The Effects of Interference Suppression by a Reconfigurable Structure at DSSS-DPSK Receiver

Transcription

1 494 N. MIOŠEVIĆ, Z. NIKOIĆ, B. DIMITRIJEVIĆ, B. NIKOIĆ, THE EFFECTS OF INTERFERENCE SUPPRESSION The Effets of Interferene Suppression y Reonfigure Struture t DSSS-DPSK Reeiver Nend MIOŠEVIĆ, Zori NIKOIĆ, Bojn DIMITRIJEVIĆ, Bojn NIKOIĆ Dept. of Teeommunitions, University of Niš, Aesndr Medvedev 4, 8 Niš, Seri {nend.miosevi, zori.nioi, ojn.dimitrijevi, ojn.nioi}@ef.ni..rs Astrt. In this pper we show the performnes of DSSS-DPSK reeiver the interferene rejetion iruit is reonfigure nd is using -struture. The resuts wi e shown for the se of pet, s we s for the ontinuous PSK interferene. The resuts show tht the proposed reonfigurtion iruit, in se of pet PSK interferene, signifinty dereses the error proiity, ompred to the system using ony -struture for sign to noise rtios of prti importne. Aso, in se of ontinuous interferene, the reonfigure struture hs equy good performne, regrdess of interferene power nd its itrte. Keywords Interferene suppression, spred spetrum system, reonfigurtion, error proiity.. Introdution The suppression of digity moduted interferene t DSSS/PSK system using ompex dptive trnsvers fiter [] is not s suessfu s the suppression of singe or mutipe tone interferene []. This is more pronouned for high interferene itrte when the interferene is widend. Beuse of this, in [3] -struture is proposed, nd it n e suessfuy ppied for the suppression of interferene with numer of different digit modution formts, regrdess of its itrte. However, in order to -struture performs we, it is neessry to interferene power e higher thn some minimum threshod vue. Therefore, in this pper we proposed reonfigure reeiver with - struture for the interferene suppression. The use of reonfigure interferene rejetion struture is espeiy importnt for ognitive nd softwre rdio [4]. Aso, it shoud e pointed out tht most of modern teeommunition systems use pet trnsmission [5]. It is of high importne to see how the pet nture of the system infuenes the interferene suppression fiters. In this pper we wi onsider the performnes of DSSS-DPSK reeiver the interferene rejetion iruit is reonfigure in ses of pet nd ontinuous interferene. Hving in mind tht the ognitive rdio systems re ment to wor in frequeny rnges tht re redy in use, there my e wide vriety of interfering modution formts. As n exmpe of interferene, PSK interferene hs een hosen.. System Mode Bo digrm of the reeiver is shown in Fig.. The usefu sign is given s s( d( d( t ) m( os( t ) () m( is the PN sequene with hip interv ; d( is the informtion dt with it interv T =, is the rrier frequeny, is the sign phse, nd is the proessing gin. Besides the usefu sign nd noise, there is PSK interferene t the input of the reeiver: i t ) J p ( t ) ( t ) os( ) () ( t i i J is the interferene power, ( is the interferene informtion dt, i is the interferene rrier frequeny, nd i is rndom phse with uniform distriution on (, ]. Vrie tht desries the pet nture of the interferene is t t, mod /,( Tp ) / / p ( (3), mod /,( Tp ) / / T s is interferene pet durtion, nd T p is time interv etween two pets. For exmpe, p( = for ontinuous PSK interferene. et us define the rtio etween T p nd T s (duty ye) s /( Tp ). Sign t the input of the reeiver is given y: x( s( i( n( (4) n( is the rndom Gussin noise with zero men nd vrine.

