User Based Resource Scheduling for Heterogeneous Traffic in the Downlink of OFDM Systems

Transcription

1 G. Indumath S. Vjayaran K. Murugesan User Based Resource Schedung for Heterogeneous Traffc n the Downn of OFDM Systems INDUMATHI.G VIJAYARANI.S Department of ECE Mepco Schen Engneerng Coege Svaas INDIA. ndupryanga@gma.com sdvjayaran@gma.com MURUGESAN.K Bharathyar Insttute of Engneerng for Women Attur INDIA. Abstract Besdes avodng nter-symbo nterference and eadng to hgh capacty wreess orthogona frequency dvson mutpexng (OFDM) provde fne granuarty for resource aocaton snce they are capabe of dynamcay assgnng sub-carrers to mutpe users and adaptvey aocatng transmt power. The current domnate ayered networng archtecture n whch each ayer s desgned and operated ndependenty resuts n neffcent and nfexbe resource use n wreess networs due to the nature of the wreess medum such as tme-varyng channe fadng. Thus we need an ntegrated adaptve desgn across dfferent ayers. In ths paper we focus on resource aocaton and schedung n wreess mutuser OFDM networs based on jont physca and medum access contro (MAC) ayer optmzaton. An adaptve cross-ayer desgn for the downn mutuser OFDM systems to maxmze the weghted sum capacty of a users where each user has mutpe heterogeneous traffc queues smutaneousy s proposed. A pacet dependent (PD) schedung scheme s empoyed at the MAC ayer whch determnes the pacet transmsson order by assgnng dfferent weghts to dfferent pacets and s shown by smuatons more effcent than the prevous methods where a pacets n a queue have the same weght. The weght desgn n PD schedung consders the deay sze and quaty of servce (QoS) prorty eve of pacets. Each user weght empoyed n resource aocaton at the physca (PHY) ayer s obtaned by summng up the weghts of seected pacets for the user. We aso deepy nvestgate the varous resource schedung schemes for comparsons. Keywords Cross-ayer desgn quaty of servce pacet schedung orthogona frequency dvson mutpexng systems. Introducton The aocaton and management of resources are cruca for wreess networs n whch the scarce wreess spectra resources are shared by mutpe users. In the current domnate ayered networng archtecture each ayer s desgned and operated ndependenty to support transparency between ayers. Among these ayers the physca ayer s n charge of raw bt transmsson and MAC ayer contros mutuser access to the shared resources. However wreess channes suffer from tmevaryng mutpath fadng; moreover the statstca channe characterstcs of dfferent users are dfferent. The sub optmaty and nfexbty of ths archtecture resut n neffcent resource use n wreess networs. We need an ntegrated adaptve desgn across dfferent ayers. Therefore crossayered desgn across the physca and MAC ayers are desred for wreess resource aocaton and pacet schedung []. For cross-ayer desgn channe-aware schedung strateges are proposed to adaptvey transmt data and dynamcay assgn wreess resources based on channe state nformaton (CSI). The ey dea of channe-aware schedung s to choose a user wth good channe condtons to transmt pacets [2]. Tang advantage of the ndependent channe varaton across users channe-aware schedung can substantay mprove the networ performance through mutuser dversty whose gan ncreases wth the number of users [3]. To guarantee farness for resource aocaton and expot mutuser dversty uttyprcng structures n networ economcs are usuay preferred for schedung desgn [4]. The growth of Internet data and mutmeda appcatons requres hgh-speed transmsson and effcent resource aocaton. To avod nter-symbo nterference orthogona frequency dvson mutpexng ISSN: Issue 5 Voume 0 May 20

