Cross Layer Design (CLD) for Wireless Networks
Future Wireless Systems
Nth Generation CellularWireless Internet AccessWireless Video/Music Wireless Ad Hoc NetworksSensor Networks Smart Homes/AppliancesAutomated Vehicle NetworksAll this and more…
Ubiquitous Communication Among People and Devices
Next Generation Network Architecture
MobilityServices
Layer
RadioAccessLayer
MobileTerminal
Layer
InternetworkingLayer
LocalServiceLayer
NetworkServiceLayer
AccessManagement
Layer
AccessInterface
Layer
WirelessInterface
Layer
MobileApplication
Layer
Internet Wireless PSTN
Radio Access Network
Radio Access NetworkMobile User Equipment(e.g. Win9X, Palm OS)
Mobile User Equipment(e.g. Win9X, Palm OS)
Application
Network Server(e.g. WinNT, Unix)
Network Server(e.g. WinNT, Unix)
IP Transport(TCP, UDP, RTP)
Internet Protocol(IP)
RadioAccess
RadioAccessModemModemEthernetEthernet
Application
IP Transport(TCP, UDP, RTP)
Internet Protocol(IP)
EthernetEthernet ATMATMInternet
TransportAgents
TransportAgents
IP
RadioResourceMgmt
RadioL1
AccessL1
RadioL2
AccessL2
AccessL1
CoreL1
AccessL2
CoreL2
Radio-Optimized IP Networking• Transparent to TCP/IP protocols• Enables deployment of IP-based consumer applications in next generation wireless systems
Our simplified model for wireless systems
Application
Presentation
Session
Transport
Network
Data Link
Physical
(MAC sublayer)
OSI Model
Physical Layer
MAC Layer
Network Layer
Transport Layer
App. Layer
Simplified wireless network layered model
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
Transport
Physical
Signal
Packet
Bits
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
Why is Wireless Hard?The Wireless Channel
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
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
Wireline Backbone
• They are formed by nodes with radios– There is no a priori notion of “links”– Nodes simply radiate energy
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
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
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
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
Cross Layer Design
General framework for cross–layer 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
Cross Layer Signaling Methods
Method I – Packet headers
Method II – ICMP Messages
Method III – Local Profiles
Method IV – Networks Services
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
QoS Requirements
Voice VideoData
Delay
Packet Loss
BER
Data Rate
Traffic
<100ms - <100ms
<1% 0 <1%
10-3 10-6 10-6
8-32 Kbps 1-100 Mbps 1-20 Mbps
Continuous Bursty Continuous
One-size-fits-all protocols and design do not work well
Wired networks use this approach, with poor results
CLD
Hardware Link Access Network Application
Delay ConstraintsRate Constraints
Energy Constraints
Adapt across design layersReduce uncertainty through scheduling
Provide robustness via diversity
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
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 > Go
An idle node listens omnidirectionally Does not know who is going to transmit to it
Pros and Cons for directional antennasAdvantagesSpatial reuseMultiple transmissions in the same neighborhood
Higher gains – better links Two distant nodes may communicate with a single hop Fewer hops in a route
DisadvantagesHigher 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
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
Performance Evaluation
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
Multilayer Design
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