Showing papers on "Bandwidth (signal processing) published in 2014"

Channel Estimation and Hybrid Precoding for Millimeter Wave Cellular Systems

Abstract: Millimeter wave (mmWave) cellular systems will enable gigabit-per-second data rates thanks to the large bandwidth available at mmWave frequencies. To realize sufficient link margin, mmWave systems will employ directional beamforming with large antenna arrays at both the transmitter and receiver. Due to the high cost and power consumption of gigasample mixed-signal devices, mmWave precoding will likely be divided among the analog and digital domains. The large number of antennas and the presence of analog beamforming requires the development of mmWave-specific channel estimation and precoding algorithms. This paper develops an adaptive algorithm to estimate the mmWave channel parameters that exploits the poor scattering nature of the channel. To enable the efficient operation of this algorithm, a novel hierarchical multi-resolution codebook is designed to construct training beamforming vectors with different beamwidths. For single-path channels, an upper bound on the estimation error probability using the proposed algorithm is derived, and some insights into the efficient allocation of the training power among the adaptive stages of the algorithm are obtained. The adaptive channel estimation algorithm is then extended to the multi-path case relying on the sparse nature of the channel. Using the estimated channel, this paper proposes a new hybrid analog/digital precoding algorithm that overcomes the hardware constraints on the analog-only beamforming, and approaches the performance of digital solutions. Simulation results show that the proposed low-complexity channel estimation algorithm achieves comparable precoding gains compared to exhaustive channel training algorithms. The results illustrate that the proposed channel estimation and precoding algorithms can approach the coverage probability achieved by perfect channel knowledge even in the presence of interference.

A fully photonics-based coherent radar system

Abstract: The next generation of radar (radio detection and ranging) systems needs to be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. Today's digital microwave components (synthesizers and analogue-to-digital converters) suffer from limited bandwidth with high noise at increasing frequencies, so that fully digital radar systems can work up to only a few gigahertz, and noisy analogue up- and downconversions are necessary for higher frequencies. In contrast, photonics provide high precision and ultrawide bandwidth, allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimetre waves, and the detection of such signals and their precise direct digitization without downconversion. Until now, the photonics-based generation and detection of radio-frequency signals have been studied separately and have not been tested in a radar system. Here we present the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR. The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radio-frequency up- and downconversion and guaranteeing both the software-defined approach and high resolution. Its performance exceeds state-of-the-art electronics at carrier frequencies above two gigahertz, and the detection of non-cooperating aeroplanes confirms the effectiveness and expected precision of the system.

Fundamentals of wireless communications

Abstract: Radio Frequency (RF) communications are an important smart grid enabler for functions such as volt/VAR control, recloser control, and feeder restorations and isolation. This paper will give a basic tutorial on the types of radio frequency communications and the benefits and liabilities of each. Specific topics to be explored will be licensed versus unlicensed frequencies, distance between remote radios and base stations, and communications architectures. Radio technology is often referred in numerical ranges or frequencies. The decision on which frequency to employ in a network depends on a few key variables. Prior to deciding which frequency for a network, the application for the radio use will assist with dictation of which frequency range to utilize. Applications such as recloser control and volt/Var control may require a radio device that can provide a high bandwidth/fast speed solution. Other SCADA applications such as sensor monitoring may only require small bandwidth and for data delivery to be at a much slower speed. Another variable when deciding on a radio network is the distance from the main SCADA hosts to end remote devices such as RTUs or PLCs. Lower end frequencies (100 MHz-900 MHz) provide further coverage and greater distance from base stations/Access Points to remote end devices, whereas higher frequencies (2.4 GHz-5.8 GHz) provide shorter distance coverage, but higher bandwidth and relay data back to SCADA hosts much faster. Determining a network's architecture should focus on either the desire of a private, licensed network or the notion of an unlicensed, less expensive network. The lower licensed frequency ranges (100 MHz, 200 MHz, 400 MHz and upper 900 MHz bands) are often referred to as MAS (Multiple Address Systems) networks and require license acquisition from the FCC once geographical coverage is determined. These licenses are granted for the lower frequencies as mentioned previously but are considered the proprietary use of the owner. Anyone operating in these frequencies will be fined/cited by the FCC. The less expensive, unlicensed network is allowable for frequencies ranging from 902MHz-928MHz, which is defined as the ISM (Industrial, Scientific, and Medical) bands. Within the unlicensed frequency band, there exist registered bands (3.65 GHz) that employ WiMax (Wireless Microwave Access for Broadband) technology that provide shorter coverage for remote devices, however, the bandwidth and speed provided by these frequencies make them just as popular for networks. Further analysis and discussion of licensed versus unlicensed radio wireless communications is proposed in this paper.

