The Expeimental Study of Possibility fo Rada Taget Detection in FSR Using L1-Based on-coopeative Tansmitte Ch. Kabakchiev 1, I. Gavanov, V. Beha 3, H. Rohling 4 1 Faculty of Mathematics & Infomatics,Sofia Univesity, Sofia, Bulgaia ckabakchiev@fmi.uni-sofia.bg Univesity of Libay Studies and Infomation Technologies, Sofia, Bulgaia i.gavanov@unubit.bg 3 Institute of Infomation & Communication Technologies,BAS, Sofia, Bulgaia beha@bas.bg 4 Depatment of Telecommunications,TU hambug-habug, Hambug,Gemany ohling@tu-habug.de Abstact: The Fowad Scatte Rada (FSR) system is a special case of bistatic ada. In such bistatic FSR, the eceive and tansmit antennas ae fixed and diected at each othe, so the taget detection takes place when the baseline is cossed. This type of ada povides a countemeasue to stealth technology because in the aea of the fowad scatte effect the tagets RCS depends only on the size and the shape of thei silhouette. Passive adas use tansmittes of oppotunity as signal souce, and theefoe they ae vey attactive due to thei inheit low cost. The advantage of consideing Global avigation Satellite System (GSS) satellites as tansmittes of oppotunity is the high availability that these satellites offe. Anywhee on eath, aound eight Global Positioning System (GPS) satellites ae continuously in view. This povides an optimum scenaio fo implementation of a GSS-FSR system. In this pape, some expeimental esults of a GPS-FSR system, whee the signal at the output of the Caie&Code tacking block is coheently integated, ae descibed and analyzed. 1. Intoduction Fowad Scatteing Rada (FSR) is a specific type of bistatic adas that opeate in the naow aea of the fowad scatteing effect whee the bistatic angle is close to 180 0, and the taget moves nea the tansmitte-eceive baseline [1-6, 11, 1]. In FSR, the Babinet pinciple is exploited to fom the fowad scatte signatue of a taget. Accoding to this pinciple, the dastic enhancement in scatteing is ceated due to the fowad scatteing effect. This type of ada povides a countemeasue to stealth technology. Due to the fowad scatteing effect, the Rada Coss Section (RCS) of tagets extemely inceases (by -3 odes) and mainly depends on the taget s physical coss section and is independent of the taget s suface shape and the absobing coating on the suface. Howeve, FSR has some fundamental limitations, which ae the absence of ange esolution and opeation within vey naow angles (±10 0 ) [1, ]. In this pape a passive Fowad Scatte Rada (FSR) system, in which GPS satellites ae exploited as non-coopeative tansmittes, is studied (Fig. 1). The civil L1 signal is tansmitted by satellites at 157.4 MHz and contains the coase acquisition (C/A) code, which is unique fo each satellite. The C/A code modulated signal is a BPSK signal with a chip ate of 1.03 MHz and the epetition inteval of 1ms. The L1 signal fequency bandwidth is.046 MHz.
The idea to apply a GPS L1 eceive to FSR fo ai taget detection is discussed in [7]. Some expeimental esults of a GPS L1 eceive concening the detection of ai tagets ae shown and discussed in [8]. A possible algoithm fo ai taget detection in a GPS L5-based FSR system is descibed in [9], and the detection pobability chaacteistics ae calculated in [10] fo the case when low-flying and pooly maneuveable (fo example, helicoptes) ai tagets ae detected on the backgound of a white Gaussian noise, o in the uban intefeence envionment o a Standoff-Jamme (SOJ). Tansmitte Taget Receive Eath Figue 1. FSR topology The aim of this study is to veify the possibility of detection of gound tagets by using a GPS L1- based FSR system when GPS satellites ae located at small elevation angles. In such a system, the signal integated at the output of the Code&Caie tacking block (message bits) of a GPS eceive can be used fo detection of tagets. In this pape, a possible algoithm fo detection of gound tagets at the output of the Code&Caie tacking block of a GPS eceive is descibed and the esults ae obtained by pocessing the expeimental ecods made by means of a GPS eceive.. Powe budget We conside the case when the taget is located close to the visible satellite-gps eceive baseline. The signal-to-noise atio at the RF font-end output of the GPS eceive is [14]: P PG σ SR ec t = = (1) 4πRtg Accoding to [3-6], the fowad scatte RCS σ of a taget depends only on the physical coss section of the taget (A tg ) and can be calculated appoximately as: 4πA tg 4π σ = = () λ λ In (), A tg is the taget physical coss section, and the paametes h and l ae geometical dimensions of a taget. In ode to obtain the SR expession at the input of a CFAR detecto in FSR, we eplace the paamete σ in (1) by its expession (). PG t SR = (3) λ Rtg At the output of the Code& Tacking loops the signal-to-noise atio is given by: PG t SR = G SP (4) λ Rtg whee G SP is the pocessing gain of the coss-coelato. Afte coheent integation of the message bits the SR can be calculated as:
