BTS_power_control

Copyright © 1997 by Ericsson Radio Systems AB2882-EN/LZT 123 4038 Rev A

New algorithm in CME 20 R6

• Quality also used as a power regulation criterion• Possible to use different amounts of pathloss

ti

BTS Power Control


BTS Power Control, Performance Gain

In addition BTS power control: • Saves battery in the BTS (if the power supply to the BTS has been cut off and the BTS is operating on battery power) • Reduces the risk of MS receiver saturation (and thus the risk of having bad speech quality)

BTS power control will reduce the number of mobiles experiencing a very low C/I ratio


BTS Power Control, Regulation Area

Regulation area

Site

Figure 1 Schematic picture of the power regulation areain a cell.


BTS Power Control

SS 1

SSDESDL

Received signal strength in the MS

Path lossRegulation area

Path loss

Output power of the BTSMaximumallowed power level

Minimumallowedpower level

Regulation area


BTS Power Control, Procedure

• Measurement preparation

• estimation of missing measurements• decide whether full or sub set shall be used (DTX)• frequency hopping compensation

(if the BCCH-carrier is in the hopping set)

• Filtering of measurements

• eliminates variations of temporary nature to ensure that the decision base for the next power order is stable

• Calculation of power order

• calculate power order to achieve desired signalstrength and quality

• apply power order constraints


BTS Power Control, MeasurementProcedure

Down link s

ignal strength

Down link q

uality

Measurement report is senteach SACCH period(every 0.480 sec.)

• Full set 100 samples• Sub set 12 samples


BTS Power Control, MeasurementProcedure

BSC

DL qualityDL signal strengthBTS power level usedDL DTX indicator

BTS power order


BTS Power Control, Filters

Filtering of measurements

• QLENDL - signal quality filter length• SSLENDL - signal strength filter length

Regulation

• power regulation starts as soon as SSLENDL is filled• the regulation interval parameter, REGINTDL, controls

the shortest time interval between two power orders


BTS Power Control

• BTS power control is performed on a time slot basis

• Power control is not performed on the BCCH carrier

• The maximum power order change is 30 dB which also is the

maximum configurable dynamic power regulation range

• If the BCCH carrier is included in the frequency hopping set, this is

compensated for in the BSC when the power orders are calculated.

One TDMA frame

76 � 76 � 76 �

76 �

76 �

76�

76�

76�

30 dB

30 dBTRX1

TRX1

TRX1


BTS Power Control

There are two possibilities in GSM to perform the MS signal strength and quality measurements when the BCCH is included in the frequency hopping set:

1) The MS shall include the BCCH-carrier in the measurements

2) The MS shall exclude the BCCH in the measurements

Which method to use is determined by the property PWRC. PWRC=0 means include BCCH-carrier, PWRC=1 exclude.

In R6.0 the BCCH-carrier is included in the measurements.


BTS Power Control, Calculation ofPower Order

The unconstrained power order:

power order = Fpl(path loss) +Fq( quality)

Fpl(path loss) = BSTXPWR - a(SSave - SSDESDL)

BSTXPWR is the output power at the locating reference pointand SSDESDL is the desired signal strength to be received in the BTS

SSave is the filtered signal strength compensated for down regulation, i.e.it is the signal strength that would have been received by the MS if no power control was used

a = LCOMPDL/100 and determines the degree of path loss compensation


BTS Power Control, Reference Point

SSDESDL

referencepoint for

PA Combiner TX feeder TX antenna gain Path loss MSRX

referencepoint for

BSPWRBBSPWRT

preferredreferencepoint for

BSPWRBSTXPWRBSPWRMIN

alternativereference point(EIRP) for

BSPWRBBSTXPWRBSPWRMIN


BTS Power Control

The transformation from rxqual to C/I is given bythe following expressions:

Q_AVE_dB = 32 - 10·Q_AVE/25 (2)

QDESDL_dB= 32 - 10·QDESDL/25(3)

b = QCOMPDL/100 and determines the degree of quality compensation

Fq( quality) = - b(Q_AVE_dB - QDESDL_dB)


BTS Power Control

Mapping of rxqual to C/I

C/I Quality (rxqual) QDESDL 32 0 028 1 1024 2 2020 3 3016 4 4012 5 508 6 604 7 70


BTS Power Control, Calculation ofPower Order

Measurementpreparation Filtering

Calculation of unconstraintpower order

Applyconstraints

Send power order (REGINTDL)

Every SACCH period


BTS Power Control, Power OrderConstraints

• If the unconstrained power order is higher than BSTXPWR, the power order is set equal to BSTXPWR.

