International Journal of Engineering Trends and Technology (IJETT) – Volume 6 Number 7- Dec 2013
Ch. Ravindra Kumar
*
, M.V.Rajesh
#
*
M.Tech Scholar,
#
Sr. Assistant professor
*#
Dept of CSE, Aditya Engineering College, Aditya Nagar, Surampalem, Andhra Pradesh
Abstract: Improving throughput and fairness of IEEE 802.11
WLAN is still an interesting research issue in networks, Even though various approaches available, but optimizing the throughput and fairness are the important parametersin
MAC layer of data link layer. In this paper we are proposing an efficient MAC scheme called ANBA. The key idea is to enable each AN to adjust its CW to approach the optimal one that can make the throughput maximum and while keeping fair channel sharing among all nodes.
I.INTRODUCTION common wireless channel with limited bandwidth in the
WLAN, it is highly desirable that an efficient and fair medium access control (MAC)scheme is employed.
However, for the 802.11 DCF, there is much room for improvement in terms of both efficiency and fairness. Cali et al. pointed out in [6] that depending on the network configuration, DCF may deliver a much lower throughput compared to the theoretical throughput limit.
Meanwhile, as demonstrated in [7], the fairness as well as throughput of the IEEE 802.11 DCF could significantly deteriorate when the number of nodes increases.
In IEEE 802 Reference model data link layer lies between the physical layer and all other main upper layers layers,datalink layer again classified intological link layer and medium access control, the functionalities of the MAC isReliable data delivery, Data access and Security. Reliable data delivery can be achieved by the various frame exchange protocols like Frame Exchange protocol and Four frame exchange protocols with RTS,CTS and ACK.Two types of access protocols are there, Decentralized and centralized protocols
Every layer has their individual importance while transmission of data packets over network from physical layer to application layer ,every layer has theier functionalities as physical layer deals with physical data connection and flow of protocol connection, data link layer works as medium between the physical layer network layer, and works as data transmission layer and
The network layer provides the functional and procedural means of transferring variable length data sequences
(called datagrams) from one node to another connected to the same network
Wireless local area networks (WLANs) have become increasingly popular and widely deployed in recent years.
Currently, the IEEE 802.11 MAC [1]–[3] standard includes two channel access methods: a mandatory contention-based one called Distributed Coordination Function (DCF) and an optional centralized one called Point Coordination Function
(PCF). Due to its inherent simplicity and flexibility, the
DCF mode is preferred and has attracted most research attention. At the same time, PCF is not supported in most current wireless cards andmay result in poor performance when working alone or together with DCF, as shown in [4], [5]. In this paper, we focus on DCF.Since all the nodes share a
II. RELATED WORK
While transmission of the data packets from the active source to destination node with send request and acknowledgements as individual frames. Every frame has their common proto type and structure of parameters and
MAC frame contains the frame control, common duration, address, sequence control, frame body and cyclic redundancy check and frame control field has set of parameters as protocol version, type, subtype and tags as
More fragments ,Retry , Power management and order
A station with a new packet to transmit monitors the channel activity. If the channel is idle for a period of time equal to a Distributed InterFrame Space (DIFS), the station transmits. Otherwise, if the channel is sensed busy (either immediately or during the DIFS), the station persists to monitor the channel until it is measured idle for a DIFS. At this point, the station generates a random backoff interval before transmitting (this is the Collision
Avoidance feature of the protocol), to minimize the probability of collision with packets being transmitted by other stations. In addition, to avoid channel capture, a station must wait a random backoff time between two consecutive new packet transmissions, even if the medium is sensed idle in the DIFS time.
For efficiency reasons, DCF employs a discrete-time backoffscale. The time immediately following an idle DIFS is slotted, and a station is allowed to transmit only at the beginning of each Slot Time. The Slot Time size, , is set equal to the time needed at any station to detect the transmission of a packet from any other station[7]. layer,
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International Journal of Engineering Trends and Technology (IJETT) – Volume 6 Number 7- Dec 2013 and it accounts for the propagation delay, for the time needed to switch from the receiving to the transmitting state (RX TX Turnaround Time), and for the time to signal to the MAC layer the state of the channel (Busy Detect
Time).
III. PROPOSED WORK
In this paper we are proposing an efficient and novel MAC scheme i.e ANBA,ANBA is MAC scheme for high throughput and fairness of IEEE 802.11 WLAN,In this approach we are dynamically adjusting the contention windows of the active nodes and it is integrated with the collision free mechanism while transmitting the frames between the source and destination over period of time,it is a DCF mechanism which deals with
 if many stations attempt to communicate at the same time, many collisions will occur which will lower the
L
L imin imin available bandwidth and possibly lead to congestive collapse.
 there are no Quality of Service (QoS) guarantees. In particular, there is no notion of high or low priority traffic.
