3G Questionary

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    S. No. Question

    1 Explain Ec/Io and RSCP; on what channel are they measured on?

    2 What does channelization codes do and function?

    3 What does the scrambling code do and function?

    4Explain the concept of Cell Breathing. How is the accounted for in the link

    Budget?

    5 Explain the different Handover types in UMTS

    6 What is an active set, monitor set and detected set?

    7What is the major difference in l ink budgets between UMTS and

    GSM/TDMA?

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    8In the Link Budget, what is a Shadow Fade Margin for and what factors

    does it depend on?

    9What is the typical maximum active set size and what needs to be consider

    when setting this?

    10What is typically the requirements (criteria) for a cell to be

    added/removed/replaced to/from/in the active set?

    11 What would you define as a pilot polluter?

    12How would you find such cells from a planning tool andfrom a drive test

    tool?

    13What would the call flow be for a Mobile Originated Call (major RRC

    messages)?

    14 What are the general triggers for an iRAT handover?

    15What is compressed mode, what is it's function, and what impact does it

    have on the network?

    16Name the 4 RRC Connected Modes (states) and describe the characteristics

    of each.

    17If 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?

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    18In Release '99, how does the network manage the throughput on the Radio

    Interface for a user/connection?

    19 What is the typical/most common bitrate that a voice call uses?

    20Depending on the RF conditions, what can the network do to manage call

    quality?

    21In HSDPA, how does the network manage the throughput on the Radio

    Interface for a user/ connection?

    22 Explain Inner and Outer loop power control and who controls them.

    23 In what cases is Open Loop Power Control used?

    24 Explain the concept of a Monte Carlo Simulation for UMTS Design

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

    26 What is the CQI in HSDPA?

    27 What is the HARQ?

    28 What is MIMO Antenna System?

    29 What are the different RABs in R99?

    30 What is TTI in WCDMA How it impact?

    31 How many PSC in WCDMA?

    32 What is the Processing Gain?

    33 What is the Power Control?

    34 what should be the idle CPICH power ?

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    35 What is rake receiver?

    36 What kind of services are available with WCDMA?

    37 Which modulation schemes are used in WCDMA?

    38 What is interleaving?

    39 What is threshold for adding and deleting a cell from Active Set?

    40 What are the types of location & routing are registration update?

    41 Which timer is involved for periodic LA & RA update and in which

    42 What is the Difference Between Ec/No and Ec/Io?

    43 What are the no. of Scrambling codes used in UL and DL?

    44 What are the types of compressed mode techniques used in 3G?

    45 What are MM Procedures?

    46 What is URA and URA_PCH state?

    47 Which channel contains Layer 1 information

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    48 Which Channel Contains Layer 3 Information

    49 What are the main KPI's

    50 Which parameter decides the preference between IFHO & IRAT HO

    51 UE goes to compress mode after which events

    52 What are the idle mode tasks of UE?

    53 Explain the cell selection criteria?

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    Answer

    Ec/Io = energy of carrier over all noise. RSCP = Receive Signal Code Power. In FDD mode (what we normally deal with) they are measured on the

    CPICH (pilot). Bonus if they know that Io is the sum of all interference: thermal/bg noise + interferers + own cell and is wideband. Bonus if they

    understand that RSCP is actually measured AFTER despreading (i.e. narrowband)

    Also known as OSVF(orthogonal variable spreadinng factor) code.Channelization codes are used for spreading and despreading of the signals, they

    also create the "channels" making it possible to distinguish between users/connections/channels. There are associated Spreading Factor and are

    allocated depending on the bandwidth required by the service.Codes have orthogonal property to minimize the interference. Chip rate is constant in

    UMTS i.e 3.84 Mcps. SF bit rate. SF=Chip rate/bit rate. .

    identity to UE/NodeB.These are reffered as Gold codes/PN codes/Scrambling codes.These codes are constructed in such a way that when corelated

    with themselves , they produce high corelation value regardless of phase shift between two.This property is called good auto correlation. when

    correlated with other PN codes the result is low but not zero.This is cause of interference in WCDMA network.PN codes are generated by linear or

    shift registers. There are 2^24 UL SC codes. In DL we have 2^18-1 SC. Out of them 8192 are least interference codes, and out of them 512 SC are used

    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 than

    the 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. It is accounted for in the Noise Rise Margin found in the Link

    Budget.

    Soft(er) Handover: connected to more than one cell on the same frequency, softer occurs when 2 cells in the active set belong to same Node-B; Intra-

    frequency Hard Handover: Occurs when Ue moves from one cell in one RNC to a cell in another RNC and the RNCs do not have an Iur link between

    each other; Inter-Frequency Hard Handover: when UE changes from one frequency to another frequency (usually due to traffic layer management or

    Quality reasons);Inter-technology (iRAT) Hard Handover: Handover from UMTS to GSM (v.v.) usually at the edge of UMTS service area but also due to

    quality reasons.

