wcdma arch 001

1 © NOKIA WCDMA_arch.PPT/ 25.1.2002 Kari Heiska, TLI361-WCDMA radioverkkosuunnittelu - luentosarja Jyvaskylän yliopistossa

UMTS Architecture, protocols and logical Channels

25.1.2002 Kari Heiska


Contents

• High level UMTS architecture• Those architecture blocks, interfaces and functions that has impact

on radio network planning (RNP)

• Radio Interface Protocol Architecture and Logical Channels• Medium Access Control (MAC)• Radio Link Control (RLC)• Packet data Convergence Protocol (PDCP)• Broadcast/Multicast Control (BMC)

• Transport Channels• Common and dedicated transport channels• Multiplexing to physical channels• Basic physical layer functions


High level UMTS architecture• UMTS designed to support different applications with different Quality of

Service profiles (QoS)• speech, video, web-browsing, …

• UMTS includes different entities• User equipment (UE)• UMTS Terrestrial Radio Access Network (UTRAN)• Core Network

• And different interfaces• Radio Interface (Uu)• CN-UTRAN Interface (Iu)

• Both Interfaces are divided into two protocols• User plane protocols to transport the service (Radio Access Bearer (RAB) Service)• Control plane protocols to control the RAB and the connection between UE and CN


High level UMTS architecture• Access Stratum

• Specific to Access Technique: Provides services through Service Access points to Non-Access Stratum

• This means: transfer of radio related information and coordinating radio resources between UE and access network

• Non-Access Stratum• Provides access link between UE and CN which consist of:1) One or more independent and simultaneous UE-CN Radio Access Bearer Services2) Only one signaling from CN to UE


High level UMTS architecture• Radio Access Bearer (RAB)

• Service provided by the Access Stratum to the Non-Access Stratum in order to transfer user data between CN and UE

• RAB is described by a set of parameters (attributes) which define the QoS profile of that particular service/application

• For example: maximum allowed delay for the packet call, maximum allowed bit error rate, minimum data rate, etc.

• One profile for one RAB• RAB service includes Radio Bearer Service and Iu bearer service• Radio Bearer Service covers Radio interface transport and uses UTRA FDD and is realized by

the Radio Link Control protocol user plane (RLC-U)• Iu bearer service includes attributes that defines CN specific QoS attributes• Radio network controller maps the RAB QoS RB QoS

TE MT UTRAN CN Iu edge CN gateway

End-to-end Service

UMTS Bearer Service ExternalBearer Service

Radio Access Bearer Service CNBearer Service

BackboneBearer Service

IuBearer Service

RadioBearer Service

UTRAService

PhysicalBearer Service

Legend:TEMT

= Terminal Equipment= Mobile Termination

Backbone Phys.Bearer Service


Protocol architecture and logical channels

• Radio interface protocols are needed to set up Radio Bearer Service• Radio interface protocols consist of three protocol layer:

• Physical layer, L1• Data link layer, L2. L2 includes

• Medium access layer (MAC)• Radio Link Layer (RLC), which includes (Includes Control (C) and user (U) planes)• Packet data Convergence Protocol (PDCP) (Includes U plane only)• Broadcast/Multicast Control (BMC), (Includes U plane only)

• Network layer, L3 • One protocol: Radio Resource Control (RRC) (C-plane only)



Transport Channels (TrCH),information transfer service, which L1offers to MAC and higher layers

Logical Channels (LoCH),MAC provides logical channels fordata transfer services to the layersabove MAC

These protocols are needed to set up, reconfigure and release the Radio Bearer services

Physical channels

L3

C-plane signalling U-plane information

L2/MAC

L1

L2/RLC

L2/BMC

PDCPPDCP L2/PDCP

RLC RLCRLC

RLCRLC

RLCRLC

RLC

cont

rol

cont

rol

cont

rol

cont

rol

control

BMC

RRC

PHY

MAC

higher L3 sub-layers

L1data amount

payl

oad

L2/

MA

C

L2/

RL

C

L1 overhead

includes higherlayer control data


• Medium Access Control (MAC)• Mapping Logical Channels onto appropriate Transport Channel providing efficient

use of transport channels

• Main MAC functions• Based on instantaneous source rate it selects the appropriate transport format

(TF) within an assigned transport format set (TFS) for active TrCH• Transport Format is based on transport format combination set (TFCS) assigned by

