GTS Scheduling Scheme for Real-Time Communication in IEEE Industrial Wireless Sensor Networks

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1 Idia Joural of Sciece ad Techology, Vol 9(7), DOI:.7485/ijst/6/v9i7/87734, February 6 ISSN (Prit) : ISSN (Olie) : GTS Schedulig Scheme for Real-Time Commuicatio i IEEE8.5.4 Idustrial Wireless Sesor Networks H. Safdarkhai ad S. A. Motamedi* Electrical Egieerig Departmet, Amirkabir Uiversity of Techology, Tehra, Ira; safdarkhai@aut.ac.ir, motamedi@aut.ac.ir Abstract Backgroud/Objectives: We have proposed a improved algorithm for the delay sesitive etworks with bulk periodic data traffic. This kid of etworks such as Idustrial etworks that should trasfer the moitorig data has a high sesitivity to delay sice these etworks should work real-time. Methods/Statistical Aalysis: Cosiderig ad studyig the idustrial etwork traffic model, a ew adaptive cetralized GTS schedulig algorithm is proposed focusig o real-time commuicatio ad reliability which are two importat issues i idustrial wireless commuicatio. Fidigs: Wireless Sesor Network (WSN) is selected for implemetig the idustrial etwork. Idustrial Wireless Sesor Network (IWSN) ad IEEE8.5.4 stadard is the most popular stadard for WSN MAC layer protocol. I this paper cosiderig the idustrial etwork data types ew GTS schedulig scheme for IEEE8.5.4 is itroduced for the delay sesitive etworks with bulk periodic data traffic. Applicatios/Improvemets: Our proposed algorithm by adaptig the characteristics of idustrial etworks ad IEEE8.5.4 stadard shows high gai i delay improvemet. Keywords: GTS Schedulig, Idustrial Wireless Sesor Network (IWSN), IEEE8.5.4, Real-Time Commuicatio. Itroductio Nowadays, wireless techologies might be of advatage i idustrial eviromets. The IEEE8.5.4 stadard was fialized i October 3 ad specifies the characteristics of the physical layer ad the MAC layer of a radio etwork stack. It is adopted as a commuicatio stadard for Low-Rate Wireless Local Area Networks (LR-WPANs). To achieve this stadard such as low cost, low power, twoway wireless commuicatio solutio, it meets the uique requiremets of sesors ad cotrol devices. Because of popular usage of this stadard ad its good specificatios, ivestigatios are made to use this stadard for idustrial applicatios which have more sesitivity i delay ad reliability tha ordiary etworks. IEEE8.5.4 stadard is week i real time ad reliable commuicatio,3. IEEE8.5.4 has two o-beaco ad beacoeabled modes i the MAC. I the o-beaco mode all the odes ca sed the data usig Carrier Sese Multiple Access/Collisio Avoidace (CSMA/CA) at ay time but i the beaco-eabled mode there is a coordiator which broadcasts the beaco to the ordiary odes. I the beaco-eabled mode there is a coordiator which broadcasts the beaco to the ordiary odes. The duratio betwee two respective beacos is called Beaco Iterval (BI) ad cotais the active regio i which data trasmissios are allowed (super frame) ad the iactive regio i which o data trasmissio would occur. The iactive regio is maily used for sleepig of the odes for eergy savig ad loger life time of the odes. IEEE protocol also provides real-time guaratees by usig Guarateed- Time Slot (GTS) mechaism i beaco-eabled mode. I this mode, as it is show i Figure, each super frame is divided to sixtee equal time slots cotaiig oly up to seve GTSs. Each ode ca allocate up to two GTSs (oe for receive ad oe for trasmit), ad oe *Author for correspodece

2 GTS Schedulig Scheme for Real-Time Commuicatio i IEEE8.5.4 Idustrial Wireless Sesor Networks Figure. Beaco iterval ad superframe structure. GTS may have more tha oe slot. The GTSs formig the Cotetio-Free Period (CFP) ad the remaiig time slots compose the Cotetio Access Period (CAP). I this research we are goig to add ew features to this stadard with some modificatio i order to improve real-time commuicatio for idustrial applicatios. From a allocatio poit of view, the cocept of a GTS allocatio is similar to a Time Divisio Multiple Access (TDMA) time slot allocatio. A reserved amout of badwidth is periodically grated for a give data flow. The amout of badwidth is determied by the duratio of the time slot ad its periodicity. However, the IEEE GTS mechaism is more flexible tha a classic TDMA sice the GTS duratio may be dyamically adjusted by settig adequately the parameters of the IEEE super frame, whereas a TDMA time slot duratio is, i geeral, fixed for a give etwork cofiguratio. May researches for ivestigatig the stadard ad evaluatig ad improvig its