Research Article Interference Cancellation Using Replica Signal for HTRCI-MIMO/OFDM in Time-Variant Large Delay Spread Longer Than Guard Interval

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1 Hindawi Publishing Corporaion Journal of Elecrical and Compuer Engineering Volume 212, Aricle D , 1 pages doi:11155/212/ Research Aricle nerference Cancellaion Using Replica Signal for HTRC-MMO/OFDM in Time-Varian Large Delay Spread Longer Than Guard nerval Yua da, 1 Chang-Jun Ahn, 2 Takeshi Kamio, 1 Hisao Fujisaka, 1 and Kazuhisa Haeiwa 1 1 Graduae School of nformaion Sciences, Hiroshima Ciy Universiy, Ozukahigashi, Asaminami-ku, Hiroshima , Japan 2 Graduae School of Engineering, Chiba Universiy, 1-33 Yayoi-cho, nage-ku, Chiba , Japan Correspondence should be addressed o Yua da, yida@chiba-ujp Received 15 July 211; Revised 22 February 212; Acceped 12 March 212 Academic Edior: Hanho Lee Copyrigh 212 Yua da e al This is an open access aricle disribued under he Creaive Commons Aribuion License, which permis unresriced use, disribuion, and reproducion in any medium, provided he original work is properly cied Orhogonal frequency division muliplexing (OFDM) and muliple-inpu muliple-oupu (MMO) are generally known as he effecive echniques for high daa rae services n MMO/OFDM sysems, he channel esimaion (CE) is very imporan o obain an accurae channel sae informaion (CS) However, since he orhogonal pilo-based CE requires he large number of pilo symbols, he oal ransmission rae is degraded To miigae his problem, a high ime resoluion carrier inerferomery (HTRC) for MMO/OFDM has been proposed n wireless communicaion sysems, if he maximum delay spread is longer han he guard inerval (G), he sysem performance is significanly degraded due o he inersymbol inerference (S) and inercarrier inerference (C) However, he convenional HTRC-MMO/OFDM does no consider he case wih he ime-varian large delay spread longer han he G n his paper, we propose he S and C compensaion mehods for a HTRC-MMO/OFDM in he ime-varian large delay spread longer han he G 1 nroducion Recenly, he sophisicaed erminal as a smar phone becomes widely used and many mulimedia services are provided [1, 2] High speed packe access (HSPA) using a wideband code division muliplexing access (W-CDMA) is used in he mobile communicaions and provides he daa services wih he maximum ransmission rae of abou 14 Mbps [3] However, since he available frequency band is limied, a HSPA canno improve he ransmission rae more han now [4] To solve his problem, orhogonal frequency division muliplexing (OFDM) and muliple-inpu muliple-oupu (MMO) are acively used [5 9] OFDM is a mulicarrier digial modulaion The OFDM signal can be ransmied in parallel by using he many subcarriers ha are muually orhogonal n MMO sysems, he signal of he several ransmi anennas is ransmied in he same frequency band Moreover, since each ransmied signal is sen over he independen channel, he space diversiy can be obained in he receiver Therefore, a long erm evoluion (LTE) has been sandardized as 39 G sysem using MMO/OFDM sysems [1, 11] An LTE provides he maximum ransmission rae of abou 5 1 Mbps Moreover, an LTE Advanced will suppor broadband daa services wih he maximum ransmission rae of abou 1 M 1 Gbps as 4 G sysems Since he received signal is changed due o he ampliude and phase variaions for a frequency selecive fading, he channel esimaion (CE) is imporan o compensae he channel variance n he convenional MMO/OFDM, he orhogonal pilo symbols-based CE is used o idenify an accurae channel sae informaion (CS) [7] However, since he orhogonal pilo-based CE requires he large number of pilo symbols and large ransmission power, he ransmission rae is degraded To miigae hese problems, a high ime resoluion carrier inerferomery (HTRC) for MMO/OFDM has been proposed [12]

