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`FOR{J
`Radio Access For Third TT
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`TESLA, INC.
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`CAVA BSN
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`x
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`MCT Cam BUTTS
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`Third EditionA,
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`Ex.1015 / Page 1 of 8
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`

`

`Copyright © 2004
`
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`A catalogue record for this book is available from the British Library
`
`ISBN 10: 0-470-87096-6 (HB)
`
`ISBN 13: 978-0-470-87096-9 (HB)
`
`Typeset in 10/12pt Times by Thomson Press (India) Limited, New Delhi.
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`
`Cor
`
`Preface
`
`Acknowl
`
`Abbrevh
`
`1 Introd
`
`Harri He
`1.1 w
`Ai
`1.2
`Sc
`1.3
`Di
`1.4
`C<
`1.5
`Referenc,
`
`2 UMT5
`
`2.3
`
`2.4
`
`Harri He
`2.1
`In
`2.2
`Pe
`2 ..
`2. :
`Pe
`2 ..
`2 ..
`2 ..
`2 ..
`C<
`2.·
`2.•
`2.·
`2.·
`Bl
`IP
`
`2.5
`2.6
`
`

`

`for UMTS
`
`Physical Layer
`
`131
`
`Jpen loop
`1e Primary
`rminals to
`earch.
`
`trries two
`he Paging
`e different
`t least one
`,m exist in
`be able to
`wever, for
`minals are
`Secondary
`
`:ording to
`1eters, but
`rate. The
`s with the
`ll carrying
`terleaving
`: convolu-
`
`1er layer 1
`
`I when no
`1als.
`
`when it is
`ita rate. In
`•n.
`
`when an
`. purposes
`
`he paging
`1el, called
`s together
`full power
`obviously
`t has been
`
`ll be used
`i is higher
`
`for common channels in general , as neither Primary nor Secondary CCPCH can use fast
`power control. Also, since they are often sent with full power to reach the cell edge, reducing
`the required transmission power level improves downlink system capacity.
`
`6.5.5 Random Access Channel (RACH) for Signalling Transmission
`
`The Random Access Channel (RACH) is typically used for signalling purposes, to register
`the terminal after power-on to the network or to perform location update after moving from
`one location area to another or to initiate a call. The structure of the physical RACH for
`signalling purposes is the same as when using the RACH for user data transmission, as
`described in connection with the user data transmission. With signalling use the major
`difference is that the data rate needs to be kept relatively low, otherwise the range achievable
`with RACH signalling starts to limit the system coverage. This is more critical the lower the
`data rates used as a basis for network coverage planning. The detailed RACH procedure will
`be covered in connection with the physical layer procedures.
`The RACH that can be used for initial access has a relatively low payload size, since it
`needs to be usable by all terminals. The ability to support 16 kbps data rate on RACH is a
`mandatory requirement for all terminals regardless of what kind of services they provide.
`
`6.5.6 Acquisition Indicator Channel (A/CH)
`
`In connection with the Random Access Channel, the Acquisition Indicator Channel (AICH)
`is used to indicate from the base station the reception of the random access channel signature
`sequence. The AICH uses an identical signature sequence as the RACH on one of the
`downlink channelisation codes of the base station to which the RACH belongs. Once the
`base station has detected the preamble with the random access attempt, then the same
`signature sequence that has been used on the preamble will be echoed back on AICH. As the
`structure of AICH is the same as with the RACH preamble, it also uses a spreading factor of
`256 and 16 symbols as the signature sequence. There can be up to 16 signatures, acknowl(cid:173)
`edged on the AICH at the same time. Both signature sets can be used with AICH. The
`procedure with AICH and RACH is described in the physical layer procedures section.
`For the detection of AICH the terminal needs to obtain the phase reference from the
`common pilot channel. The AICH also needs to be heard by all terminals and needs to be
`sent typically at high power level without power control.
`The AICH is not visible to higher layers but is controlled directly by the physical layer in
`the base station, as operation via a radio network controller would make the response time
`too slow for a RACH preamble. There are only a few timeslots to detect the RACH preamble
`and to transmit the response to the terminal on AICH. The AICH access slot structure is
`shown in Figure 6.22.
`
`6.5. 7 Paging Indicator Channel (PICH)
`
`The Paging Channel (PCH) is operated together with the Paging Indicator Channel (PICH)
`to provide terminals with efficient sleep mode operation. The paging indicators use a
`channelisation code of length 256. The paging indicators occur once per slot on the
`corresponding physical channel, the Paging Indicator Channel (PICH). Each PICH frame
`carries 288 bits to be used by the paging indicator bit, and 12 bits are left idle. Depending on
`
`

