Transcript Cross layer design for Wireless networks

Lecture 12: Cross Layer Design
(CLD) for Wireless Networks
Future Wireless Systems
Ubiquitous Communication Among People and Devices
Nth Generation Cellular
Wireless Internet Access
Wireless Video/Music
Wireless Ad Hoc Networks
Sensor Networks
Smart Homes/Appliances
Automated Vehicle Networks
All this and more…
Next Generation Network Architecture
Internetworking
Layer
Mobility
Services
Layer
Network
Service
Layer
Local
Service
Layer
Access
Management
Radio
Layer
Access
Layer
Access
Interface
Layer
Mobile
Terminal
Layer
Wireless
Interface
Layer
Mobile
Application
Layer
Internet
Wireless
PSTN
Radio Access Network
Mobile User Equipment
(e.g. Win9X, Palm OS)
Application
Network Server
(e.g. WinNT, Unix)
Radio Access Network
Radio
Resource
Mgmt
Application
IP Transport
(TCP, UDP, RTP)
Internet Protocol
(IP)
Ethernet Modem
Radio
Access
IP Transport
(TCP, UDP, RTP)
Transport
Agents
Transport
Agents
Radio Access
L2
L2
IP
Internet Protocol
(IP)
Access Core
L2
L2
Internet
Radio Access
L1
L1
Access Core
L1
L1
Radio-Optimized IP Networking
• Transparent to TCP/IP protocols
• Enables deployment of IP-based consumer applications
in next generation wireless systems
Ethernet ATM
Our simplified model for wireless systems
OSI Model
Application
Presentation
Session
Simplified wireless network
layered model
App. Layer
Transport
Transport Layer
Network
Network Layer
(MAC sublayer)
MAC Layer
Data Link
Physical
Physical
Layer
Separation principles
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Application, transport and
physical layer can be
separated if :
Application Signal
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No errors at physical layer
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No losses and delays at transport
layer
Transport
Packet
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No fluctuations in applications
rate
Physical
Bits
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Each layer being perfect from the
point of view of other layers
Challenges
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Wireless channels are a difficult and capacity-limited
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
Why is Wireless Hard?
The Wireless Channel
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Fundamentally Low Capacity: R< B log(1+SINR) bps
 Spectrum scarce and expensive
Received power diminishes with distance
Self-interference due to multipath
Channel changes as users move around
Signal blocked by objects (cars, people, etc.)
Broadcast medium – everyone interferes
d
…And The Wireless Network
Wireline Backbone
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Link characteristics are dynamic
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Network access is unpredictable and hard to coordinate
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Routing often multi-hop over multiple wireless/wired channels
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Network topology is dynamic
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Different applications have different requirements
• They are formed by nodes with radios
– There is no a priori notion of “links”
– Nodes simply radiate energy
What lead to CLD?
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Advanced applications like VOIP, Web browsing ,
multimedia conferences & video streaming demanded
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Widely varying and diverse QoS guarantees
Adaptability to dynamically varying networks & traffic
Modest Buffer requirements
High and effective Capacity utilization
Low processing overhead per packet
Video streaming high bandwidth requirements are coupled with tight
delay constraints
Cross Layer Design
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CLD is a way of achieving information sharing between all the layers in
order to obtain highest possible adaptivity of any network.
This is required to meet the challenging Data rates, higher performance
gains and Quality of Services requirements for various real time and non
real time applications.
CLD is a co-operation between multiple layers to combine the resources
and create a network that is highly adaptive
Cross Layer Design
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This approach allows upper layers to better adapt their strategies to
varying link and network conditions.
This helps to improve the end-to-end performance given networks
resources.
