Cross Layer Design in Wireless Networks Andrea Goldsmith Stanford University Crosslayer Design Panel...
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Transcript of Cross Layer Design in Wireless Networks Andrea Goldsmith Stanford University Crosslayer Design Panel...
Cross Layer Design in Wireless Networks
Andrea GoldsmithStanford University
Crosslayer Design PanelICC
May 14, 2003
Future Wireless Networks
Wireless Internet accessNth generation CellularWireless Ad Hoc NetworksSensor Networks Wireless EntertainmentSmart Homes/SpacesAutomated HighwaysAll this and more…
Ubiquitous Communication Among People and Devices
•Hard Delay Constraints•Hard Energy Constraints
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
These challenges apply to all wireless networks, but are amplified in ad hoc/sensor networks
Evolution of Current Systems
Wireless systems today2G Cellular: ~30-70 Kbps.WLANs: ~10 Mbps.
Next Generation3G 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.
“Current Systems on Steroids”
Future Generations
Rate
Mobility
2G
3G
4G802.11b WLAN
2G Cellular
Other Tradeoffs: Rate vs. Coverage Rate vs. Delay Rate vs. Cost Rate vs. Energy
Fundamental Design Breakthroughs Needed
Design objective
Want to provide end-to-end “QoS”
The challenge for this QoS is the system dynamicsScheduling can help shape these dynamics
Adaptivity can compensate for or exploit these dynamics
Diversity provides robustness to unknown dynamics
Scheduling, adaptivity, and diversity are most powerful in the context of a crosslayer design
Energy must be allocated across all protocol layers
Crosslayer Design
Hardware
Link
Access
Network
Application
Delay ConstraintsRate Constraints
Energy Constraints
Adapt across design layersReduce uncertainty through scheduling
Provide robustness via diversity
Crosslayer Techniques Adaptive techniques
Link, MAC, network, and application adaptation Resource management and allocation (power
control) Synergies with diversity and scheduling
Diversity techniques Link diversity (antennas, channels, etc.) Access diversity Route diversity Application diversity Content location/server diversity
Scheduling Application scheduling/data prioritization Resource reservation Access scheduling
Key QuestionsWhat 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?
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
TrafficGenerator
DataBuffer
SourceCoder
ChannelCoder
Modulator(Power)
Receiver
Stringent QoS constraints require that thefull dynamics of the system be represented
Channel
Cross-Layer System
Average performance metrics are misleading
The “Myth” of Averages:
Minimizing Average Delay
What if we constrain delayacross all channel gains?
Average Delay
Channel Gain in dB
Dela
y in
mill
iseco
nd
s
Hard Delay Constraints (50 ms)
Pow
er
in m
illiw
att
s
Source data rate in bits per second
50ms constraint on delayacross all channel gains
with power adaptation only
Joint source-channel coding power saving
200mW
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
Each node can only send a finite number of bits.Transmit energy minimized by maximizing bit timeCircuit 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
Network design must meet control requirements. Automated highway controllers unstable with any delay
Controller design should be robust to network faults. Need joint application and communication network design.
Automated highways,factories, and homes
Design Approach
Theory Optimizati
on Simulatio
n Testbeds
NetworkDesign
Opt
imiz
atio
n
Sim
ulat
ion
LinkDesign
DeviceDesign
ApplicationDesign
Summary Crosslayer design needed to meet requirements
and constraints of future wireless networks
Key synergies in crosslayer design must be identified
The design must be tailored to the application
Crosslayer design should include adaptivity, scheduling and diversity across protocol layers
Energy can be a precious resource that must be shared by different protocol layers
Lots of fun and challenging research problems