Performance Improvement of the DSRC System Using a Novel S and Π-Decision Demapper

Transcription

1 Wreless Sensor Network, 29,, do:.4236/wsn Publshed Onlne Noveber 29 ( Perforane Iproveent of the DSRC Syste Usng a Novel S and Π-Deson Deapper Abstrat Jeh MAR, Ch-Cheng KUO Departent of Counatons Engneerng, Yuan Ze Unversty, Tawan, Chna Eal: eejar@saturn.yzu.edu.tw Reeved Marh 3, 29; revsed June 2, 29; aepted June 23, 29 Based on the onstellaton dagra of the dfferent odulatons, a novel S and Π-deson rule s desgned for the analog deapper of the orthogonal frequeny-dvson ultplexng (OFDM) systes. The dedated short-range ounatons (DSRC) syste s hosen as an OFDM platfor to opare the perforane aong the proposed S and Π-deson deoder, hard-deson and soft-deson deoders. Sulaton results deonstrate that both the oplexty and perforane of S and Π-deson deapper used for M-ary quadrature apltude odulaton (QAM) OFDM syste an be greatly proved. The nuber of desons between the reeved sybol and onstellaton ponts an be splfed to look up table log2 M tes for M-ary QAM OFDM syste. Keywords: S and Π-deson Rule, Analog Deapper, DSRC Syste, OFDM. Introduton In the tradtonal dgtal ounaton syste where the dgtal Vterb deoder s used, the axu lkelhood deson rule s appled to both the deapper and dgtal hard-deson or soft-deson Vterb deoder. The soft-deson deoder s the reoended shee to be used n the dgtal Vterb deoder beause t provdes a odng gan over the hard-deson deoder [,2]. A splfed algorth of the soft-deson Vterb deoder for the 6-quadrature apltude odulaton (QAM) and 64-QAM onstellatons was presented n [3], whh allows the oplexty of the deapper to be antaned at alost the sae level for all the possble odes of HIPERLAN/2. In [4], t presented that for M-ary QAM systes the oplexty of the deapper n a soft-deson Vterb deoder used for bt-nterleaved oded odulaton an be sgnfantly lowered wthout oprosng the perforane. Four types of analog-nput Vterb deoders are desrbed and opared n [5], where the analog-to-dgtal onverter (A/D) onverter s nluded as part of a dgtal Vterb deoder. The analog rut flaws of the prevously used add-opare-selet (ACS) hps are nluded n the oparson. It onludes the analog Vterb deoder s able to outperfor the dgtal Vterb deoder, as well as aheve 3-bt or hgher deodng resoluton. In ths paper, we propose a new S and Π-deson deoder, where the S and Π-deson rules are desgned for the analog deapper of the orthogonal frequeny-dvson ultplexng (OFDM) systes. The ACS and path eory (PM) odules, whh are parts of the analog Vterb deoder ntrodued n [6], are used to perfor the Vterb deodng proess. The proposed S and Π-deson deapper obned wth the dgtal Vterb deoder s another alternatve to usng the S and Π-deson deoder. Beause analog Vterb deoder outperfors dgtal Vterb deoder and analog very-large-sale ntegraton (VLSI) pleentaton s n general ore area and power effent than dgtal pleentaton, the perforane oparson of the S and Π-deson deoder usng the dgtal Vterb deoder s not nluded n the paper. The dedated short-range ounatons (DSRC) syste [7], whh eploys OFDM tehnque, provdes wreless ounatons over a short dstane between the roadsde and hgh-speed oble rado unts or between hgh-speed vehles. The DSRC syste wll work n a oble envronent wth te-varyng haratersts. The te-varyng fadng effet of the DSRC syste ay not be effetvely opensated by usng the long sybol tranng and plot-based frequeny synhronzer [8]. The obned nterleavng and onvoluton odng, whh provdes the te dversty funton, ay further prove the perforane of the DSRC syste. We hoose DSRC syste as a bass for the perforane Copyrght 29 SRes.

