Kunpeng Liu

Millimeter wave MIMO channel tracking systems

We consider channel/subspace tracking systems for temporally correlated millimeter wave (e.g., E-band) multiple-input multiple-output (MIMO) channels. Our focus is given to the tracking algorithm in the non-line-of-sight (NLoS) environment, where the transmitter and the receiver are equipped with hybrid analog/digital precoder and combiner, respectively. In the absence of straightforward time-correlated channel model in the millimeter wave MIMO literature, we present a temporal MIMO channel evolution model for NLoS millimeter wave scenarios. Considering that conventional MIMO channel tracking algorithms in microwave bands are not directly applicable, we propose a new channel tracking technique based on sequentially updating the precoder and combiner. Numerical results demonstrate the superior channel tracking ability of the proposed technique over independent sounding approach in the presented channel model and the spatial channel model (SCM) adopted in 3GPP specification.

A millimeter wave channel model with variant angles under 3GPP SCM framework

Channel model is the fundamental issue to study and design millimeter wave communications, especially for beam-tracking evaluation where large-scale antenna array is applied. In this paper, a new channel model based on 3GPP spatial channel model (SCM) framework is proposed, which introduces variant arrival and departure angles. A linear variation with time is modeled to describe the angle changes where UE is assumed to move in a short range. The model well meets the requirements of beam-tracking evaluation where keeping spatial consistence. Simulations with ray-tracing tools verify the variant angles in indoor dining hall scenario.

Joint Channel Estimation and Beamforming for Millimeter Wave Cellular System

In this paper, we propose a joint channel estimation and beamforming (BF) scheme for the wide band millimeter wave (mmWave) cellular system. Specifically, low complexity compressive sensing (CS) based estimation algorithm is used to estimate the sparse mmWave channels. Based on the estimated channel, low complexity BF scheme is proposed to adapt to the channel for data communications. The algorithm is designed by considering the practical hardware and channel constraints. Furthermore, the complexity is very low without matrix inverse and singular value decomposition (SVD) compared with traditional algorithms, which is well suitable to practical realization. Finally, we show by simulations that the performance of proposed scheme is close to the optimal scheme with extremely less overhead.

Simulation study on millimeter wave 3D beamforming systems in urban outdoor multi-cell scenarios using 3D ray tracing

Urban outdoor millimeter wave communication systems will comprise of dense cell deployment and large-sized array antennas. In this paper, a millimeter wave downlink system-level simulator operating at 73 GHz, which emulates multiple base stations (BSs) and user equipments (UEs) in an outdoor street geometry, is developed. Each BS and UE are surrounded by moving obstacles (e.g., moving cars and walking pedestrians). Two-dimensional (2D) array antennas are employed at both UE and BS to form the 3-dimensional (3D) beams to combat the severe pathloss found in the spectrum. The 3D ray tracer customized to the 3D beam patterns is implemented in the simulator using the OpenGL platform. The 3D ray tracer, in our simulator, carries out the beam alignment task and produces physical channels between UE and BS. The physical channel representation characterizes useful link statistics, e.g., link blockage and co-channel interference statistics. It is shown through the simulation study that high density BS deployment with the directional 3D beamforming enhances the link quality and decreases outage probability compared to the lower density BS deployment. However, the performance degradation caused by the co-channel interference compared to the zero-interference case is still significant. Furthermore, it is observed that high density moving obstacles deteriorate both the throughput and outage performances compared to the low density case because of the increased link blockage.

AoD and AoA tracking with directional sounding beam design for millimeter wave MIMO systems

Millimeter wave multiple-input multiple-output (MIMO) systems equipped with large-sized array antennas have a great potential to boost the achievable data rates by leveraging large bandwidth available at the spectrum. In this paper, we focus on the angle of departure (AoD) and angle of arrival (AoA) tracking problem for temporally correlated sparse millimeter wave MIMO channels. With the beam space MIMO channel modeling, a low complexity two-sided channel sounding scheme for the AoD and AoA tracking is investigated. The adoption of the sparse beam space MIMO channel representation eventually converts the AoD and AoA estimation problem to the support recovery problem. For the support recovery, we employ an iterative soft thresholding algorithm which is broadly referred to as the approximate message passing (AMP) algorithm. The support recovery performance of the AMP, however, suffers from serious deterioration especially at the low SNR regime. To remedy, several directional sounding beam design schemes are proposed to ameliorate the performance of the channel tracking at the low SNR. Simulation results demonstrate that the proposed AoD and AoA tracking outperforms other benchmark schemes when compared in a low SNR setting.

On the 3D beamforming and proactive cell shaping with 3GPP 3D channel model

3-Dimensional (3D) beamforming has been recognized as a promising technique to increase the spectrum efficiency in the Multiple-Input-Multiple-Output (MIMO) systems, which provides performance benefits both in azimuth and elevation dimensions. In this paper, we investigate the typical application scenarios for 3D beamforming and provide the performance evaluation results based on the newest 3D channel model, which is established by 3rd Generation Partnership Project (3GPP). Furthermore, in this paper, we also provide a new 3D beam-forming application scheme, named as Proactive Cell Shaping, to enhance the system performance through balancing the traffic load in the Heterogeneous network (Het-Net) scenario.