05 01 Ra41205en60gla0 Rrm Overview

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LTE FDD RRM Overview

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Nokia LTE RRM Framework consists of RRM building blocks, RRM functions

and RRM algorithms.L3 RRM:

ICIC: Selects certain parts of the Frequency Spectrum of the LTE Carrier.

Exclusively for PDSCH and PUSCH on Cell Basis. Remaining channels not

affected.

DRX/DTX algorithm: To support provisioning of measurement gaps for Inter-

RAT-HO and DRX/DTX mode in later product releases. Not supported in RL09.

Differences with RRM WCDMA:

Softer and Soft handovers are not supported by the LTE systemLTE requirements on power control are much less stringent due to the different

nature of LTE radio interface i.e. OFDMA (WCDMA requires fast power control to

address the Near-Far problem and intra-frequency interferences)

On the other hand LTE system requires much more stringent timing

synchronization for OFDMA signals.


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PMI

- Single stream: 4 matrices (2x1)

- Dual stream: 2 matrices (2x2)

# streams OL CL

1 TxDiv SM single stream

2 SM SM dual stream


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The cyclic delay operation for the second antenna causes a linear phase shift along

the frequency dimension. Thus, summing the cyclically delayed signal in the receiverand the un-delayed signal from the first antenna causes a frequency selective fading

pattern

UE provides feedback in terms of:

CQI

Rank Indication (RI)number of layers to use

Precoding Matrix Indicator (PMI)set of weights to apply during precoding


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Note: CQI adaptation needs to be supported/enabled ;Tx diversity needs to be

supported/enabled. MIMOThis feature was introduced in RL10. In LTE70,UE radio capabilities, andUECQI, andUE rank information, are considered.

Performance counter for transmission mode usage is supported per cell


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DL adaptive closed loop MIMO (4x2) supports Transmit Diversity for 4 antenna

ports in Transmission Mode 4 (TM4) and in Transmission Mode 2 (TM2).3GPP has specified open loop Transmit Diversity using one codeword: Precoding

Feedback and Rank Information is not required!

Transmit Diversity using 4 antenna ports is used whenever there is no valid,

complete and consistent Channel State Information available as detected by eNodeB.

During Initialization when RRC setup is performed

No update of valid CSI reports for single layer (RI=1) and dual layer

(RI=2) transmissions since a characteristic update time.

UE does not send valid reports (e.g. Category 1 UEs).Transmit Diversity for 4 antenna ports is implemented as a combination of SFBC

(Space Frequency Block Coding) with FSTD (Frequency Switched Time Diversity).


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This feature allows to hand over a UE in RRC_Connected mode between two LTE

cells operating on different carriers (frequencies/bands).The trigger for this procedure is:better neighbor cell (frequency) coverage; better neighbor cell (frequency) quality;limited serving cell (frequency) andsufficient neighbor cell (frequency) coverage

Intra LTE inter-frequency handover is classified as :

Hard handover: Connection to one cell only at the same time gap assisted

measurements are usually required

Network controlled and UE assisted handover: network takes decision based onmeasurements delivered by UE

Backward handover: The resources at target cell (frequency) are reserved in

advance

Handover performed via X2 or S1 interface: Data forwarding between serving and

target eNB may be applied


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source cell thresholds (RSRP), target cell thresholds (RSCP, EcN0), hysteresis,

time to trigger and speed dependent scaling are operator configurable.Handover preparation

The Flexi Multiradio BTS initiates a handover after receiving a measurement

report form the UE by sending a S1AP:HANDOVER REQUIRED message to the

MME.

The Flexi Multimode BTS takes the first target cell indicated by the UE

measurements for the handover.

The MME responds to this with a S1AP:HANDOVER COMMAND message

indicating that the resources at the target have been reserved.Handover execution

The Flexi Multiradio BTS sends after this a RRC:Mobility from EUTRA

command message to the UE, which forces to the to a WCDMA cell.

The Flexi Multimode BTS performs handover retries to other target cells

provided by the UE measurements in case of unsuccessful handovers.


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A1: activate interRAT measurements

A2: deactivate inter RAT measurements

B2:Inter RAT measurements

Data forwarding is not supported for NACC

Measurements are triggered early enough to take to take the necessary

actions on the UE side (in contrast to triggering the RL10 redirection

procedure performed in critical conditions related to LTE coverage end

without prior measurements of 2G/3G)


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LTE55 is prerequisite for the TDD-FDD Handover.

Both features are activated with the same flag (actIfHo).

The mechanisms (evaluation of measurements reports, handover preparation,

execution, completion and data forwarding) introduced by LTE 55 are re-used in TDD-

FDD Handover.

Additionally to the original Inter-frequency Handover feature LTE1060 TDD-FDD

Handover cooperates with Inter eNB IF Load Balancing (LTE1170) if it is activated.

Both S1 (LTE54) and X2 (LTE53) handovers are supported.

In case Inter eNB Inter-frequency Load Balancing is activated, A4 is used to report

suitable inter-frequency neighbors for load balancing


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The triggers for Intra cell handover

-Following events trigger intra cell handover procedure

Intra-Cell Handover for re-keying as result of inter RAT HO from

UTRAN

Intra-Cell Handover for switch on/off TTI bundling mode

Intra-Cell Handover for key refresh due to run out of DRB ID

Intra-Cell Handover for key refresh due to PDCP sequence number

overflow

Intra-Cell Handover for key refresh due to RLC Retransmission Error


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In RL40 there was basic functionality introduced via the CRL0632

It was possible to configure Dedicated cell reselection priorities only for intra-LTE

targets frequency layer

This functionality is available at once when RL40 is on boardi.e. it did not require

setting any activation flag

In RL50 when the LTE487 Idle Mode Mobility Load Balancing feature is activated

(LNBTS:actIdleLB = true):

It was possible to configure Dedicated cell reselection priorities also for inter-RAT

targets

It was possible to configure Dedicated cell reselection priorities via the Mobility

Profiles (when also LTE490 was enabledLNBTS:actSelMobPrf = true)

In RL60 some modifications for existing mechanism were done:

Dedicated cell reselection priorities are not configurable, they are calculated with

usage of Weighted Round Robin algorithm and taking into account also priorities

configured for SIB broadcast

Instead of dedicated priorities parameters Idle Mode Mobility Load Balancing

weightsare possible to be configured


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Redirection is a mechanism to force a UE to:

switch from RRC-CONNECTED to RRC-IDLE mode and

reselect to inter-frequency/inter-RATneighbor cell for PS session

continuation and/or CS call setup (CS Fallback*)

Redirection is triggered by the radio conditions

RSRPor RSRQ (from RL35/RL50 )

in case of CS Fallback*, redirection is triggered by mobile originating or

terminating CS call

Target RAT/frequency layer is indicated to a UE by an eNB within

RRC:rrcConnectionReleasemessage

At first glance, redirection could be regarded as the last-ditch from loosing of

signaling connection between an eNB and a UE in case of either poor coverage or

extensive interference

* RRC connection release with redirection mechanism is one of the means of

realization of the CS Fallback functionality


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eHRPD (evolved High Rate Packet Data) and normal HRPD (EV-DO) overlapin mostfunctionalities

Both are 3G CDMA technology

The difference is that eHRPD data is routed through the LTE core instead of thePDSN


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05 01 Ra41205en60gla0 Rrm Overview

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