02 UTRAN Structure

7/31/2019 02 UTRAN Structure

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UMTS Terrestrial

Radio Access Network

(UTRAN)

[email protected]

063361
mailto:[email protected]:[email protected]


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UTRAN Structure & Interface


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UMTS Architecture

CN

UTRAN

UE

Uu

Iu

UTRAN UMTS Terrestrial Radio Access NetworkCN Core NetworkUE User Equipment


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UTRAN Architecture

RNS

RNC

Node B Node B

Iub Iub

Core Network

RNS

RNC

Node B Node B

Iub Iub

Iu Iu

Iur

UTRAN consists of many Radio Network Subsystems (RNSs) belonging to one operator.A RNS consists of one Radio Network Controller and one or more Node B(s) (base stations).The operation of RNC is similar to the GSM BSC. i.e., responsible for radio resourceallocation, execution of handover, terrestrial channel management and mapping between radioand terrestrial channels.

The only main difference between UTRAN and GSM architectures is that, in the case ofUTRAN, there is a logical connection between RNCs.


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Radio Interface protocol architecture (Layer Model) -------- Iu-CS


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Radio Interface protocol architecture (Layer Model) -------- Iu-PS

Iu UP Protocol

Layer


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Radio Interface protocol architecture (Layer Model) -------- Iub


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Radio Interface protocol architecture (Layer Model) -------- Iub


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Radio Interface protocol architecture (Layer Model) -------- Uu

L2/MAC

L2/RLC

L1

MAC

RRC

PHY

TransportChannels

LogicalChannels

C-plane signaling U-plane information

GC Nt DC

GC General ControlNT NotificationDC Dedicated ControlRRC Radio Resource ControlRLC Radio Link Control

MAC Medium Access Control

RLC

BMC

PDCP

L3

PDCP Packet Data ConvergenceProtocol

BMC Broadcast and Multicast Control


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Issues to Radio Interface Layers

The radio interface has two planes: C-plane signalling and U-plane information

and three layers: physical layer (L1), data link layer (L2) and network layer (L3). Service Access Points (SAPs) marked by circles. Each layer offers services through SAPs to upper layers. A service is defined by a

set of service primitives (operations) that a layer provides to upper layers. All physical functions such as spreading, modulation, multiplexing, mapping transport

channels to physical channels, etc., are located in layer 1. In the C-plane, layer 2 contains two sub-layers; MAC and RLC. In the U-plane, in

addition to MAC and RLC, two additional service dependent protocols exists; PDCPand BMC protocols. The main functions of MAC include mapping of logical channels onto transport

channels, priority handling between data flows and identification of UEs (userequipments) on common transport channels. The RLC main functions include ARQ,segmentation and reassembly and flow control.

PDCP exist only for packet switched domain services. It main function is headercompression.

BMC is used to transmit over the radio interface messages originating from cellBroadcast Centre (broadcast and multicast services).

Layer 3 consists of one protocol, RRC, which belongs to the control plane. Its mainfunction is to setup, modify and release layer 2 and layer 1 protocol entities. RRCmessages carry in their payloud also all higher layer signalling such as MM, CM andSM.

Gc, Nt and Dc are SAPs between RRC and higher layer protocols which are

independent of the access network.


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UTRAN Channel


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Definition of Channels

Logical Channel Type of information to be transmitted e.g., traffic or controllogical channels.

Transport Channel How and with what format data is transmitted through

physical links.

Physical Channel Unit of radio resource of a radio system e.g., frequency

band, time slot, code, etc.

RF Channel Fixed frequency band of a radio system.

The MAC sublayer is responsible for mapping logical channels onto transport

channels.

The physical layer is responsible for mapping transport channels onto physical

channels.


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Logical Channels

Broadcast Control Channel (BCCH)

Paging Control Channel (PCCH)

Dedicated Control Channel (DCCH)

Common Control Channel (CCCH)

Control Channel (CCH)

Dedicated Traffic Channel (DTCH)Traffic Channel (TCH)

Common Traffic Channel (CTCH)

Interface between L2/MAC & upper layers

Classified by the transferred information


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Transport channels

Common Channels (CCHs) Dedicated Channel (DCH)

(Uplink/Downlink)

Common PacketChannel(CPCH)(Uplink)

BroadcastChannel (BCH)

(Downlink)

Forward-Access

Channel (FACH)

(Downlink)

PagingChannel (PCH)

(Downlink)

Random-Access

Channel (RACH)

(Uplink)

Downlink SharedChannel(DSCH)(Downlink)

Interface between Physical Layer & L2/MAC

Classified by the transferred information & transfer methods on the physical layer


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Transport ChannelsA common channel is a channel (resource) used by all users or a group of users in a cell. In the

downlink a common channel is a point-to-multipoint channel and in the uplink the channel iscontended by users.

A dedicated channel is a point-to-point channel allocated to a specific user.

BCCH is a downlink channel used to broadcast system and cell-specific information over the entirecell.

