05-03-2011, 03:55 PM
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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 page 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
