Wave Communication Systems Research Articles

Hybrid Precoding Design for Reconfigurable Intelligent Surface Aided mmWave Communication Systems

In this letter, we focus on the hybrid precoding (HP) design for the reconfigurable intelligent surface (RIS) aided multi-user (MU) millimeter wave (mmWave) communication systems. Specifically, we aim to minimize the mean-squared-error (MSE) between the received symbols and the transmitted symbols by jointly optimizing the analog-digital HP at the base-station (BS) and the phase shifts (PSs) at the RIS, where the non-convex element-wise constant-modulus constraints for the analog precoding and the PSs are tackled by resorting to the gradient-projection (GP) method. We analytically prove the convergence of the proposed algorithm and demonstrate the desirable performance gain for the proposed design through numerical results.

Low Harmonic Distortion DFB Laser for Broadband Analog Applications

$1.35~\mu $ m AlGaInAs/InP DFB lasers with low harmonic distortion and high frequency response bandwidth have been demonstrated for broadband analog applications. By optimizing active layers and setting Bragg wavelength 10 nm blue shifted of the gain peak wavelength, the device has a threshold current of 8.5 mA, 3-dB frequency response bandwidth of 21 GHz at 60 mA and 28GHz at 90 mA, second harmonic distortion of −23 dB and 1.5 ps group delay time up to a modulation frequency of 25 GHz. These highly linear and high frequency response bandwidth DFB lasers are realized for broadband analog applications and will become the key transmitters for the future 5G millimeter wave communication systems.

WSDSBL Method for Wideband Channel Estimation in Millimeter-Wave MIMO Systems with Lens Antenna Array

In millimeter wave (mmWave) communication systems, Channel State Information(CSI) is extremely essential for beamforming. The traditional Successive Support Detection (SSD) algorithm can achieve high wideband channel estimation accuracy, but it only used least square (LS) algorithm to recover the detected channel part, the estimation accuracy is low under low SNR regions. To tackle this problem, in this paper, inspired by the classic Support Detection (SD) channel estimation scheme in narrowband, we propose an efficient Wideband Support Detection Sparse Bayesian Learning (WSDSBL) channel estimation scheme. For every subcarrier, we first detect the support of the wideband beamspace channel of the subcarrier, then we use the Sparse Bayesian Learning (SBL) scheme to recover it. Simulation results show that the proposed WSDSBL channel estimation algorithm is better than conventional wideband channel estimation schemes in MSE performance and achievable sum-rate performance, especially in low SNR regions.

Wireless Secure Signal Transmission for Distributed Intelligent Surface-Aided Millimeter Wave Systems

The optimization of the secrecy rate of the distributed intelligent reflecting surfaces (IRSs)-assisted millimeter wave (mmWave) communication system is studied in this paper. In this system, the users are served by multiple IRSs, and by adjusting the switch state of each IRS and optimizing the phase shift of the IRS to maximize the secrecy rate of the system. The problem is described as a joint IRS control, transmit beamforming design problem. Our objective is to maximize the secrecy rate of the distributed IRSs-aided system under the transmit power constraint of the access point (AP). Since the problem is non-convex, one alternating optimization algorithm is proposed for solving this problem. We use the successive convex approximation (SCA) algorithm to solve it, and the solution that is obtained by the SCA algorithm guarantees to converge to a stable point that satisfies the Karush-Kuhn-Tucker (KKT) conditions. Moreover, by using the dual method, we obtain the IRS switch. For the IRS phase shifts optimization problem, a low-complexity majorization-minimization (MM) algorithm is used to solve this problem. Numerical results show that the proposed scheme can achieve higher secrecy rate compared with the single IRS-aided scheme.

