Millimeter-wave Performance Research Articles

Transceiver Optimization for mmWave Line-of-Sight MIMO Systems Using Hybrid Arrays

The performance of millimeter wave (mmWave) line-of-sight multiple input multiple output (LOS MIMO) systems using hybrid arrays of planar subarrays was studied. We characterized the achievable maximum spatial multiplexing gain for such LOS MIMO systems by the measures of spectral efficiency and effective degree of freedom (EDoF). By proposing a joint plane-wave and spherical-wave-based general 3D channel model, we derived the optimal design parameters in the analog domain, i.e., the optimal subarray separation products, and analyzed their sensitivity on the system performance. We also gave analytical eigenvalue expressions of the equivalent LOS MIMO channel matrix, which are applicable to the case of a non-optimal design, as well as the upper and lower bounds of the EDoF for system performance evaluation. A piecewise uniform quantization codebook was further designed for quantizing phase shifter values in practical applications. The numerical and simulation results show that planar subarrays are superior to traditional arrays in terms of spectral efficiency and EDoF in Ricean fading channels because they are more robust to the change in the communication distance and the deviation from the optimal design. The use of hybrid arrays of planar subarrays effectively removes the limitation of mmWave LOS MIMO systems using traditional arrays, through which, the conventional Rayleigh distance criterion has to be satisfied to achieve the optimal performance.

Minimally Equicorrelated MIMO Modelling for NLOS MM Wave Performance Improvement

The 5G physical layer has evolved rapidly. With transmissions at 28, 38, and 72 GHz, millimeter (MM) wave communications are at the core of it. Such links provide improved data rates to an increased number of users availing around 20 GHz of free spectrum. Directional arrays in multiple-input multiple-output (MIMO) setups facilitate beamsteered transmissions. Maximal ratio combining (MRC) receivers aid MM wave signaling and link metrics are analyzed in terms of antenna correlations. The system model is evaluated assuming a short range, non-line-of-sight (NLOS) MM wave user under independently correlated, Rayleigh conditions. This paper showcases analytical closed form expressions for received signal, output signal- to-noise ratio (SNR), line-of-sight (LOS), probability density function (PDF), and NLOS average capacity of the proposed MM wave link. The derivations exhibit capacity alterations with transceiver correlations. MM wave correlation matrices have unique dependency on steering vectors or corresponding transmission angles. This does not apply to millimeter wave.

Impact of Finite-Resolution Precoding and Limited Feedback on Rates of IRS Based mmWave Networks

Intelligent reflecting surfaces (IRSs) can enhance the system performance of millimeter wave (mmWave) networks. In practice, phase shifts at the base station and the IRSs are digitally controlled and have discrete values. The channel state information (CSI) feedback also has a limited rate. This work analyzes the spectral efficiency performance of an IRS based mmWave network in which the beamsteering codebooks are used for the passive precoding and analog precoding, and the zero-forcing precoder is used for digital precoding. To capture the features of mmWave channels and reflect the impact of passive and analog precoding, a channel correlation based codebook is employed to quantize the effective channels. Upper-bounds are derived for the spectral efficiency losses due to finite-resolution beamsteering codebooks and limited CSI feedback. It is found that the spectral efficiency loss due to finite-resolution beamsteering codebooks does not depend on the transmit power in large signal-to-noise ratio regimes, while the spectral efficiency loss due to limited CSI feedback increases with the transmit power. Then, the asymptotic performance is analyzed when the numbers of transmit antenna elements and reflecting elements go to infinity. Simulations verify the derivations and findings.

Modelling and Analysis of Performance Characteristics in a 60 Ghz 802.11ad Wireless Mesh Backhaul Network for an Urban 5G Deployment

With the widespread deployment of 5G gaining pace, there is increasing interest in deploying this technology beyond traditional Mobile Network Operators (MNO) into private and community scenarios. These deployments leverage the flexibility of 5G itself to support private networks that sit alongside or even on top of existing public 5G. By utilizing a range of virtualisation and slicing techniques in the 5G Core (5GC) and heterogeneous Radio Access Networks (RAN) at the edge, a wide variety of use cases can be supported by 5G. However, these non-typical deployments may experience different performance characteristics as they adapt to their specific scenario. In this paper we present the results of our work to model and predict the performance of millimeter wave (mmWave) backhaul links that were deployed as part of the Liverpool 5G network. Based on the properties of the 802.11ad protocol and the physical characteristics of the environment, we simulate how each link will perform with different signal-to-noise ratio (SNR) and Packet Error Rate (PER) values and verify them against real-world deployed links. Our results show good convergence between simulated and real results and provide a solid foundation for further network planning and optimization.

