Adaptive Imbalances Correction in LINC Transmitters. Paloma García, Jesús de Mingo, Antonio Valdovinos and Alfonso Ortega

Transcription

1 Adapi Imbalac Corrcio i LINC Tramir Paloma arcía, Jú d Migo, Aoio Valdoio ad Alfoo Orga Uiriy of Zaragoza, Elcroic Egirig ad Commuicaio Dp., Zaragoza, Spai. -mail: paloma@uizar., migo@uizar., oi@uizar., orga@uizar. Abrac: Th LIar amplificaio uig Noliar Compo (LINC chiqu i a wllkow powr amplifir liarizaio mhod o rduc adjac chal irfrc i a ocoa lop modulaio ym. I major drawback i h ihrid iiiy o gai ad pha imbalac bw h wo amplifir brach. I hi papr wo ol adapi fulldigial ba bad mhod ar dcribd which corrc ay gai ad pha imbalac i LINC ramir. Thir mai adaag i h abiliy o rack h ipu igal ariaio ad adap o h chag of amplifir oliar characriic.. Iroducio Th growig dmad for mobil commuicaio ric ad h limi of h frqucy pcrum ha icrad h u of pcrally ffici modulaio, mo of which ha o-coa lop. A a rul of ramir oliarii (maily from h powr amplifir h ramid igal pcrum xpad io adjac chal, a ffc kow a ACI (Adjac Chal Irfrc. Som ym ar ry rrici wih rgard o puriou miio i h adjac chal. I ordr o m hi rrici rquirm, h LINC claical liarizig chiqu for powr amplifir i propod ( Fig.. I major drawback i ihrid iiiy o gai ad pha imbalac bw h wo amplifir brach [,]. Th prd ol mhod u adapi igal procig chiqu ad i mai adaag i o rack ipu igal ariaio ad poibl chag du o mpraur ariaio ad compo agig, amog ohr. I i carrid ou i ba-bad ad i full-digial. Thorough imulaio wr carrid o alua ral opio. Sigal Compo Sparaor (SCS i Quadraur Modulaor q i Quadraur Modulaor q o Fig. Schmaic diagram of h LINC ramir. Imbalac ffc i a LINC ramir O of h rao ha h LINC ramir ha o b ud widly i h difficuly o achi accura gai ad pha machig rquird bw h wo pah. Error i gai ad/or pha machig will cau o o icompl cacllaio of uwad lm i widbad pha modulad igal. A a rul, a larg umbr of uwad puriou produc appar i h oupu pcrum, a obrd priouly [,,3,4,8]. Th ffc of gai ad pha imbalac bw h wo pah may b aalyzd a follow. Th ourc igal may b wri i complx gral forma a [7] jρ c c cmax < ( Th ourc igal i parad io wo coalop igal by a Sigal Compo Sparaor (SCS a how i Fig.. Th igal ar calculad a [ ] ( [ ] whr i a igal ha i i quadraur o h ourc igal. c max j (3 Thu ad Th amplifir of ach pah i characrizd by a lldpd complx gai, wih a oupu igal i ach pah gi by ( ( o o (4 whr ad ar h complx babad rpraio of h iaaou ipu complx modulaio lop of h powr amplifir i ach pah. I Fig., h powr amplifir ipu igal, ad, rpr h corrpodig badpa igal of ach pah. Thrfor, if h D-o-A corr ad quadraur modulaor ar uppod o b idal, ha i, ad, h oupu igal i complx forma h bcom o o o ( ( (5

2 Th cod rm i (5 impli ha hr i a uwad ridual igal du o imprfc cacllaio (i d o zro a h gai ad pha machig ar prfcd. Th rm iroduc irfrig powr i h adjac chal limiig h pcrum fficicy of h ym. Th aim of hi mhod i o rduc h facor [ ( ( ] a much a poibl. 