Research on Blanket Jamming to Beidou Navigation Signals Based on BOC Modulation

Transcription

1 Int. J. Communiations, Network and System Sienes, 6, 9, Published Online May 6 in SiRes. Researh on Blanket Jamming to Beidou Navigation Signals Based on BOC Modulation Pei Wang,,3, Xiaohun Lu,, Rui Wang 4 National Time Servie Center, Chinese Aademy of Sienes, Xi an, China Key Laboratory of Preision Navigation and Timing Tehnology, Chinese Aademy of Sienes, Xi an, China 3 University of Chinese Aademy of Sienes, Beiing, China 4 Xi an Monitoring Station, SAPPRFT, Xi an, China Reeived April 6; aepted 4 May 6; published 3 May 6 Abstrat Aiming at the issue of influene of blanket amming on performanes of Beidou navigation signals, through studying Beidou signals based on the BOC modulation tehnology, establishing a blanket amming mathematial model, and performing modeling and simulation on multiple amming tehnologies, to attain the amming urves of time domains and frequeny domains of Beidou signals, and the orrelation urve of the signal-to-amming rate and the bit error rate under blanket amming, and thus realizing evaluation on the amming performane. Keywords Beidou Navigation Signals, Blanket Jamming, BOC. Modeling Analysis on Signals of Beidou Navigation System The binary offset arrier (BOC) tehnology, as a researh hotspot in the field of navigation, has been experimented in navigation signals of the Amerian GPS system and the European Galileo system [] []. Compared with the traditional way of spread spetrum modulation, the novel BOC modulation way has the advantages of improving the utilization rate of navigation frequeny bands, restraining the multipath error of signals, reduing the oherene loss of signals, improving the pseudorange measurement auray, enhaning the anti-amming performane of signals, et.. The Beidou global navigation signal system will also adopt the BOC modulation tehnology [3]-[5]... BOC Basi Model BOC modulation referred to auxiliary modulation on ode signals generated by a satellite by taking a square wave as the subarrier, then modulating to the main arrier, that is, multiplying the signal St () and the subarrier with the frequeny being f s, to split the frequeny spetrum of signals into two parts, whih are positioned on the right and left parts of the frequeny of the main arrier [6]. That is: How to ite this paper: Wang, P., Lu, X.C. and Wang, R. (6) Researh on Blanket Jamming to Beidou Navigation Signals Based on BOC Modulation. Int. J. Communiations, Network and System Sienes, 9,

2 S () t = A D() t P() t S ()os( t π ft + ϕ) () BOC In whih, A refers to the signal amplitude; Dt () refers to the message data; Pt () refers to the PRN sequene; SC () t refers to the subarrier signal. The priniple of BOC signals is shown in Figure, in whih, f refers to the rate of the spread spetrum ode, and f s refers to the rate of the subarrier. After the navigation data are modulated to the spread spetrum ode, a retangular subarrier is then modulated to generate a BOC signal, and finally the BOC signal is modulated to the main arrier of the navigation signal frequeny band to be transmitted. BOC (4, ) is taken as an example. Figure is the time domain waveform of PRN odes being subeted to BOC (4, ) modulation, it is observed that the blue full line represents the extended ode sequene ( f ), and the red dotted line represents the ode sequene ( f s ) after modulation. Figure 3 is the power spetral density of the signal... Power Spetrum and Autoorrelation Funtion of BOC Signals In referene to promotion of the spetrum formula of BPSK modulation signals, the power spetral density of the normalization baseband of BOC (f s, f ) modulation an be attained as [6]: C G ( f) = f BOC π f π f sin sin fs f π f π f os f s () navigation signal BOC signal spread spetrum signal retangular subarrier Figure. Shemati diagram of BOC signal modulation. BOC(4, ).5 Code sequene Chips Figure. Waveform of BOC (4, ) modulation signals. 36

