WRST 2/2+ IndexModule Objectives
At the end of the module you will be able to:
Describe the principles of Load Control and it's parameters in detail
Differentiate controllable, semi-controllable & non-controllable loads
Describe the relationships of Load Control with AC & PS
Identify the parameters influencing BTS load measurements
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BTS Measurements and Reporting
LC is a cell based RRM Function, utilising cell specific:
thresholds set by RNP,
in association with AC & PS
LC updates load status using resource measurements & estimations provided by AC & PS
Continuously feeds cell load information to the other RRM functions, e.g. PS & AC
LC
AC
PS
RM
RNC
BTS Measurements and Reporting
Actual prevailing load in the cell depends on multiple factors
Number of active connections
Properties of the connections
SHO condition
Different methods can be applied to measure/estimate load conditions, e.g.
Throughput Based Load Estimation
Power Based Load Estimation
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DL uses Power Measurements and calculations for RRM decisions
UL uses Power & Throughput estimations and calculations for RRM decisions
å
Throughput based threshold
PRx_Own
PTx_Own
Radio Interface Load
The BTS measures the total received power (PrxTotal) and the total transmitted power (PtxTotal) on cell basis
The BTS reports PrxTotal & PtxTotal of each cell to the RNC
LC updates
Cell load status for each cell based on RADIO RESOURCE INDICATION
Non-controllable UL (PrxNC) & DL (PtxNC) load in cell
Semi-controllable UL (Prx_SC) & DL (Ptx_SC) load in the cell (related to PS Streaming)
AC and PS algorithms work on the current cell load status provided by LC
Denying call admission (AC) & throttling back NRT traffic (PS) are the overload actions
After scheduling PS provides LC with PrxNRT, PtxNRT & LNRT estimates
After admitting RT RAB, AC provides LC with NC load increase estimate
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System noise PrxNoise is the sum of all stationary noises:
thermal noise
PrxNoise can vary place to place & even time to time
PrxNoise setting affects the capacity of cell:
PrxNoise too low: overestimation of cell load and can lead to unnecessary call blocking
PrxNoise too high: underestimation of cell load and can lead to overload situation
RNC provides Autotuning-Tool to measure unloaded system noise:
PrxUnloaded; it adjusts PrxNoise parameter based on these measurements
PrxTotal = PrxUnloaded when own cell considered unloaded / very low load;
LRT UnloadedRT & LNRT UnloadedNRT & no EDCH users in the cell
UnloadedRT & UnloadedNRT are RNC parameters (values for NRT: 1 %, RT: 2 %)
LRT & LNRT: UL load factor for own cell RT (AC estimates) & PS users (PS estimates)
PrxNoise updated by the autotuning algorithm based on PrxUnloaded
PrxNoise autotuning step size limited by PrxNoiseMaxTuneAbsolute
PrxNoise
PrxNoiseAutotuning
PrxNoiseMaxTuneAbsolute
255 dB: Autotuning is not limited
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UL Preventive & Overload Thresholds
PrxTarget =
load factor
PtxOffset: WCEL; 0 .. 6; 0.1; 1dB
PtxCellMax WCEL: 0…50; 0.1; 43dBm
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BTS Measurements and Reporting
PtxTotal – Transmitted Carrier Power
PtxNonHSPATransmitted Code Power of all codes not used for HSDPA
Nokia Private NBAP
Nokia Private NBAP
Nokia Private NBAP
Acknowledged PRACH preambles
Nokia Private NBAP
Provided HSDPA Bitrate
Provided HSUPA Bitrate
Required Power
RRM in RNC needs this information for Streaming mapped on HSPA
(NST – Non Scheduled Transmission)
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WBTS sends measurements periodically according setting of RRM parameter
The RNC can order BTSs to report cell-based and connection-based measurements only if internal thresholds are exceeded.
However, a report is sent at least once per 10 reporting periods (RNP parameters).
The filtering functionality decreases the amount of measurement messages between the BTS and the RNC and thus decreases the load of RNC computer units.
Internally RNC repeats the cell based measurements every WBTS: RRIndPeriod to provide RRM functions a continuous flow of measurements
Reporting period
RADIO RESOURCE MEASUREMENT REPORT
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WBTS can filter a measurement report (not sent to RNC) –
only inform RNC about important load changes
reduce common NBAP signaling on IuB interface
RNC provides load threshold and value change threshold to WBTS
Parameter settings for
WBTS & NB/RSxxx send periodic measurement reports with code power measurement results from all Radio Links (UEs in Cell_DCH)
Depending on allocated service type WBTS applies different reporting frequency
CS Services and SRB
WBTS: DedicatedMeasRepPeriod; Range: 0.5..5 s; step 0.5 s; default = 2.5 s
CS Data Services
WBTS: DediMeasRepPeriodCSdata; Range: 0.5..5 s; step 0.5 s; default = 1.5 s
PS Data Services
WBTS: DediMeasRepPeriodPSdata; Range: 0.5..5 s; step 0.5 s; default = 0.5 s
Remark:
NSN recommended to set all 3 values to 2.5 s
and to reduce the averaging windows in RNC
(Technical Note RNC SW 131)
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Florian Reymond
RANPAR, HSUPA measurements included & some minor additions (e.g. parameters related to SIRerror filtering & reporting)/ S. Cardamone, review & deletion of alpha trimmed filter (JI)
Florian Reymond
Thorsten Hagedorn
Benedikt Aschermann