as) United States
`a2) Patent Application Publication 10) Pub. No.: US 2008/0002660 A1
`
` Jeonget al. (43) Pub. Date: Jan. 3, 2008
`
`
`US 20080002660A1
`
`(54) METHOD FOR MAINTAINING UPLINK
`TIMING SYNCHRONIZATION IN A MOBILE
`
`(22)
`
`Filed:
`
`Jun. 21, 2007
`
`COMMUNICATION SYSTEM AND USER
`EQUIPMENT APPARATUS FOR THE SAME
`
`(30)
`
`Foreign Application Priority Data
`
`Jun. 22, 2006
`
`(KR) oe cece eeeeenees 56417/2006
`
`(75)
`
`Inventors: Kyeong-In Jeong, Hwaseong-si (KR);
`Ju-Ho Lee, Suwon-si (KR); Yong-Jun
`Kwak, Yongin-si (KR); Sung-Ho Choi,
`Suwon-si (KR); O-Sok Song, Suwon-si
`(KR); Gert Jan Van Lieshout, Staines
`(GB); Himke Van Der Velde, Staines
`(GB)
`
`Correspondence Address:
`THE FARRELL LAW FIRM,P.C.
`333 EARLE OVINGTON BOULEVARD
`SUITE 701
`UNIONDALE,NY 11553 (US)
`
`(73) Assignee: SAMSUNG ELECTRONICS CO.,
`LTD., Suwon-si (KR)
`
`(21) Appl. No.:
`
`11/766,498
`
`Publication Classification
`
`(31)
`
`Int. CL
`(2006.01)
`HO4T 3/06
`(52) US. Che
`eceeessssssssnssnsssnsesssenesnsensssneeaneesees 370/350
`
`ABSTRACT
`(57)
`. .
`oo.
`.
`.
`Disclosed is a method for maintaining uplink timing syn-
`chronization by a User Equipment (UE) in a mobile com-
`munication system, without uplink transmission of a pre-
`amble from a UE or without transmission of uplink timing
`difference information from an Evolved Node B (E-NB) to
`solve the inefficient use problem of radio resources, occur-
`ring due to periodic transmission of uplink signaling and
`downlink signaling during maintenanceofthe uplink timing
`synchronization, and a UE apparatus for the same.
`
`SELECT/GENERATE PREAMBLE
`CODE TO BE USEDIN UL TIMING
`SYNCH PROCEDURE
`
`UL SYNC RES (pre-amble codeid,
`
`UL timing adjustmentinfo, etc) (422)
`
`REFERENCE UL TIMING
`
`
`
`
`
`AONWd340SICONIWILWNF1VeSGISNOO
`
`(LZ¥)03103130
`
`1, STORE DL TIMING OF 461 AS
`REFERENCE DL TIMING
`2, ADJUST UL TIMING BASEO ON
`RECEIVED UL TIMING
`ADJUSTMENT INFO
`3. STORE ADJUBTED UL TIMING AS
`
`UL SIGNALING/DATA
`
`1
`
`APPLE 1005
`
`1
`
`APPLE 1005
`
`

`

`Patent Application Publication
`
`Jan. 3,2008 Sheet 1 of 7
`
`US 2008/0002660 Al
`
`16
`
`
`2,
`cneo1
`|E-Node BEAN cp|
`
`
`FIG.1A
`(PRIOR ART)
`
`2
`
`

`

`Patent Application Publication
`
`Jan. 3,2008 Sheet 2 of 7
`
`US 2008/0002660 Al
`
`IP Network
`
`114
`
`
`
`
`: Fast Scheduling
`* HARQ
`‘ ARQ
`* AMC
`
`FIG.1B
`(PRIOR ART)
`
`3
`
`

`

`Patent Application Publication
`
`Jan. 3,2008 Sheet 3 of 7
`
`US 2008/0002660 Al
`
`T_pro 2=3.33us
`
`T_pro 1=0.33us sl,
`
`Time
`
`
`1 OFDM Symbol
`
`UL@UE#1
`
`202 UL@UE#2
`
` Not maintain orthogonality
`
`between UE#1 and UE#2
`
` ahs
`
`(PRIOR ART)
`
`4
`
`

