Handover Control in CDMA Radio Networks

1. Handover Control in CDMA Radio Networks Hongying Yin Feb. 11th 2003 Helsinki University of Technology hongying.yin@nokia.com 1S-72.333 Post–graduated Course in Radio Communication, H. Yin

2. Content • Handover • Soft handover • Softer handover • Inter-frequency handover • Intra-frequency handover • Inter-system handover • Cell info for Handover Measurement Reporting • Neighbour cell definitions • Cell List • Measurement Reporting Criteria • Intrafrequency measurements • Interfrequency and Intersystem Measurements • UE Internal Measurements • ReportingMeasurement Results 2S-72.333 Post–graduated Course in Radio Communication, H. Yin

3. 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. 3S-72.333 Post–graduated Course in Radio Communication, H. Yin

4. Soft Handover (2/2) 4S-72.333 Post–graduated Course in Radio Communication, H. Yin

5. 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. 5S-72.333 Post–graduated Course in Radio Communication, H. Yin

6. Softer Handover (2/2) 6S-72.333 Post–graduated Course in Radio Communication, H. Yin

7. 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). 7S-72.333 Post–graduated Course in Radio Communication, H. Yin

8. Hard/Interfrequency Handover 8S-72.333 Post–graduated Course in Radio Communication, H. Yin

9. Hard/Intrafrequency Handover 9S-72.333 Post–graduated Course in Radio Communication, H. Yin

10. Inter-System Handover 10S-72.333 Post–graduated Course in Radio Communication, H. Yin

11. 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. 11S-72.333 Post–graduated Course in Radio Communication, H. Yin

12. Handover Measurement Reporting- WCDMANeighbour 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) 12S-72.333 Post–graduated Course in Radio Communication, H. Yin

13. Handover Measurement Reporting- GSMNeighbour Cell List Info • Cell Global ID CGI = MCC + MNC + LAC + CI • BCCH frequency • Base Station ID Code BSIC = BCC + NCC 13S-72.333 Post–graduated Course in Radio Communication, H. Yin

14. 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. 14S-72.333 Post–graduated Course in Radio Communication, H. Yin

15. 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 15S-72.333 Post–graduated Course in Radio Communication, H. Yin

16. 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. 16S-72.333 Post–graduated Course in Radio Communication, H. Yin

17. 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 17S-72.333 Post–graduated Course in Radio Communication, H. Yin

18. 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. 18S-72.333 Post–graduated Course in Radio Communication, H. Yin

19. Report of the Measurement Results- Time-to-Trigger Mechanism • Frequent reporting  excessive signalling load • Each report event can be connected with timer 19S-72.333 Post–graduated Course in Radio Communication, H. Yin

20. 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. 20S-72.333 Post–graduated Course in Radio Communication, H. Yin

21. Exercise • Explanation of what is soft handover, softer handover and hard handover. 21S-72.333 Post–graduated Course in Radio Communication, H. Yin

22. 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) 22S-72.333 Post–graduated Course in Radio Communication, H. Yin

23. References • Jaana Laiho, Achim Wacker, and Tomás Novosad: “Radio Network Planning and Optimisation for UMTS”, Wiley 2002. • Jens Zander and Seong-Luyn Kim: “Radio Resource Management for Wirless Networks”, Artech House 2001. • Holma & Toskala: "WCDMA for UMTS, Radio Access for Third Generation Mobile Communications", John Wiley & Sons. • T. Ojanpera &etc. ”wideband CDMA for Third Generation Mobile Communications” , Artech House Publishers. • Gordon L. Stüber: ”Principle of Mobile Communication”, 2nd edition, Kluwer Academic Publishers. • Nokia Internal training materials for CDMA/WCDMA/UMTS. 23S-72.333 Post–graduated Course in Radio Communication, H. Yin