Lei Tian

Beijing University of Posts and Telecommunications | BUPT · Wireless Technology Innovation Institute

In the sixth-generation (6G), with the further expansion of array element number and frequency bands, the wireless communications are expected to operate in the near-field region. The near-field radio communications (NFRC) will become crucial in 6G communication systems. The new mid-band (6-24 GHz) is the 6G potential candidate spectrum. In this pa...

Terahertz (THz) communication is considered to be a key enabling technology for 6G due to its abundant available spectrum resources. One pre-requisite for implementing THz communication systems is to understand and model the THz radio channel in 6G deployment scenarios. However, new radio characteristics in THz bands (e.g., channel sparsity, near-f...

Triggered by the introduction of higher frequencies (above 24 GHz), there has been a long-standing debate in the radio propagation community on whether higher frequency radio channels are sparser relative to channels below 6 GHz. Here, sparsity implies a few dominant multipath components containing the vast majority of the electromagnetic energy. T...

To realize the sixth-generation (6G) vision may require additional spectrum to support the framework and objectives. The sub-6 GHz of fifth-generation (5G) can be used for spectrum refarming, but we also need to find more spectrum with larger bandwidth. This article focuses on the new mid-band (6-24 GHz) that 6G is concerned with, and gives several...

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 o...

Technology research and standardization work of sixth generation (6G) has been carried out worldwide. Channel research is the prerequisite of 6G technology evaluation and optimization. This paper presents a survey and tutorial on channel measurement, modeling, and simulation for 6G. We first highlight the challenges of channel for 6G systems, inclu...

Terahertz (THz) communication is envisioned as the possible technology for the sixth-generation (6G) communication system. THz channel propagation characteristics are the basis of designing and evaluating for THz communication system. In this paper, THz channel measurements at 100 GHz and 132 GHz are conducted in an indoor office scenario and an ur...

The 6 GHz band plays a crucial role in the development of the 6 G. A profound comprehension of channel reciprocity is essential for designing time division duplexing/frequency division duplexing (TDD/FDD) systems within this band. Firstly, in an indoor corridor scenario, precise and impartial measurements are conducted for both the uplink (UL) and...

Terahertz (THz) channel propagation characteristics are vital for the design, evaluation, and optimization for THz communication systems. Moreover, reflection plays a significant role in channel propagation. In this letter, the reflection coefficient of the THz channel is researched based on extensive measurement campaigns. Firstly, we set up the T...

In order to support the future digital society, sixth generation (6G) network faces the challenge to work efficiently and flexibly in a wider range of scenarios. The traditional way of system design is to sequentially get the electromagnetic wave propagation model of typical scenarios firstly and then do the network design by simulation offline, wh...

The tripolarized MIMO system can provide one more degree of freedom and have a more compacted size over a dual-polarized MIMO system, which is attractive for high-capacity wireless communication systems. In this paper, we analyze and model channel properties for tripolarized MIMO systems based on experimental channel measurements in typical indoor...

Terahertz (THz) communication has been envisioned as a key enabling technology for sixth-generation (6G). In this paper, we present an extensive THz channel measurement campaign for 6G wireless communications from 220 GHz to 330 GHz. Furthermore, the path loss is analyzed and modeled by using two single-frequency path loss models and a multiple-fre...

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 c...

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 signifi...

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 p...

The bands 3.5 and 28 GHz are both very important for the fifth-generation (5G) wireless communication system. To model their propagation characteristics and study their channel properties, we conduct measurements at these two frequencies in indoor and outdoor scenarios. The measured bandwidths at 3.5 and 28 GHz are 100 and 400 MHz, respectively. To...

In this paper, the Gaussian mixture model (GMM) is introduced to the channel multipath clustering. In the GMM field, the expectation-maximization (EM) algorithm is usually utilized to estimate the model parameters. However, the EM widely converges into local optimization. To address this issue, a hybrid differential evolution (DE) and EM (DE-EM) al...

Three dimensional (3D) Multiple Input and Multiple Output (MIMO) is one of the most promising techniques for the 5th generation (5G) mobile communication system. To support its research, the property of elevation angle in 3D channel model should be accurately modeled. Conventionally, 3D channel is modeled with an assumption that the mean elevation...

Cluster-based channel model is the main stream of fifth generation mobile communications, thus the accuracy of clustering algorithm is important. Traditional Gaussian mixture model (GMM) does not consider the power information which is important for the channel multipath clustering. In this paper, a normalized power weighted GMM (PGMM) is introduce...

In this letter, a novel angular sampling method–random offset sampling (ROS) is proposed for the simulation of ray-based physical reference channel models. This new method employs an asymmetrical random angular offset to the equal power sampling method, which makes the simulated channel match the spatial-temporal characteristics of the reference ch...

