KR101785873B1 - Method and apparatus for handover in mobile communication system - Google Patents

Abstract

A handover method and apparatus in a mobile communication system capable of reducing a service disconnection time due to a handover and providing a high QoS by selecting a neighboring cell capable of providing high throughput as a target cell are disclosed. A handover method in a mobile communication system includes receiving signal strength information for a neighboring cell from a wireless terminal; Determining a target cell candidate group for handover of the wireless terminal using the signal strength information; Estimating QoS information for the target cell candidate group; And selecting a handover target cell from the target cell candidate group using the QoS information, wherein the QoS information includes a service disconnection time according to a handover and a service disconnection time with respect to data stored during the service disconnection time, And transmission time information.

Description

TECHNICAL FIELD The present invention relates to a handover method and apparatus in a mobile communication system,

The present invention relates to a handover method and apparatus in a mobile communication system, and more particularly, to a handover method and apparatus capable of providing a high QoS.

Generally, in a mobile communication system, a mobile station can perform a handover from a serving cell of a serving cell currently serving to a target cell of a target cell.

In a LTE system, a serving cell determines a target cell to which a wireless terminal will handover based on a received signal reference power (RSRP) of the wireless terminal. At the time of handover, the connection between the serving cell and the wireless terminal is disconnected, and the connection between the target cell and the wireless terminal is established.

While the connection between the serving cell and the wireless terminal is disconnected, the wireless terminal experiences a service disconnection time that is not connected to any of the base stations, and this is referred to as HIT (Handover Interruption Time). During the service disconnection time, since the wireless terminal can not receive data, the serving cell transmits data to the target cell, and the target cell stores the data in the buffer. When the wireless terminal and the target cell are connected to each other, the target cell transmits the data stored in the buffer to the wireless terminal.

The data to be transmitted to the wireless terminal during the handover is stored in the target cell and is not lost. However, since the wireless terminal can not receive data during the service disconnection time, the wireless terminal is provided with a service in which data transmission is delayed, Can not provide high QoS service.

Therefore, it is necessary to study a handover method that can provide high QoS by reducing data transmission delay due to handover.

A related prior art document is Korean Patent Publication No. 2010-0079094.

The present invention provides a handover method and apparatus in a mobile communication system capable of reducing a service disconnection time due to a handover and providing a high QoS by selecting a neighbor cell as a target cell capable of providing high throughput .

According to an aspect of the present invention, there is provided a method for transmitting a signal to a wireless terminal, the method comprising: receiving signal strength information for a neighboring cell from a wireless terminal; Determining a target cell candidate group for handover of the wireless terminal using the signal strength information; Estimating QoS information for the target cell candidate group; And selecting a handover target cell from the target cell candidate group using the QoS information, wherein the QoS information includes a service disconnection time according to a handover and a service disconnection time with respect to data stored during the service disconnection time, The present invention provides a handover method in a mobile communication system including transmission time information.

According to another aspect of the present invention, there is provided a method for estimating QoS information for neighboring cells using radio resource information for neighboring cells in a serving cell and a serving cell, And selecting a handover target cell from among the neighboring cells using the QoS information, wherein the QoS information includes a service disconnection time according to a handover and a transmission time to data stored in the wireless terminal during the service disconnection time And a handover method in a mobile communication system including information.

According to another aspect of the present invention, there is provided an apparatus including: an information receiver for receiving signal strength information on a neighboring cell from a wireless terminal; A candidate group determining unit for determining a target cell candidate group for handover of the wireless terminal using the signal strength information; An information estimator for estimating QoS information for the target cell candidate group; And a target cell selector for selecting a handover target cell in the target cell candidate group using the QoS information, wherein the QoS information includes a service disconnection time and a movement time including information on a transmission time of data stored during the service disconnection time A handover apparatus is provided in a communication system.

According to the present invention, a high QoS can be provided by determining a target cell to be handed over by considering a service disconnection time due to a handover and a data transmission speed of a neighboring cell.

Also, according to the present invention, the data stored in the target cell is transmitted to the mobile station by determining the resource allocation priority such that the handover target cell is in proportion to the size of the HOL (Head Of Line) delay value and in inverse proportion to the delay threshold value It is possible to reduce the buffered packet delivery time (BPDT) and utilize radio resources efficiently.

1 is a view for explaining a concept of a handover method in a mobile communication system according to an embodiment of the present invention.
2 is a diagram for explaining a handover method in a mobile communication system according to an embodiment of the present invention.
3 is a diagram for explaining a handover method in a mobile communication system according to another embodiment of the present invention.
4 is a diagram for explaining a handover apparatus in a mobile communication system according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

The present invention is an invention that can provide a high QoS by reducing a delay of a data transmission time due to a handover, which is highly influenced by a user experience of a user of a mobile terminal in a mobile communication system.

