Efficient Spectrum Sharing in the Presence of Multiple Narrowband Interference

Transcription

1 Eent Spetrum Sharng n the Presene Multple Narrwand Intererene Demsthenes Vuyukas Department Inrmatn and Cmmunatn Systems Engneerng Unversty the Aegean Karlvass 83, Sams, Greee e-mal: dvuyu@aegean.gr Astrat. In ths paper, we study the spetrum usage eeny y applyng wdeand methds and systems t the exstng analg systems and applatns. The essental mtvatn ths wrk s t dene the prspetve exstene etween analg FM and dgtal Spread Spetrum systems n an eent way sharng the same requeny and. The ptental verlad Spread Spetrum (SS) system an spetrally nde wthn the exstng narrwand Frequeny Mdulated (FM) radastng system upn several lmtatns, rgnatng a key mtvatn r the use the FM rad requeny and n many applatns, enmpassng wreless persnal and sensrs netwrks. The perrmane the SS system due t the verlayng analg FM system, nsstng multple narrwand FM statns, s nvestgated n rder t derve the relevant t errr pralty and maxmum ahevale data rates. The SS system uses dret sequene (DS) sprea dng, thrugh maxmal length pseudrandm sequenes wth lng spreadng des. The SS sgnal s evaluated thrughut theretal and smulatn-ased perrmane analyss, r varus types spreadng senars, r derent arrer requeny set (Δ) and sgnalt-ntererene rats, n rder t derve valuale results r uture develpng and plannng an verlay senar. Key-Wrds: Spread Spetrum, Dret Sequene (DS), Analg FM, Intererene, Bt - Errr-Rate. 1. Intrdutn Nwadays and uture trends wreless systems are manly twards develpng new wreless tehnlges s as t supprt hgher data rates wth mnmum sts. Ths s ahevale apart rm ther y demandng addtnal aess t the spetrum. The spetrum sarty s the mst serus hallenge ang the wreless ndustry tday and t s nly gng t get wrse durng the next years. Majr amplshments have already een develped n the area Cgntve Rad (CR) r spetrum sensng, spetrum sharng, dynam spetrum aess t prmary and sendary users and etween Rad Aess Tehnlgy (RAT) [1],[]. But, spetrum regulatn stll remans where many spetrum ands are unused and sme them are heavly ngested allated t spe applatns and peratrs. Enalng the prvsn serves and applatns n an eent way makng use the natural resure rad spetrum an e realzed y ntrdung prnples wdeand SS tehnques n real exstng regulatn. The spetrum verlay etween Dret Sequene Spread Spetrum (DSSS) systems and FM rad radastng serves an nrease spetral eeny and mmunatn apaty wthn a gegraphal area. Ant-jammng, ant-ntererene, prvay and lw pwer spetral densty are sme the advantages that the SS tehnque enmpasses and strengthen ther use t exstng shemes. Bth eld tests and analyses have prvded a perspetve as t what the apaltes suh system are. DOI : 1.511/jwmn

