Download - 3G Importants Knowledge for Interview Crack
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For 3G Interview
Best Practical & Theoretical
Knowledge
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WCDMA Frequency and Spectrum
Uplink=1920MHz -1980 MHz
Downlink= 2110MHz -2170MHz Bandwidth=60 MHz
Actual B.W assign to operator is 5MHz
And out of that 3.84 MHZ is utilize.
In WCDMA frequency reuse factor =1 because time and frequency
remains constant.
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Eb /NO= Bit energy/Noise energy
Ec/No = Chip Energy /Noise Energy.
Ec/No= Eb/No - process gain
As per Eb/No is fixed for each service for Ex: voice =2 and
video=4
Ec/N0= 2- 10= -8 for voice(for voice -8 is good limit)
Ec/N0= 4-18= -14 for video(for video -14 is good limit)
Process gain(voice) = chip rate/bit rate= 10dB Process gain (video) = chip rate /bit rate= 18dB
Chip rate = 3.84Mchips in WCDMA.
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Cyclic Redundancy Check (CRC) is used to detect if there are anyuncorrected errors left after error correction
The next part in the transmitter is Forward Error Correction (FEC).
The function of this block is to help the receiver correct bit errors
caused by the air interface.
The error-protected signal is then multiplied by a particular
channelization code to provide the necessary channel separation.
This is necessary since all the channels will be added together,
which will produce a composite data stream.
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Channelization codes
In the downlink, the channelization codes are used to separate the
different data channels coming from each cell. For the dedicated
channels, this represents the different users since only onescrambling code is used for all downlink transmission from the
cell.
In the uplink, the channelization codes are used to separate the
different data channels sent from the UE to the each cell. The
separation of the different UEs will here be done with differentscrambling codes.
The number of codes used in the downlink is restricted to 8192 in
total. This is done to speed up the process for the UE to find the
correct scrambling code. 512 of these are primary codes (the rest
are secondary codes, 15 codes per primary) divided into 64 codegroups each group containing 8 different codes. The UE can
determine which scrambling code group a cell is using by the
synchronization procedure (see chapter 5). Note that there are no
restrictions for the number of codes generated by the 24 bits start
key in the uplink case
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Data Drive
There is 3 modulation technique QPSK,16QAM,64QAM.
For high through put 16QAM and 64QAM should have high Utilization
So, if There is less Utilization of QPSK in downlink than data throughput is
also high
CQI is like SQI in speech which ensure good channel quality for data
transfer.
Retransmission of HS- DSCH(High-Speed Downlink Shared Channel) packetis high than also throughput is decreases.
In case of stationary Data Test- 2Mbits speed can be achieved
In case of moving Vehicle 800kbits to 1.2 Kbits speed can be achieved.
Application throughput is always 85% of physical layer data rate
throughput because at application level IP inclusion and overheadinformation will be there.
Latency time is round trip time from server and for 3G it should be 150 ms
for 32 bit data .
http://en.wikipedia.org/wiki/High-Speed_Downlink_Shared_Channelhttp://en.wikipedia.org/wiki/High-Speed_Downlink_Shared_Channelhttp://en.wikipedia.org/wiki/High-Speed_Downlink_Shared_Channelhttp://en.wikipedia.org/wiki/High-Speed_Downlink_Shared_Channel -
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The modulation scheme and coding is changed on a per-user basis
depending on signal quality and cell usage. The initial scheme is
Quadrature phase-shift keying (QPSK), but in good radio conditions
16QAM and 64QAM can significantly increase data throughputrates. With 5 Code allocation, QPSK typically offers up to 1.8 Mbit/s
peak data rates, while 16QAM offers up to 3.6 Mbit/s. Additional
codes (e.g. 10, 15) can also be used to improve these data rates or
extend the network capacity throughput significantly.
Data Throughput will be also depend on MS class which support
5,10 and 15 codes resp.
