The three previous industrial revolutions profoundly transformed agriculture industry from indigenous farming to mechanized farming and recent precision agriculture. Industrial farming paradigm greatly improves productivity, but a number of challenges have gradually emerged, which have exacerbated in recent years. Industry 4.0 is expected to reshape the agriculture industry once again and promote the fourth agricultural revolution. In this article, first, we review the current status of industrial agriculture along with lessons learned from industrialized agricultural production patterns, industrialized agricultural production processes, and the industrialized agri-food supply chain. Furthermore, five emerging technologies, namely the Internet of Things, robotics, artificial intelligence, big data analytics, and blockchain, toward Agriculture 4.0 are discussed. Specifically, we focus on the key applications of these emerging technologies in the agricultural sector and corresponding research challenges. This article aims to open up new research opportunities for readers, particularly industrial practitioners.

From Industry 4.0 to Agriculture 4.0: Current Status, Enabling Technologies, and Research Challenges

Cognitive Radio Technology

Envelope tracking (ET) is by now a well-established technique that improves the efficiency of microwave power amplifiers (PAs) compared to what can be obtained with conventional class-AB or class-B operation for amplifying signals with a time-varying envelope, such as most of those used in present wireless communication systems. ET is poised to be deployed extensively in coming generations of amplifiers for cellular handsets because it can reduce power dissipation for signals using the long-term evolution (LTE) standard required for fourthgeneration (4G) wireless systems, which feature high peak-to-average power ratios (PAPRs). The ET technique continues to be actively developed for higher carrier frequencies and broader bandwidths. This article reviews the concepts and history of ET, discusses several applications currently on the drawing board, presents challenges for future development, and highlights some directions for improving the technique.

ET Comes of Age: Envelope Tracking for Higher-Efficiency Power Amplifiers

A power amplifier module comprises a plurality of amplifier stages, each including a reference amplifier for emulating the operation of the amplifier. The current flowing to the base of a bipolar transistor that forms each reference amplifier depending on an input power level is detected, amplified, and supplied as base current of the transistor of the corresponding amplifier.

Power amplifier module

The study and exploration of massive multiple-input multiple-output (MMIMO) and millimeter-wave wireless access technology has been spurred by a shortage of bandwidth in the wireless communication sector. Massive MIMO, which combines antennas at the transmitter and receiver, is a key enabler technology for next-generation networks to enable exceptional spectrum and energy efficiency with simple processing techniques. For massive MIMOs, the lower band microwave or millimeter-wave band and the antenna are impeccably combined with RF transceivers. As a result, the 5G wireless communication antenna differs from traditional antennas in many ways. A new concept of the MIMO tri-band hexagonal antenna array is being introduced for next-generation cellular networks. With a total scaling dimension of 150 × 75 mm2, the structure consists of multiple hexagonal fractal antenna components at different corners of the patch. The radiating patch resonates at 2.55–2.75, 3.45–3.7, and 5.65–6.05 GHz (FR1 band) for better return loss (S11) of more than 15 dB in all three operating bands. The coplanar waveguide (CPW) feeding technique and defective ground structure in the ground plane have been employed for effective impedance matching. The deviation of the main lobe of the radiation pattern is achieved using a two-element microstrip Taylor antenna array with series feeding, which also boosts the antenna array’s bandwidth and minimizes sidelobe. The proposed antenna is designed, simulated, and tested in far-field radiating conditions and generates tri-band S-parameters with sufficient separation and high-quality double-polarized radiation. The fabrication and testing of MIMO antennas were completed, where the measurement results matched the simulation results. In addition, the 5G smartphone antenna system requires a new, lightweight phased microwave antenna (μ-wave) with wide bandwidth and a fire extender. Because of its decent performance and compact architectures, the proposed smartphone antenna array architecture is a better entrant for upcoming 5G cellular implementations.

