Recent advances in single-carrier distributed antenna network

Transcription

1 WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Wirel. Commun. Mob. Comput. ; :55 5 Publihed online November in Wiley Online Library (wileyonlinelibrary.com). DOI:./wcm. SPECIAL ISSUE PAPER Recent advance in ingle-carrier ditributed antenna network Fumiyuki Adachi *, Kazuki Takeda, Tetuya Yamamoto, Ryuuke Matukawa and Shinya Kumagai Department of Electrical and Communication Engineering, Graduate School of Engineering, Tohoku Univerity --5, Aza-aoba, Aramaki, Aoba-ku, Sendai, Miyagi , Japan ABSTRACT For the realization of future wirele network, gigabit wirele technology, which can achieve higher-than- Gbp data tranmiion with extremely low tranmit power, i indipenable. We have been tudying the ditributed antenna network (DAN) and the frequency domain wirele ignal proceing. In DAN, many antenna or cluter of antenna are patially ditributed over a ervice area, and they are connected by mean of optical fiber link with DAN ignal proceing center. A number of ditributed antenna cooperatively erve mobile uer uing patial multiplexing, diverity, array, or relaying technique. In thi paper, the recent advance in ingle-carrier DAN are introduced. Copyright John Wiley & Son, Ltd. KEYWORDS component; ditributed antenna network; tranmit antenna diverity; pace time coding; patial multiplexing; frequency domain equalization *Correpondence Fumiyuki Adachi, Department of Electrical and Communication Engineering, Graduate School of Engineering, Tohoku Univerity --5, Aza-aoba, Aramaki, Aoba-ku, Sendai, Miyagi , Japan. adachi@ecei.tohoku.ac.jp. INTRODUCTION In the early 98, cellular mobile communication ytem, which made anytime, anywhere communication poible, appeared. Cellular mobile communication ytem have evolved from narrowband network of around kbp (firt and econd generation ytem) to wideband network of around Mbp (third generation ytem). Along with the advancement of wirele technique, wirele ervice have been hifted from imple voice to data and then broadband Internet-related data ervice including video data. Now, the third generation long term evolution ytem with Mbp peak data rate are deployed in ome countrie []. A next tep i the development of broadband wirele technology that will be ued in the fourth generation ytem of a peak data rate of around Gbp. In the future fixed network, a variety of broadband network ervice will be made available by the o-called cloud computing network. Along with thi evolution of fixed network, wirele network need to further evolve in order to extend a variety of broadband network ervice available in the fixed network to wirele uer. Wirele acce network need to be enhanced to provide a gigabit wirele pipe to each uer mobile terminal (MT). However, there are a number of important technical iue to be addreed, for example, limited bandwidth, frequency-elective fading, and limited tranmit power. In thi paper, ome of the aforementioned technical iue are dicued, and then a ditributed antenna network (DAN) i introduced a a promiing olution. The gigabit wirele channel are extremely frequency elective. The received ignal pectrum i everely ditorted. An advanced equalization technique i neceary to achieve high-quality gigabit wirele data tranmiion in a trong frequency-elective channel. A promiing equalization technique i frequency domain equalization (FDE) [ ]. FDE i an attractive equalization technique that can be combined with tranmit diverity, receive diverity, beamforming, multiplexing, cooperative relaying, hybrid automatic repeat requet combining, and o on. In addition, the path lo and hadowing lo caue a evere power lo becaue the tranmit power i limited. The communication range i limited by the uplink Copyright John Wiley & Son, Ltd. 55

2 Single-carrier ditributed antenna network F. Adachi et al. (MT-to-bae tation (BS)). With the ame MT tranmit power a in the preent wirele ytem (i.e., third generation cellular ytem), the communication range of the gigabit wirele network will ignificantly hrink, and gigabit wirele ervice may be available near BS only. Therefore, a fundamental change i neceary in wirele acce network architecture. Ditributed antenna ytem or DAN [5] combined with frequency domain ignal proceing ha a potential to olve the aforementioned problem. For uplink ignal tranmiion, the ingle-carrier (SC) tranmiion i promiing becaue it ha a lower peak-to-average power ratio than multicarrier tranmiion (uing a tranmit power amplifier with the ame peak power, SC provide longer communication range than multicarrier). Therefore, we