KR101047039B1 - Power Control and User Allocation Method in Wireless Mesh Network - Google Patents

Abstract

A method of controlling transmission power and distributing users in a wireless mesh network including a plurality of access points, the method comprising: (a) calculating a first constraint from each link capacity and each user channel capacity of the wireless mesh network; (B) calculating a second constraint from the number of access users of each of the access points, and (c) a backhaul in the wireless mesh network based on the first constraint and the second constraint. And determining the transmission power of each of the access points and the number of access users of each of the access points so that the required transmission power required for the configuration of the C-P is optimized. According to this method, it is possible to improve the power efficiency of the system through user allocation and transmission power control in the wireless mesh network, and to reduce the influence of interference on other wireless communication networks without degrading the quality of service in the wireless mesh network. have.

Wireless mesh network, transmit power control, user allocation

Description

Method for Power Control and User Allocation in Wireless Mesh Network {Method for Power Control and User Allocation in Wireless Mesh Network}

The present invention relates to a power control and user distribution method in a wireless mesh network, and more particularly, an access point (AP) connected to a wireless backhaul in a wireless mesh network is a gateway. It relates to a technique for optimizing the power required to configure the backhaul by adjusting the transmission power required to transfer data and the number of users connected to each access point.

The present invention is derived from a study performed as part of the next-generation tactical defense communication source technology development project of the Ministry of Knowledge Economy [task management number: N03090062, the task name: development of next-generation tactical defense communication high-speed mobility providing technology].

Recently, communication technology has been developed to provide high-speed services for terminals (wires) wirelessly connected to access points having a certain service coverage as demand for wireless communication networks increases rapidly. In particular, a wireless local area network (WLAN), for example, a wireless LAN that conforms to the IEEE 802.11 standard, is a wireless communication network that enables wireless Internet access. This is attracting attention. The wireless mesh network is one of the solutions to the above needs, and is used to expand the service area by combining several local networks, and have an automatic configuration and restoration function in response to changes in the wireless communication environment and the wireless network. have.

In general, a wireless mesh network includes a plurality of mesh nodes. The mesh nodes are coupled by radio. A mesh node may be wirelessly connected to a leaf node by a terminal in a local network. The mesh node providing a wireless connection to the terminal may be referred to as an access point. Meanwhile, there may be a special mesh node that serves to provide access to an external backbone network. As such, a mesh node, which is an interconnection point between a wireless mesh network and an external network, may be called a gateway. . In a wireless mesh network, even when one or more mesh nodes cannot operate, other mesh nodes can communicate with each other through an appropriate path, thereby providing reliability and redundancy. In addition, wireless mesh networks are easy to configure, as there is no need for direct backhaul links to interconnects and gateways between each mesh node. For example, an access point of a wireless LAN may be wirelessly connected to form a mesh backhaul, and a mesh WLAN of an infrastructure, which is a mesh wireless network connected to the Internet through a gateway, may be constructed.

1 is a diagram illustrating an exemplary structure of a wireless mesh network. The wireless mesh network 100 includes a gateway 140, a plurality of access points 160, 162, 164, and a plurality of other mesh nodes 180, 182. The mesh nodes 180, 182 and the access points 160, 162, 164 receive traffic from the input link and forward the traffic to the output link in the wireless mesh network. Each of the access points 160, 162 and 164 and the other mesh nodes 180 and 182 may have a single radio interface or may have a multi radio interface. have. In addition, the access points 160, 162, and 164 cover a service area of a specific range, and provide wireless services to the terminals 190, 191, 192, 193, 194, 195, and 196 located within the range. do. For example, the access points 160, 162, and 164 may communicate with terminals 190, 191, 192, 193, 194, 195, and 196, respectively, connected to themselves using an interface according to the IEEE 802.11 standard. The gateway 140 provides access to the Internet 120, which may be connected to the Internet 120 by wire. In the wireless mesh network 100 including the gateway 140, traffic transmitted to the Internet 120, which is an external network, and traffic received from the Internet 120 are concentrated in the gateway 140. Traffic generated by the terminals 190, 191, 192, 193, 194, 195, and 196 may be relayed through the access points 160, 162, and 164 and / or the mesh nodes 180 and 182. 160, 162, 164 or the gateway 140 may be forwarded, and the terminals 190, 191, 192, 193, 194, 195, and 196 may communicate with each other or access the Internet 120.

In order to configure a mesh-like backhaul in a wireless mesh network, transmission power required to transmit incoming traffic by a mesh node including an access point is consumed. Here, the problem is how to optimize the required transmit power required for the configuration of the backhaul in the wireless mesh network. For example, when constructing a wireless communication system in which multiple radio access technologies (RATs) share the same frequency band in order to increase frequency efficiency, the transmission power required to construct a backhaul in a wireless mesh network is the same frequency band. Since it acts as interference to other wireless communication networks sharing the network, it is necessary to minimize the transmission power required to configure the backhaul in the wireless mesh network in order to minimize such interference.

The present invention is to recognize the above problems, the access point (AP) connected to the wireless backhaul in the wireless mesh network is connected to each access point and the transmission power required to transfer data to the gateway (gateway) It is an object of the present invention to provide a method for optimizing the required transmit power required for the backhaul configuration by adjusting the number of users.

