This document discusses base transceiver station (BTS) power control in GSM networks. It describes how BTS power control can save battery power, reduce mobile station receiver saturation, and lower the number of mobiles with low carrier-to-interference ratios. The document outlines the power control procedure, including signal measurements, filtering, power order calculation applying constraints, and interaction with other features like handover thresholds. It provides recommendations for configuring power control parameters.

1. Copyright © 1997 by Ericsson Radio Systems AB
2882-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
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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

2. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control, Regulation Area
Regulation area
Site
Figure 1 Schematic picture of the power regulation area
in a cell.
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control
SS 1
SSDESDL
Received signal strength in the MS
Path lossRegulation area
Path loss
Output power of the BTSMaximum
allowed
power level
Minimum
allowed
power level
Regulation area

3. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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 signal
strength and quality
• apply power order constraints
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control, Measurement
Procedure
Down link signal strength
Down link quality
Measurement report is sent
each SACCH period
(every 0.480 sec.)
• Full set 100 samples
• Sub set 12 samples

4. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control, Measurement
Procedure
BSC
DL quality
DL signal strength
BTS power level used
DL DTX indicator
BTS power order
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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

5. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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.

6. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control, Calculation of
Power 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 point
and 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
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control, Reference Point
SSDESDL
reference
point for
PA Combiner TX feeder TX antenna gain Path loss MSRX
reference
point for
BSPWRB
BSPWRT
preferred
reference
point for
BSPWR
BSTXPWR
BSPWRMIN
alternative
reference point
(EIRP) for
BSPWRB
BSTXPWR
BSPWRMIN

7. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control
The transformation from rxqual to C/I is given by
the 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)
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control
Mapping of rxqual to C/I
C/I Quality (rxqual) QDESDL
32 0 0
28 1 10
24 2 20
20 3 30
16 4 40
12 5 50
8 6 60
4 7 70

8. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control, Calculation of
Power Order
Measurement
preparation
Filtering
Calculation of
unconstraint
power order
Apply
constraints
Send power order
(REGINTDL)
Every SACCH period
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control, Power Order
Constraints
• 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

9. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control
The ordered power level is always increased by a
power 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
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control, Parameters
Parameter Recommended Value
Unit
Default
SACCH periods
name value value range
SDCCHREG OFF ON ON, OFF
SSDESDL –80 –105 –110 to –47 dBm
SSLENDL 5 4 3 to 15
LCOMPDL 50 20 0 to 100
QDESDL 35 0 0 to 70 dtqu
QLENDL 12 5 0 to 20
QCOMPDL 30 60 0 to 60
REGINTDL 5 1 1 to 30
PMARG 4 6 0 to 20 dB
BSPWRMIN –20 BSTXPWR –12 –20 to +50 dBm
BSTXPWR 0 to 80 dBm

10. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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:
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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.

11. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control
Neighbour cell stronger than serving cell due to BTS PC
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control
70 80 90 100 110 120 130
-90
-85
-80
-75
-70
-65
-60
-55
-50
Path loss [dB]
rxlev[dBm]
SSDESDL=75 LCOMPDL=50, 70 and 100
(___) LCOMPDL=100 (R5)
(......) LCOMPDL=70
(_ _ _) LCOMPDL=50)

12. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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]
rxlev[dBm]
SSDESDL=-80 QDESDL=35 LQOMPDL=100 QCOMPDL=30
°°°°° 0 dtqu
........ 45 dtqu
++++ 70 dtqu
R5
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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]
rxlev[dBm]
SSDESDL=80 QDESDL=10 LCOMPDL=100 QCOMPDL=30
°°°°° 0 dtqu
........ 45 dtqu
++++ 70 dtqu
R5

13. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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]
rxlev[dBm]
SSDESDL=-80 QDESDL=35 LQOMPDL=100 QCOMPDL=60
°°°°° 0 dtqu
........ 45 dtqu
++++ 70 dtqu
R5
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
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]
rxlev[dBm]
SSDESDL=-80 QDESDL=20 LQOMPDL=70 QCOMPDL=30
°°°°° 0 dtqu
........ 45 dtqu
++++ 70 dtqu
R5

14. Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control
80 90 100 110 120 130
-95
-90
-85
-80
-75
-70
-65
-60
-55
Path loss [dB]
rxlev[dBm]
SSDESDL=-80 QDESDL=35 LQOMPDL=50 QCOMPDL=30
°°°°° 0 dtqu
........ 45 dtqu
++++ 70 dtqu
R5
Copyright © 1997 by Ericsson Radio Systems AB
2882-EN/LZT 123 4038 Rev A
BTS Power Control, Mobile Traffic
Recording Graph
SSDESDL=80, LCOMPDL=100, SSLENDL=4,
QDESDL=35, QCOMPDL=30, QLENDL=8, REGINTDL=4
Maxpower=30“dB”,Conv.sign.str.0==-90dBm
Power used and signal strenght -20[RXLEV]
SACCH periods (samples)
RXLEV and
RXQUAL are
averaged over
5 samples!
Quality[RXQUAL]
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)