WO BT1002 E01 1 UMTS Key Technologies

UMTS Key Technologies

ZTE University

Content

RAKE Receiver Handover Control Compressed Mode Admission Control Load Control Code Resource Allocation Capacity Features

Multi-path characteristics of radio channel

Electromagnetic propagation: direct radiation 、 reflection 、 diffraction and scattering

Signal attenuation: Path loss ： Loss of electromagnetic waves in large scope of the

spread reflects the trend of the received signal in the spreading 。 Slow fading ： Loss because of being blocked by the building and

hill in the propagation path Fast fading ： Electromagnetic signals rapidly decline in a few

dozens wavelength ranges

Description of Fast fading distribution Rayleigh distribution ： non line-of –sight(NLOS) transmission Rician distribution ： line-of –sight(LOS) transmission

Multi-Path Effects

receiving signalreceiving signal

timetime

strengthstrength

00

sending signalsending signal

Frequency Frequency off-setoff-set caused by the movement of caused by the movement of

mobile mobile ，， that is Doppler effectthat is Doppler effect

Frequency Frequency off-setoff-set caused by the movement of caused by the movement of

mobile mobile ，， that is Doppler effectthat is Doppler effect

Sending signal Accepting signal

Interference Interference

0dB

Sending signal

-25dB

Accepting signal

fadingfading

0 + Sending signal Accepting signal

delaydelay

0 2 3 + Sending signal Accepting signal

ditheringdithering

Characteristics of Radio Propagation

RAKE Receiver can effectively overcome the multi-path RAKE Receiver can effectively overcome the multi-path

interference, consequently improve the receiving performance.interference, consequently improve the receiving performance.

RAKE Receiver can effectively overcome the multi-path RAKE Receiver can effectively overcome the multi-path

interference, consequently improve the receiving performance.interference, consequently improve the receiving performance.

RAKE Receiver

The multi-path signals contain some useful energy , therefore the UMTS receiver can combine these energy of multi-path signals to improve the received signal to noise ratio.

RAKE receiver adopts several correlation detectors to receive the multi-path signals, and then combines the received signal energy.

RAKE Receiving

d1 d2

t t t

d3

transmitti

ng

Receivin

gRake

combinationnoise

Multi-finger receiver

Traditional receiver Multi-path signals are treated as interference. The receiving performance will decline because of the

Multi-address Interference (MAI).

Precondition of Multi-finger receiver Multi-finger receiver utilizes the Multi-path Effect. Multi-finger signals can be combined through relative

process Multi-finger time delay is larger than 1 chip interval,

which is 0.26us=>78m.

Multi-finger receiver

receivertransmitter

coding decoding

Direct signal

Reflected signal

Dispersive time < 1 chip interval

Multi-finger receiver can’t supply multi-finger diversity

decodingDirect signal

Reflected signaltransmitter receiver

Dispersive time > 1 chip interval

Multi-finger receiver can supply multi-finger diversity, signal gain is improved

coding

RAKE Receiving

receiverreceiver

Single receiving

Single receiving

Single receiving

searcher calculatecalculate

combining

tt

s(t) s(t)

signal

RAKE Receiving overcomes multi-finger interference, improves receiving performance

Combination of Multi-fingers

Maximal ratio combining (MRC)

at each time delay phase shifting by adding

Finger 1

Finger 2

Finger 3

Content


What’s ？

When UE is moving from the coverage area of one site to another, or the quality of service is declined by external interference during a service, the service must be handed over to an idle channel for sustaining the service.

Handover is used to guarantee the continuity of service.

Handover is a key technology for mobile networking.

Category of Handover

Intra-RNC, inter-Node B Inter-RNC

Soft handover (SHO)

Same Node B, Inter-sector

Softer handover

Intra-frequency Inter-frequency Inter-system (UMTS&GSM) Inter-mode (FDD&TDD)

Hard handover (HHO)

UMTS system support

multiple handover technology

Handover Demonstration

Hard

Handover

Soft

Handover

A

B

C

A

B

C

A

B

C

A

B

C

A

B

C

A

B

C

Soft Handover/Softer Handover

Soft Handover

Soft-Softer Handover

Softer Handover

Hard Handover

During the hard handover procedure, all the old radio links with the UE are abandoned before new ones are established, so there must be service interruption during the HHO.

Hard handover may occur in the following main cases

When the UE is handed over to another UTRAN carrier, or another technology mode.

When soft handover is not permitted (if O&M constraint)

Hard Handover

Node B

SRNCRNC or BSC

CN

Node B or BTS

Soft/Softer Handover

The soft/softer handover allows to migrate from one cell to another without service interruption or without deleting all old radio links.

