Performance Evaluation of QoS Parameters in Dynamic Spectrum Sharing for Heterogeneous Wireless Communication Networks

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1 IJCSI Internatonal Journal of Computer Scence Issues, Vol. 9, Issue 1, No 2, January 2012 ISSN (Onlne): Performance Evaluaton of QoS Parameters n Dynamc Spectrum Sharng for Heterogeneous Wreless Communcaton Networks Kanezhl. R 1 and Chandrasekar. C 2 and NthyaRekha.S 3 1,3 Research Scholar, Department of Computer Scence, Peryar Unversty, Salem, TamlNadu , Inda 2 Assocate Professor, Department of Computer Scence, Peryar Unversty, Salem, TamlNadu , Inda Abstract Cogntve rado nodes have been proposed as means to mprove the spectrum utlzaton. It reuses the spectrum of a prmary servce provder under the condton that the prmary servce provder servces are not harmfully nterrupted. A cogntve rado can sense ts operatng envronment's condtons and t s able to reconfgure tself and to communcate wth other counterparts based on the status of the envronment and also the requrements of the user to meet the optmal communcaton condtons and to keep qualty of servce (QoS) as hgh as possble. The effcency of spectrum sharng can be mproved by mnmzng the nterference. The Utlty functon that captures the cooperatve behavor to mnmze the nterference and the satsfacton to mprove the throughput s nvestgated. The dynamc spectrum sharng algorthm can mantan the qualty of servce (QoS) of each network whle the effectve spectrum utlsaton s mproved under a fluctuaton traffc envronment when the avalable spectrum s lmted. Keywords: CR, throughput, propagaton delay, spectrum effcency, Interference. 1. Introducton It s commonly beleved that there s a spectrum scarcty at frequences that can be economcally used for wreless communcatons. By recent studes of FCC, t shows that the scared spectrum can be well utlzed and unused spectrum e whte spaces can be utlzed by the secondary users wth the advance technology of Cogntve Rado (CR)[2] to mplement the opportunstc spectrum sharng. However, as noted by the FCC, there are large portons of allotted spectrum that are unused when consdered on a tme and geographcal bass. There are portons of assgned spectrum that are used only n certan geographcal areas and there are some portons of assgned spectrum that are used only for bref perods of tme. Studes have shown that even a straghtforward reuse of such wasted spectrum can provde an order of magntude mprovement n avalable capacty. Thus the ssue s not that spectrum s scarce the ssue s that most current rado systems do not utlze technology to effectvely manage access to t n a manner that would satsfy the concerns of current lcensed spectrum users. Cogntve rado [2], [3], [4] s currently consdered as one of the most promsng solutons to the aforementoned scarcty problem by enablng a hghly dynamc, devcecentrc spectrum access n future wreless communcaton systems. A CR can adapt the operaton parameters of ts rado (frequency band, modulaton, codng etc) and ts transmsson or recepton parameters on the fly based on cogntve nteracton wth the wreless envronment n whch t operates. CR wll lead to a revoluton n wreless communcaton wth sgnfcant mpacts on technology as well as regulaton of spectrum usage to overcome exstng barrers. Cogntve rado not only adapts to the avalable spectrum but t also shows the better Qos and the channel condtons that satsfes the requrement of the effectve performance of the bandwdth. Cogntve Rado s an emergng technology provdes an way to effcent way for better utlzaton of the unused spectrum. Spectrum allocated to the prmary users s not used fully at all nstances of tmes. Hence, the number of tryng to use ths unused lcensed spectrum s ncreasng enormously. So, the dea s that the sensng the unused or empty frequences of the prmary users and that can be Copyrght (c) 2012 Internatonal Journal of Computer Scence Issues. All Rghts Reserved.

