Umts Air Interface

1U101 UMTS Network Systems Overview

UMTS Air Interface

UMTS Air InterfaceUMTS Air Interface


Contents and Session AimsContents and Session AimsUMTS Air Interface

• This session aims to explain the protocols and operation of the air interface

! To give an overview of the UMTS specific operation of the air interface

! To look at the protocol structure ! To investigate the Frame and

Timeslot structure of the major air interface channels

•Overview of the Air Interface

•Logical, Transport and Physical Channels on the Air Interface

•The Dedicated Channels


Role of the Air InterfaceRole of the Air Interface• To provide a number of bearer or physical channels to support

data transfer over the radio path.• To provide control channels to manage the cell• To provide a number of traffic channels at an acceptable error

performance and at various rates• To provide signalling channels for call set up, etc.• In providing all of this to also:

! Ensure an efficient use of the available spectrum! Minimise interference to other cells and services! Minimise the use of power, particularly from the mobile! Provide synchronisation

UMTS Air Interface


UMTS FDD Air Interface OverviewUMTS FDD Air Interface Overview

Parameter ValueMultiple Access Scheme Direct Sequence CDMADuplexing Method FDDChip Rate 3.84 McpsCarrier Spacing 5 MHzCarrier Spacing Raster 200 kHzFrame Length 10 msSlots per Frame 15Inter-cell Synchronisation NoneSpreading factor Variable (4-512)User Data Rate 8->384 kbps

UMTS Air Interface


Multiple Access SchemeMultiple Access Scheme• UMTS FDD mode makes use of a CDMA style multiple access

scheme• In the case of UMTS this is commonly referred to as Wideband

CDMA• However there are elements of FDMA and TDMA in UMTS

! Common channels for paging and packet access share codes betweenUEs (TDMA)

! Multiple carriers are used per operator (FDMA)

UMTS Air Interface


Duplexing Duplexing MethodMethod• UMTS FDD mode makes use of

Frequency Division Duplexing! The Uplink and Downlink

Channels are carried on separate carriers

• In the case of UMTS in Europe:! The Uplink band is between 1.92

and 1.98GHz! The Downlink band is between

2.11 and 2.17GHz ! The Uplink/Downlink Separation

is 190MHz

UMTS Air Interface

1.8GHz

2.05GHz

1.9GHz1.95GHz2GHz

1.85GHz

2.1GHz2.15GHz2.2GHz

190MHz2.17GHz

2.11GHz

1.98GHz

1.92GHz

UMTS Uplink UMTS Downlink


Chip RateChip Rate• The chiprate used in UMTS FDD mode is 3.84Mcps• This leads to a carrier bandwidth of approximately 5MHz• This chip rate was chosen because it:

! Could be generated simply from existing GSM clock rates! Provided a similar bandwidth to cdma2000 to allow shared use of filters etc in

UEs

• Note: Initially UMTS was specified as having a chip rate of 4.096Mcps.! You may find some old texts and papers referring to this chip rate

UMTS Air Interface


Carrier Spacing and Carrier Spacing RasterCarrier Spacing and Carrier Spacing Raster• The nominal carrier spacing for

UMTS is 5Hz• This was chosen to comply with

the American market, where spectrum has been awarded in 5MHz blocks

• It is possible to move the centre frequency of the carrier on a 200kHz raster

! We can have carrier spacings between 4.4MHz and 5.6MHz

! This may be set within the license conditions, or to the operators discretion

UMTS Air Interface

5MHz

200kHz


Adjacent Channel InterferenceAdjacent Channel Interference• Adjacent channel interference may have a significant impact on

UMTS capacity• Required attenuation (by standards)

! adjacent carrier 33dB! 2nd adjacent carrier 43dB

• Since only have 2 or 3 carriers typically at least one adjacent carrier will be transmitted by a third party

• This can partially be negated by a flexible carrier spacing based upon a 200kHz raster

UMTS Air Interface


Adjacent Operator InterferenceAdjacent Operator Interference

Distant Serving Macrocell

Close InterferringMicrocell

InterferenceSignal50dB path loss

150dB path loss

UMTS Air Interface


UK Spectrum Allocations ExampleUK Spectrum Allocations ExampleD D DE E EC C CA A A A B B B

