Studies on Novel Anti-jamming Technique of Unmanned Aerial Vehicle Data Link

Transcription

1 Chinee Journal of Aeronautic 1(008) Chinee Journal of Aeronautic Studie on ovel Anti-jamming Technique of Unmanned Aerial Vehicle Data Link Huang enzhun a, *, ang Yongheng a, Ye Xiangyang b a School of Electronic and Information, orthwetern Polytechnical Univerity, Xi an 71007, China b Telecommunication Engineering Intitute, Air Force Engineering Univerity, Xi an , China Received 14 Augut 007; accepted 6 December 007 Abtract Baed on the -ary pread pectrum (-ary-ss), direct equence pread pectrum (DS-SS), and orthogonal frequency diviion multiplex (OFD), a novel anti-jamming cheme, named orthogonal code time diviion multi-ubchannel pread pectrum modulation (OC-TDSCSS), i propoed to enhance the anti-jamming ability of the unmanned aerial vehicle (UAV) data link. The anti-jamming ytem with it mathematical model i preented firt, and then the ignal format of tranmitter and receiver are derived. The receiver bit error rate (BER) i demontrated and anti-jamming performance analyi i carried out in an additive white Gauian noie (AG) channel. Theoretical reearch and imulation reult how the anti-jamming performance of the propoed cheme better than that of the hybrid direct equence frequency hopping pread pectrum (DS/FH SS) ytem. The jamming margin of the OC-TDSCSS ytem i 5 db higher than that of DS/FH SS ytem under the condition of Rician channel and full-band jamming, and 6 db higher under the condition of Rician channel environment and partial-band jamming. Keyword: UAV data link; OC-TDSCSS; ytemview imulation; orthogonal code; anti-jamming 1 Introduction * Unmanned aerial vehicle (UAV) ha become one component of the properou modern aviation weapon ytem for it outtanding tactical and technical performance. However, in implementing tak uch a reconnaiance, urveillance, airborne warning, communication relay and electronic countermeaure, it i often ubjected to interference. A an important part of UAV ytem, the UAV data link demand the highet reliability in data tranmiion, and the mot powerful ability of anti-jamming and anti-multipath [1]. A an exiting UAV data link, the applied imple anti-jamming ytem, direct equence pread pectrum (DS-SS) or -ary pread *Correponding author. Tel.: addre: wenzhunw@ohu.com Foundation item: Aeronautical Science Foundation of China (007ZC53030) pectrum (-ary-ss), eem to be weak in anti-jamming performance, and unable to atify the requirement of UAV data link in unfavorable and complex electromagnetic environment [-3]. Recent reearche introduce the application and performance analyi on frequency hopping pread pectrum (FH-SS), multi-carrier code diviion multiple acce (C/CDA) [4-5], and hybrid direct equence frequency hopping pread pectrum (DS/FH SS) ytem [6]. They how that the hybrid DS/FH SS ytem ha an anti-jamming performance better than DS-SS, -ary SS, FH-SS and C/CD-A. Thu, to enhance the anti-jamming ability of the UAV data link in variou complex environment, the advantage of the traditional pread pectrum ytem can be utilized and optimized in the development of a new anti-jamming technology to improve the elec-

