1 umts key technologies-80

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 signal

time

strength

0

sending signal

Frequency off-set caused by the movement of mobile ，that

is Doppler effect

Sending signal Accepting signal

Interference

0dB

Sending signal

-25dB

Accepting signal

fading

0 +


delay

0 2 3 +


dithering

Characteristics of Radio Propagation

RAKE Receiver can effectively overcome the multi-path

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

d1d2

t t t

d3

transmitting ReceivingRake

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

decoding

Direct signal

Reflected signaltransmitter receiver

Dispersive time > 1 chip interval

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

coding

RAKE Receiving

receiver

Single

receiving

Single

receiving

Single

receiving

searcher calculate

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

RAKE Receiver

Handover Control

Compressed Mode

Admission Control

Load Control


Capacity Features

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 (3G&2G)

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

SRNC

RNC 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


SRNCDRNC

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.

General Procedure of Handover Control (I)

Measuring

The measurement objects are decided by RNC. Usually,

either Ec/No or RSCP (Received Signal Code Power) of P-

CPICH channel is used for handover decision.

ZTE RNC adopts Ec/No measurement, because Ec/No

embodies both the received signal strength and the

interference. The relation of Ec/No and RSCP is shown as

follows:

Ec/No ＝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 RNC

Measurement 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.

Configuring Priority for Each Cell

Source Cell

Priority 0

Priority 1

Priority 2

Tactics of Deleting Neighboring Cells in Excess of 32

The protocol specifies the upper limit of co-frequency

neighboring cell quantity to be 32 (including source

cells). When the UE is in the macro diversity state, the

quantity of neighboring cells of multiple cells in the

macro diversity may exceed the upper limit. Therefore,

a tactic is required to delete the excessive neighboring

cells. The tactics are: combining and adjusting priority

levels, selecting the cell among the cells of the same

priority, and deleting excessive neighboring cells.


Combining priority levels

If a cell is adjacent to multiple cells in an active set, the cell

may have different priority levels configured by the

background when it is adjacent to different cells. In this case,

the multiple priority levels will be combined, and the highest

priority level among them will apply.


Updating the Adjacent Cell List and Deleting Neighboring

Cells in Excess of 32 If there are more than 32 neighboring cells in the neighboring cell

list of an active set, the neighboring cells will be arranged from the

high priority level to the low priority level. The cells subsequent to

the 32nd cell will be placed into the neighboring cell reservation list.

When triggering event 1a, 1b, 1c or 1d, the UE updates the priority

level of neighboring cells in the neighboring cell list. After event 1b

occurs, if there are less than 32 neighboring cells in the

neighboring cell list, the UE will select the neighboring cells from

the high priority level to the low priority level in the neighboring cell

reservation list, and put the selected cells into the neighboring cell

list. The quantity of cells that can be selected is: min (32 – quantity

of cells existent in the neighboring cell list, quantity of cells in the

neighboring cell reservation list).

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

Pilot

Ec/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

RNSTarget

RNS

Serviing

RNSTarget

RNS

Iu Iu

Iur

RNS

Radio 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

RAKE Receiver

Handover Control

Compressed Mode

Admission Control

Load Control


Capacity Features

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.

Content

RAKE Receiver

Handover Control

Compressed Mode

Admission Control

Load Control


Capacity Features

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

Access

Threshold

Interference capacity

Service priority

Reserved 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 B

an

dw

idth

Po

we

r R

ece

ive

d b

y N

od

e B

(d

Bm

)

Ultimate Situation for different service rate

Throughput

Throughput -- The Total Bandwidth Received by Node B

Th

e T

ota

l B

an

dw

idth

Po

we

r R

ece

ive

d b

y N

od

e B

(d

Bm

)

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 cell

Service priority

Reserved capacity for

handover


Th

e T

ota

l T

ran

sm

issio

n P

ow

er

(dB

m)

Red：low speed service

Blue：high speed service

The above figure illustrates the relation between ultimate user number

corresponds to different service rate and distance under equidistant

distribution 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

RAKE Receiver

Handover Control

Compressed Mode

Admission Control

Load Control


Capacity Features

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 and

access are forbidden

2. TCP increase is

forbidden

3. RAB service rate

degrade

4. Handover out

5. Release call (call drop)

1. Handover in and access

are allowed

2. Transmitted code power

(TCP) increase is allowed

3. RAB service rate

upgrade is allowed

1. Handover in

and access are

allowed

2. 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-

spot cell with the light loaded neighbor cells, therefore to

improve the utilization of system capacity.

Cell Breathing Effect

Example for load control

Cell 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

RAKE Receiver

Handover Control

Compressed Mode

Admission Control

Load Control


Capacity Features

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, OC2

OC3, OC4

OC5, OC6, OC7

OC1 , OC2, OC3

OC1, 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

RAKE Receiver

Handover Control

Compressed Mode

Admission Control

Load Control


Capacity Features

Capacity of UMTS

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 B

an

dw

idth

Po

we

r R

ece

ive

d b

y N

od

e B

(d

Bm

)

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

Concept of Soft Capacity

System capacity and QoS can be interconverted

Capacity

All the key technologies adopted are used to try to

achieve 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

UL

Tower Mounted Amplifier (TMA)

4 Rx Div

OTSR

DL

transmission diversity (Tx Div)

high power amplifier

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 ControlMonitoring 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

1 umts key technologies-80

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