Performance evaluation of broadcast mac and aloha mac protocol for underwater wireless sensor networks

IJRET: International Journal of Research in Engineering and Technology eISSN:2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 11 | Nov-2014, Available @ http://www.ijret.org 214
PERFORMANCE EVALUATION OF BROADCAST MAC AND ALOHA
MAC PROTOCOL FOR UNDERWATER WIRELESS SENSOR
NETWORKS
Jekishan K. Parmar1
, Mrudang Mehta2
1
M. Tech Student, Department of Computer Engineering, Dharmsinh Desai University, Gujarat, India
2
Associate Professor, Department of Computer Engineering, Dharmsinh Desai University, Gujarat, India
Abstract
Broadcast MAC (BMAC) is simple yet very efficient MAC protocol for Underwater Wireless Sensor Network (UWSN). BMAC
senses the channel and if channel is free then data is transmitted. It is much desired protocol for some low traffic networks. Here
we carry out its evaluation. We also evaluate ALOHA protocol which is also for UWSN. There are various versions of ALOHA
protocol available but here we are considering the pure ALOHA where the sender just sends the data whenever it wants. BMAC
and ALOHA, both possess simplicity in their implementation as well as in their working and hence we evaluate both of them
together in similar simulation scenario. We compared the performance of these two Underwater MAC protocols on the basis of
bit-rate and number of nodes participating in the network. On completing the evaluation process we found that B-MAC performed
well in the simulation scenario that we had designed.
Keywords: BMAC, ALOHA, UWSN, Underwater MAC, Performance Evaluation, Bit-rate.
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1. INTRODUCTION
Recently Underwater Wireless Sensor Network (UWSN) has
appeared as a very important and in demand networking
aspect for various types of marine applications [1] such as
military surveillance, mine reconnaissance, ocean sampling,
and underwater navigation assistance. Various types of low
cost, medium and large scale monitoring systems have
emerged with the development of UWSN. As described in
[1], solutions of terrestrial wireless sensor network cannot be
applied to UWSN. This is due to specific challenges faced by
the acoustic channel. Some of the issues faced with acoustic
channel include low-bandwidth, propagation delay and
frequent-dependent attenuation. These all issues effect
protocol design at all layers of a network protocol stack [2].
The focus of our work is on MAC layer protocol. There are
various MAC layer protocol available for UWSN. Among
the various protocols available we describe and evaluate two
protocols, namely BMAC [3] and ALOHA [4]. Former is
based on broadcasting mechanism and the latter is based on
ALOHA idea which is tailored specifically for underwater
network environments. Both of these protocols contain
backoff mechanism when they are not able to transmit the
data successfully. Though, the manner in which they use this
mechanism differs in some ways from each other. Moreover
both protocols do not prevent collision [5]. The purpose of
evaluating these two protocols is to identify a protocol that is
suitable for a particular type of scenario as described in our
simulation experiment.
As both of these protocols are very much primary and are
expected to perform well in low traffic networks, we find
which one is suitable at scenarios where the bit-rate is low
and there are only few nodes participating in the network.
Moreover we also evaluate optimum bit-rates for both of
these nodes in a specifically designed simulation scenario.
The optimum bit-rates that we consider are based on energy
consumption which is an important factor for any type of
UWSN [1]. We also evaluate these protocols for amount of
delay caused in the network at various bit-rates.
The analysis of these protocols by considering shallow
UWSN scenarios would be also very helpful as shallow
UWSNs basically just receives the data from UWSNs that
are very deeply stationed and sends them to the onshore
stations wirelessly [11]. Moreover shallow UWSNs may
remain unused or very less utilized for several periods [11]
and so our simulation scenario is also applicable for shallow
UWSN. As concluded in [11], there is severe bandwidth as
well as power consumption limitations for a shallow UWSN
and it is one more point due to which we will try to
incorporate the same in our simulation design.
