Cross Layer Design (CLD) for Wireless Networks

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Cross Layer Design (CLD) for Wireless Networks
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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
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Next Generation Network Architecture
Internetworking Layer
Internet
Wireless
PSTN
Network Service Layer
Mobility Services Layer
Local Service Layer
Access Management Layer
Radio Access Layer
Access Interface Layer
Wireless Interface Layer
Mobile Terminal Layer
Mobile Application Layer
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Radio Access Network
Radio Access Network
Mobile User Equipment(e.g. Win9X, Palm OS)
Network Server(e.g. WinNT, Unix)
Application
Application
TransportAgents
TransportAgents
RadioResourceMgmt
IP Transport(TCP, UDP, RTP)
IP Transport(TCP, UDP, RTP)
Internet Protocol(IP)
Internet Protocol(IP)
RadioAccess
Modem
Ethernet
Ethernet
ATM

• Radio-Optimized IP Networking
• Transparent to TCP/IP protocols
• Enables deployment of IP-based consumer
  applications in next generation wireless
  systems

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Our simplified model for wireless systems
OSI Model
Application
Simplified wireless network layered model
Presentation
Session
App. Layer
Transport
Transport Layer
Network
Network Layer
(MAC sublayer)
MAC Layer
Data Link
Physical Layer
Physical
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Separation principles

• Application, transport and physical layer can be
  separated if
• No errors at physical layer
• No losses and delays at transport layer
• No fluctuations in applications rate
• Each layer being perfect from the point of view
  of other layers

Application
Signal
Transport
Packet
Physical
Bits
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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
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Why is Wireless Hard?The Wireless Channel

• Fundamentally Low Capacity Rlt B log(1SINR) 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

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And The Wireless Network
Wireline Backbone

• Link characteristics are dynamic
• Network access is unpredictable and hard to
  coordinate
• Routing often multi-hop over multiple
  wireless/wired channels
• Network topology is dynamic
• Different applications have different requirements

• They are formed by nodes with radios
• There is no a priori notion of links
• Nodes simply radiate energy

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What lead to CLD?

• Advanced applications like VOIP, Web browsing ,
  multimedia conferences video streaming demanded
• 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

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Cross Layer Design

• 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

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Cross Layer Design

• 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

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Cross Layer Design

• Wireless Networking
• Architecture Connection Vs Connectionless
• Energy efficient analysis of manets
• Traffic theory protocols
• Signal processing
• Increasing the spectral efficiency
• Reducing Bit Error Rate
• Reducing transmission energy
• Information Theory
• Developing capacity limits
• Designing efficient source coding and channel
  algorithms

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Cross Layer Design

• General framework for crosslayer design
• Maintain the layered approach but exchange
  information between layers and jointly optimize
  the performance
• Abstraction of layers
• 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
• determine SIR as a key performance measure for
  the physical layer
• Optimize powers, receivers, antennas
• MAC and Network layers
• QoS measures Delay and blocking performance
• Optimize scheduling, routes, number of users
  allowed in the network

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Cross Layer Signaling Methods

• Method I Packet headers
• Method II ICMP Messages
• Method III Local Profiles
• Method IV Networks Services

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CLD Design goal ?

• Deliver QoS
• QoS measures
• Physical layer
• BER (Bit error rate)
• MAC layer
• Access delay, throughput
• Network layer
• Delay, throughput, blocking probability, dropping
  probability
• Other important performance measures
• Energy (power consumption, network lifetime)
• User capacity

Impact all layers
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QoS Requirements
Voice
Video
Data
Delay
lt100ms
-
lt100ms
Packet Loss
lt1
0
lt1
BER
10-3
10-6
10-6
Data Rate
8-32 Kbps
1-100 Mbps
1-20 Mbps
Traffic
Continuous
Bursty
Continuous
One-size-fits-all protocols and design do not
work well
Wired networks use this approach, with poor
results
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CLD

• Hardware
• Link
• Access
• Network
• Application

Delay Constraints Rate Constraints Energy
Constraints
Adapt across design layers Reduce uncertainty
through scheduling Provide robustness via
diversity
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Examples of cross-layer integration for ad-hoc
networks

• Physical layer MAC
• Adaptive beamforming and CSMA/CA
• Adaptive modulation and MAC
• Adaptive power control and MAC
• Physical layer network layer
• Adaptive power control routing
• Adaptive power control receiver optimization
  routing
• Power control routing receiver optimization
  admission control
• Physical layer MAC routing
• Adaptive modulation MAC routing
• Adaptive beamforming MAC routing

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Case 1 Adaptive beamforming MAC routing

• In general, different MAC protocols differ based
  on
• 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 gt Go
• An idle node listens omnidirectionally
• Does not know who is going to transmit to it

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Pros and Cons for directional antennas

• Advantages
• Spatial reuse
• Multiple transmissions in the same neighborhood
• Higher gains better links
• Two distant nodes may communicate with a single
  hop
• Fewer hops in a route
• Disadvantages
• Higher gains mean also high interference at
  distanced nodes
• There are three types of links
• omnidirectional omnidirectional OO links
  smallest range
• directional omnidirectional DO links
• directional directional largest range

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Joint MAC and routing solution

• Use the same MAC for directional antennas, but
  transmit RTS over multiple hops (MMAC protocol)
• If source 1 wants to communicate with node 6
• transmits a forwarding RTS with the profile of
  node 6, using DO links
• when node 6 gets the RTS, it beamforms in the
  direction of 1, forming a
• DD link
• Transmission from 1 to 9 on DD links requires
  only 2 hops

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Performance Evaluation
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Multilayer Design

• Hardware
• Power or hard energy constraints
• Size constraints
• Link Design
• Time-varying low capacity channel
• Multiple Access
• Resource allocation (power, rate, BW)
• Interference management
• Networking.
• Routing, prioritization, and congestion control
• Application
• Real time media and QOS support
• Hard delay/quality constraints

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Cross-layer 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