UE can connecte to more than one cell simultaneously and take benefit from the macro-diversity.

Soft Handover Softer Handover

CN CN

Iur

The two Node Bs may belong to the

same RNC

The two Node Bs may belong to the Same RNC


SRNC DRNC

CN

Node B

SRNC

CN


Node B

CN

UMTS General Handover Trilogy

Measurement Control UTRAN demands the UE to start measurement through

issuing a measurement control message.

Handover decision UTRAN makes the decision based on the measurement

reports from UE. The implementation of handover decision is various for different vendors. It impacts on the system performance critically.

Handover execution UTRAN and UE execute different handover procedure

according to the handover command.

(A) RNC sends measurement control message to UE (Measurement Control)

(B) UE starts measurement task with the parameters included in the message, and reports measurement results （ Measurement Report）

(C) RNC stores the measurement results according to frequencies and cells

(D) RNC Estimates the quality of each carrier (including intra-frequency and inter-frequency)

(E) Quality

Decision

(G) Allocate resource in target cell, prepare to execute handover

(F) maintain the active set and monitored set

(H) Allocate resource in target cell, prepare to execute handover

Current carrier has good quality

Other system has good quality

Other carrier has good quality

（ I ） If handover is required, RNC sends handover command with target cell to UE

Handover Flows

General Procedure of Handover Control (I)

Measuring The measurement objects are decided by RNC. Usually,

either Ec/Io or RSCP (Received Signal Code Power) of P-CPICH channel is used for handover decision.

ZTE RNC adopts Ec/Io measurement, because Ec/Io embodies both the received signal strength and the interference. The relation of Ec/Io and RSCP is shown as follows:

Ec/Io ＝ RSCP/RSSI

In the above equation ， RSSI （ Received Signal Strength Indicator ） is measured within the bandwidth of associated channels

Filtering The measurement results should be filtered before being

reported. Measurement filtering can be regarded as a low pass filtering procedure. The following equation is applied for filtering.

Fn=(1-a)Fn-1 ＋ a*Mn

Variants definition ： Fn ： filtered measurement result ； Fn-1 ： last filtered measurement result ； Mn ： latest Ec/Io or RSCP measurement result received from

physical layer; a = 1/2(k/2), k means the “Filter coefficient”, which is included in the

Measurement Control message. It is decided by the UTRAN. F0 is initialized by the first measurement result M1.

General Procedure of Handover Control (II)

General Procedure of Handover Control (III)

Reporting Period report triggered handover

Base on the filtered measurement result

Event report triggered handover Base on the event

Soft Handover

Hard Handover

Period

Event

Measurement result filtered in

UE

Event decided in RNC

Handover decided in RNCMeasurement result filtered in UE Event decided in UE

Handover decided in RNC

General Procedure of Handover Control (IV)

Handover algorithm All the handover algorithms including soft handover,

hard handover and so on are implemented on the event decision made according to the measurement reports.

Events defined in 3GPP specifications Intra-frequency events ： 1A~1F Inter-frequency events ： 2A~2F Inter-RAT events ： 3A~3D

Note: RAT is short for “Radio Access Technology”, e.g. UMTS&GSM

Concepts Related to Handover

Active Set: A set of cells that have established radio links with a

certain mobile station. User information is sent from all these cells.

Monitored Set: A set of cells that are not in the active set but are

monitored according to the list of adjacent cells assigned by the UTRAN.

Detected Set: A set of cells that are neither in the active set nor in the

monitor set.

Soft handover event

Event Description

1AQuality of target cell improves, entering a report range of relatively activating set quality

1BQuality of target cell decreases, depart from a report range of relatively activating set quality

1CThe quality of a non-activated set cell is better than that of a certain activated set cell

1D Best cell generates change

1EQuality of target cell improves, better than an absolute threshold

1FQuality of target cell decreases, worse than an absolute threshold

An Example of SHO Procedure

Pilot Ec/Io of cell 1

time

PilotEc/Io

Connect to cell1 Event 1A Event 1C Event 1B （ add cell2 ）（ replace cell1 with cell 3 ）（ remove cell3 ）



⊿ t ⊿ t ⊿ t

RNS Relocation

Core NetworkCore Network

Serving RNS

Target RNS

Serviing RNS

Target RNS

Iu Iu

Iur

RNSRadio Network Sub-system

RNS relocation can : Reduce the Iur traffic significantly Enhance the system adaptability

Hard Handover

Hard handover measurement is much more complex for UE than soft handover measurement.

Inter-frequency hard handover requires UE to measure the signal of other frequencies.

