1111111111111111 IIIIII IIIII 11111 1111111111 11111 111111111111111 lllll 111111111111111 11111111
`US 20080051091Al
`
`c19) United States
`c12) Patent Application Publication
`Phan et al.
`
`c10) Pub. No.: US 2008/0051091 Al
`Feb. 28, 2008
`(43) Pub. Date:
`
`(54) APPARATUS, METHOD AND COMPUTER
`PROGRAM PRODUCT PROVIDING
`ENHANCED ROBUSTNESS OF HANDOVER
`IN E-UTRAN WITH PAGING OF THE
`ACTIVE UE
`
`(75)
`
`Inventors:
`
`Vinh Van Phan, Oulu (FI);
`Markku J. Vainikka, Kiviniemi
`(FI); Benoist Sebire, Tokyo (JP)
`
`Correspondence Address:
`HARRINGTON & SMITH, PC
`4 RESEARCH DRIVE
`SHELTON, CT 06484-6212
`
`(73) Assignee:
`
`Nokia Corporation
`
`(21) Appl. No.:
`
`11/895,508
`
`(22)
`
`Filed:
`
`Aug. 24, 2007
`
`Related U.S. Application Data
`
`(60)
`
`Provisional application No. 60/840,283, filed on Aug.
`25, 2006.
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`H04Q 7120
`(2006.01)
`(52) U.S. Cl. ....................................................... 455/436
`ABSTRACT
`
`(57)
`
`In a non-limiting aspect thereof, the exemplary embodi(cid:173)
`ments of this invention provide a method that includes
`starting a timer in a base station after sending a handover
`information message, and stopping the timer upon a condi(cid:173)
`tion, including either receiving an expected handover related
`message, or expiration of a maximum allowed time value of
`the timer.
`
`/1,NETWORK
`
`oGW
`
`14
`
`NETWORK
`ELEMENT (MME/UPE)
`14C
`
`13
`
`Samsung Ex. 1015
`
`

`

`SERVING CELL
`
`/
`
`1,NETWORK
`
`aGW
`
`/14
`
`NETWORK
`ELEMENT (MME/UPE)
`,,.-14C
`
`I
`
`13
`
`(')
`~
`
`.....
`
`""O
`~ .....
`('D = .....
`>
`"e -....
`"e
`.... 0 =
`""O =
`-....
`.... 0
`.....
`=
`
`O"
`
`(')
`~
`
`I
`
`"f'j
`('D
`?'
`N
`~CIO
`N
`0
`0
`CIO
`
`('D
`
`rJJ =-('D
`.....
`....
`0 ....
`....
`
`0
`
`c
`rJJ
`N
`0
`0
`CIO
`
`0
`Ul
`0
`1,0
`
`---0
`....
`....
`> ....
`
`MEM
`
`RRC
`
`p~ I
`10G/ UE I
`
`108 /
`
`112G~ I - I -1
`I I
`
`RRC
`I SOURCE
`eNODE B
`
`MEM
`
`128/
`
`DP
`
`PROG
`MEM
`
`148
`
`14A
`
`I
`
`TARGET CELL
`
`/
`
`I
`
`MEM I
`
`TARGET
`eNODE B
`
`· - -
`
`128/
`
`I
`I
`
`FIG.1
`
`Samsung Ex. 1015
`
`

`

`I
`
`UE
`
`I TARGET eNB I
`I SOURCE eNB I
`I
`I
`PACKET DATA
`PACKET DATA
`~------------------ ---------
`----------------------
`UL ALLOCATION
`
`C ...
`1. MEASUREMENT REPORTS
`
`eNB MAKES HO DECISION
`TO MOVE UE TO A CELL
`IN TARGET eNB
`
`MMELUPE
`
`LE
`
`GENO
`
`GNALLING
`L3 SI
`
`L1/L2 ~ SIGNALLING
`
`=:::===>
`___ U~_;E -------
`R DATA
`
`2. CONTEXT DATA
`{UE RAN CONTEXT)
`
`-
`
`STORE UE RAN CONTEXT.
`RECEIVE C-RNTI
`
`3. CONTEXT CONFIRM
`{NEW C-RNTI...)
`
`DL ALLOCATION
`
`A
`
`K --.
`
`4. HANDOVER COMMAND
`(NEW C-RNTl...)
`
`DETACH FROM OLD
`DELIVER BUFFERED AND
`CELL AND SYNCHRONIZE
`IN TRANSIT PACKETS
`TO NEW CELL
`TO TARGET eNB
`_J _______ _J__ ________
`- - - - -
`FIG.2A
`
`""O
`~ .....
`('D = .....
`
`(')
`
`~ .....
`
`t "e -....
`.... 0 =
`""O = O" -....
`.... 0 =
`
`(')
`
`~ .....
`
`"f'j
`('D
`?'
`N
`~CIO
`N
`0
`0
`CIO
`
`('D
`('D
`
`rJJ =(cid:173)
`.....
`N
`0 ....
`....
`
`0
`
`c
`rJJ
`N
`0
`0
`
`0
`Ul
`0
`1,0
`
`CIO ---0
`....
`....
`> ....
`
`Samsung Ex. 1015
`
`