    Active Set: the set of cells with which the UE is currently connected/communicating with; DriveTT usually show them as SC or Pilots but they are

    actually cells; Monitored Set: Cells that the UE has detected and is monitoring and are known to the network, they either don't meet the criteria or

    the active set is full; Detected Set - Cells that the UE has detected but are not known to the network as yet (missing neighbor likely).

    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 maximum power available per user (maximum power per connection) which is a starting point in

    the link budget.

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    The shadow fade margin is dependent on the target percentage area coverage, the propagation model, and the standard deviation of the lognormal

    shadowing (usually the same as the model's standard deviation if the fast fading effects are removed). The Shadow Fade Margin is a nadded margin

    placed in the link budget such that a guarenteed level of service can be offered "in the worst case"

    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)

    For addition (Event 1a), candidate cell needs to have an Ec/Io value that is within a T_ADD threshold of the primary/reference (usually the best) cell

    for a specify time hysteresis. For removal (event 1b), cell needs to have Ec/Io lower than T_DROP margin for a specific time hysteresis. For

    replacement (event 1c), cell needs to have an Ec/Io better than the worst cell in the active set by the T_REPLACE and for a specific time hysteresis.

    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 the criteria for addition into the

    Active Set but can not enter because the active set is full.Ignoring low signal conditions, if the best cell RSCP is greater than say -85dBm and there are cells not in the active set but are strong enough to be in

    the active set then they are candidate for pilot polluters. Looking at cells that have a high noise rise, high amount of traffic compared to surrounding

    cells, may also indicate a pilot polluter. Areas with high Signal strength for the (Active Set Size + 1) best pilot (like the 4th best pilot if AS size is 3). In

    DTT, areas with poor Ec/Io but good RSCP, in the monitored set contains a cell with a good Ec/Io but cannot enter the AS because it is full . Areas

    where scanner shows a strong signal for a far away cell.

    RRC Connect Request -> RRC Connection Setup -> RRC Setup Complete -> (SETUP, authentication encyrption, TMSI reallocation etc) -> CALL

    PROCEEDING-> Radio Bearer Setup -> Radio Bearer Setup Complete -> ALERT -> CONNECT -> CONNECT ACK ->DISCONNECT -> RELEASE.

    Ec/Io of best cell below a certain threshold (usually around -16 to -18 dB) or RSCP of best cell below a certain threshold (usually around -100 dBm)

    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 bitrate, it halves the SF, and therefore increases power level causing

    higher interference to the network. If the SF cannot be halved then the bitrate of the bearer decreases. If they seem knowledable, 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.

    Cell-DCH: UE has been allocated a dedicated physical channel inuplink 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 transfered 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.

    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.

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    This question is a little harder to ask, so you may need to work it differently a few times. Perhaps leading questions could be: What

    parameter/configuration does the network change on the air interface What you are trying to hear from the candidate is that the network assigns a

    radio bearer with a channelization code with a spreading factor that matches the requested service maximum bit rate.

    They should say 12.2kbps but may be different if they start talking about AMR and the different rates then the know more. Prod them to see if they

    know the Spreading Factor (SF) used for the radio bearer, should be 128.

    AMR - for good conditions use codec will low redundancy/overhead; for poor conditions use codec with lower bit rate requirement but higher

    overhead, stronger coding and more redundancy.

    Modulation (16QAM, QPSK etc), Coding (convolution coding, fire codes etc), number of codes allocated and scheduling (it's a shared resource)

    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 theNodeB to set the transmit power 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).

    1) Idle to Cell-DCH state, when a connection is setup. When UE goes into soft handover, ACTIVE SET UPDATE where the new Radio Link initial power

    settings use open loop PC.

    This is a s imulator that randomly distributes terminals/users geographically onto the network and then checks the link budget for each

    terminal/connection to see if they can successfully connect or not. The simulator modifies parameters such has UE Tx Power, BTS Tx Power,

    requested bearer (in the case that multiple bearers could support the same service) when checking if a connection can be made. In every snapshot

    the simulator runs through the list of terminals/connections and attempts to make them all connect successfully, it starts a new snapshot when the

    number of successful connections converges. The process then starts on a new snapshot.

    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 stonger pilot from a nearby cell that appears on the scanner but not on the UE, there is a possible missing neighbor. One would then verify

    that the neighbor appears in defined neighbor list from the OSS.

