(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2007/0254656 A1
`
`Dalsgaard NOV. 1, 2007 (43) Pub. Date:
`
`
`US 20070254656A1
`
`(54) APPARATUS, METHOD AND COMPUTER
`PROGRAM PRODUCT PROVIDING UPLINK
`SYNCHRONIZATION THROUGH USE OF
`DEDICATED UPLINK RESOURCE
`ASSIGNMENT
`
`Publication Classification
`
`(51)
`
`2154317/20
`
`(2006 01)
`'
`
`(75)
`
`Inventor:
`
`Lars Dalsgaard, Oulu (Fl)
`
`Correspondence Address:
`HARRINGTON & SMITH, PC
`4 RESEARCH DRIVE
`SHELTON, CT 06484-6212
`_
`.
`_
`(73) Ass1gnee:
`NOkla Corporation
`
`(21) Appl. No.:
`
`11/799,200
`
`(22)
`
`Filed:
`
`May 1, 2007
`
`Related US. Application Data
`
`(60) Provisional application No. 60/796,767, filed on May
`1, 2006.
`
`(52) US. Cl.
`
`.................................................... 455/435.1
`
`ABSTRACT
`(57)
`An assignment of an uplink resource on which to send an
`uplink synchronization signal is transmitted to a user equip-
`ment. The user equipment sends on the uplink resource an
`uplink synchronization signal. From the uplink synchroni-
`zation signal is determined a timing advance for the user
`equipment. Various indications are used to indicate to the
`user equipment that the assignment of uplink resources is for
`the purpose of sending its synchronization signal, such as
`expiration of its timing advance timer, a field in the alloca-
`tion table that assigns the uplink resources, or explicit
`signaling from the network. Methods, devices, and computer
`program products are detailed for both network and user
`equipment embodiments.
`
`10
`
`WIRELESS LINK
`
`
`
`ASSIGNMENT
`
` UL RESOURCE
`
`
`
`
`
`UL
`
`SPECIAL BURST
`
`III%I
`Lv_/
`ASSIGNED UL—SCH
`SUB—FRAME .
`GT=GUARD TIME
`
`APPLE 1026
`
`APPLE 1026
`
`

`

`Patent Application Publication
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`Nov. 1, 2007 Sheet 1 of 5
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`Patent Application Publication
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`Nov. 1, 2007 Sheet 2 0f 5
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`US 2007/0254656 A1
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`Patent Application Publication
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`Patent Application Publication
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`Nov. 1, 2007 Sheet 4 0f 5
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`US 2007/0254656 A1
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`
`
`
` }m
`} 4-20
`
`
`ACTIVE STATE AND UE IS UL SYNCHRONIZED
`
`SYNCHRONIZED RACH
`
`RESOURCE ALLOCATION (AT)
`
`NON-SYNCHRONIZED RACH
`
`ACTIVE STATE AND UE IS NOT UL SYNCHRONIZED
`
`A
`
`B
`
`
`
`C
`
`D
`
`NON-SYNCHRONIZED RACH
`
`430
`
`ALLOCATION TABLE INCLUDING UL RESOURCE ALLOCATION
`
`RACH-TYPE 0F BURST FOR ALLOWING NETWORK TO
`
`CALCULATE TIMING ADVANCE
`
`
`
` 44o
`
`ALLOCATION TABLE INCLUDING TA AND UL RESOURCE ALLOCAIIO
`
`
`
`
`
`IDLE STATE
`
`PAGING
`
`NON-SYNCHRONIZED RACH
`
`450
`
`FICA-
`
`

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`Patent Application Publication
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`Nov. 1, 2007 Sheet 5 0f 5
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`

`US 2007/0254656 A1
`
`Nov. 1, 2007
`
`APPARATUS, METHOD AND COMPUTER
`PROGRAM PRODUCT PROVIDING UPLINK
`SYNCHRONIZATION THROUGH USE OF
`DEDICATED UPLINK RESOURCE
`ASSIGNMENT
`
`REFERENCE TO RELATED APPLICATION
`
`[0001] This patent application claims priority under 35
`U.S.C. §ll9(e) from US. Provisional Patent Application
`No. 60/796,767, filed on May 1, 2006, and hereby incorpo-
`rated by reference in its entirety.