Acquisition of channel state information for mmWave massive MIMO: traditional and machine learning-based approaches

The accuracy of channel state information (CSI) acquisition directly affects the performance of millimeter wave (mmWave) communications. In this article, we provide an overview on CSI acquisition, including beam training and channel estimation for mmWave massive multiple-input multiple-output systems. The beam training can avoid the estimation of a high-dimension channel matrix, while the channel estimation can flexibly exploit advanced signal processing techniques. In addition to introducing the traditional and machine learning-based approaches in this article, we also compare different approaches in terms of spectral efficiency, computational complexity, and overhead.

Two-Step Method for Millimeter-Wave Antenna Performance Assessment in 5G Smartphones

A critical challenge for 5G is transitioning to the mm-Wave spectrum. Despite providing unprecedented data rates, mm-Waves also suffer high path loss, atmospheric absorption, and higher fluctuating channel conditions, sparking numerous paradigm shifts in the smartphone industry. Extending mm-Wave communications to smartphones requires first a comprehensive study to identify the antenna design/smartphone implementation challenges that impact the quality of communications. This work proposes a two-step assessment metric, the mmWAESI, to evaluate mm-Wave antennas’ potential and limitations regarding their impact on system performance. First, it analyzes the spatial distribution of the smartphone-integrated beam steering array’s radiated power. Then, it evaluates the antenna’s influence on the MIMO performance, using a discrete, time-variant geometrical MIMO channel simulator to recreate any mm-Wave propagation scenario. For enhanced accuracy, mmWAESI accounts simultaneously for several communication aspects: antenna type, realistic radiation patterns, mobile phone form factor constraints, phone orientation, and user influence. The method is illustrated for two different 4-element linear arrays at 39 GHz, based on patch or monopole elements, integrated into smartphones. Their performance is compared under similar conditions, revealing that, unless array switching is employed, the smartphone’s form factor and user influence will mask any potential advantage of the unperturbed array characteristics.

BPSK Modulation‐Based Local Oscillator‐Free IQ Demodulation for Millimeter Wave Imaging

The precision of local oscillator (LO) signal in in‐phase and quadrature (IQ) demodulation strongly affects the imaging performance of millimeter wave (mmWave) radars. Therefore, to eliminate the requirement for high‐precision LO, a simple yet effective digital IQ demodulation method has been proposed with the aid of a specified sampling scheme in order to eliminate the demand for LO. Based on the bandpass sampling theorem, the characteristic of the intermediate frequency signal of mmWave imaging indicates that the LO is unrequired if the sampling rate is twice of the frequency of the carrier of the intermediate signal. In this way, the in‐phase signal would be directly and accurately obtained by performing the Binary‐Phase‐Shift‐Keying (BPSK) modulation on the samples, based on which the IQ demodulation would be completed by using the Hilbert transform. The proposed method does not employ LO and thus simplifies the demodulation process and is suitable for implementation in a Field‐Programmable Gate Array (FPGA) with fewer hardware resources. To verify the method, a three‐dimensional mmWave radar imaging is carried out at the 30‐34 GHz bandwidth, where the sampling and digital IQ demodulation are realized by an ADC (AD9250) and FPGA (XC7K325T), respectively. The results show a simplified transceiver with lower requirements and the prospect of the proposed method being applied in radar imaging and other related fields.

Network Capacity Optimization for Cellular‐Assisted Vehicular Systems by Online Learning‐Based mmWave Beam Selection

Directional communication is helpful to improve the performance of millimeter Wave (mmWave) links. However, the dynamic nature of vehicular scenarios raises the complexity of directional mmWave vehicular communications. Also, a mmWave link is susceptible to blockages. Therefore, a mmWave vehicular communication system requires high environmental adaptability and context‐awareness. Due to inadequate context information and insufficient beam settings in the existing related algorithm, it is difficult to pick out the set of beams with more reasonable widths and directions, which hinders the further promotion of network capacity in vehicular networks. Therefore, we propose an improved fast machine learning (IFML) algorithm to overcome this shortcoming. In order to improve network capacity while suppressing the additional beam search overhead, a partitioned search method is designed in the IFML. Also, in order to be robust to occasional fluctuations and timely adapt to significant changes in communication environments, the IFML adopts a flexible beam performance update approach based on adjustable weight coefficient. The simulation results show that the IFML significantly outperforms the existing related algorithm in terms of aggregate received data after a certain number of online learning time periods.