3 -6 BOC(4, ) PSD (db/hz) Frequeny (MHz) x 7 Figure 3. Power spetral density of BOC (4, ) modulation signals. When fs n = is an even number, f π f π f sin os fs f GBOC ( f) = f (3) π f π f os f s fs When n = is an odd number, f Generally, the autoorrelation funtion of BOC modulation annot be easily expliitly expressed. Provided that signals take the omplex bandwidth β r as band limit ideally, the autoorrelation funtion an be defined as: βr / π fτ R( τ ) G ( ) r / BOC f e df β = (4) The number of main lobes and side lobes between the main lobes on both sides on the BOC power spetrum is determined by two parameters, i.e. f s, and f, and the speifi orresponding relation is expressed as: fs n = (5) f In whih, n represents the number of main lobes and side lobes between the main lobes on both sides, and also serves as the order of BOC modulation, f s refers to the frequeny of the subarrier, and f refers to the ode rate. Thus the number of main lobes and side lobes between the main lobes of BOC (4, ) an be alulated to be 4, as shown in Figure 3.. Researh on Jamming Tehnologies Jamming on navigation signals mainly referred to amming ountermeasure to a user reeiver, and lassified into blanket amming and deeption amming in tehnology... Blanket Jamming By launhing ertain types of amming signals, masking the frequeny spetrum of signals launhed by the ad- 37

4 verse party in a ertain way, and blanketing satellite signals reahing the antenna terminal of a reeiver, to ause a result that the adverse party annot orretly reeive satellite signals to arry out positioning, and thus the apability of the adverse party to ondut normal operation is degraded or ompletely destroyed [7]. Blanket amming inludes spot amming, bloking amming and orrelation amming. Spot amming is onduted in a manner of mainly performing amming to satellite signals in speifi ode types, to ause the signals to fail at a ertain area by adopting the frequeny spot tehnology, through perfetly aligning the amming arrier frequeny to the signal arrier frequeny [8]. Bloking amming is onduted in a manner of blanketing satellite signals reahing the antenna terminal of a reeiver through launhing amming signals, to attain the purpose of amming. Bloking amming has multiple amming systems, inluding single-tone amming, multi-tone amming, et. Generally, spot amming is regarded a speial ase of bloking amming; noise amming guarantees that uniform-bandwidth amming spetrums an be generated in bloking amming. Correlation amming has a amming system modulated with pseudo odes, that is, amming is arried out by using the harateristi that the pseudo ode sequene of amming signals and the pseudo ode sequene of navigation signals are greatly orrelated. Compared with unorrelated amming, more energy an pass the narrow-band filter of a reeiver, and therefore effetive amming realized in other way an be realized with smaller power... Deeption Jamming Referred to launhing ghost signals having the same parameters (only with different information odes) with real satellite signals to am a reeiver, to ause the reeiver to generate error loation information, and funtioning as a pseudo satellite. Deeption amming to navigation signals an be onduted in two ways: providing false navigation information or inreasing the signal propagation time delay, whih orrespond to two amming systems, i.e. the prodution amming system and forwarding amming system [9]. Prodution amming means launhing radio signals same with satellite signals by a amming soure to deeive a reeiver, to ause error deoding. Forwarding amming means re-broadasting the reeived satellite signal to onstitute a false satellite signal, to lead to error deoding by the reeiver and ause ranging error, and thus error positioning is aused..3. Single-Tone Jamming Single-tone amming referred to launhing signals at one frequeny, and therefore amming signal is a single frequeny ontinuous wave voie frequeny. Single-tone amming is also alled dot frequeny amming []..4. Multi-Tone Jamming A ammer an launh L (being greater than ) audios, whih an be randomly distributed, or positioned on speifi frequeny bands. Under the irumstanes that a speifi target anti-amming ommuniation system is very vulnerable to amming by speifi audios and the ammer reognizes the situation, audios should be used more autiously at the speifi frequenies, and should not be randomly distributed []. When the audios are at adaent hannels, independent multi-tone amming is formed, that is omb amming. Therefore, the following assumption is adopted in default no matter whih audio amming ountermeasure is disussed, that is the audio is positioned at one frequeny of a frequeny spetrum aurately, thus the amming audio an pass the filter of a reeiver, and distortion or attenuation is not generated. Independent multi-tone amming is formed in a manner of superposing n independent sine wave signals, A refers to the amplitude, Δf refers to the stepping frequeny width, and the time-domain expression is as follows:.5. Noise Jamming The generalized stationary random proess: N π ( ) (6) n= xt ( ) = A sin f + n f t t J ( t) = U os πkfm u ( t ') dt ' + w t + ϕ (7) 38