We evaluate the performance of the given protocols by
varying the number of nodes in the network. By this we can
also analyze how variation in nodes affects the performance
of a low traffic network. The results of our evaluation shows
at what value of bit-rate, there is lowest amount of energy
consumption in the network and we also investigate the cause
of it in the paper. The organization of paper is as follows.
Section II gives the detailed description of both of these
protocols. In Section III, we carry out the task of evaluating
and discussing the obtained results of our protocols. Finally
in Section IV, we conclude the paper.

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2. DESCRIPTION OF THE PROTOCOLS
2.1 ALOHA
In literature, there are different versions of ALOHA protocol.
The ALOHA protocol that is described in [4] resembles very
much to the pure ALOHA described in [6], there are also two
sub-types of ALOHA that are described in [2]. In [7] authors
have described a classic optimized version of ALOHA
protocol called slotted ALOHA for underwater networks.
The ALOHA that we are considering is the one referred in
[4].
In ALOHA, when the sender wants to transmit the data it
directly sends out the data. After sending the data it starts a
timer, this timer indicates the time since the packet was sent
and then it waits for the response from the receiver. This
response is nothing but the acknowledgment of receipt of
frame by the receiver. If the frame is received correctly by
the receiver then only it will send the response. If there is
some problem with the frame and receiver doesn’t receive it
and hence doesn’t acknowledge it then server will back off
for some specific amount of time and then resends the same
frame. If the frame is not having any problem and reaches to
the receiver successfully without any issues then the sender
will receive the response from the receiver before it goes for
back off. This time, for which the sender waits to receive the
response from receiver, is called timeout period. The value of
timeout period for the classic ALOHA that we are describing
over here is random but there is a specific timeout period for
another version called carrier-sensing ALOHA.
The time for which the carrier-sensing version of ALOHA
waits for receiving the response is described in [2]. Though,
our main focus is to find how the simplest form of ALOHA
protocol behave in the simulation scenario designed for a low
traffic network. The working of classic ALOHA and the
resulting collisions are shown in figure 1.
Fig-1: Working of ALOHA & Collisions
As given in [5], in ground communications, frame sent at
time t will collide with the frame sent in time [t-1, t+1]. This
is also shown in figure 1 where three stations have sent
frames. The first has sent at t-1, second at t and the third at
t+1. We can see that all the frames overlap each other at
some point; hence no one was able to successfully transmit.
In UWSN, we can visualize ALOHA using similar approach
but we have to consider propagation delay. Hence instead of
looking at the time which frame was sent, we look at the
arrival time on destination side. Thus, we say that
transmission of frame is successful if it does not collide with
other frames at destination side.
We can understand how differently propagation delay acts
with ALOHA by considering an example given in figure 1.
Let us consider that node 1 sends a message after time t-1.
Also, node 2 sends message at time t. Now both these
signals keep on propagating and meet eventually, which
results into constructive and destructive waves. After this,
the signals keep on propagating into that direction. At time
t+1, signals of message sent by node 1 will reach to node 2
while signal of message sent by node 2 is still continuously
propagating. Although, the message sent by node 1 is
received at node 2 without any collision. Thus, we consider
the transmission from node 1 to node 2, to be successful. It
should be noted that, this won’t be the case when you work
with radio waves, if it were radio signals then they would
get collided. Hence, we can say that working of ALOHA
differs a lot compared to ground communications in UWSN.
2.2 Broadcast MAC
B-MAC is a simple yet efficient MAC protocol when we
consider the low traffic networks [4]. B-MAC can take full
advantages of the broadcast nature of Underwater Acoustics
Channel. B-MAC also possesses a simple working
mechanism which is completely dependent on the backoff
mechanisms. Whenever a frame is to be transmitted, it will
first sense the channel whether it is free or not, if it is free
then it simply sends the data or else it will backoff. It
continues to do so until a specific backoff limit is reached.
