Recognition of OFDM Modulation Method

Transcription

1 K. ULOVEC, RECOGITIO O ODM MODULTIO METHOD Recognton o ODM Modulaton Method Karel ULOVEC Department o Rado Engneerng, Czech Techncal Unverty, Techncká, 66 7 Prague, Czech Republc xulovec@el.cvut.cz btract. Th contrbuton deal wth aynchronou noncoherent recognton o modulaton type. The man am to recognze ODM modulaton method rom ome other ngle-carrer analog and dgtal modulaton type n the preence o WG noe. The decrbed oluton o recognzer ue key eature o the receved gnal. The gnal ampltude oberved at the output o the quadrature ntermedate-requency tage. The properte o the recognzer are vered by mulaton ung Matlab. Keyword oncoherent aynchronou recognton, ODM modulaton method, WG noe, quadrature ntermedate-requency gnal, gnal key eature, correct recognton, ale alarm, mulaton.. Introducton utomatc Modulaton type Recognton (MR) could be ued a example or automatc demodulaton electon n the otware dened rado or n applcaton o pectra montorng []. It could alo mprove hybrd recever dedcated to both dgtal and analog ytem. or example, analog and dgtal audo broadcatng coext n the ame requency band below 3 MHz (ampltude modulaton v. ODM), analog and dgtal vdeo broadcatng (pecal type o ampltude modulaton v. ODM) and t uppoed that dgtal audo broadcatng wll extend to M band, n whch analog audo broadcat (requency modulaton v. ODM). Two man approache to MR could be dtnguhed, rtly maxmum lkelhood and econdly eature extracton approach []. The rt one provde optmal oluton by mnmzng the probablty o ale clacaton and the econd one baed on the derence o key eature or derent modulaton type. In th work the latter ued. ODM modulaton method baed on ung a bg number o carrer (hundred, thouand), o t called Mult-Carrer (MC) modulaton method. Each carrer modulated ung quadrature ampltude modulaton wth randomzed modulatng data. pplyng the central lmt theorem, we could clam that ODM probablty law converge to the Gauan law. The tattcal properte o ODM gnal ampltude have to be dtnct rom the tattcal properte o other modulaton type gnal. The key eature computed on the ba o ampltude gnal could be ued or ODM modulaton technque recognton. The man goal o th paper to recognze ODM rom other modulaton type; only n addton we deal wth the poblty o recognzng each rom another (next to ODM). Many technque nvolve recognton o ngle carrer modulaton type, [3]-[], only a ew technque deal wth MC modulaton, a example [6]. But technque nvolvng ODM and analog and/or dgtal Sngle-Carrer (SIC) modulaton at the ame tme are mng. In th paper the background o a gnal proceng and key eature decrbed. The tudy o key eature properte lead to determnng o threhold and thee are ued or automatc recognton o modulaton type. Becaue we uppoe no pror knowledge o gnal to be recognzed, we call the preented technque a noncoherent and aynchronou. The key eature computed rom ample o the gnal at the output o a quadrature mxer or modulaton type clacaton. The nluence o the WG noe or vercaton o the properte o recognzer condered n th work.. Background an nput gnal, we conder a number o ample (one rame) o the rado-requency (R) gnal r [k], whch have an expected central requency c (we don t know anythng about the ncomng gnal; the exact value unknown). Two gnal are at the output o quadrature Inter- Medate (IM) requency mxer havng a ueul product n the band around the requency marked m oc r '[k] = co(π k) r [k], () oc r '[k] = n(π k) r [k] () where oc the requency o the local ocllator ( m = oc - c ) and the amplng requency.

