LTE-Advanced系统的多天线和干扰协调技术研究
摘要
作为LTE的平滑演进,LTE-Advanced系统的标准化进程备受瞩口。在LTE-Advanced系统中,采用了增强型多天线MIMO、多点协作传输(CoMP)、载波聚合(CA)、异构网络(HeNet)等多项关键技术。LTE-Advanced在全面支持LTE已有功能的前提下,通过进一步对室内覆盖场景的优化、应用载波聚合技术以支持更大带宽的通信,能够显著提升网络性能。
对于LTE-Advanced系统中的多天线,下行和上行都能够支持最多八根天线,能够支持最高八个数据流的并行传输,进一步增大了系统可获得的阵列增益、复用增益和分集增益。波束赋形是LTE-Advanced系统中所采用的多天线技术之一,并且为了充分发挥波束赋形的技术优势,获得更高的可靠性和吞吐量,系统需要支持波束赋形单双流之间的动态切换,但过去的单双流自适应方案很少考虑到非理想信道这个条件的影响。本文提出一种适用于非理想信道条件下的波束赋形单双流自适应切换方案,这个方案将信道估计误差作为判断单双流切换的影响因子之一,并且单双流切换门限值的一个参数是可以根据信道变化进行动态优化的。利用信道估计误差的调整和门限值参数的优化,能实现非理想信道条件下更准确的单双流自适应。仿真结果表明,所提方案能够显著提升小区平均吞吐量,有效抵抗信道估计误差所带来的性能损失。
对于LTE-Advanced系统,在下行采用正交频分复用(OFDM),在上行采用单载波频分复用多址(SC-FDMA),能够完全消除小区内的干扰,因此小区间干扰是影响系统性能的一个重要因素。此外,异构网络中异构节点,包括中继、Pico和家庭基站的引入,使得异构网络中干扰更加复杂和难以控制,同构网络的干扰协调算法不再适用于异构网络。考虑到用户终端设备的限制,传统下行干扰协调算法并不适用于上行链路。本文提出一种应用于基站端的、基于奇异值分解的异构网络小区间干扰协调算法。这个算法利用SVD分解获取干扰用户有效信道的零空间,并按照一定的准则构造补偿矩阵,从而在对小区间干扰进行消除或协调的同时,获得完全的复用增益。仿真结果表明,所提出的算法性能优于传统的迫零(ZF)和最小均方误差(MMSE)接收算法。
As the smooth evolution of LTE system, LTE-Advanced system is now under the focus of telecommunication research. LTE-Advanced has adopted enhanced Multiple-Input Multiple-Output (MIMO), Coordinated Multiple-Point communication (CoMP), Carrier Aggregation (CA) and Heterogeneous Network (HeNet) as its key technologies. LTE-Advanced can support all the functions of LTE, further optimize the coverage of indoor scenarios, and obtain larger bandwidth with CAas well.
Up to eight antennas in the downlink and eight antennas in the uplink are supported in LTE-Advanced systems, leading to up to eight parallel data streams at the same time. So the system is able to achieve higher array gain, multiplexing gain and also diversity gain. Beamforming is one of the MIMO technologies employed in LTE-Advanced, and adaptive switching between single-stream and dual-stream is supported to develop fully of potential of beamforming. But the effect of imperfect Channel State Information (CSI) has been rarely considered in past research. In this paper, a rank adaptive beamforming scheme is proposed for TDD LTE systems with imperfect CSI, in which channel estimation error acts as one of the impact factors of switching threshold, and one parameter of the switching threshold can be dynamically optimized. With the adaptation of switching threshold and the optimization of threshold parameter, more accurate adaptive switching between single-stream and dual-stream can be obtained under imperfect CSI. It is shown by simulation results that the proposed scheme can significantly improve the average cell throughput, resisting the loss by imperfect CSI effectively.
In LTE-Advanced system, Orthogonal Frequency Division Multiplexing (OFDM) is used in the downlink, and Single-Carrier Frequency Division Multiple Access (SC-FDMA) is used in the uplink, resulting in no interference for the intra-cell. Therefore, inter-cell interference becomes one of the most important elements of system performance. With heterogeneous nodes introduced, inter-cell interference turns more complicated in HeNets, and traditional Inter-Cell Interference Coordination (ICIC) algorithms are not suit for HeNets. Besides, ICIC schemes in the downlink are unfit for the uplink due to constraint of user equipments. In this paper, an uplink co-channel interference coordination algorithm is proposed for HeNets, where the algorithm is applied at the receiver sides. In this algorithm, the zero space of interference user channel can be obtained with Singular Value Decomposition (SVD), and a supplement matrix is used according to a given metric, so this algorithm can achieve interference elimination or coordination and obtain full multiplexing gain at the same time. The simulation results show that the proposed algorithm outperforms the traditional Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) algorithms.