`

`- - - - - - - - - - - - - , - - --- - --- - - - - , - - - - - - - - - --- -
`DELIVER USER DATA (i)
`~-------------------
`
`K ......
`
`5. SYNCHRONIZATION
`I
`UL ALLOCATION + TA FOR UE
`I
`6. HANDOVER CONFIRM
`
`BUFFER PACKETS FROM
`SOURCE eNB
`
`" ..
`
`II'
`
`1-----------
`
`PACKET DATA
`--------~-------------------
`7a. HANDOVER COMPLETED
`
`FLUSH DL BUFFER,
`CONTINUE DELIVERING
`IN-TRANSIT PACKETS
`
`i--------------
`
`DELIVER USER DATA (ii)
`~------------------
`PACKET DATA
`
`------i-----------------
`
`7b. UE UPDATE TO MME/UPE
`
`I PATH SWITCHING I
`
`I
`
`I--
`
`------------------
`
`PACKET DATA
`
`FIG.2A
`FIG.2B I FIG.2
`
`FIG.28
`
`"'O
`~ .....
`('D = .....
`
`(')
`
`~ .....
`
`t "e -....
`.... 0 =
`"'O = O" -....
`.... 0 =
`
`(')
`
`~ .....
`
`"f'j
`('D
`?'
`N
`~CIO
`N
`0
`0
`CIO
`
`('D
`('D
`
`~
`
`rJJ =(cid:173)
`.....
`0 ....
`....
`
`0
`
`c
`rJJ
`N
`0
`0
`
`0
`Ul
`
`0
`1,0
`
`CIO ---0
`....
`....
`> ....
`
`Samsung Ex. 1015
`
`

`

`- - - - - --- - --- - , - - - --- - --- - --- ,- --- - ---,---- - - - - -
`DELIVER USER DATA (i)
`~-------------------
`
`BUFFER PACKErS FROM
`SOURCE eNB
`
`4o. NOTIFICATION (HO}
`
`4b. PAGING (HO)
`
`4c. PAGING (HO)
`
`4d*. NOTIFY oGW
`
`IDLE STATE PAGE
`NOTIFICATION
`4e.*
`
`DErACH FROM OLD
`CELL AND SYNCHRONIZE
`TO NEW CELL
`
`~
`"
`
`5. SYNCHRONIZATION
`I
`UL ALLOCATION + TA FOR UE
`I
`6. HANDOVER CONFIRM
`
`~ -v
`
`FIG.3A
`FIG.3B I FIG.3
`
`FIG.38
`
`(')
`
`""O
`~ .....
`('D = .....
`~ "e -....
`~ ..... .... 0 =
`""O = O" -....
`~ ..... .... 0 =
`
`(')
`
`"f'j
`('D
`?'
`N
`~
`N
`0
`0
`QO
`
`('D
`
`.i;...
`
`rJJ =(cid:173)
`('D .....
`0 ....
`....
`
`0
`
`c
`rJJ
`N
`0
`0
`
`0
`Ul
`
`0
`1,0
`
`QO ---0
`....
`....
`> ....
`
`Samsung Ex. 1015
`
`

`

`UE
`
`10
`
`SOURCE eNB
`
`12
`
`PACKET DATA
`----------
`UL ALLOCATION
`
`1. MEASUREMENT REPORTS
`
`I TARGET eNB r
`
`I
`
`PACKET DATA
`
`12'
`
`aGW
`MME/UPE
`
`14·
`
`eNB MAKES HO DECISION
`TO MOVE UE TO A CELL
`IN TARGET eNB
`
`2. CONTEXT DATA
`(UE RAN CONTEXT)
`
`LEGEND
`
`L3 SIGNALLING
`
`i
`
`L 1 /L2 SIGNALLING
`
`>
`USER DATA
`-----------
`
`X=
`
`NOT
`RECEIVED
`OR
`IMPAIRED
`
`* OPTIONAL
`
`TIMER_T2
`
`STORE UE RAN CONTEXT,
`RECEIVE C-RNTI
`
`N
`
`3. CONTEXT CONFIRM
`(NEW C-RNTI •.• )
`
`DELIVER BUFFERED AND
`IN TRANSIT PACKETS
`TO TARGET eNB
`FIG.3A
`
`TIMER_T1
`
`""O
`~ .....
`('D = .....
`
`t "e -....
`
`(')
`~
`Q;
`
`0 =
`""O = O" = (')
`~ ..... ....
`0 =
`
`"f'j
`('D
`?'
`N
`~CIO
`N
`0
`0
`CIO
`
`('D
`('D
`
`rJ'1 =(cid:173)
`.....
`Ul
`0 ....
`....
`
`0
`
`c
`rJ'1
`N
`0
`0
`
`0
`Ul
`
`0
`1,0
`
`CIO ---0
`....
`....
`> ....
`
`Samsung Ex. 1015
`
`

