KR101981089B1 - A method and apparatus for cell selection in heterogeneous wireless communication systems - Google Patents

Abstract

In a heterogeneous cell operating environment in which a femtocell is operated in a macro base station operating area, a user located at a femtocell boundary in a macro base recognizes the environment of the femtocell and selects a base station to be served by considering operation information of surrounding base stations, And the like.
A method for selecting a serving base station according to the present invention includes: receiving operational information from a macro base station including at least one of a number of multiple antennas, a frequency use band or a load state for at least one small base station; And transmitting, to the macro base station, a message requesting handover to a base station having the maximum average transmission capacity using the operation information.
According to the present invention, a user located at a boundary of a heterogeneous cell requests neighboring cell operation information including an antenna number, frequency resource utilization information, and cell load to a serving macro base station, and the serving macro base station transmits operation information And provide it to the user. Accordingly, the base user can estimate the average transmission capacity of the serving macro base station and the neighboring cells based on the received operation information, thereby improving the performance of the user at the boundary of the heterogeneous cell by selecting the base station that can provide the highest quality service .

Description

[0001] METHOD AND APPARATUS FOR CELL SELECTION IN HETEROGENEOUS WIRELESS COMMUNICATION SYSTEMS [0002]

The present invention relates to a method and apparatus for selecting a base station to be served by a UE located at a femtocell boundary in a heterogeneous network including low power nodes (LeNBs) such as femtocells in macro base station operational coverage .

More specifically, the present invention is characterized in that a UE located at a cell boundary receives operation information including information on a number of multiple antennas, a frequency band to be used, and a load state for each of at least one neighboring cell from a macro base station, And a handover to a cell having a maximum cell size.

Research on low power nodes (LeNBs) with low power to increase the coverage and capacity of a network consisting of only macro base stations has recently been actively conducted by 3GPP LTE-Advanced (LTE-A) For example, a heterogeneous network (HetNet) is configured by deploying a remote radio head (RRH), a pico, a femto, a relay, etc. in a macro cellular network. Can improve the transmission performance of the user by operating the femto base station in the indoor shadow area where the macro base station signal reaches small.

However, when the macro base station and the femto base station use the same channel, the femto base station may cause severe interference to the neighboring macro base station users. In addition, the macro base station has a wide operating area, while the femto base station has a relatively small operating area. Therefore, a user existing in the femtocell boundary area can receive a signal-to-interference plus noise ratio SINR) can be greatly changed.

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

A cell selection scheme using a received signal strength indicator (RSSI), which is a conventional base station selection scheme, is a scheme of selecting a pilot or a preamble signal received from an adjacent base station, This is a method of selecting a base station.

However, there is a problem that the above technique does not consider the difference in the operation method between the macro-femtocell. The femto base station uses fewer frequency bands than the macro base station, and when a plurality of femtocells are coexisted, the femto base station is allocated with a fractional frequency reuse (FFR) scheme to control interference therebetween, This is because there is a difference in operating methods between and. Also, considering the complexity of the femto base station, the number of transmitting and receiving antennas is limited, and the loading state of the cell may be different.

Considering this difference in operation technique, there arises a problem that the transmission capacity of each base station can be different even when the received signal strength is the same.

Therefore, in order to efficiently operate HetNet, there is a need for a technology that maximizes the transmission performance by using a method of selecting a serving base station capable of maximizing a transmission capacity calculated by considering an operating method of an adjacent base station, do.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. In particular, the present invention is characterized in that a UE located at a cell boundary receives operation information including information on a number of multiple antennas, a frequency band to be used, and a load state for each of at least one neighboring cell from a macro base station, And to select a cell to maximize transmission performance.

In order to solve the above problems, a method for selecting a serving base station in a mobile station of the present invention comprises the steps of: transmitting operation information including at least one of a number of multiple antennas, a frequency use band, ; And transmitting, to the macro base station, a message requesting handover to a base station having the maximum average transmission capacity using the operation information.

A method of selecting a serving base station of a terminal according to the present invention includes: transmitting operation information including at least one of a number of multiple antennas, a frequency band, and a load state to at least one or more small base stations to the terminal; And receiving, from the terminal, a message requesting handover to a base station having the maximum average transmission capacity using the operation information.

In addition, the terminal for selecting a serving base station of the present invention includes a transmitting / receiving unit for transmitting / receiving signals to / from a base station; And at least one of a number of antennas, a frequency band, and a load state for at least one or more small base stations from the macro base station, and transmits the operation information to the base station having the maximum average transmission capacity using the operation information The macro base station transmits a message requesting the macro base station to the macro base station.