2 IJCSI Internatonal Journal of Computer Scence Issues, Vol. 9, Issue 1, No 2, January 2012 ISSN (Onlne): accommodated to some other unlcensed (Secondary) users. Ths makes the effcent utlzaton of the avalable spectrum. Ths can be acheved by usng the Cogntve rado to dentfy and used to allocate the unused spectrum bandwdth that can allocate dynamcally by changng ther parameters keepng n vew the QoS requested by the secondary user or smply the applcaton, wthout nterferng wth the prmary users. The technques developed to date for the enhancement of heterogeneous networks concentrate on mprovng ther accessblty and QoS. Numercal smulaton results demonstrate that Throughput and Spectrum Effcency of networks employng dynamc spectrum sharng are much better than those of networks employng fxed allocaton, especally for networks under heavy traffc load, when spectrum s lmted. I have already proposed the spectral effcency n my prevous work that the call arrval rate vs spectral effcency[1]. The remanng work e Performance of QoS based on spectrum sharng usng CR nodes s carred out n the present work. The paper s organzed as follows; Secton 2 and 3 defnes cogntve rado and proposes a system model approach for ts mplementaton. In secton 4, Performance analyss has been nvestgated to mprove the system effcency. Secton 5 and 6 presents the Proposed Algorthm of the work and smulaton results wth mplementaton ssues. Fnally, conclusons are presented n Secton Cogntve Rado 2.1 Introducton A Cogntve Rado s a rado that s able to sense the spectral envronment over a wde frequency band and explot ths nformaton to opportunstcally provde wreless lnks that best meet the user communcatons requrements. CR provdes the real tme nteracton wth ts envronment. Ths provdes the way to dynamcally adapt to the dynamc rado envronment and the rado analyzes the spectrum characterstcs and changes the parameters among the users that share the avalable spectrum. Wth the approach to solve the ssue of scarcty of avalable rado spectrum, the Cogntve rado technology s gettng a sgnfcant attenton [4]-[6]. The prmary feature of cogntve rado s the capablty to optmze the relevant communcaton parameters gven a dynamc wreless channel envronment. Snce cogntve rados are consdered lower prorty or secondary users of spectrum allocated to a prmary user, a fundamental requrement s to avod nterference to potental prmary users n ther vcnty. On the other hand, prmary user networks have no requrement to change ther nfrastructure for spectrum sharng wth cogntve networks. Therefore, cogntve rados should be able to ndepently detect prmary user presence through contnuous spectrum sensng. In general, cogntve rado senstvty should outperform prmary user recever by a large margn n order to prevent what s essentally a hdden termnal problem. Ths s the key ssue that makes spectrum sensng very challengng research problem. 2.2 Cogntve Rado Parameters The Cogntve Rado system must relate the performance objectves to the transmsson parameters and the envronmental parameters n order to reach at an optmzed soluton. Whle defnng the lst of parameters we make a compromse between the large tme scale, system level parameters and the small tme scale, transmsson level parameters. Table I shows the transmsson parameters used n ths paper to generate a utlty functon. TABLE I TRANSMISSION PARAMETER LIST Parameter Name Symbol Descrpton Transmt Power P Transmsson Power Modulaton Type MT Type of Modulaton The avalable system parameters should be defned as decson varables for evolutonary algorthms calculatng generatng utlty functons. Table II shows the Envronmental parameters used n ths paper to generate a utlty functon. The BER parameter value deps on several channel characterstcs, ncludng the nose level and transmt power. Envronmental Parameters nform the system of the surroundng envronmental characterstcs. SBAC Algorthms s chosen for the allocaton algorthm due to ther fast convergence. TABLE II ENVIRONMENTALLY SENSED PARAMETER LIST Copyrght (c) 2012 Internatonal Journal of Computer Scence Issues. All Rghts Reserved.