2 14 Huang enzhun et al. / Chinee Journal of Aeronautic 1(008) tronic counter meaure of UAV data link. Thi paper propoe a novel anti-jamming technique, termed orthogonal code time diviion multi-ubchannel pread pectrum modulation (OC-TDSCSS), in which the -ary i aociated with the DS-SS and orthogonal frequency diviion multiplex (OFD). Different from the -ary ytem, the former pread pectrum i added before erial-parallel converter, and in mapping coding, the draft of orthogonal pread pectrum ubchannel i choen intead of peudorandom (P) code. Different from the DS/FH SS ytem, though the former pread pectrum employ the ame theory a DS-SS, in the DS/FH SS ytem, one hoping frequency tranmit multiple bit information, or multiple hoping frequencie tranmit one bit information, while in the new cheme aociated with -ary SS, multiple orthogonal pread pectrum ubchannel repreent one bit information. Different from the OFD ytem, a new egment of former pread pectrum i added and orthogonal pread pectrum ubchannel are adopted intead of the orthogonal ubchannel, thereby improving the pread pectrum gain and correlated characteritic between ubchannel [7]. The imulation reult confirm that the output ignal of OC-TDSCSS ytem like the Gauian white noie ignal lead to an anti-jamming performance better than the DS/FH SS ytem. Sytem Decription.1 Tranmitter model Fig.1 how the model of tranmitter, in which the input binary data equence at 1/T rate i firt encoded and multiplied by a higher rate channel P equence. The reult i a binary data equence at k/t rate. Then thee data are grouped according to k bit forming a data ymbol with = k ymbol. Each data ymbol i mapped with one of orthogonal pread pectrum ubchannel which are compoed of orthogonal pread pectrum equence modulated by binary phae-hift-keying (BPSK) in the orthogonal pread pectrum code et, and each ymbol elect repective orthogonal pread pectrum ubchannel to tranmit according to the mapping coding principle. Then orthogonal pread pectrum ubchannel are tranmitted timely through a radio frequency (RF) part. Fig.1 OC-TDSCSS tranmitter. The data ource period i denoted by T, the amplitude of qth data ource by A q, and the power of data ource denoted by P q equal A q /. In the orthogonal code et, the code length of each orthogonal equence equal, and the period i T c. For given modulator, their carrier are in an orthogonal frequency et, f ( 1,,, ), then T c = T /. Aume that the chip waveform of the pread pectrum code i a unit-amplitude rectangular pule with chip duration T c, and then p(t) i 1, 0 t Tc pt () (1) 0, Other In the orthogonal code et, the pread pectrum equence i expreed by C C(, i), C (, i) [ 1, 1] () where 1,,,, i 1,,,. Hence, the output ignal of tranmitter i S() t P C(,) i. Receiver model q 1 i1 it T pt ( ) co ft q (3) The model of a receiver i hown in Fig.. In the parallel correlated ynchronization receiver, digital matched filter (DF) are adopted. One elf-correlated peak i an output in each period of

3 Huang enzhun et al. / Chinee Journal of Aeronautic 1(008) pread pectrum ubchannel through the orthogonality of pread pectrum ubchannel and the correlation of P code. Thu, elf-correlated peak can be obtained and detected while one bit information i tranmitted. After de-mapping elf-correlated peak to pread pectrum ubchannel coding, the reult i ent to the correlator of local DS equence, and one bit information can be obtained. ithout conidering the radio frequency part, the receipt ignal in AG can be denoted by r() t S() t n() t J () t (4) where S(t) i given by Eq.(3), n(t) i an additive white Gauian noie (AG) with ingle-ided pectral denity 0, and J(t) the jamming ignal. where Q(, r) i a Gauian tochatic variable with zero-mean and T c 0 /4 variance. The fale judge probability of the jth orthogonal code and frequency i P ( j) {1 P[ Z ( Z, Z, Z, Z,, c j 1 j1 j1 Z )/ f ]} P( f ) j j (8) where P( f j ) i the fale judge probability of the jth frequency in orthogonal frequency et a 1/( 1). PZ { ( Z, Z, Z, Z,, Z )/ f} Z Z Z j 1 j1 j1 j j j j PZ ( / f j)d Z[ PZ ( j Zx, x j)] ( 1) Then Eq.(8) can be rewritten into 1 (9) 1 1 Pc ( j) {1 [ P( Z j Zx, x j)] } 1 (10) Fig. OC-TDSCSS receiver. 3 Bit Error Rate (BER) Analye in AG Channel In the cae that the receiver ha caught ynchronization in AG, aume the tranmitting ignal ymbol i the th in AG channel, thu the ignal in receiver can be expreed by r() t S( V,) t n () t (5) where n(t) i white Gauian noie with double-ided pectral denity 0 /. If coherence reception i adopted, the th correlator, denoted by Z, i the ignal ymbol of 1/ bit defined a T r C 0 c (6) n1 c Z () t (, n) p( tnt ) cof tdt After ubtituting Eq.(5) into Eq.(6), Z can be rewritten into Tc Pq Q(, r), and f f Z (7) Q(, r), or f f According to the central limit theorem, when the orthogonal code length i big enough, the ditribution of Z can be approximated by the Gauian proce. Becaue the variance of Z j Z x i = T c 0 /4, and the mean i T c (P q /) 1/, the following formula can be obtained: ( ytc P q /) 1 {, } e d PZ j Zx x j y 0 erf ( E / ) b 0 (11) where erf(x) denote the error function. After ubtituting Eq.(11) into Eq.(10), P c ( j ) can be obtained 1 1 Pc( j) {1 [erf( Eb / 0)] } (1) 1 Thu in detecting the th orthogonal code and orthogonal frequency, the fale judge probability i 1 P P ( j) P ( j), j 1,,, (13) c c c j 1 From the tranmitter model, when orthogonal code and orthogonal frequencie have been detected correctly, i.e. one bit information ha been tranmitted, the BER in AG i 1 1 Pb Pc {1 [erf ( Eb / 0)] } (14) 1

