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The Radio Network and basics of WCDMA
ObjectivesUpon completion of this chapter the student will be
able to:
Explain the main differences between the multiple access
technologies FDMA, TDMA and WCDMA
Explain spread spectrumExplain why power control is
necessaryExplain the different handover scenarios in terms of
soft, softer and hard handoverExplain the difference between FDD
and TDD modeExplain the Radio Access Products in UTRAN
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WCDMAWideband Code Division Multiple Access
High data rates in 5 MHz 384 kbps with wide-area coverage
2 Mbps with local coverage
High service flexibility support for services with variable
rate
support for simultaneous services
support of multiple parallel variable-rate services on one
connection
packet and circuit switched services
Fast and efficient packet access
Higher capacity
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Development Key Features 1WCDMA
Built-in support for future
capacity enhancements
Adaptive antennas
Advanced receiver structures for
multi-user detection
Increased coverage compared to
existing systems
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Development Key Features 2WCDMA
Supports Hierarchical
cell structures Inter-frequency
handover
No need for GPS synchronization
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USIM
USIM
SIM
BTSBTSBTSBTSBS
BTSBTSBTSBTSBS
BTSBTSBTSBTSBTS
UMTS/GSM Reference ModelUser equipment GSM BSS Core network
External
network
Cu Uu
Um
Iu
A
Iu
Gb
Iur
Abis
Iub
ME
ME
MT
SCP SMS-GMSC
RNC
RNC
BSC
UTRAN
SIM MT BTS BSC
MSC
EIR
GGSN
GMSC
SGSNAUCHLR
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Figure 1 - 6
WCDMA was chosen as the technology for UMTS public, wide-area
service, on the paired FDD bands:
TD/CDMA was chosen for private, indoor services in the unpaired
TDD band.
ETSI Decision on UMTS
1920 - 1980 MHz (uplink)2110 - 2170 MHz (downlink)
1900 - 1920 MHz2010 - 2025 MHz
(1) The WCDMA technology can also be deployedin existing
frequency bands, e.g. 900, 1800 and 1900 MHzFit into 2*5 MHz
spectrum allocations.
(2) The two modes have harmonized parameters.
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Frequency Division Multiple Access (FDMA)
Orthogonal in frequency within cell Narrow bandwidth per carrier
Continuous transmission and reception No synchronization in
time
f
t
Power
MS1 MS 2 MS 3
NMTAMPSTACS
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Time Division Multiple Access (TDMA)
Orthogonal in time within cell Increased bandwidth per carrier
Discontinuous transmission and reception Synchronization in
time
Power
t
f
MS 1MS 2
MS 3
200 kHz
GSM
PDC
D-AMPS
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Separate users through different codes Large bandwidth
Continuous transmission and reception
f
Code
t
MS 1MS 2MS 3
5 MHz
Direct Sequence Code Division Multiple Access (DS-CDMA)
IS-95 (1.25 MHz) CDMA2000 (3.75 Hz) WCDMA (5 MHz)
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WCDMATechnical characteristics
5 MHz carriers Frequency Division Duplex, FDD 3.84 Mcps chip
rate Variable spreading codes
f
t10 ms frame
4.4-5.0 MHz
P
Optimised packet access on common ordedicated channel
High spectrum efficiency
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Why Spread Spectrum ?Frequency selective fading - Frequency
Diversity
Interference Averaging
f
ChannelQuality
f
ChannelQuality
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BITS 11001
SPREADING
CHIPS 1101001001Chiprate = Spreading Factor * Symbol Rate =
Constant = 3.84 Mchip/s
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Direct Sequence Spread Spectrum Signals
TS
TC
t
t
t
d(t)
c(t)
d(t)c(t)
Information signal
Spreading Signal
Transmission Signal
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Bit-rate FlexibilityWCDMA variability principle:Power is the
commonshared physical resource
Varyinguser bit rate