`

`Patent Application Publication
`
`Feb. 28, 2008 Sheet 6 of 10
`
`US 2008/0051091 Al
`
`INITIATE OPERATION OF TIMER 12F V 4A
`IN AT LEAST ONE OF THE TARGET
`eNB 12' AND SOURCE eNB 12 AFTER
`INITIATION OF THE HO PROCEDURE
`
`1•
`
`IN EVENT TIMER 12F EXPIRES BEFORE / 48
`THE UE 10 CAN BE EXPECTED TO
`RESPOND TO A HO-RELATED MESSAGE
`SENT FROM THE SOURCE eNB 12,
`INITIATE COMMUNICATION TO THE
`UE 10 ON A PAGING CHANNEL FROM
`AT LEAST ONE OF THE TARGET eNB
`12' ONE OF THE TARGET eNB 12'
`AND SOURCE eNB 12, WHERE THE
`COMMUNICATION INCLUDES
`INFORMATION CONTAINED IN THE
`HO-RELATED MESSAGE
`
`FIG.4A
`
`Samsung Ex. 1015
`
`

`

`Patent Application Publication
`
`Feb. 28, 2008 Sheet 7 of 10
`
`US 2008/0051091 Al
`
`INITIATE OPERATION OF TIMER 12F
`IN AT LEAST ONE OF THE TARGET
`eNB 12' AND SOURCE eNB 12 AFTER
`INITIATION OF THE HO PROCEDURE
`
`I~ 4A'
`
`•
`TIMER EXPIRES BEFORE THE UE 10
`CAN BE EXPECTED TO RESPOND TO
`A HO-RELATED MESSAGE SENT FROM
`THE SOURCE eNB 12
`
`I~ 48'
`
`t
`RADIO CONNECTION IS LOST
`t
`CONTACT THE aGW 14 WITH
`NOTIFY MESSAGE
`
`t
`
`RECEIVE A PAGE NOTIFICATION
`FROM THE aGW 14
`
`t
`BEGIN IDLE STATE PAGING OF THE
`UE 10, WHERE IT IS ASSUMED THAT
`EXPIRATION OF THE TIMER_T2 1 OF
`HAS CAUSED THE UE 10 TO BE
`PLACED IN A CONDITION TO BE
`RESPONSIVE TO AN IDLE STATE PAGE,
`AND WHERE THE IDLE STATE PAGE,
`INCLUDES INFORMATION CONTAINED IN
`THE HO-RELATED MESSAGE
`
`/ 4C'
`
`/ 4D'
`
`V 4E'
`
`4F'
`I /
`
`FIG.48
`
`Samsung Ex. 1015
`
`

`

`Patent Application Publication
`
`Feb. 28, 2008 Sheet 8 of 10
`
`US 2008/0051091 Al
`
`INITIATE OPERATION ON TIMER 10F
`AFTER START OF THE HO
`PROCEDURE
`
`,,,,--SA
`v
`
`IN EVENT TIMER 1 OF EXPIRES
`BEFORE THE UE 10 RECEIVES AN
`EXPECTED HO-RELATED MESSAGE SENT
`FROM THE SOURCE eNB, BEGIN
`LISTENING TO A PAGING CHANNEL OF
`A CURRENT CELL AND, OPTIONALLY, TO
`PAGING CHANNEL(S) OF NEIGHBORING
`CELL(S)
`
`RECEIVE THE EXPECTED HO(cid:173)
`RELATED MESSAGE AND
`ASSOCIATED INFORMATION FROM
`A RECEIVED PAGE
`
`SC
`
`CONTINUE WITH THE HO
`PROCEDURE USING THE HO-
`RELATED MESSAGE AND
`ASSOCIATED INFORMATION
`RECEIVED THROUGH THE PAGING
`CHANNEL
`
`V 5D
`
`FIG.5
`
`Samsung Ex. 1015
`
`

`

`Patent Application Publication
`
`Feb. 28, 2008 Sheet 9 of 10
`
`US 2008/0051091 Al
`
`STARTING A TIMER IN A BASE STATION
`AFTER SENDING A HANDOVER
`INFORMATION MESSAGE
`~
`STOPPING THE TIMER UPON A
`CONDITION, COMPRISING EITHER:
`RECEIVING AN EXPECTED
`HANDOVER RELATED MESSAGE; OR
`
`610
`
`V 615
`
`EXPIRATION OF A MAXIMUM
`ALLOWED TIME VALUE OF THE
`TIMER
`
`FIG.SA
`
`STARTING A TIMER IN A USER
`EQUIPMENT AFTER AN INITIATION
`OF A HANDOVER PROCEDURE
`
`v--- 620
`
`!
`
`STOPPING THE TIMER UPON A
`CONDITION, COMPRISING EITHER:
`RECEIVING AN EXPECTED
`HANDOVER RELATED MESSAGE; OR
`
`1/ 625
`
`EXPIRATION OF A MAXIMUM
`ALLOWED TIME VALUE OF THE TIMER,
`WHERE AT THE EXPIRATION OF THE
`MAXIMUM ALLOWED TIME VALUE THE
`USER DEVICE BEGINS LISTENING FOR
`A PAGE TO OBTAIN HANDOVER RELATED
`INFORMATION
`
`FIG.68
`
`Samsung Ex. 1015
`
`