performace has bee performed 4,5. I geeral, IEEE allocates GTS o a First Come First Serve (FCFS) basis. But it has problems such as badwidth wastage, o delay tolerace ad moderate throughput 6. I 7,8 proposed implicit GTS allocatio mechaism, heceforth referred to as igame algorithm. It ca support higher badwidth utilizatio ad ca allow the sharig of GTS amog may devices. However, igame caot guaratee a GTS slot if the delay guaratee is less tha beaco iterval. Also, the authors have assumed that the flow characteristics of all the devices are provided prior to schedulig itself. The GTS requests are trasmitted i the CAP period itself. However, if the umber of GTS requestig devices icreases tremedously, the the chaces that a device trasmits its GTS request i the CAP is much less. This form of starvatio is ot addressed by igame. The performace of the explicit GTS allocatio i IEEE has bee evaluated 9. That work proposes a delay boud aalysis of a explicit GTS allocatio. It also aalyzes the impact of the beaco ad super frame orders o the throughput, delay ad power efficiecy of a GTS allocatio. It works uder two costraits. First of all, the umber of odes requestig the GTS must be higher tha seve ad secodly the deadlie associated with each GTS message is smaller tha the beaco iterval. I, have addressed multi cycle pollig schedulig i field bus etworks. These papers have cotributed to the schedule ability aalysis of a set of periodic tasks with deadlies equal to periods uder Rate Mootoic (RM) ad Earliest Deadlie First (EDF) schedulig policies, where the odes polled are differet from oe cycle to aother. I both approaches, the idea cosists i fidig the miimum cycle, called primary cycle, which correspods to the greatest commo divisor of all task periods, ad computig the umber of time slots eeded to trasmit periodic traffic iside each cycle, if the task set is schedulable. The last step cosists i executig tasks accordig to their priorities (usig RM or EDF) i each primary cycle. I proposed a ew GTS scheme which utilizes the CFP more efficietly tha the stadard scheme by dividig the CFP ito 6 equally sized sub slots. With smaller slots, CFP utilizatio i the ew scheme is better tha that i the stadard scheme. I 3 proposed a dyamic GTS (D-GTS) allocatio algorithm to reduce wasted badwidth. To reduce the wasted part of GTS allocatio, they proposed to allocate a D-GTS i the back off period uit rather tha a super frame slot uit. Recetly, Pervasive usage of wireless techology leads to workig o reliability ad real-time commuicatio which ca be metioed as wireless weakess agaist wired commuicatio for reliable ad delay sesitive commuicatio. I 4 used a etwork codig mechaism for trasmittig data which ehaces the reliability of the etwork. Furthermore, reducig the umber of trasmissios ad receptios i etwork odes results i the reductio of eergy cosumptio. This method has bee proposed for optimizig the parameters of reliability ad eergy cosumptio i multimedia WSNs. However this method is ivestigated i multimedia applicatios which have high traffic. I idustrial etwork the data size is ot volumious. I this paper, cosiderig the situatio of idustrial etwork traffic patter, a algorithm for schedulig of GTS slots to the odes is preseted i order to reduce delay. Vol 9 (7) February 6 Idia Joural of Sciece ad Techology

3 H. Safdarkhai ad S. A. Motamedi. Proposed Algorithm Idustrial etwork duty is to trasfer the moitorig ad cotrol data betwee the sesors ad actuators ad the cotrol room as a commader. Sice this research is workig o the idustrial etwork, studyig the specificatios ad the data types i this etwork ca help for better modificatios i order to have better performace. Real-time ad reliable commuicatio is vital i idustrial etworks because the data is importat how ever sice the data is ot massive (for example moitorig data ad alarms are usually small packets) the bit rate is ot as importat as the real-time ad reliability. Two mai data categories ca be defied i idustrial etwork. The first data type is the moitorig data. The sesors will sed the data to the commader (Moitorig room) ad the moitorig data will be aalyzed i the cetral cotrol room (Loggig ad profilig the data, aalyzig the coditio) ad i the situatio which a chage i the plat is eeded, the cotrol room (commader) should sed a commad or cotrol message to a actuator. Aother type is alarm data. I this approach the sesor oly will sed the packet (alarm packet) whe its data has get upper or lower tha a pre-defied value. This