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Q1. What is a maximum information rate that can be achieved with bandwidth

20 MHz and Signal-to-Noise Ratio equal S/N= 20?

A1. Apply Shannon-Hartley formula

where BW - bandwidth available for the communication,S - received signal power, and

N - the power of the white noise impairing the received signal.

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Q2. Describe GSM timing advance procedure and its purpose.

Timing advance is needed to cope with variations in the two-way propagation time to

terminals at different distances from the base.

Therefore, to prevent data bursts from different terminals overlapping in the input to thebase-station receivers, the base-station instructs the terminals to insert a suitable delay

between received and transmitted data bursts.

The delay is adjusted such that a transmitted burst from the terminal reaches the base-

station receiver at the right instant relative to the time-slot structure. The closer a

terminal is to the base station, the greater will be the delay inserted. Thus, regardless of

how far the terminal is away from the base, the bursts arriving to the base receiver willalways arrive roughly in the middle of the intended time slot.

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Q3. What is a purpose of training sequence of 26 bits in the middle of GSM burst?

The impulse response of the radio channel can change drastically during a GSM

Frame, speed of the variation increases with speed of terminal.This means that for each time slot, the receiver must carry out bit synchronization and

set the channel equalizer.

The setting of the channel equalizer is based on a known Training Sequence of 26 bits,

which is also used for the bit synchronization.

The sequence is constructed as follows:

The 16 bits are placed in the middle of the sequence, this bit sequence has good cycliccorrelation characteristics.

Then the last 5 bits of that 16 bit sequence are placed at the beginning of Training

Sequence , comprising the prefix and the first 5 bits of basic 16 bit sequence are

repeated at the end, comprising suffix.

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4.In what GSM network node encrypted bit stream of voice call from mobile

transmitter is decrypted?

In the Base Station. Only air interface is encrypted in GSM.

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Q5. Describe call setup procedure for mobile terminated call

The MS is called via the PCH and requests a signaling channel on the RACH.

It obtains the SDCCH through an IMMEDIATE ASSIGNMENT message on the AGCH.

Then follow authentication, start of ciphering and start of setup over the SDCCH.

An ASSIGNMENT COMMAND message gives the traffic channel to the MS, which

acknowledges its receipt on the FACCH of this traffic channel.

The FACCH is also used to continue the connection setup.

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Q6. Describe call setup for mobile originated call. (below is also the answer on Q5)

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Q7. Describe registration procedure for mobile terminal in GSM.

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Q8. What information obtained from terminal is used by network in decision for Mobile

assisted handover (MAHO)?

The terminal measures:

Signal strength from own base (TCH/BCCH)- Quality from own base (TCH)

- Signal strength from the 6 strongest neighbour cells (BCCH)

This information is transferred to base station

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Q9. Describe purpose and highlevel procedure of interleaving in GSM.

Interleaving consists of mixing up the bits of the coded data blocks.

The goal is to have adjacent bits in the modulated signal spread out over severaldata blocks. The error probability of successive bits in the modulated stream is

typically highly correlated, and the channel coding performance is better when

errors are decorrelated.

Therefore, interleaving improves the coding performance by decorrelating errors

and their position in the coded blocks.

Interleaving procedure involves segmentation and reordering of the coded datablocks. Interleaving process mixes the encoded data block of 456 bits, and groups

the bits into eight sub-blocks (half bursts). The eight sub-blocks are transmitted on

eight successive bursts (interleaving depth equals 8).

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Q10. What additional network nodes are introduced to GSM system to support packet

data services? What functions they perform?

The first node is the access point for an external data network and is known as thegateway GPRS support node (GGSN).

The GGSN routes the packets to the current location of the mobile.

The second is the node that serves the mobile stations needs and is known as the

serving GPRS support node (SGSN).

The SGSN is responsible for a mobility management context for an attached MS.It does the ciphering for packet data traffic.

The SGSN initiates the PDP context activation following request from mobile or from

network.

