Training Umts Basics

UMTS BasicsR99/HSDPA

Multiple Access ApproachesFrequency Division Multiple Access

Each User has a unique frequency

(1 voice channel per user)

All users transmit at the same time

AMPS, NMT, TACS

Use

r 1

Use

r 2

Use

r 3

Frequency

Each Transmitter has a unique spreading code

Each Data Channel has a unique orthogonal code

Many users share the same frequency and time

IS-95, cdma2000, WCDMA

Frequency

Code Division Multiple Access

SpreadSpectrumMultipleAccess

Multiple Transmitters

and

Multiple Data Channels

Each User has a unique time slot

Each Data Channel has a uniqueposition within the time slot

Several users share the same frequency

IS-136, GSM, PDC

Time Division Multiple Access

Use

r 1

Use

r 2

Use

r 3

Use

r N

Time

Orthogonal Codes

CC1, CC2CC3, CC4

CC5, CC6, CC7

CC1 , CC2, CC3CC1, CC2

CC1, CC2, CC3, CC4

Uplink: Channelization Codes used to distinguish data (and control) channels coming from each UE

Downlink: Channelization Codes used to distinguish data (and control) channels coming from each cell

(Also called channelisation)

Scrambling Codes

SC3 SC4

SC5 SC6

SC1 SC1

Cell “1” transmits using SC1

SC2 SC2

Cell “2” transmits using SC2

Downlink: Scrambling Code used to distinguish each cell (assigned by operator – SC planning)

Uplink: Scrambling Code used to distinguish each UE (assigned by network)

Downlink Scrambling Codes

• Downlink Scrambling Codes– Each Cell is assigned one and only one Primary Scrambling Code (of 512)– Secondary Scrambling Codes may be used over part of a cell, or for other data

channels

Primary SC0

Secondary Scrambling

Codes

(15)

Secondary Scrambling

Codes

(15)

Secondary Scrambling

Codes

(15)

Secondary Scrambling

Codes

(15)

Code Group #1 Code Group #64

512 Downlink Scrambling CodesEach code is 38,400 chips of a 218 - 1 (262,143 chip) Gold Sequence

Primary SC7 Primary SC504Primary SC511

Uplink Scrambling Codes

Random Access, Packet Access

• Cell-specific Scrambling Code(s)

• Code(s) are assigned by UTRAN

• Code allocation corresponds tothe cell’s DL scrambling code group

Dedicated Traffic Connection

• UE-specific Scrambling Code(s)

• Code(s) are assigned by UTRAN

Uplink Scrambling Code Type depends on the Application

Channelization and Scrambling Codes

2 data channels(voice, control)

SC3 + CC1 + CC2

2 data channels(14 kbps data, control)

SC4 + CC1 + CC2

3 data channels(voice, video, control)

SC2 + CC1 + CC2 + CC3

3 data channels(voice, video, control)SC5 + CC1 + CC2 +

CC3

4 data channels(384 kbps data, voice, video, control)

SC6 + CC1 + CC2 + CC3 + CC4

4 data channels(384 kbps data, voice, video, control)

SC2 + CC4 + CC5 + CC6 + CC7

2 data channels(voice, control)

SC1 + CC1 + CC2

1 data channels(control)

SC1 + CC3

VoiceConversation Uplink

Packet Data

Videoconference

Videoconference with Data

Pilot, BroadcastSC1 + CCP + CCB

Pilot, BroadcastSC2 + CCP + CCB

UMTS UTRAN Architecture

GSM/GPRS Core Network (CN)

Iu Iu

RNS

RNC

RNS

RNC

Node B Node B Node B Node B

Iur

IubIubIub

Iub

User Equipment(UE)

UTRAN

(UMTS Terrestrial

Radio Access Network)

PSTNISDN

Internet

Uu

3GPP TS 25.401 ¶ 6.03GPP TS 25.401 ¶ 6.0

MSCGPRS

Service Node

Iu Iu

UMTS UTRAN Architecture

UMTS - Hierarchy of Bearers

3GPP TS 23.107, QoS Concept and Architecture

TETE MTMT UTRANUTRANCN Iuedgenode

CN Iuedgenode

CNGateway

CNGateway

TETE

UMTS

End-to-End Service

TE/MT Local Bearer Service

External Bearer Service

UMTS Bearer Service

Radio Access Bearer Service CN Bearer Service

Backbone Bearer Service

Iu Bearer Service

Radio Bearer Service

UTRA FDD/TDD Service

Physical Bearer ServiceRAB

Cell Breathing in WCDMA• The more traffic on the cell, the more noise generated.• More power is required in UL and DL to achieve the

required Eb/No.• The cell shrinks because power is a finite resource.