Furthermore, when the wireless mesh network and the other wireless communication network form a wireless communication system sharing the same frequency band, different wireless access schemes may be used in the same frequency band by minimizing the required transmission power required for the backhaul in the wireless mesh network. It is an object of the present invention to provide a method for minimizing interference to a wireless communication network that is serviced using a.

The object of the present invention is not limited to the above-mentioned object, and other objects that are not mentioned will be clearly understood by those skilled in the art from the following description.

According to an embodiment of the present invention for achieving the above object, in a method for controlling transmission power and distributing users in a wireless mesh network including a plurality of access points, (a) each of the wireless mesh network Calculating a first constraint from the link capacity and each user channel capacity of the processor; (b) calculating a second constraint from the number of connected users of each of the access points; and (c) the first constraint. And determining the transmit power of each of the access points and the number of access users of each of the access points so that the necessary transmit power required for the configuration of a backhaul in the wireless mesh network is optimized based on the second constraint. A transmission power control and a user distribution method are provided.

Further, in the step (c), the required transmission power is a total transmission power that is the sum of the transmission powers of each of the access points.

In addition, the step (c) is the transmit power of each of the access points such that the objective function, which is the total transmit power that is the sum of the transmit powers of the access points, has a minimum value while satisfying the first and second constraints. And a transmission power control and user distribution method for determining the number of access users of each of the access points.

Further, in the step (a), the first constraint is that for each of the access points, the link capacity of the output link is equal to or greater than the sum of the sum of the link capacity of the input link and the user channel capacity of the access user of the access point. A transmission power control and user distribution method is provided.

Further, in the step (b), the second constraint provides a transmission power control and user distribution method, wherein the total number of connected users in the wireless mesh network is constant.

In addition, step (c) provides a transmission power control and user distribution method comprising the step of obtaining a Lagrangian function from the objective function, the first constraint and the second constraint.

In addition, in the step (c), if the Lagrange function is divided into a first function that is a function of transmission power of each of the access points and a second function that is a function of the number of access users of each of the access points, the access A transmission power control and user distribution method is provided that includes determining transmission power of each point and determining the number of access users of each of the access points.

In addition, the step (c) provides a transmission power control and user distribution method comprising the step of obtaining a Lagrangian dual function from the objective function, the first constraint and the second constraint.

In addition, when the Lagrange dual function is divided into a first function, which is a function of transmission power of each of the access points, and a second function, which is a function of the number of access users of each of the access points, A transmission power control and user distribution method is provided that includes determining transmission power of each of the access points and determining the number of access users of each of the access points.

In addition, in step (c), a transmission power control and user distribution method for determining transmission power of each of the access points using a convex optimization solution is provided.

In addition, the convex optimization solution provides a transmission power control and user distribution method, characterized in that the interior point method (interior point method).

Further, in the step (c), determining the number of access users of each of the access points may reduce the number of access users of one of the plurality of access points and access the other access points by the reduced number. A transmission power control and user distribution method characterized by increasing the number of users.

In addition, step (c) provides a transmission power control and user distribution method comprising the step of updating a first multiplier which is a Lagrangian multiplier associated with the first constraint.

In addition, the first multiplier provides a transmission power control and user distribution method for updating by using a subgradient of the Lagrange dual function for the first multiplier.

In addition, step (c) provides a method for controlling transmission power and transmitting power, including updating a second multiplier that is a Lagrange multiplier associated with the second constraint.

In addition, the second multiplier provides a transmission power control and user distribution method for updating by using the sub-gradient of the Lagrange dual function for the second multiplier.

이고, 상기 제1 제약조건은

이며,상기 제2 제약조건은

이되, K는 상기 복수의 액세스 포인트의 총수, P_i는 상기 복수의 액세스 포인트 중 i 번째 액세스 포인트의 송신 전력, A는 상기 무선 메쉬 네트워크의 복수의 링크 중 m 번째 링크가 상기 복수의 액세스 포인트 중 k 번째 액세스 포인트의 출력링크인 경우에는 m 번째 열의 엘리먼트 a_km이 1이고, 상기 무선 메쉬 네트워크의 복수의 링크 중 m 번째 링크가 상기 복수의 액세스 포인트 중 k 번째 액세스 포인트의 입력링크인 경우에는 a_km이 -1이며, 그 외의 경우에는 a_km이 0인 행렬, b는, C_ij가 i 번째 액세스 포인트에서 j 번째 액세스 포인트로의 링크의 링크 용량이고, P(i)가 i 번째 액세스 포인트의 부모(parent) 액세스 포인트들의 집합이며, B가 게이트웨이에 연결된 외부 네트워크의 용량일 때,

인 벡터, C는 상기 사용자 채널 각각의 사용자 채널 용량, n_j는 상기 복수의 액세스 포인트 중 j 번째 액세스 포인트의 접속 사용자 수, n은

인 벡터, N은 상기 무선 메쉬 네트워크의 총 접속 사용자 수인 송신 전력 제어 및 사용자 배분 방법을 제공한다.In addition, the objective function is

