Implementation of Code Shift Keying signaling technique in GALILEO E1 signal

Transcription

1 Ileentaton of Code Shft Keyng sgnalng technque n GALILEO E sgnal Axel Javer Garca eña, are-laure Boucheret, Chrstohe acaau, Jean-Lous Dadaux, Lonel Res, Stéhane Corazza, Anne-Chrstne Escher To cte ths verson: Axel Javer Garca eña, are-laure Boucheret, Chrstohe acaau, Jean-Lous Dadaux, Lonel Res, et al.. Ileentaton of Code Shft Keyng sgnalng technque n GALILEO E sgnal. NAVITEC, 5th ESA Worsho on Satellte Navgaton Technologes and Euroean Worsho on GNSS Sgnals, Dec, Noordwj, Netherlands. -8,, <.9/NAVITEC >. <hal-5> HAL Id: hal-5 htts://hal-enac.archves-ouvertes.fr/hal-5 Sutted on 9 Se 4 HAL s a ult-dsclnary oen access archve for the deost and dssenaton of scentfc research docuents, whether they are ulshed or not. The docuents ay coe fro teachng and research nsttutons n France or aroad, or fro ulc or rvate research centers. L archve ouverte lurdsclnare HAL, est destnée au déôt et à la dffuson de docuents scentfques de nveau recherche, ulés ou non, éanant des étalsseents d ensegneent et de recherche franças ou étrangers, des laoratores ulcs ou rvés.

2 Ileentaton of Code Shft Keyng sgnallng technque n GALILEO E sgnal Axel Garca eña ENAC are-laure Boucheret ENSEEIHT Chrstohe acaau ENAC Jean-Lous Dadaux Thales Alena Sace Lonel Res CNES Stéhane Corazza Thales Alena Sace Anne-Chrstne Escher ENAC Astract One of ltatons of the current GNSS sgnals s ther low data nforaton rate. Ths low data nforaton rate does not allow, for exale, the transsson of addtonal coercal servces or the transsson of redundant eheers data. The Code Shft Keyng (CSK) s a sgnalng technque secfcally desgned to ncrease the transsson t rate of a sreadng sectru sgnal. Therefore, one soluton to ncrease the data nforaton rate of the GNSS sgnals s to ntroduce the CSK technque n the. In ths aer, the leentaton of the CSK technque nto GNSS sgnals s nsected through the develoent and analyss of the lelhood rato exresson of the ts transtted nsde a CSK syol, and through the dentfcaton of the est ang etween ts elongng to a word and ts transtted nsde a CSK syol. Fnally, the act of the CSK technque on the GALILEO E sgnal s analyzed y calculatng the CSK deodulaton erforance for a gven scenaro and the drawacs of the technque on the sgnal acquston and tracng rocesses. Keywords-CSK, deodulaton erforance, BER, WER, lelhood rato, CSK ang, CSK tracng, CSK acquston I. INTRODUCTION The current and future GNSS sgnals such as GS LC, GS L5, GS LC and GALILEO E sgnals have roved the deodulaton erforance of the orgnal GS L C/A sgnal y eans of new navgaton essage structures, the leentaton of ore advanced channel codes and the ntroducton of nterleavers. One last oton stll to e exlored n order to rove the deodulaton erforance of these sgnals s the ncrease of the teoral dversty of the transtted nforaton y ncreasng the reettons of the satellte eheers data n order to allow the recever to otan the nforaton ore qucly or to accuulate the nforaton for a lower requred deodulaton C/N threshold. oreover, the ass aret of the GNSS systes s stll growng and new alcatons as well as servces whch were not thought as useful or roftale n the ast can now resent theselves as great coercal oortuntes. The role wth these future servces, as well as wth the reetton of the eheers data, s the lac of avalale sgnal transsson t rate of the GNSS sgnals. In order to ncrease the GNSS sgnals data nforaton rate, we ntroduce a sgnallng technque secally desgned to ncrease the transsson t rate of a sreadng sectru sgnal. Ths technque s nown as Code Shft Keyng or CSK. The CSK sgnallng technque conssts n crcularly shftng each transtted RN code n order to reresent wth each crcularly shfted verson of the RN code a dfferent CSK syol ang a fxed quantty of ts. Therefore, f each erod of the data channel RN code s equal to the duraton of the data syol, the t transsson rate s ncreased