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Fundamentals of WCDMA

Transcript of 1 WCDMA Fundamentals

WCDMA Fundamentals

Ashok Kumar Joshi

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NSN Siemens Networks

3G Radio Planning Essentials / NPO Capability Development

3G Data Rate evolution

WCDMA R99 3GPP 5.0 MHz 100-200 ms 384 kbps 384 kbps

WCDMA HSPA 3GPP 5.0 MHz 0 3. Take next two chips = (1,-1).(1,-1) = 1+1 = 2 = +ve => 1 4. Take next two chips = 1,-1).(1,-1) = 1+1 = 2 = +ve => 1

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Energy BoxOriginating Bit Received Bit

Duration (t = 1/Rb)

Higher spreading factor Wider frequency band Lower power spectral density

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Spreading & Processing GainUser bit rate

Power density (Watts/Hz)

R

Unspread narrowband signal

Spread wideband signal

Frequency

Bandwidth W (3.84 Mchip/sec)

W const 3.84 MchipProcessing gain:

sec

W G p dB R

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Processing Gain ExamplesVoice user (R=12,2 kbit/s)R

Power density (W/Hz)

Gp=W/R=24.98 dB Spreading sequences have a different length Processing gain depends on the user data rate

Frequency (Hz)

Packet data user (R=384 kbit/s)R

Power density (W/Hz)

Gp=W/R=10 dB

Frequency (Hz)17 NSN Siemens Networks 3G Radio Planning Essentials / NPO Capability Development

Transmission Power

Power density

High bit rate userFrequency

5MHz

Low bit rate userTime

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WCDMA Codes In WCDMA two separate codes are used in the spreadingoperation Channelisation code Scrambling code

Channelisation code DL: separates physical channels of different users and common channels,defines physical channel bit rate UL: separates physical channels of one user, defines physical channel bit rate

Scrambling code DL: separates cells in same carrier frequency UL: separates users

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DL Spreading and Multiplexing in WCDMACHANNELISATION codes:CODE 1Pilot Radio frame = 15 time slots

P-CPICH Pilot XCODE 2

BCCH User 1 User 2

BCCH

P-CCPCHXCODE 3

User 3 SUM

User 1

XCODE 4

DPCH1

+SCRAMBLING CODE X

Time

User 2

XCODE 5

DPCH2

3.84 MHz RF carrier

User 3

X

DPCH3

RF

3.84 MHz bandwidth20 NSN Siemens Networks 3G Radio Planning Essentials / NPO Capability Development

DL & UL Channelisation Codes Walsh-Hadamard codes: orthogonal variable spreading factor codes (OVSFcodes) SF for the DL transmission in FDD mode = {4, 8, 16, 32, 64, 128, 256, 512} SF for the UL transmission in FDD mode = {4, 8, 16, 32, 64, 128, 256}

Good orthogonality properties: cross correlation value for each code pair in thecode set equals 0 In theoretical environment users of one cell do not interfere each other in DL In practical multipath environment orthogonality is partly lost Interference betweenusers of same cell

Orthogonal codes are suited for channel separation, where synchronisationbetween different channels can be guaranteed Downlink channels under one cell Uplink channels from a single user Orthogonal codes have bad auto correlation properties and thus not suited in an asynchronous environment Scrambling code required to separate signals between cells in DL and users in UL21 NSN Siemens Networks 3G Radio Planning Essentials / NPO Capability Development

Channelisation Code TreeSF= 1 SF= 2 SF= 4C4(0)=[1111] C8(1)=[1111-1-1-1-1] C2(0)=[11] C8(2)=[11-1-111-1-1]

SF= 8C8(0)=[11111111]

SF=1 6 C16(0)=[.........

...

SF=25 SF=51 6 2

C4(1)=[11-1-1] C8(3)=[11-1-1-1-111]C0(0)=[1 ] C8(0)=[1-11-11-11-1] C4(2)=[1-11-1] C8(5)=[1-11-1-11-11] C2(1)=[1-1] C8(6)=[1-1-111-1-11] C4(3)=[1-1-11] C8(7)=[1-1-11-111-1]

...] C16(1)=[......... ...] C16(2)=[......... ...] C16(3)=[......... ...] C16(4)=[......... ...] C16(5)=[......... ...] C16(6)=[......... ...] C16(7)=[......... ...] C16(8)=[......... ...] C16(9)=[......... ...] C16(10)=[......... ..] C16(11)=[........... ] C16(12)=[....... ....] C16(13=[........ ...] C16(14)=[....... ....] C16(15)=[....... ....]