4 144 Huang enzhun et al. / Chinee Journal of Aeronautic 1(008) Anti-jamming Performance Analyi The current main jamming method aimed at the UAV data link are of full-band jamming, partial-band jamming, multitone jamming, and pule jamming [8]. Later, the analyi and imulation of the firt two jamming method are preented. 4.1 Performance in full-band jamming Aume that the input ignal of UAV i r() t S() t n () t (15) where n(t) i wide-band noie. Eq.(15) can alo be expreed a r t S t n t co ft n t in ft (16) I where n I (t) and n Q (t) are two mutual independent low-pa Gauian noie with double-ided power pectral denity ( 0 + jm )/, where 0 denote ingle-ided power pectral denity of thermal noie, and jm ingle-ided power pectral denity of jamming ignal. Therefore, the component near the intermediate frequency after correlation i H () t { ( tt / )co[ t ()] t 1 I Q IF d [ n ()co t t n ()in t t] co[( ) t ( t)]} IF Q IF (17) where ( ) i the elf-correlated function for orthogonal code in th ubchannel, and (t) the random modulation phae. In the receiver, the power pectrum of each ebchannel output i SR f Sinc f f fif Sinc f f f (18) where i the bandwidth of ubchannel. hen the frequency component excluding f IF have been filtered, the following equation hold. f S f R jm 0 Sinc f f f f fif d jm 0 f Sinc f f fif d f (19) ith the definition of = f f f IF, Eq.(19) can be implified into 0 jm Sinc f fif f fi F f SR f d (0) and the double-ided pectral denity of noie near f = ± f IF i n 0 jm fif SR fif (1) It how that when the ytem i ubjected to full-band jamming, the noie band i much wider than that of the ubchannel, and n / approache 0 / or jm /, meaning that broadband jamming noie poee feature imilar to the receiver inner noie. 4. Performance in partial-band jamming Compared with full-band jamming, it i eaier to generate partial-band jamming having a higher power pectral denity. Aume that i the bandwidth of radio frequency, jm the jamming bandwidth, the ubchannel bandwidth, P jm the jamming power, the rate of and jm, p the pectral denity of partial-band jamming, jm the pectral denity of full-band jamming, and 0 ingle-ided pectral denity of thermal noie. Thu the final pectral denity of noie i 0 + p, and only 0 i the effect in the remaining partial-band. The receiver ignal i r() t S() t n() t n () t () where S(t) i the ueful tranmitting ignal, n(t) the thermal noie, and n jm (t) the partial-band jamming. After correlative calculation, the output of the depectral mixer i H () t { ( tt / ) co[ t ()]} t 1 jm IF d

