Terahertz (THz) extremely large-scale MIMO (XL-MIMO) is considered a key enabling technology for 6G and beyond due to its advantages such as wide bandwidth and high beam gain. As the frequency and array size increase, users are more likely to fall within the near-field (NF) region, where the far-field plane-wave assumption no longer holds. This also introduces spatial non-stationarity (SnS), as different antenna elements observe distinct multipath characteristics. Conventional far-field stationary models with fixed path parameters fail to capture these variations. Therefore, this paper proposes a THz XL-MIMO channel model that accounts for both NF propagation and SnS, validated using channel measurement data. In this work, we first conduct THz XL-MIMO channel measurements at 100 GHz and 132 GHz using 301- and 531-element ULAs in indoor environments, revealing pronounced NF effects characterized by nonlinear inter-element phase variations, as well as element-dependent delay and angle shifts. Moreover, the SnS phenomenon is observed, arising not only from blockage but also from inconsistent reflection or scattering. Based on these observations, a hybrid NF channel modeling approach combining the scatterer-excited point-source model and the specular reflection model is proposed to capture nonlinear phase variation of different types of non-line-of-sight (NLoS) paths. For SnS modeling, amplitude attenuation factors (AAFs) are introduced to characterize the continuous variation of path power across the array. By analyzing the statistical distribution and spatial autocorrelation properties of AAFs, a statistical rank-matching-based method is proposed for their generation. Finally, the model is validated using measured data. Evaluation across metrics such as entropy capacity, condition number, spatial correlation, channel gain, Rician K-factor, and RMS delay spread confirms that the proposed model closely aligns with measurements and effectively characterizes the essential features of THz XL-MIMO channels.

Shore-based communication is an essential component of the Space-air-ground integrated network(SAGIN). However, due to complex marine environmental factors such as wave motion and tidal effects, it’s challenging to accurately model its channel characteristics. Therefore, this paper conducted a wideband shore-to-ship channel measurement experiment with 4 GHz frequency and 100 MHz bandwidth. To deeply analyze the impact of waves and tides on the channel, a ship attitude recorder was introduced for the first time to capture the real-time attitude information of the ship. Based on the measured data and combined with the Kirchhoff approximation theory, a path loss model in the nearshore area was established and proved better than the fitting effect of the two-ray model. Moreover, the delay spread of the channel was analyzed, showing that its 90% value is within 185.64 ns. The paper contributes to the development of a more realistic and detailed model of dynamic maritime channels.

In this paper, we investigate the visible light-based integrated sensing and communication (ISAC) channel characteristics in a vehicle-to-vehicle (V2V) scenario, focusing on monostatic sensing and bi-static sensing modes. The ISAC channel is divided into a target channel and a background channel. The channel impulse response (CIR) at different distances, as well as the fading characteristics, multipath correlation, and delay spread of the channel within the effective sensing distance in the two sensing modes are investigated by ray tracing simulation. The results show that with the increase of distance, the target channel received power ratio of mono-static sensing decreases by 30%, while the received power ratio of bi-static sensing is stable at about 1.06%, the target channel fading of mono-static sensing is faster than that of bi-static sensing. In addition, the linear fit coefficient of the root mean square (RMS) delay spread (DS) values for mono-static sensing is positive with a mean value of 2.95 which is greater than the mean value of 0.32 for the RMS DS values for bi-static sensing, while the linear fit coefficient of the RMS DS values for bi-static sensing is negative. Overall, the bi-static sensing system outperforms at longer distances, has a more stable target signal received power ratio, better handling target signals and background noise, reducing signal RMS DS, and improving transmission quality and anti-interference capabilities, indicating the advantages of bi-static sensing in V2V scenarios using visible light-based ISAC.

Integrated Sensing and Communication (ISAC), as a fundamental technology of 6G, empowers Vehicle-to-Everything (V2X) systems with enhanced sensing capabilities. One of its promising applications is the reliance on constructed maps for vehicle positioning. Traditional positioning methods primarily rely on Line-of-Sight (LOS), but in urban vehicular scenarios, obstructions often result in predominantly Non-Line-of-Sight (NLOS) conditions. Existing researched indicate that NLOS paths, characterized by one-bounce reflection on building wall with determined delay and angle, can support sensing and positioning. However, experimental validation remains insufficient. To address this gap, channel measurements are conducted in an urban street to explore the existence of strong reflected paths in the presence of a vehicle target. The results show significant power contribution from NLOS paths, with large Environmental Objects (EOs) playing a key role in shaping NLOS propagation. Then, a novel model for EO reflection is proposed to extend the Geometry-Based Stochastic Model (GBSM) for ISAC channel standardization. Simulation results validate the model's ability to capture EO's power and position characteristics, showing that higher EO-reflected power and closer distance to Rx reduce Delay Spread (DS), which is more favorable for positioning. This model provides theoretical guidance and empirical support for ISAC positioning algorithms and system design in vehicular scenarios.