roortonally to the nuer of ts aed y a CSK syol. In ths aer, frst we resent the fundaentals of the CSK sgnallng technque. After, we analyze the CSK technque y frst resentng ts general deodulaton erforance when usng hard decson outut deodulators. Second, we develo the theoretcal atheatcal exressons of the lelhood ratos of the ts aed y a receved CSK syol. Thrd, we analyze what s the otal ang etween the ts of the code words to e transtted and the ts aed y a sngle CSK syol. oreover, the deodulaton erforances of the GALILEO E sgnal when leentng the CSK technque for dfferent nuer of ts aed y a sngle CSK syol s resented for hard decson outut deodulators and for soft outut deodulators when the nforaton s rotected y an LDC channel code. Fnally, the drawacs ntroduced y the CSK leentaton to a odern GNSS sgnal on the acquston and tracng rocesses are resented. Note that the CSK technque s leented n the LEX sgnal of the Jaanese gloal ostonng servce, QZSS, as ndcated n the ulc released nterface secfcaton [] //$6. IEEE

3 II. CSK FUNDAENTALS The CSK fundaentals consst of the CSK defnton, of the atheatcal characterzaton, of the CSK odulator and deodulator locs schees and of the orthogonal CSK. A. CSK Defnton The Code Shft Keyng s a drect-sequence sreadsectru (DS-SS) sgnalng ethod whch overcoes the sreadng gan versus data rate ltatons []. The CSK s a for of -ary orthogonal sgnalng over a councaton channel [3] snce orthogonal sgnalng wavefors are used n order to transt log () ts. The secal characterstc of the CSK odulaton wth resect to the tycal -ary orthogonal sgnalng s that each wavefor s otaned fro a dfferent crcular hase shft of a sngle axal length RN code; where each crcular hase shft s ade y an nteger nuer of chs []. In other words, the CSK odulaton generally adots a axal-length sequence (-sequence) wth ts erod equal to as ts fundaental sequence. And each set of nut data ts s reresented y a sgnalng code, where each sgnalng code s otaned y cyclcally shftng the adoted fundaental sequence. Each cyclcally shfted sequence s assued to e a full erod verson of the fundaental sequence [4]. B. CSK atheatcal characterzaton Each sngle CSK syol odulates ts usng the CSK technque. The nuer of crcularly shfted versons of the fundaental code s equal to, where. The CSK fundaental code s called c d (t) and has a erod length equal to T whch sans over L chs. L s not necessarly equal to and the ch nterval s equal to T c. Fro ths fundaental code c d (t), the odulator generates the crcularly shfted versons of the code whch are called c d (t) to c d-+ (t). Each syol s reresented y dfferent ts, and the set of syols generates a -ary alhaet. oreover, each crcularly shfted verson of the fundaental code s also called wavefor. A atheatcal exresson of a generc crcularly shfted verson of the code s shown elow: c d x ([ t x Tc ] ( )) L Tc x.. [ ] c [ ] ( t) c od d c () d x d x odl () x : Integer nuer reresentng the code shft of the x th wavefor Once the wavefor has een selected, t s odulated at a carrer frequency, and after ts transsson through an AWGN channel the receved sgnal at the recever antenna outut can e odeled as: v ( t) s( t) + n( t) (3) s ( t ) A c ( t ) cos( t d x ω ) (4) v(t): Receved sgnal at the recever antenna outut s(t): Transtted sgnal at the transtter antenna nut n(t): AWGN wth ower equal to. C. odulator Bloc Schee The odulator schee of a CSK transtted sgnal can e odeled as shown elow: Fgure. CSK odulator Bloc Schee D. Deodulator Bloc Schee One ossle deodulator loc schee s resented. Ths deodulator loc uses Fourer and Inverse Fourer transfors [5] whereas another ossle deodulator schee uses atched flters, one flter for each crcularly shfted verson of the RN code. Nevertheless, the atheatcal exresson of the outut of each deodulator s the sae. Fgure. CSK Deodulator Bloc Schee Where w(t) s the receved sgnal at the RF/IF loc outut. Each coonent of the vector reresents the correlaton etween