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Mobile Computing COE 446 Introduction

Mobile Computing COE 446 Introduction. Tarek Sheltami KFUPM CCSE COE http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm. Principles of Wireless Networks K. Pahlavan and P. Krishnamurth. Background: # wireless (mobile) phone subscribers now exceeds # wired phone subscribers!

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Mobile Computing COE 446 Introduction

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  1. Mobile Computing COE 446Introduction Tarek Sheltami KFUPM CCSE COE http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm Principles of Wireless Networks K. Pahlavan and P. Krishnamurth

  2. Background: # wireless (mobile) phone subscribers now exceeds # wired phone subscribers! computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet access two important (but different) challenges communication over wireless link handling mobile user who changes point of attachment to network Introduction

  3. Cellular Subscribers

  4. Cellular Subscribers..

  5. Outdoor 50 – 200m Mid range outdoor 200m – 4Km Long range outdoor 5Km – 20Km Indoor 10 – 30m Characteristics of selected wireless link standards 54 Mbps 802.11{a,g} 5-11 Mbps .11 p-to-p link 802.11b 1 Mbps 802.15 3G 384 Kbps UMTS/WCDMA, CDMA2000 2G 56 Kbps IS-95 CDMA, GSM

  6. Introduction- Conventional Wireless Communications

  7. connects cells to wide area net • manages call setup (more later!) • handles mobility (more later!) Mobile Switching Center Mobile Switching Center • covers geographical region • base station (BS) analogous to 802.11 AP • mobile users attach to network through BS • air-interface: physical and link layer protocol between mobile and BS Public telephone network, and Internet MSC cell wired network Components of cellular network architecture

  8. time slots frequency bands Cellular networks: the first hop Two techniques for sharing mobile-to-BS radio spectrum • combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots • CDMA: code division multiple access

  9. Cellular standards: brief survey 2G systems: voice channels • IS-136 TDMA: combined FDMA/TDMA (north america) • GSM (global system for mobile communications): combined FDMA/TDMA • most widely deployed • IS-95 CDMA: code division multiple access

  10. Cellular standards: brief survey 2.5 G systems: voice and data channels • for those who can’t wait for 3G service: 2G extensions • general packet radio service (GPRS) • evolved from GSM • data sent on multiple channels (if available) • enhanced data rates for global evolution (EDGE) • also evolved from GSM, using enhanced modulation • Date rates up to 384K • CDMA-2000 (phase 1) • data rates up to 144K • evolved from IS-95

  11. Cellular standards: brief survey 3G systems: voice/data • Universal Mobile Telecommunications Service (UMTS) • GSM next step, but using CDMA • CDMA-2000

  12. Cellular standards: brief survey 3G+ systems: voice/data • High Speed Downlink Packet Access • Hybrid Automatic Repeat Request • Fast cell site selection • Adaptive Modulation and Coding

  13. Why HSDPA? • Comparison Between 3G & 3.5G. • Data Rate ( 2Mbps -----> 10 Mbps) • Modulation ( QPSK -----> QPSK&16QAM) • Transmission Time Interval (TTI) ( 10ms ----> 2ms )

  14. HSDPA EVOLUTION

  15. home Mobile Switching Center Mobile Switching Center home MSC consults HLR, gets roaming number of mobile in visited network call routed to home network home MSC sets up 2nd leg of call to MSC in visited network VLR HLR 1 4 2 3 MSC in visited network completes call through base station to mobile GSM: indirect routing to mobile home network correspondent Public switched telephone network mobile user visited network

  16. Handoff goal: route call via new base station (without interruption) handoff initiated by old BSS Mobile Switching Center VLR GSM: handoff with common MSC new routing old routing old BSS new BSS

  17. anchor MSC: first MSC visited during call call remains routed through anchor MSC new MSCs add on to end of MSC chain as mobile moves to new MSC IS-41 allows optional path minimization step to shorten multi-MSC chain Home MSC home network MSC MSC MSC GSM: handoff between MSCs correspondent anchor MSC PSTN (a) before handoff

  18. Home MSC home network MSC MSC MSC GSM: handoff between MSCs • anchor MSC: first MSC visited during cal • call remains routed through anchor MSC • new MSCs add on to end of MSC chain as mobile moves to new MSC • IS-41 allows optional path minimization step to shorten multi-MSC chain correspondent anchor MSC PSTN (b) after handoff

