PCT/EP2009/05 191 1 (81) Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ,
`CA, CH, CN, CO, CR, CU, CZ, DE, DK, DM, DO, DZ,
`EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, HN,
`HR, HU, ID, IL, IN, IS, JP, KE, KG, KM, KN, KP, KR,
`KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD, ME,
`MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO,
`NZ, OM, PG, PH, PL, PT, RO, RS, RU, SC, SD, SE, SG,
`SK, SL, SM, ST, SV, SY, TJ, TM, TN, TR, TT, TZ, UA,
`UG, US, UZ, VC, VN, ZA, ZM, ZW.
`
`(22) International Filing Date:
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`18 February 2009 (18.02.2009)
`
`English
`
`English
`
`(71) Applicant (for all designated States except US): NOKIA
`SIEMENS NETWORKS OY [FIZFI]; Karaportti
`3,
`02610 Espoo (FI).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): HUANG, Min [CN/
`CN]; NSN Building A, 14, Jiu Xian Qiao Road, Beijing,
`100016 (CN). DU, Lei [CN/CN]; NSN Building A, 14,
`Jiu Xian Qiao Road, Chaoyang District, Beijing, 100016
`(CN). TENG, Yong [CN/CN]; Building 11, Bao Sheng
`Li Fang Qing Yuan, Hai Dian District, Beijing, 100192
`(CN).
`
`(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`(43) International Publication Date
`26 August 2010 (26.08.2010)
`
`(51) International Patent Classification:
`H04W 74/08 (2009.01)
`
`(21) International Application Number:
`
`(10) International Publication Number
`WO 2010/094325 Al
`
`(74) Agent: RUUSKANEN,
`Juha-Pekka; PAGE WHITE
`AND FARRER, Bedford House, John Street, London
`Greater London WClN 2BF (GB).
`
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ,
`TM), European (AT, BE, BG, CH, CY, CZ, DE, DK, EE,
`ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV,
`MC, MK, MT, NL, NO, PL, PT, RO, SE, SI, SK, TR),
`OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, ML,
`MR, NE, SN, TD, TG).
`
`(54) Title: CONTROLLING TRANSMISSIONS ON COMPOSITE CARRIERS
`
`[Continued on next page]
`
`provider may
`
`Fig. 1
`
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`WO 2010/094325 AIIMMTIATUNIIU ATMATATUAMAE ITAATA AT
`
`Published:
`
`—__with international search report (Art. 21(3))
`
`IPR2022-00648
`Apple EX1020 Page 2
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`Published:
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`Controlling transmissions on composite carriers
`
`The invention relates to relay a communication system, and more particularly to
`
`controlling transmissions on composite carriers.
`
`A communication system can be seen as a facility that enables communication
`
`sessions between two or more entities such as mobile communication devices
`
`and/or other stations. The communications may comprise,
`
`for example,
`
`communication of data for carrying communications such as voice, electronic
`
`mail (email), text message, multimedia and so on. Users may thus be offered and
`
`provided numerous services via their communication devices. Non-limiting
`
`examples
`
`of
`
`these services
`
`include two-way or multi-way
`
`calls, data
`
`communication or multimedia services or simply an access to a data
`
`communications network system, such as the Internet. User may also be
`
`provided broadcast or multicast content. Non-limiting examples of the content
`
`include downloads,
`
`television and radio programs, videos, advertisements,
`
`various alerts and other information.
`
`A communication system can be provided for example by means of a
`
`communication network and one or more compatible communication devices.
`
`The communication system and associated devices typically operate in
`
`accordance with a given standard or specification which sets out what
`
`the
`
`various entities associated with the system are permitted to do and how that
`
`should be achieved. For example, the standard or specification may define if a
`
`communication device is provided with a circuit switched carrier service or a
`
`packet switched carrier service or both, and how the carriers are configured.
`
`Communication protocols and/or parameters which shah be used for
`
`the
`
`connection are also typically defined. For example,
`
`the manner how the
`
`communication device can access resources provided by the communication
`
`system and how communication shall be implemented between communicating
`
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`

`devices, the elements of the communication network and/or other communication
`
`devices is typically based on predefined communication protocols.
