Pseudo Peak Suppression in Generating Range Profile with Multi-carrier Chirp

Transcription

1 Pseudo Peak Suppresson n Generatng Range Profle wth Mult-carrer Chrp YANG Chao, ZHENG Ln,, BAI Yunhao. Key Lab. of Cogntve Rado & Informaton Processng, the Mnstry of Educaton, Guln, P. R. Chna. Sc. and Tech. on Info. Transmsson and Dssemnaton n Communcaton Networks Laboratory, Shjazhuang, P. R. Chna 47466@qq.com, gwzheng@gmal.com Abstract: - To ensure the relablty of transmsson and prevent nter-carrer nterference (ICI) between subbands, the sub-carrer frequency ncrement s usually greater than the bandwdth of sub-band for mult-carrer chrp. That wll brng on false targets generated by pseudo peaks on Hgh Resoluton Range Profle (HRRP). At the presence of false targets, t s dffcult to get the true poston of target due to the serous nfluence on target detecton. In ths paper, the mechansm of pseudo peaks generaton s analyzed and an algorthm s proposed to remove pseudo peaks whle the mage resoluton s mproved by Super-SVA, whch reduces the echo pulse wdth. Wth the pulse wdth less than an unambguous range, the HRRP wthout false targets can be obtaned. Wth the analyss and smulaton of sngle and mult-targets, the results ndcate that ths algorthm can effectvely remove false targets caused by the pseudo peaks. Key-Words: - Mult-carrer communcatons; pseudo peak; Super-SVA; HRRP, Target detecton, Chrp sgnal Introducton The combnaton wth communcaton and target detecton s an mportant applcaton area on Radarcommuncaton ntegraton. In communcaton areas, t s based on wreless network to acheve collaboratve target percepton. Mult-carrer sgnal can mprove the nformaton transmsson rate as a communcaton sgnal, and s also able to synthesze large bandwdth to obtan HRRP as a radar sgnal. Therefore, mult-carrer chrp sgnal becomes more mportant n the research area of radar communcaton ntegraton [~3]. Compared wth mult-carrer chrp, steppedfrequency chrp sgnal (SFCS) s wdely used n modern hgh-resoluton radar, whch has a low hardware complexty snce t uses a narrowband transcever. However, wthout parallel transmsson n subbands, SFCS has a lower nformaton transmsson rate than that of mult-carrer chrp. Meanwhle, due to Doppler affecton, SFCS generates lnear phase tem and quadratc phase term whch results n target range shft and echo spread [4]. Mult-carrer chrp sgnal has the characterstcs of beng nsenstve to Doppler, that s, t s mmune to Doppler nfluence n movng targets []. To obtan HRRP wth mult-carrer chrp, frst step n dgtal processng s channel dvson for dfferent sub-band. After pulse compresson, each sub-chrp sgnal becomes a coarse resoluton range profle (called coarse dstance dmenson). Then, HRRP s obtaned va IDFT appled to dfferent channels n the same coarse range gate, whch s called as fne dstance dmenson. To reduce the loss of oversamplng, hgher samplng frequency than the bandwdth of sub-band must be adopted, whch result n over-samplng result of pulse compresson. So the target pck-up algorthm has to be adopted to elmnate target s redundancy n order to obtan fne HRRP. In target extracton [6,7], a zone s pcked up from each fne dstance dmenson, called vald zone here. And there s only one vald zone for a sngle target under the deal condton. In order to ensure the relablty of transmsson and prevent nter-carrer nterference (ICI) between sub-bands, t s essental to add a guard nterval or use a tme-frequency doman roll-off shapng flter between sub-bands for mult-carrer communcaton sgnal. As a result, the carrer frequency ncrement f must be greater than bandwdth of subband B, as shown Fgure. At ths pont, the pulse wdth s greater than the unambguous range n the synthetc range profle. Hence, more than one vald zone occurs n a pulse wdth. After target extracton, false targets wll turn up nevtably n range profle, whch mpact on the target detecton. Ths paper analyzes the mechansm of pseudo peaks generaton, and proposes the algorthm of pseudo peaks suppresson based on the spectrum extrapolaton characterstcs of Super-SVA. That E-ISSN: Volume 3, 4