Multiple-input-multiple-output (MIMO) has been a promising technology in wireless communication systems. Channel models are of great importance for the development and assessment of system. With the increase of carrier frequency and MIMO size, the channel model needs to consider near-field spherical wave and spatial non-stationary characteristics, which is different from conventional far-field planar-wave-based geometry-based stochastic model (GBSM) in the 3rd Generation Partnership Project (3GPP). This paper focuses on comparing the channel characteristics and modeling in the far- and near-field region. In this work, we design the measurement campaign in the 6 GHz band (5.9-6.1 GHz) involving the unlicensed spectrum. The uniform planar array (UPA) is adopted from far-field to near-field, where the communication distance is decreasing from 21 m to 6 m (Rayleigh distance is about 14.8 m). Compared to the far-field, the spatial non-stationary phenomenon of channel parameters can be more clearly observed along the array in the near-field region. Then, we propose the extension channel model based on the channel modeling of 3GPP TR 38.901. The array domain is introduced to characterize the spatial non-stationarity of channel parameters (e.g., power, delay, angle). Subsequently, the channel characteristic parameters along the array are analyzed in the near-field range, and the non-stationary model related to the antenna array is established, including power, path loss, delay spread, angular spread, and Ricean K-factor. Finally, the model validation and parametrization are presented in detail with the actual indoor near-field MIMO channel measurements in the 6 GHz band, such as power, angle, and so on. The design and scheme of antenna array spacing are given under the influence of spatial non-stationary characteristics. These work will be helpful for the development and operation of MIMO technology in unlicensed spectra for wireless communication systems.

Extremely large-scale massive multiple-input multiple-output (XL-MIMO) is a potential enabling technology for 6th-generation (6G) communication. The XL-MIMO channel research will be important for XL-MIMO system development. In this paper, the measurement of XL-MIMO channels from 32 to 512 transmitting antenna elements in the 6 GHz band is carried out in an indoor corridor scenario. The delay spread, angular spread, and channel capacity are investigated. The results are compared with the indoor channel model in the Third Generation Partnership Project (3GPP) TR 38.901. We find that the number of antenna elements has a small impact on the delay spread and angular spread. So the spatial non-stationary effect does not need to be considered specifically in the far-field range in this scenario. In addition, the special structure of the corridor leads to a difference in the comparison of the angular spread with the 3GPP model in each dimension. The closed environment of the corridor also results in a significant gap in channel capacity performance from the i.i.d. channel. This work can provide insights into XL-MIMO applications in the 6G era.

Extremely Large-Scale Multiple-Input-Multiple-Output (XL-MIMO) communication, is recognized as a potential enabling technology for sixth-generation (6G) communication. Due to the large antenna aperture of XL-MIMO, spatial non-stationary (SnS) phenomena may occur on the array domain during deployment. This paper, relying on Ray-tracing (RT) simulations, analyzes the SnS phenomena from various perspectives of channel characteristics. Meanwhile, to accurately model the SnS phenomenon, this paper proposes a method for stationary sub-interval partitioning based on channel characteristics. It is assumed that the channel is stationary within each sub-interval, while it is non-stationary across different intervals. The method comprehensively considers factors such as channel correlation, delay spread (DS), azimuth angle spread of departure (ASD), and multipath components (MPCs) birth-death for sub-interval partitioning. By analyzing the independence of sub-intervals, this paper demonstrates that the proposed method performs better in sub-interval partitioning compared to the traditional averaging approach.

Massive multiple-input multiple-output (MIMO) is envisioned as a promising technology in 5G-Advanced and sixth-generation (6G) communication. Channel characteristics are important for the development and performance assessment of massive MIMO systems. Besides, the 6 GHz band (5925- 7125 MHz) has rapidly become the focus band of industry and academia at present. Therefore, this paper conducts the massive MIMO channel measurements in 6 GHz band in typical urban scenarios, and focuses on the massive MIMO channel characteristics in 6 GHz band. The important channel characteristic parameters such as power delay profile (PDP), delay spread, angular spread, channel capacity and data transmission rate are obtained and investigated, which are statistically different from Third Generation Partnership Project (3GPP) TR 38.901 model parameters. Besides, the impact of bandwidth on the system is important, and the great bandwidth allocation has the ability to provide higher transmission rates for future communication systems. Based on deeply exploration of the channel characteristics in 6 GHz band, this work hopes to provide some reference for the design and optimization of 6G communication systems.