`

`Patent Application Publication
`
`Feb. 28, 2008 Sheet 10 of 10 US 2008/0051091 Al
`
`SENDING A HANDOVER RELATED
`MESSAGE TO A USER EQUIPMENT
`FROM A BASE STATION
`
`[/710
`
`STARTING A TIMER AFTER SENDING
`THE HANDOVER RELATED MESSAGE
`TO THE USER EQUIPMENT
`
`720
`
`IN THE EVENT TIMER EXPIRES BEFORE V 730
`RECEIVING AN EXPECTED RESPONSE
`FROM THE USER EQUIPMENT TO THE
`HANDOVER RELATED MESSAGE,
`THE BASE STATION INITIATING A
`COMMUNICATION TO THE USER
`EQUIPMENT ON A PAGE CHANNEL.
`WHERE THE COMMUNICATION INCLUDES
`INFORMATION CONTAINED IN THE
`HANDOVER RELATED MESSAGE
`
`FIG.7
`
`Samsung Ex. 1015
`
`

`

`US 2008/0051091 Al
`
`Feb.28,2008
`
`APPARATUS, METHOD AND COMPUTER
`PROGRAM PRODUCT PROVIDING
`ENHANCED ROBUSTNESS OF HANDOVER
`IN E-UTRAN WITH PAGING OF THE
`ACTIVE UE
`
`RNTI radio network temporary identity
`
`C-RNTI cell-specific RNTI
`
`SIB system information block
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`[0001] This patent application claims priority under 35
`U.S.C. § 119(e) from Provisional Patent Application No.
`60/840,283 filed Aug. 25, 2006, the disclosure of which is
`incorporated by reference herein in its entirety.
`
`TECHNICAL FIELD
`
`[0002] The exemplary and non-limiting embodiments of
`this invention relate generally to wireless communication
`systems, methods, devices and computer program products
`and, more specifically, relate to techniques for use during
`handover.
`
`BACKGROUND
`
`[0003] Following are some acronyms used in the descrip(cid:173)
`tion below:
`
`3GPP third generation partnership project
`
`UTRAN universal terrestrial radio access network
`
`EUTRAN evolved UTRAN
`
`OFDM orthogonal frequency division multiplex
`
`Node-B base station
`
`[0004]
`
`eNB EUTRAN Node B
`
`UE user equipment
`
`[0005]
`
`aGW access gateway
`
`HO handover
`
`RLL radio link layer
`
`RNL radio network layer
`
`PHY physical (layer 1 or L1)
`
`L2 layer 2 (e.g., the RLC/MAC layer)
`
`L3 layer 3 (e.g., the RRC layer)
`
`MME mobility management entity
`
`UPE user plane entity
`
`MAC medium access control
`
`RLC radio link control
`
`RRC radio resource control
`
`RRM radio resource management
`
`LTE long term evolution
`
`UL uplink (UE to Node-B)
`
`DL downlink (Node-B to UE)
`
`BSC base station controller
`
`GSM global system for mobile communications
`
`QOS quality of service
`
`[0006] A proposed communication system known as
`evolved UTRAN or E-UTRAN, and also referred to as
`UTRAN-LTE is presently under consideration within the
`3GPP.
`[0007] Of particular interest to the exemplary embodi(cid:173)
`ments of this invention is a case ofa basic HO scenario (intra
`E-UTRAN). Reference may be had to FIG. 2, derived from
`Section 9.1.5 of 3GPP TR 25.813, 3rd Generation Partner(cid:173)
`ship Project; Technical Specification Group Radio Access
`Network; Evolved Universal Terrestrial Radio Access
`(E-UTRA) and Evolved Universal Terrestrial Radio Access
`Network (E-UTRAN); Radio Interface Protocol Aspects
`(Release 7), V7.0.0 (2006-06).
`[0008] What follows is a description of the signal flow
`shown in FIG. 2 herein, as specified in 3GPP TR 25.813
`(Release 7) for the intra-MME/UPE HO procedure.
`[0009] Step 1: The UE is triggered to send a MEASURE(cid:173)
`MENT REPORT by the rules set by system information,
`specification etc.
`[0010] Step 2: The Source eNB makes a decision based on
`the MEASUREMENT REPORT and/or RRM information
`to hand off the UE. The Source eNB prepares the target eNB
`for handover and passes relevant information in the Han(cid:173)
`dover Request.
`[0011] Step 3: The Target eNB prepares the HO with
`Ll/L2 and responds to the source eNB by providing new
`C-RNTI and possibly other parameters such as access
`parameters, SIBs, etc. After reception of the accepted prepa(cid:173)
`ration of HO, the source eNB begins forwarding data
`packets to the target eNB.
`[0012] Step 4: The UE receives a HANDOVER COM(cid:173)
`MAND with necessary parameters such as the new C-RNTI,
`possible starting time, target eNB SIBs, etc. The UE may
`need to acknowledge reception of the HO COMMAND with
`a RLC acknowledgment procedure (e.g., in GSM there is no
`acknowledgment).
`[0013] Step 5: After expiry of the starting time in the HO
`COMMAND, the UE performs synchronization to the target
`eNB and then begins acquiring the UL timing advance.
`[0014] Step 6: The network responds with UL allocation
`and timing advance. These are used by the UE to send a
`HANDOVER CONFIRM to the target eNB, which com(cid:173)
`pletes the handover procedure for the UE. It is probable that
`network needs to acknowledge reception of the HO CON(cid:173)
`FIRM with a RLC acknowledgment procedure.
`[0015] Step 7a: The target eNB informs the success of the
`HO to the source eNB, which can then clear already for(cid:173)
`warded data from its buffers. The source eNB still continues
`forwarding UE data if it has data in its buffers, or if the UPE
`still forwards data to it.
`[0016] Step 7b: The UE location information is updated to
`the MME/UPE in order to enable the UPE to forward
`packets directly to the target eNB.
`[0017] As may be appreciated, a question arises as to the
`consequences of the UE not correctly receiving the "DL
`allocation" and "HO command" at Step 4, as this is essential
`
`Samsung Ex. 1015
`
`

