01. WCDMA Fundamentals

No Slide TitleWCDMA Fundamentals
MODULE 1
Module 1 – WCDMA Fundamentals
Understand the main properties of WCDMA air interface
Recognize the main Nokia RRM functions and their main tasks
* © Nokia Siemens Networks Presentation / Author / Date
Module Contents
Overview of Nokia Radio Resource Management (RRM)
Module Contents
IMT-2000 frequency allocations
Main properties of UMTS Air Interface
Standardisation of 3G cellular networks
ITU (Global guidelines and recommendations)
IMT-2000: Global standard for third generation (3G) wireless communications
3GPP is a co-operation between standardisation bodies
ETSI (Europe), ARIB/TTC (Japan), CCSA (China), ATIS (North America) and TTA (South Korea)
GSM
EDGE
UMTS
3GPP2 is a co-operation between standardisation bodies
ARIB/TTC (Japan), CCSA (China), TIA (North America) and TTA (South Korea)
CDMA2000
IMT-2000 (International Mobile Telecommunications-2000) is the global standard for third generation ( 3G ) wireless communications as defined by the International Telecommunication Union .
IMT-2000 frequency allocations
UMTS – FDD Frequency band evolution
Release 99
I 1920 – 1980 MHz 2110 –2170 MHz UMTS only in Europe, Japan
II 1850 –1910 MHz 1930 –1990 MHz US PCS, GSM1900
New in Release 5
New in Release 6
V 824-849MHz 869-894MHz US cellular, GSM850
VI 830-840 MHz 875-885 MHz Japan
New in Release 7
VIII 880-915 MHz 925-960 MHz GSM900
IX 1749.9-1784.9 MHz 1844.9-1879.9 MHz Japan
The allocation of frequency bands for FDD WCDMA is specified by 3GPP in TS25.104.
3GPP release 99 specifies operating bands I and II. Release 5 specifies operating bands I, II and III. Release 6 specifies operating bands I, II, III, IV, V and VI.
Operating band I is at 2100 MHz and represents the core 3G spectrum allocation. Operating band II is at 1900 MHz and helps to satisfy the requirements of America. Operating band V is at 850 MHz and represents an extension band for future use.
Duplex spacings vary from 45 MHz for operating bands V and VI, to 400 MHz for operating band IV. Larger spacings increase the importance of treating the uplink and downlink propagation separately.
Nokia supports WCDMA 2100 with RAN1.5.2.ED2, WCDMA 1900 with RAN04 (Node B software WN2.ED2) and WCDMA 850 with RAS05 (Node B software WN3).
The UARFCN identifies the RF carrier on a 200 kHz raster. The 200 kHz raster can be used for fine tuning the position of the RF carrier. Operating bands II and IV, V and VI have additional RF carrier positions defined with a different UARFCN numbering scheme.
Directed Emergency Call Inter-System Handover (EMISHO) is supported by Nokia for WCDMA 1900 and 850. EMISHO allows GSM location based services to be used in American markets where there are stringent location based service requirements for emergency calls.
Nokia’s solution for WCDMA 2100 supports both 20 W and 40 W WPA. Nokia’s solution for WCDMA 1900 and 850 supports only 40 W WPA.
The majority of link budget assumptions are the same for all operating bands. Antenna gains and feeder losses tend to be lower at lower frequencies. Building penetration losses and indoor standard deviations can be assumed to be equal for each of the frequency bands although these assumptions tend to be country specific. The use of 40 W WPA for WCDMA 1900 and 850 means that downlink transmit powers are typically 3 dB greater. MHA may not be used in band V as a result of the reduced feeder loss at 850 MHz.
The air-interface propagation loss is less for the lower operating bands. In the case of Okumura-Hata, the frequency dependant terms result in approximately 12 dB difference between the WCDMA 2100 and 850 path loss figures for a specific cell range. Propagation model, clutter dependant correction factors may be assumed to increase at lower frequencies, i.e. for WCDMA 850.
The Nokia Flexi WCDMA Base Station will be available for frequencies 2100 MHz, 1700 MHz, 1800 MHz and 1700/2100 MHz in the second half of 2006. In the first half of 2007, further frequencies, including 850 MHz, 900 MHz and 1900 MHz will be available, where after other frequencies will be added based on market need.
Module Contents
UMTS Air interface technologies
UMTS Air Interface technologies
UMTS Air interface is built based on two technological solutions
WCDMA – FDD
WCDMA – TDD
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
All cells at same carrier frequency
Spreading codes used to separate cells and users
Signal bandwidth 3.84 MHz
Inter-Frequency functionality to support mobility between frequencies
Compatibility with GSM technology
WCDMA Technology
5 MHz in TDD mode
WCDMA Carrier
Frequency
Time
UMTS & GSM Network Planning
Differences between WCDMA & GSM
Multiple WCDMA carriers – Layered network
200 - 500 m
CDMA principle - Chips & Bits & Symbols
Spreading Code
Spread Signal
Bits (In this drawing, 1 bit = 8 Chips SF=8)
Baseband Data
Energy Box
Higher spreading factor Wider frequency band Lower power spectral density
BUT
Spreading & Processing Gain
Processing Gain Examples
Packet data user (R=384 kbit/s)
Power density (W/Hz)
Processing gain depends on the user data rate
Transmission Power
