Access Methods for Mobile Ad Hoc Networks

1
Access Methods for Mobile Ad Hoc Networks
(MANET)
Nishitha Ayyalapu KUID 2335165
2
Outline

• Introduction
• 2. Effect of Mobility on Protocol Stack
• 3. Challenges in Mobile Environment
• 4. Goals of MAC in MANET
• 5. Issues in Designing MAC for MANET
• 6. Performance Metrics
• General Broad Classification of MAC
• DCF of IEEE 802.11
• Performance Limitations of DCF with MANET
• Enhancement of Channel Utilization
• Enhancements in RTS/CTS Mechanism
• Enhancements in Backoff Algorithm
• Multi Channel MAC Schemes
• Transmission power control MAC Schemes
• Others.
• Conclusions
• References

3
Introduction

• Classification of Wireless Networks
• Single Hop vs. Multi-Hop Wireless Networks
• What is a MANET ?
• Need for MANETS ?

4
Classification of Wireless Networks

• Infrastructured Networks
• These are the networks with fixed gateways.
• The bridges for these networks are known as base
  stations.
• Handoffs occur.
• Eg wireless local area networks (WLANs),
  Cellular Systems
• Infrastructure-less Networks
• No fixed routers all nodes are capable of
  movement and can be connected dynamically in an
  arbitrary manner.
• Nodes of these networks function as routers which
  discover and maintain routes to other nodes in
  the network.
• Example applications of ad-hoc networks are
  emergency search-and-rescue operations, meetings
  or conventions in which persons wish to quickly
  share information, and data acquisition
  operations in inhospitable terrains.

5
Single-Hop Vs. Multi-Hop

• Single-Hop Wireless Connectivity
• Space divided into cells
• A base station is responsible to communicate with
  hosts in its cell
• Mobile hosts can change cells while communicating
• Hand-off occurs when a mobile host starts
  communicating via a new base station
• Multi-Hop Wireless Connectivity

• May need to traverse multiple links to reach
  destination.
• Mobility causes route changes

From Tutorial at CIT2000. Bhubaneshwar, Dec
20-23. Sridhar Iyer. IIT Bombay
www.it.iitb.ac.in/sri/talks/manet.ppt
6
What is a MANET ?

• A MANET can be defined as a collection of
  wireless mobile nodes (e.g., portable computers
  or PDAs) that form a dynamically changing
  network, without using any existing network
  infrastructure or centralized administration.
• Can be Single-hop or Multi-hop.
• But, Mostly Multi-hop. Hence, a mobile ad hoc
  network is sometimes also called a Multihop
  wireless network.

7
Need for MANET ?

• Do not need backbone infrastructure support
• Are easy to deploy
• Useful when infrastructure is absent, destroyed
  or impractical
• Many Applications
• Personal area networking
• cell phone, laptop, ear phone, wrist watch
• Military environments
• soldiers, tanks, planes
• Civilian environments
• taxi cab network
• meeting rooms
• sports stadiums
• boats, small aircraft
• Emergency operations
• search-and-rescue
• policing and fire fighting

8
Effect of Mobility on Protocol Stack

• Application
• - new applications and adaptations
• Transport
• - congestion and flow control
• Network
• - addressing and routing
• Link
• - media access and handoff
• Physical
• - transmission errors and interference

9
Challenges in Mobile Environment

• Limitations of the Wireless Network
• packet loss due to transmission errors
• frequent disconnections/partitions
• limited communication bandwidth
• Broadcast nature of the communications
• Limitations Imposed by Mobility
• dynamically changing topologies/routes
• lack of mobility awareness by system/applications
  
• Limitations of the Mobile Computer
• short battery lifetime
• limited capacities

10
Goals of MAC in MANET

• High channel efficiency
• Low power
• Scalability
• Fairness
• Support for prioritization
• Distributed operation
• QoS support
• Low control overhead

11
Issues in Designing MAC Protocol for MANET

• Hidden Node Problem
• A hidden node is a node which is out of range of
  a transmitter node (node A in Figure ), but in
  the range of a receiver node (node B in Figure ).
  