3 IJCSI Internatonal Journal of Computer Scence Issues, Vol. 9, Issue 1, No 2, January 2012 ISSN (Onlne): Parameter Name Symbol 2.3 Utlty Functons The system performance ndexes are descrbed n terms of utlty functons. The actual results should take balance of these utlty functons, whch can meet the QoS requrements and mprove the performance. Utlty functons are defned ndvdually consderng the current user s QoS specfcatons. Ths mples to the exstence of a trade-off among the parameters for a partcular channel. Ths s analyzed by the correspondng weghts assgned by the user to each of them. Ths s actually very useful n our decson-makng process and provdes wth a varety of solutons for the best optmzaton of a problem. Four performance measures of Data Transmsson rate, Propagaton Delay, Spectral Effcency and Throughput are consdered n ths paper and the utlty functons are desgned as n Table III: TABLE III UTILITY FUNCTIONS Descrpton Bt Error Rate BER Number of bt errors dvded by the total number of transferred bts durng a studed tme nterval. Sgnal-to- Interference Nose Rato SINR Rato of the receved strength of the desred sgnal to the receved strength of undesred sgnals (nose and nterference). Nose power N O Magntude n decbels of the Nose Power Performance Metrcs Low Propagaton Delay Mnmze RTT Maxmze Throughput Maxmze Spectral Effcency Usng the objectves n Table III as sole nputs to the utlty functons wll not suffce. It s ambguous to have the system mnmze power consumpton whle also mnmzng BER. Thus, the objectves must also contan a quantfable rank representng the mportance of each. Ths wll allow the utlty functon to characterze the trade-offs between each objectve by rankng the objectves n order of mportance. Several approaches exsts for determnng the preference nformaton of a set of objectves. 3. System Model We consder the spectrum sharng among multple servce provders, they belong to the lcensed bands. We assume that there are a number of prmary and secondary users communcatng wth ther partners smultaneously. Here, the term user wll be used broadly where t can be a moble node or base staton n a dstrbuted networks. Smultaneous communcatons among users (.e., both prmary and secondary users) wll nterfere wth each other. The enttes we wll work wth are communcaton lnks each of whch s a par of users communcatng wth each other. We wll refer to communcaton lnks belongng to secondary networks as secondary lnks. We wll also consder the nterference constrants at the recevng nodes of prmary networks whch wll be referred to as prmary recevng ponts. We assume that each prmary recevng pont can tolerate a maxmum nterference level. Also, secondary lnks have desred QoS performance n terms of BER. We assumed a model n whch S base-statons are sharng S dfferent frequency bands. Each band has a user capacty of K wth throughput of R per user. Therefore, each band can support an aggregate traffc of KR bts per second per Hertz. In theory, each base-staton acheves ths throughput va the lcensed band provded that there are K actve users and enough packets from each user to fully explot the capacty. We should note at ths pont that the proposed sharng protocol apples to both downlnk and uplnk transmssons. The access strategy used by each basestaton to serve the users could be any of the standard technques. Actve users are defned to be users of the wreless network requestng access for ther data flow. Assume each base staton {1, 2,..., S} has a random number of requests for establshng a sesson say a each dstrbuted accordng to a Posson dstrbuton wth average rate of λ. Each a s assumed to be ndepent from requests at other statons. We assume that all users and sessons have the same data rate requrements met by the rate R. 4. Performance Analyss Assume that there are M prmary recevng ponts and N secondary communcaton lnks n the consdered geographcal area. Let us denote the channel gan from the Copyrght (c) 2012 Internatonal Journal of Computer Scence Issues. All Rghts Reserved.