two categories work i differet maer ad their traffic has complete differet profile. I the moitorig data, mostly the sesors will sed their data i a periodic maer which meas they will sed their measured quatity i a costat itervals but at the other side the alarms do ot have a specified time ad i ay time a alarm ca be arise. The majority of the traffic i a idustrial etwork is the moitorig part because of the umber of moitorig sesors ad their traffic profile which produce costat data. (A moitorig sesor ca also produce a alarm but for simplicity we cosider the separated odes for moitorig ad alarm. It will ot make ay problem i our aalysis because it is possible that the source of or more traffic be just oe ode i practice. We cosider separated odes for separated traffic just for simplicity). Sice the bulk traffic is due to moitorig data which has periodic maer, maagig this part is i our focus. I idustrial applicatios, it is importat that the data received correctly ad as soo as possible i the moitorig room. Accordig to this specificatio of the idustrial etworks ad simplicity, i this paper, trasmissio of this kid of data is i spotlight. Data packets are ackowledged ad IEEE8.5.4 supports retrasmissio as reliability factors but i idustry applicatios reliability with real-time trasmissio is meaigful. Igorig retrasmissios ad assumig that i CFP period the packets will receive to their destiatio errorless, the coordiator ode should maage the GTS slots, i such a way that all costrais about the sesors data would match. Kowig that gettig a GTS slot eeds to sed a successful request packet to the coordiator ad the request should be set durig the CAP period, shows that the GTS just ca be dedicated i the beaco Iterval ext to the first CAP regio which the request is set successfully (if the coordiator has a empty GTS slot to allocate). It will be cocluded that with this algorithm the data will be delayed at least oe beaco iterval. This algorithm is suitable as a geeral method because the coordiator is ot aware about the time whe data of a ode is geerated so the ode should request for a GTS slot whe it has data. As described before i idustrial applicatios, moitorig data is produced periodically so the time of productio of the ext data ca be calculated accurately. Usig this feature we propose a ew method that the odes that has periodic data do ot follow the stadard protocol ad with a little chage which is completely easy to implemet, get a better result which meas reduce the delay of the odes data. For formulatig the problem, T i shows the itervals betwee producig the data of ode i. As a reliability parameter D i is cosidered maximum acceptable delay for ith ode. If the ode i expresses these two parameters to the coordiator, it ca calculate the time of future geerated data of that ode. Kth data productio time = KT i + T o () Where T o is the begiig offset time from the t = for ode i. For havig more flexibility i reducig the eergy cosumptio by miimum duty cycle, the super frame order ad the beaco order will adaptively choose which is possible i the stadard. BI j represets the jth beaco order ad SD represets the super frame duratio. Accordig to the above parameters the th super frame duratio is: j= BI < th sup erframe < BI + SD j j= BI = Base super frameduratio j j B J () Vol 9 (7) February 6 Idia Joural of Sciece ad Techology 3

4 GTS Schedulig Scheme for Real-Time Commuicatio i IEEE8.5.4 Idustrial Wireless Sesor Networks SD = Base super frameduratio As the iactive period will force some limitatios o real-time trasmissio, i this paper we discard this opportuity of IEEE8.5.4 which is maily used for eergy savig i ordiary wireless sesor etworks so the sesors data ca be set more quickly. For eglectig the iactive period BO=SO. As the beaco mode of IEEE is slotted first the time should be cosidered i a discrete maer. So every time quatity should map to the begiig of the ext slot. This ew discrete parameters ca be calculated usig the Expressio (3). represet ceilig fuctio i this formula. Tj i Tj = BIi + BI 6 = BI i BI 6 S (3) Where T j is the time i cotiuous maer ad T j is its mapped time to the begiig of the ext slot. We will defie discretio delay as the differece betwee these two parameters. T j BI = i i BI Discretio Delay = Tj Tj = BIi + Tj = BI i 6 6 (4) Accordig to the IEEE stadard at least the first ie slots should dedicated to the CAP ad i this paper for reliability ad aalytical purposes the periodic data is goig to be trasmitted i CFP period. I each