UMTS Postlaunch Opt

8/13/2019 UMTS Postlaunch Opt

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UMTS Network Post-launchOptimisation and Network Evolution

O056


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Factors Limiting Capacity

Cell Throughput is given by the simplified expressions for pole

capacity in kbps multiplied by the loading factor

Crucial parameters are Eb/No, inter-cell interference i,

orthogonality and loading factor (which is affected by the

Noise Rise limit).

Capacity Limit ing Factors

iN

E

iN

E

b

b

1

3840

1

3840

0

0

Uplink

Downlink


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Factors Limiting Capacity: NR limit

NR limit on uplink is directly linked to loading factor:

NR limit appears in link budget and hence affects coverage prediction.

If a network is planned so that continuous coverage would be provided

with all cells simultaneously at NR limit, then probability suggests that

coverage is over-dimensioned.

Coverage could be planned for a NR value 1 to 2 dB below the limit

but this is often used as a comfort factor margin.

Failures will then be split between Eb/No and NR.


10101);1log(10NR

NR


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Noise Rise vs. Throughput

0.00

5.00

10.00

15.00

20.00

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

Throughput (x100kbps)

NoiseRise

Series1



Steep slope -unstable

Shallow slope -stable

However, if NR is allowed to reach very high values (e.g.> 7 dB)

there is concern that the network could become unstable.

Initially, it is expected that NR will be limited to a maximum of, say, 6

dB until confidence in this approach is gained.


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Factors Limiting Capacity: FRE

Frequency re-use efficiency is the name given to theproportion of received power that comes from a cells ownusers rather than from all users including other cells.


11

1

1

cellintra

cellinter1

1

cellintercellintra

cellintra

FREi

iFRE

Frequency re-use efficiency is a useful term as it variesbetween zero and 1 as idrops from infinity to zero.


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The ideal situation is where the receiving antenna can onlysee its own users but not those of other cells. i.e. FRE = 1

The power from neighbouring mobiles close to the cell bordercause the biggest problems.


High power mobiles close to

Cell border cause FRE reduction


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A large cell serving a low subscriber density surrounded byseveral smaller cells serving high subscriber densities willexperience a low value of FRE.


A Large cell will experience low FREBecause it is surrounded by

many users of other cells


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Hotspots near the cell border will cause more problems thatevenly distributed neighbouring cells

A quantitative analysis is not always possible. A simulatoris extremely valuable in helping to develop a feel for theseriousness of potential problems.


Hot spots near cell border cause

FRE reduction


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Increasing FRE: the main weapon is to down-tiltantennas.

Overlap of coverage cannot be too small otherwise handover will fail. However, large overlaps will lead to lowFRE.

This is most effective when there is a large anglebetween the line from the antenna to the cell edge andthe horizontal.

In the case of large cells, planning to avoid hotspots nearthe cell border will reduce the incidence of low FRE.



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Factors Limiting Capacity: Eb/N0

High capacity levels depend on low levels of Eb/No being

used. ( Note BER must be acceptable ). Achieving this relies on accurate, fast power control to

compensate for fast fading.

Fast fading occurs as a mobile moves through aninterference pattern.

Interference patterns develop due to reflections.

Repetition distance depends on angle between incidentand reflected waves.


cos2


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If the mobile cannot respond to power control commands,

the UE will notice a variation in the received signal.

This will lead to BER variations that will cause the networkto require a higher target Eb/No (a fast fading margin orpower control margin will be required).

The effect can be to increase the target Eb/No from anormal value of perhaps 4 dB to 10 dB or more for fastmoving mobiles.



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Reducing the required Eb/No: Diversity systems provide an Eb/No improvement.

That means that the Eb/No over the air interfacecan be reduced and hence the air interfacecapacity increases.

Multi-user detection (MUD) reduces the effect ofmutual interference between users on the uplink.

This reduces the required transmit power per userand hence reduces the noise rise caused by agiven number of users.

As a result the pole capacity increases.



