KR101698898B1 - Hand-over method for mobile-communition service - Google Patents

Abstract

The present invention relates to a handover method for a mobile communication service. The handover method of the disclosed mobile communication system includes a step of selecting a plurality of cooperative base stations by a serving base station that has determined handover of a mobile communication terminal, a step of requesting a handover to selected cooperative base stations by a serving base station, The serving base station responding to the handover request to the serving base station, receiving the packet data by requesting multicasting by the cooperative base stations, requesting the serving base station to reset the RRC connection to the mobile communication terminal, Receiving and providing packet data to a serving base station or a cooperative base station until a predetermined handover threshold value condition is satisfied while checking a channel environment with the serving base station and the cooperative base stations in real time, If the condition is satisfied, it is determined whether any of the cooperative base stations And a step of performing a handover to the base collar. In order to adaptively change radio resources with better signal quality such as quasi-soft handover, handover is reduced by utilizing a plurality of cooperating base stations as well as a serving base station, thereby ensuring high QoS and improving frequency efficiency .

Description

[0001] HAND-OVER METHOD FOR MOBILE-COMMUNITION SERVICE [0002]

The present invention relates to a handover method for a mobile communication service, and more particularly, to a handover method of a mobile communication terminal provided with a mobile communication service, a handover supporting method of a base station for the mobile communication terminal, Over method.

As is known, in 3GPP Release 8, EPC (Evolved Packet Core), which is a network architecture, is described as one of mobile communication systems. EPC is a set of network nodes for 3GPP LTE (Long Term Evolution) system. The EPC evolves the core network of the existing 3GPP system architecture to support Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN), which is an evolved RAN, And has an efficient network structure that simplifies the network node. A wireless communication system including an EPC and an E-UTRAN may be referred to as an evolved packet system (EPS) and corresponds to an LTE mobile communication system currently in service in Korea.

Meanwhile, in the mobile communication system, a handover is performed in order to provide a continuous service even when the mobile communication terminal is moving. Such handover can be divided into a hard handover and a soft handover.

Among these, the hard handover first disconnects from the serving base station during the handover process, and performs the connection to the target base station. On the other hand, the soft handover is disconnected from the serving base station after the connection with the target base station is completed. Soft handover is superior to hard handover in terms of spectral efficiency (or capacity) because there is an interval during which handover is concurrently connected to both base stations during the handover process. However, the radio link is twice There is a further disadvantage to use.

Semisoft handover combines the advantages of hard handover and soft handover. Generally, during the handover process, the distance between the serving base station and the target base station is similar, and the fading effect of the channel is added together, so that the signals between the base stations undergo a severe change with a similar average. The quasi-soft handover opportunistically utilizes this change to adaptively change the radio quality of the signal quality among the serving base station and the target base station to obtain the diversity gain. This is called SSDT (Site Selection Diversity).

This quasi-soft handover is advantageous in that the frequency efficiency is further improved as compared with the hard handover through opportunistic signal use, while the radio resource uses the same amount as the hard handover.

In recent mobile communication systems, studies on small cells have been actively carried out to increase the capacity of a network, and accordingly, frequent handover accompanied with miniaturization of a base station service area leads to decrease in quality of service (QoS) There was a problem.

U.S. Published Patent Application No. 2013-0058246, published on March 7, 2013

According to the embodiment of the present invention, handover is reduced by using a plurality of cooperative base stations as well as a serving base station in adaptively changing radio resources with better signal quality such as quasi-soft handover, And improves the frequency efficiency.

The problems to be solved by the present invention are not limited to those mentioned above, and another problem to be solved can be clearly understood by those skilled in the art from the following description.

According to a first aspect of the present invention, there is provided a handover method of a mobile communication system, comprising: selecting a plurality of cooperative base stations by a serving base station that has determined handover of a mobile communication terminal; Requesting the serving base station to respond to the handover request to the serving base station; requesting the cooperative base stations to respond to the handover request to the serving base station; receiving the packet data by requesting multicasting by the cooperative base stations; Requesting RRC connection reconnection to the serving base station and the cooperative base stations, and requesting the RRC connection re-establishment of the serving base station and the serving base stations until the mobile communication terminal confirms the channel environment with the serving base station and the cooperative base stations in real- Or requesting and providing packet data to the cooperative base stations, And performing a handover from the serving base station to one of the target base stations when the mobile communication terminal satisfies the handover threshold value condition.

