Performance Analysis of MIMO SFBC CI-COFDM System against the Nonlinear Distortion and Narrowband Interference

Transcription

1 Performance Anayss of MIMO SFBC CI-COFDM System aganst the onnear Dstorton and arrowband Interference YSuravardhana eddy Department of ECE JTUACEAnantapur AP E-ma: K ama adu Department of ECE JTUACEAnantapur AP E-ma: Abstract Carrer Interferometry Coded Orthogona Frequency Dvson Mutpexng (CI-COFDM) system has been wdey studed n mut-carrer communcaton system The CI-COFDM system spreads each coded nformaton symbo across a sub-carrers usng orthogona CI spreadng codes The CI-COFDM system shows the advantages of Pea to Average Power ato (PAP) reducton frequency dversty and codng gan wthout any oss of communcaton throughput On the other sde a great attenton has been devoted to Mut Input Mut Output (MIMO) antenna systems and space-tme-frequency processng In ths paper we focus on two Transmt (Tx)/one eceve (x) antennas confguraton and evauate the performance of MIMO OFDM MIMO CI- OFDM and MIMO CI-COFDM systems Space Frequency Boc Codng (SFBC) s apped to MIMO OFDM MIMO CI-ODFM and MIMO CI-COFDM systems For CI-COFDM reazaton dgta mpemented CI-COFDM s used n whch nformaton conventona s encoded CI code spreadng operaton and carrer aocaton are processed by IFFT type operaton From smuaton resuts t s shown that MIMO SFBC CI-COFDM reduces PAP sgnfcanty as compared wth that of MIMO SFBC CI-OFDM and MIMO SFBC OFDM systems In arrow Band Interference (BI) channe MIMO SFBC CI-COFDM systems acheve consderabe Bt Error ate (BE) mprovement compared wth MMO SFBC CI-OFDM and MIMO SFBC OFDM system Keywords- COFDM CI PAP MIMO SFBC IITODUCTIO Orthogona Frequency Dvson Mutpexng (OFDM) technque has been adopted as the standards n the severa hgh data rate appcatons for exampe European DAB/DVB (Dgta Audo and Vdeo Broadcastng) system and hgh-rate WLA (Wreess Loca Area etwors) such as IEEE8x and IPELA II OFDM system transmts nformaton data by many sub-carrers where sub-carrers are orthogona to each other and sub-channes are overapped so that the spectrum effcency may be enhanced OFDM can easy be mpemented by the Inverse Fast Fourer Transform (IFFT) and Fast Fourer Transform(FFT) process n dgta doman and has the property of hgh-speed broadband transmsson and robustness to mut-path nterference frequency seectve fadng owever OFDM sgna has hgh PAP because of the supermposton of mut- carrer sgnas wth arge number of sub-carrers The hgh PAP maes the sgna more senstve to the nonneartes of the PA and resut n sgna dstorton when the pea power exceeds the dynamc range of the ampfer To transmt the hgh PAP sgna wthout dstorton requres more expensve ecenty a new nd of technque caed CI-COFDM has been wdey studed [-4 9] In the CI-COFDM technque each coded nformaton symbo s sent smutaneousy over a carrers and the each carrer for the symbo s assgned a correspondng orthogona CI spreadng code Ths CI/COFDM system not ony can reduce PAP sgnfcanty probem but aso acheve codng gan and frequency dversty gans wthout any oss n throughput Besdes a great dea attenton has been devoted to MIMO antenna array systems and space-tme-frequency processng [5-7] MIMO dversty technque whch exsts dversty gan and codng gan can resove the hgh n budget probem n the hgh data rate transmsson especay n the mut-path fadng channe Besdes the space-tme-frequency processng especay Aamout s dversty technque offers sgnfcant ncrease n performance at a ow decodng compexty Aamout s Space-Tme Boc Codng (STBC) method s very Internatona Journa of Eectroncs Sgnas and Systems (IJESS) ISS o Voume- Issue- 3

