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8/13/2019 Umts Wcdma Basic Concept 3g 2
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WCDMA BASICCONCEPT_2
Prepared By:A.K.M.Asaduzzaman
RF Optimization Engineer(RNO)
Radio Network Planning & Optimization Department
STAR LINK.
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Mobile Network Evolution
1G
Analogue
2G
Digital
2.5GPacket Data
2.75G
Enhanc ed Data
NMT
TACS
AMPS
GSM
CDMA
TDMA
PDC
GPRS
EDGE
CDMA 1X
WCDMA
TD-SCDMA
cdma20001X EV-DO
2M, 14M
2M
2.4M144K
1982-1996+ 1992-2002+ 2001+ 2004+ 2002-2004+
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WCDMA FDD
WCDMA FDD
Multiple access method DS-CDMA
Duplex Method Frequency Division
Frequency Band Uplink : 1920-1980MHz, Downlink : 2110-2170MHz
Base Station Synchronization Asynchronous/Synchronous operation
Chip Rate 3.84Mcps
Frame Length 10ms
Service multiplexing Multiple Services with different QoS are multiplexed on a
single connection
Multi-user detection, smart antennas Supported by standard, optional in implementation
Power Control Fast Power Control, 1.5KHz
Handover Softer, Soft & Hard Handover
Transmit Diversity Open & Closed Loop
Voice Coding AMR Voice Coding, rate 4.75kb
12.2kbps
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WCDMA Network Structure
GSM /GPRS BSS
BTS
BSC
PCUSS7
SCP
SMS
SCE
PSTN/other PLMN
Internet,Intranet
MSC/VLR GMSC
HLR/AUC
SGSN
CGBG
GGSN
PS backbone
Other PLMN
CS domain
PSdomain
NodeB
RNC
UTRAN
Iu-CS
Iu-PS
A
Gb
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UTRAN
The main task of UTRAN is to create and maintain Radio Access
Bearers (RAB) for communication between UEs and Core
Network.
UTRAN is located between two open interfaces being Uu and Iu.
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UTRAN Architecture
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UTRAN & Interfaces
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RNC (Radio Network Controller) The RNC is switching and controlling element of the UTRAN. RNC is located
between the Iub and Iu interface. It also has the third interface called Iur for
inter-RNS connections.
Referring to the Bearers, the RNC is a switching point between the Iu Bearer
and Radio Bearer(s).
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RNC Function The whole functionality of RNC can be classified into two parts:
UTRAN Radio Resource Management
UTRAN Control Functions
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Radio Resource Management
The RRM is a collection of algorithms used to
guarantee the stability of the radio path and
the QoS of radio connection by efficient
sharing and managing of the radio
resources.
The RRM algorithms to be shortly presented here are:
Handover Control
Power Control
Admission Control and Packet Scheduling
Code Management
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WCDMA Handover Scenarios
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Soft HandoverIn WCDMA system, the majority of handovers are intra-frequency soft handovers
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Concept of Soft/Softer Handover
Cell A
Cell B
Cell C
Single Link
The UE measured the CPICH Signal strenght (RSCP) and quality (Ec/No) to determine whichcell to add in the active set
Add and remove from active set is based on relative measurments
Softer handover
-two cells within the same RBS in Active Set
Soft handover
-two cells from different RBS in Active Set
Soft/Softer handover
-three cells in Active Set
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POWER CONTROL Power control is an essential feature of any
CDMA based cellular system.
In WCDMA, power control is employed in both uplink anddownlink.
Downlink power control is basically for minimising the interference to other
cells and compensating for other cells' interference as well as achievingacceptable SIR.
To manage the power control properly in WCDMA, the system uses differenttwo defined power control:
Open Loop Power Control
Closed Loop Power Control (CLPC), including Inner and Outer Loop
Power Control mechanisms
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Types of Power Control
Open Loop Power Control (OLPC): Basically used for uplink power adjusting, the UEadjusts its transmission power based on estimate of the received signal level from the
BS Common Pilot Channel (CPICH) when the UE is in idle mode and prior to PhysicalRandom Access Channel (PRACH) transmission.
Closed-Loop Power Control (CLPC):Utilised for adjusting the transmission powerwhen the radio connection has already been established. Its main target is to
compensate the effect of rapid changes in the radio signal strength and hence it shouldbe fast enough to respond to those changes.
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CELL CAPACITY
In GSM the TRX capacity calculation is very straightforward procedure but because in
WCDMA the radio interface is handled differently and the system capacity is limited by
variable factors, the capacity of the WCDMA TRX is not very easy to be determined.