Herein, the serving BS and the serving BSs may receive a plurality of MIMO (Multiple Input Multiple Output) signals according to a result of comparison between a channel environment with the mobile communication terminal and a predetermined transmission mode threshold, ) Transmission mode can be used.

The mobile communication terminal may switch to a filter corresponding to the selected MIMO transmission mode and receive the packet data when the transmission mode is selected among the plurality of MIMO transmission modes and the packet data is transmitted.

The serving base station and the cooperative base stations may use the spatial multiplexing transmission mode when the SINR (Signal-to-Interference and Noise Ratio) with the mobile communication terminal exceeds a preset transmission mode threshold.

A method for supporting handover of a base station according to a second aspect of the present invention includes: selecting a plurality of cooperative base stations when a handover of a mobile communication terminal is determined; receiving a response requesting handover to the selected cooperative base stations; Requesting RRC connection re-establishment to the mobile communication terminal; receiving packet data requested by the cooperative BSs to the mobility management node according to the handover request; When the mobile communication terminal requests the packet data until the mobile communication terminal satisfies a predetermined handover threshold value condition, and if the handover threshold value is satisfied, The mobile communication terminal performs handover to a target base station. It may comprise the step of releasing the switch.

The serving BS and the serving BSs may be configured to transmit the packet data to the mobile communication terminal in accordance with a result of a comparison between a channel environment with the mobile communication terminal and a predetermined transmission mode threshold, A transmission mode can be used.

The serving base station and the cooperative base stations may use a spatial multiplexing transmission mode when the SINR with the mobile communication terminal exceeds a preset transmission mode threshold.

According to a third aspect of the present invention, there is provided a handover method of a mobile communication terminal, comprising: receiving an RRC connection re-establishment message for handover from a serving base station; Receiving the packet data from the serving base station or the cooperative base stations and receiving the packet data until the handover threshold value is satisfied, And performing handover from the serving base station to one of the target base stations.

Here, in the step of receiving and providing the packet data, when the mobile communication terminal selects one of the plurality of MIMO transmission modes by the serving base station and the cooperative base stations and the packet data is transmitted, And may switch to a filter corresponding to the MIMO transmission mode to receive the packet data.

According to the embodiment of the present invention, handover is reduced by using a plurality of cooperative base stations as well as a serving base station in adaptively changing radio resources with better signal quality such as quasi-soft handover, And improves the frequency efficiency.

Furthermore, by using a suitable transmission mode among a plurality of MIMOs according to a channel environment, the frequency efficiency is further improved.

1A and 1B are flowcharts illustrating a handover method of a mobile communication system according to an embodiment of the present invention.
2 is a flowchart illustrating a handover support method of a base station according to an embodiment of the present invention.
3 is a flowchart illustrating a handover method of a mobile communication terminal according to an embodiment of the present invention.
4 is a graph showing simulation results of a handover method and a conventional handover method according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The following terms are defined in consideration of the functions in the embodiments of the present invention, which may vary depending on the intention of the user, the intention or the custom of the operator. Therefore, the definition should be based on the contents throughout this specification.

1A and 1B are flowcharts illustrating a handover method of a mobile communication system according to an embodiment of the present invention.

As described above, the handover method of the mobile communication system according to the embodiment includes steps (101 to 105) of selecting a plurality of cooperative base stations by the serving base station that has determined handover of the mobile communication terminal.

The serving base station further includes a step (107) of requesting a handover to the selected cooperating base stations.

And further comprising steps (109 and 111) in which the cooperative base stations respond to the handover request to the serving base station.

The cooperative base stations further include steps 113 and 115 for requesting multicasting to the mobility management node and providing packet data provided by the gateway to the cooperative base station and the serving base station.

The serving base station further includes a step (117) of requesting a mobile communication terminal to perform a radio resource control (RRC) connection reestablishment.

Next, the mobile communication terminal requests and provides packet data to the serving base station or the cooperative base stations until the mobile communication terminal realizes the channel environment with the serving base station and the cooperative base stations in real time and satisfies the predetermined handover threshold value. 123).

