時(shí)間選擇性衰落信道下的差分空時(shí)多普勒編碼

第38卷第2期中國海洋大學(xué)學(xué)報38(2):331~3342008年3PERIODICAL OF OCEAN UNIVERSITY OF CHINAMar,,2008時(shí)間選擇性衰落信道下的差分空時(shí)多普勒編碼蔚娜12,趙犁豐3,楊莘元(1.哈爾濱工程大學(xué)信息與通信工程學(xué)院,黑龍江哈爾濱150001;2.中國電波傳播研究所,山東青島266107;3.中國海洋大學(xué)電子工程系,山東青島266100)摘要:對于差分編碼的系統,接收端可利用差分編碼自身的結構來(lái)進(jìn)行解調,無(wú)需知道信道狀態(tài)信息。因此基于時(shí)間選擇性衰落信道的基擴展模型,提出一種新型的應用于時(shí)間選擇性衰落信道下多輸入多輸出系統的差分空時(shí)多普勒(DsTD)編碼方案,由該方案組成的系統可以配備任意數目的發(fā)送和接收天線(xiàn)。該DSTD系統發(fā)送端由頻譜編碼器、差分編碼器和OFDM調制器串聯(lián)組成,能提供最大空間多普勒分集增益和顯著(zhù)的編碼增益。差分編碼器中酉結構的引入可以實(shí)現線(xiàn)性空時(shí)分離的最大似然檢測,降低了譯碼的復雜度。仿真分析表明與已有差分系統相比,文中所提出的差分編碼方案可以獲得更高的分集增益。關(guān)鍵調:差分調制;時(shí)間選擇性衰落;最大空間多普勒分集;空時(shí)編碼;正交頻分復用中圖法分類(lèi)號;TN911文獻標識碼:A文章編號:1672-5174(2008)02331-05為了提高無(wú)線(xiàn)通信的可靠性和有效性,新的理論符號說(shuō)明:大寫(xiě)粗體表示矩陣(例如:X),[x]m,表示和技術(shù)不斷涌現。其中,多輸入多輸出(MIMO)系統X的第(m+1,n+1)個(gè)元素;小寫(xiě)粗體表示列向量就是近年來(lái)在無(wú)線(xiàn)移動(dòng)通信研究中的1個(gè)熱點(diǎn),尤其(x),[x]m表示x的第(m+1)個(gè)元素;IN表示NxN是基于多天線(xiàn)傳輸的空時(shí)碼,在接收端進(jìn)行適當的信單位矩陣;1N表示元素全為1的N×1向量;0表示元號處理就可以獲得分集增益和編碼增益,提高了信道素全為0的N×1向量;(·)表示轉置;(·)表示共容量12l但是絕大多數的空時(shí)碼方案都是假設在接軛;(,)表示共軛轉置;Rel,表示求實(shí)部dagx表收端能夠準確獲得信道狀態(tài)信息(CSI),并且在足夠長(cháng)示以x為對角線(xiàn)元素,其它元素為0的矩陣;⑧表示的時(shí)間內信道保持不變,這在實(shí)際的快衰落信道中是 Kronecker乘積。很難滿(mǎn)足的。如果在發(fā)送端采用差分編碼系統,在接收端進(jìn)行1信道模型譯碼時(shí)就無(wú)需知道CSI,基于此,產(chǎn)生了差分空時(shí)編碼(DSTC)。單差分空時(shí)分組編碼(SDST)方案(3能夠本文采用基擴展模型19來(lái)模擬時(shí)間選擇性衰落信在沒(méi)有CSI的情況下進(jìn)行譯碼,但當信道存在頻率偏道設n為每個(gè)分組塊中符號序列索引,N為1個(gè)分組移,為快衰落信道時(shí),性能會(huì )下降。單天線(xiàn)雙差分編碼塊中包含的符號數分組塊索引用k表示,則得到時(shí)變方案56在譯碼時(shí)可以降低對頻率偏移的敏感度,而結信道的離散表達式為:合了單天線(xiàn)雙差分編碼技術(shù)和空時(shí)編碼技術(shù)的雙差分hmp)(AN+n)=∑h"(k)(1)空時(shí)分組編碼(DDST)方案,即使對于每發(fā)送1個(gè)編碼符號信道就變化的時(shí)間選擇性衰落信道,在接收端其中,p=1,…,N2為發(fā)送天線(xiàn),=1,…N為接收同樣可以獲得較高的分集增益和編碼增益天線(xiàn),Q=2「∫mxNT1,fm為最大多普勒頻移,T,為但是文獻[7]的DT方案也只是利用了空間分符號周期,呦=2nx(q-Q/2)/N,n=0,…N-1集,而文獻[8]提出的單天線(xiàn)系統下的塊差分編碼方則接收端第υ個(gè)天線(xiàn)在第kN+n個(gè)時(shí)刻收到的信案,可以獲得多普勒分集增益。據此,本文提出了應用號為于時(shí)間選擇性衰落信道下多輸入多輸出系統的差分空r(o)(kN +n)=時(shí)多普勒編碼方案,該方案除了利用空間分集還利用U(O(N+ n)(o,)(kN+n)+了時(shí)變信道下的多普勒分集,能夠獲得更大的分集增o)(kN+n)益以塊為單位,寫(xiě)成矢量的形式為:·基金項目:國防基金(51401040703CB0102);“十一五”預研項目(11001060404)資助收稿日期:200706-18;修訂日期:20070925作者簡(jiǎn)介蔚娜(1981-),女博上。 E-mail: lenghanbingxue@sin.cm中國海洋大學(xué)學(xué)報2008年r(o)(k)=e EDo.p(k)yp(k)+5 o)(k)得到y=(INw⑧D∥")x)+η)((2)其中,y)=(IN⑧Fp)(IM⑧Rq)g其中,r(k)=[r{)(kN),…,r(劃N+N-1)];n)=(L⑧F)(IN⑧Rc){,yp)(k)為發(fā)送向量:[vP)(kN),…,v)(kN+N1)]r;yo)(k)與r)(k)有相同的結構其元素是獨立同(IN⑧Ta)(IN⑧F)x,分布的均值為0,方差每維為05的復高斯隨機變量;信道矩陣D")(k)=dg.[h(u,)(N…“,hP= pP/(P+Q)2.2差分編譯碼(kN+N-1)]};p是接收端信噪比。