Application Not AN116A Ap 11, 1997 SystVi Y E L A N I X A Dict Squnc Spad Spctu (DSSS) syst ith a Tansittd Rfnc using th32-bit vsion of SystVi by ELANIX. Intoduction Th pupos of this syst is to sho ho SystVi along ith th RF/Analog libay ay b usd fo th folloing 1 aas of dsign: 1. snt a sipl xapl of a Dict Squnc Spad Spctu (DSSS) syst that has both a tansitt and a civ that oks ith a path loss of to 1 d. 2. Although it is an infficint us of th availabl spctu, a tansittd fnc syst is usd to siplify th civ in this syst. 3. Th filts, aplifis, liiting aplifis, and ixs usd in th syst hav thi paats st to valus psntativ of Wilss Local Aa Ntok (WLAN) chip sts that a psntly availabl. 4. A Sufac Acoustical Wav (SAW) filt is quid in both th tansitt and th civ. Th spons of th SAW filts is siulatd by th custo dsign of to Finit Ipuls Rspons (FIR) filts. 5. A syst ith typical fquncy xts of 1 MHz and 2.4 GHz is scald to 1 MHz and 35 MHz. This ill pit a fast siulation. Although th us of a tansittd fnc, th odulato, and th dodulato usd in this xapl a not consistnt ith th IEEE 82.11 spcification, so potions of th spcification a ptinnt: 6. A spading cod of 11 MHz is usd. This sults in a channl idth of 22 MHz. 7. A data at of 1 MHz is usd. This givs a atio of 11:1 (cod:data). 8. To channls a opatd at th sa ti, at a spacing of 3 MHz. (Th tansittd fnc syst quis th tansitt to us to tansitting channls at th sa ti. Th 82.11 spcification allos fo to indpndnt systs opating at th sa ti, ithout intfnc, at a channl spacing of 3 MHz.) 9. This xapl confos to th IEEE 82.11 spctal ask quints fo tansission. Th sid lob is at last 3 d don fo th ain lob. 1. Th output po of ach channl is +18 d. Dtaild Dsciption of th Siulation A hypothtical xapl of a Dict Squnc Spad Spctu (DSSS) syst, using a tansittd fnc, and typical WLAN fquncis is shon in Figu 1. Fo o infoation about tansittd fnc systs plas f to Robt C. Dixon s book (Rf. 1). In addition to a syst dsciption, th book fs to an IEEE pap a study of ths systs (Rf. 2), and (Rf. 3) a U.S. patnt. To siplify th diaga, any of th aplifis and filts a not shon. A tansittd fnc syst dos not qui th us of a /9 dg odulato, but on ay b usd as long as th a spaat I and Q inputs and outputs. In Figu 2 th fquncis of ach stag hav bn st to b clos to ach oth, kping th oiginal 1 MHz and 11 MHz data and cod input fquncis. This ill allo th siulation to tak lss ti. Th 1st LO is st to a ath high 1 MHz. This allos th 2-pol filts to do a btt job of jcting th vaious LO fdthough fquncis. Also, th id band filts a nao than in Figu 1. Th n filt bandidths a id nough fo th to channls of intst, and th ducd bandidth hlps jct th vaious LO fdthough fquncis. Th full spad spctu syst is psntd in SystVi by th tokns in Figu 3. AN116A Ap 11, 1997 ag 1 of 12
Figu 1. A hypothtical xapl of a Dict Squnc Spad Spctu (DSSS) syst, using a tansittd fnc, and typical WLAN fquncis. To siplify th diaga, any of th aplifis and filts a not shon. Figu 2. Th xapl in Figu 1 is shon ith fquncy scaling to pit a fast siulation ti. Th 2 and 3-pol filt bandidths a not as id as in Figu 1. caus th vaious fquncis a clos togth, th filts a lss ffctiv in ducing out-of-band signals (th LO s). AN116A Ap 11, 1997 ag 2 of 12