A macro base station for selecting a serving base station of the MS according to the present invention comprises: a transmitting / receiving unit for transmitting / receiving signals to / from the MS; And transmitting at least one of operation information including at least one of a number of multiple antennas, a frequency use band, and a load state to at least one or more small base stations to the mobile station, and using the operation information, And a controller for controlling the terminal to receive a request message from the terminal.

According to the present invention, a user located at a boundary of a heterogeneous cell requests neighboring cell operation information including an antenna number, frequency resource utilization information, and cell load to a serving macro base station, and the serving macro base station transmits operation information And provide it to the user. Accordingly, the base user estimates the average transmission capacity of the serving macro base station and the neighboring cells based on the received operation information, thereby improving the performance of the user at the boundary of the heterogeneous cell by selecting the base station that can provide the highest quality service .

1 illustrates an example of a heterogeneous cell wireless communication network model;
2 illustrates an example of using a fractional frequency reuse (FFR) technique in which a femtocell uses some of the available bandwidths to avoid interference with neighboring femtocells within a multi-femtocell group.
3 is a diagram for explaining an influence of interference received by a user according to a load of a neighboring cell;
FIG. 4 is a flowchart illustrating a process of a UE selecting a serving base station according to an embodiment of the present invention; FIG.

It is to be understood that the present invention is not limited to the description of the embodiments described below, and that various modifications may be made without departing from the technical scope of the present invention. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

In the drawings, the same components are denoted by the same reference numerals. And in the accompanying drawings, some of the elements may be exaggerated, omitted or schematically illustrated. It is intended to clearly illustrate the gist of the present invention by omitting unnecessary explanations not related to the gist of the present invention. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a model of a heterogeneous cell wireless communication system considered in the present invention. 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, And a user 109 affected by interference from the macro base station 101 and the femto base station 105.

The entire channel band B _m (111) is made up of L subchannels (113), and the femtocell includes L _f Channel band consisting of two sub-channels (117) B _f (115). The macro base station 101 and the femto base station 103 allocate the subchannels 113 and 117 having good channel status to the user by using the instantaneous channel information of the user 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 can be operated with interference between neighboring femtocells. In this case, the received signal of the user k can be expressed as Equation (1).

Here,_k ^(l) And β_{k, f} ^(l) Denotes a channel path attenuation value between the macro base station and the femto base station f to the user k. And h_k ^(l) And g_{k , f} ^(l) (1xN_m) And (1 x N_f) Vector macro base station and femto base station f Means a channel vector from user k to user k

In addition, w ^(l) and u _f ^(l) X _M ^(l) and x _f ^(l) denote the beam weights of the macro base station and the femto base station, which are vectors N _m x 1 and N _f x 1, respectively, Means a signal transmitted using a channel. And n _k is a complex Gaussian noise with a variance of σ _k ² , ε _M ^(l) and ε _f ^(l) Denotes a utility function of the macro base station and the femto base station f for each 1 < th > subchannel having a value of {0, 1}.

When the user k receives a request from the macro base station The average transmission capacity when receiving service through the 1 < st > subchannel can be expressed as Equation (2) below.

은 각각 매크로 셀과 펨토셀 ^□f의 사용자 k가 얻을 수 있는 평균 신호 대 잡음비(signal-to-noise ratio: 이하 SNR)을, E{?}는 평균값 계산 함수를 의미한다. here,

Denotes the average signal-to-noise ratio (SNR) obtained by the user k of the macrocell and the femtocell ^□ f, respectively, and E {} denotes the average value calculation function.

를 B비트 크기의 코드북을 사용하여 양자화 하여 기지국에 보고 하는 경우, 실제 채널 정보 h_k ^~(l) 와 양자화된 채널 정보 q_k ^(l)와의 관계는 하기 <수학식 3>과 같이 표시할 수 있다.In order to generate the beam weight using the instantaneous channel information, the base station user sets the channel direction information (Channel Direction Information)

Is quantized using a codebook having a size of B bits and reported to the base station, the relationship between the actual channel information h _k ^{~ (l)} and the quantized channel information q _k ^(l) can be expressed as Equation have.

Where v _k ^(l) is an arbitrary unit norm vector in the null space of q _k ^(l) .

The macro base station user The femto base stations adjacent to < RTI ID = 0.0 > k & and the macro base station serving the user k generates the beam weight of the matching beamforming using the channel direction information reported from the user k. (I.e., w = q ^H ). In this case, the average transmission capacity of the user k can be expressed as Equation (4).

Where β (·, ·) denotes the beta function.

