This paper reviews medium access control (MAC) in wireless sensor network (WSN),and different management methods to save energy.MAC protocol controls how sensors access a shared radio channel to communicate with neighbours.

1. International Journal of Electrical & Electronics Engineering 36 www.ijeee-apm.com
IJEEE, Vol. 1, Spl. Issue 1 (March 2014) e-ISSN: 1694-2310 | p-ISSN: 1694-2426
Optimization of Transmission Schemes in
Energy-Constrained Wireless Sensor Networks
1
Vivek Rana, 2
Jaspal Singh, 3
Leena Mahajan
1,2
Rayat Institute of Engineering & Information Technology,Railmajra, Punjab, India.
3
Indo Global college of Engineering, Abhipur,Distt. Mohali,Punjab,India
1
ranavivek01@gmail.com, 2
jaspal_116@yahoo.co.in, 3
leenamahajan1997@gmail.com
Abstract- This paper reviews medium access control
(MAC) in wireless sensor network (WSN),and different
management methods to save energy.MAC protocol
controls how sensors access a shared radio channel to
communicate with neighbours. This paper discusses design
trade-offs with an emphasis on energy efficiency, latency,
fairness and throughput. One mechanism used to reduce
energy expenditure is to periodically turn off the radio
receivers of the sensor nodes in a coordinated manner. S-
MAC may require some nodes to follow multiple sleep
schedules causing them to wake up mmore often than other
nodes. A typical node in WSN consists of one or more
sensors, embedded processors, moderate amount of
memories and transmitter/receiver circuitry. These sensors
are battery powered and recharging of these nodes is very
expensive and normally not possible. The proposed
modification in MAC protocol solves the energy
inefficiency caused by idle listening, control packet,
overhead, and overhearing taking nodes latency into
consideration based on network traffic. The modified
version improves the energy efficiency, latency and the
throughput and hence increases the life span of a wireless
sensor network. Simulation experiments have been
performed to demonstrate the effectiveness of the proposed
approach. This protocol has been simulated in Qualnet 5.0.
Keywords- Wireless Sensor Network, Medium Access
Control, Energy Efficiency , latency, throughput, fairness.
I. Introduction
A wireless sensor network (WSN) of spatially distributed
autonomous sensors to monitor physical or environmental
conditions, such as temperature, sound, pressure, etc. and to
cooperatively pass their data through the network to a main
location. The more modern networks are bi-directional, also
enabling control of sensor activity. The development of
wireless sensor networks was motivated by military
applications such as battle field surveillance; today such
networks are used in many industrial and consumer
applications, such as industrial process monitoring and
control, machine health monitoring, and so on.
A WSN generally consists of a host or “gateway” that
communicates with a number of wireless sensors via a radio
link. Data is collected at the wireless sensor node,
compressed, and communicated to the gateway directly or,
if required, uses other wireless sensor nodes to forward data
to the gateway. The gateway then ensures that the data is
input into the system. The main function of a wireless
sensor network (WSN) is to collect data from environment
and send it to a reporting site where the data can be
observed and analyzed Each wireless sensor is considered a
node and presents wireless communication capability, along
with a certain level of intelligence for signal processing and
networking data. Depending on the type of application,
each node can have a specific address. Figure 1 represents a
generic block diagram of a node. It usually comprises a
sensing unit, a microcontroller to process data, and a RF
block for the wireless connection. Depending on the
network definition, the RF block can function as a simple
transmitter or transceiver (TX/RX). When designing the
nodes, it is very important to pay attention to the current
consumption as well as the processing capability. The
microcontroller’s memory is very dependent of the software
stack used.
Fig.1: Generic block diagram of a node of a WSN.
Wireless Sensor Networks (WSNs) are an important new
class of networked system.
Dealing with both scale and density is hard enough in ideal
environments. Unfortunately, we don’t have the luxury of
ideal environments with sensor networks. Because sensor
networks are intended to monitor the physical world, they
must often be deployed in natural and uncontrolled
environments. No longer can we assume the carefully
controlled temperature, abundant power, and human

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monitoring of server rooms and data centers. Instead,
wireless sensor networks must be designed to operate while
no external power is connected, unattended, irregularly
connected (radios may be turned off for significant periods
of time to conserve power), and uncontrolled environment
[1].
MAC protocols have a significant effect on the function of
WSN. MAC protocol, which builds bottom infrastructure in
sensor network systems, decides how to use wireless
channel and allocate limited wireless communication
resources for sensor nodes. MAC protocol, one of the key
network protocols that ensure effective communication in
sensor network, is in the bottom part of the sensor network
protocol and has a great impact on the performance of
sensor network [6].
