Cross layer design for Wireless networks
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Transcript of Cross layer design for Wireless networks
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Cross layer design for Wireless networks
Kavé Salamatian
LIP6-UPMC
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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
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Next generation network architecture
MobilityServices
Layer
RadioAccessLayer
MobileTerminal
Layer
InternetworkingLayer
LocalServiceLayer
NetworkServiceLayer
AccessManagement
Layer
AccessInterface
Layer
WirelessInterface
Layer
MobileApplication
Layer
Internet Wireless PSTN
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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
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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
Transport
Physical
Signal
Packet
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: 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
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…And The Wireless Network
Link characteristics are dynamic Network access is unpredictable and hard to coordinate Routing often multihop over multiple wireless/wired
channels Network topology is dynamic Different applications have different requirements
Wireline Backbone
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Design objective
Want to provide end-to-end Properties
The challenge for this system is dynamics Scheduling 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
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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
Multilayer Design
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Crosslayer TechniquesAdaptive 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
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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? 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?
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Single user example
1 2 3 4 5 6 7 8 9 1010
-6
10-5
10-4
10-3
10-2
10-1
100
WIFI : (171,133)
SNR
Packet
Err
or
Rate
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Adaptive Modulation and Coding in Flat Fading
Adapt transmission to channel Parameters: power,rate,code,BER, etc. Capacity-achieving strategy
Recent Work Adaptive modulation for voice and data (to meet QOS) Adaptive turbo coded modulation (<1 db from capacity) Multiple degrees of freedom (only need exploit 1-2) Adaptive power, rate, and compression with hard deadlines
(t)
UncodedData Bits Buffer
M()-QAM ModulatorPower: S()
To Channel(t)
PointSelector
log2 M() Bits One of theM() Points
BSPK 4-QAM 16-QAM
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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
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Wireless networks
They are formed by nodes with radios There is no a priori notion of “links” Nodes simply radiate energy
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Nodes Cooperation
Decode and forward Why not: Amplify and
Forward
Increase Signal for Receiver
Why not: Reduce Interference at Receiver
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How should node cooperates ?
Some obvious choices Should nodes relay packets? Should they amplify and forward? Or should they decode and forward? Should they cancel interference for other nodes? Or should they boost each other’s signals? Should nodes simultaneously broadcast to a group of
nodes? Should those nodes then cooperatively broadcast to
others? What power should they use for any operation? …
Or should they use much more sophisticated unthought of strategies?
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Example: Six Node Network
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Capacity Regions (Goldsmith)
(a): Single hop, no simultaneous transmissions.(b): Multihop, no simultaneous transmissions. (c): Multihop, simultaneous transmissions.(d): Adding power control (e): Successive interference cancellation, no power control.
jiijRij ,34,12 ,0
Multiplehops
Spatial reuse
SIC
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Optimal Routing
The point is achieved by the following scheduling :
MbpsRR 64.13412
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Idea: Adapt transmission rate according to channel quality Change modulation to get higher rate if channel is good Could send multiple packets at higher rates (A
suggested cscheme)
Protocol details RTS/CTS and Broadcast packets sent at lowest rate Receiver measures strength of RTS Communicates rate to sender in CTS DATA and ACK at that rate
Adaptive Rate MAC (Kumar)
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Interaction with Min Hop Routing Protocol
Most current routing protocols are min hop Consider DSDV for example Chooses long hops But long hops => low signal strength => low rates
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Switching off adaptation is better
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Routing based approach
Luigi & al.
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Routing in wireless network
« Shortest path approche is not optimal » Physical channel is instable Each transmission inject interference in the
network Interference reduce capacity
Power management is needed Make use of multi-rate and power control on WIFI card
L’architecture en couches n’est pas optimale
Cross Layer approch
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Maximise throughput
Gupta & Kumar
Throughput
Node number
Transmission range
Rate
To maximise throughput we have to maximise transmission rate and reduce interference generated by each packets
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Capacity Constraints
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Cross-Layer Approach
SIRInterface characteristics
Next-HopData-RateTransmission power
Routing metric Rate Interference Packet Error Rate
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Interference
Measurement: unrealistic More neighbor => More interference More power => More interference Defining a interference replacement function I(P) Minimise I(P) => Minimise Real interference
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Packet Error Rate (I)
MAC
Convolution Coder
Interleaver
Modulator &Scrambler
Channel
Rake Receiver
Deinterleaver
Viterbi Decoder
MAC
InterferenceNoise
(White or fading)
IP packet IP packet
Multiple AntennaMultiple Antenna
Single AntennaSingle Antenna
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Packet Error Rate (III)
LEP
BERSIRPER
f
f
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Routing Strategy
• Rate (Mbps)•Maximise
•Interference (mW)• Minimise
•PER• Minimise
•Power (mW)• trade off for optimising routing parameter
•NP-Complet Problème
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Routingless approach
Ramin & al.
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Ad-Hoc Network
Ad Hoc Networks function by multi-hop transport Nodes relay packets until they reach their destinations
Must of the traffic carried by the nodes is relay traffic The actual useful traffic per user pair is small
Intermediate nodes relay the same information Duplicated information might be received by the receiver
More intelligent relaying is needed
Which packet to relay Which information to relay
• The relay nodes must only send useful information
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Coding for erasure channels MDS (Maximum Distance Separable) codes
Get k packets, generates n-k redundant packets Each combination of k packets out of n enable to retrieve
the initial packets Generating matrix
• Each submatrix of is invertible
Reed Solomon codes are MDS We suppose that sender generates m redundant
packets We suppose that relay generates l packets
How to choose m and l to achieve the bound
( )k k k n kC I B
( )k n kB
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Achievability of the capacity bound for the more capable case
Choose a code length n. Knowing packet loss matix of the netwok R and can be determined. We chose then
The code is a MDS code The receiver is able to retrieve the k initial packets if it receives at
least k packets from sender and relay together This happen asymptotically with large n if the rate validate
the bound
10)( lkknkkk BBIC
optnlnRk ,
0)( knkkk BIWX
11 lkBWX
CXXW 1,
10)(
knkkk BIXW
WW p
1p 2p
opt
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Comments & practical consideration
Relay send only useful side information over the channel
The relay load is chosen as the minimal value which maximize the global rate
Each sender and relay can derivate the number of needed redundant packets if it know the packet loss probability matrix
The proposed scheme can be implemented very easily in WiFi based wireless network Does not need any change to physical layer
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Practical implementation
15 node distributed randomly in the environment One Sender-Receiver pair is chosen randomly each node have two cart WiFi, with different frequency
channels f1 and f2 If one node receive the packets
It can be a relay with probability p The relay nodes broadcast information in the
environment There is not any routing protocol
It is done in NS
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Topology
0 100 200 300 400 500 6000
100
200
300
400
500
600
Sender
Receiver
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Throughput and relay load
10-3
10-2
10-1
100
102
103
104
105
106
10-3
10-2
10-1
100
0
5
10
15
20
25
30
35
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Toward Software radio
• Common technology for multiple radio platforms
NetworkI/F
Dup
Channel-izer
D/AUpcon-verter
A/DLNA RF/IF Rx Chan
Tx ChanMCPA
Cellsite controller middleware
CommonDSP
platform
Antenna
ATMWideband transceiver
Inte
rfac
e
Inte
rfac
e
Inte
rfac
e
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Conclusions
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
Coming Challenges MIMO: how to take advantage of Multiple Antenna Software Radio: How to enable adaptation of physical layer
from upper layer
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Interesting Question
MIMO or Ad Hoc, that’s the question? Routing can be seen as a diversity
Not shortest path !