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Transcript of UMTS Fundamentals
Proprietary and Confidential
1: UMTS Fundamentals
Version 2.0
West Region - UMTS RF Engineering
Proprietary and Confidential Slide 2
Module 1: UMTS Fundamentals • Module Overview
1.1 Introduction
1.2 CDMA Multiple Access Fundamentals
1.3 UMTS System
• Technology & Physical Interfaces
• WCDMA Air Interface
• UMTS Key Concepts
1.4 HSDPA
1.5 HSUPA
The overall aim of Module 1 is to give a broad grounding of UMTS concepts on
which to build on in the following modules
Proprietary and Confidential
Introduction
Proprietary and Confidential Slide 4
Introduction • abc
Proprietary and Confidential
Multiple Access Fundamentals
Proprietary and Confidential Slide 6
FDMA – Frequency Division Multiple Access
frequency
time
User 1
Frame Period (we may still need
frames/timeslots for signalling)
Channel
Bandwidth
User N
Proprietary and Confidential Slide 7
TDMA - Time Division Multiple Access
freq
ue
ncy
time
User 1 User 1
Timeslot Period Frame Period
Channel
Bandwidth
Proprietary and Confidential Slide 8
FDMA/TDMA
frequency
time
Channel
Bandwidth
Timeslot Period Frame Period
User 1 User 1
Proprietary and Confidential Slide 9
CDMA - Code Division Multiple Access
frequency
time
code
Frame Period (we may still need
frames/timeslots for signalling)
Proprietary and Confidential Slide 10
Code Division Multiple Access
Identica
l codes
Tx Bit Stream
P
f
Code Chip Stream
Spreading
P
f
Channel
Air Interface
Chip Stream
P
f
Code Chip Stream
Despreading
P
f
Rx Bit Stream
P
f
Proprietary and Confidential Slide 11
Code Division Multiple Access
Rx Bit Stream
Air Interface
Chip Stream
Tx Bit Stream 1
-1
Code Chip Stream
X Spreading
Code Chip Stream
X Despreading
Proprietary and Confidential Slide 12
Code Division Multiple Access
Air Interface
Chip Stream
Tx Bit Stream 1
-1
Code Chip Stream
X Spreading
X Despreading Code Chip Stream Y
Rx Bit Stream
Proprietary and Confidential
WCDMA System Overview
Proprietary and Confidential Slide 14
WCDMA Network Topology
Iu-CS
Iub
PSTN
IP Domain
(Wap, Internet, Streaming)
GGSN 3G
SGSN
WCDMA Air Interface
Uu
Iu-PS
User Equipment (UE) & USIM
Node Bs RNC
2G Net
MSC (Voice & Video calls)
Proprietary and Confidential
WCDMA Air Interface Concepts
Proprietary and Confidential Slide 16
Key WCDMA Concepts • Key WCDMA concepts to be covered
– AIR INTERFACE OVERVIEW
– POWER CONTROL
• Open
• Closed (Fast/Slow)
– HANDOVER
• Intra-Frequency (Soft/Softer)
• Inter-Frequency (Other WCDMA carrier)
• Inter-System (3G->2G)
– RADIO RESOURCE MANAGEMENT
• Admission Control
• Load Control
• Packet Scheduler
• Resource Management
• Mobility Management
• Power Control
Proprietary and Confidential
WCDMA Air Interface Overview
Proprietary and Confidential Slide 18
WCDMA Air Interface
UMTS FDD UMTS TDD
Multiple Access
CDMA CDMA
Modulation QPSK/16QAM QPSK
Carrier Spacing 5MHz (200kHz raster)
5MHz (200kHz raster)
Frame Length 10ms/2ms 10ms
Slots per Frame
15 15
Multiple Rates Multi-code, Variable
Spreading Factor
Multi-code, multi-slot
Chip Rate 3.84Mcps 3.84Mcps
Max Data Rate 14.4Mbps 2Mbps
Synchronous No Yes
Handover Soft Hard
Proprietary and Confidential Slide 19
WCDMA Spreading Codes
SF 4
SF 8
SF 16
SF 2
• WCDMA used Orthogonal Variable Spreading Factor (OVSF) Codes to
spread user data in both the uplink and the downlink
• Spreading separates the different users in the code domain
• The maximum spreading factor used in UMTS is 512