Hutchison

One2One

Vodafone

BT Cellnet

Orange

14.6MHz 14.8MHz10MHz 10MHz 10MHz0.3MHz0.3MHz

20MHz

UMTS Air Interface


Tslot = 666.7µs = 2560 chips

Radio Frame StructureRadio Frame Structure• Radio Frame Period = Tf = 10ms• Frames are used for channel format control• 15 slots, #0…#14• Slots are use for power control• 38400 chips • Tslot = 2560 chips = 666.7µs

#0 #1 #2 #i #14

Tf = 10ms = 38400 chips

UMTS Air Interface


Superframe Superframe StructureStructure• 72 Radio Frames make a Superframe• Superframe Period Tsf = 720ms

Superframes are used for

#0 #1 #2 #i #71

Tsf = 720ms

UMTS Air Interface


Inter Cell Inter Cell SynchronisationSynchronisation• Cells in a UMTS network are not synchronised in time with

each other.• This removes the need for tight synchronisation between the

base stations• There is no need for GPS receivers at sites

! This makes implementation of picocells and their integration with the network more simple as satellite LoS is not required

• 3rd Party Transmission requirement are less stringent

UMTS Air Interface


Spreading Factor and User Data RatesSpreading Factor and User Data Rates• UMTS has been designed to provide flexibility to allow the user

to use multiple services, some of which we cannot foresee at the moment

• Rather than having a fixed bit rate and spreading factor, each of the channels on the user interface has a range of bit rates that can be used

• This makes the channels more complicated than for GSM…but certainly more flexible

UMTS Air Interface


Air Interface Access StratumAir Interface Access Stratum

L3

L2

L1

Radio Resource Control RRC

Radio Link Control RLC

Medium Access Control MAC

Physcial Layer

Control Plane Signalling

User Plane Information

Logical Channels

Transport Channels

Physical Channels

UMTS Air Interface


Physical Channels

Radio Resource Control LayerRadio Resource Control Layer• The RRC layer forms the lower

part of the OSI layer 3• It is responsible for:

! Bearer Control! Monitoring! Power Control! Measurement Reporting! Paging! Broadcast Control

L3

L2

L1




Physical Layer



Logical Channels

Transport Channels

UMTS Air Interface


Radio Resource Control Layer Functional Radio Resource Control Layer Functional EntitiesEntities

• The RRC layer resides at the RNC serving a cell or UE• The RRC Layer can be split into 3 functional entities

! Dedicated Control Functional Entity (DCFE)" One per UE in connection" All functions and signalling specific to a single UE

! Paging and Notification control Functional Entity (PNFE)" One per cell" Paging of idle mode UEs

! Broadcast Control Functional Entities (BCFE)" One per cell" Broadcasting of system information

UMTS Air Interface


Physical Channels

Radio Link Control LayerRadio Link Control Layer• The RLC layer forms the upper part

of the OSI layer 2• It is responsible for:

! Logical Link Control! Acknowledged and

unacknowledged data transfer

L3

L2

L1




Physical Layer



Logical Channels

Transport Channels

UMTS Air Interface


Physical Channels

The Medium Access Control LayerThe Medium Access Control Layer• The MAC Layer forms the lower

part of layer 2• It is responsible for:

! Random Access! Physical Link Control! Ciphering! Multiplexing and Channel Mapping

to the Physical Layer

L3

L2

L1




Physical Layer



Logical Channels

Transport Channels

UMTS Air Interface


Medium Access Control Layer Functional Medium Access Control Layer Functional EntitiesEntities

• MAC-b! Handles the broadcast channel (BCH) and is located in the Node-B in

the UTRAN

• MAC-c/sh! Handles the common and shared channels and is located in the RNC in

the UTRAN

• MAC-d! Handles the dedicated channels and is located in the RNC

UMTS Air Interface


The Physical LayerThe Physical Layer• The Physical Layer forms layer 1 of

the OSI protocol stack• It is responsible for:

! Carrying traffic and signalling across the air interface

L3

L2

L1




Physical Layer



Logical Channels

Transport Channels

UMTS Air Interface

Physical Channels


Protocol Termination in the Access StratumProtocol Termination in the Access Stratum

