TD-SCDMA向LTE TDD演进中的多天线技术
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摘要
多天线技术因为在提高系统容量与频谱效率,提升系统传输性能等方面的优越性而逐渐受到关注。无线通信也从对频率域、时间域、码域的研究逐渐拓展到空间域。多天线技术在利用空时信道环境的空间特性上具有与生俱来的优越性。
智能天线技术在多天线技术中因其优越的空间辨识能力,已经成为3G TD-SCDMA中的关键技术。具备通过波束赋形,增强期望信号,抑制干扰信号,实现空分多址(SDMA)的能力。并且随着研究的进步,逐步从窄带进入了宽带智能天线领域。
MIMO多天线技术,随着研究的深入,逐渐从单用户MIMO系统拓展到多用户MIMO系统,从室内多散射不相关应用环境拓展到室外相关信道环境中。因其高频谱效率以及优越的传输性能,已经成为LTE乃至下一代无线通信的关键技术之一。
然而当MIMO多天线技术从室内到室外,随着无线信道环境的改变,空间相关性将显著影响MIMO系统的容量与可靠性。对天线隔离度的需求也增加了工程施工的难度。因此MIMO多天线技术从开环发展到利用信道反馈进行闭环预处理的自适应阶段。能否有效降低信道相关性的影响,同时降低反馈负荷与算法复杂度,成为MIMO技术应用的关键因素。
本文先从空时无线信道出发,推导了基于统计特性空时信道模型下的空时相关系数。给出了不同参数对空间相关性的影响。同时分析了同用户多径角度扩展与多径间独立性的关系,为后续章节的研究提供基础。
在多径相互独立的前提下,本文提出了单用户波束赋形空分复用方案。第一种方案通过发射波束赋形与门限接收切换波束赋形,同时获得了空时无线信道中的空分复用增益与空间分集增益,提高系统的性能与容量。第二种方案在总结第一种方案应用局限性的前提下,提出了将双极化多天线极化分集与发射波束空分复用相结合的方案,为发射波束空分复用选择增加了更大的自由度,提升了系统性能。通过发射与接收端波束赋形的联合优化,系统减轻了反馈负荷,同时降低了复杂度。
本文还将波束赋形引入多用户MIMO中,发挥了波束赋形消除用户间干扰的优点,同时相对于迫零等算法,减轻了闭环全反馈CSI的反馈负荷,利用了复用用户的空间自由度。由于系统性能受用户间空间相关性的影响,同时考虑到系统激活用户数一般大于多用户空分复用服务用户数,在波束赋形多用户空分复用方案的基础上,结合分组多用户分集。通过多径赋形波束在用户间造成的互干扰量度来调度系统中的激活用户数,增加了系统和容量。
针对LTE下行链路时隙特征,最后给出了波束赋形多用户复用分集在系统存多个下行链路时隙的调度方案。分析了系统平均和容量与时隙数的关系,可以为实际应用中通过激活用户选择不同时隙配置提供参考。
Recent years, multi-antenna technology has got great attention because of the advantage of enhancing system capacity and spectral efficiencies. It can also improve system reliability. Research domain has also changed from frequence, time, and code to spatial domain. Multi-antenna technology has the ability to cope with the spatial character of space-time channel.
Smart antenna technology has become the key point in the third generation communication especially in TD-SCDMA because of the spatial distinguish ability. Beamforming from smart antenna, which increasing desire signal and suppressing interference, can achieve spatial divided multiple accessing (SDMA). With the developting of smart antenna, it begins entering the wildband wireless communication area.
Multiple input and multiple output (MIMO) technology has get great development. The research about MIMO has increased from single user to multiuser MIMO system. The application environment has changed from the indoor rich scattering uncorrelated channel to outdoor correlated channel. Because of the advantage in the spectral efficiencies and transmitting ability, it has become the key point in LTE and 4G.
But the channel correlation under space-time wireless environment will bring influence to the system capacity and reliability when MIMO technology has applied from indoor to outdoor. In the same time, the distance demand between antenna elements will bring the difficulty to engineering application. So MIMO technology is developing from opened loop to self adapted closed loop system relying on the feedback of channel information. How to depress the influence of channel correlation and how to decrease the feedback load and operation complication are the key points for the application of MIMO technology.
This dissertation starts from the research of space time channel. The correlation coefficient is derived under statistical channel model in LTE. It gives the influence measurement of different spatial coefficients to channel correlation. The relationship of angle spread and the correlation between different multipaths is analysed for the next chapters'research.
Supposing the independence between multipaths, two kind of beamforming spatial multiplex schemes for single user are proposed in the dissertation. The first scheme can get the multiplex and diversity plus together through self adaptation transmitting beamfroming and switch receiving beamforming. When the multipaths are not enough for spatial multiplex and spatial diversity at same time, the second secheme is proposed that combines the beamforming multiplex and dual polarized diversity to leave more multipaths for the spatial multiplex. Through the associated optimization between transmitting and receiving, the system capacity can get increase under strong correlated channel. The feedback load and operation complication can get decrease together.
Beamforming is combined into multiple users systems. The ability to depress interference between users is enhanced. Comparing with other multiple users MIMO systems such as zeroforcing, the scheme proposed in this dissertation does not need to feedback full CSI information because the spatial characters of multiplex users are completely used.
The capacity and reliability of multiple users system are affected by the correlation between multiplex users which include the spatial location, angle spread and multipath DOA. Also considering the number of active users usually large than the multiplex serving users, multiuser diversity is combined. An interference parameter is used for multiuser scheduling. Because of the multiuser diversity, the sum capacity can get improved.
