(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2008/0002660 A1
`
` Jeong et al. (43) Pub. Date: Jan. 3, 2008
`
`
`US 20080002660Al
`
`(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) ....................................... 56417/2006
`
`(75)
`
`Inventors: Kyeong-In Jeong, Hwaseong-si (KR);
`Ju_H0 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) App]. No.:
`
`11/766,498
`
`Publication Classification
`
`(51)
`
`Int. Cl'
`(200601)
`H04] 3/06
`(52) US. Cl.
`.............................................................. 370/350
`
`ABSTRACT
`(57)
`.
`.
`.
`.
`.
`.
`.
`.
`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 maintenance of the uplink timing
`synchronization, and a UE apparatus for the same.
`
`
` SELECT/GENERATE PREAMBLE
`CODE TO BE USED IN UL TIMING
`SYNCH PROCEDURE
`
`
`UL SYNC RES (Dre-amble code Id.
`
`
`UL timing adjustment info, etc) (422)
`
`I. STORE DL TI
`ING OF 412 AS
`
`
`REFERENCE IL TIMING
`
`2. ADJUST UL T MING BASED ON
`
`RECEIVED U TIMING
`ADJUSTMEN INFO
`
`3. STORE ADJU -TED UL TIMING AS
`
`REFERENCE L TIMING
`
`
`
`
`
`
`UL SIGNALING/DATA
`
`PERIOD T
`
`441
`
`UL SIGNALING/DATA
`
`>
`
`
`
`
` AONVdBHOSIGONIWIIIRBIBVHEIGISNOO
`
`
`
`
`482
`
`UL SIGNALING/DATA
`
`ING OF 461 AS
`I. STORE DL TI
`REFERENCE IL TIMING
`2. ADJUST UL lMING BASED ON
`
`RECEIVED Ul TIMING
`ADJUSTMEN INFO
`
`
`3. STORE ADJUTED UL TIMING AS
`REFERENCE L TIMING
`
`
`
`
`
`Ill?)03103130
`
`1
`
`SAMSUNG 1005
`
`SAMSUNG 1005
`
`1
`
`

`

`Patent Application Publication
`
`Jan. 3, 2008 Sheet 1 of 7
`
`US 2008/0002660 A1
`
`16
`
`
`
`FIG. 1A
`
`(PRIOR ART)
`
`2
`
`

`

`Patent Application Publication
`
`Jan. 3, 2008 Sheet 2 of 7
`
`US 2008/0002660 A1
`
`114
`
`IP Network
`
`
`
`
`
`
`' Fast Scheduling
`' HARQ
`
`- ARQ
`- AMC
`
`FIG. 1 B
`
`(PRIOR ART)
`
`3
`
`

`

`Patent Application Publication
`
`Jan. 3, 2008 Sheet 3 of 7
`
`US 2008/0002660 A1
`
`T_pro 1=0.33us
`
`T.pro 2=3.33us
`
` UL@UE#1
`UL@UE#2 Not maintain orthogonality
`
`
`between UE#1 and UE#2
`
`213
`
`(PRIOR ART)
`
`4
`
`

`

`Patent Application Publication
`
`Jan. 3, 2008 Sheet 4 of 7
`
`US 2008/0002660 A1
`
`301
`
`302
`
`GENERATE PREAMBLE CODE TO BE
`USED IN UPLINK TIMING
`
`SYNCH PROCEDURE
`
`UL SYNC FIEQ (pre-amble code) (321)
`
`UL SYNC RES (pre—amble code id.
`UL timing adjustment Info. etc) (322)
`
`
`
`CHANGE/UPDATE UL TIMING
`BASED ON RECEIVED UL TIMING
`
`ADJUSTMENT INFO
`
`f' —————————————————————— 'I
`
`
`
`
`
`
`
`
`
`UL SYNC REQ (pre-amble code) (342)
`
`
`
`
`SELECT/GENERATE PREAMBLE
`I
`CODE TO BE USED IN UL TIMING lr—341
`SYNCH PROCEDURE
`
`UL SYNC RES (pre-amble code id.
`UL timing adjustment info. etc) (343)
`
`UL SIGNALING/DATA
`
`FIG.3
`
`(PRIOR ART)
`
`I I
`
`.
`
`5
`
`