The GGSN creates the PDP context entry in routing table.

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Q11. What mobility management states are introduced with GPRS?

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Idle State

The subscriber is not reachable by the GPRS network. The subscriber is not attached to

the mobility management. In order to change state, the MS has to perform a GPRS

Attach procedure.

Standby State

The subscriber is attached to the mobility management and the location of an MS is

known on a routing area level. The MS is capable of receiving pages but cannot send

data. The network holds a valid mobility management context for the subscriber.

If the MS sends data, the MS moves to READY state.

Ready State

The subscriber is attached to the mobility management and the location of an MS isknown on a cell level. The MS is capable of receiving PTM (Point to Multi point) and PTP

(point to point) data. The SGSN can send data to the MS without paging at any time and

the MS can send data to the SGSN at any time.

GPRS Attach and Detach

With the GPRS Attach the mobile moves to READY state and the mobility management

context is established, the MS is authenticated, the ciphering key is generated, aciphered link established and the MS is allocated a Temporary Logical Link Identity (TLLI).

The SGSN gets the subscriber information from the HLR.

After a GPRS Attach, the SGSN tracks the location of the MS. The MS can send and

receive SMS, but no other data. To transfer other data it has to first activate a PDP

context.

The GPRS Detach moves the MS to IDLE state and the mobility management context isremoved .

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Q12. What is PDP context?

PDP context describes the characteristics of the packet data session.

It contains : the PDP type (e.g. IPv4),

the PDP address assigned to the MS (e.g. an IP address),

the requested QoS class and

the address of a GGSN that serves as the access point to the external network.

This context is stored in the MS, the SGSN and the GGSN.

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Q13. What is TBF (Temporary Block Flow) and what procedure associated with TBF?

The TBF is a RLC (Radio Link Control) procedure of orderly transmission of the

packet data units received from upper layers of GPRS protocol stack.

It involves RLC layer segmentation of data units into radio blocks (RNC/MAC blocks)

and ARQ (Automatic Repeat/reQuest) procedure during transfer of sequence of

radio blocks over air interface.

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Q14. Describe principle of link adaptation in EDGE ((E) GPRS).

Link adaptation consists of two step procedure.

The first step is the selection of a suitable MCS (Mobile Coding Scheme), i.e.combination of modulation type and coding rate.

The next step in the link adaptation is advanced ARQ arrangement based on is

called incremental redundancy.

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Q15. How Radio Access Bearer (RAB) in 3G is different from traffic channel in GSM?

In 2G the bearer is a traffic channel, i.e. one to one relationship.

In 3G the bearer represents a selected QoS for a specific service.

Only from the point of view of the physical layer is a bearer a type of channel.

The service is mapped to RAB (CS/PS, HSxA) according the traffic class defined for

specific service such as speech, video, web browsing, etc.

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Q16. Briefly describe the functions of UTRAN physical layer.

UTRAN physical layer is responsible for the following functions:

1. Multiplexing the Transport Blocks (TB) in Transport Format Combination (TFC)

2. Rate Matching

3. Channel Coding

4. Spreading (Channelization)

5. Scrambling

6. Modulation

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Q17. What is the function of Coded Composite Transport Channel (CCTrCH)?

The CCTrCH encodes and multiplexes all transport channels of the same type on the

physical layer.The CCTrCH creates the Transport Format Combination Set, which includes 10 x TFC

(Transport Format Combination) in which each combination is represented by a pair

(TFA,TFB) where TFA is the transport format of the DTCH channel and TFB is the

transport format of the DCCH channel:

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Q18. Describe scrambling features and its purpose in WCDMA.

Scrambling codes are basically transmitter specific, each base station sector or

mobile terminal have own code. For a cell (sector) the scrambling code is namedPrimary Scrambling Code (PSC) and used to distinguish the serving cell from the

neighbour cell. It also randomizes inter-cell interference.

Scrambling codes in UTRAN FDD are complex codes applied at chip level, so the

scrambling procedure consists of a complex multiplication of I and Q channels by

complex scrambling code.

