1 wcdma fundamentals
DESCRIPTION
Fundamentals of WCDMATRANSCRIPT
1 © NSN Siemens Networks 3G Radio Planning Essentials / NPO Capability Development
WCDMA Fundamentals
Ashok Kumar Joshi
2 © NSN Siemens Networks 3G Radio Planning Essentials / NPO Capability Development
Downlink peak rate
Network Latency
Uplink peak rate
Bandwidth
Standard
3G Data Rate evolution
Spectral efficiency, DL
Spectral efficiency, UL
WCDMA R99
3GPP
5.0 MHz
100-200 ms
384 kbps
384 kbps
0.16 bps/Hz
0.16 bps/Hz
WCDMA HSPA
3GPP
5.0 MHz
<50 ms
1.8-14.4 Mbps
1-4 Mbps
0.2-0.8 bps/Hz
0.25 bps/Hz
3.9 G estim.
3GPP
1.25-20 MHz
<10 ms
Up to 100 Mbps
Up to 50 Mbps
1.6-2.5 bps/Hz
0.6-0.8 bps/Hz
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CN
circuitswitched
(cs) domain
packetswitched
(ps)domain
UTRAN
Radio Network Subsystem (RNS)
Radio Network Subsystem (RNS)
Iub
Iub
Iur
Iu-PS
Iu-CS
Uu
Uu
UE
UE
MSC/VLR
SGSN
RNC
RNC
UTRAN
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3G-MSC/VLR
3G-SGSN
UE Node BRNC
RNC
RNS
RNS
RRC
Iur: RNSAP
Iu-PS: RANAP
Iu-CS: RANAPIub: NBAP
UTRAN Specific Signalling and Control Protocols
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Module Contents
• Standardisation and frequency bands
• Main properties of UMTS Air Interface– UMTS Air interface technologies
– WCDMA – FDD
– WCDMA vs. GSM
– CDMA principle
– Processing gain
– WCDMA codes and bit rates
– Concepts of RSCP and Ec/No
WCDMA Handovers
• Overview of NSN Radio Resource Management (RRM)
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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
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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
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WCDMA Technology
5 M Hz
3.84 M Hz
f
5+5 MHz in FDD mode5 MHz in TDD mode
Freq
uenc
y
TimeDirect Sequence (DS) CDMA
WCDMA Carrier
WCDMAWCDMA5 MHz, 1 carrier5 MHz, 1 carrier
TDMA (GSM)TDMA (GSM)5 MHz, 25 carriers5 MHz, 25 carriers
Users share same time and frequency
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UMTS & GSM Network Planning
GSM900/1800: 3G (W CDM A):
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Differences between WCDMA & GSM
WCDMA GSM
Carrier spacing 5 MHz 200 kHz
Frequency reuse factor 1 1–18
Power controlfrequency
1500 Hz 2 Hz or lower
Quality control Radio resourcemanagement algorithms
Network planning(frequency planning)
Frequency diversity 5 MHz bandwidth givesmultipath diversity with
Rake receiver
Frequency hopping
Packet data Load-based packetscheduling
Timeslot basedscheduling with GPRS
Downlink transmitdiversity
Supported forimproving downlink
capacity
Not supported by thestandard, but can be
applied
High bit rates
Services withDifferent quality
requirements
Efficient packet data
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Multiple WCDMA carriers – Layered network
F1
F2
F2
F3
F3
F3
Micro BTSMacro BTS
Pico BTSs
1 - 10 km
50 - 100 m200 - 500 m
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Spreading Code
Spread Signal
Data
Air Interface
Bits (In this drawing, 1 bit = 8 Chips SF=8)
Baseband Data
-1
+1
+1
+1
+1
+1
-1
-1
-1
-1
ChipChip
Despreading
Despreading
CDMA principle - Chips & Bits & Symbols
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Spreading and Despreading
SpreadingEach user data bit is multiplied with a sequence of 'x' code bits called CHIPS. This 'x' determines the SPREADING FACTOR!!!!The resulting spread data is at a rate of 'x' times R
DespreadingThe spread user data/chip sequence is multiplied with the same 'x' code chips to recover the original data.
