Design of an energy efficient Medium Access Control protocol

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					   Design of an energy efficient Medium Access
   Control protocol for wireless sensor networks




                                       Masters Thesis Defense
                                                Kiran Tatapudi

                   Thesis Committee
 Dr. Chansu Yu,    Dr. Wenbing Zhao,   Dr. Yongjian Fu




       Organization

Introduction
Related Work
Bulk Synchronous Medium Access
Performance Evaluation
Conclusion




                                                                 1
          Introduction

What is a Wireless Sensor Network ?




          Introduction

What is a Wireless Sensor Network ?

   a collection of cheap, low power wireless devices with limited
   processing and communication capabilities, which collectively help
   monitor physical or environmental conditions




                                                                        2
           Introduction

What is a Wireless Sensor Network ?

    a collection of cheap, low power wireless devices with limited
    processing and communication capabilities, which collectively help
    monitor physical or environmental conditions




   Applications

•Habitat Monitoring
•Home Automation
                                            SINK
•Surveillance
                                BASE STATION




           Introduction

Key Aspects

    •Sink based




                                            SINK

                                BASE STATION




                                                                         3
          Introduction

Key Aspects

   •Sink based
   •Multi-hop communication




                                        SINK

                                BASE STATION




          Introduction

Key Aspects

   •Sink based
   •Multi-hop communication
   •Time and space correlated




                                        SINK

                                BASE STATION




                                               4
          Introduction

Key Aspects

   •Sink based
   •Multi-hop communication
   •Time and space correlated (Message bursts)




   How to Arbitrate the
   medium !!


                                         SINK

                              BASE STATION




          Introduction

Medium Access Control




                                                 5
           Introduction

Medium Access Control
arbitrate the shared communication medium among competing nodes and
thus provide a robust communication channel to applications




           Introduction

Medium Access Control
arbitrate the shared communication medium among competing nodes and
thus provide a robust communication channel to applications



   802.11 ??




                                                                      6
             Introduction

Medium Access Control
arbitrate the shared communication medium among competing nodes and
thus provide a robust communication channel to applications



    802.11 ??

Unique requirements of Sensor networks
•Energy Efficiency
•Handle traffic bursts




             Related Work

Two classes of protocols :
      Contention based protocols
      Time Division Multiple Access protocols




                                                                      7
          Related Work
Contention based protocols
    CSMA for collision avoidance




Drawbacks
    Higher number of Collisions
    Re-transmissions
    Non-deterministic




          Related Work
Contention based protocols
    CSMA for collision avoidance
    ACK packets for collision detection




Drawbacks
    Higher number of Collisions
    Re-transmissions
    Non-deterministic




                                          8
          Related Work
Contention based protocols
    CSMA for collision avoidance
    ACK packets for collision detection
    Sleep schedules for energy conservation




Drawbacks
    Higher number of Collisions
    Re-transmissions
    Non-deterministic




          Related Work
Time Division Multiple Access
    Exclusive slot assignment




                                              9
          Related Work
Time Division Multiple Access
    Exclusive slot assignment
    Collision free




          Related Work
Time Division Multiple Access
    Exclusive slot assignment
    Collision free
    Automatic duty cycle




                                10
          Related Work
Time Division Multiple Access
    Exclusive slot assignment
    Collision free
    Automatic duty cycle
    Deterministic




          Related Work
Time Division Multiple Access
    Exclusive slot assignment
    Collision free
    Automatic duty cycle
    Deterministic



Drawbacks
    Synchronization Overhead
    Improper schedule formation




                                  11
             Related Work
Two-hop graph coloring for slot scheduling in TDMA
      Communications within two-hops interfere with each other, but
     beyond that the communications are safe
      Allot different slots for nodes within two-hop neighborhood and reuse
     the slots for other nodes


Example:

 1       2       3       4                      1       2       3      1




             Related Work

Two-hop coloring is not always correct

                             u            b




                                 a        v




Exploit the unique feature of sink-based sensor net to simplify the
message exchange procedure while achieving collision-free slot
schedule !!!