User Equipment Node-B Radio Network Controller

RRC RRC

RLC RLC

MAC MAC

Physical Physical

Note: Some Layer 2 functionality regarding the broadcast functionality resides in the Node-B

UMTS Air Interface


UMTS Channel Types and FunctionsUMTS Channel Types and Functions• There are three types of channel across the air interface and

access stratum that we are interested in:! Logical Channels

" Between the RLC and MAC layers

! Transport Channels" Between the MAC and Physical layers

! Physical Channels" Between Physical Layers at the Node-B and UE

UMTS Air Interface


Major Logical Channels in UMTSMajor Logical Channels in UMTS• Control Channels

! BCCH Broadcast Control Channel! PCCH Paging Control Channel! CCCH Common Control Channel! DCCH Dedicated Control Channel

• Traffic Channels! DTCH Dedicated Traffic Channel! CTCH Common Traffic Channel

UMTS Air Interface


Logical Control ChannelsLogical Control Channels• The Broadcast Control Channel (BCCH) is a downlink channel

for broadcasting system control information• The Paging Control Channel (PCH) is a downlink channel that

transfers paging information• The Dedicated Control Channel (DCCH) is a point-to-point bi-

directional channel transmitting control information between a specific UE and the UTRAN

• The Common Control Channel (CCCH) is a bi-directional channel transmitting control information between Ues and the UTRAN

UMTS Air Interface


Logical Traffic ChannelsLogical Traffic Channels• The Dedicated Traffic Channel (DCH) is a point-to-point

channel dedicated to a single UE for the transfer of user information

• The Common Traffic Channel (CTCH) is a point-to-point unidirectional channel for transfer of user information to a group of UEs

UMTS Air Interface


• Common Control Channels! BCH Broadcast Channel! FACH Forward Access Channel! PCH Paging Channel ! RACH Random Access Channel! CPCH Common Packet Channel

• Dedicated Channels! DCH Dedicated Channel! DSCH Downlink Shared Channel

Major Transport Channels for UMTSMajor Transport Channels for UMTSUMTS Air Interface


Common Transport ChannelsCommon Transport Channels• The Broadcast Channel (BCH) is a cell-wide channel that is used to

broadcast system and cell-specific information. The BCH is always transmitted over the entire cell with a low fixed bit rate.

• The Paging Channel (PCH) is a cell-wide channel that is used to carry control information to a UE when the system does not know the location cell of the UE

• The Forward Access Channel (FACH) is a downlink channel that is used to carry control information to a UE when the system knows the location cell of the UE. May also carry short user packets.

• The Random Access Channel (RACH) is an uplink control channel from the UE. May also carry short user packets

• The Common Packet Channel (CPCH) is a contention based uplink channel used for transmission of bursty data traffic.

UMTS Air Interface


Dedicated Transport ChannelsDedicated Transport Channels• The Downlink Shared Channel (DSCH) is a downlink channel

shared by several UEs carrying dedicated control or traffic data.• The Dedicated Channel (DCH) is a channel dedicated to one

UE used in uplink or downlink.

UMTS Air Interface


• Common Control Channels! P-CCPCH Primary Common Control Physical Channels (DL)! S-CCPCH Secondary Common Control Physical Channels (DL)! P-SCH Primary Synchronisation Channel (DL)! S-SCH Secondary Synchronisation Channel (DL)! CPICH Common Pilot Channel (DL)! AICH Acquisition Indicator Channel (DL)! PICH Paging Indicator Channel (DL)! PDSCH Physical Downlink Shared Channel (DL)! PRACH Physical Random Access Channel (UL)! PCPCH Physical Common Packet Channel (UL)! AP-AICH Access Preamble Acquisition Indicator Channel (DL)! CD/CA-ICH Collision Detection/Channel Assignment Indicator Channel (DL)

• Dedicated Channels! DPDCH Dedicated Physical Data Channel (DL & UL)! DPCCH Dedicated Physical Control Channel (DL & UL)

Major Physical Channels for UMTSMajor Physical Channels for UMTSUMTS Air Interface


• The Primary-Common Control Physical Channels (P-CCPCH) is used to carry broadcast information across the cell

• The Secondary-Common Control Physical Channels (S-CCPCH) is used to carry paging and forward access information across the cell

