Millimeter-wave Spectrum Research Articles

Asymmetric Millimeter-Wave Spectrum in Laser Mode Partition Noise Generated by Fiber Transmission

In this article, we report on the asymmetry of intensity noise spectrum at millimeter-wave (mm-wave) heterodyne carriers. Passively mode-locked laser diode (PMLLD) is employed for a low phase noise mm-wave photonic generation using direct detection. This optical source produces an excess intensity noise known by laser mode partition noise (LMPN) in which its spectrum usually appears as symmetric double side-bands around the beat-note. The propagation over a dispersive medium such as optical fiber can modify the spectral behavior and profile of the LMPN. This article explores the impact of fiber transmission on the distortions of the LMPN in optical and electrical spectrum. Experimental results reveal, for the first time, that the LMPN symmetry is converted to an asymmetric deformation on the generated beating carrier. The mathematical model and numerical simulation are presented to give hints for analyzing this phenomenon. The findings of the simulations and measurements demonstrate the main role of second- and third-order fiber dispersion on the LMPN profile.

Rotational spectroscopic study of S-methyl thioformate: A global laboratory analysis of ground and excited torsional states up to 660 GHz.

ContextS-methyl thioformate CH3SC(O)H is a monosulfur derivative of methyl formate, a relatively abundant component of the interstellar medium (ISM). S-methyl thioformate being, thermodynamically, the most stable isomer, it can be reasonably proposed for detection in the ISM.AimsThis work aims to experimentally study and theoretically analyze the ground and first torsional excited states for CH3SC(O)H in a large spectral range for astrophysical use.MethodsS-methyl thioformate was synthesized as a result of a reaction of methyl mercaptan with acetic-formic anhydride. The millimeter-wave spectrum was then recorded for the first time from 150 to 660 GHz with the solid-state spectrometer located at Lille.ResultsA set of 3545 lines is determined and combined with 54 previously measured lines in the microwave region, belonging to ground state ν t = 0 as well as 1391 transitions in the first excited state of torsion ν 18 = 1. Some 164 lines were also assigned to ν 18 = 2 for the A-species. A global fit was performed using the BELGI-Cs code taking into account the large splitting of A and E lines due to methyl internal rotation motion with a relatively low barrier, V3 = 127.4846(15) cm–1.ConclusionsUsing our spectroscopy work, a deep search of S-methyl thioformate was carried out in the IRAM 30m and ALMA data of different high-mass star-forming regions (Orion KL and Sgr B2). We derived an upper limit to the CH3SC(O)H column density in these regions.

Attenuation constant measurements of clear glass samples at the low terahertz band

The technical performance requirements from wireless communication networks are continuously rising. One method to satisfy the demands is increasing the carrier frequency to the millimetre wave or low terahertz band spectrum to utilise wider operation bandwidth. In order to facilitate the studies in this frequency range, the corresponding electromagnetic (EM) wave properties, channel attributes and material characteristics need to be analytically formulated. In line with these, this Letter initially presents the theoretical expressions governing the EM wave transmission across a conducting medium. Then, by using the relative parameter quantities in the proposed attenuation constant ( ) computation technique, the results of the measurements performed between 260 and 350 GHz for the clear window glass samples of different thicknesses are given. This Letter concludes with the evaluation of the outcomes.

Adaptive 5G Architecture for an mmWave Antenna Front-End Package Consisting of Tunable Matching Network and Surface-Mount Technology

Adaptive 5G architecture consisting of three functional sections (four antenna components, tunable matching network (TMN), and radio frequency (RF) front-end package) is proposed, analyzed, and verified. In the 5G millimeter-wave (mmWave) spectrum, the RF performance is highly dependent on the specific antenna package technology. However, compact antenna packages, oftentimes, result in undesired interference between the antenna elements. This eventually leads to severe RF performance degradation. For the first time in the literature, an mmWave 5G RFIC and the TMN are integrated for efficient operation that is applicable to real-life 5G mobile devices. Moreover, the proposed antenna-in-package (AiP) architecture enables independent frequency control at multiple frequencies. The proposed solution is simulated and measured at the system level. As a result, the devised AiP solution exhibits a simulated effective isotropic radiated power (EIRP) of 22.05–23.96 dBm at the cumulative distribution function (CDF) of 50% by applying the conducted power of 17 dBm (per channel), and the peak gain of the antenna exhibits 13.7 dBi at 27 GHz (state A) and 12.6 dBi at 28 GHz (state B) with an amplifier having an output power of 5 dBm.