3. Modl of Corrcio Mhod-I A chmaic diagram of h imulaio modl i dpicd i Fig.. Th ourc igal i parad io h wo coa-lop igal by a SCS. Th igal ar muliplid by diffr complx coffici, o for ach brach (K ad K. Th coffici ar compud o rduc h Adjac Chal Irfrc by ma of a adapi algorihm. Thi algorihm d a rfrc of h oupu igal o upda h complx coffici. Two rfrc igal, o for ach pah, r ad r ar obaid by ma of a dowcorio proc of h oupu igal o ad o rpcily, whr ad ar h dowcorio gai i ach L L pah. Thy ar calculad o adju h rag of alu of h quadraur dmodulaor ipu. Fig.. Simulaio modl Th adapaio cririo of h algorihm i o miimiz h ma-quard-rror i ach pah. Th rror igal for ach pah (dfid by (6 i h diffrc bw h coa-lop igal grad by h SCS block ad h rfrc igal of h oupu igal. Sigal Compo Sparaor (SCS K K r r ( K ( L r Quadraur Modulaor q i Quadraur Modulaor Quadraur Dmodulaor ( r ( K (6 L whr idal D-o-A, A-o-D corr, quadraur modulaor ad dmodulaor ar aumd. i q Quadraur Dmodulaor Th co fucio o miimiz ar dfid a L L o o o J E J E (7 Whr E[.] do h aiical xpcaio opraor. Th gradi of h co fucio i calculad a J J J j (8 K Kr Ki Wih K Kr jki, Whr Kr do h ral par ad Ki h imagiary par of K. For h co fucio J o aai i miimum alu, all h rm of h gradi mu b imulaouly qual o zro. Applyig om approximaio, w fially g for ach pah h rul * r J E, (9 k K Thrfor, uig h iaaou ima of h gradi, h updad alu of h adapi coffici a im m i compud by uig h impl rcuri rlaio ( m ( m r K ( ( ( m K m µ m, K ( Whr h poii ral-alud coa µ (p-iz, corol h pd of corgc ad h miadjum (fial xc rror of h algorihm. Th ourc igal for imulaio wa a π/4-dqpsk modulad igal filrd wih a quard-roo raid coi wih a.35 roll-off facor a 36 Kbp, which corrpod o a TETRA igal. Th amplifir i characrizd by a complx gai uig a mmoryl modl [6,8], which dpd o h ipu igal ll. Th complx gai of h amplifir i xracd from maurm of AM-AM ad AM-PM corio of a Miubihi M68749 amplifir (wih a drir a 39 MHz (5 Ω ym. A polyomic rgrio i ud o modl h amplifir complx gai of ach pah. M Φ jφ M ( (, ( α 8α 76α,,, α 9354α,4, α 64α 6,6,7.4β.5β 7.67β,,, β β,4, β β 6,6,7 * ( (3

3 Normalizd Powr Diy Spcrum (db Normalizd Powr Diy Spcrum (db Th amplifir i pah i imulad wih h coffici α ad β. Th amplifir i pah wa imulad iroducig ral imbalac i om coffici of h gai ad pha poliomy. Sral wr carrid ou by modifyig h facor α,j ad β,j amog a ± %. Fig. 3 how h ormalizd ipu S(f ad oupu S o (f powr pcrum diy for a 3- Wa oupu powr amplifir udr diffr gai ad pha imbalac bw boh brach of h LINC ramir (wihou applyig h corrcio mhod Frqucy (ormalizd o ymbol ra Fig. 3. Normalizd Powr Diy Spcrum of imulad ipu S(f ad oupu S o(f wih ral gai ad pha imbalac bw boh brach of a LINC ramir wihou corrcio mhod. (a a 3dB, φ a º, (b a db, φ a 5º,(c a db, φ a 3º, (d a.7db, φ a º,( a.5db, φ a º Fig. 3 illura h ffc of gai ad pha imbalac ad h d for a mhod o achi gai ad pha machig a prd i hi papr. Fig. 4 compar h ormalizd ipu ad oupu powr pcrum diy wih ad wihou h prd adapi corrcio mhod ad wih a gai imbalac of approximaly.5 db ad a pha imbalac aroud 5º bw h amplifir i pah ad h o i pah. Th ACI i improd afr applyig h corrcio mhod wih accura gai ad pha machig bw h wo pah. Th ACI i h fir adjac chal wihou corrcio i aroud 35 dbc, bu -7 dbc wih h corrcio mhod (35 db improm Fig. 4. Normalizd Powr Diy Spcrum of imulad ipu S(f ad oupu S o(f wih ad wihou corrcio (a S(f So(f S(f So(f wihou corrcio So(f wih corrcio Frqucy (ormalizd o ymbol ra (b (c (d ( 3. Limiaio of h corrcio algorihm I h priou imulaio h