(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2010/0260140 A1
`
` Zhu (43) Pub. Date: Oct. 14, 2010
`
`
`US 20100260140A1
`
`(54) APPARATUS, METHOD AND COMPUTER
`figgflsligfigiligggijzciabmgggiccnss
`HANDOVER
`
`75
`
`(
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`:
`
`Zh B
`“’ cum“
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`CN
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`Y
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`“an
`) men or
`Correspondence Address;
`Nokia, Inc.
`:02} C?;e7°5tg;‘; D518“, MS 2'5'520
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`
`(73) Assignee:
`
`NOKIA CORPORATION, Espoo
`(FD
`
`(21) APP1~ N05
`
`12/443531
`
`(22) PCT Filed:
`
`Sep. 21, 2007
`
`(86) PCT No.:
`
`PCT/IB07/02761
`
`§371 (c)(1)S
`(2), (4) Date:
`
`May 12, 2010
`
`Related US. Application Data
`(60) Provisional application No. 60/847,764, filed on Sep.
`27’ 2006'
`Foreign Application Priority Data
`
`(30)
`
`................................... 60/847764
`(US)
`Sep. 27, 2006
`Publication Classification
`
`(51)
`
`Int Cl
`(2009.01)
`H04W 4/00
`(52) use. ........................................................ 370/331
`
`ABSTRACT
`(57)
`A method is provided including sending a source Node-B a
`target Node-B cell-specific unique identifier for a user equip-
`ment to be handed over to the target Node-B, sending the
`source Node-B a predetermined access preamble sequence
`for the user equipment to be handed over to the target Node-B,
`and in response to receiving the predetermined access pre-
`amble sequence from the user equipment, sending the user
`equipment handover related information in association with
`the cell-specific unique identifier for handing over to the
`target Node-B.
`
`
`
`
`
`ACCESS PREAMBLE (+MESSAGE)
`
`IMING INFORMATION
`
`a
`— U
`M U
`“ T
`
`PLINK DATA RESOURCE ALLOCATION
`
`
`
`
`L DATA TRANSMISSION
`
`APPLE 1027
`
`APPLE 1027
`
`

`

`Patent Application Publication
`
`Oct. 14, 2010 Sheet 1 0f 6
`
`US 2010/0260140 A1
`
`l
`
`I
`
`l
`
`
`
`
`
`
`
`
`
`
`
`ACCESS PREAMBLE (+MESSAGE)
`
`TIMING INFORMATION
`
`‘
`
`UPLINK DATA RESOURCE ALLOCATION
`
`UL DATA TRANSMISSION
`
`FIG.1A
`
`ACCESS PREAMBLE
`
`TIMING INFORMATION AND SR RESOURCE ALLOCATION
`
`SCHEDULING REQUEST
`
`UPLINK DATA RESOURCE ALLOCATION
`
`UPLINK DATA TRANSMISSION
`
`FIG.1 B
`
`
`
`
`
`I
`
`
`
`
`
`
`
`
`
`

`

`Patent Application Publication
`
`Oct. 14, 2010 Sheet 2 0f 6
`
`US 2010/0260140 A1
`
`_J
`
` 14C
`
`
`2
`Lu
`2 S?-
`F‘
`
`FIG.2
`
`o E
`
`l—
`E
`2
`m5
`
`0Q
`
`<<
`
`—,_
`
`ELL:2
`
`1.NEI'WORK
`
`/
`
`SERVING
`
`

`

`Patent Application Publication
`
`Oct. 14, 2010 Sheet 3 0f 6
`
`US 2010/0260140 A1
`
`1O
`
`T—NODE B
`
`'
`
`12
`
`12
`
`S—NODE B
`
`
`
`
`
`1.HAND OVER TRIGGERED T-NODE B
`
`2.CONTEXT TRANSFER
`
`3.HAND OVER START
`
`
`
`4.PREAMBLE
`
`5.ACKNOWLEDGEMENT WITH THE FREQUENCY
`AND SIGNATURE INDEX OF THE PREAMBLE
`
`-TA, POWER ADJUSTMENT, T—C-RNTI
`
`
`
`6.UL—SCH ALLOCATION USING T—C—RNTI
`
`
`
`7.UL TRANSMISSION ON SCH
`
`—C—RNT| + RANDOM ACCESS CAUSE
`
`+ BUFFER STATUS + DL CQI
`
`
`
`10.CONTEXT TRANSFER SUCCESSFUL
`
`
`
`8a.UL—SCH ALLOCATION USING T—C—RNTI
`IF NODE—B FAILS IN RECEPTION
`
`0R
`
`8b.UL—SCH ALLOCATION USING C—RNTI
`
`IF NODE—B SUCCEEDS IN RECEPTION
`
`9.TRANSMISSION ON SCH
`
`
`
`
`
`
`
`
`FIG.3
`
`

