BASIC CONCEPTS OF WCDMA

UMTS AIR INTERFACE

UMTS AIR INTERFACE

WCDMA – FDD TECHNOLOGY• Multiple access technology is wideband CDMA

(WCDMA)• All cells at same carrier frequency• Spreading codes used to separate cells and users• Signal bandwidth 3.84 MHz

• Multiple carriers can be used to increase capacity• Inter-Frequency functionality to support mobility between

frequencies

• Compatibility with GSM technology• Inter-System functionality to support mobility between GSM

and UMTS

ACCESS TECHNOLOGY EXPLANATION

• Multiple Access means “Many users share the same medium”

• There are a number of different Multiple Access (MA) strategies :

• Time Division Multiple Access (TDMA)• Frequency Division Multiple Access (FDMA)• Code Division Multiple Access (CDMA)

TDMA

freq

uen

cy

time

User 1 User 1

Timeslot Period Frame Period

Idealised TDMA (with no guard periods)

Available Frequency Band

FDMA

freq

uen

cy

time

User 1

Frame Period (we may still need frames/timeslots for signaling)

Channel Bandwidth

Idealised FDMA (with no guard bands)

CDMA - DIRECT SEQUENCE SPREAD SPECTRUM

freq

uen

cy

time

code

Frame Period (we may still need frames/timeslots for signaling)

WCDMA TECHNOLOGY

5 MHz

3.84 M Hz

f

5+5 MHz in FDD mode5 MHz in TDD mode

Freq

uenc

y

TimeDirect Sequence (DS) CDMA

WCDMA Carrier

WCDMAWCDMA5 MHz, 1 carrier5 MHz, 1 carrier

TDMA (GSM)TDMA (GSM)5 MHz, 25 carriers5 MHz, 25 carriers

Users share same time and frequency

UMTS & GSM NETWORK PLANNING

GSM900/1800: 3G (W CDM A):

SC PLANNING

TRANSMISSION POWER

Frequency

5MHz

Power density

Time

High bit rate user

Low bit rate user

- Radio Frame: 38400 chip = 10ms = 15 Time Slots

- Time Slot: 2560 chip = 666,6 us (Slots are used for periodic functions (e.g. Power Control), they are not used for channel separation)

- Chip Rate: 3.84 Mcps

- Chip Time: 0.2604 us

WCDMA SPREADING OPERATION• In WCDMA two separate codes are used in the spreading

operation– Channelisation code– Scrambling code

Data

Bit rate

Chanelization code (SF)

scrambling code

chip rate chip rate

Chanelization (increases signal BW)- using orthogonal codes

Scrambling (doesn’t affect signal BW)- using pseudo noise code

Downlink Spreading Factor

Uplink Spreading Factor

Channelisation and Scrambling Codes

Scrambling & Channelization Codes

CONCEPTS OF RSCP AND EC/NO

• Two Important Terms

– RSCP– Ec/No, Ec/Io

TOTAL RECEIVED POWER IO• In a WCDMA network the User Equipment (UE) receives signals from

many cells• Io* = The sum total of all of these signals (dBm)• *Note: Sometimes Io is referred to as No, RSSI

RECEIVED POWER OF A CPICH• Using the properties of SCs the UE is able to extract the respective CPICH

levels from the sites received• RSCP = The Received Power of a Particular CPICH (dBm) • Ec = Energy per Chip

Ec2Ec1

THE CPICH QUALITY (EC/IO)• From the previous two measures we can calculate a signal quality for each

CPICH (SC) received• Ec/Io = Ec - Io (dB)• *Note: Sometimes Ec/Io is referred to as Ec/No

Ec1 Ec2

Logical Channels

RLC

MAC

Physical Layer

Logical Channels

Transport Channels

Physical Channels

Dedicated Logical Channels

Dedicated Traffic Channel (DTCH)

Dedicated Control Channel (DCCH)

Common Logical Channels

Broadcast Control Channel (BCCH)

Paging Control Channel (PCCH)

Common Control Channel (CCCH)

Common Traffic Channel (CTCH)

RLC Radio Link Control

MAC Medium Access Control

RNC Radio Network Controller

Logical ChannelsDTCH is a point-to-point channel, dedicated to one UE, for the transfer of user information. DTCH can exist both in the downlink and uplink.

