KR20130068458A - Method and apparatus for handover in wireless communication system - Google Patents

Abstract

PURPOSE: A handover method in a wireless communication system and a device thereof are provided to reduce an unnecessary handover in a femto cell by reducing unnecessary scanning processes during the handover in a hierarchical cellular network. CONSTITUTION: A macro cell base station converts position information of a neighbor base station, current position information of a terminal, future position information of the terminal into coordinates(S306). The macro cell base station converts position coordinates of the base station into a coordinate system having the future position coordinates and the current position coordinates as an X-axis(S308). The macro cell base station generates a neighbor base station list according to an angle and a radius of the terminal and designates the current position coordinates and the future position coordinates as a central line. The macro cell base station transmits the neighbor base station list to the terminal(S320). [Reference numerals] (AA) Yes; (BB) Select the IT resources corresponding to the selected network resources; (S302) Start; (S304) Request a cloud service; (S306) Allocate one way resources?; (S308) Select IT resources; (S310) Inquiry about variable network resources for distributed IT resource connection; (S312) Select network resources; (S314) Provide the cloud service; (S316) Allocate network-oriented two way resources; (S318) Select an IT resource candidate; (S320) Request the network resources

Description

METHOD AND APPARATUS FOR HANDOVER IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to a handover method and apparatus in a wireless communication system, and more particularly, to a handover method and apparatus in a communication system in which a macro cell includes a plurality of femto cells.

Small cellular networks such as micro-cells with a radius of 50 to 100 meters, femto cells with a radius of 10 to 50 meters, and Wi-Fi hotspots are currently available as an alternative to macro cellular systems within a radius of 1 km. There is a lot of research going on. These small cells are expected to provide a high quality wireless data access service for users who reside indoors because they are installed in indoor environments with low noise and low base station cost. As a result, many mobile operators are building a hierarchical cellular network in which many small cells are installed in one macro cell. This hierarchical cellular network has the advantage of greatly improving the processing capacity and the number of concurrent users of the system compared to the existing single macro cellular network because several small base stations simultaneously provide connectivity within a single macro cell. have.

In general, in a mobile communication system, when a signal of a macrocell base station is weak at a cell edge, a femtocell base station corresponding to a small base station is installed to increase network capacity. At this time, the femtocell base station may be arbitrarily installed by the user, not the service provider. Therefore, it is difficult to predict how many femtocell base stations are installed and how they are distributed in a single macrocell area. In this case, in the conventional handover method, the macrocell base station broadcasts to each terminal including a plurality of femtocell base stations in the Rulon macrocell base station in the neighboring base station list with a strong RSSI (Received Signal Strength Indication). . When the terminal receives the neighbor base station list, the terminal scans the candidate base station included in the neighbor base station list. Therefore, as the number of femtocell base stations or candidate macrocell base stations included in the neighbor base station list increases, the number of scanning increases.

As in the conventional handover, when the terminal selects a target base station from a neighbor base station list prepared by RSSI and handovers, excessive handover may be caused.

In addition, in general, the serving base station to which the terminal is connected does not store information on the speed or location of each terminal in the cell. However, since the coverage area of the femto cell is small, a terminal moving at a predetermined speed or more causes an unnecessary excessive number of handover processes when it is negotiated with the femto cell base station. Handover is a task that consumes a lot of network resources. Frequent handovers between macro cells and small cells place a significant load on the macro cell base station.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a handover method and apparatus capable of reducing unnecessary scanning during handover in a hierarchical cellular network and reducing unnecessary handover in a femtocell.

According to an embodiment of the present invention, a method for controlling handover of a terminal in a base station of a wireless communication system in which a macro cell includes a plurality of femto cells is provided. The handover method may include obtaining location information of a neighboring base station and current location information of the terminal, predicting future location information of the terminal based on current location information of the terminal, location information of the neighboring base station and the terminal. Converting current position information of the terminal and future position information of the terminal into coordinates, converting position coordinates of the neighboring base station into a coordinate system having the current position coordinates of the terminal and the future position coordinates of the terminal as the x-axis, and Generating a neighbor base station list according to a radius and an angle of the terminal, and transmitting the neighbor base station list to the terminal based on the current position coordinates of the terminal and the future position coordinates of the terminal.

According to an embodiment of the present invention, in a communication environment including a plurality of femto cells in a macro cell, the number of neighboring base station lists that are excessively large may be reduced, and excessive handover between femto cells may be minimized. In the case of a terminal moving at a predetermined speed or more, it is possible to negotiate with the macro cell base station, thereby reducing unnecessary handover due to negotiation with the femtocell base station.