Figu 3. SystVi s opning indo vi of th Dict Squnc Spad Spctu syst, shoing fou tasysts: A tansitt, and th civ don convsions. Th TRANSMITTER -- Modulato Th tansitt potion of th syst is containd in tasyst tokn (Figu 4). Th input cod and data a supplid by N (psudoando) tokns. Th spctu of th cod souc (and th EX-OR gat) is th classic sin_x / x that has its sid lob don 13 d fo th pak of th ain lob. To t th IEEE 82.11 spctal ask quints of a -3 d sid lob axiu, a 7.7 MHz 5-pol uttoth filt is usd to duc th sid lobs to b don to about 36 d blo th ain pak. Non-linaity of th vaious ixs and aplifis ill caus this 36 d valu to go toads th 3 d valu. To kp this spctal goth to a iniu in SystVi, an aplifi-ultipli tasyst is usd instad of th usual activ-ix tokn. Th haonics of th squa av LO of th activ ix can alias ith SystVi s sapl at. This can caus th sid lob to b only don about 25 d fo th pak (Rf. 4). Th activ-ix ill b usd in th civ potion of th syst h th -25 d sid lobs can b tolatd. In Appndix A, Figus 14, 15, and 16 sho ho th aplifi paats a st to achiv th dsid odulato output aplitud of both th ain lob and sid lob. Th output of th tansitt is shon in Figus 1 and 11. Each filt is pcdd by an attnuato to odl th filt s loss. An additional attnuato in ach path is usd to st th final output aplitud. Th FIR filts hav a cnt fquncy of 1 MHz. S Appndix fo th dsign dtails of th FIR filt. AN116A Ap 11, 1997 ag 3 of 12
SAW Filt Siulation Th sufac acoustic av (SAW) filt folloing th odulato is odld by using a 1 MHz FIR filt that is st fo a 2 d ippl in its pass band. Th 2 d valu causs th filt to hav a sooth oundd top instad of th usual flat top. Th paats usd in stting this filt (and th civ s 13 MHz filt) can b found in Appndix, Figus 17, 18, and Tabls 1 and 2. Th sids of ths FIR filts a not as stp as th intndd SAW filts. To allo fo a fast siulation 111 taps a usd. Mo taps ould poduc a shap cutoff filt and incas th siulation ti. Sinc th FIR filt has a 1 d loss, an attnuato is usd bfo th filt to inst th dsid nois figu into th syst. This attnuato-bfo-a-filt plan is usd fo ost of th filts in th syst. Th attnuato aft th FIR filt is usd to st th po output of th channl to +18 d. An aticl pint fo Micoavs & RF (Rf. 5) dtailing a o accuat siulation of a SAW filt is availabl fo ELANIX. IF to RF Convt An aplifi-ultipli tasyst is usd again instad of th usual activ-ix tokn (Figu 6). This ti th aplifi paats hav bn st to th data book valus fo th dsid ix. Usually, not all th paats quid by SystVi a listd in a data sht, and it ay b ncssay to convt a data sht input fncd paat to an output fncd paat. Fo hlp on dtining th valu of a issing paat, o input to output paat convsion, plas f to AENDIX C of th SystVi -- A Guid to th RF / Analog Libay. Tansitt o -ap and o Aplifi Folloing th IF to RF Convt is a chain of a pap, and a po aplifi intspsd ith th 2-pol filts. oth tansitting channls a sud to allo th us of only on attnuato in psnting th path loss. Continud on pag 6. AN116A Ap 11, 1997 ag 4 of 12
Figu 4. Th tansitt sction, including to ix-odulato tasysts and to ix-up-convt tasysts. Figu 5. Th paats fo th aplifi in th ix-odulato tasyst hav bn dtind xpintally by th syst shon in Appndix A. With a givn input, th output sid lobs a don th dsid aount. Figu 6. Th paats fo th aplifi in th ix-odulato tasyst hav bn st to th data book valus fo an up-convting ix. AN116A Ap 11, 1997 ag 5 of 12
