Design Issues In Adhoc Wireless MAC Protocol

YEAR- 2018-19
SUBMMITTED TO
CSA DEPARTMENT
SUBMMITTED BY
DUSHHYANT KUMAR
MEDIUM ACCESS CONTROL 1

 The major issues that affect the design,
deployment, & performance of an ad hoc
wireless network system are
 Medium Access Control (MAC)
 The primary responsibility of a Medium Access Control
(MAC) protocol in ad hoc wireless networks is the
distributed arbitration for the shared channel for
transmission of packets.
 The major issues to be considered in designing a MAC
protocol for ad hoc wireless networks are as follows :
MEDIUM ACCESS CONTROL
3

1. Distributed Operation
2. Synchronization
3. Hidden Terminals
4. Exposed terminals
5. Throughput
6. Access delay
7. Fairness
8. Real-time Traffic support
9. Resource reservation
10. Ability to measure resource availability
11. Capability for power control
12. Adaptive rate control
13. Use of directional antennas
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Distributed Operation
 Ad hoc wireless network do not have central coordinator to
distribute bandwidth fairly among nodes.
 Therefore nodes must be scheduled in a distributed fashion for
gaining access to the channel and for this exchange of control
information among nodes is required.
 Therefore the MAC protocol design should be fully distributed
and must make sure that the additional overhead incurred due to
this control information exchange is not Elevated.
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Distributed Operation
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Synchronization
 Synchronization is very important for bandwidth reservations by
nodes.
 The MAC protocol must take into consideration the
synchronization between nodes in the network.
 The MAC protocol design should take into account the
requirement of time synchronization. Synchronization is
mandatory for TDMA-based systems for management of
 transmission and reception slots. Synchronization involves usage
of scarce resources such as bandwidth and battery power.
 The control packets used for synchronization can also increase
collisions in the network.
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8
Time Synchronization
Nodes
Nodes
Wireless Network
Wireless Network

 Hidden Terminals
 Hidden terminals are nodes that are hidden(or not reachable) from
the sender of a data transmission session, but are reachable to the
receiver of the session.
 In such cases, the hidden terminal can cause collisions at the receiver
node.The presence of hidden terminals can significantly reduce the
throughput of a MAC protocol used in ad hoc wireless networks.
 Exposed terminals
 Exposed terminals, the nodes that are in the transmission range of the
sender of an on –going session, are prevented from making a
transmission.
 In order to improve the efficiency of the MAC protocol, the exposed
nodes should be allowed to transmit in a controlled fashion without
causing collision to the on-going data transfer.
9

Throughput
 The MAC protocol employed in ad hoc wireless networks should
attempt to maximize the throughput of the system.
 The important considerations for throughput enhancement are
 Minimizing the occurrence of collisions.
 Maximizing channel utilization and Minimizing control overhead.
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Access delay
 The average delay that any packet experiences to get transmitted.
The MAC protocol should attempt to minimize the delay.
Fairness
 Fairness refers to the ability of the MAC protocols to provide an
equivalent share or weighted share of the bandwidth to all
competing nodes.
 Fairness can be either node-based or flow based.
 The former attempts to provide an equal bandwidth to all
competing nodes where the later provides an equal share for
competing data transfer session.
12

 In ad hoc wireless network fairness is important due to the multi-
hop relying done by the node.
13
FairnessDistribution

Real-time Traffic support
 In a contention-based channel access environment, without any
central coordination, with limited bandwidth, and with location-
dependent contention, supporting time- sensitive traffic such as
voice, video, and real-time data requires explicit support from the
MAC protocol.
Resource reservation
 The provisioning of QoS defined by parameters such as
bandwidth, delay, and jitter requires reservation of resources such
as bandwidth,buffer space,and processing power.
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Ability to measure resource availability
 In order to handle the resources such as bandwidth efficiently and
perform call admission control based on their availability, the
MAC protocol should be able to provide an estimation of resource
availability at every node.
 This can also be used for making congestion control decisions.
15

 Capability for power control
 The transmission power control reduces the energy consumption at
the nodes, causes a decrease in interference at neighboring nodes,
and increases frequency reuse.
 Support for power control at the MAC layer is very important in the ad
hoc wireless environment.
 Adaptive rate control
 This refers to the variation in the data bit rate achieved over a
channel.
 A MAC protocol that has adaptive rate control can make use of a high
data rate when the sender and receiver are nearby & adaptively
reduce the data rate as they move away from each other.
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 Use of directional antennas
 This has many advantages that include increased spectrum reuse,
Reduction in interference and Reduced power consumption.
 MAC protocols that use omni directional antennas do not work with
directional antennas.
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Adaptive Rate Control

Topology control with Directional Antennas
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Design Issues In Adhoc Wireless MAC Protocol

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