• DL Speech uses SF=128
• DL 384k used SF=8
Proprietary and Confidential Slide 20
WCDMA Scrambling Codes (SC)
• After spreading the bit stream is scrambled
• In the uplink – one SC per UE
• In the downlink – (typically) one SC per sector
• Spreading separates the different base stations in the code domain
Spreading Code
Spreading
User Bit Stream
Scrambling
Scrambling Code
TX Bit Stream
Proprietary and Confidential Slide 21
WCDMA Code Summary Synchronisation Codes Channelisation Codes Scrambling Codes, UL Scrambling Codes, DL
Type
Gold Codes, Primary
Synchronization Codes (PSC)
and Secondary Synchronization
Codes (SSC)
Orthogonal Variable Spreading
Factor (OVSF) codes,
sometimes called Walsh codes
Complex-Valued Gold Code
Segments (long) or Complex-
Valued S(2) Codes (short)
Complex-Valued Gold Code
Segments
Length 256 chips 4-512 chips 38400 chips /256 chips 38400 chips
Duration 66.67 µs 1.04 µs - 133.34 µs 10 ms / 66.67 µs 10 ms
Number of
codes
1 primary code / 16 secondary
codes
= spreading factor, 4 ... 256 UL,
4 ... 512 DL16,777,216
512 primary / 15 secondary for
each primary code
Spreading No, does not change bandwidth Yes, increases bandwidth No, does not change bandwidth No, does not change bandwidth
UsageTo enable terminals to locate
and synchronise to the cells'
main control channels
UL: to separate physical data
and control data from same
terminal. DL: to separate
connection to different terminals
in a same cell
Separation of terminal Separation of sectors
Proprietary and Confidential Slide 22
WCDMA Logical Channels
• Control Channels
– BCCH Broadcast Control Channel
– PCCH Paging Control Channel
– CCCH Common Control Channel
– DCCH Dedicated Control Channel
• Traffic Channels
– DTCH Dedicated Traffic Channel
– CTCH Common Traffic Channel
Proprietary and Confidential Slide 23
WCDMA Transport Channels
• Common Channels
– BCH Broadcast Channel
– FACH Forward Access Channel
– PCH Paging Channel
– RACH Random Access Channel
– CPCH Common Packet Channel
• Dedicated Channels
– DCH Dedicated Channel
– DSCH Downlink Shared Channel
Proprietary and Confidential Slide 24
WCDMA Physical Channels
• Common Control Channels
– P-CCPCH Primary Common Control Physical Channels (DL)
– S-CCPCH Secondary Common Control Physical Channels (DL)
– P-SCH Primary Synchronisation Channel (DL)
– S-SCH Secondary Synchronisation Channel (DL)
– CPICH Common Pilot Channel (DL)
– AICH Acquisition Indicator Channel (DL)
– PICH Paging Indicator Channel (DL)
– PDSCH Physical Downlink Shared Channel (DL)
– PRACH Physical Random Access Channel (UL)
– PCPCH Physical Common Packet Channel (UL)
– AP-AICH Access Preamble Acquisition Indicator Channel (DL)
• Dedicated Channels
– DPDCH Dedicated Physical Data Channel (DL & UL)
– DPCCH Dedicated Physical Control Channel (DL & UL)
Proprietary and Confidential Slide 25
WCDMA Transport -> Physical Channel Mapping
BCH PCH CPCH RACH FACH DSCH DCH
DPDCH
DPCCH
PDSCH
S-CCPCH
P-CCPCH
PCPCH
PRACH
S-SCH
CPICH
AICH
PICH
AP-AICH
CD/CA-ICH
P-SCH
Physical Channels
Transport Channels Spreading/Modulation
Proprietary and Confidential
WCDMA Air Interface Key Concepts
Proprietary and Confidential Slide 27
Scrambling Codes & CPICH
• The Common Pilot Indication 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 cell
• It is this “beacon” that is used by the phone for its cell measurements for
network acquisition and handover purposes (Ec, Ec/Io).