5 u t is the zero-mean generalized u t and uniformly distributed, π, U refers to the amplitude of noise frequeny modulation signals, w refers to the enter frequeny of noise frequeny modulation signals, and K FM refers to the slope of frequeny modulation. Gaussian noise and sinusoidal signals are used for noise frequeny modulation, and amming signals are formed after filtering and power amplifiation. The effetive bandwidth of signals subeted to noise frequeny modulation is only orrelated to the amplitude effetive value of modulation noise, and the frequeny modulation oeffiient, and barely orrelated to the bandwidth of modulation noise. The generalized stationary random proess: Called noise frequeny modulation amming, in whih modulation noise ( ) stationary random proess, ϕ is a random variable mutually independent to ( ) between [ ] ( ) J( t) = U + U t os wt+ ϕ Called noise amplitude modulation amming, in whih U ( ) n (8) n t refers to generalized stationary random noise, of whih modulation noise is a zero mean, and the variane being σ n, and being distributed between [ U, ], ϕ refers to a random variable whih is uniformly distributed between [, π ], and mutually independent to Un ( t ), and U and w are onstants. From the expression of noise amplitude modulation, it is observed that noise amplitude modulation amming is generated due to generation of band-limited noise fundamentally. Firstly, a set of mutually-independent Gaussian white noise is generated, and then the Gaussian white noise passes a band-limited filter to produe required band-limited noise []. The noise amplitude modulation signal and the orresponding power spetrum an be attained through amplitude modulation by means of band-limited Gaussian noise. Noise amplitude modulation amming an be defined as narrow-band amming, as the frequeny spetrum width thereof is only twie that of modulation noise. Requirement on a modulator is high with inrease of the spetrum width of modulation noise, thereby leading to a too ompliated iruit whih is diffiult to realize. In addition, the frequeny spetrum width of noise amplitude modulation is also limited by the limited bandwidth of an osillating tube. The generalized stationary random proess: t is the zero-mean generalized sta-, π, and mutually inde- J( t) = U os wt + KFMU( t) + ϕ Called noise phase modulation amming, in whih modulation noise Un ( ) tionary random proess, ϕ is a random variable uniformly distributed between [ ] pendent to Un ( t ), and U, w and K are onstants. FM (9) The total power of phase modulation waves is equal to the arrier power. When the effetive phase shift D is very small, the power spetrums form a bump funtion at the enter frequeny, and are distributed uniformly within the bandwidth F around the enter frequeny, and energy is onentrated at the enter frequeny; when the effetive phase shift is inreased, the energy at the enter frequeny is onverted into side frequeny energy, however, the bandwidth is unhanged; when the effetive phase shift D is greater than, energy is mainly distributed in side frequenies, the spetrum width is broadened, and the power spetrum is low. The effetive frequeny bandwidth of noise phase modulation signals is orrelated to the frequeny bandwidth of modulation signals, the amplitude of modulation signals, and the phase modulation oeffiient [3] [4]. 3. Jamming Simulation of Beidou Navigation System The amming analysis program is mainly onduted in a manner that a Beidou navigation signal generating module and a amming signal generating module are integrated through a human-omputer interation interfae, the parameters of different amming modules an be adusted aording to requirements, the waveform harateristis of time domains and frequeny domains of Beidou navigation signals generated by the Beidou navigation signal generating module, and the hosen amming signals an be observed in real time, the two an be simulated into a signal reahing the reeiver terminal through amming analysis software in an integrating way, and the time domains and frequeny domains of the signal are displayed. By integrating the Beidou navigation signal soure with the amming modules, bit error rates under different amming onditions are attained through further simulation and the amming effet is analyzed. Blanket amming has great amming power, so the pseudorange measurement preision of a reeiver an not only be redued, even error deoding an be aused diretly, thereby leading to inapability of positioning by 39

6 the reeiver. Multiple blanket amming effets are analyzed and simulated mainly in the aspets of time domain and frequeny domain simulation and bit error rate simulation. Setting the information ode rate to be. MHz, the BOC modulation subarrier frequeny to be 4 MHz, the spread spetrum ode rate to be MHz, the intermediate frequeny arrier to be MHz, the sampling frequeny to be 44 MHz, the signal-to-amming rate to be db, and the transmit information bit to be,. When being free from amming, time domain and frequeny domain simulation of signals reeived by a reeiver as shown in Figure 4 and Figure 5. Setting the Gaussian noise variane 4 MHz, amming signals with different signal-to-amming rates are applied respetively, Monte Carlo statistial experiments are onduted, and independent statistis are performed for times to obtain the simulation result as shown in Figures 6-. Figures 6- are time domain and frequeny domain graphs of signals reeived by the input terminal of a reeiver under the effet of three types of noise, and the amming effets of amming signals on time domains and frequeny domains an be observed visually. Figures -4 is a urve, of whih bit error rates of three types of σ =, the amming power to be 4 W, and the amming frequeny to be.5 Amplitude Time points Figure 4. Time domain graph of amming-free BOC modulation signals Fenquene(MHz) Figure 5. Frequeny domain graph of amming-free BOC modulation signals. 4

