Performance Enhancement of UWB Power Control Using Ranging and Narrowband Interference Mitigation Technique

Transcription

1 The nternatona Ara Journa of nformaton Technoogy, Vo. 6, No., Ar 9 69 Performance Enhancement of UWB Power Contro Usng Rangng and Narrowand nterference Mtgaton Technque Rashd Saeed, Sara Khatun, Borhanuddn A 3, and Mohamad Aduah Teeom Maaysa, Research and Deveoment nnovaton Centre, Maaysa Deartment of Comuter and Communcatons Engneerng, Unversty Putra Maaysa, Maaysa Astract: Power contro s a crtca arameter for the desgn and evauaton of UWB-ased WPAN networs due to ts dstruted contro nature and non-fxed tooogy. The man ssues n UWB PC are the channe gan fuctuatons nduced y ndoor channe fuctuaton and nterference arsng from narrowand systems. n ths aer we ntroduce a ont PHY/MAC technque for DS-UWB ower contro desgn y exotng the hgh tme resouton of the UWB sgna for channe gan mrovement and mtgate the narrowand nterference to reduce transmtted ower. The resuts ndcate that the roosed aroach acheves etter BER and throughut over revous wors. Keywords: Utra-wdeand, ower contro, narrowand nterference, NB, TOA. Receved Juy 9, 7; acceted Decemer 4, 7. ntroducton Utra-WdeBand (UWB) Technoogy w ay a ey roe n short range wreess connectvty. Ths s due to the otenta advantages of UWB transmssons such as ow ower consumton, very hgh data rate, mmunty to mutath fadng, ess comex transcever hardware, and ocaton caates. Utra-wdeand as a hysca ayer technque rngs many features to the networ. nterest n UWB s motvated y features due to extremey wde andwdth (severa GHz); otenta for sgnfcant mutath cature, fne tme resouton, hgh data rate, and ow ower transmsson. These features aso rng severa chaenges to UWB hysca ayer and uer ayers desgn, for nstance the need for the recever to have a ong acquston tme due to the very short use, the need to oerate wth a dynamc nterference rofe from other sectrum users (narrowand systems) as we as UWB networ users, arsng from the arge andwdth UWB hysca ayer n the networ and durng the transmsson, the MAC ayer needs to reconfgure the Power Contro (PC) from tme to tme due to channe gan varaton, wreess channe fuctuaton, and nodes moty. For roust PC desgn, rangng etween nodes shoud e erformed for adatve channe gan estmaton []. UWB suffers from Narrow Band nterference (NB) due to the arge andwdth that UWB sreads over. PC s consdered as an effectve way n DS-UWB ased systems to comat MU, guarantee the requred SNR at the recever. However, ths s not true n Mute Rado nterference (MR) envronments. For exame, when a n exerences dee narrowand nterferer, ower contro sgnfcanty ncreases ts transmsson ower to ee the same SNR at the recever. Ths arge transmsson ower ntroduces arge nterference to other ns and reduces the system caacty [6]. So for accurate ower contro desgn, NB shoud e mtgated. n [5] the roactve and adatve aroach for rate assgnment and ower contro roems has een examned. The aer dscussed tradeoffs etween throughut and range to romote farness n the networ y ower contro otmzaton. However, the effect of moty on the rotoco was not nvestgated, where ony statonary nodes are consdered. An uncoordnated MAC rotoco for UWB networs wth rate adataton and nterference mtgaton to mrove throughut and energy consumton was resented n [3]. The musve nterference was mtgated at the hysca ayer as we as at the n ayer. However, the rangng caaty was not used. Uncoordnated UWB taored MAC agorthm medum access networs (UWB) was descred n [] ased on ure Aoha wth synchronzaton. (UWB) exoted rangng caaty offered y UWB PHY ayer. Dstance nformaton etween transmtter and recever was coected durng contro acet exchange. Mut User nterference (MU) was modeed ased on acet cosons. n [3], a Dynamc Channe Codng (DCC) ased rotoco was extended y ncororatng a mode for a UWB moe ad-hoc networs hysca ayer as we as new MAC ayer rotocos. Jont PHY/MAC ayer desgn was deveoed wth the dea of arrangng the hysca ayer and the MAC rotoco such that