Example:
Spreading code 1 = (1, -1)
Data to spread = (1,-1,1,1)
• Data after spreading = (1, -1).(1), (1,-1).(-1), (1,-1).1, (1,-1).1 = (1,-1, -1,1,1-1,1,-1)
• Despreading : Multiply the received signal with same spreading code
• ( 1, -1, -1, 1, 1, -1, 1, -1).(1,-1)– 1. Take first two chips = (1,-1).(1,-1) = 1+1 = 2 = +ve => 1
– 2. Take next two chips = (-1,1).(1,-1) = -1 -1 = -2 = -ve => 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 Box
Frequ
ency
Ban
d
Duration (t = 1/Rb)
Po
wer
/Hz
Originating Bit Received Bit
Higher spreading factor Wider frequency band Lower power spectral density
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FrequencyPow
er d
ensi
ty (
Wat
ts/H
z)
Unspread narrowband signal Spread wideband signal
Bandwidth W (3.84 Mchip/sec)
User bit rate R
sec84.3 MchipconstW
R
WdBGp Processing gain:
Spreading & Processing Gain
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Frequency (Hz)
Voice user (R=12,2 kbit/s)
Packet data user (R=384 kbit/s)
Pow
er
den
sity
(W
/Hz)
R
Frequency (Hz)
Gp=W/R=24.98 dB
Pow
er
den
sity
(W
/Hz)
R
Gp=W/R=10 dB
• Spreading sequences have a different length• Processing gain depends on the user data rate
Processing Gain Examples
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Transmission Power
Frequency
5MHz
Power density
Time
High bit rate user
Low bit rate user
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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
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DL Spreading and Multiplexing in WCDMA
User 3
User 2
User 1
BCCH
Pilot X
CODE 1
X
CODE 2
X
CODE 3
X
CODE 4
X
CODE 5
+
X
SCRAMBLINGCODE
RF
SUM
User 2
User 1
BCCH
Pilot
Radio frame = 15 time slots
Time
User 3
3.84 MHzRF carrier
3.84 MHz bandwidth
CHANNELISATION codes:
P-CPICH
P-CCPCH
DPCH1
DPCH2
DPCH3
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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
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Channelisation Code Tree
C0(0)=[1]
C2(1)=[1-1]
C2(0)=[11]
C4(0)=[1111]
C4(1)=[11-1-1]
C4(2)=[1-11-1]
C4(3)=[1-1-11]
C8(0)=[11111111]
C8(1)=[1111-1-1-1-1]
C8(2)=[11-1-111-1-1]
C8(3)=[11-1-1-1-111]
C8(0)=[1-11-11-11-1]
C8(5)=[1-11-1-11-11]
C8(6)=[1-1-111-1-11]
C8(7)=[1-1-11-111-1]
C16(0)=[............]C16(1)=[............]
C16(15)=[...........]
C16(14)=[...........]
C16(13=[...........]
C16(12)=[...........]
C16(11)=[...........]
C16(10)=[...........]
C16(9)=[............]
C16(8)=[............]
C16(7)=[............]
C16(6)=[............]
C16(5)=[............]
C16(4)=[............]
C16(3)=[............]
C16(2)=[............]
SF=1
SF=2
SF=4
SF=8
SF=16
SF=256
SF=512
...
