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ECE 5221 Personal Communication Systems

ECE 5221 Personal Communication Systems. Prepared by: Dr . Ivica Kostanic Lecture 2: Basics of cellular system architecture (Chapter 2.1 and 2.2). Spring 2011. Outline . Outline of cellular system architecture Elements of the cellular system architecture Support for mobility – Handoff

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ECE 5221 Personal Communication Systems

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  1. ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 2: Basics of cellular system architecture (Chapter 2.1 and 2.2) Spring 2011

  2. Outline • Outline of cellular system architecture • Elements of the cellular system architecture • Support for mobility – Handoff • Automatic roaming Important note: Slides present summary of the results. Detailed derivations are given in notes.

  3. Layout of the Cellular Comm. System Circuit switched part of cellular system

  4. Mobile Subscriber Unit • Usually the only part of the system that users are aware of • Traditionally used for voice • Becoming more data centric • Performs any functions • Voice processing • CS/PS Call management • Packet data transfer • May be multi-band • May be multi-technology Block diagram of voice processing in mobile unit

  5. Base Station Controller • Two implementations • Multiple BSCs • BSC within MSC • Responsibility of BSC • Radio resource management • Handoff between cells

  6. Base Transceiver Station • Base station • Bank of radios • Responsible for radio link between system and the mobile • Base station provides communication resources over given coverage area • The number of users that can be served = number of BTS resources • BTS connects to the core network (BSC) through T1/E1 lines • May be configured as omni-directional or sectored Block diagram of a base station

  7. Base Station Antenna Configuration • Omnidirectional (Omni) Antennas • Coverage pattern is a circle • Usually located in low-traffic (rural) areas • Directional Antennas • Coverage directed to a specific area • Increase system capacity • 60º, 90º and 120º are the most common

  8. Base Station Coverage Classification • Coverage depends on; • transmit power • antenna gains • antenna height

  9. Monopole - 80’ - 150’ - small amount of land required - limited loading Guyed Tower - up to 1500’ - heavy loading can be a problem Self Supporting - 100’ - 300’ - heavy loading Towers

  10. Circuit vs. packet switching • Legacy cellular technologies (1G and 2G) • are circuit switched • Dial-up type connections • A single user occupies a channel for the entire transmission • Requires time-oriented billing • GSM transmissions are bursty • Bursty nature favors data services Modern cellular networks (3G and 4G) is packet switched technology More appropriate for data services Continuous flow is not required Access is based on demand only Several users can be multiplexed Billing based on negotiated QoS and usage

  11. Cellular architecture CS/PS (2G->3G)

  12. Handoff • Fundamental requirement for mobility support • Two types: hard handoff and soft handoff • Hard Handoff … ‘Break before make!’ • Analog Handoff - obsolete • MAHO (Mobile Assisted Handoff) • Soft Handoff … ‘Make before break!’ • currently just in CDMA systems • Soft handoff is MAHO • Type of implemented handoff depends on air interface technology

  13. MAHO All modern technologies use MAHO

  14. Hard HO and Soft HO Hard handoff Type of handoff – function of air interface Soft handoff more reliable Soft handoff – resource intense Soft handoff

  15. Automatic Roaming Current location of a mobile – kept in a VLR When mobile turns on – it registers As a part of registration – HLR is updated with the current mobile’s VLR When the mobile is called, based on the HLR entry, the call is located to the MSC of the mobile’s current VLR The mobile is paged within the area or sub-area of current VLR

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