`

`Patent Application Publication
`
`Jan. 3, 2008 Sheet 5 of 7
`
`US 2008/0002660 A1
`
`IMEI
`
`Em
`
`SELECT/GENERATE PREAMBLE
`CODE TO BE USED IN UL TIMING
`SYNCH PROCEDURE
`
`411
`
`412 é UL SYNC REQ (Dre-amble code) (421)
`UL SYNC RES (pre-amble code id.
`UL timing adjustment info, etc) (422)
`
`
` 1. STORE DL TI
`ING OF 412 AS
`REFERENCE IL TIMING
`
`
`2. ADJUST UL T MING BASED ON
`
`RECEIVED U TIMING
`
`ADJUSTMEN INFO
`
`UL SIGNALING/DATA
`
`451
`
`UL SIGNALING/DATA
`
`
`
`
`
`
`'
`
`:
`Z0
`20
`
`632
`O 2
`o
`A2190
`
`UJITI
`-I>-
`028%;
`v—i
`m0?
`m r—
`Ugm
`2C
`Cr-
`_<
`
`482
`
`6
`
`

`

`Patent Application Publication
`
`Jan. 3, 2008 Sheet 6 of 7
`
`US 2008/0002660 A1
`
`RECEIVE UL TIMING ADJUSTMENT INFO
`
`501
`
`UPDATE AND STORE DL TIMING DURING UL
`
`TRANSMISSION BEFORE RECEPTION
`501 AS REFERENCE DL TIMING
`
`511
`
`ADJUST UL TIMING BASED ON UL TIMING
`ADJUSTMENT INFO RECEIVED IN 501
`
`512
`
`UPDATE AND STORE UL TIMING ADJUSTED IN
`512 AS REFERENCE UL TIMIN
`
`13
`
`5
`
`541
`
`52'
`
`
` PERIOD ARRIVED?
`
`N0
`
`MAINTAIN LAST ADJUSTED
`UL TIMING (UL TIMING
`ADJUSTED IN 512 CR 533)
`
`YES
`
`MEASURE DL TIMING
`
`531
`
`CALCULATE TIMING DIFFERENCE
`BETWEEN DL TIMING MEASURED IN
`531 AND REFERENCE DL TIMING
`
`ADJUST UL TIMING BY APPLYING DL TIMING
`DIFFERENCE CALCULATED IN 532 TO
`REFERENCE UL TIMING
`
`532
`
`533
`
`END
`
`FIGS
`
`7
`
`

`

`Patent Application Publication
`
`Jan. 3, 2008 Sheet 7 of 7
`
`US 2008/0002660 A1
`
`631
`
`DL
`
`MEASURER
`
`REFERENCE
`
`
`UL/DL TIMING
`
`MANAGER
`
`
`
`UL TIMING
`
`ADJUSTER
`
`
`
` E-NB
`
`
`MESSAGE
`
`DECRYPTER
`
`601
`
`MESSAGE
`
`TRANSCEIVER
`
`FIG.6
`
`8
`
`

`

`US 2008/0002660 A1
`
`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 be classi-
`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
`CDM scheme basically uses codes, it tends to suffer from a
`lack of resources due to a limit of orthogonal code resources.
`Accordingly, an OFDM scheme has emerged as an altema-
`tive to the CDM scheme.
`
`[0006] The OFDM scheme is 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 frequency efficiency, 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 scheme is now under discussion in 3rd Genera-
`tion Partnership Project (3GPP) as the next generation
`mobile communication system that will replace Universal
`%obile 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 terminal in the exist-
`ing 3GPP system serves as a Node B for managing cells, 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 manner of 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 gateway for 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 GGSN follow the 3GPP standard, 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. AUE 101, or
`a terminal, accesses an IP network by the E-RAN 110. The
`E-NBs 120 to 128 correspond to the existing Node Bs in the
`UMTS system, 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,
`because all user traffics, 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
`HARQ technique is used to increase transmission efficiency.
`It is expected that to realize a data rate of a maximum of 100
`Mbps, LTE will use OFDM as a wireless access technology
`in a 20-MHz bandwidth.
`
`FIG. 2 illustrates an uplink timing synchronization
`[0013]
`procedure in a 3GPP LTE system to which OFDM is applied.
`
`[0009] Referring to FIG. 1A, a UE 11 indicates 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 (UEZ) is located far from the
`E-NB. T_prol indicates a propagation delay time in wireless
`
`9
`
`

