International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 11 - Apr 2014
A Survey on MAC Protocols in WSN
Ritesh Kumar#1 , Mritunjay Kumar Rai*2
#
M.Tech, Electronics and Communication Engineering, LPU, Jalandhar, Punjab, India
*
Associate Professor, Department of ECE, LPU, Jalandhar, Punjab, India
Abstract- A Wireless Sensor Network (WSN) is a collection of
several small, low powered, low cost sensor nodes. These sensors
are capable of performing multiple functions when applied at the
desired location. There are some Medium Access Control (MAC)
protocols for the WSN which are used to control the medium
access in the network. In this paper various MAC protocols are
discussed. The various characteristics of the MAC protocols are
also discussed.
Keywords- WSN, MAC, MAC protocols.
I.
by using the inter-mediate nodes between the source node and
the destination node. This way of transmission of data is
known as multi-hoping [4].
Internet
INTRODUCTION
Sink node
Nowadays there are so many small and tiny devices
are available which have the capability of sensing the data
from the surrounding environment and transmitting the sensed
data over a wireless medium. The creation of such capable
devices has led to a number of future applications to be
implemented. These sensing devices are called as sensors. So
we can compose a network by using such small sensors. The
network composed of such kind of devices is known as
wireless sensor network.
A wireless sensor network is the collection of nodes
organized in cooperative manner [4]. The nodes used in the
network are the sensor nodes which are used for the
communication by using the wireless media. The wireless
media may be either radio frequency waves, infrared medium
or any other media in which there is no use of the wires is
done. The sensor nodes are arranged randomly and the nodes
may communicate with each another to establish an ad-hoc
network [4]. In wireless sensor network the sensor nodes
monitor different conditions at different locations and
different conditions may be some kind of heat or
temperatures, stress, strain, level of noise, movement of
vehicle, the objects’ presence, the atmospheric conditions like
humidity, lightning condition etc, and any current
characteristics like the speed and direction of any object and
shape of objects [1].
A sensor node basically consists of a sensor module,
a battery, a processor and a radio device. A wireless sensor
network consist a large number of sensor nodes, and These
nodes are generally low power nodes and are capable to do
multiple functions, operate in an unmanned atmosphere with
the limited capability of computation and sensing [2]. These
sensor nodes are self-powered nodes and used to detect the
special events and process their data to a base station.
In case if a sensor node is unable to establish the
communication with any of the other node, then it means that
they are not within the range with one another. In such
situations, the data can be transmitted to the destination node
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User
Sensor Nodes
Fig 1: Wireless Sensor Network
Some basic functions must be performed by the wireless
sensor network which is same for all the WSN. These basic
functions are [14]:
 Sensing.
 Processing.
 Storage of data.
 Communication.
There is no previously existing network infrastructure
required to form such kind of network. In such networks we
can add or remove the nodes as per requirement. This property
is known as the flexibility of the network. Due to this property
we have to deal with several forceful changes in the topology
of the network such as the path updation, updation of the tree
of the network etc. in a wireless sensor network the sensor
node collects and then send it to the sink. The data sink may
be connected to the world via internet where the information
may be required [4]. Basically sensor nodes are small and less
costly so they are used in large number. The resources are
limited because sensor nodes are small, limited energy,
bandwidth, and computational speed. The battery is limited so
the lifetime of the sensor node is also limited therefore this is
the reason that lifetime of the sensor network is limited. Thus
energy efficiency is a major issue for sensor networks [3].
In this paper we have introduced different sections. We
have briefly described about MAC in section II. The Different
MAC protocols used in WSN are explained in detail in section
III. There are some characteristics of the MAC protocols
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 11 - Apr 2014
related to the wireless sensor networks which are introduced
in section IV.
II.
MEDIA ACCESS CONTROL
The Media Access Control (MAC) is a protocol for
data communication. MAC is basically the sub-layer of data
link layer. The data link layer is the second layer in open
systems interconnection (OSI) model. The main functions of a
MAC sub-layer include taking decision when a node can
access the shared medium, framing, addressing and flow
control etc. It also resolves the probable conflicts between
competing nodes. It makes possible for several nodes in the
network to communicate within a multipoint network,
typically a local area network (LAN) or metropolitan area
network (MAN). The mechanism of addressing is known as
the MAC address or physical address. The MAC address is
generally a unique serial number that is assigned to every
network adapter. This address makes it feasible to deliver the
data packet to its destination within the network. The MAC
sub-layer provides an interface between the physical layer and
logical link control sub-layer of data link layer [10].
III.
MAC PROTOCOLS FOR WSN
MAC protocol in a WSN coordinates when and how
the nodes in the network access the wireless channel. Idle
listening, overhearing, collisions, and the control packets
overheads are the main sources of energy wastage [7].