不失一般性,本差分編碼器取N個(gè)NP×1向量s0,…,sN-1作為文只考慮1個(gè)分組塊,因此為了表述方便,下文中的分輸入(Na=(N/N4-1),合理設置使N/N為大于1組塊索引k略去不寫(xiě)。的整數),首先把s(i=0,…,N,-1)分成N個(gè)P又已知循環(huán)矩陣可以被IFFT矩陣對角化),因1維子塊s,m(m=1,…,N),令Cm是這些向量通過(guò)此DP)可以寫(xiě)成以下形式:以下復正交設計得到的矩陣:D(A)=FNHU,P)FE(3)其中,H(",P)是1個(gè)N×N循環(huán)矩陣,其第一列為[hS),…h(huán)",…,hgn),…,h出]r;FN為N點(diǎn)8F-圓87a□F歸一化FFT矩陣,[FN]nn√°2m”/N。1由(3)式可知,在發(fā)送端和接收端分別進(jìn)行FFTF和IFFT變換,可以把時(shí)間選擇性衰落信道轉換成頻率選擇性衰落信道,所以:F了一[R一L8∑Hp)la(p)+;()(4)圖1基帶DSTD系統Fig 1 Baseband DSTD system其中,g)=F,)=F(),p)=FAw)N-12系統模型∑[A1⑧5,m+B1⑧sm](7)圖1是DSTD系統收發(fā)端的框圖發(fā)送端由3部分A,B,是NxN4實(shí)矩陣M在本文中的值遵循式組成:頻諧編碼器,差分編碼器和OFDM調制;接收端(8),且N=N,包括與發(fā)送端3部分對應的逆過(guò)程。N2,若N4=2,4,8,2.1OFDM調制與解調若對于頻率選擇性衰落信道,引入OFDM結構,這樣8,若N1=5,6,7可以解決塊間干擾,并且可以以塊為單位進(jìn)行譯碼,還可以把經(jīng)過(guò)在發(fā)送端加入和接收端去掉循環(huán)前綴而變取X0=I⑧IP,則:成循環(huán)矩陣的信道矩陣對角化,因此差分編譯碼器之x82…x只間的信道等效為X= D(I⑧F)(Iw⑧R)Hp)I⑧ToTNt. m(I6②F)=I⑧D!(p(S)其中,其中TcaP=[T1,IP,T2],(1)T1=[0a2)x(P-a/2),lo2],D,(a)= diagix(,Rap= [Opx(Q/),IP,OPx(Q/)]從而得到在N4個(gè)天線(xiàn)上發(fā)送的碼字矩陣為:D{n)=dag{[Hp(0),…,H(,p)(P-1)]X=[x(),x(Hr(np)(p)=∑h(q-Q/2)p/P其中,2期娜,等:時(shí)間選擇性衰落倩道下的差分空時(shí)多普勒編碼333xp)=[x.3,…,x)1.0,…,x.,…,x8),N]T為a,m即可完成譯碼。因為在實(shí)際的系統中有N個(gè)發(fā)送天線(xiàn),所以實(shí)際發(fā)送又假設星座符號集況中每個(gè)信息符號包含 Bits,的碼字矩陣為:則經(jīng)過(guò)LCD映射之后,|<|=2則隨著(zhù)R或者P的由(6)式把第個(gè)天線(xiàn)上的接收矢量分為(M,(11)增大,譯碼復雜度都會(huì )增加因此為了減小譯碼復雜X=TX=LIN,0x(N-N)」X度,采用分組的方法3假設P=N(Q+1),則進(jìn)一步把d,m分成N個(gè)NP×1子塊ym(m=0,…,N),則:組d,m(g),(g=0,…,N-1),d,m(g)映射成為=∑(D}”)x2,…,x1m+CD碼s,m(g),則:xn(g)=D:(g)Cn(g)==/:(Dx.)Th()+n)x(1(g)…xg)1.m(g)其中,Dx=LINp0Px-N)D,h(v)=[h1)r,…,hpN)TT,h,)是D胃對角線(xiàn)上的元素組成的列向量。其中,[xm(g)]=[xm]+系由(9)式得到:D。=D:DCn(13)3仿真分析這里,Dc∑A,⑧D,m+B,⑧D仿真中假設每個(gè)符號塊發(fā)送N=48個(gè)符號,每對則結合式(12)、(13)可以推出:天線(xiàn)之間的信道有(Q+1)=3個(gè)復指數基,并且信道(14)的基擴展模型參數是獨立同分布的均值為0,方差為其中wm)=ηm-Dηm1,本文假sm取自模為常/(Q+1)的復高斯隨機變址。采用本文提出的方法對數且能址歸一化的星座A,所以D是酉陣,不難得2發(fā)1收(2副發(fā)送天線(xiàn)1副接收天線(xiàn))以及2發(fā)2收的到wm)的元素是獨立同分布的均值為0,每維方差為1系統分別進(jìn)行了仿真,并與文獻[8]的結果進(jìn)行比較。的高斯隨機變量。圖2、圖3分別對應R=1、R=2,由圖中誤比待率曲線(xiàn)對于N個(gè)接收天線(xiàn),有:yn=[ym),…,ym)的斜率可以看出,文獻[8]的方案所獲得的分集增益同理有:ym=(囟D)ym1+wn(15)(即:(Q+1))是3,本文2發(fā)1收系統和2發(fā)2收系統獲得分集增益(即:NN,(Q+1))分別是6和12,可見(jiàn)wn與yn有相同結構。本文提出的差分編碼方案較文獻[8]獲得了更高的分令:x1,m=gm1集增益,不僅獲得時(shí)間選擇性衰落信道提供的多普勒{[∑[a,⑧D…,[an⑧D!]×x+分集,還同時(shí)獲得了多副收發(fā)天線(xiàn)提供的空間分集?！芠b⑧D"1],…∑[b,D}]}其中,a.n,b,n為N×1列向址,分別對應A,B10在文獻圖8]Dn(n= dingY21(n)},ym1(n)是P×1列向量,一本文N=2N=1并且:ym)1=[ym)1(0),…,y)1(N4-1)]T。