1 S-72.333 Post–graduated Course in Radio Communication, H. Yin

Handover Control in CDMA Radio Networks

Hongying YinFeb. 11th 2003

Helsinki University of Technologyhongying.yin@nokia.com

2 S-72.333 Post–graduated Course in Radio Communication, H. Yin

Content1. Handover

• Soft handover• Softer handover• Inter-frequency handover• Intra-frequency handover• Inter-system handover

2. Cell info for Handover Measurement Reporting• Neighbour cell definitions• Cell List

3. Measurement Reporting Criteria• Intrafrequency measurements

• Interfrequency and Intersystem Measurements• UE Internal Measurements

4. Reporting Measurement Results

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Soft Handover (1/2)

In a soft handover, a terminal is connected simultaneously to more than one base station via several handover branches. The group of base stations communicating with the terminal during soft handover is called the active set.

Based on signal strength decisions involving various thresholds, branches can be added to or removed from the connection at any time, in other words base stations can be added to or removed from the active set. Such actions are referred to as ”active set update” procedures.

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Soft Handover (2/2)

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Softer Handover (1/2)

A softer handover is performed between two adjacent sectors of the same base station.

In downlink, soft and softer handover is very similar from the terminal point of view (signal replicas are simply combined in the Rake receiver).

In uplink, there is a major difference between soft and softer handover. – In soft handover branches, signal replicas can only be

combined within the Radio Network Controller (RNC) – In softer handover branches, signal replicas can be

combined earlier - within the base station.

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Softer Handover (2/2)

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Hard Handover

This type of handover is well-known from GSM. A hard handover may take place:

Between channels carried by two different frequencies within the same cell or adjacent cells (both cases are referred to as interfrequency handovers);

Between UTRA FDD and UTRA TDD channels (intermode handover);

Between UMTS and GSM channels (intersystem handover)

In addition, in such situations where the Iur interface between two RNCs is not available for soft handover, a hard handover can be performed - using the same frequency - from a cell belonging to one RNC to a cell belonging to the other RNC (intrafrequency handover).

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Hard/Interfrequency Handover

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Hard/Intrafrequency Handover

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Inter-System Handover

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Handover Measurement Reporting- Neighbour cell definitions

Intrafrequency neighbour list:The UE must be able to monitor at least 32 cells on the same WCDMA

carrier frequency as the serving cell.

Interfrequency neighbour list:The UE must be able to monitor at least 32 cells in all on two WCDMA

carrier frequencies in addition to the serving cell.

Intersystem neighbour lists:A separate list is needed for each neighbouring PLMN. Max of 32

interfrequency neighbour must be supported by UE.

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Handover Measurement Reporting- WCDMA Neighbour Cell List Info

Global RNC Identifier (PLMN id MCC and MNC, RNC id)

Cell ID Location Area Code (LAC) Routing Area Code (RAC) UTRA Absolute Radio Frequency Channel Number

(UARFCN) Scrambing code of the Primary Common Pilot Channel

(P-CPICH)

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Handover Measurement Reporting- GSM Neighbour Cell List Info

Cell Global ID CGI = MCC + MNC + LAC + CI

BCCH frequency Base Station ID Code

BSIC = BCC + NCC

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Measurement Reporting Criteria- Intrafrequency Measurements

Mobile Equipment Handover Type (MEHO) RAN broadcasts the measurements reporting

criteria for intrafrequency measurements in BCCH.

When criteria is fulfilled, UE reports the measurement results to RNC.

RNC makes the HO decisions.

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Measurement Reporting Criteria- Interfrequency and Intersystem Measurements

Network Handover Type (NEHO) Interfrequency and Intersystem measurements are

made only when RNC sends orders. A separate measurements reporting criteria is sent to

UE. UE will periodically reports the results to RNC. The measurement is controlled by:

– Reporting duration– Reporting interval

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Measurement Reporting Criteria- UE Internal Measurements

UE internal measurements criteria are controlled:– cell-by-cell basis

and

– parameters common to all cells in the whole RNC. Network sends the measurement information

on DCCH rather than BCCH. UE reports the measurement results to RNC

when the measurement criteria is fulfilled.

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Measurement Results Reporting

Event-triggered intrafrequency measurement report

Periodic intrafrequency measurement report Interfrequency measurement report Intersystem measurement report Measurement reports on common channels Quality deterioration report

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Measurement Results Reporting - Reporting of the Intrafrequency Measurements

UE is constantly monitoring – P-CPICH Ec/I0 neighbor cells– Evaluating the reporting criteria

UE sends an event-trigger report when one of the events is fulfilled.

Some other factors also taken into accounts during the measurements.

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Report of the Measurement Results- Time-to-Trigger Mechanism

Frequent reporting excessive signalling load

Each report event can be connected with timer

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Report of the Measurement Results- Event-Triggered/Periodic Reporting

Event-triggered reporting results in an access stratum update.

If access stratum can not be updated because of lack of capabilities or HW resources, UE will send periodic report.

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Exercise

Explanation of what is soft handover, softer handover and hard handover.

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Abbreviation and Definition

BCCH: broadcast control channel CPICH: common pilot channel DCCH: dedicated control channel Ec/I0: ratio in decibels (dB) of the pilot energy accumulated over one PN chip

period (Ec) to the total power spectral density in the received bandwidth (I0) FDD: frequency division duplex Iur: logical interface for the interconnection of two radio network controller (RNC)

components of the UMTS terrestrial radio access network (UTRAN) system. MCC: mobile country code MNC: mobile network code TDD: time division duplex UMTS:   Universal Mobile Telecommunications System UTRA:   UMTS terrestrial radio access Uu: Radio interface between the UMTS terrestrial radio access network (UTRAN)

and user equipment (UE)

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References

1. Jaana Laiho, Achim Wacker, and Tomás Novosad: “Radio Network Planning and Optimisation for UMTS”, Wiley 2002.

2. Jens Zander and Seong-Luyn Kim: “Radio Resource Management for Wirless Networks”, Artech House 2001.

3. Holma & Toskala: "WCDMA for UMTS, Radio Access for Third Generation Mobile Communications", John Wiley & Sons.

4. T. Ojanpera &etc. ”wideband CDMA for Third Generation Mobile Communications” , Artech House Publishers.

5. Gordon L. Stüber: ”Principle of Mobile Communication”, 2nd edition, Kluwer Academic Publishers.

6. Nokia Internal training materials for CDMA/WCDMA/UMTS.