PG t SR = GSPM (5) λ R tg whee M is the numbe of integated bits of a message. Fo example, in [8], the SR has been calculated at the coss-coelato output fo the case of a GPS L5 signal and a small taget (h=1m and l=1m). The SR values have been calculated as a function of the distance to the taget R tg. The SR values obtained ae plotted in Fig., whee paametes of the GPS L5 signal ae: caie fequency f o =1176MHz (λ=0.551m); fequency bandwidth ΔF=0.46MHz, the GPS L5 signal powe nea the Eath s suface P t =-154dBW. Figue. SR at the coelato output integated within 0msec 3. Signal pocessing The geneal block-scheme of a possible algoithm fo detection of tagets when they ae located close to the visible satellite-gps eceive is shown in Fig 3. Pilot signal L1(n) Code &Caie Tacking Acquisition I P Sign(I P ) Coheent Integation I P (x1ms) Powe Estimation (I P ) CFAR Detection Figue3. FSR signal pocessing Accoding to this block-scheme, a visible GPS satellite is acquied and tacked ove the complete duation of ecoded signals. The tacking Code&Caie loops opeate with 1-ms integation time. This means that with evey millisecond, a coelation value is obtained, whose magnitude is diectly popotional to the satellite signal powe being tacked (noise neglected). We conside the case when the acquisition and tacking algoithms of a GPS eceive ae implemented in MATLAB. The tacking loops ensue that the pompt coelato is synchonized with the incoming pseudoandom (PR) code. Moeove, they also synchonize the eceive s local oscillatos, both in tems of fequency and phase with the satellite signal caie. In this way, the
coelation magnitude emains in the eal pat (I P component), and just the sign changes caused by the navigation bits would emain, which ae also wiped out. The absolute values of the Ip component at the output of the Code&Caie tacking block ae then integated duing milliseconds. The powe of the integated signal is futhe used fo detection of tagets by means of the CFAR thesholding. 4. Expeimental esults The aim of this expeiment is veify the possibility fo detection of stationay gound tagets using FSR that exploits GPS satellites at low elevation angles as tansmittes. In this expeimental study, the GPS L1-based ecoding system consists of two diffeent GPS eceives. The fist GPS eceive (Antais AEK-4R) will be used to detemine the location of the satellites while the othe softwae GPS eceive (GSS_SRR) will be used to ecod and stoe GPS signals fom diffeent tagets. Fig.4. Expeimental scenaio Fig. 5. Satellite constellations Using the eceive AEK-4R, we can monito the location of satellites (Fig. 5) and choice an appopiate satellite, the signal fom which will be ecod by the GSS_SRR signal ecoding system. Fo example, the satellite 8 fom Fig.5 and Fig. 6, whose elevation is in the ange of 40 0 is used fo the expeimental testing. Duing the expeiment, the eceive GSS_SRR ecods the signals eceived fom the satellite 8 when moving along staight path behind a lage building as shown in Fig.4. This lage building is located close to the baseline between the satellite 8 and the GSS_SRR signal ecoding system. The expeimental ecods ae futhe pocessed using MATLAB. All visible satellites acquied by the acquisition algoithm ae shown in Fig.6. The Ip component at the output of the Code&Caie tacking block of the sattelite 8 is shown in Fig.7. The coheent integation of the I P component powe is made duing 1000, 00 and 0 ms, and esults of integation ae shown in Fig.8, Fig.9 and Fig.10. It can be seen that the shadow signal due to the taget (lage building) can be exploited fo detection of the taget (lage building). It can be also seen that the integation time influences the CFAR detection, i.e. the longe time of integation the moe stable CFAR detection.