• A hidden node does not hear the data sent from a
  transmitter to a receiver (node C is hidden from
  node A). When node C transmits to node D, the
  transmission collides with that from node A to
  node B.
• The hidden nodes lead to higher collision
  probability. Generally, the probability of
  successful frame transmission decreases as the
  distance between source and destination increases
  and/or the traffic load increases.

From Medium access control protocols for
wireless mobile ad hoc networks issues and
approaches, Teerawat Issariyakul, Ekram Hossain,
and Dong In Kim, Wirel. Commun. Mob. Comput.
2003 3935958 (DOI 10.1002/wcm.118) http//cite
seer.ist.psu.edu/cache/papers/cs2/137/httpzSzzSzw
ww.win.trlabs.cazSzteerawatzSzpublicationszSzWCMC
_Dec03MAC_survey.pdf/issariyakul03medium.pdf
12
Issues in Designing MAC Protocol for MANET

• Exposed Node Problem
• An exposed node (node C is exposed to B in Figure
  ) is a node which is out of range of a receiver
  (node A), but in the range of the corresponding
  transmitter (node B).
• Node C defers transmission (to node D) upon
  detecting data from node B, even though a
  transmission from node C does not interfere with
  the reception at node A.
• The link utilization may be significantly
  impaired due to the exposed node problem. This
  would impact the higher layer protocol (e.g. TCP)
  performance considerably.

From Medium access control protocols for
wireless mobile ad hoc networks issues and
approaches, Teerawat Issariyakul, Ekram Hossain,
and Dong In Kim, Wirel. Commun. Mob. Comput.
2003 3935958 (DOI 10.1002/wcm.118) http//cite
seer.ist.psu.edu/cache/papers/cs2/137/httpzSzzSzw
ww.win.trlabs.cazSzteerawatzSzpublicationszSzWCMC
_Dec03MAC_survey.pdf/issariyakul03medium.pdf
13
Issues in Designing MAC Protocol for MANET

• Radio Link Vulnerability
• Wireless channel capacity is limited due to high
  bit-error rate.
• Causes noise, interference, free space loss,
  shadowing and multipath fading.
• The radio link vulnerability may tremendously
  impact the utilization of the radio channel (s)
  and the service fairness among different mobile
  nodes (and flows).
• Control Measures Forward error correction (FEC)
• Automatic repeat request (ARQ)
  have been developed.
• Unfortunately, they result in inefficient
  bandwidth utilization. Again, increase in
  transmission power to combat with the above
  undesirable radio propagation properties can
  broaden interference region, thereby resulting in
  the reduction of spatial reuse.
• Capture Effect
• Capture is an ability of a mobile node to
  perfectly receive a signal (presumably one with
  the dominating signal level) in the presence of
  more than one simultaneous transmissions.
• Improves the utilization of the channel, but it
  may cause unfairness among mobile nodes.

14
Performance Metrics

• Throughput and Delay
• Throughput is generally measured as the
  percentage of successfully transmitted radio link
  level frames per unit time. Transmission delay is
  defined as the interval between the frame arrival
  time at the MAC layer of a transmitter and the
  time at which the transmitter realizes that the
  transmitted frame has been successfully received
  by the receiver.
• Fairness
• Generally, fairness measures how fair the
  channel allocation is among the flows in the
  different mobile nodes. The node mobility and the
  unreliability of radio channels are the two main
  factors that impact fairness.
• Energy Efficiency
• Generally, energy efficiency is measured as the
  fraction of the useful energy consumption (for
  successful frame transmission) to the total
  energy spent.
• Multimedia Support
• It is the ability of an MAC protocol to
  accommodate traffic with different service
  requirements such as throughput, delay and frame
  loss rate.
• Vulnerable Period
• Time interval during which for a node to transmit
  a packet successfully without collisions, other
  interfering nodes should not attempt to transmit
  during the nodes transmission time