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
UL: separates users
User 3
User 2
User 1
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
Physical Layer Bit Rates (DL)
Half rate speech
Full rate speech
128 kbps
384 kbps
2 Mbps
(QPSK modulation)
Rb_phy includes DPDCH (User data + L3 control) + Error protection + DPCCH (L1 control)
Spreading factor
Maximum user data rate with ½-rate coding (approx.)
512
7.5
15
2880
5760
5616
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 rate
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 SF=2 – 4)
Initial expected capability 1.46 Mbps
Coding rate
DL & UL Scrambling Codes
512 Primary 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
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
Scrambling Codes & Multipath Propagation
RAKE Receiver
Delay 1
connection
Output
t
Cell-1
Cell-1
Cell-1
Cell-2
Code is the combines scrambling (cell 1 or 2) and spreading code (physical channel)
Channelisation and Scrambling Codes
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
Uplink: Separation of mobile
Length
Downlink also 512 chips
Different bit rates by changing the length of the code
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
Number of codes
Uplink: 16.8 million
Spreading
Module Contents
Load control
Admission Control
Packet Scheduler
Resource Manager
Power Control
Handover Control
Radio Resource Management
RRM is responsible for optimal utilisation of the radio resources:
Transmission power and interference
Logical codes
The trade-off between capacity, coverage and quality is done all the time
Minimum required quality for each user (nothing less and nothing more)
Maximum number of users
The radio resources are continuously monitored and optimised by several RRM functionalities
service quality
cell coverage
cell capacity
RRM Functionalities
Load Control (LC)
LC performs the function of load control in association with AC & PS
LC updates load status using measurements & estimations provided by AC and PS
Continuously feeds cell load information to PS and AC;
Interference levels (UL)
Load Control – Load Status
Overload
Admission Control (AC)
Checks that admitting a new user will not sacrifice planned coverage or quality of existing connections
Admission control handles three main tasks
Admission decision of new connections
Take into account current load conditions (from LC) and load increase by the new connection
Real-time higher priority than non-real time
In overload conditions no new connections admitted
Connection QoS definition
Connection specific power allocation (Initial, maximum and minimum power)
Packet Scheduler (PS)
PS allocates available capacity after real-time (RT) connections to non-real time (NRT) connections
Each cell separately
PS selects allocated channel type (common or dedicated)
PS relies on up-to-date information from AC and LC
Capacity allocated on a needs basis using ‘best effort’ approach
RT higher priority
Resource Manager (RM)
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
Users within one cell
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 increase 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
Uplink power control target
minimised UL transmit power and interference
UE1
UE2
min(Prx1)
min(Prx2)
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
Power Control types
UL Outer Loop
Closed Loop Power Control
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 utilise both
Fast closed loop power control
Outer loop power control
Both work according to similar principles as the dedicated channel power control
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
Softer handover
MS handover within one base station but between different sectors
Hard handover
MS handover between different frequencies or between WCDMA and GSM
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 planning parameters
Radio link performance is improved during soft handover
Soft handover consumes base station and transmission resources
BS1
BS2
BS3
Hard handover
Hard handovers are typically performed between WCDMA frequencies and between WCDMA and GSM cells
GSM/GPRS
GSM/GPRS
f1
f2
f1
f2
f2
f2
HSPA mobility
Serving cell change for HSDPA data channel
Connected only to one cell at a time
HSUPA
Soft handover utilised for uplink channels as required due to near-far problem
Only Serving Cell can allocate more UL capacity/power
HS-SCCH
HS-PDSCH
DPCH
DPCH
Serving
Module 1 – WCDMA Fundamentals
Summary
Radio interface technology of UMTS is WCDMA with FDD and TDD versions
WCDMA networks can be built on European, US-based and Asian/Japanese frequency bands
WCDMA air interface utilises combination of two spreading codes
Radio Resource Management is responsible of efficient utilisation of radio resources while offering required quality of service to users
GSM900/1800:
Time
(DPDCH) and control channels
(DPCCH) from same terminal
Downlink: Separation of downlink
cell
Length
4
of the code
66.7
m
dvanced
Number of codes
code = spreading factor
Uplink: 16.8 million
Short
Spreading
bandwidth

01. WCDMA Fundamentals

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