2 J. MAR ET AL. 269 oparson aong dfferent deoders. Based on the analog-nput Vterb deoder, the odng gan of the DSRC syste aheved by replang the hard-deson and soft-deson deoders wth the proposed S and Π-deson deoder wll be onfred wth the sulatons. The rest of ths paper s organzed as follows. In Seton II, several hannel deodng shees are desrbed. The proposed S and Π-deson deoder s depted n detal for the bnary phase-shft keyng (BPSK), quadrature phase-shft keyng (QPSK), 6-QAM and 64-QAM OFDM sgnals of the DSRC systes. Seton III brefly desrbes the base band odel of the DSRC syste, whh s used to opare the bt error rate () perforane of the DSRC syste for the dfferent deoders. Sulaton results are gven n Seton IV, whh show the odng gan aheved by the proposed S and Π-deson deoder opared to the hard-deson and soft-deson deoders. Fnally, onlusons are drawn n Seton V. 2. S and Deson Deoder for the OFDM Systes In the tradtonal dgtal ounaton syste, the dgtal Vterb deodng uses a axu lkelhood rule whh s deal for an addtve whte Gaussan nose (AWGN) hannel. For a hard-deson Vterb deoder, the saples athng to a sngle bt of a ode word are quantzed to the two levels zero and one, a deson s ade as whether eah transtted bt n a ode word s zero or one. The odng gan of the soft-deson Vterb deoder for the hard-deson Vterb deoder n Raylegh fadng hannel nreases to about 2dB []. A four-level dsrete syetr hannel odel [2] s used for the soft-deson deoder. The deapper assgns one of four values to eah reeved sgnal. The path etrs n the Vterb algorth are alulated by weghtng the square of the Hang dstane between the soft-deson and the referene value. The four-level soft-deson Vterb deoder s alost exatly as shown for the harddeson ase wth the only dfferene beng the nreased nuber of path etrs. The blok dagra of the proposed S and Π-deson deoder for the OFDM syste s shown n Fgure, where t onssts of a S and Π-deapper and an analog Vterb deoder. The S and Π-deson deoder s a nonunfor nfnte-level quantzaton deoder. The S and Π-deson deapper assgns an analog oplex value to the analog Vterb deoder for eah reeved sgnal z(y) aordng to a obnaton of S and Π funtons, as shown n Fgure 2. The Π funton [9], as shown n Fgure 2(a), s defned as follows: Szy ((); MRM, R/2, M) forzy () M ((); zy RM, ) S( z( y); M, M R/2, M R) for z( y) M where z(y) represents ether ˆ I ( y ) or ˆ Q ( y) and y s the reeved sgnal after hannel opensaton. The onstellaton deoder estate the th sybol ganed through the reeved sgnal after hannel opensaton, ˆ ˆ ˆ Y ( y) I ( y) jq ( y), an be found n the sgnal spae dagras [] for BPSK, QPSK, 6-QAM and 64-QAM, respetvely, where the values of Iˆ ( y ) and ˆ Q ( y ) are serally deoded aordng to the odulaton type. The Π-funton goes to zero at the ponts () z( y) M R (2) whle the Π-funton goes to.5 at the rossover ponts R zy ( ) M (3) 2 Note the paraeter R s now equal to one, whh s the total wdth at the rossover ponts; paraeter M s now equal to zero, whh s the ddle pont of the Π-funton. The S-funton, as shown n Fgure 2(b), s defned as follows: S( z( y);,, ) for z( y) z( y) zy ( ) for z( y) 2 2( ) for z( y) 2 2( ) for z( y) For BPSK odulaton, the value of ˆ I ( y ) s n the nterval of (-,) of onstellaton dagra. Fro BPSK onstellaton dagra, the orgnal one bt bnary data (b ) s deded as ˆb usng the S-deson rule. Usng (4) for α=-, β= and γ=, the values of ˆb are produed as follows: ˆb =- for z(y) -; ˆb = for z(y) ; ˆb = S( z( y)) for -<z(y)<. For QPSK, the values of ˆ I ( y) and ˆ Q ( y) n the onstellaton dagra are found b n the ntervals (-, ). (2) The orgnal two-bt vetor = (b, b ) s also estated usng the S-funton as a deson rule. The S-deson rule n (4) for α=-, β= and γ= s used to deterne ˆb fro the reeved I-hannel sgnal part ˆ I ( y ) and deterne ˆb fro the Q-hannel sgnal part ˆ Q ( y). (4) Copyrght 29 SRes.

