as) United States
`a2) Patent Application Publication co) Pub. No.: US 2007/0149206 Al
`(43) Pub. Date: Jun. 28, 2007
`
`Wanget al.
`
`US 20070149206A1
`
`(54)
`
`(75)
`
`METHOD AND SYSTEM FOR ADJUSTING
`UPLINK TRANSMISSION TIMING FOR
`LONG TERM EVOLUTION HANDOVER
`
`Inventors: Jin Wang, Central Islip, NY (US);
`Stephen E. Terry, Northport, NY (US)
`
`Correspondence Address:
`VOLPE AND KOENIG,P.C.
`DEPT. ICC
`UNITED PLAZA, SUITE 1600
`30 SOUTH 17TH STREET
`
`PHILADELPHIA, PA 19103 (US)
`
`(73)
`
`Assignee:
`
`TECHNOLOGY
`INTERDIGITAL
`CORPORATION, Wilmington, DE
`(US)
`
`(21)
`
`Appl. No.:
`
`11/612,837
`
`(22)
`
`Filed:
`
`Dec. 19, 2006
`
`Related U.S. Application Data
`
`(60)
`
`Provisional application No. 60/753,124,filed on Dec.
`22, 2005. Provisional application No. 60/839,267,
`filed on Aug. 21, 2006.
`
`Publication Classification
`
`(51)
`
`Int. CL
`(2006.01)
`H04Q 7/20
`(52) U.S. Ch.
`ceecccccssssssscsssseestesesenseeeee 455/450; 455/502
`
`(57)
`
`ABSTRACT
`
`A method and system for adjusting uplink transmission
`timing when sending an initial
`transmission to a target
`cell/Node-B of an evolved universal terrestrial radio access
`network (E-UTRAN) immediately after handover from a
`source cell/Node-B of the E-UTRAN.In one embodiment,
`a user equipment (UE) autonomously computes and applies
`a timing advance (TA) value based on the current source
`cell/Node-B timing value, cell/Node-B beacon channelref-
`erence signal measurements and knowledge ofthe relative
`time difference, (if any), between the source and target
`cells/Node-Bs.
`In another embodiment,
`the UE sends a
`scheduling request message or real data packets with the
`computed TA value applied to the uplink transmission
`timing to the E-UTRANvia pre-allocated non-contention
`based uplink radio resources. In an alternate embodiment,
`the UE sends a scheduling request message with the new
`computed TA value applied to the UL transmission timing to
`an E-UTRANvia a synchronous random access channel
`(RACH).
`
`
`
`
`COMMAND
`HANDOVER
`MESSAGE
`
`225
`
`|
`
`|
`|
`
`I
`i
`
`USER
`
`
`
`EQUIPMENT
`
`__N
`(UE)
`
`INTIAL
`205
`
`
`Leteacinnnanaaed TRANSMISSION TON J
`
`
`
`TARGET CELL/NODE-B
`Ng
`UE ADJUSTS TIMING
`ADVANCE
`|
`;
`(TA)
`=
`{USING PRE-
`7
`ADVANCE
`(TA) VALUE TO
`ACCESS TRANSMISSION
`ALLOCATED UPLINK [|
`)
`TO TARGET CELUNODE-g
` RADIORESOURCES
`|
`BASED ON REFERENCE
`OR USING
`TARGET
`SIGNALS OF SOURCE
`SYNCHRONOUS
`=|
`
`
`
`CELUNODE-B AND RANDOM ACCESS—| CELUNODE-B |
`TARGET CELLNODE-B
`CHANNEL (RACH)
`220
`i
`BEACON CHANNELS
`ac i
`
`i
`'
`j
`i
`
`
`SOURCE
`CELLNODE-B
`
`215
`|
`EVOLVED UNIVERSAL
`|
`TERRESTRIAL RADIO
`ACCESS NETWORK
`(E-UTRAN)
`210
`|
`
`
`|
`i
`
`
`
`APPLE 1024
`APPLE 1024
`
`

`

`Patent Application Publication Jun. 28,2007 Sheet 1 of 3
`
`US 2007/0149206 Al
`
`
`
`
`
`
`USER
`EQUIPMENT
`(UE)
`
`i i i i i i i
`
`|
`
`| i i i i i i i i
`
`
`
` SOURCE
`CELL/NODE-8
`246
`
`EVOLVED UNIVERSAL
`TERRESTRIAL RADIO
`ACCESS NETWORK
`(E-UTRAN)
`210
`
`BEACON CHANNELS
`
`TARGET
`CELL/NODE-B
`220
`
`
`
`COMMAND
`HANDOVER
`MESSAGE <<
`oN 995
`
`
`
`
`
`
`
`
`USER
`
`
`EQUIPMENT
`(UE)
`\.
