Duan Thi Thanh Thao vd Dtg 86(10): 27-32 Tap chi KHOA HOC & CONG NGHE KHA NANG SLT DUNG DO THIET HAI KHOANG CACH DD DE DANH GIA TAC DONG CUA M E O PHI TUYEN GAY BOI B Q KHUECH DAI CONG SUAT PHAT TRONG CAC HE THONG 256-QAM Doan Thj Thanh Thao'*, Doan Thanh Hai\ D6 Huy Khoi' 'Truang DH CNTT&TT- DHTN, 'Truang DH Ky thudt Cong nghiep - DH TOM TAT Bai bao gidi thieu each xac djnh tham so thiet hai khoang each dd (distance degradation) de danh gia phi tuyen ciia cac bg khuech dai cong suat va khao sat sy phu thugc ciia lugng thiet hai ty so tin tren tap SNRD (Signal-to-Noise Ratio Degradation) vao thong so dd he thong dieu che 256-MQAM dan song mang Dong thdi bai bao cung ggi md mgt hud'ng nghien ciiu mdi cho viec tinh toan mgt each giai tich xac suat loi bit, nham danh gia tac dong ciia meo phi tuyen dugc gay bdi eac bg khuech dai eong suat he thong dieu che da song mang Til' khoa: MQAM, meo phi tuyen, thiet hgi khodng cdch, lugng thiet hgi ti so tin tren tgp GIOI THIEU CHUNG Cac tac dong ciia meo phi tuyen gay boi cac bo khuech dai cong suat phat Cac tae ddng ciia meo phi tuyen gay bdi bg KDCS cac he thdng vd tuyen sd MQAM gdm: Trai rdng phd va gay tap am phi tuyen, tae ddng djeh chuyen vj tri cac tin hieu tren mat phang pha, tac dgng gay ISI phi tuyen Cach danh gia tac dong ciia meo phi tuyen gay bdi bo khuech dai cong suat phat Meo phi tuyen gay bdi KDCS cae he thdng M-QAM ed the lam giam mdt each nghiem trgng chat lugng cd the dat tdi dugc ciia he thdng Cae nghien cuu chi tiet [5], [7] eho thay rang eac meo AM/AM va AM/PM tac ddng tdi chat lugng he thdng theo Idi tang cudng lan {synergistic), tire la suy giam chat lugng he thdng tinh tdi ca meo AM/AM lan AM/PM thi ldn hon tdng suy giam chat lugng cua he thdng tinh tdi hoac ehi meo AM/AM hoac ehi meo AM/PM Tae ddng tdi chat lugng he thdng eiia meg phi tuyen duge danh gia qua thiet hai ty sd tin/tap (SNRD - Signal-to-Noise Ratio Degradation) tinh tai mdt gia trj nao dd ciia xac suat ldi bit ciia he thdng Tinh tang cudng tac ddng ndi tren cd the dien dat bdi: Danh gia anh hudng eiia meo phi tuyen gay bdi KDCS tdi chat lugng he thdng cae he thdng vd tuyen sd M-QAM la mdt van de nan giai Do tinh chat phu'c tap eiia he thdng, viec tinh toan mdt each giai tich la mdt nhiem vu khdng the thye hien dugc va ndi chung, md phdng may tinh thudng dugc xem la giai phap hieu qua nhat viec khao sat eae he thdng ed eae phan tir phi tuyen Trong cdng trinh ciia Amadesi [8], ben canh viec de xuat sii' dung BO (Back-Off) nhu mdt thdng sd meo phi tuyen, Amadesi P va cac cdng sy da tien hanh md phdng he thdng 16QAM vdi mdt sd bd khuech dai TWT va da tim dirge cdng thiic gan dimg kinh nghiem de tinh toan SNRD tai BER = 5.10"': SNRD A.e -K.HO a [dB] (2) dd: A = 3,25,sin(2;riS'/9,5 + 5;r/36) + 5,75 [dB]; ^ = , - 0,05ln(l+e5'-"''*'"''^') [dB"']; a= 1,1 [dB]; BO [dB] la liii cdng suit loi (Back-Off) va S [dB] la chenh leeh giii'a cdng suit dieu kien hoan toan tuyen tinh va cdng suat bao hoa cua bd KDCS (vdi ciing cdng suit Idi vag ung vdi gia trj cdng suit bao hoa) Mac dau cdng thiic da tim duge td tuong ddi khdp vdi kiem tra thye te (sai sd ciia viee (1) lam