2 7 The nternatona Ara Journa of nformaton Technoogy, Vo. 6, No., Ar 9 cosons may e reaced y rate reducton. Due to the advantages of used TH-UWB, t has een adoted to come out wth an nterference mtgaton scheme that reduces the mact of strong nterferers. n ths aer we ntroduce a ont PHY/MAC desgn for DS-UWB ower contro desgn y exotng the hgh tme resouton of the UWB sgna for hgh rangng estmaton accuracy usng Tme-Of-Arrva (TOA) agorthm for Non-Lne-Of-Sght (NLOS) envronments and mtgate the narrowand nterference to reduce transmtted ower usng douet Gaussan use shae. The rest of the aer s organzed as foows. n secton, the UWB sgna mode s resented; secton 3 dscusses the ower contro desgn evauaton. Sectons 4 and 5 resent rangng estmaton and narrowand nterference anayss and mtgaton; resectvey. Smuaton numerca resuts and dscussons are dscussed n secton 6. Fnay, secton 7 concudes the aer.. UWB Sgna Mode A Gaussan douet s comrsed of a ar of searated nd Gaussan's monocyce, a ostve use foowed y a negatve use. Ths offers two degrees of freedom, tme searaton etween the two uses n the douet and tme searaton etween douets. = ( ( ) () ( t The nd Gaussan dervatve G ( t ) can e exressed as: ( t µ ) σ ( t µ ) = G ( AG ex πσ () σ where the arameter σ determnes the monocyce wdth T. The effectve tme duraton of the waveform that contans 99.99% of the tota monocyce energy s T =7σ centered onµ = 3. 5σ. The factor A G s ntroduced so that the tota energy of the monocyce s normazed to unty,.e., G ( dt =. Wth sectrum anayss of equaton the (ESD): P( ω) = 4πe.( wt ). e ( ωt ).[ cosωt n ] (3) Snceω = πf, the nu frequences n ESD are, π ( ft n ) =,π,...,π.., then f = ( T n ), where =,. Usng equatons, and 3, the douet Gaussan use n tme doman and frequency doman are shown n Fgures and, resectvey. The nu frequences of Gaussan douet n Fgure can e controed y reguatng the oston of the second Gaussan use (the frst use ( ) egns at t t =, the second one ( egns at t = Tn ). From the fgure we can see that the PSD s sewed. As dected n Fgure there notch sectra n the douet waveform whch can e used to mtgate nterference from other systems. Fgure. Tme-doman reresentaton for Gaussan douet use wth tme deay etween the uses T n =.n sac. Nomazed PSD[d] Normazed amtude FCC emsson mt Frequency [Hz] Fgure. Power sectra densty of douet Gaussan use and FCC emsson mt for ndoor systems. 3. Power Contro Desgn Power contro s the rocess of determnng the transmtted ower of each communcaton termna n the UWB networ. Adustng the transmtted ower s extremey mortant for UWB ad-hoc networs ecause the transmttng node needs to sense the Sgna-to-nterference and Nose-Rato (SNR) at recevng node []. f the SNR s ower than the target vaue then the transmttng node ncreases ts transmtted ower and vce versa so as to mrove the tota system erformance. A measure of the n quaty (reated to t error rates) s the SNR oserved at the recever []. ndeed the n throughut s an ncreasng functon of the SNR. Thus, the n ower contro s an ncreasng functon of the SNR overa. To smfy the dscusson, we ase our formuaton of the ower contro roem drecty on the SNR and consder the aove roems of moty and NB. Let SNR= t(nsec) σ rec + P ( g ( Q P g ( + σ m m =,, (4)