`INTIAL
`205
`
`
`TRANSMISSION TO™
`
`UE ADJUSTS TIMING
`TARGET CELL/NODE-B
`ADVANCE (TA} VALUE TO
`(USING PRE-
`ACCESS TRANSMISSION
`ALLOCATED UPLINK
`TO TARGET CELUNODE-8
`RADIO RESOURCES
`BASED ON REFERENCE
`OR USING
`SIGNALS OF SOURCE
`SYNCHRONOUS
`CELL/NODE-B AND
`FANDOM ACCESS
`TARGET CELL/NODE-B
`CHANNEL (RACH)
`
`

`

`Patent Application Publication Jun. 28,2007 Sheet 2 of 3
`
`US 2007/0149206 Al
`
`
`
`
`
`ENABLE AND PERFORM TIMING ADVANCE FOR A USER
`2
`EQUIPMENT (UE} IN A SOURCE GELL/NODE-B OF ANEVOLVED
`=77 S08
`
`UNIVERSAL TERRESTRIAL RADIO ACCESS NETWORK (E-LITRAN).
`|
`THE E-UTRAN MEASURES AND CALCULATES THE TIMING ADVANCE
`
`VALUE AND SIGNALS THE TIMING ADVANCE VALUE TOTHE UE.
`
`
`
`
`
`THE UE APPLIES THE TIMING ADVANCE VALUE OF STEP 310 WHEN _
`TRANSMITTING TO THE SOURCE CELL/NODE-B.
`
`-
`
`ale
`
`~ 310
`
`7
`
`_*
`PERFORM OG _
`en HANDOVER?ae
`
`320
`
`
`
`THE SOURCE CELL/NODE-B SENDS A HANDOVER COMMAND
`
`
`MESSAGE (OPTICNALLY INCLUDING PRE-ALLOCATED UPLINK RADIO |
`RESOURCE OR SYNCHRONOUS RANDOM ACCESS CHANNEL (RACH) |__. 395
`
`
`INFORMATION) TO THE UE TO INITIATE HANDOVER.
`
`CELL/NODE-B BASED ON BEACON CHANNEL Ri
`
`THE UE PERFORMS ONE OR MORE MEASUREMENTS TO DETERMINE THE
`DIFFERENCE IN PROPAGATION DELAYS BETWEEN THE SQURCE CELL/NODE-B AND p—™ 330
`A TARGET
`
`
`
`
`
`THE UE AUTONOMOUSLY COMPUTES A NEW TIMING ADVANCE VALUE BASED ON |
`305
`THE CURRENT SOURCE CELL/NODE-B TIMING VALUE, THE MEASUREMENTS=7
`
`
`PERFORMEDIN STEP 330 AND KNOWLEDGE OF THE RELATIVE TIME DIFFERENCE |
`
`
`(F ANY} BETWEEN THE SQURCE CELL/NODE-B AND THE TARGET CELL/NODE-B.
`|
`
`
`
`340
`
`THE UE APPLIES THE NEWTIMING ADVANCE VALUE TO ADJUST THE UPLINK |
`TRANSMISSION TIMING WHEN SENDING AN INITIAL TRANSMISSION TO THE b-
`TARGET CELL/NODE-B EITHER THROUGH THE USE OF PRE-ALLOCATED
`|
`UPLINK NON-CONTENTION BASED RADIO RESOURCES OR A SYNCHRONOUS |
`
`
`RACH, AS INDICATED BY THE HANDOVER COMMAND MESSAGE.
`
`
`
`
`
`

`

`Patent Application Publication Jun. 28,2007 Sheet 3 of 3
`
`US 2007/0149206 Al
`
`A USER EQUIPMENT (UE} AUTONOMOUSLY COMPUTES A TIMING
`RONEAE VALUE.
`
`THE UE SENDS A SCHEDULING REQUEST MESSAGE THROUGH A
`SYNCHRONOUS RANDOM ACCESS CHANNEL (RACH) TO AN
`EVOLVED UNIVERSAL TERRESTRIAL RADIO ACCESS NETWORK (E-
`UTRAN) WITH THE COMPUTED TIMING ADVANCE VALUE APPLIED.
