Generation Wireless Communication Systems Research Articles

Low-complexity MU-MIMO-GFDM joint receivers

ABSTRACT The Multiple-Input Multiple-Output (MIMO) scheme uses multiple antenna configurations to achieve high throughput data transmission in current communication systems. The new generation wireless communication system considers using generalised frequency division multiplexing (GFDM) due to its advantages such as lower out-of-band (OOB) emission and peak-to-average power ratio (PAPR), etc. However, inter-symbol interference (ISI) and inter-carrier interference (ICI) occur due to GFDM utilises the pulse shaping filter. This paper proposes a low-complexity joint minimum mean square error (MMSE) receiver to suppress ISI, ICI, and multi-user interference (MUI) for multi-user MIMO-GFDM (MU-MIMO-GFDM) system. The conventional approach is to design the equalisation and the GFDM demodulation separately. This paper jointly designs the equalisation and demodulation process that significantly reduces the complexity and enhances the error rate performance. This paper also analyzes the closed-form expression and two low-complexity methods for the proposed receiver. The simulations demonstrate the effectiveness of the proposed low-complexity multi-user MIMO-GFDM receivers.

Cooperative 3D Beamforming for Small-Cell and Cell-Free 6G Systems

Three dimensional (3D) resource reuse is an important design requirement for the prospective sixth generation (6 G) wireless communication systems. Hence, we propose a cooperative 3D beamformer for use in 3D space. Explicitly, we harness multiple base station antennas for joint zero forcing transmit pre-coding for beaming the transmit signals in specific 3D directions. The technique advocated is judiciously configured for use in both cell-based and cell-free wireless architectures. We evaluate the performance of the proposed scheme using the metric of Volumetric Spectral Efficiency (VSE). We also characterized the performance of the scheme in terms of its spectral efficiency (SE) and Bit Error Rate (BER) through extensive simulation studies.

A design of impedance transformer with tunable center frequencies using filter synthesis approach

Microwave impedance transformer (IT) with center frequency tunable capability is one of great research issue for better utilization of frequency spectrum resources and system miniaturization of next generation wireless communication systems. This article presents a filter synthesis approach for designing IT with center frequency tunable capability using single dc-bias controlled tunable resonators. The proposed IT provides bandpass filtering response and is designed by properly coupling quarter-wave tunable resonators with alternate J- and K-inverters. The J-inverters are realized using a parallel-coupled line, whereas K-inverter is implemented with T-type short-circuited TL. Using filter theory, analytical design equations are derived to calculate the circuit parameters. The center frequency of the proposed IT is tuned over a wide frequency tuning range (FTR) by changing the varactor diode capacitance of quarter-wave resonators. For experimental demonstration, a prototype of 25-to-50 Ω IT is designed, simulated, and measured. The measured results confirmed that the center frequency of the proposed IT is tuned from 2.05 to 2.91 GHz (860 MHz or 34.68% FTR) with an insertion loss variation of 2.57 to 1.76 dB.

5G Cognitive Radio Networks Using Reliable Hybrid Deep Learning Based on Spectrum Sensing

Spectrum sensing is critical in allowing the cognitive radio network, which will be used in the next generation of wireless communication systems. Several approaches, including cyclostationary process, energy detectors, and matching filters, have been suggested over the course of several decades. These strategies, on the other hand, have a number of disadvantages. Energy detectors have poor performance when the signal-to-noise ratio (SNR) is changing, cyclostationary detectors are very complicated, and matching filters need previous knowledge of the main user (PU) signals. Additionally, these strategies rely on thresholds under particular signal-noise model assumptions in addition to the thresholds, and as a result, the detection effectiveness of these techniques is wholly dependent on the accuracy of the sensor. In this way, one of the most sought-after difficulties among wireless researchers continues to be the development of a reliable and intelligent spectrum sensing technology. In contrast, multilayer learning models are not ideal for dealing with time-series data because of the large computational cost and high rate of misclassification associated with them. For this reason, the authors propose a hybrid combination of long short-term memory (LSTM) and extreme learning machines (ELM) to learn temporal features from spectral data and to exploit other environmental activity statistics such as energy, distance, and duty cycle duration for the improvement of sensing performance. The suggested system has been tested on a Raspberry Pi Model B+ and the GNU-radio experimental testbed, among other platforms.