`

`US 2008/0051091 Al
`
`Feb.28,2008
`
`2
`
`to the success/failure of the HO and, as a consequence, to
`providing the required or desired QoS.
`
`SUMMARY
`
`[0018]
`In an exemplary aspect of the invention there is a
`method that comprises starting a timer in a base station after
`sending a handover information message, and stopping the
`timer upon a condition, comprising either receiving an
`expected handover related message, or expiration of a maxi(cid:173)
`mum allowed time value of the timer.
`[0019]
`In another exemplary aspect of the invention there
`is a method that comprises starting a timer in a user
`equipment after an initiation of a handover procedure, and
`stopping the timer upon a condition, comprising either
`receiving an expected handover related message, or expira(cid:173)
`tion of a maximum allowed time value of the timer, where
`at an expiration of the maximum allowed time value the user
`equipment begins listening for a page to obtain handover
`related information.
`[0020]
`In yet another exemplary aspect of the invention,
`there is a computer readable medium encoded with a com(cid:173)
`puter program executable by a processor to perform actions
`that comprise starting a timer in a base station after sending
`a handover information message, and stopping the timer
`upon a condition, comprising either receiving an expected
`handover related message, or expiration of a maximum
`allowed time value of the timer.
`[0021]
`In yet another exemplary aspect of the invention,
`there is a computer readable medium encoded with a com(cid:173)
`puter program executable by a processor to perform actions
`that comprise starting a timer in a user equipment after an
`initiation of a handover procedure, and stopping the timer
`upon a condition, comprising either receiving an expected
`handover related message, or expiration of a maximum
`allowed time value of the timer, where at an expiration of the
`maximum allowed time value the user equipment begins
`listening for a page to obtain handover related information.
`[0022]
`In yet another exemplary aspect of the invention,
`there is an apparatus that comprises a handover control unit
`coupled to a transmitter configured to start a timer in a base
`station after sending a handover information message, and
`the handover control unit coupled to a receiver configured to
`stop the timer upon a condition, comprising either receiving
`an expected handover related message, or expiration of a
`maximum allowed time value of the timer.
`[0023]
`In another exemplary aspect of the invention, there
`is an apparatus that comprises a handover control unit
`configured to start a timer in a user equipment after an
`initiation of a handover procedure, and the handover control
`unit coupled to a wireless receiver configured to stop the
`timer upon a condition, comprising either receiving an
`expected handover related message, or expiration of a maxi(cid:173)
`mum allowed time value of the timer, where at an expiration
`of the maximum allowed time value the wireless receiver of
`the user equipment is further configured to begin listening
`for a page to obtain handover related information.
`[0024]
`In still another exemplary aspect of the invention
`there is an apparatus that comprises means for starting a
`timer in a base station after sending a handover information
`message, and means for stopping the timer upon a condition,
`comprising either receiving an expected handover related
`message, or expiration of a maximum allowed time value of
`the timer.
`
`[0025]
`In another exemplary aspect of the invention, there
`is an apparatus that comprises means for starting a timer in
`a user equipment after an initiation of a handover procedure,
`and means stopping the timer upon a condition, comprising
`either receiving an expected handover related message, or
`expiration of a maximum allowed time value of the timer,
`where at an expiration of the maximum allowed time value
`the user equipment begins listening for a page to obtain
`handover related information.
`[0026]
`In yet another exemplary aspect of the invention,
`there is a method that comprises sending a handover related
`message to a user equipment from a base station, starting a
`timer after sending the handover related message to the user
`equipment, and in the event the timer expires before receiv(cid:173)
`ing an expected response from the user equipment to the
`handover related message, the base station initiating a com(cid:173)
`munication to the user equipment on a page channel, where
`the communication includes information contained in the
`handover related message.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0027] The foregoing and other aspects of embodiments of
`this invention are made more evident in the following
