2. 2
There are two main concept in Nortel CDMA protect when it
comes to BTS Transmit power management
Digital Domain
Analog Domain
The BTS has a finite amount of RF power available to
provide CDMA services
Available power needs to be used wisely to provide the
maximum capacity and least interference possible throughout
the network.
Understanding of such parameters will help to alleviate traffic
related performance degradation in the Bakrie network
Overview
3. 3
BTS “Domains”
The BTS forward link has two “domains”; the digital
domain and the analogue domain.
The digital domain refers to algorithms involving the
digital “gains” that control the output level of each
Channel Element.
The analogue domain refers to the total BTS output
power from all active CEs in the sector controlled by
an attenuator in the upconverter and
measured/reported at DPM output.
Reported total power is in units of 1/16th dBm at the
DPM output
4. 4
BTS Power Management Block Diagram
CE
(pilot)
CE
(traffic)
CE
(traffic)
CE
(sync)
CE
(paging)
PilotGain
SyncGain
PagingGain
Traffic Gain
from SBS
Traffic Gain
from SBS
TXPilotGain
TXMaxGain
TXMinGain
TXInitGain
Dup
TPTL
Algorithm
HPA
TxPwrFilterDecayConst
TPEFilterDecayExponential
Feed to:
SectorTxPower
BTSPerformanceData
Power
Limiting
Alogorithm
(WiltBloss)/BBWStepSize
WiltBlossStepPeriod
(TxPowerMax)/PowerTooHighThreshold
TxAttenNormal
Feed to calculations for:
ExcessForwardLinkCapacity
Call and Handoff Blocking
BTSPerformanceData
(CallBlockingThreshold
HandoffBlockingThreshold
MinPilotToTotalPwrRatio)
ForwardPowerEstimationEnabled
TPTLEnabled
TPTLTargetPowerOffset
5. 5
The Digital Domain and Forward Power Control
The power output of any channel element is controlled by
digital gain.
This include both Traffic CE as well as Overhead CEs
(paging/sync/pilot)
The overhead channels are fixed values datafilled at the BTS
on a per-sector basis.
The traffic channels vary within a defined range as required
by forward link power control. The range for the traffic channel
gains is datafilled relative to a reference power
(FwdPwrCtrlRefGain) within Flexible_power_control_array
Changing the Pilot gain for a sector has no effect on the other
individual overhead channels of that sector but will affect the
call/handoff blocking levels and intercell interference.
The Paging and Sync channel powers can be set
independent from Pilot, but set proportional to pilot so that the
mobile can properly demodulate those channels
6. 6
The Digital Domain and Forward Power Control
It is the SBS FwdPwrCtrlRefGain value that is used to calculate
the digital gains for the traffic channel.
Therefore, even if the pilot gain at one sector of a BTS is
lowered by, say, 1dB, the SBS will continue to send digital
gains in the range same range to traffic channel before.
Hence, if the Max Tx power was set to be -1dB in relation to
the Pilot and now the Pilot is lowered by 1dB, the Max Tx
power is now effectively 0dB in relation to the Pilot.
For example, with a FwdPwrCtrlRefGain of 192, an upper limit
of -1dB (-4 in datafill) from reference and a lower limit of -15dB
(-60) from reference, the selector will send digital gains in the
range 188 to 132.
7. 7
TxMinGain is the minimum digital gain that can be set for the
forward link. This value prevents the transmit gain from decreasing
to a level from which it would be difficult to recover in the event of
sudden fading or other interference. High values of this parameter
would waste capacity, while low values would increase the
possibility of dropped calls. Value is used as an offset from
FwdPwrCtrlRefGain
TxMaxGain sets the maximum digital gain that can be set for the
forward link. This value prevents the transmit gain from increasing
to a level that no longer provides any gain in performance. Setting
this parameter too low, however, increases the likelihood of
dropped calls. Value is used as an offset from FwdPwrCtrlRefGain
TxInitGain is the forward link power target used at the beginning of
a call for the FCH. Generally the value of this parameter is set fairly
high to ensure successful call setup but with fast forward power
control in the 1xRTT product, power get adjusted down reasonably
quickly. Value is used as an offset from FwdPwrCtrlRefGain
The Digital Domain and Forward Power Control
8. 8
BTS “ Power Domain” Diagram
Digital Domain (bits^2, 1/16dB, 1/16dBm) Analogue Domain
Current Traffic in bits2
Call Blocking
10
(-MinPilotToTotalPwrRatio/160)
Digital Reference
HandoffBlockingThreshold
ExcessForwardLinkCapacity
=
(Digital
Reference
-
Traffic
-
Overhead)
bits
2
CallBlockingThreshold
Total O’Head
Pilot + Paging + Sync
PilotGain
9. 9
The forward link CallBlockingThreshold and HandoffBlockingThreshold
are datafilled in terms of a “bits-squared” value.
