WO2013191460A1

WO2013191460A1 - Method and apparatus for selecting cell in heterogeneous cell wireless communication system

Info

Publication number: WO2013191460A1
Application number: PCT/KR2013/005393
Authority: WO
Inventors: 이효진; 박정수; 변용석; 이용환; 김기일; 김윤선; 배태한
Original assignee: 삼성전자 주식회사; 서울대학교산학협력단
Priority date: 2012-06-19
Filing date: 2013-06-19
Publication date: 2013-12-27
Also published as: KR20130142274A; KR101981089B1

Abstract

The present invention relates to a method for improving transmission performance, by a user located on a femtocell boundary in a macro base station selecting a base station to be serviced by recognizing the user's environment and considering operating information of neighboring base stations, in a heterogeneous cell operation environment in which a femtocell within an operating area of the macro base station is operated. A method for a terminal selecting a serving base station, according to the present invention, comprises the steps of: receiving from the macro base station the operating information which includes at least one of the number of multi-antennas, a frequency usage band, or a load status of at least one small base station; and transmitting to the macro base station a message for requesting a handover to a base station having the maximum average transmission capacity by using the operating information. According to the present invention, the user located at a boundary of heterogeneous cells can request from a serving macro base station neighboring cell operating information, which includes the number of antennas, frequency resource utilization information, and cell load, and the serving macro base station can receive the operating information of relevant neighboring cell through a backhaul network and provide same to the user. As a result, the user can estimate the average transmission capacity of the serving macro base station and the neighboring cell on the basis of the operating information that is received, and select the base station that can provide the best service, thereby improving the performance of the user located at the heterogeneous cell boundary.

Description

Method and apparatus for selecting a cell in a heterocell wireless communication system

The present invention relates to a method and apparatus for selecting a base station to be serviced by a UE located at a femtocell boundary in a heterogeneous network including low power nodes (LeNBs) such as femtocells within a macro base station operating area. It is about.

More specifically, the present invention, the UE located at the cell boundary receives operation information from the macro base station, including information on the number of multiple antennas, frequency bands used, load status for each of at least one or more adjacent cells, the average transmission capacity The present invention relates to a method and an apparatus capable of handing over to a maximum cell.

Research on low power nodes (LNBs) with low power to increase coverage and capacity of a macro BS only network (Macro BS only Network) has been actively conducted in 3GPP LTE-Advanced (LTE-A). For example, a heterogeneous network (HetNet) is formed by deploying a remote radio head (RRH), pico, femto, relay, etc. in a macro cellular network. The femto base station can be operated in an indoor shadow area where the macro base station signal reaches a small amount to improve the transmission performance of the user.

However, when the macro base station and the femto base station serves using the same channel, the femto base station has a problem that can cause severe interference to the neighbor macro base station user. In addition, the macro base station has a large operating area, while the femto base station has a relatively small operating area, so users existing in the femtocell boundary area receive a signal-to-interference plus noise ratio according to the change of location. SINR) may vary greatly.

Therefore, it is important to determine which base station the user who is located in the cell boundary area will receive service to improve performance.

In the conventional cell selection scheme, a cell selection technique using a received signal strength indicator (RSSI) is used to receive a service from a base station having the largest RSSI of a pilot or preamble signal received from a neighboring base station. This is a method of selecting a base station.

However, there is a problem that the technique does not take into account the difference between operating methods between macro-femtocells. Femto base stations use fewer frequency bands than macro base stations, and when multiple femtocells coexist, channels are allocated in a fractional frequency reuse (FFR) manner to control interference between them. This is because the operation method is different from the. In addition, the femto base station has a limited number of transmit / receive antennas in consideration of mounting complexity, and a cell loading situation may occur differently.

In consideration of such a difference in operating techniques, a situation arises in which a transmission capacity that each base station can actually provide even in a location where the received signal strength is the same.

Therefore, for efficient operation of HetNet, there is a need for a technique for maximizing transmission performance by using a method of selecting a serving base station capable of maximizing a transmission capacity calculated by an intelligent terminal in consideration of an operation technique of a neighboring base station. do.

The present invention is to solve the above problems. In particular, the present invention, the UE located at the cell boundary receives the operating information from the macro base station including information on the number of multiple antennas, frequency bands used, and load status for each of at least one neighboring cell from the macro base station, the average transmission capacity is the maximum The purpose is to maximize the transmission performance by selecting a cell.

The method for selecting a serving base station by the terminal of the present invention for solving the above problems, the macro base station to the operating information including at least one of the number of multiple antennas, frequency use bands or load conditions for at least one small base station Receiving from; And sending a message to the macro base station to request a handover to the base station having the maximum average transmission capacity by using the operation information.