Th Rciv -- LNA, and RF to IF Convt Th civ is copisd of th tasysts, on fo ach fquncy convsion. Th Lo Nois Aplifi (LNA) and fist don convt is shon in Figu 7. An activ ix is usd ith noal paats xcpt fo th -8 d LO lakag. It ncssay to duc aount of th LO lakag bcaus th fquncis of ach stag hav bn st to b clos to ach oth aking th stop bands of th vaious filts lss ffctiv. Liiting Aplifis and d-spading Mix Th input to th scond don convsion stag (Figu 8) is spaatd into to channls using to FIR filts (1 MHz and 13 MHz, s Appndix ). Dciato tokns (dciat by 2) a usd aft th FIR filts to duc th nub of sapls psnting th data. This also ducs th syst sapl at by 2. Th sult is a fast siulation and plotting ti. Th is a scond dciation by at th output of th tasyst. Sinc th liiting aplifis hav a high gain (45 d), th filts btn th aplifis a shon as having no loss in thi pass band. Th output of th d-spading ix is shon in Figu 12. Th 3d Don Convsion -- Costas Loop Th input signal (Figu 12) to th Costas Loop in Figu 9 is a 3 MHz cai odulatd ith th oiginal 1 MHz data. Th loops Voltag Contolld Oscillato (VCO) is th Fquncy Modulato (FM) tokn. Th VCO s gain paat (2.4 MHz/volt) has bn st to b consistnt ith a Mini-Cicuits TM OS-5 lina tuning VCO. Th output of th in-phas (I) and quadatu (Q) ixs is follod by a pai of p-filts. Ths sipl 2-pol filts ov ost of th high sid fquncis of th ixs, hil th lativly high 1 MHz cutoff fquncy allos th loop to lock-in apidly. Th pai of filts (5 khz 5-pol ssl) usd fo th sinks poduc y appaling plots. Th classic RC loop filt (fding th FM tokn) is follod by an invting op-ap gain of -1/4. (Whn using an op-ap ak su that th fdback capacito is an appopiat valu.) Figu 13 shos th ovlaid plots. Th Q output is a sall aplitud avy lin, th I output is th filtd data that follos th oiginal shap-dgd input data. Th input data has bn dlayd to lin up in this ovlay. Also, ith th Costas loop, th phas of th I output ay b ith o 18 dgs lativ to th input data. Noally, a data ncoding sch is usd that is insnsitiv to th /18 dg output of th Costas loop. Figu 7. Th fist don-convt of th civ includs th fist activ ix usd in th siulation. AN116A Ap 11, 1997 ag 6 of 12
Figu 8. Th scond don-convt of th civ fatus a pai of liiting aplifis in ach of th to channls. caus of th 3 dciato tokns in th syst, th output at of th syst is ¼ (256 6 sapls/sc) of th input at (1.24 9 sapls/sc). Figu 9. Th thid don-convt is a Costas-Loop Dodulato. Th dciatos in this syst a usd just to duc th nub of sapls displayd in th output plot (savs so coput oy and spds th plotting). AN116A Ap 11, 1997 ag 7 of 12
SystVi by ELANIX SystVi by ELANIX o Spctu of Tx output (d 5 ohs) o Spctu of Costas input (d 5 ohs) 275.+6 3.+6 325.+6 35.+6 375.+6 4.+6 6.+6 14.+6 22.+6 3.+6 38.+6 46.+6 1-1 -1 o o -2-2 -3 d -3 d -4-4 -5-5 -6-6 275.+6 3.+6 325.+6 35.+6 375.+6 4.+6 6.+6 14.+6 22.+6 3.+6 38.+6 46.+6 Fquncy in Hz (Rs = 62.5+3 Hz) Fquncy in Hz (Rs = 62.5+3 Hz) Figu 1. Th output of th tansitt. A 22 MHz id data-xo-cod channl at 32 MHz, and a 22 MHz id cod-only channl at 35 MHz. Th to attnuatos in th tansitt hav bn st to giv ths output aplituds. Figu 12. Th d-spad output of th 2nd don convsion, 2 MHz id cntd at 3 MHz. SystVi by ELANIX SystVi by ELANIX Moving Avg of 6 (N = Ovlay of Data input, I output, Q output 275.+6 3.+6 325.+6 35.+6 375.+6 4.+6 5.-9 2.5-6 4.5-6 6.5-6 8.5-6 1.5-6 12.5-6 14.5-6 1 1.5 1 o -1 A 5.-3-2 p l i t d -3 u d -5.-3-4 -1-5 -6-1.5 275.+6 3.+6 325.+6 35.+6 375.+6 4.+6 5.-9 2.5-6 4.5-6 6.5-6 8.5-6 1.5-6 12.5-6 14.5-6 Fquncy in Hz (Rs = 62.5+3 Ti in Sconds Figu 11. foing a 5-point oving avag on th spctu in Figu 1 claly shos th paks a at about -7 d. las s AENDIX C fo dtails on this aplitud. Figu 13. Th pfct shapd input data along ith th Costas loop I (data) and Q (na zo) output. AN116A Ap 11, 1997 ag 8 of 12