`

`Patent Application Publication
`
`Jan. 3,2008 Sheet 4 of 7
`
`US 2008/0002660 Al
`
`301
`
`302
`
`
`
`GENERATE PREAMBLE CODE TO BE
`USED IN UPLINK TIMING
`SYNCH PROCEDURE
`
`
`
`
`
`CHANGE/UPDATE UL TIMING
`BASED ON RECEIVED UL TIMING
`
`
`ADJUSTMENT INFO
`
`I
`SELECT/GENERATE PREAMBLE
`|
`
`| CODE TO BE USED IN UL TIMING 1~341
`|
`SYNCH PROCEDURE
`a em ee eee ee es er ee ee
`
`UL SYNC REQ (pre-amble code) (342)
`
`UL SYNC RES (pre-amble codeid,
`UL timing adjustmentinfo, etc) (343)
`
`
`
`UL SIGNALING/DATA
`
`
`
`
`FIG.3
`(PRIOR ART)
`
`5
`
`

`

`Patent Application Publication
`
`Jan. 3,2008 Sheet 5 of 7
`
`US 2008/0002660 Al
`
`SELECT/GENERATE PREAMBLE
`CODE TO BE USED IN UL TIMING
`SYNCH PROCEDURE
`412~O UL SYNC REQ (pre-amble code) (421)
`UL SYNC RES (pre-amble code id,
`UL timing adjustmentinfo, etc) (422)
`
`41]
`
`
`
`AONVd3¥OSI0DNIWILTNJTVVYICISNOO
`
` =
`
`1, STORE DL TIMING OF 412 AS
`
`O (12)03103130
`
`482
`
`6
`
`

`

`Patent Application Publication
`
`Jan. 3,2008 Sheet 6 of 7
`
`US 2008/0002660 Al
`
`RECEIVE UL TIMING ADJUSTMENT INFO
`
`}-~-501
`
`UPDATE AND STORE DL TIMING DURING UL
`TRANSMISSION BEFORE RECEPTION
`501 AS REFERENCEDL TIMING
`
`ADJUST UL TIMING BASED ON ULTIMING
`ADJUSTMENT INFO RECEIVEDIN 501
`
`511
`
`512
`
`UPDATE AND STORE UL TIMING ADJUSTED IN
`512 AS REFERENCE ULTIMIN
`
`13
`
`5
`
`521
`
`
` PERIOD ARRIVED?
`
`NO
`
`MAINTAIN LAST ADJUSTED
`UL TIMING (UL TIMING
`ADJUSTED IN 512 OR 533)
`
`531
`
`532
`
`YES
`
`MEASUREDL TIMING
`
`CALCULATE TIMING DIFFERENCE
`BETWEEN DL TIMING MEASUREDIN
`531 AND REFERENCE DL TIMING
`
`ADJUST UL TIMING BY APPLYING OL TIMING
`DIFFERENCE CALCULATEDIN 532 TO
`REFERENCE UL TIMING
`
`END
`
`FIG,.O
`
`7
`
`

`

`Patent Application Publication
`
`Jan. 3,2008 Sheet 7 of 7
`
`US 2008/0002660 Al
`
`631
`
`OL
`MEASURER
`
`
`
`
`
`REFERENCE
`UL TIMING
`
`
`UL/DL TIMING
`ADJUSTER
`MANAGER
`
`
`
`
`
`
`
`
`MESSAGE
`MESSAGE
`TRANSCEIVER
`
`DECRYPTER
`
`
`
`
`E-NB
`
`FIG.6
`
`8
`
`