Extremely-large-scale multiple-input multiple-output (XL-MIMO) technology, offering vast spatial degrees of freedom by deploying a huge number of antennas, is a promising enabling technology to empower sixth-generation mobile networks (6G). The XL-MIMO channel model is a prerequisite of XL-MIMO technology optimization, system design, and performance evaluation. In this paper, we provide an overview of challenges and ongoing research in XL-MIMO channel measurement, characterization, and modeling. In particular, characterizing and modeling near-field effects and spatial non-stationarity (SnS) are discussed. Also, the channel modeling methods that can describe these new channel characteristics are surveyed. Furthermore, open issues in XL-MIMO channel measurement, characterization, and modeling are presented to give insights into future XL-MIMO channel research.

In the 5G-Advanced and beyond systems, multi-frequency cooperative networking will become an inevitable development trend. However, the channels have not been fully investigated at multi-frequency bands and in multi-scenarios by using the same channel sounder, especially for the sub-6 GHz to millimeter-wave (mmWave) bands. In this paper, we carry out channel measurements at four frequency bands (3.3, 6.5, 15, and 28 GHz) in two scenarios including Urban Micro (UMi) and Outdoor-to-Indoor (O2I) with the same channel sounder. The channel characteristics are extracted and modeled, including path loss (PL), shadow fading, frequency dependence of cluster features, root mean square (RMS) delay spread (DS), Ricean K-factor, and the correlation properties. We mainly focus on the analysis of large-scale parameters and more consideration of the link budget coverage problem. We present the frequency dependence model of the channel characteristics. Among them, in the non-line-of-sight (NLoS) condition, it is found that except for theoretical value brought by higher frequency, additional path loss increment will be generated. Based on these channel characteristics, the impact on performance of the wireless system is analyzed including cell coverage radius, data rate and bit error rate (BER). The results can give an insight into the spectrum selection and optimization in 5G-Advanced and beyond multi-frequency communication systems.

太赫兹信道传播特性对太赫兹通信系统的设计、评估和优化至关重要。此外, 反射在信道传播中起着重要作用。本文基于大量的信道测量工作, 对太赫兹通道的反射系数进行研究。首先, 建立从220 GHz到320 GHz的太赫兹信道测深平台, 入射角范围从10°到80°。根据实测的传播损耗, 分别计算玻璃、瓷砖、木板、石膏板和铝合金五种建筑材料的频率和入射角的反射系数。研究发现, 由于缺乏与太赫兹相关的参数, 导致非金属材料的菲涅耳模型无法成功地拟合实测数据。因此, 通过改进菲涅耳模型与洛伦兹和德鲁德模型, 提出一个频角二维反射系数模型。该模型表征了反射系数的频率和入射角, 与实测数据的均方根误差较小。总的来说, 这些结果对于太赫兹通道的建模做出贡献。

Beamforming is an essential part of the fifth-generation (5G) mobile communication technology. And it will continue to play an indispensable role in the sixth-generation (6G) system. Due to unequal numbers of radio frequency (RF) chains between the base station (BS) and the user equipment (UE), asymmetric beam patterns exist between BS and UE. In this case, characteristics of downlink (DL) channel and uplink (UL) channel need to be explored. In this paper, channel measurements have been performed in an indoor office at 39 GHz. In the measurement campaign, a directional antenna and an omnidirectional antenna are used to simulate BS and UE respectively. In the line-of-sight (LOS) case, we find that path loss (PL) exponent of UL is 0.3 smaller than DL and intercept of UL is 5 dB larger than DL. The measured PL of UL is higher than DL in most cases. And the difference in measured PL between DL and UL decreases with increasing distance. Meanwhile, the root-mean-square (RMS) delay spread (DS) value of UL is larger than DL under most circumstances and the mean value of the difference is 0.9 ns. In the non-line-of-sight (NLOS) case, PL exponent of UL is 0.2 smaller than DL, and the intercept of UL is 2 dB larger than DL. The difference in measured PL and RMS DS between DL and UL becomes narrowed due to blockage effect. The results of the paper are conductive to get a further understanding of asymmetric channel in millimeter-wave.

Millimeter-wave technology is the key technology to support the connection and throughput of the Industrial Internet of Things (IIoT). And the channel model is the basis for the evaluation, optimization, and deployment of the wireless communication system. To model the millimeter-wave channel characteristics in the IIoT scenario, we conduct measurements in a factory-like scenario at 28 GHz. In measurements, antenna heights are set to be higher or lower than most of the metal machines, separately. Based on the collected data, we analyze the large-scale fading and small-scale fading characteristics, including path loss, delay spread (DS), and angular spread (AS). These channel characteristics are statistically modeled. The effects of antenna heights on these channel characteristics are also investigated. Furthermore, we study the distance dependence of the DS and AS.