have been invetigating the potential of SC-DAN [5]. In thi paper, we firt give an overview of DAN in Section and then preent pace time-coded diverity combined with one-tap FDE for SC-DAN downlink and uplink in Section. In Section, patial multiplexing for SC-DAN i preented. Finally, Section 5 offer concluion.. OVERVIEW OF DISTRIBUTED ANTENNA NETWORK In DAN, a hown in Figure, the conventional BS i replaced by the ignal proceing center (SPC), and many antenna or cluter of antenna are patially ditributed around the SPC o that ome antenna can alway be viible from an MT with a high probability. Antenna or antenna cluter are connected to an SPC by mean of optical fiber link or wirele link. A number of ditributed antenna cooperate and act a patial multiplexing, antenna diverity, relay, or antenna array. Probably the mot powerful application i ditributed tranmit/receive antenna diverity combined with FDE. The problem that reult from ditance-dependent path lo and hadowing lo a well a from the intantaneou ignal power variation due to fading can imultaneouly be mitigated.. DIVERSITY For DAN uplink and downlink tranmiion, it i deirable to ue a many ditributed antenna a poible, wherea the number of MT antenna i limited to one or two becaue there i not enough pace to equip too many antenna at an MT. A a promiing DAN downlink tranmit diverity technique, we have developed a frequency domain pace time block-coded joint tranmit/receive diverity (FD-STBC-JTRD) combined with tranmit FDE []. The FD-STBC-JTRD i an extenion of joint tranmit diverity/tranmit FDE [] by adding antenna diverity reception and achieve an N dan N mt th order (full) diverity gain, where N dan and N mt repreent the number of ditributed tranmit antenna and that of MT receive antenna, repectively. The FD-STBC-JTRD allow the ue of up to N mt D MT receive antenna while requiring only imple addition, ubtraction, and conjugate operation at an MT receiver and thu alleviate the computational complexity problem of MT receiver. Although the number of MT receive antenna i limited to N mt D, FD-STBC-JTRD allow the ue of an arbitrary number of ditributed tranmit antenna, N dan. There are two type of tranmit FDE weight: minimum mean quare error (MMSE) weight and maximum channel capacity weight. For the uplink tranmiion, frequency domain pace time tranmit diverity (FD-STTD) [8] i promiing. Thi i becaue FD-STTD allow the ue of an arbitrary number N dan of ditributed receive antenna although the number N mt of MT tranmit antenna i limited. A combination of FD-STBC-JTRD for downlink and FD-STTD for uplink i uitable for DAN. In Section., we preent the ignal repreentation for SC-DAN downlink uing FD-STBC-JTRD. Section. introduce the tranmit FDE weight for FD-STBC-JTRD. The SC-DAN uplink uing FD-STTD i decribed in Section.. Section. dicue the computer imulation reult. Section.5 compare the uplink and downlink performance in term of bit error rate (BER). DAN SPC Spatial multiplexing/ diverity Relay Ditributed antenna Optical fiber link Figure. Ditributed antenna network (DAN). SPC, ignal proceing center. 55 Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm

3 F. Adachi et al. Single-carrier ditributed antenna network #N dan Data mod. N c -Point FFT STBC- JTRD encoder N c -Point IFFT +GI # # SPC N dan ditributed antenna (a) SPC tranmitter #N mt # N mt receive antenna GI N c -Point FFT STBC- JTRD decoder N c -Point IFFT Data demod. (b) MT receiver Figure. Downlink tranmitter/receiver tructure uing frequency domain pace time block-coded joint tranmit/receive diverity (FD-STBC-JTRD): (a) ignal proceing center (SPC) tranmitter and (b) mobile terminal (MT) receiver. FFT, fat Fourier tranform; GI, guard interval. Table I. J, Q, and coding rate R. No. of tranmit antenna No. of receive antenna J Q Coding rate Arbitrary / / The SC ignal tranmiion i a block tranmiion. In thi paper, a block ize of N c ymbol i aumed... FD-STBC-JTRD (downlink) The FD-STBC-JTRD tranmitter/receiver tructure uing N dan ditributed tranmit antenna and N mt MT receive antenna i illutrated in Figure. At the SPC, a equence of J block of N c ymbol each i tranformed by an N c -point fat Fourier tranform (FFT) into a equence of J frequency domain ignal and then encoded into N dan (the number of ditributed tranmit antenna) tream of Q-coded frequency domain ignal block each. FD-STBC-JTRD decoding at an MT receiver need addition, ubtraction, and conjugate operation only. A combination of J, Q, and coding rate R are hown in Table I for N mt D to. The achievable diverity gain increae with increaing N mt ; however, the coding rate