When the backoff limit is reached it simply drops the
frames. When the receiver receives the frame by B-MAC it
does not send any ACK.
The only issue that rests with B-MAC is the number of
collisions. The other problem that B-MAC faces is the
“reply storm” problem [3]. It can be described by
considering a situation where, CTS frames are broadcasted
on network layer. When this broadcast of CTS is heard by
all the nodes in the network, all of them will try and send
RTS at the same time, this simultaneous issuing of large
number of RTS frames is described as reply storm problem.
This problem is due to the handshake nature of the MAC
protocols. This reply storm problem is also the only reason
for large number of collisions in B-MAC.
2.3 Comparison of B-MAC and ALOHA
There is very limited description of B-MAC found in
literature but its capability to give optimum performance
with geo-routing based protocol as well as its characteristic
of working efficiently in low traffic networks [4] makes it
our point of focus.
Moreover, one more important point to be noticed is that
Broadcast MAC and ALOHA both use back off mechanisms
and there is also a facility of acknowledgment from receiver
in ALOHA which cannot be found in Broadcast MAC.
Hence we consider ALOHA protocol for comparative
evaluation with B-MAC.

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We need to find whether the acknowledgment which is a
part of ALOHA, consumes more bandwidth or not. If it
would be consuming more bandwidth then it should have
higher overall energy consumption as receiving node will
also waste energy in generating acknowledgment as
transmitting it back while it is expected that in B-MAC with
various bit-rates the overall energy consumption of network
should remain lower compared to ALOHA as there are no
extra frames in the form of acknowledgment generated in it
and so less energy would be consumed.
3. PERFORMANCE EVALUATION
We analysed few scenarios for evaluation of MAC protocols
for UWSN before deciding parameters for the simulation
scenario. We analysed scenarios that were configured in [2],
[8] and [9] and then designed the simulation scenario for our
low traffic network as described in following section.
3.1 Network Simulation Configurations
The simulation scenario that we have considered consists of
five nodes, from which one acts as a sink node and other all
are mobile wireless nodes participating in a UWSN as shown
above in figure 2. The network configurations will be as that
of a low traffic network. We will be also varying the number
of nodes just by increasing by a number of one up to a total
of eight nodes. Moreover, the sink node which is attached to
the surface buoy will remain stationary throughout the
simulation time.
Fig-2: Visualization of Simulation Scenario
In our simulation we have considered our nodes to possess
the physical properties like transmission power, receiving
power, idle power, frequency and transmission range same as
that of LinkQuest UWM1000 acoustic modem [10]. Also the
dimensions of our network are 100m X 100m X 10m and so
we have a shallow underwater acoustic network [11] with a
depth of 100m. Bandwidth and energy consumption are also
considered as impediments in this kind of shallow UWSN as
described by [11]. Hence, we also get chance to understand
the performance of B-MAC and ALOHA in this kind of
network which has very high latency. Thus, if either B-MAC
or ALOHA performs well in this kind of scenario we can
expect them to work more efficiently in general UWSN.
To simulate the scenario that is being described we are using
Aqua-Sim which is an NS2 based simulator [4]. The default
value of sound propagation in the physical underwater
acoustic channel is given as 1500 m/sec in Aqua-Sim. The
mobility and wireless functionality are provided
independently by Aqua-Sim which works in parallel with
CMU-wireless package of NS2. Any changes that are made
to Aqua-Sim are confined to itself and it is mentioned in [4]
that it is an independent simulator, which is designed
completely like NS2 in C++. The configuration of our
simulation is summarized in table 1 below.
Table 1: Simulation Confgurations
Parameter Value
Number of nodes 5
Transmission power 2 W
Receiving power 0.75 W
Transmission range 90 m
Data packet size 60 bytes
Control packet size 5 bytes
Speed of node 0.5 m/sec
Maximum speed of node 3 m/sec
Minimum speed of node 0 m/sec
Bit-rate
10 kbps (varying by 10
kbps up to 100 kbps )
Interval 10
Simulation time 600 sec
Most of the parameters that are given in the table 1 above
have been discussed by us so far. But, the type of traffic
generation has not been discussed so far. Hence, we describe
the traffic generation over here.
