GHz Signal Research Articles

Features of 5G mobile network integration on the example of the SD-Core and SD-Fabric project

Mobile networks move at a relentless pace, and they are built around two standards: 4G and 5G. Indeed, 5G is a new stage in the development of mobile technologies, which will provide better speed and coverage than the current 4G. 5G operates on a 5GHz signal and is tuned to speeds up to 1Gbps for dozens of users. In addition, 5G uses a new frequency band, along with other new technologies that use much higher radio frequencies (28 GHz compared to 4G's 2.5 GHz) to transfer more data at higher speeds, with reduced downloads and less delay. This new mmWave interface allows more devices to be used within the same cluster; 4G can support about 4,000 devices per km2, while 5G will support about a million. This means that more streaming data from various video services, voice calls and other services will be transmitted on mobile networks.
 The fifth generation mobile communication standard (5G) is a new stage in the development of technologies, which is designed to expand the possibilities of Internet access through radio access networks.

Multiple-access relay stations for long-haul fiber-optic radio frequency transfer.

We report on the realization of a long-haul radio frequency (RF) transfer scheme by using multiple-access relay stations (MARSs). The proposed scheme with independent link noise compensation for each fiber sub-link effectively solves the limitation of compensation bandwidth for long-haul transfer. The MARS can have the capability to share the same modulated optical signal for the front and rear fiber sub-links, simplifying the configuration at the repeater station and enabling the transfer system to have the multiple-access capability. At the same time, we for the first time theoretically model the effect of the MARS position on the fractional frequency instability of the fiber-optic RF transfer, demonstrating that the MARS position has little effect on system's performance when the ratio of the front and rear fiber sub-links is around 1:1. We experimentally demonstrate a 1 GHz signal transfer by using one MARS connecting 260 and 280 km fiber links with the fractional frequency instabilities of less than 5.9 × 10-14 at 1 s and 8.5 × 10-17 at 10,000 s at the remote site and of 5.6 × 10-14 and 6.6 × 10-17 at the integration times of 1 s and 10,000 s at the MARS. The proposed scalable technique can arbitrarily add the same MARSs in the fiber link, which has great potential in realizing ultra-long-haul RF transfer.

A sub-30 GHz differential-frequency tripler in 22-nm FDSOI technology for FMCW spectrum

In this work, a wide-band Frequency-Tripler is designed to cover Frequency-Modulated Continuous Wave radar (FMCW) in 22-nm CMOS-FDSOI Technology. The designed frequency Tripler upconverts sub-30 GHz signal to cover a wide-band FMCW spectrum (72–84 GHz). In this paper, the silicon validated results of a VCO combined with the proposed frequency Tripler are presented. The design architecture, EM simulation results, measurement setup and silicon result of our fabricated die are covered in this paper. The designed circuit consumes 20 mA of current at the supply voltage of 800 mV. The Tripler works in the input frequency range from 24 GHz to 32 GHz, delivering a wide-band frequency output of 72–96 GHz. The differential output of VCO is capacitively coupled with the input of the multiplier.

High-Bandwidth Arbitrary Signal Detection Using Low-Speed Electronics

The growing demand for bandwidth and energy efficiency requires new solutions for signal detection and processing. We demonstrate a concept for high-bandwidth signal detection with low-speed photodetectors and electronics. The method is based on the parallel optical sampling of a high-bandwidth signal with sinc-pulse sequences provided by a Mach-Zehnder modulator. For the electronic detection and processing this parallel sampling enables to divide the high-bandwidth optical signal with the bandwidth <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B$</tex-math></inline-formula> into <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> electrical signals with the baseband bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B/(\text{2}\,N)$</tex-math></inline-formula> . In proof-of-concept experiments with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N=3$</tex-math></inline-formula> , we present the detection of 24 GHz optical signals by detectors with a bandwidth of only 4 GHz. For ideal components, the sampling and bandwidth down-conversion does not add an excess error to the signals and even for the non-ideal components of our proof-of-concept setup, it is below 1%. Thus, the rms error for the measurement of the 24 GHz signal was reduced by a factor of about 3.4 and the effective number of bits were increased by 1.8.