对于LTE-Advanced系统中的多天线,下行和上行都能够支持最多八根天线,能够支持最高八个数据流的并行传输,进一步增大了系统可获得的阵列增益、复用增益和分集增益。波束赋形是LTE-Advanced系统中所采用的多天线技术之一,并且为了充分发挥波束赋形的技术优势,获得更高的可靠性和吞吐量,系统需要支持波束赋形单双流之间的动态切换,但过去的单双流自适应方案很少考虑到非理想信道这个条件的影响。本文提出一种适用于非理想信道条件下的波束赋形单双流自适应切换方案,这个方案将信道估计误差作为判断单双流切换的影响因子之一,并且单双流切换门限值的一个参数是可以根据信道变化进行动态优化的。利用信道估计误差的调整和门限值参数的优化,能实现非理想信道条件下更准确的单双流自适应。仿真结果表明,所提方案能够显著提升小区平均吞吐量,有效抵抗信道估计误差所带来的性能损失。
对于LTE-Advanced系统,在下行采用正交频分复用(OFDM),在上行采用单载波频分复用多址(SC-FDMA),能够完全消除小区内的干扰,因此小区间干扰是影响系统性能的一个重要因素。此外,异构网络中异构节点,包括中继、Pico和家庭基站的引入,使得异构网络中干扰更加复杂和难以控制,同构网络的干扰协调算法不再适用于异构网络。考虑到用户终端设备的限制,传统下行干扰协调算法并不适用于上行链路。本文提出一种应用于基站端的、基于奇异值分解的异构网络小区间干扰协调算法。这个算法利用SVD分解获取干扰用户有效信道的零空间,并按照一定的准则构造补偿矩阵,从而在对小区间干扰进行消除或协调的同时,获得完全的复用增益。仿真结果表明,所提出的算法性能优于传统的迫零(ZF)和最小均方误差(MMSE)接收算法。
As the smooth evolution of LTE system, LTE-Advanced system is now under the focus of telecommunication research. LTE-Advanced has adopted enhanced Multiple-Input Multiple-Output (MIMO), Coordinated Multiple-Point communication (CoMP), Carrier Aggregation (CA) and Heterogeneous Network (HeNet) as its key technologies. LTE-Advanced can support all the functions of LTE, further optimize the coverage of indoor scenarios, and obtain larger bandwidth with CAas well.
Up to eight antennas in the downlink and eight antennas in the uplink are supported in LTE-Advanced systems, leading to up to eight parallel data streams at the same time. So the system is able to achieve higher array gain, multiplexing gain and also diversity gain. Beamforming is one of the MIMO technologies employed in LTE-Advanced, and adaptive switching between single-stream and dual-stream is supported to develop fully of potential of beamforming. But the effect of imperfect Channel State Information (CSI) has been rarely considered in past research. In this paper, a rank adaptive beamforming scheme is proposed for TDD LTE systems with imperfect CSI, in which channel estimation error acts as one of the impact factors of switching threshold, and one parameter of the switching threshold can be dynamically optimized. With the adaptation of switching threshold and the optimization of threshold parameter, more accurate adaptive switching between single-stream and dual-stream can be obtained under imperfect CSI. It is shown by simulation results that the proposed scheme can significantly improve the average cell throughput, resisting the loss by imperfect CSI effectively.
In LTE-Advanced system, Orthogonal Frequency Division Multiplexing (OFDM) is used in the downlink, and Single-Carrier Frequency Division Multiple Access (SC-FDMA) is used in the uplink, resulting in no interference for the intra-cell. Therefore, inter-cell interference becomes one of the most important elements of system performance. With heterogeneous nodes introduced, inter-cell interference turns more complicated in HeNets, and traditional Inter-Cell Interference Coordination (ICIC) algorithms are not suit for HeNets. Besides, ICIC schemes in the downlink are unfit for the uplink due to constraint of user equipments. In this paper, an uplink co-channel interference coordination algorithm is proposed for HeNets, where the algorithm is applied at the receiver sides. In this algorithm, the zero space of interference user channel can be obtained with Singular Value Decomposition (SVD), and a supplement matrix is used according to a given metric, so this algorithm can achieve interference elimination or coordination and obtain full multiplexing gain at the same time. The simulation results show that the proposed algorithm outperforms the traditional Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) algorithms.