gan diing SNRD nhd ban 0,25 dB), cdng trinh td it hieu qua cdng thirc thiet ' 'Tel: 0984 984199, Email: thaonguyen@yahoo.com lap dugc chi la vdi SNRD tinh tai mgt gia trj SNRD,'(AM/AM va AM/PM) > SNRDA SNRD 27 Dodn Thi Thanh Thao vd Dtg Tap ehi KHOA HOC & CONG NGHE kha ldn cua BER la 5.10""", thye tl tinh toan thiet ke ddi hdi phai cd kha nang tinh SNRD tai BER tdi tan cac gia trj 10"^ tham chi tdi 10"' hoac nhd ban Han thi nua, gia thiet meo AM/PM la 3°/dB dugc su' dung md phdng may tinh cua Amadesi chi gan dimg vdi cae TWT va hoan toan khdng phii hgp vdi cac SSPA Cudi cimg, sa dd dieu che thich hgp vdi cdng thu'c tim dugc chi la 16-QAM va khdng cd kha nang md rdng cdng thuc cho eac he thdng 64-QAM hay 256-QAM Trong [11], S Pupolin va L J Greenstein da gia thiet mdt each vd doan rang cac cym diem xuat hien tren chdm tin hieu thu dudi tac dgng ciia meo phi tuyen gay bdi KDCS (the hien ISI phi tuyen) cd phan bd chuan Dya tren gia thiet va sii' dyng khai trien chudi Volterra, S Pupolin va L J Greenstein da thiet lap cac cdng thue xac djnh cae tham sd thdng ke eua tin hieu thu, tren eo' sd dd cd the tinh toan mgt each giai tich xac suat Idi bit eiia he thdng Giai phap nay, nhu da thay, thude vao Idp giai phap tya giai tich (do dya tren gia thiet ve phan bd ciia ISI) va kit qua tinh toan ehi la ket qua gan diing Dieu giai thich cho viee ket qua tinh toan cua S Pupolin va L J Greenstein da trinh bay [11] ehi sat vdi ket qua md phdng MonteCarlo d nhung gia trj kha Idn ciia BER Mdt han che ntia ciia phuong phap da dugc dl xuat bdi S Pupolin va L J Greenstein la khai trien chudi Volterra chi cd thi tinh bing phuong phap sd ddi vdi cae meo phi tuyIn tdi bac ba ma thdi, viee tinh toan ddi vdi eac meo phi tuyen tdi bae hay hon nii'a se ddi hdi bd nhd may tinh qua ldn den mu'c khdng thye tl dieu kien cdng nghe nhu hien Trong dd, vdi viec ap dyng cae phuong phap tuyen tinh boa bd KDCS thi meo bac thu'dng giam nhd tdi mirc cac phin meo bae hay hon nua khdng the bd qua dugc Cac nghien cii'u chi tiet han nua [2, 10] da ehi rang ham mat xac suat pdf {probability density/unction) ciia ISI phi tuyen khdng phai chuan mdt each ty nhien Pdf cua ISI phi tuyen van cd the lam gan dimg bang mdt phan bd chuan, nhien vdi ky vgng va phuong 28 86(10): 27-32 sai khac vdi ky vgng va phuang sai thuc sy ciia ISI xac djnh bang djnh nghTa Dieu cung gdp phan ly giai sy sai khac tuong ddi ldn giua ket qua tinh toan dugc ciia S Pupolin va L J Greenstein va ket qua md phdng Monte-Carlo tai nhung gia trj thap cua BER Cac nghien ciiu hien van dang dugc tien hanh nham tim each xac djnh cac tham sd thdng ke (ky vgng va phuang sai) mdt each tryc tiep tii' eac tham sd phi tuyen cua bd khuech dai, hoac nham tim kiem mdt phan bd xac suat mdi cho ISI phi tuyen cac he thong M-QAM vdi bg KDCS phi tuyen Trong cdn chua xac djnh dugc each tinh xac suat ldi bit cua he thdng mdt each giai tich vdi mdt meo phi tuyen nao dd, thi anh hudng ciia meo phi tuyen gay bdi bg khuech dai cdng suat van cd the tinh mgt each gan dimg theo eac cdng thiic thuc nghiem da duge tim [9, 10] Tac ddng ciia meo phi tuyen cd the danh gia qua SNRD gay bdi