WCDMA RF Planning Principals

WCDMA RF Planning Principals

Content •WCDMA Air Interface Basics •Capacity and Coverage Planning

Content

WCDMA AIR INTERFACE

3G Network Planning Areas

• 3G Network Planning could be divided to • Radio Network Planning • Access Transmission Planning • CS core Network Planning • PS Core Network Planning

MGW

3GUEC

RNC Iu-cs

BTS

Radio Planning

3G-SGSN

Iub,Iur

Iu-ps

Transmission Planning

Gn

Core Planning

PS Domain Inter-PLMN Backbone Network

3G-GGSN Gn

Data Network (Internet)

IP

Firewall

UMTS Air Interface technologies • UMTS Air interface is built based on two technological solutions • WCDMA – FDD • WCDMA – TDD

• WCDMA – FDD is the more widely used solution • FDD: Separate UL and DL frequency band

• WCDMA – TDD technology is currently used in limited number of networks • TDD: UL and DL separated by time, utilizing same frequency

• Both technologies have own dedicated frequency bands • This course concentrates on design principles of WCDMA – FDD solution, basic planning principles apply to both technologies

WCDMA – FDD technology • Multiple access technology is wideband CDMA (WCDMA) • All cells at same carrier frequency • Spreading codes used to separate cells and users • Signal bandwidth 3.84 MHz

• Multiple carriers can be used to increase capacity • Inter-Frequency functionality to support mobility between frequencies

• Compatibility with GSM technology • Inter-System functionality to support mobility between GSM and UMTS

Frequency

WCDMA Technology Users share same time and frequency WCDMA Carrier 3 .8 4 M H z

f 5 M H z

5+5 MHz in FDD mode 5 MHz in TDD mode

WCDMA 5 MHz, 1 carrier

TDMA (GSM) 5 MHz, 25 carriers

Direct Sequence (DS) CDMA

Time

UMTS & GSM Network Planning G S M 9 0 0 /1 8 0 0 :

3 G (W C D M A ):

Highbetween bit rates Differences WCDMA & GSM WCDMA Carrier spacing Frequency reuse factor Power control frequency

Services with Different quality requirements

5 MHz 1 1500 Hz

GSM 200 kHz 1–18 2 Hz or lower

Quality control

Radio resource management algorithms

Network planning (frequency planning)

Frequency diversity

5 MHz bandwidth gives multipath diversity with Rake receiver

Frequency hopping

Packet data Downlink transmit diversity

Efficient packet data

Load-based packet scheduling Supported for improving downlink capacity

Timeslot based scheduling with GPRS Not supported by the standard, but can be applied

Multiple WCDMA carriers – Layered network 1 - 10 km

F3 F2 F2 F3

200 - 500 m

50 - 100 m

Micro BTS

F3 Pico BTSs

F1 Macro BTS

CDMA principle Chips & Bits & Bits (In this drawing, 1 bit = 8 Chips  SF=8) Symbols +1

Baseband Data

-1

Chip

Chip +1

Spreading Code

-1 +1

Spread Signal

-1

Air Interface De

e r p s

g n i ad

+1 -1 +1

Data

-1

b

= const Received Bit

Fr eq

ue n

cy

Ba nd

Power/Hz

Energy per bit = E Energy Box Originating Bit

Duration (t = 1/Rb) •

Higher spreading factor  Wider frequency band  Lower power spectral density • •

BUT Same Energy per Bit

Power density (Watts/Hz)

Spreading & Processing Gain User bit rate

R

Unspread narrowband signal

Spread wideband signal

Frequency

Bandwidth W (3.84 Mchip/sec)

W  const  3.84 Mchip Processing gain:

W G p  dB  R

sec

Processing Gain Examples Voice user (R=12,2 kbit/s) Power density (W/Hz)

R

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)

Power density (W/Hz)

R

Gp=W/R=10 dB

Frequency (Hz)

Transmission Power Power density Frequency

High bit rate user

5MHz

Low bit rate user Time

Characteristic to WCDMA • RAKE receiver takes advantage of multipath propagation • Fast power control keeps system stable by using minimum power necessary for links • Soft handover ensures smooth handovers, reduced probability of dropped calls

Multiservice Environment • Data speed • In R99 bit rate varies from 8 kbps up to 384 kbps • Variable bit rate also available • Bit rate gradually grows up to 21 Mbps (RU20)

• Service delivery type • Real-time (RT) & non real-time (NRT)

• Quality classes for user to choose • Different error rates and delays

• Traffic asymmetric in uplink & downlink • Common channel data traffic • Inter-system handovers

Air Interface • Capacity and coverage coupled - “cell breathing” • Neighbour cells coupled via interference • Soft handover • Fast power control • Interference limited system (e.g. GSM frequency limited)