UMTS employs compressed mode technology to support inter-frequency measurement.

Content


Purpose of Compressed Mode

In order to support inter-frequency and inter-RAT handover, UE is required to perform inter-frequency and Inter-RAT measurement periodically.

The UE with one transceiver does not have the opportunity to perform inter-frequency measurement during the service period (especially the voice call) , because the transceiver is busy in transmitting and receiving the signals all the time.

Compressed mode can provide idle slot based transmission time window, which can be used for inter-frequency measurement, for the UEs in connected state, e.g. CELL_DCH.

Compressed Mode

Compressed Mode Transmission Diagram

Transmit gaps（Maximum 7 slots = 4.7ms） 1 frame（10ms）

10ms

Generation of Compressed Mode Frame

Puncturing Lower the symbol rate of physical channel when

processing the rate matching procedure

SF halving Employ half SF, e.g. employ SF64 to replace

SF128

High layer scheduling Decrease the bit rate from up layer

Content


Admission Control

The admission control is employed to admit the access of incoming call. Its general principal is based on the availability and utilization of the system resources.

If the system has enough resources such as load margin, code, and channel element etc. the admission control will accept the call and allocate resources to it.

Purpose of Admission Control

When user initiates a call , the admission control should implement admission or rejection for this service according to the resource situation.

The admission control will sustain the system stability firstly and try the best to satisfy the new calling service’s QoS request, such as service rate, quality (SIR or BER), and delay etc. basing on the radio measurement.

Admission control is the only access entry for the incoming services, its strategy will directly effect the cell capacity and stability, e.g. call loss rate, call drop rate.

Admission Control in Uplink

Itotal_old+ΔI >Ithreshold

The current RTWP (Received Total Wide Power) value of cell, which is reported by Node B

AccessThreshold

Interference capacityService priorityReserved capacity for handover

Iown-cell

0~N

Iother-cell

The forecasted interference including the delta interference brought by the incoming service is calculated by the admission algorithm, and its result depends on the QoS and transmission propagation environment

Different ultimate user numbers Different interference threshold under different ultimate

user number conditions Different ultimate throughputs

Quantity of Subscriber

Quantity of Subscriber-- The Total Bandwidth Received by Node B

Th

e T

ota

l Ba

nd

wid

th P

ow

er

Re

ceiv

ed

by

No

de

B (

dB

m)

Ultimate Situation for different service rateThroughput

Throughput -- The Total Bandwidth Received by Node B

The

Tot

al B

andw

idth

Pow

er R

ecei

ved

by N

ode

B (

dBm

)Admission Control in Uplink

Admission Control in Downlink

Ptotal_old+△P>=Pthreshold Access Threshold

The forecasted TCP value including delta power required for the incoming service is calculated by the admission algorithm, and its result depends on the QoS and transmission propagation environment.

The current TCP value of cell, which is reported by Node B（ Transmitted Carrier Power*Pmax ）

Max TCP of cellService priorityReserved capacity for handover


Th

e T

otal

Tra

nsm

issi

on P

ower

(dB

m)

Red ： low speed serviceBlue ： high speed service

The above figure illustrates the relation between ultimate user number The above figure illustrates the relation between ultimate user number

corresponds to different service rate and distance under equidistant corresponds to different service rate and distance under equidistant

distribution conditiondistribution condition

The above figure illustrates the relation between ultimate user number The above figure illustrates the relation between ultimate user number

corresponds to different service rate and distance under equidistant corresponds to different service rate and distance under equidistant

distribution conditiondistribution condition

Admission Control in Downlink

The service can be either one-direction or bi-direction type. For bi-direction service, it is admitted only after both uplink and downlink are admitted.

Admission control is the only access entry for the incoming services, its strategy will directly effect the cell capacity and stability, e.g. call loss rate, call drop rate.

Admission Control Analysis

Content


Load control

The purpose of load control is to keep the

system load under a pre-planned threshold

through several means of decreasing it, so as to

improve the system stability.

The speed and position

changing of UE may

worsen the wireless

environment.

Increased transmitted

power will increase the

system load.

