Umts Wcdma Basic Concept 3g 2

8/13/2019 Umts Wcdma Basic Concept 3g 2

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WCDMA BASICCONCEPT_2

Prepared By:A.K.M.Asaduzzaman

RF Optimization Engineer(RNO)

Radio Network Planning & Optimization Department

STAR LINK.


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Mobile Network Evolution

1G

Analogue

2G

Digital

2.5GPacket Data

2.75G

Enhanc ed Data

NMT

TACS

AMPS

GSM

CDMA

TDMA

PDC

GPRS

EDGE

CDMA 1X

WCDMA

TD-SCDMA

cdma20001X EV-DO

2M, 14M

2M

2.4M144K

1982-1996+ 1992-2002+ 2001+ 2004+ 2002-2004+


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WCDMA FDD

WCDMA FDD

Multiple access method DS-CDMA

Duplex Method Frequency Division

Frequency Band Uplink : 1920-1980MHz, Downlink : 2110-2170MHz

Base Station Synchronization Asynchronous/Synchronous operation

Chip Rate 3.84Mcps

Frame Length 10ms

Service multiplexing Multiple Services with different QoS are multiplexed on a

single connection

Multi-user detection, smart antennas Supported by standard, optional in implementation

Power Control Fast Power Control, 1.5KHz

Handover Softer, Soft & Hard Handover

Transmit Diversity Open & Closed Loop

Voice Coding AMR Voice Coding, rate 4.75kb

12.2kbps


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WCDMA Network Structure

GSM /GPRS BSS

BTS

BSC

PCUSS7

SCP

SMS

SCE

PSTN/other PLMN

Internet,Intranet

MSC/VLR GMSC

HLR/AUC

SGSN

CGBG

GGSN

PS backbone

Other PLMN

CS domain

PSdomain

NodeB

RNC

UTRAN

Iu-CS

Iu-PS

A

Gb


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5

UTRAN

The main task of UTRAN is to create and maintain Radio Access

Bearers (RAB) for communication between UEs and Core

Network.

UTRAN is located between two open interfaces being Uu and Iu.


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6

UTRAN Architecture


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7

UTRAN & Interfaces


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RNC (Radio Network Controller) The RNC is switching and controlling element of the UTRAN. RNC is located

between the Iub and Iu interface. It also has the third interface called Iur for

inter-RNS connections.

Referring to the Bearers, the RNC is a switching point between the Iu Bearer

and Radio Bearer(s).


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RNC Function The whole functionality of RNC can be classified into two parts:

UTRAN Radio Resource Management

UTRAN Control Functions


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10

Radio Resource Management

The RRM is a collection of algorithms used to

guarantee the stability of the radio path and

the QoS of radio connection by efficient

sharing and managing of the radio

resources.

The RRM algorithms to be shortly presented here are:

Handover Control

Power Control

Admission Control and Packet Scheduling

Code Management


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11

WCDMA Handover Scenarios


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Soft HandoverIn WCDMA system, the majority of handovers are intra-frequency soft handovers


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Concept of Soft/Softer Handover

Cell A

Cell B

Cell C

Single Link

The UE measured the CPICH Signal strenght (RSCP) and quality (Ec/No) to determine whichcell to add in the active set

Add and remove from active set is based on relative measurments

Softer handover

-two cells within the same RBS in Active Set

Soft handover

-two cells from different RBS in Active Set

Soft/Softer handover

-three cells in Active Set


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POWER CONTROL Power control is an essential feature of any

CDMA based cellular system.

In WCDMA, power control is employed in both uplink anddownlink.

Downlink power control is basically for minimising the interference to other

cells and compensating for other cells' interference as well as achievingacceptable SIR.

To manage the power control properly in WCDMA, the system uses differenttwo defined power control:

Open Loop Power Control

Closed Loop Power Control (CLPC), including Inner and Outer Loop

Power Control mechanisms


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Types of Power Control

Open Loop Power Control (OLPC): Basically used for uplink power adjusting, the UEadjusts its transmission power based on estimate of the received signal level from the

BS Common Pilot Channel (CPICH) when the UE is in idle mode and prior to PhysicalRandom Access Channel (PRACH) transmission.

Closed-Loop Power Control (CLPC):Utilised for adjusting the transmission powerwhen the radio connection has already been established. Its main target is to

compensate the effect of rapid changes in the radio signal strength and hence it shouldbe fast enough to respond to those changes.


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CELL CAPACITY

In GSM the TRX capacity calculation is very straightforward procedure but because in

WCDMA the radio interface is handled differently and the system capacity is limited by

variable factors, the capacity of the WCDMA TRX is not very easy to be determined.