2 G. Indumath S. Vjayaran K. Murugesan (OFDM) s desrabe for wreess hgh-speed communcatons. OFDM-based systems are tradtonay used for combatng frequency-seectve fadng. From a resource aocaton pont of vew however mutpe channes n an OFDM system naturay have the potenta for more effcent MAC snce subcarrers can be assgned to dfferent users [5]. Another advantage of OFDM s that adaptve power aocaton can be apped for a further mprovement. The basc probem that we need to sove n ths paper s how to effectvey aocate resources on the downn of Internet protoco (IP)- based OFDM networs by expotng nowedge of CSI and the characterstcs of traffc to enhance the system throughput and guarantee quaty of servce (QoS). Secton II presents the system mode and probem formuaton. The maxmumm weghted sum capacty (MWSC) based resourcee aocaton s dscussed n Secton III. Channe aware jont channe and queue aware pacet dependent resource schedung schemes are anaysed n Secton IV. Secton V shows the smuaton resuts and Secton VI draws the concuson. assume that each user has I traffc queues wth heterogeneous deay constrants for the queues. Defne Ω as the ndex set of subcarrers aocated to user. Wthout oss of generaty and for smpcty we assume that each subcarrer s aocated to ony one user [7]. Let p n denote the power aocated to user on subcarrer n h n the correspondng channe gan and N 0 the snge-sded power spectra densty of addtve whte Gaussan nose (AWGN). Assumng perfect channe estmaton the achevabe nstantaneous data rate of user u on subcarrer n s expressed as B R n og 2( + p n. γ n) N () where 2 h n γ n N0B / N (2) s the channe-to-nose power rato for user on subcarrer n. The tota achevabe nstantaneous data rate of user s gven by R R n n Ω (3) 2 System Mode & Probem Formuaton We consder a genera downn tme dvson dupexng (TDD) OFDM system where the base staton can acqure the channe state nformaton (CSI) through the upn dedcated pots from a mobe statons at the begnnng of each tme sot and use t for resource aocaton and schedung. The subcarrer and power controer at the PHY ayer performs subcarrer and power aocaton and the traffc controer at the MAC ayer performs data schedung. Wth a cross-ayer desgn the QoS nformaton obtaned by the traffc controer s transferred to the subcarrer and power controer for resource aocaton and the resource aocaton resuts are feedbac to the traffc controer n the base staton for schedung of the data to be sent out n each sot. The cross-ayer schedung archtecture s depcted n the Fg.. We assume a tota bandwdth of B whch s dvded nto ndependent subcarrerss and shared by K users. The tota transmt power from the base staton s assumed to be P t. The OFDM sgnang s tme-sotted and each tme sot s of ength T sot [6]. We consder a quas-statc fadng channe where the channe gan s constant durng each sot and s ndependent of the channe for other sots. We Fg. Cross-ayer schedung archtecture We empoy a genera maxmum weghted sum capacty (MWSC) based cross-ayer desgn whch s to maxmze the weghted sum of a users nstantaneous capactes [8]. Lettng W denote the weght for user whch contans the QoS nformaton and s determned by schedung at the MAC ayer the cost functon to be maxmzed s gven by J K W R Subject to (C) p n 0 (C2) (C3) K Ω n n T R T Q sot p p (4) ISSN: Issue 5 Voume 0 May 20

3 G. Indumath S. Vjayaran K. Murugesan (C4) Ω... Ω { 2 }...N (C5) Ω Ω φ ( j) j where Q s the queue ength of user. The constrant n (C3) s to guarantee that no more resource s aocated to the user f the user aready obtans suffcent resources to send a data out n current sot to avod waste of resources. The above user based cross-ayer desgn can be easy extended to the queue based cross-ayer desgn by repacng the user ndex wth the queue ndex. Assumng that a users have w queues each.e I w there are tota number of wk queues n the system. The queue based MWSC cross-ayer desgn s to maxmze the foowng cost functon. wk J W R (5) The MWSC based cross-ayer desgn s genera n that the weghts W and W can be obtaned by usng a wde range of schedung schemes. 3 Maxmum Weghted Sum Capacty Based Resource Aocaton To mae a good trade off between compexty and performance we propose a suboptma resource aocaton agorthm whch performs subcarrer aocaton and power aocaton separatey. We frst perform subcarrer aocaton assumng equa power across a subcarrers and then perform power aocaton. Wth equa power on each subcarrer the subcarrer aocaton shoud assgn subcarrer n to user rather than user j f W R n > W jr j n. After subcarrer aocaton power aocaton s performed by usng Karush-Kuhn-Tucer (KKT) condtons. Let Φ denote the user ndex set. The dynamc agorthm to mpement the suboptma MWSC based subcarrer and power aocaton s descrbed as foows ) Intaze the set for a users and for a subcarrers pt Φ { 2... } R Ω φ 0 p n N 2) For a the subcarrers fnd * ( n) arg max W R { } n Φ 3) Assgn subcarrer n to user * ( n ) and then update * ( n ) carrer ndex and data rate. 4) Aocate the power to subcarrer by (6) (7) p n W p T + K m q Ω m K m W m Ω m γ m q γ * ( n) * 0 ( n) (8) 5) For a subcarrers f power s ess than zero for partcuar user than there s no enough power for subcarrer n whch has sma weght and/or sgna to nose rato thus subcarrer n w be gnored for power aocaton. 