Open-loop Beamforming Research Articles

Multi-Node Open-Loop Distributed Beamforming Based on Scalable, High-Accuracy Ranging

We present a distributed antenna array supporting open-loop distributed beamforming at 1.5 GHz. Based on a scalable, high-accuracy internode ranging technique, we demonstrate open-loop beamforming experiments using three transmitting nodes. To support distributed beamforming without feedback from the destination, the relative positions of the nodes in the distributed array must be known with accuracies below <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /15$ </tex-math></inline-formula> of the beamforming carrier frequency to ensure that the array maintains at least 90% coherent beamforming gain at the receive location. For operations in the microwave range, this leads to range estimation accuracies of centimeters or lower. We present a scalable, high-accuracy waveform and new approaches to refine range measurements to significantly improve the estimation accuracy. Using this waveform with a three-node array, we demonstrate high-accuracy ranging simultaneously between multiple nodes, from which phase corrections on two secondary nodes are implemented to maintain beamforming with the primary node, thereby supporting open-loop distributed beamforming. Upon movement of the nodes, the range estimation is used to dynamically update the phase correction, maintaining beamforming in a dynamic array. We show the first open-loop distributed beamforming at 1.5 GHz with a three-node array, demonstrating the ability to implement and maintain phase-based beamforming without feedback from the destination.

Smart Beamforming for Direct LEO Satellite Access of Future IoT.

Non-terrestrial networks (NTN) are expected to play a key role in extending and complementing terrestrial 5G networks in order to provide services to air, sea, and un-served or under-served areas. This paper focuses the attention on the uplink, where terminals are able to establish a direct link with the NTN at Ka-band. To reduce the collision probability when a large population of terminals is transmitting simultaneously, we propose a grant-free access scheme called resource sharing beamforming access (RSBA). We study RBSA for low Earth orbit (LEO) satellite communications with massive multiple-input multiple-output (MIMO). The idea is to benefit from the spatial diversity to decode multiple overlapped signals. We have devised a blind and open-loop beamforming technique, where neither the receiver must carry out brute-force search in azimuth and elevation, nor are the terminals required to report channel state information. Upon deriving the theoretical throughput, we show that RBSA is appropriate for grant-free access to LEO satellite, it reduces the probability of collision, and thus it increases the number of terminals that can access the media. Practical implementation aspects have been tackled, such as the estimation of the required statistics, and the determination of the number of users.

Achieving High Spectrum Efficiency on High Speed Train for 5G New Radio and Beyond

Realizing high mobile data rates in high mobility scenarios has been an important yet challenging target for wireless communications. One typical scenario of such "double high" communications is the HST, which has been one of the most representative infrastructures in more and more countries, especially in China. However, the current SE in HST communications according to the measurements is far from satisfactory to meet the data rate demand generated by the intensive users on HSTs. To address this issue, potential technologies to improve the SE performance of HST communications under various CSI assumptions are presented in this article. Specifically, two open loop beamforming methods with the help of location information (i.e., the location based MIMO precoding and the location assisted MIMO precoder cycling) are first proposed, which are shown to be robust to HST channel variations. Then, we study closed loop beamforming strategies, where channel prediction is proposed to be the key to obtain the essential CSI (e.g., channel matrix or channel covariance) with a low overhead. As HSTs usually go through complicated environments, a big data aided adaptation mechanism between the investigated methods is further proposed. Numerical results demonstrate that the proposed approaches are capable of achieving over 10x SE performance than the current HST transmission strategies and worthy to be studied and discussed in the future 5G New Radio (NR) standardization. It is anticipated that communications with high data rates in high mobility scenarios will be well supported for HSTs in the 5G era.

Open-Loop Beamforming Technique for MIMO System and Its Practical Realization

The concept of close-loop beamforming for MIMO system was well known proposed the singular value decomposition on channel matrix. This technique can improve the capacity performance, but the cost of feedback channel and the complexity processing discard the interest of implementation. Therefore, this paper aims to investigate the benefit of using an open-loop beamforming for MIMO system in practical approaches. The low-profile concept of open-loop beamforming which is convenient for implementation is proposed by just inserting Butler matrices at both transmitter and receiver. The simulation and measurement results indicate that the open-loop beamforming with Butler matrix outperforms the conventional MIMO system. Although, the close-loop beamforming offers a better performance than open-loop beamforming technique, the proposed system is attractive because it is low cost, uncomplicated, and easy to implement.