CQI- Channel quality indication may include carrier level received
signal strength indication (RSSI) and bit error rate (BER). I
Channel quality indicators are messages that are sent on acommunication system (such as a mobile communication system)
that provide the remote connection (e.g. base station) with channel
quality information
http://en.wikipedia.org/wiki/Phase-shift_keyinghttp://en.wikipedia.org/wiki/QAMhttp://en.wikipedia.org/wiki/QAMhttp://en.wikipedia.org/wiki/QAMhttp://en.wikipedia.org/wiki/QAMhttp://en.wikipedia.org/wiki/Phase-shift_keyinghttp://en.wikipedia.org/wiki/Phase-shift_keyinghttp://en.wikipedia.org/wiki/Phase-shift_keyinghttp://en.wikipedia.org/wiki/Phase-shift_keyinghttp://en.wikipedia.org/wiki/Phase-shift_keying -
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Notes on quantities denoting signal power
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KEY PERFORMANCE INDICATORS
Accessability (Call set-up success rate)
Retainability (Dropped calls)
Mobility (Handover success rate)
Integrity (BLER and throughput)
Integrity- quality
Integrity-throughput
What is the major difference in link budgets between UMTS and GSM/TDMA?
In UMTS you generally have a link budget for each service (voice, data, video etc),
in GSM you usually only use 1 for voice. Each service has a different Eb/No target.
In UMTS you have to consider the target traffic load you will have and add a
noise-rise margin, in GSM you may have a slight interference margin but notnormally related to traffic. In UMTS some services (like voice) will show up as
uplink limited but other services (like HSDPA, 384kbps service) will show as
downlink limited. In UMTS you usually have to consider that all users use the
same power from the BTS therefore the more number of users the lower the
maximumpower available per user (maximum power per connection) which is a
starting point in the link budget.
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KPI Requirements Formula
CPICH RSCP -95dBm N/A(nbr_of_samples_RSCP>=-95dBm)/
(tot_nbr_of_samples_RSCP)
CPICH Ec/Io -12dB N/A (nbr_of_samples_EcIo>=-12dB)/(tot_nbr_of_samples_EcIo)
Voice call setup
success rateMin % 98%
(nbr_of_successful_voice_call_setup)/
(nbr_of_voice_call_attemp)
Voice call setup time
(Mobile to 1764440)
10s 99%
(nbr_of_voice_call_setup_time10s)/
(nbr_of_successful_voice_call_setup)
voice_call_setup_time =[T(CC_alerting) - T(first_RRC_connection_request)]
9s 95%
(nbr_of_voice_call_setup_time9s)/
(nbr_of_successful_voice_call_setup)
voice_call_setup_time =[T(CC_alerting) - T(first_RRC_connection_request)]
Voice call drop rate Max % 2%(nbr_of_voice_call_drop)/
[(call_duration_time)/90sec]
PDP activation
successful rateMin % 99%
(nbr_of_PDP_context_activation_accept)/
(nbr_of_PDP_context_activation_request)
PDP activation delay 2s 99%
(nbr_of_PDP_activation_delay2s)/
(nbr_of_PDP_context_activation_accept)PDP_activation_delay= [T(PDP_context_activation_accept)-
T(PDP_context_activation_request)]
PS 384k FTP DL Avg Throughput 280kbps(downloaded_data_kbit)/
(data_session_duration)
PS 384k FTP UL Avg Throughput 280kbps(uploaded_data_kbit)/
(data_session_duration)
HSDPA FTP Avg Throughput 4.5Mbps(downloaded_data_kbit)/
(data_session_duration)
HSUPA FTP Avg Throughput 1.1Mbps(uploaded_data_kbit)/
(data_session_duration)
KPI calculation
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Case 1: Drop due to missing neighbor
Problem: Detected Nighbor (DN)
UE sends a Measurement Report that contains an event1a means adding a new RL
(cell) to Active Set If the reported cell is not in the current neighbor cell list and the reported Ec/No is
better than the best serving cell Ec/No in AS by some dBs (set by a RNC parameter)
If for any reason the new cell can not be added to AS, call will be released
2. If the UE reconnects to the network immediately after call drop and the scramble of
the cell that UE camps on is different from that upon call drop, missing neighbor cell
is probable. Confirm it by measurement control (search the messages back from call
drop for the latest intra-frequency measurement control message. Check the
neighbor cell list of this measurement control message)
3. UEs might report detected set information. If corresponding scramblling code
information is in the monitor set before call drop, the cause must be missingneighbor cell.
