Design of an energy efficient Medium Access Control protocol for wireless sensor networks Thesis Committee Masters Thesis Defense Kiran Tatapudi 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 Surveillance SINK 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 Data flow BIGSLOT Three-way Handshaking PADV, PSEL, SCH messages GG G P 1 P 2 D 1 D 2 GD (a) 7-node scenario GG GG GG receives G P 1 receives G receives G P 1 &P 2 P 2 receives D 1 &D 2 D 1 D 2 P 2 P 1 D 1 receives GD GD slot s D1 slot s P1 slot s G BIGSLOT 0 BIGSLOT 1 BIGSLOT 2 A TDMA frame in data phase (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 P 1 &P 2 D 1 &D 2 GD PADV PSEL SCH G can start (upstream) communication at frame F 3. P 1 & P 2 can start (upstream) communication at frame F 4. Frame F 0 Frame F 1 Frame F 2 Frame F 3 Frame F 4 Sleep schedule of D 1 Receive PADV s Send PSEL Receive SCH Send SCH Receive PSEL s Send PADV 15
Bulk Synchronous Medium Access Design Issues Orphan Nodes Bulk Synchronous Medium Access Design Issues Orphan Nodes Tree Convergence 16
Performance Evaluation Number of orphan nodes 90 80 70 60 50 40 30 20 10 0 Scheduling phases (15) 2dB 4dB 6dB 8dB 10dB SD=0dB 2dB 4dB 6dB 8dB SD=4dB 10dB 2dB 4dB 6dB 8dB SD=6dB 10dB (Z0) 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