從而,,m= arg max S, m∈ AR Rel z:),51,mThe proposed algorithm Na2, N=2152025信噪比 Signal noise ratio/ei=0,…,N-1;m=1,…,Na2.3頻譜編譯碼圖2R=1時(shí)各系統性能比較如圖1所示,取自星座的信息符號流d分成Fig 2 Performance comparison with R=1NN個(gè)P×1子塊d,m(i=0,…1;m=1,Na),每個(gè)子塊分別映射成為P×1為維LCD碼12)s,m,接收端只要將差分譯碼得到的3,n逆映射中國海洋大學(xué)學(xué)報2008年[2] Tarokh V, Jafarkhani H, Calderbank A R. Space-time block codefrom orthogonal designs [J]. IEEE Trans Inform Theory, 1999, 45(7):1456-1467.[3]Hochwald B M, Sweldens W. Differential unitary space-time modula-[]. IEEE Trans On Communications, 2000, 48( 12):2041[4]Information Theory, 2000, 46(7): 2567-2578|△-文獻圖[5] FGini, Giannakis G B. Generalized differential encoding一本文N=2N=1signal processing perspective [J]. IEEE Trans On Signal PnThe proposed algorithm N=2 N 1D1998,46(11):2967-2974proposed algorithm N-2.N-2[6] Pent M. Doubly differential PSK scheme in the presence of Dopplershift[C]. France: Digital Communications in Avionics, AGARD信噪比 Signal noise ratio/dBProe,1978,43:I-43.II[7] Liu, Z, Giannakis G B, Hughes B L. Double differential space-time圖3R=2時(shí)各系統性能比較block coding for time- selective fading channels [J]. IEEE Trans OnFig 3 Performance comparison with R=2Communications,2001,49(9):1529-1539[8] Ma X, Giannakis G B, Bing Lu. Block differential encoding for rapid4結語(yǔ)ly fading channels [J]. IEEE Trans On Communications, 2004, 52(3):416425本文提出了時(shí)間選擇性衰落信道下任意收發(fā)天線(xiàn)[9Max. Giannakis G B. Maximum-Diversity transmissions over time.數的差分空時(shí)多普勒(DSTD)編譯碼系統。在差分編Selective Wireless Channels [C]. USA: Proc of Wireless Communica-碼中引入基于分組正交設計的酉結構可以使最大似然tions and Networking Conf, Orlando, FL, 2002[10] Golub G H, Loan C F van. Matrix computations [M]. Maryland碼在時(shí)間和空間上分離,并且頻譜編碼中LCD碼的Johns Hopkins Univ Press, 3rd Edition, 1996引入可以降低譯碼的復雜度。仿真結果表明在沒(méi)有[1! Tirkkonen O. Hottinen A. Square-matrix embeddable space-timeCSI的情況下,系統可以同時(shí)獲得空間和多普勒分集block codes for complex signal constellations [J]. IEEE Trans增益以及顯著(zhù)的編碼增益Theory,2002,48(2):384-395[12] Li Hongbin. Differential space-time modulation ower frequencyselec參考文獻tive channels[J]. IEEE Trans On Signal Processing, 2005, 53(6):22282242[1] Tarokh v, Seshadri N. Calderbank AR. Space-time codes for high [13] Liu Z, GiannakisG B. Block differentially encoded OFDM withdata rate wireless communicatiomaximum multipath diversity [J]. IEEE Trans Wireless Commun.struction [J]. IEEE Trans Inform Theory, 1998, 44(3): 744-7652003,2(5):420-4(下轉302頁(yè))中國海洋大學(xué)學(xué)報2008年Distribution of Branchiostoma belcheri and Amphiura vadicola in Relation toBottom Grain Size in Dafangji Waters, MaomingLU Huo-Sheng, SHEn