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Factors Limiting Capacity: Orthogonality

Dramatic effect on downlink capacity.


i

1N

E3840CapacityPole

0

b

C


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Example: Eb/No = 4 dB, i= 0.6, 12200bps


2548

1.0

1914

0.8

153412801100963Pole Capacity

0.60.40.20Orthogonality

Pole Capacity

(kbps)

1000

2000

Orthogonality0.5 10


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Loading Factor

Loading Factor = Actual Throughput

Pole Capacity

C it Li i t i F t


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What can be done to improve orthogonality?

Currently, very little.

No guidance regarding placing of sites to

maximise orthogonality known about.

In future there may well be but:- the only outcome

would be the recommendation to move cells (not a

welcome recommendation as it means start

planning the network from the beginning).


Capacit Limit ing Factors


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Factors Limiting Capacity: Hard Blocking

So far we have

discussed air

interface capacity or

soft capacity.

We could suffer also

from hard blocking

due to hardware and

fixed network

constraints.


Channel elements?

E1 links?



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Factors Limiting Capacity: Hard Blocking

There is no value in

increasing the soft

capacity of the air

interface above the

networks hard

capacity.

Often the network will

be launched with a low

level of hard

capacity.


Channel elements?

E1 links?



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Methods of Increasing Cell Capacity

Zero resource:

Adjusting configuration to reduce mutual interference

Adjusting network and cell parameters in order to optimise

performance.

New resource requirements:

Adding channel elements

Increasing capacity of fixed network

Implement diversity and/or multi-user detection.




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Network Capacity

Capacity calculations have been per cell.

Network is of many cells.

Can we just multiply the capacity per cell by the

number of cells?

Do we just add more cells to increase network

capacity?

Very expensive option

Diminishing returns set in: higher site density results inincreasing interference.

Procedure needs to be structured for maximum

benefit.




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Network Capacity

Possible procedure

Address hard capacity issues.

Use pico-cells to provide an in-building solution

Deploy micro-cells to service hot spots

Further sectorise (e.g. six cells per sector)

Provision extra carriers on some sites (a sector

with 2 carriers is, logically, 2 cells in UMTS).

Deploy extra sites in the macro-cell layer.

Note: Priority of deployment of diversity/MUD

is a topic of discussion.


Reducing Mu tual Interference


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Reducing Mutual Inteference

The lower the interference the higher the capacity.

Because of the single frequency used in a UMTS layer, there isan Interference feedback loop.

This means that interference, rather than just adding to thebackground noise level, consumes a proportion of the networkresource (power on the DL, noise rise on the UL).




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High Sites

Often, what is apparently sensible planning can lead to the

emergence of high sites. In the situation shown a distant site posed an interference threat

in the area of interest.


Area of interest

InterferingCell Intendedserving cell



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High Sites

The first action to be taken would be to increase the down tilt of

the interfering cell. Care must be taken to ensure that it still provides coverage

where it is intended.


Area of interest


CoverageArea



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High Sites

Other possible solutions include reducing the cell power of the

interfering cell. This should be done with great care as it will affect the downlink

coverage and capacity in its wanted coverage area.


Area of interest


CoverageArea



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Examples of Antenna Tilt

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

No Tilt MechanicalDowntilt

Electrical

Downtilt

Electrical Downtilt +

Mechanical Uptilt

g

Problem



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Limitations on Downtilt

If the antennas aremounted centrally on aroof,

The amount of down-tiltachievable can be limitedby the site geometry

Plan

Block Image

g



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The Optimum Value of Down Tilt

Although a lot of interference will reduce network capacity, too

little overlap can lead to hand over failures.

g

Too much interference:network capacity

reduced.

Too little overlap:hand over failures.

Network Parameters


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Optimising Network Parameters

Parameters that can be changed:

RNC - global

Node B

Cell

There are thousands of parameters that eachinfluence network functions.

We will look at some that are among the mostsignificant.

Network Parameters


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BLER Target

Setting a low value of BLER (e.g. 0.3%) will produce

a high quality digital communication channel

But: this will in turn require a high Eb/No so each

channel will use a lot of network resource.

Optimising a network is supporting as many satisfiedcustomers as possible; this means providing a

service that is just good enough.