oductivity Th ti to un th full Tx/Rx siulation on a 166 MHz ntiu Using th 32-bit vsion 1.9 of SystVi by ELANIX, Inc. and Windos 95 is suaizd blo. Syst sapls Data bits Ti (inuts) Nub of Loops 16,384 16 1.9 1 131,72 512 15.4 1 Conclusion Th as of siulating a dict squnc spad spctu (DSSS) tansitting and civing syst has bn shon. SystVi by ELANIX is qually at ho ith fquncy hopping spad spctu (FHSS) systs. Mo Infoation Rfncs 1. R. C. Dixon, Spad Spctu Systs, Tansittd-Rfnc Mthods, pags 23-231, publishd by Wily-Intscinc. 2. R. M. Gagliadi, A Gotical Study of Tansittd Rfnc Counications Systs, IEEE Tans. Co. Tch., Dcb 1964. 3. R.W. Mifflin, and J.. Whl, Tansittd Rfnc Synchonization Syst, U.S. atnt 3,641,433 Fbuay 8, 1972. 4. SystVi xapl fils, ix-sin.svu and ixpn.svu, locatd in th folloing dictoy: c:\sysvu_32\exapls\rflib 5. Lay uns, Micoavs & RF (agazin) Fbuay 1997, Accuatly Modl SAW Filt havio pags 85, 86, 88, and 89. Fo o infoation on SystVi siulation softa plas contact: ELANIX, Inc. 5655 Lindo Canyon Road, Suit 721, Wstlak Villag CA 91362. Tl: (818) 597-1414 Fax: (818) 597-1427 o visit ou b ho pag ( http://.lanix.co ) to don load an valuation vsion of th softa that can un a siplifid vsion (dsss.v.svu) of this siulation as ll as oth us ntd dsigns. AN116A Ap 11, 1997 ag 9 of 12
AENDIX A Figu 14. Th tst syst usd to st th aplifi paats poducing a ain lob pak of -24 d and a sid lob that is don 36 d. SystVi by ELANIX SystVi by ELANIX o Spctu of Sink 3 (d 5 ohs) Moving Avg of 1 (N = 25) 26.+6 34.+6 42.+6 5.+6 58.+6 66.+6 74.+6 26.+6 34.+6 42.+6 5.+6 58.+6 66.+6 74.+6-1 -1-2 -2-3 -3 o o -4-4 d -5 d -5-6 -6-7 -7-8 -8 26.+6 34.+6 42.+6 5.+6 58.+6 66.+6 74.+6 26.+6 34.+6 42.+6 5.+6 58.+6 66.+6 74.+6 Fquncy in Hz (Rs = 25.+3 Hz) Fquncy in Hz (Rs = 25.+3 Hz) Figu 15. Th output spctu of th ix shoing a spctal lin at ach null du to th aplifi s Out I2 t. Figu 16. foing a 25-point oving avag on th spctu in Figu 17 claly shos that th sid lob is don 36 d. AN116A Ap 11, 1997 ag 1 of 12
AENDIX Figu 17. Th SystVi FIR dsign indo. In anoth dsign indo, a Haing indo is applid to th dsign. Figu 18. Th sulting sooth ounding of th top du to using a 2 d ippl facto in th dsign indo. aats fo th to diffnt FIR Filts.782.918.136.1172 Rlativ fq. (Faction of sapl at) 8 94 16 12 Actual fq. (MHz) 1.2 Gain in d at cnt fq. -45 Out of band loss in d, lo sid -45 Out of band loss in d, high sid 2 Rippl in d 1 Rcondd taps 111 Taps usd Us Haing indo Rsulting bandidths: -3 d +/- 8.5 MHz -45 d +/- 3 MHz Tabl 1. SystVi paats fo th 1 MHz FIR filt.175.1211.1329.1465 Rlativ fq. (Faction of sapl at) 11 124 136 15 Actual fq. (MHz) 1.2 Gain in d at cnt fq. -45 Out of band loss in d, lo sid -45 Out of band loss in d, high sid 2 Rippl in d 1 Rcondd taps 111 Taps usd Us Haing indo Rsulting bandidths: -3 d +/- 8.5 MHz -45 d +/- 32 MHz Tabl 2. SystVi paats fo th 13 MHz FIR filt AN116A Ap 11, 1997 ag 11 of 12
AENDIX C Figu 19. Th tst syst usd to hlp in stting th +18 d output aplitud of th tansitt. SystVi by ELANIX SystVi by ELANIX o Spctu of 2 (d 5 ohs) Moving Avg of 3 (N = 5) 5 1.+6 2.+6 3.+6 4.+6 5.+6 33.+6 34.+6 35.+6 36.+6 37.+6-5 -5-1 o -1 o -15-15 -2 d d -2-25 -25-3 -3-35 -35-4 1.+6 2.+6 3.+6 4.+6 5.+6 33.+6 34.+6 35.+6 36.+6 37.+6 Fquncy in Hz (Rs = 62.5+3 Hz) Fquncy in Hz (Rs = 62.5+3 Hz) Figu 2. Th +18 d ton is cntd on th spad signal. Figu 21. A zood-in vi, aft pfoing a 5-point oving avag on th spctu in Figu 2. Th pak has an aplitud of about -7 d. (Th 5- point oving avag has ovd th +18 d ton fo th plot.) AN116A Ap 11, 1997 ag 12 of 12