`

`US 2008/0002660 Al
`
`Jan. 3, 2008
`
`METHOD FOR MAINTAINING UPLINK TIMING
`SYNCHRONIZATION IN A MOBILE
`COMMUNICATION SYSTEM AND USER
`EQUIPMENT APPARATUS FOR THE SAME
`
`PRIORITY
`
`[0001] This application claims priority under 35 U.S.C. §
`119(a) to a Korean Patent Application filed in the Korean
`Intellectual Property Office on Jun. 22, 2006 and assigned
`Serial No. 2006-56417, the contents of which are incorpo-
`rated herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`[0002]
`
`1. Field of the Invention
`
`invention relates to a method for
`[0003] The present
`maintaining uplink timing synchronization (sync)
`in an
`Orthogonal Frequency Division Multiplexing (OFDM)sys-
`tem and a User Equipment (UE) apparatus for the same.
`
`[0004]
`
`2. Description of the Related Art
`
`[0005] The mobile communication scheme can beclassi-
`fied into Time Division Multiplexing (TDM), Code Division
`Multiplexing (CDM) and Orthogonal Frequency Multiplex-
`ing (OFM) schemes according to a multiplexing method.
`The CDM scheme is most popularly used in the current
`mobile communication system, and can be subdivided into
`a synchronous and an asynchronous CDM scheme. Since the
`CDMschemebasically uses codes, it tends to suffer from a
`lack of resources due to a limit of orthogonal code resources.
`Accordingly, an OFDM schemehas emerged as an alterna-
`tive to the CDM scheme.
`
`[0006] The OFDM schemeis for transmitting data using
`multiple carriers, and is a type of Multi-Carrier Modulation
`(MCM)scheme that converts a serial input symbol stream
`into parallel streams, and modulates each of the parallel
`streams with a plurality of orthogonal sub-carriers,
`i.e.
`sub-carrier channels, before transmission. The OFDM
`scheme is similar to the conventional Frequency Division
`Multiplexing (FDM)scheme, but it maintains orthogonality
`between multiple sub-carriers during transmission and over-
`laps frequency spectra. Therefore, the OFDM scheme has
`high frequencyefficiency, is robust against frequency selec-
`tive fading and multi-path fading, and can reduce Inter-
`Symbol Interference (ISI) with use of a guard interval. In
`addition, the OFDM scheme enables simple design of a
`hardware equalizer and is robust against impulse noises, so
`it can obtain the optimal
`transmission efficiency during
`high-speed data transmission.
`
`[0007] A Long Term Evolution (LTE) system employing
`the OFDM schemeis now under discussion in 3° Genera-
`tion Partnership Project (3GPP) as the next generation
`mobile communication system that will replace Universal
`Mobile Telecommunication System (UMTS), which is the
`3 generation mobile communication standard.
`
`[0008] FIGS. 1A and 1B illustrate examples of a wireless
`mobile communication system to which reference will be
`made by the present
`invention, particularly illustrating
`examples of a 3GPP LTE system.
`
`participating in communication with a terminalin the exist-
`ing 3GPP system serves as a Node B for managingcells, and
`also serves as a Radio Network Controller (RNC) that
`controls a plurality of Node Bs and radio resources. In the
`E-RAN 14, an Evolved Node B (E-NB) 12 and an Evolved
`RNC (E-RNC) 13 can be separately implemented in the
`physically different nodes, or can be merged in a single