Micro-strip Patch 2.4 GHz Wi-Fi Antenna Design For WLAN 4G- 5G Application

In this study, an antenna with a frequency of 2.4 GHz has been designed that can be used in new generation wireless communication systems, which are in high demand with the development of technology. The designed antenna has Wi-Fi operating frequency range according to IEEE 802.11 standards. While choosing the antenna design, micro-strip antenna was preferred due to their geometry, lightness, low cost of production and compactness. While designing the antenna, the CST microwave studio program was deemed appropriate to be used and the necessary measurements were made. It has been deemed appropriate to use copper in the ground and patch parts of the antenna design. ROGERS 5880 (RT5880), for micro-strip circuit applications, was preferred as the substrate material. The dielectric coefficient of the selected material is 2.2. Its thickness is taken as 0.81 mm. As a result of the design, most of the intended goals were achieved. The gain of the designed antenna is measured as 2.73 dBi return loss value 30 dB and the bandwidth as in the 2.33-2.48 GHz range. These results are acceptable according to the standards. The 2.4 GHz antenna designed in this study can be used for Wi-Fi studies according to the experimental results.

Terahertz Communications: Challenges in the Next Decade

Thanks to the abrupt advances in semiconductor technologies, particularly in terms of the operating frequency, the last decade has seen various efforts and trials in attempts to achieve high-throughput wireless communications at terahertz (THz) frequencies. Through the use of several potential device technologies, not only III-V heterojunction bipolar and high-electron-mobility transistors but also silicon complementary metal-oxide-semiconductors and photonic technologies, high data rates of 100 Gbps or more have been successfully demonstrated. Meanwhile, the next generation of wireless communications systems, so called 6G, is already being discussed in research communities worldwide. A terabit per second peak data rate is envisioned, which essentially requires huge spectral resources. The recent considerable attention to 6G communications is implicitly focused on THz communications but is more than a technical curiosity unlike in the past. In this article, we briefly review the progress of THz communications made in the last decade and discuss some of the most challenging issues that need to be overcome for future wireless systems at THz frequencies, including not only the 6G network but also short-range connectivity and fixed wireless links.

Markov‐based analysis for cooperative HARQ‐aided NOMA transmission scheme in 5G and beyond

AbstractIn the fifth generation (5G) wireless communication system, the non‐orthogonal multiple access (NOMA) scheme has recently been proposed as a possible candidate for improving spectral efficiency. We look at power‐domain NOMA in this study, in which, multiple simultaneous transmissions are allowed at the same channel with different transmission powers. To achieve reliable transmissions in NOMA, the hybrid automatic repeat request (HARQ) scheme can be integrated into NOMA. The performance of a downlink NOMA system using the Type I HARQ method is investigated in this research. This type of HARQ does not entail expensive device which is considered one of the requirements for a massive 5G‐based Internet of Things network. Unfortunately, in the literature, it has been shown that deriving closed‐form expressions for the outage probabilities of HARQ‐aided NOMA systems is intractable due to the incorporation of multiple fractional random variables. Consequently, in this article, we follow a simple yet efficient methodology to study our considered HARQ‐aided NOMA system. The HARQ‐assisted NOMA system on the downlink is modeled as an absorbing discrete‐time Markov chain (DTMC). Thereafter, under perfect and imperfect channel estimation, we use this model to examine system performance in terms of outage probability and estimated number of retransmissions. Interestingly, we demonstrate that our DTMC‐based analysis is straightforward, repeatable, and accurate. Moreover, in this article, we propose a cooperative HARQ (CHARQ) scheme for the downlink NOMA system. According to CHARQ, the users cooperate with the base station in the retransmission process that will result in improving the performance of NOMA. Monte Carlo simulations have been conducted to not only verify the accuracy of our DTMC‐based analysis, but also manifest the superiority of CHARQ over HARQ.