Industrial Internet of Things (IIoT) is an emerging area that fifth-generation (5G) mobile communication system penetrates industrial manufacturing applications. The indoor factory has larger space and there are a lot of metal machine tools distributed in it, which makes its radio propagation characteristics and corresponding channel models significantly different from those of the indoor office and indoor hotspot. To support the design and the evaluation of the IIoT techniques, the 3rd Generation Partnership Project (3GPP) released the first 5G IIoT standard model in October 2019. In this article, we give a detailed explanation of this IIoT model and compare it with other indoor models. First, we introduce the standardization of 3GPP IIoT channel model and its motivation. Second, four IIoT subscenarios, which are classified according to the clutter density and antenna height, are described. Third, the potential frequency bands of 5G IIoT are summarized. Fourth, the models of channel parameters, including the path loss and the line-of-sight (LOS) probability, the root mean-square (RMS) delay spread, and the angular spread, are given. Among them, the models of path loss and LOS probability take the antenna height and clutter density into consideration. The model of RMS delay spread changes from frequency-dependent to volume-dependent in order to catch the size variation of factories. Finally, two newly added key channel characteristics, dual mobility and absolute time of arrival, which help to describe the robot movement and positioning, are also presented.

This paper presents an empirical study of the uplink and downlink azimuth angle of arrival (AoA) in an urban micro (UMi) scenario at 28 GHz. At present, most UMi measurements are conducted in the downlink and then the uplink situation is inferred assuming channel reciprocity. Although the channel correlation coefficient of the uplink and downlink can be as high as 0.8, this does not mean that they are the same. Only a real uplink measurement can accurately describe its channel conditions, and this is what this study does. A receiver equipped with a rotatable horn antenna is mounted at the base station and the user terminal, respectively, in simulating the uplink and downlink. To improve the angular resolution, we extract the multipath components (MPCs) using the space-alternating generalized expectation-maximization algorithm. Also, a spatial lobe approach is used to cluster the MPCs in the power angular spectrum. By matching MPCs with objects in the environment, we find that direct propagation and first-order reflections are dominant in line-of-sight and non-line-of-sight cases. By comparing our measurement with those in standard channel models, we verify that the AoA of clusters follows a Gaussian distribution in the uplink and downlink. In addition, a two-dimensional Gaussian distribution for ray AoA and power is established to reflect their correlation.

Previous studies have shown that introducing real principal component analysis (PCA) into wireless MIMO channel modeling can effectively improve its accuracy. However, wireless channel data is mostly in the form of complex-valued channel impulse response (CIR) and thus real PCA is very difficult to recover the phase of channel. Under such a motivation, this paper proposes a novel complex PCA-based MIMO channel modeling methodology. First, we prove that PCA can be used to analyze the measured complex-valued CIR data with the principle of maximizing the converted channel power. Then the representative channel features are extracted, which are utilized to reconstruct the CIR finally. An indoor measurement with 32 × 56 antennas is performed for validation. The results clearly show that the proposed channel model is more accurate compared to the real PCA-based model, and is tightly close to the measured channel. Moreover, the proposed methodology is robust with the increase of antennas, which provides insights into massive MIMO channel modeling in the future.

With the commercialization of fifth generation networks worldwide, research into sixth generation (6G) networks has been launched to meet the demands for high data rates and low latency for future services. A wireless propagation channel is the transmission medium to transfer information between the transmitter and the receiver. Moreover, channel properties determine the ultimate performance limit of wireless communication systems. Thus, conducting channel research is a prerequisite to designing 6G wireless communication systems. In this paper, we first introduce several emerging technologies and applications for 6G, such as terahertz communication, industrial Internet of Things, space-air-ground integrated network, and machine learning, and point out the developing trends of 6G channel models. Then, we give a review of channel measurements and models for the technologies and applications. Finally, the outlook for 6G channel measurements and models is discussed.

Identifying Line-of-Sight (LOS) and Non-LOS (NLOS) channel conditions is a big concern in many works. In this paper, we aim to achieve channel classification for millimeter wave (mmWave) systems. The results of mmWave measurement conducted at 28 GHz in typical shopping mall scenario are presented. Specifically, we analyzed the identification performance of single- valued feature extracted from channel impulse response (CIR), and confirmed that rise-time is an attractive features for identification, particularly precise for wideband mmWave signal. Furthermore, a classification algorithm Gradient Boosting Decision Tree (GBDT) is used for LOS/NLOS identification. Experimental results demonstrate an overall detection accuracy of 97.9\%, which shows that our method has a better classification performance than the single feature classifier. Moreover, extensive experimental evaluation considering various propagation distances and obstruction diversity have validated the feasibility of this method.