If, if the user k is receiving the service through the l-th sub-channel from the femtocell ^□ f, the average transmission capacity of the user _k can be approximately expressed as follows with <Equation 5>.

As in the case of the macro base station, ^□f When the signal is transmitted using the matched beamforming according to the channel information reported from the user k, the average transmission capacity of the user k can be approximated as Equation (6).

2 shows an example of using a fractional frequency reuse (FFR) technique in which a femtocell 201 uses some of the available bandwidths to avoid interference with adjacent femtocells 205 in the multiple femtocell group 203. [

Referring to FIG. 2, a total of L sub-channels 207 are divided into D frequency division bands {B ₁ , B ₂ ,. , B _D } 209, and each frequency division band includes L _f sub-channels 211. In FIG. 2, a set of femtocells using the sub-band B _d is denoted by S _d . The utilization function of the femtocells belonging to the S _d for the subchannels not belonging to the frequency division band B _d is zero. That is, Equation (7) holds for _l ? S _d .

)에 속한 부채널을 통해 서비스 받는다. 상기

에 대하여 하기 <수학식 8>이 성립한다.The macro-base station user k located in the femtocell boundary region is a frequency division band with the smallest average interference effect

) Through the subchannel belonging to the channel. remind

&Quot; (8) &quot;

은 각각 주파수 분할대역 B_d과

에 속한 부채널이다.
Here,

Respectively The frequency division bands B _d and

Lt; / RTI &gt;

 Therefore, the average transmission capacity of the macro base station user k can be expressed by Equation (9).

The user k the femtocell _^□ f (∈S ^□ _d) when receiving a service from, may be interference effects from the neighbor femtocell using a band such as a frequency divided band B of the serving femtocell using _{□ d.}

를 통해 서비스 받는 사용자 k의 평균 전송 용량은 하기 <수학식 10>과 같이 근사적으로 나타낼 수 있다. In this case,

The average transmission capacity of the user k that is served through the service center k can be approximated as shown in Equation (10).

FIG. 3 schematically illustrates the influence of interference received by a user depending on the load of a neighboring cell. 3, since the number of subchannels to be used is smaller than the number of allocated subchannels in the case of a small-sized cell 301, the neighboring user 305 is notified of the interference using the instantaneous channel information of the serving user 303 You can assign subchannels with less impact.

On the other hand, the cell 307 having a large load has a large influence of interference because there is no room to consider the neighboring user 305.

When the macro base station allocates the subchannel to the user using the instantaneous channel information, the utilization function? _M ^(l) for the subchannel l follows the Bernoulli distribution as shown in Equation (11).

Where P _M denotes the probability that the macro base station will occupy the corresponding band as a load of the macro base station, and U _M denotes the number of macro base station users.

에 대한 활용 함수

는 하기 <수학식 12>와 같이 나타낼 수 있다.Similarly, the sub-channel of the femtocell _^□ f (∈S ^□ _d)

Utilization function for

Can be expressed by Equation (12) below.

Where p _f is a femto base station _□ ^□ f Of the probability of the femto base station ^□ f occupy the band as the load, _f L is the number of available subchannels per femtocell, U _{□ f} represents the number of users a femto base station.

The average transmission capacity when the user k receives the service from the macro cell in the case of considering the neighboring cell interference characteristic that the probability of interference comes in accordance with the Bernoulli distribution can be approximated as shown in Equation (13) below .

Here, ^? F satisfies the following Equation (14) among the femtocells belonging to S _d Is the femtocell that has the greatest interference impact to user k.

On the other hand, femtocell users located at the boundary of heterogeneous cells are most affected by interference from macro base stations. Therefore, when the user k is a femtocell ^□ f has to ask the transmission capacity when receiving service from a number to be displayed and the approximated as <Equation 15>.

According to Equation (13) and Equation (15), it can be seen that the transmission performance of the user k can be changed by not only the received signal strength of the serving cell and neighboring cells but also various operational environment factors.

At this time, the base station h _k which can provide the best service satisfies the following <Equation 16> with respect to all neighboring femtocell and the entire sub-channels.

Therefore, in order to select a base station capable of maximizing the transmission capacity of a user located at a cell boundary, the user terminal needs to receive the number of antennas, frequency resource utilization information, and cell load of the serving cell and neighboring cells from the serving base station. The terminal that receives this information can select the cell that can provide the optimal service to the user considering the environmental factors.

