PLA University of Science and Technology, Nanjing, Jiangsu, China

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1 016 d Iteratioal Coferece o Mechaical, Electroic ad Iformatio Techology Egieerig (ICMITE 016) ISB: A Improved Iterferece Suppressio Algorithm Based o Regular WPT i the DSSS Satellite Commuicatio System Yaghui Tog, Daoxig Guo, Fagju Liu, Heg Wag PLA Uiversity of Sciece ad Techology, ajig, Jiagsu, Chia sagfg@163.com Keywords: satellite commuicatios, Fourier trasform, DSSS, wavelet pacet trasform, iterferece suppressio Abstract. Direct Sequece Spread Spectrum (DSSS), which is a typical spread spectrum techology with the characteristic of ati-jam, is widely used i satellite commuicatio systems. evertheless, its processig gai is always limited because there are some restrictios o badwidth ad techiques i a practical system. Whe the iterferece is over threshold, it will lead to performace degradatio Trasform domai processig techology does improve the system's atiiterferece ability. Fourier trasform possesses a certai aalyzig ability i the time ad frequecy domai, ad wavelet pacet trasform has a better oe. Both of their results of sigal processig are ot satisfied due to the limited capability of the iterferece detectio ad suppressio. Through comparig ad summarizig the traditioal algorithm, a ovel iterferece suppressio algorithm which combies wavelet pacet trasform with Fourier trasform is put forward i this paper. Simulatio results reveal that the proposed iterferece suppressio algorithm sigificatly improves the ati-jammig capability the DSSS satellite commuicatio system Itroductio Spread spectrum commuicatio is a emergig high commuicatio techology. It is widely applied to military commuicatio systems because of its strog ati-jammig ability ad multiple accessig performace. However, the ati-iterferece capabilities of DSSS system is limited to the processig gai. The performace of the system largely degrades whe the iterferece power is higher tha the jammig margi. It is of great sigificace to employ sigal processig techiques to improve the ati-jammig performace of DSSS system. Curretly, two classes of iterferece suppressio schemes have bee extesively used: time domai processig techiques [1,] ad trasform domai processig structures [3,4]. Time domai processig techiques ca elimiate the arrowbad iterferece completely because it estimates the iterferece exactly ad is miused from the received sigal ad the iterferece free DSSS sigal is left. But it eeds a covergece time to reach the optimal solutio, which is appropriate for slow-altered iterferece. O the other had, the trasform domai suppressio ca quicly trac the chagig iterferece, such as Fourier trasform ad Wavelet pacet trasform, by maig use of the differet characters which is displayed i frequecy domai ad the suitable algorithm to detect ad suppress iterferece. As a sigificat algorithm i trasform domai, Fourier trasform plays a importat role i trasformig time-domai sigal of spread spectrum to frequecy-domai sigal, which provides us a easier way to detect ad suppress the iterferece [5]. Compared with the Fourier trasform, wavelet pacet trasform has a more superior performace--it ca trac the spectrum varieties of iput sigal, ad the the iterferece is localized i a defiite frequecy domai. So the applicatio of wavelet pacet trasform to iterferece-excisio has aroused itesive iterest. Through comparig ad summarizig the traditioal algorithm, a ovel iterferece suppressio algorithm which combies wavelet pacet trasform with Fourier trasform is put forward i this paper. Firstly, we use Fourier trasform to detect ad suppress iterferece primarily before sigal recostructio. The, we mae further judgmets ad suppressio o the recostructed sigal by usig wavelet pocet trasform i order to elimiate residual iterferece better. 439

2 I. System model The iterferece suppressio ad oise suppressio model, which is built based o Fourier trasform ad wavelet pacet trasform, is show i Fig. 1. The sigal from the groud receiver usually icludes spread spectrum sigal compoet, arrowbad iterferece ad oise r ca be expressed as: compoets. The received sigal r sj (1) where the s deotes spread spectrum commuicatio sigal usig the BPSK modulatio, J presets the arrow-bad iterferece sigals, deotes the additive white Gaussia oise sigal with a mea zero ad the variace. Thus, the sigal s based o direct sequece spread spectrum system ca be expressed as: s Ps0 Pcos0 (1) where P represets power level of the spread spectrum sigal, is the biary iformatio bits, s0 P is the spreadig sequece, 0 is carrier frequecy, is the phase. Iformatio iput Upli Iformatio output Satellite traspoder iterferece Fourier trasform Trasform domai sigal processig Wavelet pacet Atitrasform Orietatio ad iterferece suppressio Orietatio ad iterferece suppressio Iverse Fourier trasform Wavelet pacet trasform Figure 1. Schematic of DSSS iterferece suppressio satellite commuicatio based o Fourier trasform ad wavelet pacet trasform. II Theoretical aalysis (1) Fourier trasform aalysis basic The arrowbad iterferece is detected ad suppressed by FFT based o the power distributio differece betwee itself ad the DSSS sigal i frequecy domai. Discrete Fourier Trasform (DFT) ad its iverse trasform (IDFT) are defied usig the followig sequece of fuctios with recursio: 1 j 1 W 0 0 X( ) x( ) e x( ), 0,1,..., 1 (3) j 1 x ( ) X( e ) X( ), 0,1,..., 1 0 W (4) 0 where it requires multiplicatios ad 1 complex multiplicatios to calculate a X. The amout of calculatio is so huge that Fast Fourier trasform is itroduced. The x( ) sequece is divided ito a eve sequece x 1 ( ) ad a odd sequece x ( ), ad the legth of them is / : x( ) x ( ) x ( ) (5) the 1 440

