"4G LTE" Radio Measurements Event Parameters

4G Long Term Evolution LTE  Radio Measurements Performance Events

4G LTE Events MEASUREMENT & Performance.

- LIST -
ü  List of detected preambles
•        The eNB shall report a list of detected PRACH preambles to higher layers. Higher layer utilize this info for the RACH procedure
ü  Transport BLER
•        The ACK/ NACKs for each transmission of the HARQ process are reported to the MAC. Based on these ACK/NACKs the higher layers compute the BLER for RRM issues.

TIPS:-

• LINK:- 4G LTE, Handover Measurements
• LINK:- 4G LTE Evolution,4G channels & LTE Techniques

ü  TA
•        The eNB needs to measure the initial timing advance (TA) of the uplink channels based on the RACH preamble.
ü  Average RSSI
•        Measured in UL by eNB. It can be used as a level indicator for the UL power control. The RSSI measurements are all UE related and shall be separately performed for ( TTI intervals)

--- UL data allocation (PUSCH)

--- UL control channel (PUCCH)
--- Sounding reference signal (SRS)
ü  Average SINR
•        In UL the eNB measures SINR per UE. The average SINR can be used as a quality indicator for the UL power control
ü  UL CSI
•        Channel state information per PRB for each UE. The CSI shall be the received signal power averaged per PRB.

Intra LTE measurements ( from LTE to LTE)

ü  UE measurements
• CQI measurements
• Reference Signal Received Power (RSRP)
• Reference Signal Received Quality (RSRQ)
ü  eNB measurements
• Non standardized (vendor specific):TA, Average RSSI, Average SINR, UL CSI, detected  PRACH preambles, transport channel BLER
• Standardized:DL RS Tx Power, Received Interference Power, Thermal Noise Power

 Measurements from LTE to other systems

ü  UE measurementsare mainly intended for handover
• UTRA FDD:CPICH RSCP, CPICH Ec/No and carrier RSSI
• GSM:GSM carrier RSSI
• UTRA TDD:carrier RSSI, RSCP, P-CCPCH
• CDMA2000:1xRTT Pilot Strength, HRPD Pilot Strength

REFERENCE SIGNAL RECEIVED POWER (RSRP)

SAMPLES:-

ü  The received power on the resource elements that carry cell-specific reference signals

REFERENCE SIGNAL RECEIVED POWER (RSRP)

REFERENCE SIGNAL RECEIVED POWER (RSRP)

The received power on the resource elements that carry cell-specific reference signals

REFERENCE SIGNAL RECEIVED POWER (RSRP)

• The higher the maximum transmit power of eNodeB, the higher is the RS power.

• Besides, the RS power also affected by the RS power boosting constant, Pb. A larger value of Pb results in larger increase in RS power, better channel estimation & PDSCH demodulation performance.

REFERENCE SIGNAL RECEIVED POWER (RSRP)

There is dependency between RS power and Max Total Tx Power. The relation is given by

PRS = PTx, Max – 10* log (NRB *12)+ 10*log (Pb+1)

where    PRS          = RS power per RE (dBm)

------ PTx, Max     = Max eNodeB power per Tx  (dBm)

------ NRB             = number of resource block

<<<<<  Pb             = RS power boosting constant (actual value range = 0~3)

Recommended value:- Single antenna = 0, double____antenna =1)

Reference Signal Received Quality (RSRQ)

The relation of N times the Reference Signal Received Power divided by the total received power in the channel bandwidth. Within the RSRQ also the noise and interference contributions are considered.

Reference Signal Received Quality (RSRQ)

4G LTE MEASUREMENT ( EVENTS )

SAMPLES

TIMING ADVANCE (TA )

When UE wish to establish RRC connection with eNB, it transmits a Random Access Preamble, eNB estimates the transmission timing of the terminal based on this. Now eNB transmits a Random Access Response which consists of timing advance command, based on that UE adjusts the terminal transmit timing.

3GPP TA Requirements

• Timing Advance adjustment delay 

UE shall adjust the timing of its uplink transmission timing at sub-frame n+6 for a timing advancement command received in sub-frame n.