`
`TECHNICAL FIELD
`
`[0002] The exemplary and non-limiting embodiments of
`this invention relate generally to wireless communications
`systems, methods, computer program products and devices
`and, more specifically, relate to techniques for achieving
`uplink temporal synchronization of user equipment.
`
`BACKGROUND
`
`[0003] The following abbreviations are herewith defined:
`
`3GPP
`A"
`
`
` {ACH
`
`third generation partnership project
`allocation table (also called physical downlink shared control
`channel PDCCH)
`cell radio network temporary identifier
`C-RNTI
`downlink (node B to UE)
`D n
`discontinuous reception
`D {X
`general packet radio service
`G’RS
`global system for mobile communication
`GSM
`hand over
`{0
`instant messaging service
`MS
`long term evolution
`GTE
`medium access control
`MAC
`base station
`Node B
`)
`packet timing advance control channel
`"CCH
`random access channel
`radio link identifier
`{DID
`radio network control
`{NC
`radio resource control
`{{C
`shared channel
`SCH
`timing advance
`TA
`temporary block flow
`T 3F
`user equipment
`J 3
`uplink (UE to node B)
`J2
`universal mobile telecommunications system
`JMTS
`UMTS terrestrial radio access network
`JTRAN
`E-UTRAN evolved UTRAN, also referred to as UTRAN-LTE and as
`3.9G
`voice over internet protocol
`
`VoIP
`
`[0004] UTRAN-LTE is defined as a packet-based trans-
`mission system only. This implies that there will not be a
`so-called dedicated connection mode (or circuit switched
`mode) as exists in some currently deployed systems.
`[0005] As currently defined the uplink air
`interface
`resources are divided between an UL-SCH and a contention
`
`based RACH. A Node-B may provide an allocation on the
`UL-SCH if the UE can be identified (such as with RLlD/
`C-RNTI) and if the TA of the UE has been so recently
`controlled by the Node-B such that it can be considered to
`be valid. If the UE has no valid TA it is not allowed to
`
`transmit on the UL-SCH. The random access procedure may
`be used by the UE for initial network access,
`for TA
`adjustment, for transfer from LTE-lDLE to LTE-ACTIVE
`state, for uplink resource requests and during HO. One of a
`
`synchronous or non-synchronous random access procedure
`is used, depending on the validity of UE’s TA.
`[0006]
`Further reference with regard to the RACH channel
`can be made to, for example, Annex B of 3GPP TR 25.813,
`V0.83, 3rd Generation Partnership Project, Technical Speci-
`fication Group Radio Access Network; Evolved Universal
`Terrestrial Radio Access (E-UTRA) and Evolved Universal
`Terrestrial Radio Access Network (E-UTRAN), and Radio
`interface protocol aspects (Release 7).
`[0007] One proposal for UTRAN-LTE is that the UE will
`receive the UL-SCH resource allocations from the network
`
`through an AT, where the UE would receive the AT at certain
`instants in time determined at least in part by the current
`DRX period of the UE (which may be defined by the
`network).
`[0008]
`It should be noted that in the general case resource
`(s) are assigned to the UE by the network through the use of
`DL control signaling. The exact format and content of this
`control signaling is not particularly germane to an under-
`standing of the invention, and in fact may be subject to
`revision.
`
`[0009] However, if the currently used DRX period of the
`UE is long (e.g., seconds) the TA used by the UE before the
`DRX period may no longer be valid for use in transmission
`in the UL-SCH. If the UE no longer has a valid TA it is not
`allowed to transmit
`in the UL-SCH before the UE has
`received a new TA value from the network.
`
`[0010] More generally, if the time from the last update of
`the TA is long, however the TA may be updated, then the TA
`may not be valid. The use of DRX periods to ascertain the
`potential validity or invalidity of the current TA of the UE is
`but one non-limiting example.
`[0011]
`It has been proposed that the procedure for achiev-
`ing a valid TA (when no valid TA is available) includes
`transmission by the UE on the non-synchronized RACH
`channel. However, this approach, which utilizes a contention
`based resource (where the possibility of collisions, backoffs
`and re-transmissions may occur), may introduce an unde-
`sirable and unpredictable delay.
`[0012] Another issue relates to a requirement in 3.9G that
`the UE in the Active state shall always be UL synchronized.