6) Repeat the step 3 and 4 unt the power s greater than zero. n 4 Resource Schedung Schemes The weght of the MWSC based cross-ayer desgn descrbed n secton III contan the QoS nformaton and can be obtaned from schedung at the MAC ayer. In ths secton we w anayse the varous resource schedung schemes and then pacet based schedung scheme s proposed. Notce that a schedung schemes are performed n every tme sot and the weghts are updated n every sot as we. 4. Maxmum Sum Capacty The maxmum sum capacty (MSC) rue s a channe aware schedung scheme that maxmzes the tota throughput n the system [9]. The weght s gven by w (9) Athough the MSC rue maes the most effcent use of the bandwdth t can ead to unfarness and nstabty especay for non symmetrca channe condtons and non unform traffc patterns. 4.2 Proportona Farness (PF) The PF schedung s a channe aware schedung rue amng to maxmze average data rate of user [0]. The weght s gven by w R (0) 4.3 Modfed Largest Weghted Deay Frst Schedung The modfed argest weghted deay frst (MLWDF) [] schedung scheme s a queue based scheme desgned usng the cost functon gven by (5) and t can eep the deays of most queues beow a bound. Lettng U and T HOL respectvey denote the deay toerance and HOL pacet deay for queue defne ISSN: Issue 5 Voume 0 May 20

4 G. Indumath S. Vjayaran K. Murugesan δ as the maxmum aowed probabty that T HOL > U. The weght of queue s gven by THOL og( δ) w U R () Substtutng (9) nto (5) t can be deduced that wth M-LWDF the queue whch has a hgher HOL pacet deay reatve to the deay bound a hgher nstantaneous data rate reatve to the average data rate and a hgher requrement for outage probabty s gven a hgher prorty to be served. 4.4 Exponenta Rue (EXP) The EXP schedung [0] rue s desgned for snge carrer CDMA networs wth a shared downn channe and t s a queue based schedung scheme. The structure of the EXP rue s very smar to the M-LWDF but wth dfferent weghts. The mutchanne verson s gven by T HOL w exp R + T HOL (2) 4.5 Maxmum deay utty schedung (MDU) The so-caed MDU [0] schedung scheme s to maxmze the utty functons wth respect to the deay. Defne f ( T ) as a decreasng utty HOL functon of the average HOL pacet deay Q THOL for queue where Q λ THOL denote λ the average queue ength the average arrva rate and the short-term average HOL deay of queue cacuated n current sot respectvey. Smar to M- LWDF MDU s a queue based schedung scheme wth the weght n (5) expressed as f ( THOL ) w. λ THOL (3) 4.6 Pacet Dependent Schedung (PD) The mechansm of the conventona queue based schedung such as M-LWDF and MDU s to assgn the same weght to a pacets n a queue and serve the seected queues unt ether the data or PHY ayer resources are exhausted durng each sot. Ths however eads to neffcency f some pacets n the unseected queues are more urgent than some pacets n the currenty served queues. We now anayse a pacet dependent (PD) schedung scheme whch assgns dfferent weghts to dfferent pacets contaned n the same queue. The pacet weghts are determned based on the deay pacet sze and QoS prorty eve of the pacets. Therefore t s more fexbe and effcent than the queue based schedung. Defnng U as the deay toerance for queue of user a pacet wthn ths queue w be dropped f ts watng tme s arger than U. In genera the deay toerance of the voce varabe bt rate (VBR) vdeo and BE traffc queues s set to be ow medum and hgh respectvey. A guard nterva G s ntroduced to reduce the pacet drop rate whch means that the urgent pacets beongng to queue of user shoud be gven a hgh prorty wthn the ast G duraton before they tmeout. Lettng t c [0 ) denote the