DOTS: A Propagation Delay-aware Opportunistic MAC Protocol for Underwater Sensor Networks IEEE ICNP 2010 (18.2%) Youngtae Noh, Mario Gerla (UCLA, CS) Paul Wang (JPL, Caltech) Uichin Lee (KAIST, KSE) Dustin Torres (UCLA, EE) Speaker: Wun-Cheng Li

Outline Introduction Goal DOTS DESIGN ▫ Delay Map Management ▫ Transmission Scheduling ▫ Schedule Recovery ▫ Guard Time Simulation Conclusion 2

Introduction The world's oceans cover over 70 % of its surface ▫ Underwater Wireless Sensor Networks (UWSNs) 3

Introduction Underwater sensor network technology can be applied in many fields ▫ Data acquisition ▫ Underwater exploration ▫ Unattended environmental monitoring systems ▫ Prevention of natural disasters ▫ Military purpose 4

Introduction Transmission rate ▫ WSN: 3 x 10 8 m/s ▫ UWSN: 1500 m/s  Propagation delay 5 A B Propagation delay

Problem Long propagation delay 6 RTS CTS DATA RTS CTS A B C

Related work Temporal Reuse Spatial Reuse 7 x y z y x u v time t = 0 Tx Rx Tx Rx

Related work Slotted FAMA 8 RTS CTS DATA RTS CTSDEFERS TRANSMISSIONS A B C Maximum Propagation Delay+CTS

Related work DACAP ▫ A non-synchronized protocol that allows each node to use different handshaking. ▫ To delay the data transmission to avoid collision did not consider the opportunity of simultaneous transmission 9

Related work CS-ALOHA ▫ Each node transmits whenever the channel is idle without performing the RTS/CTS handshaking process. ▫ Although carrier sensing ALOHA offers a higher throughput, it wastes much more power on collisions. 10

Goal Expected to increase opportunities for simultaneous transmission and reduce the possibility of collision 11

Assumptions DOTS protocol makes the assumption of time synchronization amongst all nodes in the network. 12

DOTS DESIGN Delay Map Management ▫ By passively observing neighboring transmissions, each node can maintain a delay map  Source  Destination  Timestamp  Delay 13 Propagation delay = t‘ - t RTS S D U time tt'

DOTS DESIGN 14 RTS DATA CTS DATA ACK time y x u v

DOTS DESIGN 15 RTS CTS DATA time RTS CTS DATA ACK DATA ACK y x u v

DOTS DESIGN 16 RTS CTS DATA time RTS CTS DATA ACK DATA ACK DATA ACK y x u v

DOTS DESIGN Schedule Recovery ▫ When two or more transmission schedules conflict at a node by network dynamics ▫ This algorithm can use the timestamp knowledge in its delay map database to give preference to one of the transmission schedules. 17

DOTS DESIGN Guard Time ▫ DOTS uses a guard time to support node mobility caused by the ocean currents.  2* (average movement distance/speed of sound) 18

Simulation Simulation topology 19

Simulation QualNet 20 Parameter Settings 3D region430m × 430m × 430m Nodes10 transmission range750m Data size 512bytes /1kbytes Data rate 50kbps Data generation rate 0.25~30 Run lasts 1 hour Number of runs 50 Nodes move maximum speed 0.3m

Simulation line topology 21 Data size (512bytes) Data size (1kbyte)

Simulation star topology 22 Data size (512bytes) Data size (1kbyte)

Simulation star topology 23

Simulation random topology 24

Simulation random topology 25

Conclusions This paper proposed a MAC protocol DOTS that achieves better channel utilization by harnessing both temporal and spatial reuse. Simulations results have shown that DOTS outperforms S-FAMA and DACAP protocol. 26

Thank you! 27