DESIGN OF A HIGH DYNAMIC GPS RECEIVER

Transcription

1 DESIGN OF A HIGH DYNAMIC GPS RECEIVER Item Type text; Proceeding Author Bochuan, Zhang; Yanhong, Kou; Qihan, Zhang; Qing, Chang Publiher International Foundation or Telemetering Journal International Telemetering Conerence Proceeding Right Copyright International Foundation or Telemetering Download date 7/06/08 7:4:5 Lin to Item

2 DESIGN OF A HIGH DYNAMIC GPS RECEIVER Zhang Bochuan Kou Yanhong Zhang Qihan Chang Qing School o Electronic and Inormation Engineering, Beihang Univerity, Beiing, P. R. China, ABSTRACT High dynamic and multi-channel digital GPS eiver can handle the ignal with high dynamic range, low S/N ratio and rereh data quicly. A hardware deign o high dynamic GPS digital eiver i given. Baed on analyi o the eect that high dynamic movement mae on the eiving ignal, a cheme o at-acquiition high dynamic GPS eiver i preented. Exact oning o the orbit parameter and the atellite cloc parameter are integrated with appropriate algorithm. A DDLL i ued to piely etimate the C/A code delay, a CPAFC loop and a Cota loop to piely etimate the carrier requency and phae. The DDLL i aited with carrier phae. The experimental reult how that the eiver meet the deign requet. KEYWORDS Global Poition Sytem (GPS), high dynamic, digital ignal proceing, eiver, acquiition. INTRODUCTION When the eiver doe not tore almanac or there i no available almanac becaue o not woring or a long time, the eiver will go through a cold tart. When the almanac prediction error i not tolerable, the eiver will expend a long time to acquire

3 GPS ignal, get ephemeri, then get the poition exactly. However, exact oning o the orbit parameter, the atellite cloc parameter and the eiver cloc parameter, integrated with appropriate algorithm can eiciently horten the poitioning time or GPS eiver. In order to eive the ignal on high dynamic condition, we mut careully deign the ot loop part in the module o digital ignal proceing o the eiver, which i one o the ey part o a high dynamic eiver. DETERMINING THE RECEIVER TIME Becaue the time error o the cloc t(t) can be expreed by a polynomial whoe independent variable i the time t, t(t) can be pread at t []. t t = t t + δ ( t t ) + α( t t) () Where, δ i the error o the requency drit, α i the crytal aging velocity, that i gotten at t. Ater getting the time error, we can determine the eiver time. The GPS time parameter o the eiver include wee number o the current GPS time WN (current wee number) and Z count, that i, TOW count. Becaue the navigation data expre wee number by 0 bit, the larget number o wee that expreed by the 0 bit i 04, which i ambiguou. For oning the Greenwich time o obervation point with the wee count o GPS time, we mut calculate the true wee count integrated with other parameter. The wee number o the 0 bit can expre , o the eiver mut ubtract 04 rom the wee that derived rom the ent Greenwich time o obervation dot. Becaue o the leap econd, there i 3 econd dierence between

4 UTC time and GPS time ater So the wee number o the 0 bit can expre At the ame time, time converion rom Greenwich time to GPS time mut conider the time zone o the eiver. ( y 980) doy[ m ] + d + D 6 WN = 04 () 7 d = ( y 980) doy [ m ] + d + D D = y + ( y 980)%4 = 0 or m, then 4 D t ec = ( d%7) ( hh TimeZone) mm (3) i t ec 0, then WN and t = t ec ec Z _ Count = INT[ t / 6] + (4) ec Where, y, m,d, hh, mm, i the year, month, day, hour, minute, econd o the imulate time; t ec i the econd number at the beginning o the GPS wee epoch. % i the modular arithmetic; doy[] = {0,3,59,90,0,5,8,,43,73,304,334}; TimeZone i the time zone o the imulator. DOPPLER SHIFT COMPONENTS OF THE RECEIVER Our eiver utilize GP00 and GP0 o Zarlin Semiconductor. The requency o the atellite ignal i irtly down converted to the MHZ intermediate requency ignal. Then the intermediate requency ignal i under-ampled by a 5.75 MHZ cloc and output the digital ignal. The digital ignal are expreed: = M r( t) A C [( id )( T τ )] D [( id )( T τ )]in[π ( ) T φ ] + n( t) i i i i i id i i = where A i the ignal intenity, D i (t) i the ephemeri data o the I atellite, (t) i i the preading code o the i atellite, τ i i the delay value o atellite ignal C i (5)