Wherein the first constraint is

The second constraint is

Where K is the total number of the plurality of access points, P _i is the transmit power of the i th access point of the plurality of access points, and A is the m th link among the plurality of links of the wireless mesh network. In the case of the output link of the k-th access point, when the element a _km of the m-th column is 1, and the m-th link of the plurality of links of the wireless mesh network is the input link of the k-th access point of the plurality of access points, a a _km -1, and the other cases, a _km of zero matrix, b is a, C _ij is the i link capacity of the link to the second access point to the second access point j, P (i) is the i-th access point A set of parent access points, where B is the capacity of an external network connected to the gateway,

Is a vector, C is the user channel capacity of each of the user channels, n _j is the number of access users of the j-th access point of the plurality of access points, n is

In vector, N provides a transmission power control and user distribution method, which is the total number of connected users of the wireless mesh network.

의 해로부터 결정하되, P는

인 벡터이고,

가 상기 액세스 포인트 각각의 송신 전력의 최대값일 때, P_i는

를 만족하며,

는 상기 제1 제약조건과 연관된 라그랑쥬 승산자인 제1 승산자인 송신 전력 제어 및 사용자 배분 방법을 제공한다.Further, in step (c), the transmit power of each of the access points is

Is determined from the solution of

Is a vector

When P is the maximum value of the transmit power of each of the access points, P _i is

Satisfying

Provides a transmit power control and user distribution method that is a first multiplier that is a Lagrange multiplier associated with the first constraint.

,

에 의하여 n을 갱신하는 단계를 포함하되, u는

벡터의 엘리먼트 중에서 최대값인 엘리먼트의 인수이고, v는

벡터의 엘리먼트 중에서 최소값인 엘리먼트의 인수이며,

은 모든 엘리먼트가 1인 벡터이고,

는 상기 제1 제약조건과 연관된 라그랑쥬 승산자인 제1 승산자이고,

는 상기 제2 제약조건과 연관된 라그랑쥬 승산자인 제2 승산자인 송신 전력 제어 및 사용자 배분 방법을 제공한다.Also, in the step (c), determining the number of access users of each of the access points

,

By updating n, wherein u is

Is the argument of the largest element of the vector, and v is

Is the argument of the minimum element among the elements of the vector,

Is a vector with all elements 1

Is a first multiplier that is a Lagrange multiplier associated with the first constraint,

Provides a transmit power control and user distribution method that is a second multiplier that is a Lagrange multiplier associated with the second constraint.

에 의하여 갱신하되,

는 상기 제1 제약조건과 연관된 라그랑쥬 승산자인 제1 승산자,

는 상기 제2 제약조건과 연관된 라그랑쥬 승산자인 제2 승산자,

은 상기 제1 승산자를 갱신한 값,

은 상기 제2 승산자를 갱신한 값,

는 상기 제1 승산자를 갱신하기 위한 스텝 사이즈(step size),

는 상기 제2 승산자를 갱신하기 위한 스텝 사이즈인 송신 전력 제어 및 사용자 배분 방법을 제공한다.Further, the step (c) may include a first multiplier that is a Lagrange multiplier associated with the first constraint and a second multiplier that is a Lagrange multiplier associated with the second constraint.

Updated by

Is a first multiplier that is a Lagrange multiplier associated with the first constraint,

Is a second multiplier that is a Lagrange multiplier associated with the second constraint,

Is a value of updating the first multiplier,

Is a value of updating the second multiplier,

Is a step size for updating the first multiplier,

Provides a transmission power control and user distribution method that is a step size for updating the second multiplier.

Specific details according to still another embodiment of the present invention are included in the following description and drawings.

According to an embodiment of the present invention, there is an effect of improving the power efficiency of the system through user allocation and transmission power adjustment in a wireless mesh network.

In addition, according to an embodiment of the present invention, there is an effect that can reduce the effect of interference on other wireless communication networks in the wireless mesh network without deterioration of service quality.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. 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. It is provided to fully inform the scope of the invention, and the invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout. In addition, when it is determined that the detailed description of the related well-known configuration or function may obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention;

2 is a diagram illustrating a configuration of a wireless communication system according to an embodiment of the present invention.

The wireless communication system 200 is a system that services a plurality of wireless access methods using the same frequency band. Referring to FIG. 1, a wide area network (WAN) such as a cellular network and a local area network (LAN) such as a wireless LAN are provided. area networks can coexist. In such a case, the WAN serves as a basic network providing basic services, such as voice and low-speed data communication, anytime and anywhere to a terminal connecting to the WAN through a WAN base station 220 covering a relatively wide service area, and the LAN is Access points 260, 261, 262, 263, 264, 265, and 266 may be used in serviceable areas or areas where service is required. Each may be easily installed to serve as an optional network for providing a high speed data communication service to a terminal connected to a LAN. At this time, the access points (260, 261, 262, 263, 264, 265, 266) of the LAN are wirelessly connected to each other in terms of cost or maintenance to form a wireless network backhaul, but the access point (260, 261, All traffic relayed through 262, 263, 264, 265, and 266 may be delivered to the gateway 240. Meanwhile, the gateway 240 may provide a connection to an external network, for example, the Internet. The gateway 240 may be connected to the Internet, for example, by wire. In addition, when the terminal is wirelessly connected to the gateway 240, it may be regarded as a special access point having an interface with an external network. At this time, the traffic generated by the terminal connected to the access point (260, 261, 262, 264, 265, 266) of the LAN constituting the wireless mesh network to the gateway 240, the frequency sharing between the LAN and WAN Interference may occur.