the receved sgnal and a crcularly shfted verson of the fundaental RN code. Assung that w(t) can e atheatcally odeled as: w ( t) s( t) + n( t) (5) n(t): Addtve narrow-and Gaussan nose wth a ower n B N B: RF/IF flter andwdth The atheatcal exresson of the outut of the CSK deodulator loc schee s: y ± + n x.. n x n : Indeendent narrow-and Gaussan noses wth ower equal to R s N R s : CSK syol transsson rate E. Borthogonal and Orthgonal CSK In addton to use crcularly cyclc shfts of the fundaental RN code to encode log () ts, we can also use the olarty of the fundaental RN code n order to (6)

4 a one extra t wth the sae nuer of crcularly cyclc shfts as done n the -ary orthogonal sgnalng technque. Therefore, n ths aer, we call orthogonal CSK the CSK ethod nsred fro the -ary orthogonal sgnalng technque and orthogonal CSK to the CSK ethod nsred fro the -ary orthogonal sgnalng. Note that a -ary orthogonal sgnalng ethod s equvalent to a /-ary orthogonal sgnalng ethod where the two olartes or sgns of the / dfferent syols are used. III. CSK ILEENTATION INTO A GENERIC GNSS SIGNAL In ths secton, the characterstcs of a CSK technque leented on a generc GNSS sgnal are analyzed. These characterstcs are the CSK deodulaton erforance when usng a hard outut decsons, the lelhood rato exressons of the CSK ts and the otal CSK ang etween the ts elongng to a word and the ts transtted nsde a CSK syol. A. CSK theoretcal hard decson deodulaton erfroance The CSK s a tye of -ary orthogonal sgnalng (OS) as verfed y [5]. Therefore, the hard deodulaton erforance n ters of BER as a functon of the E /N has already een calculated and largely coented n the lterature [6]. The sae can e sad for a orthogonal CSK wth resect to a - ary orthogonal sgnalng. The BER of an orthogonal CSK as a functon of the essage E s /N s equal to [6]: + y x / E S e dx ex y dy π π N E N BER E N S log ( ) E s /N : sgnal syol energy er syol to nose ower densty rato : roalty of orthogonal CSK syol error The BER of a orthogonal CSK as a functon of the E s /N s equal to [6]: π + ES / N π v+ E / N S e ( v+ ES / N ) BER x / dx / e v / dv (7) (8) (9) () () E s /N : sgnal syol energy er syol to nose ower densty rato : roalty of orthogonal CSK syol B. CSK lelhood ratos atheatcal exressons The ts transtted nsde the CSK syols wll very roaly e encoded wth a channel code n order to decrease the E /N requred to otan a desred BER. The ost owerful channel codes use soft nuts; therefore n order to leent these channel codes, the lelhood rato (LR) exressons of the ts transtted nsde a CSK syol have to e develoed. ) -ary orthogonal sgnalng lelhood rato exresson The lelhood rato (LR) of the transtted th t ( ) of a orthogonal CSK s defned as shown elow: ( LR( ) ( Y) Y) () Ths exresson when the transtted ts are equroale s equal to: ( Y LR ( ) ( Y ) ) (3) The nuerator and denonator roaltes cannot e drectly otaned snce the roaltes otaned fro the oservaton of the Y vector (CSK deodulator) deterne the roalty of recevng a syol rather than the roalty of recevng only one ndvdual t. The oserved roalty exresson for a gven grou of transtted ts or syol s shown elow. (, ) ( Y B ), (4) oserved Y, B (5),,,, B : Set of ts deternng the transtted syol x : Value of the x th t of the set B Fro equaton (4), the roalty of recevng Y when s equal to or to can e calculated as resented next: ( Y ) ( Y x,,,,, x, x ) (6) x xk ( x,,,, x, x ) Note that n equaton (6), the only suaton whch s not aled s the suaton havng as sundex x. The suaton havng as sundex x has to e nterreted as shown elow. ( x ( ) ( x ) ( ) + ( x ) ) ( ) Snce the ts are equroale, equaton (6) s slfed to: x x x ( Y ) ( x,,, x ), (7) Y (8)