2 2 Journal of Elecrical and Compuer Engineering Daa Pilo generaion Mapper Phase offseing Mux S/P Scrambling Scrambling FFT FFT Shifed pilo signal Shifed pilo signal +G +G D/A D/A D/A D/A uad mod uad mod U/C U/C (a) Transmier Daa P/S A/D Descrambling FFT uad G -Pilo A/D demod MLD signal Descrambling A/D FFT G uad A/D demod S/P nerference FFT τ m,n,l >T g FFT cancellaion FFT ^H m,n (k) Time FFT nerference FFT FFT windows Subracion G of pilo cancellaion signal (b) Receiver D/C D/C Figure 1: Proposed sysem n wireless communicaions, inersymbol inerference (S) and inercarrier inerference (C) are serious problems o miigae he sysem performance To preven hese problems, a guard inerval (G) is generally insered n general, G is usually designed o be longer han he delay spread of he channel However, if he maximum delay spread is longer han he G, he sysem performance is significanly degraded due o he S and C However, he convenional HTRC-MMO/OFDM does no consider he case wih he ime-varian large delay spread longer han he G n his paper, we propose he S and C compensaion mehods for a HTRC-MMO/OFDM in he ime-varian large delay spread longer han he G Unil his ime, several schemes have proposed he S and C compensaion mehods due o he large delay spread channel For example, [13] has proposed he S reducion mehod by exending he G However, since[13] has exended he G lengh, he maximum hroughpu is degraded and he ransmission power is also increased Reference [14] has proposed he S and C compensaion mehods using he urbo equalizaion However, [14] has large complexiy by he ieraive processing for he urbo equalizer Reference [15] has proposed he S and C compensaion mehods using he esimaed channel coefficiens and he CS o reproduce he inerference componens However, he packe lengh becomes longer by using he raining symbol To miigae he above-menioned problems, we propose he ime domain S compensaion mehod wih he replica signal based on he C compensaion for a HTRC-MMO/OFDM in his paper This paper is organized as follows n Secion 2, wepresen he sysem model Then, we describe he proposed sysem in Secion 3nSecion 4, we show he compuer simulaion resuls Finally, he conclusion is given in Secion 5 2 Sysem Model This secion describes he sysem model, which employs he ime-division muliplexing (TDM) ransmission for muliple users This sysem is illusraed in Figure 1 21 Channel Model We assume ha a propagaion channel consiss of L discree pahs wih differen ime delays The impulse response beween he mh ransmi and nh receive anenna h m,n (τ, ) is represened as follows: L 1 h m,n (τ, ) h m,n,l ()δ ( ) τ τ m,n,l, (1) l where h m,n,l, τ m,n,l are he complex channel gain and he ime delay of he lh propagaion pah, and L 1 l E h 2 m,n,l 1, where E denoes he ensemble average operaion The channel ransfer funcion H m,n ( f, ) is he Fourier ransform of h m,n (τ, ) and is given by H m,n ( f, ) h m,n (τ, ) exp ( j2πfτ ) dτ (2) L 1 h m,n,l () exp ( ) j2πfτ m,n,l l 22 HTRC-MMO/OFDM The ransmission block diagram of he proposed sysem is shown in Figure 1(a) Firsly, he coded binary informaion daa sequence is modulaed, and N p pilo symbols are appended a he beginning of he sequence The HTRC-MMO/OFDM ransmied signal for

