高铁车地通信中的酉空时调制技术研究

发布时间：2018-04-19 12:45

本文选题：酉空时调制 + 连续快时变　；参考：《西南交通大学》2016年博士论文

【摘要】：在高铁车地通信环境下,列车通常处于开阔地带环境且运行速度非常快,使得衰落信道呈现出明显的空间相关和连续快时变特性。在多天线系统中,酉空时调制技术由于接收端不需要知道信道状态信息而适用于高铁车地通信。论文针对高铁场景,从点对点链路、点对多点链路以及多点对多点链路三个方面研究了酉空时制系统的收发设计方案,并进行相关的性能分析。主要内容概括如下：首先,针对点对点链路,论文研究了空间相关连续快时变信道下酉空时调制系统的最优非相干接收机性能。研究表明,尽管最优非相干接收机在高信噪比区域呈现出错误平层效应,但相比不使用任何信道信息的非相干接收机,该接收机能够获得显著的性能改善。另一方面,信道的高空间相关性使得系统的编码增益在中等信噪比区域中有所损失,信道的空间相关性信息也无益于进一步改善系统性能。鉴于此,论文提出了一种仅利用列车速度信息的简化非相干接收机方案,可省略信道二阶统计特性的估计步骤,从而降低系统的计算复杂度。论文推导了简化非相干接收机的成对错误概率理论公式。仿真结果与分析表明简化非相干接收机的误码性能远优于不使用任何信道相关性信息的次优非相干接收机,并且十分接近最优非相干接收机。其次,论文提出一种空间相关连续快时变信道下酉空时调制系统的预编码器和接收机的联合设计方案。预编码器基于信道的发送空间相关矩阵进行设计,以最小化高信噪比条件下信道估计的均方误差为优化目标；接收机的设计则同时利用了信道的发送／接收空间相关矩阵和时间相关矩阵,并根据最大似然准则得到最优的非相干接收机。仿真结果表明,相比单一的最优非相干接收机,所提方案的误码性能得到明显改善；当信道的发送空间相关性和归一化多普勒频移大到一定程度时,其性能超过空间独立连续快时变信道下的最优非相干接收机。此外,论文推导了所提方案的成对错误概率的理论公式,仿真结果验证了推导的正确性。再次,论文提出一种空间独立连续快时变信道下基于导频序列的酉空时调制系统的相干接收方案。在导频位置的信道估计误差方差和信道时间相关矩阵均已知的前提条件下,通过最大似然法则获得了最优的相干接收机。仿真结果表明所提方案改善了中低信噪比区域的最优非相干接收机的误码率性能。高铁场景中的列车运行速度变化范围相当宽,对应的多普勒频移也发生大幅度变化。在这种情况下,酉空时码的相干接收性能比传统的空时编码具有更好的鲁棒性,因此进一步验证了酉空时码更适用于高铁通信。针对点对多点链路,基于一种新型的信号乘积传输方案,论文研究了两用户MIMO广播信道下的的收发端设计方案,并详细分析了两用户的误码性能。不同用户有不同的移动速度,从而有不同的信道估计能力。在该场景中,假定移动速度高的用户(称为非相干用户)不知道任何信道状态信息,而移动速度低的用户(称为相干用户)已知完美信道状态信息。在发送端,非相干用户的期望信号采用酉空时调制方式,相干用户的期望信号采用空间全复用方式。在接收端,非相干用户采用基于最大似然的最优非相干接收方案,而对于相干用户,提出基于最大似然和最小均方误差的两种硬检测方案和基于条件期望最大化的一种软检测方案。仿真结果对比了不同用户和不同接收方案的误码性能。此外,推导了相干用户和非相干用户的误码率公式,得到相关的精确解以及上界。最后,针对多点对多点链路,论文提出了两用户MIMOX信道下的一种酉空时调制与盲干扰对齐相结合的传输方案,实现了发送端和接收端均不需要信道状态信息的干扰对齐。假设非相干用户经历时间选择性的平坦瑞利衰落信道而相干用户经历频率选择性的静态信道,该方案利用信道的这种异构性实现干扰对齐。由于非相干用户无法知道信道状态信息,因此需要采用非相干方式进行信号传输,在本文所提的方案中,非相干用户和相干用户的期望信号均采用酉空时调制。我们所提的方案比传统的正交传输方案具有更大的分集增益,从而获得更好的误码性能。
[Abstract]:In the communication environment of high speed railway, the train is usually in the open zone environment and runs very fast, which makes the fading channel show obvious spatial correlation and continuous fast time-varying characteristics. In the multi antenna system, the unitary space-time modulation technology is suitable for the high speed railway communication because the receiver does not need to know the channel state information. High speed scene, from three aspects of point to point link, point to point link and multi point to multipoint link, the transceiver design scheme of unitary space-time system is studied, and related performance analysis is carried out. The main contents are as follows: firstly, the unitary space-time modulation system under the space-dependent and fast time-varying channel is studied for point to point link. The performance of the optimal non coherent receiver shows that, although the optimal non coherent receiver presents an erroneous flat layer effect in the high signal to noise ratio region, the receiver can achieve significant performance improvement compared to the non coherent receiver without any channel information. On the other hand, the high spatial correlation of the channel makes the system coding gain. In the middle signal to noise ratio region, the spatial correlation information of the channel is not beneficial to further improve the system performance. In view of this, a simplified non coherent receiver scheme which only uses the train speed information is proposed, which can omit the estimation step of the two order statistical characteristics of the channel, thus reducing the computational complexity of the system. The theoretical formula of the error probability of a simplified incoherent receiver is simplified. The simulation results and analysis show that the error code performance of the simplified incoherent receiver is far superior to the suboptimal incoherent receiver without using any channel correlation information, and is very close to the optimal incoherent receiver. Secondly, a spatially correlated fast time variation is proposed in this paper. A joint design scheme for the precoder and receiver of the unitary space-time modulation system. The precoder is designed based on the transmission space correlation matrix of the channel to minimize the mean square error of the