`node, in the mannerof the existing 3GPP system. Although
`in the following description the E-NB 12 and the E-RNC 13
`are physically merged in a single node of the E-RAN 14,the
`same can be applied to when the E-RNC 13 is separately
`implemented in the physically different node.
`
`[0010] An Evolved Core Network (E-CN) 15 is a node
`provided by merging functions of a Serving GPRS Support
`Node (SGSN) and a Gateway GPRS Support Node (GGSN)
`in the existing 3GPP system into one function. The E-CN 15,
`interposed between a Packet Data Network (PDN) 16 and
`the E-RAN 14, serves as a gatewayfor allocating an Internet
`Protocol (IP) address to the UE 11 and connecting the UE 11
`to the PDN 16. Definitions and functions of the SGSN and
`
`the GGSNfollow the 3GPPstandard, and a detailed descrip-
`tion thereof will be omitted herein.
`
`[0011] Referring to FIG. 1B, an Evolved UMTS Radio
`Access Network (E-RAN) 110 is simplified to a 2-node
`configuration of Evolved Node Bs (E-NBs) 120, 122, 124,
`126 and 128, and anchor nodes 130 and 132. A UE 101, or
`a terminal, accesses an IP network by the E-RAN 110. The
`E-NBs 120 to 128 correspondto the existing Node Bsin the
`UMTSsystem, and are connected to the UE 101 over a
`wireless channel. Unlike the existing Node Bs, the E-NBs
`120 to 128 perform more complex functions.
`In LTE,
`becauseall usertraffics, including real-time services such as
`Voice over IP (VoIP), are serviced over a shared channel,
`there is a need for devices for gathering status information
`of UEs and performing scheduling depending thereon, and
`the E-NBs 120 to 128 manage the devices.
`
`[0012] Generally, one E-NB controls a plurality of cells. In
`addition, the E-NB performs Adaptive Modulation & Cod-
`ing (AMC) that determines a modulation scheme and a
`channel coding rate according to channel status of a UE.
`Similar to High Speed Downlink Packet Access (HSDPA),
`High Speed Uplink Packet Access (HSUPA) and Enhanced
`Dedicated CHannel
`(E-DCH) of UMTS, even in LTE,
`Hybrid Automatic Repeat reQuest (HARQ)is performed
`between the E-NB 120 to 128 and the UE 101. However,
`because LTE cannot meet various Quality of Service (QoS)
`requirements only with HARQ, Outer-ARQ in an upper
`layer can be performed between the UE 101 and the E-NBs
`120 to 128. HARQ,as is well known, refers to a technique
`for soft-combining previously received data with retrans-
`mitted data without discarding the previously received data,
`thereby increasing a reception success rate. In high-speed
`packet communication, such as HSDPA and EDCH,
`the
`HARQtechnique is used to increase transmissionefficiency.
`It is expectedthat to realize a data rate of a maximum of 100
`Mbps, LTE will use OFDMas a wireless access technology
`in a 20-MHz bandwidth.
`
`FIG.2 illustrates an uplink timing synchronization
`[0013]
`procedure ina 3GPP LTE system to which OFDMis applied.
`
`[0009] Referring to FIG. 1A, a UE 11indicates a terminal
`for the 3GPP LTE system, and an Evolved Radio Access
`Network (E-RAN) 14, a radio base station device directly
`
`[0014] Referring to FIG.2, a first UE (UE1) is located near
`an E-NB, and a second UE (UE2) is located far from the
`E-NB. T_prol indicates a propagation delay time in wireless
`
`9
`
`