3 1 (1) X( ) x ( ) W x ( ) W, 0,1,..., 1 (6) Due to W W, / 1 1 / / X( ) x ( ) W x ( ) W X ( ) W X ( ), 0,1,..., 1 (7) where 1 ( ) X ad X ( ) are DFT of / correspodig to x ( ) ad x ( ). Both of X ( ) ad 1 1 X ( ) are the cycle of /, ad W / is equal to X( ) X1( ) W X( ), 0,1,..., / 1 (8) X( ) X1( ) W X( ), 0,1,..., / 1 (9), W X ca be give as: () Wavelet pacet aalysis basis of DSSS sigal 1) Theoretical calculatio Wavelet pacet trasform has a excellet localizatio features i time-frequecy ad multiresolutio aalysis ability. Whe the iterferece chages i real-time, the iterferece will be located quicly ad efficietly i a limited sub-bad ad the will be elimiated through the relevat suppressio algorithm. The trasform process of Wavelet pacet is defied usig the followig sequece of fuctios with recursio: U t h U t U t g U t (10) where 1 Z Z U0 t is the scalig fuctio of t, 1 t, U t, Z is ow as Wavelet Pacet Group of U0 t, g 1 hl 1, Z U t is the mother wavelet of h, Z ad respectively represets a low-pass filter coefficiet group ad high-pass filter set of coefficiets of quadrature mirror filters QMF with supportig legth L, ad satisfy the followig coditio: hahb ab, Z h Z (11) Wavelet pacet is i discrete form i practical applicatios. A followig recursive discrete wavelet pacet trasform was give by C.K.Chui[6]: 441

4 Sl 1 i hisl z 1 Sl 1 i gisl z (1) The correspodig iverse discrete wavelet pacet trasform is give as follows: S i h i S g i S l l1 l1 z z (13) where l represets the correspodig layers of wavelet pacet decompositio, idicates the lateral odes positio of the correspodig level; S represets the decompositio sequece of ode at the layer of l. The received sigal ca be separated to a uiform or o-uiform spectral subbad by exploitig wavelet pacet trasform. ) Wavelet decompositio As show i Fig., the received spread spectrum sigal is decomposed by wavelet pacet of M-ary L 1 i order to get a rule wavelet pacet decompositio tree. The umber of odes is M i every layer, where M is a ary umber, L is the decompositio level. (0,0) l (1,0) (1,1) (,0) (,1) (,) (,3) (3,0) (3,1) (3,) (3,3) (3,4) (3,5) (3,6) (3,7) Figure. Diagram of rule wavelet pacet decompositio tree (decompositio level 3) ad the correspodig uiform badwidth of decompositio. he problem about precisio, cosistecy ad efficiecy of the algorithm still exists. Future wor will be focused o the developmet of a sophisticated method of derivig a optimized highprecisio matchig result uder the ifluece of oise. III. THE ITERFERECE POSITIOIG AD SUPPRESSIO ALGORITHM O THE BASIS OF WAVELET PACKET TRASFORM The steps of the proposed iterferece suppressio method of combiig Fourier trasform with wavelet pacet trasform are as follows: STEP 1 DSSS sigal is processed with FFT trasform, ad the value i of sigal spectral compoets ca be achieved ad the set a detectio threshold G whose value is the sum of the stadard deviatio ad the media of i. If i satisfies the coditio i G, it idicates that the value of the spectral compoet is maily composed of iterferece ad it will be set as zero directly; The remaiig compoets are without ay processig. Fially, the DSSS sigal will be recostructed. STEP As is show i the Fig., the recostructed DSSS sigal is evely decomposed to a rule wavelet pacet usig wavelet pacet trasform algorithm, ad the read coefficiet of each ode, calculate the variace of coefficiet ad get the miimum variace mi. Fially, reset the 44