We are enhancing the Dynamic ContentionWindows
Adjustment ( DCWA) approach named as ANBA,Initially it initializes the parameter Backoff counter (BC) to transmit the frame by the node with a random value selected sequentially from the set of range 0 to CW,which leads to avoiding the ideal interval in short time period,the active node calculates the average idle interval as Li(t) and it is given as
L i
*
(t) = α L i
(t) + (1 – α) L i
*
(t - 1)
Where L i
*
(t-1) is the smoothing process of L i
(t-1) which is the last observed average idle interval, and α is the smooth coefficient ranging from 0 to 1. The node with large CW chooses a larger RV by a very high probability than the node with small CW. So, L i
(t) observed by the node with large CW is smaller than L i
(t) observed by the node with small CW by a very high probability. Therefore, the node with large CW should have smaller optimal range [L imin
,
L imax
] than the node with small CW. The optimal range
[L imin
, L imax
] is:
= L
* imin
- CW
= L
* imax i
/ CW max
- CW i
/ CW max
Where CW i
is the current CW of the node, CW max
is the maximum value of CW, and [L
* imin
, L
* imax
] is the basic optimal range. Thus, the optimal range [L imin
, L imax
] is the from [L
* imin
, L
* imax
] to [L
* imin
+ 1, L
* imax
+ 1]. When the
CWi is large, [L imin
, L imax
] is small. As a result, the node with large CW i
has a higher priority than the node with small CWi in decreasing the size of CW, while the node with small CW i has higher priority than the node with large
CW i
in increasing the size of CW. In the next sections, we select the range [5, 7] or [6, 8] as the optimal range to achieve or approach the maximum normalized throughput
ρ max
. Therefore, [L imin
, L imax
] can be [5, 6], as a result [L imin
,
L imax
] is from [5, 7] to [6, 8].
If L * (t) is smaller than L imin
, the CW is increased by η incr
. If L
*
(t) is larger than L imax
, the CW is decreased by
η decr.
The
ηincr and η decr are defined as follows.
η incr
= F
1
/CW max
-CW min
(CW max
-CW i
)
η decr
= F
2
/CW max
-CW min
(CW i
-CW min
)
Where CW i
is the current CW of the node, CW min and CW max
are the minimum CW and the maximum CW, respectively, F
1
and F
2
are the maximum increased value and the minimum decreased value, respectively. The
ANBA scheme is described more formally
ANBA Approach :
If(RV >16 && BC ==0 {
/*smooth processing of L i
(t) */
L i
* (t)=αL i
(t)+(1α)L i
*(t- 1)
/*obtain the optimal range(L iminx
L imax
*/
L min
=L* imin
-CW i
/CW max
L imin
=L* imax
-CW i
/CW max
/*Adjust the CW*/
η incr
= F
1
/CW max
-CW min
(CW max
-CW i
)
η decr
= F
2
/CW max
-CW min
(CW i
-CW min
)
If(L* i
(t)<L imin
) {
CW i
= CW i
+ η incr
}
Else if(L* i
(t)>L imax
) {
CW i
=CW i
= η decr
}
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International Journal of Engineering Trends and Technology (IJETT) – Volume 6 Number 7- Dec 2013
Else Fairness
CW i
=CW i
<<2)+2
IV.
RESULT ANALYSIS
To evaluate the fairness of ANBA, we adopt the following Throughput fairness index (FI): An explanation [20] that is commonly accepted.
FI=( ∑
I
T i
/ i
)
2
/n ∑
I
(T i
/ i
)
2
Here, we compare the throughput of four schemes, i.e. IEEE 802.11 DCF, DOB, Idle sense and proposed scheme ANBA, as function of the average frame length where each node always has packets in its buffer waiting for transmission.
Fig.1 shows the normalized throughput when the number of nodes is varying from 10 to 100 and the frame lengths is 250 bytes.
Where T i
is the throughput of flow i during the transmission time T, φ i
is the weight of flow i.
Here, we assume all nodes have the same weight in simulation. Normally, a higher FI means a better Fairness. We compute the FI every 10 seconds and calculated the mean value, which can reflect the short-term fairness.
Fairness Index of IEEE 802.11 DCF, DOB, Idle sense, and ANBA are shown in fig. 2 for 250 bytes.
Figure 1 Normalized Throughput vs. No. of Active Nodes at frame length = 250 bytes
From the fig. 1, it can be observed that the throughput of IEEE 802.11 DCF significantly deteriorate when the number of nodes increases, while the throughput of DOB, Idle sense and
ANBA are insensitive to the number of the active nodes. To sum up, the throughput performance of
ANBA is the best among these four schemes.
ANBA uses the average idle interval to adapt
CW to approach the optimal CW, which can efficiently lead to high throughput.