`
`In a wireless communication system at least a part of communications between
`
`at least two stations occurs over a wireless link. Examples of wireless systems
`
`include public land mobile networks (PLMN), satellite based communication
`
`systems and different wireless local networks, for example wireless loca! area
`
`networks (WLAN). The wireless systems can typically be divided into cells, and
`
`are therefore often referred to as cellular systems.
`
`A user can access the communication system by means of an appropriate
`
`communication device. A communication device of a user is often referred to as
`
`user equipment
`
`(UE). A communication device is provided with an appropriate
`
`signal
`
`receiving and transmitting apparatus for enabling communications,
`
`for
`
`example enabling access to a communication network or communications
`
`directly with other users. The communication device may access a carrier
`
`provided by a station, for example a base station of a cell, and transmit and/or
`
`receive communications on the carrier.
`
`A carrier may comprise a composite carrier, i.e. a carrier that
`
`is provided by a
`
`plurality of sub or component carriers. Composite carriers may be provided by
`
`utilising what is known as carrier aggregation.
`
`In carrier aggregation a plurality of
`
`carriers are aggregated to increase bandwidth. Such carriers are known as
`
`aggregated carriers, each aggregated carrier comprising a plurality of component
`
`carriers.
`
`The popularity of communication devices or user equipment (UE) has increased
`
`considerably in the recent years and the number of user devices in active use is
`
`believed to increase even further in the future. Thus the number of users who
`
`may want to access a communication system at substantially the same time is
`
`also
`
`believed
`
`to increase. The
`
`available
`
`bandwidth
`
`provided
`
`by
`
`the
`
`communications systems has also been increased, to provide more capacity to
`
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`

`meet the increased demand. This has resulted in a situation where it is possible
`
`that a large number of user devices perform random access in a system, and
`
`more particularly, a carrier provided by the system.
`
`An example of a modern communication system that is attempting to solve the
`
`problems associated with the increased demands for capacity is an architecture
`
`that
`
`is known as the long-term evolution (LTE) of
`
`the Universal Mobile
`
`Telecommunications System (UMTS) radio-access technology and that is being
`
`standardized by the 3rd Generation Partnership Project
`
`(3GPP). The various
`
`development stages of the 3GPP LTE specifications are referred to as releases.
`
`The aim of the standardization is to achieve a communication system with, inter
`
`alia,
`
`reduced latency, higher user data rates,
`
`improved system capacity and
`
`coverage, and reduced cost for the operator. A further development of the LTE
`
`is referred to as LTE-Advanced. The LTE-Advanced aims to provide further
`
`enhanced services by means of even higher data rates and lower latency with
`
`reduced cost. A feature of the LTE-Advanced is that
`
`it
`
`is capable of providing
`
`aggregated carriers.
`
`In systems where composite or aggregated carriers are available a problem is
`
`that the communication devices accessing the system are limited into the original
`
`component carrier they are assigned to. For example,
`
`the design of random
`
`access procedure in the medium access control
`
`(MAC) layer in LTE-A may
`
`become problematic. A n approach inherited directly from the earlier versions of
`
`the 3GPP,
`
`in particular from Release 8 of the LTE,
`
`is to execute the whole
`
`random access process from preamble transmission to contention resolution
`
`within a single component carrier. However, as the number of communication
`
`devices that want to access the system is increased at the same time as the
`
`bandwidth provided in LTE-A is also increased, there is possibility that a large
`
`number of communication devices perform random access in one carrier.
`
`Because of this, and the nature of the carrier assignment by the random access
`
`procedure, preamble collisions can become more likely. Also, use of the same
`
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`carrier for the subsequent communications may result in longer access delays
`
`and heavier load in the uplink channel resources.
`
`It
`
`is noted that
`
`the above discussed issues are not
`
`limited to any particular
`
`communication environment, but may occur in any appropriate communication
`
`system where composite carriers may be provided.
