KR101571879B1 - Method for performing handover between base station with different bandwidth - Google Patents

Abstract

A method for performing a handover according to the present invention is a method for performing handover between base stations having different bandwidths, the method comprising the steps of matching a downlink center frequency between a serving base station and a target base station equally, Determining a handover to the target BS, requesting handover to the MS, and transmitting the handover command to the serving BS through a radio resource control (RRC) reconfiguration message, To the terminal.

Description

[0001] METHOD FOR PERFORMING HANDOVER BETWEEN BASE STATION WITH DIFFERENT BANDWIDTH [0002]

The present invention relates to a method for performing inter-base station handover in a non-identical bandwidth.

When constructing an LTE (Long Term Evolution) wireless network, the mobile communication system can construct a broadband base station in a traffic high density area and a narrowband base station in a traffic density area in order to construct an investment-efficient wireless network.

Here, in a Frequency Division Duplex (FDD) system, a downlink (DL) and an uplink (UL) center frequency are generally matched at the time of handover in a boundary region between base stations having different bandwidths, Can be over-processed.

However, when the downlink and uplink center frequencies of the base stations having different bandwidths can not be synchronized at the same time, frequency boundaries are generated in the boundary areas of the two base stations and an inter-frequency handover process should be performed.

In addition, such inter-frequency handover has a problem of data rate degradation in the border region compared to the same frequency handover due to frequent frequency transition for another frequency search, and there is a problem that call truncation and handover fail.

The present invention proposes a handover performing method capable of performing handover of the same frequency when the downlink and uplink center frequencies of the base stations having different bandwidths can not be synchronized at the same time.

A method for performing a handover between a serving base station and a target base station in a method for performing handover between base stations having different bandwidths includes the steps of matching a downlink center frequency between the serving base station and the target base station, Determining handover to the target BS, requesting handover to the MS, and transmitting a handover command through a radio resource control (RRC) reconfiguration message to the serving BS To the terminal.

The step of requesting handover may include requesting a handover to a Mobility Management Entity (MME), and receiving a handover accept message of the target BS from the MME.

The receiving from the MME may include receiving a handover command message including the handover acceptance message from the MME when the MME receives the handover acceptance message including radio resource information for handover from the target base station Step < / RTI >

The handover acceptance message may include uplink frequency information for the target base station.

The step of matching the downlink center frequency may include matching the downlink center frequency using a center frequency of a synchronization channel for acquiring synchronization between the base stations having different bandwidths.

The step of equalizing the downlink center frequency may include changing only the downlink center frequency without changing the uplink center frequency between base stations having different bandwidths.

A method for performing a handover between a serving base station and a target base station in a method for performing handover between base stations having different bandwidths includes the steps of matching a downlink center frequency between the serving base station and the target base station, Transmitting a handover accept message including radio resource information for handover of the MS, and completing radio resource control (RRC) reconfiguration with the MS.

The step of receiving the handover request may include receiving a handover request for the UE from a Mobility Management Entity (MME).

The step of transmitting the handover accept message may include transmitting frequency band information of the target base station in the handover acceptance message when an asymmetric frequency division duplex (FDD) gap (GAP) is set .

The handover acceptance message may include uplink frequency information for the target base station.

The step of matching the downlink center frequency may include matching the downlink center frequency using a center frequency of a synchronization channel for acquiring synchronization between the base stations having different bandwidths.

According to the present invention, handover can be effectively performed between base stations having different bandwidths by matching the downlink center frequency and providing the uplink center frequency through a handover accept message.

1 is a diagram illustrating a mobile communication system for performing handover between base stations having a same bandwidth.
FIG. 2 is a diagram illustrating an inter-frequency handover between base stations having a non-identical bandwidth. FIG.
3 is a diagram showing an operation state at the time of inter-frequency handover.
4 is a flowchart briefly illustrating an operation procedure for performing a handover to a target base station having a different bandwidth in a serving base station according to an embodiment of the present invention.
5 is a diagram illustrating a synchronization channel for matching downlink center frequencies according to an embodiment of the present invention
FIG. 6 is a diagram illustrating intra-frequency handover between base stations having non-identical bandwidths. FIG.
7 is a flowchart illustrating a handover performing method 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. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when an element is referred to as "comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise.

Throughout the specification, a terminal is referred to as a mobile station (MS), a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS) terminal, an AT, a user equipment (UE), or the like, and may include all or some of functions of a terminal, MT, SS, PSS, AT, UE,

In addition, a base station (BS) includes a node B, an evolved node B, an eNodeB, an access point (AP), a radio access station (RAS) a base transceiver station (BTS), a mobile multihop relay (MMR) -BS, or the like, and may include all or some of functions of a Node B, an eNodeB, an AP, a RAS, a BTS, and an MMR-BS.

