Narrow-band Interference Suppression in DSSS Systems Using Efficient Adaptive Filters

Transcription

1 009 Internatonal Conerene on Communaton and Moble Computng Narrow-band Intererene Suppreon n DSSS Sytem Ung Eent Adaptve Flter Abtrat In th paper, we preent a novel adaptve ntererene uppreon method by ombnng wth tme-doman lter and requeny-doman lter. Demontrated by mulaton reult, the method an gnantly mprove the perormane o DSSS reever ervng at the narrow-band ntererene envronment. The mprovement o reultng SNR ater NBI uppreon wll urther enhane along wth the nreang o ntererene ntente. Compared wth the mple ntererene nullng and ampltude lmtng proeng, the propoed method ha le omplexty and better real-tme perormane wthout long muh gnal perormane. 1. Introduton Dret equene pread petrum ( DSSS ) ommunaton tehnque oer a promng oluton to an overrowded requeny petrum amd growng demand or moble and peronal ommunaton erve, beaue t poee a number o attratve eature, uh a ant-dturbane, prvay, multpath adng retane, nreang tranmon apaty, et. In the moble and peronal ommunaton ytem, DSSS ytem hare the ame requeny band wth the extng narrow-band requeny ommunaton ytem. Thereore the perormane would nevtably be aeted by narrow band ntererene (NBI). Sne NBI beome a wdeband gnal ater depreadng, the ytem nherently an uppre NBI to a ertan extent by ung an approprate bandpa lter[1]. However, the omparable perormane baed on the aumpton that dret pread (DS) gnal power great enough, or the petrum o DS gnal muh wder than the NBI. That, the ant-ntererene apablty o a DSSS ytem dretly proportonal to the preadng gan o tel. In ae o the preadng gan dereae or ntererene gnal trong, th n turn may aue the perormane to be omewhat unatatory. However, pratally and preondtonally, nether moble nor peronal ommunaton ytem wll allow DS gnal tranmttng power o ntrudng the extng narrowband ommunaton ytem. In addton, when uh ator o ommunaton rate and ytem engneerng pratablty are taken nto onderaton, the yle o the PN equene an not nreae unboundedly, and the ame, the de-pread module at the reever an not unlmtedly expand NBI petrum n DS ommunaton ytem. All thee ator onront the DSSS wth nablty o reetng NBI. In order to mprove the ytem ant-dturbane on ondton that the ytem tel wll not nreae the preadng gan, an approprate NBI uppreon tehnque need be employed pror to de-preadng,. NBI uppreon tehnology At preent, baed on dgtal gnal proeng tehnology, NBI uppreon tehnology an be roughly orted by tme-doman lterng algorthm and tranorm doman lterng algorthm. Thee algorthm wth xed parameter exert good retrant on the NBI whh tattally tatonary. However, due to the omplex rado envronment and the ontnuouly hangng o the ntererene gnal, the tattal haratert are alway hangng whh lead to the at that the algorthm o xed parameter an not eetvely uppre the tme-varyng NBI. Thu the parameter o the lter mut be updated ontnuouly. It a omplated and tme-onumng proe to olve the parameter through the tattal haratert. I the bt rate too at, the alulaton may not meet the need o real-tme proeng. So /09 $ IEEE DOI /CMC

