Wireless channel capacity estimation in the THz band

The advent of context-aware environments and related applications demands a high degree of connectivity, with new spectral bands and related radio resource management functionalities in the current 5G bands and foreseen in future 6G wireless communication systems. This, in turn, poses new challenges in the implementation of wireless transceivers and radiating systems, in terms of device integration, miniaturization and element isolation, among others. High-performance miniature devices are presented and studied in this work, aided by metamaterial-inspired complementary resonators. A single particle is used to build a single layer, double layer, double frequency resonators and power dividers. A complete characterization of each equivalent circuit is also analyzed, showing great agreement between analytical circuit models and full-wave electromagnetic simulations. By adding more particles, different diplexers and triplexers in the multi-layer configuration are proposed. The flexibility in the design is the key advantage, as all devices are easily tunable and the output lines can be built in different layers, enabling frequency scalability from RF to millimeter wave ranges. Nevertheless, they are only a sample of all possible combinations of devices that can be designed for integration in future wireless communication systems.

As the world warms up to the idea of millimeter wave (mmWave) communication and fifth generation (5G) mobile networks, realization slowly dawns that the data rate, latency, throughput, and other performance metrics that are used to assess a new wireless communication technology will not be enough to support the demands of envisioned futuristic applications. Thus there is an eagerness to further climb up the frequency ladder to use the large swathes of available spectrum in the 0.1 - 10 THz band which is expected to act as the key technology enabler to fulfill the requirements of the sixth generation (6G) wireless communication and possibly even beyond. Channel measurement and modeling are crucial to the design and deployment of future wireless communication systems and researchers across the world are putting their best foot forward to accelerate the process. The present article presents comprehensive assimilation of research efforts in the context of THz channel sounding. A detailed overview of the current channel sounding techniques is first introduced followed by their relevance to THz band channel measurement. An in-house novel channel sounder developed for THz band measurement is also briefly introduced in this context. The paper next provides elaborate dissemination of various measurement campaigns in the band of interest followed by the modeling techniques that are available in the literature and are being adopted for the THz band. Post the description of different challenges and future research directions in the context of sounding, measurement, and modeling the article is concluded.

On Industrial MAC Protocols: State of the Art Systems and Recent Approaches

The potential synergy between quantum communications and future wireless communication systems is explored. By proposing a quantum-native or quantum-by-design philosophy, the survey examines technologies such as quantumdomain (QD) multi-input multi-output, QD non-orthogonal multiple access, quantum secure direct communication, QD resource allocation, QD routing, and QD artificial intelligence. The recent research advances in these areas are summarized. Given the behavior of photonic and particle-like Terahertz (THz) systems, a comprehensive system-oriented perspective is adopted to assess the feasibility of using quantum communications in future systems. This survey also reviews quantum optimization algorithms and quantum neural networks to explore the potential integration of quantum communication and quantum computing in future systems. Additionally, the current status of quantum sensing, quantum radar, and quantum timing is briefly reviewed in support of future applications. The associated research gaps and future directions are identified, including extending the entanglement coherence time, developing THz quantum communications devices, addressing challenges in channel estimation and tracking, and establishing the theoretical bounds and performance tradeoffs of quantum communication, computing, and sensing. This survey offers a unique perspective on the potential for quantum communications to revolutionize future systems and pave the way for even more advanced technologies.

As the demand for higher data throughput continues to grow, next-generation wireless communication systems are expected to deliver per-link data rates in the range of tens to hundreds of gigabits per second. Photon-assisted generation of terahertz (THz) signals can support larger modulation bandwidths in future ultrahigh-speed wireless communication systems. Orthogonal frequency-division multiplexing (OFDM) has emerged as a promising candidate for future THz communication systems owing to its capability to combat frequency-selective fading and suppress inter-symbol interference (ISI). The least-squares (LS) method is widely used for channel estimation due to its simplicity and low computational complexity. However, it is highly sensitive to noise and interference, resulting in limited estimation accuracy. In this work, we proposed an LS maximum ratio combining (MRC) scheme that combines the SNRs of I- and Q-branch pilot-based channel estimations using the MRC technique to enhance the accuracy of channel estimation and equalization. We experimentally demonstrate 16-GBaud QPSK wireless transmission over 4.6 km at 137.5 GHz using a photon-assisted terahertz IQ-mixer communication system. By employing LS-MRC, we achieve more than 2 dB gain, significantly improving link performance. To the best of our knowledge, this is the first experimental demonstration of high-gain performance achieved through the use of I/Q mixer and LS-MRC techniques in a D-band terahertz communication system.

