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8/13/2019 Conference PDF

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High Throughput MAC Protocol for Mobile Ad Hoc Networks

Rakesh Sharma. M1 M.tech(CE), G. pradeep reddy

2M.tech(CE), O.ravikumar

3M.tech(CE),

Gerardine Immaculate Mary 4Asst.prof(SR)

School of electronics engineering, VIT university, vellore-632014

[email protected], [email protected],[email protected], [email protected]

ABSTRACT:

One way to improve the throughput of a mobile ad hoc network at the media access layer is to allow

as much as concurrent transmission among neighbouring nodes. In this paper we present a high

throughput MAC protocol, called Concurrent Transmission MAC (CTMAC), which supports concurrent

transmission. To safeguard concurrent transmission, collision avoidance information is included in the

control packets and used by neighbouring nodes to schedule their transmissions. Also, to avoid the

collision between DATA packets and ACK packets, a new ACK sequence mechanism is proposed.

Simulations are done in NS-2. The simulation results shows that a significant gain in throughput can be

obtained by CTMAC protocol compared with the existing IEEE 802.11 MAC protocol.


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High Throughput MAC Protocol for Mobile Ad Hoc Networks

ABSTRACT:

One way to improve the throughput of a

wireless ad hoc network at the media access

layer is to allow as much as concurrent

transmission among neighbouring nodes. In this

paper we present a high throughput MAC

protocol, called Concurrent Transmission MAC

(CTMAC), which supports concurrent

transmission. To safeguard concurrent

transmission, collision avoidance information is

included in the control packets and used by

neighbouring nodes to schedule their

transmissions. Also, to avoid the collision

between DATA packets and ACK packets, a

new ACK sequence mechanism is proposed.

Simulations are done in NS-2. The simulation

results shows that a significant gain in

throughput can be obtained by CTMAC

protocol compared with the existing IEEE

802.11 MAC protocol.

INTRODUCTION

Mobile ad hoc networks (MANET) have gained a

significant attention in the past several years. How

to efficiently utilize the channel remains a great

challenge. IEEE 802.11 DCF [1] has been regarded

as the basic Media Access Control (MAC) protocol

for MANETs. It is based on CSMA/CA (carrier

sense multiple access collision avoidance).With

extension to allow for the exchange of RTS/CTS

(request-to-send/clear-to-send) packets between the

transmitter and receiver before actual transmission

of DATA packets.

IEEE 802.11 DCF is overly restrictive, it prohibitsconcurrent transmission among neighbouring nodes

even when the transmission is possible. In

MANET, a packet can be received successfully

even if there exist other interfering packets, only if

its instantaneous power is larger than instantaneous

joint interference power by minimum threshold

factor. The threshold factor is called signal-to

interference-and noise ratio (SINR).

Fig. 1.scenario

In Fig 1 when the node i sends packets to node j,

after exchanging control packets between node i

and j, the transmissions u to v and m to n both

prohibited until the end of transmission i to j. Thusin fig 1 without considering ACK packets as long

as the required SINR is fulfilled then the DATA

packets of other transmissions can be transmitted

simultaneously. But the ACK packets also collide

with each other or with the DATA packets. For this

to avoid an ACK sequence mechanism has been

proposed. Thus potential concurrent transmission

between neighbouring nodes in a MANET is

possible, which is the main topic of the paper. The

proposed CTMAC protocol has some key features.

First, after successfully exchange of control packets

CTMAC inserts additional control gap (ACG)

between RTS/CTS and DATA packet. The ACG

offers neighbouring nodes to exchange their control

packets and schedule concurrent transmission.

Second, in CTMAC collision avoidance

information is inserted in control packets. This

information used in conjunction with the received

signal strength of the packets by the potentially

interfering nodes to dynamically determine whether

it is possible to schedule their transmission.

Third ,to avoid collision between DATA and ACK

packets CTMAC introduces a new sequence

mechanism.

Finally in CTMAC the concurrent transmission is

controlled locally by the node sin the vicinity of

transmitting/receiving node, depending on the

information they overhear. Thus CTMAC is

asynchronous and does not require any central

control. It is suitable for large scale of ad hoc

networks.


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II. PRELIMINARIES

One essential requirement of CTMAC is that the

schedule transmission should not collide with the

existing transmission. To achieve this, CTMAC

needs to maintain some necessary information. InCTMAC, each node maintains a new data structure

called Active Neighbour List (ANL). ANLi records

node is knowledge about the active nodes in is

vicinity. For every active node in is vicinity, ANLi

contain following information.

{ , , ,

D, }

Where

is the address of the active nodeu.

is the estimated channel gain betweennode i and u.

and are the starting times ofDATA and ACK packets of the

transmission between node u and v.

