WCDMA for UMTS Training
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Transcript of WCDMA for UMTS Training
WCDMA for UMTS
by Dr. Hatem MOKHTARICirta Consulting LLC
Contents• History of the WCDMA Standard• Spectrum Allocation• Bearer Services• CDMA Principles• WCDMA• Radio Access Network Architecture• Physical Layer• Radio Interface Protocols• Packet Transmission• TDD Mode• Network Planning
CDMA Principles
• CDMA System Overview
• Direct Sequence CDMA
CDMA Principles
• In FDMA and TDMA systems, traffic channels cannot share the same radio channel at the same time
• In Code Division Multiple Access (CDMA) systems, traffic channels share the same radio channel and are distinguished by a Code:
CDMA Principles
• Frequency hopping (FH) CDMA where traffic channels hop across the same group of narrow-band channels with a different hop sequence
The Code determines the hop sequence:
• Direct Sequence (DS) CDMA where traffic channels are spread across the same wide-band radio channel using a pseudo-random bit sequence (PRBS). The Code determines the PRBS
F1:F2:F3:F4:F5:F6:F7:F8:F1:F2:F3:F4:F5:F6:F7:F8:F1:F2:F3:F4:F5:F6:F7:F8:F1:F2:F3:F4:F5:F6:F7:F8:F1:F2:F3:F4:F5:F6
FH sequence
time
CDMA PrinciplesDS CDMA System Overview
Demodulation
PRBS/PN
A
f Received signal
A
f Signal recovery
A
f Baseband signal
A
f
W
Transmitted signal
Transmission
Modulation
PRBS/PN
r
WCDMA
• Main Parameters in WCDMA
• Spreading and Despreading
• Rake Reception
• Power Control
• Handovers
WCDMAMain Parameters in WCDMA
• WCDMA is a wideband Direct-Sequence Code Division Multiple Access system (DS-CDMA).
• The chip rate of 3.84 Mchips/s gives a carrier bandwidth of approximately 5MHz
• WCDMA supports highly variable user data rates. The concept of bandwidth on demand.
• WCDMA supports 2 basic modes of operation:• FDD where separate 5 MHz carrier frequencies
are used for uplink and downlink• TDD where only one 5 MHz carrier is time
shared between uplink and downlink
WCDMAMain Parameters in WCDMA
• WCDMA supports the operation of asynchronous base stations.
• WCDMA employs coherent detection on the uplink and downlink based on the use of pilot symbols or common pilot.
• The WCDMA air interface has been designed to allow advanced CDMA receiver concepts, e.g. multiuserdetection and smart adaptive antennas.
• WCDMA is designed to work in conjunction with GSM.
WCDMASpreading and Despreading
1
-1
1
-1
1
-1
1
-1
1
-1
Chip
Despreading
Data
Spreading Code
Spread Signal = Data x Code
Spreading Code
Data = Spread Signal x Code
Symbol
Spreading
Spreading and Despreading in DS-CDMA
WCDMA
Interfering Signal
Wanted Signal
The CDMA Correlation Receiver
Desired Spread Signal
Spreading Code
Data after Despreading
Data after Integration
Interfering Spread Signal
Interfering Sig. After Despreading
Interfering Sig. After Integration
1
-1
1
-1
1
-18
-8
1
-11
-18
-8
Spreading and Despreading
WCDMA
Example of Processing Gain
If the data rate of a speech service is 12.2 Kb/sProcessing Gain = 10 x log (3.84x106/12.2x103) = 25 dB
After despreading Eb/No should be >= 5 dB for speechDesired C/I of the spread signal = 5 - processing Gain = -
20 dBIn this case the wanted signal power can be 20 dB below
thelevel of the interference or system noise.
Spreading and Despreading
Physical Layer
• Channels• Interface Between Higher Layers and Physical
Layer• Transport Channels• Uplink Physical Channels• Downlink Physical Channels• Transport Channel to Physical Channel
Mapping• Dedicated Physical Channels
Physical Layer
Channels
•RF Channel
•Physical Channel
•Transport Channel (New in UMTS)
•Logical Channel
Physical LayerInterface Between Higher Layers and Physical Layers
TRANSMITTER RECEIVER
Transport Block
Transport BlockTFI TFI
Transport Block & Error Indication
Transport Block & Error Indication
TFITransport Block & Error Indication
Transport Block & Error Indication
Transport Block
Transport BlockTFI
Higher Layers
Physical Layer
Coding & MultiplexingTFCI TFCI Decoding
Decoding & Demultiplexing
Physical Control Ch
Physical Data Ch
Physical Control Ch
Physical Data Ch
Transport Ch 1 Transport Ch 2
Physical LayerTransport Channels
Common Channels (CCHs) Dedicated Channel (DCH)
(Uplink/Downlink)
Broadcast Channel (BCH) (Downlink)
Forward Access Channel (FACH) (Downlink)
Paging Channel (PCH) (Downlink)
Random Access Channel (RACH) (Uplink)
Common Packet Channel (CPCH) (Uplink)
Downlink Shared Channel (DSCH) (Downlink)
Physical LayerUplink Physical Channels
Dedicated Physical Channels Common Physical Channels
Dedicated Physical Control Channel (Uplink DPCCH)
Dedicated Physical Data Channels (Uplink DPDCH)
Physical Random Access Channels (PRACH)
Physical Common Packet Channel (PCPCH)
Physical LayerDownlink Physical Channels
Dedicated Physical Channel (Downlink DPCH) (Time multiplex of downlink DPDCH and downlink DPCCH
Common Physical Channels
Common Pilot Channel (CPICH)
Primary CPICH
Secondary CPICH
Primary Common Control Physical Channel (P-CCPCH)
Secondary Common Control Physical Channel (S-CCPCH)
Synchronisation Channel (SCH)
Physical Downlink Shared Channel (PDSCH)
Acquisition Indication Channel (AICH)
Page Indication Channel (PICH)
Physical LayerTransport Channel to Physical Channel Mapping
Transport Channels
Physical Channels
BCH FACH DCHRACHPCH
SCHP-CCPCH
DSCHCPCH
S-CCPCHCPICH DPCCH
DPDCHPRACH
PCPCH PDSCH
PICH
AICH
Physical Layer
Dedicated Physical Channel (DPCH)
DPCH
DPDCH DPCCH
DPDCH - Dedicated Physical Data Channel
•Carries dedicated transport channels
DPCCH - Dedicated Physical Control Channel
•Carries control information at layer 1 (known pilot, transport format combination indicator (TFCI), feedback information and transmit power control (TPC) command.
Physical LayerUplink DPCH Frame Structure
0 1 2 3 12 13 14…...
10ms
Pilot TFCI FBI TPC
Data
2560 chips
DPCCH
DPDCH
Physical Layer
DPDCH Spreading Factor
DPDCH Channel bit rate (Kb/s)
Maximum user data rate with ½ rate coding
(approx.) 256 15 7.5 kb/s
128 30 15 kb/s
64 60 30 kb/s
32 120 60 kb/s
16 240 120 kb/s
8 480 240 kb/s
4 960 480 kb/s
4 with 6 parallel codes 5740 2.3 Mb/s
Uplink DPDCH data Rates