A Bit-Map-Assisted Energy- Efficient MAC Scheme for Wireless Sensor Networks Jing Li and Georgios Y. Lazarou Department of Electrical and Computer Engineering, Mississippi State University ACM IPSN’04

Outline Introduction Introduction Related work Related work Bit-Map-Assisted (BMA) MAC Bit-Map-Assisted (BMA) MAC Energy-efficient TDMA Energy-efficient TDMA Analysis of BMA Analysis of BMA Performance evaluation Performance evaluation

Introduction Design of a MAC protocol for WSNs must consider the following factors Design of a MAC protocol for WSNs must consider the following factors Energy efficiency Energy efficiency Scalability Scalability Highly localized and distributed solution Highly localized and distributed solution Dynamic and autonomous network operation Dynamic and autonomous network operation Self-organizing ability Self-organizing ability

TDMA(1) Clustering solutions are often used with TDMA Clustering solutions are often used with TDMA Advantages of TDMA Advantages of TDMA TDMA performs well under high load conditions TDMA performs well under high load conditions TDMA performs well in terms of bandwidth efficiency and average packet latency TDMA performs well in terms of bandwidth efficiency and average packet latency

TDMA(2) Disadvantages Disadvantages Nodes have to turn on the radio during their scheduled slots Nodes have to turn on the radio during their scheduled slots Hard for TDMA schemes to change the time slot allocations and frame length dynamically Hard for TDMA schemes to change the time slot allocations and frame length dynamically

Major Source of Energy Waste Idle listening Idle listening Almost % of the energy consumed in receive mode Almost % of the energy consumed in receive mode Collision Collision retransmission retransmission Overhearing Overhearing Control packet overhead Control packet overhead

Goal An intra-cluster communication bit-map- assisted (BMA) MAC protocol for large- scale cluster-based WSNs is proposed An intra-cluster communication bit-map- assisted (BMA) MAC protocol for large- scale cluster-based WSNs is proposed Reduce the energy wastes due to idle listening Reduce the energy wastes due to idle listening Reduce the collisions while maintaining a good low-latency performance Reduce the collisions while maintaining a good low-latency performance

Illustrated of BMA MAC Each round Each round Totally k sessions N slots (N cluster members)

Set-up Phase 1. Each node decide whether it could become a cluster head based on its energy level 2. Elected cluster heads broadcast an advertisement to all other nodes by using non-persistent CSMA 3. Non-cluster head nodes join the cluster

Steady Phase Contention period Contention period Cluster member contents for a data slot during its scheduled slot Cluster member contents for a data slot during its scheduled slot Data transmission period Data transmission period Each source node turn on its radio and sends its data to cluster head during its data slot Each source node turn on its radio and sends its data to cluster head during its data slot All non-source nodes have their radio off during the data transmission period All non-source nodes have their radio off during the data transmission period

TDMA & E-TDMA Set-up phase Contention period Steady phase Frame …… Frame k frames Each frame consists of N time slots Each frame consists of N time slots A node always turns on its radio during its slot when using TDMA A node always turns on its radio during its slot when using TDMA A node keeps its radio off during its allocation when using E-TDMA A node keeps its radio off during its allocation when using E-TDMA

Illustration of a Single Cluster

Analysis of BMA(1) Let n i source nodes in the i th session/frame Let n i source nodes in the i th session/frame The event whether a node has data to transmit can be viewed as a Bernoulli trial The event whether a node has data to transmit can be viewed as a Bernoulli trial p: the possibility that a node has data to transmit p: the possibility that a node has data to transmit Therefore, n i is a Binomial random variable Therefore, n i is a Binomial random variable Expectation of the number of source number in n i sessions

Analysis of BMA(2) power consumption during power consumption during P t : transmit mode P t : transmit mode P r : receive mode P r : receive mode P i : idle mode P i : idle mode Time required to transmit/receive Time required to transmit/receive T d : a data packet T d : a data packet T c : a control packet T c : a control packet T ch : cluster head to transmit a control packet T ch : cluster head to transmit a control packet

Analysis of BMA(3) Energy consumption by a source in a session Energy consumption by a source in a session Energy consumption by a non-source node in a session Energy consumption by a non-source node in a session Energy consumption by a cluster head in a session Energy consumption by a cluster head in a session

Analysis of BMA(4) Total energy consumed in a cluster in the i th session Total energy consumed in a cluster in the i th session Total energy dissipated during each round Total energy dissipated during each round Average system energy consumed Average system energy consumed Average packet latency Average packet latency

Performance Evaluation Based on analytic computations Based on analytic computations Radio transceiver uses Radio transceiver uses 462 mW for transmitting 462 mW for transmitting 346 mW for receiving 346 mW for receiving 330 mW for idle listening 330 mW for idle listening Data rate is 24Kbps Data rate is 24Kbps Control packet is 18 bytes and data packet is 250 bytes Control packet is 18 bytes and data packet is 250 bytes

Average Packet Latency (N = 10, k = 4)

Total Cluster Energy Consumption vs. p (N = 10, k = 4)

Total Cluster Energy Consumption vs. k (N = 10, p = 0.3)

Total Cluster Energy Consumption vs. N (k = 4, p = 0.3)

Total Cluster Energy Consumption vs. data packet size (N = 10, k = 4, p = 0.3)

Conclusion In term of average packet latency, BMA is superior In term of average packet latency, BMA is superior BMA is superior for the cases of low and medium traffic loads, relatively few sensor nodes per cluster and relatively large data size BMA is superior for the cases of low and medium traffic loads, relatively few sensor nodes per cluster and relatively large data size

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