The generation of traffic will be done using Poisson process
with rate λ packets per second. The interval value supplied
over here will be playing part in the generation of traffic.
With this interval value as 10 we will have λ = 0.1 which can
be considered as low traffic generation rate as given in [2].
3.2 Performance Metrics
The performance metrics that we have considered here are
cumulative delay and overall energy consumption. Our entire
focus while evaluating the performance of these protocols is
on overall energy consumption. We aim to find the bit-rate at
which there is the least consumption of energy by the
network. We can then consider that bit-rate as an optimum
bit-rate for that protocol in the context of overall energy
consumption. At present, it is very difficult to get underwater
acoustic modems with bit-rates greater than 35-40 kbps but
we expect that in future there may be modems with higher
bit-rates and good performance. Hence, we aim to evaluate
the MAC protocols to find the bit-rate at which lowest
overall energy consumption takes. Thus, we consider overall
energy consumption and cumulative delay as our
performance metrics.
 Energy Consumption [12]. We consider energy
consumption during the communication period which
depends on various factors like implementation of
hardware, sleep control and MAC protocols [12], but
we use communication time to evaluate energy
consumption. The communication time is the total
time spent in communication of sensor networks in

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the simulation including transmission time and
receiving time of all nodes in networks.
 Cumulative Delay. The sum of the time taken by all
the packets that are generated in the network to reach
from source to destination is called Cumulative
Delay.
3.3 Simulation Results
We carried out several simulations with scenario described
above. In following figure 3, the results of simulations for
cumulative delay by varying bit-rates are being shown for
ALOHA.
Fig-3: Bit-rate vs. Cumulative delay for ALOHA
The result shown above describes ALOHA simulation
results for cumulative delay against various bit-rates. We
can see that cumulative delay goes on decreasing
continuously till 65 kbps of bit-rate value but it increases a
little at 70 kbps, just before the least value is encountered
around 75 kbps of bit-rate and after that it increases to
become stable at the value of 13.68 sec at bit-rate of 95
kbps. Hence in the results we found that cumulative delay
decreases rapidly till the bit-rate value of 65 kbps but after
that it just keeps on hovering around 13 sec except at 75
kbps. Similarly for overall energy consumption simulation
results are plotted in figure 4.
Fig-4: Bit-rate vs. Overall energy consumption for ALOHA
From the above figure 4, we see that overall energy
consumption is decreasing either rapidly or slowly but only
up to the bit-rate value of 70 kbps, after that it becomes
nearly constant with value around 41 J. Also it should be
noted that even between bit-rate values of 50 kbps and 70
kbps, the energy consumption is only around 44 J which is
nearly half of what is found at 20 kbps. Hence, we can say
that, with increase in bit-rate the energy consumption goes
on decreasing but it gets stabilized at a point. Thus, increase
of bit-rate does play a part when we consider overall energy
consumption.
From the results of ALOHA against bit-rate as given in
figure 3 and figure 4, we can say that, the cumulative delay
becomes pretty much stable after 75 kbps and it also stops
decreasing after 65 kbps. Also, we find that after 70 kbps,
there is not any significant decrease in energy consumption.
Fig-5: Bit-rate vs. cumulative delay for B-MAC
Figure 5, shows the cumulative delay caused in the network
when B-MAC protocol is used. Here the continuous drop or
continuous variation in values of cumulative delay is found
up to bit-rate value of 50 kbps after which the cumulative
delay is nearly constant at a value around 12 sec. In the
following figure 6, overall energy consumption of network
against varied bit-rate values is considered.