Accordingly, the embodiment of the present invention enables to optimize the transmission power required for the configuration of the backhaul in the wireless mesh network and to reduce the influence of interference between the LAN and the WAN. In particular, according to an embodiment of the present invention, by configuring the backhaul in the wireless mesh network by adjusting the number of users that can access each access point of the wireless mesh network and the transmission power required for the backhaul at each access point of the wireless mesh network A method is provided for optimizing the required transmit power required by.

On the other hand, according to an embodiment of the present invention, the transmission power required for the configuration of the backhaul is optimized in consideration of various restrictions existing in the wireless mesh network according to the actual wireless communication environment. For example, there may be a limit on the number of users connecting to each of the access points, which may be the case where there is an upper limit or a lower limit on the number of access users of each access point, that is, the sum of the number of access users of each access point, i.e. There may be a case where an upper limit or a lower limit exists in the total number of connected users in the wireless mesh network, or the total number of users in the wireless mesh network may be constant. In addition, an upper limit may exist for the transmit power of each access point. In addition, there may be a limitation in transmitting data by the backhaul in the wireless mesh network. For example, the capacity of each output link of the access point may be determined by the capacity of each of the one or more input links and one or more terminals connected to the access point. It must be at least the sum of the capacities of each transmitting user channel.

3 is a diagram illustrating a restriction on the capacity of an output link of an access point in a wireless mesh network according to an embodiment of the present invention.

Referring to FIG. 3, in the wireless mesh network, the j th access point 300 receives traffic from the i th access point 320 and the i ′ th access point 322, and the terminal _j 340 of n _j users is connected. It transmits data through each user channel and forwards traffic to the kth access point 360. For example, as shown in FIG. 3, the maximum value of the traffic that the i th access point 320 and the i ′ th access point 322 delivers to the j th access point 300 is determined by the j th access point 300. If the capacity of the user channel for transmitting the data to the j th access point 300, the terminal capacity of each of the input links C _ij and C _i'j , n _j user terminals 340, j The link capacity C _jk of the output link from the first access point 300 to the k th access point 360 satisfies the following equation.

를 이용할 수 있고, 지향성 안테나를 사용하여 백홀을 구성하는 경우에는 단순한 신호 대 잡음비로서

를 이용할 수 있다. 여기서, h_m은 m 번째 링크의 송신단에 해당하는 액세스 포인트 및 수신단에 해당하는 액세스 포인트 사이의 채널 이득이고, h_nm은 n 번째 링크의 송신단에 해당하는 액세스 포인트와 m 번째 링크의 수신단에 해당하는 액세스 포인트 사이의 간섭 채널 이득이며, σ²는 잡음 전력이다. 한편,

은 m 번째 링크의 송신단에 해당하는 액세스 포인트의 송신 전력으로서, 예컨대 무선 메쉬 네트워크를 이루는 각각의 액세스 포인트에 대하여

라는 제한이 있을 수 있다.In the wireless mesh network, each link capacity and each user channel capacity may be obtained according to channel characteristics. For example, Shannon's channel capacity equation can be used, or a modulation coding set (MCS) given according to the modulation scheme and code rate used for each link, in which case the signal-to-noise ratio also depends on the characteristics of the channel. . For example, when a non-directional antenna is used, since a transmission signal of another link acts as interference with respect to one link, as a signal-to-noise plus interference ratio,

If the backhaul is formed using a directional antenna, the signal to noise ratio

Can be used. Where h _m is the channel gain between the access point corresponding to the transmitting end of the m th link and the access point corresponding to the receiving end, and h _nm is the access point corresponding to the transmitting end of the n th link and the receiving end of the m th link. The interference channel gain between access points, sigma ² is the noise power. Meanwhile,

Is the transmission power of the access point corresponding to the transmitting end of the mth link, for example, for each of the access points forming the wireless mesh network.

There may be a limit.

More generally, according to an embodiment of the present invention, a set of child access points, which are access points that forward traffic to a j th access point in a wireless mesh network, is referred to as C (j), and the j th access point is referred to as traffic. When a set of a parent access point that is an access point transmitting P is called P (j), as long as the channel capacity of each user channel between the terminal accessing the j th access point and the j th access point is C, the output link Constraints on can be described as in the following equation.

On the other hand, when the j-th access point is the mesh node at the end, there is no incoming traffic and only the output link, the constraint on the output link can be expressed by the following equation.

On the other hand, the gateway functions to forward traffic to the external network and is not affected by the number of access users. Therefore, when the j th access point is a gateway having an interface to an external network, when the capacity of the external network connected to the gateway is B, the following equation may be obtained.