am dowcorio gai i ach pah wa aumd, ha i, L L. Th pracical implmaio of hi balac bw boh dowcorio brach i chologically ry difficul, alhough i i air ha bw LINC ramir brach. Thu, w aalyzd h ffc of h imbalac (uppodly liar, bw h dowcorio brach. Fig. 5 how h prformac obaid i h imulaio wh a gai ( ad pha ( φ imbalac facor bw L ad L i iroducd. A xpcd, ACI udr ral codiio icra coidrably, wih gai ad pha imbalac bw dowcorio brach. (.5 db ad φ º, Normalizd Powr Diy Spcrum (db S(f So(f wihou corrcio So(f wih corrcio ad ral dow imbalac. db φ 5 º Frqucy (ormalizd o ymbol ra Fig. 5. Normalizd Powr Diy Spcrum of imulad ipu S(f ad oupu S o(f wih ad wihou corrcio mhod ad wih ral imbalac bw dowcorio brach. 4. Modl of Corrcio Mhod-II O way o ol hi problm i o ha oly o fdback brach, hu obaiig a igl rfrc igal of h powr oupu igal, o. Thi rfrc igal ca b pli io wo igal uig a SCS block o obai h wo rror igal (o for ach pah, dd for h adapi algorihm. Fig. 6 how h w propod archicur. Sigal Compo Sparaor (SCS K r K r SCS i Quadraur Modulaor q i Quadraur Modulaor r q Quadraur Dmodulaor Fig.6. Simulaio modl of mhod II. db φ º.5 db φ º o o L o

4 I hi ca, h rror igal i ach pah i r r ( whr r ad r ar obaid from r uig a Sigal Compo Sparaor block Aumig idal D-o-A ad A-o-D corr ad quadraur modulaor ad dmodulaor, h rfrc igal r i r r r o K L ( K L (5 Magiud im (µ Fig. 8. Eoluio of h rror igal i ach pah. A i h priou mhod, h adapaio cririo of h algorihm i ud o miimiz h ma-quardrror i ach pah. Thrfor h co fucio o miimiz i dfid a (7. Applyig om approximaio, for ach pah w obai h am rul a (9. Thrfor, h updad alu of h adapi coffici a im m ca b compud uig h am rcuri rlaio a (. Th prformac of hi w mhod i illurad i Fig.7. Th ACI i h fir adjac chal wihou corrcio i aroud 35 dbc, bu blow 64 dbc uig h w corrcio mhod ( 3dB improm. I g wor ha h priou mhod, bu i do o dpd o h dowcorio gai imbalac ad oly o fdback dmodulaio brach i dd. Normalizd Powr Diy Spcrum (db S(f So(f wih corrcio So(f wihou corrcio Frqucy (ormalizd o ymbol ra Fig. 7. Normalizd Powr Diy Spcrum of imulad ipu S(f ad oupu S o(f wih ad wihou corrcio mhod II Th pd of corgc ca b maurd by aalyzig h im oluio of h rror igal ad. Th p iz paramr, µ, wa cho o rduc h ACI (up o -6dBc i h fir adjac chal a quickly a poibl ( Fig. 8. Th corgc im (< µ i uiabl i ordr o b implmd i a ral im ym. 4.. Modulaor ad Dmodulaor Mialigm Prfcly balacd quadraur modulaor ad dmodulaor wr aumd i hi archicur, which lad o aohr pracical coidraio. Th quadraur imbalac (ampliud ad pha cra a ridu i h adjac chal, icraig h ACI [9]. Fig. 9 how h dgradaio of h ACI wh hr ar imbalac i h quadraur modulaor. Simulaio wr carrid ou wih ral ampliud ad pha imbalac. Th rul ar ry promiig for imbalac alu corrpodig o commrcial quadraur modulaor (ampliud rror bw.5 db ad db ad pha rror bw º ad 5º. W alo aalyzd h ffc of a ubalacd quadraur dmodulaor i hi archicur. Som imulaio wr carrid ou wih commrcial gai ad pha rror bu hir ffc o h I/Q dmodulaor wa o igifica. Normalizd Powr Diy Spcrum (db So(f wihou corrcio So(f wih corrcio ad ral imbalac Frqucy (ormalizd o ymbol ra Fig. 9. Normalizd Powr Diy Spcrum of imulad ipu S(f ad oupu S o(f wih ral gai ad pha imbalac i h quadraur modulaor.