II. RELATED WORK
A. Proposed S-MAC Protocol Design Challenges
It is necessary to establish communication links between
nodes because a great number of sensor nodes are
distributed to the medium in Wireless Sensor Networks. For
this reason, MAC protocol has two aims in WSNs. The first
is to build a sensor network infrastructure. The second is to
share the communication medium in a fair and efficient
way [8].
Attributes that should be taken into consideration in the
design of MAC protocol are listed on below :
Energy efficiency: Energy efficiency is the most important
issue when designing a new MAC protocol in WSNs
because the network’s lifetime is determined by the nodes’
energy.
Latency: The elapsed time for sending a MAC-layer data
packet successfully is called “Latency”.
Throughput: The ratio of the messages served by
communication systems is called “Throughput”.
Robustness: Robustness is composed of the attributes
including reliability, usability, and durability. It shows the
protocol’s degree of resistance to errors and false
information.
Scalability: Capability of communication system regardless
of the number of sensor nodes performing a transaction and
the size of the network is called “Scalability”.
Stability: The ability of communication system to handle
the issue of traffic congestion in the medium that changes
constantly is called “Stability”. A stable MAC protocol
should handle sudden loads that can exceed maximum
channel capacity.
Fairness: Bandwidth is limited in most of WSNs
applications, but the base station must receive data equally
from all the nodes. Channel capacity should be fairly shared
among the nodes without reducing the efficiency of the
network.
The main goal in our S- MAC protocol design is to reduce
energy consumption, while supporting good scalability,
fairness and collision avoidance. Our protocol tries to
reduce energy consumption from all the sources that we
have identified to cause energy waste. To achieve the
design goal, we have developed the S-MAC that consists of
three major components: periodic listen and sleep, collision
and overhearing avoidance, and message passing. A
modification of the protocol is then proposed to eliminate
the need for some nodes to stay awake longer than the other
nodes. The modified version improves the energy
efficiency, latency, fairness and the throughput and hence
increases the life span of a wireless sensor network.
Wireless sensor networks use battery-operated computing
and sensing devices [3]. We expect sensor networks to be
deployed in an ad hoc fashion, with nodes remaining
largely inactive for long time, but becoming suddenly
active when something is detected. These characteristics of
sensor networks and applications motivate a MAC that is
different from traditional wireless MACs such as IEEE
802.11 in several ways [2, 4]: energy conservation and self-
configuration are primary goals, while per-node fairness
and latency are less important. S-MAC uses a few novel
techniques to reduce energy consumption and support self-
configuration. It enables low-duty-cycle operation in a
multi-hop network. Nodes form virtual clusters based on
common sleep schedules to reduce control overhead and
enable traffic-adaptive wake-up. S-MAC uses in-channel
signaling to avoid overhearing unnecessary traffic. Finally,
S-MAC applies message passing to reduce contention
latency for applications that require in-network data
processing.
B. S-MAC Protocol
S-MAC [9] is a CSMA –based MAC protocol designed
with a modified IEEE 802.11. Its primary goal is power
consumption. S-MAC supports message transition so that
large-sized packets can be sent more efficiently. The
innovations in this protocol are periodical listening,
reducing collision, preventing unintentional receiving, and
message transition. Nodes generally sleep instead of
continuously listening to the medium. Listening and
sleeping times are stable and periodic. There should be a
strict synchronization so that the nodes can move together.
The timing diagram of S-MAC is shown in Figure 2.
Fig. 2. Timing diagram of S-MAC
The Sensor MAC (S-MAC) protocol was introduced in [5]
to solve the energy consumption related problems of idle
listening, collisions, and overhearing in WSNs using only
one transceiver. S-MAC considers that nodes do not need to
be awake all the time given the low sensing event and
transmission rates. S-MAC [3] reduces the idle listening
problem by turning the radio off and on periodically. Nodes
are synchronized to go to sleep and wake up at the same
time. In order to address the issue of synchronization over
multi-hop networks, nodes broadcast their schedules to all
its neighbors. This is performed sending a small SYNC
frame with the node schedule periodically. S-MAC divides
time in two parts: the active (listening) part and the inactive
(sleeping) part. The active part is divided at the same time
in two time slots. During the first time slot, nodes are
expected to send their SYNC frames to synchronize their
schedules. The second time slot is for data transmission in
which the S-MAC protocol transmits all frames that were
queued up during the inactive part. In order to send SYNC

3. International Journal of Electrical & Electronics Engineering 38 www.ijeee-apm.com
frames over the first time slot or RTS–CTS–DATA–ACK
frames over the second time slot, nodes obtain access to the
media utilizing the same contention mechanism included in
IEEE 802.11, which avoids the hidden terminal problem
and does a very good job avoiding collisions too. However,
nodes using the IEEE 802.11 protocol waste a considerable
amount of energy listening and decoding frames not
intended for them [4]. In order to address this problem, S-
MAC allows nodes to go to sleep after they hear RTS or
CTS frames. During the sleeping time, a node turns off its
radio to preserve energy.