`

`Patent Application Publication
`
`Oct. 14, 2010 Sheet 4 0f 6
`
`US 2010/0260140 A1
`
`
`
`1O
`
`T-NODE B
`
`'
`
`12
`
`12
`
`S—NODE B
`
`1.HAND OVER TRIGGERED T—NODE B
`
`2.CONTEXT TRANSFER
`
`3.HAND OVER START-C-RNTI
`
`
`IN T-NODE—B + PREAMBLE IN T-NODE-B
`
`
`-TA, POWER ADJUSTMENT
`
`7.CONTEXT TRANSFER SUCCESSFUL
`
`4.PREAMBLE IN T—NODE—B
`
`5.ACKNOWLEDGEMENT WITH THE FREQUENCY
`AND SIGNATURE INDEX OF THE PREAMBLE
`
`6.TRANSM|SSION ON SCH
`
`FIG.4
`
`

`

`Patent Application Publication
`
`Oct. 14, 2010 Sheet 5 0f 6
`
`US 2010/0260140 A1
`
`RECEIVING A HO REQUEST AT THE
`SOURCE NODE—B FROM A UE
`
`5A
`
`
`
`
`
`
`
`OPERATING THE SOURCE NODE—B
`TO ASSIGN THE UE A TARGET
`
`NODE—B CELL—SPECIFIC UNIQUE
`IDENTIFIER, AND A PREDETERMINED
`ACCESS PREAMBLE SEQUENCE,
`IN
`CONJUNCTION WITH A HO START
`MESSAGE FOR HANDING OVER THE
`
`
`
`
`
`
`
`
`
`UE TO THE TARGET NODE—B
`
`5B
`
`FIG.5
`
`SENDING A SOURCE NODE—B A TARGET
`
`NODE-B CELL-SPECIFIC UNIQUE
`IDENTIFIER FOR A UE TO BE HANDED
`
`OVER TO THE TARGET NODE—B
`
`SENDING A SOURCE NODE—B A
`
`PREDETERMINED ACCESS PREAMBLE
`
`SEQUENCE THAT WILL BE ASSIGNED BY
`THE SOURCE NODE—B TO THE UE
`
`IN RESPONSE, TO RECEIVING THE
`PREDETERMINED ACCESS PREAMBLE
`SEQUENCE FROM THE UE, SENDING
`THE UE HO—RELATED INFORMATION,
`IN ASSOCIATION WITH THE
`CELL—SPECIFIC UNIQUE IDENTIFIER,
`FOR HANDING OVER TO THE TARGET
`
`
`
`”00H
`
`FIG.6
`
`

`

`Patent Application Publication
`
`Oct. 14, 2010 Sheet 6 0f 6
`
`US 2010/0260140 A1
`
`SENDING A MESSAGE TO A SOURCE
`
`NODE-B TO INITIATE A HO TO A
`
`TARGET NODE—B
`
`
`
`RECEIVING FROM THE SOURCE
`
`NODE—B A TARGET NODE—B CELL-
`
`SPECIFIC RADIO NETWORK TEMPORARY
`IDENTIFIER AND A PREDEI'ERMINED
`ACCESS PREAMBLE SEQUENCE,
`IN
`CONJUNCTION WITH A HO START
`
`MESSAGE
`
`TRANSMITTING THE PREDEI'ERMINED
`ACCESS PREAMBLE TO THE TARGET
`NODE—B ON A RANDOM ACCESS
`
`CHANNEL
`
`FIG.7
`
`