Increasing the BLER target (to, say, 1%) will

increase capacity. Assessment on impact is often subjective.

Network Parameters


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BLER Target - Packet Services

Values of 0.3% and 1% are typical for Circuit

Switched (CS) services (e.g. voice, VT).

For packet switched (PS) services, delays and re-

transmissions can be tolerated.

BLER can be much higher. Crucial parameter

SERVICE

REL 99

Target BLER Max DCH Power

dBm

AMR(12.2Kbps) 1% 31.5

PS (64Kbps) 5% 36.5

PS (384 Kbps) 5% 37

FER

NEb

1

0


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Release 5ServerRNCNode-B

UE

RLC retransmissions

TCP retransmissions

MAC-hs retransmissionsFaster

retransmissionsallows us to have ahigherretransmissionprobability whilemaintaining userdelay.

This leads to andecrease in Eb/No.

Frame Erasure Rate (FER) = 1Correctly received data framesTotal Transmitted data frames

Eb/No = Eb/No

1- FER

Network Parameters


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Cell Pilot Power

Pilot power dictates: cell coverage

soft hand over regions

UL soft hand over gain is maximised if UL path loss is

equal.

If MHAs are employed, pilot power should be equal at the

mast head, not at PA output.

Network Parameters


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Maximum DL Power per Bearer

DL users share the power available to traffic channels

(typically 16 Watts or 42 dBm).

Allowing one user to use all this power would mean the cell

is blocked to other users; a limit is imposed.

Network Parameters


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If demand is low, it is best to have a high limit so that

coverage is maximised.

Network Parameters


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If demand is high, a lower limit will maximise throughput

(and hence revenue) at the expense of coverage in areas

of high path loss or interference.



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NR limit on uplink is directly linked to loading factor:

NR limit appears in link budget and hence affects coverage prediction.

If a network is planned so that continuous coverage would be provided

with all cells simultaneously at NR limit, then probability suggests that

coverage is over-dimensioned.

Coverage can be planned for a NR value 1 to 2 dB below the limit - this

is often used as a comfort factor margin.

Failures will then be split between Eb/No and NR.

10101);1log(10NR

NR

Hard Capacity


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Hard Capacity

Because the air interface in UMTS networks is new, mostattention is paid to maximising the interference-limited

capacity of the air interface itself (the soft capacity).

However, there must be sufficient capacity in the hardware

of the fixed network to support the demand generated bythe cells.

This includes considering:

Channel Elements at the Node B

Capacity of the interfaces

Capacity of the RNCs

Hard Capacity


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Hard Capacity - Channel Elements

Each bearer requireshardware in the form of

channel elements (Ces) in

the Node B. The number of

CEs required depends on

the data rate, for example:

Voice: 1 CE

64 kbps: 3 CEs

128 kbps: 5 CEs

384 kbps: 8 CEs

Hard Capacity


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Hard Capacity - Channel Elements

Allocation is shared acrosscells and carriers.

Provision must be made to

accommodate soft hand

over. Softer hand over imposes

no additional burden.

Hard Capacity


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Hard Capacity - HSDPA

HSDPA is not amagic solution.

Interference limitations

still exist.

HSDPA only possiblein areas of low

interference.

Aggregate network

capacity should beincreased.

HSDPAPossible

NoHSDPA

Hard Capacity


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Hard Capacity - HSDPA

Ultimate constraint isthe 3840 kcps chip

rate.

QPSK allows 2 bits per

symbol. High Speed Downlink

Packet Access

(HSDPA) uses 16 QAM

which allows 4 bits persymbol.

Hard limit is doubled.

QPSK

16 QAM


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HSDPA architecture and channel structure

A HS-PDSCH corresponds to one channelling

code of fixed spreading factor SF=16, and thereare 15such codes reserved for HS-DSCHtransmission.

Multi-code transmission and code multiplexing arefacilitated for, i.e. UE can be assigned multiple-codes depending on its capability or several UEcan be multiplexed using different codes.