The method for selecting a serving base station of the terminal by the base station of the present invention comprises the steps of: transmitting operation information including at least one or more of the number of multiple antennas, frequency use bands or load conditions for the at least one small base station; And receiving, from the terminal, a message for requesting handover to a base station having a maximum average transmission capacity using the operation information.

Furthermore, the terminal for selecting a serving base station of the present invention includes a transceiver for transmitting and receiving a signal with the base station; And receiving operation information from the macro base station including at least one of a number of multiple antennas, a frequency using band, or a load state of the at least one small base station, and handing over to the base station having the maximum average transmission capacity using the operation information. And a controller for controlling to transmit a message requesting the message to the macro base station.

And a macro base station for selecting a serving base station of the terminal of the present invention includes a transceiver for transmitting and receiving a signal with the terminal; And transmitting operation information including at least one of the number of multiple antennas, a frequency using band, or a load state of the at least one small base station to the terminal, and handover to the base station having the maximum average transmission capacity using the operation information. And a control unit controlling to receive a request message from the terminal.

According to the present invention, a user located at a heterogeneous cell boundary requests neighboring cell operation information, including antenna number, frequency resource utilization information, and cell load, from a serving macro base station, and the serving macro base station operates information of the neighboring cell through a backhaul network. Can be obtained and provided to the user. Accordingly, the user can improve the performance of the user at the heterogeneous cell boundary by estimating the average transmission capacity of the serving macro base station and the neighbor cell based on the received operation information and selecting the base station that can provide the best quality service. Can be.

1 is a diagram illustrating an example of a heterogeneous wireless communication network model.

FIG. 2 is a diagram illustrating an example in which a femtocell uses a fractional frequency reuse (FFR) technique using some bands of all available bands to avoid interference with adjacent femtocells in a multi-femtocell group.

3 is a view for explaining an interference effect received by a user according to a load of an adjacent cell.

4 is a flowchart illustrating a process of selecting a serving base station by a UE according to an embodiment of the present invention.

It is apparent that the present invention is not limited to the description of the embodiments described below, and various modifications may be made without departing from the technical gist of the present invention. In describing the embodiments, descriptions of technical contents which are widely known in the technical field to which the present invention belongs and are not directly related to the technical gist of the present invention will be omitted.

On the other hand, the same components in the accompanying drawings are represented by the same reference numerals. In the accompanying drawings, some components may be exaggerated, omitted, or schematically illustrated. This is to clarify the gist of the present invention by omitting unnecessary description that is not related to the gist of the present invention. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a heterogeneous cell wireless communication system model considered in the present invention. Referring to FIG. 1, a heterogeneous cell wireless communication system includes a macro base station 101, a plurality of macro base station users 103, a femto base station 105, and a femto base station user 107. A user 109 subjected to interference from the macro base station 101 and the femto base station 105.

The full channel band B _m 111 is composed of L subchannels 113, and a femtocell uses a channel band B _f 115 composed of L _f subchannels 117, which are some of them. The macro base station 101 and the femto base station 103 respectively assign

subchannels

113 and 117 having good channel conditions to the user by using the instantaneous channel information of the user. The macro base station 101 and the femto base station 105 improve transmission performance by using a transmission beamforming technique using N _m and N _f antennas, respectively.

The femtocell in the system may be operated while affecting interference with a plurality of femtocells installed nearby. In this case, the received signal of the user k may be expressed as Equation 1 below.

Equation 1

here

Wow

Denotes a channel path loss value between the macro base station and the femto base station f from the user k , respectively. And

Wow

Are each

and

A channel vector from the macro base station and the femto base station f, which is a vector, to the user k .

Also

and

Are each

and

The beam weights of the macro base station and the femto base station f which are vectors,

and

Denotes a signal transmitted by the macro base station and the femto base station f using the l-th subchannel, respectively. And

Is

Represents a complex Gaussian noise with a variance of

and

Denotes a utility function of the macro base station and the femto base station f for each l- th subchannel having a value of {0, 1}.

When the user k receives a service from the macro base station through the l-th subchannel, the average transmission capacity may be expressed by Equation 2 below.

Equation 2

here,

Wow

Are macro cell and femtocell, respectively.

Is the average signal-to-noise ratio (SNR)

Means an average value calculation function.

Channel direction information by a base station user to generate beam weights using instantaneous channel information

Is quantized using a B-bit codebook and reported to the base station, the actual channel

And quantized channel information

The relationship with can be expressed as shown in Equation 3 below.

Equation 3

here

Is

An arbitrary unit norm vector in the null space of the.

