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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

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.
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


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

STAY TUNED>>

TO BE CONTINUED:-






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