Jiahui Li

Robust and Low Complexity Hybrid Beamforming for Uplink Multiuser MmWave MIMO Systems

In a millimeter-wave (mmWave) multiple-input multiple-output (MIMO) system, a large number of antennas can be placed into a very limited space. It is not practical to equip each antenna with one independent radio frequency (RF) chain. Fortunately, the hybrid analog/digital beamforming (HBF) can be utilized to greatly reduce the number of RF chains, while providing an acceptable performance. However, the conventional multiuser MIMO beamforming algorithms cannot be directly applied to the mmWave system with HBF structure. In this letter, based on the idea that interuser interference reduction should be done for both analog beamforming and digital beamforming, we propose a novel HBF algorithm for the uplink multiuser scenario, which has low computational complexity. Simulations indicate that the proposed algorithm performs very close to the full digital algorithm, and its robustness is verified by comparisons with other existing algorithms under two different channel assumptions.

Measurement-based RSS-multipath neural network indoor positioning technique

Significant developments in indoor positioning techniques based on location fingerprint have been seen recently. RSS (received signal strength) is the most frequently-used indoor fingerprint information. The precision and accuracy of indoor positioning can be improved if we make better use of channel state information and apply more effective matching algorithms. In this study, a method for multipath similarity measurement using multipath time delay and amplitude is proposed. We expand the positioning fingerprint based on the proposed multipath similarity measurement method. Neural network technique is an effective classification and prediction method. An RSS-multipath joint neural network positioning technique is proposed to improve the indoor positioning performance. Distributed MISO (Multiple-Input Single-Output) channel measurement campaign using the THU channel sounder is carried out in indoor environments. Analysis of the experimental results shows that the proposed RSS-multipath joint neural network positioning technique outperforms classical fingerprint algorithms and can improve the positioning accuracy effectively.

Energy-efficient Butler-matrix-based hybrid beamforming for multiuser mmWave MIMO system

In order to reduce the cost and power consumption of radio frequency (RF) chains in a millimeterwave (mmWave) multiple-input multiple-output (MIMO) system, hybrid analog/digital beamforming (HBF) can be utilized to reduce the number of RF chains. The HBF consists of an analog beamforming (ABF) stage and a digital beamforming (DBF) stage. The ABF is always realized by using phase shifters and the DBF is done in a low-dimensional digital domain. However, phase shifters have several drawbacks, such as high power consumption and inconsistency of insertion loss. In this paper, we propose an energy-efficient HBF structure to handle these problems, which utilizes the Butler phase shifting matrix in the ABF stage. With the Butlermatrix- based ABF, several fixed beam directions can be obtained, and the best beam directions of different Butler matrices can be chosen by using exhaustive search. To reduce the high complexity of exhaustive search, we further provide a low complexity HBF algorithm. Simulations under the conditions of perfect channel state information (CSI) and estimated CSI verify the effectiveness of our proposed Butler-matrix-based HBF structure and related algorithms.

Uplink sum-throughput evaluation of sectorized multi-cell massive MIMO system

In this paper, a sectorized multi-cell massive multiple-input multiple-output (MIMO) system is considered with a spatially correlated channel model. Since sum-throughput per cell is an important index for evaluating a multi-cell system, we derive the ergodic achievable uplink sum-throughput per cell of the sectorized system and give the deterministic approximation of it based on the large random matrix theory. Numerical results indicate that sum-throughput per cell can be greatly increased compared to the conventional multi-cell massive MIMO system, which validates the effectiveness of the sectorized system. Moreover, it can be seen that the deterministic approximation is consistent with the result of Monte-Carlo simulation.

Path Loss Model Based on Cluster at 28GHz in the Office and Corridor Environments

This paper presents 28GHz path loss model based on cluster obtained from channel measurement campaigns with rotating platforms and directional antennas in the office and corridor environments. As the sequence number of cluster increases, the path loss exponents (PLEs) increase while shadow factors also have the growing tendency. The PLE of all-clusters is the least because of multi propagation paths, and the LOS PLEs of corridor scenario are less compared with that of office scenario because of corridors long and narrow structure. This path loss model not only contains cluster characteristics, but also unites directional and omnidirectional model into the same framework, which to some extent improves the 5G mmWave channel model.