Chun-Yan, FENG BoCollege of Fisheries, Guangdong Ocean University, Zhanjiang 524006, ChiAbstract: Distribution of Branchiostoma belcheri and Amphiura uadicola is analyzed based on marine biolog-ical surveys conducted in Dafangji waters, Maoming during august 2003 to May 2004. both branchiostomabelcheri and Amphiura uadicola distribute in clusters. Their inter-species relationship proves to be positive inspatial distribution, and they do not compete strongly. branchiostoma belcheri is mainly distributed in sandwith median diameter (Md,)from 0.4 to 2.2 and its density is large for Mdo ranging from 0. 5 to 1.5 andsmall in the remaining intervals of Mdo. It is greater than 100 ind/m where the granularity of 0.36-0. 78mmgroup is greater than 50 percent and less than 50 ind/m otherwise. Amphiura uadicola is mainly distributedsand with Mdo ranging from 0.2 to 0. 8. Its density is dramatically greater where the granularity in 0. 360 78 mm group lies from 60 to 80 percent than where the granularity of the same group if from 10 to 50 per-Key words: Branchiostoma belcheri; Amphiura vadicola the median diameter Inter-species relationship責任編輯于衛上接334頁(yè))Differential Space-Time-Doppler Coding over Time-Selective ChannelsWEI Na. 2, ZHAO Li-Feng, YANG Shen-Y(1. College of Information and Communication Engineering, Harbin Engineering UnHarbin 150001, China; 2China Research Institute of Radiowave Propagation, Qingdao 266107, China; 3. Department of Electronics and EngineeringOcean University of China, Qingdao 266100, China)Abstract: Differential encoding is known to simplify receiver implementation because it by-passes chanel estimation. Relying on a basis expansion model for time-selective channels, we derive a new differential space-time-doppler modulation scheme for systems that are equipped with an arbitrary number oftransmit and receive antennas and operate in time-selective channels. The proposed dStd modulator con-sists of a concatenating spectral encoder differential encoder and OFDM modulator that offer full spatio-doppler diversity and significant coding gain. A unitary structure is imposed on the differential encoder toadmit linear, decoupled maximum likelihood ML)detection in space and time. Simulation results showthat the proposed! dStd codes achieve higher diversity gain in time-selective channels than some existingdifferential schemesKey words: differential modulation; time-selective fading: maximum spatio-doppler diversity; space-time coding: OFDM責任編輯陳呈超