5 Huang enzhun et al. / Chinee Journal of Aeronautic 1(008) n() t { C(,) i p( tt )co[( ) t 1 i1 ( t)]} n ( t) { C(, i) d jm 1 i1 pt ( T ) co[( ) t ( t)]} IF d IF (3) where the econd term i the noie caued by coaction of the thermal noie and the depectral reference waveform, and the bandwidth i much wider than that of the pectral waveform, which ha been dicued in Section 4.1. Hereafter, two cae are conidered a follow: Cae one when jm <, i.e. one of the ub-channel i jammed, for the ingle ubchannel, the output of depectral mixer i H1 t co[ IFtd( t)] n t {cco[( IF ) t ( t)]} n ( t) cco[( ) t ( t)] jm IF (4) where i the elf-correlated function for the orthogonal code of the ingle ubchannel, and c the orthogonal code of the ingle ubchannel. The power pectral denity of the third term, generated by jamming, i the convolution of jamming pectral denity and pread pectrum waveform pectral denity. Along the imilar line cited in Section 4.1, it can be deducted that the output pectral denity in partial-band jamming i determined by p fjm jm / SfIF Sinc f x dx fjm jm / (5) where 1,,,. In uch cae, receiver can till obtain 1 elf-correlated peak and receive data normally while only one ubchannel i ubjected to interference. Cae two when jm >, for implifying analyi, if ubchannel central frequency fall in the jamming frequency band, the ubchannel i ubjected to complete jamming. Herein, when ubchannel i not in the jamming frequency band, the noie double-ided pectral denity of the depectral correlator output i 0 /; otherwie, it i ( 0 + p )/, and the average BER i E E P 1 P ( ) P ( ) b b a b b 0 0 jm (6) where P b ( ) i determined by Eq.(14). In uch cae, receiver can till obtain a majority of elf-correlated peak and recover the data a long a the number of interferential ubchannel i le than half of the number of ubchannel. 5 Simulation and Dicuion In the imulation, the OC-TDSCSS ytem parameter are aumed a follow: the ource rate i 8 Kbp; the former pread pectrum egment adopt BPSK modulation; the length of former pread pectrum code i 64 with a chip rate of 51 kc/; the number of ub-channel 16 with a chip rate of 048 kc/; the ytem bandwidth i Hz, and the intermediate frequency 85 Hz. The DS/ FH SS ytem parameter are choen a follow: the ource rate i 8 Kbp; the length of DS-SS code 64 with a chip rate of 1 04 kc/; the number of hopping frequency 16; the FH rate hop/, 1bit per two hopping; the ytem bandwidth i Hz, and the intermediate frequency.36 Hz. The jamming ignal parameter are taken a follow: the full-band jamming ignal i applied by Gauian white noie ignal with an alterable gain amplifier; the partial-band jamming ignal i adopted by DS- SS ignal with a bandwidth of Hz. In the BER performance analyi, the imulation i baed on the ATLAB platform and the onte Carlo method with a ampling rate of one per chip. In the anti-jamming ability analyi, the imulation i baed on the ytemview dynamic platform with a ampling rate of 500 Hz and ampling number of The Rician channel i choen with a Rician factor of 11 db, and the maximum Doppler frequency hift i 500 Hz [9]. The onte Carlo imulation reult of BER in AG channel are hown in Fig.3, from which it i clear that the imulation curve accord well with that of the theoretical reult, and when E b / 0 i equal to or larger than 9 db, the two curve are uperimpoed thu leading to the theoretical credibi-

6 146 Huang enzhun et al. / Chinee Journal of Aeronautic 1(008) lity of the ytem BER. Fig.6 Self-correlated peak of OC-TDSCSS under full-band jamming (1, 4, 7, 11 ubchannel). Fig.3 BER performance with theoretic and onte Carlo imulation in AG channel. The output pectrum of OC-TDSCSS ytem and DS/FH SS ytem are decribed in Fig.4 and Fig.5, repectively, which how that the tranmitted ignal of OC-TDSCSS ytem look like the Gauian white noie ignal in line with the theoretical reult, while in the DS/FH SS ytem, there are 16 ditinct envelop without the characteritic of Gauian white noie ignal. Fig.6 how the elf-correlated peak of OC-TDSCSS ytem of the ubchannel 1, 4, 7, 11 under the condition of full-band jamming. The program run two time. The ignal-to-noie ratio (SR) i 0 db; the jamming to ignal ratio (JSR) i db and 4 db. In the cae of JSR db, the elf-correlated peak can be extracted completely and the ytem can recover the data rightly, but thi i completely different with 4 db. Fig.7 how the elf-correlated peak of DS/FH SS ytem under the condition of full-band jamming. The program run two time. The SR i 0 db; the JSR i 17 db and 19 db. In the cae of JSR 17 db, the elf-correlated peak can be extracted completely and the data can be recovered rightly, but, for 19 db, the elf-correlated peak of the 3rd, 4th, 6th, 8th, 1th, 13th hopping cannot be detected normally leading to the loing of ynchronization. Therefore, the jamming margin of the OC- TDSCSS ytem i 5 db more than that of the DS/FH SS ytem under the condition of Rician channel and full-band jamming. Fig.4 Output ignal pectrum of OC-TDSCSS ytem. Fig.7 Self-correlated peak of DS/FH under full-band jamming. Fig.5 Output ignal pectrum of DS/FH ytem. Fig.8 decribe the output pectrum of the OC-TDSCSS ytem under the condition of partial-band jamming, which how that the eight anterior ubchannel are covered by the major lobe of jamming ignal pectrum, and the eight poterior