`

`US 2008/0002660 A1
`
`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 UE1 is located nearer to the E-NB compared to
`the UE2,
`it has less propagation delay time. In FIG. 2,
`T_prol 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 UE1 and the UE2 are powered on or are in
`an idle mode, uplink timing synchronization of the UE1, the
`UE2 and of UEs in 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-NB receiving the uplink OFDM symbols
`are shown by reference numerals 211, 212 and 213. That is,
`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-NB receives an OFDM
`symbol from the UE2 are different from each other. There-
`fore, the uplink symbols transmitted from the UE1 and the
`UE2 serve as interference components to each other, as they
`have no orthogonality, and the E-NB may not successfully
`decode the uplink symbols 201 and 202 transmitted from the
`UE1 and the UE2, due to the interference and the discrep-
`ancy between the start 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
`match the start timing 221 in which it receives and decodes
`uplink OFDM symbols, the timing 222 in which it receives
`an uplink OFDM symbol from the UE1, and the timing 223
`in which it receives an uplink OFDM symbol from 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.
`
`In step 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 includes trans-
`mitting to a Node B an uplink sync request message includ-
`ing a preamble code, receiving from the Node B an uplink
`sync 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 A1
`
`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 included in 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, and trans-
`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 according to 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 1B illustrate conventional configu-
`rations of an OFDM mobile communication system to which
`reference will be made by the present invention;
`
`[0027] FIG. 2 illustrates an uplink timing synchronization
`procedure in an OFDM mobile communication system;
`
`[0028] FIG. 3 illustrates an example of an uplink timing
`synchronization procedure;
`
`[0029] FIG. 4 illustrates a method of maintaining UL
`timing synchronization in an OFDM system according to the
`present invention;
`
`[0030] FIG. 5 illustrates an operation of a UE according to
`the present invention; and
`
`[0031] FIG. 6 illustrates a UE apparatus according to the
`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
`
`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 UE periodically 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. Upon receipt of the
`UL timing 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 measurement for 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 channel for 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 sync channel.
`
`FIG. 4 illustrates generally a method of finding UL
`[0037]
`timing according to the present invention, and more particu-
`larly a method of finding UL timing by applying a difference
`between DL timing and Reference DL timing to Reference
`UL timing.
`
`[0038] Referring to FIG. 4, steps 411, 421 and 422 indicate
`execution of an initial UL timing synchronization procedure.
`That is, in step 411, a UE 401 generates a preamble code to
`be used for a UL timing synchronization procedure. If the
`UE 401 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 which it 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).
`
`In step 431, the UE 401 adjusts UL timing using 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 manner of steps 341, 342 and 343 ofFIG. 3 to recheck
`UL timing 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 timing is 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 performs in step 432 UL signaling/data
`transmission with the adjusted UL timing.
`
`In FIG. 4, for the DL timing measurement of step
`[0042]
`412 for Reference DL timing setting, 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 DL at 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 used as it is.
`
`FIG. 5 illustrates an operation of a UE to which an
`[0046]
`embodiment of 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 advance info) from an E-NB. In step 511,
`the UE sets 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 UE sets 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 has arrived.
`
`If the UL timing adjustment period has arrived, the
`[0048]
`UE measures DL timing through measurement in 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 has not arrived, the UE maintains
`the last adjusted UL timing in step 541.
`
`[0049] Although not shown in FIG. 5, as described above,
`the UE does not exclude any other possible time for which
`it sets Reference DL timing in step 511. For example, the UE
`can set, as Reference DL timing, the DL timing for which it
`has received UL timing difference information over the DL.
`
`FIG. 6 illustrates a UE apparatus to which an
`[0050]
`embodiment of the present invention is applied.
`
`[0051] Referring to FIG. 6, the UE includes a message
`transceiver 601, a message decrypter 611, a Reference
`UL/DL timing 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/DL timing
`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 number of signaling transmissions between the
`UE and the E-NB is reduced, thereby reducing overhead of
`UL/DL signaling