The I and Q channels could be of different amplitudes at the input of scrambler. Thescrambling equalize the I and Q component at the output of the scrambler. This

reduces the Peak to Average Ration of modulated signal in amplification process.

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Q19. What is the physical concept of WCDMA timeslot and how it different from GSM

time slot in its purpose?

The 10 ms radio frame is subdivided in 15 time slots, each one having 2560 chips. Here,

the concept of time slot is not at all the same as in TDMA systems, since in UTRAN FDDthere is no user multiplexing from slot to slot in the dedicated physical channels. On the

contrary, each time slot corresponds to a power control cycle, which means that the

power amplifier should be able to modify the transmitted power on a time slot basis

according to the commands that are received in the downlink direction. This ensures a

power control rate of 1500 Hz. (Lecture 7)

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Q 20. Describe how mobile terminal synchronize to WCDMA network.

The Synchronisation Channel (SCH) is the first physical channel that a mobile terminal

detects when it is switched on. Terminal achieves the frame and slot synchronisation +determines a primary scrambling code (PSC) of the camped cell.

The synchronisation channel consists of a primary SCH and a secondary SCH both

transmitted over P-CCPCH, once per time slot, during the initial 256 chip period of the

slot in which the BCH is switched off.

The Primary SCH uses a 256-chip spreading sequence identical in every cell.

The secondary SCH code words vary from one base station to another, with a total of 16sequences in use, each secondary sequence is used to generate respective scrambling

code. Slot and chip level synchronisation is achieved by means of correlation of PCH chip

sequence with expected sequence, the separation of the peaks in correlation function

relates to the slot duration.

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21. Describe briefly four RRC states in WCDMA .

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Cell_DCH.

Dedicated transport channel both in uplink and downlink directions is allocated to the

terminal, so that it can transmit either signalling or data information.

Cell_FACH.

There is NO dedicated transport channel, so the terminal can only transmit through the

RACH or CPCH in the uplink and receive through the FACH in the downlink.

Cell_PCH. The terminal cannot transmit in the uplink direction in neither the dedicated

nor in the common transport channels. Terminal can simply decode the information

from the broadcast and paging channels. The mobile location is known at the cell level.

URA_PCH. Cell_PCH, similar to CELL_PCH with the difference that the mobile positionis known on a registration area basis, so that the terminal does not require informing

the network when it performs a cell reselection procedure between cells of the same

registration area.

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Q22. What are the major functions of Radio Resource Management (RRM)?

it performs a cell reselection procedure between cells of the same registration area.

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Q23. What are the key functionalities of HSPA?

1. Shared-Channel Transmission based on Channel Dependent Scheduling

2. Physical layer retransmission supported by HARQ with Soft Combining

3. Fast link adaptation over short transmission time interval (TTI)

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Q24. How HSPA impacted the functionalities of NodeB?

New functionalities for fast HSPA scheduling, priority handling and retransmission

control has to be supported by the Base Station. The result is an introduction of new

protocol entity MAC-hs into NodeB.

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Q25. What are the key differences between Release 99 DCH and HS-DSCH (High Speed

Downlink Shared Channel)?

When compared to DCH, the key difference is the replacement of power control with

link adaptation and L1 HARQ. Also the multicode operation has been extended.

Feature

Variable spreading factor

Fast power control

Adaptive modulation and coding

Fast L1 HARQ

DCH

Yes

Yes

No

No

HS-DSCH

No

No

Yes

YesBTS based scheduling No Yes

Multi-code operation Yes Yes, extended

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Q26. Describe principle of Fast Link Adaptation in HSDPA

1. Mobile measures the signal strength on common Pilot Channel (CPICH) and

estimates channel quality on data channel.

2. Mobile reports CQI (Channel Quality Indicator) on HSDPA control channel (HS-

DPCCH) to NodeB. The reported CQI relates to a biggest transport block size which

can be transmitted with BLER

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Q27. What information is carried by F-DPCH (FractionalDPCH)?