The mobile communication terminal further includes a step (125-129) of performing handover from the serving base station to one of the target base stations when the mobile communication terminal satisfies the handover threshold value condition.

The base station further includes a step (131-137) of releasing a resource for the mobile communication terminal except for the base station to which the mobile communication terminal has been attached via the handover.

Thereafter, the mobile communication terminal further includes a step (139) of receiving the packet data provided by the gateway from the attached base station.

2 is a flowchart illustrating a handover support method of a base station according to an embodiment of the present invention.

As shown in the figure, the handover supporting method of the base station according to the embodiment includes a step (201) of selecting a plurality of cooperating base stations when the handover of the mobile communication terminal is determined.

The method further includes a step 203 of requesting handover to the selected cooperating base stations and receiving a response.

The method further includes a step (205) of requesting the mobile communication terminal to perform RRC connection re-establishment.

The method further includes a step (207) of receiving the packet data requested by the cooperative base stations to the mobility management node according to the handover request.

The mobile communication terminal further includes a step 209 of providing the packet data until the mobile communication terminal confirms the channel environment with the serving base station and the cooperative base stations in real time until the mobile communication terminal satisfies a predetermined handover threshold value.

The method further includes a step (211) of releasing a resource for the mobile communication terminal that has performed the handover from the serving base station to any one of the target base stations, after the handover threshold condition is satisfied.

3 is a flowchart illustrating a handover method of a mobile communication terminal according to an embodiment of the present invention.

As shown in the figure, the handover method of the mobile communication terminal according to the embodiment includes a step 301 of receiving an RRC connection re-establishment message for handover from the serving base station.

Receiving the packet data from the serving base station or the cooperative base stations until the predetermined condition of the handover threshold is satisfied while checking the channel environment with the plurality of cooperative base stations and the serving base station included in the RRC connection reestablishment message in real time, (303).

Next, a handover from the serving base station to one of the target base stations is performed (307) when the handover threshold condition is satisfied.

Hereinafter, a handover method for a mobile communication terminal, a handover support method for a base station and a handover method for a mobile communication system according to an embodiment of the present invention will be described in detail with reference to FIGS. 1A and 1B to 4 Let's take a look.

First, the serving base station to which the mobile communication terminal is attached receives the packet data for the mobile communication terminal from the gateway, and transmits the received packet data to the mobile communication terminal (101).

The mobile communication terminal receiving the mobile communication service through the step 101 measures the propagation environment for the base stations located around the mobile communication terminal including the serving base station and transmits a report on the measured propagation environment to the serving base station. For example, the mobile communication terminal can measure and report SINR (Signal-to-Interference and Noise Ratio) with respect to radio waves transmitted from each base station (103).

Then, the serving base station, based on the radio environment report provided from the mobile communication terminal, judges whether the result of comparison with the predetermined threshold satisfies the handover evaluation index when there is a base station having better radio environment than itself, If the evaluation index is satisfied, the handover of the mobile communication terminal is determined (105).

Next, in step 105, the serving base station selects a plurality of base stations satisfying the handover evaluation index as a cooperative base station (201) and transmits a handover request message to the selected cooperating base stations (107).

The cooperative base stations that have received the handover request message determine the availability of the service by checking resources held by the cooperative base stations. If there is a service capability, the cooperative base stations perform admission control to permit handover (109) The serving base stations transmit the handover request response message to the serving base station (111, 203).

In operation 111, the cooperative base stations request multicasting to the MME in order to receive the user data (113), and the mobility management node transmits a multicasting request to the gateway The gateway transmits the packet data for the mobile communication terminal to the serving base station and the serving base stations in a multicasting manner (115).

On the other hand, in step 111, the serving BS, which has received the handover request response message from the cooperative base stations, requests the mobile communication terminal to perform RRC connection resetting. At this time, the RRC connection re-establishment request message includes information about the cooperating base stations that have performed the admission control in step 109 (117, 205, 301).