• The Primary-Synchronisation Channel (P-SCH) is used during cell search to provide timing information

• The Secondary-Synchronisation Channel (S-SCH) is used during cell search to provide information about the primary scrambling codes in use in the cell

• The Common Pilot Channel (CPICH) is used to provide the phase reference for downlink channels

• The Acquisition Indicator Channel (AICH) is used to acknowledge random access requests

Common Physical Channels for UMTSCommon Physical Channels for UMTSUMTS Air Interface


• The Paging Indicator Channel (PICH) is used to enable discontinuous reception of the S-CPCCH

• The Physical Downlink Shared Channel (PDSCH) carries traffic to one or more users• The Physical Random Access Channel (PRACH) is a contention based channel used for

random access and to transmit small packets of information• The Physical Common Packet Channel (PCPCH) is an extension to the RACH used to carry

larger packets of information on the uplink• The Access Preamble Acquisition Indicator Channel (AP-AICH) is used to indicate the reception

of a preamble signature for Random Access• The Collision Detection/Channel Assignment Indicator Channel (CD/CA-ICH) is used to indicate

collisions and channel assignment for packet access

Common Physical Channels for UMTSCommon Physical Channels for UMTSUMTS Air Interface


Dedicated ChannelsDedicated Channels• The Dedicated Physical Data Channel (DPDCH) is used to

carry user information• The Dedicated Physical Control Channel (DPCCH) is used to

carry dedicated control information regarding its associated DCHs

UMTS Air Interface


Mapping of Logical Channels to Transport Mapping of Logical Channels to Transport ChannelsChannels

BCH PCH CPCH RACH FACH DSCH DCH

BCCH PCCH DCCH CCCH CTCH DTCH

Logical Channels

Transport Channels

UMTS Air Interface


Mapping of Transport Channels to Physical Mapping of Transport Channels to Physical ChannelsChannels

BCH PCHCPCHRACH FACH DSCH DCH

DPDCH

DPCCH

PDSCH

S-CCPCH

P-CCPCH

PCPCH

PRACH

S-SCH

CPICH

AICH

PICH

AP-AICH

CD/CA-ICH

P-SCH

Physical Channels

Transport Channels Spreading/Modulation

UMTS Air Interface


UMTS Air Interface Physical ResourceUMTS Air Interface Physical Resource• Code Plane

! Separation within cell by channelisation codes! Separation between cell by scrambling codes

• Frequency Plane! Multiple carriers available

• Phase Plane! IQ multiplexing of channels on the UL

• Space Plane! Adaptive antennas

• Time Plane! Time multiplexing of channels on DL! Packet Access

UMTS Air Interface


Codes in UMTSCodes in UMTS• We have already talked generically about codes in CDMA• In UMTS there are a number of different types of codes:

! Synchronisation Codes" To enable an unsynchronised UE to synchronise and determine the

scrambling code of the cell

! Channelisation Codes" To spread and channelise within a UE or cell

! Scrambling Codes" To separate the UEs and cells

UMTS Air Interface


Synchronisation CodesSynchronisation Codes• These are short duration Gold codes• They have length 256 chips and duration 66.67µs• There is 1 primary code and 64 secondary codes

UMTS Air Interface


Channelisation Channelisation CodesCodes• These are short Orthogonal Variable Spreading Factor (OVSF)

codes• They are of length 4 - 512 chips long (1.04-133.34µs)

dependant upon the channel and required bit rate of the service• There are between 4 and 512 codes dependant on the length

of the code• OVSF codes are orthogonal

UMTS Air Interface


• Orthogonal Variable Spreading Factor Codes can be defined by a code tree:

• Where ! SF = Spreading Factor of code (maximum 512 for UMTS)! k = code number = 0<=k<=SF-1

SF = 1 SF = 2 SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,4,0 =(1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

OVSF codesOVSF codesUMTS Air Interface


SF = 1 SF = 2 SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,4,0 =(1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

IN USE

IN USESF = 1 SF = 2 SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,4,0 =(1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

IN USE

Code Usage EfficiencyCode Usage Efficiency• Any codes further down the trunk

of a branch in use cannot be used• Any codes further out from the

branch in use cannot be reused

• By filling up branches of the code tree before starting new branches a greater capacity can be achieved