`

`US 2010/0260140 A1
`
`Oct. 14, 2010
`
`APPARATUS, METHOD AND COMPUTER
`PROGRAM PRODUCT PROVIDING
`NON-SYNCHRONIZED RANDOM ACCESS
`HANDOVER
`
`TECHNICAL FIELD
`
`[0001] The exemplary and non-limiting embodiments of
`this invention relate generally to wireless communication
`systems, methods, devices and computer program products
`and, more specifically, relate to techniques for handing off a
`mobile device from one fixed wireless network node to
`another.
`
`BACKGROUND
`
`[0002] Certain abbreviations that may be found in the
`description and/or in the Figures are herewith defined as
`follows:
`
`3GPP third generation partnership project
`[0003]
`[0004] UTRAN universal terrestrial radio access network
`[0005] EUTRAN evolved UTRAN
`[0006] OFDM orthogonal frequency division multiplex
`[0007] Node-B base station
`[0008]
`eNB EUTRAN Node B
`[0009] C-RNTI cell-specific radio network temporary
`identifier
`
`T—C-RNTI temporary cell-specific radio network
`[0010]
`temporary identifier
`[0011]
`S-Node-B source node B
`[0012]
`T—Node-B target node B
`[0013] TDD time division duplex
`[0014]
`FDD frequency division duplex
`[0015] TA timing advance
`[0016] UE user equipment
`[0017]
`SC-FDMA single carrier, frequency division mul-
`tiple access
`[0018] LTE long term evolution
`[0019] UL uplink (UE to Node-B)
`[0020] DL downlink (Node-B to UE)
`[0021] H0 handover
`[0022] LCR low chip rate
`[0023] LCR-TDD LCR-time division duplex
`[0024] RU resource unit
`[0025] RACH random access channel
`[0026] MAC medium access control
`[0027]
`SCH shared channel
`[0028] A proposed communication system known as
`evolved UTRAN (E-UTRAN, also referred to as UTRAN-
`LTE or as E-UTRA) is under discussion within the 3 GPP. A
`working assumption is that the DL access technique will be
`OFDM, and the UL access technique will be SC-FDMA.
`[0029] A random access procedure has been discussed for
`the E-UTRA system. For example, according to Rl-06l651,
`3GPP TR25.814, V1.5.0,
`the random access procedure
`includes synchronized random access and non-synchronized
`random access. The non-synchronized random access proce-
`dure would be mainly used when the UL has not been syn-
`chronized, or after synchronization between the UE and the
`Node-B has been lost. This applies to both initial access and
`H0.
`
`[0030] As is stated in Section 9.1.2.113 of 3GPP TR25.
`814, “Non-synchronized random access procedure”, prior to
`attempting a non-synchronized random access, the UE shall
`synchronize to the downlink transmission.
`
`[0031] Two approaches for the random access procedure
`are considered.
`
`[0032] Approach #1: FIG. 9.1.2.1.l.3-l (shown herein as
`FIG. 1A) outlines this approach, where the Node B responds
`to the non-synchronized random access attempt with timing
`information to adjust the uplink transmission timing and an
`assignment of uplink resources to be used for transmission of
`data or control signaling (possibly including any message
`payload (e.g. UE ID) not included in the preamble) using the
`shared data channel. It may be noted that the timing informa-
`tion can also be combined with the uplink data resource
`allocation. Furthermore, the uplink data resource allocation
`may be implicitly indicated by associating a reserved time
`frequency region with a preamble sequence.
`[0033] Approach #2: FIG. 9.1.2.1.13-2 (shown herein as
`FIG. 1B) outlines this approach, where the Node B responds
`to the non-synchronized random access attempt preamble
`with timing information and resource allocation for transmis-
`sion of scheduling request (and possibly any additional con-
`trol signaling or data). The UE then sends the scheduling
`request at the assigned time-frequency resource using the
`shared data channel or physical random access channel (for
`co-existing LCR-TDD based frame structure). The Node B
`adjusts the resource allocation according to the scheduling
`request from the UE.
`[0034] Reference may also be had to Rl-06l901, Non-
`synchronized random access procedure, 27-30 Jun. 2006,
`Nokia, and to Rl-061893, Preamble-based shared channel ID
`assignment during initial access, 27-30 Jun. 2006, IPWire-
`less,
`for describing proposed non-synchronized random
`access procedures.
`
`SUMMARY
`
`In an exemplary aspect of the invention, there is a
`[0035]
`method comprising sending a source Node-B a target Node-B
`cell-specific unique identifier for a user equipment to be
`handed over to the Target Node-B, sending the source Node-B
`a predetermined access preamble sequence for the user equip-
`ment to be handed over to the target Node-B, and in response
`to receiving the predetermined access preamble sequence
`from the user equipment, sending the user equipment han-
`dover related information in association with the cell-specific
`unique identifier for handing over to the Target Node-B.
`[0036]
`In another exemplary aspect of the invention, there
`is a computer readable medium encoded with a computer
`program executable by a processor to perform actions com-
`prising sending a source Node-B a target Node-B cell-spe-
`cific unique identifier for a user equipment to be handed over
`to the Target Node-B, sending the source Node-B a predeter-
`mined access preamble sequence for the user equipment to be
`handed over to the target Node-B, and in response to receiving
`the predetermined access preamble sequence from the user
`equipment, sending the user equipment handover related
`information in association with the cell-specific unique iden-
`tifier for handing over to the Target Node-B.
`[0037]
`In another exemplary aspect of the invention, there
`is an apparatus comprising a wireless transmitter, a wireless
`receiver, a handover control unit coupled to an interface and
`configurable to send to a source Node-B a target Node-B
`cell-specific unique identifier for a user equipment to be
`handed over to the target Node-B and to also send the source
`Node-B a predetermined access preamble sequence for the
`user equipment to be handed over to the target Node-B, and
`the handover control unit coupled to said wireless receiver
`
`

