CHARACTERIZATION OF INTERFERENCE EFFECTS ON GPS SIGNAL CARRIER PHASE ERROR

Transcription

1 Aghar abatabae Balae, Joel Barne, Andrew G.Depter. Charaterzaton of nterferene effet on GPS gnal arrer-phae error. Proeedng of SSC 005 Spatal Intellgene, Innovaton and Prax: he natonal bennal Conferene of the Spatal Sene Inttute, Septeber, 005. elbourne: Spatal Sene Inttute. ISBN CHARACERIZAION OF INERFERENCE EFFECS ON GPS SIGNAL CARRIER PHASE ERROR Aghar abatabae Balae, Joel Barne and Andrew G.Depter Shool of Surveyng and Spatal Inforaton, Unverty of New South Wale KEYWORDS: GNSS Reever, Code rang Loop, Carrer rang Loop, Carrer Phae Error, CW Interferene ABSRAC Autrala now ha a nuber of ontnuouly operatng referene taton (CORS networ for real-te neat (RK GPS. Eah taton n the networ, however, vulnerable to rado frequeny (RF nterferene, whh an degrade the auray of orreton provded to networ uer. Depte the portane of the effet of nterferene on GPS gnal arrer phae error and peudorange, the proble ha not been olved depte gnfant reearh effort. In th paper frtly analytal tehnque are ued to how the relatonhp between the nterferene frequeny and the qualty of the reeved gnal, a etated by the reever. hen the relatonhp between th etate and the arrer loop phae error nvetgated and found to be effetve n aeng the effet of narrowband nterferene on the arrer phae error. Next the theoretal predton are opared wth the experental reult. BIOGRAPHY OF ASGHAR ABAABAEI BALAEI Aghar abatabae Balae wa born n ehran, Iran, on arh 6, He reeved the B.S., and.s., degree n eletral engneerng fro Sharf Unverty of ehnology, ehran, Iran, n 1998, and 000, repetvely. Currently, He dong h PhD at Shool of Surveyng and Spatal Inforaton, Unverty of New South Wale, Sydney, Autrala. H urrent reearh atvte are foued on the haraterzaton and deteton of oure of nterferene and ultpath n GPS (Global Potonng Syte.he projet upported by the Cooperatve Reearh Centre n Spatal Inforaton. Stohat Sgnal Proeng, Etaton heory, and Global potonng yte are h favorte reearh top.

2 1. INRODUCION Interferene aong the feared event n ontnuouly operatng referene taton (CORS networ for real-te neat (RK GPS. he haraterzaton of the effet of nterferene a eaure of the ueptblty of GPS reever to varou type of unntentonal nterferene or ntentonal jang. hee effet range fro dereaed auray to loof-lo, whh obvouly underable n all applaton but atatroph n oe rtal applaton uh a tng, eergeny loaton and navgaton. hee haraterzaton help u to derve the axu level of nterferene that an be tolerated n dfferent part of a GPS reever on one hand and alo enable the degner to equp ther produt wth oe nterferene tgaton tehnque to nreae the level of nterferene that wll aue the loe the lo. hee effet have been exaned n relaton to Autoat Gan Control n GNSS reever n [Batde 003]. In [Spler 1996], quantzer effet n the preene of nterferene have been nvetgated. A pre-orrelaton nterferene deteton ntrodued n [art 004], whh another pont affeted by rado frequeny nterferene (RFI. Pot-orrelaton effet of RFI ha been evaluated by [Betz 000, Hegarty 1997]. In [Betz 000], a ethod to etate the pot-orrelaton arrer to noe denty rato n the preene of narrowband nterferene preented and ued n the delay lo loop noe perforane, derved n [Derendon 199]. In that ethodology, onderng reever pef detal uh a ntegraton te and oherent or nonoherent proeng ha been avoded. In [Hegarty 1997], a loed relatonhp between the ode and arrer-trang jtter varane and the gnal to noe rato ued to derve the axu tolerable n-band nterferene level for avaton applaton of GNSS. In th paper we wll derve a relatonhp between the pot-orrelaton arrer to noe rato and the frequeny and power of the nterferene n eton. In eton 3, arrer phae jtter varane evaluated. In eton 4, the relatonhp derved n eton evaluated by ulaton ung an etaton preented n [Parnon 1996] and opared wth another etaton whh ued for arrer phae lo deteton n the ae referene. Fnally the reult are dued n the lat eton.. POS CORRELAION CARRIER O NOISE RAIO (C/N0 In th eton, expreon for the pot-orrelaton arrer to noe denty (C/No derved. A hgh C/No ean that the reever operatng on or near the orrelaton pea. We ntend to how that th pea affeted by two fator: he nonohereny between the reeved ode and the arrer phae and thoe generated loally n the reever, and the frequeny dfferene between the ontnuou wave (CW nterferene and the arrer. Fgure 1 how a blo dagra of a orrelaton proe. he ode frt trpped off the gnal and then the arrer taen off (by gettng ultpled by the reever generated repla. Fnally t wa paed through the dup ntegraton whh hown by the low pa flter n the dagra (LPF.