Regions of Active Damping Control for LCL Filters

Abstract: The control of a grid-connected voltage source inverter with an inductive-capacitive-inductive (LCL) filter is a very challenging task, since the LCL network causes a resonance phenomenon near to the control stability boundary. While many active damping methods have been proposed to overcome this issue, the role that pulse width modulation transport delay plays in the effectiveness of these strategies is still not fully resolved. This paper presents a theoretical discrete time-analysis framework that identifies three distinct regions of LCL filter resonance, namely, a high resonant frequency region where active damping is not required, a critical resonant frequency where a controller cannot stabilize the system, and a low resonant frequency region where active damping is essential. Suitable controllers are then proposed for the two stable regions, with gain calculations that allow for the greatest system bandwidth and damping. Simulation and experimental results verify the presented analysis.

Multiband Carrierless Amplitude Phase Modulation for High Capacity Optical Data Links

Abstract: Short range optical data links are experiencing bandwidth limitations making it very challenging to cope with the growing data transmission capacity demands. Parallel optics appears as a valid short-term solution. It is, however, not a viable solution in the long-term because of its complex optical packaging. Therefore, increasing effort is now put into the possibility of exploiting higher order modulation formats with increased spectral efficiency and reduced optical transceiver complexity. As these type of links are based on intensity modulation and direct detection, modulation formats relying on optical coherent detection can not be straight forwardly employed. As an alternative and more viable solution, this paper proposes the use of carrierless amplitude phase (CAP) in a novel multiband approach (MultiCAP) that achieves record spectral efficiency, increases tolerance towards dispersion and bandwidth limitations, and reduces the complexity of the transceiver. We report on numerical simulations and experimental demonstrations with capacity beyond 100 Gb/s transmission using a single externally modulated laser. In addition, an extensive comparison with conventional CAP is also provided. The reported experiment uses MultiCAP to achieve 102.4 Gb/s transmission, corresponding to a data payload of 95.2 Gb/s error free transmission by using a 7% forward error correction code. The signal is successfully recovered after 15 km of standard single mode fiber in a system limited by a 3 dB bandwidth of 14 GHz.

Filtered-OFDM - Enabler for Flexible Waveform in the 5th Generation Cellular Networks

Abstract: The underlying waveform has always been a shaping factor for each generation of the cellular networks, such as orthogonal frequency division multiplexing (OFDM) for the 4th generation cellular networks (4G). To meet the diversified and pronounced expectations upon the upcoming 5G cellular networks, here we present an enabler for flexible waveform configuration, named as filtered-OFDM (f-OFDM). With the conventional OFDM, a unified numerology is applied across the bandwidth provided, balancing among the channel characteristics and the service requirements, and the spectrum efficiency is limited by the compromise we made. In contrast, with f-OFDM, the assigned bandwidth is split up into several subbands, and different types of services are accommodated in different subbands with the most suitable waveform and numerology, leading to an improved spectrum utilization. After outlining the general framework of f-OFDM, several important design aspects are also discussed, including filter design and guard tone arrangement. In addition, an extensive comparison among the existing 5G waveform candidates is also included to illustrate the advantages of f-OFDM. Our simulations indicate that, in a specific scenario with four distinct types of services, f-OFDM provides up to 46% of throughput gains over the conventional OFDM scheme.

