Xuefeng Yin

Future railway services-oriented mobile communications network

The future development of the railway is highly desired to evolve into a new era where infrastructure, trains, travelers, and goods will be increasingly interconnected to provide high comfort, with optimized door-to-door mobility at higher safety. For this vision, it is required to realize seamless high data rate wireless connectivity for railways. To improve the safety and comfort of future railways, wireless communications for railways are required to evolve from only voice and traditional train control signaling services to various high data rate services including critical high-definition (HD) video and other more bandwidth-intensive passenger services, such as onboard and wayside HD video surveillance, onboard real-time high data rate services, train multimedia dispatching video streaming, railway mobile ticketing, and the Internet of Things for railways. Corresponding mobile communications network architecture under various railway scenarios including inter-car, intra-car, inside station, train-to-infrastructure and infrastructure- to-infrastructure are proposed in this article. Wireless coverage based on massive MIMO for railway stations and train cars is proposed to fulfill the requirement of high-data-rate and high spectrum efficiency. The technical challenges brought by the massive MIMO technique are discussed as well.

Device-to-device channel measurements and models: a survey

Channel measurements and modelling have been long considered as the foundation for effective and efficient wireless communication system designs. Recently, there has been an explosive growth of research work dedicated to the so-called device-to-device (D2D) communications. In the mean time, however, measurements and modelling of D2D channels seem to somewhat fall behind. To promote research on these aspects, in this study, the authors provide a critical overview of the current state of research on D2D channels, and comprehensively discuss future trends and research directions.

A 3D Geometry-Based Stochastic Channel Model for UAV-MIMO Channels

Unmanned Aerial Vehicles (UAVs) have been a promising platform in realizing high-speed wireless networks. As an emerging scenario, the UAV communication is distinct from widely used cellular systems or vehicular networks, requiring the development of practical yet easy-to-use channel models. In this paper, for the first time we introduce the geometry-based stochastic model (GBSM) to UAV channel modeling, and propose a new three- dimensional (3D) GBSM for UAV Multi-Input Multi- Output (UAV-MIMO) channels. Based on the proposed model, we derive and investigate the space-time correlation function (STCF) under a 3D moving and scattering environment. The usefulness of this model is verified by the comparison between the theoretical results and some measurement data.

A General Framework for BER Analysis of OFDMA and Zero-Forcing Interleaved SC-FDMA over Nakagami-m Fading Channels with Arbitrary m

In this letter, bit error rate (BER) analysis is presented for both orthogonal frequency-division multiple access (OFDMA) and zero-forcing (ZF) interleaved single-carrier frequency-division multiple access (SC-FDMA) systems over Nakagami-m frequency-selective fading channels with arbitrary m. Specifically, the analytical BER is derived for both cases based on a general framework, that is by exploiting the statistics of the equalized noise. In comparison with the exiting alternatives, the proposed BER analysis has only half of the computational complexity for the OFDMA system and is more general for the SC-FDMA case.

Channel maps and stochastic models in elevation based on measurements in operating networks

In this contribution, a channel measurement campaign recently carried out in the Jiading campus of Tongji University, Shanghai, China, is introduced. The downlink signals of an active Universal Mobile Telecommunications System (UMTS) were collected at more than 4000 locations and processed to extract channel impulse responses (CIRs). The signal to noise power ratios (SNRs), delay spread, Doppler frequency spread, and the status of line-of-sight (LoS) existence are calculated and used to generate channel maps, i.e. geographic maps overlaid with spots at measurement locations being color-coded by the values of channel parameters. The variations of channel parameters with respect to the co-elevation in NodeBs are investigated. Relationships between the delay, Doppler frequency spreads and the LoS occurrence rate at specific co-elevations are analyzed. Based on these results, a new method is proposed which is applicable for generating realistic CIRs in time and frequency domains that satisfy the elevation-dependent statistics extracted from the measurements.

Experimental spatial correlation characteristics of propagation channels in indoor environments

Spatial auto- and cross-correlation characteristics of propagation channels are investigated for four indoor scenarios using measurement data. In addition to the well-known spatial auto-correlation effect, significant cross-correlation between channels is also observed. We found that non-zero spatial cross-correlation among channels may occur in three scenarios with possibly different mechanisms. These results should be considered when establishing realistic models for the spatial cross-correlation behavior of channels.

Interference measurement and analysis of full-duplex wireless system in 60 GHz band

With co-time co-frequency full duplex (CCFD) in 60 GHz band, self interference (SI) has different characteristics due to larger wireless path loss and beamformed system compared to current band under 6 GHz (normal band). In this paper, we present real SI channel measurement results and analysis to consider indoor CCFD in 60 GHz band. The results show that the narrow beam antennas can effectively suppress the direct leakage component but increase the root mean square (RMS) delay spread of the SI channel due to reflections from nearby objects. The effect of phase noise on SI cancellation is demonstrated since a high-frequency oscillator is used. At the end, we show the key factors of SI cancellation based on the measurement results for implementation of CCFD in 60 GHz band.

Dynamic range selection for antenna-array gains in high-resolution channel parameter estimation

In this paper, a method of choosing direction estimation range is proposed for high-resolution channel parameter estimation by using the Space-Alternating Generalized Expectation-maximization (SAGE) algorithm. The proposed method applies in cases where directional multi-antenna arrays are used for channel measurements. In the method, the direction estimation range is determined by specifying appropriate values for the dynamic range of array gain (DRAG) of directional arrays. A simple rationale is provided for calculating the lower-bound of DRAG. Both simulation and measurement results demonstrate that when the DRAG is properly selected, the estimation errors retains at an acceptable level and the spurious paths, i.e. the estimated path without its counterpart in reality, appear with low possibilities.

Investigation of multi-link spatial correlation properties for cooperative MIMO channels

In this paper, a comprehensive investigation of multi-link spatial correlation properties for cooperative multiple-input multiple-output (MIMO) wireless channels is presented. The impact of interested and important parameters, e.g., local scattering density (LSD) and environment-related parameters, on multi-link spatial correlation properties is completely investigated. Some interesting observations are found and useful conclusions are made. They are helpful for better understanding cooperative MIMO channels and for setting up more purposeful measurement campaigns.