`
`Embodiments of the invention aim to address one or several of the above issues.
`
`In accordance with an embodiment
`
`there is provided a method for controlling
`
`transmissions on a composite carrier comprising at least two component carriers,
`
`comprising receiving a message from a device attempting to transmit on the
`
`composite carrier,
`
`including in a response an indication of at
`
`least one
`
`component carrier to be used by the device for a subsequent transmission, and
`
`sending the response to the device.
`
`In accordance with another embodiment
`
`there is provided a method for
`
`transmitting by a device on a composite carrier comprising at
`
`least
`
`two
`
`component carriers, comprising receiving a message from a provider of
`
`the
`
`composite carrier, determining based on the message at least one component
`
`carrier to be used by the device for at least one subsequent transmission, and
`
`transmitting on the determined at least one component carrier.
`
`In accordance with another embodiment there is provided a control apparatus for
`
`a communication system capable of providing a composite carrier comprising at
`
`least
`
`two component carriers. The control apparatus is configured to control
`
`transmissions on the composite carrier based on information regarding an
`
`attempt by at least one device to transmit on the composite carrier, to include in a
`
`message to the at
`
`least one device an indication of at
`
`least one component
`
`carrier
`
`to be used by the at
`
`least one device for at
`
`least one subsequent
`
`transmission, and to send the message to the at least one device.
`
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`In accordance with another embodiment there is provided a control apparatus for
`
`a communication device adapted for communications on a composite carrier
`
`comprising at least two component carriers. The control apparatus is configured
`
`to control transmissions based on a message received from a provider of the
`
`composite carrier, wherein the control apparatus is configured to determine
`
`based on the message at
`
`least one component carrier to be used by the
`
`communication device for at least one subsequent transmission and to instruct
`
`transmission on the determined at least one component carrier.
`
`In accordance with a more detailed embodiment,
`
`the indication is included in a
`
`random access response. The index of at least one component carrier may be
`
`included in a response message. An indication of a component carrier for a
`
`subsequent preamble retransmission or a scheduled transmission may be
`
`included.
`
`Loading on component carriers may be distributed by sending different
`
`indications in response to different received messages and/or messages from
`
`different devices.
`
`A n indication associated with a component carrier may be included in a message
`
`periodically in the time domain or dynamically in response to load or another
`
`predefined event.
`
`The composite carrier and the component
`
`carriers provide may carrier
`
`aggregation in accordance with the specifications by the third generation
`
`partnership project.
`
`In accordance with an embodiment a response is received from the provider of
`
`the composite carrier within a predefined period. At least one component carrier
`
`to be used for the at
`
`least one subsequent
`
`transmission can be determined
`
`based on the response. The determining may comprise determining if
`
`the
`
`received message includes an indication of at least one component carrier to be
`
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`

`

`used by the device for at least one subsequent transmission on the composite
`
`carrier. The determining may comprise determining if
`
`the received message
`
`contains a backoff
`
`indicator. The determining may comprise determining if the
`
`received message contains information regarding at least one component carrier
`
`to be used by the device for at
`
`least one subsequent
`
`transmission on the
`
`composite carrier.
`
`In the absence of such information, a default component
`
`carrier may be determined or a component carrier may be selected in random.
`
`In accordance with an embodiment a message for controlling communications on
`
`a composite carrier comprising at least two component carriers is provided. The
`
`message comprises a medium access control protocol data unit configured to
`
`carry in at least one subheader thereof an indicator of a component carrier to be
`
`used by a communication device for at least one subsequent transmission.
`
`A computer program comprising program code means adapted to perform the
`
`method may also be provided.
`
`Various other aspects and further embodiments are also described in the
`
`following detailed description and in the attached claims.