3 ' 27 J. MAR ET AL. I ˆ( x ) Q ˆ ( x ) I ˆ( x ) ˆ b () Qx ˆ( ) Fgure. Blok dagra of the S and Π-deson deoder. The onstellaton dagra of 6-QAM s shown n Fgure 3, where the values of ˆ I ( y ) and ˆ Q ( y ) for 6-QAM odulaton are found n the ntervals of (-3, -,, 3), respetvely. The essage ponts n eah quadrant are assgned wth Gray-enoded four-bt vetor b (3) = (b b b 2 b 3 ). The frst two bts (b b ) and last two ts (b 2 b 3 ) n b b (3) are transtted n I and Q-hannel, respetvely. Both frst two bts (boldfae) of the I-hannel fro left to rght essage ponts and last two bts (Noral) of the Q-hannel fro botto to top essage ponts have the sae 8-bt pattern n Fgure 3. The frst four odd bts are and the seond four even bts are an be estated by usng the S and Π ' -deson rule, respetvely, as shown n Fgure 4. The Π ' -deson rule as shown n Fgure 4(a) s defned as Π(x) S(x) x (b ) Fgure 2. (a) Π-deson rule; (b) S-deson rule. x (a ) z( y) -3 S( z( y);-3,-2,-) -3 z( y) - ' ( zy ( )) - z( y) - S( z( y);,2,3) z( y) 3 zy ( ) 3 (5) where the S-funton s defned n (4). The frst two bts ( ˆb ˆb ) and the last two bts ( ˆb ˆb 2 3 ) of the deapper output for eah essage pont are estated fro the values of ˆ I ( y ) and ˆ Q ( y ), respetvely. The S-deson rule s used to deterne ˆb and ˆb 2 and the Π'-deson rule s used to detern e ˆb and ˆb 3. The nuber of deson needed to obtan S and Π-deson deapper output n 6-QAM OFDM syste s four. The sae desgn prnple of the S and Π-deson deapper used for 6-QAM s appled for 64-QAM. The values of ˆ I ( y ) and ˆ Q ( y) n the onstellaton dagra for 64-QAM odulaton are found n the ntervals of (-7, -5,-3, -,, 3, 5, 7), respetvely. Slarly, the sx-bt vetor ˆ (4) b = ( ˆb ˆb ˆb ˆb ˆb ˆb ) for eah essage pont of 64-QAM odulaton s de Fgure 3. The onstellaton dagra of 6-QAM. ( z( y)).5 S( z( y)) z(y) (a) z(y) 2 3 (b) Fgure 4. (a) Π ' -deson rule; (b) S-deson rule for 6-QAM. Copyrght 29 SRes.