RRC• Priority handling between data flows

• TFC for which high data rate transport channel will be selected• Priority handling between UE(s)

• Multiplexing and demultiplexing of RLC PDUs (protocol data units) onto Transport Blocks (TB). One Radio frame consists of one or several Transport blocks

• Traffic Volume measurements and reporting to RRC � TrCH switching decisions from RRC



MAC to physical layer

LoCH1 LoCH2 LoCH3 LoCH4

100 B 10B 50B 60B

different incoming data amounts

TFS

TF1

TF2

TFN

MAC

TF TF TF TF

RRC

TFCS

The combination of current TrCHs determine the TFCS in RRC

All possible available combinations produced by the admission control (AC) in RNC

TFS is a collection of possible TF of transport channel 1

TrCH1 TrCH2 TrCH3 TrCH4


TransportBlock Set(TBS) DCH2

T T I

DCH1T T I

T B

T B

T BT B

Transport Block

Transport Block

Transport Block

T B

T B

Transmission Time Interval

T T I

T T I

T T I

Transport Format (TF)• Dynamic part (TB size, TBS

size)• Semi static part (TTI, CRC,

etc…)(TFI)

Transport Format Set (TFS)• TB´s same static part• Variable dynamic part

Data exchange example between MAC and the physical layer (2 DCH)Transport

FormatCombination

(TFC)

MAC• ChoosesTFC/TFCS• Controls thedynamicpart/TB's/TTI

Transport FormatCombination Set

(TFCS)


Formats and Configurations

• Transport Block (TB)• Basic data unit between L1 and L2 (MAC)• L1 adds CRC to each TB

• Transport Block Set (TBS) • Consists of transport Blocks from L1 and L2 within the same time

instant

• Transport Block Size• Number of bits in TB, which is fixed within a TBS

• Transport Block Set Size • Number of bits in TBS

• Transmission Time Interval (TTI)• Periodicity at which a TBS is transferred by the physical layer.

Multiple of minimum interleaving period. So MAC delivers one TBSto the physical layer every TTI


Formats and Configurations• Transport Format (TF)

• Format offered between L1 and MAC for the delivery of a TBS during a TTI on a given TrCH. Consist of dynamic part (TB size, TBS size) and semi static part (TTI, coding, …)

• Transport Format Set (TFS)• A set of TFs associated with a TrCH. Same semi static part in all TF

inside one TFS• Example

• DCH: TB size of 336 bits (320 (payload)+16 (RLC header))• 2 TB per TBS, 10 ms TTI � 336×2/10=67.2 kbps, user bit-rate

320×2/10=64 kbps• Variable rate either by changing TBS size or TB size per TTI

• Transport Format Combination (TFC)• Combination of currently valid TFs submitted to L1 simultaneously

on a CCTrCH of a UE


Formats and Configurations• Transport Format Combination Set (TFCS)

• Set of TFCs on a CCTrCH• MAC (L2 control) chooses the TFC to be transmitted. This means

that it can change the bit rate very quickly without asking fromRRM algorithms (L3 control). L3 controls the semi static part which is the same inside TFS

• Transport Format Indicator (TFI)• Label for TF: Includes TF attributes used for communication

between L1 and MAC (L2)

• Transport Format Indicator (TFCI)• Used to inform the receiving side of the currently valid TFC• L1 builds TFCI from TFs of each transmitted TrCH and puts the

information to dedicated physical control channel (DPCCH) transmitted on air

• With TFCI the receiving side is able to identify TFC


Formats and Configurations

RAB1 RAB2 RABn

Transport

format

set

Transport FormatCombination x

Transport FormatCombination x+1

Transportformat


• Logical Channels• The type of information defines the type of logical channels• Two types of logical channels: control channels and traffic channels

• BCCH: Broadcast Control Channel. Broadcasting system control information in downlink (DL)

• PCCH: Paging Control Channel. Paging information in DL when network does not know the mobile location

• CCCH: Common Control Channel. Carries common control information (UL and DL)

• DCCH: Dedicated Control Channel. Point-to-point channel for dedicated control information (UL and DL)

• DTCH: Dedicated Traffic Channel. Point-to-point channel for user information (UL and DL)

• CTCH: Common Traffic Channel. Dedicated user information for all or a group of specified UEs (DL)