Filterless Radio-Over-Fiber System to Generate 40 and 80 GHz Millimeter-Wave

A filterless radio-over-fiber system to generate 40 and 80 GHz millimeter-wave was proposed by using two Mach-Zehnder modulators (MZMs). The two MZMs are biased at the maximum transmission point to suppress odd-order sidebands. By adjusting the modulation index of the two MZMs and the radio frequency drive signals, only the two 2nd and 4th order sidebands are retained. Subsequently, by adjusting the polarization direction to generate 40 and 80GHz frequency millimeter-wave signal. Detailed theoretical analyses and simulations are provided. The simulation results show that the 40 GHz millimeter-wave signal was obtained with 30 dB optical sideband suppression ratio (OSSR) and the 80 GHz millimeter-wave signal was obtained with 25 dB OSSR. Thanks to the higher OSSR, the generated MMW signal is not greatly affected by power fluctuations during transmission or frequency tuning. Furthermore, the effects of the modulation index, bias voltage and extinction ratios deviate from the ideal value on millimeter-wave performance are also analyzed and verified, showing the proposed scheme is relatively flexible from the limitation of filter fixed bandwidth and economical.

An $E$ -Band Power Amplifier With 26.3% PAE and 24-GHz Bandwidth in 22-nm FinFET CMOS

This paper presents the design and optimization of an $E$ -band power amplifier (PA) implemented in Intel’s 22FFL FinFET process. Layout optimization and characterization of the PA unit cell yielding optimal millimeter-wave (mmW) performance of the active device are described. A holistic optimization methodology is also presented which co-optimizes efficiency of the active devices and passive networks by incorporating passive losses earlier in the design process. The measured PA achieves a peak gain of 18.6 dB with a 3-dB bandwidth of 62–86 GHz (24 GHz). At 75 GHz, the measured $P_{\mathrm {sat}}$ , OP1dB, and peak power added efficiency (PAE) are +12.6 dBm, +5.7 dBm, and 26.3%, respectively. The PA can amplify a 6-Gb/s 16-QAM signal at an average $P_{\mathrm {out}}$ of +5 dBm with a PAE of 10% and −26-dB EVM(rms) and a 9-Gb/s 64-QAM signal at an average $P_{\mathrm {out}}$ of +1.3 dBm with a PAE of 5% and −28.3-dB EVM(rms). The compact layout of the PA yields a core area of 0.054 mm2, enabling compact integration.

Low-Complexity Reconfigurable MIMO for Millimeter Wave Communications

The performance of millimeter wave (mmWave) multiple-input multiple-output (MIMO) systems is limited by the sparse nature of propagation channels and the restricted number of radio frequency chains at transceivers. The introduction of reconfigurable antennas offers an additional degree of freedom on designing mmWave MIMO systems. This paper provides a theoretical framework for studying the mmWave MIMO with reconfigurable antennas. Based on the virtual channel model, we present an architecture of reconfigurable mmWave MIMO with beamspace hybrid analog-digital beamformers and reconfigurable antennas at both the transmitter and the receiver. We show that employing reconfigurable antennas can provide throughput gain for the mmWave MIMO. We derive the expression for the average throughput gain of using reconfigurable antennas in the system, and further derive the expression for the outage throughput gain for the scenarios where the channels are (quasi) static. Moreover, we propose a low-complexity algorithm for reconfiguration state selection and beam selection. Our numerical results verify the derived expressions for the throughput gains and demonstrate the near-optimal throughput performance of the proposed low-complexity algorithm.

Modeling and Analysis of D2D Millimeter-Wave Networks With Poisson Cluster Processes

This paper investigates the performance of millimeter wave (mmWave) communications in clustered device-to-device (D2D) networks. The locations of D2D transceivers are modeled as a Poisson Cluster Process. In each cluster, devices are equipped with multiple antennas, and the active D2D transmitter (D2D-Tx) utilizes mmWave to serve one of the proximate D2D receivers. Specifically, we introduce three user association strategies: 1) uniformly distributed D2D-Tx model; 2) nearest D2D-Tx model; and 3) closest line-of-site (LOS) D2D-Tx model. To characterize the performance of the considered scenarios, we derive new analytical expressions for the coverage probability and area spectral efficiency (ASE). Additionally, in order to efficiently illustrating the general trends of our system, a closed-form lower bound for the special case interfered by intra-cluster LOS links is derived. We provide Monte Carlo simulations to corroborate the theoretical results and show that: 1) the coverage probability is mainly affected by the intra-cluster interference with LOS links; 2) there exists an optimum number of simultaneously active D2D-Txs in each cluster for maximizing ASE; and 3) the closest LOS model outperforms the other two scenarios but at the cost of extra system overhead.