• The lowest allowed power order is given by the maximum of a) maximum configurable BSTXPWR - 30, and b) BSPWRMIN


BTS Power Control

The ordered power level is always increased by apower margin, PMARG at:

• At assignment of a TCH.• At assignment failure or handover

failure.• At intra-cell handover and subcell

change.

Note! PMARG affects both up and down link power control


BTS Power Control, Parameters

Parameter Recommended ValueUnitDefault

SACCH periods

name value value range

SDCCHREG OFF ON ON, OFFSSDESDL –80 –105 –110 to –47 dBmSSLENDL 5 4 3 to 15LCOMPDL 50 20 0 to 100QDESDL 35 0 0 to 70 dtquQLENDL 12 5 0 to 20QCOMPDL 30 60 0 to 60REGINTDL 5 1 1 to 30PMARG 4 6 0 to 20 dBBSPWRMIN –20 BSTXPWR –12 –20 to +50 dBm

BSTXPWR 0 to 80 dBm


Interactions With Other Features

• the down link target quality, QDESDL,• the thresholds triggering bad quality urgency handovers,

QLIMDL• the intracell handover area defined by QOFFSETDL• the length of the locating quality filter QLENSD• the power control quality filter, QLENDL

The strategy should be to achieve power regulation before intra-cell handover or bad quality urgency handover occur.

This can be achieved by a well balanced combination of:


Current Parameter Recommendations

• quality filter length QLENDL, 5 SACCH periods• target quality, QDESDL, 0 dtqu• use quality compensation factor QCOMPDL 60 as a start

• use SSDESDL = -105 to -100 by measuring signal strength at cell border, start with a safe setting and lower while monitoring system performance (STS-counters)

• signal strength filter, SSLENDL, 4 SACCH periods• use partly path loss compensation, LCOMPDL, 20• use regulation interval, REGINTDL= 1 SACCH period.


BTS Power Control

Neighbour cell stronger than serving cell due to BTS PC


BTS Power Control

70 80 90 100 110 120 130-90

-85

-80

-75

-70

-65

-60

-55

-50

Path loss [dB]

rxle

v [d

Bm

]

SSDESDL=75 LCOMPDL=50, 70 and 100

(___) LCOMPDL=100 (R5)

(......) LCOMPDL=70

(_ _ _) LCOMPDL=50)


BTS Power Control

80 85 90 95 100 105 110 115 120 125 130-100

-95

-90

-85

-80

-75

-70

-65

-60

Path loss [dB]

rxle

v [d

Bm

]

SSDESDL=-80 QDESDL=35 LQOMPDL=100 QCOMPDL=30

°°°°° 0 dtqu

........ 45 dtqu

++++ 70 dtqu

R5


BTS Power Control

80 85 90 95 100 105 110 115 120 125 130-95

-90

-85

-80

-75

-70

-65

-60

Path loss [dB]

rxle

v [d

Bm

]

SSDESDL=80 QDESDL=10 LCOMPDL=100 QCOMPDL=30

°°°°° 0 dtqu

........ 45 dtqu

++++ 70 dtqu

R5


BTS Power Control

80 85 90 95 100 105 110 115 120 125 130-100

-95

-90

-85

-80

-75

-70

-65

-60

Path loss [dB]

rxle

v [d

Bm

]


°°°°° 0 dtqu

........ 45 dtqu

++++ 70 dtqu

R5


BTS Power Control

9702729

80 85 90 95 100 105 110 115 120 125 130-100

-95

-90

-85

-80

-75

-70

-65

-60

Path loss [dB]

rxle

v [d

Bm

]


°°°°° 0 dtqu

........ 45 dtqu

++++ 70 dtqu

R5


BTS Power Control

80 90 100 110 120 130-95

-90

-85

-80

-75

-70

-65

-60

-55

Path loss [dB]

rxle

v [d

Bm

]


°°°°° 0 dtqu

........ 45 dtqu

++++ 70 dtqu

R5


BTS Power Control, Mobile TrafficRecording Graph

SSDESDL=80, LCOMPDL=100, SSLENDL=4, QDESDL=35, QCOMPDL=30, QLENDL=8, REGINTDL=4

Max

pow

er=3

0 “d

B”,

Con

v.si

gn. s

tr. 0

<==

> -9

0 dB

m

Power used and signal strenght -20[RXLEV]

SACCH periods (samples)

RXLEV andRXQUAL areaveraged over5 samples!

Qu

alit

y [R

XQ

UA

L]

3

0

1

6

5

4

2

-1

7

15

0

5

30

25

20

10

-5

35

40

� PWR_DL -converted

� RXLEV_F_DL - ave_of_

� RX_Q_F_LD - ave_of_

SSDESDL=-80 dBm(<==>10 in this graph)

Documents

BTS_power_control