A 200–240 GHz Sub-Harmonic Mixer Based on Half-Subdivision and Half-Global Design Method

For the terahertz harmonic mixer, a design model based on Half-Subdivision and Half-Global Design Method (HS-HGDM) with a single functional unit is proposed. The single functional unit circuit of the mixer, such as LO or IF Low Pass Filter (LPF), is designed by Subdivision Design Method (SDM), and the rest circuits of the mixer are designed by Global Design Method (GDM). The harmonic mixer based on this model is characterized by simple circuit structure, low conversion loss, small circuit size and high stability. In this paper, an improved Compact Suspended Micro-strip Resonators (CSMRs) filter is developed for the IF part of sub-harmonic mixer. The remaining circuits consist of some basic transmission units, such as the High-Z Low-Z impedance Transmission Lines (H-Z L-Z TLs) applied for main circuit, and full/reduced height WR4.3/WR8 applied for providing RF/LO signal. In RF frequency range 200–240 GHz, a Single Sideband (SSB) conversion loss of 7.36±0.76 dB operating at IF frequency 1.8 GHz, and a Double Sideband (DSB) noise temperature below 1034 K with the LO power of 2–5 mW and the LO frequency of 107 GHz were achieved. This broadband sub-harmonic mixer operates at room temperature, which makes it applicable to sub-millimeter wave or terahertz wireless communication systems and imaging inspection systems.

RadChat: Spectrum Sharing for Automotive Radar Interference Mitigation

In the automotive sector, both radars and wireless communication are susceptible to interference. However, combining the radar and communication systems, i.e., radio frequency (RF) communications and sensing convergence, has the potential to mitigate interference in both systems. This article analyses the mutual interference of spectrally coexistent frequency modulated continuous wave (FMCW) radar and communication systems in terms of occurrence probability and impact, and introduces RadChat, a distributed networking protocol for mitigation of interference among FMCW based automotive radars, including self-interference, using radar communications. The results show that RadChat can significantly reduce radar mutual interference in single-hop vehicular networks in less than 80 ms.

Study of Total Electron Content and Electron Density Profile from Satellite Observations During Geomagnetic Storms

Total Electron Content (TEC) and electron density profile are the key parameters in the mitigation of ionospheric effects on radio wave communication system. In this study, the variations of TEC and electron density profile have been analyzed using satellite data from four different latitude-longitude sectors (13°N -17°N, 88°E - 98°E), (30°N - 50°N, 95°W - 120°W), (26°S - 29°S, 163°W - 167°W,) and (45°S - 60°S, 105°W-120°W) during different geomagnetic storms. The interplanetary magnetic field (Bz), solar wind velocity (Vsw), solar wind pressure (Psw) and geomagnetic indices, aurora index -AE, Kp and disturbed stormed time index (Dst) are also analyzed to distinguish their effects on TEC and electron density. The geomagnetic indices and solar wind parameters are correlated with the TEC and electron density. The study showed that the value of TEC and electron density vary significantly with different latitude, longitude, altitude and solar activities. The result also concludes that the electron density profile increases with the altitude, acquired peak value around 250km-300km and decreased beyond the altitude of 300 km.

Wideband Waveguide-to-Microstrip Transition for mm-Wave Applications

Introduction. Increased data rate in modern communication systems can be achieved by raising the operational frequency to millimeter wave range where wide transmission bands are available. In millimeter wave communication systems, the passive components of the antenna feeding system, which are based on hollow metal waveguides, and active elements of the radiofrequency circuit, which have an interface constructed on planar printed circuit boards (PCB) are interconnected using waveguide-to-microstrip transition.Aim. To design and investigate a high-performance wideband and low loss waveguide-to-microstrip transition dedicated to the 60 GHz frequency range applications that can provide effective transmission of signals between the active components of the radiofrequency circuit and the passive components of the antenna feeding systemMaterials and methods. Full-wave electromagnetic simulations in the CST Microwave Studio software were used to estimate the impact of the substrate material and metal foil on the characteristics of printed structures and to calculate the waveguide-to-microstrip transition characteristics. The results were confirmed via experimental investigation of fabricated wideband transition samples using a vector network analyzer Results. The probe-type transition consist of a PCB fixed between a standard WR-15 waveguide and a back-short with a simple structure and the same cross-section. The proposed transition also includes two through-holes on the PCB in the center of the transition area on either side of the probe. A significant part of the lossy PCB dielectric is removed from that area, thus providing wideband and low-loss performance of the transition without any additional matching elements. The design of the transition was adapted for implementation on the PCBs made of two popular dielectric materials RO4350B and RT/Duroid 5880. The results of full-wave simulation and experimental investigation of the designed waveguide to microstrip transition are presented. The transmission bandwidth for reflection coefficient S11 < –10 dB is in excess of 50…70 GHz. The measured insertion loss for a single transition is 0.4 and 0.7 dB relatively for transitions based on RO4350B and RT/Duroid 5880.Conclusion. The proposed method of insertion loss reduction in the waveguide-to-microstrip transition provides effective operation due to reduction of the dielectric substrate portion in the transition region for various high-frequency PCB materials. The designed waveguide-to -microstrip transition can be considered as an effective solution for interconnection between the waveguide and microstrip elements of the various millimeter-wave devices dedicated for the 60 GHz frequency range applications.