Hereinafter, a method for performing inter-base station handover of a non-identical bandwidth according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 7. FIG.

1 is a diagram illustrating a mobile communication system for performing handover between base stations having a same bandwidth.

Referring to FIG. 1, a serving base station 200 and a target base station 300 are connected to a Mobility Management Entity (MME) 400, And performs handover from the serving base station 200 to the target branch station 300.

Herein, the serving BS 200 refers to a BS having a current RAS 100 and a radio bearer, and the target BS 300 disconnects a radio bearer with the source BS 200 and newly sets up a radio bearer A base station to which a handover is to be performed.

When constructing an LTE (Long Term Evolution) wireless network, the mobile communication system can construct a broadband base station in a traffic high density area and a narrowband base station in a traffic density area in order to construct an investment-efficient wireless network. Here, in a Frequency Division Duplex (FDD) system, the downlink (DL) and the uplink (UL) center frequencies between different bandwidth systems are matched at the time of handover in a boundary region between base stations having different bandwidths, Frequency handover processing is generally performed.

The LTE system is a 3GPP technology standard and is an OFDMA (Orthogonal Frequency Division Multiple Access) super high-speed and broadband mobile communication technology. LTE systems are capable of selectively using 1.4, 3, 5, 15 and 20 MHz bandwidths. The LTE system is divided into an FDD system using downlink and uplink using different frequencies, and a TDD (Time Division Duplex) system using the same frequency on downlink and uplink and time division. In the LTE FDD system in the 3GPP technical standard, the FDD gap between the center frequency of the downlink and the center frequency of the downlink is defined as shown in Table 1 below.

E-UTRA operating band TX - RX Carrier center frequency separation One 190 MHz 2 80 MHz. 3 95 MHz. 4 400 MHz 5 45 MHz 6 45 MHz 7 120 MHz 8 45 MHz 9 95 MHz 10 400 MHz 11 48 MHz 12 30 MHz 13 -31 MHz 14 -30 MHz 17 30 MHz 18 45 MHz 19 45 MHz 20 -41 MHz 21 48 MHz

In this case, when a specific block of the uplink frequency band can not be used due to the frequency allocation policy or other reasons, or when the center frequencies between the base stations having different bandwidths of the wide band and the narrow band can not be matched, Frequency boundaries are generated in the area and inter-frequency handover processing should be performed.

FIG. 2 is a diagram showing another frequency handover between base stations having a non-identical bandwidth, and FIG. 3 is a diagram showing an operating state at the time of handover between different frequencies.

If the mobile communication system fails to use a specific block in the uplink frequency band due to a frequency allocation policy or other reasons, if the center frequency between the base stations having different bandwidths of the wide band and the narrow band can not be matched, A frequency boundary is generated in the frequency band, and handover processing between other frequencies is performed as shown in FIG.

When the signal level of the serving base station 200 is lower than a predetermined level, the terminal 100 periodically searches and measures the target base station 300 using another frequency to the serving base station 200 .

At this time, a gap measurement pattern (Measurement Gap Pattern) can be used according to 3GPP standards as shown in Table 2 below to search for another frequency.

Gap Pattern Id Measurement Gap Length (MGL, ms) Measurement Gap Repetition Period (MGRP, ms) 0 6 40 One 6 80

Here, Pattern 1 uses 6 ms for every other frequency measurement every 40 ms, and Pattern 2 uses 6 ms for another frequency measurement every 80 ms. At this time, when pattern 1 is used, data can not be received for 6 ms every 40 ms period, and data frequency degradation of 13% (6 / (40 + 6)) occurs because another frequency must be searched.

When the signal of the target base station 300 is better than the signal of the serving base station 200, the serving base station 200 issues a handover command to the mobile station 100, (300).

In this case, as shown in FIG. 3, the inter-frequency handover has a problem of data rate degradation in the border region compared to the same frequency handover, and quality degradation such as call truncation and handover failure due to frequent frequency transition for other frequency search .

Therefore, in the LTE FDD system having different bandwidths, when the UL center frequency can not be moved due to a specific reason, only the DL frequency can be moved and the same frequency handover can be performed Thereby solving the above problems.

A procedure for performing handover in the serving BS will be described in detail with reference to FIG.