FACH is a downlink channel used to carry control information to a mobile station when the systemknows the location cell of the mobile station. FACH may also carry short user packets.

PCH is a downlink channel used to carry control information to a mobile station when the systemdoes not know the location cell of the mobile station. It is used to inform the mobile station of

incoming calls.

RACH is a uplink channel used to carry control information. It is used for initiating a call (initialaccess to the serving BS). RACH may also carry short user packets.

CPCH is a uplink channel used to carry infrequent medium sized packets.

DSCH is a downlink channel used to carry infrequent medium and large sized packets and can beshared in time between several users.


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Mapping Logical Channels ontoTransport Channels

BCH PCH DSCHFACHRACH DCH

BCCH-

SAP

DCCH-

SAP

CCCH-

SAPPCCH-

SAP

DTCH-

SAP

Transport

Channels

MAC SAPs

USCH(TDD only)

CPCH(FDD only)

CTCH-

SAP

SHCCH-

SAP

(TDD only)


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Uplink Physical channels

Common Physical ChannelsDedicated Physical Channels

Dedicated Physical Data Channels(Uplink DPDCH)

Dedicated Physical Control Channel

(Uplink DPCCH)) Physical Random Access Channel(PRACH)

Physical Common Packet Channel(PCPCH)


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Downlink Physical Channels

Common Physical Channels

Dedicated Physical Channel (Downlink DPCH)A time multiplex of a downlink DPDCH and a downlink DPCCH

Common Pilot Channel

(CPICH)

Primary CPICH

Secondary CPICH

Primary Common ControlPhysical Channel(P-CCPCH)

Secondary Common ControlPhysical Channel(S-CCPCH)

SynchronisationChannel(SCH)

Physical DownlinkShared Channel(PDSCH)

Acquisition IndicationChannel(AICH)

Page IndicationChannel(PICH)


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Mapping Transport Channels ontoPhysical Channels

BCH FACH PCH RACH DCH DSCH

P-CCPCH

S-CCPCH

PRACH

Transport

channels

CPCH

Physical

channelsAICH

PICH

PDSCH

SCH

DPCCH

DPDCH

PCPCHCPICH


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RACH Procedure I

Access Preamble

Control Part

Data Part

Message Part

4096 chips

Structure of the random access transmission

0P 1PjP

1,2)(Nmsec10*N


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RACH Procedure II

The MS receives from the BCH the available sub-channels(Access slots), scrambling codes and signatures.

The MS selects randomly one of the RACH sub-channelsfrom the group its access class allows it to use. It alsoselects a signature randomly from the available signatures.

A 1 ms access preamble is transmitted using the selectedsignature.

The MS monitors the Acquisition Indication Channel (AICH)to see whether the BS has received the preamble.

If no AICH is detected, the MS increases the accesspreamble transmission power by a fixed amount given by theBS and transmits it again in the next available access slot.

When an AICH is detected, the MS transmits the 10 ms or 20

ms massage part of the RACH.


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RACH Procedure III

Data bitsNdata

Control

slotT 0..3)(kbits2*10chips,2560 k

Slot 0 Slot 1 Slot i Slot 14

ms10TframeradiopartMessage RACH

Structure of the random-access message part

bitsNdata TFCIN

Data

Pilot

bits

TFCI


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CPCH Procedure I

Access Preamble

Collision ResolutionPreamble

Control Part

Data Part

Message Part

4096 chips

Structure of the CPCH random access transmission

0P P1jP jP

msec10 msec10*N


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CPCH Procedure II

It is similar to the RACH procedure. The main differenceis the Collision Detection (CD) which has a similarstructure to that of the access preamble.

The operation follows the RACH procedure until the MS

receives the AICH. After that a CD preamble with thesame power level using a different signature is sent tothe BS. On the receipt of this preamble, the BS thensends back a CD-Indication Channel (CD-ICH).

After the MS receives the correct CD-ICH, it transmits

the message which may last over several frames. The use of a CD preamble reduces the probability of

collision on layer 1.


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Dedicated Physical Channels (DPCH)

DPDCH

DPCCH

Dedicated Physical Data Channel

Dedicated Physical Control Channel

DPDCH - Carries dedicated transport channels

DPCCH - Carries control information at layer 1 ( known pilot,transport format combination indicator (TFCI) feedbackinformation (FBI) and transmit power control (TPC)

command

DPCH

The pilot bits are used for channel estimation in the receiver.The TPC bits carry the power control commands.The FBI bits are used when closed loop transmission diversity is used in the downlink.The TFCI indicates the transport format of the DPDCH in the same frame.


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DPDCH

bitsNdata

bitsNdata

bitsNTFCI bitsNFBI bitsN TPCDPCCH

slotT 0..6)(kbits2*10chips,2560k

Frame structure for uplink DPDCH/DPCCH

ms10T:frameradio1 f


Data

Pilot TFCI FBI TPC

Uplink DPCH Procedure I


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Uplink DPCH Procedure IITransmission time is divided into radio frames. The size of a radio frame is 10

ms consisting of 15 time slots.

