Rapid Acquisitio n of Doppler Shift in Satellite Co mmunicatio ns

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1 7 3 7 ATA ELETRONIA SINIA Vol. 31 No. 7 July 3 1, 1, (1., 184 ;., 444) :., PN,.,,. : ; ; ; : TN9 : A : 3711 (3) 7155 Rapid Acquisitio of Doppler Shift i Satellite o mmuicatio s HUAN Zhe 1,LU Jiahua 1,YAN Shizhog (1. Departmet of Electroic Egieerig, Tsighua Uiversity, Beijig 184, hia ;. School of ommuicatios Egieerig, hogqig Uiversity, hogqig 444, hia) Abstract : I this paper,a rapid acquisitio scheme of Doppler shift is proposed for a LEO satellite spreadspectrum commui catios system. Based o the use of digital matched filter (DF) ad automatic frequecy cotrol (AF) loop,two characteristics of the DF are exploited to reduce the mea acquisitio time (AT) of Doppler shift,amely,the rapid acquisitio property of PN code ad a high sesitivity of maximum correlatio value to frequecy offset. A expressio of the AT is derived,ad a suboptimal decisio of acquisitio is give out from umerical results. Fially,the performace of the proposed acquisitio scheme is compared with the tradi tioal serial scheme,showig a sigificat improvemet achieved. Key words : satellite commuicatios ;digital matched filter ;automatic frequecy cotrol loop ;Doppler shift acquisitio 1 (LEO),., LSI, (DF) DA. DF,.,,,,,., NO,.,,. [13 ],,,. (AF),,, NO,., AF. AF,,( ) PLL [4 ]., AF,..,, AF,. AF.,, ;,.,., :39 ; : hia Academic Joural Electroic Publishig House. All rights reserved.

2 7 : 153,DF PN, AF. PN (1). DF AF. AF, NO,,. PN,PN,PN., PN. 1,. 1, : r( t) = sc ( t - ) cos[ ( c + ) t ++] + ( t) (1) s c ; ; ( BPSK,= ) ; c ( t) PN ; ( t) N /., DF : y I = st c c K + k + i c K+ k cos( kt c ++ ) + I ( k + i) c K + k y Q = s T c c K + k + i c K + k si( kt c ++ ) + Q ( k + i) c K + k DF ; K t = PN ; I ( k) Q ( k), () E[ I ( k) ] = E[ Q ( k) ] =, E[ I ( k) ] = E[ Q ( k) ] = T c N /, E[ I ( k) I ( j) ] = E[ Q ( k) Q ( j) ] = ( j k) ; T c PN. PN PN H 1 ;, H. H 1,() : y I = = E[ y I ] + N I y Q = s T c cos( kt c ++ s T c si( = E[ y Q ] + N Q kt c ++ ) + ) I ( k) c K + k Q ( k) c K + k N I N Q, [5 ] : (3) = N T c / (4), 1, DF, : N : E[ y I ] + E[ y Q ] = st c si( kt c ) + st c Z = y I + y Q (5) cos( kt c ) = st si(ft c ) c (6) si(f T c ) µ 1f T c ν 1,: SNR loss log 1 [si c (ft c ) ] (7) (7) : DF PN,( PN ). 3,,. DF,,. :.,f. f,.,d, NO.,NO,AF,T s ( ),(),., B s,( ),B s / DF, DF, AF., hia Academic Joural Electroic Publishig House. All rights reserved.