3 Journal of Elecrical and Compuer Engineering 3 he mh ransmi anenna can be expressed in is equivalen baseband represenaion as follows: s m () N p+n d 1 i N 2S c 1 g( it) u m (k, i) N c k [ ] j2π( it)k exp, where N d and N p are he number of daa and pilo symbols, N c is he number of subcarriers, is he effecive symbol lengh, S is he average ransmission power, and T is he OFDM symbol lengh, respecively The frequency separaion beween adjacen orhogonal subcarriers is 1/ and can be expressed by using he kh subcarrier of he ih modulaion symbol d m (k, i)wih d m (k, i) 1forN p i N p + N d 1 as follows: (3) u m (k, i) c PN (k) d m (k, i), (4) where c PN is a long pseudonoise (PN) sequence as a scrambling code o reduce he peak-o-average power raio (PAPR) G is insered in order o eliminae he S due o a mulipah fading, and hence, we have T + T g, (5) where T g is he G lengh n communicaion sysems, ε is generally considered as 4 or 5, where ε /T g n his paper, we assume ε 4 n (3), he ransmission pulse g() isgiven by g() { 1 for Tg oherwise (6) For i N p 1, he ransmied pilo signal of he kh subcarrierfor he mh ransmi anenna elemen is given by ( ( ) ) ζ 1 j2π m +2μ Tg k m exp for i d m (k, i) μ ζ oherwise, (7) where ζ ε/2, m mod (m, ζ), and x sands for he ineger lower and closer o x, respecively n his case, he HTRC-MMO/OFDM pilo signal can muliplex he same impulse responses from he ransmi anenna elemens in each receive anenna elemen in ζ imes on he ime domain wihou overlapping o each oher For example, if we consider ε 4 and 2 ransmi anenna elemens, we obain N c 1 k d (k,) {1,,,1,} and N c 1 k d 1(k,) {1,, 1,,,1,, 1, } as he pilo signal of he firs and second ransmi anenna elemens from (7) as shown in Figure 2(a) n his case, since each pilo signal conains componens, we can idenify he half of ransmission power compared wih he convenional MMO/OFDM sysem using he orhogonal pilo However, if τ m,n,l > T g, he convenional HTRC-MMO/OFDM can no obain an accurae CS, where τ m,n,l is he maximum delay spread for he mh ransmi and nh receive anenna To solve his problem, we propose he new channel esimaion using a HTRC-MMO/OFDM Firsly, in he ransmier, we shif he channel impulse responses of (7) as follows: ( ( ) ) ζ 1 j2π 2 m + μ Tg k m exp for i d m (k, i) μ ζ oherwise (8) n (8), he channel impulse responses are shifed as shown in Figure 2(a) This operaion enables esimaing he maximum delay spread longer han he G and o obain an accurae CS in he receiver The received srucure is illusraed in Figure 1(b) By applying he FFT operaion, he received signal r n () is resolved ino N c subcarriers The received signal for he nh receive anenna r n () in he equivalen baseband represenaion can be expressed as follows: r n () m h m,n (τ, )s m ( τ)dτ + n n (), (9) where M is he number of ransmi anennas and n n () is addiive whie Gaussian noise (AWGN) wih a single-sided power specral densiy of N for he nh receive anenna, respecively The kh subcarrier r n (k, i)isgivenby r n (k, i) 1 [ ] it+ts j2π( it)k r n () exp d 2S it N c 1 N c m e 1 Ts { u m (e, i) [ exp j2π ] (e k) h m,n (τ, + it)g( τ) ( j2πeτ exp ) } dτ d + n n (k, i), (1) where n n (k, i) is AWGN noise wih zero mean and a variance of 2N / Afer abbreviaing, (1) can be rewrien as follows: r n (k, i) 1 2S N c N c 1 m e Ts [ exp j2π u m (e, i) ] (e k) { h m,n (τ, + it)g( τ) ( ) } j2πeτ exp dτ d + n n (k, i) 2S N c m ( ) k H m,n, it u m (k, i) + n n (k, i) (11)

4 4 Journal of Elecrical and Compuer Engineering Pilo generaion Phase offseing S/P FFT FFT Shif Shif +G +G Tx1 Tx2 T g 2T g 3T g T g 2T g 3T g Tx1 Tx2 From Tx2 (G par) From Tx2 (G par) From Tx1 From Tx2 T g T g 2T g 3T g 4T g G Wih shif FFT From Tx1 From Tx2 (a) Transmier /4 T g Wihou shif T g Time windows [, T g + τ m,n,l 1 ] [T g,2t g + τ m,n,l 1 ] Time windows [2T g,3t g + τ m,n,l 1 ] [3T g,4t g + τ m,n,l 1 ] Averaging Averaging T g Subracion Subracion FFT FFT Wih shif CS from Tx1 CS from Tx2 T g T g 2T g 3T g 4T g Wihou shif T g T g (b) Receiver Figure 2: The concep of a HTRC-MMO/OFDM o apply he maximum delay spread longer han he G for 2 ransmi anenna elemens and ε 4 Afer descrambling, he oupu signal r n (k, i) for he nh receive anenna elemen is given by r n (k, i) c PN(k) c PN (k) 2 r n(k, i) 2S N c m ( ) k H m,n, it d m (k, i) + n n (k, i), (12) where ( ) is a complex conjugae and c PN(k)/ c PN (k) 2 is he descrambling operaion, respecively Observing (11)and (12), he noise componens are he same noaion n his paper, he descrambling operaion is o roae he phase of each subcarrier by using a PN code Since ε /T g, a HTRC-MMO/OFDM can muliplex he same impulse responses in ζ imes on he ime domain Afer he pilo signal separaion, he pilo signal is convered o he ime domain signal r n ()againas N p 1 N 2P c 1 [ ] j2π( it)k r n () r n (k, i) exp i N p 1 i N c 2P k N c m N c 1 h m,n (τ, + it) [ ] j2π( it)k exp + ñ n () k d m (k, i) N p 1 M 1 2P L 1 h m,n,l ( + it) N i c m l 1 ζ 1 δ ( ) τ τ m,n,l τ (2 m+μ)tg ζ + ñ n(), μ (13) where P is he ransmission pilo signal power and ñ n () is he noise componen, respecively Here, if τ m,n,l > T g, since

5 Journal of Elecrical and Compuer Engineering 5 he channel impulse responses of he differen ime window overlap he desired channel impulse responses, he accurae CS can no be obained Therefore, we process as follows A he receiver, in Figure 2(b), he overlapped channel impulse responses show he same ampliude for he ransmied pilo signal wihou he shif in he differen ime window n his case, we can no esimae he maximum delay spread On he oher hand, he overlapped channel impulse responses show he differen ampliude for he ransmied pilo signal wih he shif in he differen ime window Therefore, we can esimae he maximum delay spread from he differen ampliude in he differen ime windows Nex, we eliminae he channel impulse responses of he differen ime window Thechannel impulse responses ofhe differen ime window can be eliminaed by using he channel impulse responses of he G These channel impulse responses do no conain he channel impulse responses of he differen ime window This is because he pilo signal of he G is he head of packe and i does no conain he channel impulse responses of he differen ime window Therefore, we can eliminae he channel impulse responses of he differen ime window From he above process, he frequency response of he kh subcarrier beween he mh ransmi and nh receive anenna Ĥ m,n (k)forτ m,n,l > T g is obained by Ĥ m,n (k) N c ζ 2P N c 1 m e Ts L 1 L 1 l l L 1 ζ 1 μ 1 h m,n,l ( + ρt ) δ ( τ τ m,n,l τ (2 m+μ)tg ) δ ( ) ( ) j2πeτ τ τ m,n,l exp dτ d + η m,n (k) for L T g, ρ m, ζ (14) where η m,n (k) is AWGN componen wih E[ η m,n (k) ] 2 E[ n n (k, i)/ζ ] 2 σ 2 /ζ 3 Proposed Sysem 31 Rewrien Marix Form Afer he pilo signal separaion, (13) forτ m,n,l T g can be rewrien in he marix form as follows: R i,n λ i,m,n FD i,m + N i,n, (15) m where λ i,m,n is he N c N c ime-domain channel marix for he ih symbol beween he mh ransmi and nh receive anenna, N i,n is he N c 1 noise marix, and F is he FFT operaion, respecively However, (15) forτ m,n,l > T g is rewrien as follows: ( ) R i,n λisi,i 1,m,n FD i 1,m + λ ici,i,m,n FD i,m + Ni,n, (16) m where λ isi,i 1,m,n, λ ici,i,m,n denoe he S and C channel marices for he (i 1)h and ih symbols beween he mh ransmi and nh receive anenna, respecively Observing (16), since he received signal R i,n conains he S and C erms, hese equalizaion processing are necessary 32 S and C Equalizaion n τ m,n,l > T g, since he firs daa symbol of R i,n does no conain he S [16], (16) for i is obained as R,n λ ici,,m,n FD,m + N,n (17) m However, he daa symbols for i > have he S Here, he S equalizaion is performed by using he previous deeced symbol D i 1,m,n and he esimaed S channel marix λ isi,m,n The esimaed S channel marix λ isi,m,n consiss of he esimaed channel impulse response The esimaed channel impulse response ĥm,n,l ()δ(τ τ m,n,l ) is obained by he channel response Ĥ m,n (k) afer he FFT operaion, where L l L 1 Therefore, he S equalized signal R i,n is given by R i,n R i,n m m λ isi,m,n FD i 1,m λ ici,i,m,n FD i,m + Ñ i,n, (18) where Ñ i,n is he noise erm wih he residual S Afer he FFT operaion, by using maximum likelihood deecion (MLD), he deeced signal D i [ D i,,, D i,m,, D i,m 1 ] T is obained as follows: D i arg min D N 1 F 1 2 R i,n Ĥ m,n D i,m, (19) n m where ( ) T is he ranspose operaion, N is he number of receive anennas, D i,m is he consellaion of he symbol replica candidaes as C 1 m c D i,m,c, C is he modulaion level, and Ĥ m,n is he marix form of Ĥ m,n (k), respecively From (19), S is eliminaed from he received signal However, he orhogonaliy is desroyed by he deeced signal due o he S compensaion f C is eliminaed from (19), he deeced signal D i,m canbemoreaccuraelydeeced 33 Replica Signal nserion Based on C Equalizaion To eliminae he C, we consider he orhogonaliy reconsrucion wih insering he deeced signal afer he S

6 6 Journal of Elecrical and Compuer Engineering compensaion The C equalized signal R i,n wih insering eliminaed he par of signal using he previous deeced symbol D i,m is given by R i,n R i,n + m m λ ici,m,n F D i,m λ i,m,n FD i,m + N i,n, (2) where λ ici,m,n is he esimaed C channel marix and N i,n is he noise erm wih he residual S and residual C, respecively λ ici,m,n consiss of he esimaed channel impulse responses ĥm,n,l ()δ(τ τ m,n,l ) Afer he FFT operaion, he deeced signal D i [ D i,,, D i,m,, D i,m 1 ] T is obained as follows: D i arg min D N 1 F 1 2 R i,n Ĥ m,n D i,m (21) n m Observing (19) and(21), since C is eliminaed, D i,m is he more accuraely deeced signal compared wih D i,m 34 Complexiy Comparison Here, we compare he complexiy of he convenional and proposed mehods Firsly, we show he complexiy of [14] The auhors of [14] have proposed he S and C compensaions using he urbo equalizaion From Table 1 of [14], he complexiy of [14] is given by { C [14] NNs MN c +4N c NM 2 +3N c NM +NN c log 2 N c +6N(N s + L)MN c } Nd NN c N d { M(7Ns +4M +6L +3) +log 2 N c }, (22) where N s is he number of sampling poins for G and effecive symbol Nex, we show he complexiy of our proposed mehod Firsly, he complexiy of (18) is obained by C isi NN c (N d 1)C M + {MN c (N d 1)} log N c (23) For (23), he firs erm is he complexiy of MLD and he second erm is he complexiy of FFT Nex, he complexiy of (2) is obained by C ici NN c N d C M + MNN c N d log N c {NN c (N d 1) + NN c }C M + [{MN c (N d 1)} + MN c ] log N c (24) For (24), he firs and second erms are he complexiy of MLD and FFT of (23) Finally, he complexiy of (21)is C MLD NN c N d C M {NN c (N d 1) + NN c }C M (25) Therefore, he complexiy of he proposed mehod is obained by C pro C isi + C ici + C MLD N c { N(3Nd 1)C M + M(N d 1) log N c } (26) For example, when M N 2, N c 64, N d 2, N s 8, L 2, and C 4, he complexiies of [14] and he proposed mehod are 332 and 1356 from (22) and (26) Therefore, he proposed mehod is small compared wih [14] 4 Compuer Simulaed Resuls n his secion, we show he performance of he proposed mehod Figure 1 shows he simulaion model of he proposed sysem n his simulaion, we assumed ha 2 2and 4 4 MMO sysems On he ransmier, he pilo signal is assigned for each ransmier using (8) n his case, he proposed sysem can muliplex he same impulse responses from he ransmi anenna elemens in each receive anenna elemen in ζ imes on he ime domain These have been found o be efficien for he ransmission of he OFDM signal over he frequency selecive fading channel Afer serial o parallel (S/P) convered, he coded bis are PSK modulaed, and hen he pilo signal and daa signal are muliplexed wih he scrambling using a PN code o