Transcript Multilayer Approach to Mobile Networking (SNRC)

Cross Layer Design in
Wireless Networks
Andrea Goldsmith
Stanford University
Crosslayer Design Panel
ICC
May 14, 2003
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
Challenges
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Wireless channels are a difficult and capacitylimited broadcast communications medium
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Traffic patterns, user locations, and network
conditions are constantly changing
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Applications are heterogeneous with hard
constraints that must be met by the network
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Energy and delay constraints change design
principles across all layers of the protocol stack
These challenges apply to all wireless networks,
but are amplified in ad hoc/sensor networks
Evolution of Current
Systems
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Wireless systems today
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Next Generation
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2G Cellular: ~30-70 Kbps.
WLANs: ~10 Mbps.
3G Cellular: ~300 Kbps.
WLANs: ~70 Mbps.
Technology Enhancements
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Hardware: Better batteries. Better circuits/processors.
Link: Antennas, modulation, coding, adaptivity, DSP, BW.
Network: Dynamic resource allocation. Mobility support.
Application: Soft and adaptive QoS.
“Current Systems on Steroids”
Future Generations
Rate
4G
802.11b WLAN
3G
Other Tradeoffs:
Rate vs. Coverage
Rate vs. Delay
Rate vs. Cost
Rate vs. Energy
2G
2G Cellular
Mobility
Fundamental Design Breakthroughs Needed
Design objective
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Want to provide end-to-end “QoS”
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The challenge for this QoS is the system dynamics
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Scheduling can help shape these dynamics
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Adaptivity can compensate for or exploit these dynamics
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Diversity provides robustness to unknown dynamics
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Scheduling, adaptivity, and diversity are most
powerful in the context of a crosslayer design
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Energy must be allocated across all protocol layers
Crosslayer Design
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Hardware
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Link
Delay Constraints
Rate Constraints
Energy Constraints
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Access
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Network
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Application
Adapt across design layers
Reduce uncertainty through scheduling
Provide robustness via diversity
Crosslayer Techniques
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Adaptive techniques
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Diversity techniques
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Link, MAC, network, and application adaptation
Resource management and allocation (power control)
Synergies with diversity and scheduling
Link diversity (antennas, channels, etc.)
Access diversity
Route diversity
Application diversity
Content location/server diversity
Scheduling
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Application scheduling/data prioritization
Resource reservation
Access scheduling
Key Questions
 What
is the right framework for crosslayer design?
What are the key crosslayer design synergies?
 How to manage its complexity?
 What information should be exchanged across layers, and
how should this information be used?
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 How
do the different timescales affect adaptivity?
 What
are the diversity versus throughput tradeoffs?
 What
criterion should be used for scheduling?
 How
to balance the needs of all users/applications?
Single User Systems
Receiver
Traffic
Generator
Channel
Data
Buffer
Source
Coder
Channel
Coder
Modulator
(Power)
Cross-Layer System
Stringent QoS constraints require that the
full dynamics of the system be represented
Average performance metrics are misleading
The “Myth” of Averages:
Delay in milliseconds
Minimizing Average Delay
What if we constrain delay
across all channel gains?
Average Delay
Channel Gain in dB
Power in milliwatts
Hard Delay Constraints (50 ms)
50ms constraint on delay
across all channel gains
with power adaptation only
200mW
Joint source-channel
coding power saving
Source data rate in bits per second
Crosslayer design in
multiuser systems
• Users in the system interact (interference,
congestion)
• Resources in the network are shared
• Adaptation becomes a “chicken and egg” problem
• Protocols must be distributed
Energy-Constrained Nodes
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Each node can only send a finite number of bits.
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Short-range networks must consider transmit,
circuit, and processing energy.
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Transmit energy minimized by maximizing bit time
Circuit energy consumption increases with bit time
Introduces a delay versus energy tradeoff for each bit
Sophisticated techniques not necessarily energy-efficient.
Sleep modes save energy but complicate networking.
Changes everything about the network design:
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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 highways,
factories, and homes
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Network design must meet control requirements.
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Automated highway controllers unstable with any delay
Controller design should be robust to network faults.
Need joint application and communication network design.
Design Approach
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Theory
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Optimization
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Simulation
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Testbeds
Application
Design
Network
Design
Link
Design
Device
Design
Summary
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Crosslayer design needed to meet requirements and
constraints of future wireless networks
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Key synergies in crosslayer design must be identified
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The design must be tailored to the application
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Crosslayer design should include adaptivity, scheduling
and diversity across protocol layers
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Energy can be a precious resource that must be shared
by different protocol layers
Lots of fun and challenging research problems