Considering the frame structure of LTE, a downlink slot divided Multiuser scheduling scheme is proposed at last. The relationship between average system capacity and the number of slots is analysed. It can give a reference for the configuration of active users and slots.
智能天线技术在多天线技术中因其优越的空间辨识能力,已经成为3G TD-SCDMA中的关键技术。具备通过波束赋形,增强期望信号,抑制干扰信号,实现空分多址(SDMA)的能力。并且随着研究的进步,逐步从窄带进入了宽带智能天线领域。
MIMO多天线技术,随着研究的深入,逐渐从单用户MIMO系统拓展到多用户MIMO系统,从室内多散射不相关应用环境拓展到室外相关信道环境中。因其高频谱效率以及优越的传输性能,已经成为LTE乃至下一代无线通信的关键技术之一。
然而当MIMO多天线技术从室内到室外,随着无线信道环境的改变,空间相关性将显著影响MIMO系统的容量与可靠性。对天线隔离度的需求也增加了工程施工的难度。因此MIMO多天线技术从开环发展到利用信道反馈进行闭环预处理的自适应阶段。能否有效降低信道相关性的影响,同时降低反馈负荷与算法复杂度,成为MIMO技术应用的关键因素。
本文先从空时无线信道出发,推导了基于统计特性空时信道模型下的空时相关系数。给出了不同参数对空间相关性的影响。同时分析了同用户多径角度扩展与多径间独立性的关系,为后续章节的研究提供基础。
在多径相互独立的前提下,本文提出了单用户波束赋形空分复用方案。第一种方案通过发射波束赋形与门限接收切换波束赋形,同时获得了空时无线信道中的空分复用增益与空间分集增益,提高系统的性能与容量。第二种方案在总结第一种方案应用局限性的前提下,提出了将双极化多天线极化分集与发射波束空分复用相结合的方案,为发射波束空分复用选择增加了更大的自由度,提升了系统性能。通过发射与接收端波束赋形的联合优化,系统减轻了反馈负荷,同时降低了复杂度。
本文还将波束赋形引入多用户MIMO中,发挥了波束赋形消除用户间干扰的优点,同时相对于迫零等算法,减轻了闭环全反馈CSI的反馈负荷,利用了复用用户的空间自由度。由于系统性能受用户间空间相关性的影响,同时考虑到系统激活用户数一般大于多用户空分复用服务用户数,在波束赋形多用户空分复用方案的基础上,结合分组多用户分集。通过多径赋形波束在用户间造成的互干扰量度来调度系统中的激活用户数,增加了系统和容量。
针对LTE下行链路时隙特征,最后给出了波束赋形多用户复用分集在系统存多个下行链路时隙的调度方案。分析了系统平均和容量与时隙数的关系,可以为实际应用中通过激活用户选择不同时隙配置提供参考。
Recent years, multi-antenna technology has got great attention because of the advantage of enhancing system capacity and spectral efficiencies. It can also improve system reliability. Research domain has also changed from frequence, time, and code to spatial domain. Multi-antenna technology has the ability to cope with the spatial character of space-time channel.
Smart antenna technology has become the key point in the third generation communication especially in TD-SCDMA because of the spatial distinguish ability. Beamforming from smart antenna, which increasing desire signal and suppressing interference, can achieve spatial divided multiple accessing (SDMA). With the developting of smart antenna, it begins entering the wildband wireless communication area.
Multiple input and multiple output (MIMO) technology has get great development. The research about MIMO has increased from single user to multiuser MIMO system. The application environment has changed from the indoor rich scattering uncorrelated channel to outdoor correlated channel. Because of the advantage in the spectral efficiencies and transmitting ability, it has become the key point in LTE and 4G.
But the channel correlation under space-time wireless environment will bring influence to the system capacity and reliability when MIMO technology has applied from indoor to outdoor. In the same time, the distance demand between antenna elements will bring the difficulty to engineering application. So MIMO technology is developing from opened loop to self adapted closed loop system relying on the feedback of channel information. How to depress the influence of channel correlation and how to decrease the feedback load and operation complication are the key points for the application of MIMO technology.
This dissertation starts from the research of space time channel. The correlation coefficient is derived under statistical channel model in LTE. It gives the influence measurement of different spatial coefficients to channel correlation. The relationship of angle spread and the correlation between different multipaths is analysed for the next chapters'research.
Supposing the independence between multipaths, two kind of beamforming spatial multiplex schemes for single user are proposed in the dissertation. The first scheme can get the multiplex and diversity plus together through self adaptation transmitting beamfroming and switch receiving beamforming. When the multipaths are not enough for spatial multiplex and spatial diversity at same time, the second secheme is proposed that combines the beamforming multiplex and dual polarized diversity to leave more multipaths for the spatial multiplex. Through the associated optimization between transmitting and receiving, the system capacity can get increase under strong correlated channel. The feedback load and operation complication can get decrease together.
Beamforming is combined into multiple users systems. The ability to depress interference between users is enhanced. Comparing with other multiple users MIMO systems such as zeroforcing, the scheme proposed in this dissertation does not need to feedback full CSI information because the spatial characters of multiplex users are completely used.
The capacity and reliability of multiple users system are affected by the correlation between multiplex users which include the spatial location, angle spread and multipath DOA. Also considering the number of active users usually large than the multiplex serving users, multiuser diversity is combined. An interference parameter is used for multiuser scheduling. Because of the multiuser diversity, the sum capacity can get improved.
Considering the frame structure of LTE, a downlink slot divided Multiuser scheduling scheme is proposed at last. The relationship between average system capacity and the number of slots is analysed. It can give a reference for the configuration of active users and slots.
引文
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