A hybrid photonic link for concurrent transmission of millimeter wave and Sub 6 Ghz wave using polarization modulator

AbstractA stable, simple, compact, and economical photonic link which enables the sending of millimeter‐wave (mm‐wave) along with Sub‐6 GHz wave signal simultaneously is proposed in this study. Instead of using the conventional high‐cost Mach Zehnder modulation‐based link, here a cost‐efficient polarization modulator is used. The polarization modulator is used to obtain the tuneable frequency response and also to get a better performance compared to the Mach Zehnder modulator‐based system which is widely used. The concept of free space optics is introduced in this proposed system to guarantee a higher power efficiency and a higher data transmission. The advantages of mm‐wave signals and Sub‐6 GHz wave signals can be obtained in parallel by the simultaneous transmission of both signals through the multiplexed link. A 16‐QAM modulation is employed for RF signal in both mm‐wave and Sub6 GHz signal. The performance of the designed link is verified by bit error rate (BER) and the simulation gives a very small value of BER which indicates the least probability of error.

High-performance dual-band radio-over-fiber link for future 5G radio access applications

For the fronthaul between the baseband unit and the remote radio unit (RRU), radio over fiber (RoF) is promising to replace the Common Public Radio Interface in beyond fifth-generation and the sixth-generation wireless communication systems. The weight, size, and power consumption of the RRU can be greatly reduced, along with easy support for the millimeter-wave band. In this paper, a dual-band RoF link is proposed, where flexible switching between high-frequency (28 GHz) and low-frequency (3.5 GHz) RF channels is realized through polarization control. Single-sideband modulation is performed on 28 GHz signals to avoid periodic power fading during long-distance fiber transmission. By adjusting the DC bias, the third-order intermodulation distortion component in the 3.5 GHz signal is suppressed, and the spur-free dynamic range (SFDR) is improved. Experimental results show a channel isolation of above 43 dB. The link gain of the 28 GHz signal channel is flat, and the SFDR of the 3.5 GHz signal channel can reach 118.6 d B ⋅ H z 4 / 5 . In the case of RF vector signal transmission, the adjacent channel power ratio of the 3.5 GHz signal channel is optimally up to 48 dB, and the error vector magnitude is 2.9%.

10 GHz generation with ultra-low phase noise via the transfer oscillator technique

Coherent frequency division of high-stability optical sources permits the extraction of microwave signals with ultra-low phase noise, enabling their application to systems with stringent timing precision. To date, the highest performance systems have required tight phase stabilization of laboratory grade optical frequency combs to Fabry–Pérot optical reference cavities for faithful optical-to-microwave frequency division. This requirement limits the technology to highly controlled laboratory environments. Here, we employ a transfer oscillator technique, which employs digital and RF analog electronics to coherently suppress additive optical frequency comb noise. This relaxes the stabilization requirements and allows for the extraction of multiple independent microwave outputs from a single comb, while at the same time, permitting low-noise microwave generation from combs with higher noise profiles. Using this method, we transferred the phase stability of two high-finesse optical sources at 1157 and 1070 nm to two independent 10 GHz signals using a single frequency comb. We demonstrated absolute phase noise below −106 dBc/Hz at 1 Hz from the carrier with corresponding 1 s fractional frequency instability below 2 × 10−15. Finally, the latter phase noise levels were attainable for comb linewidths broadened up to 2 MHz, demonstrating the potential for out-of-lab use with low SWaP lasers.

A Study on Propagation Models for 60 GHz Signals in Indoor Environments

The millimeter-waves band will enable multi-gigabit data transmission due to the large available bandwidth and it is a promising solution for the spectrum scarcity below 6 GHz in future generations of mobile networks. In particular, the 60 GHz band will play a crucial role in providing high-capacity data links for indoor applications. In this context, this tutorial presents a comprehensive review of indoor propagation models operating in the 60 GHz band, considering the main scenarios of interest. Propagation mechanisms such as reflection, diffraction, scattering, blockage, and material penetration, as well as large-scale path loss, are discussed in order to obtain a channel model for 60 GHz signals in indoor environments. Finally, comparisons were made using data obtained from a measurement campaign available in the literature in order to emphasize the importance of developing accurate channel models for future wireless communication systems operating in millimeter-waves bands.