Abstract This paper reports a longitudinal study on the retrospective evaluation of perceived usability. We propose a retest method based on SUS questionnaires to reduce the multiple-observation effects typically present in longitudinal research. We designed different forms of the SUS questionnaire to eliminate memory effects and distributed duplicate SUS copies to subjects. We first measured the alternative-form reliability of duplicate in Experiment I ($\textbf{r =0.814}$). We then found that the duplicates we designed significantly reduce memory effects compared to the standard SUS questionnaire. Experiment II involved tests on the retrospective evaluation of perceived usability at five measurement points after initial use. The retrospective evaluation of perceived usability changes over time. After 5 min (at point ${\mathrm{T}}_2$), we found that each subject’s retrospective evaluation changed significantly regardless of whether the task had higher or lower usability levels. Moreover, the `directions’of this change tended to differ. This indicates that time is an important factor in perceived usability evaluation. Our results altogether indicate that time affects the retrospective evaluation of perceived usability as well as the accuracy of perceived usability evaluation, which suggests that the process of perceived usability assessment requires strict time constraints.

Massive multi-input and multi-output (MIMO), which uses large-scale antenna arrays to improve spatial efficiency, strengthen performance robustness, etc., is one of primary technologies of 5G wireless communication. To gain further insights into the massive MIMO channel, measurements with the virtual antenna array of the same structure (256 antennas at transmitter and 16 antennas at receiver) are performed in an urban macrocell scenario (UMa) at different frequencies (3.5 & 6 GHz) with different bandwidths (100 & 200 MHz). The enormous collected channel impulse responses enable us to present comparative results including the power delay profile, delay spread and extract angular parameters via SAGE algorithm. Furthermore, angle spread values are illustrated as a direct reflection of massive MIMO channel propagation, then we present comparative channel capacity results. Collectively, these results will shed light on the design of massive MIMO system in UMa environments.

This paper presents the wideband channel characteristics of 28 GHz in urban microcell (UMi) scenario based the measurement in Beijing. Both the omnidirectional-antenna-based measurement and the horn-antenna-based measurement are performed with bandwidth up to 800 MHz. The standard deviation of shadow fading (σS ) is studied and is compared with that value in standard protocol. Unlike traditional method, the σS is calculated with data captured in each single route in this paper. It is found that in a specific environment, the standard model obtained by traditional method overestimate the σS of this frequency band to a large extent both in line of sight (LOS) environment and non line of sight (NLOS) environment. In addition, the 3-Dimensional angle information is estimated with the space alternating generalized expectation-maximization (SAGE) algorithm. The angle spread of arrival (ASA) and the angle spread of departure (ASD) are investigated and the cluster characteristics at different rotation measurement sites are analysed. It is found that dimension of parameter space that used in clustering algorithm has a great impact on the clustering result of the recognizable multipaths.

The millimeter-wave communication is a key component in future broadband cellular networks. In this paper,a virtual multi-antenna measurement was conducted in an indoor line-of-sight scenario using a broadband channel sounder with 400 MHz bandwidth at 28 GHz. In the measurement,with an omni- directional antenna located in a fixed position at transmitter, horn antenna at receiver is rotated 360° in azimuth with the step of 2°, 3°, 5°, 8° and 10°, respectively. Then, the space- alternating generalized expectation-maximization (SAGE) algorithm was utilized to extract channel parameters from the measured results, including number of multipath components (MPCs) in azimuth domain, power azimuth spectrum (PAS) and root mean square azimuth spread of arrival angles (ASA). Finally, we compare these estimated parameters. This work aims to reveal the effects of the rotating step on the estimated results using SAGE algorithm in the virtual multi- antenna measurement. It is found that the number of estimated MPCs in azimuth domain decreases obviously as the rotating step rises, which further affects PAS and ASA. When with the step of 5°, the estimated ASA value is closest to the reference value of 3GPP TR 38.900.

It is necessary to study the spatial evolution of clusters in massive multiple-input multiple-output (MIMO) mobile channel, which is one of the important features in cluster-based models. In this paper, we analyze the data collected from the massive MIMO mobile measurement campaign, with a 256-element virtual array at 3.5 GHz in line of sight (LoS) and non line of sight (NLoS) conditions, respectively. Firstly, the cluster-level angular power spectrums (APS), azimuth of departure (AoD) and azimuth of arrival (AoA), are shown to display the variation of clusters along with the measurement route. Secondly, the evolution of cluster number is presented, showing the changes of appearance and disappearance of the clusters, and the corresponding model based on birth-death process is built. Finally, the cumulative density functions (CDF) of radii of visibility regions (VR) are calculated, which are used to study the variations of VRs along with the measurement route, and lognormal distribution fits the CDFs well.