3 C/A Code rang Loop S+I+N Carrer Frequeny ADC Referene Carrer Carrer rang Loop ADC: Analog to Dgtal Converter LPF: Low Pa Flter NCO: Nueral Controlled Ollator S+I+N: Sgnal + Interferene + Noe C/A: Coure Aquton I: In-phae Q: Quadra-phae 90 Referene Carrer LPF NCO LPF I Q Fgure 1. Correlaton proe on gnal, noe and nterferene he reeved GPS CA ode gnal n the preene of nterferene an be odeled a [Kaplan 1996], S(t = P D(t.PN(t.n(πf t + θ ( t + n (t + I(t D (1 where P the trantted gnal power, D(t the data odulaton at 50bt/, and f the arrer frequeny. PN(t the peudorando ode odulaton, n (t the theral noe whh whte and Gauan and I(t the n band CW nterferene defned by : I(t = Jn(π f t + θ ( t ( where J the nterferene power. he front end bandwdth ondered wde enough to pa eentally all of the gnal and nterferene power. he theral noe ha power petral denty N 0. he referene ode and arrer (Fgure 1, whh are generated by the ode and arrer trang loop, are ondered not to be oherent wth the reeved ode and arrer of the gnal.

4 RPN (t = PN(t -τ (3 RCAR (t n(π fˆ ˆ t + θ = (4 where τ the ode phae dfferene and fˆ and θˆ are the etate of arrer frequeny and phae. After ultplyng the gnal wth the referene ode and arrer n the orrelaton proe, the reult paed through the ntegrator wth the duraton of d whh uually hoen a the navgaton data hp duraton. he followng analy to evaluate the gnal, nterferene and noe after the proe. o ae the oputaton eaer, we onder the output orrepondng to the gnal a (I + j.q. At the pont before the ntegraton (I + jq (t =. j(πδf t+ δθ P.PN(t.PN(t -τ e (5 Δθ j (I + jq (f = e P R PN (f, τ * δ ( f + Δf (6 where ˆ Δ f = f - f and Δθ = θ θ ˆ (I + jq (t = j τ jπ j e CC jδ ( f Δf = R ( τ. δ ( f + + Δf (7 where the hp perod and C the th oeffent of the fourer tranfor of PN(t and After the ntegraton we have : R = C C. + j= j (I + jq (f = d. R ( τ.n(( + Δf d (8 where d the ntegraton duraton te. If we onder the dfferene between the etated frequeny and the atual one to be le than the reproal of the ntegraton duraton, equaton (8 wll be plfed to: (I + jq (f d. R ( τ = 0.n( δfd (9 he output orrepondng to the nterferene before the ntegraton wll be