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Weak Coverage
Weak coverage usually refers to weak RSCPUplink or downlink DCH power helps to confirm the weak coverage is in uplink or
downlink by the following methods.
If the uplink transmission power reaches the maximum before call drop, the uplink
BLER is weak ,the call drop is probably due to weak uplink coverage.
Out of Uplink coverage may be caused by not only by low CPICH_RSCP
But also by high UL_RSSI
If the downlink transmission power reaches the maximum before call drop and the
downlink BLER is weak, the call drop is probably due to weak downlink coverage
High downlink RSSI received by UE is an indication of weak coverage during that time UE tries to
increase its target SIR to listen to the network.
Multipath propagation yields signal paths of different lengths with
different times of arrival at the receiver. Typical values of time
delays (s) are 0.2 in Open environment, 0.5 Suburban and 3 in
Urban.
When coded data rates of services are incompatible,
Rate Matching is used to equalize the data rates.
Rate Matching may be performed by:
Padding with extra bits Puncturing of bits using a pseudo-random algorithm
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Case 2: Drop due to Poor Coverage (low RSCP)
Problem: Poor DL coverage
When UE gets to an area with low RSCP ( < -105 dBm)
regardless Ec/No values there is high risk for drop.UE will likely ramp up the transmitted power and reach its
max power. The UL BLER will probably increase and SIR
target cannot maintain anymore, finally the call drops.
Explain the concept of Cell Breathing. How is the accounted for in the linkBudget?
Ans: Io or No (the interference part of Ec/Io and Eb/No) increase as the traffic on
the network increases since everyone is using the same frequency. Therefore as Io
or No increases the UE or BTS needs to use more power to maintain the same
Eb/No or Ec/Io. When the power required is more thanthe maximum power
allowed, the connection cannot be made. Users at the cell edge are usually the firstto lose service, hence the service area of a cell shrinks. As traffic decreases the
reverse happens and the service area increases. They should say that it is accounted
for in the Noise Rise Margin found in the Link Budget.
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Interference
In downlink, when the active set CPICH RSCP is greater than 85 dBm and the active setEc/Io is >=12 dB, the call drop is probably due to downlink interference
Downlink interference usually refers to pilot pollution
Interference in Uplink is detected when the Uplink RTWP exceeds a certain
configurable Threshold. In general Expected level of RTWP is formed by sum of the the
following components.
1.Thermal noise floor (KTB =-108.132dBm)2.Node B noise figure (Typically 1.8 dB for our equipment)
3.Noise raise due to load (50% load in Uplink corresponds to 3 db)
4.Compensation for inaccuracies in Radio N/W algoriths (2dB)
WHAT IS THE PILOT POLLUTION ?
Area where the SIR (Signal interference ratio) is too low and below the expected value
(Ec/Io >= -12 dB), there is too much interference => the mobile cannot understand thepilot channel
HOW TO REDUCE THE PILOT POLLUTION PROBLEM ?
Maximise the signal inside the best server
Minimise the energy overshoot from the neighbor cells with some RF consideration (tilt,
azimuth,)
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Pilot Pollution
Excessive strong pilots exist at a point, but no one is strong enough to be primary pilot.
1. Definition of strong pilot (CPICH_RSCP > ThRSCP)
2. Definition of Excessive CPICH_Number > ThN
3. Definition of "no best server strong enough
CPICH_RSCP1st-CPICH_RSCP(ThN+1)th < ThRSCP_Relative
Following is the case from cluster Mongkok West
Probable Solution : adjust engineering parameters of an antenna so that a best server forms around the
antenna. For handover problems caused by pilot pollution, adjust engineering parameters of other antennas so
that signals from other antennas becomes weaker and the number of pilots drops
For this case reduce antenna height of site SGI.
Many definitions: A cell that has a high signal strength at a location but is not part of the active set. A cell that
meets thecriteria for addition into the Active Set but can not enter because the active set is full.
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1.UE fails to receive active set update command (Delayed Handover)
After UE reports measurement message, the Ec/Io of original cell signals decreases
sharply. When the RNC sends active set update message, the UE powers off the
transmitter due to asynchronization. The UE cannot receive active set update message.This may be due to,
Ec/Io of original cell decreases sharply and that of the target cell increases greatly
(Turnings)
2. The best server changes frequently. Two or more cells alternate to be the best server.
The RSCP of the best server is strong. The period for each cell to be the best server isshort.
