TPTL Power Management Leg Metro

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TPTL and Power Management in Legacy and Metro Cells

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Transmit Power Tracking Loop• TPTL works to stabilise BTS transmit power against

temperature and component aging effects.• TPTL functions as follows:

– Assess all the digital gain settings for overhead channels and current traffic channels

– From these, calculate an expected power output.– Using the power detector, measure the actual power output.– If there is a difference, adjust the gain of the transmit chain to

compensate.


Power Sensor

• Physically located just after the power amplifier but readings are offset to allow for components beyond the PA– The list of components included in this offset are different

between Legacy and Metro Cell so any comparison measurements need to allow for this.

• For both types of BTS, commissioning procedures include a confirmation of sensor performance.


BTS Power Management Block Diagram

Dup

TPTLAlgorithm

HPA

PowerLimitingAlgorithm

TxAttenNormal

TPTLEnabledTPTLTargetPowerOffset

CE(pilot)PilotGain

CE(traffic)

CE(traffic)

CE(sync)

CE(paging)

SyncGain

PagingGain

Traffic Gainfrom SBS (WiltBloss)/BBWStepSize

WiltBlossStepPeriod(TxPowerMax)/PowerTooHighThreshold

Traffic Gainfrom SBS

TXPilotGainPTXupperPTXstartPTXlowerPrTXerror

TPEFilterDecayExponential

TxPwrFilterDecayConst

Feed to:SectorTxPowerBTSPerformanceData

Feed to calculations for:ExcessForwardLinkCapacityCall and Handoff BlockingBTSPerformanceData(CallBlockingThresholdHandoffBlockingThresholdMinPilotToTotalPwrRatio)

ForwardPowerEstimationEnabled


BTS Commissioning

• TPTL was designed to operate in a specific range to avoid attempts to compensate for genuine hardware defects

• In Legacy BTSs, wider tolerances on the RF components and power sensor means that the TPTL range needs to be “centered” to avoid running out of range.–Achieved by disabling TPTL and choosing a

TXAttenNormal value to achieve certain conditions

–Not required on Metro Cells• As soon as TPTL is re-activated, the output power is adjusted

based on the power sensor measurements.–This can be confirmed on an active Legacy BTS

(TPTL running)• Make a small change to TXAttenNormal and allow the slow TPTL

loop to settle – the BTS output power will come back to its original value

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BTS Power Control


BTS “Domains”• The BTS forward link has two “domains”; the digital domain

and the analog domain. The digital domain refers to algorithms involving the digital “gains” that control the outputlevel of each Channel Element. The analog domain refers to the total BTS output power controlled by an attenuator in the up converter and reported at the following locations:– Metro Cell

• DPM output (NBSS7.x and NBSS8.0)

• PAM Output (NBSS 9.0)

– 1st generation BTSs (Legacy)• RFFE Antenna 0 on the 1900MHz Mini BTS


The Digital Domain and Forward Power Control• The power output of any channel element is controlled by a digital

gain.• 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 pilot power. – For example, with a pilot gain of 216, an upper limit of -1dB pilot

(PTxUpper) and a lower limit of -15dB pilot (PTxLower), the selector will send digital gains in the range 192 to 38.

• Note that the pilot gain is datafilled both per-sector at the BTS PilotGain) and as a global parameter at the SBS (TXPilotGain) as a forward power control reference value.– It is the SBS TXPilotGain 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 to 192, the SBS will continue to send digital gains in the range 192 to 38. I.e., for this sector alone, the traffic channels are now effectively 0dB pilot to -14dB pilot.


The Digital Domain: ExcessForwardLinkCapacity• The forward link Call and HandoffBlockingThresholds are datafilled in terms of

ExcessForwardLinkCapacity which is a “bits-squared” value.• ExcessForwardLinkCapacity is calculated as follows:

– 1. Square the pilot gain (e.g. 2162 is 46656)– 2. Divide by MinPilotToTotalPowerRatio (e.g. 46656 divided by -7.5dB (in linear terms)

is 262365). This number is referred to as the “digital reference”.– 3. Sum up the bits-squared over all channel elements– 4. Subtract item 3. from item 2. The result is the ExcessForwardLinkCapacity.

• If the ExcessForwardLinkCapacity is less than the CallBlockingThreshold, then block new calls (pre-NBSS8: just send BTS Ack. NBSS8: send reorder).

• If the ExcessForwardLinkCapacity is less than the HandoffBlockingThreshold, then block handoffs (send Handoff Direction without the new sector - mobile will ask again with a new PSMM).

• Note that there is no action if the “digital reference” is crossed although EFLC will never be reported as a negative number.