`
`THE E-UTRAN COMPUTES A REFINED (LE.,MORE ACCURATE)
`TIMING ADVANGEVALUE BASED ON INFORMATION IN THE
`SCHEDULING REQUEST MESSAGE,
`
`_—~ 405
`
`——~ AQ
`
`~ 41S
`
`109
`
`)
`
`:
`
`|
`
`|
`
`DOWNLINK RADIO RESOURCES.
`
`iF NECESSARY, THE E-UTRAN SENDS THE REFINEDTIMING
`
`ADVANCE VALUE TO THE UE IN A DOWNLINK SIGNALING MESSAGE
`AND ASSIGNS UPLINK AND/OR DOWNLINK RADIO RESOURCES
`FOR USE BY THE UE FOR SUBSEQUENT DATA TRANSMISSIONS.
`
`|
`THE UE INITIATES DATA TRANSMISSION USING THE REFINED
`TIMING ADVANCE VALUE AND THE ASSIGNED UPLINK AND/OR=b-—~ 425
`
`

`

`US 2007/0149206 Al
`
`Jun. 28, 2007
`
`METHOD AND SYSTEM FOR ADJUSTING
`UPLINK TRANSMISSION TIMING FOR LONG
`TERM EVOLUTION HANDOVER
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`[0001] This application claims the benefit of U.S. Provi-
`sional Application No. 60/753,124 filed Dec. 22, 2005 and
`US. Provisional Application No. 60/839,267 filed Aug. 21,
`2006, which are incorporated by reference as if fully set
`forth.
`
`FIELD OF INVENTION
`
`[0002] The present invention relates to wireless commu-
`nication systems. Moreparticularly, the present invention is
`related to a timing adjustment procedure for synchronizing
`data transmissions between a wireless transmit/receive unit
`
`(WTRU), (1.e., a user equipment (UE)), and a target cell/
`evolved Node-B (eNB) immediately after handover from a
`source cell/eNB to the target cell/eNB in a long term
`evolution (LTE) system.
`
`BACKGROUND
`
`[0003] The objective of evolved universalterrestrial radio
`access (E-UTRA) and evolved universal terrestrial radio
`access network (E-UTRAN) is to develop a radio access
`network (RAN) for providing a high-data-rate, low-latency
`and packet-optimized improved system capacity and cover-
`age. FIG. 1 shows a wireless communication system 100
`which includes at least one cell/Node-B 105 that commu-
`nicates with at least one UE 110. In order to achieve this
`
`objective, an evolution of the radio interface as well as the
`radio network architecture is being considered, such as a
`long term evolution (LTE) system. However, there are no
`existing dedicated channels in an LTE system,soall services
`are provided over shared and common channels. Further-
`more, system frame number-system frame number (SFN-
`SFN) measurements maynot be available in the LTE system.
`This causes problems with synchronized communications
`between the UE 110 and the cell/Node-B 105 during han-
`dover in the LTE system.
`
`[0004] A timing advance (TA) enables the UE 110 to send
`its uplink (UL) bursts earlier than what the UE 110 perceives
`at the start of an UL timeslot for transmission, so that the UL
`bursts are received at the cell/Node-B 105 within a time
`window that allows accurate detection and minimizes, or
`eliminates, signal degradation. Single channel frequency
`division multiple access (SC-FDMA)is a new radio access
`technologythat has a stringent performance requirement for
`ULsynchronization. Thus, an appropriate and accurate TA is
`critical in LTE UL transmission.
`
`[0005] Handoverrequires that TA be adjusted for the LYE
`110 in the case where the UE 110 maintains shared channel
`connectivity or use of the synchronous PRACH ina target
`cell/Node-B with minimum delay whichis especially impor-
`tant for time sensitive services such as voice over IP (VoIP)
`and interactive gaming, etc. The LTE system should avoid
`requiring an asynchronous random access channel (RACH)
`access burst to establish the TA during handover since this
`procedure increases the delay in establishing a connection in
`the target cell and is not an efficient use of physical resources
`relative to use of an UL shared channel. In the Third
`
`Generation Partnership Project (3GPP), TA during handover
`is achieved through measuring SFN-SFN timing difference
`between old and new radiolinks associated with old and new
`Node-Bs. However, in an LTE system, there is no new radio
`link set in parallel to the old radio link during handover, and
`an SFN-SFN for timing difference measurement may not
`exist. Thus, acquiring TA with less delay is desired during
`handover in an LTE system.