Design and Testbed Implementation of Blind Parameter Estimated OFDM Receiver

Designing an intelligent or adaptive transceiver system is becoming a promising technology for upcoming generations of wireless communication systems due to its adaptivity, spectrum efficiency, and low-latency characteristics. However, there is no work available until now that characterizes and demonstrates complete adaptation in the physical layer for orthogonal frequency-division multiplexing (OFDM) systems. In this article, we propose and implement sequential blind parameter estimation methods for OFDM signals using radio frequency (RF) testbed setup in a realistic scenario. The estimations include the number of subcarriers, symbol duration, cyclic prefix, oversampling factor, symbol timing offset (STO), and carrier frequency offset (CFO). The proposed algorithms also include blind modulation classification for linearly modulated signals over a frequency-selective fading channel. The parameter estimation has been carried out through a cyclic cumulant process. The modulation formats are classified by using normalized fourth-order cumulant in the frequency domain. The STO and CFO are estimated by a proposed modified maximum likelihood algorithm. The performances of parameter estimations, modulation classification, and synchronization are measured through analytical, simulation, and measurement studies. The overall performance of the OFDM system is provided in terms of the received constellation diagram and bit error rate (BER) over an indoor propagation environment.

A Review of Orbital Angular Momentum Vortex Waves for the Next Generation Wireless Communications

The next-generation wireless technology that can fulfill such a demand, namely the fifth-generation (5G) technology, should provide 1000 times larger capacity. Moreover, sixth-generation (6G) communication, which represents a significant upgrade from the fifth-generation (5G) network and is anticipated to operate from 100 GHz to 3 THz band, will be required in the years after 2030 due to newly developed data-hungry applications and the greatly expanded wireless network. To meet the ever-growing demands of wireless carriers, an efficient wireless access method that can improve wireless area throughput without expanding bandwidth or cell size is required. Radio Frequency (RF) Orbital Angular Momentum vortex waves (which is now on referred to as OAM waves) to address the concerns mentioned above have attracted much attention in recent years. Due to their orthogonality, different OAM waves of different modes can be multiplexed in the same frequency channel, which can greatly increase the channel capacity. Using the orthogonal modes, a new type of multiple access scheme known as Mode Domain Multiple Access (MDMA) can be used by multiple users using the same frequency channel without additional resources such as frequency and time. As a result, the channel capacity for the next generation wireless communication systems can be enhanced as well as the overall spectrum efficiency can be improved. This review paper begins with an overview of the next generation communication such as 5G communication technology and beyond. This paper first briefly discusses the theory of OAM waves and several methods to generate OAM waves. Various different designs have also been analyzed for their ability to generate OAM waves and discussion on several restrictions and solutions to resolve. Open concerns and development trends are discussed for possible future RF OAM antenna upgrades. This study also proposes that for next generation wireless communication employing OAM, the typically used Uniform Circular Array (UCA) could be paired with the Multiple-Input-Multiple-Output (MIMO) system to improve performance in dense or urban areas for multiusers. In addition, the purity of OAM-modes needs to be considered for efficient utilization of the OAM system for future communications at the radio domain.

Separate least mean square based equalizer with joint optimization for multi-CAP visible light communication

Visible light communication (VLC) is expected to be a potential candidate of the key technologies in the sixth generation (6G) wireless communication system to support Internet of Things (IoT) applications. In this work, a separate least mean square (S-LMS) equalizer is proposed to compensate low-pass frequency response in VLC system. Joint optimization is employed to realize the proposed S-LMS equalizer with pre-part and post-part by introducing Lagrangian. For verification, the performance of VLC system based on multi-band carrier-less amplitude and phase (m-CAP) modulation with S-LMS equalizer is investigated and compared with that without equalizer, with LMS equalizer and with recursive least squares (RLS)-Volterra equalizer. Results indicate the proposed equalizer shows significant improved bit error ratio (BER) performance under the same conditions. Compared to the RLS-Volterra equalizer, S-LMS equalizer achieves better performance under low data rate or high signal noise ratio (SNR) conditions with obviously lower computational complexity.

