7064705 khoi-phuc-dinh-thoi-tan-so-va-da-song-mang-trong-tin-hieu-msk

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Khoi-Phuc-Dinh-Thoi-Tan-So-Va-Da-Song-Mang-Trong-Tin-Hieu-MSK

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  • 1. Kho lun tt nghipNg Th Nguyn_K46DBI HC QUC GIA H NI TRNG I HC CNG NGHNg Th NguynKHI PHC NH THI, TN S V PHA SNG MANG TRONG TN HIU MSK KHO LUN TT NGHIP I HC H CHNH QUY Ngnh: in t_Vin ThngH NI-2005i hc Cng ngh-HQG H Ni1

2. Kho lun tt nghip Ng Th Nguyn_K46DBI HC QUC GIA H NI TRNG I HC CNG NGHNg Th NguynKHI PHC NH THI, TN S V PHA SNG MANG TRONG TN HIU MSK KHO LUN TT NGHIP I HC H CHNH QUY Ngnh: in t_Vin Thng Cn b hng dn: Tin s Trnh Anh V H NI-2005i hc Cng ngh-HQG H Ni2 3. Kho lun tt nghip Ng Th Nguyn_K46DB Li cm nEm xin c by t lng bit n chn thnh v su sc nht ti thyTrnh Anh V. Thy tn tnh hng dn v ch bo cho em trong sut qu trnh lmlun vn.Em cng xin gi li cm n ti ton th cc thy c gio trong khoa int_ vin thng cng nh cc thy c trong trng i Hc Cng Ngh_ i HcQuc Gia H Ni gip , to mi iu kin cho em trong qu trnh hc tp v lmkho lun tt nghip. Cui cng, xin cm n nhng ngi thn, bn b ng vin v gip ti hon thnh kho lun tt nghip ca mnh. H Ni ngy29 thng5 nm 2005Sinh vinNg Th Nguyni hc Cng ngh-HQG H Ni3 4. Kho lun tt nghipNg Th Nguyn_K46DB Tm tt ni dungTrong phn m u kho lun khi qut cc k thut iu ch s (nhPSK, QPSK, OQPSK, MSK v GMSK) v qu trnh gii iu ch cc tn hiu .Tip kha lun s dng Matlab 7.0 m phng qu trnh khi phctn hiu MSK (Minimum shift keying) ti ni thu trong iu kin knh truyn chtlng km, t c ci nhn ton cnh qu trnh khi phc tn hiu MSK qua knhtruyn c nh hng ca nhiu trong thc t.Trong m hnh m phng ni n cc yu t ng vai tr nh hng ncht lng truyn dn tn hiu MSK trn ng truyn l cc tham s dch nh thi khiu pha, dch tn s, dch pha v trn knh truyn cn c cng n Gausian trng(AWGN). Tai ni thu, trc khi gii iu ch tn hiu MSK phi khc phc tt c ccnh hng ca nhiu trn ng truyn. C th, phi khi phc nh thi k hiu pha,khi phc tn s sng mang sau khi phc pha mang.Ngoi ra kho lun c s dng thm cng c BERtool trong Matlab 7.0 tnh ton li bit BER trn ng truyn, t minh ho tnh phc tp ca vn khi phc li tn hiu khi i qua knh truyn cht lng km trong thc t.H Ni, ngy 28 thng 5 nm 2005i hc Cng ngh-HQG H Ni4 5. Kho lun tt nghip Ng Th Nguyn_K46DBLi m uNgy nay k thut truyn dn tn hiu s c s dng trong hu ht cc lnhvc truyn thng do tnh u vit hn hn truyn dn tn hiu tng t. Trn thc tng truyn dn lun lun c tp m (n Gaussian), bng tn gii hn v cc giaothoa tn hiu khc nhau i vi cc mi trng, vt liu truyn dn khc nhau. iuny dn n lm sai lch, mo dng tn hiu v gy li trn ng truyn. V vy vicnghin cu t m cc dng tn hiu v gy li trn ng truyn, phng php ng bnhm lm gim sai st trn ng truyn l nhng k thut c s rt quan trng.K thut truyn dn ni chung c th chia lm hai loi: Truyn dn bng tnc s, truyn dn qua iu ch sng mang. Trong truyn thng tin s qua knh bngtn c s, tn hiu mang thng tin c truyn trc tip trn knh, tuy nhin hu htcc knh truyn thng u l bng tn gii hn. Do cn chuyn tn hiu qua knhbng cch dch tn s ca tn hiu mang thng tin ph hp vi bng tn ca knh, cnh vy tn hiu in t mi chm suy gim v truyn i c xa. K thut iu ch sln sng mang tn s thch hp mi trng truyn dn s tng tm hot ng ca ccthit b vin thng vi mt chi ph ti thiu.Kho lun hn ch trong vic nghin cu chi tit m hnh m phng v lthuyt k thut v khi phc nh thi, khi phc tn s sng mang v khi phc phamang trong tn hiu MSK (Minimum shift keying) trn bng tn c s. Km theo mphng trong