With the introduction of HS-DSCH, additionalintelligence in the form of an HSDPA Medium

Access Control (MAC) layer is installed at theNode B, thus leading to shorter delay with packetdata when retransmissions are needed.


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HSDPA UE categories

Category Max. number of

HS-DSCH codes

Modulation Max. data rate

[Mbit/s]

1 5 QPSKand 16-QAM 1.2

2 5 QPSK and 16-QAM 1.2








10 15 QPSK and 16-QAM 14.4

11 5 QPSK only 0.9

12 5 QPSK only 1.8

The UE is a member of one of 12 categories, this is a function of the hardwarecapabilities.
http://en.wikipedia.org/wiki/16-QAMhttp://en.wikipedia.org/wiki/16-QAMhttp://en.wikipedia.org/wiki/16-QAMhttp://en.wikipedia.org/wiki/QPSK


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HSDPA architecture and channel structure

HSDPA represents an evolution of the WCDMA radiointerface, which uses very similar methods to those employedin EDGE evolution of the GSM radio interface.

To implement the HSDPA feature, new channels areintroduced in the 3GPP physical layer specifications:

High Speed Physical Downlink Shared Channel (HS-PDSCH)

High Speed Shared Control Channel (HS-SCCH)

High Speed Dedicated Physical Control Channel (HS-DPCCH)

The transport channel carrying the user data with HSDPAoperation is denoted as the High Speed Downlink SharedChannel (HS-DSCH)

The HS-DSCH is mapped onto a pool of physical channels

(i.e. HS-PDSCH), to be shared among HSDPA users in atime multiplexed manner.


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HS-SCCH: High Speed Shared Control Channel (DL)

When HSDPA is operated using Time multiplexing, then only one HS-SCCH can be configured. ONLY one user receives data at a time.

14

13

12

1110

9876543210

10ms

HS-

SCCH

HS-DSCH

Demodulation info

USER1

The HS-SCCH has a two slotsoffset compared with HS-DSCH.

USER

2

Demodulation info

USER

3

Demodulation info


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HS-SCCH: High Speed Shared Control Channel (DL)

14

13

12

1110

9876543210

10ms

HS-

SCCH

HS-SCCHHS-DSCH

USER1

USER

1

When there is a need to have code

multiplexing, then more than ONEHS_SCCH needs to be included. A singleterminal may consider at MOST fourcodes


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Code Multiplexing

The higher the data rates and terminal capabilities the smaller the need for codemultiplexing.

Use of code multiplexing is not necessarily where carrier shared with DCH traffic.

OR

When there is a desire to have HSDPA data users operating with reasonable datarates384Kbps and more

Up to15codesreserved forHS-PDSC

H


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Code Multiplexing

Up to 15 codes may be used in the Node B

UE typically support 5 To maximize spectral efficiency3 parallel users with 5 codes

Code multiplexing used for large number of HSDPA users with LOW data rate ieVoIP.

Up to15codesreserved forHS-PDSC

H


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Channels Allocated to One HSDPA User

UE

NodeB

1-4xHS-SC

CH

HS-DPCC

H

HS-PDSCH: High-Speed PhysicalDownlink Shared Channel (DL)

Actual HSDPA data for HS-DSCHtransport channels

1-15 codes per channel

QPSK or 16QAM modulation

HS-SCCH: High Speed Shared ControlChannel (DL)

Informs the UE how and when toreceive the HS-PDSCH

HS-DPCCH: High Speed DedicatedPhysical Control Channel (UL)

MAC-hs ACK/NACK information Channel Quality Information

(CQI)

In-bui ld ing solut ions


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In-building Solutions

Cells with indoor antennas can help

with coverage problems.

Most importantly, they add to the

network capacity and serve an

indoor hotspot.

Eg; 20 floor, 200 people per floor(4000 people): 800 subscribers, 20

Erlangs offered.

If this is VT, this would be typical for

a sectored Node B. A macro-cell

may contain several such buildings.

In-building solutions can alleviate

macro-cell capacity problems.



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Frequency allocation

Advantageous if same

frequency as macro-cell layer

can be used.

Spectral efficiency maximised

Hand over between indoor and

outdoor environment simplified.