current tme for the th pacet that beongs to queue of user and arrves at tme t [0 t c ] the deay s gven by S t c t. Thus the tme eft that the pacet becomes urgent s denoted by C whch s expressed as U S G (4) C If < 0 S U G C.e. > t means that the pacet s urgent and w tmeout wthn the guard nterva of G. Hence the pacets wth C <0 shoud be gven a hgh prorty durng ths guard nterva. Further et D denote the pacet sze (n bts) of the pacet that beongs to queue of user and arrves at tme t. Defne β [ ) as the QoS prorty eve for queue of user. In genera the QoS prorty eves for the voce traffc queues vdeo traffc queues and BE traffc queues are hgh medum and ow respectvey. We desgn W the weght of the to-be-served pacets that beong to queue of user and arrve at tme t by usng the foowng equaton W β D β D /( C + ) ( C ( C 0) < 0) (5) Accordng to (5) the PD schedung scheme assgns a hgher weght to the pacets n a queue whch have a hgher QoS prorty eve a arger data amount and a fewer tme eft to become urgent. The pacets wth hgher weghts w be transmtted frst regardess f they are n the same queue or not. Each pacet s assgned a unque sequence number whch ensures that t can be reassembed durng transmsson. Therefore the PD schedung scheme s more fexbe and effcent than queue based schedung schemes where a pacets n the same queue are assgned the same weght. ISSN: Issue 5 Voume 0 May 20

5 G. Indumath S. Vjayaran K. Murugesan If C 0.e. S U G the weght n (5) ncreases wth the decrease of C. In partcuar we have 2 W / C β D /( C + ) (6) Ths mpes that wth a arge vaued C.e. a reatvey sma pacet deay the varaton of the weght W s ess senstve to the varaton of C. In ths case the QoS prorty eve and data amount pay a more mportant roe n weght cacuaton. On the other hand the fewer tme eft for the pacet to become urgent the arger the pacet deay and the faster the weght ncreases. If C < 0.e. S > U G t means that the pacets arrvng at tme t w tmeout n ess than G and shoud be gven a hgh prorty durng the guard nterva to avod the drop of pacets. In ths case W n (5) mantans ts maxmum vaue whch s determned by the data amount and QoS prorty eve of the pacets. For nstance f two voce pacets (of the same QoS prorty eve) both fa n the guard nterva the pacet wth a arger data amount w be assgned a hgher weght. On the other hand f two pacets are of the same data amount the pacet wth a hgher QoS prorty eve w obtan a hgher weght. Usng (5) the weght W n (4) for the current sot s gven by I W W (7) The PD schedung scheme can aso be easy combned wth the queue based MWSC resource aocaton whose compexty s hgher than that of the user based MWSC wth heterogeneous traffc. 5 Smuaton Resuts We use smuaton resuts to demonstrate performance of the varous resource schedung schemes for a system wth a tota transmt power P T W a sot duraton of T sot 2 msec and a tota bandwdth of B 5 MHz whch s dvded nto N 52 subcarrers. We assume that each user has I 3 queues: voce VBR vdeo and BE traffc queues. The deay toerance U for voce vdeo and BE traffc s set to be 00 msec 400 msec and 000 msec respectvey. The guard nterva G s set to be 0 msec for a types of traffc. The pacets arrve at an nterva of msec.the pacet arrva rates of voce and BE traffc are constanty 64 Kbps and 500 Kbps respectvey. The pacet arrva rate of the varabe bt rate (VBR) vdeo traffc foows a truncated exponenta dstrbuton n each state wth the maxmum mnmum and mean of 420 Kbps 20 Kbps and 239 Kbps respectvey where the duraton of each state foows an exponenta dstrbuton wth mean 60 msec. It can be cacuated that the average pacet szes for voce vdeo and BE traffc are 64 bts 239 bts and 500 bts respectvey. The QoS prorty eves β for the voce vdeo and BE traffc are respectvey set to be and as a resut of testng to provde the best performance. The channe s modeed to be of sx ndependent Rayegh fadng paths wth an exponentay deay profe and a root-mean-square (RMS) deay spread of 0.5 µsec. The sgna-to-nose rato (SNR) s defned as the average rato of the receved sgna power to nose power for each user. In the foowng we present a performance comparson of varous resource schedung schemes used n MAC ayer. In the PHY ayer