Beamforming techniques have become an integral part of the fifth-generation(5G) of mobile communication systems and continue to evolve for providing high spectral efficiency, spatial diversity, and beamforming gain in millimeter-wave and terahertz(THz) communication for future 6G networks. This paper presents a comprehensive overview of beamforming algorithms from statistical signal processing and optimization perspectives. The fundamentals of beamforming for wireless communication and several representative beamforming algorithms for single-stream and multi-stream transmission are discussed.
A visible-light-communication system incorporating a receiver containing an array of SPADs is described. Initial results suggest that the receiver is shot noise limited and when OOK is used a data-rate of 200 Mb/s is achievable.
In this letter, we present the design and implementation of a pixelated electro-absorption modulator-based modulating retroreflector (MRR) for high-speed optical wireless communications. The modulator is based on a multiple quantum well structure embedded in an asymmetric Fabry-Perot cavity. This MRR was used in an outdoor link, operating at 150 Mb/s with a bit error rate (BER) of 1.22 × 10 -6 at a range of 200 m. The system was also tested in laboratory-controlled conditions achieving a data rate of 200 Mb/s with a BER of 2 × 10 -4 . To the best of our knowledge, this is the fastest retroreflective free-space optics demonstration in both the indoor and outdoor environments.
We demonstrate the development, performance, and application of a GaN-based micro-light emitting diode ( $\mu$ LED) array sharing a common p-electrode (anode), and with individually addressable n-electrodes (cathodes). Compared to conventional GaN-based LED arrays, this array design employs a reversed structure of common and individual electrodes, which makes it innovative and compatible with n-type metal-oxide-semiconductor (NMOS) transistor-based drivers for faster modulation. Excellent performance characteristics are illustrated by an example array emitting at 450 nm. At a current density of 17.7 kA/cm $^2$ in direct-current operation, the optical power and small signal electrical-to-optical modulation bandwidth of a single $\mu$ LED element with 24 $\mu$ m diameter are over 2.0 mW and 440 MHz, respectively. The optimized fabrication process also ensures a high yield of working $\mu$ LED elements per array and excellent element-to-element uniformity of electrical/optical characteristics. Results on visible light communication are presented as an application of an array integrated with an NMOS driver. Data transmission at several hundred Mb/s without bit error is achieved for single- and multiple- $\mu$ LED-element operations, under an on – off -keying modulation scheme. Transmission of stepped sawtooth waveforms is also demonstrated to confirm that the $\mu$ LED elements can transmit discrete multilevel signals.
Device-to-device (D2D) communication that delivers a dedicated channel with low latency and high spectral efficiency has been considered an essential solution for vehicle-to-vehicle (V2V) communication. To achieve such D2D-V2V communication, the beam-steering technique using optical wavelengths can be an attractive candidate due to the advanced optical wireless technologies for point-to-point applications. Recently, there has been research on high-performance optical beam-steering techniques based on microelectromechanical systems mirrors and spatial light modulators in quasi-static indoor environments. Due to the optomechanical complexity, size, and cost, however, their suitability for D2D-V2V applications is problematic. In this work, a cost-effective optical beam-steering system based on a fluorescent reflector and stereo vision for D2D-V2V is introduced. Proof-of-concept demonstration using off-the-shelf devices and components shows that the proposed system can support +-30-deg field of view with a data rate of 300 Mb/s.
This letter presents a visible light communication (VLC) system based on a single 50- μm gallium nitride light emitting diode (LED). A device of this size exhibits a 3-dB modulation bandwidth of at least 60 MHz - significantly higher than commercially available white lighting LEDs. Orthogonal frequency division multiplexing is employed as a modulation scheme. This enables the limited modulation bandwidth of the device to be fully used. Pre- and postequalization techniques, as well as adaptive data loading, are successfully applied to achieve a demonstration of wireless communication at speeds exceeding 3 Gb/s. To date, this is the fastest wireless VLC system using a single LED.
In this paper, we study a family of solid-state, organic semiconductors for visible light communications. The star-shaped molecules have a boron-dipyrromethene (BODIPY) core with a range of side arm lengths which control the photophysical properties. The molecules emit red light with photoluminescence quantum yields ranging from 22% to 56%. Thin films of the most promising BODIPY molecules were used as a red colour converter for visible light communications. The film enabled colour conversion with a modulation bandwidth of 73 MHz, which is 16 times higher than that of a typical phosphor used in LED lighting systems. A data rate of 370 Mbit/s was demonstrated using On-Off keying modulation in a free space link with a distance of ∼15 cm.
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