Mutual interference must be

minimised whilst engineering

soft hand over region.



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The lower the interference the higher the capacity.

Because of the single frequency used in a UMTS layer, there isan Interference feedback loop.

This means that interference, rather than just adding to thebackground noise level, consumes a proportion of the networkresource (power on the DL, noise rise on the UL).



54/91


The walls of the building will help

provide isolation between theindoor and outdoor cells, thusimproving capacity.

Problem areas are those wherethe path loss to both cells issimilar.

Presence of walls makes itpossible to make this regionnegligibly small.

Similar, in principle, to a macro-cellstructure with gaps in coveragelow interference (but HO failuresbut people dont walk throughwalls).


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Th D d Z Eff t l ti ?



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The Dead Zone Effect: solutions?

Unlikely to provide a solution by

engineering the radio environment:low path loss to best server isgenerally a good thing

Possibilities

All affected operators deploy a picocell within a particular building.

Operators allow hand over to picocell carriers from affected cells.

Macro cell pilot:

-105 dBm

Pico cell

interference: -57 dBm

H d O



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Hand Over

A hand over region needs to be

provided. Sudden changes in signal level

from a cell can lead to calls beingdropped.

Required hand over region is nearthe door.

Hand over region:

Large enough to allow hand over.

Should be where subscriberdensity is low, as hand over regionis area where mutual interferenceis highest.

Preventing sudden changes insignal strength at the HO regionrequires appropriate siting of pico-cell and macro-cell antennas.

Required handover region

H d O



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Hand Over

Contour of equal pilot strength

(between macro-cells and pico-cell)should be engineered to be justoutside, rather than just inside thebuilding.

This is because subscriber density islikely to be much higher inside thebuilding.

This needs to be checked bymeasurements.

This will lead to the path loss to thepico-cell, for subscribers within thebuilding, being much less than that to

the macro-cell. This is a good thing as it means the

pico-cell will have a negligible impacton macro-cell capacity.

Contour of equalpilot strength.

I l ti th i b ildi l ti



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Implementing the in-building solution

Design and implementation of in-

building solutions is an area ofexpertise in its own right.

The following provides an outline of thedecisions and choices regarding thedesign of the pico-cell.

A high level overview of the relativeadvantages of the different options isprovided.

Th Ch i Th N d B



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The ChoicesThe Node B

Single Node B Multiple CompactNode Bs Repeater toexternal Node B

Th Ch i Th N d B



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Single Node B

Easy capacity expansion (justadd more cards).

Staff familiar with equipment,as Node B can be the same asfor the macro-cell.

Centralised system could beprone to faults.

Node B could be physicallylarge to accommodate.

Th Ch i Th N d B



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Multiple CompactNode Bs

More robust to faults as it isdistributed.

Can lead to superior coverage.

Smaller physical size.

Capacity expansion can beharder.

Staff may need extra trainingon new type of Node B.

Th Ch i Th N d B



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Repeater toexternal Node B

Cheapbut no solution tonetwork capacity problems.

The Choices Antenna S stems



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The ChoicesAntenna Systems

Distributed PassiveAntennas

Distributed ActiveAntenna System Radiating Cable

The Choices Antenna Systems



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Distributed PassiveAntennas

Closeness of antenna to UEallows low radiated power.

Most suitable antenna can bechosen for each locationallowing good control of

radiation.

Cables can be lossy andexpensive.

Installation of heavy cable canbe difficult.




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Low grade CAT 5 cable can beused instead of feeder makinginstallation easier.

Lower feeder losses

Restricted to low transmitpower.

Power supply required at eachantenna location. Distributed Active

Antenna System




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Easiest to model/predict linkloss.

Produces even coverage.

Can be hidden from view.

Often the most expensivesolution.

Not suited for all shapes

(better for longitudinal shapes). Precision installation required

to maximise benefits.

Radiating Cable

Field Measurements to Check on Implementation



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Field Measurements to Check on Implementation

Scanner measurements can be used to assess:

Coverage

Hand over region

Isolation from macro-cell. Ideally the macro-cell and thepico-cell should not interfere with each other.