Fig.3: S-MAC frame
C. Problems with S-MAC
The following two problems have been identified in S-
MAC [3] protocol with multiple schedules.
1. Longer listen period
2. Sleep delay
1. Longer listen period
While choosing and maintaining the listen and sleep
schedule some nodes may have to keep wake during the
listen time of more than one schedule [3]. This happens, for
example, if a node,
(A): Before
(B): After
Fig.4: Sleep schedule before and after node M join the network
When it starts up, finds some of its neighbors following one
schedules and the rest following another. The nodes
following a shared schedule are said to form a virtual
cluster. Figure 4 shows an example of this situation. Before
node M starts up, two isolated virtual clusters of nodes
exist. Nodes A, B and C follow one schedule (schedule 1);
and nodes X, Y and Z follow another schedule (schedule 2).
The circle around a node indicates the communication
range of the node. When M starts, during its initial listening
spanning a synchronization period, it receives sync frames
corresponding to both the schedules. M will then adopt one
of the schedules (e.g. schedule 2) as its own, and announce
this schedule in its sync frames. However, it will also have
to wake up during the listen time of the other schedule.
Thus M has higher duty cycle, and consumes more energy.
2. Sleep delay
Sleep delay introduce extra end to end delay called sleep
delay [3]. Sleep delay increases communication latency in
multihop networks, as intermediate nodes on a route do not
necessarily share a common schedule. In a nutshell, the
difficulty is to make a trade off between sleep delay and
optimal active periods.
D. Proposed Modification in S-MAC
In this section we propose a modification of the S-MAC
protocol. The following features were included in the S-
MAC design:
 RTS/CTS for hidden terminal problem.
 Both virtual and physical carrier sense.
 Back off and retry.
 RTS/CTS/ACK.
 Broadcast packets are sent directly without using
 The RTS/CTS reserves the medium for the entire
message.ACK is used for immediate error
recovery.
 Node goes to sleep when its neighbor is
communicating with another node. Each node
follows a periodic listen/sleep schedule.
 At boot up time each node listens for a fixed Sync
period and then tries to send out a sync packet. It
suppresses sending out of sync packet if it happens
to receive a sync packet from a neighbor and
follows the neighbor's schedule.
 A node can choose its own schedule instead of
following others, the schedule start time is user
configurable.
 Neighbor Discovery: in order to prevent that two
neighbors cannot find each other due to following
complete different schedules, each node
periodically listen for a whole period of the
SYNCPERIOD.
 Duty cycle is user configurable.
III. RESULT AND DISCUSSION
The objective of this discussion is to compare the S-MAC
and the modified proposed S-MAC protocol in terms of
energy efficiency, latency, fairness, security and
throughput. We need to have set of protocols to perform
successful communication among different nodes. There
are more steps for design a MAC protocol. First,
researchers have to decide that in which application do they
use this protocol. Because there are more priority such as
energy efficiency, latency, fairness, throughput, security. If
your first priority is energy efficiency, you can neglect to

4. www.ijeee-apm.com International Journal of Electrical & Electronics Engineering 39
more security. Because, each work for security causes that
consumption and delay. Otherwise, if you develop a
protocol which will be use in military or healthcare
applications, you have to provide security requirements. In
order to meet the application level security requirements,
the individual nodes must be capable of performing
complex encrypting and authentication algorithms. Long
mechanism of encryption and decryption should not be kept
as they consume more energy. In WSNs, energy efficiency
is the main task. After measuring the effect of the
parameters like power, lifetime of sensor network, memory,
security and type of radio communication on different
protocols, it can be concluded that these evaluation
parameters should be kept in mind while designing MAC
protocol. Simulation results of the WSN models are
presented under varying network load conditions followed
by performance comparisons and analysis.
A. Measurement of Energy Consumption
We measured the energy consumption in the ten-hop
network. In each test, the source node sends a fixed amount
of data, 20 messages of 100-bytes each. Figure 5 shows that
S-MAC with periodic sleep consumes much more energy
over MAC without sleep, but the proposed MAC achieves
better energy efficiency than the S-MAC protocol.