4 IJCSI Internatonal Journal of Computer Scence Issues, Vol. 9, Issue 1, No 2, January 2012 ISSN (Onlne): transmttng node of secondary lnk to recevng node of s secondary lnk j by g ( j, ) whle the channel gan from the transmttng node of secondary lnk to prmary recevng p pont j as g ( j, ). If N denotes the total nose and nterference at the recevng sde of secondary lnk, for wreless access system, the correspondng effectve bt-energy-to-nose spectral densty rato can be wrtten as s W ( j, ) N R s g j 1, j ( j, ) Pj N Where W s the spectrum bandwdth, R s the transmsson rate of secondary lnk. Here, W / R s the processng gan whch s usually requred to be larger than a partcular value. The processng gan s smply equal to one for other multple access technologes and μ denotes the SINR. Now, f a partcular modulaton scheme s employed, there wll be an explct relaton between BER and SINR. Thus, for a specfc requred BER level of secondary lnk, μ s requred to be larger than a correspondng value. Hence, the QoS requrement for secondary lnk can be expressed as g P μ ³γ,=1,2,...,N T Now, let j be the mnmum nterference level tolerable by prmary recevng pont j. The nterference constrant for prmary recevng pont j can be wrtten as N =1 g P T,j=1,2,...,M p (j,) j where total nterference at the prmary recevng pont j should be smaller the tolerable lmt. We wll assume that transmsson rate of secondary lnk can be adjusted n an allowable range wth mnmum and maxmum values are R, mn max R respectvely. Also, power of secondary lnk s max constraned to be smaller than the maxmum lmt P. 5. Proposed Algorthm The proposed work, QoS of Spectrum sharng among multple Servce Provders s carred out n a long-term spectrum Assgnment scheme. The functon coordnates and negotates the spectrum assgnments between multple Servce Provders for large geographcal areas. The spectrum assgnments are updated perodcally and t s explaned wth the help of the proposed algorthm named SBAC (Selecton of Best Avalable Channel). 6. Smulaton Results Algorthm : SBAC BS mn (moble node s request to Base Staton) CR BS ncr CR current _ channel _ avalable _ lst ncr prob current _ channel _ avalable / total _ channel ch_frq f frmax< ch_frq frmax frq f frmn> ch_frq frmn ch_frq nter frmax frmn cost t *60* c 1 1 ch _ u (10* 1* prob) 2*log 3* nter cost cu _ lst[ cu _ count ] ch _ u f ( cu _ count! 0) cu _ lst f max cu _ lst max ch _ lst channel _ max max The Cogntve Rado receves the RF envronment at ts recever and nvolves tself n a decson-makng process to accommodate a new user requestng the spectrum allocaton. Ths requres a decson-makng consderng certan factors, such as the secondary user s requrements as parameters lke, ts Channel codng, data transmsson rate, etc. The user needs the spectrum to carry out ts communcatons and specfes ts QoS requrements to the cogntve rado that also gets the nformaton about the RF envronment from a sensng module. Copyrght (c) 2012 Internatonal Journal of Computer Scence Issues. All Rghts Reserved.

5 IJCSI Internatonal Journal of Computer Scence Issues, Vol. 9, Issue 1, No 2, January 2012 ISSN (Onlne): The utlty functon represents the rado s behavoral trats for the decson-makng process to acheve the requred optmzaton. There can be many possble trats that can be consdered n ths regard but we shall consder only some of the basc trats for the rado n ths research. Some of the possble trats that can be consdered are the occuped bandwdth, spectral effcency, throughput and delay. We shall just consder a few parameters only, n order to mantan the smplcty n the research. These are the frequency bands, power and BER. But for communcaton between them the max data rate s affected by the nose n the system, and ths wll dep on the nose of the propagaton medum, the nose fgure of the RX, the power level of the TX, the transmsson loss, and the maxmum tolerable error rate. Satsfactory data transmsson can be acheved wth hgher nose at a lower bt rate because of the statstcal nature of the