Discrete Lens Array Research Articles

Low Complexity Beam Selection Scheme Based on Estimated CSI

The beam selection technology based on the discrete lens array (DLA) can greatly reduce the number of RF chains required by mmWave massive multiple-input multiple-out (MIMO) system. However, the performance of the existing beam selection schemes is on the premise of perfect channel state information (CSI). While in practical situation, accurate channel state information must be obtained by the base station before beam selection. In this paper, the channel estimation scheme based on support detection (SD) is used to estimate the state information of large-scale channel by utilizing the structural characteristics of beamspace. Then on the basis of group-iteration (GI) algorithm, we propose the group-iteration beam selection scheme based on estimated CSI. The simulation results show that this scheme can achieve the performance close to beam selection scheme based on perfect CSI, and compared with the traditional beam selection schemes, the proposed scheme also shows performance advantages.

Beam Selection for mmWave Massive MIMO Systems Under Hybrid Transceiver Architecture

Hybrid analog/digital precoding is a promising technology to cut down hardware cost in massive multi-input multi-output systems at millimeter wave frequencies. In this letter, we propose a joint beam selection scheme for analog domain precoding under discrete lens array. By considering channel correlation among users, the proposed scheme is able to avoid inter-user interference and maximize system sum rate. Moreover, a bio-inspired ant colony optimization-based algorithm is proposed to obtain a near-optimal solution with dramatically reduced computational complexity. Finally, simulations show the advantages of the proposed scheme in improving system sum rate.

Fast Channel Tracking for Terahertz Beamspace Massive MIMO Systems

The recent concept of beamspace multiple input multiple output (MIMO) with discrete lens array can utilize beam selection to reduce the number of radio-frequency chains (RF) required in terahertz (THz) massive MIMO systems. However, to achieve the capacity-approaching performance, beam selection requires information on a beamspace channel of large size. This is difficult to obtain since the user mobility usually leads to the fast variation of THz beamspace channels, and the conventional real-time channel estimation schemes involve unaffordable pilot overhead. To solve this problem, in this paper, we propose the a priori aided (PA) channel tracking scheme. Specifically, by considering a practical user motion model, we first excavate a temporal variation law of the physical direction between the base station and each mobile user. Then, based on this law and the special sparse structure of THz beamspace channels, we propose to utilize the obtained beamspace channels in the previous time slots to predict the prior information of the beamspace channel in the following time slot without channel estimation. Finally, aided by the obtained prior information, the time-varying beamspace channels can be tracked with low pilot overhead. Simulation results verify that to achieve the same accuracy, the proposed PA channel tracking scheme requires much lower pilot overhead and signal-to-noise ratio (SNR) than the conventional schemes.

Virtual channel space-time processing with dual-polarization discrete lens antenna arrays

This paper discusses channel capacity improvements with optimal multiantenna wireless communications using a discrete lens array (DLA) at the analog front end. It is first shown that optimal signaling over multiantenna channels via virtual spatial models (VSMs) has a direct hardware correspondence in a multibeam spatially fed antenna architecture. A multibeam dual-polarized DLA is designed and characterized, and the effects of measured antenna radiation patterns on calculated capacity are quantified. In particular, the paper examines: 1) effects of cross-polarization for a dual-polarized multibeam array; 2) effects of beam overlap in a multibeam array; and 3) effects of gain variations for different scan angles. It is demonstrated that adding an ideal dual-polarized array achieves a capacity improvement of up to 88% compared to the single-polarization case. In practice, the two polarizations are weakly coupled, and the measured cross-polarization level of -14 dB decreases the capacity of the system by less than 2%. Furthermore, it is shown that a dual-polarized multibeam DLA is nearly insensitive to polarization rotation in a rich scattering environment, whereas single-polarized antennas incur a capacity degradation of up to 24%. Finally, capacity decrease due to measured nonuniform amplitudes on the antenna aperture is shown to be less than 10%.