Translates into Varying power level Varying spreading factor
B
i
t
r
a
t
e
P
o
w
e
r
l
e
v
e
l
S
p
r
e
a
d
i
n
g
f
a
c
t
o
r
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Service FlexibilityMultiple Parallel Services
For a single user, multiple services with different variability
can be mixed easily on a single physical resource
Bitrate
Power level
Bitrate
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WCDMA Resource Allocation The common shared resource in WCDMA is
power Varying user bit rate is mapped to variable power and
spreading on
a single code Different services can be mixed on a single code
for a user Resource allocation is more decentralized
CA
CC
Power levels from MS
Received power levels at BTS
CB
CA
CA
CA
CC
CB CB
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SF ChiprateMchips/s
User BitrateUplink
3,84
3,84
3,84
3,84
3,84
3,84
3,84
256
128
64
32
16
8
4
15
30
60
120
240
480
960
3,84
3,84
3,84
3,84
3,84
3,84
3,84
3,84
512
256
128
64
32
16
8
4
15
30
60
120
240
480
960
1920
SF ChiprateMchips/s
User BitrateDownlink
SF ChiprateMchips/s
User BitrateUplink
3,84
3,84
3,84
3,84
3,84
3,84
3,84
256
128
64
32
16
8
4
15
30
60
120
240
480
960
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Channelization Codes (CC)
CC1 & CC2 CC3,CC4 & CC5
In the Downlink Orthogonal Codes are used to distinguish
betweendata channels from the same Base Station
CC1,CC2,CC3 CC1 & CC2
In the Uplink Orthogonal Codes are used to distinguish between
data channels from the same mobile
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Channelisation Code tree Adapts user bit-rate to code length
C1 = {1}
C2.1 = {1 1}
C2.2 = {1 -1}
C4.1 = {1 1 1 1}
C4.2 = {1 1 -1 -1}
C4.3 = {1 -1 1 -1}
C4.4 = {1 -1 -1 1}SF = 1 SF = 2 SF = 4
OVSF
Channelization codes of different length, depending of the bit
rate
Ensures orthogonality even with different rates and spreading
factors
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Channelisation Code tree Adapts user bit-rate to code length
C2.1 = {1 1}
C4.2 = {1 1-1-1}
C8.3 = {11-1-111-1-1}
C8.4 = {11-1-1-1-111}
SF = 2 SF = 4 SF = 8
Unusable codesC2.1 = {1 1}Using C4.1
C4.1 = {1111}C8.1 = {11111111}
C8.2 = {1111-1-1-1-1}
Using C8.4
Unusable code
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Code Correlation
+1 0 -0.5Divide byCode Length
-1 +1 1 +1 +1 1 +1 -1 -1 +1 1 +1 +1 1 +1 -1 -1 +1 1 +1 +1 1 +1
-1Orthogonal code
in Transmitter
x x x
-1 +1 1 +1 +1 1 +1 -1 -1 +1 -1 +1 -1 -1 +1 -1 -1 +1 1 +1 +1 1 +1
-1TransmittedSequence= = =
+1 +1 +1 +1 +1 +1 +1 +1 -1+1 -1 +1 +1 -1 +1 1 +1 1 1 1 +1 1 1
-1
8 0 -4Integrate
Result
Integrate Integrate Integrate
= = =
-1 +1 1 +1 +1 1 +1 -1 +1 +1 +1 +1 +1 +1 +1 +1 -1 -1 +1 1 +1 +1 1
+1Orthogonal Codeused in Receiver
x x x
Case I: Correlation using Channelisation Codes(a) Same
Channelisation Code; (b) Different Channelisation codes; (c) Same
code with non-zero time offset
Transmitter
Receiver
Input Data +1 +1 +1(a) (b) (c)
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Pseudo Noise (PN) Codes
PN code 1
PN code 3
PN code 1
PN code 4
BS 1 transmits on PN code 1
PN code 2
PN code 5
PN code 2
PN code 6
BS 2 transmits on PN code 2
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Uses modulus addition (XOR)1 mod 1 = 00 mod 0 = 01 mod 0 = 10
mod 1 = 1
Generation of Pseudo Noise (PN)Codes
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Code Correlation
Input Data +1 -1 +1
+1 -1 +1Divide byCode Length
Case II: Auto-correlation using a PN CodeReceiver and
Transmitter use identical code at same time offset
+1 1 +1 +1 1 -1 +1 -1 +1 1 +1 +1 1 -1 +1 -1 +1 1 +1 +1 1 -1 +1
-1PN code usedin Transmitter
x x x
+8 -8 +8Integrate
Result
Integrate Integrate Integrate
TransmittedSequence +1 1 +1 +1 1 -1 +1 -1 -1 +1 -1 -1 +1 +1 -1
+1 +1 1 +1 +1 1 -1 +1 -1
= = =
+1 +1 +1 +1 +1 +1 +1 +1 -1 1 1 1 1 1 1 -1 +1 +1 +1 +1 +1 +1 +1
+1= = =
+1 1 +1 +1 1 -1 +1 -1 +1 1 +1 +1 1 -1 +1 -1 +1 1 +1 +1 1 -1 +1
-1PN CodeUsed in Receiver
x x x
