power control in umts.ppsx

8/10/2019 Power Control in UMTS.ppsx

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23 November 2014Slide Title | CONFIDENTIAL 2006

Agenda

Why you need power control?

What is power control?

Types of power control

Interference vs. power control


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To minimize the interference in the system

So, efficient power control is needed to increase the

performance of network

A good power control mechanism can handle more

number of customers at a given point of time

Why do you need power control?


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Why do you need power control? (continued)

This will avoid near-far effect


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Logical channels

The situation is different in the downlink direction

The down link signal transmitted by one base station orthogonal Signals which are orthogonal do not interfere each other

Signal reflections cause non-orthogonal interference in a base station

hence causes interference

Moreover, signals sent from different base stations are non orthogonalin nature thus increase the interference

Bottom line here is we need to have power control mechanism in both theuplink and down link

Why do you need power control? (continued)


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Types of power control

There are two types of power control

Open loop power control

The transmitting entity shall measure the channel interference

and sets its power accordingly

Closed loop power control The quality measurements are done at the receiving entity and

the results are sent back to the transmitting entity with the feed

back so that it can adjust the power accordingly

It can not react quick to the channel conditions


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The closed-loop power control in the UTRAN can be further

divided into two processes: inner-loop and outer-loop powercontrol.

The outer-loop power control sets the signal-to-interference

ratio (SIRtarget) and the inner-loop power control adjusts the

peer entity transmit power so that the measured SIR fulfills theSIRtarget requirement.

This adjustment is done with transmit power control (TPC)

commands.

Types of power control (continued )


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TPC bit is transmitted in every time slot

There is no neutral TPC signal

All power control signal either have an increase or decrease

command

TPC mechanism


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The receiving entity (UE or Node B) measures the SIR and compares

it to the SIRtarget. If received SIR > SIRtarget then the TPC bit is set

to 0 (reduce power) in the peer entity. Otherwise it is set to 1 (increase

power). This TPC bit is transmitted to the peer entity once every time

slot.

Inner-loop power control is also known as fast power control. The

basic principles of Inner-loop power control are similar in both the UE

and in the UTRAN.



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SIR is measure every 667 micro second period

Based on this information a decision can be made to increase or decrease

the power



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Power ControlOpen Loop

Use to determine uplinktransmit power to use for

initial (random!!) access,using downlink powerreference and broadcastinformation

CPICH downlink transmitpower

uplink interference

constant value

UE will measure receivedpower of pilot (CPICHRSCP), and calculates initialpower

UEs close to Node-B should

transmit with lesser powercompare to UEs far away toNode-B


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Power ControlClosed Inner Loop

1500 times per second

(1500 Hz) Maintains Signal to Noise

ratio

Fading, Shadowing, etc

Control interference

Inner loop power control

in soft handover scenario

Decrease UL transmit

power, even if one DL radio

link commands to decrease

Increase UL transmit

power, only when all DL

radio links commands to

increase

UE

Received

TPC Cmd

SIR

Measurement

+/- dB

Node-B

Received

TPC Cmd

SIR

Measurement

+/- dB

power control in umts.ppsx

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