C-MAC: A TDMA-based MAC Protocol for Underwater Acoustic Sensor
Networks
Yutao Ma, Zhongwen Guo, Yuan Feng, Mingxing Jiang,Guanglei Feng
Department of Computer Science, Ocean university of China
{ mac863, guozhw,fengyuan, jiangmingxing,llc863}@ouc.edu.cn
Abstract
Different from terrestrial wireless networks that use
radio channel, underwater networks utilize acoustic
channel, which poses great research challenges in
medium access control (MAC) protocol design due to
its low available bandwidth and high propagation
delay characteristics. In addition, the high bit-error,
high transmission energy cost, and complex multi-path
effects in underwater environment make it even harder.
In this paper, a suitable MAC protocol, named C-MAC
(cellular MAC) for underwater acoustic sensor
networks (UWANs) is proposed. C-MAC is a TDMA-
based MAC protocol, which divides networks into
many cells. Each cell is distributed a time slot; nodes
in a cell, can only transmit packets in the cell’s time
slot. Experiments show the protocol can avoid collision,
minimize the energy consumption, and increase the
throughput efficiency.
1. Introduction
UWANs are expected to have a significant impact
on the efficiency of many civil and military
applications [1]. Generally speaking, traditional
terrestrial wireless networks utilize the radio channel.
Due to the high rate of absorption of radio in the water,
we prefer acoustic in the underwater environment [2, 3].
But the special characteristic of acoustic brings
tremendous challenges to not only the application of
UWANs but also the design of the system [4, 5, 6].
First of all, the extremely low speed of sound in
underwater causes its propagation delay to be very high
(about 0.67msec/m). T his is very high compared to
terrestrial wireless networks which are often assumed
negligible propagation delay. Secondly, it suffers from
high bit error rate and significant attenuation which
depends on frequency, so the available b andwidth is
particular limited. In addition, it is difficult to pr edict
the underwater environment which is changing all the
time.
Recently a lot of MAC protocols have been
proposed that attempt to supply sufficient systems
despite the special characteristic of UWANs. PCAP
uses RTS-CTS handshake mechanism to avoid
collision [7]. PCAP allows senders to do other actions
while waiting for the CTS frame from receiver. When
offered load increases, the throughput of PCAP
becomes inefficient. Slotted FAMA is also
handshaking based protocol which uses time slot to
avoid c ollision [8]. All frames can only b e transmitted
at the beginning of each time slot. Nodes must be
synchronized in slotted FAMA. The long slot length
requirement reduces the throughout of the protocol. In
[9] the author proposed a distributed, energy efficient
protocol based on CSMA. It allows node to sleep in the
long propagation time, and synchronization is also
needed. Its main problem is that it assumes latency
constant. In [10] the author proposed Aloha-CA which
uses a short advance notification packet (NT F) as the
pre-engagement of dada packet. Similar with other
Aloha protocols, when offered load is very high, good
performance of protocol becomes unavailable.
2ˊ
Protocol description
This dissertation is talking about a MAC pro tocol
based on TDMA. Time is segmented into many cycles
which are repeated continuously, and each cycle
consists of seven time slots. A time slot is made up of
data transfer phase and protection phase. The length o f
protection phases is equal to the largest expected
propagation delay in the network. Each d ata transfer
phase is long enough to transmit a maximum length
packet.
Fig.1 shows the typical transfer sequence of a cycle
for the protocol. A cycle is composed of seven different
time slots using numbers to mark in the figure. Panes
with number stand for the data transfer phase; and the
2009 International Conference on Networks Security, Wireless Communications and Trusted Computing
978-0-7695-3610-1/09 $25.00 © 2009 IEEE
DOI 10.1109/NSWCTC.2009.130
728
2009 International Conference on Networks Security, Wireless Communications and Trusted Computing
978-0-7695-3610-1/09 $25.00 © 2009 IEEE
DOI 10.1109/NSWCTC.2009.130
728