`
`in SC-FDMA systems to
`[0006] TA is very important
`achieve the acceptable performance requirement. This
`becomesa problem during handover, as the UE 110 has to
`achieve fast synchronized communications with the cell/
`Node-B 105 after a network commanded handoveris imple-
`mented, and the UE 110 has to achieve fast cell selection to
`maintain a satisfactory quality of service (QoS). Unsynchro-
`nized transmissions cause high UL interference and thus
`degrade the system performance. Thus, a fast timing adjust-
`ment mechanism for synchronizing transmission immedi-
`ately after handover would be advantageous for LTE.
`
`[0007] Because there is no dedicated channel established
`in an LTE system, only shared channels are to be used,
`which makesit difficult to maintain a tight synchronization.
`Thus, the handover of the UE 110 to a new cell/Node-B has
`to be performed using other channels such as an asynchro-
`nous primary RACH (PRACH)to acquire the TA between
`both cells/Node-Bs. By using the asynchronous PRACH for
`timing adjustment after handover, the UE 110 has to go
`through a contention based access procedure in order that
`the cell/Node-B 105 can successfully detect the PRACH
`sequence and then signal to the UE 110 the proper TA. This
`results in an unnecessary delay in establishing shared chan-
`nel connectivity in the target cell/Node-B. Thus, a respon-
`sive timing adjustment mechanism during handover would
`be advantageous for LTE to avoid the need for asynchronous
`RACHaccess procedure that incurs delay, (i.e., a handover
`“blackout period” is avoided).
`
`It would therefore be advantageous if a procedure
`[0008]
`existed relating to the timing adjustment for synchronized
`communications between the UE 110 and the cell/Node-B
`
`105 during a handover process that does not possess the
`limitations of conventional systems.
`
`SUMMARY
`
`[0009] The present invention is related to a method and
`system for adjusting UL transmission timing when sending
`an initial transmission to a target cell/Node-B of an E-UT-
`RAN immediately after handover from a source cell/Node-B
`of the E-UTRAN.In accordance with one embodiment of
`the present invention, the UE autonomously computes and
`applies a TA value based on beacon channel reference
`signals which are received from the source and target
`cells/Node-Bs and knowledgeoftherelative time difference,
`(if any), between the source and target cells/Node-Bs. In
`another embodiment, the UE sends a scheduling request
`message or real data packets with the computed TA value
`applied to the UL transmission timing to an E-UTRANvia
`pre-allocated non-contention based UL radio resources
`which are negotiated and reserved from the target cell/
`Node-B to the source cell/Node-B in advance of handover.
`
`In an alternative embodiment, the UE sends a scheduling
`request message with the new computed TA value applied to
`the UL transmission timing to an E-UTRANvia a synchro-
`
`

`

`US 2007/0149206 Al
`
`Jun. 28, 2007
`
`nous RACH. Then, the E-UTRAN computesarefined,(1.e., both the source andtarget cells are supported by a common
`
`more accurate), TA value in response to the scheduling
`Node-B it is more likely that these cells may be synchro-
`nized with each other.
`request message and, if necessary, the E-UTRANsignals the
`refined TA value to the UE, and assigns UL and/or downlink
`(DL)radio resources to be usedin thetarget cell/Node-B for
`the UE. If the refined TA value is signaled, the UE initiates
`data transmission using the refined TA value and the
`assigned radio resources after the EUTRANsignaling in the
`target cell is processed.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0010] A more detailed understanding of the invention
`may be had from the following description of a preferred
`embodiment, given by way of example and to be understood
`in conjunction with the accompanying drawings wherein:
`
`FIG. 1 showsa conventional wireless communica-
`[0011]
`tion system which includes at least one Node-B that com-
`municates with at least one UE;
`
`[0012] FIG. 2 shows a wireless communication system
`including a UE and a E-UTRAN with source and target
`cells/Node-Bs in accordance with the present invention;
`
`[0013] FIG. 3 is a flow diagram of an autonomous timing
`advance LTE handover procedure implemented in the sys-
`tem of FIG. 2 by accessing a target cell/Node-B using
`pre-allocated radio resources
`in accordance with one
`embodiment of the present invention; and
`
`[0014] FIG. 4 is a flow diagram of an autonomous timing
`advance LTE handover procedure implemented in the sys-
`tem of FIG. 2 in which the target cell/Node-B is accessed
`using synchronous RACHaccess in accordance with another
`embodiment of the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`[0015] When referred to hereafter, the terminology “user
`equipment (UE)” includes but is not limited to a wireless
`transmit/receive unit (WTRU), a mobile station, a fixed or
`mobile subscriber unit, a pager, a cellular telephone, a
`personal digital assistant (PDA), a computer, or any other
`type of user device capable of operating in a wireless
`environment.