`Such a requirement would in practice mean that there would
`be a need for constant DL/UL transmissions in order to
`
`allow the network to maintain the UL synchronization (TA)
`of the UE up-to-date, and could require scheduled DL/UL
`transmission for no other reason than keeping the UE TA
`current. As can be appreciated, this approach is not efficient
`in terms of UE power consumption and bandwidth utiliza-
`tion.
`
`is really
`[0013] Yet another issue relates to whether it
`necessary for all connection types and services to maintain
`UL synchronization at all times. One justification for main-
`taining UE UL synchronization is that there is a need for fast
`connection setup time (short delay), and another is to
`maintain a constant regular UL/DL data flow with short
`intervals (e.g., VolP). In other situations, however, such as
`normal WEB browsing or email download, the setup time
`may not be as important and the data may be transmitted in
`a bursty (aperiodic) manner.
`[0014]
`It is noted that in the currently deployed GSM HO
`procedure, when the UE receives a HO command to a new
`cell and does not have a valid TA for the new cell, the UE
`is not allowed to transmit a normal UL burst in the new cell.
`Instead, the UE must transmit a shorter duration burst that
`
`

`

`US 2007/0254656 A1
`
`Nov. 1, 2007
`
`leaves a large part of the time slot as a guard time or guard
`band around the burst. The network measures the propaga-
`tion delay from the received short burst and sends an
`appropriate TA value to the UE. The UE can then start to use
`the newly assigned TA value when transmitting a normal UL
`burst.
`
`[0015] The use of the PTCCH in the GPRS is another
`already deployed procedure for assuring that the UE has UL
`synchronization. However, the use of this procedure is only
`valid when the UE has an active TBF, which means that
`there is an already established UL/DL connection between
`the network and the UE.
`
`SUMMARY
`
`In an exemplary embodiment of the invention there
`[0016]
`is a method which includes transmitting to a user equipment
`an assignment of an uplink resource on which to send an
`uplink synchronization signal,
`receiving from the user
`equipment on the uplink resource the uplink synchronization
`signal, and determining from the uplink synchronization
`signal a timing advance for the user equipment.
`[0017]
`In an exemplary embodiment of the invention there
`is a method which includes receiving from a network device
`an assignment of an uplink resource on which to send an
`uplink synchronization signal, and transmitting on the
`assigned uplink resource the uplink synchronization signal.
`[0018]
`In yet another exemplary embodiment of the inven-
`tion there is a computer program product embodied on a
`memory and executable by a processor to perform opera-
`tions, including transmitting to a user equipment an assign-
`ment of an uplink resource on which to send an uplink
`synchronization signal, receiving from the user equipment
`on the assigned uplink resource the uplink synchronization
`signal, and determining from the uplink synchronization
`signal a timing advance for the user equipment.
`[0019]
`In yet another exemplary embodiment of the inven-
`tion there is a network element, which includes a transmitter
`adapted to transmit to a user equipment an assignment of an
`uplink resource on which to send an uplink synchronization
`signal, a receiver adapted to receive from the user equipment
`on the assigned uplink resource the uplink synchronization
`signal, and a processor adapted to determine from the uplink
`synchronization signal a timing advance for the user equip-
`ment.
`
`In still another exemplary embodiment of the
`[0020]
`invention there is a user equipment, which includes a
`receiver adapted to receive from a network device an assign-
`ment of an uplink resource on which to send an uplink
`synchronization signal, a processor coupled to a memory
`and adapted to determine the uplink synchronization signal,
`and a transmitter adapted to transmit on the uplink resource
`the uplink synchronization signal.
`[0021]
`In yet another exemplary embodiment of the inven-
`tion there is an apparatus which includes means for trans-
`mitting to a user equipment an assignment of an uplink
`resource on which to send an uplink synchronization signal,
`means for receiving from the user equipment on the assigned
`uplink resource the uplink synchronization signal, and
`means for determining from the uplink synchronization
`signal a timing advance for the user equipment.
`[0022]
`Further,
`in the exemplary embodiment of the
`invention above the means for transmitting comprises a
`
`transmitter, the means for receiving comprises a receiver,
`and the means for determining comprises a processor.
`
`DESCRIPTION OF THE DRAWINGS
`
`[0023] 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.
`[0024]
`FIG. 1 shows a simplified block diagram of various
`electronic devices that are suitable for use in practicing the
`exemplary embodiments of this invention.
`[0025]
`FIG. 2 illustrates the protocol stacks of an UMTS
`packet data service for control signaling and transmission of
`user data.
