31519066 wcdma air interface fundamentals
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OBJECTIVES
Describe the requirements and drivers behinds the W-CDMA Air Interface.
List the layers UMTS radio Air Interface protocol stackand 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 correctionemployed by UMTS Air interface
Channelizations in UMTS Source Identification: Scrambling codes/Gold Codes
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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..
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3G SERVICES
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3G CHARACTERISTICS - Asymmetric
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3G CHARACTERISTICS Concurrent Services
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3G CHARACTERISTICS ALWAYS ON
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W-CDMA INTERFACE
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SPECTRUM FOR UMTS
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UMTS MODES
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UMTS RADIO PROTOCOL STACK
Layer-1
Layer-2L
Layer-2U
Layer-3
OSI
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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..
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RADIO PROTOCOL STACK FUNCTIONS
RLC Functions (Layer-2U): Segmentation and assembly
Transfer of user data
Error correction through retransmission optimized for physicallayer
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 neededfor better spectral efficiency
RRC Functions: Broadcast of system information Radio Resource handling
Control of requested QOS
UE measurements reporting and control of the reporting
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W-CDMA Channel Architecture
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OBJECTIVE
UMTS W-CDMA Channels Structure
Map channels to radio interface protocol
stack
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CHANNELS OVERVIEW
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Gift ANALOGY
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Channel Overview Cont
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UMTS RADIO INTERFACE CHANNELS
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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)
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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 Lucents initial release)
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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)
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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
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W-CDMA PHYSICAL LAYER PROCESSING
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W-CDMA PHYSICAL LAYER PROCESSING
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W-CDMA PHYSICAL LAYER PROCESSING
Protecting Data/User Information:
Forward error correction mechanism are applied to allow addinginformation to the data streams enabling receiver to correct the errorsduring decoding process.
Achieved by digital coding techniques such as:
Convolution coding:
Can use 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 fornon 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
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W-CDMA PHYSICAL LAYER PROCESSING
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)