To this end, the present invention estimates a service disconnection time according to a handover, estimates a time when data stored in a target cell is transmitted to the wireless terminal during a service disconnection time, and estimates a target cell to be handed over based on the estimated time And selects among the neighboring cells of the serving cell. According to the present invention, if a handover is performed by selecting a target cell that can minimize the service disconnection time and the data transmission time to the wireless terminal, the user of the wireless terminal can be provided with the optimal QoS.

The present invention can use resource information for a serving cell and a neighbor cell to estimate a service disconnection time and a data transmission time to a wireless terminal. The present invention is performed in a base station of a serving cell that provides a service to a wireless terminal, and information necessary for selecting a target cell can be provided from a wireless terminal and a neighboring cell.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram for explaining the concept of a handover method in a mobile communication system according to an embodiment of the present invention. The average throughput 130 of a serving cell over time, the time of first and second neighboring cells 0.0 > 110 < / RTI > In Fig. 1, the case where two neighboring cells are used is described as an embodiment.

Referring to FIG. 1, when a handover is determined in a serving cell connected to a wireless terminal, the connection between the wireless terminal and the serving cell is broken and a service disconnection time (HIT) occurs. After the service disconnection time, the data stored in the neighboring cell is transmitted to the wireless terminal. Each of the neighboring cells can transmit the stored data to the wireless terminal by increasing the throughput using the available wireless resources. Since the available radio resources are different for each neighboring cell, the throughput for data transmission also varies, as shown in FIG. 1, and the time required for data transmission depends on the throughput of neighboring cells.

Therefore, the serving cell according to the present invention is configured such that the service disconnection time (HIT ₁ , HIT ₂ ) for the first and second neighboring cells and the time (BPDT ₁ , BPDT ₂ ) and determines a target cell to be handed over from the first and second neighboring cells based on the estimation result.

Buffered Packets Delivery Time (BPDT) is a concept newly introduced in the present invention and is a concept introduced to convert the transmission rate of a neighboring cell into a time dimension. Service disconnection time and throughput should be considered in order to provide optimal QoS, but service disconnection time and transmission speed (throughput) are different in dimension. Therefore, the present invention can treat the service disconnection time and throughput in the same time from the viewpoint of time by introducing a time dimension BPDT depending on the throughput. The higher the throughput, the shorter the BPDT. The lower the throughput, the longer the BPDT.

Referring back to FIG. 1, the serving cell determines a target cell to be handed over from the first and second neighboring cells, considering the estimated service disconnection time and BPDT, as described above. As shown in FIG. 1, although the service disconnection time (HIT ₁ ) for the first neighboring cell is longer than the service disconnection time (HIT ₂ ) for the second neighboring cell, Is higher than the throughput 120 of the neighboring cell so that the BPDT ₁ of the first neighboring cell is smaller than the BPDT ₂ of the second neighboring cell so that the serving cell can determine the first neighboring cell as the target cell.

The serving cell uses the radio resource information of the neighboring cell to estimate the service disconnection time and the BPDT, and the necessary information can be provided from the neighboring cell.

As a result, according to the present invention, a high QoS can be provided by determining a target cell to be handed over by considering a service disconnection time due to a handover and a data transmission rate of a neighboring cell.

FIG. 2 illustrates a handover method in a mobile communication system according to an embodiment of the present invention. The handover method of FIG. 2 is performed in a base station of a serving cell.

The base station of the serving cell according to the present invention estimates the QoS information for the neighboring cells using the radio resource information of the neighboring cells around the serving cell and the serving cell (S210). The QoS information includes a service disconnection time (HIT) according to a handover and a transmission time (BPDT) information of data stored in neighboring cells to a wireless terminal during a service disconnection time. The QoS information estimation method is described in more detail in Fig.

Then, the base station of the serving cell selects the handover target cell from neighboring cells using the QoS information (S220). The base station of the serving cell can select a neighboring cell in which the sum of the service disconnection time and the transmission time BPDT is the smallest among the neighboring cells as the handover target cell.

FIG. 3 is a view for explaining a handover method in a mobile communication system according to another embodiment of the present invention. The handover method of FIG. 3 is performed in a base station of a serving cell.

The base station of the serving cell according to the present invention receives the signal strength information on the neighboring cell from the wireless terminal (S310). The wireless terminal measures signal strength for a neighboring cell and transmits signal strength information (RSRP) to the serving cell.

