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UMTS Overview
Strategy & Support
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UMTS Overview
1. Introduction to UMTS
2. UMTS Network Architecture
3. WCDMA Wireless Technology
4. WCDMA Air Interface Principles
5. Coverage and Capacity Principles
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UMTS Overview
Introduction to WCDMA/UMTS
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1980s 1990s 2000 +
same business, new machine new business, new machine
Services
Network
New mobile businesses
Wideband/multimedia
1 2nd
generationdigital
stgenerationanalogue 3 generationwideband
rd
Basic mobile telephony
Evolution to 3G systems
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Consumer demand forwideband services
Increased network capacity
More airtime Access anytime, anyplace
Wireless postcard
Imaging
Mobile transactions
More Subscribers
UMTS Drivers
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UMTS Spectrum Allocation
900 MHz 880 915 925 960
EGSM
890 915 935 960
GSM
890 902.5 935 947.5
902.5 915 947.5 960
VFE GSM 900
1800 MHz 1710 1785 1805 1880
GSM
1756 1761 1763.5 1766 1851 1856 1858.5 1861
RX RX TX TX
1751 1756 1761 1763.5 1846 1851 1856 1858.5
RX RX TX TX
1850 1910 1930 1990
1900 MHz GSM/
TDMA/CDMA
1920 1980 2110 2170
UMTS/W-CDMA
MobiNil GSM 900
RX
RX
MobiNil GSM 1800
TX
TX
RX TX
TX
TX
TXRX
RX
TXRX
RX
VFE GSM 1800
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UMTS Overview
UMTS Network Architecture
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3G Radio Access Network - Highlights
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GSM/GPRS Core Network (CN)
Iu Iu
RNS
RNC
RNS
RNC
Node B Node B Node B Node B
Iur
Iub IubIub Iub
User Equipment
(UE)
UTRAN
(UMTS
Terrestrial
Radio Access
Network)
PSTN
ISDNInternet
Uu
3GPP TS 25.401 6.0
MSCGPRS
Service Node
Iu I
u
UMTS and UTRAN
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UMTS Overview
CDMA Wireless Technology
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TDMA Frequency
Time
Time
Frequency
CDMA Frequency
Code
Frequency
TimeCode
Time
Frequency
FDMA Frequency
Radio Access Technologies
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RateData
RateCodePN
Both signals combined
in the air interface
PN Code 1Frequency
Amplitude
Signal 1
PN Code 2Frequency
Amplitude
Signal 2
Spread SpectrumProcessing Gain
PN Code 1 Signal 1 is reconstructed
Signal 2 looks like noise
Both signals are
received together
AT THE RECEIVER...
Two Transmitters at the same frequency
Spread Spectrum Multiple Access
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In WCDMA, all cells may use the same carrier frequency but different
scrambling codes. This means no frequency planning, but scrambling codeand power planning instead!
FDMA/TDMA (reuse > 1) CDMA/WCDMA (reuse = 1)
One Cell Frequency Reuse
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Correlation of channel codes in receiver
1 Carrier (5MHz)
Power
Own channel correlates well, i.e. peaks (Signal) Other channels appear as noise (Interference) More users increased interference
Signal (Eb)
Interference (No)
Power need to be adjusted to retain the Signal to Interference Ratio (SIR)I.e. fulfilling the BLER requirements for that specific service
CDMA Rx Concept (1/2)
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PN3 PN4
PN5 PN6
PN1 PN1
Cell Site 1 transmits using PN code 1
PN2 PN2
Cell Site 2 transmits using PN code 2
Uplink: PN Code used to distinguish each Mobile StationDownlink: PN Code used to distinguish each Base Station
Scrambling Code Planning
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OC1, OC2OC3, OC4
OC5, OC6, OC7
OC1 , OC2, OC3OC1, OC2
OC1, OC2, OC3, OC4
Uplink: Orthogonal Codes used to distinguish data channels
coming from each Mobile Station
Downlink: Orthogonal Codes used to distinguish data channels
Coming from each Base Station
Channelization Codes
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OVSF Code Space: 8 users; one 8-bit code per user
Chip Rate = 3.840 Mcps
480 kb/s 480 kb/s 480 kb/s 480 kb/s 480 kb/s 480 kb/s 480 kb/s 480 kb/s
1
11 10
1111 1100 1010 1001
11111111 11110000 11001100 11000011 10101010 10100101 10011001 10010110
OVSF Codes
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OVSF Code Space: 5 users; one user has 4x data bandwidth