An ultra-wideband surface plasmonic filter in microwave frequency

Abstract: We propose an ultra-wideband plasmonic waveguide based on designer surface plasmon polaritons (DSPPs) with double gratings. In such plasmonic metamaterials, the DSPP waves in the region of lower frequencies of the dispersion curve can be tightly confined and hence effectively broaden the operating bandwidth. Based on such features, we design and fabricate a high performance DSPP filter, in which a transducer consisting of microstrip, slotline, and gradient corrugations is employed to feed electromagnetic energies into the plasmonic waveguide with high efficiency. The simulated and measured results on reflection and transmission coefficients in the microwave frequency demonstrate the excellent filtering characteristics such as low loss, wide band, and high square ratio. The high performance DSPP waveguide and filter pave a way to develop advanced plasmonic integrated functional devices and circuits in the microwave and terahertz frequencies.

Wideband Fabry-Perot Resonator Antenna With Two Complementary FSS Layers

Abstract: This paper presents a novel design of a Fabry-Perot (FP) resonator antenna with a wide gain bandwidth in X band. The bandwidth enhancement of the antenna is attributed to the positive reflection phase gradient of an electromagnetic band gap (EBG) structure, which is constructed by the combination of two complementary frequency selective surfaces (FSSs). To explain well the design procedure and approach, the EBG structure is modeled as an equivalent circuit and analyzed using the Smith Chart. Experimental results show that the antenna possesses a relative 3 dB gain bandwidth of 28%, from 8.6 GHz to 11.4 GHz, with a peak gain of 13.8 dBi. Moreover, the gain bandwidth can be well covered by the impedance bandwidth for the reflection coefficient ( ${\rm S} _{11}$ ) below $-10~{\rm dB}$ from 8.6 GHz to 11.2 GHz.

22.4 A 1GS/s 10b 18.9mW time-interleaved SAR ADC with background timing-skew calibration

Abstract: SARs are one of the most energy-efficient ADC architectures for medium resolution and low-to-medium speed. To improve the limited bandwidth of SAR ADCs, the time-interleaved (TI) structure is often used [1,2]. However, TI ADCs have several issues caused by mismatches between channels, such as offset, gain, and timing-skew errors. Unlike the other errors, timing-skew causes errors that increase with input signal frequency. Considering that the TI structure is typically employed to increase bandwidth, timing-skew can be a dominant error source of TI ADCs. Recent works [1,3] have demonstrated a background timing-skew calibration using a dedicated additional channel as a timing reference. In this work, we present a TI SAR ADC that enables background timing-skew calibration without a separate timing reference channel and enhances the conversion speed of each channel.

Strong environmental coupling in a Josephson parametric amplifier

Abstract: We present a lumped-element Josephson parametric amplifier designed to operate with strong coupling to the environment. In this regime, we observe broadband frequency dependent amplification with multi-peaked gain profiles. We account for this behavior using the “pumpistor” model which allows for frequency dependent variation of the external impedance. Using this understanding, we demonstrate control over the complexity of gain profiles through added variation in the environment impedance at a given frequency. With strong coupling to a suitable external impedance, we observe a significant increase in dynamic range, and large amplification bandwidth up to 700 MHz giving near quantum-limited performance.

High Bandwidth Visible Light Communications Based on a Post-Equalization Circuit

Abstract: A research in extending bandwidth of the visible light communication (VLC) system that uses phosphorescent white LED has been reported in this letter. Slow response of the phosphorescent component limits the modulation bandwidth of white LED to the lower MHz range. In this letter, we present a post-equalization circuit that contains two passive equalizers and one active equalizer. With blue-filtering and the post-equalization circuit, a bandwidth of 151 MHz has been achieved in our VLC system, which allows OOK-NRZ data transmission up to 340 Mb/s. The VLC link operates at 43 cm using a single one Watt white LED, and the bit-error-ratio was below 2×10-3, which is within the forward error correction limit.