5 The ndvdual ters of equaton (8) can e deterned snce they are the roalty of the Y vector oservaton when a deterned grou of ts, B, s transtted. Usng equaton (4), the revous exresson can e exressed as ( Y ) ( Y B n, ) n (9) B n,: Set of ts aed y syol n. The t of syol n s equal to. The condtoned roalty of the Y vector oservaton can e odeled as a roduct of the condtoned roaltes of the oservaton of each ndvdual Y vector coonent snce the Y vector coonents are ndeendent aong the: the nose of each Y vector coonent s ndeendent fro the nose of any other coonent. The condtoned roalty of the Y vector oservaton can e exressed as: ( Y B ) ( y B ) ( y B ) ( y B ) () Fro equaton (6), the condtoned roalty of each ndvdual coonent oservaton can e odeled as a Gaussan varale wth varance equal to, and wth a ean that deends on the transtted grous of ts, B n: the ean of the y coonent oservaton s equal to f the transtted grou of ts, B n, s aed y the -ary orthogonal syol ; n other words, f s equal to n. Otherwse the ean s. The roaltes of the oservaton of the Y vector coonents when the grou of ts, B n, s transtted are: ( y B n ) y ex πσ σ ex πσ σ ( y ) Therefore, exresson () s equvalent to: ( B n ) n n Y ex y ex ( y n ) πσ σ σ Fnally, equaton (9) can e wrtten as shown elow: ( Y x ) K( Y ) x K( Y ) ex πσ σ () () y ex σ (3) y (4) The suaton of the second ter of equaton (3) eans the suaton of all the y coonents whch reresent a syol, or grou of ts, B, havng x. Fnally, snce K(Y) has the sae value for and, the fnal exresson of the lelhood rato of the ts aed y a -ary orthogonal syol s: LR( ) y y ex ex σ σ (5) Fnally, an algorth to seed the ts lelhood rato calculaton s resented:. Calculatng and storng all the exonental values: T ex(y / ). Settng the value 3. For to - a. Calculatng the lelhood rato. T + T T -. T + T + + T -. LR( ) /. Calculatng the new T values. For to (/ ) T T + T + c. Settng the new value: / Ths algorth s llustrated and justfed n the fgure dslayed elow. In ths exale, 4 ts are odulated n a 6- ary orthogonal syol. Fgure 3. 6-ary orthogonal sgnallng exale - Bts lelhood rato calculaton for 4 ts ang an orthogonal sgnal ) -ary orthogonal sgnalng lelhood rato exresson In the case of a -ary orthogonal sgnalng, the search of the ts lelhood raton exresson s dfferent fro the t ndcatng the olarty of the transtted wavefor to the ts selectng the transtted wavefor. The atheatcal notaton for a orthogonal CSK ang s: R {,,, } β (6), {, B } R β (7) R : Set of nut ts for a orthogonal CSK syol : Value of the t settng the wavefor olarty B - : Set of - nut ts for a orthogonal CSK syol x : Value of the x th t of the set B - The lelhood rato exresson of the t settng the wavefor olarty s calculated usng equaton (3): ( Y β ) LR ( β) ( Y β ) (8)

6 In ths case, the oserved roalty at the deodulator outut s: (,,, ) ( Y R ) β (9) oserved Y, Therefore, denotng each dfferent grou of transtted ts aed y the /-ary orthogonal syol as B n and denotng each dfferent grou of transtted ts y the -ary orthogonal syol as R n, the condtoned roalty of the oservaton of the Y vector coonent y can e odeled as: ( y R n ) y ex πσ σ ex πσ σ ( y + β ) n n Consequently, exresson (Y R n) s equal to: ex πσ σ ( R n ) Y y ex β y σ / n (3) (3) The lelhood rato exresson of the t settng the wavefor olarty can e found fro equatons (9), (8) and (3): / / y ( ) ex y LR β ex σ σ (3) The lelhood rato exressons of the ts selectng the transtted wavefor are calculated tang nto account the roalty of havng receved the t equal to or equal to. (, ) ( β Y ) + ( Y, β ) ( β Y ) (, β ) ( β Y ) + ( Y, β ) ( β Y ) Y Y LR( ) β (33) The ters (Y, ) can e calculated as showed n equaton (9) usng equaton (4) for the -ary orthogonal sgnalng case. The only dfference s found when snce the value of y has ts sgn nversed n ths case. ( Y x, β β ) ( ) ( ) Y R n, x, β β n Thus, (Y, ) can e exressed fro (3) and (34) as: ( Y x, β ) K( Y, β ) x ex (.5 β ) σ y (34) (35) / K ( Y, β ) ex y πσ σ (36) As efore, K(Y,) has the sae value for and for. Therefore, the lelhood rato exresson s: / / y ex σ y ex σ LR( ) / y y + ex ex σ σ / y y ex + ex σ σ y ex σ y ex σ 3) Lelhood ratos atheatcal exresson verfcaton We have sulated the transsson of a CSK