The macro base station a femto base station adjacent to the user k are the beams of the user one form the k weights beam without consideration of the with the channel, the macro base station that is serving the user k is the forming mating beam using the reported receiving channel direction information from the user k Generate weights (i.e.

). In this case, the average transmission capacity of the user k may be expressed as Equation 4 below.

Equation 4

here

Denotes a beta function.

If the user k is femtocell

When the service is received through the l-th subchannel from, the average transmission capacity of the user k may be approximately expressed as in Equation 5 below.

Equation 5

As in the macro base station, femtocell

The user based on the received channel information reported from the k when transmitting a signal using a matched beamforming average transmission capacity of the user k can be approximated as expressed as follows in <Equation 6>.

Equation 6

FIG. 2 illustrates an example of using a fractional frequency reuse (FFR) technique in which a femtocell 201 uses some bands among all available bands to avoid interference with adjacent femtocells 205 within a multi-femtocell group 203.

Referring to FIG. 2, the total L subchannels 207 are divided into _D frequency half-bands {B ₁ , B ₂ , ....., B _D } 209, and each frequency division band is L _f subbands. Channel 211. In FIG. 2, a set of femtocells using split band B _d among the frequency division sets is represented by S _d . The utilization function of the femtocells belonging to S _d for subchannels not belonging to the frequency division band B _d is zero. In other words,

With respect to Equation 7 is established.

Equation 7

The macro base station user k located at the femtocell boundary region has a frequency division band having the least average interference effect (eg,

Receive service through subchannel belonging to). remind

With respect to Equation 8 is established.

Equation 8

here

and

Are each frequency division bands

and

Subchannels belonging to

Therefore, the average transmission capacity of the macro base station user k can be expressed as Equation 9 below.

Equation 9

The user k is femtocell

Frequency service, used by the serving femtocell

Interference may be affected from adjacent femtocells using the same band.

In this case, the subchannel

The average transmission capacity of the user k serviced through can be approximated as shown in Equation 10 below.

Equation 10

3 is a diagram illustrating the interference effect received by a user according to the load of an adjacent cell. Referring to FIG. 3, in the case of a cell 301 having a small load, the number of subchannels to be used is smaller than the number of subchannels allocated, thereby interfering with the neighbor user 305 using the instantaneous channel information of the serving user 303. Subchannels can be allocated with less impact.

On the other hand, the cell 307 with a high load cannot afford to consider the neighboring user 305 and thus has a large interference effect.

When the macro base station allocates a subchannel to a user using instantaneous channel information, a utilization function for the subchannel l

Follows the Bernoulli distribution as shown in Equation 11 below.

Equation 11

here

Is the load of the macro base station, which is the probability that the macro base station occupies the corresponding band,

Denotes the number of macro base station users.

Similarly, femtocell

Subchannel of

Utilization function for

May be represented as in Equation 12.

Equation 12

here

Femto base station

That band as the load of the femto base station

The probability of occupying this,

Is the number of available subchannels per femtocell,

Denotes the number of femto base station users.

In this case, when considering the neighbor cell interference characteristic that the probability of interference follows the Bernoulli distribution, the average transmission capacity when the user k receives the service from the macro cell may be expressed by the following Equation (13). .

Equation 13

Where femtocells

silver

Among the femtocells belonging to the following Equation 14, the femtocell having the greatest interference effect on the user k .

Equation 14

On the other hand, femtocell users located at heterogeneous cell boundaries are most affected by the macro base station. Thus the user k is femtocell

When the transmission capacity at the time of service is obtained from Equation 15, it can be approximated and expressed as shown in Equation 15 below.

Equation 15

According to Equation 13 and Equation 15, the user k may know that the transmission performance may be changed by various operating environment factors as well as the reception signal strength of the serving cell and the adjacent cells.

At this time, the base station that can provide the optimal service

Satisfies Equation 16 for all adjacent femtocells and all subchannels.

Equation 16

Therefore, in order for a user located at a cell boundary to select a base station capable of maximizing transmission capacity, the user terminal needs to receive a number of antennas, frequency resource utilization information, and cell load of the serving cell and neighbor cells from the serving base station. Receiving such information, the terminal can select a cell that can provide an optimal service to itself in consideration of environmental factors.

4 is a flowchart illustrating a procedure in which a serving macro base station receives information on a neighbor cell in order for a user to select a serving base station according to an exemplary embodiment of the present invention.

In step 410, the terminal 401 is in the service coverage of the macro base station 403. The adjacent base station 405 is in a state of affecting interference with the UE 401.

In step 420, the user, i.e., the UE 401, receives the preamble signal of the neighboring base station 405 that affects interference, and in step 425 detects the ID of the neighboring base station 405.

