the already- ). ≪ / RTI > 10. The method of claim 9,
Wherein the first trust message and the second trust message are updated while repeating the transmission of the first trust message and the receipt of the second trust message. delete

Images