reduce to / when N mt D and. Thi ugget that the channel capacity or throughput may be maximized at N mt D. Later, for the ake of brevity, only the ignal repreentation for N mt D (therefore, J D Q D ) i preented (for N mt D and []). However, the computer imulation reult on the channel capacity will be hown for N mt D to confirm that N mt D maximize the channel capacity. When N mt D, a pair of N c ymbol block (J D ) to be tranmitted are tranformed by N c -point FFT into a pair of frequency domain ignal fd.k/;d.k/i k D N c g.q D /, which i repreented by D.k/ D ŒD.k/ D.k/ T : D.k/ i then encoded into N dan pair of frequency domain-coded ignal block a S tbc-jtrd.k/ D S ;.k/ S ;.k/ : S ;Ndan.k/ S ;.k/ S ;.k/ : 5 S ;Ndan.k/ DW.k/D tbc-jtrd.k/ () where S qn.k/, q D,ithekth frequency component at the nth tranmit antenna. In Equation (), D tbc jtrd.k/ i the encoding matrix of ize for N mt D,givenby D.k/ D tbc-jtrd.k/ D D.k/ D.k/ D.k/ () Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm 55

4 Single-carrier ditributed antenna network F. Adachi et al. W(k/ i the tranmit FDE weight matrix of ize N dan, given a where H.k/ D W.k/ D A.k/H H.k/ () H;.k/ H ;.k/ H ;Ndan.k/ H ;.k/ H ;.k/ H ;Ndan.k/ and./ H denote the Hermitian tranpoe. In Equation (), A.k/ i introduced to keep the tranmit power intact after the encoding and will be dicued in Section.. H m;n.k/ in Equation () i the channel gain between the nth ditributed tranmit antenna and the mth MT receive antenna. An N c -point invere FFT (IFFT) i applied to fs.k/i k D N c g to obtain N dan pair of N c ymbol block to be tranmitted from N dan ditributed antenna. At the MT receiver, a uperpoition of N dan pair of coded N c ymbol block i received by N mt D antenna. The received ignal are tranformed by N c -point FFT into frequency domain ignal, fr m;.k/ and R m;.k/i m D g, which can be expreed uing the matrix form a R:.k/ R R.k/ D ;.k/ R :.k/ R ;.k/ (5) E D H.k/S tbc-jtrd.k/ C N.k/ T where N;.k/ N.k/ D N ;.k/ N ;.k/ N ;.k/ i the noie matrix with fn m;q.k/i m D ; q D g being independent zero-mean complex Gauian variable having variance N =T,whereN denote the ingleided power pectrum denity of additive white Gauian noie and T denote the data ymbol duration. The FD-STBC-JTRD decoding for N mt D i carried out to obtain the frequency domain ignal vector OD.k/ D h i T D O.k/ OD.k/ correponding to the tranmitted ignal vector D.k/ D ŒD.k/D.k/ T a " R;.k/ C R OD.k/ D ;.k/ # R ;.k/ R;.k/ E X NX dan D A.k/ Hm;n.k/D.k/ () T md nd " N;.k/ C N C ;.k/ # N ;.k/ N;.k/ Finally, N c -point invere FFT i applied to tranform n O D.k/I k D N c o into a pair of oft deciion N c ymbol block (J D ). () () It can be clearly een from Equation () that the downlink FD-STBC-JTRD uing N dan ditributed tranmit antenna and N mt MT receive antenna can achieve an N dan N mt.d /th order (full) diverity gain. In the following, we conider an SC-DAN with N dan ditributed antenna and N mt MT antenna... Tranmit FDE weight for FD-STBC-JTRD (downlink) Two type of tranmit FDE weight are preented: joint water filling and maximal ratio tranmiion (WF-MRT) weight [9] and MMSE weight [].... Joint WF-MRT weight. The joint WF-MRT weight i the one that maximize the channel capacity. The problem formulation of channel capacity maximization under the tranmit power contraint can be written from Equation () a max C D NX c B log fa.k/g C E wf-mrt A.k/ tbc-jtrd c N kd A NX mt NX C Hm;n.k/ A.t. N c X kd md nd tbc-jtrd N dan X nd NX mt The olution of Equation (8) i denoted by k D N c g and i given by A wf-mrt tbc-jtrd.k/ D N mt P N dan P Hm;n.k/ md Hm;n.k/ A D N c (8) n A wf-mrt tbc-jtrd.k/i md nd 8 ˆ< max.e =N / ' D ; N mt P N dan P ˆ: Hm;n.k/ md nd 9 >= (9) 5 >; where D i et o a to atify the tranmit power contraint hown in Equation (8). Subtituting Equation (9) 55 Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm

5 F. Adachi et al. Single-carrier ditributed antenna network into Equation () give the joint WF-MRT weight. The channel capacity C (bp/hz) for the given channel realization i given a C D NX c log N c kd C E N mt P N dan P N Hm;n.k/ md nd 8 9 ˆ< >= max ˆ: '.E D =N / C ; Nmt P N dan P 5 A jh m;n.k/j >; md nd ()... MMSE weight. The MMSE weight i the one that minimize the mean h i T quare error between OD.k/ D D O.k/ OD.k/ and D.k/ D ŒD.k/ D.k/ T. Similar to Equation (8), finding the MMSE weight can be formulated a min fa.k/g e D N c X kd N mt X md NX c E OD m.k/ D m.k/ N mt A mme.k/ tbc-jtrd kd md NX dan Hm;n.k/ A D N c nd n () With Equation () being olved, A mme tbc-jtrd.k/i k D N c g i given a [] A mme tbc-jtrd.k/ D N mt P N dan P N