`

`US 2010/0260140 A1
`
`Oct. 14, 2010
`
`and configurable to send to the user equipment Via said wire-
`less transmitter, in response to receiving the predetermined
`access preamble sequence from the user equipment, handover
`related information in association with the cell-specific
`unique identifier for handing over to the target Node-B.
`[0038]
`In still another exemplary aspect of the invention,
`there is an apparatus comprising means for sending a source
`Node-B a target Node-B cell-specific unique identifier for a
`user equipment to be handed over to the target Node-B and for
`sending the source Node-B a predetermined access preamble
`sequence for the user equipment to be handed over to the
`target Node-B, and means for sending the user equipment
`handover related information in response to receiving the
`predetermined access preamble sequence from the user
`equipment, in association with the cell-specific unique iden-
`tifier for handing over to the target Node-B.
`[0039]
`In yet another exemplary aspect of the invention,
`there is a method ofperforming a handover comprising send-
`ing a message to a source Node-B to initiate a handover to a
`target Node-B, receiving from the source Node-B a target
`Node-B cell-specific radio network temporary identifier and a
`predetermined access preamble sequence,
`in conjunction
`with a HO start message, and sending the predetermined
`access preamble sequence to the target Node-B on a random
`access channel.
`
`In still another exemplary aspect of the invention,
`[0040]
`there is an apparatus comprising a transceiver coupled to a
`processor configurable to send a message to a source Node-B
`to initiate a handover to a target Node-B, the transceiver
`configurable to receive from the source Node-B a target
`Node-B cell-specific radio network temporary identifier and a
`predetermined access preamble sequence,
`in conjunction
`with a HO start message, and the transceiver further config-
`urable to send the predetermined access preamble sequence
`to the target Node-B on a random access channel.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0041] The foregoing and other aspects of embodiments of
`this invention are made more evident
`in the following
`Detailed Description, when read in conjunction with the
`attached Drawing Figures, wherein:
`[0042]
`FIGS. 1A and 1B reproduce FIG. 9.1.2.1.l.3-l and
`FIG. 9.1.2.1 .1 .3-2, respectively, from 3GPP TR25.814,V1.5.
`0.;
`FIG. 2 shows a simplified block diagram of various
`[0043]
`electronic devices that are suitable for use in practicing the
`exemplary embodiments of this invention;
`[0044]
`FIG. 3 is a message flow diagram that illustrates a
`result of directly applying a two-step non-synchronized ran-
`dom access procedure to a HO situation;
`[0045]
`FIG. 4 is a message flow diagram that illustrates a
`result of applying a one-step non-synchronized random
`access procedure to the HO situation in accordance with
`exemplary embodiments of this invention;
`[0046]
`FIG. 5 is a logic flow diagram that is illustrative of a
`method, and the operation ofa computer program product, for
`the Source Node-B shown in FIG. 2;
`[0047]
`FIG. 6 is a logic flow diagram that is illustrative of a
`method, and the operation ofa computer program product, for
`the Target Node-B shown in FIG. 2; and
`
`FIG. 7 is a logic flow diagram that is illustrative of a
`[0048]
`method, and the operation ofa computer program product, for
`the UE shown in FIG. 2.
`
`DETAILED DESCRIPTION
`
`[0049] By way of introduction, R1 -06 l 901, Non-synchro-
`nized random access procedure, Nokia, 27-30 Jun. 2006,
`discusses a non-synchronized random access procedure in
`accordance with 3GPP TR25.814. A bare preamble with no
`attached message part is transmitted first. The preamble sig-
`nature carries no information on the requested resources. This
`information is included to the message send on the SCH,
`allocated after the Node-B observes the preamble. A two-step
`procedure is proposed, wherein the network assigns to the
`observed preamble a temporary identifier that is used for
`allocating UL resources for the transmissions following the
`preamble. In addition, the preamble collisions are resolved in
`an early phase of the random access procedure.
`[0050] As is further stated, the non-synchronized random
`access procedure must be used if the UE TA may be invalid.
`If UE has C-RNTI, the purpose of the non-synchronized
`random access can be: (1) resource request, (2) handover, and
`(3) network initiated adjustment of TA. The causes (2) and (3)
`could also be handled using a scheduled resource with a large
`guard time. If the UE does not have C-RNTI, the possible
`causes are a move to LTE-ACTIVE state, and an update ofthe
`location area. In these cases, UEs are identified with TMSI,
`IMSI, or IMEI.
`[0051] According to the proposal in Rl-06l 901, when the
`Node-B observes a preamble, it assigns a temporary C-RNTI
`(T—C-RNTI) for the preamble’s time, frequency and signature
`index and sends that in the acknowledgement ofthe preamble.
`T-C-RNTI is of the same length as C-RNTI, and only a small
`fraction of, the total number of C-RNTIs are needed for the
`temporary use. The UL-SCH resources are allocated with
`T-C-RNTI for the first transmission(s) after the preamble,
`which means that these allocations can be handled like any
`other allocations. That is beneficial considering the signaling
`of all the UL SCH allocations. With T-C-RNTI, Node-B can
`also order retransmissions of the first message(s).
`[0052] The T-C-RNTI is said can be released after the UE
`has sent its already existing C-RNTI, or when a permanent
`C-RNTI is assigned for the UE in the cell association proce-
`dure (T—C-RNTI could also become the permanent C-RNTI in
`this phase), or when the random access procedure fails and a
`sufficiently long time has passed since T-C-RNTI was used
`for allocation.
`
`Instead of an explicit assignment of T-C-RNTI, also
`[0053]
`considered is a system where the preamble’s time, frequency
`and signature would map to a T-C-RNTI in a manner that the
`UE also knows. This is said would save transmission of T-C-
`
`RNTI in the preamble acknowledgment, but may consume an
`unnecessarily large part ofthe C-RNTI space. In this method,
`a C-RNTI would be reserved for every possible preamble
`frequency and signature index for a period of several tens of
`ins (equal to the duration of cell association procedure), as
`compared to the case where the Node-B does the selection,
`where T-C-RNTIs are reserved only for the observed pre-
`ambles.
`
`[0054] Also of potential interest is Rl-061893, Preamble-
`based shared channel ID assignment during initial access,
`IPWireless, 27-30 Jun. 2006, where it is acknowledged that
`before data transmission over UL-SCH may occur, the UE
`must be assigned a C-RNTI (or an ID serving an equivalent
`
`