`
`[0016] When referred to hereafter, the terminology “cell/
`Node-B” includes but
`is not
`limited to a cell and/or a
`Node-B, an LTE eNB, a cell and/or a base station, a site
`controller, an access point
`(AP), or any other type of
`interfacing device capable of operating in a wireless envi-
`ronment.
`
`It should be understood by one ofskill in the art
`[0017]
`that there are different types of handover, such as an intra-
`Node-B handover and an inter-Node-B handover. In the
`
`intra-Node-B handovercase, because the handover happens
`between two cells within one Node-B, a handover occurs
`from a source cell to a target cell, but the handoveris within
`a common Node-B and does not occur from a source
`
`Node-B to a target Node-B. In the inter-Node B handover
`case, a handover occurs from onecell, (i.e., a source cell),
`belonging to a source Node-B, to another cell, (i.e., a target
`cell), belonging to a target Node-B. In this case, the terms
`“cell” and “Node-B”are interchangeable. A handover from
`a source cell to a target cell may apply to both cases. When
`
`[0018] An application specific integrated circuit (ASIC)
`may be utilized to implement the present invention. The
`present invention is applicable to a radio resource manage-
`ment (RRM)and a radio resource controller for a WTRU,
`base station, network or system, at the physicallayer, (digital
`baseband), or network layer, as softwareor as a digital signal
`processor (DSP). The present invention is applicable to the
`following air interfaces: wideband code division multiple
`access
`(WCDMA),
`frequency division duplex (FDD),
`CDMA2000 ((Ix Evolution-Data Only (IXEV-DO), Ix Evo-
`lution data and voice (IxEV-DV), CDMA, enhanced UL,
`high speed downlink packet access (HSDPA), and LTE
`based systems.
`
`[0019] The present invention is related to an LTE_Active
`state,
`for both intra/inter-Node-B handover cases. The
`present
`invention provides a method and procedure by
`which a UE can autonomously measure and calculate a TA
`value so that the synchronous transmission can be immedi-
`ately applied in the target cell following handover. Thus,
`application of the asynchronous PRACH procedure in the
`target cell to update the TA value can be avoided.
`
`[0020] During a non-handover situation, a TA value is
`determined by the E-UTRAN from the ULtransmissions,
`and a TA adjustment value is signaled to the UE when
`necessary. When handover from a source, (i.e., current),
`cell/Node-Bto a target, (i.e., new), cell/Node-B occurs, the
`UE can autonomously determine the TA value for starting
`transmissions in the target cell/Node-B, using either pre-
`allocated UL non-contention based radio resources or a
`synchronous RACH for access to the target cell/Node-B.
`Otherwise,if the TA is not adjusted for the target cell, no TA
`value is applied in the target cell/Node-B and the asynchro-
`nous PRACHprocedure must be usedforthe first transmis-
`sion in the target cell.
`
`If absolute TA signaling is applied, the EEUTRAN
`[0021]
`must always know the applied TA value in the UE. When a
`new calculated TA is autonomously determined by the UE,
`the UE mustreport the TA after the autonomous adjustment.
`It is also possible for the E-UTRANto request the applied
`TA in a measurement report. Once handoveris complete, the
`nominal TA procedure applies again.If relative TA signaling
`is applied, it is not necessary to signal the new calculated TA
`to the E-UTRANfollowing autonomous TA adjustments by
`the UE.
`
`In accordance with the present invention, a han-
`[0022]
`dover refers specifically to a hard handover between syn-
`chronous cells/Node-Bs or between cells/Node-Bs where
`
`the relative time difference is known. The present invention
`provides a UE autonomous TA measurementand calculation
`method, as well as a procedure for LTE handoverto achieve
`synchronous communication with reduced delay and less
`interference. The knowledgeof the relative time difference
`(if any) between the source and target cells/Node-B should
`be signaled to the UE in order to compute a new TA value.
`In a preferred embodimentthe relative time difference or
`indication that the cells are synchronized with each other is
`signaled in the handover command.
`[0023] Depending on which TA information element (IE)
`in a radio resource control (RRC) command is enabled,
`
`

`

`US 2007/0149206 Al
`
`Jun. 28, 2007
`
`either the pre-allocated UL non-contention based radio
`resource from a target cell/Node-B, or the synchronous
`RACH,will be used during the handoverprocess to access
`the target cell/Node-B. Optionally,
`the E-UTRAN deter-
`mines which one of the two access functions will be used.
