Cross layer design for Wireless networks

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					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               Internet   Wireless   PSTN
     Layer

              Network
              Service
   Mobility    Layer
   Services
    Layer       Local
               Service
                Layer
             Access
           Management
    Radio     Layer
    Access
     Layer     Access
              Interface
                Layer
              Wireless
              Interface
    Mobile      Layer
   Terminal
                   Mobile
    Layer       Application
                   Layer
  Radio Access Network

   Mobile User Equipment            Radio Access Network                    Network Server
   (e.g. Win9X, Palm OS)                                                   (e.g. WinNT, Unix)


         Application          Radio                                          Application
                              Resource
                              Mgmt
         IP Transport                                                        IP Transport
       (TCP, UDP, RTP)                                                     (TCP, UDP, RTP)

      Internet Protocol          Transport        Transport                Internet Protocol
             (IP)                 Agents           Agents                         (IP)

                              Radio Access        Access Core
                               L2     L2     IP     L2    L2
                    Radio                                       Internet
  Ethernet Modem                                                            Ethernet ATM
                   Access
                              Radio Access        Access Core
                               L1     L1            L1    L1

Radio-Optimized IP Networking
    • Transparent to TCP/IP protocols
    • Enables deployment of IP-based consumer applications
      in next generation wireless systems
Separation principles
 Application, transport and
  physical layer can be              Application Signal
  separated if :
  No errors at physical layer
  No losses and delays at            Transport   Packet
   transport layer
  No fluctuations in applications
   rate                               Physical    Bits
  Each layer being perfect from
   the point of view of other
   layers
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


                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                                            Multilayer Design
   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
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
                     0
                                              WIFI : (171,133)
                    10




                     -1
                    10




                     -2
                    10




                     -3
                    10
Packet Error Rate




                     -4
                    10




                     -5
                    10




                     -6
                    10
                          1   2   3   4   5              6       7   8   9   10
                                                      SNR
Adaptive Modulation
and Coding in Flat Fading

 Uncoded                           Point                   M(g)-QAM
 Data Bits   Buffer               Selector                 Modulator
                                                           Power: S(g)
                                             One of the
                      log2 M(g) Bits         M(g) Points                  To Channel
                g(t)                                             g(t)

 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      Increase Signal for
 Why not: Amplify and     Receiver
  Forward                 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   (a): Single hop, no simultaneous
                                        transmissions.
                                   (b): Multihop, no simultaneous
                                        transmissions.
                                   (c): Multihop, simultaneous
                                        transmissions.
                                   (d): Adding power control
 Multiple
                                   (e): Successive interference
                  Spatial   SIC
 hops                                    cancellation, no power
                  reuse
                                         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

                               Next-Hop
   SIR                         Data-Rate
   Interface characteristics   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                                                  Viterbi
  Coder                                                      Decoder


Interleaver                                                Deinterleaver


Modulator &
 Scrambler              Interference                       Rake Receiver
                                            Noise
                                       (White or fading)
              Channel
                          Single Antenna

                        Multiple Antenna
Packet Error Rate (III)




                    BER 
      PERSIR  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 ( n k ) 
                                                  
        • Each submatrix of   Bk( nk )   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 ) Bk l is a MDS code
                                    1

     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( n k )   
                                                1
                                                                         
                                                             X 1  W  Bk l
                                                                        1


                                                                   p2
                                    p1

          W                                              p                                  W
                   
         X  W  I k k Bk0( nk )                                    W  X , X 1  C
 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      -2         -1    0
   10       10         10    10




 35

 30

 25

 20

 15

 10

   5

   0
     -3      -2         -1    0
   10       10         10    10
Toward Software radio
Antenna


                                      Rx
Dup LNA RF/IF      A/D                Chan




                                                 Interface
                         Interface




                                                                        Interface
     Wideband                                                Common
                                     Channel-                  DSP                  Network ATM
     transceiver                     izer                                             I/F
                                                             platform
           Upcon-                     Tx
    MCPA          D/A
           verter                     Chan



                                             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 !

				
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