3g interview questions

INTERVIEW

3G

Atunu Gorai

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.

WCDMA Frequency and Spectrum

Uplink=1920MHz -1980 MHz

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.

Cyclic Redundancy Check (CRC) is used to detect if there are any uncorrected 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.

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 one scrambling 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 different scrambling 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 code groups 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

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) packet is 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 overhead information will be there.

Latency time is round trip time from server and for 3G it should be 150 ms for 32 bit data .

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 throughput rates. 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 a communication system (such as a mobile communication system) that provide the remote connection (e.g. base station) with channel quality information

Notes on quantities denoting signal power

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 not normally 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.

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 rate Min % 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 rate Min % 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

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 missing neighbor cell.

Weak Coverage

Weak coverage usually refers to weak RSCP Uplink 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

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 first to 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.

Interference

In downlink, when the active set CPICH RSCP is greater than 85 dBm and the active set Ec/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 the pilot 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,)

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.

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 is short. 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

17

Radio Interface Protocol Architecture

Radio

Interface

Protocol

Architecture

Transport Channel (SAP)

Physical Channels

Logical Channel

L3

contr

ol

contr

ol

contr

ol

contr

ol

Logical

Channels

Transport

Channels

C-plane signalling U-plane information

PHY

L2/MAC

L1

RLC

DCNtGC

L2/RLC

MAC

RLC

RLCRLC

RLC

RLCRLC

RLC

Duplication avoidance

UuS boundary

BMC L2/BMC

RRC

control

PDCPPDCP L2/PDCP

DCNtGC

Packet Data Convergence Protocol:

Is only for PS domain services.

18

Radio Interface protocol architecture

L2/MAC

L2/RLC

L1

RLC

MAC

L3 RRC

PHY

Transport Channels

Logical Channels

C-plane signalling U-plane information

GC Nt DC

RLC RLC

RLC

GC NT DC RRC RLC MAC

General Control Notification Dedicated Control Radio Resource Control Radio Link Control Medium Access Control

UTRA Protocol Architecture

19

Logical Channel Structure

Synchronisation Control Channel (SCCH)

Broadcast Control Channel (BCCH)

Paging Control Channel (PCCH)

Dedicated Control Channel (DCCH)

Dedicated Control Channel (DCCH)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)

20

Channels

Transport Channels: Dedicated Transport Channel (DCH), UL/DL, mapped to DCCH and DTCH Broadcast 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.

21

Channels Physical 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 DSCH Physical 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)

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, 5.9 kbps 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.

23

Link Budget

Cell range & cell capacity are limited by the same parameters:

Interference in uplink

Power in downlink

Cell breathing phenomenon

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

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 all the scrambling codes within the code group.

26

Slot Synchronization

P-SCH1

P-SCH3

P-SCH2

P-SCH1 S-SCH1 P-CCPCH P-CCPCH


P-SCH3 S-SCH3 P-CCPCH P-CCPCH P-CCPCH

1 Slot = 667ms

UE synchronizes on the strongest correlation peak

27

Frame Synchronization

..

2560 chips

acp

Slot # ?

P-SCH acp

Slot #?

16 11 S-SCH

acp

Slot #?

2 Group 4 Slot 12,13,14

slot number Scrambling Code 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

28

Slot Synchronization

P-SCH1

P-SCH3

P-SCH2



P-SCH3 S-SCH3 P-CCPCH P-CCPCH P-CCPCH

1 Slot = 667ms

UE synchronizes on the strongest correlation peak

29

Cell Information

P-SCH: Coverage indication, Slot Synchronization

S-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,256,1 Primary Scrambling Code

Transmitted during 9/10th slot

Bit Rate: 12.3 kbps RLC Mode: transparent

Mac-B: transparent

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

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_RACH P_MAX, 0)

for FDD cells: Srxlev > 0 AND Squal > 0

for TDD cells: Srxlev > 0

for GSM cells: Srxlev > 0

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

33

Cell Reselection Procedure

Squal

SintraSearch

SinterSearch

SinterRAT Measurement on same frequency Measurement on

other frequencies Measurement on

other RAT

If Squal = CPICH_Ec/No qQualMin < Threshold Associated measurements are performed

Thresholds are broadcasted in SIB 11

In UMTS02, 2 types of measurements are done: Intra frequency and inter RAT

Th

rese

ho

lds

giv

en a

s ex

am

ple

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 C0

qualMeas CPICH_EcNo or

CPICH_RSCP

CPICH_EcNo N.A. Static

tReselection CellSelectionInfo Int [0..31] (s) 31 6 C2

35

Measurements

The different types of air interface measurements are:

Intra-frequency measurements: measurements on downlink physical channels at the same frequency as the active set. A measurement object corresponds to one cell.