`The UEcalculates the timing difference from the source and
`target cells/Node-Bs by measuring reference signals on
`beacon channels received from different cells/Node-Bs. The
`UE then autonomously determines the TA to apply in UL
`transmission to a new target cell/Node-B upon handoverto
`avoid the asynchronous PRACH procedure requirement.
`The UE can use an assigned UL channel with TA applied for
`direct transmission for a resource request, or it can use a
`synchronous RACH for a resource request and then start
`data transmission after radio resource allocation from the
`target cell/Node-B is completed. When the E-UTRAN
`directs the UE to handoverto a new target cell/Node-B, the
`E-UTRANwill direct the UE to apply the computed TA in
`the new cell/Node-B. Atall other times, it is the E-UTRAN
`that determines the TA value. This avoids the need for
`requiring an asynchronous RACH access procedure to a
`target cell/Node-B, or a source cell/Node-B SFN-SFN
`reporting associated with the E-UTRAN handover com-
`mand.
`
`[0024] FIG. 2 shows a wireless communication system
`200 including a UE 205 and an E-UTRAN 210 in accor-
`dance with the present
`invention. The E-UTRAN 210
`includes a source cell/Node-B 215 anda target cell/Node-B
`220.
`
`[0025] UE Autonomous TA Measurement During LTE
`Handover
`
`If the UE 205 performs autonomous TA during
`[0026]
`handover, it must determine the value of its one-way propa-
`gation delay. Let L denote the radio frame length, t, denote
`the clock time at the cell/Node-B i, p, denote the one-way
`propagation delay from the cell/Node-B 1 to the UE 205, and
`( )L denote the module operation by L. Since, through cell
`search, the UE 205 only knowsthe sum of(t;)L and p, for a
`cell/Node-B i that the UE 205 is not connected to, the UE
`205 has to know either (t,)L or p, to solve the other.
`
`Suppose the distance between the UE 205 and the
`[0027]
`cell/Node-B 1 is D,. The coarse DL timing that the UE 205
`detects, (in the first cell search step), for the cell/Node-B 1,
`is (t,)L+P;+tp,;, where Tp; is the multipath that generates a
`peak for timing detection. The propagation delay p,=D,/c is
`therefore not affected by the frequency. The tp; part
`depends on both frequency and environment. After refined
`timing detection, (the secondor third step of cell search), at
`least part of multipath delay can be resolved.
`
`[0028] Lett, denote the residual multipath delay which
`is shorter than t,,. Then,
`the fine DL timing becomes
`(t)L+p;+tp,. If tp, is very small, it can be arguedthatfine
`DL timing=(t,)L+p,, which is independent of frequency. It
`can temporarily be assumed that tp, is very small in the
`following analysis.
`
`Inorder for the UE 205 to align its UL transmission
`[0029]
`with other UEs at the cell/Node-B i, the UE 205 needs to
`perform TA by the amount of 2p,. In this way,
`the UL
`transmitted signals of the UE 205 are receivedat the time of
`RTQ), which is given by:
`RTO=Qitp-2ptpitun,
`
`Equation (1)
`
`where T;, 1s the maximum multipath delay in the UL and
`depends on frequency as well.
`
`[0030] Acyclic period (CP) is used in an OFDMAsystem
`to avoid inter-timeslot interference. Thus, it functions as a
`guard period. The use of a CP, (that covers the length of
`Ty), ensures that the UL receives signals from UEs which
`are aligned in time and keepsthe orthogonality among them.
`
`[0031] According to the preferred embodiment, there are
`two options to realize a TA calculation at the UE 205.
`
`In one option, if the source andtarget cells/Node-
`[0032]
`Bs 215 and 220 in the E-UTRAN210 are not synchronized,
`(so far it is the assumption in LTE), the source cell/Node-B
`i signals the UE 205 the clock difference module by frame
`length, (.e., (t;-t;);,), between the source cell/Node-B i and
`the target cell/Node-B j when the cell/Node-B i signals the
`UE to handover to the target cell/Node-B j. By knowing
`(t),; p; 18 solved. If the cells/Node-Bs 215 and 220 are
`synchronized, then (t;);=(t;),. The TA is solved as well.
`[0033]
`In another option,
`the UE 205 measures signal
`strength of the reference signals (pilots), synchronization
`channels (SCH)or other DL channels. Based on the mea-
`surement, the UE 205 determinesits distance from the target
`cell/Node-B 220 in the E-UTRAN 210 and computes the
`propagation delay. However, usually it is known that dis-
`tance can not be accurately and reliably derived from signal
`strength or path loss measurement. Signal strength fluctuates
`with fading, which can be mitigated, (however, not elimi-
`nated), by collecting measurements over a long time inter-
`val.