reduce he PAPR The OFDM ime signal is generaed by he FFT operaion and is ransmied o he frequency-selecive and ime-varian radio channel afer he cyclic exension has been insered The ransmied signal is subjec o he broadband channel propagaion n his simulaion, we assume ha OFDM symbol period is 5 μs and guard inerval is 1 μs forε 4, and L 2, 3 pah Rayleigh fadings The maximum Doppler frequency is 1 Hz n he receiver, guard inerval is erased from he received signal and he received signal is convered S/P The parallel sequences are passed o he FFT operaor and conver he signal back o he frequency domain Afer he descrambling and FFT operaion, each impulse response for all combinaion of he ransmi and receive anenna elemens can be esimaed by exracing and averages ζ imes impulse responses using he ime windows wih (14) n τ m,n,l > T g, he HTRC-MMO/OFDM pilo signal conains he overlapped channel impulse responses from he differen ime window However, he pilo signal of he G does no conain he overlapped channel impulse responses By using his signal, he channel impulse responses of he differen ime window are eliminaed from he overlapped channel impulse responses as shown in Figure 2(b) The frequency domain daa signal is deeced and demodulaed by using he MLD algorihm Since he deeced daa signal conains he S and C, hese equalizaion processing are necessary The S equalizaion is performed wih he previous deeced symbol and esimaed S channel marix as (18) From (18), S is eliminaed However, he orhogonaliy is desroyed by he deeced signal due o he S compensaion To reconsruc he orhogonaliy, he C equalizaion is performed by using he replica signal inserion as (2) Finally, he daa

7 Journal of Elecrical and Compuer Engineering E b /N per received anenna (db) E b /N per received anenna (db) No S and C No compensaion (2 pah) Convenional mehod (2 pah) Proposed mehod (2 pah) No compensaion (3 pah) Convenional mehod (3 pah) Proposed mehod (3 pah) Figure 3: The of he convenional and proposed mehods for 2 2 MMO sysem a Doppler frequency of 1 Hz No S and C No compensaion (2 pah) Convenional mehod (2 pah) Proposed mehod (2 pah) No compensaion (3 pah) Convenional mehod (3 pah) Proposed mehod (3 pah) Figure 4: The of he convenional and proposed mehods for 4 4 MMO sysem a Doppler frequency of 1 Hz Table 1: Simulaion parameers Daa modulaion PSK Daa deecion MLD Symbol duraion 5 μs Frame size N p 1, 2, N d 2 FFize 64 Number of carriers 64 Guard inerval 16 sample imes Fading 2, 3 pah Rayleigh fading Doppler frequency 1 Hz Anennas (M, N) (2, 2), (4, 4) signal is deeced as (21) The packe consiss of N p 1, 2 pilo symbols and N d 2 daa symbols Table 1 shows he simulaion parameers Figures 3 and 4 show he of he convenional and proposed mehods for 2 2and4 4MMOsysemsa Doppler frequency of 1 Hz The number of maximum delay spread is 4 and 16 in 2 2 and 4 4 MMO sysems, respecively From he simulaion resuls, he performance for no S and C compensaion is increased abou 22 and 3 imes compared wih no S and C case in 2 2and4 4 MMO sysems, respecively For he convenional mehod, he performance shows he error floor in high E b /N This is because he residual S and C are remained The proposed mehod shows approximaely he same performance compared wih no S and C case Therefore, he proposed mehod can eliminae he S and C Nex, we compare he 2- and 3-pah models The 2-pah model conains he channel impulse responses of he differen ime window in he ime domain HTRC- MMO/OFDM pilo signal However, hey do no overlap he desired channel impulse responses On he oher hand, he 3- pah model overlaps he desired channel impulse responses Therefore, he channel impulse responses of he differen ime window are eliminaed by using he channel impulse