CPICH
Proprietary and Confidential Slide 28
3G Coverage Measurements
• The majority of 3G coverage measurements are based upon measurements
of the CPICH
• Golden Rule: If the UE can’t see the CPICH the UE can’t see the cell.
• Initial 3G network optimisation will be performed purely from CPICH
measurements
• Three key related measurements for 3G optimisation are
• Ec - The Received Signal Level of a particular CPICH (dBm)
• Io - The Total Received Power (dBm)
• Ec/Io - The CPICH Quality (The ratio of the above two values)
Proprietary and Confidential Slide 29
Total Received Power Io
• In a WCDMA network the User Equipment (UE) may receive signals from
many cells whether in handover or not
• Io* = The sum total of all of these signals + any background noise (dBm)
*Note: Sometimes Io is referred to as No, RSSI or ISSI
Io
Proprietary and Confidential Slide 30
Received Power of a CPICH (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)
*Note: Sometimes RSCP is referred to as Ec
Ec1 Ec2
Proprietary and Confidential Slide 31
The CPICH Quality (Ec/Io)
• From the previous two measures we can calculate a signal quality for each
CPICH (SC) received
• Ec/Io = RSCP - Io (dB)
*Note: Sometimes Ec/Io is referred to as Ec/No
RSCP1 RSCP2
Proprietary and Confidential Slide 32
Example
• From the above three measurements we can calculate for each pilot the
RSCP level for that particular pilot
RSCP1 = -80 - 5 = -85dBm
RSCP2 = -80 - 10 = -90dBm
Ec/Io1= -5dB Ec/Io2 = -10dB
Io=-80dBm
Proprietary and Confidential Slide 33
Ec, Io and Ec/Io Measurement • All commercial scanners and test UEs are capable of making Ec, Io and Ec/Io
measurements
• It is these measurements that are used for coverage analysis and basic
optimisation
Proprietary and Confidential Slide 34
Power Control
Proprietary and Confidential Slide 35
Power Control • The near far problem
– In any CDMA network, the power of the BTS and UE must be tightly controlled
to avoid interference to other BTSs/UEs
Proprietary and Confidential Slide 36
Power Control • Types of Power Control
– Open Loop Power Control – Used to set the initial transmit power of the BTS/UE
– Closed Loop Power Control – Used to control power of uplink/downlink DCHs
• Inner Loop (Or Fast Power Control) used to control TX Power (UL/DL)
• Outer Loop (Or Slow Power Control) used to control SIR Targets (UL/DL)
Proprietary and Confidential Slide 37
Open Loop Power Control • Open Loop Power Control (UPLINK)
– Open Loop Power Control – Used to set the initial transmit power of the BTS/UE
– UPLINK: Uses a measure of DL path loss to provide estimate uplink path loss
– UPLINK: CPICH measurement by the UE along with the reported BTS Noise
Floor are used to determine the initial TX power of the UE
Preamble_Initial_power = CPICH_Tx_power – CPICH_RSCP + UL_interference + UL_required_CI
CPICH_Tx_power
UL_Interference
UL_required_CI
CPICH_RSCP
Proprietary and Confidential Slide 38
Open Loop Power Control • Open Loop Power Control (DOWNLINK)
– Open Loop Power Control – Used to set the initial transmit power of the BTS/UE
– DOWNLINK: Uses a measure of DL path loss to set initial DL TX power
PPDPCH_Initial = Eb/No - PG + CPICH_Tx_Power – CPICH_Ec/Io
CPICH_Tx_power
CPICH_Ec/Io
Eb/No
PG
Proprietary and Confidential Slide 39
Closed Loop Power Control • Closed Loop Power Control
– Enables the BTS/UE to rapidly adjust their DCH TX powers to track the
changing channel conditions (path loss & interference) in order to maintain the
required SIR at the receiving UE/BTS
– Uses feedback (power control commands) in the opposite link to adjust Tx
power accordingly
Proprietary and Confidential Slide 40