5 (I + jq (f = jπτ jδθ e Ce δ ( f + Δf where Δ f = f - fˆ (10 and after the ntegraton (I jq (f = d.c n.n(d. Δf + (11 where C n the n th oeffent of the petral lne of C/A ode and we have Δ f. he effetve C/No n the preene of nterferene ay be expreed a [Betz 004]: n d C L = L N + I C/No (1 n 0 where C the reeved power of the gnal, L the proeng gan n the dered gnal, N 0 the theral noe power petral denty, L n the proeng gan n the noe and I the effetve nterferene. Subttutng equaton (,3 nto (4 yeld the expreon for effetve C/No: ( C/No = L N n 0 d R ( τ.n( Δf 0 + (d.c.n(d. Δf n d (13 In the next eton, th atheatal expreon analyzed n evaluaton of the effet of nterferene paraeter on the arrer phae error varane. 3. CARRIER PHASE ERROR Perforane of tandard ode-trang loop n the preene of CW nterferene wa tuded n [Sapao-Neto 1996] and later the effet of narrowband nterferene on GPS ode trang auray wa nvetgated n [Betz 000]. In [Levtt 1979] and [Sue 1998] t ha been hown that n oherent ounaton yte that ue a nuodal arrer and phae lo loop (PLL to tra the arrer phae, nterferene ha a gnfant effet and th effet wa evaluated on the PLL n [Karı 000]. Reult n [Spler 1996] how that the ode loop ore robut than the arrer loop n the preene of nterferene and unfortunately ot reever rely on the PLL to eep the reeved gnal wthn the reever pa band flter, and o the PLL deterne reever threhold. Experent n th eton are done by DataFuon oftware reever [Data Fuon Corporaton 004]. h oftware reever allow external nterferene to be added at any pont n the reever. h ha the advantage of dablng all of the effet of other fator le front-end band wdth and early late pang. he nterferene wa added to the gnal at the pont rght before the orrelaton. h alo enable the effet of nterferene to be nvetgated, whh aue the reever to fal even to aqure the gnal a CW jaer are ore daagng durng the aquton proe than durng gnal trang. In Fgure, the varane of

6 arrer-phae jtter nvetgated n ter of arrer to noe denty rato. In Fgure arrer to noe rato ondered for the gnal n the abene of any nterferene to nvetgate the haraterzaton of nterferene n ter of t power. Fgure. Coparon of varane of arrer phae jtterng veru C/No for two dfferent nterferene power. In Fgure 3, frequeny of CW jaer ondered. A t wa explaned n eton II n dervng equaton (13, t wa aued that the frequeny dfferene between the nterferene and the nearet CA ode petru dra lne le than the reproal of the loop bandwdth ( d and the nterferene outde th band were not ondered. he fat that the ore the frequeny dfferene Δ f the le would be the effet and the ore power needed to aue lo of lo. ( Fgure 3. Coparon of varane of arrer-phae jtterng veru nterferene power for three nterferene dfferent n frequeny (frequeny dfferene fro the nearet CA ode petru dra lne growng n the dreton of the array In [Betz 000], effet of narrowband nterferene on the ode trang auray evaluated. It ha been hown that, for CA ode reever, narrowband nterferene at frequene away fro band enter an degrade ode trang auray ore than nterferene havng the ae power at band enter, even though the reever eaured gnal to noe rato degrade ore when narrowband nterferene frequeny loated at band enter. h phenoenon and the fat that CW nterferene an affet the arrer loop f t loe to the frequeny of one of the CA petru dra lne an be an explanaton of the behavor of varane of arrer-phae jtterng n the preene of CW nterferene veru the frequeny offet of the nterferene fro the band enter (Fgure 4 and 5.

7 Fgure 4. Carrer-phae jtterng varane whle nterferene frequeny loe to the band enter :deltaf= Δf n equaton (13 Fgure 5. Carrer-phae jtterng varane whle nterferene frequeny far fro the band enter: deltaf= Δf n equaton (13 4. CW INERFERENCE SENSIIVIY OF LOCK DEECION ECHNIQUES he arrer trang loop reove the lne of ght dyna effet on the arrer and provde t to the ode trang loop. he ode trang loop alo fnd the ode phae and provde t to the arrer loop. Lo happen when thee two loop onverge ultaneouly and th when ther operaton ha onverged to the orrelaton pea. Beaue of nterferene there ght be oe other loal orrelaton pea and th ay aue the loop to dverge fro the an one. For lo deteton, [Parnon 1996] ha preented two tehnque (E 1 and E one for ode lo deteton and the other for arrerphae lo deteton. hee two tehnque are evaluated here n the preene of CW nterferene. A the nowledge of ode lo the ae a the nowledge of the reeved gnal power, an etaton of C/No ondered for the deteton of the ode lo. h etaton expreed by: Cˆ E1= N o µ ˆ NP 1 = 10log (14 ( µ NP where = 1 K ˆµ the ean value of the noralzed power for K perod. NP NP K = 1 NP = NBP WBP the noralzed power. WBP = ( I + Q the wdeband power for aple. =1