`

`US 2010/0260140 A1
`
`Oct. 14, 2010
`
`purpose%.g. MAC ID) to identify the user on the SCH. The
`user’s shared channel ID is referred to as the “MAC-ID”, and
`two possibilities are considered: Explicit MAC-ID assign-
`ment and Implicit MAC-ID assignment.
`[0055]
`In the explicit MAC-ID assignment case the net-
`work explicitly assigns a MAC-ID. The MAC-ID is commu-
`nicated to the UE either Via a common channel (using higher
`layer IDs for user addressing), or Via special channels linked
`to the random access procedure and used to carry responses to
`the initial access request (termed RACH-associated channels
`in Rl-061893).
`time/frequency
`instances,
`in both
`[0056] However,
`resources need to be set aside, either for the common channels
`or for the RACH-associated signaling channels. This may be
`slow or non-responsive to RACH load. Furthermore, initial
`access delay is increased due to the need for the MAC-ID
`assignment prior to the commencement of shared channel
`communications.
`
`For the case ofthe implicit MAC-ID assignment the
`[0057]
`initial MAC-ID is implicitly assigned at a very early stage of
`the connection by means of linking the selected access pre-
`amble with one of a set of MAC-IDs reserved in the cell for
`initial access.
`
`In contrast to the explicit approach, by adopting the
`[0058]
`implicit MAC-ID assignment it is said that the resource grant
`messages in initial access procedure may take the same form
`as any other UL grant message, there is no need for an explicit
`intermediate MAC-ID assignment prior to the use of the
`UL-SCH (reduced initial access latency), the need for spe-
`cially-defined physical/transport channels is avoided (re-
`duced system complexity), and the need for a reservation of
`time/frequency resources for RACH-associated or common
`downlink channels is avoided (improved resource efficiency
`in the presence of varying RACH load).
`[0059]
`It is stated that an initial implicit assignment of
`MAC-ID may be followed at a later stage by an explicit
`MAC-ID assignment, once the UE is authenticated and
`admission is granted.
`is said to be preferred in
`[0060]
`In the approach that
`R1 -061893, by selecting a preamble and transmitting this on
`a particular RACH channel,
`the UE has effectively also
`selected a MAC-ID from a pool ofreserved MAC-IDs and has
`conveyed this selection to the eNode-B. There is therefore a
`set of MAC-IDs (which constitutes a sub-set of the cells total
`MAC-ID space) that is linked to initial access and the MAC-
`IDs contained within it are reserved by the eNode-B specifi-
`cally for this purpose.
`[0061] After using the MAC-ID, which is implicitly asso-
`ciated with the selected preamble, for initial shared channel
`communications,
`it is envisaged that the Node-B would,
`within a short period of time, explicitly assign a more perma-
`nent MAC-ID to the UE such that the MAC-ID originally
`selected can be released and used by other UEs for initial
`access. Thus, a UE would occupy an initial access MAC-ID
`only for a short period of time until the eNode-B reassigns a
`more permanent MAC-ID. This is termed here the temporary
`ID lifespan. During this period of time, it is necessary to
`prevent other UEs from selecting the same temporary MAC-
`ID. This is achieved by sub-dividing the reserved MAC-ID
`region into orthogonal sets, each set being applicable for one
`ofthe “L” available random access instances that exist within
