【作者】 刘留；

【导师】 李承恕；

【作者基本信息】 北京交通大学 ， 通信与信息系统， 2010， 博士

【摘要】 近年来我国高速铁路及轨道交通取得了举世瞩目的建设成就。与此同时,列车与地面之间的无线通信数据量(包括面向用户的宽带数据业务和列车控制信息)也呈迅速上升趋势。现在普通列车和高速列车上的乘客,仅能通过无线蜂窝网络(2G和3G系统)进行通信,但这些通信体制并不支持高速移动下的宽带无线接入。本论文以时速为350km/h-500km/h高速铁路宽带无线接入为研究对象,着重研究了高速铁路宽带无线接入的系统结构设计和物理层信号处理等关键技术,主要内容包括：针对高速铁路车地间宽带无线接入的业务特点,总结归纳了现有无线通信系统的优点与不足,提出了一种新型的车地间宽带无线数据传输架构——High Speed and Mobile Cell (Himocell)架构,评估了Himocell的优点与不足。同时研究了高速铁路无线信道的特点——时间频率双选择性衰落,探讨了其信道建模方法。针对高速列车车载通信系统对通信收发信机尺寸体积不敏感的特点,研究了空间域方法对抗Doppler频偏技术。在高速列车上架设线性天线阵列,利用天线阵列对接收信号进行空间采样确定虚拟不动点,该虚拟不动点相对地面静止,没有Doppler频偏,消除了时间选择性衰落的影响。本文提出一种时变瑞利信道条件下的最优虚拟点分集接收机方案,该方案在对抗Doppler频偏的同时,接收端可以获得分集增益。针对多载波传输的特点,研究了多载波OFDM技术在时变多径信道下的信道估计技术。为了进一步提高信道估计的准确度和改善系统的误码性能,本文提出一种基于梳状导频的变换域频率分集式信道估计算法,该信道估计算法的精度随着分集导频组的增加而提高,在时变信道中性能也有明显改善。然后,研究了多载波OFDM技术在时变多径信道下的子载波间干扰消除技术。在分析经典子载波间干扰消除技术的基础上,本文提出一种联合信道估计的子载波间干扰消除方法,该方法采用“二项导频”,联合前后两个OFDM符号进行子载波间干扰消除。仿真结果表明,新型子载波干扰消除方法在性能和频谱效率上均优于经典方法。Doppler频率偏移是高速移动条件下影响宽带无线系统性能的主要原因之一。本文在总结归纳经典Doppler分集的基础上,深入研究了一种定向天线扇区接收实现Doppler分集的方法,该方法在完成Doppler频率补偿的同时,可以获取较好的Doppler分集增益。理论分析和仿真结果表明,在快速时变频率选择性衰落信道下,该方案可以有效提高宽带通信系统的传输性能。参照IEEE802.11a标准,开发了基于FPGA软件无线电平台的宽带无线系统原型机。本文优化了OFDM接收机中帧同步、符号定时、信道估计等算法,这些优化使系统运算复杂度下降、处理延迟缩短、硬件资源占用量减少,提高了系统处理效率。更多还原

【Abstract】 The development of China Railway High Speed attracts the world’s attention. There is a technology bottleneck between high mobility scenario and broadband wireless data transmission either the services for the passengers’ wireless demands or for railway control system in High-Speed Railway Communication (HRC). While the mobile telecommunications technology evolved from the second generation to what is known today as beyond third generation (B3G), the same occurred with the telecommunication systems used in HRC. In this paper we will focus on the key technologies to enhance the performance of the broadband wireless access under high speed conditions.The wireless communication demands for the high speed railway is analyzed, and then the advantages and disadvantages are referred. We propose an architecture called High Speed and Mobile Cell (Himocell) to fulfill the broadband wireless needs for High-Speed Railway. The superiorities and drawbacks are evaluated. Additionally, the wireless channel of HRC is studied that the wireless channel of HRC is a double selective fading channel.Doppler spread is particularly detrimental to wireless communication performance especially for transmitting a long packet. In this case, the packet experiences rapidly varying fading compared with transmitting over the static channel. To deal with this problem, the uniform linear antenna (ULA) was proposed to compensate Doppler spread. The ULA consists of a linear antenna array which can be used as space samplers to estimate a virtual point that does not move during packet transmission but without the diversity gain. In this paper, we propose the optimal time diversity position with the ULA compensator over the time-varying Rayleigh fading channel. During transmission, this scheme can not only keep the channel quasi-static but also achieve the optimal time diversity by setting the virtual diversity receiving points at zeros of the time autocorrelation function. When combined with the orthogonal space time block code (STBC), it is proved that this scheme performs even better than that over the static channel with Monte Carlo simulation.Orthogonal frequency division multiplexing (OFDM) should estimate and track the wireless channel in the double selective fading channel. Generally, the comb-pilot number is more than the wireless channel order which makes the noise suppression difficult. We will propose a novel frequency diversity channel estimation method via groups of pilots combining which can reduce the noise. Doppler frequency offset due to the high speed movement destroys the orthogonality of the subcarriers resulting in the intercarrier interference (ICI), and degrades the performance of the system at the same time. We will propose a novel OFDM channel estimation algorithm with ICI mitigation based on the ICI self-cancellation scheme. With this method, more accurate channel estimation is obtained by comb-type double pilots and then ICI coefficients can be obtained to mitigate the ICI on each subcarrier under the assumption that the channel impulse response (CIR) varies in a linear fashion. The theoretical analysis and simulation results show that the BER and spectral efficiency performances are improved significantly under high-speed mobility conditions (350km/h-500km/h) in comparison to the classical ICI self-cancellation scheme.The sectorized antenna can be employed for Doppler mitigation and obtaining Doppler diversity gain. In this paper we will focus on the performances of this directional antenna. We will present the preferable partition scheme for the omnidirectional antenna and the Doppler compensation frequency. And the uncorrelated property of the signal received from the different sectorised antennas will be demonstrated which is utilized for Doppler diversity gain. Finally, it is proved by the simulation results that this architecture will show superior performance under high-mobility conditions.Fast verification of the prototype design upon software radio platform has become one of the most important content in communication assessment. This paper introduces the fundamental method of float-point and fixed-point simulation and rapid prototype design flow. Then some key issues such as OFDM frame synchronization, symbol timing, channel estimation, and so on are optimized, which significantly reduced the usage of hardware resources. The validness is illustrated here with experimental results from the implementation of OFDM burst frame transceiver.更多还原