3 Performance Enhancement of UWB Power Contro Usng Rangng and Narrowand nterference 7 rec where σ s the nose ower, P ( and g ( are the ower and channe gan etween node to node, resectvey, {,,3..., N},, and m m σ s the narrowand nterference whch affects the quaty of the rado n, roducng more acet osses, and resut n an overa rate reducton and an ncreased energy consumton. nterference has a arge mact on the system erformance and needs to e taen nto account as eary as n the desgn hase. ( s modeed as a comnaton of dstance x x, ath oss (α ) and Rayegh fadng (mutath) channe Γ ( where and ( g = K X = g ( X α g Γ ( (5) s the set of narrowand nodes that can cause nterference at UWB node ; g ( t ) s a reference vaue for ower gan evauated at D= m. To cacuate the dstance etween the nodes we can wrte: x x = cτ. (6) where c s the seed of ght and τ s the estmated tme of receved sgna at node, gven y []: τ = τ TOA + ε (7) where τ TOA s the tme-of-arrva and ε s the tme offset otaned from mean acquston tme, whch s the tme the recever need to synchronze wth the transmtter for more accurate TOA estmaton. TOA technque comutes dstance ased on the estmaton of the roagaton deay etween transmtter and recever. n order to do that the maxmum ehood estmator was used as foows [6]: ( r( s( t τ d )) d N Tos ˆ τ ( r) = arg mn( e ) (8) ToA( ML) τ R where N s the Power Sectra Densty (PSD) of the nose and Tos s the oservaton nterva over whch the estmaton s erformed. We can wrte that, for each n there s a ower SNR threshodγ T, refectng a certan QoS the n has to mantan n order to oerate roery [8]. Therefore, we requre that: SNR= σ rec + P ( g Q =,, ( P g ( + σ m m T γ ( (9) for every {,, 3..., N},. The term P g Q =,, ( s nown as MU, where n DS-UWB, each code has the effect of modfyng the transmtted sgna n such a way that a reference recever s caae of soatng the usefu sgna from other users sgnas, whch are seen as nterferng sgnas to the recever. The ossty of removng ths undesred nterference many deends on the characterstcs of the codes used for searatng data fows, and on the degree of system-eve synchronzaton. n reastc scenaros devces do not acheve dea synchronzaton and codes ose orthogonaty due to dfferent roagaton deays on dfferent aths, the recever mght not e caae of cometey removng the resence of the undesred sgnas, and as a consequence, system erformance s affected y MU. A detaed anayss of MU has een dscussed extensvey n [8]. UWB communcaton system arameters (such as the numer of users, t rates and acheved SNR) reresent the resources made avaae y the UWB hysca ayer (such as use shae, andwdth, rocessng gan, and numer of uses er. By adustng these system arameters, t s osse to desgn a hgh throughut MAC rotoco for UWB. The wde range of vaues of the UWB arameters enaes the desgn of hghy adatve PHY/MAC desgn whch may e matched to a wde range of servce requrements [6]. n addton to focusng on the resources to e managed, osse constrants mosed y the UWB technoogy tsef must e taen nto account. n the next secton we w dscuss rangng estmaton etween nodes and narrowand nterference mtgaton for more roust ower contro desgn. 4. Rangng Desgn The fne tme resouton of UWB sgnas enaes otenta acatons n hgh-resouton of channe gan adataton. The nove asect of UWB TOA s that the mutath tme-sread n many channes of nterest s often to tmes the nherent tme resouton of the UWB sgna detected n a matched fter recever. Some of the arameters that have een tradtonay used for dstance cacuaton are the Receved Sgna Strength ntensty (RSS), the Ange Of Arrva (AOA) and TOA [6]. Amongst these arameters, RSS s the east adequate n the case of UWB ecause of the cumuatve musve sgnas strength due to mutath and requres a ste-secfc ath oss mode [7]. The estmaton of AOA, on the other hand, requres mute antennas (or at east an antenna caae of eam formng) at the recever. Ths requrement mes sze and comexty demands that are often not comate wth the ow-cost, sma-sze

