Performance Comparison between 6-Port and 5-Port homodyne circuits for DOA Estimation

Transcription

1 Procdings of th 4th WSEAS Int. Confrnc on Elctromagntics, Wirlss and Optical Communications, Vnic, Italy, Novmbr 20-22, Prformanc Comparison btwn 6-Port and 5-Port homodyn circuits for DOA Estimation Ayman Abdallah, Soubhi Abou Chahin, Kamal Sabbah, ouhammd Rammal, Guillaumm Nvux, Patrick Vaudon Abstract In this papr, w propos two approachs to provid dirction of arrival using homodyn dtction systms tchnologis lik six-port and fiv port rflctomtrs. Th choic of th rflctomtrs' typ bcoms critical in paralll of th circuit capability, i.. in trms of th numbr of signals to b dtctd simultanously. W prsnt our study by implmnting USIC algorithm at th output of two diffrnt homodyn rcivrs. Th rsults ar dducd from th simulation of th charactristics of ach systm, using th Advancd Dsign Systm (ADS) and ATAB. 1. Introduction Th problm of localization of sourcs radiating nrgy by obsrving thir signal rcivd at spatially sparatd snsors is of considrabl importanc, occurring in many filds, including radar, sonar, mobil communications, radio astronomy, and sismology.[1] Thus a varity of mthods, using htrodyn or homodyn tchniqus, for th Dtction Of Arrivals (DOA) stimation ar usd including spctral stimation, minimum-varianc distortionlss rspons stimator, linar prdiction, maximum ntropy, and maximum liklihood [2]. In addition to prvious mthods th most famous mthods usd in DOA ar ignstructur mthods, including many vrsions of USIC algorithms [3], minimum norm mthod [4], ESPRIT mthod [5], and th wightd subspac fitting mthod. Whil th most rcntly publishd paprs dscrib th DOA for thr signals at most [6], [11], th main goal of this papr is to implmnt USIC algorithm with two typs of homodyn dtction circuits. W us ths typs of circuits bcaus of thir simplicity, low cost and high fficincy in th dtction of arrivals. Th purpos is to compar th quality of th dtctd angls, in trm of prcision, for both circuits, spcially whn th numbr of th incoming RF signals incrass till svn. This papr consists of six main sctions. Sction 2 prsnts a gnral introduction of smart antnnas. Sction 3 dscribs 5-port and 6-port homodyn rcivrs and thir calibration tchniqus. Sction 4 xplains th thory of th USIC algorithm. Th simulation rsults as function of local oscillator powr, for 6- port and 5-port circuits, ar prsntd in sction 5. Finally th main conclusions ar summarizd in sction Smart antnnas dsign systms Smart antnnas ar ssntial parts of th nw gnration mobil systms. Thy can b usd to xploit spatial and spctral charactristics of th incoming signals to provid highly accurat location information [1]. Th dirction of arrival (DOA) algorithm is on of th most important parts of such tchniqus. A smart antnna systm can contain an antnna array that rcivs th incoming signals to dtrmin thir arrival angls and to control th transmittd signals. RF 2 RF 1 Array A2 Array A1 Phas Shiftr Control Bus R 1 R n Figur 1: Smart antnnas systm. Figur 1 rprsnts a smart antnna systm which can dtct th DOA for two RF signals simultanously. To do so, an antnna array A 1, that has thr patchs, rcivs th incoming wavs from th signals RF 1 and RF 2. Th output of ach patch is dirctly connctd to a rflctomtr (R i ). From th linarizd and calibratd outputs of th rflctomtrs, thr or four dpnding on his typ; fiv or six ports rspctivly, w can obtain thr low frquncy complx nvlops (ratio of incoming signal to a rfrnc signal). Ths ar th inputs for th USIC algorithm. This algorithm provid as an n D S P Transmission Rcption