Mobility and Blockage-Aware Communications in Millimeter-Wave Vehicular Networks

Mobility may degrade the performance of next-generation vehicular networks operating at the millimeter-wave spectrum: frequent mis-alignment and blockages require repeated beam training and handover, and incur enormous overhead. Nevertheless, mobility induces temporal correlations in the communication beams and in blockage events. In this paper, an adaptive design of beam training, data transmission and handover is proposed, that learns and exploits these temporal correlations to reduce the beam training overhead and optimally trade-off throughput and power consumption. At each time-slot, the serving base station (BS) decides to perform either beam training, data communication, or handover when blockage is detected, under uncertainty in the system state. The decision problem is cast as a partially observable Markov decision process, and the goal is to maximize the throughput delivered to the UE, under an average power constraint. To address the high dimensional optimization, an approximate constrained point-based value iteration (C-PBVI) method is developed, which simultaneously optimizes the primal and dual functions to meet the power constraint. Numerical results demonstrate a good match between the analysis and a simulation based on 2D mobility and 3D analog beamforming via uniform planar arrays at both BSs and UE, and reveal that C-PBVI performs near-optimally, and outperforms a baseline scheme with periodic beam training by 38% in spectral efficiency. Motivated by the structure of the C-PBVI policy, two heuristics are proposed, that trade complexity with sub-optimality, and achieve only 4% and 15% loss in spectral efficiency.

A Comprehensive Survey on Moving Networks

The unprecedented increase in the demand for mobile data, fuelled by new emerging applications and use-cases such as high-definition video streaming and heightened online activities has caused massive strain on the existing cellular networks. As a solution, the fifth generation (5G) of cellular technology has been introduced to improve network performance through various innovative features such as millimeter-wave spectrum and Heterogeneous Networks (HetNets). In essence, HetNets include several small cells underlaid within macro-cell to serve densely populated regions like stadiums, shopping malls, and so on. Recently, a mobile layer of HetNet has been under consideration by the research community and is often referred to as moving networks. Moving networks comprise of mobile cells that are primarily introduced to improve Quality of Service (QoS) for the commuting users inside public transport because QoS is deteriorated due to vehicular penetration losses and high Doppler shift. Furthermore, the users inside fast moving public transport also exert excessive load on the core network due to large group handovers. To this end, mobile cells will play a crucial role in reducing the overall handover count and will help in alleviating these problems by decoupling in-vehicle users from the core network. This decoupling is achieved by introducing separate in-vehicle access link, and out-of-vehicle back-haul links with the core network. Additionally side-haul links will connect mobile cells with their neighbors. To date, remarkable research results have been achieved by the research community in addressing challenges linked to moving networks. However, to the best of our knowledge, a discussion on moving networks and mobile cells in a holistic way is still missing in the current literature. To fill the gap, in this article, we comprehensively survey moving networks and mobile cells. We cover the technological aspects of moving cells and their applications in the futuristic applications. We also discuss the use-cases and value additions that moving networks may bring to future cellular architecture and identify the challenges associated with them. Based on the identified challenges, we discuss the future research directions.

Energy-Efficient Beam Management in Millimeter-Wave Shared Spectrum

Efficient transmit and receive beam management is necessary in millimeter-wave spectrum due to the inherently directional nature of antenna array transmissions in this regime. Energy efficiency of beam sweeping is further complicated when operating in shared or unlicensed spectrum, since receiving nodes are unaware if their designated transmitter has actually gained access to the medium. This article studies energy-efficient beam management from the perspective of a mobile node or user equipment (UE) that seeks to optimize the overall beam-sweeping period and the properties of each individual beam. Beam sweeping has an associated energy expenditure since the UE utilizes multiple RF chains to form the beams and incurs a processing overhead due to signal detection per beam. Two case studies are analyzed for UE beam management: downlink reception from a base station and uplink channel sensing based on directional listen-before-talk. The subsequent insights are particularly relevant for fifth-generation cellular networks that are currently being designed for operation in millimeter-wave shared spectrum.

Distributed directional cooperative MAC (DD-CoopMAC) protocol for improving VBR throughput in IEEE 802.11ad WLAN

The IEEE 802.11ad-based wireless local area network (WLAN) has emerged out as a promising network technology that is capable of operating on millimetre wave spectrum. This network is being used in many applications and can be extended to serve many different streams of the networking industry. However, the network still has some glitches with respect to throughput, overhead, etc., which need to be handled to make it more reliable and efficient. In this paper, distributed directional cooperative medium access control (DD-CoopMAC) protocol for improving variable bit rate (VBR) throughput in IEEE 802.11ad WLAN is proposed. In this protocol, information about network stations is intelligently collected; based on this, the relay stations are selected for transmission. Simulation results illustrate that this protocol aids in enhancing the throughput and reducing the related overhead. Also, simulation results show that the proposed DD-CoopMAC has given high throughput and less MAC delay compared with D-CoopMAC and IEEE 802.11ad.