• Timing Advance adjustment accuracy 

The UE shall adjust the timing of its transmissions with a relative accuracy better than or equal to ±4* TS seconds to the signalled timing advance value compared to the timing of preceding uplink transmission. The timing advance command is expressed in multiples of 16* TS and is relative to the current uplink timing.

In GSM

= Dist = TA * bit-period * light-speed / 2

=bit-period = 48/13 (3.69) μs

=light-speed = 300000 km/s

In 4G LTE

(No DL TA)

Maintenance of Uplink Time Alignment

The UE has a configurable timer timeAlignmentTimer which is used to control how long the UE is considered uplink time aligned

• When a Timing Advance Command MAC control element is received  then UE applies the Timing Advance Command and start or restart timeAlignmentTimer.

• When a Timing Advance Command is received in a Random Access Response message then one of following action is performed by UE.

-- if the Random Access Preamble was not selected by UE MAC then UE applies the Timing Advance Command and starts or restarts timeAlignmentTimer.

-- else if the timeAlignmentTimer is not running then UE applies the Timing Advance       Command starts timeAlignmentTimer; when the contention resolution is considered not     successful  then UE stops timeAlignmentTimer.

-- else ignore the received Timing Advance Command.

• When timeAlignmentTimer expires UE flushes all HARQ buffers, notifies RRC to release PUCCH/SRS and clears any configured downlink assignments and uplink grants.

Timing Advance Command MAC Control Element

3GPP 36.321

The Timing Advance Command MAC control element is identified by MAC PDU subheader with LCID value =  11101 (Timing Advance Command)

• R: reserved bit, set to "0"

• Timing Advance Command: This field indicates the index value TA (0, 1, 2… 63) used to control the amount of timing adjustment that UE has to. The length of the field is 6 bits.

SAMPLES

Signalled granularity = 16 Ts = 0.52 μsec (corresponding to 78 m).

In GSM we got about 553m granularity.

Ts is basic time unit defined by 3GPP

Ts. = 1 / (2048 x 15000) sec = 1 / 30.720.000 = 0.0325520833 e-6

- 15000 = 15 kHz is passband for a subcarrier in LTE

-         2048 FFT-size

Radio frame Tf = 307200 x Ts = 10ms = 20 timeslots (in FDD)

1 timeslot = 15360 Ts

2048 x Ts  = 1/15kHz

 UMTS bandwidth is 5 MHz and it operates at a high chip rate 3.84 Mcps/s, which contributes to the better resolution in timing measurements compared to GSM. The timing resolution in.UMTS with one sample per chip is ∼0.26 µs which corresponds to the propagation distance of

∼78 m.

The frequency of TA is sent dependent on speed of the UE. If UE speed

72km/h = 20m/s à update every 4s

500km/h = 130m/s à max every 2s

NodeB measuring TA based on

Recevide PUSCH on TTI basis

CQI reports on PUCCH

4G LTE MEASUREMENT

CQI

CQI

Cell Selection/ReSelection

When the UE is switched on, it attempts to establish a contact with a public land mobile network (PLMN) using a certain radio access technology.

The overall process is divided into three sub-processes:

• PLMN selection and reselection to search for an available mobile network.

• Cell selection and reselection to search for a suitable cell belonging to the selected PLMN.

• Location registration to register the UE’s presence in a registration area.

PLMN Selection

When an UE is switched on, it attempts to make contact with a PLMN. The selection of the PLMN could be either automatically or manually.

• Automatic mode: Utilizes a list of PLMN to be selected in priority order.

• Manual mode: The mobile station indicates available PLMN to the user. 

Normally the UE operates on its home PLMN. At home PLMN, the MCC & MNC match with PLMN identity stored in USIM.

If the UE loses its present PLMN coverage, a new available PLMN is selected automatically or manually.

 PLMN Selection

Service types

LIMITED SERVICE: emergency calls on an acceptable cell.