Matlab 7.0 c th so snh c im mnh, im yu v xc sut libit trong k thut iu ch tn hiu MSK. Tn hiu MSK khi cho qua b lc Guassianlm trn tn hiu, tr thnh tn hiu GMSK l phng php iu ch ch yu trongGSM.Do thi gian c hn nn kho lun s khng trnh khi thiu st, em rtmong nhn c cc kin gp ca thy c.i hc Cng ngh-HQG H Ni 5 6. Kho lun tt nghipNg Th Nguyn_K46DBChng I: TNG QUAN MT S K THUT IU CH SCc h thng tin di ng hin i s dng cc k thut iu ch s. Cc tinb trong cng ngh tch hp c ln (VLSI) v x l s (DSP) lm cho h truyn dndng iu bin s hiu qu hn h truyn dn tng t. iu ch s cho ta nhiu uim hn iu bin tng t. Mt s u im bao gm tnh khng nhiu tt hn vkho hn cho s khng hon hin ca knh truyn, d dng hn cho vic ghp knhcho cc loi thng tin khc nhau (th d nh ting ni, d liu, hnh nh) v bo mttt hn. Hn na, iu bin s thch hp vi cc m kim tra li s m chng phthin v hoc sa cc li truyn, tr gip s iu phi tn hiu phc tp v cc k thutx l nh l m ngun, bo mt v lm bngnhm ci thin hiu sut ca kt nithng tin ton cc. Trong cc h thng tin khng dy, tn hiu iu bin (th d bn tin) c thc biu din nh mt chui theo thi gian cc k hiu hoc xung, trong mi khiu c m trng thi gii ni. Mi k hiu biu din bng n bt thng tin, trong m =log 2 n bit/k hiu. Mt s trong cc k thut ny c nhng s khc nhau tinh t giachng v mi k thut thuc vo mt h cc phng php iu bin c lin quan. Thd, kho dch pha (PSK) c th hoc tch sng kt hp hoc tch sng vi phn v cth c 2,4,8 hoc c th c nhiu mc hn (v d n=1,2,3 hoc nhiu bit hn) cho mtk hiu, ph thuc vo cch trong thng tin c pht ra trong mt k hiu n. 1.1 Kho dch pha (PSK)Trong loi iu ch ny gi l 2-pha (chia 2) hay PSK pha c s 2 (BPSK).Sng mang hnh sin c hai gi tr pha c xc nh bi tn hiu d liu c s hai.Dng sng hnh sin li ra ca b iu ch l cng hay ngc pha (c ngha lch pha180 0 ) vi tn hiu li vo v l hm s ca tn hiu d liu.S 0 (t) = A cos ( t) tng ng vi bit 0 S 1 (t) = A cos ( t + ) tng ng vi bit 1i hc Cng ngh-HQG H Ni6 7. Kho lun tt nghipNg Th Nguyn_K46DB Trong PSK c s M, pha sng mang ly 1 trong M gi tr kh d v vimi n (M=2 n ) bit ca chui bit c m ho trong mt dng tn hiu c truynnh sau: S(t) = A sin ( t + ) Trong = 2(i-1) /Mi = 1,2, , M. 1.2. Kho dch pha vung gc (QPSK) Trong loi iu ch ny gi l iu ch 4-PSK, kho dch pha 90 0 hay iuch vung pha. Kho dch pha 90 0 c hiu sut rng di gp hai ln BPSK v 2 bitc truyn i trong mt k hiu iu bin tin. Pha ca sng mang ly 1 trong 4 gi trcch u nhau nh l 0, /2, v 3 /2 trong mi gi tr pha ng vi mt cp duynht ca bn tin. Chui bit nh phn li vo {d k }, d k = 0,1,2, b iu ch vi tc 1/T(bits/s), sau c bin i ni tip-song song thnh hai dng bit d I (t) v d Q (t) (ccdng cng pha v lch pha 90 0 ), mi dng c tc bt R s = R b /2 hay bng na tc ca d liu u vo. Dng d I (t) c gi l dng bit chn, dng d Q c gi ldng bit l: d I (t) = d 0 , d 2 , d 4 , d Q (t) = d 1 , d 3 , d 5 , Tn hiu sng mang c th nh ngha l:S(t) = 1/ 2 d I (t)cos(2 f o t + /4) + 1/ 2 d Q (t)sin (2 f c t + /4)Hay c th vit di dng nh sau:S(t) = Acos[2 ft + /4 + (t)].Hai chui c s hai c iu bin ring r bng hai sng mang d I (t), d Q (t)chng lch pha nhau 90 0 . Hai tn hiu iu bin, mi tn hiu c coi l mt tn hiuBPSK, c ly tng li sinh ra mt tn hiu QPSK. Vy QPSK l s kt hp haii hc Cng ngh-HQG H Ni7 8. Kho lun tt nghipNg Th Nguyn_K46DBBPSK vung pha vi nhau. Chui xung d I (t) iu ch vi hm cosine bin 1 v -1,tng ng vi pha c hai trng thi l 0 0 v 180 0 . Tng t nh vy chui xungd Q (t) iu ch vi hm sine tng ng vi pha c hai trng thi l 90 0 v 270 0 . Hnh 1.Mt trong bn gi tr pha ca sng