Millimeter-Wave Downlink Coverage Extension Strategies

Traditionally, the uplink and downlink in a cellular network are associated with the same base station and the same frequency band since it promotes simpler network design, maintenance, and operation because of reduced complexity. However, when deploying millimeter-wave (mmWave) spectrum, network coverage has limitations hinging on the nature of the mmWave propagation characteristics relative to the traditional sub 6 GHz frequency bands. In this article, we present a method for an extension of the mmWave downlink coverage by demonstrating the benefits of decoupling the reverse and forward link frequencies and by leveraging macro-type radio deployment heights to maximize the line-of-sight coverage. The accompanying link budget analysis and coverage simulations quantify the benefit of the coverage extension methodology to be as much as 6.8 dB while extending possible coverage range distance to greater than 2 km.

Joint Beam Training and Data Transmission Design for Covert Millimeter-Wave Communication

Covert communication prevents legitimate transmission from being detected by a warden while maintaining certain covert rate at the intended user. Prior works have considered the design of covert communication over conventional low-frequency bands, but few works so far have explored the higher-frequency millimeter-wave (mmWave) spectrum. The directional nature of mmWave communication makes it attractive for covert transmission. However, how to establish such directional link in a covert manner in the first place remains as a significant challenge. In this paper, we consider a covert mmWave communication system, where legitimate parties Alice and Bob adopt beam training approach for directional link establishment. Accounting for the training overhead, we develop a new design framework that jointly optimizes beam training duration, training power and data transmission power to maximize the effective throughput of Alice-Bob link while ensuring the covertness constraint at warden Willie is met. We further propose a dual-decomposition successive convex approximation algorithm to solve the problem efficiently. Numerical studies demonstrate interesting tradeoff among the key design parameters considered and also the necessity of joint design of beam training and data transmission for covert mmWave communication.

Dedicated Short-Range Communications: Performance Evaluation Over mmWave and Potential Adjustments

Vehicle-to-vehicle (V2V) communication has proven to enhance road safety and transportation systems. Currently, there are two approaches to enable transmission between moving vehicles. The first one is the 3rd Generation Partnership Project (3GPP) cellular vehicle-to-everything (V2X) specifications. Another approach is based on the IEEE 802.11 family of standards. The latter group is commonly known as dedicated short-range communications (DSRC). While the 3GPP V2X may provide higher throughput by the adoption of the millimeter-wave (mmWave) spectrum, its reliability depends on the availability of the infrastructure. On the other hand, DSRC is more intensively deployed. However, the supported throughput is significantly lower compared to the new radio (NR)-based technology. This drawback can be overcome by exploiting the mmWave bands by DSRC. In this letter, we evaluate the performance of the 802.11p technology at 28 GHz. Besides, several equalizing techniques are applied in order to improve the multipath immunity of the considered setup.

Self-adaptive power control with deep reinforcement learning for millimeter-wave Internet-of-vehicles video caching

Video delivery and caching over the millimeter-wave (mmWave) spectrum is a promising technology for high data rate and efficient frequency utilization in many applications, including distributed vehicular networks. However, due to the short handoff duration, calibrating both optimal power allocation of each base station toward its associated vehicles and cache allocation are challenging for their computational complexity. Heretofore, most video delivery applications were based on on-line or off-line algorithms, and they were limited to compute and optimize high dimensional objectives within low-delay in large scale vehicular networks. On the other hand, deep reinforcement learning is shown for learning such scale of a problem with an optimized policy learning phase. In this paper, we propose deep deterministic policy gradient-based power control of mmWave base station (mBS) and proactive cache allocation toward mBSs in distributed mmWave Internet-of-vehicle (IoV) networks. Simulation results validate the performance of the proposed caching scheme in terms of quality of the provisioned video and playback stall in various scales of IoV networks.

Two Novel Meander-Perforated Plane EBG Structures For 5G Applications

With the advance of 5G network, antennas are required to meet better performance as it’s the key element of 5G network. Meta-surface structure has been demonstrated to be an effective method to improve the performances of an antenna. Whereas, most of the meta-surface structures cannot be applied to 5G applications properly according to the recent research. In this paper, we propose two novel meander-perforated plane (MPP) electromagnetic bandgap (EBG) structures which are named TMPP-EBG and GMPP-EBG. The meander-shape slot of TMPP and GMPP is etched on the top and ground layer respectively. The two novel MPP-EBG structures can be applied to millimeter-wave 5G spectrum from 24GHz to 28GHz. Compared with the conventional mushroom-like EBG structure, the simulated results presented that TMPP-EBG enhances the bandwidth of S21 from 1GHz to 2.5GHz with the same size and GMPP-EBG achieves 14% size reduction with the same resonant frequency.