Wideband 3D Frequency Selective Rasorber

Abstract: This communication presents a 3D frequency selective rasorber (FSR) with bandpass filtering response and wideband absorption characteristics. By loading an array of lumped resistors at one side of a microstrip-line based bandpass frequency selective structure (FSS), multiple resonators, including lossy resonators, are constructed. The bandpass performance with high selectivity is provided by resonators in the substrate region of the microstrip line. The absorption characteristic is obtained by the lossy resonators at the resistor-loaded side of the air region. All reflected waves at the resistor-loaded side can be effectively absorbed by appropriately choosing the resistance value. Physical mechanism of the FSR is analyzed with the aid of an equivalent circuit model and current distributions. As an example, a prototype of the designed FSR is fabricated and tested. Experimental results show that the insertion loss at the center frequency is 2.4 dB and a bandwidth of 114% for the absorption better than 10 dB in the upper rejection band is achieved under the normal incidence.

Visible Light Communications: 170 Mb/s Using an Artificial Neural Network Equalizer in a Low Bandwidth White Light Configuration

Abstract: In this paper, we experimentally demonstrate for the first time an on off keying modulated visible light communications system achieving 170 Mb/s using an artificial neural network (ANN) based equalizer. Adaptive decision feedback (DF) and linear equalizers are also implemented and the system performances are measured using both real time (TI TMS320C6713 digital signal processing board) and offline (MATLAB) implementation of the equalizers. The performance of each equalizer is analyzed in this paper using a low bandwidth (4.5 MHz) light emitting diode (LED) as the transmitter and a large bandwidth (150 MHz) PIN photodetector as the receiver. The achievable data rates using the white spectrum are 170, 90, 40 and 20 Mb/s for ANN, DF, linear and unequalized topologies, respectively. Using a blue filter to isolate the fast blue component of the LED (at the cost of the power contribution of the yellowish wavelengths) is a popular method of improving the data rate. We further demonstrate that it is possible to sustain higher data rates from the white light with ANN equalization than the blue component due to the high signal-to-noise ratio that is obtained from retaining the yellowish wavelengths. Using the blue component we could achieve data rates of 150, 130, 90 and 70 Mb/s for the same equalizers, respectively.

Directional Modulation Based on 4-D Antenna Arrays

Abstract: Four-dimensional (4-D) antenna arrays are formed by introducing a fourth dimension, time, into traditional antenna arrays. In this paper, a time-modulated 4-D array with constant instantaneous directivity is proposed for directional modulation. The main idea is that the 4-D array transmits correct signal without time modulation in the desired direction, while transmitting time-modulated signals in other directions. As longs as the time modulation frequency is less than the bandwidth of the transmitted signal, the time-modulated signals cannot be demodulated correctly due to the aliasing effect, implying that time-modulated signals go distorted. Thus, the 4-D array can be used to transmit direction-dependent signals in secure wireless communications. The proposed idea is verified by experiments based on AM signal transmission through the 4-D array. Moreover, BPSK signal transmission through the 4-D array is studied and the bit error rate (BER) performance is investigated. Simulation results show that the BERs of time-modulated BPSK (TM-BPSK) signals transmitted through the sidelobes of the 4-D array are much higher than those of BPSK signals and almost keep unchanged even under higher SNR. Finally, two enhanced methods are presented to improve the feasibility of directional modulation by using random time sequences and random time modulation frequency.

MEMS Reconfigurable Optimized E-Shaped Patch Antenna Design for Cognitive Radio

Abstract: Reconfigurable antennas offer attractive potential solutions to solve the challenging antenna problems related to cognitive radio systems using the ability to switch patterns, frequency, and polarization. In this paper, a novel frequency reconfigurable E-shaped patch design is proposed for possible applications in cognitive radio systems. This paper provides a methodology to design reconfigurable antennas with radio frequency microelectromechanical system (RF-MEMS) switches using particle swarm optimization, a nature-inspired optimization technique. By adding RF-MEMS switches to dynamically change the slot dimensions, one can achieve wide bandwidth which is nearly double the original E-shaped patch bandwidth. Utilizing an appropriate fitness function, an optimized design which works in the frequency range from 2 GHz to 3.2 GHz (50% impedance bandwidth at 2.4 GHz ) is obtained. RF-MEMS switch circuit models are incorporated into the optimization as they more effectively represent the actual switch effects. A prototype of the final optimized design is developed and measurements demonstrate good agreement with simulations.