4 J. MAR ET AL. 27 " " terned usng the, 2 and S-deson rules, whh are desgned wth 24-bt pattern, whh s generated fro frst three bts fro left to rght essage ponts and last three bts fro botto to top essage ponts, for both I and Q-hannels. The frst 8-bt pattern an be deterned fro the S-deson rules as shown n Fgure 5(a). The seond ddle 8-bt pattern " an be estated b y usng the -deson funton whh s defned as z( y) -5 ( ( );-5,-4,-3) -5 ( ) -3 '' S z y z y ( z( y)) -3 z( y) 3 - S( z( y);3,4,5) 3 z( y) 5 z( y) 5 The thrd 8-bt pattern an be estated fro the " 2 -deson rule as shown n Fgure 5(b), whh s defned as z( y) -7 S( z( y);-7,-6,-5) -7 z( y) -5-5 z( y) 3 - S( z( y);-3,-2,-) 3 z( y) '' ( z( y)) zy ( ) 2 Szy ( ( );,2,3) zy ( ) 3 3 z( y) 5 - Szy ( ( );5,6,7) 5 zy ( ) 7 7 z( y) The frst three bts ( ˆb ˆb ˆb 2 ) and the last three bts ( ˆb 3 ˆb 4 ˆb 5 ) of eah essage pont are estated fro the values of Iˆ ( y) and Qˆ ( y), respetvely. The S-deson rule s used to deterne ˆb and ˆb 3, Szy (()) '' ( zy ( )) '' ( zy ( )) (a) z(y) () Fgure 5. (a) S-deson rule; (b) deson rule for 64-QAM. (b) '' -deson rule () (6) (7) '' 2 - " the -deson rule s used to deterne ˆb and ˆb 4 " and the 2 -deson rule s used to deterne ˆb 2 and ˆb 5. The nuber of desons needed for S and Π deapper n 64-QAM OFDM syste s sx. It s onluded that for Gray enoded M-ary QAM OFDM systes, the nuber of desons for analog S and Π-deapper an be redued to log2 M. If the S, Π, Π' and Π '' deson rules are alulated and stored n the table, eah deapper deson an be splfed as to look up table. The analog Vterb deoder desgned n Fgure s a 64-state deoder wth a trae bak length of 24, 48, 96 and 44 for BPSK, QPSK, 6-QAM and 64-QAM, respetvely. The analog oplex values of the onstellaton deodng vetors ( ˆ () b ) gan ed through the obnatonal S and Π-deson rules are nput to analog denterleaver and analog Vterb de- n turn. The analog denterleaver [] perutes oder the analog deapper output aordng to the swthng order perfored n the nterleaver. The analog Vterb deoder onssts of the analog ACS odule and a dgtal PM odule [6]. ACS odule perfors the alulaton of the analog path etrs. The transtted essage bts are deoded by PM odule usng the trae bak through the trells arhteture. The deodng algorth and the sequene ontrol for analog Vterb deoder rean dental wth the dgtal Vterb deoder. 3. Base Band Model of the DSRC Syste The blok dagra of the DSRC syste s shown n Fgure 6. The protool data unt (PDU) trans are appled to the physal layer for transsson. A 27 pseudorando sequene s used to srable the data out of the bnary sequene before the onvolutonal enodng. The purpose of the srabler s to prevent a long sequene of s or s to ad the tng reovery at the reever. The generator polynoal [] of the pseudorando sequene s 4 7 g( D) DD D (8) where D s the unt-delay. The dfferent ntalzaton value s deded by the frst 7 bts of eah PDU tran. The srabled data sequene s enoded wth a rate /2 on- as volutonal ode wth the generator polynoal g () (D) for the upper onneton and g (2) (D) for the lower onneton follows: () g ( D) D D D D (9) (2) g ( D) DD D D () where D s the unt-delay for onvolutonal odes and the lowest-order ter n the polynoal athes the nput stage of the shft regster. The punturng pattern [] s Copyrght 29 SRes.