`
`FIG. 3A illustrates operation of a method in accor-
`[0026]
`dance with the exemplary embodiments of this invention,
`while FIG. 3B shows a conventional approach.
`[0027]
`FIG. 4 illustrates currently known techniques for a
`network to acquire the TA of a UE, as well as a RACH
`procedure proposed for use in UTRAN-LTE, in addition to
`an UL synchronization procedure in accordance with an
`embodiment of this invention.
`
`is
`FIG. 5 illustrates a logic flow diagram that
`[0028]
`descriptive of a method and an operation of a network device
`for implementing the exemplary embodiments of this inven-
`tion invention.
`
`is
`FIG. 6 illustrates a logic flow diagram that
`[0029]
`descriptive of a method and an operation of a user equipment
`for implementing the exemplary embodiments of this inven-
`tion.
`
`DETAILED DESCRIPTION
`
`[0030] The exemplary embodiments of this invention
`relate to and are described below in the context of UTRAN-
`
`LTE. More specifically, the exemplary embodiments of this
`invention address the area of UE UL synchronization, and an
`ability for the network to estimate the UL synchronization
`for the UE. However, it should be appreciated that at least
`some aspects of the exemplary embodiments are applicable
`to other types of wireless communication systems such as
`GSM, HSPDA, or any packet-switched system.
`[0031] Reference is made first to FIG. 1 for illustrating a
`simplified block diagram of various electronic devices that
`are suitable for use in practicing the exemplary embodi-
`ments of this invention. In FIG. 1 a wireless network 1 is
`
`adapted for communication with a UE 10 via a Node B (base
`station) 12, also referred to herein as an eNodeB. The
`network 1 may include a RNC 14, or other radio controller
`function, which may be referred to as a mobility manage-
`ment entity MME or gateway (see 3GPP TS 36.300 V1.0.0).
`The UE 10 includes a data processor (DP) 10A, a memory
`(MEM) 10B that stores a program (PROG) 10C, and a
`suitable radio frequency (RF) transceiver 10D for bidirec-
`tional wireless communications with the Node B 12, which
`also includes a DP 12A, a MEM 12B that stores a PROG
`12C, and a suitable RF transceiver 12D. The Node B 12 is
`coupled via a data path 13 to the RNC 14 that also includes
`a DP 14A and a MEM 14B storing an associated PROG 14C.
`[0032] As will be described below, at least the PROGs
`10C and 12C 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. For example, the PROG 12C includes
`
`

`

`US 2007/0254656 A1
`
`Nov. 1, 2007
`
`program instructions that direct the Node B 12 to signal the
`UE 10, such as in a data structure sent as an AT, for assigning
`to the UE 10 a dedicated uplink resource (e.g., an UL-SCH
`sub-frame) in which to transmit a special synchronization
`burst to be used by the Node B 12 for calculating a TA value,
`as well as to receive the special burst from the assigned UL
`resource for use in calculating the TA value. The PROG 10C
`includes program instructions that direct
`the UE 10 to
`transmit the special burst in the assigned UL resource.
`[0033] Reference is now made to FIG. 2, where FIG. 2
`shows the protocol stack used for control signaling between
`the mobile station MS and the core network CN. Mobility
`management MM, call control CC and session management
`SM of the mobile station MS are signaled on the highest
`protocol layers between the mobile station MS and the core
`network CN in such a manner that the base stations BS and
`the radio network controller RNC located in between are
`
`transparent to this signaling. The radio resources manage-
`ment of radio links between mobile stations MS and base
`
`stations BS is carried out by a radio resource management
`system RRM which transmits control data from the radio
`network controller RNC to the base stations BS. These
`
`functions associated with the general management of a
`mobile system form a group called core network protocols
`(CN protocols), also known as Non-Access Stratum. Cor-
`respondingly,
`the signaling related to the radio network
`control between the mobile station MS, the base station BS
`and the radio network controller RNC is carried out on
`
`protocol layers called radio access network protocols (RAN
`protocols), i.e. Access Stratum. These include transfer pro-
`tocols of the lowest level, whose control signaling is trans-
`ferred to the higher levels for further processing. The most
`essential one of the higher Access Stratum layers is the radio
`resource control protocol RRC which is responsible for
`example for establishing, configuring, maintaining and
`releasing logical connections between the mobile station MS
`and the radio network UTRAN and for transmitting control
`information from the core network CN and the radio net-
`work RAN to the mobile stations MS. In addition, the radio
`resource control protocol RC is responsible for allocating
`sufficient capacity according to the instructions of the radio
`resource management system RRM to a user terminal con-
`nection in an application-based capacity allocation,
`for
`example.