    CQI is the channel Quality Indicator, Which is calculated on the Basis of RF invoirment, and the and code allocation is done on the basis of CQI.This is the Hybrid Automatic repeat request Technique for the retransmission of the lost frame which is used by the HSDPA. Which help to recover the

    lost frame by two partially lost frame.

    this is the multiple input multiple output antenna technique system which improves the n/w throughput over the air interface

    cs-12.2 for speech,cs-64 for video calls ,ps-16 ps-64 ps 128 ps-384 for data services

    it is the transmission time interval for sending one frame for WCDMA it is 10ms

    0-511, Total 512

    ratio of chip rate to bit rate , lower bit rate services will offer higher processing gain

    power control is the mechanism of maintaining minimal power level with acceptable QOS for each service

    10% of the Total Power

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    A rake receiver is a radio receiver designed to counter the effects of multipath fading. It does this by using several "sub-receivers" called fingers, that

    is, several correlators each assigned to a different multipath component. Each finger independently decodes a single multipath component; at a later

    stage the contribution of all fingers are combined in order to make the most use of the different transmission characteristics of each transmission

    path

    conversational, background, streaming, interactive

    QPSK. HPSK, BPSK, 16QAM, 64QAM

    Interleaving is the technique used to distribute the data so as to make the error correction accurate at the reciever end.

    For addition 3 dB and for deletion 6dB

    1. IMSI attach / detatch 2. Normal LA & RA updating 3. Periodic LA & RA updating

    Timer t3212 is involved and is contained in SIB1Ec/No- Interference caused by combination of the Non-Orthogonality of Codes, thermal noise & all other noises present in the Channel. Ec/Io-

    Interference caused by only due to non-orthogonality of codes in the channel.

    Scrambling codes in uplink- 2^24-1. Scrambling codes in Downlink- 2^18-1= 8192.

    Three Types- 1. Puncturing 2. SF/2 3. Higher Layer Scheduling.

    MM common procedures: 1. TMSI reallocation procedure. 2.authentication procedure. 3. Identification procedure. 4. MM Information Procedure. 5.

    Abort Procedure. 6. Normal Location Update. 7. Periodic Location update. 8. Imsi attach.

    URA or UTRAN Registration Area is a colection of cells that are used for fast moving UE's in Connected mode when they are not transferring any data.

    In this case the UE is in CELL_PCH state. Everytime a fast moving UE in CELL_PCH state changes the cell, a CELL UPDATE needs to be performed to let

    the UTRAN know of the new position of the UE. This is done because in the connected mode (CELL_PCH), UE is known at cell level rather than UTRAN

    level as in IDLE state. I f too many CELL UPDATES are performed, it defeats the purpose of UE being in CELL_PCH. Hence in this case the UE is put in

    URA_PCH state. Now the UE will perform CELL UPDATE only when the URA is changed for a UE. The drawback is that when UE needs to be paged the

    paging area is now extended to many cells belonging to the URA.

    Also Note that the CELL_PCH state is actually a subset of the URA_PCH state. It is possible to define overlapping URAs to be used in the URA_PCH

    state. Thus, the UTRAN operator could define that each cell is a separate URA in addition to other larger URAs. Then the operator could assign smallone-cell URAs for slow-moving mobiles, and larger URAs for mobiles with greater mobility. The small URAs could nicely perform the task of the

    CELL_PCH state. However, it has been decided to keep these states separate.

    The URAs can be overlapping or even hierarchical. The same cell may belong to several different URAs, and the UEs in that cell may have been

    registered to different URAs. SIB 2 contains a list of URA identities indicating which URAs this cell belongs to. This arrangement is done to further

    reduce the amount of location update signaling because now the UEs moving back and forth in the boundary area of two URAs do not have to update

    their URA location information if the boundary cells do belong to both URAs.

    DPCCH, Layer-1 contains information regarding Power control, Spreading-Despreading, Multiplexing-Demultiplexing, Scrambling

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    DPDCH

    Accessibility, Retainability, Intra Frequency HOSR, Intra Frequency HOSR, IRAT HOSR

    Handovertype

    Compress mode starts at events 2d (RSCP or EC/No base) & 6d (Tx power base)

    1. PLMN selection & reselection, 2.Cell selection & reselection, 3. LA & RA registration, 4.

    Paging procedure, 5. Reading System information

    Squal = Qqualmeas - qQualMin > 0, Srxlev = Qrxlevmeas - qRxLevMin - Pcompensation > 0, where ,Pcompensation = max (maxTXpowerUL -

    P ;0 ), qQualMin - Minimum required quality value and is sent in SIB3 for serving cell and SIB 11 for adjacent cell, qRxLevMin - Minimum required

    signal strength and is sent in SIB3 for serving cell and SIB 11 for adjacent cell, maxTXpowerUL - Maximum transmission power during random access

    on the RACH and is sent in SIB3, P - UE maximum output power according to its class

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