The capacity of a cell depends on the downlink Scrambling Code amount assigned for the cell

(minimum is 1). Every downlink Scrambling Code then has a set of Channelisation Codes under it

and every call/transaction requires one Channelisation Code to operate.

In WCDMA technology, all the users share the common physical resource, being frequency band in

5 MHz slices. All users of the WCDMA TRX co-exist on the frequency band at the same moment of

time and different transactions are for the people is the capacity of the WCDMA TRX.

Some assumptions:

All the subscribers under the TRX coverage area are equally distributed so that they have equal

distances to the TRX antenna.The Power level they use is the same and thus the interference they cause is on the same level.

Subscribers under the TRX use the same baseband bit rate, i.e. also the same Symbol Rates.

GSM d WCDMA C i


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GSM and WCDMA Comparison

Separate users through different codes

Continuous transmission and reception

Code planningNo Frequency Planning

Variable Cell Radius: Cell Breathing

Radio Link: 1 UE Many Node-Bs

Power is Capacity

Scrambling Code Planning

Hard/Soft/Softer Handover

Orthogonal in time within a cellTime Slot Synchronization in time

Frequency planning

Fixed Cell Radius

Radio Link: 1 MS 1 RBS

# of Frequencies limit capacity

BSIC Planning

Hard Handover

GSM WCDMA

BTS Node B

BSC RNCMS UE


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Scrambling Code

Scrambling codes

GOLD sequence.

Uplink scrambling codes Uplink scrambling codes are used to distinguish different UEs

Downlink scrambling codes

For downlink physical channels, a total of 218-1 = 262,143 scrambling codes

can be generated.

Only scrambling codes k = 0, 1, , 8191 are used.

8192 codes are divided into 512 groups, each of which contains 16 scrambling

codes.

The first scrambling code of each group is called primary scrambling code

(PSC), and the other 15 ones are secondary scrambling codes (SSC).


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Scrambling Codes & CPICH

The Common Pilot Channel (CPICH) is broadcast from every cell

It carries no information and can be thought of as a beacon constantly transmitting

the Scrambling Code of the cell It is this Beacon that is used by the phone for its cell measurements for network

acquisition and handover purposes (Ec, Ec/Io).

Beacon: A signaling or guiding device, such as a lighthouse, located on a coast. A radio transmitter that emits acharacteristic guidance signal.

CPICH


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Comments Majority of the measurements are based on CPICH.

Thumb rule is that, if UE cant see the CPICH, it cant see the cell. Initial optimisation is purely based on the CPICH measurements.

In the Downlink, WCDMA cells are identified by their SC.

Its like a BCCH in GSM but the difference is in using same frequency.


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Concepts of RSCP and Ec/No

Three Important Terms

RSCP (Received signal code power) Ec/Io ( Energy per chip/ Noise density)

Eb/No (Energy per bit/Noise density)


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Handover Types

Intra-Frequency Handovers Softer Handover

Handover between sectors of the same Node B (handled by BTS)

Soft Handover

MS simultaneously connected to multiple cells (from different Node Bs)

Hard Handover

Arises when inter-RNC SHO is not possible (Iur not supported or Iur congestion) Decision procedure is the same as SHO (MEHO and RNC controlled)

Inter-Frequency Handover Can be intra-RAN, intra-RNC, inter-RNC

Inter-RAT Handover

Handovers between GSM and WCDMA (NEHO)


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Handovers in WCDMA - Softer HO Softer handover occurs between sectors of the same site


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Soft handover occurs between sectors of the different sites

For both softer and soft it is the Ec/Io levels used to determine whether a

cell should be added or removed from the active set

Handovers in WCDMA - Soft HO


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Handovers - Inter frequency HO Inter frequency handover occurs between two WCDMA carriers

Will be used once operator deploys its second carrier, for microcell layer orcapacity purposes


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Handovers - Inter system HO Inter system handover occurs between 3G and 2G sites

As with all handovers, accurate adjacencies will be required

3G 2G


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OVSF and PN Code UsageOVSF Code PN Code

Usage Uplink :Separate physical data

(DPDCH) & control channels

(DPCCH) from the same

terminal

Downlink :Separate downlink

connections to different UEswithin the cell

Uplink :Separation of UEs

Downlink :Separation of cells

Length Uplink : 4256 chips

Downlink : 4512 chips

Uplink/Downlink :

10ms = 38400 chips

Number of codes Number of codes under one

scrambling factor = spreading

factor

Uplink : Several Million

Downlink : 512

Code Family Orthogonal Variable Spreading

Factor (OVSF)

