NC-OFDM系统导频设计方法研究
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摘要
随着通信技术、因特网及多媒体技术的发展,人们迫切地希望移动通信能够提供更加丰富的服务,如图像传送、音视频点播等数据及多媒体业务,电信运营商也期待着未来的通信网络能够方便地加载新业务而无需频繁更换网络架构及设备。在这种需求背景下,4G移动通信系统的研发工作目前在各国正如火如荼地展开。
Non-Contiguous OFDM(NC-OFDM)作为一种适用于离散频谱环境的频谱高效调制技术,它不仅具备传统OFDM的抗多径衰落和高速传输的优点,在频谱聚合、功率控制以及频谱分配方面也具有很强的灵活性,因此它被认为是4G移动通信系统中最具竞争力的一个候选的传输技术。
NC-OFDM打破了传统通信系统需要在一段连续频谱下进行数据传输的限制,但是也给它的各种关键技术带来了新的挑战。其中,导频设计问题是几个亟待解决的关键问题之一。在传统的OFDM系统中,一般采用等间隔等功率分配的导频序列,然而,由于频谱的非连续性,这种导频序列无法应用于NC-OFDM系统。因此,研究NC-OFDM系统的导频设计问题具有重要的理论意义和实用价值。
本文在分析和总结现有工作的基础上,讨论了NC-OFDM系统的技术特点及其所面临的新挑战,并重点研究了其中的导频设计问题,通过理论分析和仿真实验,给出了一些低计算复杂度的导频设计方法,主要包括:
1. SISO-NC-OFDM系统的导频设计方法基于最小二乘(LS)信道估计,在最小化归一化符号估计均方误差(SENMSE)的准则下,推导了系统的最优导频功率、数据功率和导频位置的约束关系,在此基础上,提出了一种次优的导频设计方法,它先分配每块不连续频带的导频数目,再通过一种简易的搜索方法求出它们的次优位置。
2.独立信道下MIMO-NC-OFDM系统的导频设计方法基于LS信道估计,在最小化数据子载波频域信道响应均方误差(DSCFR MSE)的准则下,采用交错导频的设计思想,推导了每根发送天线的最优导频功率和导频位置的约束关系,在此基础上,提出了两种次优的导频设计方法,通过依次求解每根发送天线的较优导频位置来逼近理论最优解。
3.相关信道下MIMO-NC-OFDM系统的导频设计方法基于线性最小均方误差(LMMSE)信道估计,在最小化DSCFR MSE的准则下,给出了与原MIMO-NC-OFDM系统等价的系统模型,在此基础上,采用交错导频的设计思想,提出了一种次优的导频设计方法,它先分配每根发送天线的导频总功率,再依次求解每根发送天线的较优导频位置。
With the development of communication, Internet and multimedia, more and more users hope that wireless communication systems can provide richer mobile services, such as image transmission, audio and video on demand, multimedia services. Telecom operators also expect that the wireless networks in the future can easily expand some new services without frequent replacement of network infrastructure and equipment. Drived by this demand, the research on the 4G mobile communication systems is currently being developed around the world.
As an effective spectrum utilization technology, Non-Contiguous OFDM (NC-OFDM) can be used in the environment of discrete spectrum. It has not only the traditional OFDM advantages of against multipath fading and high speed transmission, but also the flexibility in spectrum aggregation, power control and spectrum allocation. Therefore, it is considered as one of the most competitive candidate transmission technology in 4G mobile communication systems.
NC-OFDM looses the restriction that traditional communication system should work within a continuous spectrum, and in the meanwhile, some technical challenges are brought. Especially, the pilot design is one of the key technologies to be resolved. In traditional OFDM systems, equispaced and equipowered pilot sequence is generally used. However, this pilot sequence cannot be applied to NC-OFDM systems due to the non-continuous spectrum. Therefore, the study on the pilot design for NC-OFDM system has the theoretical and practical significance.