Photonic crystal terahertz wave logic AND-XOR gate

Terahertz wave logic gates are one of the key devices required in terahertz wave communication systems and signal processing systems. In this paper, we design a logic gate to realize the function of AND gate and XOR gate. The logic AND-XOR gate is based on two large photonic crystal ring resonators, one small ring resonator and photonic crystal branch waveguides. The structure is analyzed and simulated by treating the plane wave expansion and finite difference time domain methods. The steady-state field distributions and output power characteristics of the gate are analyzed. The simulation results show that the designed device with the feasibility can be used in terahertz wave integrated digital circuit.

Beamforming with Precoders Based Millimeter Wave Communication System

The 5G communications are used with baseband Precoders and Beamforming. The Technology is needed to update, all available characteristics in the present Wireless Communication System (WCS). The Hybrid Beamforming systems are across in the RF and Digital domain. In the mmWave MIMO system, the numbers of antennas has increased to improve the Spectral Efficiency of the system. The proposed algorithms observe that system performance for different SNR range.

Hybrid Beamforming With Dynamic Subarrays and Low-Resolution PSs for mmWave MU-MISO Systems

Analog/digital hybrid beamforming architectures with large-scale antenna arrays have been widely considered in millimeter wave (mmWave) communication systems because they can address the tradeoff between performance and hardware efficiency compared with traditional fully-digital beamforming. Most of the prior work on hybrid beamforming focused on fully-connected architecture or partially-connected scheme with fixed-subarrays, in which the analog beamformers are usually realized by infinite-resolution phase shifters (PSs). In this paper, we introduce a novel hybrid beamforming architecture with dynamic subarrays and hardware-efficient low-resolution PSs for mmWave multiuser multiple-input single-output (MU-MISO) systems. By dynamically connecting each RF chain to a non-overlap subarray via a switch network and PSs, we can exploit multiple-antenna and multiuser diversities to mitigate the performance loss due to the use of practical low-resolution PSs. An iterative hybrid beamformer design algorithm is first proposed based on fractional programming (FP), aiming at maximizing the sum-rate performance of the MU-MISO system. In an effort to reduce the complexity, we also present a simple heuristic hybrid beamformer design algorithm for the dynamic subarray scheme. Extensive simulation results demonstrate the advantages of the proposed hybrid beamforming architecture with dynamic subarrays and low-resolution PSs compared to existing fixed-subarray schemes.

Superhigh-Resolution Recognition of Optical Vortex Modes Assisted by a Deep-Learning Method.

Orbital angular momentum (OAM) has demonstrated great success in the optical communication field, which theoretically allows an infinite increase of the transmitted capacity. The resolution of a receiver to precisely recognize OAM modes is crucial to expand the communication capacity. Here, we propose a deep learning (DL) method to precisely recognize OAM modes with fractional topological charges. The minimum interval recognized between adjacent modes decreases to 0.01, which as far as we know is the first time this superhigh resolution has been realized. To exhibit its efficiency in the optical communication process, we transfer an Einstein portrait by a superhigh-resolution OAM multiplexing system. As the convolutional neuron networks can be trained by data up to an infinitely large volume in theory, this work exhibits a huge potential of generalized suitability for next generation DL based ultrafine OAM optical communication, which might even be applied to microwave, millimeter wave, and terahertz OAM communication systems.