Collisions happen if the two or additional nodes attempt to
transmit the data at same time. When a sensor node listens the
channel to check whether there is data related to it, idle
listening occurs. Overhearing occurs when a node receives the
message which is not destined to it but to any other node in
the network. Transmissions of the control packets may also
cause the wastage of energy because these packets do not
convey any useful data or information. These issues must be
carefully taken into consideration while designing the energy
efficient MAC protocols.
MAC protocols are basically divided into two classes
- contention-based MAC protocols and scheduled or schedule
based MAC protocols. Contention-based protocols are also
called as random protocols or unscheduled protocols [9].
These protocols enable nodes accessing the medium
independently from the other. They have more wastage of
energy, so in terms of use of energy resources they are
inefficient [5]. Schedule-based MAC protocols are also called
as collision-free protocols or contention-free protocols. These
protocols are more efficient in terms of energy as compared to
contention-based protocols.
A. CONTENTION BASED MAC PROTOCOLS
In contention based MAC protocols the medium
access is distributed. No central coordination in these
protocols for the nodes to access the medium. Some protocols
are discussed here.
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1) Sensor MAC (S-MAC)
S-MAC refers to the Sensor-MAC [5]. Its function is
to place a node in a medium listening state. If a node listens
nothing then it transmits a SYNC packet with a schedule
which defines the sleeping and listening periods. All the nodes
receiving this sync packet will adopt that particular schedule.
A node maintains the table with the schedules of neighbouring
nodes. When the listen period starts, a node which is ready to
transmit a packet will have to execute a procedure. The
transmitting node will transmit a request to send (RTS) frame
and then the receiver node replies with a clear to send (CTS)
frame. All the nodes that are not involved in the
communication will go into the sleep state till the
communicating nodes are transmitting the data packets and
acknowledgement packets. Due to sleeping of nodes the
energy consumption reduces but it introduces the latency
because communication with sleeping nodes will have to wait
until they wake up [5]. S-MAC protocol is less energy
consuming. The reason behind this is that in S-MAC there is
sleep period. So during this period the nodes consume less
energy. The control messages like RTS and CTS cause the
overheads and increase energy consumption.
2) Berkeley MAC (B-MAC)
B-MAC refers to Berkeley Media Access Control for
low-power sensor networks [8]. It uses an adaptive preface for
the reduction in idle listening, which is a major source of
energy consumption in several protocols. When the node has a
packet to transmit, it has to wait during a backoff period
before checking the medium or the channel. If the medium is
free then only node transmits the packet otherwise a second
(congestion) backoff begins. Every node must check the
channel regularly by using low-power listening (LPL). If the
channel is found free and the node has no data, then the node
returns to sleep state [8]. The main benefit of using B-MAC in
wireless sensor network is that in this RTS, CTS, ACK, or any
other control messages frames are not used by default, but we
can be add them. In B-MAC the adaptive preface results in
large overheads [8].
3) Predictive Wake-up MAC (PW-MAC)
PW-MAC is the abbreviated from of Predictive
Wake-Up MAC [8]. It is the improvement on S-MAC and BMAC protocols. PW-MAC uses the pseudo random schedules.
Therefore all the nodes in the network will not wakeup and
will transfer the data at the same time. This helps in avoiding
the collisions. A node that has just woke-up transmits a short
beacon message. The other nodes receiving this beacon get
inform that it is wake up. Now sender can easily transmit the
data packet and also can request information from receiver.
The receiver information may include current time and current
seed (start value) for the pseudo random schedules used by the
receiver. With the help of seed in a linear congruential
generator (LCG), the transmitter node in PW-MAC can make
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the prediction that when the receiver node will wake up [11].
The major benefit of using PW-MAC is that sleeping until the
receiver is wake up results in decrement in the duty cycles in
the sender. PW-MAC includes overhead because of beacons
and idle listening.
B. SCHEDULE BASED MAC PROTOCOLS
These protocols access the medium by defining a
schedule for the transmission, reception or being idle by the
nodes in the network. It means that a node can communicates
during specific allotted time slot and remain idle rest of the
time. Scheduling-base protocols use several approaches as
discussed below.
1) LOW-ENERGY ADAPTIVE CLUSTERING
HIERARCHY PROTOCOL (LEACH)
LEACH protocols include different characteristics
for communication in WSN [13]. These characteristics may
include routing, application, MAC, and physical
characteristics. LEACH acknowledges all the nodes are
synchronized. They can control their power of transmission,
and they can also reach one base station if required. The nodes
have also enough capability of processing for the
implementation of different MAC protocols and to perform
the signal processing function such that all information can be
assembled only in single message. Nodes are organized in
clusters and the cluster heads (CHs) are elected. After that
transmission of information starts. In each cluster direct
sequence spread spectrum (DSSS) with different code is used
in order to minimize the interference [13].