2 RDIOEGIEERIG, VOL. 7, O., PRIL Both gnal r [k] and r [k] are ltered to uppre uele product o mxng ung a IR (nte Impule Repone) lter. The requency ampltude repone o the ued lter depcted n g.. ltered gnal are degnated a r [k] and r [k]. It are rom g. that ytem bandwdth B yt = m. Sgnal r [k] an n-phae component gnal and r [k] a quadrature component gnal o the complex ntermedate gnal. rom component gnal r [k] and r [k] we compute ampltude gnal a ( r [k]) ( [k ) m [ k] = + r. (3) ] To compenate gnal attenuaton caued by the mxng and lterng we dvde gnal m [k] by t tandard devaton, whch lead to normalzed gnal (ndex n mean that the gnal normalzed, o a not to be conued wth noe) m n [k] = td{ m m [k] [k]} k =,,..., where td{} denote tandard devaton. rom component gnal we compute the pectrum o the gnal a (DT agn Dcrete ourer Tranorm) Sm [w] = DT( r [k] + jr [k]) = = Real { S [w]} + j Imag{ S [w]} m and ampltude o the pectrum a S r [w] = m w =,,..., ( Real{ S [w]}) + ( Imag{ S [w]}) m w =,,..., m (4) (). (6) We normalze the pectrum ampltude mlarly a beore X m n [w] = S r E{( [w] S r [w]) } w =,,..., One rame (havng ample) o the oberved gnal repreent one realzaton agned by ndex. Three key eature are choen or clacaton o modulaton type, rt the 4 th order moment (or one realzaton ) 4 4 = ( [k]) m n k = (7) M, () key eature (or one realzaton ) m n k = = [k], (9) and key eature S (or one realzaton ) w = S = X m n[w]. () When ndng threhold we need mean value and tandard devaton over I realzaton. We compute them accordng to I E k k, () { } = = = I I { } = td k = ( k E{ k} ) () I = where k tand or M 4, and S repectvely. a (db) - - B yt m m 3 m B R C m OSC g.. The requency ampltude charactertc (marked blue) o the IR lter to uppre underable product o mxng (note: output product o mxng are colored green, nput gnal are colored red; even no leakage o the nput gnal condered theoretcally, the charactertc relect a real tuaton wth poble leakage o the nput gnal). 3. Smulaton We ue mulaton to very capablte o the above mentoned key eature to recognze (manly) the ODM modulaton technque. ne type o modulaton are choen: M-SC (mpltude Modulaton-Suppreed Carrer) M (mpltude Modulaton) M-B (requency Modulaton-arrow Band) M-WB (requency Modulaton-Wde Band) PM (PM, Phae Modulaton) 4SK (4-tate requency Sht Keyng) 4PSK (4-tate Phae Sht Keyng) 6QM (6-tate Quadrature mpltude Modulaton) and a a matter o coure ODM two cae o ODM gnal are mulated; the rt wth bandwdth o approx. 9. khz (marked a ODM n narrow ) and the other wth bandwdth o approx. 77 khz (marked a ODM w wde ). ' m

3 K. ULOVEC, RECOGITIO O ODM MODULTIO METHOD It worth notng, the ODM n gnal correpond to the DRM (Dgtal Rado Mondale) gnal (Mode ) and the bandwdth value or ODM w choen almot between khz and khz thee range expected or an extended ytem o DRM (DRM+). Modulatng parameter or the ODM gnal are hown n Tab.. The modulatng gnal or other modulaton type generated randomly, the maxmal requency and ymbol rate are repectvely khz and 49 Bd, except o M and M-B, both wth maxmal requency o 4. khz. r [k] = mod k= [k] ( [k]) mod + n[k] k =,,..., (3) where mod [k] tand or the modulated gnal and, a a reult o the channel nluence, ample o Gauan noe n[k] are added to t. or Sgnal-to-oe Rato (SR) we ue the denton accordng to the devaton ODM number o carrer modulaton on ub-carrer ODM ymbol rate (Bd) gnal bandwdth (Hz) n 9 64-QM 4,7 94 w 3 64-QM 4,7 77 Tab.. Modulatng parameter or ODM gnal. The carrer requency c ha the value o khz and the amplng requency 4 Hz. Mnmally 73 ample o each modulated gnal are generated, correpondng to the tme duraton o approx. 39 m (exact value n the cae o dgtal modulaton are nluenced by the ymbol rate). I = realzaton o each gnal are generated. We ue a channel wth addtve Gauan noe to examne the properte o the key eature and later on or the vercaton o the recognton technque. To compenate unknown gnal attenuaton caued by a rado channel we ue normalzaton. Sample o the R gnal r [k] could be decrbed a value (-) value (-) key eature M 4 key eature u n σ SR = log (4) σ where σ u correpond to the devaton o the ueul gnal and σ n correpond to the devaton o the noe gnal. Becaue o normalzaton n (3) we obtan σ u =. The amount o the noe gnal could be determned rom n SR σ = () It worth notng that the ytem bandwdth and the value o amplng requency are taken nto account when SR computed and ample o noe are generated by a random generator wth Gauan probablty law wth zero mean value and the unt devaton (marked a norm (;) [k]) n[ k] = norm(; )[k] SR Byt k =,,..., mean value (-) mean value (-) key eature M 4. key eature. - (6) value (-). key eature S - M-B noe SK PM 49 4 M-WB PSK 49 QM 49 M 4 ODM w M-SC ODM n mean value (-). key eature S g.. Value o key eature n dependence on realzaton; Mean value o key eature n dependence on SR.