Then, in response to the RRC connection reset request message, the mobile communication terminal attaches the cooperative base stations as target base stations (119), and receives and provides packet data to the target base stations including the serving base stations and the cooperation base stations (121, 123 , 303). (207, 209) provides packet data received from the gateway to the mobile communication terminal in view of the serving base station or the cooperative base stations,

Here, the mobile communication terminal selects a base station having a better propagation environment from the serving base station and the cooperative base stations while checking the channel environment with the serving base station and the cooperative base stations in real time, and receives and receives packet data from the selected base station. The request and the reception of such packet data are performed until a predetermined handover threshold condition is satisfied. For example, the predetermined handover threshold value condition is a case where the SINR with a base station among the target base stations exceeds a preset handover threshold value, and it is preferable to perform handover to the base station at this time.

In addition, the serving base station and the serving base stations compare the channel environment with the mobile communication terminal and a preset transmission mode threshold value, and select a transmission mode among a plurality of transmission modes of MIMO (Multiple Input Multiple Output) according to the comparison result do.

The MIMO system has various transmission modes unlike the single input single output (SISO) system. For example, the MIMO transmission modes defined in 3GPP standards include Open Loop Spatial Multiplexing (OL-SM), Closed Loop Spatial Multiplexing (CL-SM), Beamforming (BF), and Transmit Diversity (TD). Each of these transmission modes exhibits different efficiencies depending on the channel environment. Generally, in the case of the spatial multiplexing (SM), the SINR is sufficiently ensured and the gain is high in the rich-scattering environment. In the case of BF and TD, in the environment with low SINR and scattering, .

Accordingly, the target base stations adaptively switch the MIMO modes according to the channel conditions according to the SINR, the channel rank, etc. with the mobile communication terminal. For example, the target BSs may use the spatial multiplexing transmission mode if the SINR exceeds the predetermined transmission mode threshold value, and otherwise, the Orthogonal Space-Time Block Code (OSTBC) transmission mode may be used.

Here, the mobile communication terminal switches to a filter corresponding to the transmission mode selected by the target base stations and receives the packet data. For example, in the case of the spatial multiplexing transmission mode, the packet data can be received by switching to a ZF (zero-forcing) filter or a minimum mean squared error filter. In the case of the orthogonal space-time block code transmission mode, May switch to a Maximal Ratio Combining (MRC) filter to receive packet data.

Next, the mobile communication terminal determines handover (125, 305) if the propagation environment with any one of the target base stations satisfies a predetermined handover condition (125, 305), and after the handover is determined, the mobile communication terminal detaches the source base station . Here, since the serving base station corresponds to the source base station, the mobile communication terminal and the serving base station are detached (127, 307).

Then, the mobile communication terminal transmits a handover confirmation message to the handover-based base station (129). FIG. 1B illustrates a case where handover is performed to the cooperative base station #N according to the embodiment.

The cooperative base station #N transmits a handover completion message to the mobility management node (131), and transmits a packet path reset message to the gateway (133).

In addition, the gateway transmits a resource release command to the remaining base stations except for the base station attached through the handover through the handover (135), and the corresponding base stations release resources for the mobile communication terminals (137, 211 ).

Thereafter, the mobile communication terminal receives the packet data provided by the gateway from the attached base station (139).

The simulation is performed to verify the effect of the handover method of the mobile communication system according to the embodiment of the present invention, and the simulation environment is shown in Table 1 below.

Cell radius 50 m Path loss exponent 3.68 Path loss constant 43.8 dB Shadowing standard deviation 8 dB BS Tx power 20 dBm Noise power density -166.83 dBm / Hz Channel bandwidth 10 MHz Number of cells 61 Frequency reuse factor One Tx antenna correlation 0.1

The result of this simulation is the graph of Fig. In FIG. 4, Hard handover is a conventional technique, and Semisoft handover is a handover method according to the present invention. In both 2X2 MIMO and 2X4 MIMO, the handover method according to the embodiment of the present invention showed a frequency efficiency improvement of about 60% in the cell-edge region compared to the prior art.

Combinations of the steps of each flowchart attached to the present invention may be performed by computer program instructions. These computer program instructions may be loaded into a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus so that the instructions, which are executed via a processor of a computer or other programmable data processing apparatus, Lt; / RTI > These computer program instructions may also be stored in a computer usable or computer readable memory capable of directing a computer or other programmable data processing apparatus to implement the functionality in a particular manner so that the computer usable or computer readable memory It is also possible to produce manufacturing items that contain instruction means for performing the functions described in each step of the flowchart. Computer program instructions may also be stored on a computer or other programmable data processing equipment so that a series of operating steps may be performed on a computer or other programmable data processing equipment to create a computer- It is also possible for the instructions to perform the processing equipment to provide steps for executing the functions described in each step of the flowchart.