2 makes pulse wdth less than an unambguous range by ncreasng bandwdth of echo sgnal. The algorthm can avod the generaton of false targets and mprove the resoluton of the target. The results of computer smulaton are gven n agreement wth the analyss. HRRP syntheszng prncple wth mult-carrer chrp The mathematc expresson of mult-carrer chrp transmtted sgnal s gven by N f t ut expjf ft () N where t u t rect expjkt T T and ut s the baseband sgnal of the chrp.k BT s the frequency-modulaton slope of a subband chrp, B s the bandwdth of subband chrp, and T s the symbol wdth. N and are the number and the ndex of carry frequences respectvely. f s the ntal carrer frequency, f s the carrer frequency ncrement of subband chrp. The tme-frequency dagrams of sgnal are as shown n Fgure. B f f t Fg.: The tme-frequency dagrams of sgnal The echo sgnal of mult-carrer chrp s expressed as: N ft ut t T () exp j f f t t where t u t rect j kt T T exp f Consderng the nsenstvty to Doppler for mult-carrer chrp, the target s supposed to be a statonary. So the echo delay of target s t Rc, where R s the range of target and c s the lght speed. After channel dvson, the baseband sgnal s gven by f t ut t N exp j f f t (3) Usng pulse compresson [] on baseband sgnal of dfferent channel, Equaton (3) becomes t R/ c S t kt rect T kt R c kt t R / c j j f R c expjf R/ c sn t / exp k t R/ c exp / 4 exp / Samplng S t at t Rc, and t yelds: S kt j exp exp (4) R exp 4 c j f Rc j f Rc () Takng N-pont IDFT of S Rc wth respect to, we can obtan the HRRP of the target as follows: S IDFT kt sn l Nf R/ c N sn l / N f R/ c (6) 3. Mechansm of pseudo-peak generaton Fgure s the dmensonal range profle under B f. In the fgure, the horzontal axs represents the coarse dstance dmenson, on whch the nterval between each slash s samplng range resoluton r s, rs cts, where T s s the samplng nterval. The slash axs represents the fne dstance dmenson, and dfferent slash corresponds to dfferent dstance gate, whose length s called the sngle pont unambguous range r I. Each rough lne E-ISSN: Volume 3, 4

3 s a vald zone of dfferent dstance gate on the fne dstance dmenson, whch s same as r s n length. When all slashes connect up n order, HRRP can be obtaned. n a sngle pulse, and the sngle pont dstance unambguous range s equal to 4 tmes length of an vald zone. However, there are 3 samplng ponts fallng nto the vald zone n a sngle pulse. As a result, two false targets wll turn up n HRRP, whch mpact on the target detecton. 4. Super-SVA on mult-carrers chrp 3. Super-SVA.8.8 t s d e n F rs r I r Coarse dstance dmenson τ Fg.: The dmenson range profle under B= f It assumes that r 4r s n Fgure, where r s the dstance resoluton of a pulse. As shown n coarse dstance dmenson, there are only 4 samplng ponts between the center of manlobe and frst zero pont. Meanwhle, the sngle pont dstance unambguous range s equal to 4 tmes length of a vald zone, that s ri 4rs, whch locates on dfferent place n each dstance gate. In the case, the only one samplng pont n a sngle pulse can fall nto the vald zone. so there s only one samplng pont to be saved for each target after target extracton Samplng pont (a) x Frequency x x -4 6 (c) Samplng pont.4 (b) Frequency x (d) A m p l e n F r Coarse dstance dmenson s r τ Fg.3: The dmenson range profle under B< f It assumes that B f s 7, f f s 4,when B f shown n Fgure 3. In Fgure 3, there are 7 samplng ponts between the center of manlobe and frst zero pont r I Frequency x Samplng pont (e) (f) Fg.4: The sgnal processng flow chart of Super-SVA (a) The echo sgnal from pulse compresson (b) The result after SVA (c) The spectrum after SVA (d) The nverse ampltude weghtng operaton (e) The reshaped spectrum (f) The result after Super-SVA Super-SVA s a super-resoluton method developed on the bass of SVA [,], the basc E-ISSN: Volume 3, 4