UE may camp to obtain limited service like emergency call. The minimum set of requirements for initiating an emergency call in a UTRAN network are:

• The cell is not barred.

• The cell selection criteria are fulfilled.

NORMAL SERVICE: for public use on a suitable cell.

UE may camp on to obtain normal service. Such a cell shall fulfill all the following requirements:

• The cell is part of the selected / registered / equivalent PLMN

• The cell is not barred

• The cell is not part of a forbidden registration area

• The cell selection criteria are fulfilled

• In case of CSG cell it is part of the white list

OPERATOR SERVICE: For operators only on a reserved cell.

Reserved cell: When the cell status "reserved for operator use" is indicated and the Acces Class of the UE is 11 or 15 the UE may select/re-select this cell if in Home-PLMN

Barred cell: When cell status "barred" is indicated the UE is not permitted to select/re-select this cell, not even for limited services.

This information is set by office data.

PLMN Selection

Cell Selection/Reselection

Cell Selection

Upon PLMN selection, UE uses “cell selection” for fast cell searching to camp on. To receive system information UE tunes to the control channels. This procedure is known as "camping on the cell”.

The UE will then register its presence in the registration area of the chosen cell by NAS (Non Access Stratum) registration procedure.

DID YOU KNOW:-

• NAS ( Non Access Stratum )
• AS ( Access Stratum )

NAS registration procedure means the upper layer information is transmitted from UE to CN via AS (Access Stratum). The NAS offers the E-UMTS service to the users. Cell selection is performed in RRC idle mode.

The cell will be decided as suitable if it fulfils the cell selection criteria.

The purpose of camping on a cell is:

• To enable UE reception of system information from the selected PLMN

• To allow UE an RRC connection, accessing the network on the cell control channel.

• To receive paging and respond to paging messages on a tuned control channel in the registration area. The PLMN knows the tracking area of the cell in which the registered UE is camped.

Control Plane Protocol Stack

Cell RE-Selection

If the UE finds a "better" cell, UE reselects it and camps on it. After camping on, UE monitors the system information to get the quality threshold and performs measurements for the cell reselection evaluation procedure. The UE evaluates whether or not a better cell exists.

The E-UTRAN controls the quality measurements for cells to be reselected. The UE measurements are triggered according to the serving cell quality level and the threshold indicated in the system information. The measurement must satisfy different requirements for intra frequency, inter frequency or inter RAT (Radio Access Technology) quality estimations.

Cell selection is performed in RRC idle mode. The camping on a cell in idle mode enables the UE to receive information from the network. UE stays in idle mode until it transmits a request to establish an RRC connection. After receiving the RRC connection set up, the mode changes into connected mode.

TIPS:-

• E-UTRAN in 4G LTE
• RRC ( Radio remote Connection ) in 4G LTE

Cell RE-Selection

CRITERIA Selection

PLMN Selection

The UE scans all RF channels in the UTRAN band according to its capabilities to find available PLMNs.

On each carrier, the UE searches for the strongest cell according to the cell search procedure (refer cell searching) and read its system information in order to find out which PLMN the cell belongs to.

If the UE can read the PLMN identity, the PLMN and the measured signal strength is reported to the NAS: if: signal >= - x dBm (high quality PLMN); without the measured signal strength if < x dBm.

 

Cell-Search in LTE

PLMN Selection

Cell-Search in LTE,Reference Signals

CELL Selection

After selecting a PLMN, the cell selection process starts. The UE selects a suitable cell and the radio access mode based on idle mode measurements and cell selection criteria. The UE searches a suitable cell of that PLMN to camp on according to the following steps:

1) The UE creates a candidate list of potential cells to camp on by using one of the two search procedures:

• Initial Cell Selection UE scans all RF channels in the UTRAN band to find a suitable cell. On each carrier, UE searches for the strongest cell and reads its system information. Once the UE has found the suitable cell for the selected PLMN, the UE creates a candidate list consisting of this cell and its neighboring cells as received in measurement control information.