meo phi tuyen, xac djnh tai mgt sd gia trj thudng quan tam cua BER (10"\ 10"^ 10"^) Theo [9,10], cac cdng thu'c ddi vdi he thdng 16- va 64-QAM cd dang sau: SNRD ^a.dd^+ b.dd [dB] (3) a, b la cac hang sd da tim qua md phdng he thong vdi mdt loat bd KDCS thye te va dugc cho cac bang va 2, dd la tham sd thiet hai khoang each gay bdi meo phi tuyIn ciia bd KDCS [6] se dugc giai thich chi tiet myc Sai sd cua SNRD tinh theo (3) la kha nhd, sai sd mgi trudng hop da kilm tra deu nhd hon 0.2 dB tai miic BER = 10"'' va tai mire BER = 10"^ (tuong duong vdi muc BER ma Amadesi P da su' dyng) sai sd cdn nhd hon ntia, dudi 0.1 dB Bang L Cac gia trj eiia a va b tai eae gia trj khac ciia BER vdi 64-QAM [6] Muc BER a b 10"-^ 25.3 0.47 10-* 45 10"* 55 2.46 Dodn Thi Thanh Thao vd Dtg Bang Cac gia trj ciia a va b tai cac gia trj khac cua BER vdi 16-QAM [5] Muc BER a b 10"' 0.3 5.5 10"'' 0.6 10.2 10"" 1.325 10.875 DO THIET HAI KHOANG CACH DD Trong trudng hgp chi danh gia rieng tac ddng CLia meo phi tuyen gay bdi bd KDCS may phat (chat lugng ty le ldi bit dd cd thi sii' dyng nhu la mdt dudng bao dudi - lower bound - ciia chat lugng he thdng thye, nhit la meo phi tuyen trdi hon), cac bd phan khac cua he thdng xem nhu dugc thiet ke hoan hao, vay mgi tae dgng khac xem nhu khdng cd: a) Ddng bd sdng mang va ddng bd ddng hd hoan hao; b) Cac mach lgc phat va thu cd dap ung tdng cdng thda man tieu ehuan Nyquist thu' nhat (bd Igc phat la bd lgc can bae hai cosine nang ndi tiep sau mdt mach siia dang xung x/sinx nham bien tin hieu NRZ d Idi bd dieu ehe eac xung Dirac ed bien dugc dieu che, mach Ige thu la mdt bd Ige can bae hai cosine nang), mdi trudng truyen duge gia thiet la ly tudng, nghTa la ed ham truyen bang vdi mgi tan sd va vay khdng gay ISI tuyen tinh; c) He thdng khdng bj nhieu Tac ddng gay trd ngai viee truyen dan tin hieu ehi cdn lai: a) Meo phi tuyen gay bdi bd KDCS may phat; b) Tap am nhiet eiia may thu quy dau vao may thu va dugc md hinh hda bdi mgt ngudn tap am cdng trang chuan (AWGN - Additive White Gaussian Noise) So' dd khdi cua mdt he thdng nhu vay dugc trinh bay tren hinh ve B6 dil? 11 eke Bd loc L> |ihitl -• Bo KDCS 86(10): 27-32 Tap ehi KHOA HOC & CONG NGHE Bg lgc Gi:u Ihii dien che Hinh L So khoi he thong M-QAM chi tinh den tac dgng meo phi tuyen Nhu da trinh bay muc 1, viec danh gia chi rieng anh hudng ciia meo phi tuyen gay bdi bd khulch dai cdng suat may phat ddi vdi cac he thdng vd tuyen sd sir dung dieu che AfQAM cung da rat nan giai Trong [7], tac gia da de xuit mdt thdng so vl phi tuyen ciia cac bd KDCS may phat (bit luan bd KDCS la TWT hay SSPA) cac he thong M-QAM Thdng sd dugc ggi la thiet hai khoang each dd {distance degi-adation), la lugng thiet hai tinh trung binh tren toan tap tin hieu cua khoang each tii' diem tin hieu tdi bien quyet djnh gan nhat gay bdi tac ddng djeh chuyen cac diem tin hieu tren bieu dd chdm Vdi mdt bd KDCS va vdi mdt liii cdng suat dinh BO,, (Peak Back-Off) da cho, dd cd thi xac djnh de dang dugc nhu sau: -I" Tir cac dac tuyen AG{POM) va Acp{Poui) ciia bd khuech dai cho bdi eae nha san xuat va tii' gia trj liii cdng suat dinh BOp, xac djnh cac gia trj