beaco, based o the umber of data, the coordiator dedicates the slots from the ed of super frame. This may force extra delay for the data. So i this paper we assumed that i each beaco the coordiator dedicate all 7 GTS slots so the first CFP data ca be set i th slot. The Figure shows a template of each super frame i our method i this paper. Remidig that the coordiator kows the time of data geeratio of each ode, it ca predict the situatio of further super frames. First for the simplicity, cosider the situatio of schedulig a super frame which cotais just oe data. At this simplified situatio two coditios may occur.. T j is i the CAP regio. As show i Figure 3 the red slot is the actual time ad the gree slot is the scheduled time. The T j is i the CFP regio. Figure 4 shows the case that the data is geerated i slot which ca be directly the CFP. Now the followig expressio ca calculate the schedulig delay forced to this packet because of the stadard limitatio. BI Schedulig Delay = max Tj, BIi + Tj + ( Tj T j ) (5) I a real situatio which more tha oe data ca exist for trasmittig i the th beaco, GTS slots will schedule i the FCFS maer accordig to the time of the data geeratio but this procedure is just for the same priority data which meas that the first CFP will dedicate to the first data geerated. This simple procedure will be performed just if the ext data matches its tolerable delay i the case it will be set i the secod GTS, otherwise the data with less tolerable will schedule first. The tolerable delay will show the priority of the data ad i the same Figure 3. Simple sceario with sigle data i superframe geeratig i CAP regio. Figure. CAP CFP Template of each superframe i our algorithm. Figure 4. Simple sceario with sigle data i superframe geeratig i CFP regio. 4 Vol 9 (7) February 6 Idia Joural of Sciece ad Techology

5 H. Safdarkhai ad S. A. Motamedi coditio the data with higher priority should schedule first. Figure 5 is showig a graphical example for 3 data slots. Cosider the set T as below T T, T T,, T is discrete time of = { (j, ) l } (k, ) (, 3) j, trasmissio of ode j which is the first data i the th BI ad T k, shows that the secod data i th BI dedicated to ode k. So the total delay for T jm, ca be calculated i the followig expressio. (mth data i th super frame). BI TotalDelay = max Tjm,, BIi + sig T (m )BI, Tjm, + jm BI i 6 (6) If the umber of data which should be set i the th beaco becomes greater tha 7, the additioal data will be i the queue for the ext super frame. For the data which will be kept i the queue the total delay ca be calculated m + 7 m BI Total Delay = BIi + m i = (7) Sice the coordiator is goig to decide about each BI ad SD at the begiig of each beaco iterval i a way that maximize the performace cosiderig the delay costrait of the odes data, it calculates the sum of total delay for the data of all odes that have data i that super frame. Also it calculates if extedig the super frame by icreasig the SO ad BO will cause ay ode data that caot match its tolerable delay. (Because the umber of GTS slots i each super frame is fixed, extedig its legth will possibly icrease the umber of data i that super frame ad queue delay will play more importat role i the total delay expressio). Figure 6 shows a sceario which extedig the super frame duratio, ca lead to lower delay. For clarity, just oe data is show i the Figure. If data productio time is i the slots to 8 of the secod super frame i (a), it ca be scheduled quicker i the exteded super frame (b). The gree slots show the first possible GTS slot for that data i each case. Cosider Total Delay,k The sum of total delay of all data i the super frame with SO=K of ode i. The Cost so=k is the sum of the total delay of all odes for SO=K. (SO=~4). Cost No. of Nodes = TotalDelay, so= k i k (8) Cosumig that the coordiator is a ode with higher processig power ad ca calculate the costs all alog the previous super frame, this procedure ca be easily performed by coordiator. I the case the process uit is limited, the calculatios for SO=~3 have acceptable result. 3. Simulatio ad the Results Accordig to the itroduced adaptive scheme for selectig Bo ad SO parameters of the stadard, coordiator ca calculate the total delay of each data by the theoretical expressios derived. It will repeat this calculatios for BO= to 3. Ad will select the best BO with lowest cost i the case the tolerable delay of all odes match. B e a co B e a co B e a co (a) Beaco Figure 5. Schedulig of GTSs i a superframe with more tha oe data. (b) Figure 6. Compariso total delay of a data i two differet BO ad SO selectio. (a) Cosiderig two successive superframe with BO=SO=. (b) Cosider oe superframe with Bo=SO=. Vol 9 (7) February 6 Idia Joural of Sciece ad Techology 5