`

`US 2008/0002660 Al
`
`Jan. 3, 2008
`
`transmission up to the UE1, and T_pro2 indicates a propa-
`gation delay time in wireless transmission up to the UE2.
`Because the UE1is located nearer to the E-NB compared to
`the UE2,
`it has less propagation delay time. In FIG. 2,
`T_pro1 is 0.33 us, and T_pro2 is 3.33 us.
`
`In one cell (indicated by a circle in FIG. 2) of the
`[0015]
`E-NB, when the UF1 and the UE2 are powered onor are in
`an idle mode, uplink timing synchronization of the UEF1, the
`UE2and of UEsin the cell, detected by the E-NB, are not
`matched to each other. Reference numeral 201 indicates
`timing synchronization for uplink transmission of an OFDM
`symbol of the UE1, and reference numeral 202 indicates
`timing synchronization for uplink transmission of an OFDM
`symbol of the UE2. When propagation delay times of uplink
`transmission of the UE1 and the UE2 are considered,
`timings at the E-NBreceiving the uplink OFDM symbols
`are shownby reference numerals 211, 212 and 213. Thatis,
`the uplink symbol 201 of the UE1 is received at the E-NB
`with a propagation delay time in the timing 212, and the
`uplink symbol 202 of the UE2 is received at the E-NB with
`a propagation delay time in the timing 213.
`
`Since uplink timing synchronizations for the UE1
`[0016]
`and the UE2 have not been acquired (matched) yet for the
`timings 212 and 213, start timing 211 in which the E-NB
`receives and decodes an uplink OFDM symbol, timing 212
`in which the E-NB receives an OFDM symbol from the
`UE1, and timing 213 in which the E-NBreceives an OFDM
`symbol from the UE2 are different from each other. There-
`fore, the uplink symbols transmitted from the UE1 and the
`UE2serve as interference components to each other, as they
`have no orthogonality, and the E-NB maynot successfully
`decode the uplink symbols 201 and 202 transmitted from the
`UE1and the UE2, due to the interference and the discrep-
`ancy betweenthestart timing 211 and the reception timings
`212 and 213 of uplink symbols.
`
`[0017] Therefore, the E-NB matches uplink symbol recep-
`tion timings of the UE1 and the UE2 through the uplink
`timing synchronization procedure. After completion of the
`uplink timing synchronization procedure,
`the E-NB can
`matchthe start timing 221 in which it receives and decodes
`uplink OFDM symbols, the timing 222 in whichit receives
`an uplink OFDM symbol from the UF1, and the timing 223
`in whichit receives an uplink OFDM symbolfrom the UE2.
`After matching the timings, the E-NB can maintain orthogo-
`nality between the uplink symbols transmitted from the UE1
`and the UE2, and thus can successfully decode the uplink
`symbols 201 and 202 transmitted from the UE1 and the
`UE2.
`
`[0018] FIG. 3 illustrates an example of an uplink timing
`synchronization procedure.
`
`Instep 311, a UE 301 generates a preamble code to
`[0019]
`be used in the uplink timing synchronization procedure. If
`the UE 301 is constructed such that multiple preamble codes
`can be used in the uplink timing synchronization procedure,
`the UE 301 generates one of the multiple preamble codes.
`The ‘preamble code’ is a type of code sequence agreed upon
`between the UE 301 and an E-NB 302, and the UE 301
`transmits the preamble code over the uplink using radio
`resources allocated by the E-NB 302 in step 321 (UL SYNC
`REQ). Upon receipt of the preamble code, the E-NB 302
`calculates a correlation between the preamble code and
`candidate preamble codes available for uplink timing syn-
`
`chronization during a sliding window having a certain
`constant
`interval,
`to find the timing and preamble code
`indicating the highest correlation. In addition, the E-NB 302
`calculates a difference between the then-reception timing
`and the timing in which it should actually have received the
`preamble code, and provides in step 322 the UE 301 with an
`IDentifier ID) of the found preamble code and information
`on the uplink timing difference using a response message
`(UL SYNC RES). In step 331, the UE 301 changes and
`updates the uplink transmission timing using the informa-
`tion on the uplink timing difference, received through the
`response message. From this time one, uplink signaling and
`data transmission is achieved using the changed and updated
`uplink timing.
`
`Steps 341, 342 and 343 indicate a process of
`[0020]
`re-performing the uplink timing synchronization procedure
`in steps 311, 321 and 322 to recheck the changed and
`updated timing, and can be omitted.
`
`[0021] The uplink timing synchronization procedure
`shown in FIG. 3 should be periodically performed because
`the UE in the mobile communication system continuously
`moves, and thus the distance difference between the UE and
`the E-NB may change over time. When the periodic uplink
`timing synchronization procedure is performed,
`the UE
`periodically generates a preamble code used for the uplink
`timing synchronization procedure and transmits the pre-
`amble code to the E-NB over the uplink, and the E-NB
`should find an uplink timing difference by receiving and
`decrypting the periodic uplink preamble code, and provide
`the uplink timing difference information to the UE over the
`downlink. Therefore, overhead of the uplink signaling/
`downlink signaling occurs, causing inefficient use of radio
`resources.
`
`SUMMARY OF THE INVENTION
`
`[0022] An aspect of the present invention is to address at
`least the problems and/or disadvantages and to provide at
`least the advantages described below. Accordingly, an aspect
`of the present invention is to provide a method of maintain-
`ing uplink timing synchronization without uplink transmis-
`sion of a preamble from a UE or without transmission of
`uplink timing difference information from an E-NB to solve
`the inefficient use problem of radio resources, occurring due
`to periodic transmission of uplink signaling and downlink
`signaling during maintenance of the uplink timing synchro-
`nization, and a UE apparatus for the same.
`
`[0023] According to the present invention, there is pro-
`vided a method for maintaining uplink timing sync in a
`mobile communication system. The method includestrans-
`mitting to a Node B an uplink syne request message includ-
`ing a preamble code, receiving from the Node B an uplink
`syne response message in response to the request message,
`adjusting uplink timing according to uplink timing adjust-
`ment information included in the response message, and
`storing the adjusted uplink timing as reference uplink timing
`for uplink signaling or data transmission; after storing the
`reference uplink timing, periodically measuring downlink
`timing, and calculating a difference between the measured
`downlink timing and previously stored reference downlink
`timing, determining the uplink timing using the calculated
`difference of the downlink timing and the reference uplink
`timing, receiving a request message for readjustment of the
`
`10
`
`10
`
`