The capacity of a cell depends on the downlink Scrambling Code amount assigned for the cell
(minimum is 1). Every downlink Scrambling Code then has a set of Channelisation Codes under it
and every call/transaction requires one Channelisation Code to operate.
In WCDMA technology, all the users share the common physical resource, being frequency band in
5 MHz slices. All users of the WCDMA TRX co-exist on the frequency band at the same moment of
time and different transactions are for the people is the capacity of the WCDMA TRX.
Some assumptions:
All the subscribers under the TRX coverage area are equally distributed so that they have equal
distances to the TRX antenna.The Power level they use is the same and thus the interference they cause is on the same level.
Subscribers under the TRX use the same baseband bit rate, i.e. also the same Symbol Rates.
GSM d WCDMA C i
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GSM and WCDMA Comparison
Separate users through different codes
Continuous transmission and reception
Code planningNo Frequency Planning
Variable Cell Radius: Cell Breathing
Radio Link: 1 UE Many Node-Bs
Power is Capacity
Scrambling Code Planning
Hard/Soft/Softer Handover
Orthogonal in time within a cellTime Slot Synchronization in time
Frequency planning
Fixed Cell Radius
Radio Link: 1 MS 1 RBS
# of Frequencies limit capacity
BSIC Planning
Hard Handover
GSM WCDMA
BTS Node B
BSC RNCMS UE
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Scrambling Code
Scrambling codes
GOLD sequence.
Uplink scrambling codes Uplink scrambling codes are used to distinguish different UEs
Downlink scrambling codes
For downlink physical channels, a total of 218-1 = 262,143 scrambling codes
can be generated.
Only scrambling codes k = 0, 1, , 8191 are used.
8192 codes are divided into 512 groups, each of which contains 16 scrambling
codes.
The first scrambling code of each group is called primary scrambling code
(PSC), and the other 15 ones are secondary scrambling codes (SSC).
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Scrambling Codes & CPICH
The Common Pilot 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).
Beacon: A signaling or guiding device, such as a lighthouse, located on a coast. A radio transmitter that emits acharacteristic guidance signal.
CPICH
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Comments Majority of the measurements are based on CPICH.
Thumb rule is that, if UE cant see the CPICH, it cant see the cell. Initial optimisation is purely based on the CPICH measurements.
In the Downlink, WCDMA cells are identified by their SC.
Its like a BCCH in GSM but the difference is in using same frequency.
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Concepts of RSCP and Ec/No
Three Important Terms
RSCP (Received signal code power) Ec/Io ( Energy per chip/ Noise density)
Eb/No (Energy per bit/Noise density)
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Handover Types
Intra-Frequency Handovers Softer Handover
Handover between sectors of the same Node B (handled by BTS)
Soft Handover
MS simultaneously connected to multiple cells (from different Node Bs)
Hard Handover
Arises when inter-RNC SHO is not possible (Iur not supported or Iur congestion) Decision procedure is the same as SHO (MEHO and RNC controlled)
Inter-Frequency Handover Can be intra-RAN, intra-RNC, inter-RNC
Inter-RAT Handover
Handovers between GSM and WCDMA (NEHO)
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Handovers in WCDMA - Softer HO Softer handover occurs between sectors of the same site
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Soft handover occurs between sectors of the different sites
For both softer and soft it is the Ec/Io levels used to determine whether a
cell should be added or removed from the active set
Handovers in WCDMA - Soft HO
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Handovers - Inter frequency HO Inter frequency handover occurs between two WCDMA carriers
Will be used once operator deploys its second carrier, for microcell layer orcapacity purposes
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Handovers - Inter system HO Inter system handover occurs between 3G and 2G sites
As with all handovers, accurate adjacencies will be required
3G 2G
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OVSF and PN Code UsageOVSF Code PN Code
Usage Uplink :Separate physical data
(DPDCH) & control channels
(DPCCH) from the same
terminal
Downlink :Separate downlink
connections to different UEswithin the cell
Uplink :Separation of UEs
Downlink :Separation of cells
Length Uplink : 4256 chips
Downlink : 4512 chips
Uplink/Downlink :
10ms = 38400 chips
Number of codes Number of codes under one
scrambling factor = spreading
factor
Uplink : Several Million
Downlink : 512
Code Family Orthogonal Variable Spreading
Factor (OVSF)
Gold code
Bandwidth Spreading increase transmission
bandwidth
No change in transmission
bandwidth
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Spreading and De-spreading
information pulse interference White noise
The improvement of time-domain information rate means that the bandwidth of spectrum-domain
information is spread.