responses of he G From he simulaion resuls, he 2-pah model shows he beer performance han ha of he 3- pah model in low E b /N means ha CS degrades due o he eliminaed processing of he overlapped channel impulse responses in he 3-pah model Figures 5 and 6 show he of he proposed mehod for 2 2and4 4MMOsysemsaDopplerfrequencyof 1HzThenumberofmaximumdelayspreadis4and16in2 2and4 4 MMO sysems, respecively For he proposed mehod wihou he noise, he noise is no added in he channel impulse responses of he G From he simulaion resuls, he 2- and 3-pah models wihou he noise show he approximaely same performance Therefore, he 3-pah model wih he noise degrades due o he noise of he G Figures 7 and 8 show he versus he number of maximum delay spread for he convenional and proposed mehods wih 2 2and4 4 MMO sysems a Doppler frequency of 1 Hz Here, E b /N per received anenna is 2 and 15 dbs in 2 2and4 4 MMO sysems, respecively n 2 2 MMO sysem, he performances of no S and C compensaion and convenional mehod are increased

8 8 Journal of Elecrical and Compuer Engineering E b /N per received anenna (db) 2 pah 3 pah 3 pah (w/o) Figure 5: The of he proposed mehod for 2 2MMOsysem a Doppler frequency of 1 Hz Number of maximum delay spread No compensaion (2 pah) Convenional mehod (2 pah) Proposed mehod (2 pah) No compensaion (3 pah) Convenional mehod (3 pah) Proposed mehod (3 pah) Figure 7: The versus he number of maximum delay spread for he convenional and proposed mehods wih 2 2 MMO sysem a Doppler frequency of 1 Hz E b /N per received anenna (db) 2 pah 3 pah 3 pah (w/o) 1 6 Figure 6: The of he proposed mehod for 4 4MMOsysem a Doppler frequency of 1 Hz abou 5 imes On he oher hand, he performance of he proposed mehod is increased abou 2 imes Therefore, he proposed mehod can suppress he S and C due o he changing of he number of maximum delay spread n 4 4 MMO sysem, he performance of no S and C compensaion and he convenional mehod are increased abou 17 and 8 imes On he oher hand, he performance of he proposed mehod is increased abou 4 imes and he proposed mehod can suppress he S and C as 2 2 MMO sysem However, he performance Number of maximum delay spread No compensaion (2 pah) Convenional mehod (2 pah) Proposed mehod (2 pah) No compensaion (3 pah) Convenional mehod (3 pah) Proposed mehod (3 pah) Figure 8: The versus he number of maximum delay spread for he convenional and proposed mehods wih 4 4 MMO sysem a Doppler frequency of 1 Hz

9 Journal of Elecrical and Compuer Engineering 9 Throughpu (Mbps) E b /N per received anenna (db) T g 32 (2 2) Convenional mehod (2 2) Proposed mehod (2 2) T g 32 (4 4) Convenional mehod (4 4) Proposed mehod (4 4) Figure 9: The hroughpu of he convenional and proposed mehods for 2 2 and 4 4 MMO sysems a Doppler frequency of 1 Hz of he proposed mehod wih he 2-pah model is increased abou 36 imes compared wih 3-pah model This is because he channel impulse responses of he G for he second ime domain HTRC-MMO/OFDM pilo symbol are overlapped from he firs pilo symbol in 4 4MMOsysem Figure 9 shows he hroughpu performance of he convenional and proposed mehods for 2 2and4 4 MMO sysems a Doppler frequency of 1 Hz The number of maximum delay spread is 4 and 16 in 2 2and4 4 MMO sysems, respecively The hroughpu T p is given by T p N d N c C R M ( ) ( ) 1 Pper, (27) Np + N d T where R is he coding rae and P per is he packe error rae (PER), respecively The exension of he G lengh is he simple mehod o preven he problem of he maximum delay spread [13] However, he hroughpu performance is degrade wih his mehod This is because he number of carriers N c decreases for (27) when he OFDM symbol lengh T is he same as no S and C case n his simulaion, N c decreases from 64 o 48, and he G lengh