`
`The invention will now be described in further detail, by way of example only, with
`
`reference to the following examples and accompanying drawings, in which;
`
`Figure 1 shows a n example of a communication system in which the
`
`embodiments of the invention may be implemented;
`
`Figure 2 shows an example of a communication device;
`
`Figure 3 shows an example of a controller for a base station;
`
`Figures 4 and 5 are flowcharts illustrating certain embodiments;
`
`Figure 6 shows a signalling flow for a contention based random access
`
`procedure;
`Figure 7 shows a signalling flow for a non-contention based random
`
`access procedure;
`
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`Figure 8 shows an example for the timing of random access preamble and
`
`random access response windows;
`Figure 9 shows an example for operation of a communication device in a
`
`random access response window without carrier aggregation;
`
`Figure 10 shows an example of carrier aggregation;
`
`Figure 11 shows an example of a protocol data unit consisting of a header
`
`and random access responses;
`
`Figure 12 shows an example for operation of a communication device in a
`
`random access response window with carrier aggregation; and
`
`Figures 13 and 14 show two examples for the use of a component carrier
`
`indication.
`
`In the following certain exemplifying embodiments are explained with reference
`
`to wireless or mobile communication systems serving mobile communication
`
`devices. Before explaining in detail
`
`the certain exemplifying embodiments,
`
`certain general principles of a wireless communication system and mobile
`
`communication devices are briefly explained with reference to Figures 1 and 2 to
`
`assist in understanding the technology underlying the described examples.
`
`A communication device can be used for accessing various services and/or
`
`applications provided via a communication system In wireless or mobile
`
`communication systems the access is provided via an access interface between
`
`mobile communication devices 1 and an appropriate wireless access system 10.
`
`A mobile device 1 can typically access wirelessly a communication system via at
`
`least one base station 12 or similar wireless transmitter and/or receiver node of
`
`the access system. A base station site typically provides one or more cells of a
`
`cellular system.
`
`In the figure 1 example the base station 12 is configured to
`
`provide a cell, but could provide,
`
`for example,
`
`three sectors, each sector
`
`providing a cell. Each mobile device 1 and base station may have one or more
`
`radio channels open at the same time and may receive signals from more than
`
`one source.
`
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`A base station is typically controlled by at least one appropriate controller so as
`
`to enable operation thereof and management of mobile communication devices
`
`in communication with the base station. The control entity can be interconnected
`
`with other control entities. In Figure 1 the controller is shown to be provided by
`
`block 13 . The controller is typically provided with memory capacity and at least
`
`one data processor 14.
`
`It shall be understood that the control functions may be
`
`distributed between a plurality of controller units.
`
`In the Figure 1 example the base station node 12 is connected to a data network
`
`20 via an appropriate gateway 15 . A gateway function between the access
`
`system and another network such as a packet data network may be provided by
`
`means of any appropriate gateway node,
`
`for example a packet data gateway
`
`and/or an access gateway. A communication system may thus be provided by
`
`one or more interconnect networks and the elements thereof, and one or more
`
`gateway nodes may be provided for interconnecting various networks.
`
`A communication device can be used for accessing various services and/or
`
`applications. The communication devices can access the communication system
`
`based on various access techniques, such as code division multiple access
`
`(CDMA), or wideband CDMA (WCDMA). The latter
`
`technique is used by
`
`communication systems based on the third Generation Partnership Project
`
`(3GPP) specifications. Other examples include time division multiple access
`
`(TDMA),
`
`frequency division multiple access (FDMA), space division multiple
`
`access (SDMA) and so on. A non-limiting example of mobile architectures where
`
`the herein described principles may be applied is known as the Evolved
`
`Universal Terrestrial Radio Access Network (E-UTRAN). Non-limiting examples
`
`of appropriate access nodes are a base station of a cellular system, for example
`
`what
`
`is known as NodeB or enhanced NodeB (eNB) in the vocabulary of the
`
`3GPP specifications. The eNBs may provide E-UTRAN features such as user
`
`plane Radio Link Control/Medium Access Control/Physical
`
`layer protocol
`
`(RLC/MAC/PHY) and control plane Radio Resource Control
`
`(RRC) protocol
`
`terminations towards mobile communication devices. Other examples include
`
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`base stations of systems that are based on technologies such as wireless local
`
`area network (WLV\N) and/or WiMax (Worldwide Interoperability for Microwave
`
`Access).