4 7 The nternatona Ara Journa of nformaton Technoogy, Vo. 6, No., Ar 9 constrants assocated wth acatons such as wreess sensor networs, whch UWB technoogy s artcuary suted for. Gven a transmtted sgna s (, the corresondng receved sgna can e wrtten as: r ( = h( * s( + n( () where h( s the channe muse resonse and n ( s AWG nose. f the sgna roagates over a erfect channe the muse resonse can e wrtten as: h( = A( d) δ ( t τ ( d)) () where d s the dstance etween the transmtter and the recever. The receved sgna can e wrtten as: r ( = A( d) s( t τ ( d)) + n( () Equaton ndcates that dstance d can e estmated from ether attenuaton A(d) or deay τ (d). The use of A(d) versus τ (d) determnes the method for estmatng dstance; Receved Sgna Strength ntensty (RSS) versus TOA, resectvey. The TOA technque comutes dstance ased on the estmaton of the roagaton deay etween transmtter and recever. TOA s the most commony used dstance estmaton method n the radar fed. Assume that a snge UWB use s transmtted over a mutath channe, then the receved sgna can e exressed as the sum of the frst sgna ath, other mutath comonents and nose: L r( = α ( t τ ) + α ( t τ ) + n( (3) = whereτ < τ <... < τ. L s the numer of mutaths, where L are unnown. We aso assume that the deay and channe coeffcent for the strongest mutath comonent, τ and α, are determned eforehand y means of a correaton technque; for exame, they can e estmated y exhaustvey searchng osse deay ostons, and choosng the one wth maxmum correaton outut [8]. A two-ste agorthm as n [7], can e emoyed frst to otan a rough estmate of the sgna deays and then to see the strongest comonent n the oc. Then, consder the sgna comonents ncudng and ror to the strongest ath and truncatng the r ( to t, we can wrte : T r ( = r(, r ( = α ( t+ τ ) + T t M α ( t+ τ ) + n ( ) t = (4) where T s the douet Gaussan use wdth (, M s the numer of mutath comonents efore the strongest comonent. f M =, then τ =, α =, ± and the second term n equaton (4) s gnored. n ( t ) s whte Gaussan nose truncated to the tme nterva (, T ] [4]. After wde-and fterng and samng r ( t ), we can wrte the vector r as: M r = α τ + α n + = τ (5) where τ s a vector consstng sames from (t + τ ) wth the same ength of r. Snce n s a whte Gaussan vector, then we can wrte the estmate τ as: M τˆ = α τ α arg max τ α r,m, mn α τ, = τ (6) where α = [ α... α M ] and τ = [ τ... τ M ]. The comutaton of TOA estmaton y equaton 6 was evauated y usng the teraton n Fgure 3 coded y MATLAB 7.4. The threshods of the agorthm, θ and θ, are mortant threshods that determne the α erformance of the estmator. Therefore, those crtca threshods can e seected ased on some statstca nformaton otaned from channe muse resonse n secfc envronment [8]. set n =, δ =, andµ = n= n+, fnd δ n Fnd µ... µ ] [ n nn µ nn θ α ˆ τ = δ n δ n n = r δ n δ θ arg max < < τ = n µ,..., µ µ [ µ... µ ] = arg mn r nn n ( n ) n = δ µ δ Fgure 3. Tme-of-arrva estmaton agorthm fow chart. 5. nterference Anayss and Mtgaton UWB systems are ae to co-exst wth narrowand technooges due to reguaton y FCC n Fa., as shown n Fgure. However, conversey the nfuence of narrowand sgnas on the UWB system can e sgnfcant, and n the extreme case, these sgnas may am the UWB recever cometey [8]. Even though narrowand sgnas nterfere wth ony a sma fracton of the UWB sectrum, due to ther T δ τ

5 Performance Enhancement of UWB Power Contro Usng Rangng and Narrowand nterference 73 reatvey hgh ower wth resect to the UWB sgna, the erformance and caacty of UWB systems can e affected consderay. Recent studes show that the BER erformance of the UWB recevers s greaty degraded due to the mact of NB [6] as shown n Fgure 4. Consder the resence of narrowand nterferer sgna wthn the DS-UWB system. Then the sgna at the recever can e wrtten as: r( S g n a P o w e r (W a t Nu Nc ( ) ( ) = A Ec = = + n( +σ GPS PCS c UN-SM and SM and EEE8.a EEE8./g FWA ( ) UWB h ( ) ( * ( t T c FCC art 5 mt (-4.3 dbm/mhz) 5.6 Frequency (GHz) T f (7) Fgure 4. Sectrum crossover of the narrowand nterferers n UWB systems. where N u s numer of users, attenuatons due to ass oss, E ( ) ( c) A reresent the s the energy er transmtted use for user. Ths s modeed wth douet Gaussan use (. n ( s the Gaussan rocess wth two sded ower sectra densty N and σ = A n ( s the varance of narrowand nterference, n ( s the narrowand nterference, ( s