In this paper, we propose a drone assisted radio access networks architecture in which drone-cells are leveraged to relay data between base stations and users. Based on the state-of-the-art drone-to-user and drone-to-base station (D2B) channel models, we first analyze the user coverage and the D2B backhaul connection features of drone-cells. We then formulate the 3-D drone-cell deployment problem with the objective of maximizing the user coverage while maintaining D2B link qualities, for a given number of drone cells being deployed. To solve the problem, the particle swarm optimization (PSO) algorithm is leveraged for its low computational cost and unique features suiting the spatial deployment of drone-cells. We propose a per-drone iterated PSO (DI-PSO) algorithm that optimizes drone-cell deployments for different drone-cell numbers, and prevents the drawbacks of the pure PSO-based algorithm derived from related works. Simulations show that the DI-PSO algorithm can achieve higher coverage ratio with less complexity comparing to the pure PSO-based algorithm.

Multiple Drone-Cell Deployment Analyses and Optimization in Drone Assisted Radio Access Networks

Two single fed low-profile cavity-backed slot antennas and an antenna array for circular polarization (CP) applications are introduced. By employing the substrate-integrated waveguide (SIW) and half-mode SIW (HMSIW) techniques in antenna designs, low-profile cavity-backed structures are realized using the low-cost standard printed circuit board process. First, a novel spoon-shaped slot antenna is proposed to realize CP radiation based on the SIW cavity. Then, to minimize the antenna size and achieve the impedance bandwidth enhancement, the HMSIW cavity is introduced to realize a cavity-backed semicircle slot antenna (SSA). The equivalence between the edge of the HMSIW cavity and the longitude slot curved on the surface of the SIW cavity is proposed to guide the design process of the SSA. In addition, two hybrid modes are used to improve the impedance bandwidth of the SSA. Furthermore, a sequential rotation antenna array is introduced to validate the feasibility of the SSA for antenna array application. Finally, the proposed antennas and the antenna array are designed and fabricated at 28 GHz. The measured and simulated results agree very well.

Low-Profile Circularly Polarized Cavity-Backed Antennas Using SIW Techniques

Using aperture-fed stacked curl elements, a full corporate-fed millimeter-wave planar broadband circularly polarized antenna array is proposed. First, the stacked curl element is aperture-fed, using the substrate-integrated waveguide (SIW) feeding network. This element is designed under a specific boundary condition, which leads to an excellent agreement of impedance bandwidth and axial ratio (AR) bandwidth between the designed element and the corresponding antenna array. Simulation results show that the antenna element achieves 35.8% impedance bandwidth and 37.8% 3 dB AR bandwidth with a maximum gain of 8.2 dBic. Then, a $2\times 2$ subarray is designed to achieve 33.1% impedance bandwidth. Next, the full-corporate SIW feeding scheme is utilized to construct the $8\times 8$ broadband antenna array. Finally, the $8\times 8$ antenna array is fabricated and its performance is evaluated. Measurement results show that its impedance bandwidth is 35.4%, 3 dB AR bandwidth is 33.8%, and 3 dB gain bandwidth is 32.2% with a peak gain of 23.5 dBic. Considering these three types of bandwidth together, its overall bandwidth is 30.6%. Good efficiency of about 70% is obtained because of the low-loss full-corporate SIW feeding scheme. A $4\times 4$ multibeam array is also simulated to verify the multibeam potential of the proposed antenna array.

Millimeter-Wave Planar Broadband Circularly Polarized Antenna Array Using Stacked Curl Elements

Millimeter-wave communications have recently attracted significant interest in future wireless networks regarding its wide bandwidth that achieves high data rates. However, the major challenge lies in the beam alignment problem that may induce a substantial loss in the received power, notably when narrow beams are employed. Therefore, this paper jointly addresses the problem of beam alignment and power allocation in a non-orthogonal multiple access (NOMA) mmWave system. Unlike the conventional orthogonal multiple access (OMA), we study the case where two users are joined for NOMA transmission. Next, to mitigate this combined issue, we propose an optimization formulation owing to maximize the sum rate. We compare two types of antennas: sectorized and lemniscate antenna patterns under NOMA and OMA schemes. Simulation results prove the performance of NOMA-lemniscate based beam alignment and power allocation scheme compared to the conventional OMA scheme.