Loosely-synchronized code division multiple access (LS-CDMA) technology is an excellent CDMA technology and very suitable to be applied in the future wireless communication systems. When the multiple input multiple output (MIMO) technique is integrated, better performance and system capacity can be achieved. But the computational complexity of classical detection algorithm based on exhaustive searching, such as maximum-likelihood (ML) rule, is too high and inconvenient to realisation. Although sphere-decoding (SD) algorithm is able to greatly decrease the detection complexity due to the sphere-constrained searching, the decoding complexity is very high especially when the constellation has a lot of points and the number of antennas is large. A modified detection algorithm based on SD method is proposed in this paper, for the sake of further decreasing the complexity. It decodes according to the signal-noise-ratio (SNR). The detector outputs the zero-forcing (ZF) detection results when the SNR is relatively high, otherwise it subtracts these decoded signals from the original receiving signals and then decodes them by SD algorithm. The simulation results shows that the performance of such modified algorithm has little difference as compared with that of SD algorithm.

Recently, there has been a growing interest in leveraging multiple orthogonal orbital angular momentum (OAM) beams to enhance the data capacity of communication systems. Concurrently, as the availability of traditional frequency bands becomes increasingly constrained, attention has shifted from millimeter waves to the terahertz (THz) range due to its extensive and underutilized spectrum. However, the transition to operating frequencies in the THz range presents significant challenges for the design of OAM metasurface antennas. These challenges include the simplification of feeding networks, improved integration with semiconductor devices, provision of sufficiently large antenna apertures, and minimization of diffraction during OAM wave propagation. To address these challenges, we propose an OAM metasurface antenna operating at 312 GHz, specifically designed to generate multiplex <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l= \pm 1$</tex> OAM modes. Additionally, since we utilize high-order Bessel beams to carry OAM information, the resulting quasi-diffraction-free OAM waves are expected to find widespread applications in future terahertz wireless communication systems.

Purpose To fulfill the demand of high-speed communication with high quality of service, the future underwater wireless communication system needs the implementation of MIMO-OFDM system in an underwater environment. But the capacity of MIMO-OFDM system falls due to interference from multiple users called multiuser access interference (MAI) at its receiver. Therefore, this study aims to focus on the suppression of MAI through multiuser detection (MUD) to enhance system capacity. Design/methodology/approach MUD in this research is accomplished in cylindrical shaped space in an UWA network using global optimum solution obtained from jet propulsion behavior and swarm behavior of marine invertebrate animal called tunicates. In other words, MUD in this research is accomplished in a cylindrical shaped space using binary version of tunicate swarm algorithm. Findings Bit error rate analysis using MATLAB simulation reveals that the proposed binary version of tunicate swarm optimizer (TSO) outperforms over conventional detectors and existing bioinspired algorithms such as Spotted Hyena Optimizer and Particle Swarm Optimizer in the same domain in an underwater acoustic network. Research limitations/implications The work is carried out in a cylindrical shaped space for the swarm behavior of tunicate. In this dimension, the fitness function is evaluated in which the proposed TSO gives better performance for interference to noise ratio at 10 and 20 dB. Practical implications TSO generates better optimal solution in comparison to other competitive algorithm in cylindrical search space and is capable of solving real case optimization problem having cylindrical search spaces. Social implications Proper MUD at the receiver in a MIMO-OFDM-UWA communication system will fulfill the demand for multimedia services and high-speed reliable communication in underwater environment. Originality/value The originality in this work is MUD is accomplished using a binary version of metaheuristic paradigm called TSO in an underwater acoustic environment. The modeling and setup of an underwater network is done using World Ocean Simulation System.