Probable solution:
Lower the triggering time for event 1a
adjust antennas to expand the handover area
adjust the antenna to form a best server
reduce Ping-pong handover by setting the handover parameter of 1B event
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17
Radio Interface Protocol Architecture
Radio
Interface
Protocol
Architecture
Transport Channel (SAP)Physical Channels
Logical Channel
L3
control
control
control
control
Logical
Channels
Transport
Channels
C-plane signalling U-plane information
PHY
L2/MAC
L1
RLC
DCNtGC
L2/RLC
MAC
RLCRLC
RLC
RLC
RLCRLC
RLC
Duplication avoidance
UuS boundary
BMCL2/BMC
RRC
control
PDCPPDCP L2/PDCP
DCNtGC
Packet Data Convergence Protocol:
Is only for PS domain services.
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Radio Interface protocol architecture
L2/MAC
L2/RLC
L1
RLC
MAC
L3RRC
PHY
TransportChannels
LogicalChannels
C-plane signallingU-plane information
GC Nt DC
RLCRLC
RLC
GC
NTDCRRCRLCMAC
General Control
NotificationDedicated ControlRadio Resource ControlRadio Link ControlMedium Access Control
UTRA Protocol Architecture
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Logical Channel Structure
Synchronisation Control Channel (SCCH)
Broadcast Control Channel (BCCH)
Paging Control Channel (PCCH)
e ca e on ro anne
Common Control Channel (CCCH)
Control Channel (CCH)
Dedicated Traffic Channel (DTCH)Traffic Channel (TCH)
ODMA Dedicated Control Channel (ODCCH)
ODMA Common Control Channel (OCCCH)
ODMA Dedicated Traffic Channel (ODTCH)
Common Traffic Channel (CTCH)
Shared Channel Control Channel (SHCCH)
(TDD)
(ODMA)
(ODMA)
(TDD)
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Channels
Transport Channels:
Dedicated Transport Channel (DCH), UL/DL, mapped to DCCH and DTCHBroadcast Channel (BCH), DL, mapped to BCCH
Forward Access Channel (FACH), DL, mapped to BCCH, CCCH, CTCH, DCCH and DTCH
Paging Channel (PCH), DL, mapped to PCCH
Random Access Channel (RACH), UL, mapped to CCCH, DCCH and DTCH
Uplink Common Packet Channel (CPCH), UL, mapped to DCCH and DTCH
Downlink Shared Channel (DSCH), DL, mapped to DCCH and DTCH
The speech service in UMTS will employ the Adaptive
Multi - rate technique.
This is a single integrated codec with eight source rates:
12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kbps. To
facilitate interoperability with existing cellular networks
some of the modes are the same as in existing networks.
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ChannelsPhysical Channels:
Primary Common Control Physical Channel (PCCPCH), mapped to BCH
Secondary Common Control Physical Channel (SCCPCH), mapped to FACH, PCH
Physical Random Access Channel (PRACH), mapped to RACH
Dedicated Physical Data Channel (DPDCH), mapped to DCH
Dedicated Physical Control Channel (DPCCH), mapped to DCH
Physical Downlink Shared Channel (PDSCH), mapped to DSCHPhysical Common Packet Channel (PCPCH), mapped to CPCH
Synchronisation Channel (SCH)
Common Pilot Channel (CPICH)
Acquisition Indicator Channel (AICH)
Paging Indication Channel (PICH)
CPCH Status Indication Channel (CSICH)Collision Detection/Channel Assignment Indication Channel (CD/CA-ICH)
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AMR
The bit rate of the AMR speech connection is controlled by the
radio access network depending on the air interface loading and the
quality of the speech connections. During high loading, such as
during busy hours it is possible to use lower AMR bit rates to offer
higher capacity while providing slightly lower speech quality. Also
if the mobile is running out of the cell coverage area and using its
maximum transmission power a lower AMR bit rate can be used to
extend the cell coverage area.
Adaptive multi-rate also contains error concealment. The purpose
of frame substitution is to conceal the effect of lost speech frames.