the tme-nvarant asynchronous mutath channe muse resonse for user. * denotes convouton, and A, A reresent the attenuatons due to ath oss, whch are functons of the transmtterrecever dstance. n order to evauate the narrowand nterference anaytcay, we construct a dscrete tme equvaent mode of the narrowand nterference y samng n ( every T s seconds, wth T s << Tc. The vector contanng the dscrete same s gven as: h T [ n ), n ( T ),..., n ( N ) T ] n R n (, (8) = s w s where T s s the samng tme, N w = Tw Ts s the numer of sames n oservaton wndow T w over whch the recever oerates. The ower sectra densty of the narrowand nterference can e wrtten as: ) S n N, f B f f + B ( f ) = (9), otherwse where f and B are the centra frequency and andwdth of the narrowand nterference, resectvey, and N s the Power Sectra Densty (PSD) of the nterference wthn ts andwdth. We consder two tyes of n-band nterference (B); an EEE8.a system wth centra frequency f =5.3GHz, and andwdth B =MHz, fxed Wreess Access (FWA) networ wth centra frequency f =3.9GHz and andwdth B =6MHz [6]. The autocorreaton functon of n ( s therefore gven y: N R ( τ ) = R ( τ ) () where R ( τ ) = B cos(πf τ ) sn c( πbτ ), and we can evauate NB varance as: N σ = A R () Puse shang s an emergng aroach for a more effcent usage of the recous rado sectrum resources and to ft to FCC sectrum mas. t consders an exanded vew of the wreess channe y managng and adatng use arameter dmensons of tme, frequency, sace, ower, and codng. n the next secton, we w dscuss use shang n order to sefadat the UWB use arameters and mnmze nand narrowand nterference tycay; WLAN and FWA. 5.. Puse Shang for Sectrum Adataton n the anayss heren, we assume an A Rae (ARae) recever, whch conssts of mute correators emoyng the temate sgna of v( = ( ( t τ ), τ s the excess deay of the th ath. When aroratey synchronzed and assumng the use shae ( nown to the recever, the correaton outut over a symo nterva of the th ath, denoted y r =,,..., N ), s gven y: where ˆ ( ) ( ) ( r r = ˆ s + n + n () s estmated at detector, and s, n, n th ath for the are the symo nterva of the transmtted sgna, narrowand nterference sgna, and AWGN sgna, resectvey. s = AN s r ( [ r ( r ( t τ )] (3) = AN m ( δ ) s

6 74 The nternatona Ara Journa of nformaton Technoogy, Vo. 6, No., Ar 9 N s n = ( t+ T + c T ) v( dt (4) = N s = f n = n( t+ T + c T ) v( dt (5) f The correaton matrx of the nterference sames { n n } R * n = E are coected over a symo nterva at dfferent aths. Snce the UWB sectrum w e ascay constant over the frequency range of NB centered at f [4], then (, ) eement of can e derved as: R n ], c c R n [ = N P ( f ) [ R () R ( ε ) R ( ε )] (6) where P r ( f ) s r n n n s the ower sectra densty of the receved use r ( at the frequency f. We can concude that the effect of NB on UWB systems s maxmum when the NB center frequency overas wth nomna center frequency of UWB sectrum. To mtgate the resence of narrowand nterference n UWB recever a notch fter shoud e aced after the ARae to fter out the nterference art around f = ( P ( ) ) from the use ower sectrum r f P r ( f ). Then we can wrte the transfer functon of the notch fter as: B B H ( f ) = u f f + u f f (7) and muse resonse as: πf t ( B h( = δ ( B e sn c (8) where B reresents the wdth of the sectra notch, whch s set to e suffcenty arger than the andwdth of the narrowand nterference. Ths can e erformed y a fter an [8]. Havng notched out the nterference, the remanng sgna s restored to the tme doman y erformng nverse fourer transform, whch can e exressed as: r ( = A ( t T c T ) n( (9) notch notch f c + πf t ( B ( = ( P ( f ) B e sn c (3) r r where t s n nanosecond and B s n ggahertz. For suresson of tyca NB, B << ; moreover, due to the ow ower of UWB transmsson system, P r ( f ) s aso of a sma vaue. So the notched use s exected to e ony sghty dfferent from r (. The rest of the sgna rocessng taes ace n tme doman. 