Parameter Planning

7/30/2019 Parameter Planning

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Commercial-in-Confidence

Parameter PlanningParameter Planning

Parameter Planning


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Contents and Session AimsContents and Session Aims

Overview of Parameter Planning

Power Control

Handover ParametersAdmission ControlPilot Power Planning

Neighbour RelationshipsCode Planning

Parameter Planning


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Overview of Parameter Planning forOverview of Parameter Planning for

UMTSUMTSParameter planning is the task of optimising the

parameters that control the behaviour of the network

Parameter planning does not usually involve modifying thephysical equipment of the networkExamples of parameter planning from GSM include:

! Frequency planning

! HSN planning

Parameter Planning


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Parameter planning for UMTSParameter planning for UMTS

The parameters with which we can modify theperformance of the network in UMTS are mainly heldwithin the RNC

As with GSM the user interfaces to the RNC are notdefined within the 3GPP standards

This means that different vendors may have slightlydifferent parameter sets, although there may be a lot ofoverlap

Many of those parameters detailed here are thosesuggested by the FRAMES project, 3GPP standards andNokia texts

Parameter Planning


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Power ControlPower Control

There are two different levels of power control in UMTS! Outer Loop Power Control

! Inner Loop Power Control

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Outer LoopOuter Loop

The purpose of the Outer Loop power control is to set andadjust the Eb/No target for the service dependant upon theachieved BER/FER

The BER/FER target will be associated with the serviceitself

However it may be possible to set:!The Measurement Frequency

!The Sampling Period

Parameter Planning


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Inner LoopInner Loop

The purpose of the Inner Loop power control is to achievethe targetEb/No over the air interface

The inner loop power control is dependant upon which oftwo algorithms are used! Algorithm 1

" A single power control bit is used to indicate a power rise/lower

! Algorithm 2" A set of five power control bits are used, preceded by a series of 4

zero valued bits. Only if all bits indicate a power rise/lower is thepower modified

Parameter Planning


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Inner Loop ParametersInner Loop Parameters

Parameter Planning

Parameter PC Algorithm Typical Values Description

OL_PC_PWR_STEP Open Loop 1dB Power Increase for AccessPreamble failure

OL_PC_TRIALS Open Loop - Maximum Number of Access Preamble Trials

CL_PC_REP_INTERVAL Closed Loop -

CL_PC_PWR_STEP Closed Loop 0.5dB (1dB also possible) Power Step for Closed LoopPower Control Algorithm

UL Power Control Algorithm Closed Loop Algorithm 1/Algorithm 2 Choice of uplink powercontrol algorithm


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HandoverHandover

Soft Handover is used in UMTS

Soft handover is where multiple cells are simultaneously

connected to a single UEThe size of the handover zone can be set by modifying the

handover parameters

Parameter Planning


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Parameter Planning

Handover ParametersHandover Parameters

Parameter Typical Values Description

WINDOW_ADD 3dB The active set window. All cells within the active set windoware added to the active set until AS_MAX_SIZE is reached

WINDOW_DROP 5dB Cells within the active set falling below this threshold are

removed from the active set

WINDOW_REPLACE 3dB If the size of the active set is AS_MAX_SIZE then a member isreplaced when this threshold is breached.

PS_MINIMUM - The minimum pilot strength of an active set pilot

AS_MAX_SIZE - The maximum size of the active set

HCS_LAYER_UP/DOWN - Thresholds to select a higher/lower cell layer

HCS_LAYER_REPLACE - Thresholds to replace the current layer (frequency) used with adifferent cell layer


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Handover Decisions in UMTSHandover Decisions in UMTS

Pilot Ec/Io

WINDOW_ADD

WINDOW_DROP

Direction of Travel

Add Time Delay Drop Time DelayReplace Time Delay

WINDOW_REPLACE

Active set = 1Cell A

= 2Cell A and Cell B

= 2Cell A and Cell C

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Handover ParametersHandover Parameters

An example of how terminology may vary:! WINDOW_ADD = AS_THRESHOLD - AS_THRESHOLD_HYST

!