• Stored Information Cell Selection (optionally) This procedure requires information stored from previously received measurement control information elements (cell parameters, carrier frequencies, etc). After the UE has found a suitable cell for the selected PLMN, candidate list is created same as the initial cell selection process.

2) Each cell on the candidate list is evaluated according to the selection criteria S as described below.

3) After selecting a suitable cell (S criterion fulfilled) for camp on, UE reports this event to NAS for registration procedures. If the registration is successful, the UE enters into "camped normally“ state.

 

If the UE is unable to find any suitable cell in the selected PLMN, the UE enters to "any cell selection" state.

Camped normally state : UE obtains normal service and performs the following tasks:

• Select and monitor the PCH of the cell.

• Performs system information monitoring.

• Performs necessary measurements for the cell reselection evaluation procedure.

• Execute the cell reselection procedure

If after cell reselection evaluation process a better cell is found, the cell reselection is performed. If no suitable cel is found, the UE enters to next state “any cell selection”

Any cell selection: UE searches an acceptable cell of any PLMN to camp on. If an acceptable cell is found, the UE reports to NAS and camp on this cell obtaining limited service. And UE enters to “camp on any cell” state. If the UE can’t find any acceptable cell, it stay in this state.

Camped on any cell state: UE obtains limited service and periodically searches for a suitable cell in the selected PLMN. If a suitable cell is found the states changed to Camped normally.

PLMN, CELL Selection & ReSelection Flowchart

CRITERIA Cell Selection

S-CRITERION

The cell selection criterion S is a pre-condition for suitable cells.

Suitable Cells:-

Cell Selection Criterian "S"

CRITERIA Cell Re-Selection

R-CRITERION

The cell reselection evaluation process depends on whether Hierarchical Cell Structure (HCS) is used or not.

In order to perform cell reselection UE measures and ranks the neighbor cells.

For each type of neighbor cells (Intra-Frequency; Inter-Frequency; Inter-RAT, i.e. GSM) thresholds are definable. Measurements of neighbor cells will be triggered if these thresholds are reached.

HIGH MOBILITY / MEDIUM MOBILITY / NORMAL MOBILITY:

For faster moving UEs the procedure alters - speed dependent scaling rules are applied.

If the number of (different cells) cell reselections during the past time period T^CRmax exceeds N^CR_H, high mobility has been detected. If the number exceeds N^CR_M, and not N^CR_H, medium mobility has been detected.

In high/medium-mobility states, a UE:

• multiplies Qhyst by "Speed dependent ScalingFactor for Qhyst for high/medium mobility state" if sent.

• multiplies Treselection^RAT by "Speed dependent ScalingFactor for Treselection^RAT for * mobility state for RAT cells. (RAT = EUTRAN, UTRAN, GERAN).

Neighbor Cell Measurement

For inter-frequency and inter-system measurements, depending on the UE capability, the network allocates measurement gaps during which no data are sent for the UE, so that the UE could perform the necessary measurements using a single receiver.

During the measurement gaps, the particular UE cannot be scheduled for data transmission, but the vacant resources could still be used for other UEs, because of the shared channel mechanism.

FOR INTRA-FREQUENCY AND EQUAL PRIORITY INTER-FREQUENCY CELLS:

(Re-) Selected cell is a suitable cell (e.g. fulfills the S criterion) and is the best ranked cell (has the highest R).

The UE shall however reselect the new cell, only if the following conditions are met:

• The new cell is better ranked than the serving cell during a time interval Treselections

• more than 1 second has elapsed since the UE has camped on the current serving cell.

The cell-ranking criterion R is defined as shown below:

Note:-

s – indicates the serving cell,

n – indicates the candidate cell.

Neighbor Cell Measurement

Ranking of Cell

FOR INTER-FREQUENCY AND INTER-RAT NEIGHBOUR CELLS:

If UE camps longer than 1 sec in the serving cell and:

- a higher priority neighbor fulfills (during Treselection^RAT):

S^{nonServingCell,x} > Thresh^high 􀃆 reselect neighbor cell.