DCCH is a point-to-point bi-directional channel that transmits dedicated control information between an UE and the network. This channel is established through RRC connection setup procedure.

BCCH is a downlink channel for broadcasting system control information.

PCCH is a downlink channel that transfers paging information.This channel is used when the network does not know the location cell of the UE, or the UE is in the cell connected state (utilizing UE sleep mode procedures).

CCCH is a bi-directional channel for transmitting control information between network and UEs. This channel is commonly used by the UEs having no RRC connection with the network, and by the UEs using common transport channels when accessing a new cell after cell reselection.

CTCH is a point to multipoint unidirectional channel for transfer of dedicated user information for all or a group of specified UEs.

Transport Channels

RLC

MAC

Physical Layer

Logical Channels

Transport Channels

Physical Channels

Dedicated Transport Channels

Dedicated Channel (DCH)

Common Transport Channels

Broadcast Channel (BCH)

Paging Channel (PCH)

Forward Access Channel (FACH)

Random Access Channel (RACH)

Downlink Shared Channel (DSCH)

Common Packet Channel (CPCH)

RLC Radio Link Control

MAC Medium Access Control

RNC Radio Network Controller

Transport ChannelsDCH is a channel dedicated to one UE used in uplink or downlink.

BCH is a downlink channel used for broadcast of system information into an entire cell.

PCH is a downlink channel used for broadcast of control information into an entire cell allowing efficient UE sleep mode procedures. Currently identified information types are paging and notification. Another use could be UTRAN notification of change of BCCH information.

FACH is a common downlink channel without closed loop power control used for transmission of relatively small amount of data.

RACH is a contention based uplink channel used for transmission of relatively small amounts of data, e.g., for initial access or non-real time dedicated control or traffic data.

DSCH is a downlink channel shared by several UEs carrying dedicated control or traffic data.

CPCH is a contention based uplink channel used for transmission of bursty data traffic. This channel only exists in FDD mode. CPCH is shared by the UEs in a cell and therefore it is a common resource. It is fast power controlled.

Physical ChannelsRLC

MAC

Physical Layer

Logical Channels

Transport Channels

Physical Channels

Dedicated Physical Channels

Dedicated Physical Channel (DPCH)

- Dedicated Physical Data Channel (DPDCH)

- Dedicated Physical Control Channel (DPCCH)

Common Physical Channels

Common Pilot Channel (CPICH)

Synchronisation Channel (SCH)

Primary Common Control Physical Channel (PCCPCH)

Secondary Common Control Physical Channel (SCCPCH)

Physical Random Access Channel (PRACH)

Physical Downlink Shared Channel (PDSCH)

Physical Common Packet Channel (PCPCH)

Acquisition Indicator Channel (AICH)

Page Indicator Channel (PICH)

Physical ChannelsThe DPCH = DPDCH + DPCCH carries the DCH in the downlink and uplink.

CPICH is a fixed rate (30 Kbps, spreading factor = 256) downlink physical channel that carries a pre-defined bit/symbol sequence

SCH is a downlink signal used for cell search. The SCH consists of two sub-channels, Primary and Secondary SCH.

PCCPCH is a fixed rate (30 Kbps, spreading factor = 256) downlink physical channel used to carry the BCH.

SCCPCH is a downlink physical channel used to carry FACH and PCH.

PRACH is an uplink physical channel used to carry RACH.

PDSCH is a downlink physical channel used to carry the DSCH.

PCPCH is an uplink physical channel used to carry CPCH.

AICH is a downlink physical channel used to carry acquisition indicators. Acquisition indicator AI_s corresponds to signature s on the PRACH or PCPCH.

PICH is a fixed rate (spreading factor = 256) downlink physical channel used to carry the page indicators. The PICH is always associated with a SCCPCH to which a PCH transport channel is mapped.