Dan Fei

Measurement-Based Characterizations of Indoor Massive MIMO Channels at 2 GHz, 4 GHz, and 6 GHz Frequency Bands

Massive MIMO has been chosen as one of the candidate technologies of the fifth-generation mobile communication system (5G), and channel modeling of massive MIMO is of great importance. The most direct and effective approach to investigate the propagation characteristics of massive MIMO channels is channel measurements. However, there are only few measurements of massive MIMO channels, and there still lacks deep investigations of massive MIMO channel characteristics. In this paper, we present a measurement campaign of indoor massive MIMO channels, by using a linear large-scale array with 64 elements. The measurements are conducted at 2 GHz, 4 GHz, and 6 GHz, respectively, with a bandwidth of 200 MHz. Both LOS and NLOS propagation scenarios are considered in the measurements. The basic channel parameters are extracted, including path loss, delay spread, and coherence bandwidth. The non-stationarity of radio channels, which is reflected by the variations of delay spread and coherence bandwidth over different array locations, is discussed. The impact of carrier frequency on the above channel parameters is further discussed. The results would be useful for the design of massive MIMO system in the indoor environments.

Massive MIMO channel measurements and analysis at 3.33 GHz

As an important candidate technologies of 5th generation mobile communication system (5G), massive MIMO is able to make full use of space resources, and effectively improves the spectrum efficiency, thus helps to solve the current condition of the shortage of spectrum resources. In order to study the massive MIMO technology, the radio channel characteristics, which is different to the conventional MIMO systems, must be captured. Therefore, in this paper, a measurement campaign at the 3.33 GHz frequency band is carried out in an outdoor scenario using a large virtual antenna array with 64 elements. Based on the measured data, we analyze the behaviors of the typical channel parameters including power delay profile (PDP), power azimuth-delay spectrum (PADS), power delay spectrum (PDS), power azimuth spectrum (PAS), delay spread (DS) and azimuth spread (AS). The results show that the non-stationary of the channel over the large array size occur both in delay and spatial domains. The results is useful to develop the massive MIMO channel model and design the 5G communication system.

TD-LTE Downlink Performance Assessment in High Speed Scenarios

Long Term Evolution (LTE) is expected to substitute the Global System for Mobile Communications (GSM) as the radio access technology for railway communications. Recently, especial attention has been devoted to high-speed trains since this particular environment poses challenging problems in terms of performance simulation and measurement. In order to severely decrease the cost and complexity of high-speed measurement campaigns, we have proposed a technique to induce effects caused by highly-time varying channels on Orthogonal Frequency-Division Multiplexing (OFDM) signals while conducting measurements at low speeds. In this work, we employ this technique to evaluate LTE transmissions in a Time-Division Duplex (TDD) fashion, which is more convenient for the railway environment due to a number of reasons (e.g., better flexibility in frequency choice and the importance of the uplink transmissions for railway control communications). We assess the performance obtained in high- speed scenarios up to 500 km/h.

Parameter estimation using SAGE algorithm based on Massive MIMO channel measurements

This paper presents the channel measurements for Massive MIMO communications in indoor scenario at 6 GHz. The channel parameters are jointly estimated using sliding-window SAGE algorithm over the antenna array. The estimated results in delay and angular domains are presented. Considering the large size of antenna array at the transmitter side, the non-stationary phenomenon in the space domain is observed.

Work in progress: LTE system performance evaluation in high-speed environment

In the case of high-speed railway environment, the performance of mobile communication system is a key issue, which will affect the reliability and efficiency in the wireless communication. In this paper, a LTE system of MIMO based on hardware-in-the-loop (HIL) technology is built to evaluate the performance of LTE system. It contains a transmitter, a receiver and a radio channel emulator with software defined radio (SDR) technology. This system, including figures of the Error Vector Magnitude (EVM) and the Error Bit Ratio (BER), will be obtained under different speeds (80~400km/h) and different scenarios (WINNER C2, WINNER D2 and WINNER D2a). Then, the analysis of relationship between EVM and BER are detailed. At last, environmental factors are inferred which may affect the high-speed mobile communication quality.

Path loss characteristics for vehicle-to-infrastructure channel in urban and suburban scenarios at 5.9 GHz

This paper investigates path loss characteristics for Vehicle-to-Infrastructure (V2I) communications in urban and suburban scenarios. We carried out measurements at 5.9 GHz. The transmitter antenna heights are 3.5 m and 1.5 m and the position of the receiver antenna is on the roof of the car. Then we analyzed the path loss characteristics by using the measured data. The results are helpful for the V2I communications system design.

Adaptive beamforming based on subband structure in smart antennas

Beamforming is a signal processing technique in which multiple antennas are used to weight the signals so that they can be added constructively in the desired direction, and destructively in the interference direction. In this paper, adaptive beamforming based on subband decomposition structure is investigated in smart antenna arrays and the performance of the proposed adaptive beamforming scheme is analyzed. An efficient subband structure with the reduced sampling rate of signal is given, which leads to the great reduction of computation complexity. Simulation results indicate that the adaptive beamforming based on subband structure works well and has comparative performance to the conventional fullband algorithms.

Development of LTE-based channel tester for high-speed scenario

This paper focuses on a channel testing scheme based on public LTE network for high-speed scenario. To simplify the deployment of channel testing for high-speed scenario, public LTE CRS in downlink can be utilized so that setting up a transmitter is avoided. A receiver system was designed and the testing was carried out on a high-speed train. Before the field testing a verification for receiver via radio communication tester and channel simulator was done. The result are helpful for the receiver design.

Semi-blind adaptive beamforming based on constant modulus algorithm for smart antennas

Adaptive beamforming plays an important role in smart antenna systems. Nonblind adaptive algorithm utilizes the known training sequence to update the weights of antenna array at the cost of low transmission efficiency. Without sending training sequences, blind adaptive algorithm is a solution to implement beamforming and increase the transmission efficiency. Two classic blind algorithms are studied, namely constant modulus (CM) algorithm and Least squares-constant modulus (LS-CM) algorithm. Considering the advantages of the nonblind and blind algorithms, a semi-blind adaptive beamforming based on CM algorithm is proposed in this paper. Simulation results indicate it has comparable performance compared with nonblind adaptive algorithm, while it only needs the training sequence in the first iteration.

Channel measurements and modeling for 5G communication systems at 3.5 GHz band

The fifth generation (5G) communication has recently attracted much interest. In this paper we present radio channel measurements on campus at 3.5 GHz, which is the candidate frequency band for the 5G communications. The measurement setup is based on software radio units with a bandwidth of 30 MHz, and the measurements were conducted on campus of Beijing Jiaotong University, China. We discuss the power delay profile, path loss, shadowing, and delay spread. It is found that the path loss exponent is up to 6.16 due to high carrier frequency. A lognormal distribution is used to model the shadowing effect, and the standard deviation is 4.21 dB. Furthermore, the root-mean-square delay spread is around 45 ns in the measured campus environments. The results can be applied to the 5G communication system design.