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 Course Information
 Term project on anything related to wireless
 Literature survey, analysis, or simulation
 Must set up website for your project (for proposal and report
 Course Syllabus
 Overview of Wireless Communications
 Security
 Review of Physical Media issues
 Power issue
 routing Algorithms
 Is there a future for wireless?
Some history
 Radio invented in the 1880s by Marconi
 Glimmers of Hope
 Internet and laptop use exploding
 2G/3G wireless LANs growing rapidly
 Low rate data demand is high
 Military and security needs require wireless
 Emerging interdisciplinary applications
 Future Wireless Networks
 Design Challenges
 Wireless channels are a difficult and capacity-limited broadcast communications medium
 Traffic patterns, user locations, and network conditions are constantly changing
 Applications are heterogeneous with hard constraints that must be met by the network
 Energy and delay constraints change design principles across all layers of the protocol stack
 Multimedia Requirements
 Wireless Performance Gap
 Evolution of Current Systems
 Wireless systems today
 2G Cellular: ~30-70 Kbps.
 WLANs: ~10 Mbps.
 Next Generation
 3G Cellular: ~300 Kbps.
 WLANs: ~70 Mbps.
 Technology Enhancements
 Hardware: Better batteries. Better circuits/processors.
 Link: Antennas, modulation, coding, adaptivity, DSP, BW.
 Network: Dynamic resource allocation. Mobility support.
 Application: Soft and adaptive QoS.
 Future Generations
 Crosslayer Design
 Hardware
 Link
 Access
 Network
 Application
 Current Wireless Systems
 Cellular Systems
 Wireless LANs
 Satellite Systems
 Paging Systems
 Bluetooth
 Cellular Systems:
Reuse channels to maximize capacity
 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
 Cellular Phone Networks
 3G Cellular Design:
Voice and Data
 Data is bursty, whereas voice is continuous
 Typically require different access and routing strategies
 3G “widens the data pipe”:
 384 Kbps.
 Standard based on wideband CDMA
 Packet-based switching for both voice and data
 3G cellular struggling in Europe and Asia
 Evolution of existing systems (2.5G,2.6798G):
l GSM+EDGE
l IS-95(CDMA)+HDR
l 100 Kbps may be enough
 What is beyond 3G?
 Wireless Local Area Networks (WLANs)
 Wireless LAN Standards
 802.11b (Current Generation)
 Standard for 2.4GHz ISM band (80 MHz)
 Frequency hopped spread spectrum
 1.6-10 Mbps, 500 ft range
 802.11a (Emerging Generation)
 Standard for 5GHz NII band (300 MHz)
 OFDM with time division
 20-70 Mbps, variable range
 Similar to HiperLAN in Europe
 802.11g (New Standard)
 Standard in 2.4 GHz and 5 GHz bands
 OFDM
 Speeds up to 54 Mbps
 Satellite Systems
 Cover very large areas
 Different orbit heights
 GEOs (39000 Km) versus LEOs (2000 Km)
 Optimized for one-way transmission
 Radio (XM, DAB) and movie (SatTV) broadcasting
 Most two-way systems struggling or bankrupt
 Expensive alternative to terrestrial system
 A few ambitious systems on the horizon
 Paging Systems
 Broad coverage for short messaging
 Message broadcast from all base stations
 Simple terminals
 Optimized for 1-way transmission
 Answer-back hard
 Overtaken by cellular
 Bluetooth
 Cable replacement RF technology (low cost)
 Short range (10m, extendable to 100m)
 2.4 GHz band (crowded)
 1 Data (700 Kbps) and 3 voice channels
 Widely supported by telecommunications, PC, and consumer electronics companies
 Few applications beyond cable replacement
 Emerging Systems
 Ad hoc wireless networks
 Sensor networks
 Distributed control networks
 Ad-Hoc Networks
 Peer-to-peer communications.
 No backbone infrastructure.
 Routing can be multihop.
 Topology is dynamic.
 Fully connected with different link SINRs
 Design Issues
 Ad-hoc networks provide a flexible network infrastructure for many emerging applications.
 The capacity of such networks is generally unknown.
 Transmission, access, and routing strategies for ad-hoc networks are generally ad-hoc.
 Crosslayer design critical and very challenging.
 Energy constraints impose interesting design tradeoffs for communication and networking.
 Sensor Networks
Energy is the driving constraint
 Nodes powered by nonrechargeable batteries
 Data flows to centralized location.
 Low per-node rates but up to 100,000 nodes.
 Data highly correlated in time and space.
 Nodes can cooperate in transmission, reception, compression, and signal processing.
 Energy-Constrained Nodes
 Each node can only send a finite number of bits.
 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.
 Sleep modes save energy but complicate networking.
 Changes everything about the network design:
 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
 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
 There is no methodology to incorporate random delays or packet losses into control system designs.
 The best rate/delay tradeoff for a communication system in distributed control cannot be determined.
 Current autonomous vehicle platoon controllers are not string stable with any communication delay
 Spectrum Regulation
 Spectral Allocation in US controlled by FCC (commercial) or OSM (defense)
 FCC auctions spectral blocks for set applications.
 Some spectrum set aside for universal use
 Worldwide spectrum controlled by ITU-R
 Standards
 Interacting systems require standardization
 Companies want their systems adopted as standard
 Alternatively try for de-facto standards
 Standards determined by TIA/CTIA in US
 IEEE standards often adopted
 Worldwide standards determined by ITU-T
 In Europe, ETSI is equivalent of IEEE
 Main Points
 The wireless vision encompasses many exciting systems and applications
 Technical challenges transcend across all layers of the system design
 Wireless systems today have limited performance and interoperability
 Standards and spectral allocation heavily impact the evolution of wireless technology