引文
[1]Harri Holma, Antti Toskala, "WCDMA for UMTS-HSPA Evolution and LTE (Fourth Edition)", John Wiley & Sons Ltd.
[2]Stefenia Sesia, Issam Toufik, Matthew Baker, "LTE-The UMTS Long Term Evolution:From Theory to Practice", A John Wiley and Sons, Ltd, Publication.
[3]沈嘉,索十强,全海洋,“3GPP长期演进(LTE)技术原理与系统设计”,人民邮电出版社,2008。
[4]沈嘉,"LTE-Advanced关键技术演进趋势”,移动通信,2008年8月(下)。
[5]万彭,杜志敏,“LTE和LTE-Advanced关键技术综述”,现代电信科技,2009年9月第9期,P33-P36。
[6]3GPP TS 36.211 v10.1.0, "Physical Channels and Modulation (Release 10)", March 2011.
[7]3GPP TR 36.819 v11.0.0, "Coordinated Multi-Point Operation for LTE Physical Layer Aspects (Release 11)", September 2011.
[8]姜静,孙云锋,田开波,“一种空间分集方法及装置”,申请号：200910076109.2。
[9]文雪,汪凡,"OFDM系统的分集发射方法与装置”,申请号：200910137474.X。
[10]Tian Chunchang, Yang Wenqian, Fang Liang, "On the Performance of Eigen Based Beamforming in LTE-Advanced", in Proc. IEEE Personal, Indoor and Mobile Radio Communications (PIMRC), Tokyo, May 2010.
[11]Mugen Peng, Xiang Zhang, Wenbo Wang, "Performance of Dual-Polarized MIMO for TD-HSPA Evolution Systems", IEEE Systems Journal, Vol.5, Issue. 3, September 2011.
[12]耿鹏,江海,傅强,“自适应数据流模式切换方法”,申请号：200710143488.3。
[13]缪德山,秦飞,潘学明,“多流波束赋形传输时rank自适应传输方法、系统及设备”,申请号：200810240390.4。
[14]缪德山,孙韶辉,秦飞,“多流波束赋形传输时信道的秩的估计方法、系统及装置”,申请号：200810240391.9。
[15]Sen Wang, Dacheng Yang, Yafeng Wang, "A Novel Single-/Multi-layer Adaptive Scheme for Eigen Based Beamforming in TD-LTE Downlink", in Proc. IEEE Vehicular Technology Conference Fall, San Francisco, CA, December 2011.
[16]F. Javier Lopez-Martinez, Eduardo Martos-Naya. Jose F. Paris. "Generalized BER Analysis oF QAM and Its Application to MRC Under Imperfect CSI and Interference in Ricean Fading Channels", IEEE Transactions on Vehicular Technology, Vol.59, Issue.5, June 2010.
[17]F. Javier Lopez-Martinez, Eduardo Martos-Naya, Jose F. Paris. "BER Analysis for MIMO-OFDM Beamforming with MRC under Channel Prediction and Interpolation Errors", in Proc. IEEE Global Telecommunications Conference, Honolulu, HI, December 2009.
[18]Du Yang, Lie-Liang Yang, Lajos Hanzo, "Imperfect Channel Knowledge Based Ergodic Channel Capacity of Transmit Beamforming", in Proc. IEEE Vehicular Technology Conference Fall, Anchorage, AK, September 2009.
[19]Robert W. Heath, Jr. and Arogyaswami J. Paulraj, "Switching Between Diversity and Multiplexing in MIMO Systems", IEEE Transaction on Communications, Vol.53, Issue.6, JUNE 2005.
[20]M.A. Khojastepour, N. Prasad, S. Wang, X. Wang, M. Madihian, "Quantized Multi-Rank Beamforming for MIMO-OFDM Systems", IEEE Journal on Selected Areas in Communications, Vol.26, Issue.6, August 2008.
[21]Dhananjaya Ponukumati, Feifei Gao, Mathias Bode, "Multicell Downlink Beamforming with Imperfect Channel Knowledge at Both Transceiver Sides" IEEE Communications Letters, Vol.15, Issue.10, October 2011
[22]Jing Jin, Chongsheng Lin, Qixing Wang, "Effect of Imperfect Channel Estimation on Multi-user Beamforming in LTE-Advanced system", in Proc. IEEE Personal, Indoor and Mobile Radio Communications, Taipei, September 2009.
[23]Aamod Khandekar, Naga Bhushan, Ji Tingfang, "LTE-Advanced: Heterogeneous Networks", in Proc. Wireless Conference,2010 European, Lucca, June 2010.