2 The mutual ntererene, whh n spe ndtns hgh densty emes unavdale, the estmatn ntererene nse serves as a measure r aeptng ther exstene. Ths verlay nept has een demnstrated n th PCS and [3] and ellular and [4]. In the prpsed wrk [5], t has een prpsed a CDMA netwrk that s permtted t e verlad n tp exstng mrwave narrw-and users that upy a part the spread-spetrum system andwdth (BW). In at, t hs s anther advantage CDMA ver ether TDMA r FDMA, eause ths wll nrease the verall spetrum apalty. Hwever, suh an applatn must e nsdered areully, eause the CDMA (wde -and) users and the narrw-and users an nterere wth eah ther. Analyss Ultra-Wde-Band (UWB) systems reveals that sgnals are sutale r underlay mmunatns and the desgn these systems are very prmsng, where t s neessary the understandng the eets ntererene t and rm narrw-and systems [6]. Smulastng methds and tehnques [7],[8] have een develped r smultaneus transmssn dgtal data wth analg FM, ver requeny ands n the MHz range. Sme these new methds are mpatle wth the standards analg FM r terrestral radast, whle thers are desgned r new requeny ands. The methd hyrd n and n hannel ( HIBOC) has een used, n rder t transmt dgtal aud smultaneusly wth analg FM, usng requeny-rthgnal analg and dgtal transmssn ver a ttal system andwdth 4 khz. Reent advanes n wreless mmunatns and eletrns have enaled the develpment varus types shrt-range wreless mmunatn systems, suh as WLANs, Bluetth, Hgh data rate WPANs, Lw pwer WPANs, Bdy area netwrks (BANs) and RFID - tehnlges wth a varety applatns (e.g., mmeral, hme, health, mltary, et.). Mst these systems as well as the wreless sensrs netwrks, utlze the spread spetrum tehnque r the physal layer [9]. The unusual applatn requrements sensr netwrks make the he transmssn meda mre hallengng. One ptn r rad lnks s the use ndustral, sent and medal (ISM) ands, whh er lense ree mmunatn n mst untres. These requeny ands suer rm lmtatns and harmul ntererene rm exstng applatns and applatns that may emerge n the uture [1]. Anther ptn r rad lnks s the use the already uped requenes, n an verlay senar utlzng the ultra lw pwer transmssn the sensr ndes. Expltatn ths spetrum verlay nept n the physal layer n the eld wreless persnal and sensr netwrks, an nrease mmunatns apaty and spetral eeny, ut may ause the llwng types ntererene: ) ntererene rm the narrwand FM statns t the SS system and ) ntererene rm the verlad wdeand SS system n the FM reevers. The rst s the spe ths paper. The later ase was nvestgated and the rrespndent results were presented n [11]. The perrmane the Dret Sequene Spread Spetrum system s examned ne verlad n tp the exstng rad and multple FM statns. The pralty errr r varus FM ntererng ndtns s derved r the ase sngle and multple spread spetrum users. The smulatn the prpsed nguratn r the estmatn the errr rate, ams r the est apprah a realst system, as well as r the knwledge the prdued sgnals at the utput eah mdule. Cnsequently, ased n the analyss and ardng t mathemat analytal mdels eah mdule, the smulatn the whle system s realzed, takng nt nsderatn all the stmulated urrenes that are aused due t nn-deally peratn the passve and atve elements. Mrever, the Addtve Whte Gaussan Nse (AWGN) s taken nt aunt r the Spread Spetrum system and als r eah FM statn. In Setn, the Spread Spetrum system s rely desred n the rm used n ths paper. The ttal ntererene analyss r sngle and multple SS due t multple narrwand ntererene users s perrmed n Setn 3, whle the FM pwer spetrum apprxmatn s 6

3 presented n Setn 4 alng wth sme ther prpertes n the ntext lsed-rm mathematal expressns. Setn 5 ntans sme ndatve numeral results r sngle and multple SS users, whle n Setn 6 smulatn results r a sngle SS user are presented. Fnally, a re dsussn and nludng remarks are gven n Setn 7.. Desrptn Spread Spetrum System The spread spetrum sgnal s gven y [1] as K K s()() t = s ()() t s= P t t t + k k k k k k k ( k ) (1) k = 1 k = 1 where P k s the reeved pwer the k-th spread spetrum, τ k s the tme delay the sgnal unrmly dstruted nt [,T], θ k s the phase angle unrmly dstruted n [,π], k (t) s the mdulatng dgtal sgnal the k-th user gven y { a 1, n } () k k ()() = n T n= t a p t nt where n = ± < < + and pt s the retangular pulse T duratn, wth P[ k (t)=1]=p[ k (t)=-1]=.5, and ω ο s the arrer requeny the sgnal. (t) s the spreadng de gven y () k k ()() = n T n= where () t { ± 1 } k t p t nt s ne hp randm nary sequene { n }, whh nssts ndependent dentally dstruted (..d) randm varales wth equal pralty, T s the spreadng de hp duratn and p s the hp waverm, assumed retangular. 3. Intererene Analyss 3.1 Sngle SS user We nsder the reever mdel as depted n Fgure 1. The ttal reeved sgnal s rrupted y nse and ntererene r()()()() t = s t + t + n t () where (t) dentes the ntererene and n(t) s the zer-mean whte Gaussan nse. Assumng that de synhrnzatn has een estalshed and we have peret hannel estmatn, the nput t the demdulatr s ( ) ( ) ( ) ( ) ( ) ( ) r () t = s t t + t t + n t t (3) 1 T Input WdeBand r(t) r 1 (t) x(t) Flter T ( ) dt Sampler (t=t ) Desn Deve Output (t) PN Sgnal Generatr g ()s t T ( t + ) Clk Fgure 1: DS reever mdel wth BPSK mdulatn 63