BS 1 BS 2

Fully loaded systemUnloaded system

QoS classes

• Radio Access Bearers are mapped onto these classes.

Traffic class Conversational classconversational RT

Streaming classstreaming RT

Interactive classInteractive best effort

BackgroundBackground best

effort

Fundamentalcharacteristics

· Preserve timerelation (variation)between information

entities of thestream

· Conversationalpattern (stringentand low delay )

· Preserve timerelation(variation)betweeninformationentities of thestream

· Requestresponse pattern

· Preservepayload content

· Destination isnot expectingthe data withina certain time

· Preservepayload content

Example of theapplication

- voice - streaming video - Web browsing - background down- load of emails

Common Pilot Channel

Pilot Symbol Data (10 symbols per slot)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 Frame = 15 slots = 10 mSec

1 timeslot = 2560 Chips = 10 symbols = 20 bits = 666.667 uSec

Sends the scrambling code of the cell

Used for channel estimation

Design targets: Ec/Io >= -16dB, RSCP >= -105dBm

P-CPICH

Downlink Transport Channels (L2)• Common Transport Channels

– BCH (Broadcast Channel)• Continuous transmission of system and cell information

– PCH (Paging Channel)• Carries control information to UE when location is unknown

– FACH (Forward Access Channel)• Used for transmission of idle-mode control information to a UE

• Dedicated Transport Channels– DCH (Dedicated Channel)

• Carries dedicated traffic and control data to one UE• Used for BLER measurements

Uplink Transport Channels (L2)

• Common Transport Channels– RACH Random Access Channel

• Carries access requests, control information, short data

• Dedicated Transport Channels– DCH Dedicated Channel

• Carries dedicated traffic and control data from one UE• Used for BLER measurements

WCDMA Physical Channels

BaseStation

(BS)

UserEquipment

(UE)

P-CCPCH- Primary Common Control Physical ChannelSCH - Synchronization Channel

CPICH - Common Pilot Channel

Channels broadcast to all UE in the cell

DPDCH - Dedicated Physical Data Channel

DPCCH - Dedicated Physical Control Channel

Dedicated Connection Channels

PICH - Page Indicator Channel

Paging Channels

S-CCPCH - Secondary Common Control Physical Channel

AP-AICH - Acquisition Preamble Indicator Channel

CD/CA-AICH - Collision Detection Indicator Channel

CSICH - CPCH Status Indicator Channel

PRACH - Physical Random Access Channel

AICH - Acquisition Indicator Channel

Random Access and Packet Access Channels

Channels

UE States• Idle mode

– No connection to radio network (No RRC connection established)– This minimizes resource utilization in UE and the network

• CELL_FACH mode– User Equipment (UE) in Connected Mode (has an RRC Connection to radio network) – UE uses the common transport channels RACH or FACH– If the parameter interFreqFDDMeasIndicator = 1, the UE will evaluate cell reselection

criteria on inter-frequency cells (0)

• CELL_DCH mode– User Equipment (UE) in Connected Mode (has an RRC Connection to radio network)– UE uses dedicated channels for transmitting data and signalling

System Information• System parameters are broadcast on BCCH. It has information regarding Idle

Mode Behaviour.

• The System Information elements are broadcast in System Information Blocks (SIB’s). Each SIB contains a specific collection of information.