0
5
10
15
20
25
30
35
0 1 2 3 4 5 6 7 8 9 1011
EnenrgyConsumption(J)
Message Inter- Arrival Time (S)
No
Sleep
S-MAC
FIG.5: Energy Consumption
B. Measurement of Average Message Latency
Since S-MAC makes the trade-off of latency for energy
savings, we expect that it can have longer latency under
both the high and low traffic loads due to the periodic sleep
on each node as shown in figure 6(A) and figure 6(B). We
consider two extreme traffic conditions, the lowest traffic
load and highest traffic load. Under the lowest traffic load,
the second message is generated on the source node after
the first one is received by the sink. To do this, a
coordinating node is placed near the sink. When it hears
that the sink receives the message, it signals the source
directly by sending at the highest power. In this traffic load,
there is no queuing delay on each node. Compared with the
MAC without sleep, the extra delay is only caused by the
periodic sleep on each node. Under the highest traffic load,
all messages are generated and queued on the source node
at the same time. So there is a maximum queuing delay on
each node including the source node. The latency of the
proposed MAC protocol is nearly equal to that of MAC
without periodic sleep but still it doesn’t reach the shortest
latency.
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7 8 9 10 11
Averagelatency
NumberOf Hops
No Sleep
S-MAC
Mod S-MAC
FIG.6 (A): Average Message Latency under the lowest traffic load
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7 8 9 10 11
AverageLatency(S)
Number Of Hops
No Sleep
S-MAC
Mod S-MAC
FIG. 6(B): Average Message Latency under the highest traffic load
C. Measurement of Throughput
Just as S-MAC may increase latency, it may also reduce the
throughput. Therefore we next evaluate throughput in the
same 10-hop network. We first consider throughput for the
highest traffic load, which is the same as that when
measuring the latency in the highest traffic load. It delivers
the maximum possible number of bytes of data in a unit
time. The results in figure 5 show that for S-MAC as well
as for proposed S-MAC, throughput drops as the number of
hops increases, due to the RTS/CTS contention in the
multihop network.
0
10
20
30
40
50
60
70
80
90
0 1 2 3 4 5 6 7 8 9 10 11
Throughput(Bytes/s)
MessageInter-Arrival Period (S)
No Sleep
S-MAC
Mod S-MAC
FIG.7: Throughput over 10-hops under varying traffic loads.

5. International Journal of Electrical & Electronics Engineering 40 www.ijeee-apm.com
IV. FUTURE SCOPE OF WORK
During this work we realized that the MAC protocols for
the wireless sensor networks are a hard and extensive area.
Although modification in S-MAC protocol has been
proposed, there is possible future work for system
performance optimization. Therefore, some of the planned
work has to be rationalized away for future work. We see
clear paths for future work:
 Verification through implementation and extensive
simulations.
 Formal descriptions to address other type of MAC
protocols and extension of components.
 Cross layer optimization is an area that needs to be
explored more extensively.
REFERENCES
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[5] IEEE Standard 802.11. (1999) “Wireless LAN Medium Access Control
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AUTHORS
Vivek Rana graduated in Electronics
& Communication Engineering from
Rayat Institute Of Information and
Technology, Railmajra, Punjab. Now
he is a student of M-Tech in
Electronics & Communication
Engineering in Rayat institute of
information and Technology Railmajra, Punjab. His active
research interests include wireless sensor network, Wireless
communication, computer networking & semiconductor
devices.
Jaspal Singh graduated in
Electronics & Communication
Engineering from Baba Banda
Singh Bahadur Engineering
College, Fatehgarh Sahib, Punjab.
He has received his M-Tech degree
in Electronics & Communication
Engineering from Thapar Institute
of Engineering and Technology,
Patiala, Punjab. He is working as Associate Professor and
HOD in ECE department in Rayat Institute of Engineering
and Technology, Railmajra, Punjab. He is a life member of
ISTE. His active research interests include intelligent
sensor network, wireless sensor network, Optical wireless
communication, Wireless communication & network,
microwave engineering, semiconductor devices
Leena Mahajan graduated in
Electronics & Communication
Engineering from Institute of
Electronics and Telecommunication
Engineering , New Delhi. She has
received her M-Tech degree in
Electronics & Communication
Engineering from Baba Banda Singh
Bahadur Engineering College,
Fatehgarh Sahib, Punjab. She has a
very rich experience of 13 years in Telecom sector. She has
served many organizations like Himachal Futuristic
Communications Limited, Chambaghat, Himachal Pradesh,
India, Punjab Communications Limited, Mohali, Punjab,
India. Presently she is working as Assistant Professor in
Indo Global College of Engineering, Abhipur, Punjab,India.
She is a corporate life member of IETE. She is guiding
many thesis of M Tech students. She has published many
national and international papers on WSN and
Managememt . Her active research interests include
intelligent sensor network, wireless sensor network, Optical
wireless communication, Wireless communication network
& switching devices.
.