6 GTS Schedulig Scheme for Real-Time Commuicatio i IEEE8.5.4 Idustrial Wireless Sesor Networks We have used MATLAB for simulatio ad compariso of our proposed algorithm with the stadard. For geerality ad better compariso the start time ad data iterval of each ode is chose radomly durig each simulatio 5. For precise compariso, the same radom data will use for both the stadard ad our algorithm so the result is ot depedat to the iitial radom data. We have chose the data iterval greater tha the base super frame duratio so every ode ca produce at most oly oe data i every super frame. This limitatio is because of the reliability of the etwork ad prevetio of istability. Otherwise havig odes with o limit traffic geeratio ca lead the etwork to a cogested situatio. We have assumed that the data packets are small size ad ca be set durig just oe slot. It is a acceptable assumptio because i idustrial etwork which we focus o that as a delay sesitive etwork the data is just moitorig data so the packet size is small. Here are the assumptios i a brief. Cosider periodic data geeratio traffic. Radom start time for each ode. Radom data iterval for each ode. Packet size is small ad ca be set durig oe slot. Base super frame Duratio=5.36ms. BO=SO. Because the delay is so importat i idustrial etwork the iactive regio is omitted. The simulatio has geerated 5 data for each ode ad rus for beaco iterval so all the packets ca be set. I this paper the delay defiitio is the time differece betwee the time the data is geerated ad the time the data is set successfully. For better depictio of the effectiveess of the proposed algorithm the average delay improvemet ca be defied by the followig formula. Averagedelay improvmet = N s ta dard Averagedelay i Im proved Avera ge I (9) N Where, N is the total umber of odes i the etwork, stadard Average delay is the average delay that ode i have usig the stadard ad Improved Average Delay is the average delay that ode i have usig the our improved algorithm. For ivestigatig the effect of umber of odes o the average delay, the simulatio has bee ru for differet umber of odes ad the results has bee depicted i the Figure 7. Average Delay Improvmet (ms) Number of Nodes Figure 7. odes. Average Delay Improvemet for differet Number of Nodes Average delay improvemet via umber of As show i Figure 7, the improvemet grows as the umber of odes grows. Growig the umber of odes will icrease the etwork traffic. The umber of odes should be limited so the etwork does ot get cogested. I a cogested etwork the queues of all odes will grow as the time passes so the etwork will get ustable. Figure 7 completely shows real effectiveess of our algorithm i the improvig the delay. For better depictio of the algorithm effect, Figure 8 ad Figure 9 illustrate the delay ad delay improvemet of a sample ode i a etwork with 4 odes. 4 ode etwork is selected sice it has the lowest average delay improvemet ad as the umber of odes grow the average delay improvemet will grow too. The reaso of this improvemet is that i the etwork with more odes, the traffic will grow ad the schedulig algorithm ad adaptive SO selectio algorithm ca demostrate its role more obvious. Our proposed algorithm focuses o the periodic data but our algorithm will have a positive effect o the delay of alarms ad the data packets which their geeratio time is ot specified too. Cosiderig that this kid of traffic is trasmitted i the CAP regio, usig the proposed algorithm will omit the GTS request packets which accordig to the stadard will sed i CAP regio. These requests are a bulk traffic for this regio ad by its omissio the traffic i this regio decreases cosiderably. The Delay i this regio is also related to the etwork traffic i this regio so, for showig this fact aother simulatio has bee doe usig MATLAB to simulate the effect of the etwork via the traffic i the CAP regio. Figure depicts the average delay for the packets that are sedig i CAP regio via the mea rate of geeratig the traffic i the odes. λ u shows the mea rate of packet geeratio of each ode i each superframe. So as the λ u icreases the traffic of a ode i each superframe icreases ad therefore the 6 Vol 9 (7) February 6 Idia Joural of Sciece ad Techology

