Houjin Chen

Position-Based Modeling for Wireless Channel on High-Speed Railway under a Viaduct at 2.35 GHz

This paper presents a novel and practical study on the position-based radio propagation channel for High-Speed Railway by performing extensive measurements at 2.35 GHz in China. The specification on the path loss model is developed. In particular, small scale fading properties such as K-factor, Doppler frequency feature and time delay spread are parameterized, which show dynamic variances depending on the train location and the transceiver separation. Finally, the statistical position-based channel models are firstly established to characterize the High-Speed Railway channel, which significantly promotes the evaluation and verification of wireless communications in relative scenarios.

A highly efficient channel sounding method based on cellular communications for high-speed railway scenarios

AbstractAn efficient channel sounding method using cellular communication systems is proposed for high-speed railway (HSR) propagation environments. This channel measurement technique can be used conveniently to characterize different HSR scenarios, which can significantly improve the measurement efficiency. Based on downlink signals of wideband code division multiple access (WCDMA) and the long term evolution (LTE), principles and methodologies of HSR channel sounding are presented. Using the WCDMA signal, a measurement campaign is conducted in real-world HSR scenarios and statistical characterizations are provided using a radio network analyzer. Due to the limits of the radio network analyzer, afterwards, a software defined radio (SDR)-based channel data recorder is developed allowing users to collect the signals from different wireless cellular systems. Especially, the estimation accuracies are validated in lab by the faded signals emitted from a vector signal generator. The results show that the channel data recorder provides a particularly good match to the configured fading channels. Therefore, this measurement method can be employed to investigate the HSR channel, and to establish the channel models under the various HSR scenarios.

Channel capacity investigation of a linear massive MIMO system using spherical wave model in LOS scenarios

Massive multiple-input multiple-output (MIMO) is a key technology for the 5th generation (5G) of wireless communication systems. The traditional plane wave channel model (PWM) is often not suitable for the large antenna structure, and in certain cases should be replaced by the more accurate spherical wave model (SWM). By using the spherical wave characterization method, this paper investigates the channel capacity performance of a linear massive MIMO system in line-of-sight (LOS) scenarios. Two types of access settings, the point to point (PTP) system and multi-user (MU) system, are considered. In the PTP setting, a geometrical optimization is performed to obtain configurations that are able to generate a full rank channel matrix for a linear massive MIMO system, which yields full spatial diversity even in LOS scenarios. Compared with the approximate and commonly applied rank-1 PWM, this is very useful for fixed wireless access and radio relay systems requiring high throughput. For the MU case, we compare the eigenvalue distributions of the LOS channels using the plane wave and spherical wave characterization method, and sum rate results are obtained by Monte Carlo simulations. The results show that MU systems using the more realistic and accurate SWM can achieve a higher sum rate than results from the PWM. This is beneficial and informative when designing massive MIMO wireless networks.摘要摘要大规模多天线是未来第五代移动通信系统的关键技术之一,当天线尺寸较大时,传统的球面波信道模型并不适合用于准确的描述传播环境。本文使用更为准确的球面波信道模型,研究了直射场景下大规模线性多天线系统(点对点接入和多用户接入两种架构)的信道容量特征。在点对点接入架构中,本文提出了一种基于位置的系统优化方式,相对于平面波信道模型获得的信道秩为1的结果,该优化方式可以让多天线系统在直射场景下获得信道满秩,从而获得全部空间分集增益;在多用户接入架构下,本文比较了球面波和平面波信道模型下的信道的特征值分布特征,通过使用蒙特卡洛仿真方法研究了系统的信道和速率,仿真结果表明,使用球面波信道模型的信道和速率高于平面波信道模型的信道和速率。创新点本文使用更为准确的球面波信道模型,研究了直射场景下大规模线性多天线系统(点对点接入和多用户接入两种架构)的信道容量特征。在点对点接入架构中,本文提出了一种基于位置的系统优化方式,相对于平面波信道模型获得的信道秩为1的结果,该优化方式可以让多天线系统在直射场景下获得信道满秩,从而获得全部空间分集增益;在多用户接入架构下,本文比较了球面波和平面波信道模型下的信道的特征值分布特征,通过使用蒙特卡洛仿真方法研究了系统的信道和速率,仿真结果表明,使用球面波信道模型的信道和速率高于平面波信道模型的信道和速率。

The dynamic evolution of multipath components in High-Speed Railway in viaduct scenarios: From the birth-death process point of view

Based on the realistic channel measurement on High-Speed Railway (HSR) in viaduct scenarios at 2.35 GHz, the dynamic evolution of multipath components is investigated from the birth-death process point of view. Due to the distinction in the amount of resolvable multipath signals, the channel is divided into five segments and can be completely parameterized by several sets of statistical parameters associated with the type of environment and scenario. Then the four-state Markov chain, describing the birth-death number variation of the detected propagation waves, is employed to specialize the temporal stochastic properties. Furthermore, the steady probabilities and transition probabilities are provided which will facilitate the development and evaluation of wireless communication systems under HSR.