5 272 J. MAR ET AL. X x x Bnary Data Srabler Convolutonal Enoder Inteleaver Mapper S/P Plot Inserton Y IFFT y Cyl Prefxng y P/S h Te-Varng Channel Output Data Desrabler Analog Vterb Deoder Analog DeInteleaver S and Π Deapper D/A P/S Channel Estaton FFT Reove CP S/P + AWGN w Fgure 6. The blok dagra of the DSRC base band odel. used to ake a rate 3/4 onvolutonal ode fro the rate /2 onvolutonal ode. A onvolutonal ode ay orret any well-spaed errors, whle beng unable to handle an error burst ntrodued by the fadng hannel. The blok nterleaver or denterleaver par [] appled to the DSRC syste an spread the burst error aross onto nonadjaent subarrers and apped alternately onto less and ore sgnfant bts of the onstellaton. After proessng the srabler, onvoluton enoder and nter- leaver, followed by appng to BPSK or QAM onstellaton ponts, the transttng data strea s dvded nto several parallel bt streas. An OFDM sgnal s bult usng an 64-ponts nverse fast Fourer transfor (IFFT). The nput vetor to the IFFT s gven as X [ X,, X,,..., X, ] T () N where X,k represents the k th subarrer of the th OFDM sybol and N s 64 n the DSRC syste. The IFFT output sgnal vetor s x [,,,,..., ] T x x, x N (2) where x,n s the n th saple pont of the th OFDM sybol. N n, k, exp( 2 ) IFFT k, N k x X j nk X (3) The yl prefxes (CP), whh are produed wth the opes of the last parts of the OFDM sybol, are prepended to the front of eah vetor x. The yl prefxng output sgnal vetor s represented as x T [ x,, x,,..., x, Nq] (4) [ x, x,..., x, x, x,..., x ]T N, q N, q N,,, N, where x n, s the n th saple pont of the th OFDM sybol and q s the length of the CP. Therefore, the reeved sgnal vetor s gven by [,,,..., T y x h w y y, y, Nq] (5) Where stands for lnear onvoluton, h and w are the hannel pulse response vetor and the addtve whte Gaussan nose (AWGN) vetor for the th OFDM sybol, respetvely. y n, s the n th saple pont of the th OFDM sybol n the th reeved sgnal vetor y. The hannel pulse response vetor h [ h h,...,h ] T an be represented by [2]:,,,, N h n, 2 j fd N Tn h e ( ), n N (6) where h s the oplex pulse response of the th OFDM sybol n the th path; f D s the th -path Doppler frequeny shft, whh ay ause nterarrer nterferene (ICI) for the reeved sgnals; T s the saple perod; λ s the delay spread ndex; and τ s the th -path delay te noralzed by saplng te. After reovng the CP, the reeved sgnal vetor y s T T y [ y, y,..., y ] [ y, y,..., y ],,, N, q, q, Nq (7) where y, n s the n th saple pont of the th OFDM sybol. The deodulated reeved sgnal vetor s Y,..., Y ] T [ Y,, Y,, N (8) where Y N 2 j nk N k, yn, e FFT yn, n (9) Suppose the guard nterval s longer than the length of the hannel pulse response, that s, there s no ntersybol nterferene between the OFDM sybols, the deodulated saple vetor Y an then be represented as [3] Y XH I W (2) H [,,,,..., H, ] T H H N (2) I [ I, I,..., I ] T (22),,, N sn( f T) H h e e, k N k, 2 j l j fd T D N fd T (23) Copyrght 29 SRes.

