WCDMA 3G ( Inter-Frequency ) Handover Principle and Parameters:-

WCDMA ( Inter-Frequency ) Handover Principle and Parameters:-

Inter-Frequency Handover:-

1.     Inter-Frequency Handover Overview

2.     Inter-Frequency Handover Procedure

3.     Signaling Procedures for Inter-Frequency Handover

Characters of Inter-Frequency Handover:-

·       The carrier frequency of the current cell and target cell are different

·       Based on the triggering causes of handover

Inter-frequency handover can be categorized into four types:-

ü  Coverage-based

ü  QoS-based

ü  Load-based

ü  Speed-based

Coverage-based inter-frequency handover

If a moving UE leaves the coverage of the current frequency, the RNC needs to trigger the coverage-based inter-frequency handover to avoid call drops

• LINK:- 3G wcdma IRAT handover detail BLOG

QoS-based inter-frequency handover

According to the Link Stability Control Algorithm, the RNC needs to trigger the QoS-based inter-frequency handover to avoid call drops.

Load-based inter-frequency blind handover

To balance the load between inter-frequency con-coverage cells, the RNC chooses some UEs and performs the inter-frequency blind handover according to user priorities and service priorities.

Speed-based inter-frequency handover

When the Hierarchical Cell Structure (HCS) applies, the cells are divided into different layers according to coverage. The macro cell has a larger coverage and a lower priority, whereas the micro cell has a smaller coverage and a higher priority. Inter-frequency handover can be triggered by the UE speed estimation algorithm of the HCS. To reduce the frequencies of handover, the UE at a higher speed is handed over to a cell under a larger coverage, whereas the UE at a lower speed is handed over to a cell under a smaller coverage.

Inter-Frequency Handover

A.Inter-Frequency Handover Overview

B. Inter-Frequency Handover Procedure

i.          Coverage-based inter-frequency handover

ii.        QoS-based inter-frequency handover

iii.       Load-based inter-frequency handover

iv.       Speed-based inter-frequency handover

v.         Blind handover Based on Event 1F

vi.       Inter-frequency anti-PingPong

vii.     Inter-frequency handover retry

3.Signaling Procedures for Inter-Frequency Handover

i.       Coverage-based inter-frequency handover:-

The handover procedure is divided into four phases: handover triggering, handover measurement, handover decision, and handover execution.

In the triggering phase:-

The RNC notifies the UE to measure through an inter-frequency measurement control message. If the quality of the pilot signal in the current cell deteriorates, the CPICH Ec/No or CPICH RSCP of the UMTS cell that the UE accesses is lower than the corresponding threshold, and the UE reports event 2D.

In the measurement phase:-

If the RNC receives a report of event 2D, the RNC requests the NodeB and UE to start the compressed mode to measure the qualities of inter-frequency neighboring cells, and the RNC sends an inter-frequency measurement control message.

In the measurement phase, the method of either periodical measurement report or event-triggered measurement report can be used.

In the decision phase:-

After the UE reports event 2B, the RNC performs the handover. Otherwise, the UE periodically generates measurement reports, and the RNC makes a decision after evaluation.

In the execution phase:-

The RNC executes the handover procedure.

Coverage-based inter-frequency handover

MEASUREMENT EVENTS

When the estimated quality or strength of the currently used frequency is below a certain threshold,2D Event will be triggered, Then RNC will initiate the compress Mode to start inter-frequency or Inter-RAT handover measurement.

• LINK:- 3G wcdma IRAT handover detail BLOG

During compress mode, if the estimated quality of the currently used frequency is above a certain threshold, 2F Event will be triggered, Then RNC will stop the compress Mode.

MEASUREMENT EVENTS

Compressed Mode

Purpose

Measure the inter-frequency cell or Inter-RAT cell under FDD mode

Categories

Downlink compressed mode

Uplink compressed mode

Realization Methods

SF/2

Higher layer scheduling

Compressed Mode control is a mechanism whereby certain idle periods are created in radio frames during which the UE can perform measurements on other frequencies. The UE can carry out measurements in the neighbouring cell, such as GSM cell and FDD cell on other frequency. If the UE needs to measure the pilot signal strength of an inter-frequency WCDMA or GSM cell and has one frequency receiver only, the UE must use the compressed mode.

Each physical frame can provide 3 to 7 timeslots for the inter-frequency or Inter-RAT cell measurement, which enhances the transmit capability of physical channels but reduces the volume of data traffic.

In DL, during compressed mode ,UE receiver can test signal from other frequency. In order to avoid the effect cause by UE transmitter, compress mode is also used in UL.

The compressed mode includes two types, spreading factor reduction (SF/2) and high layer approaches. The usage of type of compressed mode is decided by the RNC, according to spreading factor used in uplink or downlink.