T g increases from 16 o 32 On he oher hand, he proposed mehod can mainain he number of carriers N c From(27), he maximum hroughou for no S and C case is abou 488 and 931 Mbps in 2 2and4 4MMOsysems, respecively Therefore, he proposed mehod shows he bes hroughpu performance and can achieve he maximum hroughpu performance as he same no S and C case 5 Conclusion n his paper, we have focused on he large delay spread channel and proposed he S and C compensaion mehods for a HTRC-MMO/OFDM n he proposed mehod, we have performed he ime domain S compensaion mehod wih he replica signal based on he C compensaion From he simulaion resuls, he proposed mehod has achieved he approximaely same performance like he case wih no S and C Moreover, he proposed mehod can suppress he S and C due o he changing of he number of maximum delay spread Finally, he proposed mehod has shown he bes hroughpu performance and can achieve he same maximum hroughpu performance compared wih no S and C case References [1] 21 Whie paper informaion and communicaions in Japan, hp://wwwsoumugojp/johosusinokei/whiepaper/ ja/h22/pdf/indexhml [2] H Shoki and Y Tanabe, How fas will be required, how fas can be realized in fuure wireless communicaions? ECE B Pluse, no 11, pp 12 22, 29 [3] F Adachi, H Tomeba, and K Takeda, nroducion of frequency-domain signal processing o broadband single-carrier ransmissions in a wireless channel, ECE Transacions on Communicaions, vol E92-B, no 9, pp , 29 [4] S Abea, Toward LTE commercial launch and fuure plan for LTE enhancemens (LTE-Advanced), in 12h EEE nernaional Conference on Communicaion Sysems (CCS 1), pp , November 21 [5] L J Cimini, Analysis and simulaion of a digial mobile channel using orhogonal frequency division muliplexing, EEE Transacions on Communicaions, vol 33, no 7, pp , 1985 [6] J A C Bingham, Mulicarrier modulaion for daa ransmission: an idea whose ime has come, EEE Communicaions Magazine, vol 28, no 5, pp 5 14, 199 [7] A van Zels, R van Nee, and G A Awaer, Space division muliplexing (SDM) for OFDM sysems, in 51s Vehicular Technology Conference (VTC ), pp , May 2 [8] Koffman and V Roman, Broadband wireless access soluions based on OFDM access in EEE 8216, EEE Communicaions Magazine, vol 4, no 4, pp 96 13, 22 [9] Y Ogawa, T Ohgane, and T Nishimura, MMO echnologies for ulra high-speed wireless ransmission, ECE B Plus,no 11, pp 32 38, 29 [1] A Ghosh, R Raasuk, B Mondal, N Mangalvedhe, and T Thomas, LTE-advanced: nex-generaion wireless broadband echnology, EEE Wireless Communicaions,vol17,no3,pp 1 22, 21 [11] K Zheng, L Huang, G Li, H Cao, W Wang, and M Dohler, Beyond 3G evoluion, EEE Vehicular Technology Magazine, vol 3, no 2, pp 3 36, 28 [12] C J Ahn, Achievable hroughpu enhancemen based on modified carrier inerferomery for MMO/OFDM, Digial Signal Processing, vol 2, no 5, pp , 21 [13] N Gejoh and Y Karasawa, OFDM ransmission characerisic in mulipah environmen where he delay spreading

10 1 Journal of Elecrical and Compuer Engineering exceeds he guard inerval analyzed based on he ETP model, ECE Transacions on Communicaions, vol J85-B, no 11, pp , 22 [14] S Suyama, H Suzuki, and K Fukawa, A MMO-OFDM receiver employing he low-complexiy urbo equalizaion in mulipah environmens wih delay difference greaer han he guard inerval, ECE Transacions on Communicaions, vol E88-B, no 1, pp 39 46, 25 [15] D Van Nguyen, nerference cancellaion for MMO-OFDM sysems in he case of insufficien guard inerval lengh, in 1s nernaional Conference on Communicaions and Elecronics (CCE 6), pp , Ocober 26 [16] Y da, C J Ahn, T Kamio, H Fujisaka, and K Haeiwa, An inerference cancellaion scheme for TF-OFDM in imevarian large delay spread channel, Radioengineering, vol 18, no 1, pp 75 82, 29