Transmitter
Receiver
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Code Correlation
Input Data +1 -1 +1
+1 1 +1 +1 1 -1 +1 -1 +1 1 +1 +1 1 -1 +1 -1 +1 1 +1 +1 1 -1 +1
-1
+1 1 +1 +1 1 -1 +1 -1 -1 +1 -1 -1 +1 +1 -1 +1 +1 1 +1 +1 1 -1 +1
-1
-1 +1 1 +1 +1 1 -1 +1 +1 -1 +1 1 +1 +1 1 -1 -1 +1 +1 +1 1 -1 +1
+1
-1 1 1 +1 1 +1 1 -1 -1 1 1 +1 +1 +1 +1 -1 -1 1 +1 +1 +1 +1 +1
-1
PN code usedin Transmitter
TransmittedSequence
PN CodeUsed in Receiver
-4 0 2Integrate
Result
-0.5 0 0.25Divide by
Code Length
Case III: Cross-Correlation using PN CodesReceiver and
Transmitter use different codes
x x x
Integrate Integrate Integrate
= = =
x x x
= = =
Transmitter
Receiver
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PN & Orthogonal Codes
2 Data channelsPN1 + OC1 + OC2
2 Data channelsPN3 + OC1 + OC2
1 Data channelPN1 + OC3
2 Data channelsPN4 + OC1 + OC2
User 1 User 2
3 Data channelsPN5+OC1+OC2+OC3 3 Data
channelsPN6+OC1+OC2+OC3
User 3 User 4BS2
BS1
Pilot, BroadcastPN1 + OCp + OCb
Pilot, BroadcastPN2 + OCp + OCb
3 Data channelsPN2+OC1+OC2+OC3
3 Data channelPN2+OC4+OC5+OC6
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Channelisation Codes = Short Codes = Walsh Codes :
Code sequence repeated for each new data bitCode sequence length
= bit length (in time)
+ Orthogonal codes if perfect synchronization+ Good
cross-correlation properties
Scrambling Codes = PN-Codes = Long Codes :
Code sequence length >> bit (in time)Code Planning
needed
+ Good auto-correlation properties+ Low cross-correlation
Code Properties, summary
Identifies the transmitter
Separate different data channels & data rates
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0 1 0
+1
-1
+1
+1
-1
-1
Bipolardata
sequence
1 Bit
Bits/s
Chips/s
Chip
Code(1-1 1-1)
Signal
Chips/s
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10 kb/s
3.84 Megachip/s
DS-CDMA - Principle
BITS
11001BITS
11001CHIPS
1
WBI
WBI
WBI = WideBand InterfererNBI = NarrowBand Interferer
frequency
Power
f
P
f
P
f
P
f
P2
3 4 51 2
3
4
5
5 MHz
NBI
MOD DEM LP DET
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WCDMA Transport Channels
Common Control Channels BCCH Broadcast Control Channel (DL) FACH
Forward Access Channel (DL) PCH Paging Channel (DL) RACH Random
Access Channel (UL)
Dedicated Channels DCH Dedicated Channel (DL & UL)
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Transport-to-physical Channel Mapping
Secondary Common Control Physical Channel (Secondary CCPCH)
Secondary Common Control Physical Channel(Secondary CCPCH)
Physical Random Access Channel (PRACH)
Dedicated Physical Data Channel (DPCCH)
Dedicated Physical Control Channel (DPCCH)
Synchronization Channel (SCH)
Primary Common Control Physical Channel(Primary CCPCH)BCCH
FACHBCCH
RACH
DCH
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Pilot (TFI)TPC
Uplink Dedicated Physical Channels
DPDCH
DPCCH
Data
Slot 14Slot iSlot 2Slot 0
Frame 1 Frame 2 Frame i Frame 72
10 ms
One super frame = 720 ms
Q Mux
I Mux
2560 Chips, 10x2k bits
Transport Format IndicatorTransmit Power Control
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Downlink Dedicated Physical Channels
Slot 14Slot iSlot 2Slot 0
Frame 1 Frame 2 Frame i Frame 72
10 ms
One super frame = 720 ms
IQ MuxData Data(TFI)TPCPilot
DPDCHDPCCH
2560 Chips, 10x2k bits
Transport Format Indicator
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Primary Common Control Physical Channel
Slot 14Slot iSlot 2Slot 0
Frame 1 Frame 2 Frame i Frame 72
10 ms
One super frame = 720 ms
Data Pilot 8 bitsTx off
256 chips
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Secondary Common Control Channel
Slot 14Slot iSlot 2Slot 0
Frame 1 Frame 2 Frame i Frame 72
10 ms
One super frame = 720 ms
Data Data(TFCI) Pilot
2560 Chips, 20 * 2k bits (k=0..6)
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PRACH allocated for RACH access slot
Access slot #1
Access slot #2
Access slot #i
Access slot #8
Random access transmission
Random access transmission