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Physical Layer Bit Rates (DL) - HSDPA 3GPP Release 5 standards introduced enhanced DL bit rates withHigh Speed Downlink Packet Access (HSDPA) technology Shared high bit rate channel between users High peak bit rates Simultaneous usage of up to 15 DL channelisation codes (In HSDPA SF=16) Higher order modulation scheme (16-QAM) Higher bit rate in same band 16-QAM provides 4 bits per symbol 960 kbit/s / code physical channel peakrate

HSDPACoding rate Coding rate 1/4 QPSK 2/4 3/4 2/4 16QAM 3/4 5 codes 600 kbps 1.2 Mbps 1.8 Mbps 2.4 Mbps 3.6 Mbps 10 codes 1.2 Mbps 2.4 Mbps 3.6 Mbps 4.8 Mbps 7.2 Mbps 15 codes 1.8 Mbps 3.6 Mbps 5.4 Mbps 7.2 Mbps 10.7 Mbps

4/423 NSN Siemens Networks

4.8 Mbps

9.6 Mbps

14.4 Mbps

3G Radio Planning Essentials / NPO Capability Development

DL & UL Scrambling CodesDL Scrambling Codes Pseudo noise codes used for cell separation 512 Primary Scrambling Codes

UL Scrambling Codes Two different types of UL scrambling codes are generated Long scrambling codes of length of 38 400 chips = 10 ms radio frame Short scrambling codes of length of 256 chips are periodically repeated toget the scrambling code of the frame length Short codes enable advanced receiver structures in future

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Scrambling Codes & Multipath Propagation

Scrambling code C1

C1+2

Scrambling code C2

UE has simultaneous connection to two cells (soft handover)25 NSN Siemens Networks 3G Radio Planning Essentials / NPO Capability Development

RAKE ReceiverCell-1 Rx Cell-1 Rx Cell-1 Rx Cell-2 Rx t Delay 1 Delay 2 Code used for the connection Delay 3 Finger Finger Finger Output Finger

Combination or multipath components and in DL also signals from different cells26 NSN Siemens Networks 3G Radio Planning Essentials / NPO Capability Development

Channelisation and Scrambling CodesChannelisation code Usage Uplink: Separation of physical data (DPDCH) and control channels (DPCCH) from same terminal Downlink: Separation of downlink connections to different users within one cell Length 4256 chips (1.066.7 s) Downlink also 512 chips Different bit rates by changing the length of the code Number of codes Number of codes under one scrambling code = spreading factor Orthogonal Variable Spreading Factor Uplink: (1) 10 ms = 38400 chips or (2) 66.7 s = 256 chips Option (2) can be used with advanced base station receivers Downlink: 10 ms = 38400 chips Uplink: 16.8 million Downlink: 512 Long 10 ms code: Gold code Short code: Extended S(2) code family Spreading Yes, increases transmission bandwidth No, does not affect transmission bandwidth Scrambling code Uplink: Separation of mobile Downlink: Separation of sectors (cells)

Code family

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Concepts of RSCP and Ec/NoTwo Important Terms

RSCP Ec/No, Ec/Io

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Scrambling Codes & CPICH

CPICH

The Common Pilot Channel (CPICH) is broadcast from every cell It carries no information and can be thought of as a beacon constantly transmitting the ScramblingCode of the cell WCDMA cells are identified by their SC. Its like a BCCH in GSM

It is this beacon that is used by the phone for its cell measurements for network acquisition andhandover purposes (Ec, Ec/Io).29 NSN Siemens Networks 3G Radio Planning Essentials / NPO Capability Development

Total Received Power Io

IoIn 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

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Received Power of CPICH : RSCP

RSCP 1

RSCP 2

RSCP

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

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CPICH Quality (Ec/Io)

Io

RSCP

From the previous two measures we can calculate a signal quality for each CPICH (SC) received Ec/Io = (Energy per chip / Noise spectral density) = RSCP/RSSI *Note: Sometimes Ec/Io is referred to as Ec/No32 NSN Siemens Networks 3G Radio Planning Essentials / NPO Capability Development

Relation between Ec/Io and Eb/No

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Handover typesNode BNode B Node BSector 1Sector 1 f1 Sector 2 f1

Frequency f1

Frequency f1

Sector 3 f1

Sector 3

Soft Handover Node B BTS

Softer Handover

RNCUMTS

RNCIur

GSM900/1800

Node B

Node B