Purpose of Load Control

Overload control

Serious overload threshold

Overload recovery threshold

Admission control threshold

Common overload threshold

Cell load

Overload control

Normal state

Common overload

state

Serious overload

state

4. The load is smaller than the overload recovery threshold

3. The load exceeds the serious overload threshold

6. The load is smaller than the serious overload threshold. but greater than the common overload threshold

5. The load exceeds the serious overload threshold.

1. The load exceeds the common overload threshold

2. The load is smaller than the overload recovery threshold

Load Control Flows

Start

DecisionLight loaded Over loaded

Normal loaded

1.Handover in andaccess are forbidden2. TCP increase isforbidden3. RAB service ratedegrade4. Handover out5. Release call (call drop)

1. Handover in and access are allowed2. Transmitted code power (TCP) increase is allowed3. RAB service rate upgrade is allowed

1. Handover in and access are allowed2. TCP increase is allowed

Load Control in Uplink

Triggers RTWP (Received Total Wide-band Power) value from

measurement report exceeds the uplink overload threshold; Admission control is triggered when rejecting the access of

services with lower priority due to insufficient load capacity in uplink.

Methods for decreasing load Decrease the target Eb/No of service in uplink; Decrease the rate of none real time data service; Handover to GSM system; Decrease the rate of real time service, e.g. voice call; Release calls.

Methods for increasing load Increase the service rate.

Load Control in Downlink

Triggers TCP (Transmitted Carrier Power) value from measurement report

exceeds the downlink overload threshold; Admission control is triggered when rejecting the access of

services with lower priority due to insufficient load capacity in downlink.

Methods for decreasing load Decrease the downlink target Eb/No of service in downlink; Decrease the rate of none real time data service; Handover to coverage-shared light loaded carrier; Handover to GSM system; Decrease the rate of real time service, e.g. voice call; Release calls.

Methods for increasing load Increase the service rate.

Cell breathing is one of the means for load control

The purpose of cell breathing is to share the load of hot-The purpose of cell breathing is to share the load of hot-

spot cell with the light loaded neighbor cells, therefore to spot cell with the light loaded neighbor cells, therefore to

improve the utilization of system capacity.improve the utilization of system capacity.

The purpose of cell breathing is to share the load of hot-The purpose of cell breathing is to share the load of hot-

spot cell with the light loaded neighbor cells, therefore to spot cell with the light loaded neighbor cells, therefore to

improve the utilization of system capacity.improve the utilization of system capacity.

Cell Breathing Effect

Example for load control

Cell Breathing EffectCell Breathing Effect With the increase of activated

terminals and the increase of high

speed services, interference will

increase. The cell coverage area will shrink. Coverage blind spot occurs Drop of call will happen at the edge

of cell

Coverage and

capacity are

interrelated

Content


UMTS Code Resource

Channelized Code (OVSF code) Uplink Channelized Code Downlink Channelized Code

Scrambling Code Uplink Scrambling Code Downlink Scrambling Code

Function of OVSF Code

OC1, OC2OC3, OC4

OC5, OC6, OC7

OC1 , OC2, OC3OC1, OC2

OC1, OC2, OC3, OC4

Uplink: distinguish different radio channels from the same UE.

Downlink: distinguish different radio channels from the same NodeB.

Function of Scrambling code

Downlink: distinguish different Cells Uplink: distinguish different UEs

PN3 PN4

PN5 PN6

PN1 PN1

Cell Site “1” transmits using PN code 1

PN2 PN2

Cell Site “2” transmits using PN code 2

Why Code Resource Planning?

The OVSF (Orthogonal Variable Spreading Factor) code tree is a scarce resource and only one code tree can be used in each cell. In order to make full use of the capacity, and support as many connections as possible, it is important to plan and control the usage of channel code resource.

Downlink scrambling code allocation should be planned to avoid the interference between neighboring cells.

The uplink scrambling codes are sufficient, but RNC should plan the codes to use for avoiding allocating same code to different users in inter-RNC handover scenario.

Code Resource Planning

The uplink and downlink scrambling code can be planned easily by computer.

The uplink channelized code does not need planning, for every UE can use the whole code tree alone.

Therefore, only the downlink channelized code is planned with certain algorithm in RNC.

Each cell has one primary scrambling code, which correlates with a channel code tree. All the users under this cell share this single code tree, so the OVSF code resource is very limited.

The downlink channelized code tree is a typical binary tree with each layer corresponds to a certain SF ranging from SF4 to SF512.

SF = 1 SF = 2 SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,4,0 =(1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

Generation of Channelized Code

OVSF Code Tree

SF=8

SF=32

SF=16

Channelized Code Characters

Code allocation restriction ： The code to be allocated must fulfill the condition that its

ancestor nodes including from father node to root node and offspring nodes in the sub tree are not allocated;

Code allocation side effect ： The allocated node will block its ancestor nodes and

offspring nodes, thus the blocked nodes will not be available for allocation until being unblocked .

Strategy of Channelized Code Allocation

Full utilization The fewer the blocked codes, the higher code tree

utilization rate.

Low Complexity Short code first.