6. Smuaton Resuts and Dscusson MATLAB 7.4 was used to smuate and anayze the system erformance n ths aer. Tae. Smuaton arameters. Parameter Vaue Numer of uses er t ( N ) Frame duraton ( T f ) ns Bt tme ( T ) ns Numer of chs er t ( N c ) Chs duraton ( T c ) ns samng nterva ( T s ).5ns Shang factor for the use (σ ).5ns Puse wdth ( T ).5ns Tme deay etween the uses n douet ( T n ).ns Path attenuaton exonent (α ) for LOS.7 Path attenuaton exonent (α ) for NLOS 3. 5 Fgure 5 shows the rangng estmaton error for NLOS envronments versus E N wth douet Gaussan use wdth T =. 5ns and varous search regons and reatve strength threshods. Resuts showed that n NLOS, seecton of sutae threshods eads to etter rangng erformance. For nstance, n dense mutath NLOS t s etter for the recever to seect hgh search regon threshod and ow reatve strength threshod due to the hgher roaty of drect-ath detecton at these vaues. However, hgher E N transmsson wth ower threshods st gves good erformance. Rangng estmaton error (m) θ τ =ns,θ α =.5 θ τ =ns,θ α =.5 θ τ =ns,θ α =.5 θ τ =ns,θ α =.5 θ τ =ns,θ α =.75 θ τ =ns,θ α = E /N (db) Fgure 5. Rangng estmaton error for NLOS channe versus E N wth use wdth T =.5ns and varous search regon and reatve strength threshods. The resuts n Fgure 6 wth θ τ = ns and α =.5 θ was comared wth [9] for D ndoor ostonng technque sutae for muse rado networs n mutath envronment. Snce the recevers n [9] are exected to record tmes ony and s nsenstve to amtude or hase wth gven

7 Performance Enhancement of UWB Power Contro Usng Rangng and Narrowand nterference 75 Channe muse Resonse (CRs), t gves ow estmaton error at ower SNR. However, an accurate roagaton mode s requred to estmate dstance reay, whch s very dffcut n ndoor envronment due to nodes moty and varatons of channe ehavour, snce Cramer-Rao Lower Bound (CRLB) does not gve soutons for ow ower NLOS envronments, CRLB contrutes hgh rangng estmaton error [4]. The roosed agorthm outerforms the NLOS Generazed Maxmum Lehood (NLOS-GML) [8]. Fgure 7 shows the frequency doman of the roosed use shae wth notches n the vctm frequences whch s erformed y randomzng the oarty of the transmtted uses and then shftng and adustng the center frequency of the douet use. Narrowand nterference deends on three factors: carrer frequency of the NB system, dstance etween NB node from UWB node and on the numer of NB nodes [8], where the aggregate NB can e cacuated as: Rangng estmaton error (m) roosed NLOS-GML D NLOS-CRLB E /N (db) Fgure 6. Rangng estmaton error (REE) for NLOS wth use wdth T =. 5ns and θ ns, θ 5. τ = α =. = λ χ n A( d ) (3) agr m m Where λ factor descres NB carrer frequency ocaton from UWB center frequency, m s the numer of NB nodes, and A d ) s the overa oss etween ( m the m th NB node at dstance d m from the seected UWB node. Ths can e soved y usng Mnmum Mean Square Error (MMSE) comnng wth ow numer of Rae fngers [6]. Fgure 8 shows the effect of Rangng Estmaton Error (REE) n ower contro erformance. Reca the resuts n Fgure 6, the rangng estmaton error at E N = db for the roosed method s (REE=.3m), NLOS-GML s (REE=.4m), D s (REE=.7m), and for NLOS CRLB s (REE=.84). From the fgure the hgh REE eads to wrong ower contro cacuaton whch eads to Hgh Bt Error Rate (BER). m Normazed ESD Frequency [Hz] x 9 Fgure 7. Normazed energy sectra densty for UWB douet Gaussan use to mtgate WLAN and FWA nterference. Bt error Rate (BER) Target SNR (γ T )(db) REE=.3m REE=..4m REE=.7m REE=.84m Fgure 8. UWB ower contro erformance under varous REE wth N = and N u = nodes. Fgure 9 shows the ower contro erformance for conventona DS-UWB, OFDM-UWB, and DS-UWB after use shang. The roosed method outerforms EEE8.5.3a roosed systems, OFDM-UWB and DS-UWB, due to nterference mtgaton effects. Bt error Rate (BER) Target SNR (γ T )(db) FWA f notch=3.9ghz WLAN f notch=5.8ghz DS-UWB OFDM-UWB Proosed Method Fgure 9. UWB ower contro erformance under varous UWB systems wth N = and N u = nodes. Fgure shows the erformance of UWB ower contro system as evauated from equaton 9 wth varous numer of nodes (,, 3, 4, and 5 nodes). For hgh numer of users (3, 4, and 5) the BER s saturated due to ncreased numer of acet cosons, heavy oads n the medum and MutUser nterference (MU). Ths roem can e soved y adotng sace dversty that can e rovded y rangng agorthm [4]. Another method to avod