Phase Shift Optimization Algorithm for Achievable Rate Maximization in Reconfigurable Intelligent Surface-Assisted THz Communications

Terahertz (THz) band communications are considered a crucial technology to support future applications, such as ultra-high bit rate wireless local area networks, in the next generation of wireless communication systems. In this work, we consider an ultra-massive multiple-input multiple-output (UM-MIMO) THz communication system operating in a typical indoor scenario where the direct link between the transmitter and receiver is obstructed due to surrounding obstacles. To help establish communication, we assume the aid of a nearby reconfigurable intelligent surface (RIS) whose phase shifts can be adjusted. To configure the individual phase shifts of the RIS elements, we formulate the problem as a constrained achievable rate maximization. Due to the typical large dimensions of this optimization problem, we apply the accelerated proximal gradient (APG) method, which results in a low complexity algorithm that copes with the non-convex phase shift constraint through simple element-wise normalization. Our numerical results demonstrate the effectiveness of the proposed algorithm even when considering realistic discrete phase shifts’ quantization and imperfect channel knowledge. Furthermore, comparison against existing alternatives reveals improvements between 30% and 120% in terms of range, for a reference rate of 100 Gbps when using the proposed approach with only 81 RIS elements.

Calculating Beamforming Vectors for 5G System Applications

The growing demand for broadband Internet services is forcing scientists around the world to seek and develop new telecommunication technologies. With the transition from the fourth generation to the fifth generation wireless communication systems, one of these technologies is beamforming. The need for this technology was caused by the use of millimeter waves in data transmission. This frequency range is characterized by heavy path loss. The beamforming technology could compensate for this significant drawback. This paper discusses basic beamforming schemes and proposes a model implemented on the basis of QuaDRiGa. The model implements a MIMO channel using symmetrical antenna arrays. In addition, the methods for calculating the antenna weight coefficients based on the channel matrix are compared. The first well-known method is based on the addition of cluster responses to calculate the coefficients. The proposed one uses the singular value decomposition of the channel matrix into clusters to take into account the most correlated information between all clusters when calculating the antenna coefficients. According to the research results, the proposed method for calculating the antenna coefficients allows an increase in the SNR/SINR level by 8–10 dB on the receiving side in the case of analog beamforming with a known channel matrix.

A Novel 3D Non-Stationary GBSM for 6G THz Ultra-Massive MIMO Wireless Systems

Terahertz (THz) communication is now being considered as one of possible technologies for the sixth generation (6G) wireless communication systems. In this paper, a novel three-dimensional (3D) space-time-frequency non-stationary theoretical channel model is first proposed for 6G THz wireless communication systems employing ultra-massive multiple-input multiple-output (MIMO) technologies with long traveling paths. Considering frequency-dependent diffuse scattering, which is a special property of THz channels different from millimeter wave (mmWave) channels, the relative angles and delays of rays within one cluster will evolve in the frequency domain. Then, a corresponding simulation model is proposed with discrete angles calculated using the method of equal area (MEA). The statistical properties of the proposed theoretical and simulation models are derived and compared, showing good agreements. The accuracy and flexibility of the proposed simulation model are demonstrated by comparing the simulation results of the relative angle spread and root mean square (RMS) delay spread with corresponding measurements.

Maximizing the Set Cardinality of Users Scheduled for Ultra-Dense uRLLC Networks

Ultra-reliability and low latency communication has long been an important but challenging task in the fifth and sixth generation wireless communication systems. Scheduling as many users as possible to serve on the limited time-frequency resource is one of a crucial topic, subjecting to the maximum allowable transmission power and the minimum rate requirement of each user. We address it by proposing a mixed integer programming model, with the goal of maximizing the set cardinality of users instead of maximizing the system sum rate or energy efficiency. Mathematical transformations and successive convex approximation are combined to solve the complex optimization problem. Numerical results show that the proposed method achieves a considerable performance compared with exhaustive search method, but with lower computational complexity.

Sub-terahertz (THz) antenna for Internet of Things and 6G Communication

Abstract 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 mm3 for 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.