Figure 2 : Fairness index vs. the no. of Active Nodes at 250 bytes
Observed Fairness of ANBA is significantly improved over the IEEE 80.211 and Idle Sense. It can also be seen that as the number of nodes rises, the Fairness drops quickly for the IEEE
802.11 DCF. ANBA ensures that all the nodes use about the same CW that is around the optimal
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International Journal of Engineering Trends and Technology (IJETT) – Volume 6 Number 7- Dec 2013 value as shown figs 2. Hence we sum up; the proposed ANBA scheme can guarantee the better
Fairness among the IEEE 802.11, DOB and Idle sense.
V. CONCLUSION
We are concluding our research work gives the optimal results than the traditional approaches, with efficient MAC scheme i.e ANBA scheme by providing the optimal throughput and fairness with dynamic contention window mechanism and every active adjust their idle time dynamically
REFERENCES
[1] IEEE Std. 802.11-1999, Wireless LAN medium access control (MAC) and physical layer (PHY) specifications,
Reference number ISO/IEC 8802-11,1999(E), IEEE Std.
802.11, 1999 ed., 1999.
[2] B.P. Crow, I. Widjaja, J.G. Kim, and P.T. Sakai, “IEEE
802.11 wireless local area networks,” IEEE Commun.
Mag., vol.35, pp.116–126, Sept. 1977.
[3] C. Fullmer and J. Garcia-Luna-Aceves, “Floor acquisition multiple access (FAMA) for packet-ratio networks,” Proc. SIGCOMM’95, pp.262–273, Cambridge,
MA, 1995.
[4] M.A. Visser and M.E. Zarki, “Voice and data transmission over an 802.11 wireless network,” IEEE
PIMRC’95, pp.648–652, 1995.
[5] J.Y. Yeh and C. Chen, “Support of multimedia services with the IEEE 802-11 MAC protocol,” Proc. ICC’02, pp.600–604, 2002.
[6] F. Cali, M. Conti, and E. Gregori, “Dynamic tuning of the IEEE 802.11 protocol to achieve a theoretical throughput limit,” IEEE/ACM Trans. Netw., vol.8, no.6, pp.785–799, Dec. 2000.
[7] G. Bianchi, “Performance analysis of the IEEE 802.11 distributed coordination function,” IEEE J. Sel. Areas
Commun., vol.18, no.3, pp.535–547, March 2000.
[8] F. Cali, M. Conti, and E. Gregori, “Dynamic tuning of the IEEE 802.11 protocol to achieve a theoretical throughput limit,” IEEE/ACM Trans. Netw., vol. 8, no. 6, pp. 785-799, Dec. 2000.
[9] P. Yong, H. Wu, S. Cheng, and K. Long, “A new selfadapt DCF algorithm,” IEEE GLOBECOM’02, vol. 1, pp.
87-91, Nov. 2002.
[10] X. Tian, X. Chen, T. Ideguchi, Y. Fang, “Improving
Throughput and Fairness in WLANs through Dynamically
Optimizing Backoff,” IEICE Transactions, 88-B(11): 4328-
4338, 2005.
[11] G. Bianchi and I. Tinnirello, “Kalman Filter
Estimation of the Number of Competing Terminals in an
IEEE 802.11 Network,” IEEE INFOCOM’03, vol. 2, pp.
844-852, April 2003.
[12] H. Ma, H. Li,P . Zhang,S . Luo,C. Yuan, and X. Li,
“Dynamic Optimization of IEEE 802.11 CSMA/CA Based on the Number of Competing Stations,” ICC’04, vol. 1, pp.
191-195, June 2004.
[13] L. Bononi, M. Conti, and E. Gregori, “Runtime
Optimization of IEEE 802.11 Wireless LANs
Performance,” IEEE Transactions on Parallel and
Distributed Systems, vol. 15, no. 1, pp. 66-80, January
2004.
[14] Q. Ni, I. Aad, C. Barakat, and T. Turletti, “Modeling and Analysis of Slow CW Decrease for IEEE 802.11
WLAN,” In Proc. of the 14th IEEE Proceedings on
Personal, Indoor and Mobile Radio Communications
(PIMRC), vol. 2, pp. 1717-1721, 2003.
[15] A. Chandra, V. Gumalla, and J.O. Limb, “Wireless
Medium Access Control Protocols,” IEEE
Communications Surveys & Tutorials, vol. 3, no. 2, pp. 2-
15, 2000.
BIOGRAPHIES
Ch. Ravindra Kumar is a student of Aditya
Engineering College, Surampalem. Presently he is pursuing his M.Tech [Computer Science
& Engineering]. He received his B.Tech from
Aditya Engineering College, affiliated to JNTU
University, Kakinada in the year 2009. His area of interest includes Computer Networks, image processing Data mining on Big Data, Nano Technology.
M.V.Rajesh, well known and excellent teacher received M.Tech (CSE) from JNTU,
Kakinada. He is presently working as a Sr.
Assistant professor in Dept of CSE at Aditya
Engineering College. He has 8.5 years of industrial and teaching experience. He published a couple papers both in national and international Conferences & journals. His area of interest includes Computer Networks and Software Engineering. He guided so many projects in ongoing trends.
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