Beam Training for Millimeter-Wave Communication Based on Tabu Table Enhanced Rosenbrock Algorithm

The codebook-based beamforming for millimeter-wave (mm Wave) communication systems is usually used to compensate the severe attenuation of the mm Wave region. The beam training process based on pre-specified beam codebooks is considered a global optimization problem in 2-D planes formed by the potential beam index. The Rosenbrock algorithm (RA) is adopted to implement optimum beam searching whereas the simulated annealing (SA) algorithm is used to solve the problem of falling into the local optimum, due to the unavailable gradient information of the objective function. However, the RA implements rounding to the integer which leads to the problem of repeated search and beam space discontinuity caused by beam index will impair the powerful local search ability. Thus, in this paper, an enhanced RA based on tabu search and combined with SA algorithm is proposed as an alternative solution for beam search success rate. The proposed algorithm reduces the search times by forbidding the repeat search with tabu table and design of neighbor region. Moreover, to prevent the search failure, the search candidate index is defined to keep the local search ability of the original algorithm and wrap around of beam index is applied to maintain continuity of the search direction. Experimental simulations show that the proposed technique can improve the search efficiency in terms of reduced steps and increase search success rate during the beam training procedure compared to existing techniques.

Beamforming Design for Large-Scale Antenna Arrays Using Deep Learning

Beamforming (BF) design for large-scale antenna arrays with limited radio frequency chains and the phase-shifter-based analog BF architecture, has been recognized as a key issue in millimeter wave communication systems. It becomes more challenging with imperfect channel state information (CSI). In this letter, we propose a deep learning based BF design approach and develop a BF neural network (BFNN) which can be trained to learn how to optimize the beamformer for maximizing the spectral efficiency with hardware limitation and imperfect CSI. Simulation results show that the proposed BFNN achieves significant performance improvement and strong robustness to imperfect CSI over the conventional BF algorithms.

Low-Complexity Hybrid Precoding for Multi-User MmWave Systems With Low-Resolution Phase Shifters

Large-scale antennas systems have been attracted significant attention to provide considerable array gains for millimeter wave (mmWave) communications systems. However, huge hardware complexity and power consumptions make the conventional precoding architectures impractical to realize. Recently, hybrid precoding structures for mmWave communications systems are widely investigated to save the cost and achieve satisfactory performance. Unfortunately, most existing precoder designs lie in the assumption of infinite or high-resolution phase shifters (PSs), which are also difficult to realize in real-world. Motivated by this fact, a low complexity hybrid precoder and combiner design for multi-user systems with two-bit resolution PSs is proposed in this paper, which provides an appropriate trade-off between energy efficiency and system sum-rate. Specifically, the candidate sets for analog beamforming are constructed by introducing the auxiliary variables, in which the number of elements is the same as that of antennas. Accordingly, the computational complexity of searching optimal beamformer is significantly reduced over proposed codebooks. Then, to avoid high complexity singular value decomposition (SVD) of channel matrix, we propose a rank-1 approximate decomposition algorithm based-on principal component analysis technique. At last, the user scheduling algorithm is presented to further improve the performance in multiuser-scenario. Simulation results verified the effectiveness of the proposed algorithms, the performance of which is close to the optimal unquantized precoder.

A novel beam design method for mmWave multi-antenna arrays with mutual coupling reduction

To overcome the mutual coupling (MC) of multiple antennas in millimeter wave (mmWave) communication systems, a novel beam design method with low complexity is proposed in this paper. Firstly, an equivalent channel model incorporating the effect of MC is analyzed and established, and then an optimal precoding / combiner vector for beamforming is derived. On this basis, by using greedy geometric (GG) algorithm, a novel hybrid beam design method is proposed. Finally, the performance of proposed method is analyzed and compared with other traditional ones. The simulation results show that the proposed method has better suppression of the MC effect as well as lower complexity.