`
`Figure 2 shows a schematic, partially sectioned view of a communication device
`
`1 that can be used for communication on a carrier 11 comprising a plurality of
`
`component carriers, for example with at ieast one base station. An appropriate
`
`mobile communication device may be provided by any device capable of sending
`
`and receiving radio signals. Non-limiting examples include a mobile station (MS),
`
`a portable computer provided with a wireless interface card or other wireless
`
`interface facility, personal data assistant
`
`(PDA) provided with wireless
`
`communication capabilities, or any combinations of these or the like.
`
`A mobile communication device may be used for voice and video calls,
`
`for
`
`accessing service applications provided via a data network. The mobile device 1
`
`may receive signals via appropriate apparatus for
`
`receiving and transmitting
`
`radio signals. In Figure 2 a transceiver is designated schematically by block 7 .
`
`The transceiver may be provided for example by means of a radio part and
`
`associated antenna arrangement. The antenna arrangement may be arranged
`
`internally or externally to the mobile device. A mobile device is also typically
`
`provided with at least one data processing entity 3 , at least one memory 4 and
`
`other possible components 9 for use in tasks it is designed to perform. The data
`
`processing, storage and other entities can be provided on an appropriate circuit
`
`board and/or in chipsets. This feature is denoted by reference 6 . The user may
`
`control the operation of the mobile device by means of a suitable user interface
`
`such as key pad 2 , voice commands,
`
`touch sensitive screen or pad,
`
`combinations thereof or the like. A display 5 , a speaker and a microphone are
`
`also typically provided. Furthermore, a mobile device may comprise appropriate
`
`connectors (either wired or wireless)
`
`to other devices and/or for connecting
`
`external accessories, for example hands-free equipment, thereto.
`
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`Figure 3 shows an example of a controller apparatus 30 comprising at least one
`
`memory 3 1, at least one data processing unit 32, 33 and an input/output interface
`
`34. The controller 30 may be configured to execute an appropriate software code
`
`to provide the control functions as explained below in more detail. The controller
`
`30 can be provided for controlling one single composite carrier or a number of
`
`composite carriers provided by a base station in accordance of the principles of
`
`the below explained embodiments.
`
`A n embodiment for controlling transmissions on a composite carrier comprising
`
`at
`
`least
`
`two carriers is shown in the flowchart of Figure 4 . A controller,
`
`for
`
`example the controller 30 of Figure 3 , of a provider of the composite carrier
`
`receives a message at 100 from a device attempting to access the composite
`
`carrier. The message can be, for example, a request for random access. The
`
`provider can be, for example, a base station or another communication device.
`
`The controller 30 of the provider is configured to control the composite carrier or
`
`carriers that shall be used by the device for subsequent transmissions. Thus at
`
`102 the controller includes in a response an indication of at least one component
`
`carrier of a composite carrier to be used by the device for at least a subsequent
`
`transmission on the composite carrier. The selected component carrier may be
`
`the same as used at 100, or the controller may determine that at least different
`
`component carrier than what was used for the sending of the message at 100
`
`shall be used. The response with this information of the at least one component
`
`carrier
`
`is then sent
`
`to the device at 104. The device may then transmit
`
`accordingly on the composite carrier, and the transmission is received by the
`
`provider of the composite carrier at 106.
`
`Another embodiment
`
`for controlling transmissions on a composite carrier
`
`comprising at least two carriers is shown in the flowchart of Figure 5 . A controller,
`
`for example controller 3 of the mobile communication device of Figure 2 , receives
`
`a message at 202 from a provider of a composite carrier the device is attempting
`
`to access. The message can be,
`
`for example, a response to a request
`
`for
`
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`

`random access sent by the device to the provider at 200. The controller may
`
`then determine at 204, based on the message it
`
`received, at
`
`least one
`
`component carrier that is to be used by the device for at least one subsequent
`
`transmission on the composite carrier. After the determination of the component
`
`carrier the device can transmit on the determined at least one component carrier
`
`at step 206.