4 is a flowchart briefly illustrating an operation procedure for performing a handover to a target base station having a different bandwidth in a serving base station according to an embodiment of the present invention. At this time, the following flowchart will be described using the same reference numerals in conjunction with the configuration of FIG.

Referring to FIG. 4, the mobile communication system adjusts the downlink center frequency between the serving base station 200 and the target base station 300 to be equal to each other (S100) according to an embodiment of the present invention.

In order to equalize the downlink center frequencies between the serving base station 200 and the target base station 300 having different bandwidths, the mobile communication system according to an exemplary embodiment of the present invention transmits a center frequency Can be used to match the downlink center frequency.

5 is a diagram illustrating a synchronization channel for matching a downlink center frequency according to an embodiment of the present invention.

The mobile communication system according to an embodiment of the present invention may use different bandwidths as shown in FIG. At this time, the mobile communication system can use a synchronization channel (SCH) having the same bandwidth even if the bandwidth is different. Here, the synchronization channel is a channel for acquiring the signal synchronization of the base station, and always transmits the synchronization signal at the center frequency of each bandwidth. Then, the synchronization signal can be transmitted in a channel of 1.4 MHz bandwidth of each bandwidth.

Therefore, the mobile communication system according to an embodiment of the present invention can equalize the center frequency of the downlink to perform handover at the same frequency between base stations having different bandwidths through the synchronization channel.

The serving base station 200 receives the measurement result of the target base station 300 from the terminal 100 and determines handover of the terminal 100 to the target base station 300 at step S110.

At this time, the serving BS 200 requests handover of the MS 100 to the MME 400 and transmits uplink frequency information for the target BS 300 through the handover acceptance message of the target BS 300 (S120).

Then, the serving base station 200 transmits a handover command to the mobile station 100 through a radio resource control (RRC) reconfiguration message (S130).

FIG. 6 is a diagram illustrating intra-frequency handover between base stations having non-identical bandwidths. FIG.

The handover method according to an exemplary embodiment of the present invention is a method for performing handover processing of the same frequency between base stations having different bandwidths in a situation such as restriction of use of a constant band of an uplink frequency, Only the downlink center frequency is changed to be the same as that of the other bandwidth systems.

In addition, the handover performing method according to an embodiment of the present invention transmits uplink frequency information in the handover acceptance message of the target base station 300 in order to smooth handover between the two base stations having different bandwidths. In this case, since the same FDD gap is used, if the downlink center frequency is the same, the uplink center frequency can not be transmitted to the UE because the center frequency is fixed.

Therefore, the method of performing handover according to an embodiment of the present invention enables handover between two base stations having different bandwidths by including an uplink frequency in a handover acceptance message.

Hereinafter, a process of performing a handover of a UE from a serving BS to a target BS will be described in detail with reference to FIG.

7 is a flowchart illustrating a handover performing method according to an embodiment of the present invention. At this time, the following flowchart will be described using the same reference numerals in conjunction with the configuration of FIG.

7, when the MS 100 reports a measurement result of the target BS 300 to the serving BS 200 and the serving BS 200 determines a handover to the target BS 300 (S200, S202).

When the handover is determined, the serving base station 200 requests handover to the target base station 300 from the MME 400, and the MME 400 transmits a handover request message to the target base station 300 (S204, S206).

The target base station 300 sets a radio resource for handover for the handover request of the MME 400 and transmits the set radio resource information to the MME 400 through a Handover Request Acknowledge message . Then, the MME 400 stores the content in the handover command message and transmits the handover command message to the serving base station 200 (S210).

At this time, the target base station 300 performs a procedure for confirming whether or not the asymmetric FDD gap function is set. If the asymmetric FDD gap function is set, the target base station 300 transmits frequency information used by its own cell in the handover request acknowledgment message (S208).

If there are no cells with different FDD gaps, the target base station 300 deactivates the asymmetric FDD gap function so as not to transmit the uplink frequency information of the target base station 300 in the handover acceptance message, Reduction and efficient use of radio resources.

The MME 400 transmits the handover information in the handover acceptance message received from the target base station 300 to the serving base station 200 as a handover command message (S212).

The serving base station 200 transmits a handover command to the mobile station through an RRC reconfiguration message and handover the target mobile station 100 to the target base station 300 in step S214.

That is, in the handover performing method according to an embodiment of the present invention, the target base station 300 transmits the uplink frequency information of the target base station 300 in the handover acceptance message responded by the target base station 300, Over.

In the normal case of using the same FDD Gap recommendation value, in the Mobility Control Info, which is the information field of the target base station 300 in the RRC connection reconfiguration message, which is the handover message, Do not transmit frequency information.