5 4.. Mhod Viabiliy Accordig o h imulaio prd, h mhod prform wll wih imbalac i h quadraur modulaor ad dmodulaor. I hi cio w dicu h pracical faibiliy of h mhod. Digial block of h dig (uch a SCS ad h calculaio o upda h adapi coffici K ad K ca b implmd i a powrful Digial Sigal Procor (DSP dic. Maximum opimizaio of h implmaio of h algorihm i carrid ou approachig om DSP faur, uch a pd or pcial irucio for igal procig. Th algorihm mu b rarchd i ordr o dcra h umbr of irucio o rduc h compuaioal load ad iroduc miimum dlay i h ym. Aohr impora ffc ca b h quaizaio i h SCS block. Th dig i carrid ou accordig o h rquirm dcribd i [5], ad hrfor h ffc of h quaizaio will b miimum. Th Sigal Compo Sparaor i implmd i a fixd-poi DSP of a fii word lgh (6 bi. Accordig o [5] hi word lgh i uiabl ough o obai a ACI up o 6 dbc i h fir adjac chal. Th ffc quaizaio will o b a problm i a ral dig wih a righ choic of D-o-A ad A-o-D corr i h curr wid rag of commrcial dic (.g. 4 or 6 bi. Aohr idal iuaio ha ha b aumd i h priou imulaio corrpod o h ozro loop dlay. Th rfrc igal r i a dlayd ad auad rio of amplifir oupu o. Th dlay mu b compad for h adapi algorihm o corrcly compar wih r. Th am DSP dic gra igal ad r, whr ar obaid from h ourc igal ad r from h fdback igal r. Thu, h dlay compaio ca b aily obaid by comparig h ampl wih h calculad loop dlay. Thrfor h dlay producd by h corrcio circui ha o b imad bfor iroducig h adapi algorihm. A rough imaio ca b carrid ou wih h horical im dlay of h compo i h dig or by applyig om of h loop dlay imaio chiqu propod by ohr auhor [6,8,,] or wih om priou calibraio. 5. Cocluio A ol mhod o corrc gai ad pha imbalac i LINC ramir wa dcribd. Uig a imulaio w howd ha i i poibl o rduc h ACI o m h rrici pcificaio of h TETRA digial commuicaio ym. Th ym corg quickly oward ry low irfrc ll i adjac chal. A a rul of i adapi chiqu, hi mhod ca rack h ipu igal ariaio ad poibl chag du o ariaio i opraig codiio. Accordig o h imulaio, h adapi coffici quickly rach i opimal alu, hrfor hi mhod could b implmd i a ral ym by ma a uiably powrful DSP dic. Ackowldgm Thi work ha b uppord by h CICYT (Spai udr gra TIC-48. REFERENCES [] F. J. Caadall ad A. Valdoio, Prformac Aalyi of QAM Modulaio Applid o h LINC Tramir, IEEE Tra. o Vh. Tch., Vol. 4, No. 4, Nombr 993, pp [] F. J. Caadall ad J.J. Olmo, O h bhaiour of h LINC Tramir, i Proc. 4 h IEEE Vh. Tch. Cof, Orlado. May pp 9-34 [3] L. Sudröm. Auomaic adjum of gai ad pha imbalac i LINC ramir, Elcro. L., Vol. 3, o 3, pp , Fb, 995. [4] Xuju Zhag ad Lawrc E. Laro, ai ad pha rror-fr LINC ramir, IEEE Tra. o Vh. Tch., Vol. 49, No. 5, Spmbr, pp [5] L. Sudröm, Th Effc of Quaizaio i a Digial Sigal Compo Sparaor for LINC Tramir, IEEE Tra. o Vh. Tch., Vol. 45, No., May, pp [6] S.A. Maa, Volrra aalyi of pcral rgrowh, IEEE Microwa uidd Wa L, ol. 7, pp. 9-93, July 997 [7] Hzl, S.A., A. Bama, ad J.P. Mcha, LINC ramir, IEEE Elcroic Lr, ol. 7, o, pp , May 99 [8] J. d Migo ad A. Valdoio, Prformac of a Nw Digial Babad Prdiorr Uig Calibraio Mmory, IEEE Tra. o Vh. Tch., Vol. 5, No. 4, July, pp [9] J. K. Car, Th ffc of quadraur modulaor ad dmodulaor rror o adapi digial prdiorr for amplifir liarizaio, IEEE Tra. o Vh. Tch., Vol. 46, May 997, pp [] J. K. Car, Nw mhod for adapaio of quadraur modulaor ad dmodulaor i amplifir liarizaio circui, IEEE Tra. o Vh. Tch., Vol. 46, No 3, Aug. 997, pp [] Y. Nagaa, Liar amplificaio chiqu for digial mobil commuicaio Proc. 39 h IEEE Vh. Cof., pp59-64, May 989