`
`The determining may comprise, for example determining if the response includes
`
`an indication of at least one component carrier that shall be used by the device
`
`for at least one subsequent transmission on the composite carrier. The controller
`
`may also determine if the response contains a backoff indicator subheader or the
`
`like, and then decide which component carrier to use accordingly. A backoff
`
`indicator, or alike indicator, is typically used for indicating the configuration when
`
`the preamble retransmission after a certain time delay is to be executed followed
`
`by a random access failure.
`
`In accordance with a possibility the controller can determine if the response
`
`contains information regarding at least one component carrier to be used by the
`
`device for at least one subsequent transmission on the composite carrier. If it is
`
`determined that such information cannot be found, the controller can decide to
`
`use a default component carrier, for example select a carrier based on index that
`
`is derived based on the index of the component carrier used at step 200 and/or
`
`at step 202, or select a component carrier in random. The component carrier
`
`index can be derived e.g. by increasing or decreasing the value of the index of
`
`the component carrier used at 200 by a predefined integer. Another appropriate
`
`function may also be used to achieve a desired distribution of component carrier
`
`assignments.
`
`More detailed examples of operation in accordance with certain embodiments will
`
`now be explained below with reference to transmissions in access systems such
`
`as those based on the 3GPP Long Term Evolution (LTE). In the LTE releases up
`
`to release 8 only one carrier may be provided for use for communications
`
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`

`between a base station,
`
`for example an enhanced Node B (eNB), and a
`
`communication device. In accordance with the 3GPP specifications the random
`
`access procedure can take two distinct
`
`forms,
`
`i.e. contention based and non-
`
`contention based access. Contention based access is typically applicable to all
`
`random access events. Non-contention based access that is typically applicable
`
`to only handover and downlink (DL) data arrival when uplink (UL) synchronisation
`
`status is non-synchronised. A contention based random access (RA) process
`
`typically includes four steps, as shown for example in Figure 6 . Figure 7 , in turn
`
`shows the three typical steps for non-contention based random access. Each of
`
`the steps corresponds to a message either from the communication device (UE)
`
`to the base station (eNB), or from the base station (eNB) to the user device (UE).
`
`A n illustration of the timing of random access preamble and random access
`
`response window is shown in Figure 8 . The preamble message 4 1 of Figures 6
`
`and 7 from the communication device UE to the eNB is typically called random
`
`access (RA) preamble. The following message from the eNB to the user
`
`communication device (UE)
`
`is called random access response,
`
`this being
`
`denoted as message 42 in Figures 6 , 7 and 8 . Once the random access
`
`preamble,
`
`i.e. message 4 1, is transmitted,
`
`the communication device UE shall
`
`monitor Physical Downlink Control Channel
`
`(PDCCH)
`
`in the following
`
`Transmission Time Interval (TTI) window for random access response (RAR), i.e.
`
`for message 42. A concept of random access response window (RAR window) is
`
`defined as a subframe window when the communication device UE monitors the
`
`PDCCH for a possible random access response after transmission of a random
`
`access preamble. The communication device UE would stop monitoring after
`
`successful reception of a random access response corresponding to the random
`
`access preamble transmission or when random access response window
`
`expires. For example,
`
`in the current 3GPP specifications,
`
`the length of
`
`the
`
`window can be set from 2 ms to 10 ms, and the offset can be 2 ms.
`
`If the reception of the random access response is successful, a first Scheduled
`
`Transmission, or message 43,
`
`is sent from the device UE to the station eNB
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`according to uplink grant contained in the random access response. A message
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`called Contention Resolution, shown as message 44 in Figure 6 , can also be
`
`sent from the eNB to the UE if the eNB accepts the random access requirement
`
`of this UE.
`
`A typical behaviour of a communication device (UE) during random access
`
`response window according to the current 3GPP LTE specifications is illustrated
`
`in the flowchart of Figure 9 . As shown, after a communication device enters a
`
`random access window at 90, it can receive a response at 92. The response can
`
`include a backoff indicator subheader. Presence of this is determined at 95, and
`
`the process
`
`continues such that
`
`the backoff parameter
`
`is
`
`set
`
`in the
`
`communication device either in accordance with the response at 95 or to 0 at 96.