Each layer is characterized by some key parameters, that are passed to the
adjacent layers to help them determine the best operation modes that best
suit the current channel, network and application conditions
Cross Layer Design
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Wireless Networking
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Signal processing
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Architecture: Connection Vs
Connectionless
Energy efficient analysis of manets
Traffic theory & protocols
Increasing the spectral efficiency
Reducing Bit Error Rate
Reducing transmission energy
Information Theory
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Developing capacity limits
Designing efficient source coding and
channel algorithms
Cross Layer Design
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General framework for cross–layer design
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Maintain the layered approach but exchange information between layers and jointly
optimize the performance
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Abstraction of layers
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General models for different layers
 capture important parameters which influence other layers
 Identify the cross-layer information that has to be exchanged between layers
Implement adaptation protocols at each layer, using the information exchange between the layers
Several tools for analysis and optimization at different layers
 Physical layer
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determine SIR as a key performance measure for the physical layer
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Optimize powers, receivers, antennas
MAC and Network layers
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QoS measures: Delay and blocking performance
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Optimize scheduling, routes, number of users allowed in the network
Cross Layer Signaling Methods
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Method I – Packet headers
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Method II – ICMP Messages
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Method III – Local Profiles
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Method IV – Networks
Services
CLD Design goal ?
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Deliver QoS
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QoS measures
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Physical layer
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MAC layer
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Access delay, throughput
Network layer
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BER (Bit error rate)
Delay, throughput, blocking probability, dropping probability
Other important performance measures
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Energy (power consumption, network lifetime)
User capacity
Impact all layers
QoS Requirements
Voice
Delay
Packet Loss
BER
Data
Video
<100ms
-
<100ms
<1%
0
<1%
10-3
10-6
10-6
Data Rate
8-32 Kbps
Traffic
Continuous
1-100 Mbps
Bursty
1-20 Mbps
Continuous
One-size-fits-all protocols and design do not work well
Wired networks use this approach, with poor results
CLD
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Hardware
Link
Access
Network
Application
Delay Constraints
Rate Constraints
Energy Constraints
Adapt across design layers
Reduce uncertainty through scheduling
Provide robustness via diversity
Examples of cross-layer integration for adhoc networks
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Physical layer + MAC
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Physical layer + network layer
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Adaptive beamforming and CSMA/CA
Adaptive modulation and MAC
Adaptive power control and MAC
Adaptive power control + routing
Adaptive power control + receiver optimization + routing
Power control + routing + receiver optimization + admission control
Physical layer + MAC + routing
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Adaptive modulation + MAC + routing
Adaptive beamforming + MAC + routing
Case 1: Adaptive beamforming + MAC +
routing
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In general, different MAC protocols differ based on
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How RTS/CTS is transmitted (omni, directional)
Transmission range of directional antennas
Channel access schemes
Omni or directional NAVs
The antenna gains are different for omnidirectional
(Go) and directional transmission (Gd): Gd > Go
An idle node listens omnidirectionally
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Does not know who is going to transmit to it
Pros and Cons for directional antennas
Advantages
Spatial reuse
Multiple transmissions in the same neighborhood
Higher
gains – better links
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Two distant nodes may communicate with a single hop
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Fewer hops in a route
Disadvantages
Higher gains mean also high interference at distanced nodes
There are three types of links
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omnidirectional – omnidirectional : OO links – smallest range
directional – omnidirectional: DO links
directional –directional – largest range
Joint MAC and routing solution
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Use the same MAC for directional antennas, but transmit RTS
over multiple hops (MMAC protocol)
If source 1 wants to communicate with node 6
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transmits a forwarding RTS with the profile of node 6, using DO links
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when node 6 gets the RTS, it beamforms in the direction of 1, forming a
DD link
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Transmission from 1 to 9 on DD links requires only 2 hops
Performance Evaluation
Multilayer Design
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Hardware
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Link Design
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Resource allocation (power, rate, BW)
Interference management
Networking.
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Time-varying low capacity channel
Multiple Access
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Power or hard energy constraints
Size constraints
Routing, prioritization, and congestion control
Application
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Real time media and QOS support
Hard delay/quality constraints
Multilayer Design
Cross-layer 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