Wireless Communications

Transcription

1 Wireless Communications Lecture 6: Mobility Management Module Representive: Prof. Dr.-Ing. Hans D. Schotten Lecturer: Dr.-Ing. Bin Han Institute of Wireless Communication (WiCon) Department of Electrical and Computer Engineering TU Kaiserslautern SS 2018

2 Outline 1 Overview of Mobility Management 2 Mobile Location Management 3 Mobile Registration 4 Handover H. D. Schotten & B. Han Wireless Communications 2/ 14

3 Overview of Mobility Management Mobility in Mobile Communications Radio mobility: handover Network mobility: location updating & paging System boundaries: cell area location area (LA) mobile switching center (MSC) area Public Land Mobile Network Register with the visitor location register (VLR) when MS visits a new LA Each cell has a cell global identification (CGI) Wireless PLMN MCC: Mobile Country Code MNC: Mobile Network Code LAC: Location Area Code CI: Cell identification LAI: Location Area Identification Cell Global Identification H. D. Schotten & B. Han Wireless Communications 3/ 14

4 Overview of Mobility Management Mobility Management Keeping track of the subscriber s status and location to deliver calls to it Authorizing a subscriber for service in a given service area Key component: subscriber s service profile Dynamic data such as current location and status Permanent data such as service profile, international mobile subscriber identity (IMSI), etc. H. D. Schotten & B. Han Wireless Communications 4/ 14

5 Overview of Mobility Management Mobility Management Functions Automatic roaming Mobile station (MS) service qualification MS location management MS state management Home location register (HLR) & VLR fault recovery Authentication Intersystem handover H. D. Schotten & B. Han Wireless Communications 5/ 14

6 Mobile Location Management Location Update Location Update (LU) Concept: the network keeps track of the MS s location Trade-off: LU cost vs. paging cost Methods: Periodic LU LU-on-LA-crossing Hybrid location management LU Procedures Intra-VLR LU Inter-VLR LU using temporary mobile subscriber identity (TMSI) Inter-VLR LU using IMSI IMSI-attached procedure that is triggered when the mobile is powered on in the LA where it was powered off H. D. Schotten & B. Han Wireless Communications 6/ 14

7 Mobile Location Management Mobility Models What to Describe The occurrence of mobility-relevant procedures such as LU and handover Different Mobility Models Fluid model Assumes traffic flow to be like the flow of a fluid Applicable to areas with a large population Impractical when individual movement patterns are desired Markovian model Also known as the random walk model Describes individual movements No concept of trips Gravity model Describes human movement behavior in regions of varying sizes Many parameters required in the calculations H. D. Schotten & B. Han Wireless Communications 7/ 14

8 Mobile Registration Overview Primarily: MS service qualification & MS location management Must be performed to enable network services for subscribers (exceptions such like emergency calls) Unique to wireless networks (wired system: fixed subscriber locations) Different types, the support varies in different systems (AMPS 1 / TDMA / CDMA / GSM): Distance-based registration Geopraphic-based registration Parameter change registration Periodic registration Power-down registration Power-up registration Timer-based registration 1 Advanced Mobile Phone Systems H. D. Schotten & B. Han Wireless Communications 8/ 14

9 Mobile Registration Example: Call Flows for the MS Registration in ANSI-41 Standard Source: V. K. Garg, Wireless Communications and Networking H. D. Schotten & B. Han Wireless Communications 9/ 14

10 Mobile Registration Mobile Registration Procedures in GSM Overview Location Management Registration Handover Thanks Token-Based Registration Old VLR new VLR Token for enhanced security IMSI Attach and IMSI Detach Attach: at power-up Detach: at power-off On the RAN level: involving RACH + AGCH + SDCCH Paging One-to-one communication between BSS and MS Preconditions: MS locally registered, TMSI acquired Paging channels preset w.r.t. broadcast information BSS broadcasts the paged TMSI over the paging channel Paged MS requests a SDCCH over the RACH to response page BSS immediately assigns a SDCCH channel to the MS and informs it over the AGCH MS responses the page over the SDCCH H. D. Schotten & B. Han Wireless Communications 10/ 14

11 Handover Concept and Techniques Handover (or handoff ): a mobile moves from one cell area to another during an active call, the call must be switched from one channel to another. What may change (e.g. in TDMA): channel carrier frequency, time slot, BSS Triggers: signal strength deterioration, traffic congestion, etc. Synchronous or asynchronous (higher delay due to resynchronization) Different techniques: mobile-controlled handover (MCHO) - most popular for low-tier radio systems (indoor) network-controlled handover (NCHO) - low-tier CT-2+ and high-tier AMPS mobile-assisted handover (MAHO) - most high-tier > 2G systems H. D. Schotten & B. Han Wireless Communications 11/ 14

12 Handover Types System Change Intrafrequency handover: f c,new = f c,old Interfrequency handover: f c,new f c,old Intersystem handover: different radio systems (always interfrequency) Procedure Hard handover: old connection terminated new connection established Soft handover: new connection established old connection terminated Softer handover: DL through one sector, UL through multiple sectors Soft-softer handover: simultaneous soft and softer handovers H. D. Schotten & B. Han Wireless Communications 12/ 14

13 Handover Process and Algorithms Algorithm Parameters Upper threshold Lower threshold Handover margin Algorithms RSS type RSS plus threshold type RSS plus handoff margin type H. D. Schotten & B. Han Wireless Communications 13/ 14

14 Thank you for your active attendance through the entire semester! We wish everyone of you success in the examination and joyful summer holidays! H. D. Schotten & B. Han Wireless Communications 14/ 14