15
General Broad Classification of MAC

• Fixed-Assignment Channel Access
• In this, nodes are statically allocated a certain
  time slot (frequency band or spread spectrum
  code), as is the case for most of voice-oriented
  wireless networks.
• TDMA
• FDMA
• CDMA
• Random Access Methods
• Here the sender dynamically competes for a time
  slot with other nodes. This is a more flexible
  and efficient method of managing the channel in a
  fully distributed way, but suffers from
  collisions and interference.
• Pure Aloha
• Slotted Aloha
• Carrier-Sensing Mechanisms(-for MANET-Why?)

16
Basic DCF (Distributed Coordination Function) of
IEEE 802.11 MAC

• 802.11 MAC
• The 802.11 MAC is designed to provide mandatory
  asynchronous data service along with an optional
  time-bounded service that is only usable in an
  infrastructured wireless networks with access
  points.
• The asynchronous data service is usable by both
  ad hoc networks and infrastructured wireless
  networks
• Distributed coordination function (DCF)
• The mandatory basic asynchronous service is
  provided by a method known as carrier sense
  multiple access with collision avoidance
  (CSMA/CA) and an optional channel reservation
  scheme based on a four-way handshake between the
  sender and receiver nodes.
• These two methods provides the mechanism for
  achieving distributed coordination amongst
  uncoordinated wireless terminals that do not use
  a fixed access point (i.e, infrastructureless
  networks), and are known as the Distributed
  coordination function (DCF).
• Therefore DCF provides two access Mechanisms
• 1. Two-Way Handshake i.e., DATA/ACK.
• 2. Four-Way Handshake i.e., RTS/CTS/DATA/ACK

17
DCF of IEEE 802.11 MAC

• Key Elements
• ACK
• - For Collision Detection
• 2. RTS/CTS and NAV
• - For Solving Hidden Terminal Problem
• IFS
• - For Prioritized Access to the Channel
• Backoff Algorithm with Contention Window
• - To Provide Fair Access with Congestion Control

18
DCF

• ACK for Collision Detection
• ACKnowledgement (ACK) packets enable a mobile
  node to determine whether its transmission was
  successful or not.
• The sender is made aware of the collision after
  it times out waiting for the corresponding ACK
  for the packet transmitted.
• If no ACK packet is received or an ACK is
  received in error, the sender will contend again
  for the medium to retransmit the data packet
  until the maximum allowed number of
  retransmissions has been tried.
• If all fails, the sender drops the packet
  consequently leaving it to a higher level
  reliability protocol.
• 2. RTS/CTS and NAV for Solving Hidden Terminal
  Problem
• Four-way handshake based on Request-To-Send (RTS)
  and Clear-To-Send (CTS) packets is used to avoid
  collisions from the nodes hidden in the
  vulnerable region.
• By exchanging the two short control packets
  between a sender and a receiver, all neighboring
  nodes recognize the transmission and back off
  during the transmission time advertised along
  with the RTS and CTS packets.
• Network Allocation Vector (NAV)
• Increased Control Overhead.
• RTSThreshold

19
DCF

• IFS for Prioritized Access to the Channel
• Inter-Frame Spacing (IFS) is the time interval
  during which each node has to wait before
  transmitting any packet and is used to provide a
  prioritized access to the channel.
• DCF IFS (DIFS) is larger than SIFS and is used
  when initiating a data transfer. When RTS/CTS is
  used, the RTS packet can be transmitted after
  waiting for DIFS duration of time.
• Short IFS (SIFS) is the shortest and is used
  after receiving a DATA packet to give the highest
  priority to an ACK packet. All other frames (CTS,
  DATA, and ACK) use SIFS before attempting to
  transmit.