2 Performance Anayss of MIMO SFBC CI-COFDM System aganst the onnear Dstorton and arrowband Interference effcent when deay spread s bg or channe s tme varaton s very sma durng the coded contnuous OFDM symbos and OFDM sub carrer number s sma On the other hand when Dopper spread s bg or channe s tme varaton s arge and channe s non frequency seectve the nter-sub carrer s channe frequency response s neary constant n the OFDM system wth many sub carrers the SFBC method s more effcent for the hgh quaty transmsson In recent tmes some studes n the area of CI- OFDM system wth MIMO have been performed [8-] There STBC method s apped n some agorthms and MIMO CI-COFDM system s utzed to compensate the BE penaty caused by Dopper frequency or frequency seectve fadng In ths paper we focus on two Tx / one x antenna and two Tx/ two x antenna confguratons we evauate the performance of MIMO OFDM MIMO CI-OFDM and MIMO CI-COFDM system on the bass of MIMO technque theoretca anayss when PA nonnearty or BI are ncuded SFBC codng s apped n MIMO OFDM MIMO CI-OFDM and MIMO CI-COFDM systems For CI-COFDM reazaton dgta mpemented CI-COFDM s used n whch nformaton s coded by conventona encoder and CI code spreadng operaton and carrer aocaton are separatey processed by smpe IFFT type operaton [] As a resut MIMO CI-COFDM system outperforms MIMO SFBC OFDM and MIMO SFBC CI-COFDM systems sgnfcanty n the exstence of both PA nonnearty and BI IISYSTEM DESCIPTIO In ths paper SFBC transmt dversty technque s apped nto the OFDM system Smpy the Tx/x and Tx/x antenna confguraton are consdered to compare the system performance of the MIMO OFDM and MIMO CI-COFDM system Frst we dscuss the tradtona MIMO SFBC OFDM structure wth Tx/x and Tx/x antenna a) Tx/x SFBC OFDM system Fg MIMO SFBC OFDM transcever dagram wth x dversty When Tx antennas and x antenna are consdered assumng the system transmts data symbos - on carrers - respectvey the encodng agorthm s Tx f f Tx Channe coeffcents between the Tx Tx antenna and x antenna s respectvey eceved sgnas at the xantenna s for th () th carrers respectvey () So receved sgna n frequency doman s as foows Let s assume that adjacent two carrers have same channe characterstc such as Then decodng agorthm s as foows ^ ^ ^ ( ) () where means the conjugate transpose of and Internatona Journa of Eectroncs Sgnas and Systems (IJESS) ISS o Voume- Issue- 4

3 Performance Anayss of MIMO SFBC CI-COFDM System aganst the onnear Dstorton and arrowband Interference Internatona Journa of Eectroncs Sgnas and Systems (IJESS) ISS o Voume- Issue- 5 (3) b) Tx/x SFBC OFDM system Fg MIMO SFBC OFDM transcever dagram wth x dversty Channe coeffcents between the Tx Tx antenna and x antenna s respectvey and Tx Tx antenna and x antenna s respectvey eceved sgnas at the two x antennas are defned as x antenna x antenna th carrer th carrer So receved sgnas n frequency doman are expressed as foows (4) Let s assume that adjacent two carrers have same channe characterstc such as Then decodng agorthm s as foows (5) where (6) IIIMIMO SFBC CI-COFDM In MIMO SFBC CI-COFDM system at the transmtter the ncomng bts are channe coded wth ntereaver and mapped nto transmtted data symbos correspondng to arbtrary moduaton such as 6QAM In the CI spreadng process can be expressed as foows j ft j e e t C π Δθ Δ ) ( Δ π θ (7) where s the tota number of subcarrers f Δ means the carrer spacng and θ Δ s the assgned base ^ ^ ^ ) (

4 Performance Anayss of MIMO SFBC CI-COFDM System aganst the onnear Dstorton and arrowband Interference spreadng phase offset for the th parae data ere for genera expresson we defne CI spreadng sequence seres for the th parae data as π π π j j j ( ) [ c ] { c c c } { e e e } (8) Before passng through nonnear PA the th Tx antenna sgna for one entre MIMO SFBC CI-COFDM symbo s as: S (9) j π Δf t j Δθ j f t () t x e e π c e p() t j π f c t j π Δ f t e s e channe state estmaton assumng the channe responses are nown or can be estmated accuratey at the recever each symbo stream s phase offset due to spreadng s removed from each carrer by CI codes despreadng The obtaned vectors from each carrer are then combned by certan combnng strategy The combnng strategy s empoyed to hep restore orthogonaty between symbo streams mnmzng nterference and maxmzng frequency dversty benefts In the fadng channe Mnmum Mean-Square Error Combnng (MMSEC) can be used to mnmze nter-symbo- nterference from other spreadng codes and nose [ 8]Fnay the receved data sampes are dentereaved and are gven to the decson devce whch uses hard decson Vterb Agorthm (VA) where x s tme doman SFBC coded data on the th carrer and th Tx antenna fc s the center frequency and p (t) s the puse shapng for the bt duratont b We defne x e j Δ θ as s In the MIMO SFBC CI-COFDM recever sde the r th x receved sgna can be expressed as: r c L L r jπ fc t r j π Δf t jφ r e α s e e n L r r jπ Δf t jδθ jπf ct jφ r α x e e e e n () j π f t r j π Δf t r () t e h s e n () t () t () t where L ndcates number of transmt antennas and here we consder L r () t s the r th x antenna receved r sgna h s the tme doman response of the th carrer from th Tx antenna to r th x antenna when r channe s frequency seectve fadng channe r α φ and r are the fade parameter and phase h offset of respectvey n r (t) and s the Addtve Whte Gaussan ose (AWG) wth power spectra densty / from th Tx antenna r th x antenna The above receved sgna s separated nto ts orthogona sub-carrers through FFT process After Fg3 MIMO SFBC CI-COFDM transcever dagram wth x dversty IVPEAK to AVEAGE POWE ATIO In the case of two transmt antennas each of dmensona OFDM symbo s transmtted from Tx and Tx antenna respectvey Generay PAP of the transmtted OFDM sgna s defned as Internatona Journa of Eectroncs Sgnas and Systems (IJESS) ISS o Voume- Issue- 6