`

`132
`
`WCDMA for UMTS
`
`4096 chips
`
`1024 chips
`
`Access slot
`
`AICH
`
`3
`
`20 ms (two frames)
`
`Figure 6.22. AICH access slot structure
`
`the paging indicator repetition ratio, there can be 18, 36, 72 or 144 paging indicators per
`PICH frame . How often a terminal needs to listen to the PICH is parameterised, and the
`exact moment depends on running the system frame number (SFN).
`For detection of the PICH the terminal needs to obtain the phase reference from the
`CPICH, and as with the AICH, the PICH needs to be heard by all terminals in the cell and
`thus needs to be sent at high power level without power control. The PICH frame structure
`with different Pl repetition factors is illustrated in Figure 6.23 .
`
`512-4096 chips
`
`Pl
`
`PICH
`
`I
`
`I
`
`-256 chips
`
`I
`
`I
`
`I
`288 bits
`bits
`> - - - - - - - - - - - - - - - - -- -- -~
`
`_1_2_id1e
`
`Figure 6.23. PICH structure with different PI repetition rates
`
`10 ms
`
`6.5.8 Physical Channels for the CPCH Access Procedure
`
`For the CPCH access procedure, a set of CPCH specific physical channels has been
`specified. These channels carry no transport channels, but only information needed in the
`CPCH access procedure. The channels are:
`
`• CPCH Status Indication Channel (CSICH);
`• CPCH Collision Detection Indicator Channel (CD-ICH) ;
`• CPCH Channel Assignment Indicator Channel (CA-ICH);
`• CPCH Access Preamble Acquisition Channel (AP-AICH).
`
`T
`Fig1
`use1
`acc1
`dov
`l
`ICI-
`16
`1
`cha
`als<
`
`6.(
`
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`opt
`im1
`tra
`pre
`
`6.l
`
`Th
`Joe
`ne
`al
`1 '
`en
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`ra1
`co
`
`cc
`cc
`cc
`te
`
`cc
`th
`CC
`
`g
`
`

`

`134
`
`WCDMA for UMTS
`
`Pt
`
`The SIR target for closed loop power control is set by the outer loop power control. The
`latter power control is introduced in Section 3.5 and described in detail in Section 9.2.2.
`On the terminal side, what is expected to be done inside a terminal in terms of (fast) power
`control operation is specified rather strictly. On the network side there is much greater
`freedom to decide how a base station should behave upon reception of a power control
`command, as well as the basis on which the base station should tell a terminal to increase or
`decrease the power.
`
`6.6.2 Open Loop Power Control
`
`In UTRA FDD there is also open loop power control, which is applied only prior to initiating
`the transmission on the RACH or CPCH. Open loop power control is not very accurate, since
`it is difficult to measure large power dynamics accurately in the terminal equipment. The
`mapping of the actual received absolute power to the absolute power to be transmitted shows
`large deviations, due to variation in the component properties as well as to the impact of
`environmental conditions, mainly temperature. Also, the transmission and reception occur at
`different frequencies, but the internal accuracy inside the terminal is the main source of
`uncertainty. The requirement for open loop power control accuracy is specified to be within
`±9 dB in normal conditions.
`Open loop power control was used in earlier CDMA systems, such as IS-95 , being active
`in parallel with closed loop power control. The motivation for such usage was to allow
`comer effects or other sudden environmental changes to be covered. As the UTRA fast
`power control has almost double the command rate, it was concluded that a 15 dB
`adjustment range does not need open loop power control to be operated simultaneously.
`Additionally, the fast power control step size can be increased from 1 dB to 2 dB , which
`would allow a 30 dB correction range during a 10 ms frame .
`The use of open loop power control while in active mode also has some impact on link
`quality. The large inaccuracy of open loop power control can cause it to make adjustments to
`the transmitted power level even when they are not needed. As such, behaviour depends on
`terminal unit tolerances and on various environmental variables, running open loop power
`control makes it more difficult from the network side to predict how a terminal will behave
`in different conditions.
`
`6.6.3 Paging Procedure
`
`The Paging Channel (PCH) operation is organised as follows. A terminal, once registered to
`a network, has been allocated a paging group. For the paging group there are Paging
`Indicators (Pl) which appear periodically on the Paging Indicator Channel (PICH) when
`there are paging messages for any of the terminals belonging to that paging group.
`Once a PI has been detected, the terminal decodes the next PCH frame transmitted on the
`Secondary CCPCH to see whether there was a paging message intended for it. The terminal
`may also need to decode the PCH in case the PI reception indicates low reliability of the
`decision. The paging interval is illustrated in Figure 6.24. "
`The less often the Pis appear, the less often the terminal needs to wake up from the sleep
`mode and the longer the battery life becomes. The trade-off is obviously the response time to
`the network-originated call. An infinite paging indicator interval does not lead to infinite
`battery duration, as there are other tasks the terminal needs to perform during idle mode as
`well.
`
`6.
`
`T
`w
`p,
`v;
`st
`fc
`
`•
`
`•
`
`•
`
`•
`•
`•
`
`•
`
`p
`
`V
`t,
`
`C
`I
`a
`r
`
`