The base station of the serving cell determines a target cell candidate group for handover of the wireless terminal using the signal strength information (S320). Neighboring cells whose signal strength is equal to or greater than the threshold value can be determined as the target cell candidate group.

The base station of the serving cell estimates the QoS information for the target cell candidate group (S330). The QoS information includes a service disconnection time (HIT) according to a handover and a transmission time (BPDT) information of data stored in a neighbor cell to a wireless terminal during a service disconnection time.

In step S330, the serving cell BS estimates the service disconnection time and BPDT of neighbor cells included in the candidate group using the radio resource information of the target cell candidate group.

)은 [수학식 1]과 같이 RACH의 로드(load)에 비례하는 형태의 수학식으로 모델링 될 수 있다.The serving cell base station may estimate a service disconnection time using resource information of a RACH (Random Access Channel) of a neighboring cell as an embodiment. When the load of the RACH is large, the time required for the wireless terminal to access the neighboring cell must be increased, so that the service disconnection time

Can be modeled as a formula proportional to the load of the RACH as shown in Equation (1).

Where p denotes the RACH load, and a and b are constants that may vary according to the embodiment.

In order to estimate the BPDT, the serving cell BS calculates the available throughput for transmitting the stored data using the radio resource information of the target cell candidate group. The available throughput and service disconnection time are used to estimate the BPDT.

)을 계산할 수 있다.In one embodiment, the serving cell base station may determine, as an available radio resource, a code rate (R _h ) determined according to the number of subcarriers (s) and MCS (Modulation and Coding Scheme, ), The constellation size (M _h ), the duration of the OFDM symbol (S _OFDM ), and the number of OFDM symbols (N _RB ) in the resource block. Based on the available radio resources described above, the serving cell base station can calculate the available throughput, e.g., using Equation (2)

) Can be calculated.

)을 추정할 수 있다.Then, the serving cell BS calculates the sum of the service disconnection time and the BPDT using Equation (3)

) Can be estimated.

항이 BPDT에 대응되며,

이다. 그리고

는 도 1에 도시된 바와 같이, 다른 무선 단말들로 데이터를 전송하는데 이용되는 쓰루풋이며,

는 버퍼에 저장된 데이터를 무선 단말로 전송하기 위한 쓰루풋이 추가된 쓰루풋이다.

및

각각은 가용 무선 자원에 기반하여 [수학식 2]를 통해 계산될 수 있다.Equation (3) is an equation for calculating an estimated time for neighboring cell i among the candidate cell candidates,

Term corresponds to BPDT,

to be. And

Is a throughput used for transmitting data to other wireless terminals, as shown in Fig. 1,

Is a throughput added with throughput for transmitting the data stored in the buffer to the wireless terminal.

And

Each can be calculated through Equation (2) based on available radio resources.

)과, BPDT₁의 곱으로 표현될 수 있다. 그리고 서빙 셀의 쓰루풋(110)이

라면, 전술된 조건에 의해 BPDT₁은

와 같이 표현될 수 있다.Since the data that can not be transmitted during the service disconnection time is transmitted during the BPDT time, the BPDT uses the condition that the amount of data B not transmitted during the service disconnection time and the amount of data A to be transmitted during the BPDT time are the same Can be calculated. For example, in FIG. 1, the amount of data that can not be transmitted during the service disconnection time HIT1 of the first neighboring cell may be expressed as a product of the service disconnection time HIT1 and the throughput 110 of the serving cell, The amount of data to be transmitted during _one hour of the neighboring cell in the BPDT is the throughput for transmitting the stored data

) And BPDT ₁ , respectively. And the throughput 110 of the serving cell

, Then the BPDT ₁ is set to < _{RTI ID} = 0.0 _>

Can be expressed as

3, the base station of the serving cell selects a handover target cell from the target cell candidate group using the QoS information estimated in step S330 (S340), instructs the radio terminal to perform handover to the handover target cell do.

The base station of the serving cell can select the neighboring cell in which the sum of the service disconnection time and the transmission time is minimum as the handover target cell in the target cell candidate group. At this time, the serving cell base station can select the handover target cell by calculating the pareto optimal solution to Equation (3).

Meanwhile, according to the present invention, the handover target cell can determine the resource allocation priority for the wireless terminal based on the HOL (Head Of Line) delay value and the delay threshold value for the wireless terminal. That is, when the wireless terminal performs handover to the handover target cell determined according to the present invention, the handover target cell can minimize the BPDT for the wireless terminal by assigning a high resource allocation priority to the wireless terminal.

The HOL delay value is a delay value of a first packet of a queue for transmitting and receiving data between a handover target cell and a wireless terminal, Since the delay value is large, the handover target cell assigns a high priority to a wireless terminal having a large HOL delay value, so that the BPDT can be reduced by first allocating wireless resources to the handover wireless terminal.