Controlling the dynamic range of a Josephson parametric amplifier

Abstract: One of the central challenges in the development of parametric amplifiers is the control of the dynamic range relative to its gain and bandwidth, which typically limits quantum limited amplification to signals which contain only a few photons per inverse bandwidth. Here, we discuss the control of the dynamic range of Josephson parametric amplifiers by using Josephson junction arrays. We discuss gain, bandwidth, noise, and dynamic range properties of both a transmission line and a lumped element based parametric amplifier. Based on these investigations we derive useful design criteria, which may find broad application in the development of practical parametric amplifiers.

Fourier-domain beamforming: the path to compressed ultrasound imaging

Abstract: Sonography techniques use multiple transducer elements for tissue visualization. Signals received at each element are sampled before digital beamforming. The sampling rates required to perform high-resolution digital beamforming are significantly higher than the Nyquist rate of the signal and result in considerable amount of data that must be stored and processed. A recently developed technique, compressed beamforming, based on the finite rate of innovation model, compressed sensing (CS), and Xampling ideas, allows a reduction in the number of samples needed to reconstruct an image comprised of strong reflectors. A drawback of this method is its inability to treat speckle, which is of significant importance in medical imaging. Here, we build on previous work and extend it to a general concept of beamforming in frequency. This allows exploitation of the low bandwidth of the ultrasound signal and bypassing of the oversampling dictated by digital implementation of beamforming in time. By using beamforming in frequency, the same image quality is obtained from far fewer samples. We next present a CS technique that allows for further rate reduction, using only a portion of the beamformed signal's bandwidth. We demonstrate our methods on in vivo cardiac data and show that reductions up to 1/28 of the standard beamforming rates are possible. Finally, we present an implementation on an ultrasound machine using sub-Nyquist sampling and processing. Our results prove that the concept of sub-Nyquist processing is feasible for medical ultrasound, leading to the potential of considerable reduction in future ultrasound machines' size, power consumption, and cost.

The Compression of Electric Signal Waveforms for Smart Grids: State of the Art and Future Trends

Abstract: In this paper, we discuss the compression of waveforms obtained from measurements of power system quantities and analyze the reasons why its importance is growing with the advent of smart grid systems. While generation and transmission networks already use a considerable number of automation and measurement devices, a large number of smart monitors and meters are to be deployed in the distribution network to allow broad observability and real-time monitoring. This situation creates new requirements concerning the communication interface, computational intelligence and the ability to process data or signals and also to share information. Therefore, a considerable increase in data exchange and in storage is likely to occur. In this context, one must achieve an efficient use of channel communication bandwidth and a reduced need of storage space for power system data. Here, we review the main compression techniques devised for electric signal waveforms providing an overview of the achievements obtained in the past decades. Additionally, we envision some smart grid scenarios emphasizing open research issues regarding compression of electric signal waveforms. We expect that this paper will contribute to motivate joint research efforts between electrical power system and signal processing communities in the area of signal waveform compression.

On the performance of multichannel digital backpropagation in high-capacity long-haul optical transmission.

Abstract: The performance of digital backpropagation (DBP) equalization when applied over multiple channels to compensate for the nonlinear impairments in optical fiber transmission systems is investigated. The impact of a suboptimal multichannel DBP operation is evaluated, where implementation complexity is reduced by varying parameters such as the number of nonlinear steps per span and sampling rate. Results have been obtained for a reference system consisting of a 5×32 Gbaud PDM-16QAM superchannel with 33 GHz subchannel spacing and Nyquist pulse shaping under long-haul transmission. The reduction in the effectiveness of the algorithm is evaluated and compared with the ideal gain expected from the cancellation of the nonlinear signal distortion. The detrimental effects of polarization mode dispersion (PMD) with varying DBP bandwidth are also studied. Key parameters which ensure the effectiveness of multichannel DBP are identified.

