基于AF-CDC-OFDM的差分網(wǎng)絡(luò)編碼

李民政, 歐陽繕, 謝躍雷, 肖海林

(1. 桂林電子科技大學(xué)廣西信息科學(xué)實(shí)驗(yàn)中心, 廣西 桂林 541004;

2. 西安電子科技大學(xué)電子工程學(xué)院, 陜西 西安 710071)

?

基于AF-CDC-OFDM的差分網(wǎng)絡(luò)編碼

李民政1,2, 歐陽繕1, 謝躍雷1, 肖海林1

(1. 桂林電子科技大學(xué)廣西信息科學(xué)實(shí)驗(yàn)中心, 廣西 桂林 541004;

2. 西安電子科技大學(xué)電子工程學(xué)院, 陜西 西安 710071)

摘要：在多子載波、頻率選擇性衰落、雙向中繼轉(zhuǎn)發(fā)信道中提出多中繼協(xié)作的基于AF-CDC-OFDM的差分網(wǎng)絡(luò)編碼方法。通過多個(gè)協(xié)作中繼的分布式循環(huán)延時(shí)編碼及功率放大處理,兩路終端發(fā)送的差分編碼分組可獲得完全的協(xié)作分集和頻率分集增益。兩路終端在檢測對方的發(fā)送信號之前需要消除自干擾信號,為此,提出基于統(tǒng)計(jì)相關(guān)的自干擾分量估計(jì)方法。仿真結(jié)果表明，提出的差分網(wǎng)絡(luò)編碼能夠獲得完全的分集增益性能,對應(yīng)的自干擾分量相關(guān)統(tǒng)計(jì)估計(jì)算法在慢衰落信道中與干擾分量完全消除的檢測性能相比,僅有0.5 dB的信噪比損耗。

關(guān)鍵詞：差分網(wǎng)絡(luò)編碼; 循環(huán)延時(shí)編碼; 放大轉(zhuǎn)發(fā)

0引言

雖然雙向中繼信道(two way relay channel, TWRC)中物理層網(wǎng)絡(luò)編碼(physical network codes, PNC)提高了傳輸效率,但相干檢測使PNC所需的信道估計(jì)開銷更大,挑戰(zhàn)更高[1-4]。在此情況下,差分網(wǎng)絡(luò)編碼成為更現(xiàn)實(shí)的選擇。基于解碼轉(zhuǎn)發(fā)(decode and forward, DF)的差分網(wǎng)絡(luò)編碼對中繼而言接收的是雙向疊加信號,當(dāng)雙向發(fā)送符號和信道狀態(tài)信息(channel status information,CSI)均不可知時(shí),可通過雙向CSI的二階矩構(gòu)建中繼檢測方法,以此完成雙向接收信號的檢測和差分網(wǎng)絡(luò)編碼的實(shí)施[5-6]。其缺點(diǎn)是中繼檢測復(fù)雜度高、處理環(huán)節(jié)繁雜、開銷大。為此,文獻(xiàn)[7-9]提出了基于模擬網(wǎng)絡(luò)編碼(analog network codes,ANC)的差分編碼方案,中繼僅需放大轉(zhuǎn)發(fā)(amplify and forward, AF)雙向疊加信號,以此保障兩路終端能有效接收轉(zhuǎn)發(fā)信號。這種編碼方法可有效降低中繼的處理復(fù)雜度,兩路終端在消除自干擾分量后,能夠以傳統(tǒng)差分檢測方法得到對方的發(fā)送信息。文獻(xiàn)[10-13]結(jié)合最佳中繼選擇策略提出了可獲得高分集增益的差分ANC方案。文獻(xiàn)[14-15]提出了基于ANC的差分空時(shí)編碼方法,獲得了完全的協(xié)作分集增益。然而,快衰落、多中繼、多子載波通信環(huán)境中,結(jié)合正交頻分復(fù)用(orthogonal frequency division multiplexing,OFDM)的差分網(wǎng)絡(luò)編碼研究比較少見,文獻(xiàn)[16]提出了平坦衰落信道中結(jié)合OFDM和循環(huán)延時(shí)編碼(cyclic delay codes,CDC)的差分ANC方案,但兩路終端的差分檢測仍然需要知道自身到中繼的CSI,因此,這種差分網(wǎng)絡(luò)編碼并非完全的差分檢測,也只能獲得協(xié)作分集增益。