Fig-6: Bit-rate vs. Overall energy consumption for B-MAC
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Overallenergyconsumption
(J)
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The overall energy consumption of network goes on
decreasing rapidly till 50 kbps apart from a steep increase
and decrease between 30 kbps and 40 kbps. Moreover, after
50 kbps the overall energy consumption of the network
stabilizes with value of 40-42 J. Thus, we can say that after
50 kbps of bit-rate, the effect of increase in bandwidth
doesn’t affect the overall energy consumption.
From the results of B-MAC as given in figure 5 and figure 6
we can say that after 50 kbps there isn’t any significant
amount of change in cumulative delay as well as overall
energy consumption.
Next, we analyse the behaviour of ALOHA and B-MAC
protocols with increase in the number of network nodes in
the scenario that is described in figure 2. The increase that
we’ll be doing would be only by one node at a time. We do
the increase in this manner as we want to maintain the low
traffic state of the network, if we increase the node rapidly
then though we keep rates of traffic low, the overall traffic of
the network will get increased. Thus, now the ALOHA and
B-MAC protocols will be evaluated for same performance
metrics but by varying number of nodes in the network.
Figure 7 shows, cumulative delay for ALOHA and figure 8
shows overall energy consumption for the same.
Fig-7: Number of nodes vs. cumulative delay for ALOHA
Fig-8: Number of nodes vs. Overall energy consumption for
ALOHA
In this figure 7 and figure 8 for cumulative delay as well as
overall energy consumption we find the results to be very
much relatable. Both the energy consumption and cumulative
delay are increasing with increase in number of nodes in
ALOHA. But, the increase in energy consumption is not very
rapid till the number of nodes are 4 but after increasing the
number of nodes beyond 4; the increase is very sharp and
rapid.
Fig-9: Number of nodes vs. Cumulative delay for B-MAC
In B-MAC, we see that cumulative delay is not increasing as
regularly as it was in ALOHA. When there is only 1 node in
the network the cumulative delay experienced by B-MAC is
10.6s and that of ALOHA is 11.1s. When number of nodes is
increased to 2, cumulative delay for B-MAC is 11.1s and for
ALOHA it is 13.3s. Thus there is not much difference in
cumulative when number of nodes is 1 or 2. When number of
nodes are 4, the cumulative delay for B-MAC is 16.1s and
for ALOHA, it is 19.8s. Now, for amount of nodes we find
more difference in cumulative delay of both. Thus, up to the
point when number of nodes are 3 or 4, the increase in
cumulative delay is less and then it increases rapidly.
Now in figure 10, the overall energy consumption of B-
MAC protocol for various numbers of nodes is being shown.
Here, also the rate of increase of energy consumption is very
slow till the number of nodes is four but after that the
increase is quick as well as steady till number of nodes are
raised to 8. But, in the network when number of nodes is to
its highest number i.e. 8, the energy consumption done by
ALOHA is 379 J and by B-MAC it is 230 J. Hence B-MAC
consumes 61% less energy when number of nodes are 8.
0
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30
40
50
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Cumulativedelay(s)
No. of nodes
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250
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350
400
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Overallenergyconsumption(J)
No. of nodes
0
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30
40
50
60
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Cumulativedelay(s)
no. of nodes

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Fig-10: Number of nodes vs. Overall Energy consumption
in B-MAC
Also the average energy consumption by B-MAC is 109 J,
while for ALOHA it is 137 J which is 21% higher than B-
MAC.
Both of the above protocols are giving similar kind of
performance when we note their results against number of
nodes. Hence, we observe similarity in their behaviour to
tackle the increasing number of nodes, though B-MAC does
consume (about 21%) less amount of energy than ALOHA
in overall.
From the above observations, in the context of energy
efficiency and latency, we can say that ALOHA performs
well when bit-rate is around 65 kbps to 75 kbps and B-MAC
performs well when bit-rate around 50 kbps. The reason for
this is that with increase in bit-rate the amount of time that a
node is spending for transmission will get reduced due to
quick transmission of packet as with high bit-rates node
transmits quickly and goes back to its idle state and hence
the energy spent behind the task of transmission of packet is
reduced, which in turn results into decrease in overall energy
consumption of network.