3 154 3., B s AF. NO, NO PN, DF.,., (1 < ), ( ),.,T s. 1, : ;, ;, ( ).. (, D), : H 1 ( Z) = P Df Z T b + T s H ( Z) = P FAf Z T b H 3 ( Z) = P f Z T b H 4 ( Z) = Z T s P Df P FAf P f ; T b ; ; T s. : H( Z) = [ H ( Z) H 4 ( Z) + H 3 ( Z) ] i H 1 ( Z) i = H 1 ( Z) = 1 - H 3 ( Z) - H ( Z) H 4 ( Z) P Df + P FAf + P f = 1, H (1) = 1., (8) (9) : E[ Tf ] = 5 5 Z l( H( Z) ) Z = 1 = H ( Z) Z = 1 (8) (9) = 1 P Df [ T b + P FAf T s ] + T s (1) 4 DF PN, f =. H 1, Ricia [6 ] : m = f H1 ( x) = x exp - x + m I xm, x (11) s T c H 1 DF ; (4). H, PN,DF, Rayleigh [6 ] : f H ( x) = x exp - x x (1) f, H 1, (14) [7 ], m (6). f i,no f ( = 1) f i : f ( ) = f i - f (13), H 1 : ff ( ) ( x) = x exp - x + m I xm = 1 (14) m st c si c[f ( ) T c ] ( µ 1,f T c ν 1). m, Rayleigh.,, : (1) 1/ T c,h 1 ; () ( ), Rayleigh. = k ( k = 1) : f ( k) = f i - f B s = k (15) k,f k : p( k) = ff ( k) ( y) =1 k y f ( x) dx dy (16) f ( x).,d D f k : P D ( k) = m = D m ( P( k) ) m (1 - P( k) ) - m (17) k 1, f i P k,: P Df = P k P D ( k) = P k m = D m,: P FAf = P k =1 k P( k) m (1 - P( k) ) - m (18) P F ( ) (19) P F ( ),D D f ( = 1, k) : : P F ( ) = m = D P( ) = m ( P( ) ) m (1 - P( ) ) - m () f ( y) f ( x) dx dy ( = 1, k) =1 k y hia Academic Joural Electroic Publishig House. All rights reserved.

4 7 : 155, = D = 1, (18) (19) : P Df = P k P( k) (1) P FAf = P k (1 - P( k) ) (),, B s (, D) f dmax, [ f i - f dmax, f i + f dmax ], f i. [4 AF (.. 5/ T ] b ), (3). athcad 3, : E c = N = - 1dB, = 13, R b = 1/ T b = 1kHz, f dmax = 8kHz, = ceil [f dmax / B s ]. E c = st c ; R b ( PN R c = R b ) ;ceil ( ) : ceil ( x) = N + 1 x > N, N. ceil ( x) = N x = N, B s AF. B s =. R b, = 14. (7),. 1 R b =. 1/ Hz, DF. 14dB., P k = 1/ ( k = 1) (3) P( k) P Df ( 4 5). 4, k = 7, f, P( k) k = 7., k [,13 ], 4. :,,,.,. k = 1, f <, ( ), P( k) k = 1.,,. P ( k) k = f k 5 6 ( = D = 1) 5 f, P Df ( = D = 1). P Df f P( k),,,. B s, P Df ( ). DF PN. 51 (1),T s,t s AF., B s,b s T s,. B s T s,, (, D). [8 ] AF,, T s AF, T s = T b = ms., (, D), f (6). 6, (, D)., (, D) (4,), = 4, D =, B s = khz, 6, 1kHz, E( Tf) 4ms hia Academic Joural Electroic Publishig House. All rights reserved.

5 156 3,, NO (FW) NO (1), AF,FW,NO,.,B s = khz,no T s = ms,, : gtf = 15ms. 6 gtf = + 1 T s (4),,,,. PN, PN,,,.. : [ 1 ] arco Luise,et al. arrier frequecy recovery i alldigital modems for burstmode trasmissios[j ]. IEEE Tras ommu,1995,43 (/ 3/ 4) : [ ] B Lovell,et al. The statistical performace of some istataeous fre quecy estimator[j ]. IEEE Tras ASSP,199,4 (7) : [ 3 ] Umberto egali,et al. Dataaided frequecy estimatio for burst digi tal trasmissio[j ]. IEEE Tras ommu,1997,45 (1) :3-5. [ 4 ] Fracis D Natali. AF trackig algorithms[j ]. IEEE Tras ommu, 1984,3 (8) : [ 5 ] Eric W Siess,et al. Acquisitio of direct sequece sigals with modula tio ad jammig [J ]. IEEE Joural o selected areas i ommu, 1986,SA - 4 () :54-7. [ 6 ] Adreas Polydoros,et al. A uified approach to serial search spread spectrum code Acquisitiopart : a matched - filter receiver [J ]. IEEE Tras ommu,1984,3 (5) : [ 7 ]. [ D ]. :,1. [ 8 ] P N Steve. A ivestigatio of carrier recovery techiques for PSK : modulated sigals i DA ad multipath mobile eviromets [ D]. Virgiia :Virgiia polytechic istitute ad state uiversity,1997.,1969 8,, 1,:.,1963 7,,, 6,:, hia Academic Joural Electroic Publishig House. All rights reserved.

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