Bandwidth shaping of microresonator-based frequency combs via dispersion engineering

Abstract: We investigate experimentally and theoretically the role of group-velocity dispersion and higher-order dispersion on the bandwidth of microresonator-based parametric frequency combs. We show that the comb bandwidth and the power contained in the comb can be tailored for a particular application. Additionally, our results demonstrate that fourth-order dispersion plays a critical role in determining the spectral bandwidth for comb bandwidths on the order of an octave.

Reduced Complexity Digital Back-Propagation Methods for Optical Communication Systems

Abstract: Next-generation optical communication systems will continue to push the ( bandwidth · distance) product towards its physical limit. To address this enormous demand, the usage of digital signal processing together with advanced modulation formats and coherent detection has been proposed to enable data-rates as high as 400 Gb/s per channel over distances in the order of 1000 km. These technological breakthroughs have been made possible by full compensation of linear fiber impairments using digital equalization algorithms. While linear equalization techniques have already matured over the last decade, the next logical focus is to explore solutions enabling the mitigation of the Kerr effect induced nonlinear channel impairments. One of the most promising methods to compensate for fiber nonlinearities is digital back-propagation (DBP), which has recently been acknowledged as a universal compensator for fiber propagation impairments, albeit with high computational requirements. In this paper, we discuss two proposals to reduce the hardware complexity required by DBP. The first confirms and extends published results for non-dispersion managed link, while the second introduces a novel method applicable to dispersion managed links, showing complexity reductions in the order of 50% and up to 85%, respectively. The proposed techniques are validated by comparing results obtained through post-processing of simulated and experimental data, employing single channel and WDM configurations, with advanced modulation formats, such as quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16-QAM). The considered net symbol rate for all cases is 25 GSymbol/s. Our post-processing results show that we can significantly reduce the hardware complexity without affecting the system performance. Finally, a detailed analysis of the obtained reduction is presented for the case of dispersion managed link in terms of number of required complex multiplications per transmitted bit.

Theoretical modeling and analysis of mechanical impact driven and frequency up-converted piezoelectric energy harvester for low-frequency and wide-bandwidth operation

Abstract: Vibration energy harvesters are capable of generating significant amount of power at higher frequencies rather than generating at low frequencies. Moreover, as low frequency vibrations (1–30 Hz) around the ambient environment are discursive in nature, resonance based power generators are limited to use within this low frequency range. In this paper, a mechanical impact driven and frequency up-converted wide-bandwidth piezoelectric vibration energy harvester has been proposed and demonstrated theoretically and experimentally. It converts low frequency environmental vibrations into high frequency vibration by mechanical impact. A low frequency flexible driving beam with horizontally extended tip mass, upon excitation, hits two high frequency rigid piezoelectric generating beams at the same time causing a change in the driving beam's effective stiffness that allows the device to offer approximately 180% increased −3 dB bandwidth and more than 62% of the maximum power generation within the remaining operating frequency range as well. The overall bandwidth is 7.5 Hz within 7–14.5 Hz frequency range generating a minimum peak power of 233 μW. A maximum of 378 μW peak power from one generating beam is achieved under 6 ms −2 acceleration at the resonant frequency of 14.5 Hz. Output of both generating beams connected in series produces 734 μW peak power under the same operating condition with the corresponding power density 38.8 μW cm −3 . The experimental results show some discrepancy with the theoretical results due to mechanical loss during impact and the process variations in the beam formation and assembling. The theoretical and experimental results reveal that the proposed configuration has the potential of powering small portable, handheld wireless smart devices from low frequency, specially human motion related vibrations.