RAKE Receiver Cell-1

Rx

Finger

Rx

Finger

Rx

Finger

Rx

Finger

Cell-1 Cell-1

Delay 3

Code used for the connection

Delay 2

t

Delay 1

Cell-2

• Combination or multipath components and in DL also signals from different cells

Output

Power Control in WCDMA • Fast power control is vital for WCDMA performance. It aims UE to control the transmitted power on the same level with received power. This leads to minimised interference and small power consumption • Power is controlled by parameters and needs to be defined during network optimisation

UE3 UE1 UE2

UE1

With Optimum Power Control

UE2 UE3 UE4

Received power at BS

UE4

Received power at BS

Without Power Control

UE1

UE2

UE3

UE4

Effect on Tx & Rx Power on Interference Levels Downlink transmission power = Interference to the network

Uplink transmission power = Interference to other cells

Uplink received power = Interference to own cell users

Since every Tx and Rx power is causing interference to others, PC is necessary to limit the interference

Handovers in WCDMA Hard handover: UE handover between different frequencies or between WCDMA and GSM Soft handover: UE handover between different base stations Softer handover: UE handover within one base station but between different sectors • Soft handover keeps simultaneous connection to different base stations thus providing a way to improve call quality during handover. (SHO gain) • Soft handover feature has a direct impact on network capacity and therefore is a trade-off between quality and capacity. It has also an effect to coverage due cell breathing. (SHO overhead)

Received signal strength Base station BS1

Diversity (SHO gain)

BS1 Threshold

BS2 BS2 BS3

BS3

Distance from BS1

Received signal strength

Soft/softer handover • UE is simultaneously connected to 2 to 3 cells during soft handover • Soft handover is performed based on UE cell pilot power measurements and handover thresholds set by radio network BS1 Soft handover planning parameters • Radio link performance is improved during soft handover BS1 Thresholdstation and transmission • Soft handover consumes base resources BS2

BS2 BS3

Distance from BS1

BS3

Hard handover • Hard handovers are typically performed between WCDMA frequencies and between WCDMA and GSM GSM/GPRS GSM/GPRS GSM/GPRS GSM/GPRS cells Inter-System handovers (ISHO)

ff1 1

ff1 1 Inter-Frequency handovers (IFHO)

ff2 2

ff2 2

ff2 2

ff2 2

Other to own cell interference – little • Low other to own cell interference can be achieved by planning clear idominance (1/2) areas: • The cell coverage (and overlap) must be well

controlled

• The cell should cover only what it is supposed to cover • Low(er) antenna hights and down tilt of the antennas • Use buildings and other environmental structures to isolate cells' coverage • Use indoor solutions to take advantage of in building isolation

• Avoid sites "seeing" the buildings in especially horizon especially over the water or otherwise open area

> 3 km

< 300 m

Other to own cell interference-little i • The DL load equation dictates the maximum capacity (2/2)  DL 

nk

 n 1

Eb / Non   1   n   i   v n W / Rn

• Basically the other to own cell interference (i ) tells how much there is overlapping between cells. • Some overlapping is needed in order to guarantee safe handovers BUT excessive overlapping must be avoided

WCDMA Codes • In WCDMA two separate codes are used in the spreading operation • 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

DL Spreading and Multiplexing in WCDMA CHANNELISATION codes:

Radio frame = 15 time slots

Pilot

CODE 1

Pilot

X

BCCH

P-CPICH

User 1

CODE 2

BCCH

X

User 2

P-CCPCH

User 3 SUM

CODE 3

User 1

X

DPCH1

+

CODE 4

User 2

X

Time

3.84 MHz RF carrier

SCRAMBLING CODE

DPCH2

CODE 5

User 3

X

DPCH3

X

3.84 MHz bandwidth

RF

DL & UL Channelisation Codes • Walsh-Hadamard codes: orthogonal variable spreading factor codes (OVSF codes) • 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 the code 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 between users of same cell

• Orthogonal codes are suited for channel separation, where synchronisation between 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 UL

Channelisation Code Tree SF=1

SF=2

SF=4

SF=8 C8(0)=[11111111]

C8(1)=[1111-1-1-1-1] C2(0)=[11] C8(2)=[11-1-111-1-1] C4(1)=[11-1-1] C8(3)=[11-1-1-1-111] C8(0)=[1-11-11-11-1] C4(2)=[1-11-1] C8(5)=[1-11-1-11-11]

C2(1)=[1-1]

C16(0)=[........... .] C (1)=[........... 16

C4(0)=[1111]

C0(0)=[1 ]

SF=16

C8(6)=[1-1-111-1-11] C4(3)=[1-1-11] C8(7)=[1-1-11-111-1]

.] 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)=[......... ..]