4 The nput quantty t the desn deve, durng the perd T the data sgnal, s T T ( ) ()()s()()()s ( ) ( ) Z = r1 ()s t t + dt = P t t t + + t + n t t t + dt = (4) T T T ()()s()()s()()s ( ) ( ) ( ) = P t t t + + t t t + dt + n t t t + dt We assumed that = / >> 1/ T, s that the dule requeny term ( s ( t ) 1 s ( t ) 1) + + s neglgle, suppressed y the andpass lter llwng the demdulatr. Frm equatns (), (3), (4) and the at that (t) s nstant ver the perd T we have where T Gp 1 ()() T + + n = ± + + n n=, () { 1 } Z P t p t nt dt S S PT S S The de hp sequene { n } t ± (5) T Gp 1 pt () t nt dt = GpT = T (6) n= T ( ) S = ()()s t t t + dt (7) T ( ) Sn = n()()s t t t + dt (8) an e mdeled as a randm nary sequene, mprses y statstally ndependent symls wth equal pralty, s unrrelated (whte) and therere E[ nm ] = E[ n ] E[ m ] r n m and these ndtns mply that E[ n ] = and E n = 1. Peret de, phase and syml synhrnzatn are assumed. Susttutng the spreadng de nt (7), we tan where Lkewse where ( n+ 1) T S G p 1 = J (9) n n n= ( ) Jn = ()()s t pt t nt t + dt (1) nt ( n+ 1) T S G p 1 = N (11) n n n n= ( ) Nn = n()()s t pt t nt t + dt (1) nt The equatn (5) an als e wrtten as S S + y where S s the desred sgnal and y = S + Sn dentes the ttal addtve ntererene plus Gaussan nse. The rst term the rght-hand sde the equatn s determnst and ts value s gven y equatn (5). The terms S are ndependent randm varales wth zer mean value unrmly unded and 64

5 var Internatnal Jurnal Wreless & Mle Netwrks (IJWMN) Vl. 4, N. 5, Oter 1 { } S wth G p, s applyng the Central Lmt Therem (CLT) [14] mples that S nverges n a Gaussan dstrutn wth zer mean value and varane 1. Cnsequently, the dstrutn S s almst Gaussan when s large. We must underlne, that r the present analyss lng sequenes have een utlzed wth large pressng gan. Therere, the send term s a summatn tw zer-mean ndependent Gaussan varales, ndatng that y wll have an almst zer-mean Gaussan dstrutn and varane gven y { y } { S } { S } var = var + var. Based n CLT and Gaussan apprxmatn, the pralty n errr depends n the statstal haratersts the ntererene. The nal pralty errr wll e gven y [14] 1 E er T Pe = (13) var{ S} + var{ Sn} and the ttal sgnal-t-nse rat at the utput the rrelatr y E [ S] SNRD = (14) var S + var S Gp { } { } where E = PT s the reeved t energy (t), P s ts mean pwer and er s the mplementary errr untn. Based n the prevus dentns, the varane the varale y s { } { } { } var var var y = y = S + Sn = E S + E S n = GpE J n + GpE N n Suppse that θ s an ndependent randm varale unrmly dstruted n ver [ ] n (15),. The statnary n(t) and a hange varales mples that the varane N n s N T E N n = (16) 4 N where s the tw-sded nse pwer spetral densty (PSD) and we assumed that = / >> 1/ T. Fr the alulatn the varane ntererene, llwng the nse predure results t [13] T 1 n ()()s p T E J = T R R d (17) where R () s the autrrelatn () t, Rp () s the autrrelatn untn the PN sequene. Τhe lmts the ntegral an e extended t nnty eause the ntegrand s trunated. Beause R () transrm Rp (), yeld the llwng [15] s an even untn, the nvlutn therem and the knwn Furer 1 n ()sn ( ) E J = T S T d (18) where S () s the PSD the ntererene ater passage thrugh the wdeand andpass lter. I S s the PSD the ntererene at the nput the wdeand andpass lter and H() ' () s ts transer untn, then ' S ()()() = S H. Suppse that the eets the wdeand 65