From Medium Access Control Mechanisms in Mobile
Ad Hoc Networks , Chansu Yu, Ben Lee, Sridhar
Kalubandi, Myungchul Kim, http//web.engr.oregonst
ate.edu/benl/Publications/Book_Chapters/MCH_MAC_A
dHoc05.pdf
20
DCF

• 4. Backoff Algorithm with CW to Provide Fair
  Access with Congestion Control
• IFS is followed by an additional waiting time
  defined by the backoff algorithm. After waiting
  for the IFS duration, each competing node waits
  for a backoff time, which is randomly chosen in
  the interval (0, CW), defined as contention
  window.
• The main purpose of the backoff algorithm is to
  reduce the probability of collisions when
  contention is severe.
• DCF employs Binary Exponential Backoff
  Algorithm. The flow chart of algorithm is as
  below

21
DCF
Flow Chart of BEB Algorithm in DCF
From Medium Access Control Mechanisms in Mobile
Ad Hoc Networks , Chansu Yu, Ben Lee, Sridhar
Kalubandi, Myungchul Kim, http//web.engr.oregonst
ate.edu/benl/Publications/Book_Chapters/MCH_MAC_A
dHoc05.pdf
22
Performance Limitations of DCF with MANET

• Though RTS/CTS option of DCF reduces hidden
  terminal problem, it exacerbates exposed node
  problems
• Though it simple to implement, it can be
  overly conservative, leading to low spatial
  re-use, low energy efficiency and as well as high
  co-channel interference.
• Additional Control Overhead
• Collisions of Control Packets
• Radio Interference
• Capture Effect
• Low Spatial re-use
• BEB suffers from both fairness and efficiency
• According to Simulation Results
• The theoretical throughput is bounded by around
  80 when the typical DCF parameters are used
  (with propagation delay of 1 ms and packet size
  of 50msec5msec). In reality, DCF operates very
  far from the theoretical limits due to collisions
  and control overhead associated with RTS/CTS and
  the backoff algorithm.
• In a multihop MANET, the situation becomes
  worse. It was shown that end-to-end throughput is
  at most 1/4 of the channel bandwidth even without
  any other interfering nodes. This is mainly due
  to collisions among intermediate forwarding nodes
  of the same data stream
• In addition, the control overhead of DCF
  aggravates the situation and the maximum
  throughput is reduced to about 1/7 of the channel
  bandwidth

23
Enhancement of Channel Utilization

• 1. Enhancing RTS/CTS Mechanism
• 2. Enhancing Exponential Backoff Algorithm
• a.) Conservative CW Restoration to Reduce
  Collisions
• - MILD
• b.) Dynamic Tuning of CW to Minimize the
  Collision Probability
• 3. Multi Channel MAC Schemes
• a.) Schemes with a Common Control Channel
• - BTMA
• - DBTMA
• b.) Schemes without a Common Control Channel
• - ICSMA
• - JMAC
• Transmission power control MAC Schemes
• - PCMA
• - BPCMP
• 5. Others.

Enhancing Temporal Channel Utilization
Enhancing Spatial Channel Utilization
24
Enhancement of Channel Utilization

• Enhancements in RTS/CTS Mechanism
• Optimal Setting of RTSThreshold to Tradeoff
  between Control and Collision Overhead
• Better idea would be to adjust the parameter
  depending on the traffic and the collision
  probability.
• Simulation Results (by Khurana and Weinmiller)
• optimal RTSThreshold 200-500 bytes.
• 2. Enhancements in Backoff Algorithm
• a.) Conservative CW Restoration to Reduce
  Collisions
• Goal is to address the fairness and collision
  problem in the DCF backoff algorithm

From Medium Access Control Mechanisms in Mobile
Ad Hoc Networks , Chansu Yu, Ben Lee, Sridhar
Kalubandi, Myungchul Kim, http//web.engr.oregonst
ate.edu/benl/Publications/Book_Chapters/MCH_MAC_A
dHoc05.pdf
25
Enhancement of Channel Utilization

• Solutions MILD back off algorithm.
• MILD (Multiplicative Increase Linear Decrease)
• Bharghavan et al. proposed a Multiplicative
  Increase and Linear Decrease (MILD) algorithm
  where the contention window size increases
  multiplicatively on collisions but decreases
  linearly on successful transmission.
• In MILD, the backoff interval is increased by
  a multiplicative factor (1.5) upon a collision
  and decreased by 1 step upon a successful
  transmission, where step is defined as the
  transmission time of a RTS frame.
• The linear decrease sometimes is too
  conservative, and it suffers performance
  degradation when the traffic load is light or the
  number of active nodes changes sharply because of
  the additional delay incurred to return the CW to
  CWmin.
• Used in MACAW protocol.