Sectorization based pilot reuse for improving net spectral efficiency in the multicell massive MIMO system

A sectorization method using the uniform circular array (UCA) is proposed to improve the net spectral efficiency (SE) of the multicell massive MIMO system, which is an important index for evaluating the performance of a communication system. We derive the ergodic achievable uplink net SE per cell of a general sectorized system and obtain its deterministic approximation based on the large random matrix theory. Different weight matrices are considered for the sectorized system and the one with the best performance is utilized for further analysis. The consistency of the deterministic approximation with the result of Monte-Carlo simulation is proved at the same time. At last, numerical results indicate that the net SE per cell can be greatly improved compared to the conventional multicell massive MIMO system, which validates the effectiveness of the sectorization method. Moreover, comparisons with other pilot reuse methods are also made in this paper.创新点本文研究了采用均匀圆形阵列的大规模MIMO系统,并在该场景下提出了一种基于扇区化技术的导频重用策略,该策略可以大大提升多小区大规模MIMO系统净频谱效率。此外,文章基于大规模随机矩阵理论,推导得到了一般性扇区化多小区系统上行可达频谱效率确定性近似表达式,并通过数值仿真验证了该表达式的准确性,其意义在于可以广泛应用于此类型场景下的系统设计以及优化,同时节省了蒙特卡洛仿真所花费的大量时间。

Joint Beam and Channel Tracking for Two-Dimensional Phased Antenna Arrays

Analog beamforming is a low-cost architecture for millimeter-wave (mmWave) mobile communications. However, it has two disadvantages for serving fast mobility users: (i) the mmWave beam in the wireless channel and the beam steered by analog beamforming have small angular spreads which are difficult to align with each other and (ii) the receiver can only observe the mmWave channel in one beam direction and rely on beam-probing algorithms to check other directions. In this paper, we develop a beam probing and tracking algorithm that can efficiently track fast-moving mmWave beams. This algorithm has several salient features: (1) fading channel supportive: it can simultaneously track the channel coefficient and two-dimensional (2D) beam direction in fading channel environments; (2) low probing overhead: it achieves the minimum probing requirement for joint beam and channel tracking; (3) fast tracking speed and high tracking accuracy: its tracking error converges to the minimum Cramer-Rao lower bound (CRLB) in static scenarios in theory and it outperforms several existing tracking algorithms with lower tracking error and faster tracking speed in simulations.

Path loss model based on cluster at 28 GHz in the indoor and outdoor environments

This paper presents 28 GHz path loss model based on cluster obtained from channel measurement campaigns with rotating platforms and directional antennas in the indoor and outdoor environments. The transmitter (TX) and receiver (RX) both sweep a large range of angles in the azimuth and elevation plane on account of covering main propagation paths and measuring burden. As the sequence number of cluster increases, the path loss exponents (PLEs) increase while shadow factors also have a growing tendency. The PLE of all-clusters is the least because of multi propagation paths, and the LOS PLEs of corridor scenario are less compared with that of office scenario because of corridor’s long and narrow structure. This improved model not only considers cluster characteristics, but also unites directional and omnidirectional models into the same framework, which to some extent improves the 5G mmWave channel model.

Dynamic base station selection strategies based on location fingerprinting

Energy consumed at base stations accounts for a large part in wireless communication systems. Dynamic base station selection technique can reduce energy consumption on base station side. Location fingerprinting technique is widely used in indoor and outdoor positioning. Location fingerprint database can also be used for base station selection. In this study, dynamic base station selection strategies based on location fingerprinting are proposed and the theoretical evaluation is carried out. Distributed channel measurement campaign using the THU channel sounder is carried out and the experimental results show that the proposed base station selection strategies have a high accuracy rate and can reduce energy consumption effectively.

A solution to get antenna pattern based on axis calibration between different mm-wave measurement platforms

Mm-wave is expected to be one of the important technologies for 5G wireless communication system, and it is necessary for us to study its radio propagation characteristics, which is helpful for channel modeling. Since we have to carry out a large number of channel measurement campaigns, obtaining the antenna pattern of mm-wave horn antenna on different rotating platforms in different scenarios is an important but difficult work. In this paper, we propose an axis calibration method that just needs to measure the antenna pattern once in the anechoic chamber and do a simple measurement in the practical application scenario, then the exact antenna pattern on different rotating platforms can be calculated out based on previous measured antenna pattern in the anechoic chamber, which can save much measuring time. What is more, we also use simulation and practical channel measurement experiment to validate the accuracy of the proposed method, and the relationship between SNR and axis error is analyzed.