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Basic Concept of 3G Network
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3G rel99 Architecture (UMTS)
- 3G Radios
SS7
IP
BTS
BSCMSC
VLR
HLRAuC
GMSC
BSS
SGSN GGSN
PSTN
PSDN
CN
CD
GcGr
Gn Gi
Abis
Gs
B
H
BSS Base Stat ion System
BTS Base Transceiver Station
BSC Base Station Controller
RNS Radio Network System
RNC Radio Network Controller
CN Core Network
MSC Mobile-service Switching Controller
VLR Visitor Location Register
HLR Home Location Register
AuC Authentication Server
GMSC Gateway MSC
SGSN Serving GPRS Support Node
GGSN Gateway GPRS Support Node
AE PSTN
2G MS (voice only)
2G+ MS (voice & data)
Gb
3G UE (voice & data)
Node B
RNC
RNS
Iub
IuCS
ATM
IuPS
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WCDMA Specification
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Spreading process in WCDMA
1st Step: Channelization Variable Rate Spreading ( According to user data rate)
2nd Step: Scrambling Code Fixed Rate Spreading (3,840 Kchips)
S
Channelization
Code
Scrambling
Code
3,840 Kcps
Coding
&
Interleaving
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Downlink (NodeB to UE )
Scrambling Code:Identifies cell (sector). Channelization Code:Identifies user channels in cell (Sector).
Scrambling Code A
Scrambling Code B
Scrambling Code C
Channelization
Code 1
Channelization
Code 2 Channelization
Code 3
ChannelizationCode 1 Channelization
Code 2
Channelization
Code 2
Channelization
Code 1
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Up Link (UE to NodeB )
Scrambling Code:Identifies user terminal.
Channelization Code:Identifies channels in user terminal.
Scrambling Code A
Scrambling Code B
Scrambling Code C
Channelization
Code 1
Channelization
Code 2
Channelization
Code 1
ChannelizationCode 1
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Orthogonal Variable Spreading Factor [OVSF] codes are the channelization codes used for
signal spreading in the uplink and downlink
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The code used for scrambling of the uplink Channels may be of either long
or short type, There are 224 long and 224 short uplink scrambling codes.
Uplink scrambling codes are assigned by higher layers.
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.
In the downlink direction 512 of scrambling codes are used to identify the
cells in the downlink so downlink planning is required
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Different Handover in 3G
1. Intra-system handovers
MS handover within one cell between different sectors: Softer handover
MS handover between different BS:
Soft handover
Hard handover
2. Inter-frequency handovers
Hard handover
3. Inter-system handovers
Handover between WCDMA GSM900/1800: Hard handover
Handover between WCDMA/FDD TDD: Hard handover
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Intra-system handovers
1. Intra-system handovers
I. Softer handover
II. Soft handoverIII. Hard handover
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Softer Handover
Softer handover refers to handover between cells with same frequency
and in same nodeB.
As we can say HO between Cell A to Cell B of SITE0001 at f1 or f2
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Soft Handover
Soft handover refers to adding a new serving cell and deleting the old one
after stabilization. Services continue in the handover without any
interruption. Its also known by term make before break.
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Hard Handover
Hard handover refers to deleting the old serving cell and then adding a
new serving cell. Services break off during the handover. Its also known by
term break before make.
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Events in 3G
Event Description
Event 1AQuality of target cell improves, entering a report range of relativelyactivating set quality
Event 1BQuality of target cell decreases, depart from a report range of relativelyactivating set quality
Event 1CThe quality of a non-activated set cell is better than that of a certain activatedset cell
Event 1D Best cell generates change
Event 1E Quality of target cell improves, better than an absolute threshold
Event 1F Quality of target cell decreases, worse than an absolute threshold
Event correlative to soft handover
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Events in 3GEvent Description
Event 2A Best band generates change
Event 2BQuality of currently-used band is worse than an absolute threshold andthat of non-used band is better than an absolute threshold
Event 2C Quality of non-used band is better than an absolute threshold
Event 2D Quality of currently-used band is worse than an absolute threshold
Event 2E Quality of non-used band is worse than an absolute threshold
Event 2F Quality of currently-used band is better than an absolute threshold
Event correlative to hard handover
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Events in 3G
Event Description
Event 3AQuality of currently-used UTRAN operator is worse than an absolutethreshold and quality of other radio systems is better than an absolutethreshold
Event 3B Quality of other radio systems is worse than an absolute threshold
Event 3C Quality of other radio systems is better than an absolute threshold
Event 3D Best cell in other systems generates change
Event correlative to handover between systems
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Common Pilot Channel (CPICH)
The CPICH is a fixed rate (30 kbps, SF=256) downlink physical channel that carries a pre-defined bit
sequence.
There are two types of Common pilot channels, the Primary and Secondary CPICH. They
differ in their use and the limitations placed on their physical features
Primary CPICH
Secondary CPICH
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Primary CPICH
An important area for the primary common pilot channel is the measurements for the
handover and cell selection/reselection. The use of CPICH reception level at the terminal for
handover measurements has the consequence that, by adjusting the CPICH power level, the
cell load can be balanced between different cells. Reducing the CPICH power causes part of
the terminals to hand over to other cells, while increasing it invites more terminals to hand
over to the cell, as well as to make their initial access to the network in that cell.
The Primary Common Pilot Channel (P-CPICH) has the following
characteristics:
The same channelization code is always used for the P-CPICH.
The P-CPICH is scrambled by the primary scrambling code.
There is one and only one P-CPICH per cell.
The P-CPICH is broadcast over the entire cell.
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Secondary CPICH
Secondary CPICH may be phase reference for the secondary CCPCH.
A Secondary Common Pilot Channel (S-CPICH) has the following
characteristics:
An arbitrary channelization code of SF=256 is used for the S-CPICH.
A S-CPICH is scrambled by either the primary or a secondary scrambling code.
There may be zero, one, or several S-CPICH per cell.
A S-CPICH may be transmitted over the entire cell or only over a part of the cell.
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Area type DenseUrban
Urban Suburb Rural
Speech 92 93 95 95 %
144 kb/s NRT 85 85 85 85 %
GSM1800 speech 85 85 85 85 %
Cell range 1 1.6 2.3 5.2 km
Factors affecting cell size include:
Frequency band - 2000MHz muchhigher than GSM networks.
Traffic types - WCDMA user datarates drop off as the user moves
further away from the Node B
User levels - Demand for mobileservices will increase, leading tomuch greater user densities
Fast DataUsers
Voice andSlow Data
Users
average projected coverage
WCDMA Cell Coverage