Mobile Computing COE 446 Introduction Tarek Sheltami KFUPM

Mobile Computing COE 446 Introduction Tarek Sheltami KFUPM CCSE COE http: //faculty. kfupm. edu. sa/coe/tarek/coe 446. htm Principles of Wireless Networks K. Pahlavan and P. Krishnamurth 03 March 2021 1

Introduction Background: n n n # 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 n n communication over wireless link handling mobile user who changes point of attachment to network 03 March 2021 2

Cellular Subscribers 03 March 2021 3

Cellular Subscribers. . 03 March 2021 4

Characteristics of selected wireless link standards 54 Mbps 5 -11 Mbps 802. 11{a, g} 802. 11 b . 11 p-to-p link 802. 15 3 G UMTS/WCDMA, CDMA 2000 384 Kbps 2 G IS-95 CDMA, GSM 56 Kbps Indoor Outdoor Mid range outdoor Long range outdoor 10 – 30 m 50 – 200 m – 4 Km 5 Km – 20 Km 03 March 2021 5

Introduction- Conventional Wireless Communications 03 March 2021 6

Components of cellular network architecture MSC cell q connects cells to wide area net q manages call setup (more later!) q handles mobility (more later!) q covers geographical region q base station (BS) analogous to 802. 11 AP q mobile users attach to network through BS q air-interface: physical and link layer protocol between mobile and BS Mobile Switching Center Public telephone network, and Internet Mobile Switching Center wired network 03 March 2021 7

Cellular networks: the first hop Two techniques for sharing mobile-to-BS radio spectrum n combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots frequency n CDMA: code division multiple bands access 03 March 2021 time slots 8

Cellular standards: brief survey 2 G systems: voice channels n n IS-136 TDMA: combined FDMA/TDMA (north america) GSM (global system for mobile communications): combined FDMA/TDMA n n most widely deployed IS-95 CDMA: code division multiple access 03 March 2021 9

Cellular standards: brief survey 2. 5 G systems: voice and data channels n for those who can’t wait for 3 G service: 2 G extensions n general packet radio service (GPRS) n evolved from GSM n data sent on multiple channels (if available) n enhanced data rates for global evolution (EDGE) n also evolved from GSM, using enhanced modulation n Date rates up to 384 K n CDMA-2000 (phase 1) n data rates up to 144 K n evolved from IS-95 03 March 2021 10

Cellular standards: brief survey 3 G systems: voice/data n n Universal Mobile Telecommunications Service (UMTS) n GSM next step, but using CDMA-2000 03 March 2021 11

Cellular standards: brief survey 3 G+ systems: voice/data n High Speed Downlink Packet Access n Hybrid Automatic Repeat Request n Fast cell site selection n Adaptive Modulation and Coding 03 March 2021 12

Why HSDPA? v Comparison Between 3 G & 3. 5 G. ü Data Rate ( 2 Mbps -----> 10 Mbps) ü Modulation ( QPSK -----> QPSK&16 QAM) ü Transmission Time Interval (TTI) ( 10 ms ----> 2 ms )

HSDPA EVOLUTION

GSM: indirect routing to mobile home network HLR 2 home MSC consults HLR, gets roaming number of mobile in visited network correspondent home Mobile Switching Center 1 VLR 3 Mobile Switching Center 4 home MSC sets up 2 nd leg of call to MSC in visited network mobile user visited network 03 March 2021 Public switched telephone network call routed to home network MSC in visited network completes call through base station to mobile 15

GSM: handoff with common MSC n VLR Mobile Switching Center old routing old BSS 03 March 2021 n Handoff goal: route call via new base station (without interruption) handoff initiated by old BSS new routing new BSS 16

GSM: handoff between MSCs n home network correspondent Home MSC anchor MSC PSTN MSC n (a) before handoff 03 March 2021 anchor MSC: first MSC visited during call n 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 17

GSM: handoff between MSCs n home network correspondent Home MSC anchor MSC PSTN MSC n (b) after handoff 03 March 2021 anchor MSC: first MSC visited during cal n 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

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

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

Networks n Potential of networking: n move bits everywhere, cheaply, and with desired performance characteristics n Break the space barrier for information n Network provides “connectivity” 03 March 2021 21

What is “Connectivity” ? n n 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. n Tradeoff: Performance characteristics worse than true physical link! 03 March 2021 22

Connectivity. n n Building Blocks n links: coax cable, optical fiber. . . n nodes: general-purpose workstations. . . Direct connectivity: n point-to-point n multiple access 03 March 2021 23

Connectivity. . n Indirect Connectivity n n switched networks => switches inter-networks => routers 03 March 2021 24

Connectivity … n Internet: Best-effort (no performance guarantees) n Packet-by-packet n n A pt-pt physical link: n n Always-connected Fixed bandwidth Fixed delay Zero-jitter 03 March 2021 25

Wired and Wireless Multiple Access n n n 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 03 March 2021 26

Wired and Wireless Multiple Access. . n n 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 03 March 2021 Data Oriented 27

Wired and Wireless Multiple Access. . n n n 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. 03 March 2021 28

ALOHA-Based Wireless Random Access Techniques (Pure ALOHA) n n n 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 03 March 2021 29

ALOHA-Based Wireless Random Access Techniques (Pure ALOHA). . n n Advantages n Simple n No synchronization between MTs Disadvantage n Low throughput under heavy load conditions n 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 03 March 2021 30

ALOHA-Based Wireless Random Access Techniques (Slotted ALOHA). . n n n 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 03 March 2021 31

ALOHA-Based Wireless Random Access Techniques (R-ALOHA). . n n 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 03 March 2021 32

ALOHA-Based Wireless Random Access Techniques. . n Disadvantages of ALOHA-based Random Access: n n n 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 03 March 2021 33