Multiple-input and multiple-output (MIMO) is a promising technology that realizes the enormous capacity in future wireless communication systems. For multi-stream detection there are many algorithms. In this paper, we investigate the diversity gain's influence on detection performance of these algorithms. Through three groups simulation with different diversity, we verify that the diversity changes the performance gap between different detection algorithms. The simple detection may be adopted with the same performance as the complicated detection in some practical systems.

A low-complexity two-stage receiver for space–time block-coded CDMA MIMO systems

With the progress of internet of things (IoT), devices with a wireless ad-hoc function are being increasingly used. For future wireless communication systems, the use of millimeter waves, which are strongly affected by shadowing, is considered. We focus on energy-efficiency [bits/J] that combines throughput and energy consumption, which is expected to be important in future wireless communication systems, to realize smart IoT in a shadowing environment. In this paper, we compare the effects of two parameters, including shadowing deviation values, on energy-efficiency in three dimensions for both AODV and OLSR protocols in a shadowing environment using network simulator, ns3.

In this paper, we study the fundamental limits on the data rate of multiple antenna systems in a Rayleigh fading environment. With <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> transmit and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> receive antennas, up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> independent channels can be established in the same bandwidth. We study the distribution of the maximum data rate at a given error rate in the channels between up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> transmit antennas and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> receive antennas and determine the outage probability for systems that use various signal processing techniques. We analyze the performance of the optimum linear and nonlinear receiver processor and the optimum linear transmitter/receiver processor pair, and the capacity of these channels. Results show that with optimum linear processing at the receiver, up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M/2</tex> channels can be established with approximately the same maximum data rate as a single channel. With either nonlinear processing at the receiver or optimum linear transmitter/receiver processing, up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> channels can be established with approximately the same maximum data rate as a single channel. Results show the potential for large capacity in systems with limited bandwidth.

Sub-terahertz (THz) technology is expected to deliver exceptional data rates for future sixth generation wireless communication systems especially for intelligent communication among devices falling under the Internet of Things (IoT) category. Moving from current 5G millimeter wave (mmW) technology towards THz spectrum will eventually provide unprecedented solutions that will guarantee higher transmission rates and channel capacity for any wireless communication system. With various electronic and wireless components working together to fulfill this promise, high gain antennas having compact profile is one such technology that will aid in achieving sub-THz communication while offering low path and power losses with reliable and fast data transfers. In this context, this work proposes a novel deformed patch antenna operating in the sub-THz spectrum i.e. at 300 GHz band. The proposed antenna is fed via a microstrip line following the proximity coupled feeding technique. Utilizing this technique provides a wide impedance bandwidth with a broadside radiation pattern having minimum side lobe levels of around −12 dB and a directivity of 10–15 dBi for the single and array elements respectively. The proposed design has a small footprint of 1.5 × 1.5 × 0.06 mm3for the single element while the array element has dimensions of 6 × 5 × 0.06 mm3. Both the designs have been simulated in Computer Simulation Technology-Microwave Studio (CST-MWS) and the results verified via high-frequency structure simulator (HFSS) simulator. The results confirm the viability of the proposed designs to be potential candidates for future sixth generation and IoT based applications.

In the 21st-century, wireless communication and high-speed communication incorporating computation power, mobile network/Internet access capability, and consumer electronics, will become emerging technologies. To realize high-performance wireless and high-speed communication systems, system-on-chip (SoC) is becoming one of the most important technologies for future WLAN and wireless communications systems. The paper discusses the development and status of the technique first, then gives the detailed design process, especially the HW/SW codesign and verification problems. The paper gives the conclusion that the SoC technique can reduce the cost and improve the performance of WLAN, which will become more and more important with the wide use of WLAN and will drive the development of WLAN likewise.

Trichromatic-color-sensing metasurface with reprogrammable electromagnetic functions