A broad-band V-band power amplifier using a reduced access-resistance transistor layout in 65-nm CMOS

To improve millimeter-wave amplifier performance, we propose a transistor layout that reduces the gate access resistance. The proposed layout trades overlap capacitance for reduced gate access resistance, as shown by transistor parameter extraction. The proposed transistor layout improves the maximum available power gain by 1.5 dB at 67 GHz. The extrapolated maximum frequency of oscillation (f max) also increases by 23 % from 91.3 to 112.5 GHz. Using the improved transistor layout, we design a V-band power amplifier that has enhanced performance. The power amplifier fabricated using the proposed transistor achieves 15.1 dB of small-signal gain, 16.5 GHz of 3-dB bandwidth, and an output power of 7.8 dBm at 61.5 GHz. Compared to an amplifier using conventional layout, the small-signal gain is improved by 3.7 dB and the output power is increased by 3 dBm at 61.5 GHz.

Microstructure and Millimeter-Wave Attenuation Performance of Exfoliated Graphite with Different Expanding Volume

Exfoliated graphite with different expanding volume (EV) was prepared by two-step intercalation, in which the mixture of nitric acid and phosphoric acid, and that of nitric acid and acetic acid were employed as intercalating agent step by step, and potassium permanganate was used as oxidant. Its microstructure was analyzed by scanning electron microscope, and its millimeter-wave attenuation performance was measured by a static method. The results show that the exfoliated graphite forms more microcellular structures and its layers become thinner with the increasing of EV, the interlayers are fully opened and there are more tiny graphite flakes with size distribution between several microns and several ten microns. The millimeter-wave attenuation performance enhances with the increasing of EV, and the 3mm wave attenuation value rises from 5.7dB to 8.68dB When EV increases from 233ml/g to 450ml/g, which is mainly attributed to the full expansion of exfoliated graphite to form larger scattering cross section and the absorption of more tiny graphite flakes with size distribution between several microns and several ten microns.

膨胀石墨体积膨胀率对毫米波衰减性能的影响

Exfoliated graphite is a potential military passive interfering material,which can attenuate infrared and millimeter-wave simultaneously.Exfoliated graphites with different expanding volumes were prepared by two-step intercalation,in which the mixture of nitric acid and phosphoric acid,nitric acid and acetic acid were employed as intercalating agent,and potassium permanganate was used as oxidant.The microstructures of exfoliated graphites with different expanding volumes were analyzed by scanning electron microscope.The millimeter-wave attenuation performances of exfoliated graphites with different expanding volumes were measured by a static method.The results show that the exfoliated graphites′ sheets become thinner with the increasing of expanding volume,the interlayers are fully opened and there are more tiny graphite flakes with size distribution between several microns and several ten microns.And the millimeter-wave attenuation performance enhances with the increasing of expanding volume.When the expanding volume increases from 233mL/g to 450mL/g,the 3mm wave attenuation value rises from 5.7dB to 8.68dB.

InAlN Barrier Scaled Devices for Very High $f_{T}$ and for Low-Voltage RF Applications

We report excellent low-voltage (5 to ~ 10 V drain bias) microwave and millimeter-wave performance of deeply scaled InAn/AlN/GaN devices with field-plate gate of ~ 50-nm length, MBE regrown ohmic contacts, and sub-500-nm S-D spacing on four different wafers. These four wafers include also T-gate (no field-plate) devices with very thin passivation and smaller gate (~ 30 nm), which had (for reference) high fT/fmax of ~270/230 GHz, respectively, both for D- and E-mode devices. Their counterparts with field-plate gates (same gate geometry but with underlying dielectric) and 50-nm gates had lower fT/fmax but excellent performances at 10 GHz with up to 67%-69% power-added efficiency (PAE) at 6 V bias and 30 GHz with up to 14.4 dB associated gain and 2.6 W/mm and 39.6% PAE at 8 V bias. The noise figure of these devices at 10 GHz was ~ 0.25 dB with 3 V drain bias. We have measured the linearity [third-order intercept (TOI)] of 300- μm devices on another wafer with 90-nm field-plate gates: at 5 GHz and 5 V bias the devices had 31-dBm TOI with 0.31 W/mm, 18.5-dB gain, and 27.1% PAE.