26
Enhancement of Channel Utilization

• b.) Dynamic Tuning of CW to Minimize the
  Collision Probability
• Cali et al. observed that the collision
  probability increases as the number of active
  nodes increases.
• There is need for dynamic control of this
  collision probability, but the static backoff
  algorithm of DCF does not address.
• Adaptive contention schemes has been proposed,
  where optimal setting of CW, and thus the optimal
  backoff time for the next transmission can be
  achieved by estimating the number of active nodes
  in its vicinity at run time.
• Each node can estimate the number of empty
  slots in a virtual transmission time by observing
  the channel status, the number of active nodes
  can be computed and exploited to select the
  appropriate CW without paying the collision
  costs.
• Summary
• From 2

27
Enhancement of Channel Utilization

• Multi Channel MAC Schemes
• In IEEE 802.11 protocols ,schemes use only one
  channel for all kinds of packets, such as RTS/
  CTS/ DATA/ ACK. To avoid the collisions, the
  bidirectional exchanges of these packets
  significantly limit the spatial reuse due to the
  coupling of hidden and exposed terminal problems.
• The other approach to reduce collisions between
  different kinds of packets is to exploit the
  advantage of multiple channels, and transmit
  different kinds of packets over different
  separate channels
• a.) Schemes with a Common Control Channel
• These schemes use a separate channel for
  transmitting control packets, such as RTS and
  CTS, and one or more channels for transmitting
  data and acknowledgements, i.e., DATA and ACK.
• - BTMA (Busy Tone Multiple Access)
• - DBTMA (Dual Busy Tone Multiple Access)
• b.) Schemes without a Common Control Channel
• Unlike those schemes that use a common control
  channel, this kind of schemes does not rely on
  it. Instead, they are flexible in arranging
  different channels for RTS/ CTS/ DATA/ ACK to
  reduce collisions.
• - ICSMA (Interleaved CSMA)
• - JMAC (Jamming based MAC)

28
Enhancing Channel Utilization

• BTMA (Busy Tone Multiple Access)
• BTMA scheme splits the single common channel
  into two sub-channels a data channel and a
  control channel.
• Base station broadcasts an out of band busy tone
  signal to keep the hidden terminals from
  accessing the channel when it senses a
  transmission.
• Does not address exposed nodes problem and also
  it requires additional channels and transceivers.
• The busy tone channel must be close to the DATA
  channel and hence can have similar channel gain
  to that of the DATA channel, and there must also
  be enough spectral separation between these
  channels to avoid inter-channel interference.

29
Enhancing Channel Utilization

• DBTMA (Dual Busy Tone Multiple Access)
• Splits one common channel into two
  sub-channels
• One Data channel For Data Packets.
• One Control Channel Two Control Packets
  (RTS and CTS) Two busy tones (BTt and BTr).
• Transmit Busy Tone BTt
• Set by the transmitter node to indicate that
  it is transmitting on the data channel. All nodes
  that sense BTt do
• not attempt to receive. And all exposed nodes
  are prevented from becoming new receivers.
• Receive Busy Tone BTr
• Set by the Receiver node to indicate that it
  is receiving on the data channel. All the nodes
  that sense BTr do
• defer their transmissions. i.e, All Hidden
  nodes are prevented from becoming new
  transmitters.
• Exposed Terminals can sense BTt but not BTr
  so that they can safely reuse the space by
  transmitting
• their packets.
• Drawback No ACKs are sent to acknowledge a
  transmitted DATA packet, makes it worst suited
  for unreliable