mang tng ng vi hai bit d liu hayhai bt trn mt k hiu. Tc k hiu trong QPSK l mt na tc bit. C hainhnh d liu c th c mang i vi mt lng nh nhau trong di bng thng hnch.Trong QPSK, pha sng mang c th thay i ch mt ln duy nht trongmi 2T(s), trong khong T(s) pha sng mang gi nguyn khng i.i hc Cng ngh-HQG H Ni8 9. Kho lun tt nghip Ng Th Nguyn_K46DB Hnh 2. Tn hiu QPSK c tip nhn my thu v c gii iu ch BPSK ringi vi d I (t) v ring i vi d Q (t). Sau d I (t) v d Q (t) kt hp li theo nguyn lbin i song song - ni tip khi phc nguyn dng dng d liu pht. Bin ca mt tn hiu QPSK l khng i mt cch l tng. Tuy nhinkhi cc tn hiu QPSK c to dng xung, chng mt i tnh cht hnh bao khng i.S dch pha ngu nhin radian c th gy ra hnh bao ca tn hiu i qua s 0 vochnh lc . Bt k loi khuych i hn ch bi mch cng hay phi tuyn ca vicqua im khng u mang li cc bp bn c lc trc , v trung thc catn hiu cc mc in th nh b mt i trong khi pht. ngn cn vic pht li ccbp sng bn v m rng ph th bt buc l cc tn hiu QPSK c khuych i chdng cc b khuych i tuyn tnh, mc du chng c hiu sut km. Mt dng bini ca QPSK gi l QPSK lch (OQPSK) t nhy vi hiu ng c hi ny v cho skhuych i c hiu sut ln.1.3 Kho dch pha lch vung gc (OQPSK)Bo hiu OQPSK tng t nh QPSK vi s xp t theo thi gian cadng bit chn v l. Trong tn hiu QPSK, s chuyn dch ca cc dng bit chn v lxy ra ti cng thi im, nhng trong bo hiu OQPSK, cc dng bit chn v l d I (t)v d Q (t) lch i trong s xp t tng i bi mt chu k bit (na chu k ca khiu). Do s xp t ca d I (t) v d Q (t) trong QPSK chun, cc s chuyn pha xy rach ti mi T s = 2T b giy v s cc i khi 180 0 nu c mt s thay i v gi tr cac hai d I (t) v d Q (t). Tuy nhin, trong bo hiu OQPSK s chuyn bt (v do c si hc Cng ngh-HQG H Ni 9 10. Kho lun tt nghip Ng Th Nguyn_K46DBchuyn pha) xy ra ti mi T b giy. V cc thi im chuyn pha ca d Q (t) v d I (t) blch i T b , bt k thi im cho no ch c mt trong hai dng bt c th thay icc gi tr. iu ny ng rng s dch pha cc i ca tn hiu pht ra ti thi imbt k cho trc b hn ch ti 90 0 . V vy, do s chuyn pha xy ra mau hn (nghal sau mi T b giy thay cho 2T b giy), bo hiu OQPSK loi b s chuyn pha 180 0 . Hnh 3. Cc dng sng lch theo thi gian tc dng vo cc nhnh cng pha v lchpha 90 0 ca mt b iu bin OQPSK. Hnh 4.i hc Cng ngh-HQG H Ni10 11. Kho lun tt nghipNg Th Nguyn_K46DBV cc chuyn pha 180 0 c loi tr, s to xung ca tn hiu OQPSK skhng lm cho hnh bao tn hiu i qua im khng. Nhng cc thay i hnh bao l tng k v nh vy s khuych i hn ch bng hay phi tuyn ca cc tn hiuOQPSK khng pht li cc nhnh bn cao tn nhiu nh trong QPSK. V vy, schim ph gim i ng k, trong khi cho php s khuych i RF hiu qu hn.TsGii iu ch OQPSK th dng d I (t) b lm tr T b = tr li c cng2trng thi thi gian gc nh d Q (t).1.4 K thut iu ch tn hiu MSK trong thng tin v tuyn1.4.1 Phng php iu ch v biu din tn hiu MSK GSM s dng phng php iu ch kho dch pha cc tiu Gaussian GMSK(Gaussian Minimum Shift Keying). y l phng php iu ch bng hp da trn kthut iu ch dch pha. Tuy nhin ta ch xt n phng php iu ch kho dch phacc tiu MSK (Minimum Shift Key) m phng php iu ch GMSK c pht trinda trn phng php MSK. Kho dch cc tiu (MSK) l mt loi c bit ca khodch tn s pha lin tc (CPFSK), trong lch tn s nh bng 1/2 tc bit. Nicch khc MSK l kho dch tn (FSK) pha lin tc vi ch s iu bin 0.5, ng vikhong cch tn s cc tiu cho php hai tn hiu FSK l trc giao kt hp v tn khodch cc tiu ng s tch bit tn s cc tiu cho php tch sng trc giao.Ta c th trnh by sng mang c iu ch ca tn hiu MSK nh sau:S(t) = A*cos ( ct + t + 0 ) Trong : A l bin khn