Characterization of microwave and terahertz dielectric properties of single crystal La2Ti2O7 along one single direction

New generation wireless communication systems require characterisations of dielectric permittivity and loss tangent at microwave and terahertz bands. La2Ti2O7 is a candidate material for microwave application. However, all the reported microwave dielectric data are average value from different directions of a single crystal, which could not reflect its anisotropic nature due to the layered crystal structure. Its dielectric properties at the microwave and terahertz bands in a single crystallographic direction have rarely been reported. In this work, a single crystal ferroelectric La2Ti2O7 was prepared by floating zone method and its dielectric properties were characterized from 1 kHz to 1 THz along one single direction. The decrease in dielectric permittivity with increasing frequency is related to dielectric relaxation from radio frequency to microwave then to terahertz band. The capability of characterizing anisotropic dielectric properties of a single crystal in this work opens the feasibility for its microwave and terahertz applications.

Internet of Things and Next Generation Wireless Communication Systems

Next generation wireless communication systems will connect billions of Internet of Thing (IoT) devices and user elements along with billions of people, enable machine-to-ma-chine communications across heterogeneous and dynamic environment, and provide low-latency computing and storage resources on demand at the deep edge as well as in the cloud. Tremendous research and development efforts have already been emphasized on the enabling technologies toward next generation wireless systems to support a variety of critical and personalized services in multiple application domains, including industry use cases, environment, transportation, education, public health and safety, and defense. Wireless communication networks have been greatly advanced by exploiting technologies such as millimeter wave, dynamic spectrum sharing, massive MIMO, beam forming, network slicing and virtualization, and artificial intelligence and machine learning. These technology breakthroughs can empower wireless networks to support extreme high capacity, massive connectivity, and ultra-low latency communications for new use cases identified for next generation wireless systems. In order to design and deploy wireless communication systems with IoT devices across heterogeneous and dynamic environments to provide next generation wireless services, however, there are many critical technical challenges yet to be addressed. In this issue of IEEE Wireless Communications, we are pleased to present two feature topics to bring together researchers, industry practitioners, and individuals working on the related areas to address some of these technical challenges for IoT and next generation wireless systems. One feature topic on “Massive Machine-Type Communications for IoT” includes four articles, and was organized by guest editors W. Ji, T. Ebrahimi, Z. Li, J. Yuan, D. O. Wu, and Y. Xin; the other feature topic on “Emerging Visual IoT Technologies for Future Communications and Networks” includes six articles, and was organized by guest editors L. Liu, E. G. Larsson, P. Popovski, G. Caire, X. Chen, and S. R. Khosravirad. Thanks to the two guest editor teams who did an excellent job in editing these two feature topics for our readers. Please stay tuned for new developments in the research area of IoT and next generation wireless communications and read the editorials and the papers in the feature topics.

Accelerating Simulations of Large Scale Phased-Array Systems

Next generation wireless communications systems operating at millimeter-wave frequencies are utilizing phased arrays of increasing electrical size to overcome path loss. The size of these arrays can make simulations become infeasible due to the amount of computation and memory required. Here we discuss parallelization and hardware acceleration methods to overcome these obstacles for large scale phased array systems. The acceleration of these methods was quantified using an orthogonal frequency division multiplexing frequency-domain simulator.

Efficient and Robust Image Communication Techniques for 5G Applications in Smart Cities

A wide range of multimedia applications must be supported by the modern fifth generation (5G) wireless communication systems for realizing the diverse applications in smart cities. The diverse applications such as real-time monitoring of roads, smart homes, smart industries, etc., for a sustainable smart city emphasizes a robust and efficient image transmission. In this paper, the influence of maximal ratio combining (MRC) on the reception of images with different orthogonal frequency division multiplexing (OFDM) versions is studied. The different OFDM versions considered here are the fast Fourier transform (FFT) based OFDM and discrete cosine transform (DCT) based OFDM. A comparison between diverse modulation levels for the images transmitted through different OFDM methodologies, along with variation in a number of receiving antennas for MRC, is proposed for additive white gaussian noise (AWGN) and Rayleigh fading channels. The diverse modulation levels used are binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-PSK, and 16-PSK. The parameters that are used to compare different versions of OFDM for MRC antenna configurations are signal-to-noise ratio (SNR) vs. bit error rate (BER) and peak signal-to-noise ratio (PSNR) at the receiver as an estimation parameter for the received image quality.

Channel aware receiver for next generation wireless communication system

Channel aware receiver for next generation wireless communication system