...

SF=256 SF=512

Physical Layer Bit Rates (DL) Spreading factor 512 256 128 64 32 16 8 4 4, with 3 parallel codes

Channel symbol rate (ksps) 7.5 15 30 60 120 240 480 960 2880

RSymbol

Channel bit rate (kbps) 15 30 60 120 240 480 960 1920 5760

W  SF

DPDCH channel bit rate range (kbps) 3–6 12–24 42–51 90 210 432 912 1872 5616

Maximumuser data rate with ½rate coding (approx.) 1–3 kbps 6–12 kbps 20–24 kbps 45 kbps 105 kbps 215 kbps 456 kbps 936 kbps 2.3 Mbps

Rb _ phy  2  RSymbol (QPSK modulation)

Half rate speech Full rate speech 128 kbps 384 kbps 2 Mbps

Physical Layer Bit Rates (DL) HSDPA • 3GPP Release 5 standards introduced enhanced DL bit rates with High 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) HSDPA • Higher order modulation scheme (16-QAM)  Higher bit rate in same Coding 55codes 10 15 Codingrate rate Coding Codingrate rate codes 10codes codes 15codes codes band 1/4

600 kbps

1.2 Mbps

1.8 Mbps

3/4 3/4

1.8 1.8Mbps Mbps

3.6 3.6Mbps Mbps

5.4 5.4Mbps Mbps

2/4 2/4

2.4 2.4Mbps Mbps

4.8 4.8Mbps Mbps

7.2 7.2Mbps Mbps

3/4 3/4

3.6 3.6Mbps Mbps

7.2 7.2Mbps Mbps

10.7 10.7Mbps Mbps

4/4 4/4

4.8 4.8Mbps Mbps

9.6 9.6Mbps Mbps

14.4 14.4Mbps Mbps

600 kbps 1.2 Mbps 1.8 Mbps • 16-QAM provides 41/4 bits per symbol  960 kbit/s / code physical channel 2/4 1.2 2.4 3.6 peakQPSK rate QPSK 2/4 1.2Mbps Mbps 2.4Mbps Mbps 3.6Mbps Mbps

16QAM 16QAM

Physical Layer Bit Rates (UL) HSUPA • 3GPP Release 6 standards introduced enhanced UL bit rates with High Speed Downlink Packet Access (HSUPA) technology • Fast allocation of available UL capacity for users – High peak bit rates • Simultaneous usage of up to 2+2 UL channelisation codes (In HSUPA 22xxSF2 SF2++ SF=2Coding – 4) rate 11xxSF4 22xxSF4 22xxSF2 Coding rate SF4 SF4 SF2 2 x SF4 1/2 1/2

480 480kbps kbps

960 960kbps kbps

1.92 1.92Mbps Mbps

2 x SF4 2.88 2.88Mbps Mbps

3/4 3/4

720 720kbps kbps

1.46 1.46Mbps Mbps

2.88 2.88Mbps Mbps

4.32 4.32Mbps Mbps

4/4 4/4

960 960kbps kbps

1.92 1.92Mbps Mbps

3.84 3.84Mbps Mbps

5.76 5.76Mbps Mbps

Content

COVERAGE & CAPACITY PLANNING

Uplink Coverage Planning – Uplink Link budget

• Uplink- From UE to BTS

RX RXRX RX RX RXRX RX RX RXRX RX

EbNo values with diversity MHA assumed to negate cable loss in UL.

Allowed propagation loss

153.7

151.9

When load increase for 50% to 80% =>’cell breathing’ effect

Coverage Planning – Downlink Link budget DL EbNo without diversity

WCDMA Uplink Load Equation • Complete version of the uplink load equation is:

UL

jN

1   1  a * i  W j 1 1  Eb / No j . R j . j

Where, N, is the number of simultaneously active users W, is the chip rate i.e. 3.84 Mcps Rj, is the L2 user bit rate e.g. 12.2 kbps Eb/Noj is the Eb/No requirement for the jth user e.g. 4.4 dB for speech j is the activity factor for the jth user e.g. 0.67 for speech (includes DPCCH overhead) a, is the rise in uplink inter-cell interference ratio e.g. 0.7 dB i, is the uplink inter-cell interference ratio e.g. 0.65 (for 3-sectorised Macro)

Capacity calculation example-Uplink • From UL load equation we can calculate load caused by one single 12.2 speech user.