f
Sf
The spectrum before spreading
information
f0
The spectrum before despreading
information
Interference/noise
Sf
f0 f f0
The spectrum after despreading
information
Interference/noise
Sf
f
The spectrum after spreading
information
f0
Sf
f
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Principle of RAKE Receiver
RAKE receiver help to overcome on the multi-path fading and enhance
the receive performance of the system
Receive set
Correlator 1
Correlator 2
Correlator 3
Searcher correlatorCalculate the
time delay and
signal strength
Combiner The combined
signal
tt
s(t) s(t)
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Common Technical Terms
Bit, Symbol, Chip:
A bit is the input data which contain information
A symbol is the output of the convolution, encoder, and the block
interleaving
A chip is the output of spreading
Processing Gain:
Processing gain is the ratio of chip rate to the bit rate.
Closely related to spreading factor, SF.
Forward direction/ Downlink : Information path from base station to
mobile station
Reverse direction/ Uplink : Information path from mobile station to
base station
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WCDMA System
Spreading
Spreading (OVSF code)
SF 4512, depends on data rate
Scrambling (Gold Code)
Modulation
QPSK
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HandoverSofter handover
- Handover between intra-frequency cells under the control of the same BTS
- Radio link connection to new target cell is created before existing connection
being deleted.
Soft handover- Handover between intra-frequency cells under the control of the differentBTSs
Hard handover
- Condition of hard handover:
Intra-frequency handover, cells controlled by different RNCs and no Iurinterface between them
Inter-frequency handover
Inter-system handover
Interruption in voice or data communication occurs but this interruptiondoes not effect the user communication
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Soft/Softer Handover
Combine all the
power from each
sector
Power received from
a single sector
Selection combination in the RNC during soft handoff
Maximum ratio combination in the NodeB during softer handoffs
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Common Pilot
Channel(CPICH) Common Pilot Channel (CPICH)
Carries pre-defined sequence.
Fixed rate 30KbpsSF=256 Can use STTD on this channel
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1. Synchronization Procedure
Cell SearchSlot synchronization
Frame synchronization and
code-group identification
Scrambling-code
identification
UE uses PSC to acquire slot
synchronization to a cell
UE uses SSC to find frame
synchronization and identify
the code group of the cell
found in the first step
UE determines the primary scrambling
code through correlation over the
CPICH with all codes within the
identified group, and then detects the
P-CCPCH and reads BCH information
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WCDMA Handover Principal
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Why mobile systems need handover?
UE mobility
The mobile system is composed of
cells which the coverage ability is
limited.
Provide continuous service in
mobile system is the basic element
in QoS.
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The Purpose of Handover
Providing the continuous service in mobile system is the basic element in QoS.
The load balance: sharing the resource
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The Basic Concepts of
Handover Active Set
Monitored Set
Detected set
Event reporting Event reporting to Periodic reporting
Periodic reporting
Radio Link (RL)
Radio Link Set (RLS)
Combination way:
maximum ratio combination selection combination
The soft handover gain
CPICH
Soft handover, softer handover, hard handover
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Types of Handover
According to the signaling characters:
Soft handover (softer handover)
Hard handover
According to the properties of source cell and target cell
Intra-frequency handover
Inter-frequency handover
Inter-mode handover (FDD TDD)
Inter-system handover (UMTS GSM/CDMA2000)
According to the purpose of handover
Based on Coverage
Based on Load (Optional)
Based on mobility of UE (Optional)
Based on Service (Optional)
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The Characters of Different
HandoversComparison between soft handover and
hard handover:
Item Soft Handover Hard Handover
The numbers of RL in
active set after
handover
Several One
Interruption during
handover
No Yes
The frequencies of cells Only possible in
Intra-frequency
cells
Occurs in Intra-frequency
cells or Inter-frequency cells
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The Characters of DifferentHandovers
Comparison between soft handover and
softer handover:
During softer handover, the uplink signaling are combined in NodeBby maximum ratio combination, but during soft handover they are
combined in RNC by selection combination.
Compare to later one, the maximum ratio combination give more
gain. So the performance of maximum ratio combination is better.
Since softer handover is completed in NodeB, it does not consume a
lot of transport resource of Iub.
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Soft Handover
RNC
NodeB 2NodeB 1
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Softer Handover
RNC
NodeB
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Hard Handover
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Thank you