[24]Aleksandar Damnjanovic, Juan Montojo, Yongbin Wei, "A Survey on 3GPP Heterogeneous Networks", IEEE Wireless Communications, Vol.18, Issue.3, June 2011.
[25]Gary Boudreau, John Panicker, Ning Guo, "Interference Coordination and Cancellation for 4G Networks", IEEE Communications Magazine, Vol.47, Issue.4, April 2009.
[26]Mazin Al-Shalash, Farid Khafizov, Zhijun Chao, "Uplink Inter-Cell Interference Coordination Through Soft Frequency Reuse", in Proc. IEEE Global Telecommunications Conference, Miami, December 2010.
[27]David Lopez-Perez, Ismail Guvenc, Guillaume De La Roche, "Enhanced Intercell Interference Coordination Challenges in Heterogeneous Networks", IEEE Wireless Communications, Vol. 18, Issue.3, June 2011.
[28]Rui Wang, Yinggang Du, "Het-Net Throughput Analysis with Picocell Interference Cancellation", in Proc. IEEE International Conference on Communications Workshops, Kyoto, June 2011.
[29]Young-Jun Hong, Namyoon Lee, Bruno Clerckx, "System Level Performance Evaluation of Inter-cell Interference Coordination Schemes for Heterogeneous Networks in LTE-A System", in Proc. IEEE GLOBECOM Workshops, Miami, December 2010.
[30]O. Simeone, E. Erkip, S. Shamai Shitz, "Robust Transmission and Interference Management For Femtocells with Unreliable Network Access", IEEE Journal on Selected Areas in Communications, Vol.28, Issue.9, December 2010.
[31]Jacek Gora, Klaus I. Pedersen, Agnieszka Szufarska, "Cell-Specific Uplink Power Control for Heterogeneous Networks in LTE", in Proc. IEEE Vehicular Technology Conference Fall, Ottawa, September 2010.
[32]Omer Bulakci, Simone Redana, Bernhard Raaf, "Impact of Power Control Optimization on the System Performance of Relay Based LTE-Advanced Heterogeneous Networks", Journal of Communications and Networks, Vo1. 13, Issue.4, Augest 2011.
[33]Patrick Marsch, Gerhard Fettweis, "Uplink CoMP under a Constrained Backhaul and Imperfect Channel Knowledge", IEEE Transactions on Wireless Communications, Vol.10, Issue.6, June 2011.
[2]Stefenia Sesia, Issam Toufik, Matthew Baker, "LTE-The UMTS Long Term Evolution:From Theory to Practice", A John Wiley and Sons, Ltd, Publication.
[3]沈嘉,索十强,全海洋,“3GPP长期演进(LTE)技术原理与系统设计”,人民邮电出版社,2008。
[4]沈嘉,"LTE-Advanced关键技术演进趋势”,移动通信,2008年8月(下)。
[5]万彭,杜志敏,“LTE和LTE-Advanced关键技术综述”,现代电信科技,2009年9月第9期,P33-P36。
[6]3GPP TS 36.211 v10.1.0, "Physical Channels and Modulation (Release 10)", March 2011.
[7]3GPP TR 36.819 v11.0.0, "Coordinated Multi-Point Operation for LTE Physical Layer Aspects (Release 11)", September 2011.
[8]姜静,孙云锋,田开波,“一种空间分集方法及装置”,申请号：200910076109.2。
[9]文雪,汪凡,"OFDM系统的分集发射方法与装置”,申请号：200910137474.X。
[10]Tian Chunchang, Yang Wenqian, Fang Liang, "On the Performance of Eigen Based Beamforming in LTE-Advanced", in Proc. IEEE Personal, Indoor and Mobile Radio Communications (PIMRC), Tokyo, May 2010.
[11]Mugen Peng, Xiang Zhang, Wenbo Wang, "Performance of Dual-Polarized MIMO for TD-HSPA Evolution Systems", IEEE Systems Journal, Vol.5, Issue. 3, September 2011.
[12]耿鹏,江海,傅强,“自适应数据流模式切换方法”,申请号：200710143488.3。
[13]缪德山,秦飞,潘学明,“多流波束赋形传输时rank自适应传输方法、系统及设备”,申请号：200810240390.4。
[14]缪德山,孙韶辉,秦飞,“多流波束赋形传输时信道的秩的估计方法、系统及装置”,申请号：200810240391.9。
[15]Sen Wang, Dacheng Yang, Yafeng Wang, "A Novel Single-/Multi-layer Adaptive Scheme for Eigen Based Beamforming in TD-LTE Downlink", in Proc. IEEE Vehicular Technology Conference Fall, San Francisco, CA, December 2011.