4 RDIOEGIEERIG, VOL. 7, O., PRIL 3 The requency o IM gnal m uppoed to be 6 Hz. To be prece, we decmate equence o the ample ater the ntermedate IR lterng (each econd ample ued), o that the new amplng requency ( = /). The number o ample n one rame and 36. Dependence o value on realzaton and dependence o mean value on SR are hown n g. or all three key eature. It very vual, how value o key eature could be ued or the recognton o modulaton type. The tudy o thee dependence, and here not preented tandard devaton o key eature, lead to the determnaton o threhold. It not poble to decrbe th determnaton n th paper n detal. We can ee the value o threhold n Tab. -4. group group 36 rom to rom to M-SC,3 -, - ODM,,3,7, 3 noe,74,,76,7 4 QM,376,74,3,76 M,3,376,6,3 6 M-B, M- WB, SK, PM, PSK -,3 -,6 Tab.. Threhold o the key eature M rom to rom to M-B, M- WB, SK, PM,,96 -,96 - PSK M,943,96,939,96 3 QM,97,943,96,939 4 noe,9,97,9,96 ODM,63,9,69,9 6 M-SC -,63 -,69 group Tab. 3. Threhold o the key eature. rom to rom to noe,7 -, - mod. gnal 36 -,7 -, Tab. 4. Threhold o the key eature S. It evdent that the o-called angle modulaton (or M 4 n group 6 and or n group ) could not be recognzed each rom other by the propoed technque (a example M-B could not be recognzed rom PSK and o on). nother key eature (derved rom a requency or a phae) mut be ued or th purpoe we need t. But t ha no mpact on recognton ODM rom each o thee angle modulaton and t ate to the man am. When ung key eature M 4 and (a clear rom Tab. and 3) t poble to recognze group o modulaton type and noe gnal. We can recognze only between a noe gnal and a modulated gnal ( group) wth the help o key eature S (ee Tab. 4). 4. Reult reult o mulaton, probablte o the correct recognton, probablte o the ale alarm and the conuon matrx or ome SR rato value between - db and db are preented n Tab. -9 and g Conuon matrxe are tool or the demontraton o the properte o the recognzer. Type o ued modulaton are algned n row, meanwhle recognzed group o modulaton type are n column (uually one group mean one type, but not alway, ee Tab. -4). The probablty o the correct recognton computed a a number o realzaton wth correct clacaton; t mean that the gnal modulated by the ame type o modulaton a recognzed (the bet value ). The probablty o the ale alarm computed a number o realzaton wth the wrong clacaton; t mean that a gnal modulated by a derent type o modulaton than recognzed (the bet value ). We can tart wth the key eature M 4 (Tab. and 6, g. 3 and 4). We ound out rom the preented reult, that the decrbed recognzer ha very good reult n the ODM modulaton technque recognton. ODM (group ) recognzed already or SR = db (and hgher) and no ale alarm or SR = db (and hgher). The reult are not atactory or the modulaton n group and 6. But the man am dcrmnaton o ODM modulaton technque. The decrbed recognzer ueul or modulaton type M-SC, ODM, QM and noe (note that only WG noe teted). or other M and angle modulaton type another known technque mut be ued or recognton. There no chance to recognze partcular modulaton type n group o angle modulaton. The reult are almot the ame or the = and = 36. When we compare the reult or the key eature and M 4 we can ay that they are very mlar. The key eature S eem to be very good or the clacaton o a noe gnal (but only WG teted). Only good clacaton and no ale alarm are or all the teted cae. That the reaon why only one conuon matrx or SR = - db preented and no other probablte are computed.