Random access transmission
Random access transmission
1.25 ms
Offset of access slot #i
Frame Boundary
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Uplink Spreading and Modulation
DPDCH
DPCCH
CCH,di
CCH,di
Q
I
IQMux
I+jQCscramb
QPSKmodulation
Multi-code transmissionAdditional data channels DPDCHs added to
either I or Q
CCH,di:Channelization codes (OVSF codes, 4-256
chips)Cscramb:Scrambling code (long Gold code, 38400 chips, or
short VL Kasami code, 256 chips)
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Downlink Spreading and Modulation
DPDCH/
DPCCH
S Pbits to
symbols
Cch
QPSKmodulation
OVSF codes ensure DL orthogonality even with different rates and
spreading factors for different users
Cch: Channelization codes (OVSF codes, 4-256 chips)Cscramb:
Downlink scrambling code (Gold code, 38400 chips)
Cscramb
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WCDMA Packet AccessOptimized dual mode scheme with adaptive mode
selection based on packet-traffic characteristics
Small infrequent packets appended to Random-Access Request
Large or frequent packets transmitted on dedicated channel
Random-AccessRequest Small packet
Random-AccessRequest Small packet
Arbitrary time
Random-Access Channel
Random-AccessRequest
Packet Packet Packet
Random-Access Channel
Dedicated ChannelRelease of channel
T Time-out
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Initial Cell search
Matchedfilter
Slot-wise accumulation
Find Maximum
Tslot
One Ray from Base Station AOne Ray from Base Station B
Timing moduloTslot
Step one: Slot synchronizationStep two: Frame synchronization
and code group
identificationStep three: Scrambling code identification
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Cell Search, Asynchronous System (WCDMA)
Current cell
New cell
MF output
Synch. codeScrambling code
Synch. codeScrambling code
random
est
256 chip/s
3.84 chip/s
10 ms
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Handover
Intra-frequency handover within same carrier
Soft handover between different BSs
Softer handover between sector at same BS
Inter-frequency handover between two carriers
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Inter-frequency Handover
Inter-frequency measurements needed in both scenarios ETSI WCDMA
has a slotted mode for inter-frequency
measurements, thereby supporting the scenarios above
HCS-scenario
Handover f1 f2 always needed between layers
Handover f1 f2 needed sometimes at Hot Spot
Hot-spot scenario
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Support for Inter-frequency Handover
Needed for: Hot-spot cells with
additional carriers Hierarchical Cell
Structures (HCS) Handover to GSM
Two measurement approaches:
Dual-receiver approach for mobile terminals with receiver
diversity
Slotted downlink for low-complexity terminals
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f = 10 ms Idle time for IF measurements
SF=SF0
SF=SF0/2
SF=SF0 SF=SF0
SF=SF0/2
SF=SF0
WCDMA Downlink Slotted Transmission
Enables measuring on neighboring cells by changing spreading
factor
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Multipath FadingA B C
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Multipath Propagation
10
2
3
Time Dispersion
10 2 3
Radio Environment
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The RAKE-receiver principle
COM
B
I
N
E
R Power measurements of neighbouring BS
Sum of individual multipath components
Finger #1
Finger #2
Finger #3
Searcher Finger
Finger #N
Buffer/delayCorrelators
Channel
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Implemented in both the UE and Base-stations
Improves signal reception by- Multipath diversity (from a single
BS)- Macro diversity (in soft handover mode)
Enables Soft handover by
measuring signal strength (or quality) from neighboringcells
The RAKE-receiver,summary
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Power Control
What? The Transmitter adapts the output power according to
Path
Loss Why?