7 H. Safdarkhai ad S. A. Motamedi Delay ms IEEE Our Prposed Algorithm Packet Number Figure 8. Delay of each packet (ms) i stadard ad our proposed algorithm. Delay Improvemet (ms) Packet Number Figure 9. delay(uitbackoff) Delay improvemet of each packet (ms)..5.5 λ (packet/sd) u Figure. Average delay i trasmissio i CAP regio via the rate of geeratio of packets i odes i each super frame. traffic of the etwork will icrease ad it ca be see that for the λ u above the.7 the etwork is gettig saturated. Accordig to Figure reducig the traffic i CAP regio ca lead to cosiderable average delay reductio, ad i our improved algorithm with omissio of the GTS request packets of the odes that should be set i CAP regio, the traffic of CAP has reduced cosiderably ad this will decrease the delay of the packets which should be sed i this regio. 4. Coclusio We have proposed a improved algorithm for the delay sesitive etworks with bulk periodic data traffic. This kid of etworks such as idustrial etworks that should trasfer the moitorig data has a high sesitivity to delay sice these etworks should work real-time. With studyig the IEEE stadard structure ad the characteristics of the idustrial etworks, the GTS request for all periodic data packets are omitted ad the coordiator ca calculate each ode data time. Also a adaptive SO parameter selectio is itroduced which coordiator will select the best SO for correspodig super frame which leads to best performace. The results show that our proposed algorithm without forcig a big chage to stadard (really easy to implemet) ad just by adaptig to the characteristics of idustrial etworks has a high gai i delay improvemet. The gai is related to the traffic so it is related to the data iterval of the odes ad also the umber of odes producig periodic data. Also it is show that omissio of the bulk traffic of GTS request i CAP regio results i cosiderable reductio of traffic i CAP regio ad it reduces the delay of data trasmissio i CAP regio. 5. Refereces. Willig A, Matheus K, Wolisz A. Wireless techology i idustrial etworks. Proceedigs of the IEEE. 5; 93(6):3 5.. Willig A. Recet ad emergig topics i wireless idustrial commuicatios: A selectio. IEEE Trasactios o Idustrial Iformatics. 8 4(): Kumar SA, Ilago P. Data fuellig i wireless sesor etworks: A comparative study. Idia Joural of Sciece ad Techology. 5 Mar ; 8(5): Mohammadi R, Ghaffari A. Optimizig reliability through etwork codig i wireless multimedia sesor etworks. Idia Joural of Sciece ad Techology. 5 May 8; 8(9): Rao S, Keshri S, Gagwar D, Sudar P, et al. A survey ad compariso of GTS allocatio ad schedulig algorithms i IEEE wireless sesor etworks. 3 IEEE Coferece o Iformatio ad Commuicatio Techologies (ICT); JeJu Islad, 3. p Park P, Fischioe C, Johasso K H. Performace aalysis of GTS allocatio i beaco eabled IEEE th Aual IEEE Commuicatios Soicety o Sesor, Mesh ad Ad Hoc Commuicatios ad Net-works, SECON 9; Rome. 9. p Koubaa A, Alves M, Tovar E. i-game: A implicit GTS allocatio mechaism i IEEE for time-sesitive wireless sesor etworks. 8th Euromicro Coferece o Real-Time Systems; Dresde. 6. p.. 8. Koubaa A, Alves M, Tovar E, Cuha A, et al. A implicit GTS allocatio mechaism i IEEE for time-sesitive Vol 9 (7) February 6 Idia Joural of Sciece ad Techology 7

8 GTS Schedulig Scheme for Real-Time Commuicatio i IEEE8.5.4 Idustrial Wireless Sesor Networks wireless sesor etworks: theory ad practice. Real-Time Systems. 8; 39(-3): Che J, Ferreira LL, Tovar E. A explicit GTS allocatio algorithm for IEEE IEEE 6th Coferece o Emergig Techologies ad Factory Automatio (ETFA);.. Cavalieri S, Moforte S, Corsaro A, Scapellato G, et al. Multicycle pollig schedulig algorithms for fieldbus etworks. Real-Time Systems. 3; 5(-3): Buttazzo GC. Rate mootoic vs. EDF: Judgmet day. Real- Time Systems. 5; 9():5 6.. Cheg L, Bourgeois AG, Zhag X. A ew GTS allocatio scheme for IEEE etworks with improved badwidth utilizatio. IEEE Iteratioal Symposium o Commuicatios ad Iformatio Techologies, ISCIT 7; Sydey, NSW. 7. p Sog JK, Jego-Dog R, et al. A dyamic GTS allocatio algorithm i IEEE for QoS guarateed real-time applicatios. IEEE Iteratioal Symposium o Cosumer Electroics ISCE 7; Irvig, TX. 7. p Mohammadi R, Ghaffari A. Optimizig reliability through etwork codig i wireless multimedia sesor etworks. Idia Joural of Sciece ad Techology. 5; 8(9): Kasaeipoor A, Ghasemi B, Amiossadati SM. Covectio of Cu-water aofluid i a veted T-shaped cavity i the presece of magetic field. Iteratioal Joural of Thermal Scieces. 5; 94: Vol 9 (7) February 6 Idia Joural of Sciece ad Techology