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

In step 410, the terminal 401 is within the service coverage of the macro base station 403. [ The neighbor base station 405 is in a state of having an interference influence to the UE 401. [

In step 420, the user, i.e., the UE 401 receives the preamble signal of the neighbor base station 405 which influences the interference, and detects the ID of the neighbor base station 405 in step 425. The UE 401 then requests the serving macro base station 403 for the number of antennas, frequency resource utilization information, and cell load (load) information for the neighbor base station using the detected neighbor base station 405 ID in step 430 .

In step 440, the serving macro base station obtains information on the neighbor base station 405 through a backhaul network. And informs the user of the operation information in step 440.

Then, the user 401 derives the transmission capacity for the service in the serving cell 403 and the neighboring cell 405 based on the operation information received in step 455. In step 460, a base station with the maximum transmission capacity is selected.

Based on the derived transmission capacity, the UE that has selected the base station that can provide the best service to the base station can request the serving base station to perform base station conversion in step 470.

The embodiments of the present invention disclosed in the present specification and drawings are merely illustrative of specific embodiments of the present invention and are not intended to limit the scope of the present invention in order to facilitate understanding 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 are possible in addition to the embodiments disclosed herein

101, 403: macro base station
103, 109, 305, 401: UE
105, 201, 205, 405: small base stations

Claims (16)

A method for a terminal to select a serving base station in a heterogeneous network,
Receiving a preamble signal from at least one or more small base stations;
Obtaining an ID of the at least one small base station from the preamble signal;
Transmitting a message requesting the operation information to the macro base station, the message including the ID of the at least one small base station;
Receiving, from the macro base station, the operation information including at least one of a number of multiple antennas, a frequency use band, and a load state for the at least one small base station; And
And transmitting, to the macro base station, a message requesting handover to a base station having the maximum average transmission capacity using the operation information. delete The method of claim 1, wherein the step of transmitting a message requesting handover comprises:
Determining a frequency band having the smallest interference from other base stations among the frequency bands;
Calculating an average transmission capacity of the small base station in the frequency band;
Selecting a base station having the maximum average transmission capacity; And
Further comprising the step of transmitting a message requesting handover to a base station having the maximum average transmission capacity and a frequency band with the smallest interference. 4. The method of claim 3, wherein calculating the average transmission capacity comprises:

Is used. &Lt; / RTI &gt; A method for selecting a serving base station of a mobile station in a heterogeneous network,
Receiving from the terminal a message requesting operation information including at least one ID of the small base station;
Transmitting the operation information including at least one of a number of multiple antennas, a frequency use band, and a load state to at least one or more small base stations to the terminal; And
And receiving, from the terminal, a message requesting handover to a base station having a maximum average transmission capacity using the operation information. delete 6. The method of claim 5, wherein the step of receiving the handover request message comprises:
Further comprising the step of receiving, from the mobile station, a message requesting handover from a base station having the maximum average transmission capacity to a frequency band having the smallest interference from the other base station. 8. The method as claimed in claim 7, wherein the base station,

And the terminal determines the terminal using the formula.
A terminal for selecting a serving base station in a heterogeneous network,
A transmission / reception unit for transmitting / receiving signals to / from a base station; And
The method comprising: receiving a preamble signal from at least one or more small base stations, acquiring an ID of the at least one small base station from the preamble signal, including an ID of the at least one small base station, Wherein the mobile station receives the operation information including at least one of a number of multiple antennas, a frequency use band, and a load state for the at least one small base station from the macro base station, And a control unit for controlling the macro base station to transmit a message requesting handover to the macro base station. delete 10. The apparatus according to claim 9,
A base station having a maximum average transmission capacity is selected by calculating an average transmission capacity of the small base station in the frequency band and determining a frequency band having the smallest interference from other base stations among the frequency use bands, And controls to transmit a message requesting a handover to a base station having a maximum interference and a frequency band having the minimum interference.
12. The apparatus according to claim 11,

Wherein the average transmission capacity is calculated using a formula.
A macro base station for selecting a serving base station of a mobile station in a heterogeneous network,
A transmitting and receiving unit for transmitting and receiving signals to and from the terminal; And
The method comprising: receiving at least one ID of at least one small base station, receiving a message requesting operation information from the terminal, and transmitting the operation information including at least one of a number of multiple antennas, And a control unit for controlling the base station to receive a message requesting handover to a base station having a maximum average transmission capacity from the mobile station using the operation information. delete 14. The apparatus of claim 13,
And controls to receive, from the MS, a message requesting a handover from a BS having the maximum average transmission capacity to a frequency band having the smallest interference.
16. The base station as claimed in claim 15, wherein the base station,

Wherein the mobile station determines by using the equation: &lt; EMI ID = 1.0 &gt;

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