`Detailed Description, when read in conjunction with the
`attached Drawing Figures, wherein:
`[0028] FIG. 1 shows a simplified block diagram of various
`electronic devices that are suitable for use in practicing the
`exemplary embodiments of this invention.
`[0029] FIG. 2 illustrates an Intra-MME/UPE HO, and is
`derived from FIG. 9.1.5 in 3GPP TR 25., 813 7.0.0, 2006-
`06).
`[0030] FIG. 3 illustrates an Intra-MME/UPE HO that is
`enhanced in accordance with the exemplary embodiments of
`this invention.
`[0031] FIG. 4A is a logic flow diagram that is illustrative
`of a method executed by an eNB in accordance with the
`exemplary embodiments of this invention.
`[0032] FIG. 4B is a logic flow diagram that is illustrative
`of a further method executed by an eNB in accordance with
`the exemplary embodiments of this invention.
`[0033] FIG. 5 is a logic flow diagram that is illustrative of
`a method executed by a UE in accordance with the exem(cid:173)
`plary embodiments of this invention.
`[0034] FIG. 6A is a logic flow diagram that is illustrative
`of a method executed by a base station in accordance with
`the exemplary embodiments of this invention.
`[0035] FIG. 6B is a logic flow diagram that is illustrative
`of a method executed by a user equipment in accordance
`with the exemplary embodiments of this invention.
`[0036] FIG. 7 is a logic flow diagram that is illustrative of
`a method executed by a base station in accordance with the
`exemplary embodiments of this invention.
`
`DETAILED DESCRIPTION
`
`[0037] The exemplary embodiments of this invention
`address the foregoing and other problems, and provide
`support for a seamless and lossless HO in E-UTRAN that
`enhances the robustness of the HO against at least the
`situation discussed above, that is, the failure of the UE to
`correctly receive the HANDOVER COMMAND in Step 4
`of FIG. 2.
`[0038] Reference is made first to FIG. 1 for illustrating a
`simplified block diagram of various electronic devices that
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`are suitable for use in practicing the exemplary embodi(cid:173)
`ments of this invention. In FIG. 1 a wireless network 1 is
`adapted for communication with a UE 10 via at least one
`Node B or base station 12 and also referred to herein as an
`eNode B 12 or eNB 12. The network 1 may include at least
`one Network Element 14 coupled to the eNode B 12 via a
`data link 13. The Network Element 14 may include the
`MME and UPE functionality, and in general may be referred
`to as the aGW 14. Herein the Network Element 14 may be
`referred to interchangeably as the MME/UPE 14 or as the
`aGW 14.
`[0039] The UE 10 includes a data processor (DP) l0A, a
`memory (MEM) 10B that stores a program (PROG) lOC,
`and a suitable radio frequency (RF) transceiver lOD for
`bidirectional wireless communications with the eNode B 12,
`which also includes a DP 12A, a MEM 12B that stores a
`PROG 12C, and a suitable RF transceiver 12D. The eNode
`B 12 is coupled via the data path 13 to the aGW 14
`(containing the MME/UPE functionality) that also includes
`at least one DP 14A and a MEM 14B storing an associated
`PROG 14C. At least one of the PROGs l0C, 12C and 14C
`is assumed to include program instructions that, when
`executed by the associated DP, enable the electronic device
`to operate in accordance with the exemplary embodiments
`of this invention, as will be discussed below in greater detail.
`[0040] Also shown in FIG. 1 is at least one second eNode
`B, referred to as 12'. During a HO event the eNode B 12 may
`be considered the Source eNode B, i.e., the eNode B to
`which the UE 10 is currently connected and communicating
`in the associated serving cell, and the eNode B 12' may be
`considered the Target eNode B, i.e., the eNode B to which
`the UE 10 is to be connected and communicating with in the
`target cell after the HO procedure is completed. Note that in
`practice the serving cell and the target cell may at least
`partially overlap one another.
`[0041] Each eNode B 12, 12' may be assumed to include
`a HO control function or unit 12E. Each eNode B 12, 12'
`may be further assumed to include a Timer unit 12F, referred
`to below as Timer_Tl, that operates in conjunction with the
`HO unit 12E. The UE 10 may be assumed to include a HO
`control function or unit lOE and an associated Timer l0F
`also referred to below as Timer_T2. The HO units l0E, 12E
`and Timer units l0F, 12F are constructed and operated in
`accordance with the exemplary embodiments of this inven(cid:173)
`tion, as described in greater detail below. Each eNode B 12,
`12' may also be assumed to include a RRC function 12G, the
`operation of which in certain exemplary embodiments of
`this invention is discussed below. A corresponding RRC