In the case of using the FDD Gap of the same recommended value, handover processing is normally performed without transmitting frequency information. Therefore, unnecessary frequency information is not transmitted in the handover message, thereby reducing the amount of call processing messages, Efficient use of radio resources is possible.

Table 3 is a handover call processing message, and is an example of an RRC connection reset message.

- ASN1START
RRCConnectionReconfiguration :: = SEQUENCE {
rrc-TransactionIdentifier RRC-TransactionIdentifier,
criticalExtensions CHOICE {
c1 CHOICE {
rrcConnectionReconfiguration-r8 RRCConnectionReconfiguration-r8-IEs,
spare7 NULL,
spare6 NULL, spare5 NULL, spare4 NULL,
spare3 NULL, spare2 NULL, spare1 NULL
},
criticalExtensionsFuture SEQUENCE {}
}
}
RRCConnectionReconfiguration-r8-IEs :: = SEQUENCE {
measConfig MeasConfig OPTIONAL, - Need ON
mobilityControlInfo MobilityControlInfo OPTIONAL, - Cond HO
dedicatedInfoNASList SEQUENCE (SIZE (1..maxDRB)) OF
DedicatedInfoNAS OPTIONAL, --Cond nonHO
radioResourceConfigDedicated RadioResourceConfigDedicated OPTIONAL, - Cond HO-toEUTRA
securityConfigHO SecurityConfigHO OPTIONAL, - Cond HO
nonCriticalExtension RRCConnectionReconfiguration-v890-IEs OPTIONAL
}
RRCConnectionReconfiguration-v890-IEs :: = SEQUENCE {
lateNonCriticalExtension OCTET STRING OPTIONAL, - Need OP
nonCriticalExtension RRCConnectionReconfiguration-v920-IEs OPTIONAL
}
RRCConnectionReconfiguration-v920-IEs :: = SEQUENCE {
otherConfig-r9 OtherConfig-r9 OPTIONAL, - Need ON
fullConfig-r9 ENUMERATED {true} OPTIONAL, - Cond HO-Reestab
nonCriticalExtension RRCConnectionReconfiguration-v1020-IEs OPTIONAL
}
RRCConnectionReconfiguration-v1020-IEs :: = SEQUENCE {
sCellToReleaseList-r10 SCellToReleaseList-r10 OPTIONAL, - Need ON
sCellToAddModList-r10 SCellToAddModList-r10 OPTIONAL, - Need ON
nonCriticalExtension SEQUENCE {} OPTIONAL - Need OP
}
SCellToAddModList-r10 :: = SEQUENCE (SIZE (1..maxSCell-r10)) OF SCellToAddMod-r10
SCellToAddMod-r10 :: = SEQUENCE {
sCellIndex-r10 SCellIndex-r10,
cellIdentification-r10 SEQUENCE {
physCellId-r10 PhysCellId,
dl-CarrierFreq-r10 ARFCN-ValueEUTRA
} OPTIONAL, - Cond SCellAdd
radioResourceConfigCommonSCell-r10 RadioResourceConfigCommonSCell-r10 OPTIONAL, - Cond SCellAdd
radioResourceConfigDedicatedSCell-r10 RadioResourceConfigDedicatedSCell-r10 OPTIONAL, - Cond SCellAdd2
...,
[[dl-CarrierFreq-v1090 ARFCN-ValueEUTRA-v9e0 OPTIONAL-Cond EARFCN-max
]]
}
SCELLToReleaseList-r10 :: = SEQUENCE (SIZE (1..maxSCell-r10)) OF SCellIndex-r10

SecurityConfigHO :: = SEQUENCE {
handoverType CHOICE {
intraLTE SEQUENCE {
securityAlgorithmConfig SecurityAlgorithmConfig OPTIONAL, - Cond fullConfig
keyChangeIndicator BOOLEAN,
nextHopChainingCount NextHopChainingCount
},
interRAT SEQUENCE {
securityAlgorithmConfig SecurityAlgorithmConfig,
nas-SecurityParamToEUTRA OCTET STRING (SIZE (6))
}
},
...
}
- ASN1STOP

Table 4 is an example of the mobility control information included in the RRC connection reconfiguration message.