`
`In order to calculate the TA adjustment, the UE
`[0034]
`must be signaled either the relative time difference between
`the source andtarget cells/node-Bs, or must be informed that
`the cells are synchronized.
`
`[0035] UE Autonomous TA Procedure in LTE Handover
`
`[0036] A UE autonomous TA procedure is initiated upon
`reception of a handover command from the E-UTRAN 210,
`or fast cell selection coordinated between the UE 205 and
`the source and target cells/Node-Bs 215 and 220. The UE
`205 detects the time difference in reception of the reference
`signal from beacon channels of the source and target cells/
`Node-Bs 215 and 220. The timeoffset is added to the last TA
`
`value in the source cell/Node-B 215 upon handover to the
`target cell/Node-B 220.
`
`[0037] Referring to FIG. 2, the UE 205 uses a reference
`signal from a beacon channelof the source cell/Node-B 215
`and a reference signal of a beacon channel of the target
`cell/Node-B 220to infer the difference in range between the
`UE 205 and the source and target cells/Node-Bs 215 and
`220. The reference signals may be any type of signal with
`reference characteristics. The UE 205is then able to autono-
`
`mously determine the amount of TA to apply to the target
`cell/Node-B 220 upon handoverby adjusting the sourcecell
`TA bytherelative difference between the source and target
`cell reference signals. The beacon channel may bea broad-
`cast channel, a synchronization channel (SCH), andthe like.
`
`FIG. 3 is a flow diagram of a UE autonomous TA
`[0038]
`LTE handover procedure 300 implemented in the system
`200 of FIG. 2 in accordance with the present invention. In
`step 305, TA for the UE 205 is enabled and performed in the
`source cell/Node-B 215 of the E-UTRAN 210. This is
`
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`US 2007/0149206 Al
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`Jun. 28, 2007
`
`enabled by RRC signaling from the network (E-UTRAN)
`side. In step 310, the E-UTRAN measures andcalculates the
`TA value and signals the TA value to the UE 205. In step
`315, the UE 205 applies the TA value of step 310 when
`transmitting to the source cell/Node-B 215. By using this TA
`value, the UE 205 is able to adjust its UL transmission
`timing. In step 320, the E-UTRAN 210 determines when it
`is time to perform a handover from the source cell/Node-B
`215 to the target cell/Node-B 220. When the E-UTRAN 210
`determines that a handoveris to be performed in step 320,
`the source cell/Node-B 215 of the E-UTRAN 210 sends a
`
`handover command message 225, (1.e., RRC signaling), to
`the UE 205 to initiate handover of the UE 205 (step 325).
`The handover command message 225 includes an indication
`of the relative time difference between the source and target
`cells or an indication that the cells are synchronized, and
`may include pre-allocated UL radio resource information
`which is used to establish initial transmission 230 to the
`
`target cell/Node-B 220. The autonomous TA procedure can
`be explicitly or implicitly inferred from the handover com-
`mand message 225. The handover command message
`enables an initial transmission 230 from the UE 205 to the
`target cell/Node-B 220 to occur during handover, either
`through the use of pre-allocated UL radio resources from the
`target cell/Node-B 220 or through the use of a synchronous
`RACH. When the initial
`transmission 230 to the target
`cell/Node-B 220 uses pre-allocated UL radio resources,
`information regarding the pre-allocated UL radio resources
`is contained inside the handover command message 225.
`This RRC signaling may also indicate that a different
`non-UE autonomous TA measurement approach should be
`used during handover. In this case, the RRC signaling must
`also explicitly or implicitly specify if no UE autonomous TA
`adjustment process is required.
`[0039]
`Still referring to FIGS. 2 and 3, in step 330, the UE
`205 performs one or more measurements to determine the
`difference in propagation delays between the source cell/
`Node-B 215 and the target cell/Node-B 220 based on
`reference signals transmitted on beacon channels of the
`source cell/Node-B 215 and the target cell/Node-B 220. In
`step 335, the UE 205 autonomously computes a new TA
`value based on the current source cell TA value, the mea-
`surements performed in step 330, and knowledge of the
`relative time difference between the source cell/Node-B 215
`and the target cell/Node-B 220 or knowledgethat the source
`cell/Node-B 215 and the target cell/Node-B 220 are syn-
`chronized, (i.e., there is no significant relative timing dif-
`ference between the source cell/Node-B 215 andthe target
`cell/Node-B 220). In step 340, the UE applies the new TA
`value to adjust the UL transmission timing when sending an
`initial transmission 230 to the target cell/Node-B 220 using
`either pre-allocated uplink non-contention based radio
`resources or a synchronous RACH, as directed by the
`handover command message 225.