2 Procdings of th 4th WSEAS Int. Confrnc on Elctromagntics, Wirlss and Optical Communications, Vnic, Italy, Novmbr 20-22, Eignvalus output a matrix that is th rsult of projcting th b2 a1 b1 a5 a2 b5 b3 a3 b4 a4 V3 V4 V5 Figur3. Fiv-port rflctomtr In cas of six-port, a couplr is rquird to provid a rfrnc powr from th ocal Oscillator (O) input for normalization as shown in figur4. P 3 P 4 P 5 signal plan ovr th nois plan as shown in figur2. Figur 2: DOA of 2 signals using ADS Figur 2 rprsnts th rsult of simulation for th DOA of two incoming RF signals from a and Th simulation is mad using ADS (in a noislss nvironmnt) to dsign th thr rflctomtrs in addition to circuits for simulating th incoming signals [7]. As a conclusion, to dtct N signals N+1 patchs and rflctomtrs in addition to biggr capability of th DSP programs. 3. Homodyn rcivrs Th architcturs of th homodyn rcivrs ar simpl, with low nrgy consumption and small numbr of componnts. Actually, thr ar two typs of homodyn rcivrs that ar usd as ntwork analyzrs which ar fiv-port rflctomtrs and sixport rflctomtrs. Ths rflctomtrs prcisly dtrmin th complx ratio btwn two input signals. 3.1 Six-port and fiv-port rflctomtrs 50Ω a 1 Dirctiv couplr D 3 Figur 4: rflctomtr six-ports Ths dvics prmit th masurmnt of th rflction cofficint Γ of a dvic undr tst or th ratio of two RF input signals (complx nvlop). Th output dtctd powrs ar submittd to linarization and calibration functions to gt Γ or th ral part I(t) and imaginary part Q(t) of th complx nvlop. 3.3 Dsigning powr dtctors for th homodyn rcivrs Th powr dtctor HSS2852 is mad as shown in figur 5. HF C.a 1 T.a 1 D 4 Ring 5 accss D 5 D.U.T a 2 D 6 P 6 50Ω C R b 2 DC Th six-port and fiv-port rflctomtrs ar microwav masurmnt dvics that wr first introducd by G. F. Engn [8]. Th fiv-port rflctomtr consists of a fiv-port microstrip ring with thr Schottky powr dtctors as shown in figur 3. Figur 5: Powr dtctor It is locatd at ach of th output of th homodyn rcivrs. It convrts RF signals to ow frquncy signals or to DC signals. Th rlation btwn input powr and th output voltag of this dtctor is prsntd in figur 6.

3 Procdings of th 4th WSEAS Int. Confrnc on Elctromagntics, Wirlss and Optical Communications, Vnic, Italy, Novmbr 20-22, inarizd Outputs Ral Outputs Figur6: inarization of powr dtctors For low input powr, th law of opration of diod dtctor is quadratic, th output voltag is linarly dpndant of input powr. Howvr, for highr input powr (-15dBm), th output voltag is proportionnal to th amplitud of input signal (nvlopp dtctor), so a linarization function is rquird [10], [11]. powrs to th local oscillator and th tst masurmnt port. Th thortical valu of th rflction cofficint is 0.25 (-12dB) sinc th coupling cofficint of th couplr is -8dB. A good agrmnt is obtaind with th simulatd rsults and as consqunc it can b usd with high fficincy for our systms. Two mthods ar usd to calibrat th fiv port rflctomtr [9], [14]. Th first on uss th fiv port as a I(t), Q(t) dmodulator. This mthod dtcts th complx nvlop of two RF signals at th input of th fiv-port systm. This nvlop will b srvd as input for USIC algorithm to gt th DOA as mntiond bfor. Whil th scond mthod prmits to obtain th rflction cofficint. As in cas of sixport, th thortical magnitud is 1 which agrs with th rsult of th application of a mobil short circuit, as shown in figur 8. Im(Γ) 3.4 Calibration of th homodyn rcivrs any calibrating mthods wr proposd for th six port rflctomtr. Som of thm dtrmin th constants of th rflctomtr by using crtain known loads with matrix calculations. An accurat tchniqu is th six port to four port rduction mthods, providd by Engn. Th main goal of th rduction is to provid th complx ratio btwn th incidnt wavs of two of th four dtctors as function of th four masurd powrs. In this papr w us this mthod providd by Widmann [10]. Figur7 prsnts th calibration mthod. R(Γ) Figur8: Calibration of a fiv port rflctomtr 4. USIC algorithm q 5 q 4 Th multipl signal classification (USIC) [3] mthod is a rlativly simpl and fficint ignstructur that uss subspac dcomposition mthod for stimation of th frquncis of complx sinusoids obsrvd in additiv whit nois [12]. For m rciving antnnas, a signal y(m) can modld as: y P ( ) ( m) A j 2π F K m + φk = n( m)(1) K = 1 K + Figur7: Calibration of a six port rflctomtr Figur7 prsnts th rsult of th simulation of a mobil short circuit. This mobil short circuit is obtaind by applying 0dBm and -20dBm as input q 6 Whr A k, F k, Φ k, ar rspctivly th amplitud, th phas and th frquncy of ach of th P incoming sourc. An N-sampl vctor y=[y(m),..., y(m+n 1)] of th noisy signal can b writtn as: y = x + n = Sa + n (2)