the MWSC based suboptma resource aocaton dscussed n secton III s empoyed. The parameters taen for comparsons are average system throughput and average pacet deay. Average system throughput s defned as the average transmtted bt per second n the system. Average pacet deay s the average tme that a pacet must wat when tryng to access a communcaton networ. The proportona farness rue s used n system where farness s the man crtera. Fg.2 and Fg.4 demonstrate the mpact of the number of users on performance of dfferent resource schedung schemes wth 50 users. Fg. 2 shows the mpact of the number of users on the average system throughput. PD demonstrates sgnfcant performance advantages over other schedung schemes except MSC snce t depends on the nstantaneous data rate t schedues the pacet wth best channe condtons n each subcarrer. As the users ncreasng and hgher mut-user dversty the tota ce data rate of MSC agorthm s gettng ght ncrease. However the MSC agorthm does not thn about the user average data rate requrements. In partcuar the system throughput acheved by PD ncreases wth the ncrease of the number of users due to enhanced mutuser dversty. Wth gven resources when the number of users ncreases there s a hgher degree of freedom for resource aocaton resutng n enhanced mutuser dversty. Fg.3 shows the zoomed verson of Fg.2 ISSN: Issue 5 Voume 0 May 20

6 G. Indumath S. Vjayaran K. Murugesan Fg.2 Impact of number of users on average system throughput Fg.3 Zoomed verson of fg. 2. On the other hand the ncrease n the number of users woud cause the ncrease n the weght dfference of the HOL pacets of varous queues and thus the average system throughput decreases. Ths mpact on the average system throughput s more sgnfcant wth MDU M-LWDF EXP than wth PD. Wth PD the pacets wth arger weghts are served frst on pacet bass whchever queues they beong to whereas wth MDU M-LWDF EXP a pacets n a queue whch has a arger weght are served frst on queue bass. Therefore average system throughputs of MDU M-LWDF EXP beneft ess from mutuser dversty. Wth a arge number of users the average system throughput acheved by PD s much hgher than that acheved by MDU M-LWDF EXP schedung schemes. Fg.4 Impact of number of users on average pacet deay Fg. 4 shows the mpact of the number of users on the average pacet deay. The EXP schedung s poor compared to the M-LWDF and the MDU approaches. Ths s due to the mechansm of the EXP rue. If one user has a arger deay than others the weght of ths user becomes very arge because of the exponenta functon used n the weght and then ths user may occupy a of the subcarrers wth hgh probabty. Because the frequency-seectve fadng s present assgnng the whoe bandwdth to one user s ess effcent. As can be seen the M-LWDF wors we compared to EXP. However snce the MDU pocy uses the average queue engths (deays) as the weghts whch s a more moderate way the MDU pocy can aocate resources more effcenty compared to M-LWDF. PD acheves a much ower deay than M-LWDF MDU EXP snce t determnes the pacet transmsson order by assgnng dfferent weghts to dfferent pacets and therefore s more effcent than the conventona queue dependent schedung. Fg.5 Impact of SNR on average system throughput ISSN: Issue 5 Voume 0 May 20

7 G. Indumath S. Vjayaran K. Murugesan Meanwhe snce PD aocates more resources to QoS traffc t acheves up to two tmes ower deays for QoS traffc than M-LWDF and MDU. downn mutuser muttasng OFDM systems wth heterogeneous traffc. The proposed PD schedung scheme provdes sgnfcant performance advantages over the queue based M-LWDF MDU EXP schedung schemes n terms of the average system throughput QoS traffc deays wth a wde range of the number of users and a moderate to hgh SNR range. Fg.6 Impact of SNR on average pacet deay Fg.5 and Fg.6 show the mpact of SNR on performance of dfferent resource schedung schemes wth 50 users. Fg.5 shows that the average system throughput for a the schemes ncreases wth the average SNR. PD outperforms MDU M-LWDF EXP schedung schemes. Fg.6 demonstrates the mpact of SNR on average pacet deay and PD outperforms a other resource schedung schemes. Thus the pacet schedung s performed better