MinPilotToTotalPowerRatio is also datafillable
ExcessForwardLinkCapacity is seen as “what is spare from the total
available” and is a derived value
The Digital Domain and Forward Power Control
10. 10
ExcessForwardLinkCapacity is calculated as follows as example:
1. Square the pilot gain (e.g. 160^2 is 25600)
2. MinPilotToTotalPowerRatio is datafilled, so if -202 is used, the Pilot
power will takeup 10^(-202/160) of Digital Reference (Total “digital” value
available)
3. Hence, Pilot power is around 5.46% of Total “digital“ value.
4. Therefore, 25600/0.056 = Digital Reference 468532
5. Sum up the bits-squared over all channel elements (overhead or traffic)
6. Subtract item 5 from item 4,result is the ExcessForwardLinkCapacity
If the ExcessForwardLinkCapacity is less than the CallBlockingThreshold,
then block new calls
If the ExcessForwardLinkCapacity is less than the HandoffBlockingThreshold
then block handoffs
The Digital Domain and Forward Power Control
11. 11
Mapping digital gain to analogue power
2542 = (0.2 * TotalTxPowerAvailable * PercentTxPowerAvailable) +
TPTLTargetPowerOffset
i.e. gain is mapped to a percentage of HPA power, not an absolute value
for case of different HPA powers on same BSC, traffic channel gains will
automatically be scaled to same percentage
same Pilot/Sync/PagingGains on BTSs with different HPA powers will
automatically be scaled to same percentage
Once this relationship has been established, we can calculate the power
equivalent to any gain or combination of gains.
Example; the output power for a) the pilot and b) the pilot + sync +
paging if the digital gains are pilot = 216, sync = 68, (half-rate) paging
= 182 and TPTLTargetPowerOffset = 0 if 2542 = 4 Watts
The pilot power corresponding to 216 is = (2162/2542) x 4 = 2.89 W
The power for all three channels is = ((2162 + 682 + (0.5 * 1822))/2542)
x 4 = 4.21 Watts
The Digital Domain and Forward Power Control
13. 13
MaxVoiceResources
MaxDataResources
Overhead Power
Handoff Power
Max.
Data
Power
Min. Guaranteed
Voice Power
Min. Guaranteed
Data Power
Dynamically
Allocated
Power
Max.
Voice
Power
0 %
20 %
20 %
40 %
0 %
100 %
80 %
60 %
100 %
80 %
60 %
40 %
Max.
Traffic
Power
Voice vs. Data Resource Allocation
Power allocation between Voice and Data
services - Radio Resource Manager (RRM)
14. 14
Power Management O&M Perspective
Attributes Exists in PowerManagement MO
TPTLTargetPowerOffset
Settable per sector carrier
1/16 dB step
TotalTxPowerAvailable
Units: 1/16 dBm
“Gettable only” (defined at factory)
PercentTxPowerAvailable
Units: 1/10 percent
Scales entire BTS output including power limiting point
Allow Carrier to have more than 100% power but reducing Num of Carrier
Would normally be set to 1000 (100%)
Datafillable for each carrier sector
PercentTxPowerTooLow
Units: 1/10 percent
Sets low power alarm threshold
15. 15
Power Management/Power Control ReCap
Despite higher HPA power, can keep same absolute powers for Pilot,
Sync, Paging
Useful for Rural/Fringe of Network situation
more headroom for peaks of Voice Activity, soft(er) handoffs
avoid triggering Power Limiting (especially Channelizer Power Limiting) and
hence maintain quality
handoff boundaries unchanged since Pilot/Sync/Paging Ratio same
will have to get used to much lower percentages for Pilot, Sync, Paging,.
pilot, sync, paging etc. expressed as % of PA power
Does changing PilotGain for a sector affect other channels?
No - traffic channels are calculated relative to FwdPwrCtrlRefGain at BSC -
paging and sync powers are independent.
Beware call blocking point is affected.
