A study of advanced upconversion techniques used in radio over fiber (ROF) is provided. With the huge increase in both the number of wireless communication subscribers and the bandwidth required per ...customer, migrating to higher frequencies, i.e., from lower radio frequency to millimeter-wave carriers, is an essential solution. However, due to the short propagation range of millimeter waves, a large number of radio access points are required for providing reliable coverage, which would increase the infrastructure costs. Hence, the transmission of RF signals between the central (or control) points and radio access points (or remote antenna units) using optical fibers is one of the major access network solutions that have been proposed for future high-bandwidth wireless communication systems. In this paper, we introduce the basics of ROF communication, including optical modulation, the optical channel, and the optical detection techniques. Then we survey the family of advanced optical upconversion techniques that exploit the nonlinearity of the ROF link. Specifically, we describe how optical upconversion can be achieved by exploiting the Mach-Zehnder modulator's nonlinearity, wavelength conversion techniques, or the photodetector's nonlinearity. The wavelength conversion techniques rely on the nonlinearities present in the fiber, in the optical amplifier, or in the electroabsorption modulator.
What is index modulation (IM)? This is an interesting question that we have started to hear more and more frequently over the past few years. The aim of this paper is to answer this question in a ...comprehensive manner by covering not only the basic principles and emerging variants of IM, but also reviewing the most recent as well as promising advances in this field toward the application scenarios foreseen in next-generation wireless networks. More specifically, we investigate three forms of IM: spatial modulation, channel modulation and orthogonal frequency division multiplexing (OFDM) with IM, which consider the transmit antennas of a multiple-input multiple-output system, the radio frequency mirrors (parasitic elements) mounted at a transmit antenna and the subcarriers of an OFDM system for IM techniques, respectively. We present the up-to-date advances in these three promising frontiers and discuss possible future research directions for IM-based schemes toward low-complexity, spectrum- and energy-efficient next-generation wireless networks.
A directional modulation (DM) technique using a phased array to produce the modulation is presented. By phase shifting each element correctly, the desired amplitude and phase of each symbol in a ...digital modulation scheme can be produced in a given direction with data rates determined by the switching speed of the phase shifters. Because this signal is direction-dependent, the technique offers security, as the signal can be purposely distorted in other directions. DM also enables an array to send independent data in multiple directions. When using an array with driven elements, the phase shifts can be determined from simple calculations rather than time-consuming simulations or measurements. Mathematical analysis and experimental results are presented.
This paper studies the inherent relationship between two widely used pulse width modulation (PWM) methods for multilevel converters, i.e., the space vector modulation (SVM) method, also called space ...vector pulse width modulation, and the nearest-level modulation method. The nearest-level modulation method directly controls the voltage of each phase, while the SVM method simultaneously deals with all phases. It is demonstrated in this paper that the two modulation methods are functionally equivalent: with proper common-mode voltage injections, the nearest-level modulation method is equivalent to the SVM method; by selecting the appropriate redundant switching sequences and the corresponding duty cycles, the SVM method is equivalent to the nearest-level modulation method. Nevertheless, the SVM method can conveniently provide more flexibility of optimizing the switching patterns, without the need of designing sophisticated common-mode voltages. An efficient and flexible modulation method for any multiphase multilevel converter is, therefore, proposed, which combines the advantages of the nearest-level modulation and the SVM methods, i.e., both with less computational burden and high flexibility of optimizing the output waveforms. Simulation and experimental results validate the analysis.