5 coefficiet of each ode with scale factor / mi i, where i is the variace of each ode. It ca i is great, i i is close to be iferred that the iterferece will be sigificatly suppressed, whe the variace other words, the scale factor / mi i mi, the coefficiet of each ode will ot be atteuated. IV. THE SIMULATIO RESULTS AD AALYSIS is small. O the other had, whe the variace I the simulatio subsectio, we spread the sigal with a pseudo-radom sequece of legth of 3 ad the modulatio scheme is BPSK modulatio, wavelet pacet decompositio taes geeratio fuctio of db16 (Daubechies wavelets), M of M-Ary taes two, the chael of AWG is tae. Because the spreadig code legth is 3, the system has a certai ati-iterferece tolerace, i order to reflect the performace of the algorithm for iterferece suppressio well, jammig-tosigal ratio (JSR) must be greater tha dB10log db, jammig-to-sigal ratio is from 0 to 50dB i simulatio process. The maximum decompositio level of wavelet pacet tree is 5 to satisfy both the suppressio performace ad the complex of decompositio. The ormalized digital frequecies of two-toe iterferece to spreadig rate are ad 1.57, phase i 0, is uiform. From the Fig.3,it ca be see that iterferece deteriorate the performace of the DS system seriously.it is difficult to cotiue to commuicate ormally without suppressio,while the trasform domai processig structures ca effectively improve the performace of the system.from the graph,we ca ow that the ihibitory effect of traditioal FFT iterferece suppressio is the worst, ad the effect of the iterferece suppressio algorithm based o wavelet pacet trasform is better tha the former, while the effect of the ovel iterferece suppressio algorithm which combies wavelet pacet trasform with Fourier trasform is the best. From the Fig.4, The traditioal FFT iterferece suppressio has ihibitio o iterferece i a certai degree. Comparatively, the iterferece suppressio algorithm based o wavelet pacet trasform preset a more excellet performace, the ati-iterferece effect of the ovel iterferece suppressio algorithm which combies wavelet pacet trasform with Fourier trasform is the best P b 10 - P b 10-3 o iterferece suppressio FFT iterferece suppressio Wavelet pacet iterferece suppressio Proposed algorithm Oly the presece of oise JSR[dB] Figure 3. The BER performace compariso versus jammig-to-sigal ratio for differet algorithms (SR = 8dB) o iterferece suppressio 10-4 FFT iterferece suppressio Wavelet pacet iterferece suppressio Proposed algorithm Oly the presece of oise SR[dB] Figure 4. The BER performace compariso versus sigal-to-oise ratio for differet algorithms(jsr = 8dB). 443

6 COCLUSIO I this paper, a ovel iterferece suppressio algorithm which combies wavelet pacet trasform with Fourier trasform is proposed. Simulatio results reveals that the cosidered iterferece suppressio algorithm achieves a more excellet performace, sice it limits the iterferece to a few umber of sub-bads to avoid damage to the useful sigal ad the elimiates the iterferece. Therefore, our proposed algorithm sigificatly ehaces the ati-iterferece ability of DSSS satellite commuicatio system. REFERECES [1].K.C. Ho, Xiaoig Lu, Vadaa Metha. Adaptive Blid arrowbad Iterferece Cacellatio for Multi-User Detectio [J]. IEEE Trasactios o Wireless Commuicatios, 007,6(3): [].Rodrigo C. de Lamare, Marti Haardt, Raimudo Sampaio-eto. Blid Adaptive Costraied Reduced-Ra Parameter Estimatio Based o Costat Modulus Desig for CDMA Iterferece Suppressio [J]. IEEE Tras o Sigal Processig, 008, 56(6): [3].Chuhai Zhag, Liju Xue, Eryag Zhag. arrow-bad iterferece suppressio i trasform domai based o adaptive multi-threshold algorithm [J]. Joural of Electroics & Iformatio Techology, 006, 8(3): [4].P. Azmi ad M. asiri-keari. Geeralised Fourier trasform-domai techique for arrowbad iterferece suppressio i CDMA commuicatio system [J]. Electroics Letters, 001, 37(10): [5].Fa-e Dig. Ivestigatio ad Implemetatio of arrowbad Iterferece Excisio i DSSS System Based o FFT [J]. Sciece Techology ad Egieerig, 009, 9(10): [6].Xu Guo-pig 1, Jiag Mig-ya 1, Yua Dog-feg 1, ad Huag Chu-hua. Rejectio of arrowbad iterferece i DSSS systems based o adaptive wavelet pacet trasform [J]. Joural of Shadog Uiversity (Egieerig Sciece), 005, 35(0):