6 J. MAR ET AL. 273 N j2 ( fd kk) 2 j K e N k, k, 2 N K j ( fd kk ) N K k I h X e e, k N (24) where W FFT{ w}. H,k s reognzed as the aurate hannel frequeny response at the k th subarrer of the th OFDM sybol, whh s ndependent of the transtted sgnals X,k. I,k s the ICI part of the reeved sgnal at the k th subarrer of the th OFDM sybol, de- on all sub- pendng on the sgnal values X,k odulated arrers. On the hghway, the axu vehle speed s 2 k/hr. The DSRC syste needs ore robust frequeny and phase synhronzaton tehnology. Four unfor plot subarrers, whh are nserted n the postons of the 6 th, 2 th, 34 th, and 48 th subarrers for eah of the transtted DSRC data sybols, are appled for the DSRC reever to estate the frequeny and trak the phase of the reeved sgnals. A plot-based frequeny synhronzer ehans nludng least squares estaton (LSE) and nterpolaton s used for equalzng the plot sgnal-aded frequeny and phase synhronzaton [4]. 4. Sulatons Paket deteton, tng synhronzaton and oarse frequeny offset estaton of the DSRC reever are perfored aordng to the algorths provded n [5]. The sulatons fous on oparng the DSRC syste perforane aong the proposed S and Π-deson deoder, hard-deson and soft-deson deoders. The DSRC syste s spefed n the GHz ITS rado serves band. In a DSRC syste, one frae has OFDM sybols [7]. The total nuber of subarrers s 64 nludng four unforly dstrbuted plot subarrers and 2 guard subarrers. Aordng to the IEEE 82.p standard, the nu nput sgnal to nose rato values of the DSRC reever for BPSK OFDM (3Mbps), QPSK OFDM (6Mbps), 6-QAM OFDM (2Mbps), 6-QAM OFDM (8Mbps), 64-QAM OFDM (24Mbps) and 64-QAM OFDM (27Mbps) odulatons are 9, 2, 7, 24, 25 and 27dB respetvely, whh are used as a bass for evaluatng the reever perforane. The 3Mbps, 6Mbps, and 2Mbps data transsson rates are ade by usng /2-rate onvolutonal ode. The 8Mbps and 27Mbps data transsson rates are produed by usng 3/4-rate onvolutonal ode. The 24Mbps data transsson rate s produed by 2/3-rate onvolutonal ode. The quantzaton loss for the dgtal deodng s also onsdered n the deodng s of Fgures 9 and 2. Based on analyss results n [6], the quantzaton loss for onvolutonal deodng relatve to the ontnuous ase for two-level, four-level and eght-level dgtal Vterb deoders are evaluated as 7.73,.78, and.52 db wth the /2-rate onvolutonal ode;.43, 2.9 and.55 db wth the 3/4-rate onvolutonal ode. These losses rean roughly onstant aross the range of plotted. Referrng to the SPICE sulaton results n [6], the loss of real analog Vterb deoder wth.2 ACS nose and % oparator offset s less than.2 db roughly opared wth the deal analog Vterb deoders. Therefore, the ACS nose and the oparator offset wll not be onsdered n the followng sulatons. In the DSRC syste, the oherene te T s alulated by T se (25) f v v f D D D where f D =f D for = and 2. The axu Doppler shft vd s gven by fd, where v D s the axu vehle speed, f s the arrer frequeny, and s the veloty of lght. Jakes hannel odel [7] s used to produe a te- varyng Raylegh fadng hannel sulator. The effets of AWGN and arrer frequeny shft are also onsdered n the DSRC hannel. Sulatons are arred out for the vehle speed v D = 2 k/hr, delay spread τ = 2 nse, data sybols and dfferent deson Vterb deoder. Fgure 7 shows when the delay spread exeeds 5 nse, the severer frequeny seletve hannel fadng wll be aused by redung oherent bandwdth. The perforane of the DSRC reever wth BPSK OFDM (3Mbps), QPSK OFDM (6Mbps), 6-QAM OFDM (2Mbps), 6-QAM OFDM (8Mbps), 64-QAM OFDM (24Mbps) and 64-QAM OFDM (27Mbps) odulatons are shown n Fgure 8 2 respetvely. Fgure 8 shows the of QPSK OFDM odulatons for Vterb deoders usng three dfferent deson rules are redued to Delay spread = ns Delay spread = ns Delay spread = 2ns -5 Delay spread = 3ns Delay spread = 4ns Delay spread = 5ns Delay spread = 2ns Fgure 7. s of the DSRC syste usng plot subarreraded equalzer n dfferent delay spread for 6-QAM OFDM odulatons. Copyrght 29 SRes.