`
`It
`
`is also determined at 97 if the random access response (RAR) contains a
`
`random access (RA) preamble identifier corresponding to the transmitted random
`
`access preamble. !f yes, the random access process is considered successful at
`
`98. If no, the random access attempt is considered unsuccessful at 99.
`
`Current proposals for carrier aggregation in LTE-A systems will now be explained
`
`briefly.
`
`In carrier aggregation two or more carriers, referred to as component
`
`carriers are aggregated such that a communication device may simultaneously
`
`receive one or multiple component carriers depending on its capabilities. For
`
`example,
`
`an LTE-Advanced mobile communication device with reception
`
`capability beyond 20 MHz can simultaneously receive on multiple component
`
`carriers. The carrier aggregation is at present considered for LTE-Advanced to
`
`support downlink transmission bandwidths larger than 20 MHz, but
`
`the use
`
`thereof is naturally not restricted by this. A requirement that has been proposed
`
`for LTE-A is that
`
`it should operate in spectrum allocations of different sizes
`
`including wider spectrum allocations than those of the current Release 8 LTE,
`
`e.g. up to 100MHz, to achieve the peak data rate of 100Mbit/s for high mobility
`
`and 1 Gbit/s for low mobility.
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`Figure 10 gives an example of the carrier aggregation. In the example a plurality
`
`Rel8 bandwidth "chunks", or component carriers, are combined together to form
`M x Rel8 bandwidth (BW). For example, given M ~ 5 , one would have 5 x 20MHz
`
`= 100MHz. A s mentioned above, Release 8 compatible communication devices
`
`can receive/transmit only on one component carrier. However, LTE-Advanced
`
`communication may also receive/transmit on multiple component carriers
`
`simultaneously, and thus reach higher bandwidths.
`
`If carrier aggregation is employed the control channel(s) can be designed in
`
`various manners. For example,
`
`in LTE-A a Physical Downlink Control Channel
`
`(PDCCH) can be provided as a separate PDCCH per assigned component
`
`carrier. Alternatively, only one global PDCCH can be provided for signalling the
`
`allocations for all component carriers jointly. In the latter alternative, a component
`
`carrier containing the PDCCH can be called "primary component carrier" and the
`
`other component carriers without
`
`the PDCCH can be called "secondary
`
`component carriers.
`
`In accordance with a proposal a physical random access channel
`
`(PRACH)
`
`resource can be provided in each component carrier of an aggregated carrier.
`
`This can be so to provide more chance for a communication device to access
`
`and larger frequency diversity, and hence to reduce collision probability.
`
`The design of random access procedure in the medium access control (MAC)
`
`layer in LTE-A may become problematic since the entire process from preamble
`
`transmission (i.e. message 4 1 of Figure 6) to contention resolution (message 44
`
`of Figure 6) may need to be executed within a single component carrier, thus
`
`increasing the possibility that a large number of communication devices perform
`
`random access in one carrier. If these communication devices are restricted into
`
`the original component carrier constantly regardless of preamble retransmission
`
`and contention resolution,
`
`they may experience larger preamble collision
`
`probability, longer access delay, and heavier load in uplink channel resource. On
`
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`the other hand, multiple component carriers can be advantageously used to
`
`improve performance of a random access procedure.
`
`In the following more detailed example a physical
`
`random access channel
`
`(PRACH)
`
`is configured in each component carrier in an advanced long term
`
`evolution (LTE-A) system. The random access response,
`
`i.e. message 42 of
`
`Figure 6 , can be modified to carry information about the component carriers.
`
`In accordance with an embodiment a new field or information element can be
`
`added into the random access response message 42 in Figures 6 and 7 , see
`
`information element "Component Carrier ID". The information can be used to
`
`indicate a component carrier where the following procedures are to be executed.
`
`For example,
`
`this information can then be used to indicate the index of
`
`component carrier where