In this thesis, the existing research is reviewed, and the technical features and new challenges in the NC-OFDM systems are also described. Specially, the pilot design is fully explored. By the theoretical analysis and simulation experiments, several pilot designs with low complexity for NC-OFDM systems are proposed. The main contributions of this thesis are as follows.
1. The pilot design for SISO-NC-OFDM systems.
By minimizing the normalized mean square error of symbol estimate (SENMSE) with least squares (LS) channel estimation, firstly analyze the constraint relations among the optimal data power, the optimal pilot power and the optimal pilot placement, and then present a suboptimal pilot design, where the number of pilot tones for each frequency band is firstly determined, and then the position of each pilot tone can be obtained through a simple search method.
2. The pilot design for MIMO-NC-OFDM systems with independent channels.
By minimizing the MSE of the channel frequency response over the data subcarriers (DSCFR MSE) with LS channel estimation, firstly derive the constraint relations between the optimal pilot power and the optimal pilot placement of each transmitted antenna by disjoint pilots placement, then give two suboptimal pilot designs which can approximate the optimum theoretical solution through sequentially solving the pilot position of each transmitted antenna.
3. The pilot design for MIMO-NC-OFDM systems in correlated channel.
By the minimizing the DSCFR MSE with linear minimum mean square error (LMMSE) channel estimation, firstly establish a new system model which is equivalent to the original MIMO-NC-OFDM system, then present a suboptimal pilot design by disjoint pilots placement. In the proposed pilot design, firstly allocate the total pilot power for each transmitted antenna, and then find out the pilot position of each transmitted antenna sequentially.
Non-Contiguous OFDM(NC-OFDM)作为一种适用于离散频谱环境的频谱高效调制技术,它不仅具备传统OFDM的抗多径衰落和高速传输的优点,在频谱聚合、功率控制以及频谱分配方面也具有很强的灵活性,因此它被认为是4G移动通信系统中最具竞争力的一个候选的传输技术。
NC-OFDM打破了传统通信系统需要在一段连续频谱下进行数据传输的限制,但是也给它的各种关键技术带来了新的挑战。其中,导频设计问题是几个亟待解决的关键问题之一。在传统的OFDM系统中,一般采用等间隔等功率分配的导频序列,然而,由于频谱的非连续性,这种导频序列无法应用于NC-OFDM系统。因此,研究NC-OFDM系统的导频设计问题具有重要的理论意义和实用价值。
本文在分析和总结现有工作的基础上,讨论了NC-OFDM系统的技术特点及其所面临的新挑战,并重点研究了其中的导频设计问题,通过理论分析和仿真实验,给出了一些低计算复杂度的导频设计方法,主要包括:
1. SISO-NC-OFDM系统的导频设计方法基于最小二乘(LS)信道估计,在最小化归一化符号估计均方误差(SENMSE)的准则下,推导了系统的最优导频功率、数据功率和导频位置的约束关系,在此基础上,提出了一种次优的导频设计方法,它先分配每块不连续频带的导频数目,再通过一种简易的搜索方法求出它们的次优位置。
2.独立信道下MIMO-NC-OFDM系统的导频设计方法基于LS信道估计,在最小化数据子载波频域信道响应均方误差(DSCFR MSE)的准则下,采用交错导频的设计思想,推导了每根发送天线的最优导频功率和导频位置的约束关系,在此基础上,提出了两种次优的导频设计方法,通过依次求解每根发送天线的较优导频位置来逼近理论最优解。
3.相关信道下MIMO-NC-OFDM系统的导频设计方法基于线性最小均方误差(LMMSE)信道估计,在最小化DSCFR MSE的准则下,给出了与原MIMO-NC-OFDM系统等价的系统模型,在此基础上,采用交错导频的设计思想,提出了一种次优的导频设计方法,它先分配每根发送天线的导频总功率,再依次求解每根发送天线的较优导频位置。
With the development of communication, Internet and multimedia, more and more users hope that wireless communication systems can provide richer mobile services, such as image transmission, audio and video on demand, multimedia services. Telecom operators also expect that the wireless networks in the future can easily expand some new services without frequent replacement of network infrastructure and equipment. Drived by this demand, the research on the 4G mobile communication systems is currently being developed around the world.