• Multiple code trees can be used from a cell but at an increased level of interference between channels

IN USE

UMTS Air Interface


Multiple Code TreesMultiple Code Trees• We can actually use multiple code trees if we run out of OVSF

codes on the downlink• This is achieved by introducing a second scrambling code• However codes on the two code trees will only be separated by

the scrambling codes, which are not orthogonal• This reduces interference rejection

UMTS Air Interface


Scrambling CodesScrambling Codes• Downlink Scrambling codes are complex valued Gold codes

! They are a 38400 chip segment from a 218 chip code, duration 10ms (1 frame)

! There are 512 primary codes and 15 secondary codes associated with each primary code

• Uplink Scrambling codes can be long or short codes" Long codes are complex valued Gold codes and are a 38400 chip

segment from a 225 chip code, duration 10ms (1 frame)– There are 16,777,216 codes…

" Short codes are complex valued S(2) codes and 256 chips long, duration 66.67µs

– There are again 16,777,216 codes

UMTS Air Interface


The Primary Synchronisation ChannelThe Primary Synchronisation Channel• The P-SCH transmits the Primary Synchronisation Code• This is a 256 chip sequence and is the same in all cells in the network• The channel is transmitted at the start of a timeslot, for the first 66.67µs• There is only ever one P-SCH per cell

P-SCH P-SCH P-SCH

256 chips66.67µs

2560 chips666.7µs

Timeslot # 0 Timeslot # 1 Timeslot # 2

P-SCH

UMTS Air Interface


The Secondary Synchronisation ChannelThe Secondary Synchronisation Channel• The S-SCH transmits the Secondary Synchronisation Code• This is a 256 chip sequence and is one of 64 possible SSCs• The channel is transmitted at the start of a timeslot, for the first 66.67µs, at the same

time as the P-SCH• The SSC indicates which group of downlink scrambling codes is in use at the cell• There is only ever one S-SCH per cell

PSC PSC PSC

256 chips66.67µs

SSC SSC SSC

2560 chips666.7µs


P-SCH

S-SCH

UMTS Air Interface


• Primary CCPCH is transmitted continuously at constant power from each cell

• Uses one of the 512 Primary Scrambling Codes• Channelisation code is same for all Primary CCPCHs• There is only one P-CCPCH per cell

30 kbps, SF=256

The Primary Common Control Physical The Primary Common Control Physical ChannelChannel

PSC PSC PSC

256 chips66.67µs

SSC SSC SSC2560 chips

666.7µs


2304 chips600µs

Data (10 bits) Pilot (8 bits)Data (10 bits) Pilot (8 bits) Data (10 bits) Pilot (8 bits)

P-SCH

S-SCH

P-CCPCH

UMTS Air Interface


The Secondary Common Control Physical The Secondary Common Control Physical ChannelChannel

• The cell communicates with UEs through the PCH and FACH! These are carried on the Secondary-CCPCH

• The SF is variable, set in the BCH, indicated on the P-CCPCH and is between 4 and 256• Fixed power

! This is why the channels are multiplexed to avoid simultaneous transmission

• TFCI, Transport Format Combination Indicator, is optional but must be supported by all UEs• Similarly Pilot bits are optional• There may be more than one S-CCPCH per cell, and frames may be offset in time by multiples

of 256 chips! E.g.one may be used to carry the FACH and one to carry the PCH

UMTS Air Interface

Pilot (0 - 16 bits per slot)

Data (10 - 1272 bits per slot)

TFCI (0 - 8 bits per slot)

1 timeslot 2560 chips, 666.7µs

S-CCPCH30-1920 kbps, SF=4-256


The Physical Random Access ChannelThe Physical Random Access Channel• The PRACH consists of two parts

! A preamble" To initiate access

! A message" Which can contain a request for a dedicated channel or a small packet of

user data2 frames = 20 ms

1 PRACH slot = 2 normal timeslots1 PRACH preamble = 4096 chips

PRACH Message

UMTS Air Interface


The PRACH PreambleThe PRACH Preamble• Selected from one of 16 preambles available on the cell• The preamble is 1ms in length• Power of transmitted preamble is based on an estimate of

downlink loss from CPICH received signal strength• It then randomly selects a slot from 15 over 2 Frames (slotted