`

`Physical Layer
`
`135
`
`,·············1······
`
`PICH
`
`S-CCPCH
`
`- - --
`-
`-
`~ - --
`Paging indicators
`'------ -- - -- ---+ ............ 1 ... .
`
`I
`I
`I
`
`I
`
`7680 chips
`Figure 6.24. PICH relationship to PCH
`
`6.6.4 RACH Procedure
`
`The Random Access procedure in a CDMA system has to cope with the near-far problem, as
`when initiating the transmission there is no exact knowledge of the required transmission
`power. The open loop power control has a large uncertainty in terms of absolute power
`values from the received power measurement to the transmitter power level setting value, as
`stated in connection with the open loop description. In UTRA the RACH procedure has the
`following phases:
`
`• The terminal decodes the BCH to find out the available RACH sub-channels and their
`scrambling codes and signatures.
`
`• The terminal selects randomly one of the RACH sub-channels from the group its access
`class allows it to use. Furthermore, the signature is also selected randomly from among
`the available signatures.
`
`• The downlink power level is measured and the initial RACH power level is set with the
`proper margin due to the open loop inaccuracy.
`
`• A 1 ms RACH preamble is sent with the selected signature.
`
`• The terminal decodes AICH to see whether the base station has detected the preamble.
`
`•
`
`In case no AICH is detected, the terminal increases the preamble transmission power by a
`step given by the base station, as multiples of 1 dB. The preamble is retransmitted in the
`next available access slot.
`
`• When an AICH transmission is detected from the base station, the terminal transmits the
`10 ms or 20 ms message part of the RACH transmission.
`
`The RACH procedure is illustrated in Figure 6.25, where the terminal transmits the
`preamble until acknowledgement is received on AICH, and then the message part follows.
`In the case of data transmission on RACH, the spreading factor and thus the data rate may
`vary; this is indicated with the TFCI on the DPCCH on PRACH. Spreading factors from 256
`to 32 have been defined to be possible, thus a single frame on RACH may contain up to 1200
`channel symbols which, depending on the channel coding, maps to around 600 or 400 bits.
`For the maximum number of bits the achievable range is naturally less than what can be
`achieved with the lowest rates, especially as RACH messages do not use methods such as
`macro-diversity as in the dedicated channel.
`
`