7 Huang enzhun et al. / Chinee Journal of Aeronautic 1(008) ubchannel by the ide lobe of jamming ignal pectrum. Here, SR i 0 db and JSR i 5 db. Fig.9 how the elf-correlated peak of OC-TDS- CSS ytem under the condition of partial-band jamming. The program run two time. The JSR i 5 db and 7 db. For JSR 5 db, the elf-correlated peak can be extracted except thoe of the 3rd, 4th, 5th ubchannel and the right data can be recovered, but, for 7 db, the elf-correlated peak of the 1t, nd, 3rd, 4th, 5th, 6th, 7th, 10th ubchannel cannot be recovered normally leading to the loing of ynchronization. Fig.10 decribe the output ignal pectrum of the DS/FH ytem under the condition of partialband jamming. It i noted that the eight anterior ubchannel are covered by the major lobe of jamming ignal pectrum while the eight poterior ubchannel by the ide lobe of jamming ignal pectrum. Here, the SR i 0 db and the JSR i 19 db. Fig.11 how the elf-correlated peak of DS/FH ytem under the condition of partial-band jamming. The program run two time. JSR i 19 db and 1 db. For JSR 19 db, the elf-correlated peak can be extracted except thoe of the 4th, 1th ubchannel and the right data can be recovered, but, for 1dB, the elf-correlated peak of the nd, 4th, 6th, 11th, 1th, 14th hopping cannot be detected normally leading to the loing of ynchronization. Therefore, the jamming margin of the OC-TDSCSS ytem i 6 db more than that of the DS/FH SS ytem under the condition of Rician channel and partial-band jamming. Fig.10 Output ignal pectrum of DS/FH ytem under partial-band jamming. Fig.8 Output ignal pectrum of OC-TDSCSS ytem under partial-band jamming. Fig.11 Self-correlated peak of DS/FH under partial-band jamming. 6 Concluion Fig.9 Self-correlated peak of OC-TDSCSS under partial-band jamming (1, 4, 7, 11 ubchannel). The paper propoe the OC-TDSCSS cheme a a novel anti-jamming technique for UAV data link, for which the ytem and mathematical model are etablihed; the ignal format derived; and the BER and anti-jamming performance in AG channel analyzed. Theoretical analyi and imulation reult demontrate that the derived ytem BER formula i correct and the propoed ytem i technically feaible. The propoed cheme poee much better anti-jamming capability than the DS/FH ytem, i.e. the jamming margin of the OC-TDSCSS ytem i 5 db more than that of the DS/FH SS ytem under the condition of Rician channel environment and full-band jamming, and

8 148 Huang enzhun et al. / Chinee Journal of Aeronautic 1(008) the jamming margin of the OC-TDSCSS ytem i 6 db more than that of the DS/FH SS ytem under the condition of Rician channel environment and partial-band jamming. Reference [1] Ye. Some key technique about modulation and coding in UAV communication. PhD thei, orthwetern Polytechnical Univerity, 00. [in Chinee] [] Scott T, King D, achino. Information aurance in the UAV/UCAV environment. Proceeding of AUVSI Unmanned Sytem orth America ; [3] urphy J, Donaldon. Digital microwave link for unmanned vehicle. Proceeding of AUVSI Unmanned Sytem orth America ; [4] Cho J Y, Kim Y H, Cheun K. A novel frequency-hopping pread-pectrum multiple-acce network uing -ary orthogonal alh equence keying. IEEE Tran on Communication 003; 51(11): [5] en L, Zhu J K, Cota E, et al. -ary C CDA in up-link for next generation mobile communication. Proceeding of IEEE 58 th Vehicular Technology Conference. 003; 4: [6] ohammad A R K, Shao D R, ohammad B S. Analytical expreion for hybrid DS/FH pread pectrum communication ytem capacity. Proceeding of IEEE International Conference on Emerging Technology. 006; [7] Oz E. A comparion of timing method in orthogonal frequency diviion multiplexing (OFD) ytem. PhD thei, aval Potgraduate School, 004. [8] Poiel R A. odern communication jamming principle and technique. orwood, A: Artech Houe, Inc, 004. [9] Jin S, Zhang X L, Zhou Q. A tatitical model for the UAV communication channel. Acta Aeronautica et Atronautica Sinica 004; 5(1): [in Chinee] Biographie: Huang enzhun Born in 1968, a Ph.D. candidate in orthwetern Polytechnical Univerity. He received the B.S. in 1994 and.s. in 1997 from Air Force Telecommunication Engineering Intitute. Hi main academic interet i radio communication. wenzhunw@ohu.com ang Yongheng Born in 1941, he i a profeor and doctor upervior in orthwetern Polytechnical Univerity. Hi main reearch interet are radio communication and navigation. wangy@nwpu.edu.cn