Inter-frequency measurements: measurements on downlink physical channels at frequencies that differ from the frequency of the active set. A measurement object corresponds to one cell.

Inter-RAT measurements: measurements on downlink physical channels belonging to another radio access technology than UTRAN, e.g. GSM. A measurement object corresponds to one cell.

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 before

the new radio links are established. Hard handover can be seamless or non-seamless. Seamless hard handover means that the handover is not perceptible to the user. In practice a handover that requires a change of the carrier frequency (inter-frequency handover) is always performed as hard handover.

Soft handover means that the radio links are added and removed in a way that the UE always keeps at least one radio link to the UTRAN. Soft handover is performed by means of macro diversity, which refers to the condition that several radio links are active at the same time.

Softer handover is a special case of soft handover where the radio links that are added and removed belong to the same Node B (i.e. the site of co-located base stations from which several sector-cells are served.

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 system load 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 active set).

The maximum active set size at the RNC is determined by the parameter MaxAciveSetSize

3 to 4 cells, the larger the active set size the more likely it is that Iub link efficiency is reduced (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_LIST belong to the Monitored Set.

Cells detected by the UE, which are neither in the CELL_INFO_LIST nor in the active set belong to the Detected Set. Reporting of measurements of the detected set is only applicable to intra-frequency measurements made by UEs in CELL_DCH state.

38

PRIMARY CELL ELECTION ALGORITHM (MONITORED SET UPDATE)

The primary cell election algorithm applies to soft HO. It is used for monitored set determination and a pointer to mobility parameter.

The Monitored Set should be updated each time the primary cell of active set changes. A measurement control message is sent (with measurement commend set to modify) is sent to the UE in order to update the monitored set. The message contains the cell to add/remove from the monitored and should follow the ACIVE SET UPDATE message.

The primary cell algorithm is called from SHO algorithm; therefore it is performed each time a MEASUREMENT REPORT is received by the SRNC.

Measurement control used for monitored set update

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 carrier or 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.

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 if

the 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

41

Physical layer Aspects Compressed Mode Methods

Three methods are available to create transmission 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

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 route

around the the base station (about 30% of the site coverage area).

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

Antenna

Cable

Sampling

Solution: Perform a calibration drive.

An overview of cluster performance based on scanner Best Serving CPICH RSCP and Ec/Io measured data.

Inner loop & Scanner

In pre-launch optimization, how are missing neighbors usually detected?

Usually you use a scanner and compare the best pilots in Ec/Io from the scanner against that of the active set and monitored set from an active UE. If there is a stronger pilot from a nearby cell that appears on the scanner but not on the UE, there is a possible missing neighbor. One would thenverify that the neighbor appears in defined neighbor list from the OSS.

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 the UE 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 100 times per sec).

45

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.

47

Drop after active set update, Cont.

BLER is getting worse

RF condition

is o.k.

48

Drop after active set update, Cont.

No Active Set Completion was sent after Active Set Update.

FINAL WORDS

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 the present 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 poor network 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 interference reduction). Keep neighbour list upto 20.

Automated tools are needed that could suggest the best possible neighbour relations, antenna heights and tilts 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

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 also possible. 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 characteristics of each. Cell-DCH: UE has been allocated a dedicated physical channel in uplink and downlink. Cell-FACH: UE listens to RACH channel (DL) and is allocated a FACH channel (UL). Small amounts of UL/DL data can be transfers in this state. The RNC tracks the UE down to the cell level and cell reselections are possible with the CELL UPDATE message. Cell-PCH: UE monitors (using discontinuous reception) a PCH channel (PCH) indicated by the PICH channel. The RNC tracks the UE down to the cell level and cell reselections are possible with the CELL UPDATE message. No data can be transferred in the UL in this state. URA-PCH: UE monitors (using discontinuous reception) a PCH channel (PCH) indicated by the PICH channel. The RNC tracks the UE down to the URA level.

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 power control 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