Mapping of logical Channels to Transport channels (TrCH)

BCH PCH DSCHFACHRACH DCH

BCCH CCCHPCCHLogicalChannels MAC SAPs

CPCH(FDD only)

CTCH

DCH

CCCH DTCH/DCCH DTCH/DCCH

TransportChannels

UpLink DownLink

BCCH Broadcast Control ChannelCCCH Common Control ChannelDTCH Dedicated Traffic ChannelDCCH Dedicated Control ChannelPCCH Paging Control ChannelCTCH Common Traffic Channel

BCH Broadcast ChannelCPCH Common Packet ChannelDCH Dedicated ChannelDSCH Downlink Shared ChannelFACH Forward Access ChannelPCH Paging ChannelRACH Random Access Channel



Protocol architecture and logical channels• Radio Link Control (RLC) protocol

• Main functions• Segmentation of data coming from higher layers (PDUs) to payload units (PU)• Buffering • Error correction by retransmission (AM mode)• Ciphering • Maintenance of QoS defined by upper layers

• Each RLC is configured by RRC to operate in one of following modes for one Radio Bearer (RB) service:

• Transparent Mode (TM)• no overhead added

• Unacknowledged Mode (UM)• no retransmission protocols in use• Received data is either marked or discarded

• Acknowledged Mode (AM)• Automatic Repeat Request (ARQ) mechanism for error correction


Protocol architecture and logical channels• Radio Link Control (RLC) protocol

• The mode is the same in uplink and in downlink• The mode is determinated by Admission Control (AC) from RAB attributes and CN

domain information• In all RLC modes CRC (cyclic redundancy check) error detection is done in L1 and the

results is delivered to RLC with the data• Radio Network Planning effects:

• In AM mode the number of retransmissions have to be taken into account. Increases the overall data amount

• The delay experienced by the user when receiving packet call depends the date amount in the RLC buffer

• L2 header in RLC: 16 bits in AM, 8 bits for UM and 0 bits from TM: User bit rate for dimensioning is given by the L1 bit-rate reduced by L2 header



• Packet data Convergence Protocol (PDCP)• User plane only• For packet switched (PS) data only• Compression of TCP/IP and RTP/UDP/IP headers. Important to have efficient data

transmission over radio• Transmitting SDUs (Service Data Unit = is for example TCP packets) to correct RLC

entity

• Broadcast/Multicast Control (BMC)• User plane only• Provides Broadcast/Multicast services• Utilized UM RLC mode (CTCH mapped to FACH)


Protocol architecture and logical channels• Radio Resource Control (RRC) Protocol (Layer 3)

• The major part of the control signaling between UE and UTRAN is RRC messages• Most of these messages are part of RRM algorithms• Connection management procedures of RRC:

• Broadcast of system information• Used to control the UE mobility• Establish, reconfigure and release Radio Bearers• Paging, Control of ciphering• Initial cell selection and cell reselection (handovers)• Controlling the UE measurement reporting criterias• Outer loop power control

• RRC states• Idle Mode

– After power on terminal stays in Idle Mode until a request to establish RRC connection– All access stratum connections are closed

• Cell_DCH– Using dedicated physical channel / physical shared channel– Terminal performs measurements

• Cell_FACH– No dedicated channel allocated to the terminal– Using FACH and RACH for signaling or small data amounts– UE listens to the BCH

• Cell_PCH– Radio network controller knows the location of the UE– Reachable via paging message

• URA_PCH– Low battery consumption state, cell update only when URA changes


Transport channels• Data generated at higher layer is carried over the air interface with transport

channels, which are mapped onto different physical channels• Variable rate transport channel in order to provide bandwidth on demand

services• Each TrCH is coupled with a TFI• Several services can be multiplexed into one Coded Composite Transport

Channel (CCTrCH)• The physical layer combines the TFI from different TrCHs to the TFCI (TFCI bits

are carrier over the air), which informs the receiver about which TrCHs (TFC/TFCS) are active for the current frame

• Only one physical control channel per connection• The transport channel may have a different number of blocks and at any

moment not all the TrCHs are necessary active• In UTRAN the interface between physical and higher layers is represented by

the Iub interface (interface between base station and base station controller)


