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June 1, 20141 Mobile Computing COE 446 Introduction Tarek Sheltami KFUPM CCSE COE Principles of Wireless.

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Presentation on theme: "June 1, 20141 Mobile Computing COE 446 Introduction Tarek Sheltami KFUPM CCSE COE Principles of Wireless."— Presentation transcript:

1 June 1, Mobile Computing COE 446 Introduction Tarek Sheltami KFUPM CCSE COE Principles of Wireless Networks K. Pahlavan and P. Krishnamurth

2 June 1, 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 June 1, Cellular Subscribers

4 June 1, Cellular Subscribers..

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

6 June 1, Introduction- Conventional Wireless Communications

7 June 1, Mobile Switching Center Public telephone network, and Internet Mobile Switching Center Components of cellular network architecture connects cells to wide area net manages call setup (more later!) handles mobility (more later!) MSC covers geographical region base station (BS) analogous to AP mobile users attach to network through BS air-interface: physical and link layer protocol between mobile and BS cell wired network

8 June 1, 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 frequency bands time slots

9 June 1, 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 June 1, 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 June 1, Cellular standards: brief survey 3G systems: voice/data Universal Mobile Telecommunications Service (UMTS) GSM next step, but using CDMA CDMA-2000

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

16 June 1, Mobile Switching Center VLR old BSS new BSS old routing new routing GSM: handoff with common MSC Handoff goal: route call via new base station (without interruption) handoff initiated by old BSS

17 June 1, home network Home MSC PSTN correspondent MSC anchor MSC MSC (a) before handoff GSM: handoff between MSCs 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

18 June 1, home network Home MSC PSTN correspondent MSC anchor MSC MSC (b) after handoff 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

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

20 20 WiMAX: A new paradigm 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

21 June 1, Potential of networking: move bits everywhere, cheaply, and with desired performance characteristics Break the space barrier for information Network provides connectivity Networks

22 June 1, What is Connectivity ? Direct or indirect access to every other node in the network Connectivity is 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 June 1, Connectivity. Building Blocks links: coax cable, optical fiber... nodes: general-purpose workstations... Direct connectivity: point-to-point multiple access

24 June 1, Connectivity.. Indirect Connectivity switched networks => switches inter-networks => routers

25 June 1, Connectivity … Internet: Best-effort (no performance guarantees) Packet-by-packet A pt-pt physical link: Always-connected Fixed bandwidth Fixed delay Zero-jitter

26 June 1, 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 June 1, 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 Voice Oriented Data Oriented

28 June 1, 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 June 1, ALOHA-Based Wireless Random Access Techniques (Pure ALOHA)Pure 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 June 1, 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 June 1, ALOHA-Based Wireless Random Access Techniques (Slotted ALOHA)..Slotted 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 June 1, ALOHA-Based Wireless Random Access Techniques (R-ALOHA)..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 June 1, 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 June 1, ALOHA-Based Wireless Random Access Techniques (Pure ALOHA)..

35 June 1, ALOHA-Based Wireless Random Access Techniques (Slotted ALOHA)..

36 June 1, ALOHA-Based Wireless Random Access Techniques (R-ALOHA)..


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