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VIEWS: 1 PAGES: 37

									Wireless ad hoc networks: cross layer
            opportunities


         NSF workshop
     Washington DC Aug 27-28

           Mario Gerla
   Computer Science Dept, UCLA
        www.cs.ucla.edu
             Ad hoc networking
                  Current Status
Leading Applications

• Tactical battlefield:
   – no infrastructure
• Civilian emergency:
   – infrastructure, if present, was destroyed
• Critical Requirements: scalability, survivability,
  100% reliable, QoS, jam protection, etc
• Non critical: Cost, Standards, Privacy
                                                                 SATELLITE
                                                                  COMMS
               SURVEILLANCE
                 MISSION
                                                                                    SURVEILLANCE
                                                                                      MISSION


                                                UAV-UAV NETWORK
                      AIR-TO-AIR
                       MISSION


                                                       STRIKE
                                                       MISSION


                   COMM/TASKING




                                                                                        COMM/TASKING
    Unmanned
Control Platform
                                     COMM/TASKING         RESUPPLY           UAV-UGV NETWORK
                                                           MISSION




                                                                                  FRIENDLY
                                                                               GROUND CONTROL
                                                                                  (MOBILE)
                                  Manned
                             Control Platform




                       Tactical Ad Hoc Network
     Emerging Landscape :
 “Opportunistic” Ad Hoc networks
Recreational, commercial, education
 applications
    •   Vehicle networks
    •   Workgroups (eg, sharing 3G via Bluetooth)
    •   Massive Network games
    •   Patient monitoring
Access to Internet?
    • available, but - “bypass it” with “ad hoc” if too costly or
      inadequate
Tolerant to delays: DTNs
Critical: Cost, Privacy, security, standards
       Car to Car communications for Safe Driving

                                                                 Vehicle type: Cadillac XLR
                                                                 Curb weight: 3,547 lbs
                                                                 Speed: 65 mph
Vehicle type: Cadillac XLR                                       Acceleration: - 5m/sec^2
Curb weight: 3,547 lbs                                           Coefficient of friction: .65
Speed: 75 mph                                                    Driver Attention: Yes
Acceleration: + 20m/sec^2                                        Etc.
Coefficient of friction: .65     Alert Status: None
Driver Attention: Yes
Etc.
                                                                                          Alert Status: None




    Alert Status: Inattentive Driver on Right
        Alert Status: Slowing vehicle ahead
        Alert Status: Passing vehicle on left


                                                                                                Vehicle type: Cadillac XLR
                                                                                                Curb weight: 3,547 lbs
                                                                                                Speed: 45 mph
Vehicle type: Cadillac XLR                                                                      Acceleration: - 20m/sec^2
Curb weight: 3,547 lbs                                                                          Coefficient of friction: .65
Speed: 75 mph                                                                                   Driver Attention: No
Acceleration: + 10m/sec^2                       Alert Status: Passing Vehicle on left
                                                                                                Etc.
Coefficient of friction: .65
Driver Attention: Yes
Etc.
  Co-operative Download: Car Torrent



Internet




                       Vehicle-Vehicle Communication




                     Exchanging Pieces of File Later
Vehicular Sensor Network (VSN)




           Roadside base station




         Vehicle-to-roadside                 Inter-vehicle
          communications                   communications



           VSN-enabled vehicle
            Sensors            Systems



           Video   Chem.   Storage Proc.
        Personal Networking: BlueTorrent




    B        B                    B

             C       C                     C
A                         A            A




                 D                 D       D
Patient Monitoring




  Nurses upload patient
  data; share data files
      in P2P mode
   1. Future expectations on wireless
            network research
• Network layer more tightly coupled with
  applications
   – Content sharing, environement sensing
• Besides data forwarding, additional services:
   –   Location aware service discovery,
   –   content based routing;
   –   P2P networking
   –   Data collection, processing, filtering, storage, dissemination
• Network layer design must interact with:
   – applications
   – PHY Layer
  2. Major recent advances/breakthroughs
             in the physical layer

• Cognitive radios (spectrum scavenging)
• MIMOs (for flexible topology designs;
  interference mitigation etc)
• Cooperative radios
• Multi radio devices (BT, 802.11, 3G, etc)
    3. Algorithms must adjust to PHY layer

“PHY layer aware” MAC, Network and Transport
  designs

Examples (based on MIMO):

•   Topology control
•   A MIMO aware MAC protocol: SPACE-MAC
•   Multi-path Routing & MIMO
•   TCP & MIMO
        MIMO Topology Control/Routing

• Topology control:
  – Exploit mode flexibility to dynamically shape topology
  – Meet different customer requirements
 Topology with high capacity          Topology with low capacity
 links: disconnected network        links: fully connected network




              300Mbps




                                                        10Mbps
                  SPACE2 MAC

 When A wishes to transmit to       B
    B
1) A sends RTS to B; F and              F
   D learn about A


2)   B responds with CTS; F
     and D learn about B
                                D
                                            A
                   SPACE MAC (cont)


                                       B

 3)   F and D beamform such                F
      that signals from/to B and
      A are nulled; then, A and
      B start talking

4)    After A and B pair is
      established, F and D pair
                                   D           A
      also can talk
         Two-Path Routing using MIMO

                        relay nodes




 S                                                        R
sender                                                  receiver


  • S sends two independent streams simultaneously to R

  • Assume 2 antennas at each node (but extendible to
    systems with more antennas).
     MIMO yields 6-fold throughput gain




 S                                                      R
sender                                            receiver


• In the traditional relay mode, the capacity is C/3.
• Simulcast achieves 6-fold throughput increase.
        TCP and MIMO in Ad Hoc Networks