[16]F. Javier Lopez-Martinez, Eduardo Martos-Naya. Jose F. Paris. "Generalized BER Analysis oF QAM and Its Application to MRC Under Imperfect CSI and Interference in Ricean Fading Channels", IEEE Transactions on Vehicular Technology, Vol.59, Issue.5, June 2010.
[17]F. Javier Lopez-Martinez, Eduardo Martos-Naya, Jose F. Paris. "BER Analysis for MIMO-OFDM Beamforming with MRC under Channel Prediction and Interpolation Errors", in Proc. IEEE Global Telecommunications Conference, Honolulu, HI, December 2009.
[18]Du Yang, Lie-Liang Yang, Lajos Hanzo, "Imperfect Channel Knowledge Based Ergodic Channel Capacity of Transmit Beamforming", in Proc. IEEE Vehicular Technology Conference Fall, Anchorage, AK, September 2009.
[19]Robert W. Heath, Jr. and Arogyaswami J. Paulraj, "Switching Between Diversity and Multiplexing in MIMO Systems", IEEE Transaction on Communications, Vol.53, Issue.6, JUNE 2005.
[20]M.A. Khojastepour, N. Prasad, S. Wang, X. Wang, M. Madihian, "Quantized Multi-Rank Beamforming for MIMO-OFDM Systems", IEEE Journal on Selected Areas in Communications, Vol.26, Issue.6, August 2008.
[21]Dhananjaya Ponukumati, Feifei Gao, Mathias Bode, "Multicell Downlink Beamforming with Imperfect Channel Knowledge at Both Transceiver Sides" IEEE Communications Letters, Vol.15, Issue.10, October 2011
[22]Jing Jin, Chongsheng Lin, Qixing Wang, "Effect of Imperfect Channel Estimation on Multi-user Beamforming in LTE-Advanced system", in Proc. IEEE Personal, Indoor and Mobile Radio Communications, Taipei, September 2009.
[23]Aamod Khandekar, Naga Bhushan, Ji Tingfang, "LTE-Advanced: Heterogeneous Networks", in Proc. Wireless Conference,2010 European, Lucca, June 2010.
[24]Aleksandar Damnjanovic, Juan Montojo, Yongbin Wei, "A Survey on 3GPP Heterogeneous Networks", IEEE Wireless Communications, Vol.18, Issue.3, June 2011.
[25]Gary Boudreau, John Panicker, Ning Guo, "Interference Coordination and Cancellation for 4G Networks", IEEE Communications Magazine, Vol.47, Issue.4, April 2009.
[26]Mazin Al-Shalash, Farid Khafizov, Zhijun Chao, "Uplink Inter-Cell Interference Coordination Through Soft Frequency Reuse", in Proc. IEEE Global Telecommunications Conference, Miami, December 2010.
[27]David Lopez-Perez, Ismail Guvenc, Guillaume De La Roche, "Enhanced Intercell Interference Coordination Challenges in Heterogeneous Networks", IEEE Wireless Communications, Vol. 18, Issue.3, June 2011.
[28]Rui Wang, Yinggang Du, "Het-Net Throughput Analysis with Picocell Interference Cancellation", in Proc. IEEE International Conference on Communications Workshops, Kyoto, June 2011.
[29]Young-Jun Hong, Namyoon Lee, Bruno Clerckx, "System Level Performance Evaluation of Inter-cell Interference Coordination Schemes for Heterogeneous Networks in LTE-A System", in Proc. IEEE GLOBECOM Workshops, Miami, December 2010.
[30]O. Simeone, E. Erkip, S. Shamai Shitz, "Robust Transmission and Interference Management For Femtocells with Unreliable Network Access", IEEE Journal on Selected Areas in Communications, Vol.28, Issue.9, December 2010.
[31]Jacek Gora, Klaus I. Pedersen, Agnieszka Szufarska, "Cell-Specific Uplink Power Control for Heterogeneous Networks in LTE", in Proc. IEEE Vehicular Technology Conference Fall, Ottawa, September 2010.
[32]Omer Bulakci, Simone Redana, Bernhard Raaf, "Impact of Power Control Optimization on the System Performance of Relay Based LTE-Advanced Heterogeneous Networks", Journal of Communications and Networks, Vo1. 13, Issue.4, Augest 2011.
[33]Patrick Marsch, Gerhard Fettweis, "Uplink CoMP under a Constrained Backhaul and Imperfect Channel Knowledge", IEEE Transactions on Wireless Communications, Vol.10, Issue.6, June 2011.