                                                                              12
              Bulk Synchronous Medium Access


Key Aspects
 Optimized for sink-based networks
 Tree structure (rooted at sink and
grouped as non-interfering sets
based on hop-count from sink)
 Parent child relationship between
two sets of nodes
 Slot-based scheduling for tree
links
 Automatic Routing




              Bulk Synchronous Medium Access


Key Aspects
 Optimized for sink-based networks
 Tree structure (rooted at sink and
grouped as non-interfering sets
based on hop-count from sink)
 Parent child relationship between
two sets of nodes
 Slot-based scheduling for tree
links
 Automatic Routing
                                BG0   BG1   BG2




                                                  13
             Bulk Synchronous Medium Access



                                   GG                      GG GG                               GG receives

                                                            G P1 receives        G receives        G
Data flow                            G
                                                         P1&P2        P2 receives
                                                                                    P2    P1
 BIGSLOT
                                      P1         P2      D1&D2 D1           D2                 D1 receives
 Three-way Handshaking
 PADV, PSEL, SCH                                           GD                                      GD
                                           D1     D2
messages                                                         slot sD1            slot sP1 slot sG

                                           GD                    BIGSLOT0 BIGSLOT1 BIGSLOT 2
                                                                        A TDMA frame in data phase
                                   (a) 7-node scenario                (b) TDMA schedule in BSMA




             Bulk Synchronous Medium Access


 Parameters for evaluating performance
       Message Latency = (hop-count) * BIGSLOT
       Energy Efficiency = ((TX slot) + (‘n’ RX slots)) / (BIGSLOT * 3)




                                                                                                             14
          Bulk Synchronous Medium Access


Parameters for evaluating performance
    Message Latency = (hop-count) * BIGSLOT
    Energy Efficiency = ((TX slot) + (‘n’ RX slots)) / (BIGSLOT * 3)




How to form such a tree !!




          Bulk Synchronous Medium Access

Tree formation & slot scheduling
                                                  G can start (upstream)
                                                  communication at frame F3.
                                    PADV
                                       PSEL                           P1 & P2 can start (upstream)
                                                                      communication at frame F4.
                                          SCH

                G
             P1&P2
            D1&D2

               GD



                      Frame F0     Frame F1       Frame F2       Frame F3       Frame F4


             Sleep
           schedule
                        Receive PADV’s                                       Send SCH
             of D1
                                  Send PSEL                         Receive PSEL’s
                                    Receive SCH                Send PADV




                                                                                                     15
          Bulk Synchronous Medium Access


Design Issues
    Orphan Nodes




          Bulk Synchronous Medium Access


Design Issues
    Orphan Nodes
    Tree Convergence




                                           16
               Performance Evaluation
                                                                                                                            90
                                      Number of orphan nodes
                                                                                                                           80

                                                                                                                           70

                                                                                                                           60

                                                                                                                           50

                                                                                                                           40

                                                                                                                           30

                                                                                                                           20

                                                                                                                           10

                                                                                                                          0




                                                                                                                  10dB
                                                                                                            8dB
                                                                                                      6dB
                                                                                                4dB
                                                                                         2dB
            Scheduling




                                                                                  10dB
                                                                                                                         (Z0)




                                                                            8dB
                                                                      6dB
                                                                4dB
                                                          2dB
            phases (15)
                                                   10dB




                                                                                               SD=6dB
                                             8dB
                                       6dB
                                4dB
                          2dB




                                                                SD=4dB
                                      SD=0dB


                                             BIGSLOT size = 25




               Conclusion

 TDMA schemes based on two-hop graph coloring algorithm fail to provide
collision-free medium access and to utilize available transmission opportunities
 BSMA is a simple, robust and energy efficient MAC protocol
 Our simulation study based on ns-2 network simulator shows that BSMA
constructs a proper tree and collision-free schedule in reasonable number of
scheduling phases




                                                                                                                                 17
Q&A




  THANK YOU




              18