Hybrid Precoding for mmWave Massive MIMO With One-Bit DAC

Hybrid beamforming is key to achieving energy-efficient 5G wireless networks equipped with massive amount of antennas. Low-resolution data converters bring yet another degree of freedom to energy efficiency for the state-of-the-art 5G transceivers. In this work, we consider the design of hybrid precoders for massive multiple-input multiple-output (MIMO) channels in millimeter-wave (mmWave) spectrum along with one-bit digital-to-analog converters (DACs) and finite-quantized phase shifters. In particular, we propose an alternating-optimization-based precoder design which recursively computes the covariance of the quantization distortion, and updates the precoders accordingly. Numerical results verify that the achievable rate improves quickly through iterations that involve updates to the weight matrix, distortion covariance of the quantization, and the respective precoders.

A Hybrid Interweave–Underlay Countrywide Millimeter-Wave Spectrum Access and Reuse Technique for CR Indoor Small Cells in 5G/6G Era

In this paper, we propose a hybrid interweave–underlay spectrum access and reuse technique for the dynamic spectrum access and reuse of the countrywide 28 GHz millimeter-wave (mmWave) spectrum to in-building small cells of each mobile network operator (MNO) in a country. For the spectrum access, the proposed technique explores both interweave and underlay spectrum access techniques, whereas, for the spectrum reuse, it considers reusing the countrywide spectrum to each three-dimensional (3D) cluster of small cells in a building. To access the countrywide spectrum, each MNO is considered by paying a licensing fee following its number of subscribers. We present the 3D clustering of in-building of small cells and derive average capacity, spectral efficiency (SE), and energy efficiency (EE). We then perform extensive numerical and simulation results and analyses for an MNO of a country consisting of four MNOs. It is shown that, for no spectrum reuse to in-building small cells, the proposed technique improves average capacity and SE by 3.63 and 2.42 times, respectively, whereas EE improves by 72.79%. However, for vertical spatial reuse of six times (as an example) to small cells in a building, average capacity, SE, and EE improve further by 21.77 times, 14.51 times, and 95.66%, respectively. Moreover, the proposed technique can satisfy SE and EE requirements for sixth-generation (6G) mobile systems by horizontal spatial reuse of the countrywide spectrum to small cells of about 40.62%, 9.37%, and 6.25% less buildings than that required by the traditional static licensed spectrum access (SLSA) technique.

The millimeter-wave spectrum and astronomical search for ethyl methyl sulfide.

Sulfur-containing molecules constitute only 8% of the molecules observed in the interstellar medium (ISM), in spite of the fact that sulfur has been shown to be an abundant element in the ISM. In order to understand the chemical behavior of the ISM and specific cases like the missing sulfur reservoir, a detailed chemical molecular composition in the ISM must be mapped out. Our goal is to investigate the rotational spectrum of ethyl methyl sulfide, CH3CH2SCH3, which ms to be a potential candidate for observation in the ISM since the simpler analogs, CH3SH and CH3CH2SH, have already been detected. Rotational spectrum of ethyl methyl sulfide has been observed before, but its experimental rotational parameters are not precise enough to allow its detection in the ISM. The rotational spectrum of ethyl methyl sulfide in the frequency range 72-116.5 GHz was measured using a broadband millimeter-wave spectrometer based on radio astronomy receivers with fast Fourier transform backends. The spectral searches and identification of the vibrational excited states of ethyl methyl sulfide was supported by high-level ab initio calculations on the harmonic and anharmonic force fields. The rotational spectra for the trans and gauche conformers of ethyl methyl sulfide was analyzed, and a total of 172 and 259 rotational transitions were observed for each one, respectively. The observation of A - E internal rotation splittings allowed the experimental determination of the V 3 hindered internal rotation barrier height for both trans and gauche species. In addition, the vibrational excited states, resulting from the lowest frequency vibrational mode ν 30 were identified for both conformers. The new experimental rotational parameters were employed to search for ethyl methyl sulfide in the warm and cold molecular clouds Orion KL, Sgr B2(N), B1-b and TMC-1, using the spectral surveys captured by IRAM 30 m at 3 mm and 2 mm.

