1. VAPR: Void Aware Pressure Routing for Underwater Sensor Networks
Youngtae Noh, Student Member, IEEE, Uichin Lee, Member, IEEE, Paul Wang, Member, IEEE, Brian Sung Chul Choi, Member, IEEE, and Mario Gerla, Fellow, IEEE
IEEE TRANSACTIONS ON MOBILE COMPUTING 2012

2. Outline
Introduction
Overview
VAPR
Simulations
Conclusions

3. Introduction
Underwater acoustic sensor networks have many applications
Environmental monitoring
Intrusion detection

4. Introduction
A large number of mobile sensor nodes are deployed in the region of interest for exploration
Acoustic transmissions consume far more energy than terrestrial radio communications
Each sensor is equipped with a variety of sensors and a low bandwidth acoustic modem

5. Introduction
Each sensor reports data to any one of the sonobuoys with acoustic multi-hop routing
Simple greedy pressure routing often fails in sparse underwater networks due to the presence of 3D voids
Each node is equipped with a variety of sensors (ex : pressure gauges) and a low bandwidth acoustic modem

6. Goal
Design an efficient routing protocol for underwater data collection
Addresses several challenges unique to underwater communications

8. Overview Enhanced beaconing Opportunistic directional data forwarding
Sonobuoys broadcast the beacon to sensor nodes
The direction is set as up when a beacon is received from a shallower depth node
Opportunistic directional data forwarding

9. Overview Enhanced beaconing Opportunistic directional data forwarding
Sonobuoys propagate their reachability information to sensor nodes
The direction is set as up when a beacon is received from a shallower depth node
Opportunistic directional data forwarding
Sensor nodes forwarding the data

10. VAPR
Assume
Sonobuoys on the surface are equipped with GPS, clocks are synchronized
Use the same sequence number for periodic beaconing
DF_dir(node) ← up
Hop_count(node) ← 0

11. VAPR
Local max node : a node whose depth level is shallower than neighboring node, but deeper than the sonobuoys
Trapped node : a node in which greedy forwarding eventually leads to a local max node
Trap area : the area in which trapped nodes reside
Regular node : the rest of the nodes

12. VAPR Enhanced beaconing 1. broadcast beacon message
→Sender’s depth, DF_dir, SN, Hop_cnt
2. check SN(↑), Hop_cnt(↓)
3. set DF_dir
Monitoring
Center
Sonobuoy
Local
Maximum n
Sobobuoy’s depth
DF_dir : UP
SN : 104
Hop_cnt : 0 a z y
a’s depth
DF_dir : UP
SN : 103
Hop_cnt : 1 x b m k
x’s depth
DF_dir : DN
SN : 101
Hop_cnt : 3
b’s depth
DF_dir : UP
SN : 102
Hop_cnt : 2 c l w
y’s depth
DF_dir : DN
SN : 100
Hop_cnt : 4

13. VAPR Enhanced beaconing
Multiple direction from different sonobuoys are received
Node updates its status based on the higher SN
SN is the same
Smaller Hop_cnt
Monitoring
Center
Sonobuoy
MC’s depth
DF_dir : UP
SN : 104
Hop_cnt : 0
Local
Maximum n
Sobobuoy’s depth
DF_dir : UP
SN : 104
Hop_cnt : 0 a
z’s depth
DF_dir : DN
SN : 99
Hop_cnt : 5 z
n’s depth
DF_dir : UP
SN : 103
Hop_cnt : 1 y
a’s depth
DF_dir : UP
SN : 103
Hop_cnt : 1 x b m k
x’s depth
DF_dir : DN
SN : 101
Hop_cnt : 3 c l w
l’s depth
DF_dir : UP
SN : 101
Hop_cnt : 3

14. VAPR Opportunistic directional data forwarding
UP-UP, DN-DN, DN-UP, UP-DN
Based on DF_dir, NDF_dir()
Choosing the nodes whose DF_dir = NDF_dir of the current node
Sonobuoy
UP-UP
DN-DN
DN-UP
UP-UP
UP-DN
UP-UP

15. VAPR Higher priority node (based on the distance) transmits a packet
Suppress forwarding to prevent redundant packet transmissions and collisions
Finding an optimal set is computationally hard

16. VAPR Greedy clustering approach (Bloom filter)
Each node knows 2-hop connectivity and neighboring nodes’ pairwise distances
Data are periodically reported to the surface S E
(Bloom filter) F A
Can hear each other
→no hidden terminals
Group F B C D

17. VAPR

18. Retransmissions(ACK)
Simulations
Simulator
QualNet
Numbers of nodes
50 ~ 550
Topology
1500 m*1500 m*1500 m
Average packet size
< 200 B
Transmission range
250 m
Transmission power
Data rate
50 Kbps
Retransmissions(ACK) 5
Number of sonobuoys
1 ~ 64(grid)
Measures the distance
Every 50 s

19. Simulations
Fraction of nodes reachable to sonobuoys

20. Simulations
PDR(1 sonobuoy scenario)

21. Simulations
Energy consumption per message(1 sonobuoy scenario)

22. Simulations
Average latency(1 sonobuoy scenario)

23. Simulations
PDR(64 sonobuoy scenario)

24. Simulations
Energy consumption per message(64 sonobuoy scenario)

25. Simulations
Greedy forwarding success rate

26. Simulations
Average PDR(beacon intervals)

27. Simulations
Energy per node per message(beacon intervals)

28. Conclusions
This paper proposed a Void Aware Pressure Routing (VAPR) protocol in sparse underwater networks has been the efficient handling of 3D voids
The simulations showed that VAPR outperforms existing schemes

29. Thanks you