compared to other queue based resource schedung schemes such as M-LWDF MDU EXP n terms of throughput and deay. 6 Concuson In ths paper we have nvestgated varous resource aocaton and schedung schemes n the wreess OFDM based downn that serves mutpe users wth heterogeneous traffc and supports varous appcatons based on jont physca and MAC ayer desgn. We have proposed an adaptve cross-ayer desgn wth the PD schedung at the MAC ayer for References: [] Aydz I. Atunbasa Y. Fer F. and Svaumar R. AdaptNet: An adaptve protoco sute for the next generaton wreess Internet IEEE Commun. Magazne vo pp [2] Vswanath P. Tse D. N. C. and Laroa R. L. Opportunstc beamformng usng dumb antennas IEEE Trans. Inform. Theory vo pp [3] Knopp R. and Humbet P. Informaton capacty and power controng snge-ce mutuser communcatons n Proc. IEEE Int. Conf. on Commun.(Seatte WA) June 995. [4] Lu X. Chong E. and Shroff N. Opportunstc transmsson schedung wth resource-sharng constrants n wreess networs IEEE J. Seect. Areas Commun. vo pp [5] Chuang J. and Soenberger N. Beyond 3G: Wdeband wreess data access based on OFDM and dynamc pacet assgnment IEEE Commun. Magazne 2000 pp [6] G.C.Song and Y.L Utty-based resource aocaton and schedung n OFDM based wreess broadband networs IEEE Commun. Mag. vo pp [7] Z.K.Shen and J.G.Andrews Adaptve resource aocaton n mutuser OFDM systems wth proportona rate constrants IEEE Trans. Wreess Commun. vo pp [8] D.Verones S.Tomasn and N.Benvenuto Cross-ayer optmzaton for mutmeda traffc n CDMA ceuar networs IEEE Trans. Wreess Commun. vo pp [9] J.Jangand K.B.Lee Transmt power adaptaton for mutuser OFDM systems IEEE J.Se. Areas Commun. vo.2 pp.7 78 Feb [0] G.C.Song Cross-ayer resource aocaton and schedung n wreess mutcarrer networs Ph.D.dssertaton Georga Insttute of Technoogy2005. [] M. Andrews et a. CDMA Data QoS Schedung on the Forward Ln wth Varabe Channe Condtons Be Labs Tech. Memo. Apr ISSN: Issue 5 Voume 0 May 20

8 G. Indumath S. Vjayaran K. Murugesan Author s Bography Mrs.G. Indumath obtaned Bacheor s degree n Eectroncs and Communcaton Engneerng and Master s Degree n Communcaton Systems both from Madura Kamaraj Unversty Madura Inda n 990 and 997 respectvey. She s currenty studyng for a Ph.D degree at the department of Informaton and Communcaton Engneerng Anna Unversty Chenna. Her current research nterests are n the areas of Wreess and Mobe communcatons and Dgta sgna Processng. She s a Lfe member n Indan Socety for Technca Educaton (LM25836) and Feow n Insttuton of Eectroncs and Teecommuncatons Engneers. She has pubshed many research papers n Internatona and Natona Journas. Her area of nterest ncudes Cross-ayer desgn resource aocaton n wreess networs. S. Vjayaran receved the B.E. degree n Eectroncs and Communcaton Engneerng from Veamma Engneerng Coege Chenna Inda n She s currenty pursung her M.E. degree n Communcaton Systems from Mepco Schen Engneerng Coege Svaas Inda. Her area of nterest s Wreess Communcatons. Dr. Karuppasamy Murugesan obtaned Bacheor s degree n Eectroncs and Communcaton Engneerng and Master s Degree n Mcrowave and Optca Engneerng both from Madura Kamaraj Unversty Madura Inda n 990 and 993 respectvey. He earned doctora degree from Anna Unversty Chenna for hs research wor n the fed of optca communcatons n the year 200. He has aso obtaned post graduate dpoma n Personne Management and Industra Reatons from Annamaa Unversty Chdambaram Inda n 997. He has pubshed more than 30 papers n reputed Natona and Internatona journas and conferences. Hs Research Interests ncude Optca Code Dvson Mutpe Access Optca Sgna Processng Technques Lghtwave Communcaton Systems Optca Codng Theory and Utrashort Lght Puse Communcatons. He s a Feow n Insttuton of Eectroncs and Teecommuncatons Engneers Lfe member n Indan Socety for Technca Educaton and Assocate Member n Insttuton of Engneers (Inda). He receved Best ISTE Chapter Secretary Award for Engneerng Coeges from ISTE (TN & P Secton) for the year He has more than 6 years of teachng experence n addton to one year of ndustra exposure. Currenty He serves as the prncpa n Bharathyar Insttute of Engneerng for Women Attur n Tamnadu ISSN: Issue 5 Voume 0 May 20