本文提出適用于頻率選擇性衰落信道的基于AF-CDC-OFDM的差分網(wǎng)絡(luò)編碼,通過多個(gè)協(xié)作中繼對雙向疊加信號進(jìn)行CDC和AF處理,使兩路終端的編碼分組可獲取完全的協(xié)作和頻率分集增益。其理想檢測的前提是兩路終端自干擾分量完全消除,為此,提出基于統(tǒng)計(jì)相關(guān)的自干擾分量估計(jì)和消除方法。理論分析和仿真結(jié)果表明,提出的差分網(wǎng)絡(luò)編碼能獲得相應(yīng)的分集性能,對應(yīng)的自干擾分量相關(guān)統(tǒng)計(jì)估計(jì)算法在慢衰落信道中是有效的。

1差分網(wǎng)絡(luò)編碼模型

圖1　基于AF-CDC-OFDM的差分網(wǎng)絡(luò)編碼模型

2差分網(wǎng)絡(luò)編碼方法

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

3誤碼性能分析

(10)

(11)

(12)

(13)

(14)

(15)

(16)

式中,|hf(l)|2(l=1,…,KL2)為獨(dú)立同分布的指數(shù)隨機(jī)變量,因此,式(16)可表示為

(17)

(18)

4仿真實(shí)驗(yàn)與性能分析

圖2為基于AF-CDC-OFDM差分網(wǎng)絡(luò)編碼在協(xié)作中繼個(gè)數(shù)K=1, 2, 3, 4時(shí),通過仿真獲得的終端T1(或T2)的BER性能。同時(shí),為了驗(yàn)證提出的自干擾分量估計(jì)(self interference component elimination,SICE)算法的有效性,圖中還給出完全消除自干擾分量(genie-aided,GA)后的BER性能。

從圖2可看出,隨著協(xié)作中繼個(gè)數(shù)K的增加,基于AF-CDC-OFDM的差分網(wǎng)絡(luò)編碼BER性能逐漸改善,分集增益也相應(yīng)增加,當(dāng)BER為10-4時(shí),對應(yīng)中繼個(gè)數(shù)K=2,3,4處的信噪比(signal-to-noise ratio, SNR)分別為20 dB,17 dB,15 dB,BER性能依次改善了約3 dB和2 dB,這與理論分析所能獲得KL1(或KL2)階分集增益的結(jié)論相一致,也表明提出的差分網(wǎng)絡(luò)編碼能夠獲得完全的協(xié)作和頻率分集性能;協(xié)作中繼個(gè)數(shù)K相同時(shí),提出的SICE方法與GA相比,BER性能相同時(shí),SNR約有0.5 dB的損耗,這表明在慢衰落信道中提出的SICE算法能有效估計(jì)和消除自干擾分量。

圖2　中繼個(gè)數(shù)K=1, 2, 3, 4時(shí)的BER

圖3為SICE算法在時(shí)變特性逐漸增強(qiáng)的信道中獲取的BER性能,仿真中對應(yīng)的信道相干時(shí)間分別為τ=100T、50T、30T,協(xié)作中繼個(gè)數(shù)K=3,自干擾分量估計(jì)統(tǒng)計(jì)所需的OFDM幀符號個(gè)數(shù)分別為J=100、200、300。

圖3　信道相干時(shí)間τ=100T、50T、30T時(shí)的BER

從圖3可以看出,隨著信道時(shí)變特性的增強(qiáng)及信道相干時(shí)間τ的降低,提出的SICE算法與GA方法相比,對應(yīng)的BER性能呈下降趨勢,即使自干擾分量估計(jì)所需的OFDM幀符號數(shù)J由100增加到300,SICE算法的BER性能也未有明顯改善。當(dāng)BER性能為10-3時(shí),GA方法所需要的SNR為15 dB,提出的SICE算法在τ=100時(shí)與GA略差0.5 dB,在τ=50時(shí)與GA略差2 dB,在τ=30時(shí)與GA略差4 dB,這表明隨著信道時(shí)變特性的加劇,通過SICE算法得到的自干擾分量的估計(jì)誤差會(huì)相應(yīng)增加。如何在快衰落信道中更好地估計(jì)和消除自干擾分量尚需要進(jìn)一步研究。