4 process s descrbed as follows. Frstly, the pulse compresson s performed on the baseband sgnal of echo, and the result s shown n Fgure 4 (a).snce SVA only saves the man lobe of the sgnal, the sgnal s equvalent to the tme doman truncaton by usng SVA, shown as the red curves n Fgure 4 (b). Thus, the frequency spectrum wll be extrapolated, and the blue and red curves represent the frequency spectrum before and after SVA respectvely shown as n Fgure 4 (c). In order to mprove resoluton and save the nformaton of target, the spread spectrum need be reshaped nto a rectangle spectrum wth the same ampltude, as shown n Fgure 4 (e), where blue and red profle represent the frequency spectrum before and after extrapolaton, respectvely. Therefore, the spread spectrum need be multpled by a frequency-doman nverse ampltude weghtng operaton, whch s the ampltude rato of extended rectangle spectrum and IFFT of a snc functon manlobe, as shown n Fgure 4 (d). Fnally, after IFFT, the resoluton of target s mproved, as shown n Fgure 4(f), where the blue and red curves represents the result before and after Super-SVA, respectvely. The above extrapolaton procedure can be repeated several tmes to get much hgher resoluton as desred. 4.. Pseudo peak suppresson by Super-SVA In mult-carrers chrp, the ntroducton of the protecton nterval makes sub-band B less than the carrer frequency ncrement f, whch results n the dstance resoluton of a pulse greater than the sngle pont unambguous range. So a sngle pulse contans more than one vald zone. Then, the vald zones are pcked up from the fne dstance dmenson and are splced n order. As a result, the false targets wll arse n HRRP. Super-SVA s appled to extend bandwdth of sub-band, whch makes pulse wdth smaller on coarse dstance dmenson. Here, the extended bandwdth notes as B '. As long as B' f, a pulse wdth can be smaller than the sngle pont unambguous range. In ths way, there s only one vald zone to be saved aganst one target n target extracton. The flow chart of proposed algorthm s shown n Fgure. Frstly, the channel dvson s performed on mult-carrers chrp echo, and the baseband echo sgnal n each channel passes through match flter. Afterward, IDFT s appled between dfferent channels of the same samplng dstance gate. To elmnate false targets generated by pseudo, Super-SVA s performed on each channel to decrease pulse wdth. After Super-SVA, the stll exstence of sdelobes can generate false targets and cover weak targets. Furthermore, RSVA [3] can be appled to suppress sdelobes under the nonnteger Nygust sampled verson. By targets extracton, there s only one vald zone n a sngle pulse. Thus, the pseudo peaks are removed. Echo sgnal Channel dvson Pulse compresson IDFT Fg.: The flow chart of mult-carrers chrp processng. Smulaton and analyss. Smulaton for sngle target envronment Here are some smulaton results. The parameters used n the smulaton are lsted n Table. Table : Smulaton parameters Sub-chrp bandwdth B MHz Pulse wdth T us Intal carrer frequency f.4ghz Increment of carrer frequency f 6MHz Number of carrers N Samplng resoluton R s.37m Sngle pont unambguous range R I.m Fne resoluton R.m R.m Target dstance After pulse compresson of baseband echo sgnal and RSVA, the result wthout Super-SVA s shown as Fgure 6, where the center of pulse locates on xmd m, and both of the frst zero pont locate on x.63m and x 8m. Snce left Super-SVA rght RSVA Target extracton HRRP E-ISSN: Volume 3, 4

5 xmd xleft 3.37 RI, there s more than one samplng pont, whose vald zone contans target, between x md and x left. Smlarly, t s the same between x md and x rght. 8 7 X: Y: Z: 79.9 dfference results from the error produced by samplng resoluton. However, the wdth of target wthout Super-SVA s c B 3m, ths shows that the wdth of target s compressed and has been smaller than R I. Therefore, only one vald zone can be pcked up. 6. X:.e+7 Y: X:.63 Y: Z: X: 8 Y: Z: Coarse dstance dmenson/m Fg.6: The ampltude dagram of coarse dstance dmenson wthout Super-SVA - X: 4e+7 Y: Frequency/Hz x 7 Fg.8: The Spread spectrum dagram wth Super-SVA 8 7 X:.3 Y: X: Y: Z: X:.63 Y: X: 7.63 Y: Dstance/m Fg.7: The HRRP wthout Super-SVA Fgure 7 shows the HRRP wthout Super-SVA, whch had a false target on each sde of target locaton R.3m, respectvely. And there s the dstance of R I from the real target to false targets. In Fgure 8, the blue profle represents the spectrum wthout Super-SVA after pulse compresson, whose bandwdth s MHz, and the red profle represents one wth Super-SVA, whose bandwdth s 8MHz. Obvously, the bandwdth s extended by 6% of the orgnal sgnal. The result wth Super-SVA s shown as Fgure 9, two frst zero ponts locates on xleft.7m and xrght 6.88m, so the wdth of target s.6m. In fact, the theoretcal wdth of target should be.87m for B 8MHz, the X:.7 Y: Z: X: 6.88 Y: Z: Coarse dstance dmenson/m Fg.9: The ampltude dagram of coarse dstance dmenson wth Super-SVA X:.3 Y: Dstance/m Fg.: The HRRP wth Super-SVA E-ISSN: Volume 3, 4