7 274 J. MAR ET AL. hard-deson four-level soft-deson S and -deson - hard deson four-level soft-deson eght-level soft-deson S and -deson Fgure 8. Coparsons of s of the QPSK DSRC syste (6 Mbts/se; 2k/h; ode-rate s /2) n ters of the dfferent deson deoders. less than -5 at the nu sgnal-to-nose rato (SNR), whh eets the requreents spefed n the IEEE 82.p standard. When the quantzaton loss for the onvolutonal deodng s onsdered, the of 6-QAM OFDM DSRC syste s shown n Fgure 9, where usng a hard- deson Vterb deoder s hgher than -5 at the nu SNR (7dB) for the ase of the 2Mbps data transsson rate. The 6-QAM OFDM DSRC syste usng the four-level and eght-level soft-deson and analog Vterb deoders wll be redued to less than -5 at the nu SNR (7dB), whh eet the requreents spefed n the IEEE82.p standard. It s noted the S and Π-deson deoders results n a odng gan of.5 db and 5.2dB opared to the eght-level and four-level soft-deson deoders, respetvely, when the quantzaton loss for the onvolutonal deodng s onsdered. Fgure shows the of 6-QAM DSRC syste usng the hard-deson de- annot be lower than -5, when the data trans- oder sson rate nreases to 8Mbps. The hard-deson urve has a floor that s generated by the hard-deson loss under the two-ray Raylegh fadng hannel envronent. The 6-QAM DSRC syste usng both the soft-deson deoder and the S and Π-deson deoders wll redue the to less than -5 at the nu SNR (24dB), whh eets the requreents spefed n the IEEE82.p standard. The S and Π-deson deoder has a.5db odng gan opared wth the four-level soft-deson deoder. Fgure shows the of 64-QAM DSRC syste under the ondtons of 8 Mbts/se data rate and 2k/h vehle speed annot be lower than -5 for three dfferent Vterb deoders. All three urves have the floors that are aused by the hgh-order 64- QAM odulaton DSRC syste operated under the fast fadng hannel. The of 64-QAM DSRC syste s shown n Fgure 2, where the quantzaton loss for the Fgure 9. Coparsons of s of the 6-QAM DSRC syste (2 Mbts/se; 2k/h; ode-rate s /2) n ters of the dfferent deson deoders wth quantzaton loss hard-deson four-level soft-deson S and -deson Fgure. Coparsons of s of the 6-QAM DSRC syste (8 Mbts/se; 2k/h; ode-rate s 3/4) n ters of the dfferent deson deoders hard-deson four-level soft-deson S and -deson Fgure. Coparsons of s of the 64-QAM DSRC syste (24 Mbts/se; 2k/h; ode-rate s 2/3) n ters of the dfferent deson deoders. Copyrght 29 SRes.