Hm;n.k/ mt C E N md nd () and G NX c n o N A mme tbc-jtrd N.k/ X mt c kd md N dan X nd Hm;n.k/ A () Subtituting Equation () into Equation () give the MMSE weight... Receive FDE weight for FD-STTD (uplink) The FD-STBC-JTRD i uitable for the downlink tranmiion. For the uplink tranmiion, FD-STTD [8] i uitable becaue FD-STTD allow the ue of an arbitrary number N dan of ditributed receive antenna, wherea the number N mt of MT tranmit antenna i limited. A pair of N c ymbol block (ubcript and repreenting even and odd block, repectively) are tranformed by N c -point FFT into frequency domain ignal repreented by D.k/ D ŒD.k/ D.k/ T. The FD-STTD encoding i expreed uing the matrix form a [8] r D.k/ D D ttd.k/ D.k/ D.k/ D.k/ () Two pair of FD-STTD codeword are tranmitted from N mt D antenna and are received by N dan ditributed antenna, followed by N c -point FFT. N dan pair of the received frequency domain ignal, fr n;.k/ and R n;.k/i n D N dan g, are expreed uing the matrix form a R ttd.k/ D where D N.k/ D R ;.k/ R ;.k/ : 5 R Ndan ;.k/ R ;.k/ R ;.k/ : R Ndan ;.k/ E H T.k/D ttd.k/ C N.k/ T N ;.k/ N ;.k/ : N Ndan ;.k/ N ;.k/ N ;.k/ : 5 N Ndan ;.k/ (5) () i the noie matrix. After the FD-STTD decoding, the frequency domain h i T ignal vector OD.k/ D D O.k/ OD.k/ aociated with D.k/ D ŒD.k/ D.k/ T i obtained a. Ditributed antenna MT of interet MT location area Figure. Antenna ditribution. MT, mobile terminal. Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm 555

6 Single-carrier ditributed antenna network F. Adachi et al. N dan P R n;.k/wn;.k/ C N dan P Rn;.k/W n;.k/ OD.k/ D nd nd N dan P R n;.k/wn;.k/ N dan P Rn;.k/W 5 n;.k/ nd nd E X NX dan D A.k/ Hm;n.k/ D.k/ T md nd N dan P N n;.k/wn;.k/ C N dan P Nn;.k/W n;.k/ C nd nd N dan P N n;.k/wn;.k/ N dan P Nn;.k/W 5 n;.k/ nd nd () Similar to the downlink cae, the MMSE weight matrix that minimize the mean quare error between OD.k/ and D.k/ i given, for the cae of N mt MT antenna, a [8] W mme ttd where A mme ttd.k/ D.k/ D A mme ttd.k/h.k/ H.k/ D N mt P N dan P N Hm;n.k/ mt C E N md nd (8) N mt P N dan P N mt md nd.. Computer imulation reult Hm;n.k/ C E N (9) Firt, the WF-MRT weight and MMSE weight are compared for SC-DAN downlink uing FD-STBC-JTRD. Then, the channel capacity and BER ditribution are evaluated for joint WF-MRT weight and with MMSE weight, repectively. Figure illutrate the DAN antenna ditribution. N D antenna are uniformly ditributed with equal ditance between adjacent antenna. An MT having N mt antenna i randomly located in the haded area. N dan antenna are elected for downlink tranmiion, on the bai of the local average received power (i.e., on the bai of the path lo plu hadowing lo). The channel i aumed to follow an L D -path frequency-elective Rayleigh fading, a log-normally ditributed hadowing having tandard deviation D : db, and a ditance-dependent path lo having path lo exponent D :5.... Comparion of WF-MRT weight and MMSE weight for SC-DAN downlink uing FD-STBC-JTRD. A comparion between the WF-MRT weight and MMSE weight i made for the cae of N dan D and N mt D. The normalized tranmit E =N i et to db (i.e., the tranmit power i the one that provide the received E =N D db at the adjacent antenna location). For both the WF-MRT and MMSE weight, the power allocation i carried out in antenna and frequency dimenion. Figure plot the channel tranfer function between tranmit antenna and n.d / and the quared value of the correponding tranmit FDE weight. Both weight allocate the tranmit power acro the tranmit antenna on the bai of maximal ratio trategy. Therefore, irrepective of the weight, le tranmit power i allocated to the tranmit antenna in a bad channel condition (Figure (a), (a), (b), and (b)), wherea more tranmit power i allocated to the tranmit antenna in a good channel condition (Figure (a) and (b)). Power allocation i carried out acro the frequencie. In cae of the WF-MRT weight, more tranmit power i allocated to the frequencie in a good channel condition (Figure (b)). Figure 5(a) plot the equivalent channel tranfer function NX mt NX dan H.k/D Hm;n.k/ A md nd wherea Figure 5(b) plot the quared value of correponding equivalent tranmit FDE weight OW.k/ D N mt X md N dan X nd Wm;n.k/ It can be een from Figure 5(b) that joint WF-MRT weight allocate more tranmit power to the frequencie in a better channel condition (ome frequencie in a bad channel condition are not ued at all). On the other hand, the MMSE weight ue the frequencie even in a poor condition.... FD-STBC-JTRD with joint WF-MRT weight. Figure plot the % outage capacity of SC-DAN downlink uing FD-STBC-JTRD with joint WF-MRT weight, below which the channel capacity fall with % probability, for the normalized tranmit E =N D db. The ue of N mt D maximize the channel capacity. Thi i a conequence of the trade-off between diverity gain and coding rate; a N mt increae, the diverity gain increae, but the coding rate R reduce to / when N mt D (Table I). 55 Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm

7 F. Adachi et al. Single-carrier ditributed antenna network Figure plot the required tranmit E =N for a % outage capacity of 5 bp/hz a a function of N dan for the cae of N mt D. Increaing N dan reduce the required tranmit E =N. The required E =N reduction by increaing N dan from to i about 5. db.... FD-STBC-JTRD with joint MMSE weight. The BER performance of SC-DAN downlink uing FD-STBC-JTRD with MMSE weight i alo evaluated. Figure 8 plot the required tranmit E =N for a % outage BER of a a function of N dan when N mt D. Increaing N dan reduce the required tranmit E =N.The required E =N reduction by increaing N dan from to i about.5 db..5. Uplink/downlink performance comparion The BER performance are compared auming FD- STBC-JTRD uing joint MMSE weight for the uplink H, (k) (a) H, (k) W, (k) (b) W, (k) joint WF-MRT MMSE H, (k) H, (k) H, (k) (a) H, (k) (a) H, (k) (a) H, (k) W, (k) W, (k) W, (k) (b) W, (k) (b) W, (k) (b) W, (k) joint WF-MRT MMSE joint WF-MRT MMSE joint WF-MRT MMSE Figure. Channel tranfer function and quared value of frequency domain equalization weight when N mt D andn dan D : (a) jh ;.k/j, (a)jh ;.k/j, (a)jh ;.k/j, (a)jh ;.k/j, (b) jw ;.k/j, (b) jw ;.k/j, (b) jw ;.k/j, and (b) jw ;.k/j.wf-mrt, water filling and maximal ratio tranmiion; MMSE, minimum mean quare error. Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm 55

8 Single-carrier ditributed antenna network F. Adachi et al. and FD-STTD uing MMSE weight for the downlink. N dan arbitrary ditributed antenna and N mt D MT antenna are aumed. The ame antenna ditribution pattern a in Section. i aumed. (E /N ) req. (db) 5 5 FD-STBC-JTRD(downlink) α=.5, σ=. L= N mt = H(k) ^ W(k) ^ (a) H(k) ˆ joint WF-MRT MMSE 5 N dan Figure. Required tranmit E /N for a % outage capacity of 5 bp/hz. FD-STBC-JTRD, frequency domain pace-time block-coded joint tranmit/receive diverity. (E /N ) req. (db) 5 5 FD-STBC-JTRD(downlink) α=.5, σ =. L = N mt = (b) W(k) ˆ Figure 5. Equivalent channel tranfer function and quared value of equivalent tranmit frequency domain equalization weight when N mt D andn dan D : (a) OH.k/ and(b)j OW.k/j. WF-MRT, water filling and maximal ratio tranmiion; MMSE, minimum mean quare error. % outage capacity (bp/hz) 5 Normalized tranmit E /N = db α=.5, σ=., L= N c =5 N mt = N mt =, N dan Figure. % outage channel capacity of ingle-carrier ditributed antenna network downlink uing frequency domain pace time block-coded joint tranmit/receive diverity with joint water filling and maximal ratio tranmiion weight. 5 N dan Figure 8. Required tranmit E =N for a % outage bit error rate of. FD-STBC-JTRD, frequency domain pace time block-coded joint tranmit/receive diverity. The complementary cumulative ditribution function of the meaured downlink and uplink BER are plotted in Figure 9 for the normalized tranmit E =N D 5 db. It can be clearly een from the figure that well-balanced downlink and uplink tranmiion can be achieved. By increaing N dan (the number of ditributed tranmit/receive antenna), the probability that the received ignal power drop due to path lo, hadowing lo, and frequency-elective fading can be more reduced and hence the BER can be ignificantly reduced.. SPATIAL MULTIPLEXING The patial multiplexing i an attractive technique to achieve highly pectrum-efficient tranmiion []. Multiple ditributed antenna in DAN can be alo ued not only for pace diverity but alo for the patial multiplexing to improve the throughput of the ytem []. Here, we conider the uplink cae uing N mt tranmit antenna and N dan receive ditributed antenna (N dan receive antenna are elected among N ditributed antenna). 558 Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm

9 F. Adachi et al. Single-carrier ditributed antenna network Prob [BER>abcia] - - Normalized tranmit E /N = 5dB α=.5, σ=., L= N c =5, N g = N mt = FD-STTD(MMSE) (uplink) FD-STBC-JTRD(MMSE) (downlink) N dan = -.E-5.E-.E-.E-.E- BER Figure 9. Uplink/downlink performance comparion. BER, bit error rate; FD-STTD, frequency domain pace time tranmit diverity; FD-STBC-JTRD, frequency domain pace time blockcoded joint tranmit/receive diverity; MMSE, minimum mean quare error... Signal detection for patial multiplexing Recently, we propoed a maximum likelihood detection (MLD) employing QR decompoition and M-algorithm (QRM-MLD) [] for the SC patial multiplexing in a frequency-elective fading channel []. The SC frequency domain maximum likelihood block ignal detection employing QR decompoition and M-algorithm (QRM- MLBD) i a powerful ignal detection cheme combined with FDE. The receiver tructure of SC frequency domain QRM-MLBD for a cyclic prefix (CP)-inerted SC (CP-SC) patial multiplexing i illutrated in Figure. Y Y Nr Multiplication of Q H QR decompoition Ŷ MLD uing M-algorithm Deciion variable Figure. Single-carrier frequency domain maximum likelihood block ignal detection employing QR decompoition and M-algorithm. MLD, maximum likelihood detection. Auming the N mt N dan patial multiplexing, the frequency domain received ignal vector at the nth receive ditributed antenna Y n D ŒY n./;:::;y n.k/;:::;y n.n c / T i expreed a Y n D E T N mt X md H n;m Fd m C N n () where F i the dicrete Fourier tranform matrix of ize N c N c, H n;m D diagœh n;m./; : : : ; H n;m.k/;:::;h n;m.n c / i the frequency domain channel matrix between the mth tranmit antenna and nth receive antenna, and N n D ŒN n./;:::;n n.k/;:::;n n.n c / T i the frequency domain noie vector. From Equation (), the N dan N c overall frequency domain received ignal Y i given by Y D fy g T fy Ndan g T T H ; F H ; F H ;Nmt F E H ; F H ; F H ;Nmt F D T : : : :: : :: 5 H Ndan ;F H Ndan ;F H Ndan ;N mt F d N : : 5 C : : 5 d Nmt E D H T d : : d Nmt N Ndan 5 C N () where H i an equivalent channel matrix of ize N dan N c N mt N c. QRM-MLBD can be applied to the SC patial multiplexing by treating a concatenation of the pace and frequency domain channel and dicrete Fourier tranform a thi equivalent channel. The QRM-MLBD conit of two tep: QR decompoition and M-algorithm. Firt, the QR decompoition i applied to the equivalent channel matrix H to obtain H D QR, whereq i an N dan N c N mt N c unitary matrix and R i an N mt N c N mt N c upper triangular matrix. The tranformed frequency domain received ignal OY D h i T Y./;:::; O OY.k/;:::; OY.N mt N c / i obtained a OY D Q H E Y D R T d : : d Nmt 5 C Q H N () It can be undertood from Equation () that the MLD can be converted to the ucceive tree earch problem and that the computational complexity can be reduced by introducing the M-algorithm into the ucceive tree earch. SC frequency domain QRM-MLBD can achieve the BER performance cloe to the MLD with ignificantly reduced computational complexity compared with the MLD. Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm 559

10 Single-carrier ditributed antenna network F. Adachi et al. CP () Data ymbol () CP () Data ymbol () N g ymbol N c ymbol DFT block (a) CP-SC TS Data ymbol () TS Data ymbol () N c ymbol N g ymbol DFT block (b) TS-SC Figure. (a) Cyclic prefix inerted ingle carrier (CP-SC) and (b) training equence-aided ingle carrier (TS-SC). DFT, dicrete Fourier tranform. However, the CP-SC block tranmiion require a fairly large number of urviving path in the M-algorithm; therefore, it computational complexity i till very high. To overcome thi problem, we uggeted uing a known training equence (TS)-aided SC (TS-SC) tranmiion, in which the known TS in the previou block act a the CP in the preent block, a hown in Figure [],[5]. The known TS i exploited in the M-algorithm to reduce the number of urviving path. Average BER patial multiplexing QRM-MLBD TS-SC MIMO CP-SC MIMO M= M= M=5 MMSED.. Computer imulation reult Firt, we compare CP-SC and TS-SC for point-to-point tranmiion uing patial multiplexing. We aume a block tranmiion of N c D ymbol. The channel i aumed to be a ymbol-paced L D -path frequencyelective block Rayleigh fading channel having uniform power delay profile. Ideal channel etimation i aumed. The average BER performance of SC frequency domain QRM-MLBD i plotted in Figure. Alo plotted i the BER performance achievable by MMSE detection. A the number M of urviving path in the M-algorithm increae, the BER performance improve. When TS-SC i ued, the required number of urviving path in the M-algorithm i greatly reduced while achieving almot the ame BER performance a CP-SC. In DAN, even antenna are ditributed over an entire cell to compare with the conventional cellular network a illutrated in Figure. Figure plot the complementary cumulative ditribution function of the computer-imulated BER when N mt D N dan D. The ingle-uer and inglecell uplink SC-DAN i conidered. The normalized tranmit E =N i et to db (i.e., the tranmit power i the QPSK N = N = Average received E b /N per antenna (db) Figure. Bit error rate (BER) performance comparion between cyclic prefix-inerted ingle carrier (CP-SC) and training equence-aided ingle carrier (TS-SC). QPSK, quadrature phae hift keying; QRM-MLBD, maximum likelihood block ignal detection employing QR decompoition and M-algorithm; MIMO, multiple input multiple output; MMSED, minimum mean quare error detection. r r / (a) DAN. r. (b) Conventional network Figure. Sytem model: (a) ditributed antenna network (DAN) and (b) conventional network. N mt D N dan D. 5 Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm

11 F. Adachi et al. Single-carrier ditributed antenna network N mt =N dan =(Spatial multiplexing) QPSK N c =, N g = -path uniform the tranmiion performance compared with the MMSE patial filtering. Prob [BER>abcia] Normalized tranmit E /N =db CN 5 MMSED QRM-MLBD M= M= M= BER DAN Figure. Complementary cumulative ditribution function of bit error rate (BER). N mt D N dan D. QPSK, quadrature phae hift keying; MMSED, minimum mean quare error detection; QRM-MLBD, maximum likelihood block ignal detection employing QR decompoition and M-algorithm; CN, conventional network; DAN, ditributed antenna network. one that provide the received E =N D db at the cell edge). MT tranmit N mt parallel data tream by uing patial multiplexing. It i aumed that N dan ditributed antenna nearet from the MT are elected a receive antenna. It can be een that DAN can ignificantly reduce the BER compared with the conventional network. When QRM-MLBD with M D i ued, DAN can reduce the outage probability by % compared with the conventional network (the outage probability i defined a the probability that the BER exceed the required BER D in thi paper). Furthermore, QRM-MLBD can reduce the BER compared with the MMSE ignal detection. The performance improvement i ignificant in DAN. 5. CONCLUSION Ditributed antenna network i a promiing wirele technology to realize gigabit wirele data tranmiion. In thi paper, we have introduced gigabit DAN combined with SC frequency domain ignal proceing. Ditributed tranmit/received diverity can olve the problem ariing from evere channel electivity and limited tranmit power. It i deirable to ue a many ditributed antenna a poible to achieve higher diverity gain while limiting the number of MT antenna to one or two o a to alleviate the complexity problem of MT. It wa hown that the balanced downlink/uplink performance can be achieved by uing FD-STBC-JTRD for the downlink and FD-STTD for the uplink. We alo preented a patial multiplexing uing TS-SC and QRM-MLBD to improve REFERENCES. Atély D, Dahlman E, Furukär A, Jading Y, Lindtröm M, Parkvall S. LTE: the evolution of mobile broadband. IEEE Communication Magazine 9; (): 5.. Falconer D, Ariyavitakul SL, Benyamin-Seeyar A, Eidon B. Frequency domain equalization for inglecarrier broadband wirele ytem. IEEE Communication Magazine ; (): 58.. Adachi F, Sao T, Itagaki T. Performance of multicode DS-CDMA uing frequency domain equalization in a frequency elective fading channel. IEE Electronic Letter ; 9(): 9.. Adachi F, Garg D, Takaoka S, Takeda K. Broadband CDMA technique. IEEE Wirele Communication Magazine 5; (): Adachi F, Takeda K, Obara T, Yamamoto T. Recent advance in ingle-carrier frequency-domain equalization and ditributed antenna network. IEICE Tranactionon Fundamental ; E9-A():.. Tomeba H, Adachi F. Frequency-domain pace-time block coded-joint tranmit/receive diverity for the ingle carrier tranmiion, In Proceeding of the th IEEE International Conference on Communication Sytem (ICCS), Singapore,.. Choi RL, Murch RD. Frequncy domain preequalization with tranmit diverity for MISO broadband wirele communication, In Proceeding of the IEEE Vehicular Technology Conference (VTC-Fall), Vancouver, Canada,. 8. Takeda K, Itagaki T, Adachi F. Application of pacetime tranmit diverity to ingle-carrier tranmiion with frequency-domain equalization and receive antenna diverity in a frequency-elective fading channel. IEE Proceeding-Communication ; 5():. 9. Matuda H, Matukawa R, Obara T, Takeda K, Adachi F. Channel capacity of ditributed antenna network uing pace-time block coded-joint tranmit/receive diverity, In Proceeding of th IEEE International Conference on Communication Sytem (ICCS ), Singapore,.. Fochini GJ, Gan MJ. On limit of wirele communication in a fading environment when uing multiple antenna. Wirele Peronal Communication 998; (): 5. Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm 5