From 2
30
Enhancing Channel Utilization

• ICSMA (Interleaved CSMA)
• It divides the entire bandwidth into two
  channels of equal bandwidth and employ one
  half-duplex transceiver for each channel and it
  is flexible in arranging different channels for
  RTS/ CTS/ DATA/ ACK to reduce collisions.
• The transmitter sends RTS and DATA on one
  channel, and the receiver responds by sending CTS
  and ACK on the other channel.
• Supports simultaneous transmissions between two
  nodes when one node is sending RTS or DATA, or
  receiving CTS or ACK from the other node, the
  latter one is also sending the same kind of
  packets at a different channel to the former one.
• JMAC (Jamming based MAC)
• In JMAC, the medium is divided into two
  channels S channel and R channel.
• S Channel RTS, DATA and jamming signal are
  transmitted.
• R Channel CTS and ACK are transmitted.
• Transmitter also sends a jamming signal on S
  channel, while it waiting or receiving CTS/ACK on
  R Channel.
• Receiver, while it is waiting or receiving
  RTS/DATA on S channel it jams the R channel to
  prevent neighboring nodes from transmitting RTS
  frames on the S channel.
• Effectively resolves Hidden Terminal problem.
• It will stop if the RTS/CTS exchange fails, it
  resolves the erroneous reservation problem in the
  IEEE 802.11 protocol.
• Drawbacks Jamming signal is of sufficient
  energy and can cause the medium to become busy.

31
Enhancing Channel Utilization

• 4. Transmission Power Control MAC Schemes
• Mobile nodes are usually powered by batteries
  that provide only a limited amount of energy, how
  to reduce the energy consumption is of great
  importance for providing QoS (quality of service)
  assurance for MANET.
• IEEE 802.11 MAC protocol though avoids the
  collisions caused by hidden terminal problem in
  MANETs, and is widely used, there is no
  consideration of power control in the protocol at
  all. Hence, consumes significant battery power
  since transmitters send all kinds of packets at
  the same transmitting power level all the time.
• Benefits from energy conserving schemes
• - Minimal Transmit power
• - Improvement in Spatial reuse
• - Reduction in Co-channel
  interference.
• One way to reduce energy consumption in MAC
  protocol design is using transmission power
  control MAC schemes.
• The main idea of these power control schemes is
  to use a maximum possible power level for
  transmitting RTS/CTS and the lowest acceptable
  power for sending DATA/ACK.
• - BPCMP (Basic Power Control
  MAC Protocol)
• - PCMA (Power Control Multiple Access)

32
Enhancing Channel Utilization

• BPCMP (Basic Power Control MAC Protocol)
• BPCMP is a power controlled MAC protocol that
  can be incorporated into the IEEE 802.11 protocol
  and which allows a node to specify its current
  transmit power level according to different
  packet types.
• Unlike IEEE 802.11 which sends all packets at
  the same power level, BPCMP sends RTS/CTS packets
  using the maximum possible power level pmax,but
  sends DATA/ACK packets at the lowest acceptable
  power level pdesired.
• The transmit power levels will affect the radio
  range, battery life time, and capacity of the
  network.
• Timing diagram and Ranges of different power
  levels in BPCMP is as below

From Autonomous Power Control MAC Protocol for
Mobile Ad Hoc Networks,Hsiao-Hwa Chen, Zhengying
Fan, and Jie Li, EURASIP Journal on Wireless
Communications and Networking Volume 2006,
Article ID 36040, Pages 110 DOI
10.1155/WCN/2006/36040 http//www.hindawi.com/GetA
rticle.aspx?doi10.1155/WCN/2006/36040
33
Enhancing Channel Utilization