1. One power control command per slot, two TPC bits=1 x QPSK symbol during 1/10of time slot period.

2. F-DPCH allows up to ten UEs to share a single channelization code for this purpose.

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Q28. Describe scheduling principle for HSUPA (E-DCH/Enhanced DCH)?

Execuited by NodeB. The basis for the scheduling framework is scheduling grants sent

by the NodeB to the UE and limiting the E-DCH data rate and scheduling requests sent

from the UE to the NodeB to request permission to transmit (at a higher rate than

currently allowed).

The NodeB need info on UE buffer status and available transmission power . This info is

provided by means of: the out-band happy bittransmitted on the E-DPCCHand in-

band scheduling information transmitted on the E-DCH.RG and AG control the UEs maximum allowed E-DPDCH to DPCCH power ratio

RG carries one bit only: UP/DOWN by one step relative to currently used max

E-DPDCH/DPCCH power ratio

AG carries a command informing the UE of the E-DPDCH/DPCCH power ratio to

be used at maximum

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Q29. The following control channels have been configured on downlink for HSDPA capable

cell:

PICH, AICH, CPICH, and PCCPCH, each require SF256 code.

Single SCCPCH with SF128 code

Single HS-SCCH with SF128 code For HDSPA traffic the 5 x SF16 codes are allocated for HS-PDSCHs traffic channels.

How many channels are available for R99 DCH traffic to support the AMR voice with SF128?

A29.

See the code tree on the next page. At SF 16 level we have only 10 codes left to use, 5allocated by HSDPA, one is occupied by branch carrying the control channels (PICH, AICH,

CPICH, and PCCPCH +SCCCPCH, HS-SCCH).

Those 10 codes produce 10*23=10*8=80 codes at SF=128 level.

In addition we have another left hand branch starting from S16 (see code tree) which

produces one code at SF=32 level -->2 codes at SF=64 --> 4 codes at SF=128 level.

In summary we have 80+4=84 channels available for voice AMR calls with SF=128.

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Q30. Describe principle and purpose of Cyclic Prefix insertion in LTE.

Lec 9.

Cyclic Prefix insertion implies that the last part of the OFDM symbol is copied and

inserted at the beginning of the same OFDM symbol. This reduces the effective OFDMsymbol rate since total duration of the symbol is increased. Also the received power

utilization is reduced due to the fact that cyclic prefix does not carry additional

information..

On positive side, the cyclic prefix insertion preserves the orthogonality of OFDM

subcarriers received over time dispersive multipath channel. The orthogonality is

essential feature for OFDM demodulation.

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Q31. Briefly describe LTE state machine.

Lec 10.

Terminal can be in two different states : RRC_CONNECTED and RRC_IDLE.

The cell to which the terminal is belongs is known and an identity of the terminal, the Cell

Radio-Network Temporary Identifier (C-RNTI), used for signaling purposes between theterminal and the network, has been configured. RRC_CONNECTED is intended for data

transfer to/from the terminal, but discontinuous reception (DRX) can be configured in order

to reduce terminal power consumption.

RRC_CONNECTED havetwo substates,

IN_SYNC and OUT_OF_SYNC,

IN_SYNC - uplink is synchronized to the network (timing advance is defined by eNodeB).

Both uplink transmission and downlink reception are possible.

OUT_OF_SYNC- uplink is not synchronized (there is no timing alignment performed). DL

reception possible, UL transmission is not possible. In order to restore Uplink

synchronization terminal needs to perform random access procedure .

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Q32. What is the minimum resource allocation unit per user in LTE?

1 x Physical resource block spread over 2 Slots = 1 Subframe = 1 Transmission time

interval (TTI)= minimum scheduling unit=resource-block pairEach TTI = 1 ms a user can be allocated to a different PRB.

Heavy data users are allocated to more than 1 x PRB. Low data users get 1 x PRB.