8 76 The nternatona Ara Journa of nformaton Technoogy, Vo. 6, No., Ar 9 mutath nterference s to ower the duty cyce of the system, and can e acheved y ncreasng the use duraton ( T ), where duty cyce s gven y [8]: f duty cyce= T f T (3) By transmttng uses wth tme deay greater than the maxmum exected mutath deay, unwanted refectons can e avoded at the recever. Bt error Rate (BER) Target SNR (γ T )(db) N u =5 nodes N u =4 nodes N u =3 nodes N u = nodes N u = nodes Fgure. Proosed UWB ower contro erformance under varous numers of nodes wth N =. n Fgure varous numer of uses er t ( N ) were examned for target SNR for gven t error rates. Resuts show that hgh numer of uses er t ead to etter SNR for gven BER. N = means t duraton ( T ) and frame duraton ( T ) are equa, whch means hgh duty cyce equa to and eads to hgh mutath nterference, hence gves saturated curve n the fgure. Bt error Rate (BER) f Target SNR (γ T )(db) N = N = N = N =3 N =4 Fgure. Proosed UWB ower contro erformance under varous numers of uses er t wth N u = nodes. n Fgure we comared etween our roosed method and other methods from the terature. n order to emhasze the mortance of an nterference mtgaton and rangng estmaton, we comare the roosed method wth DCC-MAC [3] and (UWB) [] rotocos n term of target SNR. As seen from the fgure our roosed method outerforms the other two rotocos; ths s ecause ths method consders oth rangng and nterference mtgaton. The three methods converged at ow SNR vaues ecause eow SNR=5dB the domnant nterference s the Mut- MU [8]. Bt error Rate (BER) Target SNR (γ T )(db) (UWB) DCC-MAC roosed Method Fgure. Comarson of BER erformance of our roosed method and DCC-MAC and (UWB) wth N u = and N =. Fgure 3 comares the throughut etween the roosed method and DCC-MAC and (UWB). The throughut of (UWB) decreases wth the numer of nodes ecause (UWB) needs a common contro channe for RTS-CTS handshae to access to a destnaton. n dense non-ne-of-sght areas (UWB) contrute arge rangng estmaton error. DCC-MAC outerforms (UWB) ut the erformance st degraded as the numer of nodes ncreases, comared wth the roosed system. Throughut Performance of roosed method comared wth other reated wors (UWB) DCC-MAC Proosed method numer of nodes Fgure 3. Performance comarson etween roosed method and other reated methods. Ths s due to two reasons: frst, ecause narrowand nterference s comated n the MAC ayer usng rate adataton, whch fas wth strong nterferences e EEE8.a and EEE8.6; second, when the numer of nodes grows, nodes shoud deend on ts oca resources to avod foodng the medum wth contro messages that woud ncrease MU. 7. Concuson Power contro transmsson s an essenta MAC/PHY asect n whch accurate ower contro w reduce the tota ower consumton, myng ong attery fe, and controed nterference eve n the networ. The erformance evauaton of Utra-WdeBand (UWB) ower contro desgn has een nvestgated. Severa arameters were examned to acheve otma ower contro ased on rangng estmaton and nterference