6 lter and the ntegratn ver negatve requenes are neglgle ( >> 1/ T ), then + W / 1 n ()sn ( ) W / E J = T S T d (19) where we have assumed that the andwdth the ntererene s W W / T. The PSD the ntererene S () s gven y equatn (35) at the next setn and the ttal pralty errr s gven y P e = 1 er N + T +W / S G ( )sn ( )T d p W / 3. Multple SS users The spe ths setn s t examne the perrmane the Dret Sequene Spread Spetrum system n the ase multple spread spetrum atve users and t aess the t errr pralty n the presene analg FM ntererene and multple aess ntererene (MAI), usng the smpled mprved Gaussan apprxmatn. We assume mmunatn thrugh pnt-t-multpnt transmssn, s multple aess ntererene s nsdered wth peret de, phase and syml synhrnzatn, partularly r dwnlnk transmssns. The ttal reeved sgnal n the nput the desred spread spetrum reever s K 1 K 1 (1) r()()()() t = s t ()() + s()()() t + n t = P t t t + + t + n t k k k k k k k k k = k = where s k (t) s the k-th user s transmtted sgnal, k s the data sequene r user k, k s the spreadng sequene r user k, τ k and φ k are randm delay and arrer phase terms relatve t the desred reerene user, P k s the reeved pwer user k, ω ο s the arrer requeny the sgnal, (t) the ntererng analgue FM sgnal and n(t) dentes the zer mean whte Gaussan nse the hannel. The reeved sgnal ntans the desred user, the K-1 undesred users and the ntererng FM sgnal plus nse and all sgnals are mxed dwn t aseand, multpled y the PN sequene the desred user and ntegrated ver a t perd T. The desn statst the reever r user s: whh may e expressed as where T K 1 T 1 () Z = r()()s() t t t + dt () Z = I + IMAI + I FM + In (3) T I = ()()s() P t t t dt (4) I = ()()s()()s() P t t t + t t dt (5) MAI k k k k k k k = 1 T IFM = ()()s() t t t + dt (6) 66

7 T In = n()()s() t t t + dt (7) where I s the desred ntrutn t the desn statst rm the desred user k=, I MAI s the multple aess ntererene, MAI, rm ther users, I FM s the ntrutn the ntererng verlad FM sgnal and I n s the thermal nse ntrutn. The ntrutn the FM ntererene and nse term s nvestgated and analyzed prevusly (S and S n respetvely). Sne the perrmane the Spread Spetrum system under nvestgatn s assumed t e ntererene lmted, whh means that the FM ntererng sgnal s the dmnant ntererene mpnent, the numer smultaneus users s lmted (relatve small K). Hene t s essental r the alulatn MAI t use an apprxmatn, whh s aurate r relatve small values K. Fr the alulatn the Multple Aess Intererene ntrutn and nally the verall perrmane the system, the smpled expressn the Imprved Gaussan Apprxmatn (SIGA) s used Perrmane the verlad system ased n SIGA The smpled mprved Gaussan apprxmatn t the t errr rate s ased upn the premse that the MAI nverges t a Gaussan randm varale as the numer hps per data t N emes large and r any K [16]. Based n the expansn derenes methd [17], the SIGA requres nly that the mean μ and the varane σ ψ=var(i MAI ) t e determned. Based n the Central Lmt Therem and the at that all ntererene mpnents the desn statst are assumed t e ndependent randm varales wth dstrutn, whh nverges t Gaussan r large N, the varane the desn statst, s var() Z var() = Ivar() + var() I + I (8) MAI FM n The ntrutn nse and analg FM ntererene t the desn statst s analyzed prevusly. Fr the ase peret pwer ntrl suh that all users have dental pwer levels and these pwer levels are nt randm, the mean and the varane = var() I MAI, are gven y [18] G pt = P ( K 1) 6 (9) 4 T 3G p 1 K 1 K = ( K 1) P + Gp + (3) and the pralty errr s gven y [18] E P e = E Q T y + N T T T S ( ) (31) The smpled t errr pralty expressn r the ase MAI [16], analg FM and nse ntererene s gven y 67

8 where () 1 SIGA ET 1 ET Pe er + er 3 4() 1 eq 4( 3) + Ι + + Ιeq 1 ET + er 1 4( 3) + Ι eq (3) I eq = var{ I n } + var{ I FM } = N T T T S ( ) (33) S s the lsed-rm FM pwer spetrum apprxmatn gven y equatn (35) at the and () next setn, where the FM pwer spetrum aggregatn s alulated ver the andwdth all the under-utlzed FM statns. 4. FM Pwer Spetrum Apprxmatn In rder t tan aurate results r the BER equatns (), (3) and (33), the ntererene pwer the FM spetrum at the nput the dgtal reever s requred n lsed-rm mathematal expressn. The requred pwer spetral denstes the ntererene FM sgnals are presented as a result laratry measurements and mathematal dervatns. The FM sgnal s generally a randm press and nsequently an e nly statstally presented. Speally, t haraterze the pwer spetral densty the FM sgnal we must measure the values statstal parameters, suh us mean, maxmum, mnmum and medan. The measurement nguratn nssts a spetrum analyzer, a nal antenna and a laptp mputer. The prgram n the mputer ntrls the spetrum analyzer thrugh HP-IB prt. The spetrum analyzer parameters suh as reslutn andwdth, vde andwdth, requeny span and sweep tme are assgned thrugh the Laptp PC. Three knds statns were rerded dependng n the transmtted nrmatn; ne that transmts nly mus, ne that transmts nly speeh (ve) and ne that transmts the mnatn these tw. The statstal evaluatn the prevus measurements and the dervatn a lsed-rm mathematal expressn have een studed n [13]. Further statstal pressng shwed that the Gaussan t r the estmatn the PSD the FM hannel respnds very well ardng t several ndtns the transmtted data. The equatn s gven y the llwng expressn: ( ) Gˆ m () = y + exp A m (34) where the parameters y s a nstant near the nse threshld, A s the ampltude nstant, m s the enter requeny, ω s the standard devatn and R dentes the regressn analyss the t data. All the Gaussan t parameters are gven n Tale 1, whle Fgure depts the mean rerded values and the Gaussan urve t. 68