If several frames are lost muting is used to prevent possibly
annoying sounds as a result of the frame substitution.
In P5, with AMR NB it is possible to use lower speech codec rates
than 12.2 kbps. The radio network also supports 7.95 kbps, 5.9kbps and 4.75 kbps AMR codecs. There is no adaptation in the
sense that AMR codecs are changed during an ongoing speech
connection; rather there is a possibility to adapt the rate at initial
selection.
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23
Link Budget
Cell range & cell capacity are limited by the same parameters:
3 Interference in uplink
3 Power in downlink
Cell breathing phenomenon
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Power Link Budget
Tx power + All Gains Path Loss Other losses = Rx power
Path loss = Tx Signal + All Gains Other losses Rx power
Max Path loss = Tx Signal + All Gains Other losses Rx sensitivity
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25
Initial Cell Search
The initial Cell Search is carried out in three steps:
Step 1: Slot synchronisation - using the primary synchronisation
channel.
Step 2: Frame synchronisation and code-group identification-
using the secondary synchronisation channel.
Step 3: Scrambling-code identification-identified through symbol-
by-symbol correlation over the primary CCPCH with allthe scrambling codes within the code group.
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27
Frame Synchronization
..
2560 chips
acp
Slot # ?
P-SCH acp
Slot #?
16 11S-SCH
acp
Slot #?
2Group 4
Slot 12,13,14
slot numberScramblingCode Group #0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14
Group 0 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16
Group 1 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10
Group 2 1 2 1 15 5 5 12 16 6 11 2 16 11 15 12
Group 3 1 2 3 1 8 6 5 2 5 8 4 4 6 3 7
Group 4 1 2 16 6 6 11 15 5 12 1 15 12 16 11 2
Group 61 9 10 13 10 11 15 15 9 16 12 14 13 16 14 11
Group 62 9 11 12 15 12 9 13 13 11 14 10 16 15 14 16
Group 63 9 12 10 15 13 14 9 14 15 11 11 13 12 16 10
256 chips
S-SCH
P-SCH
512 Primary Scrambling Codes divided into 64 groups
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28
Slot Synchronization
P-SCH1
P-SCH3
P-SCH2
P-SCH1S-SCH1 P-CCPCH P-CCPCH
P-SCH2S-SCH2 P-CCPCH P-CCPCH
P-SCH3S-SCH3 P-CCPCH P-CCPCHP-CCPCH
1 Slot = 667ms
UE synchronizes on the strongest correlation peak
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29
Cell Information
P-SCH: Coverage indication, Slot SynchronizationS-SCH: Frame Synchronization, Group identification
P-CPICH: Scrambling Code Identification
P-CCPCH: System Information Broadcast
Logical Channel
BCCH
Transport Channel
BCH
Physical Channel
P-CCPCH
OVSF Cch,256,1Primary Scrambling Code
Transmitted during 9/10th slot
Bit Rate: 12.3 kbps RLC Mode: transparent
Mac-B: transparent
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30
Intra-Frequency Cell Reselection
sample
Time
Quality
Serving CellServing Cell
Neighboring Cell
Neighboring Cell
Neighboring
cell criterion S
is fulfilled and is
ranked
Neighboring cell
better ranking
than Serving cell
UE perform cell
reselection
Treselections
Qmean,s + Qhyst2s
Qmean,n - Qoffset2s,n
Qqualmin
UE perform
intra-frequency
measurements
Qqualmin +
SIntraSearch
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31
Cell selection and reselection Cell Selection criteria
The cell selection criterion S is fulfilled when:
where
Squal = Qqualmeas Qqualmin
Srxlev = Qrxlevmeas - Qrxlevmin - Pcompensation
Pcompensation max(UE_TXPWR_MAX_RACHP_MAX, 0)
for FDD cells: Srxlev > 0 AND Squal > 0
for TDD cells: Srxlev > 0
for GSM cells: Srxlev > 0
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32
Cell Selection Parameters
Parameter Object Range Default Value Recommended Value Class
qQualMin CellSelectionInfo Int [-24..0]
(dB)
-10 -16 C2
qRxLevMin CellSelectionInfo Int [-115..-25]
Step = 2 (dBm)
-45 -115 C2
maxAllowedUlTxPower UlUsPowerConf Int [-50..33](dBm)
33 33 C3
P_Max = maximum UE output power (dBm) according to its class
Power Class Maximum Output Power (dBm)
1 33
2 27
3 24
4 21
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33
Cell Reselection Procedure
Squal
SintraSearch
SinterSearch
SinterRATMeasurement onsame frequency Measurement on