`
`the temporary ID lifespan.
`
`[0062] Both of these proposals may thus be considered to
`employ some type of temporary identity that is assumed by
`the UE during the non-synchronized random access proce-
`dure.
`
`[0063] The exemplary embodiments of this invention pro-
`vide an enhanced non-synchronized random access proce-
`dure for use during at least a HO case that does not require the
`UE to assume a temporary identity, at least during the HO
`procedure.
`[0064] Reference is made to FIG. 2 for illustrating a sim-
`plified block diagram of various electronic devices that are
`suitable for use in practicing the exemplary embodiments of
`this invention. In FIG. 2 a wireless network 1 is adapted for
`communication with a UE 10 via at least one Node B (base
`station) 12 (also referred to herein as an eNode B 12). The
`network 1 may include a network control element 14 coupled
`to the eNode B 12 via a data link 13. 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 bidirectional wireless communications
`with the eNode B 12, which also includes a DP 12A, a MEM
`12B that stores a PROG 12C, and a suitable RF transceiver
`12D.
`
`[0065] The eNode B 12 is typically coupled via the data
`path 13 to the network control element 14 that also includes at
`least one DP 14A and a MEM 14B storing an associated
`PROG 14C. At least one of the PROGs 10C and 12C is
`
`assumed to include program instructions that, when executed
`by the associated DP, enable the electronic device to operate
`in accordance with the exemplary embodiments ofthis inven-
`tion, as will be discussed below in greater detail.
`[0066]
`Shown for completeness in FIG. 1 is at least one
`second eNode B, referred to as 12'. During a HO event the
`eNode B 12 may be considered the Source eNode B, i.e., the
`eNode B to which the UE 10 is currently connected and
`communicating in the associated serving cell, and the eNode
`B 12' may be considered the Target eNode B, i.e., the eNode
`B to which the UE 10 is to be connected and communicating
`with in the target cell after the HO procedure is completed.
`Note that in practice the serving cell and the target cell with at
`least partially overlap one another.
`[0067] Each eNodeB 12, 12' can be assumed to include a
`handover control function or unit (HCU 12E) that operates in
`accordance with the exemplary embodiments of this inven-
`tion, as described in detail below. The HCU 12E can be
`implemented in hardware, software or a combination ofhard-
`ware and software. At any given time the HCU 12E of a
`particular eNodeB can function as a target, or as a source, or
`simultaneously as a target and a source, depending on the
`needs of the various UEs 10 serviced by the particular eNo-
`deB. In general, the eNodeBs 12, 12' can communicate with
`one another via an interface unit 12F over an interface 15. The
`
`HCU 12E interface unit 12F can be an E-UTRAN system
`compatible interface.
`[0068] Reference may be had, for example, to 3GPPTS
`36.300, Technical Specification Group Radio Access Net-
`work; Evolved Universal Terrestrial Radio Acces s (E-UTRA)
`and Evolved Universal Terrestrial Radio Access Network
`
`(E-UTRAN; Overall description; Stage 2 (Release 8) for
`describing the overall architecture and interfaces. For
`example, and referring to FIG. 4 of 3GPP TS 36.300, the
`interface 15 can be the X2 interface, and the link 13 can be
`implemented as the SI interface between eNodeBs and the
`NCE.
`
`