UL 

1 3840000

1 10

4.4 10

*12200 * 0.67



  1  10 

1.3 10

 * 0.65   1.09% 

UL EbNo= 4.4 dB with Rx diversity, 8.0 dB without Rx diversity i=65 %, tx power rise=1.3 Activity factor=0.67 Load caused by one single speech user

• If the cell has been planned with a maximum permissible uplink load of 80 % then its uplink capacity is 73 simultaneous speech users • Without Uplink Rx diversity, Load caused by one single speech user is 2.49 % Assuming same 80% UL load then Uplink capacity without diversity is 32 simultaneous speech users

WCDMA Downlink Load Equation • The downlink load equation is: jN

Eb / No j

j 1

W / Rj

 DL  (1  SHOOH )  j Where,

 1    i 

N, is the number of simultaneously active users W, is the chip rate i.e. 3.84 Mcps Rj, is the L2 user bit rate e.g. 12.2 kbps Eb/Noj is the Eb/No requirement for the jth user e.g. 7.9 dB for speech j is the activity factor for the jth user e.g. 0.63 for speech (includes DPCCH overhead) , is the downlink orthogonality e.g. 0.5 (50%) i, is the uplink inter-cell interference ratio e.g. 0.65 (65% for sectorised Macrocell) SHOOH, is the soft handover overhead e.g. 0.2

Total Downlink Transmit Power (1/2) • The total ‘traffic channel’ transmit power requirement can be expressed as: jN

PBS Where,

Eb / No j N o  L  (1  SHOOH )   j 1/ Rj j 1  1   DL

N, is the number of simultaneously active users W, is the chip rate i.e. 3.84 Mcps Rj, is the L2 user bit rate e.g. 12.2 kbps

Capacity of the cell

Eb/Noj is the Eb/No requirement for the jth user e.g. 9.5 dB for speech j is the activity factor for the jth user e.g. 0.63 for speech (includes DPCCH overhead) No is the background noise spectral density L is the average path loss between the UE’s and Node B’s antenna connectors L = IPL – (Antenna Gains – Cable Loss – Body Loss + SHO Gain) – IPL Correction Factor

Example Total Downlink Transmit Power (2/2) • The total downlink transmit power is now obtained by adding the power requirement of the common channels. • The common channels include: • P-CPICH (100 % activity) • P-SCH (10 % activity)

• S-CCPCH (up to 100 % activity) • PICH (96 % activity)

• S-SCH (10 % activity) • P-CCPCH (90 % activity)

• AICH (up to 80 % activity)

• It can be assumed that the common channels consume 20 % of the total downlink transmit power i.e. 20 W x 0.2 = 4 W/ 40Wx0.2=8W

Capacity Calculation Example - DL

•In Downlink, the calculation is done for 12.2 speech user and 128 kbps data users separately.

Result: •AMR, Number of supported AMR calls in DL is 56. •128 kbps data: Number of supported calls is 7, limiting factor is DL load which is reached before BTS max. power

Users are added as long as either 80% load or BTS max power (43 dbm/20W) is reached

From UL link budget with 80 % of load With RU20 SW, 1 FSME card has 612 channel element. 56 AMR call requires 56 CH => 1 FSME is required

Number of simultaneous users per cell

Relation between Loading and Capacity SINGLE FREQUENCY CHANNEL SINGLE CELL

70,0 60,0 50,0 40,0

UL loading 30% UL loading 50% UL loading 70%

30,0 20,0 10,0 0,0 Voice

CS 64 kbit/s

PS 64 kbit/s

PS 128 kbit/s

PS 384 kbit/s

•Higher loading means higher capacity •50% loading: Capacity ~50Erl/800 kbit/s per cell

64 kbit/s Coverage & Capacity in Macrocells

Max. path loss [dB] 180 175 170

WCDMA downlink 20W

165 160

WCDMA uplink

155 150

100

200

300

400

500

Limit is UL coverage

600

700

800 900 1000 1100 1200

Limit is DL capacity

Load [kbps]

Capacity in Macro vs. Micro Environments • Packet data throughput, calculated with CDMA capacity formulas Assumptions

Micro cell: higher orthogonality

Micro: higher isolation between cells

Results

Multipath diversity gain is smaller within Micro environment

• Downlink capacity is more sensitive to the environment because of orthogonal codes (other cell interference affects more downlink) • Micro cells provide a higher capacity due to less multipath=> better Orthogonality

Coverage Improvement Alternatives • Mast head amplifier • • • •

basic solution for optimized uplink performance compensates feeder cable loss supported by NSN's base stations can be used together with Smart Radio Concept

• 6 sectored site • utilizing narrowbeam antennas • ~ 2 dB better antenna gain than in 3 sectored site

Capacity Improvement Alternatives • 6 sectored site • ~ 80% capacity gain compared to 3 sectors (not 100% due to inter-sector interference)

• More carriers (frequencies) per sector • doubling the amount of carriers with power splitting gives roughly 60% more capacity

• Increasing BTS power 20W  40W  60W • Dedicated Indoor & Microcells to traffic hot spots to free capacity from macro layer