Sum-Rate Capacity Investigation of Multiuser Massive MIMO Uplink Systems in Semi-Correlated Channels

The recent hot research topic of a massive multiple-output (MIMO) has been primarily studied based on the assumption that channel vectors are asymptotically pairwise orthogonal. This condition is not exactly satisfied in practice. Correlation will occur among antenna elements at the base- station antenna array in a dense scattering environment, or in a LOS propagation condition. In this paper, by using the Mellin transform of the eigenvalue distribution, we derive the semi- correlated sum-rate capacity of multi-antenna channels with an arbitrary number of antennas in closed form. Afterwards, we employ two commonly- used correlation models to compare the theoretical closed-form results and the simulated results and the final results show that they match well.

Far Region Boundary Definition of Linear Massive MIMO Antenna Arrays

The plane wave assumption has been used extensively in wireless channel modeling for simplicity. However, when the plane wave model is applied to the massive multiple input and multiple output (MIMO) channel characterization, it is no longer suitable. In this paper, by using the geometrical channel parameterizations, the phase shift difference caused by the spherical wave for a large linear antenna array is investigated, and the Far Region Boundary of a Linear Massive Antenna has been proposed as a criterion to determine whether the user terminal is within the near field of this large antenna structure. Finally, by using ray-tracing method, the proposed boundary within which the propagation caused phase difference exceeds 22.5 is verified. The spherical wave model is necessary for the more accurate channel characterization.

Markov chain based channel characterization for High Speed Railway in viaduct scenarios

The non-stationary properties based on Markov chains are proposed to describe the wireless propagation mechanism of High Speed Railway (HSR) under viaduct scenarios. This Markov modeling method reveals the statistical behaviors of the persistence process corresponding to a resolvable multipath component. Based upon the channel measurement on Beijing-Tianjin HSR at 2.35 GHz, the transition probability matrix and the steady-state probability matrix of Markov chains are specified. These proposed model parameters are informative for link-level simulation and prototype verification for HSR communication systems. In addition, the non-stationary properties are first investigated by medium-scale fading entropy and run length to evaluate the degrees of activity and persistence, respectively. Finally, our Markov models are compared with the experimental results by the Kullback-Leibler (KL) distance to obtain the degree of approximation, which show that the second order model provides a good match to the measured data.

Investigation of Shadowing Effects in Typical Propagation Scenarios for High Speed Railway at 2350 MHz

Based on realistic measurements in China, shadowing characteristics at the frequency of 2350u2009MHz were investigated in typical High-Speed Railway environments. After confirming that the measured shadowing satisfies wide-sense stationarity (assessed via the reverse arrangement test method), we quantify the shadowing correlation. Three types of correlation models are compared for the shadowing characterization, and the Normalized Mean Square Error is used to determine the best matching model: a single decaying exponential function. Decorrelation distances were found to be 11.9u2009m, 17.7u2009m, and 8.3u2009m in our three HSR scenarios, respectively. The results should be useful for the evaluation and verification of wireless communication in High-Speed Railway scenarios.

Stationarity Investigation of a LOS Massive MIMO Channel in Stadium Scenarios

Massive multiple input and multiple output (MIMO) systems can increase the spectrum and energy efficiency of existing cells, and because of this, massive MIMO has been considered as a potential technique for next generation wireless communication networks. Since a thorough knowledge of the propagation channel is a prerequisite of reliable communication systems, massive MIMO channels are of great current interest. In this paper, based on realistic measurements in a stadium scenario in two frequency bands, the stationarity of three basic channel parameters is investigated by using the reverse arrangements test. The results show that channel behaviors in our higher frequency band are stationary over the linear antenna array, whereas this appears untrue at the low frequency band. This non-stationarity phenomenon in the line of sight propagation environment is mainly caused by the stronger reflection and smaller path loss at the low frequency band, which allows more and stronger multipath components, and this leads to substantial channel changes over the large size antenna array.

The Benefits of Large-Scale Attenuation over the Antenna Array in Massive MIMO Systems

Massive multiple-input multiple-output (MIMO) is a potential candidate key technology for the fifth generation of wireless communication systems. In previous research, different power loss and shadowing effects on different individual antenna elements have been neglected. When characterizing the channel of a massive MIMO system and investigating the system performance, the large scale attenuation (LSA) over the antenna array has not been previously considered. In this paper, based on our proposed accurate geometrical propagation model, the spectral efficiency (in terms of bits/s/Hz sum-rate) result of maximal ratio combining (MRC) detection is investigated. From the simulation results, we find that the sum-rate performance for the MRC detection of our proposed more realistic channel model exceeds the results using the conventional model (where the LSA effect is not included). This proposed model LSA model is beneficial and informative for the research, design, and evaluation of the next generation of wireless communication systems employing massive MIMO configurations.