Cross layer design for Wireless networks
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Transcript Cross layer design for Wireless networks
Cross layer design for
Wireless networks
Kavé Salamatian
LIP6-UPMC
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
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
Challenges
Wireless channels are a difficult and capacitylimited 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
Wireline Backbone
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
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
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
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 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?
Single user example
WIFI : (171,133)
0
10
-1
10
-2
10
Packet Error Rate
-3
10
-4
10
-5
10
-6
10
1
2
3
4
5
6
SNR
7
8
9
10
Adaptive Modulation
and Coding in Flat Fading
Uncoded
Data Bits
Point
Selector
Buffer
log2 M(g) Bits
g(t)
One of the
M(g) Points
M(g)-QAM
Modulator
Power: S(g)
g(t)
To Channel
Adapt transmission to channel
Parameters: power,rate,code,BER, etc.
Capacity-achieving strategy
Recent Work
BSPK
4-QAM
16-QAM
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
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
Wireless networks
They are formed by nodes with radios
There is no a priori notion of “links”
Nodes simply radiate energy
Nodes Cooperation
Decode and forward
Why not: Amplify and
Forward
Increase Signal for
Receiver
Why not: Reduce
Interference at Receiver
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?
Example: Six Node Network
Capacity Regions (Goldsmith)
Rij 0, ij 12,34, i j
Multiple
hops
Spatial
reuse
SIC
(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.
Optimal Routing
The point R12 R34 1.64 Mbps is achieved by the
following scheduling :
Adaptive Rate MAC (Kumar)
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
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
Switching off adaptation is better
Routing based approach
Luigi & al.
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
Maximise throughput
Gupta & Kumar
Rate
Transmission range
Node number
Throughput
To maximise throughput we have to maximise transmission
rate and reduce interference generated by each packets
Capacity Constraints
Cross-Layer Approach
Routing metric
Rate
Interference
Packet Error Rate
SIR
Interface characteristics
Next-Hop
Data-Rate
Transmission power
Interference
Measurement: unrealistic
More neighbor => More interference
More power => More interference
Defining a interference replacement function I(P)
Minimise I(P) => Minimise Real interference
Packet Error Rate (I)
IP packet
IP packet
MAC
MAC
Convolution
Coder
Viterbi
Decoder
Interleaver
Deinterleaver
Modulator &
Scrambler
Interference
Noise
(White or fading)
Channel
Single Antenna
Multiple Antenna
Rake Receiver
Packet Error Rate (III)
BER
PERSIR f
Pf E L
Routing Strategy
• Rate (Mbps)
•Maximise
•Interference (mW)
• Minimise
•PER
• Minimise
•Power (mW)
• trade off for optimising
routing parameter
•NP-Complet Problème
Routingless approach
Ramin & al.
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
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 C I k k Bk ( nk )
• Each submatrix of
Bk( nk )
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
Achievability of the capacity bound for the
more capable case
Choose a code length n. Knowing packet loss matix of the
netwok R and opt can be determined. We chose then
k
nR, l n opt
The code C I k k Bk0( n k ) Bk1l 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
W X I k k Bk0( nk )
X1 W Bk1l
1
p2
p1
W
X W I k k Bk0( n k )
p
W X , X 1 C
W
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
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
Topology
600
500
Receiver
400
300
200
100
Sender
0
0
100
200
300
400
500
600
Throughput and relay load
6
10
5
10
4
10
3
10
2
10
-3
10
-2
10
-1
10
0
10
35
30
25
20
15
10
5
0
-3
10
-2
10
-1
10
0
10
Toward Software radio
Antenna
Common
DSP
platform
Tx
Chan
Interface
UpconD/A
verter
Channelizer
Interface
Wideband
transceiver
MCPA
Rx
Chan
A/D
Interface
Dup LNA RF/IF
Network ATM
I/F
Cellsite controller
middleware
• Common technology for multiple radio platforms
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
Interesting Question
MIMO or Ad Hoc, that’s the question?
Routing can be seen as a diversity
Not shortest path !