ALOHA)• In no acknowledge then reselects signature and increases

power by 1dB and tries again

UMTS Air Interface


The PRACH MessageThe PRACH Message

• The message is either 15 or 30 slots in length! Determined by which slot the preamble was sent in

• Power as successful preamble• Data and control are code multiplexed

Pilot (8 bits per slot)

Data (10 - 80 bits per slot)

TFCI (2 bits per slot)

1 timeslot 2560 chips, 666.7µs

PRACH message

Control

Data15 - 120 kbps, SF=32-256

15 kbps, SF=256

UMTS Air Interface


AICHAICH

• The AICH indicates whether the PRACH preamble has been received• If the Node-B receives the preamble it mirrors the preamble signature

back on the AICH

2 frames = 20 ms

1 PRACH slot = 1.25ms1 PRACH preamble = 4096 chips

PRACH

AICH

Message

1 PRACH preamble = 4096 chips

UMTS Air Interface


PCPCHPCPCH• Similar to the the PRACH• Additionally a collision detection preamble is sent• The AI-ICH responds to the PCPCH access preamble• The CD/CA-ICH responds to the collision detection preamble• The message part has the same structure as an uplink DPCH

4096 chips

P0P1

Pj Pj

Collision DetectionPreamble

Access Preamble Control Part

Data part

0 or 8 slots N*10 msec

Message Part

UMTS Air Interface


b1b0

288 bits for paging indication 12 bits (undefined)

One radio frame (10 ms)

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

b287 b288 b299

PICHPICH• The PICH is the Paging Indication Channel, used to inform the UE that it

should listen to the PCH • Fixed rate (SF=256)• N Paging Indicators {PI0, …, PIN-1} are transmitted in each PICH frame,

where N=18, 36, 72, or 144. • These are mapped to 300 transmitted bits

UMTS Air Interface


UE

Dedicated Physical Channel (DPCH)Dedicated Physical Channel (DPCH)• Consists of two parts:

! DPDCH (Dedicated Physical Data Channel)" Carries the user data

! DPCCH (Dedicated Physical Control Channel)" Carries control information (pilot bits, power control and optional rate

information)

• It is different on uplink and downlink! Uplink

" Data and control code multiplexed to avoid DTX based EMC problems

! Downlink" Data and control time multiplexed DTX based EMC not a problem

UMTS Air Interface


DCH Control FieldsDCH Control Fields• Pilot

! A predetermined bit pattern utilised by the rake receiver to estimate channel conditions (5,6,7or 8 bits per slot)

! Also used for coherent demodulation of the remaining data on the DCH• TFCI - Transport Format Combination Indicator

! This is an optional field! Used where different formats (multiplexing or spreading factor) are used on a

frame by frame basis (0 or 2 bits per slot)• TPC - Transmit Power Control

! 2 bits per slot indicating an increase or decrease power• FBI - Feedback Indicator

! Used for diversity working (0,1,2 bits per slot)

UMTS Air Interface


DownlinkDownlink--Dedicated Physical Dedicated Physical Channel..Frame/Slot StructureChannel..Frame/Slot Structure

One radio frame, Tf = 10 ms

TPCNTPC bits

Slot #0 Slot #1 Slot #i Slot #14

Tslot = 2560 chips, 10*2 k bits (k=0 ..7)

Data2Ndata2 bits

DPDCHTFCI

NTFCI bitsPilot

Npilot bitsData1

Ndata1 bits

DPDCH DPCCH DPCCH

• k = 0..7• Bits per Slot, Ndata = 10*2k bits

! Ndata = 10 - 1280 bits

• Spreading Factor, SF = 256/2k

! SF = 512 - 4

• Channel Bit Rate, Rb = 15*2k kbps! Rb = 15 - 1920kbps

• The dedicated transport channel (DCH), is transmitted in time-multiplex with control information generated at Layer 1 (known pilot bits, TPC commands, and an optional TFCI)

UMTS Air Interface


Downlink Spreading and ModulationDownlink Spreading and Modulation

Serial -Parallel

DPDCH/DPCCHcch

15*2K kbpsI

Q

cos(ωωωωt)

sin(ωωωωt)

cscrambPulse

Shaping

Pulse Shaping

UMTS Air Interface


Downlink Variable Rate (DTX based)Downlink Variable Rate (DTX based)