As an effective spectrum utilization technology, Non-Contiguous OFDM (NC-OFDM) can be used in the environment of discrete spectrum. It has not only the traditional OFDM advantages of against multipath fading and high speed transmission, but also the flexibility in spectrum aggregation, power control and spectrum allocation. Therefore, it is considered as one of the most competitive candidate transmission technology in 4G mobile communication systems.
NC-OFDM looses the restriction that traditional communication system should work within a continuous spectrum, and in the meanwhile, some technical challenges are brought. Especially, the pilot design is one of the key technologies to be resolved. In traditional OFDM systems, equispaced and equipowered pilot sequence is generally used. However, this pilot sequence cannot be applied to NC-OFDM systems due to the non-continuous spectrum. Therefore, the study on the pilot design for NC-OFDM system has the theoretical and practical significance.
In this thesis, the existing research is reviewed, and the technical features and new challenges in the NC-OFDM systems are also described. Specially, the pilot design is fully explored. By the theoretical analysis and simulation experiments, several pilot designs with low complexity for NC-OFDM systems are proposed. The main contributions of this thesis are as follows.
1. The pilot design for SISO-NC-OFDM systems.
By minimizing the normalized mean square error of symbol estimate (SENMSE) with least squares (LS) channel estimation, firstly analyze the constraint relations among the optimal data power, the optimal pilot power and the optimal pilot placement, and then present a suboptimal pilot design, where the number of pilot tones for each frequency band is firstly determined, and then the position of each pilot tone can be obtained through a simple search method.
2. The pilot design for MIMO-NC-OFDM systems with independent channels.
By minimizing the MSE of the channel frequency response over the data subcarriers (DSCFR MSE) with LS channel estimation, firstly derive the constraint relations between the optimal pilot power and the optimal pilot placement of each transmitted antenna by disjoint pilots placement, then give two suboptimal pilot designs which can approximate the optimum theoretical solution through sequentially solving the pilot position of each transmitted antenna.
3. The pilot design for MIMO-NC-OFDM systems in correlated channel.
By the minimizing the DSCFR MSE with linear minimum mean square error (LMMSE) channel estimation, firstly establish a new system model which is equivalent to the original MIMO-NC-OFDM system, then present a suboptimal pilot design by disjoint pilots placement. In the proposed pilot design, firstly allocate the total pilot power for each transmitted antenna, and then find out the pilot position of each transmitted antenna sequentially.
引文
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[4]谢显中,认知无线电技术及其应用,电子工业出版社,北京,2008年4月.
[5]孙俊,MIMO传输中的信道相关性影响与天线选择算法研究,华中科技大学,2004.
[6]张贤达,矩阵分析与应用,清华大学出版社,2004年.
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[2]佟学俭,罗涛,OFDM移动通信技术原理与应用,人民邮电出版社,2003年6月.
[3]许一波,MIMO-OFDM系统中的信道估计和导频设计研究,北京邮电大学,2006年3月.
[4]谢显中,认知无线电技术及其应用,电子工业出版社,北京,2008年4月.
[5]孙俊,MIMO传输中的信道相关性影响与天线选择算法研究,华中科技大学,2004.
[6]张贤达,矩阵分析与应用,清华大学出版社,2004年.
[7]蒋金山,何春雄,潘少华,最优化计算方法,华南理工大学出版社,2005.
[8] Telatar E.“Capacity of Multiantenna Gaussian Channels,”AT & T-Bell Lab Internal Tech Memo, 1995.