A Novel High Gain Wideband MIMO Antenna for 5G Millimeter Wave Applications

A compact tree shape planar quad element Multiple Input Multiple Output (MIMO) antenna bearing a wide bandwidth for 5G communication operating in the millimeter-wave spectrum is proposed. The radiating element of the proposed design contains four different arcs to achieve the wide bandwidth response. Each radiating element is backed by a 1.57 mm thicker Rogers-5880 substrate material, having a loss tangent and relative dielectric constant of 0.0009 and 2.2, respectively. The measured impedance bandwidth of the proposed quad element MIMO antenna system based on 10 dB criterion is from 23 GHz to 40 GHz with a port isolation of greater than 20 dB. The measured radiation patterns are presented at 28 GHz, 33 GHz and 38 GHz with a maximum total gain of 10.58, 8.87 and 11.45 dB, respectively. The high gain of the proposed antenna further helps to overcome the atmospheric attenuations faced by the higher frequencies. In addition, the measured total efficiency of the proposed MIMO antenna is observed above 70% for the millimeter wave frequencies. Furthermore, the MIMO key performance metrics such as Mean Effective Gain (MEG) and Envelope Correlation Coefficient (ECC) are analyzed and found to conform to the required standard of MEG < 3 dB and ECC < 0.5. A prototype of the proposed quad element MIMO antenna system is fabricated and measured. The experimental results validate the simulation design process conducted with Computer Simulation Technology (CST) software.

On Exploiting Millimeter-Wave Spectrum Trading in Countrywide Mobile Network Operators for High Spectral and Energy Efficiencies in 5G/6G Era.

In this paper, we propose a dynamic exclusive-use spectrum access (DESA) method to improve the overall licensed millimeter-wave (mmWave) spectrum utilization of all mobile network operators (MNOs) in a country. By exploiting secondary spectrum trading, the proposed DESA method shares partly and exclusively the licensed mmWave spectrum of one MNO to another in a dynamic and on-demand basis for a certain agreement term. We formulate the proposed DESA method for an arbitrary number of MNOs in a country. We then present an iterative algorithm to find the optimal amount of shared spectrum for each MNO, which is updated at each agreement term. We derive average capacity, spectral efficiency, energy efficiency, and cost efficiency performance metrics for all MNOs countrywide and present extensive numerical and simulation results and analyses for an example scenario of a country with four MNOs each assigned statically with an equal amount of 28-GHz mmWave spectrum. By applying DESA, we show that MNOs with a lack of minimum licensed spectra to serve their data traffic can lease at the cost of payment of the required additional spectra from other MNOs having unused or under-utilized licensed spectra. Moreover, it is shown that the overall countrywide average capacity, spectral efficiency, energy efficiency, and cost efficiency can be improved, respectively, by 25%, 25%, 17.5%, and 20%. Furthermore, we show that, by applying DESA to all MNOs countrywide, the expected spectral efficiency and energy efficiency requirements for sixth-generation (6G) mobile systems can be achieved by reusing the same mmWave spectrum to 20% fewer buildings of small cells. Finally, using the statistics of subscribers of all MNOs, we present a case study for fifth-generation (5G) networks to demonstrate the application of the proposed DESA method to an arbitrary country of four MNOs.

Millimeter wave free-jet spectrum of acrolein and several isotopologues

The millimeter-wave absorption spectrum of acrolein has been investigated in the 59.6–120 GHz region with a Free-Jet Absorption MilliMeter Wave spectrometer. New measured rotational transitions belonging to the s-cis conformer and its three 13C isotopologues and those of 13C and 18O isotopologues of the s-trans conformer, observed in natural abundance, are reported.

Frequency-Adjustable Planar Folded Slot Antenna Using Fully Integrated Multithrow Function for 5G Mobile Devices at Millimeter-Wave Spectrum

This article describes a low-profile frequency-adjustable planar folded slot antenna (PFSA) system that is applicable to real-life smartphone platforms at the millimeter-wave (mmWave) 5G spectrum. Critical challenges that are attributed from the frequency discrepancy between sub-6 GHz and mmWave 5G are discussed. The multithrow topology is used to minimize the distortion of the far-field radiation pattern due to the beam squint while adjusting the resonant frequency between 27.95 and 28.65 GHz. The presented methodology entails using a multithrow switch chip directly on the transmission line, which enables a bistate function. The proposed methodology is exemplified into a 28 GHz $1 \times 4$ subarray. Measured and simulated results confirm that the frequency-adjustable PFSA features a 2.6-time enhanced impedance bandwidth and an average peak gain of 6.3 dBi while maintaining identical antenna volume in comparison to the previously reported PFSA.