5結(jié)論

在多子載波、頻率選擇性衰落、雙向中繼轉(zhuǎn)發(fā)信道中提出多中繼協(xié)作的基于AF-CDC-OFDM的差分網(wǎng)絡(luò)編碼方法。通過多個(gè)協(xié)作中繼的分布式循環(huán)延時(shí)編碼及功率放大處理,雙向終端發(fā)送的差分編碼分組可獲得完全的協(xié)作分集和頻率分集增益。雙向終端在檢測對方的發(fā)送信號之前需要消除自身干擾信號,為此,提出基于相關(guān)統(tǒng)計(jì)的自干擾分量估計(jì)消除方法。仿真結(jié)果表明，提出差分網(wǎng)絡(luò)編碼能獲得相應(yīng)的分集性能,提出的自干擾分量相關(guān)統(tǒng)計(jì)估計(jì)消除算法在慢衰落信道中是有效的。

參考文獻(xiàn)：

[1] Fang Z X, Liang F, Li L P. Performance analysis and power allocation for two-way amplify-and-forward relaying with generalized differential modulation[J].IEEETrans.onVehicularTechnology, 2014, 63(2): 937-942.

[2] Tian J G, Zhang Q, Yu F Q. Non-coherent detection for two-way cooperative communications in fast rayleigh fading channels[J].IEEETrans.onCommunications,2011,59(10):798-801.

[3] Cui T, Gao F F, Ho T. Distributed space time coding for two-way wireless relay networks[J].IEEETrans.onSignalProcessing, 2009, 57(2): 658-671.

[4] Bagheri S, Verde F, Darsena D. Randomized decode-and-forward strtegeies for two-way relay networks[J].IEEETrans.onWirelessCommunications, 2011, 10(12): 4212-4225.

[5] Cui T, Gao F, Tellambura C. Differential modulation for two-way wireless communications: a perspective of differential network coding at the physical layer[J].IEEETrans.onCommunications, 2009, 57(10): 2977-2987.

[6] Guan W, Liu K J R. Performance analysis of two-way relaying with non-coherent differential modulation[J].IEEETrans.onWirelessCommunications, 2011, 10(6): 2004-2014.

[7] Song L, Li Y, Huang A, et al. Differential modulation for bidirectional relaying with analog network coding[J].IEEETrans.onSignalProcessing, 2010, 58(7): 3933-3938.

[8] Valenti M C, Torrieri D, Ferrett T. Noncoherent physical-layer network coding with FSK modulation: relay receiver design issues[J].IEEETrans.onCommunications,2011,59(9):2595-2604.

[9] Huo Q, Song L, Li Y, et al. A distributed differential space-time coding scheme with analog network coding in two-way relay networks[J].IEEETrans.onSignalProcessing, 2012, 60(9): 4998-5004.

[10] Li Y, Louie R H Y, Vucetic B. Relay selection with network coding in two-way relay channels[J].IEEETrans.onVehicularTechnology, 2010, 59(9): 4489-4499.

[11] Krikidis I. Relay selection for two-way relay channels with MABC DF: a diversity perspective[J].IEEETrans.onVehicularTechnology, 2010, 59(9): 4620-4628.

[12] Song L, Hong G, Jiao B, et al. Joint relay selection and analog network coding using differential modulation in two-way relay channels[J].IEEETrans.onVehicularTechnology, 2010, 59(6): 2932-2939.

[13] Zhou Q F, Li Y H, Lau C M. Decode-and-forward two-way relaying with network coding and opportunistic relay selection[J].IEEETrans.onCommunications, 2010, 58(11): 3070-3076.