- no cell fulfills S^{nonServingCell,x} > Thresh^high :

S^ServingCell < Thresh^serving,low and S^{nonServingCell,x} > Thresh^x,low 􀃆 reselect neighbor cell.

Cell Reselection from WCDMA to LTE

UE must measure the LTE frequencies and detect the available LTE cell in order to perform cell reselection to LTE.

• UE measures two physical properties called for WCDMA signal. One is CPICH RSCP and CPICH EcNo. RSCP determines Srxlev and EcNo determines Squal.  

• Srxlev = Qrxlevemeas - qRxLevMin. Qrxlevemeas is RSCP level measured by UE and qRxLevMin is the value specified in SIB.

• Squal = Qqualmeas - qQualMin. Qqualmeas is EcNo level measured by UE and qQualMin is the value specified in SIB.

• The detection measurement of LTE frequencies should be done at least once every 60s for higher priority LTE frequencies.

• In following condition, detection measurements of lower priority LTE frequency is not required.

Srxlev > absPrioCellRes.sPrioritySearch1

Squal > absPrioCellRes.sPrioritySearch2

• In following condition, UE should detect once every 30s for both lower and higher priority LTE frequencies

Srxlev <= absPrioCellRes.sPrioritySearch1

Squal <= absPrioCellRes.sPrioritySearch2

• The maximum number of LTE FDD Frequencies are 4. In this case, UE should have performed measurement for detecting LTE cells on all 4 LTE frequencies once every 240 (4 x 60) s or 120(4 x 30) s depending if UE measures above or below parameter threshold absPrioCellRes.sPrioritySearch1

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Cell Reselection from LTE to WCDMA

• Measurement Criteria (From High Priority LTE Cell to Lower Priority WCDMA Cell): When LTE cell has higher priority than WCDMA, it would stay in LTE cell but it performs measurement for the low priority WCDMA if UE is under the following condition :

Srxlev of the serving cell < sNonIntraSearch (SIB3),

where Srxlev = Qrxlevmeas - qRxLevMin (SIB3),

where Qrxlevemeas = measured RSRP level, qRxLevMin = minimum RSRP level for camping

• Measurement Criteria (From High Priority LTE Cell to Lower Priority WCDMA Cell): When LTE cell has lower priority than WCDMA (WCDMA cell priority defined in SIB6 is higher than the serving cell priority),The UE always have to perform measurements on WCDMA cell. How often UE has to measure for WCDMA depends on whether Srxlev of the serving cell is greater or lower than sNonIntraSearch(SIB3). If no parameter is set (meaning in default condition), detection of WCDMA cell should be performed at least every 60 seconds.

• Reselection Criteria  (From High Priority LTE Cell to Lower Priority WCDMA Cell): If UE in LTE cell is under the following condition with the duration longer than tReselectionUtra (SIB6), it should reselect to WCDMA cell.

Srxlev of LTE cell (serving cell)  < threshServingLow (SIB3),

where Srxlev = Qrxlevmeas - qRxLevMin (SIB3),

where Qrxlevemeas = measured RSRP level, qRxLevMin = minimum RSRP level for camping

Srxlev of WCDMA cell  > threshXLow (SIB6),

where Srxlev = Qrxlevmeas - qRxLevMin (SIB3),

where Qrxlevemeas = measured RSCP level, qRxLevMin = minimum RSCP level for camping

Note : If more than one WCDMA meet this condition, UE should select to the cell with highest Srxlev

Note : If these values are not specified in SIB and UE has to apply default values, UE has to perform reselection when LTE RSRP is lower than -145 dBm and WCDMA cell is better than -119 dBm for at least 2 seconds.

• Reselection Criteria  (From Lower Priority LTE Cell to Higher Priority WCDMA Cell): If UE in LTE cell is under the following condition with the duration longer than tReselectionUtra (SIB6), it should reselect to WCDMA cell.

Srxlev of WCDMA cell  > threshXHigh (SIB6),

where Srxlev = Qrxlevmeas - qRxLevMin (SIB3),

where Qrxlevemeas = measured RSCP level, qRxLevMin = minimum RSCP level for camping