other frequencies Measurement on
other RAT
If Squal = CPICH_Ec/No qQualMin < ThresholdAssociated measurements are performed
Thresholds are broadcasted in SIB 11
In UMTS02, 2 types of measurements are done: Intra frequency and inter RAT
Threseholdsgive
nasexample
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34
Cell Reselection Parameters
Parameter Object Range Default Value Recommended Value Class
qHyst1 CellSelectionInfo Int [0..40] (dBm)Step = 2
10 4 C2
qHyst2 CellSelectionInfo Int [0..40] (dB)Step = 2
4 6 C2
qOffset1sn GSMCell Int [-50..50] (dB) 0 TBD C0
qOffset2sn UMTSFDDNeighbouring Int [-50..50] (dB) 0 TBD C0qualMeas CPICH_EcNo or
CPICH_RSCPCPICH_EcNo N.A. Static
tReselection CellSelectionInfo Int [0..31] (s) 31 6 C2
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35
Measurements
The different types of air interface measurements are:
Intra-frequency measurements: measurements on downlinkphysical channels at the same frequency as the active set. Ameasurement object corresponds to one cell.
Inter-frequency measurements: measurements on downlinkphysical channels at frequencies that differ from the frequency ofthe active set. A measurement object corresponds to one cell.
Inter-RAT measurements: measurements on downlink physicalchannels belonging to another radio access technology thanUTRAN, e.g. GSM. A measurement object corresponds to one cell.
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36
Handover (Handoff) There are following categories of handover (also referred to as handoff):
Hard handover means that all the old radio links in the UE are removed beforethe new radio links are established. Hard handover can be seamless or non-seamless. Seamless hard handover means that the handover is notperceptible to the user. In practice a handover that requires a change of thecarrier frequency (inter-frequency handover) is always performed as hardhandover.
Soft handover means that the radio links are added and removed in a way thatthe UE always keeps at least one radio link to the UTRAN. Soft handover isperformed by means of macro diversity, which refers to the condition thatseveral radio links are active at the same time.
Softer handover is a special case of soft handover where the radio links that areadded and removed belong to the same Node B (i.e. the site of co-locatedbase stations from which several sector-cells are served.
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37
Handover (Handoff) The most obvious cause for performing a handover is that due to its movement a user
can be served in another cell more efficiently (like less power emission, less
interference). It may however also be performed for other reasons such as systemload control.
Active Set is defined as the set of Node-Bs the UE is simultaneously connected to (i.e.,the UTRA cells currently assigning a downlink DPCH to the UE constitute the activeset).
The maximum active set size at the RNC is determined by the parameterMaxAciveSetSize
3 to 4 cells, the larger the active set size the more likely it is that Iub link efficiency isreduced (more than one resource for a single connection due to SHO)
Cells, which are not included in the active set, but are included in the CELL_INFO_LISTbelong to the Monitored Set.
Cells detected by the UE, which are neither in the CELL_INFO_LIST nor in the activeset belong to the Detected Set. Reporting of measurements of the detected set is onlyapplicable to intra-frequency measurements made by UEs in CELL_DCH state.
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38
PRIMARY CELL ELECTION ALGORITHM (MONITORED SET
UPDATE)
The primary cell election algorithm appliesto soft HO. It is used for monitored setdetermination and a pointer to mobilityparameter.
The Monitored Set should be updated eachtime the primary cell of active set changes. Ameasurement control message is sent (with
measurement commend set to modify) issent to the UE in order to update themonitored set. The message contains the cellto add/remove from the monitored andshould follow the ACIVE SET UPDATEmessage.
The primary cell algorithm is called from SHOalgorithm; therefore it is performed eachtime a MEASUREMENT REPORT is receivedby the SRNC.
