Mobility Support & Channel Reuse Mobility Support & Channel Reuse Mobility Support~ Handover 無線網路多媒體系統 無線網路多媒體系統 無線網路多媒體系統 無線網路多媒體系統 Wireless Multimedia System Wireless Multimedia System Wireless Multimedia System Wireless Multimedia System Lecture 5: Cellular Concepts Lecture 5: Cellular Concepts Lecture 5: Cellular Concepts Lecture 5: Cellular Concepts 中央大學 中央大學 中央大學 中央大學 吳曉光博士 吳曉光博士 吳曉光博士 吳曉光博士 Channel Allocations: Reuse Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory ChungLi Case Study ChungLi Case Study Wireless & Multimedia Network Laboratory � � � � Wireless & Multimedia Network Laboratory � � � � � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Moving Behavior ( µ 1 , σ 1 , S 1 ) ( µ 2 , σ 2 , S 2 ) ( µ 3 , σ 3 , S 3 ) ( µ 4 , σ 4 , S 4 ) Call arrive l 6 l 7 l 6 l 5 l 4 l 5 l 7 l 5 l 6 l 3 l 7 l 4 l 3 l 2 l 4 l 2 l 8 l 8 l 14 l 1 l 1 l 13 l 14 l 12 l 13 l 12 l 9 l 9 l 10 l 11 l 11 l 10 Time Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 1
Channel Assignment in Cellular System Channel Assignment in Cellular System Hand-off in Cellular Networks Hand off in Cellular Networks � Fundamental Problem: � Transfer of mobile to a new channel when it crosses cell boundary � Fixed Channel Assignment � Handoff delay � Dynamic Channel Assignment � Prioritizing handoffs to reduce probability of dropped calls � Hybrid Schemes � Handoff Strategies � Whole Channel Usage (CDMA) � Network Controlled handoff (NCHO) � Reduce the Cell Size � Mobile assisted handoff (MAHO) � Mobile controlled handoff (MCHO) Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Agenda Agenda Reading Reading � Cellular Concepts � [Katzela96]Katzela, and M. Nahgshineh,”Channel assignment � Channel Assignments schemes for cellular mobile � Handover telecommunication systems: a comprehensive survey,” IEEE � Next Lecture: 3G WCDMA design Personal Communications, June 1996 � [Pollinin96], G.P. Pollini, “Trends in handover design, “IEEE Communications Magazine, March 1996. Wireless & Multimedia Network Laboratory � � � � Wireless & Multimedia Network Laboratory � � � � � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Cellular System Concept Cellular System Concept Channel Allocation Channel Allocation MSC PSTN Pre-Cellular Post-Cellular � A given Channel Spectrum (or bandwidth) can be divided into a set of disjoint or non-interfering radio channel • Frequency Division � frequency band • Time Division � time slot � Replace single high power transmitter covering the entire service area • Code Division with low power � modulation code • Mobiles in sufficiently distant base-stations may be assigned identical channel (frequency, time slot, & code) • System capacity may be increased without adding more spectrum � Major conceptual breakthrough in spectra congestion & user capacity • Required relatively minor technological changes frequency reuse & co- channel interference, channel allocation, hand-offs Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 2
Cell Shape Cell Shape Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory � � � � Wireless & Multimedia Network Laboratory � � � � � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 3
Channel Reuse Channel Reuse � The same channel is reused simultaneously by other sets (Co- channel) k k − α signal P d t t CIR = = � − α int erference P d N k + i 0 Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Interference Interference How to improve CIR (Quality) How to improve CIR (Quality) � Increase the transmitting power (Power Control) � Increase the separating distance (Channel Reuse) − α signal P d t t CIR = = � 5 int erference − α P d + N i i 0 1 − α signal P d t t CIR = = � α int erference P d N i 0 Wireless & Multimedia Network Laboratory � � � � Wireless & Multimedia Network Laboratory � � � � � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Approaches Approaches Frequency Reuse Frequency Reuse � Each BS is allocated a subset of carrier freqs � Fixed no flexibility 6 5 � Nearby BSs are allocated a different subset to 4 avoid interference 1 7 3 � The total set is allocated to a small tesselating � Dynamic complexity 2 group of N neighboring BSs 2 • 5 Called “reuse cluster” 6 � Hybrid might be ok 4 • 1/N is the “reuse factor” 1 Area • service System capacity goes up by 7 3 N × Area cell � Used in FDMA & TDMA based systems 2 • Not required in CDMA which has universal frequency 6 5 reuse 4 � Cells idealized as hexagons • Real cell footprints are amorphous Idealized grid of 2 • Hexagon close to a circle Hexagonal cells • Not appropriate for micro-cells, highways etc. Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory � � � � � � � � Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 4
Recommend
More recommend