AGi_i va Ac?,, ddi vdi tirng vj tri tin hieu [IJ] tren chdm tin hieu (/, j = \, 2, , •slM 12) Nhd vay xac djnh dugc chdm bj meo gdm cac diem tin hieu mdi, bj djeh khdi vj tri tieu chuan tae ddng eiia AG,, va AOij Can luu y d day rang: a) Do tinh ddi xirng ciia chdm tin hieu M-QAM, chi mdt gdc phan tu can tinh den; b) Cdng suat ciia tin hieu QAM cd cdng suat ldn nhat, tuc la cdng suat dinh ciia tin hieu QAM, duge xac djnh theo P, Ps - BOp dd peak Ps la cdng suat bao hoa ciia bd KDCS, xac djnh dugc tai diem gue cua dac tuyen AM/AM Tir day cd the xac djnh de dang cdng suat tuong iing cua cae tin hieu /",_, cdn lai; + Ddi vdi tiing tin hieu [if] tren chdm tin hieu bj meo, xac djnh bang hinh bgc khoang each nhd nhat dij tii' diem tin hieu tdi bien quyet djnh gan nhat Thiet hai khoang each ddi vdi tin hieu [IJ] la dd,, = 1- d,/, + Tham sd thiet hai khoang each cua bd khuech dai la gia trj trung binh ciia thiet hai khoang each tinh tren toan tap tin hieu, tuc la: dd M Idd,^.! (4) '.y=i Viec sir dung tham sd dd cho phep so sanh eac bd khuech dai khac thude cac chiing loai khac nhau, bat luan la cac bg khulch dai dd ed hay khdng cd meo trudc Sii' dung tham 29 Dodn Thi Thanh Thao vd Dtg sd nay, theo cac cdng thire gan dung xac djnh theo ldi kinh nghiem thdng qua md phdng nhieu bg khuech dai khac nhau, vdi nhieu gia trj BO khac nhau, ngudi ta cd the tfnh tryc tiep anh hudng ciia meo phi tuyen gay bdi bg khuech dai cdng suat tdi chat lugng he thdng Mdt dieu quan trgng nu'a la vdi each xac djnh dd nhu da neu, tham sd dd cd the md rgng va sir dung dugc cho cac gia trj Mkhae SU' DUNG DO THIET HAI KHOANG CACH DD DE DANH GIA TAC D Q N G CUA MEO PHI TUYEN GAY BQ] BQ KHUECH DAI CONG SUAT PHAT TRONG CAC HE THONG 256-QAM Sii' dung thdng sd dd, chiing tdi da tien hanh md phdng bang phan mem ASTRAS vdi bd KDCS khac dugc chgn mdt each khdng cd chu y, vdi md phdng tya giai tich de dat dugc ket qua chinh xac ma thdi gian md phdng chap nhan dugc [1, 3, 4] Cac ket qua md phdng dugc trinh bay tren cac hinh ve va Tir cac ket qua md phdng nhan dugc tren eac hinh ve va 3, chiing ta cd the cd cac nhan xet sau: Khac vdi cac he thdng 16- va 64-QAM, dd SNRD theo dd bam kha chat theo mdt dirdng cong nhat he thdng 256QAM vdi cac bd KDCS khac nhau, cac dudng cong SNRD theo dd khdng nhu Dd cd the dac tinh ciia bd KDCS da khdng duge lam gan diing theo md hinh tham sd ciia Saleh mdt each can than, dan den sy sai khac qua ldn, cai ma vdi cac gia trj nhd hon ciia M ( hay 64) bdc Id it ban Van de se cdn can phai kiem ehung lai vdi sd lugng ldn hon cac bd KDCS thuc te S N R D al B E R = - v s Gtf : -SNRD= ; : [ 13.49Ot^-0.75cSJ /^- - GU CC : \- 9^ : : _X^ Lx^ 02 S N R D = 6.9i>J(^-0 45dd i i i 15 i i 25 i 0.3 Hinh SNRD tai BER = 10"' theo dd 30 86(10): 27-32 Tap chi KHOA HOC & CONG NGHE 35 ShRD a BER = 10'^vs « Hinh SNRD tai BER = 10"'' theo dd Mac dau vay, ed the thay rat rd rang SNRD vdi mgi bg KDCS da kiem tra deu cd the lam gan diing rat tdt bang mgt da thuc bac hai khdng cd sd hang bac theo dd SU PHU THUQC CUA SNRD G A Y B6\ KDCS PHAT V A O HE SO UON LQC Mdt van de can ndi ro them d day la tii' hinh ta cd the thay