The Analog Domain: Power Sensor• Immediately following the High Power Amplifier (HPA), there is a

power sensor that is calibrated to report the total power in units of 1/16th dBm at the following locations:– 1st generation:

• RFFE Antenna 0 on the 1900MHz Mini BTS

– Metro Cell:• DPM Output

• PAM Output


The Analog Domain: Power Limiting• The sensor reading is compared against a datafillable upper limit

TxPowerMax/PowerTooHighThreshold. If this threshold is exceeded,the BTS will wilt the sector by one step and re-compare the reading with TxPowerMax /PowerTooHighThreshold. This is the Power Limiting algorithm and it repeats until the power no longer exceeds TxPowerMax /PowerTooHighThreshold. This limits the output power to TxPowerMax /PowerTooHighThreshold. However, forward link power control will act in opposition to the power limiting, possibly causing an unstable situation. For this reason, this algorithm should be viewed as an HPA protection mechanism only and the blocking thresholds should be set such that Power Limiting is a rare occurrence. The FwdHandoffBlockingThreshold should be at a higher power than the FwdCallBlockingThreshold to give priority to existing calls.


Transmit Power Tracking Loop• The two domains are “linked” by TPTL according to the relationship:

2542 = 36dBm + (TPTLTargetPowerOffset/16)• Once this relationship has been established, we can calculate the

power equivalent to any gain or combination of gains.• Example; what is 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.

• Answer; Since the digital gains are voltage gains, most calculations are in terms of “bits squared” to convert to power. Therefore, if 2542

= 4 Watts, the power corresponding to 216 is:• power = (2162/2542) x 4 = 2.89 Watts• and the power for all three channels is:• power = ((2162 + 682 + (0.5 * 1822))/2542) x 4 = 4.21 Watts


BTS Power Management Block Diagram

Dup

TPTLAlgorithm

HPA

PowerLimitingAlgorithm

TxAttenNormal

TPTLEnabledTPTLTargetPowerOffset

CE(pilot)PilotGain

CE(traffic)

CE(traffic)

CE(sync)

CE(paging)

SyncGain

PagingGain

Traffic Gainfrom SBS (WiltBloss)/BBWStepSize

WiltBlossStepPeriod(TxPowerMax)/PowerTooHighThreshold

Traffic Gainfrom SBS

TXPilotGainPTXupperPTXstartPTXlowerPrTXerror

TPEFilterDecayExponential

TxPwrFilterDecayConst

Feed to:SectorTxPowerBTSPerformanceData

Feed to calculations for:ExcessForwardLinkCapacityCall and Handoff BlockingBTSPerformanceData(CallBlockingThresholdHandoffBlockingThresholdMinPilotToTotalPwrRatio)

ForwardPowerEstimationEnabled


BTS “ Power Domain” DiagramDigital Domain (bits2, 1/16dB, 1/16dBm) Analog Domain

2542 = 4000 mW = 36dBm (+ TPTLTargetPowerOffset/16)

SyncGain = 4096 bits2

PagingGain = 8978 bits2

PilotGain = 25600 bits2

Current Traffic in bits2

Call Blocking = 211532 bits2

TxPowerMax/PowerTooHighThreshold = 666 dBm*1610(-M

inPilotToTotalPwrR

atio/160) = 18.3

Digital Reference=468532 bits2

HandoffB

lockingThreshold = 0 bits 2

ExcessForwardLinkC

apacity =(D

igital Reference -Traffic -O

verhead) bits 2

CallB

lockingThreshold =257000 bits 2

Handoff Blocking = 468532 bits2

Example for:Pilot/Sync/PagingGain = 160/64/134 (half-rate paging)MinPilotToTotalPwrRatio = -202CallBlockingThreshold = 257000HandoffBlockingThreshold = 0TxPowerMax/PowerTooHighThreshold = 666TPTLTargetPowerOffset = 0

Total O’Head = 38674 bits2

29050 mW = 44.63dBm = 200%

41.63dBm = 14540 mW = 100%

13120 mW = 41.18dBm = 90%

2400 mW = 33.8dBm = 16.5%

1590 mW = 32.0 dBm = 11%

560 mW = 27.5dBm = 3.8%

250 mW = 24.0dBm = 1.7%


Power Management Changes in NBSS8.2/9.0• Major change in digital gain to analog power mapping

for the Metro Cell– 2542 no longer mapped to 4W + TPTLTargetPowerOffset– instead, 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


Power Management Attribute Changes• Attributes in PowerManagement MO• TotalTxPowerAvailable

– Units: 1/16 dBm– “Gettable only” (defined at factory)

• PercentTxPowerAvailable– Units: 1/10 percent– Scales entire BTS output including power limiting point (cf

TPTLTargetPowerOffset which leaves power limiting point unchanged)

– Would normally be set to 1000 (100%)

• PercentTxPowerTooLow– Units: 1/10 percent– Sets low power alarm threshold


Power Management Datafill Changes• To maintain same output power for traffic and

overhead channels, TPTLTargetPowerOffset can be adjusted to bring mapping back to 4W.– 1900MHz: Mapping changes to 2.9W so add +23 (+1.4dB)

to any existing TPTLTargetPowerOffset settings.

• Going forward, can choose to standardise on one set of Pilot/Sync/Paging/TXPilotGain settings for all 1900MHz BTSs.

Documents

TPTL Power Management Leg Metro