Micro cell planning

Micro-cell Plannin g


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Micro-cell planning

Typical range for macro-cell for VT is 500 metres in dense urban

environment.

Site Density for coverage approximately 2 sites/km2.

Capacity then approximately 22 Erlangs of VT per site

Macro cell layerprovidingcontinuouscoverage

Micro cellsserving hotspots.

Micro cell planning: carrier re use



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Micro-cell planning: carrier re-use

If the macro cell carrier can be re-used:

Hand over between micro and macro cells is easier.

Macro cell layerprovidingcontinuouscoverage

Micro cellsserving hotspots.

Micro cell planning: mutual interference



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Micro-cell planning: mutual interference

In the case of in-building solutions, the building walls formed a

barrier against interference. This made re-use of the macro cell carrier more straightforward.

Outdoor micro cells have no such barrier.

Potential for more serious interference issues, reducing

capacity gains

In-buildingsolution: wallsform barrieragainstinterference.

Micro cellsnobarrier againstinterference..

Micro cell planning: theory



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Micro-cell planning: theory

Suppose an area within a macro cell could accommodate only 1

Erlang of offered traffic if the macro cell capacity was dividedequally on an area basis.

Now consider the situation if this area was expected to generate 12

Erlangs of offered traffic.

Area generates12 times theexpectedtraffic.




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If carrier frequency is to be shared and no extra loading to be

placed on macro cell: Each UE should operate at 1/12thof the power that it would if it

connected to the macro cell.

Path loss to micro cell should be 11 dB less than that to macro cell.

Area generates12 times theexpectedtraffic.




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This can be arranged with pilot power settings but there are

problems: If pilot powers are left equal, then border region will be where path loss

is equal between micro cell and macro cell UL interference on macro

cell results.

If micro cell pilot is 11 dB less than that for macro cell, UEs just outside

the micro cell border will cause a lot of UL interference on the microcell.

Pilot powers equal:macro-cell affectedby UEs on border.

Micro cell pilot reduced by11 dB. Micro cell affectedby UEs just outside border.

Engineering the Micro cell



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The success of any strategy depends on the user behaviour.

Areas of high mutual interference are only problematic if thereare lots of users.

Need to engineer the micro cell accordingly

Micro cell dominance area should exceed the hotspot area.

Area of dominance ofmicro cell shouldexceed the hotspotarea.




76/91


Radiation pattern of micro cell antenna should ensure that

path loss rapidly increases once outside the dominance area.

Initial setting of pilot power and NR limit can be the same as

for macro cell. Ideally, should be possible to reduce DL power

to 37 dBm (pilot power would then have to be reduced

proportionately).

Possible Problems



77/91

Possible Problems

If there are lots of users in the border area, this will cause

interference problems.

If the micro-cell pilot power is reduced it may suffer from

interference as the UEs connected to the macro-cell will be

transmitting with relatively high power.

Users in the borderarea will cause andexperienceinterferenceproblems.

Using Scanner Measurements



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Using Scanner Measurements

With pilot powers of the micro-cell and macro-cell set to equal

levels, the strength of the micro-cell pilot should be at least 10

dB greater than the macro-cell pilot throughout the area of

high expected user density (the hotspot).

Area of expected highuser density.



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Engineering the Micro cell: field measurements

If the pilot powers are equal, the border area is at locations of

equal path loss.

Pilot strength of micro cell should be 10 dB greater than that

from macro cell at all areas of high subscriber density.

If transmit pilot power of micro cell is 6 dB less than macro cell,

then micro cell pilot can be just 4 dB greater.

When micro cell pilot is reduced, problem comes from potential

uplink interference from macro cell UEs just outside the border.

Should be possible to raise the NR limit to help with this. (E.g.

macro cell NR limit: 4 dB; micro cell NR limit: 8 dB).

Further Sectorisation of Sites

Further Sectoris ation


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Three-sectored sites

have evolved to be the

norm in urban and

suburban areas.

Each antenna controls a

120 sector.

Antenna beamwidth a

compromise between

coverage and

interference.