Measurement control used for monitored set update
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Compressed mode
Compressed mode is when the mobile goes into a slotted transmit mode whereby
it opens up an idle period (transmission gap) where it can monitor another carrieror technology (GSM). The impact is that to maintain the same bit rate, it halves
the SF, and therefore increases power level causing higher interference to the
network. If the SF cannot be halved then the bit rate of the bearer decreases. If
they seem knowledgably, ask them if they know what messages and events
trigger and configure compressed mode on/off. 2D event for on, 2F for
off. Messages would for configuration would be RADIO BEARER
RECONFIGURATION, TRANSPORT CHANNEL RECONFIGFURATION or PHYSICAL
CHANNEL RECONFIGURATION.
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Compressed Mode During inter-frequency handover the UEs must be given time to make the necessary measurements on the different WCDMA
carrier frequency. 1 to 7 slots per frame can be allocated for the UE to perform this intra frequency (hard handover).
Why is compressed mode needed?
In UTRAN FDD, transmission/reception by the mobile is continuous : no idle periods are available for monitoring other frequencies ifthe UE has only a single receiver
How is it done?
Transmission gaps are created in the radio frame in DL and/or UL to allow the UE to switch to another frequency, perform
measurements on another carrier (FDD, TDD or GSM) and switch back
Transmission gaps are positioned in one radio frame or at the boundary of 2 radio frames in regular intervals referred to as a
transmission gap pattern sequence
no more than 7 slots are used in any one radio frame to create the transmission gap.
How is it done? Two approaches can be taken in creating the transmission gaps of the transmission gap pattern sequence
Modifiy the physical layer parameters (by puncturing or spreading factor reduction) to allow all information bits to be
transmitted.
Restrict the bit rate (by higher layer scheduling) to match the fewer available transmission slots in a compressed radio frame.
In both approaches, the goal is to not loose transmission frames
Who controls it?
Compressed mode is under the control of the UTRAN
Compressed mode is configured by the RNC per UE in the form of transmission gap pattern sequences
given to the UE via RRC signalling
given to the node B via NBAP signalling
a transmission gap pattern sequence is associated with a specific measurement purpose:
FDD measurements,
TDD measurements,
GSM initial BSIC identification, GSM BSIC reconfirmation,
GSM RSSI measurement
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Physical layer AspectsCompressed Mode Methods
Three methods are available to createtransmission gaps Puncturing: additional puncturing/fewer repetitions are performed compared to
normal mode
to be used only in DL to be used only in the case of mapping to fixed positions
scrambling and channelisation code remain unchanged
Spreading Factor Reduction: SF is divided by 2 can be used in UL and DL
can be used with mapping to flexible positions
to be used only when SF>4
only 2nd DTX insertion and physical channel mapping is modified may lead to channelisation code shortage and the need to use a secondary scrambling code
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Cell Shakedown
Purpose To test Call Setup (Voice and FTP) in each cell
To test Handoffs (Soft and Softer) between Cells
Verify antenna orientation
Primary Pilot Ec/Io Scrambling Code for each cell
UE transmit power
Path Balance
Method
By driving clockwise and anticlockwise within a designated routearound the the base station (about 30% of the site coveragearea).
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Difference between Scanner data & UE Data Collection
Scanner
Primary Common Pilot Channel (P-CPICH)
scrambling code measurements
Continuous Wave (CW) measurements
Spectrum analysis Synchronization Channel (SCH) code word
measurements
UE Data/Voice/Video Calls
Layer 3 messages logging
Layer 2 messages logging (Transport channel)
RRC State logging
UE Transmit Power
SIR
Serving Cell / Active Set / Monitored Set
Events
GSM neighbor measurements
Difference in data collection
3Antenna
3Cable
3Sampling
Solution: Perform a calibration drive.
An overview of clusterperformance based on
scanner Best Serving CPICH
RSCP and Ec/Io measured
data.
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Inner loop & Scanner
In pre-launch optimization,how are missing neighborsusually detected?
Usually you use a scanner andcompare the best pilots inEc/Io from the scanneragainst that of the active set
and monitored set from anactive UE. If there is astronger pilot from a nearbycell that appears on thescanner but not on the UE,there is a possiblemissing neighbor. One would
thenverify thatthe neighbor appears indefined neighbor list from theOSS.
Explain Inner and Outer loop power control and
who controls them.