Transport channels

Transport Block

Transport BlockTFI

TrCH 1

TFCI Coding & Multiplexing

PhysicalControl CHannel

PhysicalData CHannels

Higher Layers(UTRAN: MAC/FP)

Physical Layer(Node B: L1)

TFCI Decoding Decoding & De-multiplexing

PhysicalControl CHannel

PhysicalData CHannels

TB & Error IndicationTFI

TB & Error IndicationTransport Block

Transport BlockTFI

TrCH 2

TB & Error IndicationTFI

TB & Error Indication

• Interface between higher layers and the physical layer


Transport channels

DPDCH (Dedicated Physical Data Channel)

DPCCH (Dedicated Physical Control Channel)

PRACH (Physical Random Access Channel)

PCPCH (Physical Common Packet Channel)

CPICH (Common Pilot Channel)

P-CCPCH (Primary Common Control Physical Channel)

S-CCPCH (Secondary Common Control Physical Channel)

SCH (Synchronization Channel)

PDSCH (Physical Downlink Shared Channel)

AICH (Acquisition Indication Channel)

PICH (Paging Indication Channel

dedicated channel

DCH

RACH

CPCH

BCH

FACH

PCH

DSCH

Transport Channel Physical Channel

common channels

shared channels

• Mapping of transport channels onto physical channels


Transport channels• Dedicated Transport Channels

• Only one dedicated Transport Channels, DCH• Mapped onto a DPDCH• Reserved for a single user• Carriers all the information intended for the given user coming

from higher layers, including data for the actual service (speech frames, etc...) and control information (HO commands, UE measurements, etc…)

• A separate TrCH is not needed because of the support of the variable bit rate and service multiplexing

• The dedicated physical channel is characterized by inner loop PC, fast data rate change on a frame-by-frame basis and the possibility of transmission to a certain part of the cell

• Supports soft and softer HO


Transport channels• Common Transport Channels

• Resource divided between all or a group of user in a cell (inband id is needed)

• They do not have soft/softer HO, but some of them can have fast PC (e.g. CPCH, DSCH)

• Broadcast Channel (BCH)• Is used to transmit information specific to UTRA network or for a given cell (e.g. RACH

codes, cell access slots, cell type transmit diversity methods, etc)• Is mapped onto P-CCPCH (downlink data channel, only)

• Forward Access Channel (FACH)• Carries downlink control information to terminals known to be located in the given cell• Used also to transmit downlink packet data (small packets)• There can be more than one FACH in a cell• Mapped onto S-CCPCH

• Paging Channel (PCH)• Carries data relevant to the paging procedure• The paging message can be transmitted in a single cell or many cells (URA), depending

on the system configuration• Mapped onto S-CCPCH


Transport channels• Random Access Channel (RACH)

• Carries uplink control information from the terminal, such as request to setup a connection

• Used to send small amounts of uplink packet data (NRT)• Mapped onto PRACH

• Uplink Common Packet Channel (CPCH)• Carries uplink packet-based used data• Used uplink inner loop PC (DL-DPCCH)• The transmission may last several frames in contrast with one or two frames for

the RACH message• Mapped onto PCPCH

• Downlink Shared Channel (DSCH)• Carries dedicated user data and/or control information• Can be shared in time between several users• Is a pure data channel always associated with a downlink DCH• Supports the use of downlink inner loop PC (associated UL DPCCH)• No soft-handover• Mapped onto PDSCH


Downlink TrCH coding + multiplexing

Phy

sica

lcha

nnel

segm

enta

tion

Rad

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ame

segm

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2nd

inte

rlea

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/RF

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map

ping

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codi

ng

Rat

em

atch

ing

Rat

em

atch

ing

TrB

kco

ncat

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/C

ode

bloc

kse

gmen

tati

on

CR

Cat

tach

men

t/T

B

1st

inse

rtio

nof

DT

Xin

dica

tion

1st

inte

rlea

ving

/TT

I

TrC

HMul

tipl

exin

g

CC

TrC

H

PhCH #1

PhCH #2

TrC

H#1

2nd

inse

rtio

nof

DT

Xin

dica

tion

•The transmission time interval is transport-channel specific from theset {10 ms, 20 ms, 40 ms, 80 ms}

MAC andhigher layers

Spreading/Scramblingand Modulation

DTX for Variable Rate Handling/SF after MUX

Puncturing or better repetitionStatic Rate Matching (Eb/No balancing or Es/No matching)