In this case, if the element a _km of the kth row and the mth column of the incidence matrix A, which is the K × M matrix, is defined by the following equation, the constraint on the output link is defined for all access points. It can be easily expressed. Where K is the total number of access points including gateways in the wireless mesh network, and L is the total number of links connecting such access points.

Therefore, using the above incidence matrix A, a constraint such as the following equation can be calculated from each link capacity and each user channel capacity of the wireless mesh network.

이고,

이다.here,

ego,

to be.

According to an embodiment of the present invention, when the total number of access users of each access point in the wireless mesh network is constant, the following equation may be expressed.

은 모든 엘리먼트가 1인 벡터를 나타내고, N은 무선 메쉬 네트워크 내의 총 접속 사용자 수를 나타낸다. 한편, 각각의 액세스 포인트에는 최소한의 접속 사용자 수가 존재할 수 있는데, 접속 사용자 수의 최소값을 N_min이라 할 때,

이라는 제한이 있게 된다.here,

Denotes a vector where all elements are 1, and N denotes the total number of connected users in the wireless mesh network. Meanwhile, each access point may have a minimum number of access users. When the minimum value of the access users is N _min ,

There is a restriction.

이라 할 때, 이를 다음의 수학식으로 표현할 수 있다.As described above, when constraints exist in the wireless mesh network, according to an embodiment of the present invention, the wireless mesh network is included in the wireless mesh network based on the above constraints in order to optimize the necessary transmission power required for the backhaul configuration in the wireless network. Minimize the total transmit power, which is the sum of the transmit powers of each of the access points. P _i is called the transmit power of the i th access point

This can be expressed as the following equation.

As described above, according to an embodiment of the present invention, the first constraint, which is a constraint calculated from each link capacity and each user channel capacity of the wireless mesh network, and the constraint calculated from the number of access users of each access point, respectively. The wireless mesh network is adjusted by adjusting the transmit power of each access point and the number of access users such that the objective function has a minimum value, with the total transmit power being the sum of the transmit powers of each of the access points while satisfying the second constraint. The transmission power required to configure can be optimized. For example, P and n can be obtained by numerically solving Equation 8 based on Equation 6 and Equation 7 above, thereby determining the transmission power and the number of access users of each access point.

Meanwhile, according to an embodiment of the present invention, a Lagrangian function may be obtained from the above objective function, the first constraint, and the second constraint to control the transmission power of the access points in the wireless mesh network and to allocate users. . Such Lagrange functions include a first multiplier that is a Lagrangian multiplier associated with a first constraint and a second multiplier that is a Lagrange multiplier associated with a second constraint. For example, when the first constraint is given by Equation 6 above and the second constraint is given by Equation 7, in order to minimize the total transmit power of the wireless mesh network as shown in Equation 8 above, We can get Lagrange functions like the expression.

를 제1 함수로 놓고 사용자 배분에 해당하는 n만의 함수인

를 제2 함수로 놓으면, 제1 함수에서 P에 대한 최적화 문제는 송신 전력 제어에 관한 것이고, 제2 함수에서 n의 최적화 문제는 사용자 배분에 관한 것이다. 이와 같이 라그랑쥬 함수가 제1 함수 및 제2 함수로 구분되는 경우에는 전체 최적화 문제를 액세스 포인트 각각의 송신 전력을 결정하는 부분과 액세스 포인트 각각의 접속 사용자 수를 결정하는 부분으로 나눌 수 있다. 본 발명의 실시예에 따르면, 제1 함수에 관한 송신 전력 최적화 문제는 컨벡스(convex) 최적화 문제에 해당하므로, 일반적인 컨벡스 최적화 해법, 예컨대 인테리어 포인트 방법(interior point method)을 이용하여 P를 최적화할 수 있다. 제2 함수에 관한 사용자 배분 최적화 문제는 제1 함수에 관한 송신 전력 최적화 문제와 분리하여 풀 수 있다. 여기서, 위 두 가지 최적화 문제에 공통적으로 존재하는 변수인

는 제1 제약조건과 연관된 제1 승산자로서 위 두 문제를 연결하는 파라미터(parameter)라고 해석할 수 있다.At this time, according to the embodiment of the present invention, the optimization problem as described above can be decomposed into two optimization problems. For example, in Equation 9 above, P is a function of only the transmit power.

Is the first function, and n is the only function

With the second function, the optimization problem for P in the first function relates to transmit power control, and the optimization problem for n in the second function relates to user allocation. As described above, when the Lagrange function is divided into a first function and a second function, the overall optimization problem may be divided into a part for determining transmission power of each access point and a part for determining the number of access users of each access point. According to the embodiment of the present invention, since the transmission power optimization problem related to the first function corresponds to a convex optimization problem, P can be optimized using a general convex optimization solution, for example, an interior point method. have. The user allocation optimization problem for the second function can be solved separately from the transmission power optimization problem for the first function. Here, a variable that is common to the two optimization problems

Can be interpreted as a parameter connecting the above two problems as the first multiplier associated with the first constraint.

FIG. 4 is a diagram illustrating a concept of decomposing an optimization problem regarding transmission power control and user allocation in two parts in a wireless mesh network according to an embodiment of the present invention.