2 RADIOENGINEERING, VO. 9, NO. 4, DECEMBER 495 x( Down onversion X( - struture SNRd estimtion Reonfigurtion ontro SNRd estimtion Y( X( d( Detetion After the input sign down onversion nd fitering, the reeiver performs smping. For th smpe, reeived sign my e represented in ompex form s X ( S( I( N( (5) S s ( js ( ), (6) ( s( d( d( ) m( os s ( d( d( ) m( sin ( i i (7) I ) J p ( ) ( ) exp j ( ), (8), mod,( Tp )/ / p ( (9), mod,( Tp )/ / nd ( /( T i / )) { }, T i is the interferene it durtion, m( is PN sequene {},. Within the DSP o for interferene rejetion, reonfigurtion, nd detetion, the interferene is suppressed y -struture []. The estimted vue of the input sign, fter the reonfigurtion iruit, is: D ( D ( ), d ˆ( () D ( D ( ), : D ( X ( m( ) () D ( Y ( m( ) WS ( ) {,, j, j} i i Y ( Y ( () Y ( min X ( WS ( X ( ) W ( (3),...,,,,,..., ; is the struture ength. WS ( is vrie tht represents n estimted modution ontent etween X( nd X( ). Fig.. DSSS/DSPK reeiver o digrm Sine it is nown tht the optimum (Wiener) vues of eh pir of fiter oeffiients, symmetri with respet to the entr point, re ompex onjugte [], it ws shown tht the ning of eft nd right fiter side weights sighty improves performnes [3]. Aso, in order to fiter hve gin equ to, its weights my e normized. Therefore, fiter weights re djusted with W ( ) W ( ) W ( ) W ( ) W ( ) W ( E( [ X ( WS ( ] E( Y ( ( ) represents the ompex onjugte. (4) (5) In order to derese the infuene of noise on the reonfigurtion deisions, vrie M is introdued. In the proess of deiding on the hnge of onfigurtion, esides the estimted SNR vue t the onsidered it interv, we so te into ount the estimted SNR vues from the previous (M ) it intervs. SNR is the usefu sign to noise rtio. The vue of prmeter from () determines the moment of the reonfigurtion, nd it depends on the previous stte: If R ( ) then SNRd ˆ ˆ ( SNRd( SNRd ˆ ˆ ( ) SNRd( ),. (6) SNRd ˆ ( ( )) ˆ M SNRd( ( M )), ese It mens tht the system hnges its stte ( = ) if of the test M estimted SNRs in rnh (without interferene rejetion), SN ˆ Rd, re higher thn the mthing estimted SNRs in rnh (with -struture), SN ˆ Rd.

3 496 N. MIOŠEVIĆ, Z. NIKOIĆ, B. DIMITRIJEVIĆ, B. NIKOIĆ, THE EFFECTS OF INTERFERENCE SUPPRESSION If R ( ) then SNRd ˆ ˆ ( SNRd( SNRd ˆ ˆ ( ) SNRd( ), (7) SNRd ˆ ( ( )) ˆ M SNRd( ( M )), ese Eqution (7) mens tht the system goes to the -struture interferene rejetion stte ( = ) if of the test M SNRd ˆ s re higher thn mthing SN ˆ Rd s. Here the estimted SNR is D ( ) ˆ ( ) S NRd, (8) D ( ) D ( ) D ( ) ˆ ( ) S NRd. (9) D ( ) D ( ) 3. Numeri Resuts The resuts shown in this setion re uted using Monte-Cro simution. For the foowing figures the proessing gin of the system is hosen to e =. The infuene of pet PSK interferene on the reeption of DSSS-DPSK sign is shown in Fig.. The figure shows the error proiity s funtion of sign to noise rtio in se of interferene to sign rtio J/S = 4 db. The prmeter for the urves is the rtio of pet to puse durtion of pet interferene. A set of urves eed with represent the system performne when there is no interferene rejetion iruit; urves stnd for the se of -struture interferene rejetion, nd urves show the performne of the system using the reonfigure interferene rejetion iruit. The onsidered SNR rnge my e divided into three surnges. The first surnge is from SNR to SNR, nd here the performnes of the reonfigure reeiver re ose to the ones of the reeiver without the interferene rejetion iruit nd without interferene (urve d). The seond surnge is from SNR to SNR, nd tht is the re of importne the est performne hs the reonfigurtion reeiver, nd it redues the error proiity for n order of mgnitude ompred to the -struture interferene rejetion. The third surnge is for SNR > SNR, nd tht is the re of high usefu sign powers. In this re, the performnes of the reonfigure reeiver onverge to the performnes of the -struture reeiver SNR =. =.3 =.5 SNR SNR SNR [db] Fig.. Error proiity s funtion of sign to noise rtio. The figure so shows tht the system using the reonfigure interferene rejetion iruit, s we s the system using -struture for interferene rejetion hve simir performnes for ny in rnge (.,.5). The infuene of PSK interferene power, with prmeter =.3, on the performnes of DSSS-DPSK sign reeption is shown in Fig M = M = (J / S) M = 4 d M = 3 J / S [db] Fig. 3. Error proiity s funtion of interferene to sign rtio in se of pet interferene.