One-Bit Constrained Measurements of Parametric Signals

This paper introduces a novel estimation framework for the parameters in a linear-in-the-parameters estimation problem, when one-bit measurements are processed. We consider a periodic signal, whose components have unknown amplitudes and phases. This signal is assumed to be quantized by a single comparator, under various problem settings. To provide enough information for the estimation of the signal parameters based on one-bit quantized signal measurements, the threshold in the one-bit comparator is assumed known. Several problem settings are considered. They include synchronous/asynchronous sampling, presence or absence of deterministic or stochastic dither, presence or absence of additive noise. The results obtained by applying three alternative methods are compared and analyzed. Experimental results on a two-component 1.2 GHz signal validate the theoretical analysis. It is shown that several estimation approaches are available, which provide different performance levels, in terms of final estimation accuracy and computational complexity.

A using remodulation filterless scheme of generating frequency 32-tupling millimeter-wave based on two DPMZMs

In this paper, we introduce a filterless system for generating frequency 32-tupling millimeter waves (mm waves) by using two dual-parallel MZMs (DPMZM). A 5 GHz RF signal is used to modulate DPMZM-1. After the first beat, a 20 GHz signal for remodulating DPMZM-2 is generated. Unnecessary sidebands are suppressed by the following methods in the structure of DPMZM-2. Firstly, the ±(4n-2)th-order optical sidebands are suppressed by controlling the phase difference between two Mach-Zehnder modulators (MZMs). Then, the 0th-order sideband is offset by adjusting the value of optical attenuator (OA) and optical phase shifter (OPS). Finally, the 1st and 7th-order optical sidebands nearly disappear by adjusting the modulation index of DPMZM-2 is 3.94. Remaining sidebands enter the photodetector beat frequency to obtain frequency 32-tupling mm waves. Simulation results show that its optical sideband suppression ratio (OSSR) is 27.7 dB and radio frequency sideband suppression ratio (RFSSR) is 27.96 dB, which is consistent with the theory. Using 5 GHz RF signal to drive the DPMZM-1, 160 GHz mm-wave signal was obtained. Furthermore, analyzes the effects of modulation index, optical power and attenuator value on the system performance, optimize the system performance to the best state.

Low Phase Noise Direct-Modulation Optoelectronic Oscillator

A direct-modulation OEO (DM-OEO) generating stable 10 GHz and 20 GHz signals is presented. A single loop and a dual loop approach are implemented and compared. We show an output signal of 15 dBm RF power, and a phase noise as low as −135 dBc/Hz at 10 kHz offset from the 10 GHz carrier. The 20 GHz second harmonic exhibits a noise level of −127 dBc/Hz at 10 kHz. A high spur level reduction is also obtained in the dual loop architecture.

Coherent UD-WDM RoF Fronthaul Network With D-EML Transmitter and Phase-Noise Robust Receiver

This work proposes and tests a simplified coherent uplink architecture for ultra-dense coherent analog mobile Fronthaul with phase noise cancellation based on single sideband modulation of a dual-EML. Results show optical channel spacings of only 1.5 GHz and error-free signal recovery with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \nu $ </tex-math></inline-formula> Tb = 1.2% and 3% with reaching power as low as −46dBm for 100 Mbit/s and −38 dBm for 1 Gbit/s using QPSK modulation.