• In BPCMP, the desired power level for
  transmitting DATA/ACK is determined after RTS/CTS
  handshake. The procedures for a complete
  transmission cycle are described as follows
• 1. The transmitter sends RTS packets using
  the maximum possible power level pmax.
• 2. The receiver receives the RTS at signal
  power prec, and calculates the minimum desired
• transmit power level pdata for
  transmitting data packets as follows
• where Rxthresh is the lowest acceptable
  received signal strength. Then, the receiver
  marks
• the minimum desired transmit power level
  in the control message field of CTS and sends
• CTS back to the transmitter.
• 3. Once having received CTS, the transmitter
  begins to transmit data packet using the power
• level pdata.
• 4. The receiver sends back an ACK as soon as
  it receives DATA. The transmitting power level
• for sending ACK is determined in a
  similar way as done for DATA.

34
Enhancing Channel Utilization

• Problems with BPCMP
• Using the fixed transmitting power level, pmax,
  for RTS/CTS is not energy efficient since the
  distance between the transmitter and the receiver
  may change from time to time.
• The transmission at maximum possible power level
  causes to interfere other existing radio
  applications.
• Different transmitting power levels result in
  asymmetric topologies, and thus may consume more
  energy.
• BPCMP was proposed under the assumption that
  signal attenuation between transmitters and
  receivers is kept the same in both transmission
  directions. It may make the communications
  unreliable if the assumption is not held.

35
Enhancing Channel Utilization

• PCMA (Power Control Multiple Access)
• The Power Controlled Multiple Access (PCMA)
  Protocol proposes flexible variable bounded
  power collision suppression model that allows
  variable transmit power levels on a per-packet
  basis.
• Source-destination pair uses Request power to
  send (RPTS) and Acceptable power to send (APTS)
  handshake to compute the optimal transmission
  power based on their received signal strength,
  which will be used when transmitting data
  packets.
• PCMA also uses the busy tone channel to
  advertise the noise level the receiver can
  tolerate. During data transmission periods, each
  active receiver will periodically send a busy
  tone to advertise the maximum additional noise
  power it can tolerate.
• A potential transmitter first senses the busy
  tone to detect the upper bound of its
  transmission power for all control and data
  packets.
• PCMA protocol with busy tone is as shown below

From 2
36
Enhancing Channel Utilization

• Merits of PCMA
• PCMA works effectively in energy conservation
  since it allows more concurrent data transmission
  compared with IEEE 802.11 standard by adapting
  the transmission ranges to be the minimum value
  required for successful reception on the receiver
  side.
• Results show that PCMA can improve the throughput
  performance by more than a factor of 2 compared
  to the IEEE 802.11 for highly dense networks.
• The throughput gain over 802.11 will continue to
  increase as the connectivity range is reduced.
• The power controlled transmission in PCMA helps
  increase channel efficiency at the same time
  preserving the collision avoidance property of
  multiple access protocols.

37
Enhancing Channel Utilization

• Other Possible Channel Utilization Enhancement
  Schemes
• Antenna Based Mechanisms
• Rate Adaptive MAC schemes
• Fairness Enhanced MAC Schemes
• Power off Mechanisms (another energy conserving
  MAC protocol design).
• Summary of Enhancing spatial channel Utilization
  (From 2)

38
Conclusions

• Mobile ad hoc networks are composed of nodes that
  are self-organizing and communicate over wireless
  channels usually in a multi-hop fashion. They
  exhibit dynamic topology, share limited
  bandwidth, with most nodes having limited
  processing abilities, and energy constraints.
• We have discussed about the effect of mobility
  on protocol stack, challenges in mobile
  environment and issues in designing MAC protocol
  for MANET.
• We have considered some of the Enhancement
  techniques in the design of medium access control
  protocols with DCF of IEEE 802.11 as a reference
  model.
• Each of these schemes tries to maximize network
  capacity, reduce congestion at the MAC layer, and
  ensure fairness by balancing the control overhead
  to avoid collisions.
• Key techniques used to enhance temporal
  utilization is to optimize the DCF parameters
  such as RTSThreshold and those associated with
  the backoff algorithm, which is used to avoid
  collisions in DCF.
• Key techniques used to enhance Spatial channel
  utilization are Multi Channel MAC, transmission
  power control.
• Among these, Transmission power control methods
  not only help in reducing interference but also
  in energy conservation.