LEACH protocols help in saving the energy through
sleeping mode. Cluster head rotation increases the life span of
the network by equilibrate the rate of energy usage by all the
nodes in network. Therefore any node finishes its energy
resources after long time.
2) POWER EFFICIENT AND DELAY AWARE
PROTOCOL (PEDAMACS)
In PEDAMACS there is one access point (AP),
which is also called a sink. This sink has the ability to access
all sensor nodes in single hop [12]. However, the sensor nodes
may use one or more than one hop to approach the sink node.
There are three levels of transmission power defined to reach
three distances: maximum, medium, and minimum. The
protocol has the four different phases- topology learning,
topology collection, scheduling phase and adjustment [8].
Topology learning: In this phase, the access point initially
broadcasts a packet with maximum transmission power in
order to synchronize the nodes. Then, the access point
transmits another packet with medium power which is
retransmitted through the whole network. Therefore all the
nodes in the network get the information about the topology
held by the AP presently. With the help of using the strength
of received signal and interference models, each node can
easily identify its local neighbouring nodes. Since there is no
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scheduling is done till now, so during topology learning
phase, the protocol uses a protocol which is almost similar to
802.11, with RTS and CTS frames.
Topology collection: During this phase, every node transmits
the topology information to AP by using minimum
transmission power. Therefore data may possibly transmit
through many numbers of hops. In topology collection phase
the protocol also utilise the carrier sense multiple access
(CSMA).
Scheduling phase: In this phase, the AP broadcasts the
schedule information. Thus each node in the network can
adjust their clocks and get information about the time slots
assigned to it for transmission and reception. A guard interval
between each time slot is used to compensate the nodes
synchronization errors.
Adjustment: During this phase, the AP make request and the
nodes transmit adjustment topology packets which indicate
any changes in neighbours or interferers. The nodes can also
transmit this information between scheduling phase inside the
data packets [12].
3) PRIORITY BASED MAC PROTOCOL (PRIMA)
This protocol utilizes the procedure as in LEACH
protocol to form the clusters and choose cluster heads [13]. It
also follows the same procedure to control the communication
and to keep synchronize each cluster. The CH will rotate
every fifteen minutes. Four different priorities are defined by
the PRIMA for information by establishing the application
layer to add two bits at the end of each packet. MAC layer
make the use of two different protocols which are- classifier
MAC (C-MAC) and channel access MAC (CAMAC). The CMAC attaches each packet to one of four different queues,
according to their priority. The second protocol which is
CAMAC, make use of carrier sense multiple access/collision
avoidance (CSMA/CA) and time division multiple access
(TDMA) slots. Random access slots are used in order to
permit the different sensor nodes for requesting a time slot and
CH to broadcast the different schedules. Node transmits the
data according to schedule by the use of TDMA slots with no
collisions.
IV.
CHARACTERISTICS OF MAC PROTOCOLS IN
WSN
The MAC protocols are designed to provide the access to
different nodes in the network. The MAC protocols must have
some characteristics. Some important characteristics are as
following:
1) Fairness: Since in the WSN there are a number on
different nodes which will access the medium
according to the need. So a MAC protocol should
provide the equal amount of resources to every node
in the network to increase the fairness of the network.
2) Energy efficient: Since there is limited energy source
in a wireless sensor network and the sensor nodes
have to operate by using these finite energy sources.
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Therefore the MAC protocols must consider these
energy constraints and they must be energy efficient.
3) Reliability: The most common requirement in a
WSN is to get reliability. The MAC protocol used in
the network also affects the reliability of the WSN. A
MAC protocol is reliable if it can detect and recover
the transmission errors and collisions occurring in the
network.
4) Adaptability: Since a WSN is a self managing
network and in such kind of network changes occur
frequently. The changes may be in its topology, size,
traffic etc. So a MAC protocol must be able to adapt
these changes occur in the network without
significant overheads.
V.
[11]
[12]
[13]
[14]
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Energy-Efficient Predictive-Wakeup MAC Protocol for Wireless
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S. C. Ergen and P. Varaiya, “PEDAMACS: Power Efficient And
Delay Aware Medium Access Protocol for Sensor Networks,”
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W.B. Heinzelman, A.P. Chandrakasan, and H. Balakrishnan, “An
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Lewis Adams, “Capitalizing on 802.11 for Sensor Networks”,
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CONCLUSION
The wireless sensor network is a self configuring
network. The sensor nodes are deployed randomly in the
WSN. The sensor nodes are used for data sensing at any
desired location. The communication takes place through a
wireless medium in a WSN.
In this paper we have provided the brief introduction
about the WSN. There are several MAC protocols used in the
WSN. We have discussed some MAC protocols used in the
WSN. There are some characteristics of the MAC protocols
that must be possessed by these. These characteristics are also
discussed in brief.
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