In order to meet the increasing demand on mobile data service, the fifth generation mobile communication systems (5G) expects to operate in high frequency band up to 100 GHz where the spectrum is available for wide bandwidth. Therefore, the channel characteristics and model for high frequency band up to 100 GHz are of great importance for technology evaluation and network deployment of 5G system. In this paper, wideband channel measurements were conducted in open office and shopping mall scenarios at the center frequency of 28 GHz with 800 MHz bandwidth. Channel impulse responses are obtained for directional and omni-directional channel by using horn antennas and biconical antennas, respectively. Delay characteristics are analyzed based on the measurement data. The measured delay spread is found to obey the log-normal distribution in the two indoor scenarios. The delay spread at 28 GHz in LoS case is smaller compared with that of indoor hotspot scenario in ITU-R M.2135 for below 6 GHz. Furthermore, it is found that the delay parameters are much smaller in directional channel than those in omni-directional channel.

Having the unique feature of wide continuous bandwidth, millimeter-wave communication has attracted great attention from both industry and academics. However, due to the large path loss and diffraction loss, human body shadowing (HBS) has a huge impact on millimeter- wave communication and requires intensive research. In this paper, we conduct HBS measurements in three different cases at 28 GHz by using a pair of horn antennas. Based on our measurement results, we propose a simple HBS model, and then use the double-edge and the multiple-edge diffraction method to study the characteristics of HBS. The gain of HBS is generally 10 dB or greater for the 16 m LOS link. It grows with the distance between TX and RX, and a relative small gain will be obtained when people are close to the antennas and LOS path. Furthermore, human body's direction will have great impact on the effective height, which finally causes 4.63 dB loss.

The millimeter-wave band will be one of the most key components in the next generation wireless communication system. In this paper, a radio channel measurement was conducted in an indoor office environment at 28 GHz with 500 MHz bandwidth. The channel sounder with the clock synchronization was used to measure in both line-of-sight (LoS) and none- line-of-sight (NLoS) scenarios. The channel impulse responses (CIRs) are recorded with an omnidirectional antenna at TX and a horizontal-rotating horn antenna fixed at the same height at RX as references. The space-alternating generalized expectation-maximization (SAGE) algorithm was applied to extract the channel characteristics of multipath components (MPCs) from the synthesized CIRs, and then the direct synthesized CIRs and the CIRs constructed from SAGE results were compared in terms of power delay profiles (PDPs) and power angular spread (PAS). It is found that the reconstructed results closely approximate real results. In addition, the cluster numbers and the inner-cluster root mean square (RMS) angle spreads are drawn after the clustering analysis and they cohere with the changes of the corresponding surrounding environment of the point, regardless of LoS or NLoS. The wireless channel propagation at 28 GHz is heavily dependent on the environment because the linear and reflective propagation are the main mode of transmission.

In this paper, the mobile channel propagation measurements at 3.5 GHz and 6 GHz have been performed in urban micro-cell scenario in the city of China. The measured cases include line-of-sight (LOS) and non- line-of-sight (NLOS) propagation. Statistical results and comparative analysis are presented in this paper, including power delay profiles (PDPs), path loss (PL), coverage, and root mean square (rms) delay spread (DS). It can be found that PDPs measured from campaign keep similarity in these two bands. The result based on PDPs demonstrates that, in mobile condition, the PL exponent of 6 GHz is a little greater than that of 3.5 GHz in both LOS and NLOS propagation. Moreover, as the frequency increases, the path loss will increase and the coverage will remarkably degrade. Last, the rms DS of 3.5 GHz and 6 GHz are similar in LOS case, while that of 3.5 GHz is higher in NLOS case.

In this paper, the channel propagation measurements have been performed in indoor scenario at 3.5, 6, 14, 23, 26 and 28 GHz. The measured cases include line-of- sight (LOS) and non-line-of-sight (NLOS) propagation. Statistical results and comparative analysis are presented in this paper, including path loss (PL) and root mean square (RMS) delay spread (DS). Both floating-intercept (FI) path loss model and alpha-beta- gamma (ABG) path loss model are provided. For the LOS propagation, path loss exponents at different bands are less than or closed to 2. PL exponents range from 2.7 to 4.2 in NLOS case. By fitting ABG PL model for each frequency band, the frequency dependent factors are observed as 2.21 and 2.33 in LOS and NLOS environments respectively. However, no tendency is found between the RMS DS and frequency in indoor scenarios. RMS DS seem not decreases with the increment of frequency bands. We also find that the RMS DS at any given location increases with separation distance and fluctuates seriously at larger distance.