WINDOW DROP = AS_THRESHOLD + AS_THRESHOLD_HYST! WINDOW_REPLACE = AS_THRESHOLD_REPLACE

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Reducing the WINDOW_ADDReducing the WINDOW_ADD

Reducing the WINDOW_ADD parameter will reduce thenumber of handover channels required

Typically networks will be aiming at between 20% and40% handover channels! Remember that increasing the number of handover channels used

reduces the network capacity

Reducing the WINDOW_ADD beyond a certain point willreduce the effectiveness of soft handover and lead to:! a reduction in macrodiversity gain at the cell edge

! an increased probability of handover failure

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Reducing the WINDOW_DROP andReducing the WINDOW_DROP and

WINDOW_REPLACEWINDOW_REPLACEWINDOW_DROP and WINDOW_REPLACE are used to

prevent a ping-pong effect with cells being repeatedlyadded and removed from the active set.

As such WINDOW_DROP must be larger thanWINDOW_ADD, with an added margin

Reducing WINDOW_DROP will however again reduce the

number of UEs in soft handover

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Admission ControlAdmission Control

Fast power control has the undesirable side effect ofintroducing instability in a CDMA network if the load is toohigh

An additional mobile added to the network can causeparty effects where every other mobile tries to increaseits TX Power

Headroom is required to prevent thisThe purpose of admission control is to maintain the

stability of the network by ensuring that if the loadingbecomes too high no additional mobiles are admitted to

the network

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Admission ControlAdmission Control

Admission control typically allows the user to limit:!The Uplink Noise Rise in the network or the Uplink Load

!

The Downlink TX Power or the Downlink Load!The maximum TX Power per user

These are user definable parameters

Typically a maximum uplink Noise Rise of 6dB ( a load of75%) is allowed at macrocells or 20dB in microcells

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Pilot Power PlanningPilot Power Planning

By Pilot Planning we are referring to planning the power ofthe Pilot Channel

Other control and signaling channels will typically betransmitted at a fixed offset from the pilot.The Pilot itself is used:

!To add cells to the active set in handover.

!To set the maximum extent of the cell.

!To allow for channel estimation at the receiver.

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Modifying the Pilot PowerModifying the Pilot Power

Reducing the pilot strength in anisolated cell will have the effectof reducing the cell area

Parameter Planning

Initial Area

Smaller Area after Reducing the Pilot Power


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Modifying the Pilot PowerModifying the Pilot Power

If there is more thanone cell providingcontiguous coveragethen reducing the thepilot power will havethe effect of moving thecell border towards thesite modified

Increasing the powerwill have the oppositeeffect

Note: This does notnecessarily reduce thenumber of handovers

Parameter Planning

Cell A Cell B Handover


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NeighbourNeighbourRelationshipsRelationships

Neighbour relationships will need to be defined for UMTSto enable the monitoring of neighbours within theNeighbour Set for handover

The following Neighbour relationships may be required:! Intra-frequency/layer UMTS neighbours

! Inter-frequency/layer UMTS neighbours

! Inter-mode mode UMTS TDD neighbours! Inter-technology GSM900/GSM1800 neighbours

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Code PlanningCode Planning

Code Planning is required for the downlink scramblingcodes and downlink secondary synchronisation codes

The objective of code planning is to ensure:! that code reuse is as efficient as possible

! that we can maximise the minimum reuse distance between sitessharing the same scrambling code

There are 512 downlink scrambling codes that we can useAt an average of 3 codes used per site this implies a

reuse of 170!

!

Not too difficult...

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Code PlanningCode Planning

However it should be born in mind that the SecondarySynchronisation Code may also require planning (futurestudy required)

! If this is the case there are only 64 Secondary SynchronisationCodes

" A mere 20 sites reuse pattern

Parameter Planning

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Parameter Planning

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