[14] Ma S, Zhang J K. Noncoherent diagonal distributed space-time block codes for amplify-and-forward half-duplex cooperative relay channels[J].IEEETrans.onVehicularTechnology, 2011, 60(5): 2400-2405.

[15] Alabed S J, Paredes J M, Gershman A B. A simple distributed space-time coded strategy for two-way relay channels[J].IEEETrans.onWirelessCommunications,2012,11(4):1260-1265.

[16] Xu J, Zhu S, Gao Z. Partial-differential distributed cyclic delay diversity for nonregenerative two-way relaying system[J].IEEESignalProcessingLetters, 2009, 16(7): 596-599.

[17] Bauch G. Differential modulation and cyclic delay diversity in orthogonal frequency-division multiplex[J].IEEETrans.onCommunications, 2006, 54(5): 798-801.

[18] Liu Z, Giannakis G B. Block differentially encoded OFDM with maximum multipath diversity[J].IEEETrans.onWirelessCommunications, 2003, 2(3): 420-423.

[19] Hochwald B M, Sweldens W. Differential unitary space-time modulation[J].IEEETrans.onCommunications,2000,48(12):2041-2052.

[20] Jeffrey A,Zwillinger D.Tableofintegrals,series,andproducts[M].6th ed.New York:Academic Press,2000.

李民政(1972-),男,副教授,博士,主要研究方向?yàn)閰f(xié)作分集編碼與網(wǎng)絡(luò)編碼。

E-mail:minzhengli@126.com

歐陽繕(1960-),男,教授,博士,主要研究方向?yàn)殛嚵行盘柼幚怼?/p>

E-mail:hmoyshan@guet.edu.cn

謝越雷(1974-),男,副教授,碩士,主要研究方向?yàn)橥ㄐ判盘柤瓣嚵行盘柼幚怼?/p>

E-mail:ylxie_guet@126.com

肖海林(1976-),男,教授,博士,主要研究方向?yàn)橐苿?dòng)通信與個(gè)人通信。

E-mail:hailinxiao@guet.edu.cn

網(wǎng)絡(luò)優(yōu)先出版地址：http://www.cnki.net/kcms/detail/11.2422.TN.20150104.1720.009.html

AF-CDC-OFDM based differential network coding

LI Min-zheng1,2, OUYANG Shan1, XIE Yue-lei1, XIAO Hai-lin1

(1.GuangxiExperimentCenterofInformationScience,GuilinUniversityofElectronicTechnology,

Guilin541004,China; 2.SchoolofElectronicEngineering,XidianUniversity,Xi’an710071,China)

Abstract:Based on the amplify and forward-cylic delay codes-orthogonal frequency division multiplexing (AF-CDC-OFDM) technology, a differential network coding method with multi-relay cooperation is proposed over the multi-carrier and frequency selective two-way relay channel. The two-way terminals can obtain the maximum cooperation diversity gains and frequency diversity gains through the distributed relay cyclic delay coding and power amplification processing. However, the two terminals need to eliminate the self-interference component among received signals before detecting the transmit symbol. Therefore, a self-interference elimination method is proposed with correlation statistical processing. The simulation results demonstrate that the proposed differential network encoding method can obtain the full diversity gain, and the proposed self-interference component eliminating method only has 0.5 dB SNR loss compared with the Genie-aided method over the slow fading channel.

Keywords:differential network coding; cyclic delay codes (CDC); amplify and forward (AF)

作者簡介：

中圖分類號：TN 925

文獻(xiàn)標(biāo)志碼：A

DOI:10.3969/j.issn.1001-506X.2015.07.29

基金項(xiàng)目：國家自然科學(xué)基金(61362007,61371186,61261018,61461015);廣西可信軟件重點(diǎn)實(shí)驗(yàn)室基金(KX201414);廣西自然科學(xué)基金(2013GXNSFFA019004,2014GXNSFAA118399,2014GXNSFGA118007);廣西教育廳重點(diǎn)項(xiàng)目(ZD2014052)資助課題

收稿日期：2014-07-18；修回日期：2014-11-23；網(wǎng)絡(luò)優(yōu)先出版日期：2015-01-04。