1 is a diagram illustrating a wireless communication system according to an exemplary embodiment of the present invention.
FIG. 2 is a diagram illustrating a form of handover possible in the wireless communication system as shown in FIG. 1.
3 is a diagram illustrating a method of generating a neighbor base station list according to an embodiment of the present invention.
4A and 4D are diagrams illustrating an example of a neighbor base station list generated according to the method illustrated in FIG. 3, respectively.
5 is a diagram illustrating a handover method in a wireless communication system according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. 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. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification and claims, when a section is referred to as "including " an element, it is understood that it does not exclude other elements, but may include other elements, unless specifically stated otherwise.

In the present specification, the user terminal is a mobile station (MS), a terminal (Terminal), a subscriber station (SS), a mobile terminal, a mobile subscriber station (Portable Subscriber Station, PSS), a user device (User) It may refer to an Equipment (UE), an Access Terminal (AT), or the like, and may include all or part of functions of a terminal, a mobile terminal, a subscriber station, a portable subscriber station, a user device, an access terminal, and the like.

In the present specification, a base station includes an access point (AP), a radio access station (RAS), a node B (Node B), an advanced node B (evolved NodeB, eNodeB), and a transmission / reception base station ( It may also refer to a base transceiver station (BTS), a mobile multihop relay (MMR) -BS, and the like, and may include all or a part of functions of an access point, a wireless access station, a NodeB, an eNodeB, a transmission / reception base station, an MMR-BS, and the like. It may be.

Now, a handover method and apparatus in a wireless communication system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a wireless communication system according to an exemplary embodiment of the present invention, and FIG. 2 is a diagram showing a form of handover possible in the wireless communication system as shown in FIG. 1.

Referring to FIG. 1, in a wireless communication system according to an exemplary embodiment of the present invention, a hierarchical cellular network system may include a plurality of femto cells 20a, 20b, 20c, 20d, 20e, in a macro cell 10. 20f, 20g).

The macro cell 10 has a wide cell radius, for example, a radius of about 1 km, and the femto cells 20a, 20b, 20c, 20d, 20e, 20f, and 20g have an example of a radius smaller than the radius of the macro cell 10. For example, it has a radius of 10 to 50 m.

The macro cell 10 includes a macro cell base station MBS1 managing the macro cell 10. Also, femto cells 20a, 20b, 20c, 20d, 20e, 20f and 20g manage femtocell base stations FBS1, FBS2, FBS3, FBS4, FBS5, FBS6, FBS7).

In this hierarchical cellular network system, the terminal 30 may establish a connection with the macro cell base station (MBS1) to perform communication. When one of the femtocells (for example, 20a) approaches, the femto cell base station (FBS1) To establish communication with the server.

In general, in the hierarchical cellular network system, when the signal of the macro base station MBS1 is weak at the edge of the macro cell 10, the femto cell base stations FBS3 and FBS4 are installed by the user to increase network capacity. That is, femto cell base stations (FBS1, FBS2, FBS3, FBS4, FBS5, FBS6, FBS7) can be installed arbitrarily by the user.

In such a hierarchical cellular network system, various types of handovers are possible. For example, as shown in FIG. 2, when the terminal in the femto cell 20d region, such as the terminal MS1, leaves the region of the femto cell 20d, the macro cell 10 in the femto cell 20d. Handover to) is made. In addition, when the femto cell 20d moves from the femto cell 20d to the femto cell 20c like the terminal MS2, handover from the femto cell 20d to the femto cell 20c may be performed. When the terminal in the area of the macro cell 10, such as the terminal MS3, moves out of the macro cell to another macro cell, handover from the femto cell 20a to another macro cell may be performed.

As described above, in an environment in which various types of handovers are performed, the macro cell base stations MBS1 are generally neighboring macro cell base stations MBS2 and MBS3 and a plurality of femto cell base stations FBS1, FBS2, Among the FBS3, FBS4, FBS5, FBS6, and FBS7, a base station having a threshold value exceeding a Received Signal Strength Indication (RSSI) is set as a neighbor base station list, and the created neighbor base station list is applied to all terminals (MS) in the macro cell 10. Broadcast.

When the terminal MS receives the neighbor base station list from the macro cell base station MBS1, the terminal MS scans the candidate base station included in the neighbor base station list, and the macro cell base station MBS1 performs handover among the candidate base stations based on the scanning result of the terminal. Select a target base station. At this time, if the number of candidate base stations included in the neighbor base station list is large, the number of scanning increases. In addition, the neighbor base station list does not reflect the movement direction or speed of the terminal (MS) at all, and when the target base station is selected and handed over from the candidate base stations included in the neighbor base station list created by the RSSI, excessively frequent handovers occur. May be induced.