sgnal through an AWGN channel and we have calculated the BER usng hard decsons oututs and usng the lelhood rato exressons develoed revously. The sulatons show that all the nsected ethods rovde the sae BER as a functon of the sgnal E /N at the correlator outut. Ths eans that the revous CSK ts lelhood rato exressons are verfed as the equvalent soft outut ethod of the hard decson ethod defned y the lterature [6]. The deodulaton erforance of the transsson of a CSK sgnal through an AWGN channel when 8 ts are aed y a CSK syol s resented elow. Fgure 4 shows the BER as functon of the sgnal E /N at the correlator outut. Fgure 4. BER vs E /N for a transsson eloyng CSK syols whch a 8 ts The sae results have een otaned for 6 and ts aed y a CSK syol [7]. C. Source Words ang of a CSK odulaton The leentaton of a channel code on the ts transtted y a CSK odulaton ntroduces a new nterestng eleent of study: the CSK source word ang. The source word ang s defned as the dstruton etween the ts aed y each CSK syol and the ts elongng to the sae word: whch ts aed nto a CSK syol elong to a gven word A, whch ts elong to a gven word B, etc. Therefore, one queston to e ased s whch source word ang rovdes the lowest BER. In fact, the varance of the nuer of errors of a word transtted y a CSK sgnal deends sgnfcantly on the used CSK source word ang. And, as justfed next, t can e (37)

7 uch ore nterestng to have ether a low or a large varance deendng on the transsson channel. On one hand, f the varance s low and the error correcton caacty of the leented channel code s larger than the average nuer of errors, the channel code could correct alost all the words. On the other hand, f the varance s large and the error correcton caacty of the leented channel code s uch saller than the average nuer of errors, the channel code could correct soe words whereas wth a low varance no word should e corrected. The calculaton of the varance of the nuer of errors of a word transtted nsde CSK syols s ade n three stes. The frst ste s to calculate the roalty of havng n erroneous ts aong x ts elongng to the sae acet when the transtted CSK syol as K ts and has a roalty of error equal to. The atheatcal exresson of the roalty s gven next [7]: x n K x (38) δ K δ ( n) K x ( n K ) ( ) n + ( ) n x x (n): Drac delta functon The second ste conssts n calculatng the roalty of a word of L ts havng erroneous ts, the roalty of havng erroneous t, etc, untl the roalty of havng L erroneous ts. Ths second ste s ade usng atla snce t s the raw conaton of the roaltes exressed n (38). The thrd and fnal state s the calculaton of the average and the varance of the nuer of errors of a word transtted nto CSK syols usng the roaltes deterned n ste. Fnally, the CSK source word angs deternng the lowest and largest varance of the nuer of errors of a word transtted nsde CSK syols are deterned y nsectng the results of ste 3 for a CSK syol ang 8 ts. Fgure 5 show the desred varance as a functon of the sgnal E s /N for a word of ts. ang where all the ts transtted nsde a CSK syol elong to dfferent words. oreover, t can e oserved that the largest varance elongs to the ang where all the ts transtted nsde a CSK syol elong to the sae word. The sae results have een oserved for 4, 6, and ts aed y a CSK syol [7]. IV. CSK ILEENTATION IN THE GALILEO E SIGNAL The CSK leentaton on the GALILEO E sgnal conssts n alyng the CSK technque, the crcular shft of the RN code, on the data channel and n usng the lot RN code as synchronzer n order to dentfy whch crcular shft has een transtted. In ths secton, the hard decson outut deodulaton erforance of the GALILEO E sgnal s gven, the deodulaton erforance of the GALILEO E sgnal wth an leented LDC code s resented, and the CSK nfluence on the tracng and the acquston rocess s analyzed. A. CSK hard outut deodulaton of the GALILEO E The hard outut erforance of the GALILEO E sgnal wthout leented channel code s calculated fro