`[0040] There are two optionsto use pre-allocated UL radio
`resource information to access the target cell/Node-B 220
`during handover. One option for the UE 205 is to use the
`pre-allocated UL radio resource by sending a resource
`request message and/ortraffic data to the target cell/Node-B
`220. In this case, the target cell/Node-B 220 must respond to
`the UE 205 with the newly allocated radio resource and if
`necessary a refined TA value for supporting its subsequent
`data transmission 230 to the target cell/Node-B 220. The
`other option is to use the pre-allocated UL radio resource
`
`included in the handover command messagefor direct data
`transmission. For the above two options, the amount of the
`pre-allocated radio resource will be different for different
`purposes that is to be used during handover. The selected
`option is signaled from the E-UTRAN 210 to the UE 205
`inside the DL RRCsignaling, during call setup, or inside the
`handover command message 225 as described above. In
`doing so, the adjustment of UL transmission timing syn-
`chronization to the target cell/Node-B 220 may be achieved
`immediately after the handover, without requiring an asyn-
`chronous RACH access procedure.
`[0041] Optionally, in the case absolute TA valuesare used,
`it is necessary for the UE 205 to report the autonomously
`computed TA value to the target cell/Node-B 220 when
`sending the initial transmission 230 to the target cell/Node-B
`220. The UE 205 is not required to inform the target
`cell/Node-B 220 exactly what the new TA value is in the
`case relative TA value signaling is applied.
`[0042]
`Synchronous RACH Access Procedure During
`LTE Handover
`
`FIG. 4 is a flow diagram of a synchronous RACH
`[0043]
`access LTE handover procedure 400 in accordance with
`another embodiment of the present invention. After the UE
`autonomously computes the timing advance value (step
`405), the UE sends a scheduling, (i.e., resource), request
`message through a synchronous RACH channel
`to the
`E-UTRAN 210 with the computed TA value applied (step
`410). In step 415, the E-UTRAN 210 computes a refined,
`(1.e., more accurate), TA value based on information in the
`scheduling request message received from the UE 205. If
`necessary, the the E-UTRAN 210 sendsthe refined TA value
`to the UE 205 in a DLsignaling message, and assigns UL
`and/or DL radio resources for the UE 205 for subsequent
`data transmissions (step 420). In step 425,
`the UE 205
`initiates data transmission by using the refined TA value and
`the assigned UL/DLradio resources.
`[0044] Although the features and elements of the present
`invention are described in the preferred embodiments in
`particular combinations, each feature or element can be used
`alone without the other features and elements of the pre-
`ferred embodiments or in various combinations with or
`
`without other features and elements of the present invention.
`The methodsor flow charts provided in the present invention
`may be implemented in a computer program, software, or
`firmware tangibly embodied in a computer-readable storage
`medium for execution by a general purpose computer or a
`processor. Examples of computer-readable storage mediums
`include a read only memory (ROM), a random access
`memory (RAM), a register, cache memory, semiconductor
`memory devices, magnetic media such as internal hard disks
`and removable disks, magneto-optical media, and optical
`media such as CD-ROM disks, and digital versatile disks
`(DVDs).
`Suitable processors include, by way of example, a
`[0045]
`general purpose processor, a special purpose processor, a
`conventional processor, a digital signal processor (DSP), a
`plurality of microprocessors, one or more microprocessors
`in association with a DSP core, a controller, a microcontrol-
`ler, Application Specific Integrated Circuits (ASICs), Field
`Programmable Gate Arrays (FPGAs)circuits, any other type
`of integrated circuit (IC), and/or a state machine.
`[0046] A processor in association with software may be
`used to implementa radio frequency transceiver for use in
`
`

`

`US 2007/0149206 Al
`
`Jun. 28, 2007
`
`Whatis claimedis:
`1. A wireless communication system comprising:
`
`at least one user equipment (UE); and
`an evolved universal
`terrestrial radio access network
`
`11. The system of claim 10 wherein the measurements are
`a wireless transmit receive unit (WTRU), user equipment
`performed on beacon channelreference signals of the source
`(UE), a terminal, a base station, a radio network controller,
`cell/Node-B and the target cell/Node-B.
`or any host computer. The WTRU maybe used in conjunc-
`12. The system of claim 11 wherein each beacon channel
`tion with modules, implemented in hardwa