`[0034] The exemplary embodiments of this invention may
`be implemented by computer software executable by the DP
`10A of the UE 10 and the other DPs, such as in cooperation
`with a DP in the network, or by hardware, or by a combi-
`nation of software and/or firmware and hardware.
`
`In general, the various embodiments of the UE 10
`[0035]
`can include, but are not
`limited to, cellular telephones,
`personal digital assistants (PDAs) having wireless commu-
`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-
`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.
`
`[0036] 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
`10A, 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-
`cessors based on a multi-core processor architecture, as
`non-limiting examples.
`[0037] Having thus introduced one suitable but non-lim-
`iting technical context for the practice of the exemplary
`embodiments of this invention, the exemplary embodiments
`will now be described with greater specificity.
`[0038] The exemplary embodiments of this invention pro-
`vide a method and apparatus for the network 1 to measure
`the UL TA for a certain UE 10 when UL data transfer is
`
`required. The method and apparatus may be applied to (but
`are not restricted to) a situation where the network 1 has
`knowledge beforehand that there will be a need for the UE
`10 to transmit in the UL-SCH. This may be the case when
`the network 1 desires to request measurements of some sort
`from the UE 10, as well as when the network 1 expects that
`the UE has a need for sending positive or negative acknowl-
`edgments (ACK/NACK) in the UL in response to DL traffic.
`[0039]
`In accordance with the exemplary embodiments of
`this invention a network-assigned UE 10 dedicated UL
`resource is provided for use by the UE 10 for sending a
`special burst. This burst is then used by the network 1 (for
`example, is used by the Node B 12) for measuring the TA of
`the UE 10. The burst is specifically designed to accommo-
`date a large timing uncertainty, e.g., the burst type may
`resemble the burst used on the non-synchronous RACH in
`E-UTRAN, or may resemble the access burst type known
`from GSM that
`is used in, for example, handover and
`RACH.
`
`[0040] The network 1 calculates the TA ofthe UE 10 based
`on the received special burst and thereafter informs the UE
`10 of the new TA value in a following resource assignment
`message, or through other suitable control signaling means.
`[0041] The ensuing description is made using the non-
`limiting example of the UE 10 in an E-UTRAN LTE-
`ACTIVE state, but not UL synchronized. It can be noted that
`the exemplary embodiments of this invention may be
`employed as well to the UE 10 in, for example, the E-UT-
`RAN LTE-IDLE mode, and in other situations as well
`including but not limited to similar modes of other wireless
`systems noted by example above.
`[0042] When the UE 10 is in the ACTIVE state it has
`already been assigned a unique ID by the network 1. In fact,
`all UE that are in the ACTIVE state in a given cell have been
`assigned a unique identifier. This means that the network 1
`can uniquely address the UE 10. This may be done, for
`example, through the use of an AT sent on the DL. The
`unique address assigned to the UE 10 may be referred to as
`the RLID or as the C-RNTI, as two non-limiting examples.
`[0043] When the UE 10 is in the LTE-ACTIVE state it
`may lose synchronization if it has not transmitted on the UL
`for some period of time, and further the network 1 has not
`had the opportunity to calculate and assign a new TA value.
`In this case the UE 10 should not be allowed to transmit a
`normal burst in the UL-SCH before a new and valid TA
`value has been received from network 1. The network 1
`
`calculates the TA based on a special synchronization burst
`that the UE 10 sends in the UL.
`
`

`

`US 2007/0254656 A1
`
`Nov. 1, 2007
`
`[0044] As was noted above, it has been proposed that the
`synchronization is performed using the non-synchronized
`RACH channel procedure (see FIG. 3B transmission labeled
`330)).
`[0045] More specifically, in FIG. 3B the Node B, which
`may be referred to as an eNodeB, sends in an AT an order
`for the UE 10 to transmit on the RACH 310. The UE 10
`
`responds at 320 by transmitting a preamble (the special
`synchronization burst) on the non-ized synchronized RACH.
