3g importants knowledge for interview crack

7/28/2019 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)/


HSDPA FTP Avg Throughput 4.5Mbps(downloaded_data_kbit)/


HSUPA FTP Avg Throughput 1.1Mbps(uploaded_data_kbit)/


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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18

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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19

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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20

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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21

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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40

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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41

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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42

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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43

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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47

Drop after active set update, Cont.

BLER is getting worse

RF condition

is o.k.


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48

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

3g importants knowledge for interview crack

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