7 Amplitude Time points Figure 6. Time domain graph of noise frequeny modulation Fenquene(MHz) Figure 7. Frequeny domain graph of noise frequeny modulation 6 4 Amplitude Time points Figure 8. Time domain graph of noise amplitude modulation 4

8 Fenquene(MHz) Figure 9. Frequeny domain graph of noise amplitude modulation Amplitude Time points Figure. Time domain graph of noise phase modulation Fenquene(MHz) Figure. Frequeny domain graph of noise phase modulation 4

9 - error probability SIR db Figure. Error probability performane against SIR of noise frequeny modulation. - error probability SIR db Figure 3. Error probability performane against SIR of noise amplitude modulation. - error probability SIR db Figure 4. Error probability performane against SIR of noise phase modulation. 43

10 amming hange along with signal-to-amming rates. It is observed that amming with uniform power density is formed in the passband of a filter after the reeiver is ammed by noise, due to spread spetrum gain, and the reeiver extends the amming power while amplifying the signal power. The spread spetrum gain of Beidou system is great, and great power is required to omplete amming. No signifiant differene exists among the amming effets, by ontrast, the noise amplitude modulation is low in bit error rate when the signal-to-amming rate is lower than 5 db, and the bit error rate is high when the signal-to-amming rate is greater than 5 db. The effet of blanket amming an be illustrated more obviously by noise modulation amming, a amming funtion is fulfilled, and however, great power is required to ahieve ertain amming effets. 4. Conlusion The paper mainly fouses on detailed desription and simulation on how to am the Beidou system (BOC modulation). The researh keystone lies in the definition, harateristis and superiority in terms of anti-amming of the BOC modulation method; signal soure modeling, amming modeling and BOC modulation amming modeling are ompleted; multiple amming methods are simulated and the amming results are analyzed, and aordingly the validity of the amming methods is demonstrated. Referenes [] Tan, X.Y. () Researh of Anti-Interferene and Countermeasures of GPS Used in Military Navigation. Eletronis Optis & Control, No. 4, 3-8. [] Gao, J., Li, Z.J. and Dai, G.X. () Jamming to GPS Signal. Aerospae Eletroni Warfare, No., [3] Sun, H.T., Wang, C.Q. and Feng, J.D. (4) Current Situation and Development of Anti-Jamming Tehnology of GPS System in USA. Eletro-Opti Tehnology Appliation, 9, [4] Chu, H.L. and Li, C.X. () Researh on Key Tehnologies of BOC Modulation Navigation Signal. Radio Engineering, 4, [5] Li, X.H. and Bian, Y.J. (3) Analysis of AM Phenomenon in BPSK Signal. Journal of Time and Frequeny, 6, -9. [6] Wang, L., Liu, C.H. and He, S.B. (9) Interferene Effets on BOC Signals. Chinese Spae Siene and Tehnology, 4, [7] Yang, L., Bo, Y.M. and Tian, M.H. (8) Researh of Anti-Jamming Charateristi for BOC Signal. Computer Siene, 35, [8] Bai, Y., Lu, X.C., Wang, J. and Han, T. (5) Interferene Suppression Method Based on NEW-MDCFT in Satellite Navigation System. Journal of Navigation and Position, 3, [9] Yu, H.J. and Pan, C.S. (6) The Researh and Implementation of the Bloking-Suppressing Jamming Tehnique in GPS. Transations of Shenyang Ligong University, 5, [] Xiao, J.Q. and Ji, Q. (7) A Robust Content-Based Digital Image Watermarking Sheme. Signal Proessing, 87, [] Wei, X.G. () Study of Jamming to GPS Signal Modulated by BOC. Eletroni Design Engineering, 9, [] Wo, Y., Han, G.Q. and Zhang, B. (5) A New Feature-Based Image Content Authentiation Algorithm. Chinese Journal of Computers, 8, 5-. [3] Xiang, D.S., Xiong, Y.S. and Zhu, G.M. (6) An Image Adaptive Gray-Sale Watermark Embedding and Extration Algorithm Based on Visual System. Journal of Image and Graphis,, [4] Zang, P. and Fan, Y.B. (6) Study and Comparison of Image Watermark Based on Wavelet Paket and Multi- Wavelet. Computer Engineering, 3,