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 March 31, 2017

Introduction 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 March 31, 2017

Cellular Subscribers March 31, 2017

Cellular Subscribers.. March 31, 2017

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 Indoor 10 – 30m Outdoor 50 – 200m Mid range outdoor 200m – 4Km Long range 5Km – 20Km March 31, 2017

Introduction- Conventional Wireless Communications In a conventional wireless network, the coverage area is divided into a number of cell sites. Each cell site is served by a single base station that provides wireless connectivity to the terminals in its vicinity. Base stations are interconnected in a fixed wired (or wireless) network. Thus, base stations act as central control units that carry out the MAC functions. An MTSO is in charge of keeping track of wireless subscribers and connects the wireless network to other wide-area networks, such as the PSTN or ISDN networks. March 31, 2017

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 802.11 AP mobile users attach to network through BS air-interface: physical and link layer protocol between mobile and BS cell Mobile Switching Center Public telephone network, and Internet wired network March 31, 2017

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 March 31, 2017

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 March 31, 2017

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 March 31, 2017

Cellular standards: brief survey 3G systems: voice/data Universal Mobile Telecommunications Service (UMTS) GSM next step, but using CDMA CDMA-2000 March 31, 2017

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 March 31, 2017

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

HSDPA EVOLUTION

GSM: indirect routing to mobile HLR home network correspondent 2 home MSC consults HLR, gets roaming number of mobile in visited network home Mobile Switching Center 1 call routed to home network 3 home MSC sets up 2nd leg of call to MSC in visited network Public switched telephone network VLR Mobile Switching Center 4 MSC in visited network completes call through base station to mobile mobile user visited network March 31, 2017

GSM: handoff with common MSC Handoff goal: route call via new base station (without interruption) handoff initiated by old BSS VLR Mobile Switching Center old routing new routing old BSS new BSS March 31, 2017

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 home network Home MSC correspondent anchor MSC PSTN MSC MSC MSC (a) before handoff March 31, 2017

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 home network Home MSC correspondent anchor MSC PSTN MSC MSC MSC (b) after handoff March 31, 2017

Segmenting the Telecom Market Nortel Corporate Presentation Segmenting the Telecom Market Narrowband Mobile Broadband Cellular 3G WiMAX Local Cordless WiFi Fixed POTS Dialup DSL / Cable The Evolution from Audio to Video © 2004 Nortel

Nortel Corporate Presentation WiMAX: A new paradigm 3G+ Incumbent Operator Voice and Data 30 Mbps $200 Handsets Telecom ITU Qualcomm $50 - $70 / month WIMAX Any Operator VoIP, Data, Video 100 Mbps Consumer Products Internet IEEE Intel & Others $20 - $40 / month © 2004 Nortel

Networks Potential of networking: move bits everywhere, cheaply, and with desired performance characteristics Break the space barrier for information Network provides “connectivity” March 31, 2017

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! March 31, 2017

Connectivity. Building Blocks links: coax cable, optical fiber... nodes: general-purpose workstations... Direct connectivity: point-to-point multiple access March 31, 2017

Connectivity.. Indirect Connectivity switched networks => switches inter-networks => routers March 31, 2017

Connectivity … Internet: Best-effort (no performance guarantees) Packet-by-packet A pt-pt physical link: Always-connected Fixed bandwidth Fixed delay Zero-jitter March 31, 2017

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 March 31, 2017

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 March 31, 2017

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. March 31, 2017

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 March 31, 2017

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 March 31, 2017

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 March 31, 2017

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 March 31, 2017

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 March 31, 2017

ALOHA-Based Wireless Random Access Techniques (Pure ALOHA).. March 31, 2017

ALOHA-Based Wireless Random Access Techniques (Slotted ALOHA).. March 31, 2017

ALOHA-Based Wireless Random Access Techniques (R-ALOHA).. March 31, 2017