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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)
– 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 peak
rate
Coding rateCoding rate
QPSKQPSK
Coding rateCoding rate
1/41/4
2/42/4
3/43/4
5 codes5 codes 10 codes10 codes 15 codes15 codes
600 kbps600 kbps 1.2 Mbps1.2 Mbps 1.8 Mbps1.8 Mbps
1.2 Mbps1.2 Mbps 2.4 Mbps2.4 Mbps 3.6 Mbps3.6 Mbps
1.8 Mbps1.8 Mbps 3.6 Mbps3.6 Mbps 5.4 Mbps5.4 Mbps
16QAM16QAM
2/42/4
3/43/4
4/44/4
2.4 Mbps2.4 Mbps 4.8 Mbps4.8 Mbps 7.2 Mbps7.2 Mbps
3.6 Mbps3.6 Mbps 7.2 Mbps7.2 Mbps 10.7 Mbps10.7 Mbps
4.8 Mbps4.8 Mbps 9.6 Mbps9.6 Mbps 14.4 Mbps14.4 Mbps
HSDPA
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DL & UL Scrambling Codes
DL 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 to get 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
Scrambling code C2
C 1+ 3
C1+2C1+
1
C2
UE has simultaneous connection to two cells (soft handover)
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RAKE Receiver
• Combination or multipath components and in DL also signals from different cells
Del
ay
1Code used
for theconnection
Rx
Output
Finger
t
Cell-1
Cell-1
Cell-1
Cell-2
Rx
Rx
Rx
Finger
Finger
Finger
Del
ay
2
Del
ay
3
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Channelisation and Scrambling Codes
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Concepts of RSCP and Ec/No
Two Important Terms
• RSCP
• Ec/No, Ec/Io
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Scrambling Codes & 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 Scrambling Code of the cellWCDMA 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 and handover purposes (Ec, Ec/Io).
CPICH
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Total Received Power Io
In 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
Io
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Received Power of CPICH : RSCP
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
RSCP 1 RSCP 2
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CPICH Quality (Ec/Io)
IoRSCP
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/No
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Relation between Ec/Io and Eb/No
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Handover types
Soft Handover
4
Hard/Inter-Frequency Handover
Inter-System Handover
Node B
Frequencyf1
Frequencyf1
Frequencyf1
Frequencyf2
UMTS GSM900/1800
Frequencyf1
Frequencyf1
RNC RNC
Iur
Iub Iub
Node B
Node B Node B
Node BNode B
Softer Handover
Sector 1f1
Sector 2f1
Sector 3f1
Sector 1
Sector 3
Node B
Node B BTS
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Power control (PC) in WCDMA
• Fast, accurate power control is of utmost importance – particularly in UL;
– UEs transmit continuously on same frequency Always interference between users
– Poor PC leads to increased interference reduced capacity
• Every UE accessing network increases interference– PC target to minimise the interference Minimize transmit power of each
link while still maintaining the link quality (BER)
• Mitigates 'near far effect‘ in UL by providing minimum required power for each connection
• Power control has to be fast enough to follow changes in propagation conditions (fading)
– Step up/down 1500 times/second
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Uplink power control target
Minimise required UL received power minimised UL transmit power and interference
UE1 UE2
min(Prx1)
min(Prx2)
&
About equal when
Rb1 = Rb2
Target:
Ptx1
Ptx1
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Power Control types
• Power control functionality can be divided to three main types
• Open loop power control– Initial power calculation based on DL pilot level/pathloss measurement by UE
• Outer (closed) loop power control– Connection quality measurement (BER, BLER) and comparison to QoS target
– RF quality target (SIR target) setting for fast closed loop PC based on connection quality
• Fast closed loop power control– Radio link RF quality (SIR) measurement and comparison to RF quality target
(SIR target)
– Power control command transmission based on RF quality evaluation
– Change of transmit power according to received power control command
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UL Outer LoopPower Control
Open Loop Power Control (Initial Access)
Closed Loop Power Control
RNC
BS
MS
DL Outer LoopPower Control
Power Control types
BLER target
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Power control in HSPA
• In HSDPA (DL) the transmit power from base station is kept constant and the signal modulation and coding is adapted according to the channel conditions
– 2 ms interval 500 Hz
• In HSUPA (UL)– The power control of HSUPA channels in UL utilises both
▪ Fast closed loop power control
▪ Outer loop power control
– Both work according to similar principles as the R99 power control
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Handover Control (HC)
• HC is responsible for:– Managing the mobility aspects of an RRC connection as UE moves around the
network coverage area
– Maintaining high capacity by ensuring UE is always served by strongest cell
• Soft handover– MS handover between different base stations
• Softer handover– MS handover within one base station but between different sectors
• Hard handover– MS handover between different frequencies or between WCDMA and GSM
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Thank you for your attention