`function l0G is shown in the UE 10.
`It should be noted that while the HO and timer units
`[0042]
`l0E, 12E, l0F, 12F are shown as separate elements in FIG.
`1, in practice they may form a part of the respective RRC
`functions l0G, 12G, as the RRC typically embodies the
`primary radio interface control protocol.
`[0043]
`In general, the various embodiments of the UE 10
`can include, but are not limited to, cellular telephones,
`personal digital assistants (PDAs) having wireless commu(cid:173)
`nication capabilities, portable computers having wireless
`communication capabilities, image capture devices such as
`digital cameras having wireless communication capabilities,
`gaming devices having wireless communication capabili(cid:173)
`ties, music storage and playback appliances having wireless
`communication capabilities, Internet appliances permitting
`
`wireless Internet access and browsing, as well as portable
`units or terminals that incorporate combinations of such
`functions.
`[0044] The exemplary embodiments of this invention may
`be implemented by computer software executable by the DP
`l0A of the UE 10, the DP 12A of the eNode Bs 12 and 12',
`the DP 14A of the aGW 14, or by hardware, or by a
`combination of software and hardware.
`[0045] The MEMs 10B, 12B and 14B may be of any type
`suitable to the local technical environment and may be
`implemented using any suitable data storage technology,
`such as semiconductor-based memory devices, magnetic
`memory devices and systems, optical memory devices and
`systems, fixed memory and removable memory. The DPs
`l0A, 12A and 14A may be of any type suitable to the local
`technical environment, and may include one or more of
`general purpose computers, special purpose computers,
`microprocessors, digital signal processors (DSPs) and pro(cid:173)
`cessors based on a multi-core processor architecture, as
`non-limiting examples.
`[0046] Describing now the exemplary embodiments of
`this invention in even further detail, and referring to FIG. 3,
`the HO related Timer_Tl 12F is provided at the eNBs 12, 12'
`and the Timer_T2 l0E is provided at the UE 10. Timer_Tl
`12F is defined as a HO guard timer of the eNB 12, 12', and
`in the example shown in FIG. 3 Timer_Tl is used by the
`target eNB 12', and is started at the time that the target eNB
`12' sends the Context Confirm message to the source eNB 12
`as in Step 3. Timer_Tl 12F is used to check that a signal is
`received from the UE 10 by Step 5 or 6 at the latest. Thus,
`the condition to stop Timer_Tl 12F is after successful
`completion of Step 5 or 6. In another embodiment, Timer_
`Tl 12F is used by the source eNB 12, is started after Step
`4, and is stopped when reaching Step 7a. Timer_T2 l0F is
`defined as a HO guard timer of the UE 10, and may be
`started when the UE 10 sends the Measurement Report to the
`source eNB such as at Step 1, i.e., when the UE 10 expects
`to receive HO Command from the source eNB 12 as in Step
`4. Thus, a suitable condition to stop Timer_T2 l0F is at the
`successful completion of Step 4. Both Timer_Tl and Timer_
`T2 may be considered as cell-specific network system
`parameters, and the maximum duration of Timer_Tl and
`Timer_T2 is preferably less than the allowed or expected
`HO execution time. The value for Timer_T2 may be sent to,
`and subsequently updated in, the UE 10 in, for example,
`cell-specific broadcast system information.
`[0047] As can be appreciated, if either Timer_Tl and
`Timer_T2 times out, i.e., reaches the maximum allowed time
`value measured in, for example, milliseconds or seconds,
`then it can be assumed that an error has occurred during the
`HO signaling message flow, and corrective action can be
`taken.
`[0048] For example, in the event that Timer_Tl 12F
`expires and the eNB 12 does not receive an expected
`message, and for the case where Timer_Tl 12F is applied in
`the target eNB 12' as shown in FIG. 3, the target eNB 12'
`may notify the source eNB 12 of the time-out of Timer_l
`and may provide any related information updates as shown
`in FIG. 3, for convenience, as message 4a. In response to
`this notification, the source eNB 12B may begin paging the
`ACTIVE state UE 10 in the current cell as shown in FIG. 3,
`for convenience, as message 4b. The paging can occur by
`whatever suitable technique is selected for use in E-UT(cid:173)
`RAN. In this case the content of a Paging Cause and a
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`Paging Record sent to the UE 10 may repeat all of the
`content of HO Command, including the new C-RNTI with
`the most recent valid updates. The target eNB 12' may also
`page the ACTIVE state UE 10 in the target cell and, in this
`case, the content of the paging message can be similar to that
`sent by the source eNB 12 to facilitate the HO as shown in