`

`US 2008/0002660 Al
`
`Jan. 3, 2008
`
`uplink timing from a Node B that has detected discrepancy
`of the uplink timing, readjusting the uplink timing using
`uplink timing adjustment information includedin the uplink
`timing readjustment request message, updating the reference
`uplink timing with the readjusted uplink timing, and storing
`the updated reference uplink timing, and when updating the
`reference uplink timing, updating the last measured down-
`link timing as the reference downlink timing, and storing the
`reference downlink timing.
`
`[0024] According to the present invention, there is pro-
`vided a user equipment apparatus for maintaining uplink
`timing sync. The user equipment apparatus includes a mes-
`sage transceiver for receiving a message including uplink
`timing adjustment information from a Node B, andtrans-
`mitting uplink data and signaling to the Node B according to
`uplink timing, a message decrypter for decrypting a message
`received from the message transceiver to acquire the uplink
`timing adjustment information, a reference timing manager
`for setting reference uplink timing according to the acquired
`uplink timing adjustment information, and setting the ref-
`erence downlink timing according to the downlink timing,
`an uplink timing adjuster for periodically adjusting the
`uplink timing using a difference between the downlink
`timing and the reference downlink timing, and the reference
`uplink timing, a timer for counting a period for which the
`uplink timing is adjusted, and a downlink measurer for
`measuring the downlink timing accordingto the period, and
`providing the measured downlink timing to the uplink
`timing adjuster and the reference timing manager.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0025] The above and other aspects, features and advan-
`tages of the present invention will become more apparent
`from the following detailed description when taken in con-
`junction with the accompanying drawings in which:
`
`[0026] FIGS. 1A and 1Billustrate conventional configu-
`rations of an OFDM mobile communication system to which
`reference will be made by the present invention;
`
`FIG.2 illustrates an uplink timing synchronization
`[0027]
`procedure in an OFDM mobile communication system;
`
`[0028] FIG. 3 illustrates an example of an uplink timing
`synchronization procedure;
`
`an initial UL timing synchronization procedure, the UE sets
`DownLink (DL) timing during corresponding UL transmis-
`sion before DL transmission including UL timing difference
`information from the E-NB, or DL timing during DL trans-
`mission including the UL timing difference information, as
`Reference DL timing, and sets and maintains the then-UL
`timing adjusted using the UL timing difference information
`as Reference UL timing. The UEperiodically acquires DL
`timing through measurement on a DL channel, finds a DL
`timing difference by comparing it with the Reference DL
`timing, and finds the then-UL timing by applying the DL
`timing difference to the Reference UL timing. The period
`can be short, and can be configured by the E-NB.
`
`[0034] When the UL timing has discrepancies due to
`abrupt unstableness of the DL channel, the discrepancy is
`detected by the E-NB and UL timing difference information
`can be signaled to the UE over the DL. Uponreceipt of the
`ULtiming difference information transmitted over the DL,
`the UE changes/updates Reference UL timing to the UL
`timing adjusted using the UL timing difference information,
`and changes/updates Reference DL timing to DL timing
`during corresponding UL transmission before DL transmis-
`sion including the UL timing difference information, or to
`DL timing during DL transmission including the UL timing
`difference information.
`
`To prevent the discrepancy of UL timing due to
`[0035]
`abrupt unstableness of the DL channel,
`the UE finds a
`difference between an average value of DL timing, calcu-
`lated through measurementfor the period, and the Reference
`DL timing, or finds a difference between the DL timing and
`the Reference DL timing through periodic measurement on
`the DL channel. When the difference between the average
`value of DL timing, calculated through measurement on the
`DL channelfor the period, and the Reference DL timing has
`an abnormally large value, it can be disregarded.
`
`[0036] The term ‘UL timing’ used throughout the speci-
`fication, which is the timing in which the UE transmits
`signaling/data over the UL, can be indicated as a timing
`offset (in units of actual time such as us, or in such units as
`slots, symbols, subframes or frames) with respect to a DL
`frame to which the UE has matched a DL sync channel, and
`the ‘DL timing’ indicates DL frame timing acquired through
`a DL syne channel.
`
`FIG. 4 illustrates generally a method offinding UL
`[0037]
`timing according to the present invention, and moreparticu-
`larly a methodoffinding UL timing by applying a difference
`between DL timing and Reference DL timing to Reference
`[0030] FIG.5illustrates an operation of a UE according to
`UL timing.
`the present invention; and
`
`[0029] FIG. 4 illustrates a method of maintaining UL
`timing synchronization in an OFDMsystem according to the