• Consider three flows in the same
  wireless domain
• As the flows get closer to each
                                  (100, 100)
  other:                                              FTP 1
                                                                   (600, 100)

   – Interference builds up
   – Throughput decreases                            (350, 350)
   – Fairness suffers
                                                  FTP 2
• Can MIMO Help?                    (0, 700)
                                                      (350, 700)
                                                                       (700, 700)


                                                    (350, 1050)

                                                     FTP 3
                                    (100, 1300)                     (600, 1300)
      TCP over SPACE MAC (MIMO)
   Distance = 400m (interference range)

                                 3 FTP/TCP Flows
                                  Flow 1    Flow 2   Flow 3
T hroughput (Kbits/s)

     350

     300

     250

     200

     150

     100

      50

        0
                        802.11                                SPACE-MAC
                                           MAC Protocol


Fig 0. The throughput of 3 FTP/TCP flows with the distance
between flows being 400m
            TCP over SPACE MAC (MIMO)
             Distance = 350m (tx range)

                                3 FTP Flows
                                Flow 1     Flow 2   Flow 3
Throughput (Kbits/s)

     350

     300

     250

     200

     150

     100

       50

        0
                       802.11                                Space-MAC
                                         MAC Protocol



Fig 0. The throughput of 3 FTP/TCP flows with the distance
between flows being 350m
                        Identify gaps

• Question: How to exploit the wealth of PHY
  emerging technology?
• Do not limit your scope to LINK capacity gains
• Look for cross layer optimization opportunities at
  all layers:
   – MAC
   – Network (routing, topology control, multicast, bandwidth
     scavenging, etc)
   – transport,
   – applications and PHY layer
 The End

Thank You
Simul-Cast

 Brian Choi
 Mario Gerla
                    MIMO System Model

weight vector w1 = [w11 w21 … wm1]




             W          s(t)WHVH = r(t)   V
                  Assumptions


• Fading is flat (i.e. freq. independent).
• Channel is symmetric and quasi-static.
• Two subchannels - control channel and data channel
• Rich scattering - H is full-rank
• Antenna’s capable of transmitting and receiving
  signals simultaneously.
• We ignore additive channel noise.
• Perfect sychronization between nodes
          Two Path Routing Problem

                           relay nodes




 S                                                                R
sender                                                       receiver


  •   S sends two independent streams under two paths
      simultaneously to R.
  •   Assume 2 antennas at each node (but extensible to systems
      with more antennas).
           The 6-fold Benefit of MIMO




 S                                                      R
sender                                                receiver


• If C = (capacity of a point-to-point link) in the
  traditional relay mode, the capacity is C/3.
• Simulcast achieves 6X throughput increase.
                           Sender


s(t) = [s1(t) s2(t)]
                                     B
               s1(t)
                       A
               s2(t)

                                     C



   • A wants to send a stream (s1(t)) to B and another
     stream (s2(t)) to C simultaneously.
                       Sender: Linear Coding

                                               WB
s(t) = [s1(t) s2(t)]            HAB                 rB1(t)
                                           B
               s1(t)                                rB2(t)
                            A
               s2(t)

                       WA                           rC1(t)
                                HAC        C
                                                    rC2(t)

• B receives rB(t) = s(t)WAHABWBH.
• For B to recover s1(t), B must consume 2 degrees of freedom.
                         Sender: Pre-coding


                                                             rB1(t)
                                                    B
                                                             rB2(t)
                 s1(t)                   
                            A
                 s2(t)                   
                                                             rC1(t)
                                                    C
                                                             rC2(t)

•   If A knows the channel and the steering matrices of B and C, then A can
    precode its data such that s1(t) is received at rB1(t), s2(t) is received at
    rC1(t), without interfering each other.
•   B and C needs to comsume only one DOF each.
                 Dirty Paper Coding

                                          wB1
                                            rB1(t)
                                     B
                                             rB2(t)
         s1(t)              
                  A
         s2(t)                           wC1
                                             rC1(t)
                                     C
                                             rC2(t)


Let H = HABwB1H = QR
        HACwC1H

         QR factorization, Q = unitary, R = upper triangular
                   Dirty Paper Coding


• Let r(t) = [rB1(t) rC1(t)]. Then r(t) = s(t)H.
• Multiply s(t) by QH, such that s’(t) = s(t)QH.
• Then r(t) = s’(t)H = s(t)QHH = s(t)QHQR = s(t)R

• rB1(t) = s1(t)R1,1 (no interference)
• rC1(t) = s1(t)R1,2 + s2(t)R2,2


• Sender can estimate this interference and subtract it
  from s(t) before transmitting.
          (interference!)
                       Relay Node




            used to send a stream to
            the next node
used to receive data from
the previous node
•   There is one DOF left for us to use. We use it to
    simultaneously relay the received data to the next node.
•   We set weight vectors such that they are orthogonal to each
    other.
                       Receiver

                   A    HAR

                                  R

                        HBR
                   B


• This reduces to the problem of spatial multiplexing.
• If R knows the channels and the weight vectors used
  for both streams, then R can decode the received
  data.
                 Network-wise Benefit




 S                                                                R
sender                                                        receiver


• If C = (capacity of a point-to-point link) in the traditional
  relay mode, the capacity is C/3.
• Simulcast achieves 6X throughput increase.
                 Multiple Paths

• We can run OLSR-type of routing protocol for the
  nodes to pre-determine the paths.
• This suggests a cross-layer approach (between
  network layer and MAC layer).
                   Summary

• With MIMO and Pre-coding techniques, one can
  effectively reduce the DOF consumption at the
  receiving nodes.
• We can utilize the idle DOF to relay the data
  simultaneously.
• With two independent simultaneous paths, we
  can achieve up to 6X throughput increase.

								
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