`FIG. 3, for convenience, as an optional message 4c.
`[0049] Further by example, and in the event that Timer_Tl
`12F expires and the eNB 12 does not receive an expected
`message, and for the case where Timer_Tl is used in the
`source eNB 12, the source eNB 12 begins paging the
`ACTIVE state UE in the current cell as in message 4b in
`FIG. 3. As before, the content of a Paging Cause and a
`Paging Record sent to the UE 10 may repeat all of the
`content of HO Command, including the new C-RNTI with
`the most recent valid updates.
`[0050]
`In the event that Timer_T2 l0F expires, and the UE
`10 does not receive the expected message(s) from the
`network, such as from the source eNB 12 in the current cell,
`the UE 10 begins listening to the paging channel of the
`current cell and, if possible, to the paging channel( s) of those
`neighboring cell(s) that the UE was able to measure and
`report at Step 1 in FIG. 3. In this case the UE 10 is enabled
`to receive the HO command and associated information
`from one of the received Pages and is enabled to respond to
`the received Page, and associated HO-related information,
`either from the source or target eNB 12, 12' and continue
`from Step 5 of FIG. 3. That is, the UE 10 is provided the
`expected HO Command and associated information through
`an alternate signaling mechanism (i.e., through a Paging
`channel).
`[0051]
`It can be noted that in current LTE E-UTRAN
`system concepts the paging of an IDLE state UE 10 is
`originated from the aGW 14, and the PAGING message is
`formed and sent by the RRC unit 12G of the eNB 12.
`However, in accordance with the exemplary embodiments of
`this invention the eNB RRC unit 12G is permitted to initiate
`paging of an ACTIVE state UE 10 for control purposes. The
`source eNB 12 may use the currently valid, also referred to
`as the old C-RNTI as the UE ID for paging. In the case
`where the target eNB 12' is also allowed to page the UE 10,
`as shown in message 4c of FIG. 3, the RRC function 12G of
`the target eNB 12' may use the old C-RNTI, or some other
`ID, of the UE 10, which is known from the context data
`received from the source eNB 12 in Step 2.
`[0052] However, if the radio connection is actually lost,
`and the RRC is not allowed to initiate paging of the ACTIVE
`state UE 10, it is within the scope of the exemplary embodi(cid:173)
`ments of this invention for the source or target eNB 12, 12'
`to notify the aGW 14 upon the expiry of Timer_Tl so that
`urgent paging can be initiated from the aGW 14, and
`Timer_T2 may be generalized and extended so as to force
`the UE 10 back to the IDLE state, as from the ACTIVE state,
`to listen for possible urgent paging initiated by the aGW 14.
`[0053]
`It can be noted that in this case the eNB 12 may
`send the HO command and related information to the aGW
`14 to be included in the IDLE state page, or the eNB 12 RRC
`functionality 12G may know that the IDLE state page
`initiated by the aGW 14 should include this information. In
`either case it is most desirable that the aGW 14 request only
`a subset of the eNBs located in a paging area to page the UE
`10, such as only the source eNB 12 and the target eNB 12'.
`As such, the paging notification sent from the aGW 14
`
`least the identifications of the
`preferably includes at
`involved source and target eNBs 12, 12'.
`[0054] Optional messages 4d and 4e in FIG. 3 show this
`process for an example where the target eNB 12' sends a
`Notify message to the aGW 14, and the aGW 14 sends an
`IDLE state Page Notification to both the source eNB 12 and
`the target eNB 12'. As was noted, the HO command and
`related information could be sent as part of the Notification
`message 4d. In this case it is assumed that the expiration of
`Timer_T2 l0F has triggered the UE 10 to enter the IDLE
`state so as to receive the IDLE state page from one of the
`eNBs 12, 12' so as to perform the HO recovery process.
`[0055] For the case where the UE 10 transitions back to
`the IDLE state to receive the page, it is not implied that the
`current call is dropped. For example, a temporary state
`transition to IDLE may be performed for call recovery
`purposes so as to receive the necessary HO information.
`During this period the ACTIVE context of the UE 10 may
`remain in effect, at least for some predetermined maximum
`amount of time such as one set by an associated RRC lOG
`timer.
`[0056] Note further in this regard that the UE 10 needs to
`contact the target eNB 12' to establish the radio connection
`and become RRC_ACTIVE, and during this time the target
`eNB 12 may communicate with the MME/UPE 14 to resume
`the LTE_ACTIVE state.
`[0057]
`It can be further noted that in certain previous
`systems a central node, such as the RNC in UTRAN and a
`BSC in GSM, was