4. CONCLUSIONS
In the performance evaluation of the two MAC protocols
that we carried out, our main focus was on dependency of
overall energy consumption and delay on the bit-rate of a
network.
On carrying out simulations, we found that overall energy
consumption as well as delay decreases with increase in bit-
rate, but only up to a particular point, after which it becomes
nearly constant. From the results, we can also say that if we
want to devise an acoustic modem with higher bit-rate then
the bit-rates at which B-MAC and ALOHA performed well
can be considered. When we consider all performance
criterions of bit-rate as well as overall energy consumption
and delay in the network then we can say that B-MAC
performed better than ALOHA. B-MAC consumed the least
bit-rate and energy as well as caused much less delay in the
network compared to ALOHA but again when number of
nodes in the network were increased, both performed
similarly. The difference in ALOHA and B-MAC when we
consider the bit-rate vs. overall energy consumption in the
network may be due to the methodology of providing
responses i.e. acknowledgements by the receiver on receipt
of packets which is not there in B-MAC. The generation of
acknowledgments by the receiver in the network results
extra number of generation of packets in the networks by the
nodes which causes more energy as well as bit-rate to be
consumed.
REFERENCES
[1] I. Akyildiz, D. Pompili and T. Melodia,
“Underwater acoustic sensor networks: research
challenges,” Ad Hoc Netw. 3, pp. 257–279, 2005.
[2] C. Petrioli, R. Petroccia and M. Stojanovic,“A
Comparative Performance Evaluation of MAC
Protocols for Underwater Sensor Networks,”
MTS/IEEE OCEANS 2008-Canada.
[3] D. Mirza, F. Lu and C. Schurtgers, “Efficent
Broadcast MAC for Underwater Networks,” Poster
abstract, In Proceedings of Fourth ACM
International Workshop on UnderWater Networks
(WUWNet), 2009-California, USA.
[4] Xie et al. “Aqua-Sim: An NS2 based simulator for
underwater sensor networks,” MTS/IEEE OCEANS
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[5] L.F.M. Vieira, J. Kong, U. Lee and M. Gerla,
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[6] A. S. Tanenbaum, D. J. Wetherall, Computer
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[7] A. Syed, W. Ye, and J. Heidemann, “Understanding
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[8] R. Petroccia and C. Petrioli, “Performance
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[9] F. Guerra, P. Casari and M. Zorzi, “A Performance
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[10] LinkQuest UWM1000. <http://www.link-
quest.com/html/models1.htm>.
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[12] P. Xie, JH Cui and L. Lao, “VBF: vector-based
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0
50
100
150
200
250
0 1 2 3 4 5 6 7 8
Overallenergy
consumption(J)
No of nodes

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BIOGRAPHIES
Jekishan K. Parmar just completed his
M.Tech in Computer Engineering at
Faculty of Technology, Dharmsinh Desai
University, Nadiad, Gujarat, India in May,
2014. He received his B.E. in Information
Technology from L. D. College Of
Engineering, Ahmedabad in 2012. His
research interests include Mobile Computing, Ad hoc
Networks and Wireless Sensor Network.
Mrudang T. Mehta is an Associate
Professor at Department of Computer
Engineering, Faculty of Technology,
Dharmsinh Desai University, Nadiad,
Gujarat, India. He received his M.Tech. in
Information Technology from Indian
Institute of Technology, Roorkee in 2008
and B.E. in Computer Engineering from DDIT, Nadiad in
2001. His research interests include Wireless Sensor
Network, Embedded System and Mobile Computing.

Performance evaluation of broadcast mac and aloha mac protocol for underwater wireless sensor networks

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Performance evaluation of broadcast mac and aloha mac protocol for underwater wireless sensor networks