In this paper, we investigate the statistical characteristics of the three dimensional (3D) multiple- input multiple-output (MIMO) channels and their dependency on the dynamic range in channel impulse responses (CIRs). Our study is based on empirical results obtained from the 3D MIMO channel measurement campaigns at 6 GHz in a typical urban macrocell outdoor-to-indoor scenario. The space-alternating generalized expectation-maximization (SAGE) algorithm is employed to estimate parameters of multipath components from the measured data. The measured data is divided into groups based on the dynamic range in the measured CIRs. The second-order statistics in time and spatial domains are calculated for each group. It is found that the channel statistics shows strong dependency on the dynamic range in the measured CIRs.

In the last decade, Nakagami fading shows good performance in matching measurement data under many scenarios, i.e., vehicle-to-vehicle (V2V), mobile-to-mobile (M2M) and indoor. However, little research has been done for generating of spatial-temporal correlated MIMO Nakagami fading. In this paper, we propose a generalized and accurate algorithm to generate Nakagami-m envelope channels with arbitrary temporal autocorrelation and spatial cross-correlation. Specifically the temporal autocorrelation of Nakagami channels is derived using rank matching technology, then spatial cross-correlation is introduced by Sim's algorithm. Finally, the proposed algorithm is validated with theoretical data. This algorithm is valuable for communication system simulation and emulation.

In this paper, we present the small scale characteristics of indoor office scenario based on the channel measurement at 14 GHz with 250 MHz bandwidth. The measurements were operated at more than 100 receiver locations including LOS and NLOS cases over distances up to 55 meters by utilizing a sliding correlator sounder with 125 mega-chip per second (Mcps). Besides, highly directional horn antennas and dipole antennas were used, respectively, to get the channel characteristics including power delay profile (PDP), path number and root-mean-square (rms) delay spread. The results of path number and rms delay spread measured by dipole antennas and horn antennas are different in LOS case. Compared with the results measured by horn antennas, the path number and rms delay spread value obtained by dipole antennas is bigger in LOS case, where rms delay spread values are 30 ns and 52 ns, respectively. It is reasonable that some multipath information is lost when using horn antenna to measure. In NLOS case, path number and rms delay spread only measured by dipole antennas are given.

In this paper, the channel measurements for 5th generation mobile networks (5G) potential spectrum at 3.35 GHz, 4.9 GHz and 5.4 GHz have been performed in the urban macro cell scenarios in China. The measured cases include line-of-sight (LOS) and non-line-of-sight (NLOS) propagation. After acquiring the channel impulse response from the measurement data, the empirical log-distance path loss models are derived. Free-space and ITU-R models are analysed as references. To explore the relation between path loss and carrier frequency, we revise the proposed path loss models by introducing the frequency dependence coefficient (FDC). Furthermore, when FDC is applied, a more accurate description of path loss differences among three frequencies can be obtained in NLOS case. Measurements can be implemented in more scenarios to acquire optimised channel models in the future.

This paper investigates the development of accurate and efficient classifiers to identify misbehaving users (i.e., “flashers”) in a mobile video chat application. Our analysis is based on video session data collected from a mobile client that we built that connects to a popular random video chat ser

Online video chat services such as Chatroulette and Omegle randomly match users in video chat sessions and have become increasingly popular, with tens of thousands of users online at anytime during a day. Our interest is in examining user behavior in the growing domain of mobile video, and in particular how users behave in such video chat services as they are extended onto mobile clients. To date, over four thousand people have downloaded and used our Android-based mobile client, which was developed to be compatible with an existing video chat service. The paper provides a first-ever detailed large scale study of mobile user behavior in a random video chat service over a three week period. This study identifies major characteristics such as mobile user session durations, time of use, demographic distribution and the large number of brief sessions that users click through to find good matches. Through content analysis of video and audio, as well as analysis of texting and clicking behavior, we discover key correlations among these characteristics, e.g., normal mobile users are highly correlated with using the front camera and with the presence of a face, whereas misbehaving mobile users have a high negative correlation with the presence of a face.