In general, transmission power control 400 for obtaining P to determine transmission power of each access point in a wireless mesh network is performed at the physical layer, and user allocation 420 for obtaining n to determine the number of access users of each access point. This is done at the MAC layer, so breaking up into two optimization problems as described above is advantageous in terms of overall efficiency of the wireless communication system.

Meanwhile, according to an exemplary embodiment of the present invention, transmission power control and user distribution in a wireless mesh network may be performed using a Lagrangian dual function while considering constraints existing in the wireless mesh network. For example, in order to minimize the total transmission power of the wireless mesh network while satisfying the first and second constraints, a Lagrange dual function may be obtained as shown in the following equation.

Here, the above-described optimization problem can be solved by solving the dual optimization problem defined by the following equation. As described above, according to an embodiment of the present invention, when the Lagrange dual function is divided into a function of only P corresponding to transmit power and a function of only n corresponding to user allocation, the dual optimization problem is the transmit power of each access point. It can be decomposed into an optimization problem of and an optimization problem of user allocation.

와 제2 제약조건과 연관된 라그랑쥬 승산자인 제2 승산자

를 갱신해 가면서 액세스 포인트 각각의 송신 전력과 액세스 포인트 각각의 접속 사용자 수를 결정하되 이와 같은 과정을 특정 범위 내에서 수렴할 때까지 수행함으로써 최종적으로 P와 n을 결정할 수 있다. 예컨대, 제1 승산자는 제1 승산자에 대한 라그랑쥬 듀얼 함수의 서브그래디언트(subgradient)를 이용하여 갱신할 수 있으며, 마찬가지로 제2 승산자는 제2 승산자에 대한 라그랑쥬 듀얼 함수의 서브그래디언트를 이용하여 갱신할 수 있다. 또한, 위와 같이 제1 승산자 및 제2 승산자를 갱신하면서 주어진 제1 승산자 및 제2 승산자에 대하여 P와 n을 구하는 과정은, 전술한 바와 마찬가지로 송신 전력 제어 문제와 사용자 배분 문제로 분리하여 수행될 수 있다.According to an embodiment of the invention, a first multiplier that is a Lagrange multiplier associated with a first constraint

Second multiplier, which is a Lagrange multiplier associated with the second constraint.

While updating, the transmission power of each access point and the number of access users of each access point are determined, and the same process is performed until convergence within a specific range can finally determine P and n. For example, the first multiplier may be updated using a subgradient of the Lagrange dual function for the first multiplier, and the second multiplier may use a subgradient of the Lagrange dual function for the second multiplier. Can be updated. In addition, the process of obtaining P and n for a given first multiplier and a second multiplier while updating the first multiplier and the second multiplier as described above may be divided into a transmission power control problem and a user allocation problem as described above. Can be performed.

Based on the above analysis, the following describes a transmission power control and user distribution method in a wireless mesh network according to an embodiment of the present invention with reference to FIG.

5 is a flowchart illustrating a process of controlling transmission power and distributing users in a wireless mesh network according to an embodiment of the present invention.

In FIG. 5, when the first constraint is given from Equation 6 above and the second constraint is given from Equation 7, the Lagrange function for minimizing the total transmit power of the wireless mesh network is given by Equation 9 above. The process of determining the transmit power of each of the access points and the number of access users of each of the access points is shown for the corresponding Lagrange dual function. In such a case, the problem of optimizing the total transmit power may be solved by decomposing the optimization of the transmit power and the optimization of user allocation.

Referring to FIG. 5, first, as an initialization step (t = 0), initial values of a first multiplier associated with a first constraint and a second multiplier associated with a second constraint are set, and a user forms an access point forming a wireless mesh network. An initial value of n is set to be uniformly distributed to all (S500).

Subsequently, the transmission power is optimized for the given first multiplier (S510). Referring to the first function obtained as described above from Equation 9, the optimization problem of the transmission power can be expressed by the following equation. Here, the case where there is a limit in the transmission power of each of the access points is considered.

에 대한 최적의 송신 전력인 P를 구할 수 있다.On the other hand, the above problem corresponds to the convex optimization problem, i.e., the first multiplier given using the interior point method.

P, which is the optimal transmit power for, can be obtained.

및 주어진 제2 승산자인

에 대하여

벡터의 엘리먼트 중에서 최대값인 엘리먼트의 인수를 u라고 하고 최소값인 엘리먼트의 인수를 v라고 할 때, 다음의 수학식과 같이 u 번째 액세스 포인트의 접속 사용자 수와 v 번째 액세스 포인트의 접속 사용자 수를 갱신할 수 있다. Next, the user distribution is optimized for the given first multiplier and the second multiplier (S520). Where, for example, a given first multiplier

And given second multiplier

about

When the argument of the maximum element among the elements of the vector is u and the argument of the minimum element is v, the number of access users of the u th access point and the access user of the v th access point are updated as shown in the following equation. Can be.

In this way, by updating n corresponding to the number of connected users of each access point, the users can be distributed in the direction of minimizing the value of the portion corresponding to the second function obtained from Equation 9 above. have.