Closed Loop Power Control • Closed Loop Power Control
– Closed Loop Power Control – Used to control power of uplink/downlink DCHs
– Two components to Closed Loop Power control in WCDMA
• Inner Loop (Or Fast Power Control) used to control TX Power (UL/DL)
• Outer Loop (Or Slow Power Control) used to control SIR Targets (UL/DL)
Iu-CS
Iub
Iu-PS User Equipment (UE)
& USIM Node Bs RNC
Uu
Inner Loop PC
Outer Loop PC
Proprietary and Confidential Slide 41
Closed Loop Power Control • Closed Loop: Inner Loop Power Control
– Transmit Power Control (TPC) commands (up/down) issued to UE (Uplink) and
BTS (Downlink) to maintain Target SIR every time slot (1500 Hz)
– Power control step size typically 1dB (Algorithm 1)
– Below 30km/h 1.5KHz and 1dB is fast enough to track changes
– Above 30km/h other schemes such as (Algorithm 2) maybe more suitable
User Equipment (UE) & USIM
Node Bs
Uu
Inner Loop PC
Required SIRDL Required SIRUL
Proprietary and Confidential Slide 42
Closed Loop Power Control • Closed Loop: Outer Loop Power Control
– RNC compares uplink BLER with BLER target and sets SIRUL accordingly
– UE compares downlink BLER with BLER target and set SIRDL accordingly
– Frequency 10 to 100 Hz
– Step size 0.1 to 1dB
Iub
User Equipment (UE) & USIM Node Bs RNC
Uu
Outer Loop PC
Proprietary and Confidential Slide 43
WCDMA Handovers
Proprietary and Confidential Slide 44
Handovers in WCDMA • Soft Handover
– Intra-system Handover
• Hard Handover
– Inter-frequency Handover
– Inter-system Handover
Proprietary and Confidential Slide 45
Handovers in WCDMA - Softer HO
• Softer handover occurs between sectors of the same site
Proprietary and Confidential Slide 46
• Soft handover occurs between sectors of the different sites
• For both softer and soft handover UE Ec/Io measurements are used to
determine whether a cell should be added or removed from the active set
Handovers in WCDMA - Soft HO
Proprietary and Confidential Slide 47
Soft Handover • Mechanics of Soft Handover
– In WCDMA to avoid interference the UE must be connected to its best serving
cell at all times
– Another mechanism to minimize interference is Soft Hanover – the “Make
Before Break” handover
– In order to ensure this when in-call the UE constantly monitors the CPICH signal
quality (Ec/Io) of its serving cell and its serving cell’s declared neighbors
Proprietary and Confidential Slide 48
Soft Handover • Neighbor List
– In WCDMA like GSM each cell has to declare at list of valid neighbors
• Intra-system neighbors (32 Max)
• Inter-frequency neighbors (32 Max)
• Inter-system neighbors (32 Max)
Proprietary and Confidential Slide 49
Soft Handover • The Active Set
– The Active Set is defined as the list of cells the UE is connected to during
dedicated mode
– Active set size = 1: UE Not in Soft Handover
– Active set size > 1: UE in Soft Handover
– Typically Active set size limited to 3
Proprietary and Confidential Slide 50
Soft Handover • Updating the Active Set
– Addition Window
– Drop Window
– Replacement Window
Io
RSCP1
RSCP3
RSCP4
-60dBm
-65dBm
RSCP2 -70dBm
-77dBm
-83dBm
Proprietary and Confidential Slide 51
Soft Handover • Updating the Active Set
– Addition Window
– Drop Window
– Replacement Window
Io
RSCP1
RSCP3
RSCP4
-60dBm
-65dBm
RSCP2 -70dBm
-77dBm
-83dBm
Proprietary and Confidential Slide 52
Soft Handover • Updating the Active Set
– Addition Window
– Drop Window
– Replacement Window
Io
RSCP1
RSCP3
RSCP4
-60dBm
-65dBm
RSCP2 -70dBm
-77dBm
-83dBm
Proprietary and Confidential Slide 53
Soft Handover • Updating the Active Set
– Addition Window
– Drop Window
– Replacement Window
Io
RSCP1
RSCP3
RSCP4
-60dBm
-65dBm
RSCP2 -70dBm
-77dBm
-83dBm
Proprietary and Confidential Slide 54
