WCDMA Air Interface Fundamentals

Lucent Technologies Proprietary 1

W-CDMA Air Interface Fundamentals

Prepared By: Rupy Sikka

E-mail: [email protected]

Ph: +1 (630) 2240 192

mailto:[email protected]


OBJECTIVES

• Describe the requirements and drivers behinds the W-CDMA Air Interface.

• List the layers UMTS radio Air Interface protocol stack and the responsibility of each layer

• UMTS Channel Types and their purpose• Gain understanding of UMTS Modes: FDD and TDD• Protection in UMTS:Describe the forward error correction

employed by UMTS Air interface• Channelizations in UMTS• Source Identification: Scrambling codes/Gold Codes


W-CDMA OVERVIEW-ARCHITECTURE

RNC

Iub Iub

RNS

Uu Uu

Node B Node B

Iu-CS

3G-MSC SGSN

Iu-PS

GGSN PDN/InternetPSTN

Core Network

UTRAN


WCDMA OVERVIEW-UTRAN FUNCTIONS

• UTRAN Functions:– Overall System Access Control

– Security and Privacy

– Handover

– Radio Resource Management and Control

• RNC Functions:

– Intra UTRAN Handover

– Frame Synchronization

– Radio Resource Management: Radio Bearer Control

– Outer Loop Power Control

– Radio Resource Allocation


UTRAN FUNCTIONS

• Node B

– Termination of Iub Interface from RNC

– Conduct Radio Environment Survey (BER estimate, Rx signal strength etc..)

– Inner Loop Power Control

– Open loop power control

– Radio Channel Coding/decoding

– Mapping of coded composite transport channels on physical channel

– modulation and spreading/dispreading of physical channels

– Frequency and time Synchronization

– Error detection on transport channels and indication to higher layers

– Termination of Uu interface from the UE etc..


3G SERVICES


3G CHARACTERISTICS - Asymmetric


3G CHARACTERISTICS– Concurrent Services


3G CHARACTERISTICS – ALWAYS “ON”


W-CDMA INTERFACE


SPECTRUM FOR UMTS


UMTS MODES


UMTS RADIO PROTOCOL STACK

Layer-1

Layer-2L

Layer-2U

Layer-3

OSI


RADIO PROTOCOL STACK FUNCTIONS

• Physical Layer Functions (Layer-1)– Forward error correction, coding,interleaving– Measurements– Soft handover execution– Multiplexing/mapping of services on dedicated physical code channels– Modulation, spreading, demodulation, dispreading of physical channels– Frequency and time synchronization– Fast closed-loop power control– RF processing

• MAC Layer Function (Layer-2L)– Selection of appropriate transport format– Service multiplexing on RACH, FACH and dedicated channels– Scheduling– Access resolution on RACH– Contention resolution on RACH etc..


RADIO PROTOCOL STACK FUNCTIONS

• RLC Functions (Layer-2U):– Segmentation and assembly– Transfer of user data– Error correction through retransmission optimized for physical layer– Sequence integrity– Flow control

• PDCP Function (Layer-2U)– Service specific. Exists only in the User Plane and only for services from PS

domain. Contains compression methods needed for better spectral efficiency

• RRC Functions:– Broadcast of system information– Radio Resource handling– Control of requested QOS – UE measurements reporting and control of the reporting


W-CDMA Channel Architecture


OBJECTIVE

• UMTS W-CDMA Channels Structure

• Map channels to radio interface protocol stack


CHANNELS OVERVIEW


Gift ANALOGY


Channel Overview Cont…


UMTS RADIO INTERFACE CHANNELS


LOGICAL CHANNELS

Traffic Channels - Dedicated Traffic Channel (DTCH)- Common Traffic Channel (CTCH)

Control Channels - Dedicated Control Channel (DCCH)- Common Control Channel (CCCH)- Broadcast Control Channel (BCCH)- Paging Control Channel (PCCH)


TRANSPORT CHANNELS

Dedicated Channels - Dedicated Channel (DCH)

Common Channels - Random Access Channel (RACH) - Forward Access Channel (FACH) - Broadcast Channel (BCH) - Paging Channel (PCH)

- Common Packet Channel (CPCH) - Downlink Shared Channel (DSCH)

(CPCH & DSCH are optional channels and

are not supported in Lucent’s initial release)


PHYSICAL CHANNELS

• Uplink– Dedicated Channels

• Dedicated Physical Data Channel (DPDCH)• Dedicated Physical Control Channel (DPCCH)

– Common Channels• Physical Random Access Channel (PRACH)• Physical Common Packet Channel (PCPCH)

• Downlink– Dedicated Channel

• Dedicated Physical Channel (DPCH)– Common Channels

• Common Pilot Channel (CPICH)• Primary Common Control Physical Channel (P-CCPCH)• Secondary Common Control Physical Channel(S-CCPCH)• Synchronization Channel (SCH)• Physical Downlink Shared Channel (PDSCH)• Acquisition Indication Channel (AICH)• Page Indication Channel (PICH)


UMTS RADIO CHANNEL MAPPING

BCCH

PCCH

CCCH

DCCH

DTCH

CTCH

BCH

CPCH

DSCH

DCH

RACH

FACH

PCH

P-CCPCH

S-CCPCH

P-CPICH

PRACH

DPDCH

DPCCH

PDSCH

PICH

P-SCH

S-SCH

AICH

S-CPICH

PCPCH

Logical Channels Transport Channels Physical Channels

DPCHKey: Uplink

Downlink

Bidirectional

Data Transfer

Association

Control Ch

Traffic Ch

Common Ch (no FPC)

Common Ch (FPC)

Dedicated Ch (FPC)

Info Channels

Assoc Channels

Fixed Channels


W-CDMA PHYSICAL LAYER PROCESSING





• Protecting Data/User Information:– Forward error correction mechanism are applied to allow adding information to the

data streams enabling receiver to correct the errors during decoding process.– Achieved by digital coding techniques such as:

• Convolution coding: – Can use ½ or 1/3 rating coders. – Used for services 19.2Kbps or less e.g. Voice

• Turbo Coding: – Uses two convolution coder working in parallel.– Turbo coder defined as 1/3 rate. – Additional processing relative to convolution coder.– Added delay due to additional processing makes it perfect for non real-time

services such as WEB browsing. – Used for services data rate 19.2Kbps or higher.

• Interleaving:– Reorder original coded data streams to help error correction



• Channel Separation– Uses OVSF codes

– OVSF is applied to achieve 3.84Mcps fixed channel rate

• Source Identification– Scrambling codes are used for

Node-B and UE identification

– The set of scrambling codes are known as Gold codes

– 2-24 Gold codes for UL (UE)

– 512 are assigned for DL(Node-B)

Documents

WCDMA Air Interface Fundamentals