5 Performance Anayss of MIMO SFBC CI-COFDM System aganst the onnear Dstorton and arrowband Interference max s ( t ) t < T PAP E s ( t ) () where means the transmt antenna number and means expectaton operaton To show statstca characterstcs of PAP we use Compementary Cumuatve Dstrbuton Functon (CCDF) whch s the probabty that PAP of OFDM sgna exceeds a certan threshod PAP The CCDF s defned as CCDF Pr( PAP () where P n s the average sampe power of th transmt T antenna sgna Pavg ( / T) S ( t) dt s the average power of th transmt antenna sgna We defne the observed CCDF of MIMO transmtter as CCDF Pr( PAP P avg exp( PAP ) Pn n > PAP ( CCDF ) < PAP E[ ] max < L (3) ) ) transmtter s PA or BI s nserted to the data carrers In the present wor Tx-x and Tx-x MIMO schemes are consdered PA wth certan bacoff such as 3 and 6 Tota number of sub-carrer nterrupted by BI s defned as p and p8 besdes JS of BI s db or db consdered The whoe evauaton consder wth snge path between the each Tx and x antenna and smuaton parameters are gven n Tabe Fg4 compare the CCDF of the PAP for MIMO SFBC OFDM MIMO SFBC CI-OFDM and MIMO SFBC CI-COFDMAs shown n Fg4 MIMO SFBC CI- COFDM system 5dB and 5dB PAP gans at - over MIMO SFBC CI-OFDM and MIMO SFBC OFDM when tota subcarrers number s 4 and moduaton of 6QAM Fg5 shows BE performances of MIMO SFBC based OFDM CI-OFDM and CI-COFDM when SSPA wth bacoff s consdered as the transmtter PA As seen n Fg5 5dB and 8dB S are requred at -4 of BE n the Tx-x SFBC CI-COFDM and Tx-x SFBC CI-COFDM system respectvey but -4 of BE are acheved at S of 65dB n Tx-x SFBC CI- OFDM and 3dB n Tx-x SFBC CI-OFDM but n both MIMO SFBC OFDM even f S of 3dB error foors occurs wth BE of - Tabe : Smuaton Parameters Moduaton/Detecton 6QAM/Coherent detecton FFT sze() 4 umber of sub carrers 4 Guard ntervas 56 Forward error correcton Codng rate() / Constrant ength(k) 7 Convouton codng and vterb decodng V PEFOMACE AALISES and DISCUSSIO In order to compare the transmsson performance n the MIMO SFBC OFDM MIMO SFBC CI-OFDM and MIMO SFBC CI-COFDM system we evauate the PAP and BE of MIMO SFBC OFDM MIMO SFBC CI-OFDM and MIMO SFBC CI-COFDM when Sod State Power Ampfer (SSPA) s used as each Fg4 PAP n MIMO SFBC OFDM MIMO SFBC CI-OFDM and MIMO SFBC CI-COFDM (4 6QAM) Fg6 s shows the BE vs Eb/ pot for MIMO Internatona Journa of Eectroncs Sgnas and Systems (IJESS) ISS o Voume- Issue- 7