와 제2 승산자

에 대하여 최적의 송신 전력 P^* 및 사용자 배분 n^*을 구하면 다음의 수학식과 같이 표현할 수 있다.Next, the first multiplier and the second multiplier are updated (S540). Here, the first multiplier and the second multiplier may be updated using sub-gradients of the Lagrange dual function, respectively. Given first multiplier

And second multiplier

The optimal transmission power P ^* and the user allocation n ^* can be expressed by the following equation.

으로 주어진다면, 다음의 수학식을 얻을 수 있다.Here, the second multiplier has the same value, but the first multiplier is different value

Given by, we can get

Therefore, the following relationship can be obtained from the above equations (14) and (15).

에 대한 라그랑쥬 듀얼 함수의 서브그래디언트는

로 놓을 수 있다. 전술한 바와 유사하게, 제2 승산자에 대하여 다음의 수학식과 같은 관계를 얻을 수 있다.In this case, the first multiplier

The sub-gradient of the Lagrange dual function for

Can be set as Similarly to the above, the following equation can be obtained for the second multiplier.

에 대한 라그랑쥬 듀얼 함수의 서브그래디언트는

로 놓을 수 있다. 그러므로, 제1 승산자 및 제2 승산자는 전술한 바와 같이 이전의 두 단계(S510, S520)에서 각각 구한 P와 n을 이용하여 다음의 수학식과 같이 갱신할 수 있다.In this case, the second multiplier

The sub-gradient of the Lagrange dual function for

Can be set as Therefore, as described above, the first multiplier and the second multiplier may be updated by using P and n obtained in the previous two steps S510 and S520 as shown in the following equation.

는 제1 승산자를 갱신하기 위한 스텝 사이즈(step size)이고,

는 제2 승산자를 갱신하기 위한 스텝 사이즈이다. 예컨대,

는

이고,

이며,

를 만족하는 스텝 사이즈일 수 있으며,

도 유사한 스텝 사이즈일 수 있다. 또는, 스텝 사이즈는 각각 스텝의 경과와 무관하게 일정한 값으로 유지되는 값일 수 있다.here,

Is a step size for updating the first multiplier,

Is the step size for updating the second multiplier. for example,

Is

ego,

Is,

May be a step size satisfying

Similar step size can be. Alternatively, the step size may be a value maintained at a constant value regardless of the progress of each step.

Subsequently, the process proceeds to the next step (S540).

If the process proceeds as above, it is checked whether it can be determined that convergence within a specific range (S550). As a result of the check, if it is determined that convergence, P and n are finally determined, so that the total transmission power and user allocation in the wireless mesh network are determined. If not, the above steps (S510, S520, S530, S540, S550) are repeated for the updated first multiplier and the updated second multiplier.

인 경우, 위 수학식 6을 다음의 수학식과 같이 변경하여 제1 제약조건을 산출할 수 있으며, 그에 따라 무선 메쉬 네트워크에서 백홀의 구성에 필요한 필요 송신 전력을 최적화할 수 있다.On the other hand, according to an embodiment of the present invention, when the user channel capacity is changed according to the state of the user channel communicating with the access point connected to the access point connected to the user terminal in the wireless mesh network, for example, j j access point User channel capacity for the terminal of the q th user accessing

In this case, the first constraint may be calculated by changing Equation 6 to the following Equation, thereby optimizing the necessary transmission power required for the backhaul configuration in the wireless mesh network.

On the other hand, in calculating the constraints according to the user channel capacity, the average traffic may be used instead of grasping the state of all user channels of the j th access point.

6 is a diagram illustrating a performance improvement effect of a wireless mesh network according to an embodiment of the present invention.

According to an embodiment of the present invention, it can be seen that total transmission power is reduced as compared with the case where the user distribution is uniform through total transmission power and user distribution in the wireless mesh network. Referring to FIG. 6, in the case of uniformly distributing users and adjusting only the total transmit power, the total transmit power increases exponentially as the total number of connected users increases, but according to the embodiment of the present invention, the total number of connected users increases. Thus, the total transmit power increases linearly.

Embodiments of the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer-readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic-optical 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. The medium may be a transmission medium such as an optical or metal line, a wave guide, or the like, including a carrier wave for transmitting a signal designating a program command, a data structure, or the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. I can understand that. Therefore, the embodiments described above are illustrative in all respects and should not be understood as limiting.

1 is a diagram illustrating an exemplary structure of a wireless mesh network.

2 is a diagram illustrating a configuration of a wireless communication system according to an embodiment of the present invention.

3 is a diagram illustrating a restriction on the capacity of an output link of an access point in a wireless mesh network according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating a concept of decomposing an optimization problem regarding transmission power control and user allocation in two parts in a wireless mesh network according to an embodiment of the present invention.

5 is a flowchart illustrating a process of controlling transmission power and distributing users in a wireless mesh network according to an embodiment of the present invention.

6 is a diagram illustrating a performance improvement effect of a wireless mesh network according to an embodiment of the present invention.