`In response, the eNodeB computes the TA for the UE 10 and
`sends in an AT 330 the calculated TA and the UL-SCH
`
`allocation. At 340 the UE 10 sends a unique ID on the
`UL-SCH, and at 350 the eNodeB sends a normal UL-SCH
`allocation in an AT.
`
`[0046] The exemplary embodiments of this invention
`instead provide for the special synchronization burst to be
`transmitted on an UL-SCH allocation assigned to the UE 10
`by the network 1 (see FIG. 3A 315, and FIG. 4 440), and not
`on the RACH. That is, and referring to FIG. 1, the special
`synchronization burst is sent within an UL-SCH sub-frame
`that is assigned to the UE 10 by the Node-B in, for example,
`an AT. Note that a single AT/PDCCH may allocate more than
`one UE 10 to the same UL-SCH, which may be dedicated for
`the special synchronization bursts detailed herein.
`It
`is
`within the scope if this invention that two UEs 10 may be
`assigned in the same AT/PDCCH the same UL (shared)
`resource on which to transmit their individual uplink syn-
`chronization signals. In such a case of simultaneous UL
`synchronization bursts on the same shared channel,
`the
`eNode B 12 can distinguish the UEs from one another by use
`of a separate and unique preamble used by each of the UEs
`10 on their uplink transmission of the special synchroniza-
`tion burst. In one embodiment such a unique preamble is
`signaled to each UE upon cell entry (or other control
`signalling) so that each UE is pre-allocated a unique pre-
`amble for use with the UL-SCH synchronization burst. In
`another embodiment the AT/PDCCH itself may include an
`additional field so as to make an association between a
`
`preamble and an UE’s RLID or other UE identifier used in
`the AT/PDCCH. In this embodiment, when the UE recog-
`nizes that a preamble in that new field is associated with its
`identifier, it uses that preamble on the UL-SCH synchroni-
`zation burst. In either manner,
`the preamble enables the
`eNode B to distinguish multiple UE’s sending their own
`synchronization bursts at the same time on the same shared
`channel.
`
`[0047] The special synchronization burst differs from the
`normal UL-SCH burst in the sense that a larger guard time
`(GT) is included to accommodate the unknown TA (and thus
`to avoid interfering with UL transmissions sent by other UEs
`10). The guard time may be made equal to that used in the
`non-synchronous RACH transmission (FIG. 3B, 320). When
`the eNodeB 12 receives the special burst it calculates the TA
`of the UE 10 in a conventional manner, and assigns the TA
`to the UE 10 in the DL either through (as non-limiting
`examples): normal control signaling, as part of a header in
`a normal data transmission, or in a (next) AT.
`[0048]
`In accordance with the exemplary aspects of this
`invention, and because the synchronization burst is sent on
`an UL resource dedicated to a specific UE 10, there can be
`no collisions with bursts sent by other UEs, as may occur
`when using the RACH.
`[0049] As one non-limiting example, the synchronization
`burst may comprise a cell specific pilot code sequence.
`
`Several different alternatives exist for the network
`[0050]
`1 to indicate to the UE 10 that the purpose of the assigned
`UL resource is for TA measurement. In a first non-limiting
`example this may be indicated directly in an AT that no TA
`value is available (in a TA field), and that the UE 10 should
`therefore use the assigned UL-SCH resource for sending the
`synchronization burst transmission (see FIG. 1). In a second
`non-limiting example this may be indicated based on a TA
`value lifetime timer (a software and/or hardware timer) that
`runs in both the UE 10 and in the network 1 (or through the
`use of other time measurement alternatives such as, for
`example, the duration of DRX period(s) or frame numbers).
`If the TA validity timer is exceeded the UE 10 should use the
`assigned UL-SCH resource for transmission of the synchro-
`nization burst. In a third non-limiting example the AT/PD-
`CCH or other resource allocation message can include a
`preamble associated with a UE’s temporary identifier (either
`associated in the AT itself or signaled to the UE upon the
`UE’s entry into the cell), where the presence of such a
`preamble in the AT indicates to the UE that it is to send a
`special synchronization burst on the resources allocated it in
`that AT/PDCCH. The UE then sends that preamble itself on
`the uplink allocated resource as its synchronization burst (or
`in conjunction with some other information that serves as
`the burst). As above, the same AT/PDCCH can allocate
`multiple UEs 10 for sending a synchronization burst by
`using unique preambles sent in the same AT/PDCCH and
`associated with different UEs. Note that
`the preamble
`embodiment may be used to enable the e-Node B to distin-
`guish among different UE’s synchronization bursts even
`where the AT indicates that no TA value is available or where
`
`the lifetime timer has expired.
