Analog Beamforming Architecture Research Articles

Oversampling Based Analog Beamforming for Initial Access With a Large Number of Receive Antennas

Beamforming can provide huge array gains in large-scale antenna systems under the condition that the channel state information (CSI) has been obtained by training signals. During the initial access, no CSI is available at the receiver because the communication link between the transmitter and the receiver has not been established. This paper considers the problem of obtaining the beamforming gain for receivers with the analog beamforming architecture in the initial access, assuming that a fixed beam pattern is employed. We present the necessary and sufficient condition to obtain the receive beamforming gain in the absence of CSI, and then derive the upper bound of the receive beamforming gain for different antenna spacings. It is shown that oversampling in space is needed at the receiver to obtain a non-trivial beamforming gain without CSI, since the total received signal power is proportional to the number of receive antennas. We also design the beamformer that can achieve the upper bound. Numerical results demonstrate the effectiveness of the proposed beamformer in the scenarios of downlink synchronization and random access in millimeter-wave systems.

Beamforming Design for Large-Scale Antenna Arrays Using Deep Learning

Beamforming (BF) design for large-scale antenna arrays with limited radio frequency chains and the phase-shifter-based analog BF architecture, has been recognized as a key issue in millimeter wave communication systems. It becomes more challenging with imperfect channel state information (CSI). In this letter, we propose a deep learning based BF design approach and develop a BF neural network (BFNN) which can be trained to learn how to optimize the beamformer for maximizing the spectral efficiency with hardware limitation and imperfect CSI. Simulation results show that the proposed BFNN achieves significant performance improvement and strong robustness to imperfect CSI over the conventional BF algorithms.

Energy Efficient Analog Beamformer Design for mmWave Multicast Transmission

Millimeter wave (mmWave) communication is considered as a key enabling technology for 5G cellular networks because abundant spectrum in mmWave bands can provide multi-gigabit communication service. Analog beamforming architecture, which employs energy-efficient phase shifters (PSs) instead of energy-hungry radio frequency (RF) components, has emerged as a promising solution to overcome severe propagation loss of mmWave channels. On the other hand, multicast communication is another efficient approach to address the dramatic traffic demand by utilizing the broadcast nature of the wireless medium. This paper investigates energy efficient analog beamforming in mmWave single-group multicast communication systems. We focus on max–min fair (MMF) problem and aim to design the analog beamformer to maximize the minimum signal-to-noise ratio (SNR) over all users subject to a transmit power constraint. The analog beamformer design with infinite and finite resolution PSs are both studied. While the constraints of PSs make the problem intractable, we propose an alternative low-complexity algorithm, which iteratively determines each element of analog beamformer. Furthermore, we also investigate the asymptotically optimal beamformer designs and provide asymptotic performance analysis for large-scale mmWave multicasting systems. Extensive simulation results illustrate the effectiveness of the proposed analog beamforming designs in mmWave multicast systems. Besides, numerical results also demonstrate that the asymptotic performance of the proposed scheme is close to the optimal case.

ON–OFF Analog Beamforming for Massive MIMO

This paper investigates a new analog beamforming architecture for massive multiple-input multiple-output (MIMO) systems, where each of the multiple transmit antennas is switched to be on or off to form a beam according to the channel state information at transmitters. This on–off analog beamforming (OABF) scheme has the advantages in terms of both hardware complexities and algorithmic complexities. OABF can completely remove the high-cost, power-consuming, and bulky analog phase shifters that are extensively employed by traditional analog beamforming schemes; it only requires the deployment of low-cost analog switches that are easy to implement. Moreover, we show that the beams formed by such simple antenna on–off switch operations can achieve rather good performances with low-complexity beamforming algorithms. Specifically, we first propose two optimal signal-to-noise ratio maximization algorithms to determine the on–off state of each switch under the per-antenna power constraint and the total power constraint, respectively. After that, we theoretically prove that OABF can achieve the full diversity gain and the full array gain with complexities up to a polynomial order. Numerical results are consistent with our theoretical analysis. We believe that the simple structure of OABF makes massive MIMO much easier to implement in real systems.

Amplify-and-Forward Strategies in the Two-Way Relay Channel With Analog Tx–Rx Beamforming

In this paper, we study the multiple-input-multiple-output two-way relay channel (MIMO-TWRC) when the nodes and relay use analog beamforming. Following the amplify-and-forward (AF) strategy, the problem consists of finding the transmit and receive beamformers of the nodes and relay (as well as the power allocated to each one) that achieve the boundary of the optimal rate region. To solve it, we first express the optimal node beamformers in terms of relay beamformers and then show that the optimal rate region can efficiently be characterized using convex optimization techniques. We also extend our study to the multiple-relay scenario when the source nodes are single antenna and propose a distributed algorithm to compute the relay beamforming matrices. The proposed algorithm consists of solving two different subproblems. First, each individual TWRC is optimized independently. Next, a distributed beamforming is applied to make the signals from the relays add up coherently at the source nodes. Numerical examples are provided to illustrate the performance of the proposed techniques and to compare the performance of analog beamforming architectures against conventional MIMO schemes that operate at the baseband.