Mobile Services (ST 2010) Chapter 3: Mobility Management Axel Küpper centric centric Networking - Service-centric Networking Deutsche Telekom Laboratories, TU Berlin ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST – Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service 1 Mobile Services Summer Term 2010 3 Mobility Management 3.1 Handover Management centric centric Networking - 3.2 Basics of Location Management 3.3 GSM Location Management 3.4 GPRS Location Management 3.5 UMTS Location Management ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST – Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service 2 3 Mobility Management Functions of Mobility Management Handover Management Location Management . Maintaining the traffic connection with . Mechanisms to localize users in case of a moving user when crossing cell incoming calls, short messages, or data boundaries . Requires to partition an operator’s . Occurs when the quality or the coverage area into location areas in strength of the radio signal falls below order to efficiently perform location certain parameters (signal quality management reason) . Two basic operations: Location update centric centric Networking . Occurs when the traffic capacity of a and Paging - cell has reached its maximum or is . Location Update (LU): operation approaching (traffic reason) initialized by the terminal to inform the . GSM standard identifies about 40 network about the user’s location reasons for a handover . Paging: broadcast message initialized . Handover is initialized by the mobile or by the network to locate the current ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST – by the base station cell of a user . Other term: handoff (primarily used in the U.S.) Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service 3 3.1 Handover Management Overview of the Handover Process Measurement . Measurement criteria: signal strength (between mobile and current base station as well as between mobile and neighboring Measurement base stations), distance, quality (e.g., in terms of error rates), traffic volume,.... Measurement reports exchanged between mobile and base station Decision centric centric Networking - . Decision parameters: thresholds and hysteresis margin Decision . Network-controlled, mobile-assisted, mobile-controlled handover Execution . Handover signaling ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST – . Radio resource allocation . Re-establishing connections in core and access networks Execution . Hard and soft handover . Inter-cell and intra-cell handover Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service . Inter-frequency and intra-frequency handover . Inter-system and intra-system handover 4 3.1 Handover Management Measurement: Handover Parameters centric centric Networking - ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST – . Primarily, RSS (relative signal strength) . Alternatively, or in conjunction, path loss, measurements from the serving point of carrier-to-interference ratio, bit error attachment and neighboring points of rates, block error rates, symbol error attachment are used rates, utilization have been employed as metrics in certain types of networks Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service 5 3.1 Handover Management Decision: Relative Signal Strength Base Received signal Received signal Base station A strength strength station B centric centric Networking - Distance between base stations L1 . Mobile terminal is handed off from BS A . Because signal strength fluctuates due to ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST to BS B when the signal strength at B first multipath propagation effects, this – exceeds that at A method can lead to a ping-pong effect in . If the signal strength at B first exceeds which the unit is repeatedly passed back that at A, the mobile unit is handed back and forth between two base stations to A Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service . In this figure, handover occurs at point L1 6 3.1 Handover Management Decision: Relative Signal Strength with Threshold Base Received signal Received signal Base station A strength strength station B Th1 Th2 Th3 centric centric Networking - Distance between L1 L2 L3 base stations . Handover only occurs if . For a high threshold (e.g., Th1), this scheme . the signal at the current BS is less performs the same as the relative signal than a predefined threshold, and strength scheme ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST – . the signal from a neighboring base . If the threshold is set quite low (e.g., Th3), station is stronger the mobile may move far into the new cell . Handover is avoided as long as the signal . Threshold should not be used alone because from the serving base station is strong its effectiveness depends on prior enough knowledge of the crossover signal strength Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service between the current and the candidate base stations 7 3.1 Handover Management Decision: Relative Signal Strength with Hysteresis Base Received signal Received signal Base station A strength strength station B H H centric centric Networking - Distance between L4 base stations . Handover occurs only if the new base . Once the mobile is assigned to B, it station is sufficiently stronger (by a remains so until the relative signal margin H) than the current one strength falls below –H, at which point it ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST is handed back to A – . While the mobile is assigned to base station A, the scheme will generate a . Prevents the ping-pong effect handover when the relative signal . Disadvantage: the first handover may still strength reaches or exceeds H be unnecessary if base station A still has sufficient signal strength Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service 8 3.1 Handover Management Decision: RSS with Threshold and Hysteresis Base Received signal Received signal Base station A strength strength station B Th1 H Th2 Th3 H centric centric Networking - Distance between L4 L3 base stations . Handover occurs only if . Handover occurs at L4, if the threshold is . the current signal level drops below either Th1 or Th2 a threshold, and . Handover occurs at L3 if the threshold is ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST – . the target base station is stronger at Th3 than the current one by a hysteresis . Scheme avoids the ping-pong effect and margin H execution of handover if signal from the serving base station is still strong enough Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service 9 3.1 Handover Management Execution: Hard versus Soft Handover Hard handover . “Break before make” . Connection is released before making the new connection . Causes a short cut in the connection . The terminal is linked to no more (1) (2) (3) than one base station at any given time . Primarily used in FDMA and TDMA, where different frequency ranges are centric centric Networking - used in adjacent cells Soft handover . “Make before break” . New connection is established before the old connection is released, avoiding ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST a cut in the connection – during handover . After the successful handover, the old (1) (2) (3) connection is released . Used in CDMA, where adjacent cells use Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service the same frequency range 10 3.1 Handover Management Execution: Further Handover Types Intra-frequency handover . The new carrier frequency is the same as the previous carrier frequency . Deployment: CDMA (as neighboring cells usually use the f f1 same frequency range) 1 Inter-frequency handover . Carrier frequency of the new radio access is different from the old carrier frequency centric centric Networking - . Deployment: GSM, handover between different UMTS operators f1 f2 Inter-system handover . Happens between two different radio access networks (e.g., GSM and UMTS) ST 2010 | 3 Mobility Management Mobility Management 2010 | 3 ST – . Special kind of inter-frequency handover . Deployment: areas where GSM and UMTS coexist and overlay networks UMTS GSM 900 Mobile Services Mobile Axel Küpper Axel | Technische Universität Berlin | Service 11 3.1 Handover Management Handover Control (I) Network-controlled Handover (NCHO) Mobile-assisted Handover (MAHO) . Network measures the transmission . Mobile terminal continuously measures quality via base stations and decides signal strength from serving and when handover should be executed neighboring base stations and sends the . Mobile terminal makes no measurements recorded values to the serving base . Intense signaling between the base station stations and the node that decides on . On the basis of these values, the network handover decides when handover should take place centric centric Networking . Unlike NCHO, the terminal’s situation is - . No handover signaling at the air interface . Handover process (including data taken into account, as the terminal itself transmission, channel and network does the measuring switching) takes 100-200ms . Handover time between handover decision and execution is approximately 1 second ST 2010 | 3 Mobility Management Mobility Management 2010