12 Single-carrier ditributed antenna network F. Adachi et al.. Saleh A, Rutako A, Roman R. Ditributed antenna for indoor radio communication. IEEE Tranaction on Communication 98; 5(): Kim LJ, Yue J. Joint channel etimation and data detection algorithm for MIMO-OFDM ytem, In Proceeding of the th Ailomar Conference on Signal, SytemandComputer, ; Nagatomi K, Higuchi K, Kawai H. Complexity reduced MLD baed on QR decompoition in OFDM MIMO multiplexing with frequency domain preading and code multiplexing, In Proceeding of the IEEE Wirele Communication and Networking Conference (WCNC 9), 9;.. Yamamoto T, Takeda K, Adachi F. Training equenceaided ingle-carrier block ignal detection uing QRM-MLD, In Proceeding of the IEEE Wirele Communication & Networking Conference (WCNC ), Sydney, Autralia,. 5. Yamamoto T, Takeda K, Adachi F. Training equenceaided QRM-MLD block ignal detection for inglecarrier MIMO patial multiplexing, In Proceeding of the IEEE International Conference on Communication (ICC ), Kyoto, Japan,. AUTHORS BIOGRAPHIES Fumiyuki Adachi received B.S. and Dr. Eng. degree in Electrical Engineering from Tohoku Univerity, Sendai, Japan, in 9 and 98, repectively. In April 9, he joined the Electrical Communication Laboratorie of Nippon Telegraph & Telephone Corporation (now NTT) and conducted variou type of reearch related to digital cellular mobile communication. From July 99 to December 999, he wa with NTT Mobile Communication Network, Inc. (now NTT DoCoMo, Inc.), where he led a reearch group on wideband/broadband CDMA wirele acce for IMT- and beyond. Since January, he ha been with Tohoku Univerity, Sendai, Japan, where he i a Profeor of Electrical and Communication Engineering at the Graduate School of Engineering. He wa appointed a a Ditinguihed Profeor in. Hi reearch interet are in CDMA wirele acce technique, equalization, tranmit/receive antenna diverity, MIMO, adaptive tranmiion, and channel coding, with particular application to broadband wirele communication ytem. He i a program leader of the 5-year Global COE Program "Center of Education and Reearch for Information Electronic Sytem" (- ), awarded by the Minitry of Education, Culture, Sport, Science and Technology of Japan. From October 98 to September 985, he wa a United Kingdom SERC Viiting Reearch Fellow in the Department of Electrical Engineering and Electronic at Liverpool Univerity. He i an IEICE Fellow and wa a co-recipient of the IEICE Tranaction Bet Paper of the Year Award 99, 998, and 9 and alo a recipient of the Achievement Award. He i an IEEE Fellow and wa a co-recipient of the IEEE Vehicular Technology Tranaction Bet Paper of the Year Award 98 and again 99 and alo a recipient of the Avant Garde Award. He wa a recipient of Thomon Scientific Reearch Front Award, Ericon Telecommunication Award 8, Telecom Sytem Technology Award 9, and Prime Miniter Invention Prize. Kazuki Takeda received hi B.S., M.S., and Dr. Eng. degree in Communication Engineering from Tohoku Univerity, Sendai, Japan, in, 8, and, repectively. From April 8 to March, he wa a Japan Society for the Promotion of Science (JSPS) Reearch Fellow. Since April, he ha been with Panaonic Corporation. He wa a recipient of the 9 IEICE RCS (Radio Communication Sytem) Active Reearch Award. Tetuya Yamamoto received hi B.S. degree in Electrical, Information and Phyic Engineering in 8 and M.S. degree in Communication Engineering in from Tohoku Univerity, Sendai, Japan. Currently, he i a Japan Society for the Promotion of Science (JSPS) Reearch Fellow, tudying toward hi Ph.D. degree at the Department of Electrical and Communication Engineering, Graduate School of Engineering, Tohoku Univerity. Hi reearch interet include frequency-domain equalization and ignal detection technique for mobile communication ytem. He wa a recipient of the 8 IEICE RCS (Radio Communication Sytem) Active Reearch Award. Ryuuke Matukawa received hi B.S. degree in Electrical, Information and Phyic Engineering from Tohoku Univerity, Sendai, Japan, in. Currently, he i a graduate tudent at the Department of Electrical and Communication Engineering, Graduate School of Engineering, Tohoku Univerity. Hi reearch interet include ditributed antenna network and multiple antenna technique. 5 Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm

13 F. Adachi et al. Single-carrier ditributed antenna network Shinya Kumagai received hi B.S. degree in Information and Intelligent Sytem from Tohoku Univerity, Sendai, Japan, in. Currently, he i a graduate tudent at the Department of Electrical and Communication Engineering, Tohoku Univerity. Hi reearch interet include ditributed MIMO diverity and multiplexing technique for mobile communication ytem. Wirel. Commun. Mob. Comput. ; :55 5 John Wiley & Son, Ltd. DOI:./wcm 5