6 It can be seen from Fgure that the false targets n both sde of real target have dsappeared. That means that the false targets generated by pseudo peaks can be removed effectvely by usng Super-SVA X: 9. Y: 79.9 X:.3 Y: Smulaton for mult-targets envronment We assume that three target dstances are R 9.m, R.m, R3.7m and RCS, RCS.6, RCS3.3, respectvely. The other parameters are the same as table. We can see from the smulaton results that weak targets and false targets s dffcult to be dstngushed, n mult-target envronment, as shown n Fgure (a) and. (a). Implementng Super- SVA on mult-carrer chrp, we can elmnate false target after RSVA and target extracton, as shown n Fgure (b) and Fgure (b) Dstance/m (a) X:.7 Y: 37.3 X: 9. Y: 343 X:.3 Y: 83.6 X:.7 Y: Fne dstance dmenson/m Fne dstance dmenson/m (a) 3 4 Coarse dstance dmenson/m 3 4 Coarse dstance dmenson/m (b) Fg.: The dmenson range profle under B< f. (a) The result wthout Super-SVA (b) The result wth Super-SVA Dstance/m (b) Fg.:The HRRP wthout Super-SVA (a) and wth Super-SVA (b) 6. Concluson Ths paper analyzes the causes of pseudo peaks generaton on HRRP for mult-carrer chrp. Super- SVA s appled on mult-carrer chrp to decreases pulse wdth by bandwdth extrapolaton. In target extracton, t can ensure that there s only one vald zone n the wdth of pulse n order to avod the false peaks. Compared wth the orgnal process, the algorthm can avod pseudo peaks and mprove target resoluton, just usng Super-SVA algorthm before sdelobe suppresson. Wth the smulaton n sngle target and multple targets envronment, the results confrm the valdty of the algorthm. References: [] Zhang Mng-you. The Conspectus of Integrated Radar-EW-Communcaton. Bejng: Natonal Defense Industry Press,, pp [] L Xao-bo,Yang Ru-juan and We chen. Integrated Radar and Communcaton Based on E-ISSN: Volume 3, 4

7 Multcarrer Frequency Modulaton Chrp Sgnal. Journal of electroncs &nformaton technology, Vol.3, No., 3, pp.46-4 [3] Yang Mng-le, Zhang Shou-hong,Chen Ba-xao and Zhang Huan-yng. A Novel Sgnal Processng Approach for the Mult-Carrer MIMO Radar. Journal of electroncs &nformaton technology, Vol.3, No., 9, pp.47-. [4] Long Teng. Doppler Performance Analyss of Frequency Stepped Radar Sgnal, Journal of modern radar, Vol.8, No., 996, pp [] Xong Zhang-lang, Sh Xang-quan,Wang Zhhua and Zhao zhao. Analyss of Multcarrer Radar Sgnal, Journal of modern radar, Vol.9, No., 7, pp [6] Long Teng,L Dan and WU Qong-zh. Desgn Methods for Step Frequency Waveform and the Target Pck-up Algorthm. Journal of systems engneerng and electroncs, Vol.3, No.6, pp.6-3. [7] L Dan and Long Teng. Target s Redundance Removed Algorthms of Step Frequency Radar. Journal of electroncs, Vol.8, No.6, pp [8] Le Wen,Long Teng and Han Yue-qu.Novel Sgnal Processng Methods for Movng Targets n Stepped Frequency Modulated Radar. Journal of electroncs, Vol.8, No.,, pp [9] Zhang Huan-yng, Zhang Shou-hong and L Qang. Target Extractng Algorthm and System Parameter Desgn n Stepped Frequency Modulated Radar. Journal of electroncs, Vol.3, No.6, 7, pp.3-8. [] Long Teng,Mao Er-ke and He Pe-kun. Analyss and Processng of Modulated Frequency Stepped Radar Sgnal. Journal of electroncs, Vol.6, No., 998, pp [] Zhang Huan-yng, Zha W S. Apply super-sva to stepped-frequency chrp sgnal processng based on dechrp method, nd Asan-Pacfc Conference on Synthetc Aperture Radar. X an: IEEE AESS and IEEE GRSS 9,: [] NI Chong,WANG Yanfe, XU Xanghu,et al, A super-resoluton algorthm for synthetc aperture radar based on modfed spatally varant apodzaton. Scence Chna (Physcs Mechasncs & Astronomy), Vol.4, No.,, pp [3] C. Castllo-Rubo, S. Llorente-Romano and M. Burgos-García, A new robust SVA method for every samplng rate condton, IEEE Trans. ons on Aerospace and Electronc Systems, Vol.43, No., 7, pp.7-8 Acknowledgments Ths work was supported by Natonal Natural Scence Foundaton (project 6377, project 6366) of Chna, and Foundaton of Key Lab. of Cogntve Rado & Informaton Processng, the Mnstry of Educaton n Chna (project 3ZR8), also supported by Scence and Technology on Informaton Transmsson and Dssemnaton n Communcaton Networks Lab. (Open project KX36 / ITD-U33). E-ISSN: Volume 3, 4