nose, and the tme-doman averagng of sgnals whch occurs n the RX. 6.1 Mnmze Propagaton Delay Propagaton delay s the amount of tme taken for the sgnal to travel from the ser to the recever over a medum. It can be computed as the rato between the lnk length and the propagaton speed over the specfc medum. Propagaton delay = d / s where d s the dstance travelled and s s the propagaton speed. Fg : 2 No. of Users VS Throughput The objectve of the paper represents that mprovng the communcatons qualty of the rado. Maxmzng the throughput deals wth the data throughput rate of the system. Emphaszng ths objectve, the overall system throughput should be ncreased and t s reached n the proposed work as shown n the Fg : 2. Ths refers to the ncrease n overall data throughput transmtted by the sgnal. 6.3 Mnmze RTT Round-trp tme (RTT) s the tme t takes for a clent to s a request and the server to s a response over the network, not ncludng the tme requred for data transfer. Fg : 1 No. of users VS Propagaton Delay In the proposed work, as the number of Users ncreases propagaton delay gets mnmzed as shown n the Fg : 1. Current Round-Trp Tme (RTT) of every actve connecton s estmated n order to fnd a sutable value for the retransmsson tme-out. RTT s the major contrbutng factor to latency on "fast" (broadband) connectons and t's especally mportant to mnmze the number of requests that the clent needs to make and to parallelze them as much as possble. 6.2 Maxmze Throughput The maxmum data rates of the TX and RX dep on the bandwdth of the crcuts, and smplstcally t mght seem that the least of these wll settle the ssue. Copyrght (c) 2012 Internatonal Journal of Computer Scence Issues. All Rghts Reserved.

6 IJCSI Internatonal Journal of Computer Scence Issues, Vol. 9, Issue 1, No 2, January 2012 ISSN (Onlne): As the mean call arrval ncreases the Interference gets decreased and there wll be a mnute varatons n the Interference as shown n the Fg : Maxmze Spectral Effcency() The Spectrum Effcency s s the rato of average busy channels over total channels owned by servce provders e t refers to the amount of nformaton that can be transmtted over a gven bandwdth. Fg : 3 No. of Users VS RTT In the proposed work, as the number of prorty users ncreases the RTT value decreases, as to mnmze the number of round trps that need to be made. 6.4 Mnmze Interference Interference s the key factor that lmts the performance of wreless networks. The problem may be thought of as arsng from the lmtatons of the recever: better recevers are more able to extract the desred sgnal from a nosy envronment of background radaton and other transmtters. nterference frmax frmn In ths paper, an nterference aware dynamc spectrum sharng method s appled. It dynamcally mnmzes the nter-cell nterference and sgnfcantly mproves the system performance. Fg : 4 Mean Call Arrval VS Interference Fg : 5 Mean Call Arrval VS Spectrum Effcency As the mean call arrval ncreases the channel Utlzaton also ncreases as shown n the Fg :5. Hgher Spectrum effcency s estmated because the call blockng rate s lower; thus more calls can contrbute to the spectrum utlzaton 7. Conclusons The proposed dynamc spectrum sharng algorthm has been shown to be an effectve soluton for mprovng the spectrum effcency under fluctuatng traffc loads whle mantanng the Interference and throughput n ther acceptable QoS levels. It s llustrated that ths model can be successfully employed n the key spectrum allocaton decsons n such a spectrum sharng envronment n a heterogeneous wreless network. In ths paper, we have studed the dstrbuton of the nterference generated by a secondary network to a prmary network. We have derved a general formula for the nterference takng nto account the cogntve ablty, throughput and transmt power. Also, Cogntve rado parameters, Utlty Functons, QoS and nterference constrant parameters on network performance are nvestgated and dscussed. Copyrght (c) 2012 Internatonal Journal of Computer Scence Issues. All Rghts Reserved.