4 RADIOENGINEERING, VO. 9, NO. 4, DECEMBER 497 In Fig. 3, sign to noise rtio is SNR = db, nd es,, nd re hve the sme mening s in Fig.. In the re J/S < (J/S) the est performnes hs the reeiver without the interferene rejetion iruit. By optim hoie of prmeter M (in onsidered se M = 3), in the onsidered J/S rnge, the reonfigurtion reeiver performnes n e mde to e very ose to the reeiver without n interferene rejetion iruit. In the re J/S > (J/S) the reeiver with -struture hs weer performnes thn the reonfigurtion reeiver with the optimized prmeter M (M = 3). rformnes of the reeiver in se of time ontinuous PSK interferene re shown in Fig. 4. Fig. 4 shows the error proiity s funtion of interferene to sign power rtio for SNR = db. rformnes of the reonfigure reeiver depend on the prmeter M. In se of optim vue for prmeter M (in onsidered se M = 3) for J/S < (J/S) performnes of the proposed reeiver re very ose to the reeiver without n interferene rejetion iruit. For J/S > (J/S) nd in se of optim vue for prmeter M, performnes of the proposed reeiver re very ose to the reeiver using ony -struture. re ompred on sense of error proiity. Two ses of PSK interferene re onsidered: pet nd ontinuous. In se of pet PSK interferene, for sign to noise rtios of prti importne, the use of interferene rejetion reonfigurtion struture signifinty owers the error proiity, ompred to the reeiver using -struture for the interferene suppression. The -struture, whih is deveoped for the ontinuous PSK interferene rejetion [3], needs high interferene to sign rtio for proper opertion (J/S > (J/S), (urve in Fig. 4). The reeiver without n interferene rejetion iruit nnot operte in the re of J/S > (J/S). The proposed reonfigure struture, with the optim hoie of prmeter M, hs equy good performnes regrdess of the interferene power. The shown resuts for the interferene rejetion using reonfigure struture re very importnt for ognitive nd softwre rdio. Anowedgement - This wor ws finniy supported in prt y the Ministry of Siene of Seri within the Projet "Deveopment nd reiztion of new genertion softwre, hrdwre nd servies sed on softwre rdio for speifi purpose ppitions" (TR-3). The reserh is prt of the COST tion IC83 RFCSET. M = Referenes - -3 (J / S) (J / S) J / S [db] M = M = 3 M = 4 Fig. 4. Error proiity s funtion of interferene to sign rtio in se of ontinuous interferene. 4. Conusion A reonfigure struture for the DSSS-DPSK system interferene rejetion is proposed in this pper. The system performne in the presene of PSK interferene is onsidered. The reeivers without interferene suppression iruit, with -struture for interferene suppression, nd the reeiver with the reonfigurtion using -struture [] NIKOIĆ, Z., DIMITRIJEVIĆ, B., MIOŠEVIĆ N. Rejetion of PSK interferene in DS-SS/PSK system using ompex dptive fiter nd noniner orretion reeiver. Eetronis etters, 997, vo. 33, no. 4, p [] HASAN, M. A., EE, J. C., BHARGAVA, V. K. A nrrownd interferene neer with djuste entre weight. IEEE Trns. on Communitions, 994, vo. 4, no. /3/4, p [3] GIŠIĆ, S., NIKOIĆ, Z., DIMITRIJEVIĆ, B. Adptive sef reonfigure interferene suppression shemes for CDMA wireess networs. IEEE Trnstions on Communitions, 999, vo. 47, no. 4, p [4] CHEN, K. C., PRASAD, R. Cognitive Rdio Networs, ondon: John Wiey & Sons, 9. [5] HIGUCHI, K., FUJIWARA, A., SAWAHASHI, M. Mutipth interferene neer for high-speed pet trnsmission with dptive modution nd oding sheme in W-CDMA forwrd in. IEEE Journ on Seeted Ares in Communitions,, vo., no., p Aout Authors... Nend MIOŠEVIĆ ws orn in Knjžev, Seri, in 973. He reeived the B.E.E., M.S., nd Ph.D. degrees t the University of Niš in 997,, nd 7, respe-

5 498 N. MIOŠEVIĆ, Z. NIKOIĆ, B. DIMITRIJEVIĆ, B. NIKOIĆ, THE EFFECTS OF INTERFERENCE SUPPRESSION tivey. His interests inude moie nd wireess ommunitions with spei emphsis on oopertive ommunitions. Zori NIKOIĆ ws orn in 955 in Niš. She reeived the B.E.E., M.S., nd Ph.D. degrees t the University of Niš in 979, 985, nd 989, respetivey. She is now Professor t the Futy of Eetroni Engineering, University of Niš, she tehes sis of teeommunitions, teeommunition networs, moie ommunitions, spred spetrum systems, nd wireess ommunitions. Her min fieds of interest inude moie nd wireess ommunitions. Bojn DIMITRIJEVIĆ ws orn in esov, Seri, in 97. He reeived the B.E.E., M.S., nd Ph.D. degrees t the University of Niš in 998,, nd 6, respetivey. His reserh interests inude interferene suppression in moie nd wireess ommunitions. Bojn NIKOIĆ ws orn in Niš, Seri in 98. In 7 she grduted from the Futy of Eetroni Engineering in Niš, mjor Teeommunitions nd enroed Ph.D. studies on sme futy. She is outhor of sever ppers, presented t ntion nd interntion onferenes. Currenty, Ms. Nioić is Tehing Assistnt t the Futy of Eetroni Engineering in Niš.