Gold code

Bandwidth Spreading increase transmission

bandwidth

No change in transmission

bandwidth


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Spreading and De-spreading

information pulse interference White noise

The improvement of time-domain information rate means that the bandwidth of spectrum-domain

information is spread.

f

Sf

The spectrum before spreading

information

f0

The spectrum before despreading

information

Interference/noise

Sf

f0 f f0

The spectrum after despreading

information

Interference/noise

Sf

f

The spectrum after spreading

information

f0

Sf

f


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Principle of RAKE Receiver

RAKE receiver help to overcome on the multi-path fading and enhance

the receive performance of the system

Receive set

Correlator 1

Correlator 2

Correlator 3

Searcher correlatorCalculate the

time delay and

signal strength

Combiner The combined

signal

tt

s(t) s(t)


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Common Technical Terms

Bit, Symbol, Chip:

A bit is the input data which contain information

A symbol is the output of the convolution, encoder, and the block

interleaving

A chip is the output of spreading

Processing Gain:

Processing gain is the ratio of chip rate to the bit rate.

Closely related to spreading factor, SF.

Forward direction/ Downlink : Information path from base station to

mobile station

Reverse direction/ Uplink : Information path from mobile station to

base station


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WCDMA System

Spreading

Spreading (OVSF code)

SF 4512, depends on data rate

Scrambling (Gold Code)

Modulation

QPSK


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HandoverSofter handover

- Handover between intra-frequency cells under the control of the same BTS

- Radio link connection to new target cell is created before existing connection

being deleted.

Soft handover- Handover between intra-frequency cells under the control of the differentBTSs

Hard handover

- Condition of hard handover:

Intra-frequency handover, cells controlled by different RNCs and no Iurinterface between them

Inter-frequency handover

Inter-system handover

Interruption in voice or data communication occurs but this interruptiondoes not effect the user communication


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Soft/Softer Handover

Combine all the

power from each

sector

Power received from

a single sector

Selection combination in the RNC during soft handoff

Maximum ratio combination in the NodeB during softer handoffs


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Common Pilot

Channel(CPICH) Common Pilot Channel (CPICH)

Carries pre-defined sequence.

Fixed rate 30KbpsSF=256 Can use STTD on this channel


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1. Synchronization Procedure

Cell SearchSlot synchronization

Frame synchronization and

code-group identification

Scrambling-code

identification

UE uses PSC to acquire slot

synchronization to a cell

UE uses SSC to find frame

synchronization and identify

the code group of the cell

found in the first step

UE determines the primary scrambling

code through correlation over the

CPICH with all codes within the

identified group, and then detects the

P-CCPCH and reads BCH information


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WCDMA Handover Principal


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Why mobile systems need handover?

UE mobility

The mobile system is composed of

cells which the coverage ability is

limited.

Provide continuous service in

mobile system is the basic element

in QoS.


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The Purpose of Handover

Providing the continuous service in mobile system is the basic element in QoS.

The load balance: sharing the resource


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The Basic Concepts of

Handover Active Set

Monitored Set

Detected set

Event reporting Event reporting to Periodic reporting

Periodic reporting

Radio Link (RL)

Radio Link Set (RLS)

Combination way:

maximum ratio combination selection combination

The soft handover gain

CPICH

Soft handover, softer handover, hard handover


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Types of Handover

According to the signaling characters:

Soft handover (softer handover)

Hard handover

According to the properties of source cell and target cell

Intra-frequency handover

Inter-frequency handover

Inter-mode handover (FDD TDD)

Inter-system handover (UMTS GSM/CDMA2000)

According to the purpose of handover

Based on Coverage

Based on Load (Optional)

Based on mobility of UE (Optional)

Based on Service (Optional)


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The Characters of Different

HandoversComparison between soft handover and

hard handover:

Item Soft Handover Hard Handover

The numbers of RL in

active set after

handover

Several One

Interruption during

handover

No Yes

The frequencies of cells Only possible in

Intra-frequency

cells

Occurs in Intra-frequency

cells or Inter-frequency cells


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The Characters of DifferentHandovers

Comparison between soft handover and

softer handover:

During softer handover, the uplink signaling are combined in NodeBby maximum ratio combination, but during soft handover they are

combined in RNC by selection combination.

Compare to later one, the maximum ratio combination give more

gain. So the performance of maximum ratio combination is better.

Since softer handover is completed in NodeB, it does not consume a

lot of transport resource of Iub.


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Soft Handover

RNC

NodeB 2NodeB 1


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Softer Handover

RNC

NodeB


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Hard Handover


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Thank you

Umts Wcdma Basic Concept 3g 2

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