One time slot corresponds to 2560 chips (0.667 ms), which equals to onepower control period.

DPDCH and DPCCH bits transmitted in parallel in each time slot using I and Qstreams of QPSK modulation. i.e., one QPSK symbol (phase) carries one bit ofDPDCH and one bit of DPCCH (I-Q/code multiplexing).

DPDCH carries the traffic and/or signalling (control information of higher layers.

DPCCH carries the physical layer control information (pilot, TFCI, FBI and TPCbits).

DPCCH uses a fixed spreading factor of 256. i.e., 10 bits per time slot.

DPDCH uses 7 spreading factors from 256 to 4. No. of bits per time slot can becalculated from 10 * 2 k where k = 0, , 6.


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The DPDCH and DPCCH are spread to a fixed chip rate of 3.84 Mchips/s bythe channelization codes, Cd and Cc, respectively.

The DPDCH uses Cch,SF,k code where SF is the spreading factor (256 to 4)and k is the branch no. of the code tree for the same SF (k = 0, , SF-1). The

value of k = SF/4 is used for the DPDCH.

The DPCCH uses Cch,256,0 i.e., the top branch of the code tree for SF = 256.Bd and Bc are gain factors used to adjust the relative transmitted power of theDPDCH and DPCCH.

Slong, n or Sshort, n is the scrambling code for nth mobile station. The mobilestation is identified by its scrambling code.

One DPCCH and up to six parallel DPDCHs can be transmittedsimultaneously.

Uplink DPCH Procedure III


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All uplink physical channels are subjected to scramblingwith a complex-valued scrambling code.

The DPCCH/DPDCH may be scrambled by either long orshort scrambling codes.

The long scrambling codes are from a set of Goldsequences of 38400 chips. There are 224 long uplinkscrambling codes.

The short scrambling codes are derived from a sequenceof the family of periodically extended S(2) codes. There are 224 shortuplink scrambling codes.

Uplink scrambling codes are assigned by higher layers.

Uplink Scrambling Codes


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Downlink DPCH Procedure I

bitsNdata1 bitsNTPC bitsNdata2 bitsNPilot

slotT 0..7)(kbits2*10chips,2560k


ms10T:frameradioOne f

bitsNTFCI

DPDCH DPCCH DPDCH DPCCH

Frame structure for downlink DPCH

Data1 TPC TFCI Data2 Pilot


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Downlink DPCH Procedure II

Time multiplexing of the DPDCH and DPCCH isused in the downlink.

In the downlink the spreading factors range from4 to 512, with some restrictions on the use ofspreading factor 512 in the case of softhandover.

The downlink DPDCH consists of QPSK

symbols. Each symbol consists of two bits whilein the case of uplink the DPDCH consists ofBPSK symbol (one symbol corresponds to onebit).


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A total of 2181 scrambling codes can be generated.however, only 8192 of these scrambling codes are used.

The scrambling codes are divided into 512 sets each of aprimary scrambling code and 15 secondary scrambling codes.

The downlink scrambling codes are segments of a different setof the Gold sequences.

The scrambling codes are repeated for every 10 ms radioframe.

Downlink Scrambling Codes


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SCH Procedure I

Tf = 15 x Tslot

Tslot

Primary SCH

Secondary SCH

cp Primary Synchronisation Code ( It is the same for every cell in the system)

csi,k Secondary Synchronisation Codes ( Where i=0,1.63 is the number of the scrambling

code group, and k= 0,1,14 is the slot number. Each code is chosen from a set of16 different codes of length 256).

pc

sci, 0

pc

i, 2 sc i, 14

256 chips2560 chips

sc

pc


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The synchronisation channel consists of two channels, the primaryand secondary synchronisation channels.

The primary SCH uses a code of 256 chips transmitted over everyslot.

The primary SCH code is the same for every cell in the system. The primary SCH is used for slot synchronisation. The secondary SCH consists of 64 sequences, each sequence has

a 15 code of length 256 chips. Each BS transmits a specificsequence in every frame (one code per time slot), repeatedly.

Each code sequence is associated to one downlink scrambling codegroup. The secondary SCH is used for frame synchronisation.

SCH Procedure II


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RRC Service States


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RRC Service States


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RRC Service States

-------- Idle Mode


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RRC Service States

-------- Cell_DCH State


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RRC Service States

-------- Cell_FACH State

Cell Broadcast (CB)

SMS CB Service (CBS)


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RRC Service States

-------- Cell_PCH State


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RRC Service States

-------- URA_PCH State


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UE-initiated RRC state transition


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Network-initiated state transition


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For latest changes to the UTRAN standard,please see:

www.3gpp.org

Particularly,

TS 25.211 to TS 25.214 V3.1.1 (2000-03)For FDD modeTS 25.221 to TS 25.224 V3.1.1 (2000-03)For TDD mode

02 UTRAN Structure

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