High-speed railway (HSR), as an important deployment scenario for both the present and the future mobile wideband radio communication systems, has attracted more and more attention all over the world with the rapid increasing demand of the high data rate communication service on traveling. For the purpose of capturing the wideband channel characteristics of HSR, a channel measurement campaign was conducted at the center frequency of 2.35 GHz with 50 MHz bandwith in the U-shape cutting scenario of Zhengzhou--Xian HSR line in China. Based on the field measured data, we analyze the small scale characteristics in detail, which maily include path number, root mean square delay spread (rms DS), and doppler shift. It is found that the distribution of the path number is well fitted by a Gamma distribution. The statistics of rms DS in the U- shape cutting scenario are larger than the results in other scenario of HSR. In addition, an increasing tendency of rms DS against the transmitter-to- receiver distance is observed and can be modeled by a linear function. Finally, the doppler frequency shift is verified and meets the theoretical value.

Online video chat services such as Chatroulette [1] and Omegle [2] that randomly match pairs of users in video chat sessions have become increasingly popular, with over twenty thousand online users at anytime during a day. A key problem encountered in such systems is the presence of misbehaving users ("flashers") and obscene content. Our previous works [3] [4] prove that using some image recognition methods (skin-detection, dense SIFT) and machine learning algorithms could achieve significantly higher recall and better precision for flasher detection. Nowadays, with the rapid development of advanced mobile phones with both front and back cameras, we expect mobile video chat to become a popular extension of online video chat services. However, because of the computation-intensive features used by our previous solutions and mobile phones' hardware limitations such as memory size and CPU capacity, it is difficult to directly apply our previous works to mobile platforms. As smartphones are increasingly equipped with diverse sensing capabilities, we plan to utilize this multi-dimensional sensor information to extend flasher detection on mobile platform. This project explores how we can mine accelerometer and other mobile sensor data to infer some clues to optimize flasher detection accuracy while reducing the computation demands of flasher detection on the mobile device.

Most people spend more than 90% of their time indoors; indoor air quality (IAQ) influences human health, safety, productivity, and comfort. This paper describes MAQS, a personalized mobile sensing system for IAQ monitoring. In contrast with existing stationary or outdoor air quality sensing systems, MAQS users carry portable, indoor location tracking sensors that provide personalized IAQ information. To improve accuracy and energy efficiency, MAQS incorporates three novel techniques: (1) an accurate temporal n-gram augmented Bayesian room localization method that requires few Wi-Fi fingerprints; (2) an air exchange rate based IAQ sensing method, which measures general IAQ using only CO2 sensors; and (3) a zone-based proximity detection method for collaborative sensing, which saves energy and enables data sharing among users. MAQS has been deployed and evaluated via user study. Detailed evaluation results demonstrate that MAQS supports accurate personalized IAQ monitoring and quantitative analysis with high energy efficiency.

Most people spend more than 90% of their time indoors. Indoor air quality (IAQ) influences human health, safety, productivity, and comfort. This demo introduces MAQS, a personalized mobile sensing system for IAQ monitoring. In contrast with existing stationary or outdoor air quality sensing systems, MAQS users carry portable, indoor location tracking sensors that provide personalized IAQ information. To improve accuracy and energy efficiency, MAQS incorporates three novel techniques: (1) an accurate temporal n-gram augmented Bayesian room localization method; (2) an air exchange rate based IAQ sensing method; and (3) a zone-based proximity detection method for collaborative sensing.

Distributed antenna system (DAS) is a very promising technology to enhance the capacity of indoor communication system due to the inherent macro and micro diversity. With its natural characteristics of reducing the access distance and increasing the probability of line-of-sight (LoS) coverage, DAS can greatly enhance the power efficiency, which is in accordance with the goal of green communication. In this paper, the downlink performance of an indoor DAS is investigated based on a realistic wideband multiple input multiple output (MIMO) channel model constructed with measured data at 5.25 GHz. Different transmission schemes and antenna configurations are compared from the capacity point of view. It is demonstrated that with the same total transmit power DAS with selection transmission (ST) can increase the capacity significantly compared with centralized antenna system (CAS) and DAS with equal-power transmission. The results also show that MIMO technique can improve the system performance significantly even under LoS propagation conditions for indoor scenarios, which is counterintuitive to the common sense that MIMO will suffer from great performance degradation under LoS conditions.

Coordinated multi-points (CoMP) transmission has been widely proved to be effective to combat co-channel interference by a number of theoretical literatures. However, a common assumption is made that the optical fiber required by coordination between base stations (BSs) is always ready to be used which is quite impractical in the real world. Therefore, Intra-Site CoMP, which only involves coordination between sector antennas, is much more easily implemented since the sector antennas are located together. In contrast with the previous theoretical researches, a measurement at 2.35 GHz, with a bandwidth of 50 MHz, was carried out to evaluate its spectral efficiency performance. A novel measuring method is put forward to avoid multi-BS synchronization as well as other challenges in the implementation of CoMP. It is found that Intra-Site CoMP can greatly improve the throughput of the system under the measured environment.