LTE MEASUREMENTS by UE

This post discusses about the measurements done by a LTE UE. We will be seeing various measurements done by the UE and the purpose of those measurements.

We will be also seeing how the UE reports those measurements to the network, ie E-UTRAN.

Mainly a LTE UE does measurements for the following.

1.Cell Selection/ReSelection

2.Scheduling

3.Handovers

Cell Selection/Reselection

Happens during idle mode and is decided by the UE, based on the parameters specified by the network -mainly q-RxLevMin and q-QualMin (Please refer 3gpp standard 36.304 for further details on cell selection/reselection). UE measures RSRP and RSRQ of serving cell and neighbouring cells (intra frequency or inter frequency within E-UTRAN) or the relevant parameters for other RATs

What are the relevant parameters?

RSCP & RSSI for UTRA, RSSI for GSM and pilot strength in 3gpp2 networks

Scheduling

Scheduling is a eNodeb job and how it does this job is more or less implementation dependent.However it is safe to say eNodeb scheduler makes use of information send by L1 and MACof UE .Major ones in Uplink are Buffer Status Report(BSR) and Power Headroom (UPH).RRC configures the frequency with which these informations are reported. For downlink, scheduling assignments are dependent on CQI and HARQ ACK/NACKs send by the UE.

Handovers and RRC Measurements

RRC Measurements are configured by the network when the UE is in Dedicated State.The information send by the UE is mainly used for handovers .RRCConnectionReconfiguration message is used for configuring RRC measurements. UE can be requested to measure the following

a.E-UTRAN Measurements (Intra/Inter Frequency Measurements)

b.Measurements on UTRAN

c.Measurements on GERAN

d.Measurements on CDMA (1X/EVDO)

An rrcreconfiguration request used for configuring measurements etc.

Will contain the following informations

a.Measurement object :=> frequency etc.

b.Report Config :=>event(see below), Informations needed for event===> trigger quantity, reporting quantity,threshhold,offset,reportinterval,trigger time A list of blackcells (cells in which measurements shouldnt be taken) might also be configured.

c.Measurement ID=>links mo to report. Only one measurement object is allowed for a particular frequency.So measurement ids are used for linking multiple report configurations to measurement objects

d.Quantity Config=>filter (filter coefficient etc.)

UE maintains one list for MO,REPORT and MI.

More Information

EUTRAN-May be requested to measure Serving cell, list cells or detected cells in carrier frequency specified

UTRAN- Measures Listed Cells in the measconfig

CDMA/EVDO-Listed Cells

GERAN-Detected cells-Only carrier frequency will be specified in measconfig.

Trigger Events:

A1-Serving Cell better than threshhold

A2-Serving Cell worser than threshhold

A3-Neighbour Cell offset better than Serving Cell

A4-Neighbour Cell better than threshhold

A5-Neighbour Cell better than threshhold T1,Serving Cell better than T2

B1-Inter RAT neighbour better than threshold

B2-Serving Cell worser than threshhold,InterRAT neighbor better than threshhold

Ue sends the measurement report to the network (E-UTRAN) once the event is triggered.Multiple reports may be send based on a single measconfig based on the periodicity and frequency specified.Most common information that is reported are RSRP and RSRQ, though there are other informations that might be requested or reported like speedstats or globalcellinfo or strongestcellsforson.