7 IJCSI Internatonal Journal of Computer Scence Issues, Vol. 9, Issue 1, No 2, January 2012 ISSN (Onlne): References [1] R.Kanezhl, Dr.C.Chandrasekar, S.Nthya Rekha, Channel Selecton for Spectrum Sharng usng CR Nodes, Internatonal Proceedngs of Computer Scence and Informaton Technology, IACSIT Press, 2011, vol.20, pp [2] Danjela Cabrc, Shrdhar Mubaraq Mshra, Robert W. Brodersen, Implementaton Issues n Spectrum Sensng for Cogntve Rados n Proc. 38th Aslomar Conf. Sgnals, Systems and Computers, Pacfc Grove, CA, Nov. 2004, pp [3] F. Akyldz, W. Y. Lee, M. C. Vuran, S. Mohanty, "NeXt generaton dynamc spectrum access cogntve rado wreless networks: A survey, Computer Networks Journal (Elsever), 2006, Vol. 50, pp [4] Lars Berlemann, George Dmtrakopoulos, Klaus Moessner, Jm Hoffmeyer, Cogntve Rado and Management of Spectrum and Rado Resources n Reconfgurable Network, Wreless World Research Forum, [5] Jon M. Peha, Emergng Technology and Spectrum Polcy Reform, Internatonal Telecommuncatons Unon (ITU) Workshop on Market Mechansms for Spectrum Management, ITU Headquarters, Geneva, January [6] R. Etkn, A. Parekh, and D.Tse, Spectrum sharng for Unlcensed bands, n IEEE Internatonal Symposum on New Fronters n Dynamc Spectrum Access, 2005, pp [7] T.J. Harrold, L.F. Wang, M.A. Beach, G. Salam, A. Yarmohammad, O. Holland, Spectrum Sharng and Cogntve Rado Opportuntes for Effcency Enhancement, IEEE, [8] Ammar Alshamran, Xuemn (Sheman) Shen, and Lang Xe, QoS Provsonng for Heterogeneous Servces n Cooperatve Cogntve Rado Networks, IEEE Journal on selected areas n Communcatons, Aprl 2011,Vol. 29, no. 4. [9] Lela Musavan and Sona Assa, Qualty-of-Servce Based Power Allocaton n Spectrum-Sharng Channels n the IEEE "GLOBECOM" 2008 proceedngs. [10] Ypng Xng, Chetan N. Mathur, M. A. Haleem, R. Chandramoul and K.P. Subbalakshm, Real-Tme Secondary Spectrum Sharng wth QoS Provsonng, IEEE CCNC, [11] Alreza Attar, Olver Holland, Mohammad Reza Nakha, Interference Management n Shared Spectrum for WMAX Systems n IEEE Proc. VTC Sprng, pp , [12] Kevn Fall, Kannan Varadhan., The ns Manual, The VINT Project, May 9, [13] Teerawat Issaryakul, Ekram Hossan, Introducton to Network Smulator NS2 ISBN: e- ISBN: , Sprnger She receved her B.Sc Degree from Unversty of Madras n She receved her MCA and M.Phl Degrees from Peryar Unversty and Annamala unversty, n 2001 and 2007, respectvely. Her research nterests nclude Moble computng, Spectrum and Wreless Networkng. Dr. C. Chandrasekar s a member of IEEE. He receved hs Ph.D degree from Peryar unversty. He s workng as an Assocate Professor, Department of Computer Scence, Peryar Unversty, Salem. Hs areas of nterest nclude Wreless networkng, Moble Computng, Computer Communcatons and Networks. He s a research gude at varous unverstes n Inda. He has publshed more than 40 techncal papers at varous Natonal & Internatonal conferences and 43 journals. S.Nthya Rekha s a member of IEEE. She s a Research scholar n the Department of Computer Scence, Peryar Unversty, Salem. She receved her B.Sc Degree from Bharathayar Unversty n She receved her MCA and M.Phl Degrees from IGNOU and PRIST unversty, n 2006 and 2008, respectvely. Her research nterests nclude Moble Computng, Rough set and Wreless networkng. R. Kanezhl s a member of IEEE. She s a Research scholar n the Department of Computer Scence, Peryar Unversty, Salem. Copyrght (c) 2012 Internatonal Journal of Computer Scence Issues. All Rghts Reserved.