`[0051] The timing advance is a signal derived from the
`time synchronization of the UL sequence and sent by the
`eNB 12 to the UE 10, which the UE 10 uses to advance its
`timings of transmissions to the eNB so as to compensate for
`propagation delay and thus time align the transmissions
`from different UEs with the receiver window of a eNB 12.
`
`By avoiding the overlapping of uplink transmissions, timing
`advance allows time domain multiplexing in the uplink.
`[0052] The active mode or state noted above is sometimes
`referred to as an LTE-ACTIVE or RRC_CONNECTED
`state. In such a state, network controlled UE assisted han-
`dovers are performed. In this state, the timing advance may
`be permanently maintained or only temporarily maintained.
`If temporary, the MAC knows if layer 1 is synchronized and
`which procedure to use to start transmitting in the uplink.
`Cases where the UL synchronization status may move from
`“synchronized” to “non-synchronized” include an expiration
`of a timer; non-synchronized handover; or an explicit
`request by MAC or RRC in the eNB 12. Any of these may
`cause the eNB to send a resource allocation to the UE for the
`
`synchronization burst above and cause the UE to send it so
`as to become synchronized.
`the RACH need not be
`[0053] As can be appreciated,
`utilized for achieving the UL UE synchronization, and
`thereby the procedure in accordance with the exemplary
`embodiments of this invention avoids collision risks and the
`
`uncertainty in the delay that are inherent in the use of the
`RACH-based synchronization procedure. Assuming that the
`UE 10 receives the ATs when requested it can also be seen
`that this procedure is a more efficient use of radio resources.
`[0054] Referring to FIG. 4, the signaling sequence 410
`refers to the conventional Active state when UE 10 is UL
`
`

`

`US 2007/0254656 A1
`
`Nov. 1, 2007
`
`synchronized, and the UE 10 uses the synchronized RACH
`channel for requesting resources from the network 1.
`[0055] The signal 420 is shown for completeness, but
`actually may be eliminated as the UE 10 already has UL
`synchronization. As such, the use of the non-synchronized
`RACH channel at this time would be a waste of resources.
`
`[0056] The signal 430 shows the conventional procedure,
`when the UE 10 is not UL synchronized,
`that uses the
`non-synchronized RACH channel
`to initially access the
`network.
`
`[0057] The signaling sequence 440 is in accordance with
`the exemplary embodiments of this invention (see also FIG.
`3A), where the network 1 assigns Via an AT a special UL
`resource to be used by the UE 10 for transmitting the UL
`access burst to be used by the network for TA estimation/
`calculation. The calculated TA is delivered to the UE in the
`
`in this example, via an AT, although other control
`DL,
`signaling procedures could be used as was noted above.
`[0058] The signaling sequence 450 illustrates a conven-
`tional Idle mode procedure (network 1 initiated through
`paging and UE 10 initiated through the non-synchronized
`RACH channel procedure). However, as was noted above
`the exemplary embodiments of this invention may be
`applied as well to Idle mode UL synchronization.
`[0059] There are a number of advantages that can be
`realized through the use of the exemplary embodiments of
`this invention. For example,
`the use of the exemplary
`embodiments of this invention reduces the load on the
`
`therefore, saves
`non-synchronized RACH channel and,
`radio resources as transmission on a scheduled resource is
`
`generally more efficient than transmission on a contention-
`based resource. As another example, setup delays due to
`possible RACH collisions can be reduced, as the possibility
`for a RACH collision to occur is eliminated. As another
`
`example, the use of the exemplary embodiments of this
`invention ensures an easy and controlled way for the net-
`work 1 to be able to acquire the UE TA value when the UL
`traffic needs are known.
`
`Further, it can be appreciated that the use of the
`[0060]
`exemplary embodiments of this
`invention relaxes any
`restrictions that may be imposed on the length of DRX
`periods, as it simplifies and makes more efficient a subse-
`quent UL re-synchronization of the UE 10 after a possibly
`lengthy DRX period.
`[0061] Referring to FIG. 5, there is a method