`

`for UMTS
`
`Radio Interface Protocols
`
`171
`
`l. At core network-originated call or session set-up. In this case the request to start paging
`comes from the Core Network via the Iu interface.
`
`2. To change the UE state from Cell_PCH or URA_PCH to Cell_FACH. This can be
`initiated, for example, by downlink packet data activity.
`
`3. To indicate change in the system information. In this case RNC sends a paging message
`with no paging records but with information describing a new 'value tag' for the master
`information block. This type of paging is targeted to all UEs in a cell.
`
`Initial Cell Selection and Reselection in Idle Mode
`7.8.3.3
`The most suitable cell is selected, based on idle mode measurements and cell selection
`criteria. The cell search procedure described in Chapter 6 is part of the cell selection process.
`
`7.8.3.4 Establishment, Maintenance and Release of RRC Connection
`The establishment of an RRC connection and Signalling Radio Bearers (SRB) between
`UE and UTRAN (RNC) is initiated by a request from higher layers (non-access stratum)
`on the UE side. In a network-originated case, the establishment is preceded by an RRC
`Paging message. The request from non-access stratum is actually a request to set up a
`Signalling Connection between UE and CN (Signalling Connection consists of an RRC
`connection and an Iu connection). Only if the UE is in idle mode, thus no RRC connection
`exists, does the UE initiate RRC Connection Establishment procedure. There can always be
`only zero or one RRC connections between one UE and UTRAN. If more than one
`signalling connection between UE and CN nodes exist, they all 'share' the same RRC
`connection.
`The 'maintenance' of RRC connection refers to the RRC Connection Re-establishment
`functionality, which can be used to re-establish a connection after radio link failure. Timers
`are used to control the allowed time for a UE to return to 'in-service-area' and to execute the
`re-establishment. The re-establishment functionality is included in the Cell Update proce(cid:173)
`dure (7.8.3.9).
`The RRC connection establishment procedure is shown in Figure 7 .17. There is no need
`for a contention resolution step such as in GSM [13], since the UE identifier used in the
`connection request and set-up messages is a unique UE identity (for GSM-based core
`network P-TMSI+RAI, TMSI+LAI or IMSI) . In the RRC connection establishment
`procedure this initial UE identifier is used only for the purpose of uniqueness and can be
`discarded by UTRAN after the procedure ends. Thus, when these UE identities are later
`needed for the higher layer (non-access stratum) signalling, they must be resent (in the
`higher layer messages). The RRC Connection Set-up message may include a dedicated
`physical channel assignment for the UE (move to Cell_DCH state), or it can command the
`UE to use common channels (move to Cell_FACH state). In the latter case, a radio network
`temporary identity (U-RNTI and possibly C-RNTI) to be used as UE identity on common
`transport channels is allocated to the UE.
`The channel names in Figure 7 .17 indicate either the logical channel or logical/transport
`channel used for each message.
`The RRC connection establishment procedure creates three (optionally four) Signalling
`Radio Bearers (SRBs) designated by the RB identities #1 ... #4 (RB identity #0 is reserved
`for signalling using CCCH). The SRBs can later be created, reconfigured or even deleted
`
`ed arrows
`
`1 all the
`
`'or SIBs
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`
`c, or the
`the UE
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`can also
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`
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`'or each
`)locks.
`
`,elected
`
`

`

`172
`
`WCDMA for UMTS
`
`Radio lnterfa<
`
`UTRAN/RNC
`
`UE
`
`Idle
`mode
`
`CCCH/RACH: RRC Connection request
`
`CCCH/FACH: RRC Connection set-up
`
`UTRAN
`Connected mode
`DCCH: RRC Connection set-up complete
`
`Figure 7.17. RRC connection establishment procedure
`
`with the normal Radio Bearer control procedures. The SRBs are used for RRC signalling
`according to the following rules:
`
`1. RB#l is used for all messages sent on the DCCH and RLC-UM.
`
`2. RB#2 is used for all messages sent on the DCCH and RLC-AM, except for the Direct
`Transfer messages.
`
`3. RB#3 is used for the Direct Transfer messages (using DCCH and RLC-AM), which
`carries higher layer signalling. The reason for reserving a dedicated signalling radio
`bearer for the Direct Transfer is to enable prioritisation of UE-UTRAN signalling over
`the UE- CN signalling by using the RLC services (no need for extra RRC functionality).
`
`4. RB#4 is optional and, if it exists, is also used for the Direct Transfer messages (using
`DCCH and RLC-AM). With two SRBs carrying higher layer signalling, UTRAN can
`handle prioritisation on signalling, RB#4 being used for 'low priority' and RB#3 for
`'high priority' NAS signalling. The priority level is indicated to RRC with the actual
`NAS message to be carried over the radio. An example of low priority signalling could be
`the SMS .
`
`5. For RRC messages utilising transparent mode RLC and CCCH logical channel (e.g. Cell
`Update, URA Update), RB identity #0 is used. A special function required in the RRC
`layer for these messages is padding, because RLC in transparent mode neither imposes
`size requirements nor performs padding, but the message size must still be equal to a
`Transport Block size.
`
`7.8.3.5 Control of Radio Bearers, Transport Channels and Physical Channels
`On request from higher layers, RRC performs the establishment, reconfiguration and release
`of Radio Bearers. At establishment and reconfiguration, UTRAN (RNC) performs admission
`
`control and
`Layer 1. Tht
`(Section 7.8
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`7.8.3.6 Cc
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