39
References

• 1Tutorial at CIT2000. Bhubaneshwar, Dec 20-23.
  Sridhar Iyer. IIT Bombay
• www.it.iitb.ac.in/sri/talks/manet.ppt
• 2 Medium Access Control Mechanisms in Mobile
  Ad Hoc Networks , Chansu Yu, Ben Lee, Sridhar
  Kalubandi, Myungchul Kim,
• http//web.engr.oregonstate.edu/benl/Publications
  /Book_Chapters/MCH_MAC_AdHoc05.pdf
• 3Medium access control protocols for wireless
  mobile ad hoc networks issues and approaches,
  Teerawat Issariyakul, Ekram Hossain, and Dong In
  Kim, Wirel. Commun. Mob. Comput. 2003 3935958
  (DOI 10.1002/wcm.118) http//citeseer.ist.psu.edu
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• 4 Autonomous Power Control MAC Protocol for
  Mobile Ad Hoc Networks,Hsiao-Hwa Chen, Zhengying
  Fan, and Jie Li, EURASIP Journal on Wireless
  Communications and Networking Volume 2006,
  Article ID 36040, Pages 110 DOI
  10.1155/WCN/2006/36040. http//www.hindawi.com/Get
  Article.aspx?doi10.1155/WCN/2006/36040
• 5 A Survey, Classification and Comparative
  Analysis of Medium Access Control Protocols for
  Ad Hoc Networks, Raja Jurdak, Cristina Videira
  Lopes, and Pierre Baldi, IEEE Communications
  Surveys, FIRST QUARTER 2004, VOLUME 6, NO. 1
• http//www.comsoc.org/livepubs/surveys/public/2004
  /jan/pdf/jurdak.pdf
• 6Mobile Ad Hoc Networks, Asis Nasipuri,
  http//citeseer.ist.psu.edu/cache/papers/cs/31158/
  httpzSzzSzwww.ece.uncc.eduzSzanasipurzSzpubszSza
  dhoc.pdf/mobile-ad-hoc-networks.pdf
• 7 Medium Access Control in Mobile Ad Hoc
  Networks Challenges and Solutions,Hongqiang
  Zhai, Jianfeng Wang, Xiang Chen, and Yuguang Fang
  
• http//www.ecel.ufl.edu/jwang/publications_files/
  macsurvey.pdf

40
References

• 8 E. M. Royer, S.-J.Lee, and C. E. Perkins,
  "The Effects of MAC Protocols on Ad Hoc Network
  Communication," Proc. WCNC 2000.
• http//www.hpl.hp.com/personal/Sung-Ju_Lee/abstrac
  ts/papers/wcnc2000c.pdf
• 9 Energy-efficient MAC layer protocols in ad
  hoc Networks Fang Liu, Kai Xing, Xiuzhen Cheng,
  Shmuel Rotenstreich
• Resource Management in Wireless Networking 2004
  Kluwer Academic Publishers
• http//www.seas.gwu.edu/cheng/Publication/PowerMA
  CSurvey.pdf
• 10 Mobile Ad-Hoc Networks Silvia Giordano
• http//portal.acm.org/citation.cfm?collGUIDEdlG
  UIDEid512336
• 11 An Overview of Wireless Ad hoc Networks
  Challenges and Future Yi Wang
• http//www.net-glyph.org/wangyi/papers/Mobile20
  Ad20hoc_Survey.pdf
• 12 Research Issues for Data Communication in
  Mobile Ad-Hoc Network Database SystemsLeslie D.
  Fife, Le Gruenwald
• http//www.cs.ou.edu/database/documents/fg03.pd
  f

41
Chronological MAC Protocol Classification for
MANET
From 5
42
Comparisions