8 = I + Q = 1 = 1 NBP the narrowband power for aple. Fgure 6. Frt etr for lo deteton veru: Δ f = deltaf(hz, J = Jpower n equaton (13, τ = delta(chp he ethod of detetng the phae lo ung the noralzed etate of the one of the twe the arrer-phae gven a follow E = C = NBD φ (15 NBP where NBP = I Q = 1 = 1 Baed on the duon n eton 3, phae lo deteton alo nfer ode lo. he two tehnque have been appled for the yte n Fgure 1 (the two loop are open and the referene gnal are generated anually, and etaton value have been evaluated n ter of the paraeter affetng the C/No n equaton (13. Fgure 6 and 7 llutrate the relatonhp for the frt and the eond tehnque orrepondngly. It lear that the phae deteton tehnque ore entve agant nterferene. Fgure 7. Frt etr for lo deteton veru: τ = delta, Δ f = deltaf, J = Jpower n equaton (13

9 5. DISCUSSION AND CONCLUSION In the preene of tone nterferene at the nput, the ode and arrer trang loop behave dfferently. Whle the ode loop pread the tone, the arrer loop tre to tra the opote gnal (arrer + tone nterferene. A the reult, n the arrer loop the wort ae for the nterferene the ondene of t frequeny wth the wort CA ode petru lne and n the ode loop, th wort ae when the tone nterferene frequeny at the pefed offet wth repet to the gnal arrer frequeny. he wort ae for the two loop ultaneouly happen when the wort CA petru lne around that pefed offet. h ondene happen for the CA ode of the atellte, 6,1,13,19 and 8. h wll be nvetgated further n our future wor. he dfferent behavor of ode and arrer trang loop n the preene of nterferene, alo generate oe other loal orrelaton pea whh aue ntablty n the operaton of the two loop together where eah appear to be table f ondered alone. REFERENCES Batde, F., Ao D., Ao C., Roturer B. (003 Autoat Gan Control (AGC a an Interferene Aeent ool, ION GPS/GNSS, Betz J.W, (000 Effet of Narrowband Interferene on GPS Code rang Auray, Proeedng of he Inttute of Navgaton N eetng, Anahe, CA, Betz J.W. Bryan L., tu., (004 Interyte and Intrayte Interferene wth Sgnal Iperfeton IEEE Poton Loaton and Navgaton Sypou, Data Fuon Corporaton (004 Kent Kruveda, GPS Progra anager Data Fuon Corporaton Banno Street Sute 46 Northglenn, CO 8060 USA el: X303 Fax: Derendon A. J., Fenton P., and Ford., (199 heory and perforane of narrow orrelator pang n a GPS reever, Navgaton: J. Int. Navgaton, vol. 39, no. 3, pp , Hegarty C., (1997 Analytal Dervaton of axu olerable In-Band Interferene Level for Avaton Applaton of GNSS, Navgaton: Journal of the ION, Vol. 44, No. 1, Sprng, pp. 5-34, Kaplan E., (1996 Undertandng GPS: Prnple and Applaton, Arteh Houe. Karı F, Lndey WC, (000 Effet of CW Interferene on Phae-Loed Loop Perforane IEEE ranaton on Counaton, Levtt B. K., (1979 Carrer rang Loop Perforane n the Preene of Strong CW Interferene JPL, Paadena, CA, Deep Spae Networ, art L., Van Gra F., (004 Interferene Deteton by ean of the Software Defned Rado ION GNSS 17 th Internatonal tehnal eetng of the atellte dvon, Parnon B. W., Spler J. J., Axelrad P., and Enge P., (1996 Global Potonng Syte heory and Applaton Wahngton, DC: Aer. Int. Atron. Aero. vol. 163, Sapao-Neto, Polydoro R., Sholtz A., (1996 Perforane of Standard Code-rang Loop n the Preene of Dual one Interferene, R. Counaton, IEEE ranaton on Spler J. and Natal F., (1996 Interferene Effet and tgaton ehnque, Chapter 0 of Global Potonng Syte: heory and Applaton, AIAA. Sue. K., (1998 DSN RFI Sueptblty odel Developent Progra Overvew, JPL, Paadena, CA, Deep Spae Networ Prog. Rep.4 68, Jan. Feb.