9 -3 Mean Data Gaussan Ft Plynmal Ft -35 Pwer (dbm) ,9 99,95 1, 1,5 1,1 Frequeny (MHz) Fgure : Mean value a FM statn and ts spetrum apprxmatn Tale 1: Gaussan t parameters Parameters y A m ω Values dbm dbm 1 MHz.9697 MHz R.985 The ttal FM ntererene rm all FM statns wll e the sum ther PSD s M M [ ] ' ˆ 1 ( m 1) m S () = Gm() = My + A exp m= 1 m= 1 where M s the numer the FM statns, y, A and ω are gven n Tale 1, (35) 1 s the requeny the rst FM statn and Δ m s the arrer separatn etween tw susequent statns. 69

10 5. Numeral Results Fr the alulatn the pralty errr r sngle SS user nterered y multple FM statns, we appled the CLT r the estmatn the ttal pwer spetrum all FM statns, M mplementng the mean value y m = and standard devatn m = M. M We assumed that all the FM statns, M, have the same standard devatn and thus pwer. Fr est results and wrst ase senar, we must nsder as many statns as they an t n the FM requeny and MHz. Suggestvely, we present the results n Fgure 3 t Fgure 5 applyng equatn () r a typal value pressng gan, e.g. G p = 5 = 17dB, and r a typal arrer separatn etween the FM statns, e.g. Δ m =5kHz. The results shw the pralty errr versus E / N r varus sgnal-t-ntererene rats, hp rate, FM statns M and requeny derenes Δ etween the tw systems. The results are als mpared usng the pralty 1 E errr r the deally BPSK perrmane Pe = er. N Pralty Errr, Pe Theretal BPSK = - db = -1 db = db = 1 db E/N (db) Fgure 3: Bt errr pralty r Δ=, =1Mps, M=4 and W =MHz 7

11 Pralty Errr, Pe Theretal BPSK = - db = -1 db = db P/P 1-8 J = 1 db E/N (db) Fgure 4: Bt errr pralty r Δ= /, =1Mps, M=4 and W =MHz Pralty Errr, Pe Theretal BPSK = - db = -1 db = db = 1 db E/N (db) Fgure 5: Bt errr pralty r Δ=, =5Mps, M=1 and W =5ΜΗz 71

12 As an e shwn rm Fgures 3-5, there s dependeny etween the arrer spang these tw systems, the hp rate the SS system and the numer FM statns n the requeny and. The wrst ase perrmane the SS system s urrng when the tw systems has dental enter requeny (Δ=) and the numer FM statns are large. Whle the requeny set Δ etween the enter requenes these tw systems s kept as large as pssle and urthermre the hp rate the SS system has maxmum values, n that ase the system perrms deally, even r great extent ntererene. The perrmane the SS system utlzng multple users s derved y usng equatns (3) and (33). In Fgure 6, the t errr pralty as a untn atve Spread Spetrum users s presented, r M=4 ntererng FM statns, E / N =5dB and 1dB, pressng gan G p = 5 = 17dB, hp rate =1Mps, requeny set etween the tw systems Δ= and sgnal-t-ntererene rats = -db, -1dB and db. Ardngly, Fgure 7 depts the t errr pralty as a untn atve Spread Spetrum users, r M=1 ntererng FM statns, E / N =5dB and 1dB, pressng gan G p = 5 = 17dB, hp rate =1Mps, requeny set etween the tw systems Δ=5MHz and sgnal-t-ntererene rats = - db, -1dB and db. In Fgure 8 the t errr pralty as a untn atve spread spetrum users s presented, r M=1 ntererng FM statns, E / N =5dB and 1dB, pressng gan G p = 5 = 17dB, hp rate =1Mps, requeny set etween the tw systems Δ= / and sgnal-t-ntererene rats = -db, -1dB and db Pralty Errr, P s = 5dB, = -db = 5dB, = -1dB = 5dB, = db = 1dB, = -db = 1dB, = -1dB = 1dB, = db Numer Smultaneus Users Fgure 6: Bt errr pralty r Δ=, =1Mps, M=4 and G p =5 7