the theoretcal exressons (8) and (). Ths calculaton assues that the sgnal C/N or E s /N s fxed for any nuer of ts transtted nsde a CSK syol whch eans that the E /N vares for the dfferent nuer of ts. The nuer of chs of the GALILEO E RN data code s 49 whch eans that a axu of ts are transtted wth an orthogonal CSK and a axu of ts are transtted wth a orthogonal CSK. The t transsson rate (R D ) s equal to 5 t/s. Fgures 6 and 7 show the BER of the GALILEO E sgnal for a hard decson deodulaton as a functon of the sgnal C/N at the correlator outut. Fro these fgures, t s oserved that due to the constant value of E s, a larger nuer of ts aed y a sngle CSK syol leads to a worse deodulaton erforance n ters of BER of the CSK odulaton n the GALILEO E sgnal. Fgure 5. Varance of the nuer of t errors of a word of ts transtted y 56-CSK syols wth dfferent CSK source acet angs Fro fgure 5, t can e oserved that the CSK source word ang whch otans the lowest varance of the nuer of errors of a word transtted nsde a CSK syol s the Fgure 6. BER vs C/N of the art of the GALILEO E sgnal leentng the CSK sgnallng technque for dfferent nuer of ts aed y an orthogonal CSK syol

8 Fgure 7. BER vs C/N of the art of the GALILEO E sgnal leentng the CSK sgnallng technque for dfferent nuer of ts aed y an orthogonal CSK syol B. CSK soft deodulaton erforance for GALILEO E The deodulaton erforance of the GALILEO E sgnal whch leents the CSK and whch has a channel code aled on the CSK nforaton ts s resented. Ths secton uses the lelhood exressons develoed n secton III.B. The t transsson rate of the sgnal s 5 ts/s. The sze of the nforaton word s 6 ts whch are encoded wth the LDC code of GS LC [8] resultng nto a coded word of ts. The orthogonal and orthogonal CSK are leented and the CSK source word ang rovdng the lowest and the largest varance are analyzed. For the latter ang, an nterleaver aled over the word s ntroduced n order to rea the urst of errors and, thus, to rove the deodulaton erforance. The next fgures show the BER of the GALILEO E sgnal leentng a CSK technque whch as 8 ts for each CSK syol as a functon of the sgnal C/N at the correlator outut. An deal estaton of the sgnal carrer hase and the code delay s assued. erforance dfference grows along the ncrease of the nuer of ts aed y a CSK syol as seen n [7]. oreover, t can also een oserved that the orthogonal CSK slghtly outerfors the orthogonal CSK, ut ths dfference decreases along the ncrease of the nuer of ts as seen n [7]. Fro fgures 6, 7 and 8, t can e oserved that for a BER equal to -6, the rovded gan etween a CSK confguraton ang 8 ts wthout a channel code and the sae confguraton ut wth the GS LC LDC code s aout 6.45 db for the orthogonal CSK and s aout 6.5 db for the orthogonal CSK. Ths gan decreases along the ncrease of the nuer of ts aed y a CSK syol as seen n [7] These gans can e coared to the gan ntroduced y the alcaton of the sae LDC code on a BSK sgnal wthout the CSK technque; ths gan s aout 8. db [7]. Fnally, the BER and WER of the GALILEO E sgnal leentng an orthogonal or a orthogonal CSK confguraton wth the source word ang rovdng the lowest varance and for dfferent nuer of ts aed y a CSK syol as a functon of the sgnal C/N at the correlator outut are resented. Fgure 9. BER vs C/N of the est GALILEO E sgnal CSK confguratons Fgure 8. BER vs C/N of dfferent CSK confguratons where each CSK syol as 8 ts when the sgnal s transtted through an AWGN channel Fro fgure 8, t can e seen that the CSK source word ang rovdng the lowest varance outerfors the ang rovdng the largest varance. Ths deodulaton Fgure. WER vs C/N of the est GALILEO E sgnal CSK confguratons Fro fgures 9 and, t can e seen that for any nuer of ts aed y a CSK syol, n order to otan a BER equal