In order to understand how many antennas are needed in a multiuser massive MIMO system, theoretical derivation and channel measurements are conducted; the effect of a finite number of base station (BS) antennas on the performance capability of Zero-forcing (ZF) precoding in a rich scattering channel is quantified. Through the theoretical analysis,...

With the rapid development of high-speed train (HST), the HST wireless communication systems have been attracting an increasing amount of attention. For the design, optimization, and evaluation of HST communication systems, it is vital to have an accurate channel model that can mimic the non-stationary characteristics of HST communication links. In...

The Ricean K-factor is the ratio of the power of the deterministic multipath component (MPC) and the power of all other stochastic MPCs. The classical moment-based method has been successfully used to estimate the K-factor from time series measurements. In this paper, we apply this method to estimate the K-factor for narrowband temporal selectivity...

We focus on the interference statistical metrics of matched filter transmission over line-of-sight (LoS) downlink channels. The exact moments of the interference are derived, which can be used to make approximations for user rates and gain insights into the effects of system parameters such as angle spread (AS), antenna numbers, and array spacings....

In traditional link prediction, many researches assume that endpoint influence, represented by endpoint degree, prefers to facilitate the connection between big-degree endpoints. However, after investigating the network structure, it is observed that influence is determined by the relations built through the paths between endpoints instead of the e...

Radio frequency is a valuable resource for wireless communication systems. The high-frequency band from 6 GHz up to 100 GHz, where continuous and broad spectra exist, is promising to meet the high spectrum requirement of fifth generation (5G) mobile communication systems by 2020. To date, many groups from academia and industry have contributed to d...

This paper presents results from the measurement in indoor conference scenario at 3.5 GHz and 6 GHz. The measurement was performed by using multiple-input multiple-output (MIMO) antennas including uniform planar array (UPA) at transmitter end (Tx) and omni-directional array (ODA) at receiver end (Rx). Two cases including UPA on the wall and the cei...

This paper presents the delay results of wideband wireless channel measurements conducted in urban environment for base station to vehicle at 3.35 GHz and 5.4 GHz, respectively. Channel impulse responses are collected in both line-of-sight (LOS) and non-line-of-sight (NLOS) propagation. Based on the measurement data, power delay profiles are extrac...

With the communication services evolution from the fourth generation (4G) to the fifth generation (5G), we are going to face diverse challenges from the new network systems. On the one hand, seamless handoff is expected to integrate universal access among various network mechanisms. On the other hand, a variety of 5G technologies will complement ea...

In this paper, the performance of 3D MIMO is evaluated with measurement data for the first time. The MEMO channel response for different 3D antenna configurations is extracted from measured channel matrix in the high rise scenario and the corresponding data rates are calculated. The major findings are as follows. For single user MIMO, vertically sp...

In multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, timing synchronization is important in order to find the correct start of OFDM frames and symbols at the receiver. In this paper, a joint transmit antenna selection and maximum ratio combining at the receiver (ST/MRC) are proposed to improve the timing...

In order to obtain accurate characteristics of wireless channels in the viaduct area of China, a channel measurement was taken in a railway viaduct scenario of the Zhengzhou-Xi’an passenger dedicated line with a bandwidth of 50 MHz at 2.35 GHz. The single-slope log-distance model is used to analyze the path-loss (PL), and the distribution of shadow...

In this paper, Empirical results characterizing the joint statistical properties of the shadow fading (SF), the root-mean-square (rms) delay spread (DS), and the Ricean K-factor are presented. Measurement data from high-speed railway in viaduct scenario have been analyzed. It is found that a log-normal distribution accurately fits the distribution...

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 character...

In this paper, the characteristics of clusters induced by a variety of propagation mechanisms in the link from the relay station (RS) to the mobile station (MS) are presented. Based on the results of high resolution channel parameter estimation, an automatic framework integrated with the manual intervention is utilized to perform the cluster identi...

Heterogeneous network (HetNet) is a typical deployment scenario for the IMT-Advanced system whereby the macro enhanced node B (eNB) provides the wide coverage while the lower power nodes such as micro, pico, femto, and relay nodes extend the coverage/capacity for coverage hole or hotspot. This literature addresses the spatial propagation modeling f...

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...

This article addresses the emerging challenges for the extensive application of IMT-Advanced MIMO channel model to the upcoming technologies, e.g., relay and CoMP. To verify the observation and analysis, some field measurements for MIMO channel have been carried out in down town Beijing for the UMi scenario. From the measured data, PL, delay, and A...

Femtocell, as a new emerging deployment scenario for next generation mobile wireless communication systems, has attracted more and more attention recently for providing sufficient indoor coverage and stable backhaul link. The inter- ference problem is publicly known as a key for femtocells to be widely deployed. So lots of standardizing bodies and...