
Asynchronous Reservation MAC Protocol for
Underwater Acoustic Sensor Network
Weihong Zhai, Jun Zhang*
School of Electronics and Information Engineering
South China University of Technology
Guangzhou, China
470504467@qq.com, eejzhang@scut.edu.cn
Sindhu Hak Gupta
Amity School of Engineering & Technology
Amity University
Noida, India
shak@amity.edu
Abstract—Reservation is an efficient technique to avoid data
packet collision and has been introduced to the underwater
acoustic sensor network (UASN) MAC protocols recently.
Usually synchronization among the sensor notes are required to
schedule the transmitting and receiving time in the reservation.
However, due to the high and variable propagation delay in the
underwater acoustic channels, accurate synchronization is
difficult to implement in the UASNs. In this paper, a new
reservation based MAC protocol for the UASN is proposed, in
which the synchronization requirement are loosed by employing
an asynchronous reservation scheme. A sleep/wait-up mechanism
is also incorporated into the reservation process to further
reduce the energy consumption. Simulations show that the
proposed protocol outperforms the CSMA-ALOHA and DACAP
protocols in throughput, successful rate and energy consumption.
Keywords—Underwater acoustic sensor network; MAC
protocol; Asynchronous reservation
I. INTRODUCTION
Recently, as the needs in monitoring the marine
environment for scientific exploration, commercial
exploitation and coastline protection growing, many attentions
have been attracted to the underwater acoustic sensor network
(UASN) [1]. However, the characteristics of underwater
acoustic channel, such as the limited bandwidth, high and
variable propagation delay, time-varying multi-path and
fading, high bit error rates, temporary losses of connectivity,
energy constrained, and etc, bring great challenges to the
underwater acoustic networking [2]. The MAC protocol, which
controls the nodes in a network to share the common broadcast
channel, is one of the key techniques to the underwater
acoustic networking.
Many MAC protocols for the UASN have been proposed in
the previous researches [3-10]. According to the network
architectures, they can be divided into two categories:
centralized protocols and distributed protocols. In the
centralized MAC protocols, a special node is responsible for
the entire network transmission scheduling. In the ordered
CSMA protocol [3], the coordinator finds the optimal
transmission sequence among nodes according to their
locations and informs all the nodes about this transmission
schedule. A TDMA-based scheme MAC protocol was
proposed in [4], in which the sink node schedules the
transmission sequence and notifies all the nodes through a
super frame. The efficiency reservation MAC protocol [5]
groups nodes according to their directions to the sink. Nodes
belonging to the same group can transmit their packets in a
pipelined and collision-free way. In the distributed MAC
protocols, all nodes are equal and they need to contend to
access the channel. The Aloha protocols [6] allow the nodes
send out data without negotiation. Although collision will
occur easily in this protocol, it still effective in the high delay
underwater environment by saving the negotiation time. The
CSMA that is previous used in the terrestrial network is also
adopted by many distributed UASNs [7]. In such kind of
UASNs, the network notes sense the channel before they send
out data. If the channel is busy, they back-off a random time to
avoid collisions. The FAMA [8] avoids the packet collision by
using control packets and a handshake process. The R-MAC [9]
and T-Lohi [10] are two typical reservation based distributed
MAC protocols for the UASNs. The R-MAC uses a handshake
process to contend the data transmission slot, while in the T-
Lohi, nodes contend to send a short tone to reserve the channel
in the reservation period.
The reservation technique, which is wildly used in the
terrestrial networking to avoid data packet collision, shows
good potentials in the UASNs in the previous researches.
However, in the reservation based MAC protocols,
synchronization among the sensor notes are usually required to
schedule the transmitting and receiving time. Due to the high
and variable propagation delay in the underwater acoustic
channels, accurate synchronization is difficult to implement in
the UASNs. Some techniques have been proposed to address
this problem. The R-MAC protocol uses the latency detection
and period announcement phases to synchronize nodes. Each
note needs to maps the timing of the other notes into its own
time line and carefully schedules its operation to avoid
collision. However, the synchronization will fail when the
propagation delay is varied during two latency detection
phases. In the unsynchronized T-Lohi, nodes can start
contending any time they know the channel is not busy.
However, the collision of tone-data packets and data-data
packets will also occur in such situation.
In this paper, we propose a new reservation based MAC
protocol for the UASN, in which the synchronization
requirements are loosed by employing an asynchronous
*The corresponding author.
This work was supported in part by the National Natural Science
Foundation of China under Grant numbers 61372083 and 61372080, the
Science and Technology Project of Guangzhou under Grant 2012J2200005.
2014 International Conference on Signal Processing and Integrated Networks (SPIN)
978-1-4799-2866-8/14/$31.00 ©2014 IEEE 241