Mainly to solve the Near-Far problem Goal is that all users
should experience the same SIR
How? Open Loop Power control (Initially, No signaling) Inner
Loop Power control (Signaling channel, continuously:
1500 times/s, relative changes: up or down) Outer loop Power
control (Between BTS and RNC)
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Power controlWith power control
MS Tx Power
BS Rx Power
Without power control
MS Tx Power
BS Rx Power
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Outer loop:FER/BER
Ul Eb/No target
Adjust target
QoS target
Uplink Power Control
Initial settingOpen loop:
Random AccessPMS
Closed loopPower Control:
UP/DOWN command
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Outer loop:FER/BER
Ul Eb/No target
Adjust target
QoS target
Downlink Power Control
Closed loopPower Control:
UP/DOWN Command
Open loop:Initial setting
PBS
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BS1 BS2
Power Control in Soft Handover/Handoff
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PMS
BS2BS1
UP/DOWN Command
UP/DOWNCommand
Uplink Power Control in Soft Handover
Outer loop:FER/BER
Ul Eb/No target
Adjust target
QoS target
Down + DownDown + Up
Up + Up
Decrease power
Increase power
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Closed loop Power Control:UP/DOWN
UP/DOWNCommand
UP/DOWNCommand
BS2BS1
Downlink Power Control in Soft Handoff
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Node BNode B
RNC
UTRAN Architecture
IurIub
Core Network
Node BNode B
RNC
Iu Iu
Iub
RNS RNS SRNSDRNS
Serving and Drift RNS
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Max planned interference
Max planned
load
Noise floor
Uplink interference
Load
Radio Resource Management (Admission Control AC)
The AC function will guarantee the overall system Qos by
admitting (or blocking) new users
Monitors cell load by received interference
in uplink output power in downlink
New users blocked above this point
User added
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UTRA/Time Division Duplex
Harmonized parametersto UTRA/TDD
Primarily for private, uncoordinated systems
Deployed in unpairedUMTS bands:
1900-1920 MHz and2010-2025 MHz
The proposal is still evolving
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UTRA/TDD Parameters
Identical parameters as FDD
3.84 Mcps 10 ms frame/15 slots per frame QPSK modulation, Re-use
factor of 1 Multi-code and variable
spreading factor to handle different source rates
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Uplink/downlink Allocation
Each 0.625 ms slot allocated to either uplink or downlink
transmission
One slot for downlink (BCCH) one for uplink (RACH)
Uplink/downlink asymmetry possible Same asymmetry and frame synch
needed within
continuous area in coordinated systems
One frame (10 ms)
One slot (0.625 ms) 15
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Examples of Uplink/Downlink Allocations
Symmetric allocation
One frame (10 ms)
Symmetric allocation
Multiple uplink/downlink switching-points
Single uplink/downlink switching-point
Asymmetric allocation
Asymmetric allocation
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The TDD CDMA Component
In each slot up to 8 codes are used Multi-code transmission
Different users can share the same time slot Since only few codes
used in each time slot, joint
detection is supported
One frame (10 ms)
One time slot and code
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Traffic and Common Control Burst Structure Two different bursts,
different length of mid-amble,
in different environments (delay spreads) Mid-amble used for
channel estimation
One slot (2560 chips)
Data Mid-amble Data Guard
Data Mid-amble Data Guard
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Physical Channel Format
Frame 71Frame iFrame 1Frame 0
Time-slot 0 Time-slot 2 Time-slot i Time-slot 14
10 ms
One super frame = 720 ms
Super Frame
2560 chips
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Multi-rate with variable-rates schemes
Single code transmission withvariable spreading
a mobile uses single code transmission by adapting spreading
factor as a function of data rate
a base station should broadcast a single burst per mobile
station by adapting spreading as a function of the data rate
Multi code transmission with fixed spreading
within one timeslot more than one burst can be transmitted
different spreading codes are used to allow distinction of
multiple bursts
these multiple bursts can be allocated to one, partly to one or
to different users.
Up to 8 bursts can be transmitted
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Spectrum Requirements for WCDMA The minimum spectrum allocation
is a single carrier 5 MHz Available spectrum 2 x 60 MHz
UMTS
4.4 MHzCo-ordinated
5.0 MHz Uncoordinated
3.0 MHz Uncoordinated
GSM
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Bandwidth Capabilities
WCDMA
TodayHSCSD
&GPRS
EvolvedEDGE
up to115 kbpswide areacoverage
up to2 Mbps
local areacoverage
up to384 kbpslocal areacoverage
at least 384 kbpswide areacoverage
200 kHz 5 MHz
UMTSGSM
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WCDMA ProductsRadio Network Overview
Radio NetworkController
Core Network
Radio BaseStation
Mobile terminals
Radio Access Network
Network Management system
TRAMRANOS
RadioAccessNetworkOperationSupport
Tools forRadioAccessManagement
CN/other management appl.