9 Performance Enhancement of UWB Power Contro Usng Rangng and Narrowand nterference 77 mtgaton. Rangng estmaton was evauated y tmeof-arrva technque to erform the accurate tmng detecton. A mtgaton technque usng use shang aroach was roosed, whe cogntve rado can e a toc for further studes n nterference mtgaton. For future wor on roust and adatve ower contro, more cross-ayer arameters.e., synchronzaton, shoud e consdered. References [] Benedetto D. and Gancoa G., Understandng Utra-Wdeand Rado Fundamentas, Prentce Ha, New Jersey, 4. [] Benedetto D., Nards D., Jun M., and Gancoa G., UWB : Uncoordnated Wreess Baseorn, Medum Access Contro for UWB Communcaton Networs, Comuter Journa of EEE Moe Networs and Acatons, vo. 3, no. 7, , 4. [3] Boudec L., Ruen M., and Joerg W. A MAC Protoco for UWB Low Power Moe Ad-Hoc Networs Based on Dynamc Channe Codng Wth nterference Mtgaton, Technca Reort, Swtzerand, 4. [4] Chu X. and Murch R., The Effect of NB on UWB Tme Hong Systems, Comuter Journa of EEE Transactons on Wreess Communcaton, vo. 3, no. 5, , 4. [5] Charman M., Commssoners A., and Adesten., Federa Communcatons Commsson, Technca Reort, the Unversty of North Carona,. [6] Foerster R., The Performance of a DS-UWB System n the Presence of Mutath, Narrowand nterference, and Mutuser nterference, n Proceedngs of the Conference on UWB Systems and Technooges, USA,. 87-9, 4. [7] Gezc S., Sahnogu Z., and Poor V., A Two Ste ToA Estmaton Agorthm for R-UWB Systems, n Proceedngs of 3 th Euroean Sgna Processng Conferance, Antaya,. 7-83, 5. [8] Ghavam M., Mchae L., and Kohno R., Utra Wdeand Sgnas and Systems n Communcaton Engneerng, John Wey and Sons, 4. [9] Guo W., Fer P., and Barton K., D ndoor Mang and Postonng Usng an muse Rado Networ, Kuwer Academc Pushers, Boston,. [] Hayaneh M. and Adaah T., Statstca Learnng Theory to Evauate the Performance of Game Theoretc Power Contro Agorthms for Wreess Data n Artrary Channes, n Proceedngs of EEE Wreess Communcaton and Networng Conference, New Oreans, , 3. [] Kohno Y. and Le R., Otmum Mut User Detecton n UWB Mute Access Communcatons Systems, n Proceedngs of EEE nternatona Crmna Court, UK,. 8-86,. [] Koenchery S., Townsend J., Freeersyser J., and Bro G., Performance of Loca Power Contro n Peer to Peer muse Rado Networs wth Bursty Traffc, Comuter Journa of Goecom, vo., no.,. 9-96,. [3] Manue F., Marz R., and Le Boudec Y., Managng musve nterference n muse Rado UWB Networs, n Proceedngs of nternatona Conference on Broadand Networs, Austra,. 6-7, 6. [4] Q Y. and Koayash H., A Unfed Anayss for Cramer Rao Lower Bound for Non Lne of Sght Geoocaton, n Proceedngs of nformaton Scences and Systems, San, ,. [5] Raa J., Perre B., and Crstna L., U-MAC: A Proactve and Adatve UWB Medum Access Contro Protoco, Comuter Journa of Wreess Communcatons and Moe Comutng, vo. 5, no. 5, , 5. [6] Romeo G. and Franco M., On the Coexstence of Power Controed Utra-Wdeand Systems wth UMTS and Fxed Wreess Systems, Comuter Journa of EEE Transacton on Vehcuar Technoogy, vo. 45, no.,. -, 5. [7] Saeh A. and Vaenzuea A. A Statstca Mode for ndoor Mutath Proagaton, EEE Journa of Seected Areas n Communcatons, vo. 5, no.,. 8-37,. [8] Yong J. and Schotz A., Rangng n a Dense Mutath Envronment Usng Rado Ln, EEE Journa on Seected Areas n Communcatons, vo., no. 9, ,.

10 78 The nternatona Ara Journa of nformaton Technoogy, Vo. 6, No., Ar 9 Rashd Saeed receved hs BSc and MSc n eectroncs engneerng from the Sudan Unversty of Scence and Technoogy and Eectrca Engneerng, Karary Academcs for Technoogy, Sudan n 999 and, resectvey. He receved hs PhD from Unversty Putra Maaysa n 6 n comuter and communcatons system engneerng. Sara Khatun receved her BSc and MSc n aed mathematcs and PhD on hydromagnetc staty from the Unversty of Rashah, Bangadesh n 988, 99 and 994, resectvey. She receved her second PhD n communcatons and networng from Unversty Putra Maaysa n 3. Borhanuddn A receved hs BSc n eectrca and eectroncs engneerng from Loughorough Unversty of Technoogy n 979, hs MSc and PhD n eectromagnetsm engneerngfrom the Unversty of Waes n 98 and 985, resectvey. Mohamad Aduah receved hs BSc and MSc degree n eectrca engneerng from Unversty of Mssour at Roa, USA, n 99 and 993, resectvey, and PhD degree from Unversty Maaya, Maaysa, n 999.