This paper presents a new predistortion linearization technique for high linearity and high modulation efficiency in millimeter-wave (mm-wave) CMOS power amplifiers (PA) for fifth-generation (5G) ...mobile communications. Our proposed linearizer adopts a transformer-based (i.e., inductive) self-compensated predistortion network at the input of the PA whose amplitude-modulation to phase-modulation (AM-PM) response is opposite compared with the AM-PM response of a CMOS PA, resulting in an AM-PM cancellation effect. This proposed inductive linearization method mitigates the large gain reduction problem in traditional capacitor-based linearization approaches while consuming no extra dc power or without introducing additional control circuitry. As a result, a significant improvement in power-efficiency and linearity is achieved with high-order complex modulation signals. To validate the proposed linearization method, a PA prototype in 65-nm CMOS technology was fabricated and tested, and it exhibited <1° of <inline-formula> <tex-math notation="LaTeX">\vert </tex-math></inline-formula>AM-PM<inline-formula> <tex-math notation="LaTeX">\vert </tex-math></inline-formula> distortion at <inline-formula> <tex-math notation="LaTeX">P_{\mathrm {o,1\, dB}} </tex-math></inline-formula> over 4 GHz of bandwidth (27-31 GHz). At 28 GHz, the measured saturated <inline-formula> <tex-math notation="LaTeX">P_{\mathrm {o}} </tex-math></inline-formula> and peak power-added-efficiency (PAE) was 15.6 dBm and 41%, respectively, while achieving a 6-dB <inline-formula> <tex-math notation="LaTeX">P_{\mathrm {o}} </tex-math></inline-formula> back-off PAE of 25%. To assess PA's large-signal performance for 5G communications, the prototype was measured with the 64-quadratic-amplitude modulation (QAM) signal at 2-Gb/s data rates at 28 and 30 GHz, and the PA achieves modulated-PAE of 18.2%/17.6% and average-<inline-formula> <tex-math notation="LaTeX">P_{\mathrm {o}} </tex-math></inline-formula> of 9.8 dBm/10 dBm, respectively, while maintaining <−30 dBc of adjacent-channel-power-ratio and <−25.5 dB of error-vector-magnitude. The achieved modulated-PAE at 28 and 30 GHz shows more than <inline-formula> <tex-math notation="LaTeX">2\times </tex-math></inline-formula> improvement in comparison with the recently reported 28-GHz linear CMOS PAs. Also, the PA occupies a compact active-area of 0.24 mm 2 .
In this treatise, we provide an interdisciplinary survey on spatial modulation (SM), where multiple-input multiple-output microwave and visible light, as well as single and multicarrier ...communications are considered. Specifically, we first review the permutation modulation (PM) concept, which was originally proposed by Slepian in 1965. The PM concept has been applied to a wide range of applications, including wired and wireless communications and data storage. By introducing a 3-D signal representation, which consists of spatial, temporal, and frequency axes, the hybrid PM concept is shown to be equivalent to the recently proposed SM family. In contrast to other survey papers, this treatise aims for celebrating the hitherto overlooked studies, including papers and patents that date back to the 1960s, before the invention of SM. We also provide simulation results that demonstrate the pros and cons of PM-aided low-complexity schemes over conventional multiplexing schemes.
We discuss technology options and challenges for scaling intra-datacenter interconnects beyond 1 Tb/s bandwidths, with focus on two possible approaches: pulse amplitude modulation (PAM)-based ...intensity modulation-direct detection (IM-DD) and baud-rate sampled coherent technology. In our studies, we compare the performance of various orders of PAM modulation (PAM4 to 8). In addition to these fixed PAM signaling options, a flexible PAM (FlexPAM) technique leveraging granularity in spectral efficiency (SE) is proposed to maximize link margin. For baud-rate sampled coherent technology, we propose a simplified digital signal processing (DSP) architecture to bring down power consumption of the coherent approach closer to that of IM-DD PAM. We also propose two new phase noise tolerant 2D coherent modulation formats to relax the laser linewidth requirement. In closing, a comparative study of fixed IM-DD PAM versus coherent polarization multiplexed-quadrature amplitude modulation (PM-QAM) is presented for a 1.6 Tb/s solution (200 Gb/s per dimension), with consideration of link loss/reach budget, power consumption, implementation complexity, as well as fan-out granularity.
This paper describes the operation of modular multilevel converter, an emerging and highly attractive topology for medium- and high-voltage applications. A new pulsewidth-modulation (PWM) scheme for ...an arbitrary number of voltage levels is introduced and evaluated. On the basis of this PWM scheme, the semiconductor losses are calculated, and the loss distribution is illustrated.
The near-state pulsewidth modulation (NSPWM) method, which reduces the common-mode voltage/current, is proposed for three-phase pulsewidth modulation (PWM) inverter drives. The method is described, ...its optimal voltage vectors are found, and the sequence that these vectors are applied is determined. Its voltage linearity and DC bus and AC output PWM current ripple characteristics are studied. Its output line-to-line voltage pattern is carefully studied with regard to switching transients that may cause overvoltages at the motor terminals, particularly for long-cable applications. The NSPWM method is thoroughly investigated, and its performance is compared to conventional PWM methods. Theory, simulations, and experiments show that NSPWM exhibits superior common-mode performance and satisfactory input/output PWM ripple performance characteristics. It is also illustrated that even though the method has bipolar line-to-line output voltage pulses, due to the sufficient zero-voltage time intervals for the switching transients to settle, these pulses do not cause additional overvoltages at the motor terminals compared to the conventional methods. The method is feasible for motor drives, particularly for operation in the high modulation index range, where its overall performance exceeds the performances of the state-of-the-art PWM methods.
PDF