rang tin hieu dau vao bg KDCS phat la mdt tdng cac dap u'ng xung ciia mach lgc phat gay bdi chudi symbol dau bg dieu che, chii khdng thuan la tin hieu NRZ nhu da gia djnh each tinh dd Nhu vay, tham sd dd chi la mgt tham sd danh djnh (nominal parameter) ma thdi Tae dgng cua meg phi tuyen gay bdi bg KDCS lai phy thudc vao mue tin hieu ldi vao thye te, tue la cd le phai phu thudc vao he sd udn Igc a cua mach Ige phat Mdt van de kha ly thii la, mac dii gay chenh lech khac giu'a cdng suat dinh va cdng suat trung binh, mach Igc d phan phat vdi cac he sd udn Igc khac lai hiu nhu khdng anh hudng gi tdi SNRD gay bdi meo phi tuyIn ciia bg khuech dai [9, 10] Tire la, mac dii trgng thye te cac bg lgc cd the dugc thiet kl vdi a thay ddi giai tii' 0.2 tdi 0.75, sy thay ddi he sd udn Ige nhu thi khdng anh hudng gi lim tdi SNRD xac djnh theo bilu thuc (3) Ket qua md phdng may tinh nhim kilm tra sy phy thugc giua SNRD gay bdi meo phi tuyen cua bg KDCS phat vdi a he thdng 256-QAM dugc trinh bay bang Til' ket qua bang ta cd thi thay, a thay ddi tii' dau tdi cuoi dai gia trj Dodn Thi Thanh Thdo vd Dtg Tap chi KHOA HOC & CONG NGHE thuc te (0,25 + 0,75), SNRD thay ddi rit if thudng khdng qua 0,25 dB Til' ket qua md phdng, ehung ta cd the ket luan dugc rang [6]: Ddi vdi he thdng 256QAM, SNRD gay bdi meo phi tuyen ciia bg KDCS phat eung hau nhu khdng phu thude vao he sd udn a eua bd Igc phat Bang Sy phu thugc ciia SNRD tinh tai BER = 10"Saoa[9] HPAl given in jPupo l i n Greenstein] BO [dB] a=0.25 Q'=0,5 a=0.75 7.0 25.64 25.57 25.82 7.5 25.14 25.09 25.33 8.0 24.69 24.73 24.97 HPA2 [Berman- Maleh] given in BO [dB] a =0.25 a=0.5 Q'=0.75 8.5 26.46 26.22 26.53 9.0 25.71 25.62 26.22 9.5 25.18 25.17 25.44 HP A3 given in |Keye-Geoirge-Ericj BO [dB] Q'=0.25 a=0.5 a=0.75 8.0 28.17 27.69 27.99 8.5 27,20 26.88 27.19 9,0 26,40 26.21 26.53 KET LUAN Nhu vay, ciing vdi cac he thdng 16, 64-QAM, dd van ed the sii' dyng nhu mdt thdng sd de danh gia tac ddng eiia meo phi tuyen gay bdi bd KDCS phat phi tuyen he thdng 256QAM Viec xac djnh cac he sd cua da thuc md ta quan he giua SNRD va dd ta\ cac gia trj khac eua BER se la nhiem vu ciia nha san xuat cac bd KDCS Qua nghien ciru md mdt hudng mdi de phat trien viec danh gia tac ddng cua meo phi tuyen gay bdi bd khuech dai cdng suat cac he thdng da sdng mang thdng qua kha nang su dyng thdng so dd de tinh toan giai tich ty le ldi bit 86(10): 27-32 TAI LIEU THAM KHAO [1] Nguyen Thanh Bien, Nguyin Qudc Binh (2009), "Sl symbol cin thilt mo phdng tya giai tich cac he thing 256-QAM cd bg khulch dai cong suit phat phi tuyIn", Tgp chi Nghien ci'ni khoa hoc vd cdng nghe qudn su, Vien khoa hpc va cong nghe quan sy, so 26, 2-2009 [2] Nguyin Thanh Bien (2009), "Ham mat xac suit ciia nhieu giua cac ky hieu gay bdi sai lech ding hi cac he thong M-QAM", Tgp chi Nghien cuu khoa hoc vd cdng nghe qudn su, Vien khoa hoc va cong nghe quan su, so 27, 4-2009 [3] Nguyen Quoc Binh, Nguyin Thanh Bien, Dinh Trilu Duong, Nguyen Thanh Hieu (2003), "Sl symbol diing mo phong tua giai tieh cac he thong tryuen dan so", Tgp chi Khoa hoc vd ky thudt Hoc vien ky thuat quan sy, so 104, 2003 [4], Nguyen Quoc