Idle mode Functions

• PLMN Selection• Cell Selection and

Reselection• Location Area (LA) and

Routing Area (RA) updating• Paging• System Information

Broadcast

Cell Selection

• UE looks for a suitable cell in the selected PLMN and camps on to it

• Cell search procedure– UE acquires slot synchronization using P-SCH– It acquires frame synchronization using S-SCH– Primary scrambling code is obtained from CPICH

• UE then monitors the paging and system information, performs periodical radio measurements and evaluates cell reselection criteria

• Strategies used for the cell selection process:– Initial Cell Selection: UE has no knowledge of the WCDMA radio channels

• UE scans all WCDMA radio frequency channels to find a suitable cell with the highest signal level and read BCCH

• The PLMN is determined from the mcc and mnc in the MIB in BCCH

– Stored Information Cell Selection: UE knows the carrier frequencies that have previously been used

Cell Selection Parameters

• For cell selection criteria the UE calculatesSqual = Qqualmeas - qQualMin (for WCDMA cells)Srxlev = Qrxlevmeas - qRxLevMin – Pcompensation (for all cells)

Where Pcompensation = max(maxTxPowerUL – P,0)P is output power of UE according to class

• Cell selection criteria (S criteria) is fulfilled whenSqual>0 ( for WCDMA cells only)and Srxlev>0

• Recommended valuesqQualMin= -19dBqRxLevMin= -115dBmmaxTxPowerUL = 24

Cell Reselection

• Allows UE’s to move between cells in idle and cell_FACH connected mode

• Always camp on the best cell the UE performs the cell reselection procedure in the following cases:– When the cell on which it is camping is no longer suitable– When the UE, in “camped normally” state, has found a better

neighbouring cell than the cell on which it is camping– When the UE is in limited service state on an acceptable cell

Cell Reselection Parameters

• UE ranks available cells using R criteriaR(Serving) = Qmeas(s) + qHyst(s)R(Neighbour) = Qmeas(n) – qOffset(s,n)

Qmeas is the quality value of the received signal– Derived from the averaged received signal level for GSM cells– Derived from CPICH Ec/Io or CPICH RSCP for WCDMA cells depending on the

value of qualMeasQuantity (2, Ec/Io)

qHyst(s) = qHyst1 when ranking based on CPICH RSCP (4)qHyst(s) = qHyst2 when ranking based on CPICH Ec/Io (4)qOffset(s,n) = qOffset1sn when ranking based on CPICH RSCPqOffset(s,n) = qOffset2sn when ranking based on CPICH Ec/IoThe above two values are 0 for WCDMA cells and 7 for GSM cells

Location and Routing Area updating

• Location Area = The area to which the Core Network sends a paging message for circuit switched.

• Routing Area = The area to which the Core Network sends a paging message for packet switched.

• If the Location Area Identity (LAI) or Routing Area Identity (RAI) read on system information is different to the one stored on the USIM, the UE performs a LA or RA registration update

• Three types of registration update– Normal– Periodic – according to T3212, T3312– IMSI attach/detach - used if att = 1 (1)

• UE sends “attach” or “detach” messages when the UE is powered on or off

Power Control

• Objective

– The Transmitter adapts the output power according to Pathloss

– Goal is that all users should experience the same SIR which corresponds to a target BLER.

– Regulates power output to maintain good connection quality good connection quality

– Minimize UL and DL transmitted power to reduce interference, and increase capacity

Power Control Types

Power Control Types

• 1. Open-Loop Power Control (Initially, No signaling)– Performed in the uplink and downlink to calculate a

minimum starting power for setting up a connection.– Common channels (RACH/FACH)

– UL• UE measure pilot,• read interference level from BCH, determine PL • Transmit at calculated power, • Ramp up power

– DL• BS calculate required power, • Transmit at calculated power, • Ramp up Power

• 2. Outer-Loop Power Control (slow)– maintains the required Block Error Rate (BLER) for a service by modifying

the SIR target– Dedicated channels– If the BLER measured (DL@UE, UL@RNC) is below/ above the minimum

acceptable BLER, • UE/RNC increase/reduce SIR target.• Use the new SIR target for the Inner-loop PC.

• 3. Inner-Loop Power Control UL/DL (fast)– minimizes the power and interference of ongoing connections by

maintaining a minimum SIR.– Dedicated channels– Performed 1500 times per second, – Adjust (up or down) the Tx power to reach the SIR target.

Power Control Types

Uplink Inner Loop Power Control

• If estimated UL SIR >= target UL SIR, then RBS send power DOWN command• If estimated UL SIR < target UL SIR, then RBS send power UP command• UE always power UP/DOWN in steps of 1 dB• In SHO:

• if all radio links in active set send power UP command, the UE powers UP by 1 dB• If at least one radio link in the active set sends power DOWN command, the UE powers DOWN by

1 dB.