In addition, each step may represent a module, segment, or portion of code that includes one or more executable instructions for executing the specified logical function (s). It should also be noted that in some alternative embodiments, the functions mentioned in the steps may occur out of order. For example, the two steps shown in succession may in fact be performed substantially concurrently, or the steps may sometimes be performed in reverse order according to the corresponding function.

The foregoing description is merely illustrative of the technical idea of the present invention and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (9)

A step of the serving base station determining the handover of the mobile communication terminal selecting a plurality of cooperative base stations,
Requesting handover to the selected serving base stations;
The cooperative base stations responding to the handover request to the serving base station,
Receiving the packet data by requesting multicasting by the cooperative base stations;
A step in which the serving base station requests the mobile communication terminal to perform a radio resource control (RRC) connection reset;
Receiving and providing packet data to the serving base station or the cooperative base stations until the mobile communication terminal confirms the channel environment with the serving base station and the cooperative base stations in real time and satisfies a predetermined handover threshold value, ,
Performing handover from the serving base station to one of the target base stations when the mobile communication terminal satisfies the handover threshold value condition,
In the step of receiving and providing the packet data, the serving base station and the cooperative base stations,
(MIMO) transmission mode according to a comparison result between a channel environment including SINR (Signal-to-Interference and Noise Ratio) and scattering with the mobile communication terminal and a predetermined transmission mode threshold value A handover method of a mobile communication system using one transmission mode selected.
delete The method according to claim 1,
Wherein the mobile communication terminal switches to a filter corresponding to the selected MIMO transmission mode when the transmission mode is selected among the plurality of MIMO transmission modes and the packet data is transmitted, The handover method of the mobile communication system.
The method according to claim 1,
Wherein the serving base station and the serving base stations use a spatial multiplexing transmission mode when a signal-to-interference and noise ratio (SINR) with the mobile communication terminal exceeds a preset transmission mode threshold.
Selecting a plurality of cooperative base stations if handover of the mobile communication terminal is determined;
Receiving a handover request to the selected base stations;
Requesting RRC (Radio Resource Control) connection reset to the mobile communication terminal;
Receiving the packet data requested by the cooperative BSs to the mobility management node according to the handover request;
Providing the packet data until the mobile communication terminal, which real-time checks the channel environment with the serving base station and the cooperative base stations, satisfies a predetermined handover threshold condition,
And releasing a resource for the mobile communication terminal that has performed the handover from the serving base station to one of the target base stations, when the handover threshold condition is satisfied,
In the step of providing the packet data upon request, the serving base station and the cooperative base stations,
(MIMO) transmission mode according to a comparison result between a channel environment including SINR (Signal-to-Interference and Noise Ratio) and scattering with the mobile communication terminal and a predetermined transmission mode threshold value A handover supporting method of a base station using a transmission mode selected.
delete 6. The method of claim 5,
Wherein the serving base station and the serving base stations use a spatial multiplexing transmission mode when a signal-to-interference and noise ratio (SINR) with the mobile communication terminal exceeds a predetermined transmission mode threshold value.
Receiving a Radio Resource Control (RRC) connection re-establishment message for handover from a serving base station;
Requesting packet data to the serving base station or the cooperative base stations until a predetermined handover threshold value condition is satisfied while checking the channel environment between the plurality of cooperating base stations and the serving base station included in the RRC connection reestablishment message in real time Receiving,
And performing a handover from the serving base station to one of the target base stations when the handover threshold condition is satisfied,
In the step of requesting and receiving the packet data,
The serving base station and the serving base stations may transmit a plurality of MIMOs (MIMOs) according to a comparison result between a channel environment including SINR (Signal-to-Interference and Noise Ratio) and scattering with a mobile communication terminal, Input Multiple Output) transmission mode and transmits the packet data,
Wherein the mobile communication terminal switches to a filter corresponding to the selected MIMO transmission mode and receives the packet data.
delete

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