Combined Beam Alignment and Power Allocation for NOMA-Empowered mmWave Communications

Using travelling-wave elements, two planar antenna arrays are developed for millimeter-wave wideband circularly polarized (CP) applications. First, the aperture-fed travelling-wave element is designed. Stacked curl element is printed on the surface of the substrate to realize wideband axial ratio (AR) and impedance performance. Then, two antenna arrays using substrate integrated waveguide (SIW) and microstrip feeding networks are developed, respectively. Performance comparison between these two arrays are discussed. Finally, the wideband CP antenna array which is fed by the SIW network is fabricated and measured. The measured impedance bandwidth of the array is 35.4%, 3-dB AR bandwidth is 33.8%, and 3-dB gain bandwidth is 32.2% with a peak gain of 23.5 dBic. The overall bandwidth is 30.6% and good efficiency of about 70% is obtained because of the low-loss full-corporate SIW feeding scheme.

Millimeter-wave wideband circularly polarized antenna arrays using travelling-wave elements

The wireless capacity crunch will undoubtedly continue as new innovative applications emerge, for instance, augmented reality and massive machine type communications. mmWave promises to deliver gigabits of bandwidth and unprecedented wireless capacity and has created quite the social buzz in both industry and academia. However, mmWave does come with its challenges. Some most prominent issues include high propagation loss, device immaturity, signal processing complexity, and testability. This paper aims to review the current progress on the development of the mmWave technology from seven areas of particular interest/myths with a particular focus on deployment feasibility. We also promote sensible discussions on the potential solutions. Finally, we ask the title question from a network operator’s perspective.

Is mmWave Ready for Cellular Deployment

Large scale antenna system (LSAS) has been widely recognized as one of the key technologies for next generation wireless system (5G) due to its significant performance enhancement in both energy efficiency and system capacity, however, only theoretically so far. Compared with traditional multiple antenna system, there are orders difference in number of RF chains and antenna elements, which introduces more than orders technical challenges in engineering, including cost, circuit power consumption, form factor, etc. UE-type RFIC based RF chain design together with patch antenna design is investigated to solve the problems, with comparative analysis with current bulk RRU/Antenna. Two different architectures, “SmartTile” and “PixelRF/Ant”, based on the design are proposed, followed by a peer-to-peer comparison between these two schemes in terms of synchronization, calibration, interface, etc.

https://www.ursi.org/Proceedings/ProcGA14/papers/ursi_paper2567.pdf

RF and antenna prototype for large scale antenna system

The flexible duplex (FD) technique, including dynamic time-division duplex (D-TDD) and dynamic frequency-division duplex (D-FDD), is regarded as a promising solution to achieving a more flexible uplink/downlink transmission in 5G-Advanced or 6G mobile communication systems. However, it may introduce serious cross-link interference (CLI). For better mitigating the impact of CLI, we first present a more realistic base station (BS)-to-BS channel model incorporating the radio frequency (RF) chain characteristics, which exhibit a hardware-dependent nonlinear property, and hence the accuracy of conventional channel modelling is inadequate for CLI cancellation. Then, we propose a channel parameter estimation based polynomial CLI canceller and two machine learning (ML) based CLI cancellers that use the lightweight feedforward neural network (FNN). Our simulation results and analysis show that the ML based CLI cancellers achieve notable performance improvement and dramatic reduction of computational complexity, in comparison with the polynomial CLI canceller.

Lightweight Machine Learning for Digital Cross-Link Interference Cancellation with RF Chain Characteristics in Flexible Duplex MIMO Systems

In this paper, a pruning method based on contribution of input components is proposed to optimize the structure of Feedforward neural network (FNN) model for digital predistortion of power amplifier. The optimized hyperparameters are the specific input components. The pruning algorithm is divided into two stages. The stage I is used to rough rank the importance of input components and the stage II is used to modify the results of stage I. Then, we can get an importance ranking of input components. By deleting unimportant input components, a pruned FNN model with fewer input components can be obtained. Test results show that the proposed algorithm can greatly simplify the FNN model on the premise of ensuring the predistortion performance.

A pruning method of feedforward neural network based on contribution of input components for digital predistortion of power amplifier

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Papers

Is mmWave Ready for Cellular Deployment

RF and antenna prototype for large scale antenna system

Lightweight Machine Learning for Digital Cross-Link Interference Cancellation with RF Chain Characteristics in Flexible Duplex MIMO Systems

A pruning method of feedforward neural network based on contribution of input components for digital predistortion of power amplifier