Handover Types• Soft Handover

– In DCH mode, MS has concurrent traffic connections with two BS’s• Softer Handover

– Similar to Soft Handover, but between two sectors of the same cell• Inter-Radio Access Technology (IRAT) Handover

– CS Handover from a WCDMA system to another system– Traffic and Control Channels are Disconnected and must be Reconnected (hard handover)

• Inter-frequency Handover (IFHO)– When the MS must change WCDMA carrier frequency during the Handover– Traffic and Control Channels are Disconnected and must be Reconnected (hard handover)

• Inter-RAT Cell Change– manages PS UE mobility between cells using WCDMA RAN and cells using GSM/GPRS

• Cell Reselection– manages UE mobility between WCDMA cells with same frequency, different frequency and

between WCDMA cells and GSM/GPRS cells, when the UE is in idle mode or CELL_FACH state.

WCDMA Handover Scenarios

RNS

RNC

RNS

RNC

Node B Node B Node B Node B

Iu Iu

Iur

Iub IubIub Iub

Inter-Node(Soft)

Intra-Node(Softer)

Inter-RNS(Soft with Iur;

Hard with no Iur)

UTRAN

Core Network

Soft Handover Key Points

• When fast power control is used, soft handover is essential– Allows MS to operate in most conservative power

control mode• Soft handover provides performance benefits

– “Seamless” coverage at cell fringes– Handover may be less noticeable to the user

• Soft handover also degrades system capacity– Uses redundant physical layer resources from adjacent

or overlapping cells

Measurement Handling

MeasurementHandling

RNC

MeasurementControl

Message• List of cells to measure on• Measurement criteria

• Active set (SHO)• Monitored set (cells measured by UE but which does

not belong to active set (Intra/Inter frequency and Inter-RAT frequencies)

MeasurementReport with EVENT

Measurement Reporting

1. Measure2. Filter3. Apply quality offsets to cells individualOffset4. Compare with measurement criterion5. Send measurement report with EVENT (if occurred)

f1 f1f2

WCDMA Soft Handover Process

• One finger of the RAKE receiver is constantly scanning neighboring Pilot Channels.

• When a neighboring Pilot Channel reaches the t_add threshold, the new BS is added to the active set

• When the original Base Station reaches the t_drop threshold, originating Base Station is dropped from the active set

Monitor Neighbor BS Pilots Add Destination BS Drop Originating BS

GSM handover and cell reselection Inter-frequency handover and cell reselection

Transfer ongoing calls to another RAT or WCDMA frequency

Benefits – Maintains intersystem mobility (retained UE calls and PDP contexts)– Use GSM networks as coverage fall back– Use WCDMA network to offload GSM network at high traffic load– Maintains UE radio connections when radio environment requires

move to another frequency

IRAT HO Issues

• High percentage of time in Compressed Mode

• Frequent IRAT Handovers

• Leaving UMTS too early (increase GSM load)

• Leaving UMTS too late (dropped call)

Capacity Management Functions

• Objective– Controls the load in the cells and enables the system to

provide the requested QoS and coverage for individual UE connections.

• Admission Control– responsible for controlling the utilization of dedicated

monitored resources by accepting or refusing requests for usage of these resources

• Congestion Control– responsible for detecting and resolving overload situations

on certain dedicated monitored resources

Capacity Management Monitors

DL code utilization

Compressed Mode & DL spreading

DL code tree utilization (SF for users and CCH’s)

Provides info about # of connections with a certain SF. This adds information about DL channelization usage. Also measure # of connections in compressed mode.

DLChannelizationCodes monitor

Histogram monitor

DL transmitted power

Air interface Speech Equivalent

(ASE)

UL received total wideband power

(RTWP)

DL transmitted carrier power

monitor

Downlink transmitted power, which is affected by # of users, the type of connections and radio conditions in the cell

ASE monitorEstimates UL and DL air-interface usage per radio link.

Total received UL power, i.e. information about UL interference.