Thereafter, the UE 401 requests the serving macro base station 403 for the number of antennas, frequency resource utilization information, and cell load (load) information for the neighboring base station by using the detected neighboring base station 405 ID in step 430. .

Thereafter, in step 440, the serving macro base station obtains information on the neighbor base station 405 through a backhaul network. In operation 440, the operation information is informed to the user.

Thereafter, the user 401 derives a transmission capacity for the case where the serving cell 403 and the neighbor cell 405 are serviced based on the operation information received in step 455. In step 460, the base station with the maximum transmission capacity is selected.

The UE, which selects a base station that can provide the best service to itself based on the derived transmission capacity, may request the base station transformation from the serving macro base station in step 470.

The embodiments of the present invention disclosed in the specification and the drawings are only specific examples to easily explain the technical contents of the present invention and aid the understanding of the present invention, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention can be carried out in addition to the embodiments disclosed herein.

Claims

In a method of selecting a serving base station by a terminal in a heterogeneous network,

Receiving, from the macro base station, operation information including at least one of the number of multiple antennas, frequency use bands or load conditions for the at least one small base station; And

And sending a message requesting a head over to the macro base station to the base station having the maximum average transmission capacity using the operation information.
The method of claim 1, wherein before receiving the operation information,

Receiving a preamble signal from at least one of the small base stations;

Obtaining an ID of the small base station from the preamble signal; And

And sending a message requesting the operation information including the ID of the small base station to the macro base station.
The method of claim 2, wherein the sending of the message requesting handover comprises:

Determining a frequency band having the least interference from other base stations among the frequency use bands;

Calculating an average transmission capacity of the small base station in the frequency band;

Selecting a base station having the maximum transmission capacity; And

And transmitting a message requesting a handover to a base station having the largest average transmission capacity and a frequency band having the smallest interference.
The method of claim 3, wherein calculating the average transmission capacity comprises:

Selection method characterized by using an equation.
In the heterogeneous network (Heterogeneous Network), the macro base station selects the serving base station of the terminal,

Transmitting operation information including at least one of the number of multiple antennas, a frequency using band, or a load state to at least one small base station to the terminal; And

And receiving a message for requesting handover from the terminal to the base station having the maximum average transmission capacity using the operation information.
The method of claim 5, wherein before the step of transmitting the operation information,

And receiving from the terminal a message for requesting the operation information including the ID of the small base station.
The method of claim 6, wherein receiving the message requesting handover comprises:

And receiving a message from the terminal requesting handover in a frequency band having the least interference from the base station having the maximum transmission capacity and another base station.
The base station of claim 7, wherein the average transmission capacity is maximum,

Selecting method, characterized in that determined by the terminal using an equation.
In a terminal for selecting a serving base station in a heterogeneous network (Heterogeneous Network),

Transmitting and receiving unit for transmitting and receiving a signal with the base station; And

Receive operation information from the macro base station including at least one of the number of multiple antennas, frequency bands, or load conditions of the at least one small base station from the macro base station, and handover to the base station having the maximum average transmission capacity using the operation information. And a controller for controlling to send a request message to the macro base station.
The method of claim 9, wherein the control unit,

Receiving a preamble signal from at least one small base station, obtaining an ID of the small base station from the preamble signal, and controlling the macro base station to send a message requesting the operation information including the ID of the small base station; Terminal, characterized in that.
The method of claim 10, wherein the control unit,

Among the frequency use bands, a frequency band having the least interference is determined from other base stations, the average transmission capacity of the small base station is calculated in the frequency band, and the base station having the maximum transmission capacity is selected, and the average transmission capacity is And a base station having a maximum and controlling to transmit a message for requesting handover in a frequency band having the least interference.
The method of claim 11, wherein the control unit,

The terminal characterized in that for calculating the average transmission capacity using a formula.
In the macro base station for selecting the serving base station of the terminal in a heterogeneous network (Heterogeneous Network),

Transmitting and receiving unit for transmitting and receiving a signal with the terminal; And

Sending operation information including at least one of the number of multiple antennas, frequency use bands or load conditions for at least one small base station to the terminal, and requests a handover to the base station having the maximum average transmission capacity using the operation information. And a control unit for controlling to receive a message from the terminal.
The method of claim 13, wherein the control unit,

And controlling to receive from the terminal a message requesting the operation information including the ID of the small base station.
The method of claim 14, wherein the control unit,

And controlling a base station with a maximum transmission capacity to receive a message from the terminal requesting handover to a frequency band having the least interference from another base station.
The base station of claim 15, wherein the average transmission capacity is maximum.

Macro base station, characterized in that determined by the terminal using an equation.