A Novel Approach of Design and Analysis of a Hexagonal Fractal Antenna Array (HFAA) for Next-Generation Wireless Communication

A high-frequency amplifying section (2) amplifies an input high-frequency signal with transistors (12-1) to (12-N). A measuring circuit (27) measures the amplitude of the input high-frequency signal, and a bias controlling circuit (26) continuously controls the bias impressed on the transistors (12-1) to (12-N) according to the value of the amplitude measured by the measuring circuit (27). Thus it is possible to suppress a sudden gain variation with a change in the amplitude of the input high-frequency signal.

High-frequency amplifier

Fifth-generation (5G) mobile communications will need to accommodate huge traffic demands in the near future. Massive multipleinput/multiple-output (MIMO) technology utilizing hundreds of antenna elements has drawn attention as a key antenna configuration for envisioned 5G applications. Realizing the massive MIMO concept of active phased-array antennas (APAAs) for 5G will require small-size, low-power-consumption, and highly accurate phase control over the wide-band frequency range, which poses significant challenges for the RF front end. This article describes prototyped highly integrated RF front ends for high super-high-frequency (SHF) wide-band massive MIMO in 5G.

Integrating the Front End: A Highly Integrated RF Front End for High-SHF Wide-Band Massive MIMO in 5G

The ever-increasing data rate and number of connections for mobile communication offer exciting user experiences in our everyday lives. Currently, the wireless communication frontier is shifting from the current fourth generation (4G) to the forthcoming fifth generation (5G). We expect much of society to go through a revolutionary change with the advent of the 5G era-a change that will involve not only the telecommunication industry but also a wide range of vertical sectors, including automobiles, robotics, health care, factory automation, agriculture, and education.

A GaN PA for 4G LTE-Advanced and 5G: Meeting the Telecommunication Needs of Various Vertical Sectors Including Automobiles, Robotics, Health Care, Factory Automation, Agriculture, Education, and More

In this paper, we report a DC/DC converter based on GaN HEMT's with a switching frequency of 200 MHz that can be used to generate envelope-modulated power supply voltages for use in envelope tracking power amplifiers. The converter consists of switching circuits using 0.25-um GaN HEMTs, inductor, and low pass filter, and can provide output voltages above 28V. An integrated bootstrap driver of the switching circuits is employed in order to reduce DC power consumption of the driver stage. Generation of envelope power supply voltages for 20 MHz LTE signals was demonstrated using 200 MHz switching rates with efficiency of 73%(including dissipation in final and driver stages). The chip size is 1075×990 um2.

High efficiency GaN switching converter IC with bootstrap driver for envelope tracking applications

All-digital outphasing transmitter architecture using multidimensional power coding (MDPC) is proposed for noncontiguous concurrent multiband transmission with a high power efficiency. MDPC transforms multiband digital baseband signals into multibit low-resolution digital signals that drive switching-mode PAs. A prototype digital outphasing transmitter consists of two 1-GHz bandwidth GaN Class-D PAs and a Chireix power combiner. The two GaN PAs are driven by bipolar radio frequency (RF) pulse-width modulation (PWM) signals, which are transformed from a concurrent dual-band LTE signal by MDPC. The dual-band LTE signal with 15-MHz aggregate channel bandwidth at 240 and 500 MHz frequency band is transmitted with $-$ 30 and $-$ 37 dBc out-of-band emissions, respectively. Digital outphasing achieves more than two times higher coding efficiency than conventional concurrent dual-band digital transmitters with the same PAs in Class-S operation. Measured power coding efficiencies of 35.4% and 47.1% are observed with outphasing bipolar and 3-level RF PWM signals respectively, which are encoded from the dual-band LTE signal.

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Shintaro Shinjo

Papers

High-frequency amplifier

Integrating the Front End: A Highly Integrated RF Front End for High-SHF Wide-Band Massive MIMO in 5G

A GaN PA for 4G LTE-Advanced and 5G: Meeting the Telecommunication Needs of Various Vertical Sectors Including Automobiles, Robotics, Health Care, Factory Automation, Agriculture, Education, and More

High efficiency GaN switching converter IC with bootstrap driver for envelope tracking applications

Concurrent Multiband Digital Outphasing Transmitter Architecture Using Multidimensional Power Coding