Claims (20)

A method for controlling transmission power and distributing users in a wireless mesh network including a plurality of access points, the method comprising: (a) calculating a first constraint from each link capacity and each user channel capacity of the wireless mesh network; (b) calculating a second constraint from the number of access users of each of the access points; (c) the transmission power of each of the access points and the connection of each of the access points such that the necessary transmission power required for the configuration of a backhaul in the wireless mesh network is optimized based on the first and second constraints. Steps to determine the number of users Transmission power control and user distribution method comprising a. The method of claim 1, In the step (c) The required transmit power is a total transmit power which is a sum of transmit powers of each of the access points. Transmission power control and user distribution method. The method of claim 1, Step (c) is The transmission power of each of the access points and the number of access users of each of the access points such that an objective function, which is the total transmission power that is the sum of the transmission powers of each of the access points, has a minimum while satisfying the first and second constraints. To determine Transmission power control and user distribution method. The method according to any one of claims 1 to 3, In the step (a) The first constraint is characterized in that for each of the access points, the link capacity of the output link is equal to or greater than the sum of the sum of the link capacity of the input link and the user channel capacity of the access user of the access point. Transmission power control and user distribution method. The method according to any one of claims 1 to 3, In step (b) The second constraint is characterized in that the total number of connected users in the wireless mesh network is constant. Transmission power control and user distribution method. The method of claim 3, Step (c) is Obtaining a Lagrangian function from the objective function, the first constraint and the second constraint Transmission power control and user distribution method comprising a. The method of claim 6, Step (c) is When the Lagrange function is divided into a first function that is a function of the transmission power of each of the access points and a second function that is a function of the number of access users of each of the access points, Determining transmit power of each of the access points; Determining the number of access users of each of the access points Transmission power control and user distribution method comprising a. The method of claim 3, Step (c) is Obtaining a Lagrangian dual function from the objective function, the first constraint and the second constraint Transmission power control and user distribution method comprising a. The method of claim 8, Step (c) is When the Lagrange dual function is divided into a first function that is a function of the transmission power of each of the access points and a second function that is a function of the number of access users of each of the access points, Determining transmit power of each of the access points; Determining the number of access users of each of the access points Transmission power control and user distribution method comprising a. The method according to any one of claims 7 to 9, In the step (c) Determining transmit power of each of the access points using a convex optimization solution. Transmission power control and user distribution method. The method of claim 10, The convex optimization solution is characterized in that the interior point method (interior point method) Transmission power control and user distribution method. The method according to any one of claims 7 to 9, In the step (c) The determining of the number of access users of each of the access points may include reducing the number of access users of one of the access points and increasing the number of access users of another access point by the reduced number. doing Transmission power control and user distribution method. The method of claim 8, Step (c) is Updating a first multiplier that is a Lagrangian multiplier associated with the first constraint Transmission power control and user distribution method comprising a. The method of claim 13, The first multiplier is updated by using a subgradient of the Lagrange dual function for the first multiplier. Transmission power control and user distribution method. The method of claim 8, Step (c) is Updating a second multiplier that is a Lagrange multiplier associated with the second constraint Transmission power control and user distribution method comprising a. The method of claim 15, The second multiplier updates using a subgradient of the Lagrange dual function for the second multiplier. Transmission power control and user distribution method. The method of claim 8, The objective function is

ego, The first constraint is

Is, The second constraint is

This, K is the total number of the plurality of access points, P _i is the transmit power of the i th access point of the plurality of access points, A is an element a _km in the mth column when the mth link of the plurality of links of the wireless mesh network is an output link of the kth access point of the plurality of access points, and A is one of the plurality of links of the wireless mesh network. If the m-th k-th access link type link points of the plurality of access points is a _km -1, and the other cases, a _km of zero matrix, b is, C _ij is the capacity of the i th access point link capacity of the link to the j-th access point in a P (i) is the set of i-th Access Point parent (parent) access points and the external network B is connected to gateway when,

Vector, C is the user channel capacity of each of the user channels, n _j is the number of access users of the j th access point of the plurality of access points, n is

Vector, N is the total number of connected users of the wireless mesh network Transmission power control and user distribution method. The method of claim 17, In the step (c) The transmit power of each of the access points is

Determined from year, P is

Is a vector

When P is the maximum value of the transmit power of each of the access points, P _i is

Satisfying

Is a Lagrange multiplier associated with the first constraint and is a first multiplier Transmission power control and user distribution method. The method of claim 17, In the step (c) Determining the number of access users of each of the access point is

Updating n by u is

Is an argument of the largest element of a vector, v is

Is the argument of the minimum element among the elements of the vector,

Is a vector with all elements 1

Is a first multiplier that is a Lagrange multiplier associated with the first constraint,

Is a Lagrange multiplier associated with the second constraint and is a second multiplier Transmission power control and user distribution method. The method of claim 17, Step (c) is A first multiplier that is a Lagrange multiplier associated with the first constraint and a second multiplier that is a Lagrange multiplier associated with the second constraint

Updated by

Is a first multiplier that is a Lagrange multiplier associated with the first constraint,

Is a second multiplier that is a Lagrange multiplier associated with the second constraint,

Is a value of updating the first multiplier,

Is a value of updating the second multiplier,

Is a step size for updating the first multiplier,

Is a step size for updating the second multiplier Transmission power control and user distribution method.

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