16 14 Acquisition esults ot acquied signals Acquied signals 4000 Bits of the navigation message 1 3000 000 Acquisition Metic 10 8 6 1000 0-1000 4-000 -3000-4000 0 0 5 10 15 0 5 30 PR numbe (no ba - SV is not in the acquisition list) -5000 4 6 8 10 1 14 16 18 0 Time (s) Fig. 6.Acquisition esults Fig 7. avigation message of satellite 8 13 130 Integation time=1000 ms Channel-1 10 Integation time=00 ms Channel-1 18 115 16 0log10(Ip) in db 14 1 10 0log10(Ip) in db 110 105 118 116 100 114 11 0 5 10 15 0 5 Time [s] 95 0 5 10 15 0 5 Time [s] Fig.8. Integated powe (1000ms) Fig. 9. Integated powe (00ms) 100 Integation time=0 ms 95 90 0log10(Ip) in db 85 80 75 Sat. 8 70 0 5 10 15 0 5 Time [s] Fig. 10. Integated powe (1000ms)
4. Conclusions The esults obtained show that a bistatic FSR system with a GPS-L1 based non-coopeative tansmitte can be used fo detection of gound signals. Such a FSR system uses the integated signal at the output of a Code&Caie tacking block of a standad GPS eceive. Acknowledgements This wok is patly suppoted by the poject AComIn "Advanced Computing fo Innovation", gant 316087, funded by the FP7 Capacity Pogamme (Reseach Potential of Convegence Regions) and pojects DTK 0/8.009 and IP-0-013. Refeences [1] M. Cheniakov (ed.), Bistatic Rada: Pinciples and Pactice, Wiley & Sons, 007. []. J. Willis, Bistatic Rada, Technology Sevice Copoation, 1995. [3] M. Cheniakov, R. Abdullah, P. Jancovic, M. Salous, V. Chapusky, Automatic gound taget classification using fowad scatteing ada, IEE Poc. RS, 006, vol. 153, o 5, pp. 47-437. [4] Hu Cheng, M. Antoniou, M. Cheniakov, V. Sizov, "Quasi-optimal signal pocessing in gound fowad scatteing ada, Inten. Rada Conf. RADAR 008, Rome, Italy, May 008, pp. 1-6. [5] Hu Cheng, Xiao Liang Li, M. Cheniakov, Teng Long, Analysis of signal chaacteistic and esolution in gound fowad scatteing ada, IEEE Signal Pocessing conf. ICIP 010, Beijing, China, Octobe 010, pp. 1969-197. [6] T. Long, Hu Cheng, M. Cheniakov, Gound moving taget signal model and powe calculation in fowad scatteing mico ada, Sci China, Se F-inf Sci, 009, vol.5(9), pp.1704-1714. [7] V. Koch, R. Westphal, ew appoach to a multistatic passive ada senso fo ai/space defense, IEEE AES Systems Magazine, ovembe, 1995, pp. 4-3. [8] I. Subeviola, I. Mayodome, J. Mendizabal, Expeimental esults of ai taget detection with GPS fowad scatteing ada, 01, In IEEE Geoscience and Remote Sensing Lettes, vol. 9, no. 1, Januay 01, pp.47-51. [9] V. Beha, Ch. Kabakchiev, Detectability of Ai Taget Detection using Bistatic Rada Based on GPS L5 Signals, Poc. IRS 011,1-th Inten. Rada Symp., Leipzig, Septembe 011, pp. 1-17. [10] V. Beha, Ch. Kabakchiev, H. Rohling, Ai Taget Detection Using avigation Receives Based on GPS L5 Signals, Poc. of IO GSS 011, 4th Intenational Technical Meeting of The Satellite Division of the Institute of avigation, Potland OR, Septembe 011, pp. 333-337. [11] V. Chenyak, Fundamentals of Multisite Rada Systems, Godon and Beach Science Publishes, 1999. [1] Cheniakov M., V. Sizov, M. Antoniou, E. Rashid, P. Jankovic, A. Myakinkov, A. Kuzin, Easily deployable, multi-functional ada netwok, 5th EMRS DTC conf., Edinbugh 008, pp. A7. [13] E. Glennon, A. Dempste, C. Rizos, Feasibility of ai taget detection using GPS as bistatic ada, Jounal of Global Positioning Systems, vol. 5, no. 1-, 006, pp. 119-16. [14] Ch. Kabakchiev, V. Beha, H. Rohling, Taget Detection using Fowad Scatteing Rada with GPS Receives, Fist Intenational Confeence on Telecommunications and Remote Sensing ICTRS 01, 9-31 August, 01, Sofia, Bulgaia.