2 adaptve lter tehnologe turned out to be the mantream o NBI uppreon tehnologe n DSSS []. Among thoe adaptve algorthm, adaptve lter tehnologe that eetvely retran NBI an be ategorzed to the adaptve tme-doman lterng algorthm baed on the predton / nterpolaton tehnology, the adaptve noth-lterng algorthm n tranorm doman and other auxlary algorthm [3]. Adaptve tme-doman lterng algorthm an ully nhbt the NBI n theory, but t tablty trtly requred, tll le t lower onvergene and wore real-tme ablty. A to the adaptve tranorm-doman algorthm, data equene o nomng gnal o NBI uppreon module are proeted to the requeny doman va a ertan tme-requeny tranorm unton, or ntane,. The algorthm make nullng or mlar treatment on the requeny band, where the NBI rede, loated through the omparon between ub-band gnal energy and ub-band energy threhold, o a to aheve NBI uppreon. Although the real-tme qualty relatve to tme-doman adaptve lterng method ha been gnantly mproved, the tme wndowng ntrodued beore tranormaton make the requeny doman produe muh larger de lobe, whh make t dult to ompletely remove ntererene. Moreover, when the hgher requeny reoluton requred, a longer ub- data are needed, and t wll reult n nreang omplexty and tme delay or parttonng alulaton. Sne the ubband energy threhold o ommon adaptve requeny-doman lterng algorthm uually degned to be uned value, the NBI uppreon perormane wll delne dratally when the bakground olor petrum dene. An adaptve NBI uppreon method wth tmedoman and requeny-doman ombnaton propoed to remedy the above-mentoned problem. The method preent good perormane o NBI uppreon wth low tme delay and low omplexty. 3. NBI uppreon reever ytem model Fg. 1 dept a mpled blok dagram o NBI uppreon reever, whh ombne proeng o requeny-doman lterng and tme-doman lterng. The pread petrum gnal reeved are dvded nto two way pang through the A / D onverter, and are nput to the requeny-doman proeng module and tme-doman proeng module repetvely. The requeny-doman proeng module ont o the module, ntererene deteton module, adaptve ntererene threhold generaton module, and FIR tme-doman lter oeent generaton module. The tme-doman proeng module a FIR lter module. Fgure 1. A mpled blok dagram o NBI uppreon reever The reeved an be expreed a r ( t ) = ( t ) + n ( t ) + ( t ) (1) where (t) the DS-SS gnal and an be expreed a N ( t) = a n g ( t nt ) ( t) o( π t) () n = 1 where a the meage equene, and n { = ± 1,1 n N }, g (t) the quare pule a n gnal wth unt energy durng T nterval., T the duraton o the normaton bt. o( π t) the modulaton arrer, (t) the preadng ode gnal and t an be expreed a where L ( t ) = p ( t ) (3) = 1 T the PN equene, { 1} ±, L preadng multple, p (t) a quare pule gnal wth unt energy durng T nterval., T preadng ode duraton. n (t) the Gauan whte noe whh unlateral power petral denty N 0, (t) NBI whh an be approxmated by a determnt nte um o nuod, and expreed a below K ( t) = A o( π t + φ ) (4) = 1 where K the number o ngle-requeny ntererene, A the ampltude o ngle-requeny ntererene, the requeny o ngle-requeny ntererene, φ the orgnal phae o nglerequeny ntererene. 354

3 The reeved DS gnal whh ontan narrow-band ntererene and the Gauan whte noe ampled by the A / D rtly, and then exported to module wth wndowed. The ntererene deteton module wll ompare eah ample pont rom reeved gnal petrum wth the threhold generated by the adaptve ntererene threhold generaton module. The petrum pont wth hgher ampltude. Then the enter requeny and bandwdth o the ntererene gnal are ent to FIR tme-doman lter oeent generaton module. Baed on the ntererene normaton, the module degn the FIR lter oeent and end the oeent to the FIR lter module or the tmedoman proeng part. The FIR lter wll proeed the tme-doman lterng treatment wth FIR lter oeent. In the above proeng proedure, the tme-doman proeng only deal wth FIR lterng, and more omplated proeng, uh a ntererene gnal etmaton and lter oeent degn o bath treatment are ompleted n a requeny-doman proeng part, whh an uently enhane the real-tme ablty o the ytem. Although the urrent FIR lter oeent ued n tme-doman lterng are etmated baed on the data blok omng rom the prevou tme unt, however, n an atual eletromagnet envronment, ntererene gnal vare muh le n the lag tme wth repet to preetmated value, a not to mpat on ntererene uppreon. Compared wth the mple requenydoman ntererene uppreon baed on, the omplexty o th method only hal o t, whle the real-tme perormane gnantly mproved. 4. Adaptve ntererene threhold generaton I adaptve requeny-doman lter algorthm baed on one-way nput arhteture[4] onvergent, the lter power output wll be expreed a [ ] Pout = 1 w( ) σ (5) where w( ) adaptve requeny-doman lter weght oeent, an be expreed a σ where threhold. ; In (5) and (6), σ w( ) = σ + B (6) the nput gnal power; B energy σ B, ( ) 1 σ B, ( ) 0 w, P out σ w, P out 0. When the gnal power muh maller than the energy threhold, w( ) approahng zero, the gnal energy wll be retaned; when the gnal power ar greater than the energy threhold, w( ) approahng to 1, the gnal energy wll be analogng nullng, that, the gnal energy uppreed. Obvouly, ettng o energy threhold B uh a maor ator n the adaptve requeny-doman lterng algorthm or the NBI uppreon. The adaptve ntererene threhold generaton module n th paper ued to omplete the ntererene threhold. It degned a ollow: Chooe N pont out o the reeved DS gnal, and t expreed a w ( n) = ( n) w( n) (7) where (n) the pread petrum gnal ater A / D onveron, n= 1,,, N, N the pont. w (n) the wndow unton, w (n) the gnal ater wndowed. A N omputed or w (n) and expreed by N -pont π nm / N = (8) u( m) ( n)e n = 1 w where u (m) the o (n) w, m= 1,,, N. The gnal energy o eah requeny pont expreed a m = ab um ( ) λ = Re ( um ( )) + Im ( um ( )) λ ξ (9) where λ the weghted ator, λ 1. Adaptve threhold determned by the energy o requeny pont o M number o the nearet blok and an be expreed a M N 1 B= B + η ξ (10) mn m, MN = 1 m= 1 where B the adaptve threhold, B mn the mnmum threhold denotng pread petrum gnal have no ntererene, M to the number o blok determnng the adaptve threhold, η a oeent relatve to the reeved gnal whh adutable per the dtane between tranmtter and reever. 5. Adaptve NBI uppreon mulaton The adaptve NBI uppreon method mulated n th eton to very the analye and the 355