Compressed Mode

• Link:- Detailed Intra frequency handover blog
• Link:- detailed Irat handover blog

Parameter

2D EVENT

Inter-freq CS measure start Ec/No THD

Parameter ID: InterFreqCSThd2DEcNo

The default value of this parameter is -14dB

Inter-freq R99 PS measure start Ec/No THD  

Parameter ID : InterFreqR99PsThd2DEcNo

The default value of this parameter is -14dB

Inter-freq H measure start Ec/No THD

Parameter ID : InterFreqHThd2DEcN0 

The default value of this parameter is -14dB

Inter-freq CS measure start RSCP THD

Parameter ID: InterFreqCSThd2DEcNo

The default value of this parameter is -95dBm

Inter-freq R99 PS measure start RSCP THD 

Parameter ID : InterFreqCSThd2DRSCP

The default value of this parameter is -95dBm

Inter-freq H measure start RSCP THD 

Parameter ID : InterFreqHThd2DRSCP 

The default value of this parameter is -95dBm

2D hysteresis

Parameter ID: Hystfor2D 

The default value of this parameter is 4 (2dB)

2D event trigger delay time

Parameter ID : TimeToTrig2D 

The default value of this parameter is D320 (320 ms)

2F EVENT

Inter-freq CS measure stop Ec/No THD

Parameter ID: InterFreqCSThd2FEcNo 

The default value of this parameter is -12dB

Inter-freq R99 PS measure stop Ec/No THD

Parameter ID : InterFreqR99PsThd2FEcNo 

The default value of this parameter is -12dB

Inter-freq H measure stop Ec/No THD

Parameter ID : InterFreqHThd2FEcN0  

The default value of this parameter is -12dB

Inter-freq CS measure stop RSCP THD

Parameter ID: InterFreqCSThd2FRSCP

The default value of this parameter is -92 dBm

Inter-freq R99 PS measure stop RSCP THD

Parameter ID : InterFreqR99PsThd2FRSCP

The default value of this parameter is -92dBm

Inter-freq H measure stop RSCP THD

Parameter ID : InterFreqHThd2FRSCP 

The default value of this parameter is -92dBm

2F hysteresis

Parameter ID: Hystfor2F  

The default value of this parameter is 4 (2dB)

2F event trigger delay time

Parameter ID : TimeToTrig2D 

The default value of this parameter is D1280  (1280 ms)

Handover Measurement

When the UE enters the compress mode, RNC will trigger the inter-frequency handover measurement by two additional measurement control signaling , so as to request UE test inter-frequency neighbor cell.

In this Measurement control message, RNC should inform the UE inter-frequency measurement parameter (Neighbor list, reporting mode…)

Handover Measurement

Report Mode

·       The measurement report mode of inter-frequency handover is configured through the parameter Inter-frequency measure report mode. By default ,periodically reporting is recommended.

·       The advantage of periodical measurement report is that if the handover fails, the RNC reattempts the handover to the same cell after receiving the periodical measurement report from the UE. This increases the probability of the success of inter-frequency handover.

·       Based on the measurement control message received from the RNC, the UE periodically reports the measurement quality of the target cell. Then, based on the measurement report, the RNC makes the handover decision and performs handover.

Inter-Frequency Handover

A.Inter-Frequency Handover Overview

B. Inter-Frequency Handover Procedure

i.          Coverage-based inter-frequency handover

ii.        QoS-based inter-frequency handover

iii.       Load-based inter-frequency handover

iv.       Speed-based inter-frequency handover

v.         Blind handover Based on Event 1F

vi.       Inter-frequency anti-PingPong

vii.     Inter-frequency handover retry

3.Signaling Procedures for Inter-Frequency Handover 

QoS-based inter-frequency handover

Procedure of QoS-based inter-frequency handover :

The handover procedure is divided into four phases:

ü  handover triggering

ü  handover measurement

ü  handover decision

ü  handover execution.

Besides the triggering step, the rest 3 steps are the same with Coverage-based inter-frequency handover

In the triggering phase

   If the service quality of the current cell deteriorates, the Link Stability Control Algorithm makes a handover measurement decision.

In the measurement phase

   The RNC requests the NodeB and the UE to start the compressed mode to measure the qualities of inter-frequency neighboring cells. Then, the RNC sends inter-frequency measurement control messages.

  In the measurement phase, the method of periodical measurement report or event-triggered measurement report can be used.

In the decision phase

   After receiving the event 2B measurement reports of CPICH RSCP and CPICH Ec/No of the inter-frequency cell, the RNC performs the handover.  Otherwise, the UE periodically generates measurement reports, and the RNC makes a decision after evaluation.

In the execution phase

  The RNC executes the handover procedure.

Note :

    About “Link Stability Control Algorithm” :

    When the uplink transmit power of the UE or downlink transmitted code power of the NodeB exceeds the  associated threshold  :

For AMR, a fixed  sequence of rate downsizing, inter-frequency handover, and then Inter-RAT handover are performed,

for VP ,Inter-handover handover are performed,

For BE service, rate downsizing, inter-frequency handover, and then Inter-RAT handover are performed according to the configured sequence

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