13 1 1-1 Pralty Errr, P s = 5dB, = -db E 1-4 = 5dB, = -1dB = 5dB, = db = 1dB, = -db = 1dB, = -1dB = 1dB, = db Numer Smultaneus Users Fgure 7: Bt errr pralty r Δ=5MHz, =1Mps, M=1 and G p = Pralty Errr, P s = 5dB, = -db E 1-4 = 5dB, = -1dB = 5dB, = db = 1dB, = -db = 1dB, = -1dB = 1dB, = db Numer Smultaneus Users Fgure 8: Bt errr pralty r Δ= /, =1Mps, M=1 and G p =5 73

14 The results shwed that there s a huge dependene etween the spreadng des, the requeny dstane etween the tw systems and the amunt ntererene, whle the pralty errr deterrates when the numer smultaneus users s nsderaly nreased. 6. Smulatn Results The reprted jetves ths study wll e supprted wth the help an advaned desgn smulatn system (Aglent-ADS) and evaluated n a realst envrnment. The apprah s ased ntally n theretal level and then n smulatn level. Durng the smulatn, the eet all atrs that have analytal expressn s vered, as well as these that d nt have, tryng t evaluate vald stuatns and systems [13]. The ratnale the smulatn system nssts several steps. The rst step mprses the smulatn the spread spetrum transever, where the nguratn r BPSK mdulatn s taken nt nsderatn. Speally, r the reever s desgn, the rrelatr mdel reever has een nted, as already dsussed n Setn and presented graphally n Fgure. A alratn the system has een perrmed, n rder t ensure r the auray the press n terms theretal SNR vs.. The send step s the smulatn eah FM statn separately, s as t rrespnd, as muh as pssle, t atual ndtns. Therere, t has t e taken nt aunt all the eatures that mpletely haraterze the emtted requeny mdulated sgnal (pre-emphass, devatn, et.). Lkewse, the ttal FM spetrum s reprdued upn the remmendatns ITU r FM transmssn [19], where the spetral utput appears lke the measured ne Fgure. Susequently, ths mdule FM statn s haraterzed as ndependent suunt and the RF sum all suunts prvdes the ttal multple narrwand ntererene n the prpsed system. Durng the smulatn press sgnal transmssn SS system, we dealt wth the ttal rad path, whh s haraterzed y the multpath transmssn, the prpagatn envrnment, the mvement reever and the heghts the antennas. A typal prpagatn mdel r uran envrnment was seleted, eause the prpagatn hannel eet wasn t the al mssn ths study. The prpsed mdel r the rad path hannel was nrprated nt the press s as the nal system transmtter and reever t e alrated, wthut the FM ntererene, ut wth the addtn whte nse, leadng t a prdued t errr rate smlar t the theretal nes. Integratng all FM suunts nsttutes the nal step the smulatn nguratn, whh mprses the ttal mdel FM statns n the nal system transmtter and reever, llustratng the multple narrwand ntererene t the system. Several numer nterered narrwand FM statns are nsdered durng the smulatn predure. The ttal perrmane the SS system s measured thrugh the estmatn the errr rate at the utput the SS reever. In rder the t errr rate measurements t eme mre prese and eent, the mdel SS system shuld e regulated s as t nlude all the eets ther ndvdual elements, apart rm the reever s nse. The ntrl system nse wll eme rm a ntrlled nse sure. Ths s what regulates als the quantty. The auray BER measurements s atually nly estmatn and nt the prese measurement, whh ther auray depends n the quantty reeved samples. It s als reprted as Mnte Carl apprah. Generally, the BER estmatn s usually very tmensumng press r pratal applatns. Typally, the tehnque Imprtane Samplng [],[1] s used, n rder t sustantally derease the numer requred samples. Ardng t ths tehnque durng the smulatn, the haratersts the system are derentated s as t vary the pralty densty untn. Eventually, t s the preerale tehnque r the enhanement BER measurements. 74