4 Procdings of th 4th WSEAS Int. Confrnc on Elctromagntics, Wirlss and Optical Communications, Vnic, Italy, Novmbr 20-22, Whr th signal vctor x=sa is dfind as X X X ( m) ( m + 1) = A1 A2 AP ( ) m + N 1 πf1 N 1) j 2πF2 N 1) πfp N 1) j 2π φp πf1 m πf1 1) πf2m j 2πF2 1) πfp m πfp 1) (3) Th matrix S and th vctor a ar dfind on th right-hand sid of Equation (3). Th autocorrlation matrix of th noisy signal y can b writtn as th sum of th autocorrlation matrics of th signal x and th nois as follows: π φ1 π φ2 In this sction w will rprsnt th rsults of smart antnnas systms outputs whn using six port rflctomtrs and fiv port rflctomtrs with USIC algorithm and a local oscillator powr of 0dBm. All simulations ar mad in a quasi-idal nvironmnt whr w th problm of intrfrncs [13] is not considrd. Th following figur rprsnts th DOA of two incoming RF signals. R yy = R xx = SPS + R H nn 2 + σ I n With R xx =SPS H and R nn = σ n 2 I ar th autocorrlation matrics of th signal and nois procsss, th xponnt H dnots th Hrmitian transpos, and th diagonal matrix P dfins th powr of th sinusoids as: Whr [ P P P ] H P = aa = diag, 1 2,..., 2 i A i P = is th powr of th complx nvlop. Th st of ignvctors associatd with th P largst ignvalus span th signal subspac and ar calld th principal ignvctors. Th signal vctors si can b xprssd as linar combinations of th principal ignvctors. Th scond subst of ignvctors spans th nois subspac and has σ 2 n as thir ignvalus. Sinc th signal and nois ignvctors ar orthogonal, it follows that th signal subspac and th nois subspac ar orthogonal. Hnc th sinusoidal signal vctors si which ar in th signal subspac, ar orthogonal to th nois subspac, and w hav: P Figur10: DOA of two RF signals Th abov figur shows th USIC rspons of two incoming signals to two smart antnna systms that on of thm uss six port rflctomtrs and th scond on uss fiv port rflctomtrs. Th thortical angls was and , as shown in th xprimntal rsults both smart antnna systms gav qual and prfct rsults. Th sam xprimnt was mad to dtct till 7 signals, th rsults wr: G Six-Port B Fiv-Port Figur 9: Dcomposition of th ignvalus of a noisy signal into th principal ignvalus and th nois ignvalus. Figur9 concluds that th application of th USIC algorithm can lad to sparat th incoming signals from ach othr as wll as from th whit nois, so indd a prcis dtction of arrival angls. 5. Simulation rsults 5.1 Stabl ocal Oscillator Powr cas Arrival Angl Dgr Figur11: DOA of svn RF signals Again th rsults wr qual and prcis for both systms. So, w can us any systm sinc th input O powr is stabl. 5.2 Unstabl ocal Oscillator Powr cas In this sction, w will show th rsults of simulations for DOA of 7 signals using six-port and fiv-port rflctomtr rcivrs in an unstabl powr nvironmnt for local oscillator.

5 Procdings of th 4th WSEAS Int. Confrnc on Elctromagntics, Wirlss and Optical Communications, Vnic, Italy, Novmbr 20-22, Fiv-port rcivrs cas Six-port cas: To do so, w simulatd th six-port rflctomtrs by applying 0dBm, -3dBm, -6dBm as local oscillator powr. Whil th calibration was don at 0dBm O powr, th rsults ar rprsntd in th figur blow. In this sction w followd th sam stps as in but instad of utilizing six-port rcivrs w usd fiv-port rcivrs. 0dBm -6dBm -3dBm G P_O 0dBm B P_O -3dBm R P_O -6dBm Eignvalus Arrival Angl Dgr Figur14: DOA of 2 RF signals using fiv-port rcivrs Figur12: DOA of svn RF signals for 3 six-port rcivrs Th abov figur rprsnts th rsult for DOA of svn signals for th 3 cass. To dtct th ffct of th local oscillator powr (P_O), w can mak a zoom on aras in th figur13 as shown blow. G P_O 0dBm B P_O -3dBm R P_O -6dBm Th abov pictur rprsnts th DOA for two incoming RF signals which coms from o and 33.8 o. As dscribd abov th fiv-port rflctomtrs ar calibratd on a 0dBm as a local oscillator powr. W can asily conclud that th systm prform wll if th O powr is 0dBm as in calibration. Th angl of arrivals shows larg rrors if th O powr falls down to -3dBm and -6dBm. Th rspctiv arrival angls ar -1.5 o and 15.7 o for th first cas, whil thy ar -0.4 o and 14.7 o for -6dBm. It is to b notd that th simulation is limitd for two signals du this dficincy which shows clarly th diffrnc btwn both systms. 6. Conclusions Figur13: comparison of th DOA of a RF signals for six-port rcivrs This figur shows th rspons of an incoming RF signal form a W may say that th fficincy DOA for th six-port rcivrs did not affctd badly by local oscillator powr variations (Powr instability). W may conclud from th abov rsults that ths kinds of rcivrs rsists to th P_O instability. This papr has shown th comparison prformanc of 5-port and 6-port homodyn rcivrs as applid to DOA in smart antnna rcivrs. A brif summary of structur and calibration of both systms ar dscribd. Th USIC algorithm was usd to stimat th dirction of arrival. W hav dmonstratd that svn signal dirctions can b obtaind using both systms. Th simulations wr mad as function of th local oscillator powr stability. W concludd that in a stabl nvironmnt, both rcivrs workd proprly, but in an unstabl nvironmnt only th six-port rcivrs consrvd good prformanc. 7. Rfrncs [1] Godara,.C., Application to antnna arrays to mobil communications. Part II: Bamforming and dirction of arrival considrations, IEEE Proc., 85, , [2] al Chand Godora, "Smart Antnnas", CRC PRESS C 2004.

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