If they start talking about Open and Closed
Loop PC, tell them you want Inner/Outer Closed
Loop PC. Inner loop power control is performed
by the NodeB to set the transmitpower of theUE and BTS to compensate for signal variations
due to fading or pathloss to maintain the set SIR
(occurs up to 1500 times per sec). Outer loop
power control is performed by the RNC to set
the target SIR based on the required BER/BLER
for the requested services (occurs up to 100times per sec).
D ft ti t d t
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Drop after active set update
Symptom:
Normally, the observed sequent messages in the UE side are:
UTRAN -> UE: Active set update (to request the UE to remove a cell, e.g. SC281)
UE -> UTRAN: Active set update complete
UTRAN -> UE: Measurement Control (update neighbour list)
UE -> UTRAN: Measurement report (to propose to add7)
UTRAN -> UE: Active set update (to request the UE to add SC 137)
DROP.......(since no Active set update completion was sen after 12 secs )
The radio performances no matter DL and UL are very good.
Possible solution: No solution, check this problem with UE vendor.
In Soft
Handover the UE is connected to more than one Radio Base Station
(RBS) simultaneously. At least one radio link is always active and
there is no interruption in the dataflow during the actual handover.
The signals are received in the UE and combined in the RAKE
receiver to give protection against fading.
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Soft/Softer Handover
Radio Link Addition andRadio Link Removal.
Reference:User Description and Engineering Guidelines 75/1551-HSD
101 02/1 Uen B2
Ericsson AB 2003 - All Rights Reserved
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Drop after active set update, Cont.
BLER is getting worse
RF condition
is o.k.
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Drop after active set update, Cont.
No Active Set Completion
was sent after Active Set
Update.
FINAL WORDS
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For network tuning, we need to relay on field measurements which require extensive drive tests
Finding the best possible configuration for antenna heights, tilts, azimuths and parameter setting for all thepresent cells/sectors in the network and also for any new sites that might be needed to improve coverage
Power adjustment can also be used for network tuning but can become complicated and result in poornetwork performance
Use of Remote Electrical Tilt (RET) Antenna is preferred over mechanical tilt antenna
Neighbour definition is of prime importance in UMTS network (Soft handover gain and interferencereduction). Keep neighbour list upto 20.
Automated tools are needed that could suggest the best possible neighbour relations, antenna heights andtilts by using both the field measurements and the propagation models & simulations
Skilled people, right methods and advanced tools are needed to perform 3G tuning and optimisation
Name the 4 RRC Connected Modes
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If a UE is on a data call (CELL-DCH
state) and there is in no activity for
awhile what would you expect to see
occur?
UE should go from CELL-DCH to CELL-FACH then if still no activity to either
CELL-PCH or URA-PCH (via CELL-
FACH). If they talk about
inactivity timers and mention that the
state goes from CELL-DCH straight to
CELL-PCH or URA-PCH, that is alsopossible. Bonus they say they would
see RADIO BEARER
RECONFIGURATION messages when
the states are changing.
Name the 4 RRC Connected Modes(states) and describe the characteristicsof each.Cell-DCH: UE has been allocated a dedicatedphysical channel in
uplink and downlink.Cell-FACH: UE listens to RACH channel (DL) andis allocated a FACH channel (UL). Small amountsof UL/DL data can be transfers in this state. TheRNC tracks the UE down to the cell level and cellreselections are possible with the CELL UPDATEmessage.Cell-PCH: UE monitors (using discontinuous
reception) a PCH channel (PCH) indicated by thePICH channel. The RNC tracks the UE down to thecell level and cell reselections are possible with theCELL UPDATE message. No data can betransferred in the UL in this state.URA-PCH: UE monitors (using discontinuousreception) a PCH channel (PCH) indicated by the
PICH channel. The RNC tracks the UE down to theURA level.
Power control
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Power control
In the uplink the base station measures the received Signal-to-
Interference Ratio (SIR) and compares this to a target SIR. If the
measured SIR is below the target then the base station requests the
mobile to increase its power (and vice versa). This type of powercontrol is known as the Inner-loop power control and is capable of
adjusting the transmit power in steps of, for example 1 dB at a rate
of 1500 times per second. Inner-loop power control is only
applicable for connections on dedicated channels