Measures

RTWP monitor

RBS HW utilization Monitors the available HW resources (channel elements) in the RBS)

RBS HW utilization monitor

Congestion resolve handling

CongestionControl

AdmissionControl

Cell(s)

“UL Congestion”Block new guaranteed non–HO andnew non-guaranteed non-HO requests

CongestionControl

AdmissionControl

“DL Congestion”

Block ALL new requests

Start congestion resolve actions in the cell

HSDPA

HSDPA Overview

Shared Channel Transmission– Dynamically shared in time domain

Higher-order Modulation– 16QAM (option) in complement to QPSK

2 ms

Short Transmission Time Interval (2 ms)– Reduced round trip delay

Fast Hybrid ARQ with Soft Combining– Reduced round trip delay

Fast Radio Channel Dependent Scheduling– Round Robin scheduling of users on 2 ms time basis– Proportional fair as separate option

Fast Link Adaptation– Rate adapted to radio conditions on 2 ms time basis

Release 99 Packet Data

Release 99 Downlink Limitations

High Speed Downlink Packet Access

R99 - HSDPA

HSDPA Channels

Channels For HSDPA

Downlink Uplink

HS-SCCH– Control signaling to the mobile(s)

scheduled in a 2 ms interval– One (or a few) HS-SCCH per cell– SF=128

HS-DPCCH– ACK/NAK to inform the Node B

whether a retransmission is required or not

– Channel Quality Indicator to continuously provide the Node B with channel quality knowledge used for scheduling and link adaptation

– One HS-DPCCH per HSDPA-enabled terminal in the cell

– SF=256

HS-DSCH– Supports link adaptation, hybrid ARQ

and scheduling– Always associated with a DPCH– Never in soft handover– Mapped to one or several

channelization codes of SF=16

HS-DPCCH

HS-SCCH

Code Allocation

Node B Scheduler

HSDPA Coverage

CQI

CQI Mapping Table

– HS-DSCH: High speed downlink shared channel– A-DCH DL: Associated dedicated

channel downlink• Voice/video (multi-RAB)• Release 99 signaling

– A-DCH UL: Associated dedicatedchannel uplink

• UL data transmission• TCP ACK/NACK• Voice/video (multi-RAB)• Release 99 signaling

– HS-SCCH: High speed shared control channel• HARQ signaling

– HS-DPCCH: High speed dedicated physical control channel

• HARQ ACK/NACK• CQI: channel quality indicator

HSDPA Channel overview

RNC

Iub Iub

Iu

Associated Dedicated channels

RNC

Iub Iub

Iu

Associated Dedicated channels

HSDPA Available Power

Common Channel Power (Ex: 14% for 40 W RBS)

R’99 DCH Power

MaxTransmissionPower

MaxTransmissionPower - hsPowerMargin-5%

Available HS Power

Time

• Not all the available HS power is always used for transmission.

• It is only used the amount required to fullfill the maximum TF that can be transmitted according to channel conditions

Carrier Power

HSDPA CQI

• The Channel Quality Indicator is a recommended transport block size or, equivalently, a recommended data rate.

• Channel Quality Indicator comes from C/I measurements on CPICH channel

•To avoid negative system impact due to inaccurate CQI reports, CQI adjustment is done

– Different UEs can report different CQI values for a given quality– CQI adjustment algorithm in the RBS– Processes the ACKs and NACKs received from the UE– Determines if the UE is overestimating or underestimating the channel quality– Strives to achieve a block error rate of 10% for the initial transmission

HSDPA Phase2

TTI = 2 ms

16QAM

Shared Multi-codetransmission (15 codes)

Link Adaptation

Scheduling

Features

Hybrid ARQ with Soft Combining in RBS

HSPA Evolution

Enhanced Uplink Phase1

Benefit

Higher Peak rates: 1.45 Mbps

Higher Capacity: +50%

Reduced Latency: <60 ms

TTI = 2 / 10 ms

Multi-codetransmission (1-4 codes)

Hybrid ARQ with Soft Combining in RBS

Scheduling

Features

TEMS Drop Calls

Missing Neighbor

Poor Coverage

Poor UL Coverage

UE reaches Max Power

Bad Radio Environment (Pilot Pollution)

Congestion

Not Radio

Equipment Fault

Initial Tuning Steps

Baseline Tuning