5 tranmitted, = MHz, φi i the phae o the atellite ignal. T =, =.405MHZ, M i the number o the viible atellite M = + + (6) id i the requency error that the requency drit o the eiver cloc bring, i the requency drit o the GPS atellite, i the Doppler hit o the GPS ignal that i lead by relative movement between GPS atellite and the eiver, = v + (7) Where, i the Doppler hit o the GPS ignal that are lead by relative movement v between GPS atellite and the immobile eiver along the dition that the GPS ignal tranmit, i the Doppler hit o the GPS ignal that are lead by relative movement o the mobile eiver along the dition that the GPS ignal tranmit. Reerring to the GPS-ICD-00C Interace Control Document, we can get the a = a + a t ) (8) t t ( t Where, a, a are the cloc parameter o the navigation data o the GPS atellite []. = a 0 (9) According to the orbit parameter o the GPS atellite in the ephemeri o t, we can get the orbit parameter o the GPS atellite o t. Suppoing that ix cortion parameter are all zero, we alo get the almanac o t [3]. Then we can get the poition and velocity o the GPS atellite at t. Conidering the poition o the eiver, we can t get v o t. The eiver i tationary at the obervation time, here =0. Synchronouly we can get SV o the i atellite, o the i atellite at the obervation time i got

6 = - - id SV (0) THE DESIGNING OF THE LOOP OF THE RECEIVER We adopt the erial-parallel combined technology and MLE technology to realize the at-acquiition unction. The coare etimation o C/A code delay and Doppler requency o carrier are carried out through MLE. The pie etimation o C/A code delay i achieved through DDLL. The pie requency etimation i realized through a CPAFC loop and a Cota loop. And the DDLL i aited with carrier phae. Finally the navigation data are demodulated through the Cota loop. When the eiver i in the tate o pie code and carrier tracing, or the cro product loop, we can realize requency tracing. The dicriminator i =I(-)Q()-I()Q(-)= () ( ) D( ) R[ ε ( )][ ε ( ) ] in c{ [ ( )] πt } in c{ [ ( ) ] πt } in( φ φ ) 0.5 A D d d in =, ( ) Where, A i the ignal intenity, D ( ) i the ephemeri data, c( z) in z z i the Doppler hit etimate remain. ε ( ) i the code phae etimate remain error. ( ) π φ = d T + i the phae o the carrier o the atellite ignal. T i the φ 0 d correlator integral time. φ - φ = ( ) π T, when [ ( ) ] πt d d approach zero, in c {[ ( ) ] πt} in c{ [ ( ) ] πt} d d =, in( φ -φ )= φ - φ = ( ) π T. The ilter ue a nd order Jae-Rechtin ilter with a bandwidth o B LF, the ollowing requency cortion term can be derived [4] : ω = Tω + ω nf ω = ω + ωnf () d Where T i the ampling interval o m, ω =.89B. nf LF For phae tracing and navigation data demodulation loop:

7 I =I()coθ +Q()inθ Q =Q()coθ -I()in θ θ + =ign(i )Q θ + θ + (managed by the Jae-Rechtin ilter) θ + = θ + + θ (3) Where, I ( ) = Acoφ, Q ) Ainφ φ + = d πt φ 0, ( =, ( ) A + = I Q, I give a repreentation o the current data bit. RESULTS OF THE EXPERIMENT Figure i a curve o the velocity o x,y,z dition o a moving vehicle varying with the time, which i generated by the imulator STR4750 rom SPIRENT company. peed(m/) time() [Fig.]peed data(x,y,x axi) given by STR4760 Figure how the eiver velocity correponding to the imulated maneuver with a er in Figure, where, * i the data rom the imulator. The velocity o the imulated vehicle changed rom 0 to 000m/ within 8 econd; the line with pot repreent the velocity o the eiver. We can ee that the line with * and the line with pot coincide with each other, which demontrate that the eiver poition properly on the high dynamic condition with er o g/, acceleration o 0g, velocity o 000m/. The velocity error can be limited to 0.8m/.

8 peed(m/) time() [Fig.]the peed output o the eiver(acceleration time lice) CONCLUSION The experiment in the laboratory and the engineering application validate that the deign cheme o the loop i eaible, which ha achieved the perormance requet o the eiver. The eiver can wor with an acceleration o g, a er o 4g/. Meanwhile, the cold tart time o the eiver can be limited within 5 econd. REFERENCES []Zhao JunXiang. The Study on Mathematical Model o High Dynamic and Intelligent GPS Satellite Signal Simulator otware[d].beiing: Dept o Electronic Engineering, Beiing univerity o Aeronautic and Atronautic, 003(in Chinee) []Interace Control Document ICD-GPS-00, Navatellite GPS Spaceegment / Navigation Uer Interace(Public Releae verion C).ARINC Reearch Corporation, 0 October 993. [3] Zhang Shouxin. The oundation o the extratellurian traectory urvey and the atellite orbit urvey[m]. BeiJing: National deence indutry Pre,99 [4]GPS Builder- Deigner Guide, GEC Pleey Semiconductor, GPS Group,996 [5]Global Poitioning Sytem: Theory and Application Volume [M] American Intitute o Aeronautic and Atronautic.