`present invention;
`
`FIG.6 illustrates a UE apparatus according to the
`[0031]
`present invention.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`[0032] Preferred embodiments of the present invention
`will now be described in detail with reference to the annexed
`
`drawings. In the following description, a detailed description
`of known functions and configurations incorporated herein
`has been omitted for the sake of clarity and conciseness.
`
`invention, when a UE acquires
`In the present
`[0033]
`UpLink (UL) timing synchronization with an E-NB through
`
`11
`
`[0038] Referring to FIG.4, steps 411, 421 and 422 indicate
`execution of an initial UL timing synchronization procedure.
`Thatis, in step 411, a UE 401 generates a preamble code to
`be used for a UL timing synchronization procedure. If the
`UE401 is constructed such that multiple preamble codes can
`be used in the UL timing synchronization procedure, the UE
`401 generates one of the multiple preamble codes. The
`“preamble code’ is a type of code sequence agreed upon
`between the UE 401 and an E-NB 402, and the UE 401
`transmits the preamble code over the uplink using radio
`resources allocated by the E-NB 402 in step 421 (UL SYNC
`REQ). Upon receipt of the preamble code, the E-NB 402
`calculates a correlation between the received preamble code
`and candidate preamble codes available for UL timing
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`synchronization during a sliding window having a constant
`interval, to find the timing and preamble code indicating the
`highest correlation. In addition, the E-NB 402 calculates a
`difference between the then-reception timing and the timing
`in whichit should actually have received the preamble code,
`and provides in step 422 the UE 401 with an ID of the
`preamble code and information on the UL timing difference
`using a response message (UL SYNC RES).
`
`Instep 431, the UE 401 adjusts UL timingusing the
`[0039]
`UL timing difference information received through the
`response message, and sets it as Reference UL timing. In
`addition, the UE 401 sets DL timing in step 412 as Reference
`DL timing.
`
`[0040] Here, an operation order of step 431 is subject to
`change. That is, if steps 411, 421 and 422 are re-performed
`in the mannerofsteps 341, 342 and 343 of FIG.3 to recheck
`ULtiming adjusted according to the UL timing difference
`information received in step 422, Reference DL timing is
`reset to the DL timing during the re-performed UL preamble
`code transmission, and Reference UL timingis reset to the
`UL timing adjusted according to the newly received UL
`timing difference information.
`
`[0041] After completion of the UL timing adjustment in
`step 431, the UE 401 performsin step 432 UL signaling/data
`transmission with the adjusted UL timing.
`
`In FIG. 4, for the DL timing measurementof step
`[0042]
`412 for Reference DL timingsetting, although when the UL
`timing difference information was received over the DL in
`step 422, DL timing for the DL at the time (step 421) that the
`UL transmission has occurred before the DL reception is
`measured herein by way of example, the present invention
`does not exclude any other possible time for which the DL
`timing for setting Reference DL timing is measured. For
`example, DL timing for the DLat the time (step 422) that UL
`timing difference information was received over the DL, can
`be set as Reference DL timing.
`
`In steps 441 and 451, the UE 401 measures DL
`[0043]
`timing at each time through measurement for a period T,
`calculates a difference between the measured DL timing and
`the Reference DL timing, and calculates/adjusts the UL
`timing by applying the DL timing difference to the Refer-
`ence UL timing. That is, without signaling exchange with
`the E-NB 402, the UE 401 finds DL timing through periodic
`measurement, finds a timing difference between the DL
`timing and Reference DL timing by comparing the DL
`timing with Reference DL timing, and then finds UL timing
`by applying the timing difference to the Reference UL
`timing.
`
`[0044] When UL timing is discrepant due to abrupt
`unstableness of the DL channel, the E-NB 402 detects the
`discrepancy in step 471, and transmits UL timing difference
`information to the UE 401 using a message in step 481,
`thereby sending a request for readjustment of the UL timing
`to the UE 401. Upon receipt of a UL timing readjustment
`instruction, the UE 401 resets the DL timing for the corre-
`sponding UL transmission time (step 461 in FIG. 4) as
`Reference DL timing, and resets the UL timing adjusted
`using the UL timing difference information received through
`a message in step 481, as Reference UL timing.
`
`period T and the Reference DL timing can be applied to the
`Reference UL timing in steps 441 and 451. In addition, when
`the average value of DL timing measured for the period T is
`used for finding a difference from the Reference DL timing
`as described above, the abnormally great difference can be
`disregarded without application. Even when the DL timing
`measured in steps 411 and 451 of FIG. 4, other than the
`average value of DL timing measured for the period T, is
`used for finding the difference with the Reference DL