channel estimation under the condition of high signal to noise ratio as the optimization target; the receiver's design simultaneously uses the transmission / reception space correlation matrix of the channel. The optimal non coherent receiver is obtained by the time correlation matrix and the maximum likelihood criterion. The simulation results show that the error performance of the proposed scheme is obviously improved compared with the single optimal incoherent receiver. When the transmission space correlation and the normalized Doppler frequency shift is large to a certain extent, the performance of the proposed scheme is more than space independent. The optimal non coherent receiver under the continuous fast time-varying channel. Furthermore, the thesis derives the theoretical formula of the error probability of the proposed scheme, and the simulation results verify the correctness of the derivation. Thirdly, a coherent reception scheme for the unitary space-time modulation system based on pilot sequence is proposed in the space independent and continuous fast time-varying channel. The optimal coherent receiver is obtained by the maximum likelihood rule under the premise that the variance of channel estimation error and the time correlation matrix of the channel are all known. The simulation results show that the proposed scheme improves the BER performance of the optimal incoherent receiver in the low signal to noise ratio region. In this case, the coherent reception performance of the unitary space-time code has better robustness than the traditional space-time coding in this case. Therefore, it is further verified that the unitary space time code is more suitable for the high speed communication. Based on a new type of signal multiplicative transmission scheme for point to multipoint links, the theory is discussed. This paper studies the receiver design scheme under the two user MIMO broadcast channel, and analyzes the error performance of two users in detail. Different users have different moving speeds and have different channel estimation capabilities. In this scenario, the user who assumes a high moving speed (called a non coherent user) does not know any channel state information and moves in this scene. Users of low speed (known as coherent users) have known perfect channel state information. At the sending end, uncoherent users' expected signals use unitary space-time modulation, and the expected signals of the coherent users adopt the space full multiplexing mode. At the receiving end, the non coherent users adopt the optimal non coherent reception based on the maximum like, and for the coherent users. Two hard detection schemes based on maximum likelihood and minimum mean square error and a soft detection scheme based on conditional expectation maximization are proposed. The simulation results compare the error performance of different users and different receiving schemes. In addition, the error rate formula for coherent users and incoherent users is derived, and the relevant exact solutions and upper bounds are obtained. Finally, for multipoint to multipoint links, a scheme of unitary space-time modulation and blind interference in the two user MIMOX channel is proposed, which realizes the interference alignment of both the transmitter and the receiver without the need of channel state information. The user experiences a frequency selective static channel, which uses the heterogeneity of the channel to achieve interference alignment. Because the incoherent users cannot know the channel state information, it is necessary to use the incoherent mode to carry out the signal transmission. In the proposed scheme, the uncoherent users and the expected signals of the coherent users are all unitary space-time modulation. The proposed scheme has a larger diversity gain than the traditional orthogonal transmission scheme, thus achieving better BER performance.

【学位授予单位】：西南交通大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN911.3

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