Elimination of the PMD related delay jitter in a fiber stretcher based ultra-stable microwave signal distribution system

We realize an ultra-stable microwave signal distribution system based on an optical phase-locked loop. The transmission delay jitter is accurately compensated with a piezoelectric fiber stretcher (PFS). For further eliminating the additional delay jitter originated from the polarization changes during the PFS stretching, we propose an orthogonal-polarized round-trip PFS structure. The transmission delay jitter of 24 GHz signals distributed to multiple remote ends using the proposed and the traditional PFS scheme are carefully compared and quantitively analyzed under various fiber types and lengths. With the proposed PFS structure, the relative delay jitter of two transmitted signals are decreased from 291.4 fs to merely 17.7 fs even via 200 m polarization maintaining fiber with considerable polarization mode dispersion, showing its remarkable superiority. This microwave signal distribution system can find its versatile applications in radio astronomy where multiple ultra-high relative stable microwave signals are highly desired in different locations.

On the 40 GHz Remote Versus Local Photonic Generation for DML-Based C-RAN Optical Fronthaul

Local and remote photonic millimeter wave (mmW) signal generation schemes are theoretically and experimentally evaluated in order to compare both approaches for practical deployment in a cloud radio access network (C-RAN) fronthaul network. The paper presents a full comprehensive formulation of the frequency response of a system based on a directly modulated laser transmitting data over 40 GHz signal which is generated by external carrier suppressed modulation and optical frequency multiplication. Theoretical and experimental characterization of the system response at baseband and mmW band for local and remote generation setups show very good agreement. The remote configuration leads to a higher electrical output power (i.e., 15 dB higher in 25 km fiber links) than the local generation setup in the mmW band due to the combined effect of chirp and fiber dispersion, although intermodulation distortion is higher in the former case. Transmission experiments using quadrature phase-shift keying (QPSK) signals with 250 MHz bandwidth centered at 0.5 GHz over 10 and 25 km fiber links also confirm the superior performance of the remote setup, whereas the local setup leads to similar results to optical back-to-back (OB2B) measurements, which is also validated with data signals centered at different frequencies within the laser bandwidth frequency range. Finally, experimental results show the quality of the recovered signals in terms of error vector magnitude (EVM) as a function of the received electrical power and demonstrate that no further penalties are introduced by photonic mmW signal generation with respect to electrical back-to-back (EB2B) levels.

Fingerprint Positioning Method for Dual-Band Wi-Fi Based on Gaussian Process Regression and K-Nearest Neighbor

Since many Wi-Fi routers can currently transmit two-band signals, we aimed to study dual-band Wi-Fi to achieve better positioning results. Thus, this paper proposes a fingerprint positioning method for dual-band Wi-Fi based on Gaussian process regression (GPR) and the K-nearest neighbor (KNN) algorithm. In the offline stage, the received signal strength (RSS) measurements of the 2.4 GHz and 5 GHz signals at the reference points (RPs) are collected and normalized to generate the online dual-band fingerprint, a special fingerprint for dual-band Wi-Fi. Then, a dual-band fingerprint database, which is a dedicated fingerprint database for dual-band Wi-Fi, is built with the dual-band fingerprint and the corresponding RP coordinates. Each dual-band fingerprint constructs its positioning model with the GPR algorithm based on itself and its neighborhood fingerprints, and its corresponding RP coordinates are the label of this model. The neighborhood fingerprints are found by the spatial distances between RPs. In the online stage, the measured RSS values of dual-band Wi-Fi are used to generate the online dual-band fingerprint and the 5 GHz fingerprint. Due to the better stability of the 5 GHz signal, an initial position is solved with the 5 GHz fingerprint and the KNN algorithm. Then, the distances between the initial position and model labels are calculated to find a positioning model with the minimum distance, which is the optimal positioning model. Finally, the dual-band fingerprint is input into this model, and the output of this model is the final estimated position. To evaluate the proposed method, we selected two scenarios (A and B) as the test area. In scenario A, the mean error (ME) and root-mean-square error (RMSE) of the proposed method were 1.067 and 1.331 m, respectively. The ME and RMSE in scenario B were 1.432 and 1.712 m, respectively. The experimental results show that the proposed method can achieve a better positioning effect compared with the KNN, Rank, Coverage-area, and GPR algorithms.