Next, a method of reducing unnecessary handover in a hierarchical cellular network system will be described in detail with reference to FIGS. 3 to 5.

3 is a diagram illustrating a method of generating a neighbor base station list according to an exemplary embodiment of the present invention, and FIGS. 4A and 4D are diagrams illustrating an example of a neighbor base station list generated according to the method illustrated in FIG. 3.

Referring to FIG. 3, the serving base station to which the terminal is connected generates a neighbor base station list for handover. The serving base station may be a macro cell base station MBS1 or a femto cell base station (FBS). Hereinafter, the serving base station is assumed to be a macro cell base station MBS1.

In the wireless communication system as shown in FIG. 4A, the macro cell base stations MBS1 are located in the neighboring macro cell base stations MBS2 and MBS3 or the femto cell base stations FBS1 to FBS9 in the macro cell 10 area provided by the same service provider. Information is measured using GPS or triangulation, or location information is transmitted from neighboring macro cell base stations MBS2 and MBS3 or femto cell base stations FBS1 to FBS9 in the macro cell 10 region using a separate control channel. . The terminal MS1 measures the current position information by using a triangulation technique and transmits the current position information and the moving speed information to the macro cell base station MBS1. In the following description, neighboring macro cell base stations MBS2 and MBS3 provided by the same service provider and femto cell base stations FBS1 to FBS9 in the macro cell 10 region are collectively referred to as neighbor base stations.

In this way, after acquiring the location information of the neighboring base station and the current location information of the terminal MS1 (S302), the macro cell base station MBS1 uses the current location information and the speed information of the terminal MS1 to the terminal MS1. Predict the future location information (S304).

The macro cell base station MBS1 uses a Kalman filter to predict future location information of the terminal MS1. The Kalman filter was most commonly used in the search and tracking of moving targets and was introduced by Kalman in 1960 as a technique for estimating the state variables of a linear system. The Kalman filter uses a model with a linear moving structure, ensures convergence and stability, and has a simple algorithm. Unlike a conventional algorithm, the Kalman filter is a method of processing in a time domain rather than a spectral analysis method. In general, in the case of the terminal MS1 that needs to be negotiated with the femto cell, since the constant velocity motion of a certain speed or less may be assumed, the future position of the terminal MS1 may be predicted by using the same. However, since the linear system is assumed when estimating the position of the terminal MS1, the terminal does not guarantee optimality when moving nonlinearly. This is because it is difficult to maintain the advantages of the Kalman filter without accurate knowledge of the error of the filter and the system noise. The nonlinear filter has been improved by the method of estimating the state variable of the nonlinear system through the structural improvement of the Kalman filter. This nonlinear filter is based on the linearization of the system. The extended Kalman filter (linear extended) is obtained by linearizing the initial value, obtaining an estimate from the linearized model, and then linearizing it using the newly obtained estimate at a moment. Kalman Filter). By using the extended Kalman filter, the macro cell base station MBS1 may predict the future position and speed of the terminal.

The macro cell base station MBS1 converts and stores the location information of the neighboring base station, the location information of the terminal MS1, and the future location information of the terminal MS1 into a single two-dimensional xy coordinate system (S306). At this time, the current position of the terminal MS1 received at time t is stored as the current position coordinate [(x ^t , y ^t )] in the xy coordinate system, and the future movement position coordinate of the terminal MS1 is future movement position coordinate [(x ^{t +1} , y ^{t + 1} )].

And the macro cell base station (MBS1) is a two-dimensional x'- where the position coordinates of the neighboring base station represented by the xy coordinate system as the origin of the position coordinates ((x ^t , y ^t )) of the terminal MS1 at time t through Equation 1 y 'coordinate system is converted (S308). In this case, the future moving position coordinates [(x ^{t + 1} , y ^{t + 1} )] of the terminal MS1 calculated at time t also correspond to the position coordinates of the terminal MS1 at time t [(x ^t , y ^t )] is converted into the future coordinates of the moving position of the two-dimensional x'-y 'coordinate system [(x' ^{t + 1} , y ' ^{t + 1} )].

[Equation 1]

Also two-dimensional at time t The slope θ ^t of the future moving position coordinate [(x ' ^{t + 1} , y' ^{t + 1} )] of the terminal MS1 in the x'-y 'coordinate system may be obtained as in Equation 2.

&Quot; (2) "

At this time, when the x'-y 'coordinate system whose terminal MS1 is the origin at time ^t is rotated by θ ^t , the position coordinate [(x ^t , y ^t )] of the terminal MS1 is the origin and the terminal position. The coordinate [(x ^t , y ^t )] and the future moving position coordinates of the terminal MS1 are converted into a new x "-y" coordinate system having the x axis.