Binh, Nguyen Thi Hang Nga, Dinh Tien Diing (1997), "Ky thuat mo phdng he thong thong tin va cac u'ng dung", Tgp chi Bim chinh Vien thdng, Tong cue Buu dien, 10/1997, [5], Nguyen Quoc Binh, Nguyen Thj Hang Nga (2004), "Danh gia tac dgng dong thdi ciia meo tuyen tinh va sai lech dong ho cac he thong vi ba so M-QAM", Chuyen san Cdc cdng trinh nghien ci'ni-lrien khai vien thdng vd cdng nghe thdng tin Tap chi Buu chinh vien thong, so 11, 3-2004 [6] Nguyen Thj Hang Nga (1997), "Anh hudng tao dang tin hieu tdi quay pha phu toi uu cac he thong vo tuyen tiep sue M-QAM phi tuyen", Tgp chi Khoa hoc vd ky thudt, Hoc vien ky thuat quan sy, so 81, 1997 [7] Tran Viet Tuan (1998), "Bieu dien cac bg khuech dai cong suat mo phong cac he thong vo tuyen tiep sue M-QAM", Hdi nghi todn qudc ldn thu ba ve tu dgng hod (3rd VICA), Ha ngi, 911/4/1998 [8] Amadesi P., Mura P G., Pattial F (1983), "Including a Nonlinear Amplifier and a Predistoter in a Bandlimited 16-QAM Systems" IEEE, ICC'83 [9] Binh N Q (1995), "The Influence of the Pulse Shaping on the Signal-to-Noise Ratio Degradation Caused by Nonlinear Distortion in M-QAM Systems", TEMPUS Workshop, Budapest, Jun 810, 1995 [10] Nguyen Thi Hang Nga, Nguyen Quoc Binh, Nguyen Hai Nggc (2001), "Optimum Additional Phase Shift in Nonlinear 16-QAM Systems", Joumal on Science and Technique, Military TechnicalAcademy, No 96, 2001 [11] Pupolin S., Greenstain L.J (1987), "Performance Analysis of Digital Radio Links with Nonlinear Transmit Amplifier", IEEE, Joumal on SA C, Vol SAC-5, No.3, Mar 1987 31 Dodn Thi Thanh Thao vd Dtg Tap chi KHOA HOC & CONG NGHE 86(10): - SUMMARY THE ABILITY TO USE THE DD -DISTANCE DEGRADATION TO EVALUATE THE EFFECTS OF DISTORTION CAUSED BY NONLINEAR AMPLIFIER OUTPUT POWER OF 256-QAM SYSTEMS Doan Thi Thanh Thao", Doan Thanh Hai', Do Huy Khoi' 'College of Information and Communication Technology- TNU'' College of Technology- TNU Studies show how to determine the distance degradation - dd to evaluate the nonlinearity of power amplifiers and examines the dependence of Signal to Noise Ratio - SNRD on the distance degradation dd in MQAM modulation system 256-single carrier At the same time the paper also proposes a new research direction for calculating a bit error probability analysis to assess the impact of nonlinear distortion caused by power amplifiers in the system multi-carrier modulation Key words: distance degradation, MQAM, nonlinear distort, SNRD -Signal-to-Noise Ratio Degradation ' Tel: 0984 984199 Email: ihaonguyen^yahoacom 32 ... a=0 .75 7. 0 25.64 25. 57 25.82 7. 5 25.14 25.09 25.33 8.0 24.69 24 .73 24. 97 HPA2 [Berman- Maleh] given in BO [dB] a =0.25 a=0.5 Q''=0 .75 8.5 26.46 26.22 26.53 9.0 25 .71 25.62 26.22 9.5 25.18 25. 17. .. 25.18 25. 17 25.44 HP A3 given in |Keye-Geoirge-Ericj BO [dB] Q''=0.25 a=0.5 a=0 .75 8.0 28. 17 27. 69 27. 99 8.5 27, 20 26.88 27. 19 9,0 26,40 26.21 26.53 KET LUAN Nhu vay, ciing vdi cac he thdng 16, 64-QAM,... Nga (19 97) , "Anh hudng tao dang tin hieu tdi quay pha phu toi uu cac he thong vo tuyen tiep sue M-QAM phi tuyen", Tgp chi Khoa hoc vd ky thudt, Hoc vien ky thuat quan sy, so 81, 19 97 [7] Tran