15 Fr the mplementatn the smulatn system ertan nstant parameters the unts and suunts have een used, n njuntn wth varales nes. Beause the mplexty and the large alulatng tme the smulatn, we vared nly sme the parameters the SS and FM system. At Tale, the nstant and the varale parameters the smulatn system are depted. Prr t the FM ntererene emplyment, a alratn the system has een perrmed, n rder t ensure r the aurate easlty the press (theretal SNR vs. ). Tale : Smulatn parameters Cnstant Pressng Gan (G=17dB) SS Bandwdth MHz ( =1Mps) Frequeny separatn etween tw nsequently FM arrers (5kHz) Sgnal-t-Nse Rat r SS system and eah FM statn (SNR = 1dB) Prpagatn hannel and antenna gan Varale SS Pwer FM Pwer (eah statn) E / N Varane the errr estmatr Frequeny separatn (Δ) etween the SS system and the entral requeny FM and Fgure 9 and Fgure 1 dept the results the smulatn regardng the t errr rate at the utput the rrelatr r varus rats wanted t unwanted sgnals (CIR) and requeny separatn (Δ) etween the SS system and the mddle requeny the FM and. At ths pnt, rstly we must mentn that the alulatn the pwer the ntererene nludes the pwer rm all the FM statns that are ntaned n the predetermned y the ITU requeny and and sendly, the varane the errr estmatr had the value.1. The spe value was satsatry enugh, ut partularly aggravatng r the smulatn system. Beause the tme-nsumng smulatn press, we tred t dept results mparale t the theretal nes, lke.e. the numeral results the analytal expressns n Setn 5. 75

16 1x1-1 1x1-1x1-3 Pralty Errr, Pe 1x1-4 1x1-5 1x1-6 1x1-7 1x1-8 Theretal BPSK = db =1 db = 5 db = db E/N (db) Fgure 9: Bt errr pralty r Δ=MHz, =1Mps, M=1 and Δ m =5kHz 1x1-1 1x1 - Pralty Errr, Pe 1x1-3 1x1-4 1x1-5 1x1-6 1x1-7 1x1-8 Theretal BPSK = db =1 db = 5 db = db E/N (db) Fgure 1: Bt errr pralty r Δ= /, =1Mps, M=1 and Δ m =5kHz 76

17 7. Dsussn and Cnlusns In ths study, an eent spetrum sharng apprah has een prpsed nreasng the usage real exstng regulated spetrum y applyng a wdeand spread spetrum system. In partular, the nvestgatn spetrum verlay a Dret Sequene Spread Spetrum system n the exstng narrwand FM radastng system has een presented. We nsdered the mplementatn a wdeand SS system nsstng sngle and multple users, stuated n tp an exstng nventnal multple narrwand FM system utlzng the MHz and, ausng ntererene n the SS system. We examned the amunt multple analg FM ntererene, whh wuld nt ause exessve degradatn n the -lated SS system, thrugh extensve ntererene analyss and smulatn results. The ndutng researh was ased n smulatn mmunatn systems; t s rtal t valdate the system under develpment t assure that the results are ndatve the systems peratn n a usale envrnment. The parameters these tw systems that had t e taken nt nsderatn were several enugh s as t desgnate the justatn ths study. N hannel dng has een used eause ur prmary endeavur was t ensure peratn etween these tw systems. The results ths study prvde all the prelmnary - ut neessary - lmtatns attemptng t spetrally exst tw dssmlar systems. The evaluatn errr pralty ased n smulatn predure prvdes nterestng results that are, n sme ases, lse t the results taned rm the theretal apprxmatn n setn 4, and when Fgures 9 and 1 wth Fgures 3 and 4 are mpared respetvely. Ths mples that the assumptns and apprxmatns prpsed n setn 3 and 4 and ntrdued n analytal expressns r the pralty errr, are aeptale and arely aet the taned results. Dvergenes etween theretal and smulatn results are served r hgh values sgnal-t-ntererene rat, where the smulatn predure gves mre strt ntererene levels. Fllwng the Central Lmt Therem, the Gaussan apprxmatn r the dervatn the ttal FM ntererene and the smpled expressn the Imprved Gaussan Apprxmatn (SIGA) r multple SS users, we nlude t the llwng results: - The wrst ase r the pralty errr urs when the tw systems have dentally requenes. - The requeny derene Δ has mnmal mpat t the perrmane the system, whle the numer FM statns s suently large. - As the ttal numer the FM statns s kept large nsderng small requeny separatn Δ m, the urves t-errr-rate are mprved. - The system perrmane s hghly degraded, espeally when the numer atve smultaneus users s nreasngly rapdly. - Fr mre than rughly ten users the degradatn the perrmane reahes a threshld ver whh addtnal users have n mpat n the system perrmane r the same FM ntererng ndtns. In general, ths study gves a key mtvatn r the expltatn a derent rad requeny and r the physal layer, than the nes the standards prvde, n wreless persnal and sensrs netwrks. Extended researh atvtes are urrently undertaken y the authrs n the area a detaled SS system ptmsatn, n terms dng and ntererene anellatn tehnques, n rder t estalsh the maxmum allwale t rate r the data sgnal. Hwever, the results depend als n the he radastng parameters, suh as the aeptale ntererene level n the demdulated analg FM aud sgnal (SNR degradatn), as presented n [11]. 8. Reerenes [1] Wang, J., Ghsh, M. & Challapal K. (11). Emergng Cgntve Rad Applatns: A Survey, IEEE Cmmun. Magazne, Vl. 49, N. 3, pp