R = 60kbps R = 30kbpsR = 0kbps R = 60kbps

10 ms

Pilot+TPC+TFCI Data

Note: that this diagram does not reflect the true multiplexing on the downlink

UMTS Air Interface


Uplink Dedicated Physical Data Uplink Dedicated Physical Data Channel..Frame/Slot StructureChannel..Frame/Slot Structure

• k = 0..6• Bits per Slot, Ndata = 10*2k bits

! Ndata = 10 - 640 bits

Slot #0 Slot #1 Slot # i Slot #14

1 radio frame: Tf = 10 ms

DataNdata bitsDPDCH

Tslot = 2560 chips, N data = 10*2 k bits (k=0 ..6)

• Spreading Factor, SF = 256/2k

! SF = 256 - 4

• Channel Bit Rate, Rb = 15*2k kbps! Rb = 15 - 960kbps

• Used to carry the DCH transport channel.

UMTS Air Interface


• Used to carry control information generated at Layer 1. ULUL--DPCCH(3)..Slot/Frame StructureDPCCH(3)..Slot/Frame Structure

1 radio frame: T = 10 ms

PilotNpilot bits

TPCNTPC bits

Slot #0 Slot #1 Slot # i Slot #14

Tslot = 2560 chips, 10 bits

f

DPCCHFBI

NFBI bitsTFCI

NTFCI bits

• Channel Bit Rate! Rb = 15 kbps

• Spreading Factor! SF = 256

• Bits per slot = 10

• The Layer 1 control information consists of:

! known pilot bits ! transmit power-control (TPC)

commands! feedback information (FBI)! optional transport-format

combination indicator (TFCI).

UMTS Air Interface


Uplink Spreading and ModulationUplink Spreading and Modulation

cDPDCH

I+jQ

RealDPDCH

DPCCH Imag

cos(ωωωωt)

sin(ωωωωt)

cscramb

cDPCCH

Pulse Shaping

Pulse Shaping

UMTS Air Interface


Uplink Dedicated Channel MultiplexingUplink Dedicated Channel Multiplexing• One DPCCH and up to 6 DPDCH are spread by real valued

sequences• DPCCH is spread by channelisation code cc

• DPDCH is spread by channelisation code cd,n where 1<=n<=6• After channelisation real valued signals are weighted by βc and

βd, at least one of which has amplitude 1• Only one DPCCH allowed per link

UMTS Air Interface


Uplink Dedicated Channel MultiplexingUplink Dedicated Channel Multiplexing

IΣ

j

cd,1 βd

Sdpch,n

I+jQ

DPDCH1

Q

cd,3 βd

DPDCH3

cd,5 βd

DPDCH5

cd,2 βd

DPDCH2

cd,4 βd

DPDCH4

cd,6 βd

DPDCH6

cc βc

DPCCH

Σ

S

UMTS Air Interface


Uplink Variable Rate (VSF based)Uplink Variable Rate (VSF based)10 ms

Pilot+TPC+TFCI+FBI Data

R = 60kbps R = 30kbps R = 0kbps R = 0kbps R = 30kbps

UMTS Air Interface


Why does UMTS need the CPICH?Why does UMTS need the CPICH?• UMTS already has the SCHs and pilot bits...• Why does it need a pilot channel?

! Handover measurements and cell selection/reselection! To aid channel estimation for dedicated channels! To provide channel estimation reference for common channels

UMTS Air Interface


A MultiA Multi--Rate Rate ChannelisedChannelised TransmitterTransmitter

60kbps Bit Stream

30kbps Bit Stream

15kbps Bit Stream

Pulse Shaping and Modulation

c1

c2

c3

s1All the channels are spread to the same chip rate and then added together.Note: to achieve the same Eb/No we must modify the power per chip before combining the chip streams

Power Control

x4

x2

x1

UMTS Air Interface


QuestionsQuestions• Which other physical channels are similar to the AICH?• What are the two parts of the PRACH channel?• Which layers do the Transport channels connect?• Where is the MAC layer terminated?

UMTS Air Interface

Umts Air Interface

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Transcript of Umts Air Interface