`

`US 2010/0260140 A1
`
`Oct. 14, 2010
`
`In general, the various embodiments of the UE 10
`[0069]
`can include, but are not limited to, cellular phones, personal
`digital assistants (PDAs) having wireless communication
`capabilities, portable computers having wireless communi-
`cation capabilities, image capture devices such as digital
`cameras having wireless communication capabilities, gam-
`ing devices having wireless communication capabilities,
`music storage and playback appliances having wireless com-
`munication capabilities, Internet appliances permitting wire-
`less Intemet access and browsing, as well as portable units or
`terminals that incorporate combinations of such functions.
`[0070] The exemplary embodiments of this invention may
`be implemented by computer software executable by the DP
`12A of the eNode Bs 12 and 12' in cooperation with the DP
`10A of the UE 10, or by hardware, or by a combination of
`software and hardware.
`
`[0071] The MEMs 10B, 12B and 14B may be of any type
`suitable to the local technical environment and may be imple-
`mented 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 ofgeneral purpose
`computers, special purpose computers, microprocessors,
`digital signal processors (DSPs) and processors based on a
`multi-core processor architecture, as non-limiting examples.
`[0072] Describing now the exemplary embodiments of this
`invention in even further detail, it is noted that use of the
`two-step procedure is preferred for non-synchronized ran-
`dom access. It is further noted that thus far the various pro-
`posed solutions to the non-synchronized random access pro-
`cedure have assumed its use in the initial random access case.
`
`[0073] However, the inventor has determined that, com-
`pared with the initial non—synchronized access, HO-related
`access has several differences which may be leveraged to
`increase the performance, as compared with that of directly
`applying the two-step initial access approach to the HO case.
`The exemplary embodiments of this invention thus provide a
`random access procedure that is particularly useful during
`HO, but should not be construed as being explicitly limited
`for use to only the HO case.
`[0074] As was discussed above, in order to resolve a ran-
`dom access collision during an early stage, and make the UE
`10 addressable in the SCH directly after being detected, the
`two-step procedure in the above referenced R1 -06l901 has
`been proposed. The basic approach is to reserve a T-C-RNTI
`pool from the entire C-RNTI pool, to map the non-synchro-
`nized parameters to a T-C-RNTI and to then use the T-C-
`RNTI to address the UE 10 after detecting its preamble. The
`first DL message sent by the Node-B 12 over DL-SCH would
`be used to allocate to the UE 10 a permanent C-RNTI. Further
`communication between the Node-B 12 and the UE 10 would
`
`then use the allocated C-RNTI, enabling the T-C-RNTI to be
`released back to the T-C-RNTI pool.
`[0075] By applying this proposed non-synchronized ran-
`dom access procedure to the HO case, the two step non-
`synchronized random access procedure for H0 would oper-
`ate as shown in FIG. 3. Note in particular the message flows
`labeled 5, 6, 7, 8a and 8b. The T-C-RNTI is assigned to the UE
`10 by the target Node-B 12', along with the TA and power
`adjustment parameters, in message flow 5, and is used to
`make the UL SCH transmission (message 7) before the UE 10
`is assigned the C-RNTI in message 8b.
`
`[0076] Compared with the initial non-synchronized ran-
`dom access case, there are several differences when consid-
`ering HO non-synchronized random access. For example, the
`timing and preamble sequence of the access burst may be
`made known to the target Node-B 12' before it is sent from the
`UE 10. Further, a schedule request may not be needed. Fur-
`ther still, there need not be a transition period where UE is
`addressable through T-C-RNTI.
`[0077] Considering at least the above differences, and in
`accordance with the exemplary embodiments of this inven-
`tion, an enhanced and improved one step non-synchronized
`random access procedure for use in the HO case is shown in
`FIG. 4. Note that in FIG. 4 the S-Node-B 12 assigns the UE
`10, in response to the HO trigger (message 1), a C-RNTI in
`the HO start message 3, and also assigns it a HO-specific
`preamble sequence for use by the UE 10 when sending the
`preamble to the T-Node-B 12' in message 4.
`[0078] There are several important features of note which
`are further emphasized for the method shown in FIG. 4.
`[0079]
`First, the preamble sequence space used by the UE
`10 may be divided into two groups: one for initial non-syn-
`chronized random access and the other for H0 non-synchro-
`nized random access. The dividing of sequence space for
`initial non-synchronized random access and H0 may be
`based on, for example, a load estimation of the two different
`random access traffic flows, and may be cell specific. Alter-
`natively, a new preamble sequence space may be defined
`strictly for H0 preambles. This HO-specific preamble is the
`one used during message 4 in FIG. 4, and is the one assigned
`for use by the S-Node-B 12 as part ofmessage 3.
`[0080]
`Second, it is noted that detection of the initial non-
`synchronized random access preamble is blind, and the
`Node-B detector will always detect all possible preambles in
`this group.
`[0081] Third, detection of the HO non-synchronized ran-
`dom access preamble is need-based. That is, the T-Node-B 12'
`preamble detector should have a priori knowledge result, a
`lower threshold may be used to increase the detection prob-
`ability.
`Fourth, there is no time during which the UE 10
`[0082]
`would be addressed by the T-Node-B 12' by a T-C-RNTI.
`Instead, the UE 10 is directly addressable by C-RNTI allo-
`cated as part of message 3 from the S-Node-B 12.
`[0083]
`Further, there is no need to schedule a RU for send-
`ing a resource request from the UE 10, as this information can
`be transferred through a protocol context from the source
`Node-B 12 to the target Node-B 12'.
`[0084] There are a number of advantages that can be real-
`ized by the use of the exemplary embodiments of this inven-
`tion. For example, there is a reduction in the complexity ofthe
`non-synchronized random access procedure for the HO case.
`Further, the detection of the HO preamble sent from the UE
`10 is need-based, and its parameters are pre-known to target
`Node-B 12'. In addition, no false alarms are generated by the
`use of the HO-specific non-synchronized random access pre-
`amble, and a lower threshold can be applied to increase the
`detection probability. Further,
`there is no transition time
`period during which the newly-handed over UE 10 is addres-
`sable through a C-T-RNTI, thus enabling the execution of a
`one step HO non-synchronized random access procedure.
`Additionally, it can be noted by comparing FIG. 3 to FIG. 4
`the one step technique of FIG. 4 provides a more efficient use
`of the bandwidth and radio resources.
`
`