Linearly Polarized Reconfigurable Reflectarray Surface

A simple, low-cost, linearly polarized reconfigurable reflectarray surface (RAS) is presented that can provide beam steering over a wide range of angles in one plane. The results for a prototype design demonstrated beam steering from 35° to 60° at 5.5 GHz. Simple equations describing the beam steering angle and overall size for a minimum radar cross-sectional area (RCS) are presented that aid the system designer. The concertina RAS can be manufactured using screen-printing techniques making this potentially a low-cost product that can meet the needs of widespread deployment needed by wireless systems. A sample design using an A2-sized sheet of paper increased a 5.5 GHz signal by 20 dB, eliminating a “dead spot” in the laboratory.

Microwave frequency measurement with high accuracy and wide bandwidth based on whispering-gallery mode barcode.

We propose and experimentally demonstrate a novel method for photonic-assisted microwave frequency measurement based on whispering-gallery mode (WGM) barcode, which is a dense spectrum generated by a micro-resonator that supports a large number of optical modes. The measurement relies on the relation between the microwave frequency and its unique barcode. The proposed system has the advantages of wide bandwidth, high accuracy, and multiple-frequency measurement capability. Microwave frequency measurement from 1 to 20 GHz is experimentally demonstrated with a measurement error of 40 kHz. For multi-tone signals, the frequency resolution is demonstrated to be less than 20 MHz. A dynamic multi-tone microwave signal consists of a 16-20 GHz linear frequency-modulated (LFM) signal, and a 10 GHz signal is measured to show the capability of multiple-frequency measurement. The system stability is also evaluated, and a self-reference method is proposed to maintain a long-term high-accuracy measurement.

MmWrite: Passive Handwriting Tracking Using a Single Millimeter-Wave Radio

In the era of pervasively connected and sensed Internet of Things, many of our interactions with machines have been shifted from conventional computer keyboards and mouses to hand gestures and writing in the air. While gesture recognition and handwriting recognition have been well studied, many new methods are being investigated to enable pervasive handwriting tracking. Most of the existing handwriting tracking systems either require cameras and handheld sensors or involve dedicated hardware restricting user convenience and the scale of usage. In this article, we present mmWrite, the first high-precision passive handwriting tracking system using a single commodity millimeter-wave (mmWave) radio. Leveraging the short wavelength and large bandwidth of 60-GHz signals and the radar-like capabilities enabled by the large phased array, mmWrite transforms any flat region into an interactive writing surface that supports handwriting tracking at millimeter accuracy. MmWrite employs an end-to-end pipeline of signal processing to enhance the range and spatial resolution limited by the hardware, boost the coverage, and suppress interference from backgrounds and irrelevant objects. We implement and evaluate mmWrite on a commodity 60-GHz device. The experimental results show that mmWrite can track a finger/pen with a median error of 2.8 mm and thus can reproduce handwritten characters as small as 1 cm × 1 cm, with a coverage of up to 8 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> supported. With minimal infrastructure needed, mmWrite promises ubiquitous handwriting tracking for new applications in the field of human-computer interactions.

First 75 GHz Signals from Space

First 75 GHz Signals from Space

Sub-terahertz photonic frequency divider with a large division ratio based on phase locking.

We present a photonic frequency divider with a large division ratio for microwave signals up to sub-terahertz. A high-operating frequency and a large frequency division ratio have both been achieved by phase-locking a Fabry-Perot frequency comb to the input signal that is to be divided. The input signals ranging from 50.10 GHz to 200.10 GHz are all divided to 2.5 GHz signals, which can be further divided into lower- frequency signals easily. The proposed divider is free of high-speed electrical devices, thanks to the intermediate-frequency detection and feedback control in the phase locking process. Moreover, the phase noise caused by the photonic frequency division is negligible at low offset frequencies, proving that the divider has superior long-term stability. This flexible, cost-efficient, and stable photonic frequency divider is an ideal candidate for frequency division at the remote end of a high-precision frequency transfer system.