Angle Domain Channel Tracking With Large Antenna Array for High Mobility V2I Millimeter Wave Communications

In millimeter wave communication systems, channel estimation consumes many resources, in terms of time, bandwidth, and hardware. However, the good news is that the millimeter wave channels are generally sparse in space and channel states at consecutive time slots are highly correlated in angle domain. Therefore, it is possible to track the channel state with less resources, instead of re-estimating it for every time slot. For millimeter wave communications, the antenna array form is important, and we employ a lens antenna array in this paper, because it has much lower complexity and it allows the base station to use only a few RF (Radio Frequency) chains for beamforming. Based on the lens antenna array and the spatial sparsity of the millimeter wave channels, we propose a data-aided channel tracking scheme for vehicle-to-infrastructure (V2I) communication systems, where high-mobility of mobile users is expected. The basic idea is to employ the channel estimate from the previous time slot for the data detection at the current one. After data detection, the detected data sequence can be used for channel update, and this process iterates. By doing this, the overhead of channel estimation can be reduced to great extent. We evaluate the performance of the proposed algorithm through theoretical analysis and simulations, and they both show promising results.

Symbol-Level Hybrid Precoding in mmWave Multiuser MISO Systems

Recently, symbol-level precoding has emerged as a novel efficient solution in multi-user multi-antenna downlink systems, since it can exploit multi-user interference (MUI) and transform it into useful signal. In this correspondence, we attempt to apply symbol-level precoding into the well-known hybrid precoding architecture in multi-user multi-input single-output (MU-MISO) millimeter wave (mmWave) communication systems. Particularly, we aim to design the symbol-varying digital precoder and the analog precoder with low-resolution phase shifters (PSs) to optimize symbol detection performance under the transmit power constraint and the discrete phase constraint. To handle this difficult joint optimization problem, we propose to minimize the Euclidean distance between the optimal fully-digital precoder and the hybrid precoder. An efficient iterative algorithm is developed to solve this problem. Simulation results demonstrate the advantages of symbol-level precoding and validate the effectiveness of our proposed symbol-level hybrid precoding algorithm.

Frequency selective millimeter‐wave channel estimation based on subspace enhancement algorithms

SummaryIn millimeter wave (mmW) communication systems, hybrid architecture, including the analog‐digital precoder and combiner matrices, is employed to take advantage of the multistream transceiver. In practice, mmW channel is assumed to be frequency‐selective, since the signal bandwidth is larger than the coherence bandwidth. Hence, orthogonal frequency‐division multiplexing signaling can be remedial. So far, most of the previous works on the frequency‐selective channel estimation have focused on the single measurement vector (SMV) form, whereas finding and exploiting the proper multimeasurement vector (MMV) model can improve upon the estimation procedure based on compressive sensing (CS) concepts. In fact, the estimation procedure based on the MMV model has a faster convergence speed than the SMV method specially, when the training frames are small. In this paper, we first extract the MMV model of the channel. In this model, the rank‐deficiency occurs as the number of training frames is less or equal to the sparsity level. Thus, the conventional estimation methods fail to provide the desirable performance. To overcome this issue, we propose two rank‐aware algorithms based on the enhancement of the observed signal subspace. The first algorithm assumes to know the sparsity level, while the second faces to the lack of knowledge about the sparsity level. The simulation results corroborate the fact that the proposed methods outperform the conventional CS algorithms such as Simultaneous Orthogonal Matching Pursuit.

Estimating Rain Attenuation at 72 and 84 GHz From Raindrop Size Distribution Measurements in Albuquerque, NM, USA

The raindrop size distribution (DSD) is essential information for understanding rain attenuation effects at millimeter wavelengths. The DSD was measured in Albuquerque, NM, USA, as a part of the W/V-band Terrestrial Link Experiment. An optical disdrometer from Thies Clima was used to measure both size and velocity of rain droplets. The measured DSD consistently showed a unique property of two log-linear distributions regionally separable by drop size under variable rain rates. The functional fit that best represents our measured data with rain rates under 40 mm/h is presented. Based on the DSD, rain specific attenuation is estimated at 72 and 84 GHz with Mie scattering theory. These estimated rain attenuations can be used and validated for rain attenuation analysis of the millimeter wave propagation experiments under similar climate conditions. This letter will guide millimeter wave communication system designers to estimate the rain attenuation based on their own DSD measurements.