8 J. MAR ET AL hard deson four-level soft-deson eght-level soft-deson S and -deson Fgure 2. Coparsons of s of the 64-QAM DSRC syste (27 Mbts/se; 2k/h; ode-rate s 3/4) n ters of the dfferent deson deoders wth quantzaton loss. onvolutonal deodng s onsdered and the vehle speed redues to v = 2 k/hr. It showed the 64-QAM DSRC syste usng three dfferent deoders an be redued to less than -5 at the nu SNR (27dB), whh eets the requreents spefed n IEEE82.p standard. The S and Π-deson deoder results n a odng gan of 2.5 db, 5dB and 5 db opared to the eght-level soft-deson, four-level soft-deson and hard-deson Vterb deoders, respetvely, when the quantzaton loss for the dgtal Vterb deodng s onsdered. 5. Conlusons A new S and Π-deson rule s proposed for the analog deapper of the OFDM syste. The DSRC syste s hosen as an OFDM platfor to opare the perfor- ane of the S and Π-deson deoder, whh onssts of an S and Π-deson deapper, analog denterleaver and an analog Vterb deoder, wth hard-deson and softdeson deoders. Sulaton results show the odng g an of the S and Π-deson deoder relatve to four-level and eght-level soft-deson deoders are evaluated as 5.4dB and.5 db, respetvely, wth the 6-QAM DSRC syste; and 5dB and 2.5 db wth the 64-QAM DSRC syste when the quantzaton loss for the onvoluton deodng s onsdered. Eah analog deapper output an be deterned by lookng-up S and Π table log2 M tes for M-ary QAM OFDM systes. Many other applatons related to OFDM wth the proposed S and Π-deson deoder are possble. 6. Aknowledgeent The authors would lke to aknowledge gratefully the researh grants fro Natonal Sene Counl, Tawan, NSC E Referenes [] K. M. Lee, D. S. Han, and K. B. K, Perforane of the Vterb deoder for DVB-T n Raylegh fadng hannels, IEEE Trans. Consuer Eletron., Vol. 44, pp. 994, August 998. [2] S. B. Wker, Error ontrol systes for dgtal ounaton and storage, New Jersey, Prente-Hall, In., 995. [3] F. Tosato and P. Bsagla, Splfed soft-output deapper for bnary nterleaved COFDM wth applaton to HIPERLAN/2, n Pro. IEEE Int. Conf. Counatons, Vol. 2, pp , Aprl 22. [4] E. Akay and E. Ayanoglu, Low oplexty deodng of bt-nterleaved oded Modulaton for M-ary QAM, n Pro. IEEE Int. Conf. Counatons, Vol. 2, pp. 9 95, June 24. [5] K. He and G. Cauwenberghs, Perforane of analog Vterb deodng, 42nd Mdwest Syposu on Cruts and Systes, Vol., August 999. [6] K. He and G. Cauwenberghs, Itergrated 64-state parallel analog Vterb deoder, ISCAS 2, Vol. 4, May 2. [7] Standard Spefaton for Teleounatons and Inforaton Exhange Between Roadsde and Vehle Syste 5Ghz Band Dedated Short Range Counatons (DSRC) Medu Aess Control (Ma) and Physal Layer (PHY) Spefatons, IEEE82.p, Deeber 25. [8] S. Coler, M. Ergen, and A. Baha, Channel estaton tehnques based on plot arrangeent n OFDM systes, IEEE Trans. Broadast., Vol. 48, pp , Septeber 22. [9] J. Garratano and G. Rley, Expert Systes, 2nd. Edton, PWS Publshng Copany, 994. [] J. Heskala and J. Terry, OFDM Wreless LANs: A Theoretal and Pratal Gude, Sas, 2. [] V. C. Gaudet, R. J. Gaudet, and P. G Gulak, Prograable nterleaver desgn for analog teratve deoders, IEEE Trans. Cruts Syst. II, Vol. 49, pp , July 22. [2] D. G. Manolaks, V. K. Ingle, and S. M. Kogon, Statstal and adaptve sgnal proessng, MGraw-Hll, Eduaton, 2. [3] Y. Zhao and A. Huang, A novel hannel estaton ethod for OFDM oble ounaton systes based on plot sgnals and transfor-doan proessng, n Pro. IEEE VTC, Vol. 3, pp , May 997. [4] J. Rnne and M. Renfors, Plot spang n orthogonal frequeny dvson ultplexng systes on pratal hannels, IEEE Trans. Consuer Eletron., Vol. 42, No. 4, pp , Noveber 996. [5] IEEE 82.a, IEEE standard for Wreless LAN Medu Aess Control (MAC) and Physal Layer (PHY) spe- Vol. 7, No. 9, pp , Sep- fatons, 999. [6] M. R. G. Butler and A. R. Nx, Quantzaton loss for onvolutonal deodng n Raylegh-fadng hannels, IEEE Coun. Lett., teber 23. [7] W. C. Jakes, Mrowave Moble Counatons, New York: IEEE Press, 974. Copyrght 29 SRes.