Hybrid Indirect Transmissions (HIT) for Data Gathering in Wireless Micro Sensor Networks with Biomedical Applications Jack Culpepper(NASA), Lan Dung, Melody Moh CCW 2003, IEEE Speaker : Chi-Chih Wu

Outline INTRODUCTION BASIC MODELS PROTOCOL DESCRIPTION PERFORMANCE EVALUATION CONCLUSION

INTRODUCTION Micro sensors The consumers of power Data processing Communications Major consumer of power Communications Most energy expensive applications Remote sensing

H BS INTRODUCTION Current remote sensing routing protocols increase efficiency data fusion power management systems clustering chaining z y xB BS

INTRODUCTION W. Heinzelman et al, “ Energy-Efficient Communication Protocol for Wireless Microsensor Networks ” (LEACH) Each node has a probability p of becoming a cluster-head the protocol guarantees that every node will be cluster-head only once in 1/p rounds HH BS

INTRODUCTION Stephanie Lindsey and Cauligi S. Raghavendra, “ PEGASIS:Power Efficient Gathering in Sensor Information Systems ” Chains of nodes are computed using a greedy algorithm Chain leaders are elected to fuse data and transmit the result to BS

INTRODUCTION Features of HIT Utilizing one or more clusters to reduce the number of transmissions to the remote base station Parallel, multi-hop indirect transmissions even in the presence of multiple, adjacent clusters Goals Minimize energy consumption Minimize network delay

BASIC MODELS Data Delivery Model Radio Model Analysis of Direct versus Indirect Transmissions Parallel Transmissions Analysis of TDMA versus CSMA

Data Delivery Model Sensor networks can be classified in terms of the data delivery required Continuous (HIT based) Event-driven Observer-initiated Hybrid

Radio Model A radio transceiver dissipates E elec = 50 nJ/bit

Analysis of Direct versus Indirect Transmissions A B C A B C Energy Saving

Parallel Transmissions Parallel indirect transmissions Use intelligent scheduling algorithm (TDMA) Achieves lower delay than LEACH H H

Analysis of TDMA versus CSMA CSMA wastes energe versus TDMA Collisions Overhearing Control packet overhead Idle listening Advantages of TDMA No collisions Little overhead High energy efficient Disadvantages of TDMA Time synchronization It is difficult to change the TDMA schedule

PROTOCOL DESCRIPTION HIT is consisting of two periods Cluster setup Long steady state

PROTOCOL DESCRIPTION HIT makes the following assumptions Nodes are distributed randomly Nodes are able to communicate by CSMA the result of n fusions will be independent of n, and be no more than a constant multiple of s Nodes are able to estimate distances Each sensor node has a unique node ID

PROTOCOL DESCRIPTION HIT protocol consists of the following phases Cluster-Head Election Cluster-Head Advertisement Cluster Setup Route Setup Blocking Set Computation MAC Schedule Creation Data Transmission

Cluster-Head Election Election Scheme I(a) single cluster nodes take as cluster-head turn in order of node ID Election Scheme I(b) single cluster nodes take turn as cluster-head, some nodes may not ever be cluster-head (lower levels of connectivity or energy)

Cluster-Head Election Election Scheme II(a) multiple clusters nodes are elected randomly (LEACH) Election Scheme II(b): multiple clusters nodes are elected randomly, some nodes may not ever be cluster-head (lower levels of connectivity or energy)

Cluster-Head Advertisement(CSMA/CD) Cluster-heads broadcast their status at the fixed power with the message Non-cluster-heads then compute the distance to the clusterhead and save the value as D(H, j) H e f g h b D(H,j) H-id

Cluster Setup one or more clusters will be formed, and the upstream and downstream relationship will be created. each node has only one upstream neighbor d(u, H) < d(i, H), d(i, u) < d(i, H)

H e f g h b i j d k c H e f g h b i j d k c Cluster Setup D(H,j) id D(j,u j ) d(u, H) < d(i, H), d(i, u) < d(i, H)

Route Setup all nodes broadcast its upstream neighbor ’ s information it adds i to its list of downstream neighbors for j, DOWN(j) Source-id Upstream-id D(j,u j )

Blocking Set Computation each node computes the blocking set for its downstream neighbors we say node i blocks node j if and only if d(i, ui) > d(i, uj) i blocks j does not necessarily imply that j blocks I each downstream neighbor of j blocks all other downstream neighbors of j 10 8

MAC Schedule Setup

Data Transmission This phase does not require the use of a CDMA code

PERFORMANCE EVALUATION All nodes were bestowed with 20 J of initial energy, round was fixed at 10,000. The data rate of the wireless net-work is 1 Mbit/s, the coordinates for the base station are (l/2,-200), The average size of a sensor data item, a 50-bit packet For LEACH and HITm, we specified that 1% of the nodes would be elected cluster- heads

PERFORMANCE EVALUATION

CONCLUSION We introduce a hybrid clustering and indirect transmission scheme for micro sensor networks The novel feature of parallel indirect transmissions and the complete protocol including phases of clustering, routing, and scheduling Performance evaluations showed that HIT provides energy savings over LEACH, PEGASIS, and Direct HIT also greatly reduces the delay

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