That is, the macro cell base station MBS1 converts the position coordinates of the neighboring base station indicated by the x'-y 'coordinate system by Equation 3 back to the x "-y" coordinate system (S310).

&Quot; (3) "

Thereafter, in the x " -y " coordinate system having the terminal MS1 as the origin and the current position and the future moving position of the terminal MS1 as the x-axis, the macro cell base station MBS1 generates a neighbor base station list.

First, the macro cell base station MBS1 uses the speed information of the terminal MS1 when predicting future location information of the terminal MS1 using a Kalman filter. The macro cell base station MBS1 determines the speed of the terminal MS1. It compares with the threshold value VTH (S312).

The macro cell base station MBS1 includes, in the neighboring base station list, the macro cell base station that the area of the cell reaches within the radius R3 and the angle A3 from the terminal MS1 when the speed of the terminal MS1 is greater than the threshold value VTH. (S318). At this time, the A3 angle has an angle of 90 or more from the center line between the current position and the future movement position of the terminal MS1. In this case, as shown in FIG. 4A, MBS2 and MBS3 may be included in the neighbor base station list.

On the other hand, when the speed of the terminal MS1 is less than or equal to the threshold value VTH, the macro cell base station MBS1 neighbors the femto cell base station in which the area of the cell extends within the R1 radius and the A1 angle from the terminal MS1 in one step. It is included in the base station list (S314). The angle A1 is 180 degrees from the center line of the line connecting the present position and the future moving position of the terminal MS1. In this case, as shown in FIG. 4B, FBS4 may be included in the neighbor base station list.

Next, the macro cell base station MBS1 further includes a femtocell base station in which the area of the cell extends within the R2 radius and the A2 angle from the terminal MS1 in the neighboring base station list in step S316. At this time, the angle A2 is an angle that satisfies the condition A3 <A2 <A1 with a center line between the current position and the future movement position of the terminal MS1. In this case, as shown in FIG. 4C, FBS3 and FBS5 may be further included in the neighbor base station list.

In addition, the macro cell base station MBS1 further includes a macro cell base station in the neighboring base station list in which the area of the cell is within the R3 radius and the A3 angle from the terminal MS1 in three steps (S318). In this case, the A3 angle has a value of 90 or more based on a line connecting the current position and the future movement position of the terminal MS. In this case, as shown in FIG. 4A, MBS2 and MBS3 may be further included in the neighbor base station list.

As a result, when the speed of the terminal MS1 is less than or equal to the threshold value VTH, as shown in FIG. 4, the final neighbor base station list may include FBS3, FBS4, FBS5, MBS2, and MBS3.

The macro cell base station MBS1 unicasts or broadcasts the generated neighbor base station list to the corresponding terminal (S320).

5 is a diagram illustrating a handover method in a wireless communication system according to an embodiment of the present invention.

Referring to FIG. 4, when the terminal MS1 receives a neighbor base station list (S502), the UE MS1 scans candidate base stations included in the neighbor base station list to measure a RSSI (Received Signal Strength Indicator) value (S504). One RSSI value is reported to the macro cell base station MBS1 (S506).

The macro cell base station MBS1 determines whether to perform handover by comparing the RSSI value of the candidate base station with a handover trigger condition (S508). That is, the macro cell base station MBS1 may select a candidate base station having an RSSI value satisfying a handover trigger condition among the candidate base stations as a target base station, and determine to handover to the target base station.

When the target base station is selected, the macro cell base station MBS1 instructs the terminal MS1 to handover to the target base station (S510).

When the terminal receives the handover command from the macro cell base station MBS1, the terminal starts handover with the target base station (S512).

An embodiment of the present invention is not implemented only through the above-described apparatus and / or method, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. Such an implementation can be easily implemented by those skilled in the art to which the present invention pertains based on the description of the above-described embodiments.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (1)

A method for controlling handover of a terminal in a base station of a wireless communication system in which a macro cell includes a plurality of femto cells,
Obtaining location information of a neighbor base station and current location information of the terminal;
Predicting future location information of the terminal based on the current location information of the terminal;
Converting location information of the neighboring base station, current location information of the terminal, and future location information of the terminal into coordinates;
Converting the position coordinates of the neighboring base station to a coordinate system having the current position coordinates of the terminal and future position coordinates of the terminal as an x-axis,
Generating a neighbor base station list based on a current position coordinate of the terminal and a future position coordinate of the terminal based on a radius and an angle of the terminal; and
Transmitting the neighbor base station list to the terminal;
/ RTI &gt;

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