600 427 Wireless Networks l Instructor Baruch Awerbuch

600. 427 Wireless Networks l Instructor: Baruch Awerbuch, baruch@cs. jhu. edu l TA: Herb Rubens, Herb@jhu. edu l Class Homepage: www. cs. jhu. edu/~baruch All handouts, announcements, homeworks, etc. posted to website l “Lectures” link continuously updates topics, handouts, and reading l

Outline l Course Basics l Course Syllabus l The Wireless Vision l Technical Challenges l Current Wireless Systems l Emerging Wireless Systems l Spectrum Regulation l Standards

Course Information l Term project on anything related to wireless l Literature survey, analysis, or simulation l Must set up website for your project (for proposal and report

Course Syllabus l Overview of Wireless Communications l Security l Review of Physical Media issues l Power issue l routing Algorithms

Is there a future for wireless? Some history l l Ancient Systems: Smoke Signals, Carrier Pigeons, … Radio invented in the 1880 s by Marconi Many sophisticated military radio systems were developed during and after WW 2 Cellular has enjoyed exponential growth since 1988, with almost 1 billion users worldwide today l l Ignited the recent wireless revolution Growth rate tapering off 3 G (voice+data) roll-out disappointing Many spectacular failures recently l 1 G Wireless LANs/Iridium/Metricom RIP Wireless Revolution 1980 -2003

Glimmers of Hope l Internet and laptop use exploding l 2 G/3 G wireless LANs growing rapidly l Low rate data demand is high l Military and security needs require wireless l Emerging interdisciplinary applications

Future Wireless Networks Ubiquitous Communication Among People and Devices Wireless Internet access Nth generation Cellular Wireless Ad Hoc Networks Sensor Networks Wireless Entertainment Smart Homes/Spaces Automated Highways All this and more… • Hard Delay Constraints • Hard Energy Constraints

Design Challenges l Wireless channels are a difficult and capacitylimited broadcast communications medium l Traffic patterns, user locations, and network conditions are constantly changing l Applications are heterogeneous with hard constraints that must be met by the network l Energy and delay constraints change design principles across all layers of the protocol stack

Multimedia Requirements Voice Data Video Delay <100 ms - <100 ms Packet Loss BER <1% 10 -3 0 10 -6 <1% 10 -6 Data Rate 8 -32 Kbps Continuous 1 -100 Mbps Bursty Traffic 1 -20 Mbps Continuous One-size-fits-all protocols and design do not work well Wired networks use this approach, with poor results

Wireless Performance Gap LOCAL AREA PACKET SWITCHING 100 M Ethernet 100, 000 10, 000 FDDI Ethernet 1000 100 User Bit-Rate (kbps) WIDE AREA CIRCUIT SWITCHING ATM 10, 000 wired- wireless bit-rate "gap" 1000 1 st gen WLAN Polling 2 nd gen WLAN Packet Radio ISDN wired- wireless bit-rate "gap" 28. 8 modem 9. 6 modem 2. 4 modem 1 14. 4 9. 6 cellular digital cellular 2. 4 cellular 32 kbps PCS . 1. 01 100 User Bit-Rate (kbps) 10 10 1 ATM 100, 000 1970 1980 YEAR 1990 2000 . 01 1970 1980 YEAR 1990 2000

Evolution of Current Systems l Wireless systems today l l l Next Generation l l l 2 G Cellular: ~30 -70 Kbps. WLANs: ~10 Mbps. 3 G Cellular: ~300 Kbps. WLANs: ~70 Mbps. Technology Enhancements l l Hardware: Better batteries. Better circuits/processors. Link: Antennas, modulation, coding, adaptivity, DSP, BW. Network: Dynamic resource allocation. Mobility support. Application: Soft and adaptive Qo. S. “Current Systems on Steroids”

Future Generations Rate 4 G 802. 11 b WLAN 3 G Other Tradeoffs: Rate vs. Coverage Rate vs. Delay Rate vs. Cost Rate vs. Energy 2 G 2 G Cellular Mobility Fundamental Design Breakthroughs Needed

Crosslayer Design l Hardware l Link Delay Constraints Rate Constraints Energy Constraints l Access l Network l Application Adapt across design layers Reduce uncertainty through scheduling Provide robustness via diversity

Current Wireless Systems l Cellular Systems Wireless LANs l Satellite Systems l l Paging Systems l Bluetooth

Cellular Systems: Reuse channels to maximize capacity l l l Geographic region divided into cells Frequencies/timeslots/codes reused at spatially-separated locations. Co-channel interference between same color cells. Base stations/MTSOs coordinate handoff and control functions Shrinking cell size increases capacity, as well as networking burden BASE STATION MTSO