User with 4x Bit Rate
= Unusable Code Space
480 kb/s 480 kb/s 480 kb/s 480 kb/s
1.92 Mb/s
Chip Rate = 3.840 Mcps1
11 10
1111 1100 1010 1001
11111111 11110000 11001100 11000011 10101010 10100101 10011001 10010110
OVSF Codes
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Codes(Orthogonal)
Max PowerPower
kbps*
3840
1920
960
480
240
120
15
Gross bitrate.Effective bitrate is lessdue to channel overhead
SF
1
2
4
8
16
32
256
Code 1
Code 2
Code 3
WCDMA Shared Resources
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UMTS Overview
WCDMA Air Interface Principles
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Multi-path propagation Time dispersion
h( )
0 1 2 3
0
1
2
3
The Radio Channel
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Fast (Rayleigh) Fading
time (mSec)
Composite
Received
Signal
Strength
Time between fades is related to
RF frequency
Geometry of multipath vectors
Vehicle speed:
Up to 2 fades/sec per kilometer/hour
Deep fade caused by destructive summation
of two or more multipath reflections
msec
Multipath Fading
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CDMA Mobile Station RAKE Receiver Architecture
Each finger tracks a single multipath reflectionAlso be used to track other base stations signal during soft handover
One finger used as a Searcher to identify other base stations
Finger #1
Finger #2
Finger #N
Searcher Finger
Combiner
Sum ofindividualmultipathcomponents
Power measurementof NeighboringBase Stations
The RAKE Receiver
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TX power TX power
RX power RX power
t
t t
t
Without power control With power control
Power Control Combats fast fading
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BLER = Block Error Rate
SIR = Signal to Interference Ratio
TPC = Transmit Power Control
P(Startvalue)
Open loop
P(SIR-Target,UL)
P(SIR-Target, DL)
Inner loop
DL-TPC UL-TPC
SIR-Target,DL
BLER-Measured,DL
DL-Outer loop
RNCSIR-Target,UL
SIR-Error,UL
UL-Outer loop
CDMA Power Control
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Inter-System Handover
Handover from a CDMA system to an Analog or TDMA systemTraffic and Control Channels are Disconnected and must be Reconnected
Hard Handover
When the MS must change CDMA carrier frequency during the Handover
Traffic and Control Channels are Disconnected and must be Reconnected
Soft Handover
Unique to CDMA
During Handover, the MS has concurrent traffic connections with two BSs
Handover should be less noticeable
Softer Handover
Similar to Soft Handover, but between two sectors of the same cell
Handover is simplified since sectors have identical timing
Handover
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One finger of the RAKE receiver is constantly scanning neighboringPilot Channels.
When a neighboring Pilot Channel reaches the t_add threshold, the newBS is added to the active set
When the original Base Station reaches the t_drop threshold, originatingBase Station is dropped from the active set
Monitor Neighbor BS Pilots Add Destination BS Drop Originating BS
CDMA Soft Handover
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UMTS Overview
Coverage and Capacity Principles
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GSM voice
WCDMA voice and low bit rate
64/128 kbps
WCDMA medium bit rates
128/384 kbps
The power requirement determines the service coverage in WCDMA users will require different amount of power depending on environment, service, system load
System load or rather intereference will depend on:- Number of users in other/own cells, i.e. other/own average cell power usage- distribution of users and their service usage
WCDMA high bit rate
384 kbps
Service Coverage
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The service coverage shrinks with increasing traffic in the cell
Max power High bit rate
Medium bit rates
Low bit rate
Cell Breathing
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Case B: Low power usage and high capacity
Case A Case B
Case BCase A
Node-B Power
Case A: High power usage and low capacity
Subscriber distribution impact capacity / coverage
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Time
interference
Load In Neighbouring Cell Impact Capacity / Coverage
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