A Closed-Form Design Technique for Ultra-Wideband Doherty Power Amplifiers

Abstract: This paper presents an innovative architecture to drastically enlarge the bandwidth of the Doherty power amplifier (DPA). The proposed topology, based on novel input/output splitting/combining networks, allows to overcome the typical bandwidth limiting factors of the conventional DPA. A complete and rigorous theoretical investigation of the developed architecture is presented leading to a closed-form formulation suitable for a direct synthesis of ultra-wideband DPAs. The theoretical formulation is validated through the design, realization, and test of a hybrid prototype based on commercial GaN HEMT device showing a fractional bandwidth larger than 83%. From 1.05 to 2.55 GHz, experimental results with continuous-wave signals have shown efficiency levels within 83%-45% and within 58%-35% at about 42- and 36-dBm output power, respectively. The DPA has also been tested and digitally predistorted by using a 5-MHz Third Generation Partnership Project (3GPP) signal. In particular, to evaluate the ultra-wideband and the multi-mode capabilities of the prototype, f 1 = 1.2 GHz, f 2 = 1.8 GHz, and f 3 = 2.5 GHz have been selected as carrier frequencies for the 3GPP signal. Under these conditions and at 36-dBm average output power, the DPA shows 52%, 35%, and 52% efficiency and an adjacent channel power ratio always lower than -43 dBc.

An Indoor Hybrid WiFi-VLC Internet Access System

Abstract: Visible light communications (VLC) is emerging as a new alternative to the use of the existing and increasingly crowded radio frequency (RF) spectrum. VLC is unlicensed, has wide bandwidth, supports new levels of security due to the opacity of walls, and can be combined to provide both lighting and data communications for little net increase in energy cost. As part of a lighting system, VLC is ideal as a downlink technology in which data are delivered from overhead luminaries to receivers in the lighting field. However, realizing a symmetric optical channel is problematic because most receivers, such as mobile devices, are ill-suited for an optical uplink due to glare, device orientation, energy constraints. In this paper we propose and implement a hybrid solution in which the uplink challenge is resolved by the use of an asymmetric RF-VLC combination. VLC is used as a downlink, RF is used as an uplink, and the hybrid solution realizes full duplex communication without performance glare or throughput degradation expected in an all-VLC-based approach. Our proposed approach utilizes a software defined VLC platform (SDVLC) to implement the unidirectional optical wireless channel and a WiFi link as the back-channel. Experiments with the implemented prototype reveal that the integrated system outperforms conventional WiFi for crowded (congested) multiuser environments in term of throughput, and demonstrate functional access to full-duplex interactive applications such as web browsing with HTTP.

GHz-Wide Sensing and Decoding Using the Sparse Fourier Transform

Abstract: We present BigBand, a technology that can capture GHz of spectrum in realtime without sampling the signal at GS/s -i.e., without high speed ADCs. Further, it is simple and can be implemented on commodity low-power radios. Our approach builds on recent advances in the area of sparse Fourier transforms, which show that it is possible to reconstruct a sparse signal without sampling it at the Nyquist rate. To demonstrate our design, we implement it using 3 software radios, each sampling the spectrum at 50 MS/s, producing a device that captures 0.9 GHz — i.e., 6× larger digital bandwidth than the three software radios combined. Finally, an extension of BigBand can perform GHz spectrum sensing even in scenarios where the spectrum is not sparse.

Photonic generation of W-band arbitrary waveforms with high time-bandwidth products enabling 3.9 mm range resolution

Abstract: Ultrabroadband millimeter-wave and subterahertz waveforms offer significant potential, from ultrahigh-speed communications to high-resolution radar. Electronic generation of broadband arbitrary waveforms at these frequencies suffers from limited digital-to-analog converter speed and high timing jitter. Photonic-assisted techniques, such as those based on optical shaping and frequency-to-time mapping, can overcome these difficulties. Nevertheless, previous photonic arbitrary waveform generation demonstrations are confined to microwave and low millimeter-wave frequencies due to limited optical-to-electrical conversion bandwidth. Here, by utilizing cutting-edge photodetector technology, we report the first generation, wireless transmission, and measurement of substantially complex and highly stable arbitrary waveforms in the W-band (75–110 GHz). These waveforms exhibit high time-bandwidth products up to 600, arbitrarily extendable repetition periods, and phase-noise performance substantially better than state-of-the-art electronic arbitrary waveform generators. The utility of the generated waveforms is demonstrated in multi-target ranging, where a depth resolution of 3.9 mm, unprecedented in the W-band, is achieved over more than 5 m.