18 [] Chen, K.-C. & Prasad, R. (9). Cgntve Rad Netwrks, Jhn Wley & Sns Ltd, UK. [3] Mlsten, L. B. et al. (199). On the easlty a CDMA verlay r persnal mmunatns netwrks. IEEE Trans. Cmmun., Vl. 1, N. 4, pp [4] Hmmy, H. H. & Gupta, S. C. (1996). Overlay ellular CDMA n AMPS rward and reverse lnk analyss. IEEE Trans. Veh. Tehnl., Vl. 45, N. 1, pp [5] Pkhltz, R. L., Mlsten, L. B. & Shllng, D. L. (1991). Spread spetrum r mle mmunatns. IEEE Trans. Veh. Tehnl., Vl. 4, N., pp [6] Chan, M. & Grgett, A. (9). Cexstene Between UWB and Narrw -Band Wreless Cmmunatn Systems, Preedngs the IEEE, Vl. 97, N., pp [7] Papadpuls, H. C. & Sunderg, C.-E. W. (1998). Smultaneus radastng analg FM and dgtal aud sgnals y means adaptve preanelng tehnques. IEEE Trans. Cmmun., Vl. 46, N. 9, pp [8] Chen, B. & Sunderg, C.-E. W. (). Dgtal aud radastng n the FM and y means ntguus and nsertn and preanelng tehnques. IEEE Trans. Cmmun., Vl. 48, N. 1, pp [9] Rme,r K. & Mattern, F. (4). The Desgn Spae Wreless Sensr Netwrks. IEEE. Wreless Cmmun., Vl. 11, N. 6, pp [1] Akyldz, I. F., Su, W., Sankarasuramanam, Y. & Cayr, E. (). A Survey n Sensr Netwrks. IEEE Cmmun. Magazne, Vl. 4, N. 8, pp [11] Vuyukas, D. & Cnstantnu, P. (3). Perrmane Degradatn Analg FM System Due t Spread Spetrum Overlay. IEEE Trans. Bradast., Vl. 49, N., pp [1] Pkhltz, R. L., Shllng, D. L. & Mlsten, L. B. (198). Thery Spread-Spetrum Cmmunatns - A Tutral. IEEE Trans. Cmmun., Vl. 3, N. 5, pp [13] Vuyukas, D. ( 3) Intererene Crtera r Spetral Overlay Systems etween Dret Sequene Spread Spetrum and Analg FM Sgnals. Dssertatn, Natnal Tehnal Unversty Athens. [14] Rappaprt, T. S. ( ). Wreless Cmmunatns - Prnples and Prate, nd ed., Upper Saddle Rver: Prente-Hall In. [15] Shanmugan, K. S. & Brephl, A. M. (1998). Randm Sgnals - Detetn Estmatn and Data Analyss, New Yrk: Jhn Wley & Sns. [16] Mrrw, K. R. & Lehrert, J. S. (1989). Bt-t-t errr dependene n sltted DS/SSMA paket systems wth randm sgnatures sequenes. IEEE Trans. Cmmun., Vl. 37, N. 1, pp [17] Hltzman, J. M. (199). A smple aurate methd t alulate spread spetrum multple aess errr praltes. IEEE Trans. Cmmun., Vl. 4, N. 3, pp [18] Mrrw, K. R. (1998). Aurate CDMA BER alulatns wth lw mputatnal mplexty. IEEE Trans. Cmmun., Vl. 46, N. 11, pp [19] ITU-R BS.45-3 (1), Transmssn standards r FM sund radastng at VHF, ITU Remmendatn Standards. [] Lu, D. & Ya, K. (1998). Imprved mprtane samplng tehnque r eent smulatn dgtal mmunatn systems. IEEE J. Selet. Areas n Cmmun., Vl. 6, N. 1, pp [1] Chen, J. Lu, D. Sadwsky, J. S. & Ya, K. (1993). On Imprtane Samplng n Dgtal Cmmuatns Part I: Fundamentals. IEEE J. Selet. Areas n Cmmun., Vl. 11, N. 3, pp