  19. Segmenting the Telecom Market Narrowband Broadband Mobile Cellular WiMAX 3G Local WiFi Cordless Fixed DSL / Cable Dialup POTS The Evolution from Audio to Video

  20. WIMAX Any Operator VoIP, Data, Video 100 Mbps Consumer Products Internet IEEE Intel & Others $20 - $40 / month 3G+ Incumbent Operator Voice and Data 30 Mbps $200 Handsets Telecom ITU Qualcomm $50 - $70 / month WiMAX: A new paradigm

  21. Networks • Potential of networking: • move bits everywhere,cheaply, and with desired performance characteristics • Break the space barrier for information • Network provides “connectivity”

  22. What is“Connectivity” ? • Direct or indirect accessto every other node in the network • Connectivityis the media needed to communicate if you do not have a direct pt-pt physical link. • Tradeoff: Performance characteristics worse than true physical link!

  23. Connectivity. • Building Blocks • links: coax cable, optical fiber... • nodes: general-purpose workstations... • Direct connectivity: • point-to-point • multiple access

  24. Connectivity.. • IndirectConnectivity • switched networks => switches • inter-networks => routers

  25. Connectivity … • Internet: • Best-effort (no performance guarantees) • Packet-by-packet • A pt-pt physical link: • Always-connected • Fixed bandwidth • Fixed delay • Zero-jitter

  26. Wired and Wireless Multiple Access • Most multiple access were originally developed for wired networks • Requirements for wired & wireless networks are different • The main difference between wired and wireless channels are availability of BW and reliability of transmission • The wired medium is moving toward optical media with enormous BW and very reliable transmission • BW of wireless systems always limited because of the air medium

  27. Voice Oriented Data Oriented Wired and Wireless Multiple Access.. • Wireless medium always suffers from multi-path and fading, which causes serious threat to reliable data transmission over the communication link • Wireless have evolved around voice and data application Wireless Networks

  28. Wired and Wireless Multiple Access.. • Voice oriented networks are designed for relatively long telephone conversation as the main application, therefore exchange of several Mbytes of information in both directions • Data oriented networks are designed for bursts of data (packet switching) • Wireless networks assigns a time slot, a portion of frequency, or a code to user preferably for the entire length of the conversation.

  29. ALOHA-Based Wireless Random Access Techniques (Pure ALOHA) • MT transmits an information packets when the packet arrives from the upper layers of the protocol stack • MTs say “hello” to the air interface as the packet arrives • Each packet is encoded with an error-detection code • The BS checks the parity of the received packet, if it is OK, it sends a short ACK packet • If no ACK received the packet is assumed lost in a collision and it is transmitted again with randomly selected delay to avoid repeated collisions

  30. ALOHA-Based Wireless Random Access Techniques (Pure ALOHA).. • Advantages • Simple • No synchronization between MTs • Disadvantage • Low throughput under heavy load conditions • Max throughput for pure ALOHA 18% What is the max throughput of pure ALOHA network with large number of users and transmission range of 1 Mbps? Max Throughput = 1 Mbps X 18% = 180 Kbps

  31. ALOHA-Based Wireless Random Access Techniques (Slotted ALOHA).. • Transmission time is divided into time slots • BS transmits beacon signal for time and all MTs is divided into time slots to this beacon signal • When MT generates a packet, it is buffered and transmitted at the start of the next time slot • Assuming equal length packet, either we have a complete collision or no collision • Throughput of slotted ALOHA = 36%, which is still low

  32. ALOHA-Based Wireless Random Access Techniques (R-ALOHA).. • Time slots are divided into contention periods and contention free periods • During contention interval, an MT uses very short packets to contend for the upcoming contention free intervals that will be used for transmission of the long information packets

  33. ALOHA-Based Wireless Random Access Techniques.. • Disadvantages of ALOHA-based Random Access: • The main drawback of ALOHA based contention is the lack of efficiency caused by collision and retransmission • Users don’t take into account what other users are doing when they attempt to transmit data packets • There is no mechanisms to avoid collision

  34. ALOHA-Based Wireless Random Access Techniques (Pure ALOHA)..

  35. ALOHA-Based Wireless Random Access Techniques (Slotted ALOHA)..

  36. ALOHA-Based Wireless Random Access Techniques (R-ALOHA)..

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