Tuesday, 27 October 2015

LTE KPI for E-UTRAN ( Mandatory)



KPI Category "Accessibility"

E-RAB Accessibility

Definition

A KPI that shows probability for an end-user to be provided with an E-RAB at request.
Probability success rate for E-RABs establishment. Successful attempts compared with total number
of attempts for the different parts of the E-RAB establishment.

 
RRC.ConnEstabAtt.Cause
RRC.ConnEstabSucc.Cause
S1SIG.ConnEstabAtt
S1SIG.ConnEstabSucc
ERAB.EstabInitAttNbr.QCI
ERAB.EstabInitSuccNbr.QCI
ERAB.EstabAddAttNbr.QCI
ERAB.EstabAddSuccNbr.QCI

Mapping of end-user applications towards E-RABs can be different depending on operator strategy; hence the
measurement shall be adjustable depending on operator E-RAB mapping strategy.

Table 1 Example of service mapping towards E-RABs

 
To provide Accessibility measurement from E-UTRAN that can be mapped to a service for the operator the following
measurements are defined:
A1: Initial E-RAB establishment success rate
A2: Added E-RAB establishment success rate
The establishment success rate is defined as:
 
Services can be mapped towards either Initial or Added E-RABs depending on operator strategy. If a different QoS
characteristic is required compared with the QoS characteristic provided by an existing Initial E-RAB, an Added ERAB
can be requested. QoS characteristics can be defined on an E-RAB basis; hence both Initial E-RAB establishment
success rate (A1) and Added E-RAB establishment success rate (A2) shall be available per QoS group.
With these two measures the operator can calculate the service accessibility depending on E-RAB mapping as follows:
Service mapped on Initial E-RAB = A1*100 [%]
Service mapped on Added E-RAB = A1*A2*100 [%]



KPI Category "Retainability"
E-RAB Retainability

A measurement that shows how often an end-user abnormally looses an E-RAB during the time the E-RAB is
used.
 Number of E-RABs with data in a buffer that was abnormally released, normalized with number of data session
time units.
To measure E-RAB Retainability for a single QCI (R1) is fairly straight forward.
 

However to measure the E-RAB Retainability for UEs is not as straight forward. The measurement R1 is
defined to look at the activity level of just one QCI at the time, so to use this formula and measurements in an
aggregated way to get E-RAB Retainability on UE level will not be accurate (e.g. for an UE with multiple ERABs,there might be E-RABs that are active at the same time, hence aggregating the QCI measurements for
session time will give a larger session time than the total UE session time. See picture below).
Hence a measurement E-RAB Retainability on UE level is defined (R2) to provide a measurement for the overall
E-RAB Retainability.
 
ERAB.RelActNbr.QCI
ERAB.SessionTimeUE
ERAB.SessionTimeQCI.QCI

The retainability rate is defined as:
 

As for defining an abnormal E-RAB release with end-user impact, it shall only be considered an abnormal release of the E-RABs if the eNodeB considers there to be data waiting for transfer in any of the buffers.
As for defining an E-RAB as active, an E-RAB shall be considered active if there recently has been any data
transmission in any direction

KPI Category "Integrity"

E-UTRAN IP Throughput

A KPI that shows how E-UTRAN impacts the service quality provided to an end-user.
Payload data volume on IP level per elapsed time unit on the Uu interface.
IP Throughput for a single QCI:
 
DRB.IPThpDl.QCI
DRB.IPThpUl.QCI

To make sure that only impacts from the RAN is included in this measurement, time units to be
included in 'elapsed time unit on the Uu interface 'shall only be the ones where there is data in the
buffer to be transmitted E.g.in application data flows such as a web session, there are times when there
is no data to transmit by the eNodeB due to bursty traffic pattern, then this 'eNodeB idle time' shall not
be included in 'elapsed time unit on the Uu interface '.

To achieve a Throughput measurement (below examples are given for DL) that is independent of file size it is important to remove the samples where one TTI on the radio interface is not utilized. (Successful transmission, buffer empty in (figure below).
 

IP Throughput in DL = ThpVolDl / ThpTimeDl (kbits/s)

To achieve a throughput measurement that is independent of bursty traffic pattern, it is important to make sure that idle gaps between incoming data is not included in the measurements. That shall be done as considering each burst of data as one sample.ThpVolDl is the volume on IP level and the ThpTimeDl is the time elapsed on Uu for transmission of the volume included in ThpVolDl.
 

E-UTRAN IP Latency

A measurement that shows how E-UTRAN impacts on the delay experienced by an end-user.
Time from reception of IP packet to transmission of first packet over the Uu.
 


DRB.IPLatDl.QCI

To achieve a delay measurement that is independent of IP data block size only the first packet sent to Uu is measured.
To find the delay for a certain packet size the IP Throughput measure can be used together with IP Latency (after the first block on the Uu, the remaining time of the packet can be calculated with the IP Throughput measure).
 
T_Lat is defined as the time between receiption of IP packet and the time when the eNodeB transmits the first block to Uu.
Since services can be mapped towards different kind of E-RABs, the Latency measure shall be available per QoS group.

KPI Category "Availability"

E-UTRAN Cell Availability

A KPI that shows Availability of E-UTRAN Cell.
Percentage of time that the cell is considered available.
 
RRU.CellUnavailableTime.cause
 



As for defining the cell as available, it shall be considered available when the eNodeB can provide E-RAB service in the cell.

KPI Category "Mobility"

E-UTRAN Mobility
Definition
E-UTRAN Mobility.
A KPI that shows how E-UTRAN Mobility functionality is working.
Success rate of E-UTRAN Mobility.
 
HO.ExeAtt
HO.ExeSucc
HO.PrepAtt.QCI
HO.PrepSucc.QCI


The measurement shall include both Intra E-UTRAN and Inter RAT handovers.
The measurement shall include both the preparation and execution phase of the handover.
'Entering preparation phase' is defined as the point of time when the source eNB attempts to prepare resources for an UE in a neighboring cell.'Success of execution phase' is defined as the point of time when the source eNB receives information that the UE successfully is connected to the target cell.

Budi Prasetyo

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