Also, the delay threshold value may be set to a low delay threshold value allowed for a wireless terminal, and a delay threshold value of a wireless terminal that transmits / receives data for which urgent processing is requested may be set low. In addition, the handover target cell allocates a low priority to wireless terminals having a large delay threshold, thereby lowering the priority of the wireless resources to wireless terminals requiring urgent data transmission / reception, thereby improving the efficiency of wireless resource utilization.

That is, the handover target cell determines the resource allocation priority in proportion to the size of the HOL delay value and in inverse proportion to the delay threshold value, thereby reducing the BPDT and efficiently utilizing the radio resources.

4 is a diagram for explaining a handover apparatus in a mobile communication system according to an embodiment of the present invention.

4, the handover apparatus includes an information receiving unit 410, a candidate group determining unit 420, an information estimating unit 430, and a target cell selecting unit 440. The above-described handover method can be performed in the base station of the serving cell or in the handover apparatus included in the base station of the serving cell.

The information receiving unit 410 receives signal strength information on a neighboring cell from the wireless terminal.

The candidate group determining unit 420 determines a target cell candidate group for handover of the wireless terminal using the signal strength information.

The information estimation unit 430 estimates QoS information for the target cell candidate group. More specifically, the information estimating unit 430 uses the radio resource information of the target cell candidate group and the radio resource information of the HIT estimating unit and the target cell candidate group for estimating the service disconnection time to calculate the available throughput for the target cell candidate group And estimates a transmission time (BPDT) using the available throughput and the service disconnection time.

The target cell selection unit 440 selects the handover target cell from the target cell candidate group using the QoS information. The target cell selection unit 440 may select a neighboring cell in which the sum of the service disconnection time and the transmission time is the minimum as the handover target cell in the target cell candidate group.

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

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- And various modifications and changes may be made thereto by those skilled in the art to which the present invention pertains. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (10)

Receiving signal strength information for a neighboring cell from a wireless terminal;
Determining a target cell candidate group for handover of the wireless terminal using the signal strength information;
Estimating QoS information for the target cell candidate group; And
And selecting a handover target cell from the target cell candidate group using the QoS information,
Wherein the QoS information includes a service disconnection time according to a handover and a transmission time information of data stored in the service disconnection time to the wireless terminal,
The step of estimating the QoS information
Estimating the available throughput for the target cell candidate group using the radio resource information of the target cell candidate group; And
Estimating the transmission time using the available throughput and the service disconnection time
And a handover method in the mobile communication system.
The method according to claim 1,
The step of estimating the QoS information
And estimating the service disconnection time using the radio resource information of the target cell candidate group
A handover method in a mobile communication system.
3. The method of claim 2,
The radio resource information
RACH resource information
A handover method in a mobile communication system.
delete The method according to claim 1,
The step of selecting the handover target cell
And selects a neighboring cell having the smallest sum of the service disconnection time and the transmission time as the handover target cell
A handover method in a mobile communication system.
The method according to claim 1,
The handover target cell
Determining a resource allocation priority for the wireless terminal based on a Head Of Line (HOL) delay value and a delay threshold for the wireless terminal
A handover method in a mobile communication system.
Estimating QoS information on the neighboring cells using radio resource information of neighboring cells around the serving cell and the serving cell; And
And selecting a handover target cell from the neighboring cells using the QoS information,
Wherein the QoS information includes a service disconnection time according to a handover and transmission time information of data stored in the service disconnection time to a wireless terminal,
The step of estimating the QoS information
Estimating the available throughput for the neighboring cells using the radio resource information of the neighboring cells; And
Estimating the transmission time using the available throughput and the service disconnection time
And a handover method in the mobile communication system.
An information receiver for receiving signal strength information on a neighboring cell from a wireless terminal;
A candidate group determining unit for determining a target cell candidate group for handover of the wireless terminal using the signal strength information;
An information estimator for estimating QoS information for the target cell candidate group; And
And a target cell selector for selecting a handover target cell from the target cell candidate group using the QoS information,
The QoS information includes a service disconnection time and transmission time information of data stored during the service disconnection time,
The information estimating unit
An HIT estimator for estimating the service disconnection time using radio resource information of the target cell candidate group; And
Estimating an available throughput for the target cell candidate group using the radio resource information of the target cell candidate group and estimating the transmission time using the available throughput and the service disconnection time;
The handover method comprising the steps of:
delete 9. The method of claim 8,
The target cell selector
And selects a neighboring cell having the smallest sum of the service disconnection time and the transmission time as the handover target cell
A handover apparatus in a mobile communication system.

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