6 Performance Anayss of MIMO SFBC CI-COFDM System aganst the onnear Dstorton and arrowband Interference SFBC based OFDM CI-OFDM and CI-COFDM when SSPA wth certan bacoff s consdered as transmtter PA As seen n Fg6 when bacoff 6 and 3 are supposed respectvey n Tx-x SFBC CI-COFDM and Tx-x SFBC CI-COFDM system SSPA nonnearty s amost compensated competey In Tx- x SFBC CI-COFDM outperforms a Tx-x SFBC CI-OFDM and Tx-x SFBC OFDM system by 5dB and 55dB respectvey at BE of -4 and n Tx-x SFBC CI-COFDM system gans 7dB compare wth Tx- x SFBC CI-OFDM system but n Tx-x SFBC OFDM system even f S of 3dB error foors occurs wth BE of - Fg7 s shows the BE vs Eb/ pot for MIMO SFBC based OFDM CI-OFDM and CI-COFDM when BI s nserted to data carrers As seen n Fg7 MIMO SFBC CI-COFDM system compensates a the BI affect when p s equa to 8 and JS s or respectvey In SFBC based Tx-x CI-COFDM gans 5dB over Tx-x CI-OFDM at BE of -4 In Tx-x CI- COFDM gans 5dB over Tx-x CI-OFDM at BE of -4 but n both MIMO SFBC OFDM systems even f S of 3dB error foors occurs wth BE of -3 Fg6 BE performance of MIMO SFBC OFDM COFDM when SSPA bac-off6 or 3 (4 6QAM) Fg8 s shows the BE vs Eb/ pot for MIMO SFBC based OFDM CI-OFDM and CI-COFDM when SSPA wth bacoff s consdered as the transmtter PA and aso BI s nserted to data carrers As seen n Fg8 n SFBC based Tx-x CI-COFDM and Tx-x CI-COFDM requred 85dB and 55dB respectvey at BE of -4 but n Tx-x SFBC CI-OFDM and Tx- x SFBC CI-OFDM even f S of 3dB error foors occurs wth BE of -4 and n both MIMO SFBC OFDM systems even f S of 3dB error foors occurs wth BE of - Fg5 BE performance of MIMO SFBC OFDM COFDM wth SSPA (4 6QAM) Internatona Journa of Eectroncs Sgnas and Systems (IJESS) ISS o Voume- Issue- 8

7 Performance Anayss of MIMO SFBC CI-COFDM System aganst the onnear Dstorton and arrowband Interference COFDM systems when PA nonnearty or BI are exsted From the smuaton resut MIMO SFBC CI-COFDM system outperforms MIMO SFBC CI-OFDM and MIMO SFBC OFDM sgnfcanty when systems nterrupted by the PA nonnearty or BI Therefore the MIMO SFBC CI-COFDM method can be further appcabe to the any nds of MIMO type mut-carrer communcaton systems wth many sub carrers EFEECES Fg7 BE performance MIMO SFBC OFDM OFDM wth BI (4 6QAM) Fg8 BE performance of MIMO SFBC OFDM COFDM wth SSPA and BI (p8 4 6QAM) VI COCLUSIO In ths paper we focused on the two Tx / one x antenna and two Tx / two x antenna confguratons we evauate the performance of MIMO SFBC OFDM []Zhqang Wu Zhjn Wu Wegandt DA and assar C gh performance 64-QAM OFDM va carrer nterferometry spreadng codes IEEE 58th Vehcuar Technoogy Conference 3 VTC 3- Fa Vo pp Oct 3 []Wegandt DA assar C and Wu Z The emnaton of pea-to average power rato concerns n OFDM va carrer nterferometry spreadng codes: a mutpe consteaton anayss Proceedngs of the Thrty-Sxth Southeastern Symposum on System Theory 4 pp [3]Zhquang Wu assar C and aoyao e arrowband nterference rejecton n OFDM va carrer nterferometry spreadng codes Goba Teecommuncatons Conference 4 GLOBECOM '4 IEEE Vo4 pp ov 3 Dec 4 [4]Wegandt DA Wu Z and assar C; gh-performance carrer nterferometry OFDM WLAs: F testng ICC '3 IEEE Internatona Conference on Communcatons Vo pp3 7-5 May 3 [5] Aamout SM A smpe transmt dversty technque for wreess communcatons IEEE Journa on Seected Areas n Communcatons Vo 6 Issue 8 pp Oct 998 [6]Lee KF and Wams DB A space-frequency transmtter dversty technque for OFDM systems Goba Teecommuncatons Conference GLOBECOM ' Vo3 pp ov- Dec [7]Suto K and Ohtsu T Performance evauaton of space-tme frequency boc codes over frequency seectve fadng channes IEEE 56th Vehcuar Technoogy Conference VTC - Fa Vo3 pp Sept [8]Barbosa P Zhqang Wu and assar C gh-performance MIMOOFDM va carrer nterferometry Goba Teecommuncatons Conference 3 GLOBECOM '3 Vo pp Dec 3 [9]Maehara F and Kuchenbecer -P Performance of space dversty recepton for coded carrer nterferometry OFDM IEEE 59th Vehcuar Technoogy Conference 4 VTC 4-Sprng 4 Vo pp May 4 []Wanwoo Seo and Yeonho Chung Comparatve study of OFDM system wth carrer nterferometry code and STBC n fat fadng channes The 6th Internatona Conference on Advanced Communcaton Technoogy 4 Vo pp []eung-gyoon yu and Yngshan L Dgta Impementaton and Performance Evauaton of the CI-OFDM Structure wth Low Compexty submtted to the EEE Transacton on Consumer Eectroncs May 5 []Anwar K and Yamamoto A new desgn of carrer nterferometry OFDM wth FFT as spreadng codes 6 IEEE ado and Wreess Symposum pp Jan 6 Internatona Journa of Eectroncs Sgnas and Systems (IJESS) ISS o Voume- Issue- 9