4 mulaton about ntererene nullng and ampltude lmtng lterng are alo hown or omparon at the ame tme. Smulaton parameter are et a ollow: data rate 1Kbp, the length o PN equene 103, pread petrum ode rate 103Kbp, Gold ode ued, the produton polynomal about optmzaton par o 10 3 m equene x + x + 1 and x + x + x + x + x + x + 1, arrer requeny 103MHz, amplng requeny 409MHz, mulaton odeword 100,000, the pont requeny ntererene ued, the length o / I n requeny-doman tranorm 4,096, and the other ettng to adaptve ntererene threhold module λ = 1, M = 1, η = 4. Fg. dept the reeved gnal petrum ontanng pont requeny ntererene wth ntererene requeny o = R / and SIR -35 db, denotng a dtnt ntererene popup. Fg.3 dept the ltered gnal petrum ater the FIR lter va NBI uppreon. In Fg.3, there a noteable petrum delnaton near the ntererene pont ndatng ueul uppreon to be the ntererene gnal by the ombnng method ntrodued n the paper. A a reult, a ertan amount o reeved gnal energy lot, however, the mnorty lo o energy wll barely eet on reult ater the petrum preaded. It an be urther demontrated by the latter mulaton. Fgure. Spetrum beore NBI uppreon Fg.4 dept the BER urve pre-and-pot NBI uppreon when ntererene requeny = and SIR -5dB. In Fg.4, the R / ytem ha gnantly mprovement va NBI uppreon. When BER = 10 4, the perormane omparatvely mproved by 4dB, t der wth that o theoretal urve o non-ntererene only by 0.5dB and ompete wth that o ntererene nullng and ampltude lmtng proeng o requeny-doman tranormaton by 0.5dB. Fgure 4. The ytem perormane when = and SIR -5 db R / Fg.5 dept the BER urve pre-and-pot NBI uppreon when SIR -35dB. In Fg.5, the ytem va NBI uppreon more largely mproved than that beore NBI uppreon. The NBI uppreon eet o ntererene nullng and ampltude lmtng proeng are lghtly better than FIR lterng wth repet to the reever, a hown n Fg.5. However, both method are baed on the blok tranormaton. The / I hould be long enough to mprove the requeny reoluton. It wll be a omplated and tmeonumng proe. The propoed method provde parallel proeng o tme-doman and requenydoman, o a to redue the omplexty to a hal, and to mprove real-tme perormane prevalng over eah o the two algorthm. Fgure 3. Spetrum ater NBI uppreon

5 Fgure 5. The ytem perormane when = and SIR -35 db R / Fg.6 and Fg.7 dept repetvely ytem perormane urve pre-and-pot lterng when ntererene approahng the arrer requeny,.e. = Hz. The ytem perormane ha been mproved gnantly by the lterng a hown n Fg.6 and Fg.7. ampltude lmtng proeng, the propoed method ha le omplexty and better real-tme perormane wth lght gnal long. 7. Reerene [1] Georgo B. Gannak, ed. Sgnal Proeng Advane n Wrele and Moble Communaton. Beng: Pot& Teleommunaton Pre 00 [] Zhang We,Yao Tanren, Narrow-band Intererene Reeton Tehnque n DSSS, Communaton Tehnology, Inormaton Seurty and Communaton Prvay, Chengdu, 00 (9): 4-6 [3] Zhou YanB, Gao Yng, A Summary o Adaptve Flterng Algorthm, Journal o Guangzhou Unverty, Guangzhou Unverty,Guangzhou,00 (): [4] Yang Weguang, B Guangguo, Reeton o Narrowband Intererene n DSSS Sytem Baed on Adaptve Wavelet Paket Tranorm, Journal on Communaton. Introduton to Communaton World Webte, Beng,, 1999 (7):69-75 Fgure 6. The ytem perormane when Hz and SIR -5 db = Fgure 7. The ytem perormane when Hz and SIR -35 db = 6. Conluon A novel adaptve ntererene uppreon method wth tme-doman and requeny-doman ombnaton wa propoed. The method an gnantly mprove the perormane o DSSS reever ervng at the narrow-band ntererene envronment. Smulaton reult demontrated that, when SIR -5dB, the ytem perormane only redue by 0.5dB ompared wth that o the non-ntererene ytem, but wll be mproved by 4dB prevalng over that o the ytem wthout NBI uppreon. A urther mprovement o reultng SNR va NBI uppreon wll be attaned wth the nreang o ntererene ntente. Compared wth the mple ntererene nullng and 357