Optical SEFDM System; Bandwidth Saving Using Non-Orthogonal Sub-Carriers

Abstract: We propose and demonstrate a new optical spectrally efficient frequency division multiplexing (O-SEFDM) system, where non-orthogonal and overlapping sub-carriers are employed to provide higher spectral efficiency relative to optical-orthogonal frequency division multiplexing (O-OFDM). The O-SEFDM technique can increase spectral efficiency in both the electrical and optical domains. It is experimentally shown that for bandwidth saving up to 25%, we can achieve the same performance as O-OFDM. This is the first experimental verification of 25% optical faster than the Nyquist rate. Furthermore, for approximately the same spectral efficiency, 4QAM O-SEFDM outperforms standard 8QAM by 1.6 dB. It is experimentally shown that a lower-order modulation format can achieve a better performance by replacing a higher one.

Tunable sharp and highly selective microwave-photonic band-pass filters based on stimulated Brillouin scattering

Abstract: Stimulated Brillouin scattering (SBS) in optical fibers has long been used in frequency-selective optical signal processing, including in the realization of microwave-photonic (MWP) filters. In this work, we report a significant enhancement in the selectivity of SBS-based MWP filters. Filters having a single passband of 250 MHz–1 GHz bandwidth are demonstrated, with selectivity of up to 44 dB. The selectivity of the filters is better than that of the corresponding previous arrangements by about 15 dB. The shape factor of the filters, defined as the ratio between their −20 dB bandwidth and their −3 dB bandwidth, is between 1.35 and 1.5. The central transmission frequency, bandwidth, and spectral shape of the passband are all independently adjusted. Performance enhancement is based on two advances, compared with previous demonstrations of tunable SBS-based MWP filters: (a) the polarization attributes of SBS in standard, weakly birefringent fibers are used to discriminate between in-band and out-of-band components and (b) a sharp and uniform power spectral density of the SBS pump waves is synthesized through external modulation of an optical carrier by broadband, frequency-swept waveforms. The signal-to-noise ratio of filtered radio-frequency waveforms and the linear dynamic range of the filters are estimated analytically and quantified experimentally. Lastly, a figure of merit for the performance of the filters is proposed and discussed. The filters are applicable to radio-over-fiber transmission systems.

An Automatically Mode-Matched MEMS Gyroscope With Wide and Tunable Bandwidth

Abstract: This paper presents the architecture and experimental verification of the automatic mode-matching system that uses the phase relationship between the residual quadrature and drive signals in a gyroscope to achieve and maintain matched resonance mode frequencies. The system also allows adjusting the system bandwidth with the aid of the proportional-integral controller parameters of the sense-mode force-feedback controller, independently from the mechanical sensor bandwidth. This paper experimentally examines the bias instability and angle random walk (ARW) performances of the fully decoupled MEMS gyroscopes under mismatched (~ 100 Hz) and mode-matched conditions. In matched-mode operation, the system achieves mode matching with an error frequency separation between the drive and sense modes in this paper. In addition, it has been experimentally demonstrated that the bias instability and ARW performances of the studied MEMS gyroscope are improved up to 2.9 and 1.8 times, respectively, with the adjustable and already wide system bandwidth of 50 Hz under the mode-matched condition. Mode matching allows achieving an exceptional bias instability and ARW performances of 0.54 °/hr and 0.025 °/√hr, respectively. Furthermore, the drive and sense modes of the gyroscope show a different temperature coefficient of frequency (TCF) measured to be -14.1 ppm/°C and -23.2 ppm/°C, respectively, in a temperature range from 0 °C to 100 °C. Finally, the experimental data indicate and verify that the proposed system automatically maintains the frequency matching condition over a wide temperature range, even if TCF values of the drive and sense modes are quite different.