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Nov 18, 2014
WCDMA for UMTSby Dr. Hatem MOKHTARI Cirta 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 channelscannot 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 channelshop across the same group of narrow-band channels with a different hop sequenceThe Code determines the hop sequence:FH sequenceF1: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
time
Direct Sequence (DS) CDMA where traffic channelsare spread across the same wide-band radio channel using a pseudo-random bit sequence (PRBS). The Code determines the PRBS
CDMA PrinciplesDS CDMA System OverviewA rBaseband signal f PRBS/PN Modulation
A WTransmitted signal f
Transmission
PRBS/PN
ADemodulation
A
Signal recovery
f
Received signal f
WCDMA Main Parameters in WCDMA Spreading and Despreading Rake Reception Power Control Handovers
WCDMAMain Parameters in WCDMA WCDMA is a wideband Direct-Sequence CodeDivision 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 basestations. 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. multiuser detection and smart adaptive antennas. WCDMA is designed to work in conjunction with GSM.
WCDMASpreading and DespreadingSymbol1
DataChip
-1
Spreading1 -1 1 -1
Spreading Code Spread Signal = Data x Code Despreading
1
Spreading Code Data = Spread Signal x Code Spreading and Despreading in DS-CDMA
-1 1 -1
Spreading and DespreadingWanted Signal1 Desired Spread Signal -1 1 Spreading Code -1 1 -1 8 -8
WCDMA
Data after Despreading Data after Integration
Interfering Signal1 Interfering Spread Signal Interfering Sig. After Despreading Interfering Sig. After Integration -1 1 -1 8 -8
The CDMA Correlation Receiver
WCDMASpreading and Despreading Example of Processing Gain If the data rate of a speech service is 12.2 Kb/s Processing Gain = 10 x log (3.84x106/12.2x103) = 25 dB After despreading Eb/No should be >= 5 dB for speech Desired C/I of the spread signal = 5 - processing Gain = 20 dB In this case the wanted signal power can be 20 dB below the level of the interference or system noise.
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 LayerChannels RF Channel Physical Channel Transport Channel (New in UMTS) Logical Channel
Physical LayerInterface Between Higher Layers and Physical LayersTransport Ch 1 Transport Block TFI Transport Block TFI Transport Ch 2 Transport Block Transport Block TFI Transport Block & Error Indication Transport Block & Error Indication TFI Transport Block & Error Indication Transport Block & Error Indication
Higher Layers Physical Layer TFCI Physical Control Ch Coding & Multiplexing Physical Data Ch TFCI Decoding Physical Control Ch Decoding & Demultiplexing Physical Data Ch RECEIVER
TRANSMITTER
Physical LayerTransport Channels
Common Channels (CCHs)
Dedicated Channel (DCH) (Uplink/Downlink)
Broadcast Channel (BCH) (Downlink) Forward Access Channel (FACH) (Downlink)
Paging Channel (PCH) (Downlink)
Common Packet Channel (CPCH) (Uplink) Downlink Shared Channel (DSCH) (Downlink)
Random Access Channel (RACH) (Uplink)
Physical LayerUplink Physical ChannelsDedicated Physical Channels Common Physical Channels
Dedicated Physical Control Channel (Uplink DPCCH)
Physical Random Access Channels (PRACH) Dedicated Physical Data Channels (Uplink DPDCH) Physical Common Packet Channel (PCPCH)
Physical LayerDownlink Physical ChannelsDedicated Physical Channel (Downlink DPCH) (Time multiplex of downlink DPDCH and downlink DPCCH Common Physical Channels
Synchronisation Common Pilot Page Primary Common Channel (SCH) Channel (CPICH) Control Physical Indication Physical Downlink Channel Channel (P-CCPCH) Shared Channel (PICH) Secondary Common (PDSCH) Secondary CPICH Control Physical Channel Acquisition Indication Primary CPICH (S-CCPCH) Channel (AICH)
Physical LayerTransport Channel to Physical Channel MappingTransport Channels BCH FACH PCH RACH CPCH DCH DSCH
Physical Channels
CPICH
S-CCPCH
PCPCH DPDCH
DPCCH SCH
PDSCH
AICH
P-CCPCH
PRACH
PICH
Physical LayerDedicated Physical Channel (DPCH)DPCH DPDCH DPDCH - Dedicated Physical Data Channel Carries dedicated transport channels DPCCH
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 Structure10ms
0DPDCH
1
2
3
... Data
12 13 14
DPCCH
Pilot
TFCI2560 chips
FBI
TPC
Physical LayerUplink DPDCH data RatesDPDCH Spreading Factor 256 128 64 32 16 8 4 4 with 6 parallel codes DPDCH Channel bit rate (Kb/s) 15 30 60 120 240 480 960 5740 Maximum user data rate with rate coding (approx.) 7.5 kb/s 15 kb/s 30 kb/s 60 kb/s 120 kb/s 240 kb/s 480 kb/s 2.3 Mb/s