Cellular Phone Networks San Francisco BS BS Internet MTSO PSTN New York MTSO BS

3 G Cellular Design: Voice and Data l Data is bursty, whereas voice is continuous l l Typically require different access and routing strategies 3 G “widens the data pipe”: l l l 384 Kbps. Standard based on wideband CDMA Packet-based switching for both voice and data l 3 G cellular struggling in Europe and Asia l Evolution of existing systems (2. 5 G, 2. 6798 G): GSM+EDGE l IS-95(CDMA)+HDR l 100 Kbps may be enough l l What is beyond 3 G? The trillion dollar question

Wireless Local Area Networks (WLANs) 01011011 0101 1011 Internet Access Point l l WLANs connect “local” computers (100 m range) Breaks data into packets Channel access is shared (random access) Backbone Internet provides best-effort service l Poor performance in some apps (e. g. video)

Wireless LAN Standards l 802. 11 b (Current Generation) l l 802. 11 a (Emerging Generation) l l l Standard for 2. 4 GHz ISM band (80 MHz) Frequency hopped spread spectrum 1. 6 -10 Mbps, 500 ft range Standard for 5 GHz NII band (300 MHz) OFDM with time division 20 -70 Mbps, variable range Similar to Hiper. LAN in Europe 802. 11 g (New Standard) l l l Standard in 2. 4 GHz and 5 GHz bands OFDM Speeds up to 54 Mbps In 200? , all WLAN cards will have all 3 standards

Satellite Systems l Cover very large areas l Different orbit heights l l Optimized for one-way transmission l l GEOs (39000 Km) versus LEOs (2000 Km) Radio (XM, DAB) and movie (Sat. TV) broadcasting Most two-way systems struggling or bankrupt Expensive alternative to terrestrial system l A few ambitious systems on the horizon l

Paging Systems l Broad coverage for short messaging l Message broadcast from all base stations l Simple terminals l Optimized for 1 -way transmission l Answer-back hard l Overtaken by cellular

Bluetooth l Cable replacement RF technology (low cost) l Short range (10 m, extendable to 100 m) l 2. 4 GHz band (crowded) l 1 Data (700 Kbps) and 3 voice channels l Widely supported by telecommunications, PC, and consumer electronics companies l Few applications beyond cable replacement 8 C 32810. 61 -Cimini-7/98

Emerging Systems l Ad hoc wireless networks l Sensor networks l Distributed control networks

Ad-Hoc Networks l l l Peer-to-peer communications. No backbone infrastructure. Routing can be multihop. Topology is dynamic. Fully connected with different link SINRs

Design Issues l Ad-hoc networks provide a flexible network infrastructure for many emerging applications. l The capacity of such networks is generally unknown. l Transmission, access, and routing strategies for ad -hoc networks are generally ad-hoc. l Crosslayer design critical and very challenging. l Energy constraints impose interesting design tradeoffs for communication and networking.

Sensor Networks Energy is the driving constraint l Nodes powered by nonrechargeable batteries l Data flows to centralized location. l Low per-node rates but up to 100, 000 nodes. l Data highly correlated in time and space. l Nodes can cooperate in transmission, reception, compression, and signal processing.

Energy-Constrained Nodes l Each node can only send a finite number of bits. l l Transmit energy minimized by maximizing bit time Circuit energy consumption increases with bit time Introduces a delay versus energy tradeoff for each bit Short-range networks must consider transmit, circuit, and processing energy. Sophisticated techniques not necessarily energy-efficient. l Sleep modes save energy but complicate networking. l l Changes everything about the network design: l l l Bit allocation must be optimized across all protocols. Delay vs. throughput vs. node/network lifetime tradeoffs. Optimization of node cooperation.

Distributed Control over Wireless Links Automated Vehicles - Cars - UAVs - Insect flyers l l l Packet loss and/or delays impacts controller performance. Controller design should be robust to network faults. Joint application and communication network design.

Joint Design Challenges l There is no methodology to incorporate random delays or packet losses into control system designs. l The best rate/delay tradeoff for a communication system in distributed control cannot be determined. l Current autonomous vehicle platoon controllers are not string stable with anycommunication delay Can we make distributed control robust to the network? Yes, by a radical redesign of the controller and the network.

Spectrum Regulation l Spectral Allocation in US controlled by FCC (commercial) or OSM (defense) l FCC auctions spectral blocks for set applications. l Some spectrum set aside for universal use l Worldwide spectrum controlled by ITU-R Regulation can stunt innovation, cause economic disasters, and delay system rollout

Standards l Interacting systems require standardization l Companies want their systems adopted as standard l Alternatively try for de-facto standards l Standards determined by TIA/CTIA in US l IEEE standards often adopted l Worldwide standards determined by ITU-T l In Europe, ETSI is equivalent of IEEE Standards process fraught with inefficiencies and conflicts of interest

Main Points l The wireless vision encompasses many exciting systems and applications l Technical challenges transcend across all layers of the system design l Wireless systems today have limited performance and interoperability l Standards and spectral allocation heavily impact the evolution of wireless technology