Uplink TrCH coding + multiplexing

Rat

em

atch

ing

Phy

sica

lcha

nnel

segm

enta

tion

Rad

iofr

ame

segm

enta

tion

2nd i

nter

leav

ing

/RF

Phy

sica

lcha

nnel

map

ping

Cha

nnel

codi

ng

Rat

em

atch

ing

TrB

kco

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ode

bloc

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CR

Cat

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t/T

B

Rad

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ameeq

ualis

atio

n

inte

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ving

/TT

I

TrC

HMul

tipl

exin

g

CC

TrC

H

PhCH #1

PhCH #2

TrC

H#1

MAC andhigher layers

• Data arrives to the coding/multiplexing unit in form of transport block setsonce every Transmission Time Interval

Spreading/Scramblingand Modulation

No DTX but dynamic rate matchingfor Variable Rate Handling (SF) after MUX

Puncturing or better repetition


TrCH multiplexing

• Error Detection• CRC bits for each Transmission Block (TB)• In the reception TBs are delivered to L2 with error estimation• This estimation is used 1) as a quality measure in macro diversity

combining and 2) directly in L2 for the re-transmission purposes (RLC)

• In CRC Calculation, the entire transport block is used to calculate the CRC parity bits for each transport block

• TBs fitting to code blocks

• Channel coding• Convolutional coding (1/2 or 1/3) with low data rates.• Turbo Coding (1/3) for high bit rates with high TBS size• increases the number of bits to 2× (1/2) or 3× (1/3) the incoming

TrCH bit-rate


TrCH multiplexing• Radio frame equalization for the interleaving (UL)

• 1st interleaving (TTI) for delay resistant services • 20, 40, 80 ms interleaving lengths

• Rate matching• to mach the number of bits to the bits available on a single DPCH

radio frame by puncturing or repetition• takes into account all TrCHs which are active in the frame• Rate matching attribute makes it possible to back calculate the bit-

rate of each TrCHs in the reception• 2nd interleaving over 10 ms after TrCH multiplexing

• Block interleaving for each physical channel• The number of bits given for a physical channel at this stage is

exactly the number that the spreading factor of that frame can transmit


TrCH multiplexing• Variable rate

• Performed after TrCH multiplexing to mach the total multiplexed data rate to physical channel data rate

• Downlink• In downlink the fast variable rate has been implemented by DTX (Discontinuous

Transmission). This means that if the bit rate is below the maximum (set by L3) there is a silent period in the frame

• Different TrCH don't have a dynamic impact on rate matching on other TrCH and therefore 2nd DTX for all TrCH is needed

• If the total bit rate of CCTrCH exceeds the maximum data rate of DPCH the multicode transmission is possible. This means that CCTrCH can be splitted to several physical channels with their own codes

• Uplink• Rate matching of all TrCH before multiplexing to mach the data rate to physical

channel• The variable data rate can be achieved by changing the spreading factor of the

physical channel


Example for DL DCH (Packet data 64, 128, 384 kbps)

The number of TrChs = 1Transport block size = 640 bits

Transport block Size64 kbps 640*B bits (B = 0, 1)128 kbps 640*B bits (B = 0, 1, 2)384 kbps 640*B bits (B = 0, 1, 2, …, 6)

CRC =16 bitsCoding Turbo coding, coding rate = 1/3TTI = 10 ms

#1Transport block

CRC attachment

#1 CRC

Turbo coding R=1/3

Rate matching

640

640 16

656* B

#B

#B CRC

640

640 16TrBkconcatenation

1968* B+12+NRMInsertion of DTXindication

1968* B+12+NRM+NDI1st interleaving

1968* B +12+NRM+NDI

1968*BTail bit attachment

Tail121968*B

To TrCH Multiplexing


Example:3 TrCHs3 possible TFCSs



Variable rate and QoS

• When combining two or more services (each having their own fixed parameters for channel coding, QoS target) into a physical channel and one fast closed loop power control function is used for all services, the service having highest Eb/No requirement sets the operation point

• The minimum QoS requirement is met for one service, while other services are received with "too high quality" meaning unnecessary overhead in the received signal

• Each TrCH can have different interleaving length and can therefore support for different delay requirements

• Different quality is obtained by rate matching• Higher quality required � more repetition coding applied

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