65 is the most common.

18 dBi is typical gain.




81/91


Six-sectored sites could, in

theory, double the capacity.

If mutual interference

increases, capacity may not

increase as expected.

But, if antennas are higher

gain, can increase.

iN

Eb

1

3840Capacity

0




82/91


Antenna beamwidth is

highly significant in arriving

at the optimum between

coverage and interference.

35 is seen as the most

appropriate.

21 dBi is typical gain.

Monte Carlo simulations

can quantify the likelyimprovement.

Uplink Receive Space DiversityDiversity


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Uplink Receive Space Diversity

This is not conventional space diversity.

Each antenna is connected to a separate finger of the Rake

receiver.

This is possible due to the synchronisation and channel estimationderived from the Pilot bits on the DPCCH channel.

Eb/No is improved, rather than simply an effective power gain.

Downlink Transmit DiversityDiversity


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Downlink Transmit Diversity

UMTS explicitly allows the use of transmit diversity from the base station

However it is not possible to simply transmit simultaneously from two close antennas asthis would cause an interference pattern

Mobile terminals must have the capability of implementing downlink transmit diversity .

Transmit

antenna 1

Transmitantenna 2

Multi-User DetectionDiversity


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Multi User Detection

Mid 1980s research showed that joint, optimal, maximum-likelihood decoding ofall users out performed matched filter alternatives.

The problem was the exponential increase in processing as the number ofsimultaneous users went up. ( Viterbi trellis techniques )

Current research interests

Suboptimal linear receivers

Data-aided minimum mean squared (MMSE) linear receivers

Blind ( nondata-aided ) MMSE receiver

Non-linear multiuser detection

Multistage interference cancellation, parallel and serial, PIC & SIC



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Viterbi decoding uses past symbol knowledge to weight presentand future choices

Multiuser decoding has the added complexity of having presentother user interfering symbols

Therefore some decision as to the interfering symbols must be

made

Due to the complexity, multiuser detection is more likely to existin the Node B



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Multiuser detection reduces the need for tight power control

Power control is still important to the performance of the MUDsystem

Best performance used with short spreading codes, repeating

every symbol. ( Downlink )

Can be used with long spreading codes, pseudorandomsequences which are much longer than the symbol duration.(Uplink)

Visualising the Processing Gain w/o MUDDiversity


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Visualising the Processing Gain w/o MUD

W/Hz W/Hz W/Hz

Ec

Io

Signal

Intra-cell Noise

Inter-cell Noise

Before

SpreadingAfter

Spreading With Noise

f f f

W/HzAfter

Despreading

/Correlation

f

W/Hz Eb

No

Post

Filtering

(No MUD)

f

dBW/Hz

Eb

No

Eb/No

f

Visualising the Processing Gain with MUDDiversity


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g g

W/Hz

Signal

Inter-cell Noise

After

Despreading

/Correlation

Post

Filtering

f

Other Users

Eb

No

W/Hz

f

Eb

No

W/Hz

f

Eb

No

W/Hz

f

Eb

No

W/Hz

f

Because of MUD the contribution of the other users to the

Noise is Reduced.

It is not completely eliminated because of the inaccuracies of

the Multiple access interference estimation.

Nortel UTRAN KPIs


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Nortel UTRAN KPIs

RRC Conn ect ion Establ ishm ent Fai lure

RRCConnEstabl ishm entSuccessRate (glo bal)

CauseRRCConnect ion establ ishment (per cause)

T352 Expiry

RRCConnVoice+ConvEstabl ishmentSuccessRate

RRC Connect ion Abno rmal Release Rate

RRC Abnorm al Release

Nortel KPIs


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RRC Unspecified Release Rate

RAB Establishment Failure Conversational

RAB Establishment Failure PS Interactive + PS Background

RABVoice&ConvEstablishmentSuccessRate

RABStreamingEstablishmentSuccessRate

RABPSEstablishmentSuccessRate

ISHO CS

IU Release Command CS Failure Rate

UMTS Postlaunch Opt

Documents

Transcript of UMTS Postlaunch Opt