Soft Handover • Updating the Active Set
– Addition Window
– Drop Window
– Replacement Window
Io
RSCP1
RSCP3
RSCP4
-60dBm
-65dBm
RSCP2 -70dBm
-77dBm
-83dBm
Proprietary and Confidential Slide 55
Soft Handover
Ec/Io1
Ec/Io2
Addition Window
Drop Window
Tadd Tdrop
Proprietary and Confidential Slide 56
Soft Handover
Ec/Io1
Ec/Io3
Addition Window
Drop Window
Tadd Tadd Treplace
Ec/Io2
Ec/Io4
Proprietary and Confidential Slide 57
Soft Handover • Updating the Active Set
– Addition Window
– Drop Window
– Replacement Window
Io
RSCP1
RSCP3
RSCP4
-60dBm
-65dBm
RSCP2 -70dBm
-77dBm
-83dBm
Proprietary and Confidential Slide 58
Handovers - Inter frequency HO
• Inter frequency handover occurs between two WCDMA carriers
• Used once operator deploys its second carrier, for microcell layer or capacity
purposes
Proprietary and Confidential Slide 59
Handovers - Inter system HO
• Inter system handover occurs between 3G and other systems (2G, TDD,
WiMAX)
• As with all handovers, accurate adjacencies will be required
3G 2G
Proprietary and Confidential Slide 60
Inter System Handover -3G/2G
• Inter System HO occurs at the boundary of 3G coverage
– 3G Network Edge
– In building?
– Area of poor 3G coverage
3G 2G
Proprietary and Confidential Slide 61
Inter System Handover -3G/2G
• Currently most vendors only support Intersystem HO for Voice and PS Data
services
• 3G->2G Voice HO is a real Hard Handover (seamless from user point of view)
• 3G->2G PS Data HO is effectively a reselection (disruption in data
communications for a number of seconds)
3G 2G
Proprietary and Confidential Slide 62
Inter System Handover -3G/2G Voice
• Typical Dual Mode 3G/2G UEs utilize a single TRX
• During a voice call on WCDMA TRX utilise 100%
• However during 3G/2G HO UE needs to detect 2G neighbours
• Therefore some time sharing of TRX (RX actually) is required to detect
potential 2G Handover candidates
• This time sharing mode is know as “Compressed Mode”
• During compressed mode the UE the instantaneous transmit power is
increased in the compressed frame in order to keep the quality (BER, FER,
etc.) unaffected by the reduced processing gain
3G 2G
Proprietary and Confidential Slide 63
Inter System Handover -3G/2G Voice
• During compressed mode UE attempts to detect 2G candidate cells (ARFCN)
and reports detected neighbours to RNC
• RNC may requests further verification (BSIC)
• Finally RNC will instruct UE to handover to the chosen 2G cell and the call
continues on GSM
3G 2G
Proprietary and Confidential Slide 64
Inter System Handover -3G/2G PS Data
• As with voice, during PS 3G/2G HO the UE needs to detect the 2G neighbors
• Again compressed mode is used to detect 2G candidate cells (ARFCN) and
report detected neighbours to RNC
• RNC may requests further verification (BSIC)
• Finally RNC will instruct UE to reselect to the chosen 2G cell and initiate PS
Data transfer on GSM (GPRS)
3G 2G
Proprietary and Confidential Slide 65
Radio Resource Management
Proprietary and Confidential Slide 66
Radio Resource Management • Overview of Radio Resource Management (RRM)
– Aim of RRM is to efficiently manage the Radio Resources of the WCDMA air
interface
– Different vendors have implemented different RRM strategies and algorithms
– Generally RRM functions can be group as follows
• Admission Control
• Load Control
• Packet Scheduler
• Resource Management
• Power Control
• Mobility Control
Cell Based
Connection Based
Proprietary and Confidential Slide 67
Radio Resource Management • Admission Control
– Responsible for determining if the system (Air Interface, Code Tree, Channel
Elements, Iub, RNC, Iu etc), can accept the call
• Air Interface (Uplink Load, Downlink Load/Tx Power) ?