- ASN1START
MobilityControlInfo :: = SEQUENCE {
targetPhysCellId PhysCellId,
carrierFreq CarrierFreqEUTRA OPTIONAL, - Cond HO-toEUTRA2
carrierBandwidth CarrierBandwidthEUTRA OPTIONAL, - Cond HO-toEUTRA
additionalSpectrumEmission AdditionalSpectrumEmission OPTIONAL, - Cond HO-toEUTRA
t304 ENUMERATED {
ms50, ms100, ms150, ms200, ms500, ms1000,
ms2000, spare1},
newUE-Identity C-RNTI,
radioResourceConfigCommon RadioResourceConfigCommon,
rach-ConfigDedicated RACH-ConfigDedicated OPTIONAL, - Need OP
...,
[[carrierFreq-v9e0 CarrierFreqEUTRA-v9e0 OPTIONAL - Need ON
]]
}
CarrierBandwidthEUTRA :: = SEQUENCE {
dl-Bandwidth ENUMERATED {
n6, n15, n25, n50, n75, n100, spare10,
spare9, spare8, spare7, spare6, spare5,
spare4, spare3, spare2, spare1},
ul-Bandwidth ENUMERATED {
n6, n15, n25, n50, n75, n100, spare10,
spare9, spare8, spare7, spare6, spare5,
spare4, spare3, spare2, spare1} OPTIONAL - Need OP
}
CarrierFreqEUTRA :: = SEQUENCE {
dl-CarrierFreq ARFCN-ValueEUTRA,
ul-CarrierFreq ARFCN-ValueEUTRA OPTIONAL - Cond FDD
}
CarrierFreqEUTRA-v9e0 :: = SEQUENCE {
dl-CarrierFreq-v9e0 ARFCN-ValueEUTRA-r9,
ul-CarrierFreq-v9e0 ARFCN-ValueEUTRA-r9 OPTIONAL - Cond FDD
}
- ASN1STOP

As described above, in the handover performing method according to the embodiment of the present invention, the downlink center frequency is made equal and the uplink center frequency is provided through the handover accept message, handover can be effectively performed between the base stations having different bandwidths It provides an environment that can be performed.

The embodiments of the present invention described above are not implemented only by the apparatus and method, but may be implemented through a program for realizing the function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. Such a recording medium can be executed not only on a server but also on a user terminal.

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.

100: terminal 200: serving base station
300: Target base station 400: MME

Claims (11)

In a method for performing handover between base stations with different bandwidths,
Matching the downlink center frequency between the serving base station and the target base station;
Receiving a measurement result of a target base station from the terminal,
Determining a handover to the target BS, and requesting handover to the MS; and
And the serving base station transmitting a handover command to the terminal through a radio resource control (RRC) reconfiguration message,
The step of requesting handover to the terminal comprises:
Receiving a handover acceptance message including frequency information of the target base station from the target base station when an asymmetric FDD (Frequency Division Duplex) gap (GAP) is set;
And performing a handover. The method of claim 1,
Wherein the step of requesting handover comprises:
Requesting a handover to a Mobility Management Entity (MME), and
Receiving a handover acceptance message of the target BS from the MME;
And performing a handover. 3. The method of claim 2,
Wherein the receiving from the MME comprises:
Receiving a handover command message including the handover acceptance message from the MME when the MME receives the handover acceptance message including radio resource information for handover from the target base station
And performing a handover. 4. The method of claim 3,
The handover acceptance message includes:
And uplink frequency information for the target base station. The method of claim 1,
The step of equalizing the downlink center frequency comprises:
Matching the downlink center frequency using a center frequency of a synchronization channel for synchronization acquisition between base stations having different bandwidths
And performing a handover. The method of claim 5,
The step of equalizing the downlink center frequency comprises:
Modifying only the downlink center frequency without changing the uplink center frequency between base stations having different bandwidths
And performing a handover. In a method for performing handover between base stations with different bandwidths,
Matching the downlink center frequency between the serving base station and the target base station;
Receiving a handover request for the terminal from the serving base station,
Transmitting a handover accept message including radio resource information for handover of the MS,
And completing a radio resource control (RRC) reconfiguration with the MS,
Wherein the step of transmitting the handover accept message comprises:
If an asymmetric FDD (Frequency Division Duplex) gap (GAP) is set, transmitting the frequency information of the target BS in the handover acceptance message
And performing a handover. 8. The method of claim 7,
Wherein the receiving the handover request comprises:
Receiving a handover request for the MS from a Mobility Management Entity (MME)
And performing a handover. delete 8. The method of claim 7,
The handover acceptance message includes:
And uplink frequency information for the target base station. 8. The method of claim 7,
The step of equalizing the downlink center frequency comprises:
Matching the downlink center frequency using a center frequency of a synchronization channel for synchronization acquisition between base stations having different bandwidths
And performing a handover.

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