[9] Foschini G. J.“Layered space-time architecture for wireless communication in a fading environment when using multiple antennas,”Bell Laboratories Technical Journal,Vol. 1, No. 2, pp. 741-765, 1996.
[10] Tarokh V., Seshachi N., Calderbank A. R.,“Space-time codes for high data wireless communications: performance analysis and code construction,”IEEE Trans. Inform Theory, Vol. 44, No. 2, pp. 744-765, 1998.
[11] Wolniansky P. W., Forshini G. J., Golden G. D., et al,“V-BLAST: an architecture for realizing very high data rates over the rich-scattering wireless channel,”Proc. ISSSE-98, 19998.
[12] Molisch A. F.,Steinbauer M., Toeltsch M., Bonek E., Thoma R. S.,“Measurement of the capacity of MIMO systems in frequency selective channels,”VTC 01, pp. 204-208, 2001.
[13] Khalighi M. A., Brossier J. M., Jourdain G. V., Raoof K.,“Water filling capacity of Rayleigh MIMO channels,”Personal, Indoor and Mobile Radio Communications, 2001 12th IEEE International Symposium on,pp. 155-158, 2001.
[14] Kamath M. A., Hughes B. L., Xinying Yu,“Gaussian approximations for the capacity of MIMO Rayleigh fading channels,”Signals, Systems and Computers, Conference Record of the Thirty-Sixth Asilomar Conference, pp. 614-618, 2002.
[15] Ming Kang, Alouini M.,“Impact of correlation on the capacity of MIMO channels,”ICC’03, Vol. 4, pp. 2623-2627, 2003.
[16] Ye Li, Ray Lin K. J.,“On blind equalization of MIMO channels”, ICC’96, Vol. 2, pp. 1000-1004, 1996.
[17] Ye Li, Liu K. J.,“Adaptive blind source separation and equalization for multiple-input multiple-output systems,”IEEE Trans. on Inf. Theory, Vol. 44, No. 7, pp. 2864-2876, 1998.
[18] Tehrani A.M., Hassibi B., Cioffi J.,“An estimation based approach to multiple-input multiple output(MIMO)channel equalization,”Sensor Array and Multichannel Signal Processing Workshop,Vol. 1, pp. 27-31, 2000.
[19] T. L. Marzetta,“BLAST training: Estimating channel characteristics for high capacity space-time wireless,”in Proc. 37th Annual Allerton Conf. Communication, Control and Computing, Monticello, IL, 1999.
[20] Q. Sun, D. C. Cox, H. C. Huang, and A. Lozano,“Estimation of Continuous Flat FadingMIMO Channels,”IEEE Trans. on Wireless Commun., Vol. 1, No. 4, pp. 549-553, Oct. 2002.
[21] Choi Yang-Seok, Molisch A. F., Win M. Z., Winters J. H.,“Fast algorithms for antenna selection in MIMO systems,”In Proc. IEEE VTC 2003, Orlando, Florida, USA., Vol. 3, pp. 1733-1737, 2003.
[22] Gorokhov A., Gore D., Paulraj A. J.,“Receive antenna selection for MIMO spatial multiplexing: theory and algorithms,”IEEE Trans on Signal Processing, Vol. 1, No. 11, pp. 2 796-2806, 2003.
[23] Spectrum Efficiency Working Group,“Report of the Spectrum Efficiency Working Group,”Federal Communications Commission Spectrum Policy Task Force, Tech. Rep., Nov. 2002.
[24] J. Mitola HI and G. O. Maguire,“Cognitive radio: Making Software Radio More Personal,”IEEE Personal Communications, Vol. 6, pp. 13-18, Aug., 1999.
[25] J.Mitola III,“Cognitive Radio: An Integrated Agent Architecture for Software Defined Radio,”Ph.D. Dissertation, Royal Institute of Technology, 2000.
[26] FCC,“Notice of proposed rulemaking and order,”ET Docket No. 03-222, Dec., 2003.
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