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1 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
WCDMA Fundamentals
MODULE 1
2 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Module Objectives
At the end of this module the participant will be able to: • Describe the usage of scrambling and channalisation codes
• Describe how different bit rates can be achieved
• Describe how the capacity and coverage are connected to each others
• Describe different Handover types
• Describe Power Control procedures
• Explain the tasks of Admission Control, Load Control, Packet Scheduler and interconnections between them
3 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
IMT-2000 frequency allocations
2200 MHz20001900 1950 2050 2100 21501850
JapanIMT-2000
PH
S
IMT-2000
ITU
Mob
ile
Sate
llit
eIMT-2000 IMT-2000
EuropeUMTS(FDD)DEC
T
UM
TS
(T
DD
)
GSM1800 U
MTS
(T
DD
)
UMTS(FDD)
USA
PC
S
un
licen
sed
PCSPCS
UM
TS
(T
DD
)IM
T-2
00
0
(TD
D)
Mob
ile
Sate
llit
e
Mob
ile
Sate
llit
e
Mob
ile
Sate
llit
e
Mob
ile
Sate
llit
e
Mob
ile
Sate
llit
e
Mob
ile
Sate
llit
e
Mob
ile
Sate
llit
e
4 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
UMTS & GSM Network Planning
GSM900/1800: 3G (W CDM A):
5 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Hierarchical Cell Structure
F1
F2
F2
F3
F3
F3
Micro BTSMacro BTS
Pico BTSs
1 - 10 km
50 - 100 m200 - 500 m
6 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
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
Spectral efficiency
Different quality
requirements
Efficient packet data
7 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
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
8 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Spreading Code
Spread Signal
Data
Air Interface
Chips & Bits & Symbols Bits (In this drawing, 1 bit = 8 Chips)
Baseband Data
-1
+1
+1
+1
+1
+1
-1
-1
-1
-1
ChipChip
Despreadi
Despreadi
ngng
9 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Energy Box
Freq
uenc
y Ba
nd
Duration (SF)
Pow
er
Originating Bit Received Bit
Energy per bit = const
10 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Spreading & Processing Gain
Frequency
Pow
er
den
sity
(W
att
s/H
z)
Unspread narrowband signal Spread wideband signal
Bandwidth W (3.84 Mchip/sec)
Bit rate R
sec84.3 MchipWconstSFR
SFR
W
B
BdBG
Baerer
Up
u Gp: processing gainBUu: system chip rateBBearer: bearer symbol rateSF: spreading factor
11 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Processing Gain Examples
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
12 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Transmission Power
Frequency
5MHz
Power
Time
High bit rate user
Low bit rate user
13 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
DL & UL Channalisation 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
• Orthogonal codes are suited for channel separation, where synchronisation between different channels can be guaranteed, e.g. downlink channels under one cell, uplink channels from a single user; uplink signals from different users are not time synchronised.
• Orthogonal codes have bad auto correlation properties and thus not suited in an asynchronous environment
14 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
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=256SF=512...
15 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Physical Layer Bit Rates (DL)
Half rate speechFull rate speech
128 kbps384 kbps
2 Mbps
16 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
DL & UL Scrambling Codes
DL Scrambling Codes• Pseudo noise codes used for cell separition
• Generated with the shift register of length 18 (218-1=262 143 codes can be generated)
• The first 8192 first codes from 262 143 code set are exclusively used in DL, they are organised into hierarhical groups:
• 512 Primary Scrambling Codes• 512·15 Secondary Scrambling Codes
UL Scrambling Codes• Two different types of UL scrambling codes are generated:
• Long scrambling codes created from the Gold pseudo-noise sequence (length of 38 400 chips)
• Short scrambling codes generated by the quaternary S(2) pseudo-noise sequence (256 chips are periodicaly repeted to get the scrambling code of the frame length)
• For the common physical channels long scrambling codes must be used
• For the dedicated channels both long and short scrambling codes can be used
17 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Scrambling Codes & Multipath Propagation
Sprambling code
C1
Sprambling code
C2
C 1+ 3
C1+2C1+
1
C2
18 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
RAKE Receiver
Del
ay
1Code usedfor the
connection
Rx
Output
Finger
t
Cell-1
Cell-1
Cell-1
Cell-2
Rx
Rx
Rx
Finger
Finger
Finger
Del
ay
2
Del
ay
3
19 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Channelisation and Scrambling Codes
20 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Micro Diversity
Micro Diversity Pointsmax ratio combining is used
Summed signalNode B RAKE
Receiver
MS RAKE
Receiver
21 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Macro Diversity in the RNC
Node B
Node B
Node B
S-RNC
D-RNC
Core Network
Active cell set
Macro Diversity Pointselection combining is used
22 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Radio Resource Management
service quality
cell coverage cell capacity
Optimizationand Tailoring
• RRM is responsible for optimal utilization of the radio resources:• Transmission power• Logical codes• Bandwidth
• The trade-off between capacity, coverage and quality is done all the time: as many users as possible will get the resources in such a way, that the minimum required quality is meet (nothing less and nothing more)
• By means of several RRM functionalities, the radio resources are continuously monitored and optimize.