Studies on Anisotype Si/Si1-xGex Heterojunction DDR IMPATTs: Efficient Millimeter-wave Sources at 94 GHz Window

In this paper, an attempt is made to investigate the millimeter-wave performance of anisotype Si/Si1-xGex heterojunction Double-drift region (DDR) Impact Avalanche Transit Time (IMPATT) devices operating at 94 GHz window frequency by using a generalized double-iterative computer method based on drift-diffusion model developed by the authors. Simulation study on both anisotype Np and nP type Si/Si1-xGex heterojunction DDR IMPATTs for Ge mole fractions, x = 0.1 and x = 0.3, is carried out and their mm-wave properties are compared with a Si homojunction DDR IMPATT operating at the same frequency. Results show that significant improvements in DC to RF conversion efficiency and RF power output can be achieved in Si/Si1-xGex heterojunction DDR IMPATTs as compared to their Si homojunction counterpart. It is observed that the mm-wave performance of nP Si0.7Ge0.3/Si heterojunction DDR as regards to RF power output and conversion efficiency is best among all the devices under consideration. DC to RF conversion efficiency and continuous wave (CW) RF power output of nP Si0 7Ge0 3/Si DDR are obtained as 20.04% and 731.7 mW, respectively, near 94 GHz; whereas for Si DDR, the same parameters are obtained as 10.40% and 609.3 mW, respectively.

Studies on anisotype Si/Si1-xGexheterojunction DDR IMPATTs: efficient millimeter-wave sources at 94 GHz window

AbstractIn this paper, an attempt is made to investigate the millimeter-wave performance of anisotype Si/Si1-xGex heterojunction Double-drift region (DDR) Impact Avalanche Transit Time (IMPATT) devices operating at 94 GHz window frequency by using a generalized double-iterative computer method based on drift-diffusion model developed by the authors. Simulation study on both anisotype Np and nP type Si/Si1-xGex heterojunction DDR IMPATTs for Ge mole fractions, x = 0.1 and x = 0.3, is carried out and their mm-wave properties are compared with a Si homojunction DDR IMPATT operating at the same frequency. Results show that significant improvements in DC to RF conversion efficiency and RF power output can be achieved in Si/Si1-xGex heterojunction DDR IMPATTs as compared to their Si homojunction counterpart. It is observed that the mm-wave performance of nP Si0.7Ge0.3/Si heterojunction DDR as regards to RF power output and conversion efficiency is best among all the devices under consideration. DC to RF convers...

Enhanced performance of a 60-GHz power amplifier by using slow-wave transmission lines in 40 nm CMOS technology

This paper shows the contribution of slow-wave coplanar waveguides on the performance of power amplifiers operating at millimeter-wave frequencies in CMOS-integrated technologies. These transmission lines present a quality factor Q two to three times higher than that of the conventional microstrip lines at the same characteristic impedance. To demonstrate the contribution of the slow-wave transmission lines on integrated millimeter-wave amplifiers performance, two Class-A single-stage power amplifiers (PA) operating at 60 GHz were designed in standard 40 nm CMOS technology. One of the power amplifiers incorporates only the microstrip lines, whereas slow-wave coplanar transmission lines are considered in the other one. Both amplifiers are biased in Class-A operation, drawing, respectively, 22 and 23 mA from 1.2 V supply. Compared to the power amplifier using conventional microstrip transmission lines, the one implemented with slow-wave transmission lines shows improved performances in terms of gain (5.6 dB against 3.3 dB), 1 dB output compression point (OCP1dB: 7 dBm against 5 dBm), saturated output power (Psat: >10 and 8 dBm, respectively), power-added efficiency (PAE: 16% instead of 6%), and die area without pads (Sdie: 0.059 mm2 against 0.069 mm2).

N-Polar GaN/AlN MIS-HEMT for Ka-Band Power Applications

In this letter, we demonstrate the millimeter-wave power performance from N-polar GaN-based metal-insulator-semiconductor high-electron-mobility transistors. The device consists of a GaN spacer structure with an AlN barrier to reduce the alloy scattering. High Si doping in GaN without excessive surface roughening has been achieved using a digital doping scheme with a low ohmic contact resistance of 0.16 Ω·mm. An fT and an fMAX of 56 and 130 GHz, respectively, were obtained for a 150-nm gate length. A peak output power of 1.9 W/mm with a power-added efficiency (PAE) of 14% was achieved for VDS = 20 V, and a peak output power of 2.2 W/mm with a 12% efficiency and a linear transducer power gain of 5.7 dB was achieved for VDS = 30 V at 30 GHz. The cause of the low PAE was determined to be due to the current collapse from the RF-IV measurements, and remedies have been suggested to minimize the dc-RF dispersion.