`timing, the abnormally great difference can be disregarded
`without application.In this case, the previously acquired UL
`timing can be usedasit is.
`
`FIG.5 illustrates an operation of a UE to which an
`[0046]
`embodimentof the present invention is applied.
`
`[0047] Referring to FIG. 5, in step 501, the UE receives
`UL timing difference information (UL timing adjustment
`info or UL timing advanceinfo) from an E-NB. In step 511,
`the UEsets or updates DL timing during UL transmission as
`Reference DL timing before reception of the UL timing
`difference information of step 501, and stores the DL timing.
`In step 512, the UE adjusts the UL timing using the UL
`timing difference information received in step 501. In step
`513, the UEsets or updates the UL timing adjusted in step
`512 as Reference UL timing, and stores the Reference UL
`timing. In step 521, the UE determines whether a period of
`adjusting UL timing hasarrived.
`
`Ifthe UL timing adjustmentperiod has arrived, the
`[0048]
`UE measures DL timing through measurementin step 531,
`calculates a difference between the measured DL timing and
`the Reference DL timing in step 532, and then adjusts UL
`timing by applying the calculated difference to the Refer-
`ence UL timing in step 533. However, if the adjustment
`period of the UL timing hasnot arrived, the UE maintains
`the last adjusted UL timing in step 541.
`
`[0049] Although not shownin FIG.5, as described above,
`the UE does not exclude any other possible time for which
`it sets Reference DL timingin step 511. For example, the UE
`can set, as Reference DL timing, the DL timing for whichit
`has received UL timing difference information over the DL.
`
`FIG. 6 illustrates a UE apparatus to which an
`[0050]
`embodimentof the present invention is applied.
`
`[0051] Referring to FIG. 6, the UE includes a message
`transceiver 601, a message decrypter 611, a Reference
`UL/DLtiming manager 621, a DL measurer 631, a timer 641
`and a UL timing adjuster 651.
`
`[0052] The message transceiver 601 receives signaling
`including UL timing difference information from an E-NB.
`The message decrypter 611 decrypts a message received
`from the message transceiver 601 to detect UL timing
`difference information, and the UL timing difference infor-
`mation is delivered to the UL timing adjuster 651 via the
`Reference UL/DL timing manager 621. The UL timing
`adjuster 651 adjusts UL timing using the UL timing differ-
`ence information received via the Reference UL/DL timing
`manager 621, and updates the adjusted UL timing as Ref-
`erence UL timing. The updated Reference UL timing is used
`for later setting the timing for UL message transmission via
`the message transceiver 601.
`
`[0045] Although not shown in FIG. 4, a difference
`between an average value of DL timing measured for the
`
`[0053] Upon receipt of the UL timing difference informa-
`tion via the message transceiver 601 and the message
`
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`decrypter 611, the Reference UL/DL timing manager 621
`updates the DL timing measured by the DL measurer 631 as
`Reference DL timing. The DL timing measured by the DL
`measurer 631 is DL timing when the UE transmitted the
`corresponding UL message before it receives a message
`including UL timing difference information. The timer 641
`manages a UL timing update period for matching UL timing
`synchronization, at which period the timer 641 reports
`arrival of the period to the DL measurer 631 and the UL
`timing adjuster 651. The DL measurer 631 acquires the DL
`timing, and the UL timing adjuster 651 calculates a timing
`difference by comparing the acquired DL timing with the
`Reference DL timing stored in the Reference UL/DLtiming
`manager 621, and adjusts UL timing by applying the timing
`difference to the Reference UL timing stored in the Refer-
`ence UL/DL timing manager 621.
`
`[0054] As is apparent from the foregoing description,
`according to the present invention, the UE stores UL timing
`and DL timing for the time at which it has acquired initial
`UL timing synchronization, as Reference UL timing and
`Reference DL timing, respectively, periodically finding DL
`timing, calculating a difference by comparing the DL timing
`with the Reference DL timing, and maintaining UL timing
`by applying the difference to the Reference UL timing. By
`doing so, the numberofsignaling transmissions between the
`UEand the E-NBis reduced, thereby reducing overhead of
`UL/DL signaling and enabling efficient use of radio
`resources.
`
`[0055] While the invention has been shown anddescribed
`with reference to a certain preferred embodimentthereof, it
`will be understood by those skilled in the art that various
`changes in form and details may be madetherein without
`departing from the spirit and scope of the invention as
`defined by the appended claims.
`
`Whatis claimedis:
`
`1. A method for maintaining uplink timing synchroniza-
`tion (sync) in a mobile communication system, comprising:
`
`transmitting to a Node B an uplink syne request message
`including a preamble code;
`
`receiving from the Node B an uplink sync response
`message in response to the request message;
`
`adjusting uplink timing