SENSYS 2003 2006. 9. 7 Presented by Cheolki Lee Energy-efficient, collision-free medium access control for wireless sensor networks SENSYS 2003 2006. 9. 7 Presented by Cheolki Lee 가나다라마바사

Contents Introduction Related works TRAMA (TRaffic-Adaptive Medium Access protocol) Overview of TRAMA Access modes Three components of TRAMA NP (Neighbor Protocol) SEP (Schedule Exchange Protocol) AEA (Adaptive Election Algorithm) Experiments Conclusions TRAMA

Introduction Nodes in sensor networks Major challenge Processing and communication capabilities, sensing devices Deployed in ad-hoc manner Self-organized Battery-powered Recharging is difficult, not cost-effective Major challenge Scheduling of transmissions among nodes Self adaptive to changes in traffic, node state, connectivity Prolong the battery life of each node TRAMA

Schedules of transmitting Related works (1/2) MAC protocols for multi-hop wireless networks Contention-based protocol DCF (Distributed Coordination Function ) of the IEEE 802.11b CSMA (Carrier Sense Multiple Access) + 4-way handshake Energy consumption in an idle state S-MAC Overhearing avoidance Periodic listen and sleep ☞ Probability of collision increases with the offered load Schedules of transmitting TRAMA

Related works (2/2) Scheduling-based protocol Sohrabi and Potti Combination of TDMA and FDMA or CDMA Times slots is wasted NAMA (Node Activation Multiple Access) Distributed election algorithm One transmitter per two-hop neighborhood Collision-free transmission No energy conservation mechanism TRAMA

Overview of TRAMA TRAMA (TRaffic-Adaptive Medium Access protocol) Energy efficient Collision avoidance Sleep mode when a node is not the intended receiver Collision-free channel access One node within a two-hop neighborhood Traffic adaptive Schedules influenced by traffic information Assumption A single, time-slotted channel for data/signaling packets Time is divided into two categories Random-access periods, scheduled-access periods Adequate synchronization is attained TRAMA

Time slot organization Access modes Random access periods (contention based access) Nodes transmit only signaling packets by selecting a slot randomly New nodes can join Time synchronization can be done Period length should be ‘7*1.44*N’ (99%) (N: average num of neighbors in 2-hop distance) Scheduled access periods Nodes exchange collision-free data, or schedules Time slot organization TRAMA

NP (Neighbor Protocol) Nodes exchange signaling packets A two-hop topology is gained at each node Signaling packets Incremental neighborhood updates Connectivity between neighbors Signaling packet header format TRAMA

SEP (Schedule Exchange Protocol) (1/3) Nodes exchange schedules with neighbors Schedule generation SCHEDULE_INTERVAL (ex.100) ‘Winning slots’ in [t, t+SCHEDULE_INTERVAL] Winning slots between [1000,1100] -> 1009, 1030, 1033, 1064, 1075, 1098 Intended receivers Node’s last winning slot Reserved for broadcasting the nodes’ schedule for the next interval Schedule packet ‘Intended receivers’ information using bitmap Zero bitmap When winning slot go unused (vacant slots) 14 7 5 4 1 0 1 0 14 7 5 4 1 1 1 1 TRAMA

SEP (Schedule Exchange Protocol) (2/3) Winning slot Zero bitmap Schedule packet format TRAMA

SEP (Schedule Exchange Protocol) (2/3) Data packet header format Summary of node schedule with every data packet Size of the bitmap ‘numSlots’ Whether the node is transmitting or giving up the corresponding slot No intended receiver information Data packet format TRAMA

AEA (Adaptive Election Algorithm) (1/4) Decides a transmitter and intended receivers Priority function ‘Absolute winner’ : highest priority An absolute winner uses the time slot All other nodes switch to low-power mode (u: node identifier, t: time slot) t=0 t=1 t=2 t=3 t=4 t=5 A 14 23 9 56 3 26 B 33 64 8 12 44 6 C 53 18 57 2 Priorities of node A and its two neighbors B and C TRAMA

AEA (Adaptive Election Algorithm) (2/4) State of node u is determined by U’s two-hop neighborhood information Schedules announced by u’s one hop neighbors Possible states TX (transmit) Highest priority, has data to send RX (receive) Intended receiver of the current transmitter SL (sleep) Not the intended receiver TRAMA

AEA (Adaptive Election Algorithm) (3/4) Inconsistency problem A thinks it can send B knows that D has higher priority in its 2-hop neighborhood Absolute winner Alternative winner Inconsistency problem TRAMA

AEA (Adaptive Election Algorithm) (4/4) Definition Absolute winner : tx(u) Node with the highest priority in Alternative winner : atx(u) Node with the highest priority in one hop neighbors, hidden from tx(u) Possible transmitter set : PTX(u) One-hop neighborhood that can transmit without collision Need contender set : NEED(u) Subset of PTX(u), data to send Need transmitter Node with the highest priority in NEED(u) TRAMA

Experiments (1/5) Setup Protocol parameter Qualnet network simulator 50 nodes are uniformly distributed (500m*500m) Transmission range of each node : 100m 6 one-hop neighbors, 17 two-hop neighbors on average Traffic load type Traffic statistically generated based on a exponentially distributed inter-arrival time Data gathering applications Protocol parameter SCHEDULE_INTERVAL : 100 transmission slot SMAC setting SYNC_INTERVAL : 10 sec Duty cycle : 10%, 50% TRAMA

Average packet delivery ratio for synthetic traffic Experiments (2/5) Average packet delivery ratio for synthetic traffic Schedule-based MACs achieve better delivery X: Mean interarrival time (in seconds) Y: Percentage received Average packet delivery ratio for synthetic traffic TRAMA

Experiments (3/5) Average queuing delay for synthetic traffic X: Mean interarrival time (in seconds) Y: Average delay Average queuing delay TRAMA

Percentage energy savings Experiments (4/5) Percentage sleep time for synthetic traffic X: Mean interarrival time (in seconds) Y: Percentage sleep time Percentage energy savings TRAMA

Average sleep interval Experiments (5/5) Average sleep interval for synthetic traffic X: Mean interarrival time (in seconds) Y: Average length of sleep interval (in milli-seconds) Average sleep interval TRAMA

Conclusions TRAMA offers Contributions Significant energy savings Nodes can sleep for up to 87% of the time High throughput Around 40% over S-MAC and CSMA, and 20% over 802.11 Contributions TRAMA is well suited for applications Not delay sensitive High delivery Energy efficiency TRAMA

Appendix(1/2) TRAMA

Appendix(2/2) TRAMA