D is the tag used to distinguish thetransmitter and receiver. If the control

packet is received from a transmitter then

the D tag is set to 1. If the control packet

is from the receiver, then the D tag is set

to 0. MTI is maximum tolerable interference of

a receiver node u, denoted by . This

is maximum additional interference that

node u can tolerate from a neighbouring

node during us DATA transmission.

Another requirement of CTMAC is the DATA

packet of slave transmission must be less than or

equal to the DATA packet of corresponding master

transmission.

III. PROPOSED PROTOCOL

We know describes details of CTMAC, subsection

A we explains operation. In section b describes

ACK sequence mechanism and in section C

concurrency control.

A. Basic operation of CTMAC

First let us consider the example shown in fig.1,the

operation is illustrated in fig 2. To simplify the

description , we only consider the transmission i to

j and u to v. Node i first transmits an RTS packet to

node j, including information such as scheduled

start times of DATA and ACK packets. Node j

replies with a CTS packet which consists of similar

information. After the RTS/CTS packets are

exchanged, node waits for a duration specified by

Fig.2. operation of CTMAC

ACG before sending DATA packet. During this

period node u and v can exchange control packets

and schedule their transmission. If the transmission

is successfully scheduled, then the two

transmissions can be done concurrently and starting

time of both DATA packets is same.

In CTMAC, the CTS packet of original IEEE

802.11 DCF is extended and classified into two

types: normal CTS and negative CTS packet. The

use of normal CTS packet is similar to IEEE

802.11. The negative CTS packet is send when the

slave receiver finds it is impossible for the slave

transmission according to concurrency control

rules.

However just extending the CTS packet is not

enough for concurrent transmission control. First,

the slave transmitter has no way to notify its

neighbouring nodes of adjustment. Second, the socalled cascading lock problem remains unsolved,

which may lead to un necessary channel

reservation. To solve above problem, a packet

called ATS (Abort to send) is used by slave

transmission to inform the neighbours of necessary

information. ATS has two meanings according to

the situation it is used: first is when the slave

receiver disagrees with the values scheduled by

slave transmitter. Second situation is when it is

impossible for the slave receiver to get the data

packet from the slave transmitter.


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IV. SIMULATION RESULTS:

Parameters used in simulation

Propagation model Two ray ground

Data packet size 2Kb

Data rate 2Mbps

SINR 6 dB

Receive sensitivity -94dBm

Receive threshold -82dBm

Transmit power 15dBm

Transmission range 400m

Carrier-sense range 800m

A. Line topology

Fig 5. Line topology

Consider the topology shown in fig 5.the distance

between nodes also shown in fig. Node i is

transmitting to node j, node n is transmitting to

node m. Node n always have packets to send. All

the nodes are in each other transmission ranges,

there can be only one transmission at any time

under the scheme of IEEE 802.11 DCF.

In CTMAC, both transmissions may proceed

simultaneously. At the beginning, the node is

transmission prohibits node m from correctly

receiving node ns DATA packet, because its SINR

is violated. The node m is moving towards n at

10m/s and after 5 seconds SINR is satisfied and

two transmissions can take Place. We can see the

increase in throughput from the figure 6.

Fig 6.through put of line topology

B. Random topology

We evaluate the performance of CTMAC under

random topology. We consider two simulations

under this topology one for 20 nodes and another

for 100 nodes. Assuming there are m end to end

flows in the network. For each flow, the source

node is saturated and always has packet to send. To

better understand the throughput we use end to end

throughput.

The simulation results are plotted in fig 7a and fig

7b for 20 and 100 nodes respectively.

Fig 7a.throughput of random topology for 20 nodes

Fig 7b throughput of random topology for 100

nodes.


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V. CONCLUSION:

In this paper we proposed CTMAC, a high

throughput media access control protocol for

MANET. Through simulation we evaluated and

compared the performance of CTMAC with IEEE802.11 scheme. The simulation results showed that

CTMAC increases the network throughput

compared to other protocols.

REFERENCES

1. IEEE computer society LAN MAN standards

committee Ed.international standard ISO/IES8802-

11; PART 11: wireless LAN Medium Access

Control (MAC) and physical layer (PHY)

specifications.

2. J.H.Kim and J.K.Lee capture effects of wireless

CSMA/CA protocols in Rayleigh and shadow

fading channels.

3. NS-2 software http://nsnam.isi.edu

4. communication networks and fundamental

concepts and key architectures by Leon-Garcia &

Indra Widjaja

5. T.S.Rappaport and L.B.Milstein Effects of

radio propagation path loss on DS-CDMA cellularfrequency reuse for reverse channel.

6. M.krunz POWMAC-single channel power

control protocol for throughput enhancement in

wireless ad hoc network.

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