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.
The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost polymer optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb s−1 are also outlined.
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.
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