• Code Tree – Fragmentation ?
• Processing Capacity ?
• Iub Capacity ?
• RNC Capacity ?
– May give priority to different types of calls
• Typically voice/video take precedent
– Considers reports from Load Control Entity to assist decisions
Proprietary and Confidential Slide 68
Radio Resource Management • Load Control
– Responsible for ensuring cell does not go into overload condition
– Constantly monitoring Uplink Rx power and Downlink Tx power
– Preventative action taken to avoid overload condition
– Load reports sent to Admission Control and Packet Scheduler
Proprietary and Confidential Slide 69
Radio Resource Management • Packet Schedule
– Responsible for maximizing throughput of cell/users
– Considers reports from Load Control Entity to assist decisions
– Should allocate the best bearer for the job
• HSDPA / 384k / 128k / 64k / 32k / FACH etc.
Time
Load
Load Target
CS Load
Free Capacity for
PS or HSDPA
Proprietary and Confidential Slide 70
Radio Resource Management • Resource Manager
– Responsible for ensuring efficient use of cells processing capacity
• Code use
• Channel element use
SF 4
SF 8
SF 16
384 user #1 128 user #1
384 user #2
Proprietary and Confidential Slide 71
Radio Resource Management • Power Control
– As shown earlier power control is used to maintain the quality of the radio link
– Minimizing the uplink and downlink transmission power maximizes system
capacity
Iu-CS
Iub
Iu-PS User Equipment (UE)
& USIM Node Bs RNC
Uu
Inner Loop PC
Outer Loop PC
Proprietary and Confidential Slide 72
Radio Resource Management • Mobility Manager
– Responsible for maintaining radio links with UE during mobility
• Intra-system handover
• Inter-system handover
• Link Adaptation
3G 2G 3G 3G
Proprietary and Confidential Slide 73
Key WCDMA Concepts Summary • Key WCDMA concepts to be covered
– AIR INTERFACE OVERVIEW
– POWER CONTROL
• Open
• Closed (Fast/Slow)
– HANDOVER
• Intra-Frequency (Soft/Softer)
• Inter-Frequency (Other WCDMA carrier)
• Inter-System (3G->2G)
– RADIO RESOURCE MANAGEMENT
• Admission Control
• Load Control
• Packet Scheduler
• Resource Management
• Mobility Management
• Power Control
Proprietary and Confidential
Module 1. UMTS Fundamentals Summary
Proprietary and Confidential Slide 75
Module 1: UMTS Fundamentals • Module Summary
1.1 Background & Evolution to 3G and beyond
1.2 CDMA Multiple Access Fundamentals
1.3 UMTS System
• Technology & Physical Interfaces
• WCDMA Air Interface
• UMTS Key Concepts
1.4 WCDMA Link Budgets
1.5 West Region Planning Process Overview
The overall aim of Module 1 is to give a broad grounding of UMTS concepts on
which to build on in the following modules