23 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
RRM must be able to:
• Predict the impact on interference (power) of the admitting a new user for UL & DL
• Perform appropriate actions (e.g. new call admissions, bit rate increase/decrease etc.) in accordance with prevailing load conditions
• Provide different quality of service for real time (RT) and non-real time (NRT) users
• Take appropriate corrective action when the different cell load thresholds are exceeded in order to maintain cell stability (i.e. load control)
Overload
Load TargetOverload Margin
Pow
er
Time
Estimated capacity for NRT trafficMeasured load causedby non-controllable load (RT)
Radio Resource Management
RT services must have higher quality assurance than NRT
24 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
RRM Functionalities
• AC - Admission Control
• LC - Load Control
• PS Packet Scheduler
• RM - Resource Manager
• PC - Power Control
• HC - HO Control
PC
HCConnection based functions
LC
AC
Network based functions
PS
RM
25 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Admission Control • Checks that admitting a new user will not sacrifice planned
coverage or quality of existing connections
• Determines whether or not a new RT RAB can be admitted to the RAN
• With PS decides whether to admit NRT RABs (PS handles all NRT connections)
• Also sets• UL/DL BLER, Ec/No targets• SIR target for outer loop power control• Initial DL transmission power for the channel• Radio Link Control parameters, e.g. transmission mode• Transport Channel (TrCH) parameters, e.g. TFS
• Provides RLC parameters to PS for NRT users;• Bearer class• Traffic handling priority• Transport Formats• MS capabilities
26 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Admission Control
Radio Access Bearerson the air interface Uu
Inte
rfac
e Ban
dwid
th
Allowed RangeAC Procedure
...
27 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Admission Control
Planned uplink interference margin; defines the optimum operating point up to which the AC can operate.
Defines the limit (the first UL overload threshold) for the UL interference margin, after which the BS starts its load control actions to prevent overload.
0
5
10
15
20
25
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Load
Inte
rfere
nce M
arg
in (
dB
)
Offset
28 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Load Control• Cell load is defined as a function of interference – main criterion in
WCDMA
• The load control function within RRM can be divided into:• Preventive load control (e.g. congestion)• Overload control (e.g. dropping of calls in worst case)
• The load control functionality is done by measuring both UL (received interference) and DL (transmit power) periodically on a cell basis
• Load control is performed for UL and DL separately (asymmetric traffic)
• Preventive actions are performed before the cell is overloaded (threshold y)
• Overload actions are performed after cell is overloaded (threshold x)
• RNP parameters define the thresholds for the RRM functionalities
• The thresholds define a stable functionality within a cell and with surrounding cells
29 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Load Control
Estimated capacity for NRT traffic.Measured load caused by non-controllable load (RT)
Overloadthreshold x
Load Targetthreshold y
Pow
er
Time
Preventive Load Control
Overload Control
30 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Load Control• LC performs the function of load control in association with AC &
PS (LC works as glue between these two functions)
• Updates load status using measurements & estimations provided by AC and PS
• Continuously feeds cell load information to PS and AC;• Interference levels• BTS power levels• Non-controllable load
LC
AC
PSNRT load
Load change info
Load status
31 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Packet Scheduler• A non-real time call constitutes of a bursty sequence of packets.
• In the downlink, the Packet Scheduler decides which channel to use, DCH or FACH.
• The load target can be reached by scheduling the transmission of NRT packets .
time
packet service session
packet call
reading time
packet size packet arrival interval
32 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Packet Scheduler
• PS allocation times need to be fast to accommodate changing conditions & accurate (up-to-date load info)
• Capacity requests sent via traffic volume measurement reports (governed by RNP parameters)
• PS comprises two parts: MS specific & Cell specific
power
time
non-controllable load
controllable load
Total Load
Target threshold
Overload threshold
• Responsible for scheduling radio resources for both UL and DL NRT RABs
• Scheduling period defined by RNP parameters
• PS relies on up-to-date information from AC and PS
• Capacity allocated on a needs basis using ‘best effort’ approach
33 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Packet Scheduler (PS)• PS also responsible for:
• TFCS selection• Initial channel selection based on RNP parameters & RLC buffer load;
• small amounts of NRT data sent on control channels (Cell _FACH state)
• long and frequent data sent on dedicated channels (Cell _DCH state)
• Queuing of unscheduled NRT capacity requests (queuing algorithm)
• Capacity request handling policy
• Increasing/decreasing user bit rates (governed by RNP parameters)
• PS preventive & overload actions
34 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Packet Scheduler
Radio network planning parameters
Periodical cell measurements
Periodical radio link measurements
RB setup/reconfiguration/release
information
Traffic volume measurements (triggers for
DCH allocation)
Updated power estimations
Control of traffic volume measurements
DCH allocations for NRT RB
PacketPacketschedulerscheduler