9 to -6 or a WER equal to -3 we need a C/N larger than 34 db-hz. C. Drawacs of the CSK on the GALILEO E sgnal The an dsadvantage of the CSK technque leentaton on the GALILEO E sgnal s the constant shft of the data RN code whch does not allow the use of the data channel n the acquston and n the tracng rocess. ) Tracng rocess: The new GNSS sgnals are fored y two channels, the data channel and the lot channel, n order to avod the ltaton of the axal coherent ntegraton te osed y the data syol duraton. Ths eans that the tracng of new GNSS sgnals was thought to e ade only on the lot channel. oreover, we-off technques are also allowed y the data RN code leentng the CSK technque, snce the nowledge of the transtted ts deternes the next crcular shft of the RN code. The only dfference s that a larger quantty of ts ust e nown to e ale to aly the we-off technques. To su u, the tracng rocess s not affected y the leentaton of the CSK sgnalng technque. ) Acquston rocess: The acquston rocess of the GALILEO E sgnal s affected y the leentaton of the CSK technque snce oth channels, lot and data, are used to acqure the sgnal. In order to quantfy the act of the CSK technque on the acquston rocess, we have run soe sulatons whch calculate the average acquston te of the GALILEO E sgnal when we use oth channels to acqure the sgnal wthout leentng the CSK, when we use oth channels to acqure the sgnal leentng the CSK and when we only use the lot channel. The sulatons use a coherent ntegraton te of 4s, a non-coherent ntegraton te of s, correlators and only 9 syols out of the 5 syols transtted each second y the GALILEO E sgnal leent the CSK. Fro fgure, t can e oserved that when the CSK s leented, the sgnal has to e acqured only usng the lot channel. oreover t can e seen that for C/N larger than 9 db-hz, the GALILEO E sgnal s acqured faster usng only the lot channel than usng oth channels even when the CSK technque s not leented. Fnally, t can e seen that for an average acquston te of s, we requre an extra db of C/N when we only use the lot channel than when we use oth channels and the CSK s not leented. V. CONCLUSIONS In ths aer, the Code Shft Keyng sgnalng technque has een resented as a ossle oton for the future GNSS sgnals n order to ncrease ther data transsson rate. Fgure. Average acquston te for GALILEO E OS sgnal as a functon of the data + lot C/N Ths ncrease of the data nforaton rate could e use n order to transt addtonal coercal servces or n order to transt redundant eheers data whch wll reduce the C/N needed to otan a desred BER or WER. Dfferent deodulaton erforance of the GALILEO E sgnal has een calculated for dfferent CSK confguratons, and the CSK act on the tracng and acquston rocess has een analyzed. The lelhood rato exressons of the ts transtted nsde a CSK syol has een develoed. A fast algorth has een rovded for ther calculaton. ACKNOWLEDGENT A.G.. thans to CNES, TAS-F and TéSA for the jont fnancng of the research fellowsh. REFERENCES [] Jaan Aerosace Exloraton Agency, Interface Secfcaton for QZSS (IS-QZSS) Draft V., arch 9, [] A.Y.-C. Wong, and V. C.. Leung, Code-hase-Shft Keyng: A ower and Bandwdth Effcent Sread Sectru Sgnalng Technque for Wreless Local Area Networ Alcatons, IEEE Canadan Conference on Electrcal and Couter Engneerng, 997. [3] J.D. Endsley, and R.A. Dean, ult-access roertes of transfor doan sread sectru systes, In roceedngs of the 994 Tactcal Councatons Conference, Vol., Dgtal Technology for the Tactcal Councator, 994. [4] Y.-R. Tsa, -ary Sreadng Code hase Shft Keyng odulaton for DSSS ultle Access Systes, IEEE Transactons on councatons, Vol 57, No, Noveer 9. [5] G.. Dllard,. Reuter, J. Zedler and B. Zedler, Cyclc Code Shft Keyng: A Low roalty of Intercet Councaton Technque, IEEE Transactons on Aerosace and Electronc Systes, Vol. 39, No 3, July 3. [6] J.G. roas, Dgtal Councatons, 4th ed, cgraw-hll,, [7] A.J. Garca-ena, Otsaton of Deodulaton erforance of the GS and GALILEO Navgaton essages, Dssertaton, Insttut Natonal olytechnque de Toulouse,. [8] ARINC Engneerng Servces, Navstar GS sace Segent/User segent LC nterfaces, Draft IS-GS-8, Aug 4, 6