Hai-Heng Ng, Wee-Seng Soh, Mehul Motani National University of Singapore IEEE GLOBECOM 2008

Outline Introduction MACA overview Proposed MACA-U Adaptation For Multi-hop Underwater Network Simulation Conclusion

Introduction Terrestrial wireless communication uses radio waves Latency Bandwidth MAC schemes such as Frequency Division Multiple Access (FDMA) Time Division Multiple Access (TDMA)

Introduction Underwater communication relies on acoustic waves Long latency limited bandwidth However, terrestrial MAC schemes such as Frequency Division Multiple Access (FDMA) Narrow bandwidth Time Division Multiple Access (TDMA) Time synchronization and long guard time

Introduction Existing underwater contention based MAC solutions Aloha based. Handshaking based.

Introduction Pure Aloha based. Packet S→D Data S → D D S Data S → D S D O Packet S→D Packet S→D Packet S→D ACK D→S

Introduction Pure Aloha based. Packet S→D Data S → D D S Data S → D S D A Packet S→D Packet S→D Packet S→D ACK D→S Data D → A Data D → A A

Goals The state transition rules The backoff algorithm

Introduction We examine how an existing asynchronous handshaking based protocol Goals Improvement lower throughput

P. Karn, “MACA-A new channel access method for packet radio,” in Proc. ARRL/CRRL Amateur Radio Ninth Computer Networking Conf.,September H. Matsuno, H. Ishinaka and A. Hamanaga, “A simple modification for the drastic improvement of MACA in large propagation delay situation,” in Proc. Wireless Communications and Networking Conference, September Original MACA overview RTS S→D Data S → D D S CTS D→S Data S → D QUIET S D O defer its transmission and transit to QUIET state IDLE CONTEND RTS S→D CTS D→S

MACA -State Transition Rules Event Type \State Receives RTS Receives CTS Overhears xRTS Overhears xCTS Timer Expired IDLE Transmit: CTS WFDATA Disregard packet QUIET - CONTEND Transmit: CTS WFDATA Disregard packet QUIET Transmit: RTS WFCTS Disregard packet Transmit: DATA Send Data→IDLE QUIET IDLE WFDATA Disregard packet Disregard packet QUIET IDLE QUIET Disregard packet Disregard packet QUIET IDLE

Improvement original MACA The state transition rules The backoff algorithm

MACA-U Five distinct states, IDLE, CONTEND (CTD), WFCTS, WFDATA and QUIET. WFCTS ： 2τ max + T cts τ max ： maximum propagation delay T cts ： CTS duration WFDATA ： 2τ max + T data T data ： Data packet duration QUIET QUIET_RTS QUIET_CTS

MACA-U -Timing diagram RTS B→C Data B → C C B CTS C→B WFDATA Data B → C QUIET_CTS 2τ max + T data B C D A D RTS B→C A RTS B→C WFCTS CTS C→B CTS C→B QUIET_RTS 2τ max + T cts

MACA-U -State Transition Rules Event Type \State Receives RTS Receives CTS Overhears xRTS Overhears xCTS Timer Expired IDLE Transmit: CTS WFDATA Disregard packet Set Timer : QUIET_RTS QUIET Set Timer : QUIET_CTS QUIET - CONTEND Transmit: CTS WFDATA Disregard packet Set Timer : QUIET_RTS QUIET Set Timer : QUIET_CTS QUIET Transmit: RTS Set Timer: QUIET RTS WFCTS Disregard packet Decrement BEB Transmit: DATA Send Data→IDLE Disregard packet Set Timer : QUIET_CTS QUIET Increment BEB Backoff for Retransmit IDLE WFDATA Disregard packet Disregard packet Disregard packet Disregard packet IDLE QUIET Disregard packet Disregard packet QUIET IDLE

MACA-U -State Transition Rules WFCTS RTS B→A Data B → A C B WFDATA Data C → D B C D A D RTS B→A A RTS B→A WFCTS CTS A→B CTS A→B WFDATA RTS C→D RTS C→D RTS C→D CTS D→C CTS D→C Data B → A Data C → D In WFCTS Overhears xRTS ↓ Disregard packet The system throughput can be improved

MACA-U -State Transition Rules WFCTS RTS A→B WFDATA CTS B→A Data B → A C B WFDATA Data C → D B C D A D A WFCTS RTS C→D RTS A→B RTS C→D CTS D→C CTS D→C Data C → D CTS B→A Data B → A In WFCTS Overhears xCTS ↓ QUIET RTS C→D CTS B→A Potential Data Collision

MACA-U -Backoff Algorithm Backoff algorithm is a collision resolution methodology to minimize packet collision probability. Each node doubles its backoff counter in the event of RTS failure The retransmission or contention slot duration is defined by T rts +τ max., the backoff interval, T bk

Simulation ParameterValue Grid spacing700m Maximum transmission range1.75 times the grid spacing, or 1225m EquippedHalf duplex omni-directional antenna Bit rate2400 bps Acoustic propagation speed1500 m/s Control packets lengths100 bits Data packet lengths1200, 2400, 4800 bits Backoff parametersB min = 1, and B max = 64 OtherNo ACK

Simulation

Conclusion Two areas of improvement are investigated, namely, the state transition rules, and the backoff algorithm. The simplicity and throughput stability of MACA-U More advanced underwater MAC may benchmark its performance against.