`

`US 2010/0260140 A1
`
`Oct. 14, 2010
`
`FIG. 5 is a logic flow diagram that is illustrative of a
`[0085]
`method, and the operation ofa computer program product, for
`the Source Node-B 12 shown in FIG. 2. The method com-
`
`prises: receiving a HO request at the Source Node-B from a
`UE (Block 5A); and,
`in response, operating the Source
`Node-B to assign the UE a Target Node-B cell-specific unique
`identifier, and a predetermined access preamble sequence, in
`conjunction with a HO start message for handing over the UE
`to the Target Node-B (Block 5B). The Target Node-B cell-
`specific unique identifier is comprised of a Target Node-B
`cell-specific radio network temporary identifier, and the pre-
`determined access preamble sequence is one known to the
`Target Node-B to be associated with the UE to be handed
`over. In an exemplary embodiment of the method the cell-
`specific radio network temporary identifier and the predeter-
`mined access preamble sequence are provided to the Source
`Node-B from the Target Node-B during a context transfer
`(message 2 in FIG. 4). Note that in a case where all sequences
`reserved for H0 non-synchronous random access are cur-
`rently allocated, the two-step procedure may be used as a fall
`back procedure.
`[0086]
`FIG. 6 is a logic flow diagram that is illustrative of a
`method, and the operation ofa computer program product, for
`the Target Node-B 12' shown in FIG. 2. The method com-
`prises: sending a Source Node-B