1 PRB is mapped to 12 subcarriers (180kHz) and 2 x 7(6) symbols.

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Q33. What is the purpose of downlink cell reference signal, how reference signal is

positioned in time and frequency domain?

Reference signals are used for channel estimation (signal quality and strength); thereforethey are similar in functionality to the Pilot signal in WCDMA.

The position of the reference signalsin the time domain is fixed (symbols 0 and 4 for the

FDD frame), and in the frequency domain, it depends on the Cell ID.

Distributing the reference signals in both time and frequency domains allows the UE to

complete the channel estimation in both domains.

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Q34. What is the purpose of LTE downlink scrambling and what input parameters

are used by a scrambling generator to produce downlink scrambling code?

LTE downlink scrambling implies that the block of code bits delivered by the hybrid-

ARQ functionality is multiplied (exclusive-or operation) by a bit-level scramblingsequence.

Bit level scrambling in LTE randomizes inter-cell interference thus ensuring full

utilization of the processing gain provided by the channel code and , in effect,

suppressing interference.

The scrambling sequences depend on the physical-layer cell identity.

The scrambling sequence generator is re-initialized every subframe (except for the

Physical Broadcast CHannel (PBCH)

Input to scrambling generator comprised of the identity of the cell, the subframe

number (within a radio frame) and the UE identity.

Q35 What procedures the LTE cell search includes?

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Q35. What procedures the LTE cell search includes?

LTE cell search consists of the following basic parts:

Acquisition of frequency and symbol synchronization to a cell.

Acquisition of frame timing of the cellthat is, determine the start of the downlink

frame. Determination of the physical-layer cell identity of the cell.

To assist the cell search, two special signals are transmitted on each downlink

component carrier, the Primary Synchronization Signal (PSS) and the Secondary

Synchronization Signal (SSS).

There are 504 different physical-layer cell identities defined for LTE, where each cell

identity corresponds to one specific downlink reference-signal sequence. The set of

physical-layer cell identities is further divided into 168 cell-identity groups, with three

cell identities within each group. The three identities in a group would usually be

assigned to cells under the control of the same eNodeB. Three PSS sequences are used

to indicate the cell identity within the group, and 168 SSS sequences are used to

indicate the identity of the group.

ib h i f i f h i i i f ( i

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Q36. Describe the information outcomes of the acquisition of PSS (Primary

Synchronization Signal) and SSS (Secondary Synchronization Signal) by LTE terminal.

After acquisition of PSS (Primary Synchronization Channel ) and time slot

synchronization is achieved. Terminal select one of three possible types of PSS signals

which indicate the physical cell-ID group.

After synchronizing with the SSS, the mobile has not only retrieved slot and radio

frame timing, but also detected the duplex method (TDD or FDD), CP length, and the

9-bit physical layer c-ID.

Once the terminal has acquired frame timing and the physical-layer cell identity, it has

identified the cell-specific reference signal. The behavior is slightly different depending

on whether it is an initial cell search or cell search for the purpose of neighboring cell

measurements:

In the case of initial cell searchthat is, the terminal state is in RRC_IDLE mode

the reference signal will be used for channel estimation and subsequent decoding

of the BCH transport channel to obtain the most basic set of system information. In the case of mobility measurementsthat is, the terminal is in

RRC_CONNECTED modethe terminal will measure the received power of the

reference signal. Based on the measurement report, the network will conclude

whether a handover should take place.

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Q37 What reference signals deployed in LTE uplink and what their purpose

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Q37. What reference signals deployed in LTE uplink and what their purpose,

respectively?

Two types of RS are supported on the uplink:

DeModulation RS (DM RS), associated with transmissions of uplink data on the Physical

Uplink Shared CHannel (PUSCH) and/or control signalling on the Physical Uplink ControlCHannel (PUCCH). These RSs are primarily used for channel estimation for coherent

demodulation.

Sounding RS (SRS), not associated with uplink data and/or control transmissions, and

primarily used for channel quality determination to enable frequency-selective

scheduling on the uplink.