35 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Resource Manager• Responsible for managing the logical radio resources of the RNC in
co-operation with AC and PS
• On request for resources, from either AC(RT) or PS(NRT), RM allocates:
• DL spreading code• UL srambling code
• Also looks after code tree management (to maintain orthogonality);• Initial code selection – codes concentrated to the same branch• Code re-fragmentation – dynamic reallocation of codes as users
enter/leave the system
Code Type Uplink Downlink
Scrambling codes
Spreading codes
User separation Cell separation
Data & control channels from same UEUsers within one cell
36 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Outer Loop Power Control
Power Control (PC)
Open Loop Power Control (Initial Access)
Closed Loop Power Control
RNC
BS
MS
37 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Power control in WCDMA
• Fast, accurate power control is of utmost importance – particularly in UL;• UEs transmit continuously• WCMDA often uses 1 frequency• Poor PC leads to increase interference > reduced capacity
• From BTS perspective every UE accessing network increase interference
• WCMDA capacity is proportional to interference level > minimise interference
• PC maintains link quality by adjusting UE (UL) and BTS (DL) powers every slot
• Mitigates 'near far effect', by providing minimum required power for each connection
• UEs and BTSs should always be at the lowest possible transmission power
• PC utilises Signal-to-Interference Ratio (SIR) – independently for each connection
• Provides protection against shadowing and fast fading
38 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Open Loop Power Control• Controlled by UE• Determines how much power UE should use during random
access procedure (UL)• Network informs UE of current network status;
• CPICH power (RNP parameter)• UL required C/I ratio (RNP parameter)• UL interference
• UE uses these parameters to calculate initial power of RACH preamble
• If access request is not detected power of preamble is increased in steps
• After detection of MS signal, the initial SIR is calculated in RNC
Preamble PreamblePreamble
Preamble
MS
Ou
tpu
t Pow
er
AICH
Mesage Part
RACH
39 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Fast Loop Power Control
• Located in BTS and UE• Controls the power of the dedicated physical channels• Power control changes can occur every slot (i.e. 1500 times per
second)• BTS and UE continuously compare recevied SIR with SIR target
and inform each other to either increase or decrease its power (using TPC commands)
With OptimumPower Control
WithoutPower Control
MS1
MS2
MS3
MS4
MS1 MS2 MS3 MS4
Rec
eive
d p
ower
at
BS
Rec
eive
d p
ower
at
BS
MS1MS2
MS3
MS4
40 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Closed Loop Power Control
• Adjusts the SIR for every user based on BER/FER observation. Initial, max. and min. SIR values are set by AC
• Needed to track changes in radio environment• Aims to provide required quality• UL quality evaluation is made after MDC• RNP parameters control the threshold comparison process for SIR
target and the reporting of these results• If SIR target reaches its maximum (I.e. radio conditions
deteriorate even though SIR target is inceased, system has to take action;
• inter-frequency / inter-system handover• RRC connnection release
41 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Handover Control• HC is responsible for:
• Managing the mobility aspects of an RRC connection as UE moves around the network
• Maintaining high capacity by ensuring UE is always served by strongest cell
Hard handover: MS handover between different frequencies or between WCDMA and GSM.
Soft handover: MS handover between different base stations.Softer handover: MS 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. However, this 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.
• Optimisation has an important role in controlling the handover performance during the pre-launch optimisation (initial setting). This role is especially essential in continuous optimisation when traffic increases and levelling of traffic between base stations becomes more important.
42 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Hanover Control
BS1
BS2
BS3
Received signal strength
BS3
Distance from BS1
Threshold
Base station diversity
BS2
BS1
43 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Handover Control
Intra-layerInter-layer
Intra-System
Soft(er) Handover
Hard Handover
Inter-frequency
Intra-frequency
Intra-frequency
Inter-System
(Inter-RAT)
Hard Handover
Inter-frequency
WCDMA to GSMWCDMA to GPRSGSM to WCDMAGPRS to WCDMA
WCDMA to WCDMA
Intra-layerInter-layer
Intra-layerInter-layer
Intra-layerInter-layer
Requires Compressed
Mode
44 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
Increased load 800 kbps Decreased coverage
Increased load 800 kbps Decreased coverage
Low load 200 kbps Large coverage
Low load 200 kbps Large coverage
128 kbps
64 kbps
8 kbps144 kbps
64 kbps
64 kbps
144 kbps
144 kbps
64 kbps64 kbps
• Traffic load has direct effect on the cell size
• Radio Resource Management provides means to control cell breathing in network optimisation
• Traffic load has direct effect on the cell size
• Radio Resource Management provides means to control cell breathing in network optimisation
Cell Breathing
45 © NOKIA WCDMA Fundamentals.PPT/10.06.2003 / NN
WCDMA Key Benefits
• Soft Handover• Call is connected before handover is completed, reducing the
probability of a dropped call
• Processing Gain• Basic CDMA benefit => the wider the transmitted bandwidth
compared to the user datarate the less power is needed for the transmission
• Advanced Radio Resource Management (RRM)• RRM will control call admission and packet scheduling and all
RRM building blocks are closely related to each other
• Multipath Signal Processing • Combines power for increased signal integrity => RAKE
receiver