5 4 K. ULOVEC, RECOGITIO O ODM MODULTIO METHOD recognzed group 3 4 6,933,4,63,9,,4,6,4,9,7,36,6,,,46,3,,9,9,4,4,996,4-4 7 recognzed group 3 4 6,794,76,6,74,6,,,,,,,,,,9,36 Tab.. Probablte o correct detecton and probablte o ale alarm v. SR ung key eature M 4 or =. Tab.. Probablte o correct detecton and probablte o ale alarm v. SR ung key eature or = recognzed group 3 4 6,4,,697,,,6,6,6,99,,4,6,,,6,39,,94,6 Tab. 6. Probablte o correct detecton and probablte o ale alarm v. SR ung key eature M 4 or = recognzed group 3 4 6,6,9,3,36,6,9,,99,44,96,4,,96,9,,74,9,9,,,76,9 Tab. 7. Probablte o correct detecton and probablte o ale alarm v. SR ung key eature or =.,,6,4, g. 3. Probablty and probablty v. SR or ODM modulaton, ung M 4, =.,,6,4, g. 4. Probablty and probablty v. SR or ODM modulaton, ung M 4,, = 36.,,6,4, g.. Probablty and probablty v. SR or ODM modulaton, ung, =.

6 RDIOEGIEERIG, VOL. 7, O., PRIL,,6,4, g. 6. Probablty and probablty v. SR or ODM modulaton, ung, = 36. modulated recognze group noe ODM_3 ODM_9 M-SC QM M M-B M-WB SK PM PSK Tab. 9. Conuon matrx o modulaton v. noe recognton ung S (the ame reult or all teted cae).. Concluon In th paper the noncoherent aynchronou recognton technque or clacaton o the modulaton type nvolvng all analog and dgtal ngle-carrer and ODM decrbed. The oluton ue key eature computed on the ba o ampltude gnal and t pectrum at the output o quadrature ntermedate requency tage. The decrbed method eem to be ucent or the recognton o the mult-carrer modulaton technque ODM n the preence o the Gauan noe or low value o SR ( db). the technque noncoherent and aynchronou, we don t need to know anythng about the recevng gnal, whch could be nteretng or practcal applcaton. owaday ome reult rom th work are vered ung otware dened rado (SDR) and t eem that the reult are applcable a an example or the recognton o analog M, M broadcatng and dgtal audo broadcatng Dgtal Rado Mondale. But no extenve tet have been done wth the SDR recepton yet. It planned or uture work. cknowledgement The reearch decrbed n the paper wa upported by the reearch program MSM Reerence [] DUBUC, C., BOUDREU, D., PTEUDE,., IKOL, R. n automatc modulaton recognton algorthm or pectrum montorng applcaton. In Internatonal Communcaton Conerence, Vancouver, 999. [] OCTVI,. D., WEI, S. On the clacaton o lnearly modulated gnal n adng channel. In Conerence on Inormaton Scence and Sytem, Prnceton Unverty, 4. [3] ZZOUZ, E. E., DI,, K. utomatc dentcaton o dgtal modulaton type. Sgnal Proceng, 99, vol.47, no., pp [4] SWMI,., SDLER, B. Herarchcal dgtal modulaton clacaton ung cumulant. IEEE Tranacton on Communcaton,, vol. 4, no. 3, p [] DI,. K., ZZOUZ, E. E. utomatc analog modulaton recognton. Sgnal Proceng, 99, vol. 46, p.-. [6] KMOUCHE, W. Detecton o Multcarrer Modulaton Ung 4th- Order Cumulant. IEEE, 999. bout uthor... Karel ULOVEC wa born n 977 n Prague, Czech Republc. He receved h Mater' Degree n electrcal engneerng rom the aculty o Electrcal Engneerng, Czech Techncal Unverty n Prague, n. t preent, he an atant proeor at the ame aculty and he workng on h Ph.D. the. H reearch nteret nclude broadcatng ytem, meaurement o rado tranmtter and recever and rado gnal proceng.