Allocate codes for common channels and physical shared channels prior to dedicated channels. Guarantee the code allocation for common physical

channels.

Apply certain optimized strategy to allocate codes for downlink dedicated physical channels.

An Example of Code Allocation

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

SF = 4

SF = 8

SF = 16

SF = 32

SF = 4

SF = 8

SF = 16

SF = 32

Red spots represent the codes that have been allocated；Green spots represent the codes that are blocked by the allocated offspring codes；Blue spots represent the codes that are blocked by the allocated ancestor codes;Black spots represent the codes that to be allocated;

Choose one code from

three candidates

Planning of downlink scrambling code

PN1

PN2

PN3PN7

PN6 PN4

PN5

PN7

PN6 PN4

PN5

PN1

PN2

PN3

PN1

PN2

PN3PN7

PN6 PN4

PN5

PN1

PN2

PN3PN7

PN6 PN4

PN5

PN1

PN2

PN3PN7

PN6 PN4

PN5 PN1

PN2

PN3PN7

PN6 PN4

PN5

Content


Capacity of UMTS

UL capacity is restrained by interference

DL capacity is restrained

by the power of NodeB

Power Rising

Power rising occurs because of the Multiple Access Interference (MAI) resulting from the non-orthogonal code channels.

UMTS network Meeting Room

Code channel transmit talk with dialects Channel power voice tone Promised channel quality listen clearly Channel power rise voice tone rise Power climb voice climb Collapse over the range can not hear each other

Power Rising


Quantity of Subscriber-- The Total Bandwidth Received by Node B

Th

e T

ota

l Ba

nd

wid

th P

ow

er

Re

ceiv

ed

by

No

de

B (

dB

m)

Capacity of UMTS System

Under the circumstance of single services:

=

=

=

Capacity of UMTS System

…...

X Y Z+ +

Under the circumstance of mixed services ：

UMTS Capacity Features

UMTS capacity feature UMTS capacity is Soft Capacity.

The Concept of Soft Capacity The system capacity and communication quality are

interconvertible. Different services have different capacity. Different proportion of services have different capacity

for mixed services. The capacity is also restricted to the allocation of code

resource.

Different combination of service has different capacity

Different service has

different capacity

Concept of Soft Capacity

System capacity and QoS can be interconvertedSystem capacity and QoS can be interconverted

Quality

Quality C

over

age

Cov

erag

e

CapacityCapacity

All the key technologies adopted are used to try to All the key technologies adopted are used to try to

achieve the optimal balance of the three factorsachieve the optimal balance of the three factors

All the key technologies adopted are used to try to All the key technologies adopted are used to try to

achieve the optimal balance of the three factorsachieve the optimal balance of the three factors

Crucial Factors for UMTS Network (CQC)

Coverage and Capacity

UMTS performance is determined by such factors as ： Number of users Transmission rate Moving speed Wireless environment

indoors Outdoors

The radius of cell depends on such factors as: Local radio conditions (local interference) Traffic in neighbouring cells (remote interference)

Cell Radius decrease according to the Increase of user number

Coverage/capacity VS Data Rate

Higher data rate needs higher power High data rate transmission is only available nearby the

station

>12.2 kbps

>64 kbps

>384 kbps

>144 kbps

Coverage decrease

Subscriber num increase

DL/UL: Add carrier six sectors

DL/UL: Add carrier six sectors

UL Tower Mounted Amplifier (TMA) 4 Rx Div OTSR

UL Tower Mounted Amplifier (TMA) 4 Rx Div OTSR

DL transmission diversity (Tx Div) high power amplifier

DL transmission diversity (Tx Div) high power amplifier

Add basestation

“last choice”

Add basestation

“last choice”

Optimization methods

To overcome Cell Breathing Effect caused by increased traffic and meet different requirements for capacity and coverage in different environment, following solutions can be applied:

Factors Impact on UMTS capacity

RAKE Receiver

The advanced receiving and baseband processing technology is introduced to overcome the fast fading

Power Control Reducing interference, saving power and Increasing capacity

Handover Control

Impacting the capacity through applying different proportion and algorithm of soft handover

Admission Control

Admitting a connection base on the load and the admission threshold of planned capacity

Load Control Monitoring system load and adjusting the ongoing services to avoid overload

OVSF Code The Allocation of codes impacts the maximum number of simultaneous connections.

Wireless Environment

Wireless environment such as interferences, UE position and mobility etc. can influent the cell capacity

Factors affects UMTS Capacity

WO BT1002 E01 1 UMTS Key Technologies

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Transcript of WO BT1002 E01 1 UMTS Key Technologies