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.

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.

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.

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.

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.

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.

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.

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.

Abstract: It is a tough task to greatly improve the working bandwidth for the traditional flat microwave absorbers because of the restriction of available material parameters. In this work, a simple patterning method is proposed to drastically broaden the absorption bandwidth of a conventional magnetic absorber. As a demonstration, an ultra-broadband microwave absorber with more than 90% absorption in the frequency range of 4–40 GHz is designed and experimentally realized, which has a thin thickness of 3.7 mm and a light weight equivalent to a 2-mm-thick flat absorber. In such a patterned absorber, the broadband strong absorption is mainly originated from the simultaneous incorporation of multiple λ/4 resonances and edge diffraction effects. This work provides a facile route to greatly extend the microwave absorption bandwidth for the currently available absorbing materials.

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.

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.

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.

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.

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.

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.

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.

Abstract: The simplicity and intuitive design of traditional circularly polarized (CP) patch antennas, such as the truncated corner patch antenna, has led to their widespread popularity. However, they are limited to a narrowband performance on the order of 0.1%-2% for simultaneously good S11 and axial ratio (AR). We will prove theoretically that this is a direct result of the probe reactance hindering the use of thicker substrates to increase the bandwidth. Furthermore, we propose a novel compensation technique to enhance the bandwidth capabilities of these CP patch antennas. Our method inserts a capacitive element, such as an annular gap or parallel plate, in series with the probe inductance to remove its effect. We demonstrate this technique with simulations and measurements to obtain AR- S11 bandwidth capabilities as high as 12.6%. To the authors' best knowledge, this is the first time that capacitive compensation and thick substrates have been jointly employed to enable broadband CP patch antennas.

Abstract: We present an innovative photonic strategy to generate arbitrary microwave and millimeter-wave signals with maximal time-bandwidth product capability and broadly tunable center frequency. The proposed approach incorporates high-resolution pulse shaping, optical interferometry, and the concept of frequency-to-time mapping in order to enable independent control over the temporal amplitude, temporal phase, and center frequency of the generated waveforms. Numerical simulation and experimental results validate that the time-bandwidth product of these pulses is equal to the upper bound set by the number of independent pulse shaper control elements, extending to more than twice that of conventional frequency-to-time mapping techniques. We thus demonstrate a record photonic arbitrary waveform generation time-bandwidth product of ∼589. Also, a length 15 Costas sequence realization is implemented to further portray the potentials of this technique. Detailed analysis of the repeatability and stability of these waveforms as well as higher order dispersion compensation is provided.

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.

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.

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.

Abstract: Location-aware networks are of great importance and interest in both civil and military applications. This paper determines the localization accuracy of an agent, which is equipped with an antenna array and localizes itself using wireless measurements with anchor nodes, in a far-field environment. In view of the Cramer-Rao bound, we first derive the localization information for static scenarios and demonstrate that such information is a weighed sum of Fisher information matrices from each anchor-antenna measurement pair. Each matrix can be further decomposed into two parts: a distance part with intensity proportional to the squared baseband effective bandwidth of the transmitted signal and a direction part with intensity associated with the normalized anchor-antenna visual angle. Moreover, in dynamic scenarios, we show that the Doppler shift contributes additional direction information, with intensity determined by the agent velocity and the root mean squared time duration of the transmitted signal. In addition, two measures are proposed to evaluate the localization performance of wireless networks with different anchor-agent and array-antenna geometries, and both formulae and simulations are provided for typical anchor deployments and antenna arrays.

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.

Abstract: This article investigates novel adaptive self-interference cancellation solutions and the total integrated cancellation performance of a mobile single-antenna inband full-duplex transceiver. First, novel self-adaptive digital self-interference cancellation algorithms are described, with an emphasis on tracking of time-varying self-interference coupling channel in a mobile device as well as on structural ability to suppress also nonlinear self-interference with highly nonlinear mobile power amplifiers. This leads to an advanced self-adaptive nonlinear digital canceller which utilizes a novel orthogonalization procedure for nonlinear basis functions, together with low-cost LMS-based parameter learning. The achievable self-interference cancellation performance is then evaluated with actual RF measurements using mobile device scale RF components, in particular a highly nonlinear PA. The measurements also incorporate a novel self-adaptive RF cancellation circuit in order to realistically assess the total integrated cancellation performance. The reported results show that highly efficient self-interference cancellation can be achieved also in a mobile device, despite a heavily nonlinear PA and limited computing and hardware resources. The proposed cancellation solutions, when integrated together, show that 100 dB of self-interference can be cancelled using a 20 MHz LTE waveform, while the SI can be attenuated by over 110 dB with a narrower bandwidth of 1.4 MHz, all measured at 2.4 GHz ISM band. Furthermore, these results are achieved using a highly nonlinear transmitter power amplifier and fully adaptive canceller structures which can track a rapidly changing coupling channel in a mobile full-duplex device.

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.

Abstract: In an MIMO radar network, the multiple transmit elements may emit waveforms that differ on power and bandwidth. In this paper, we are asking, given that these two resources are limited, what is the optimal power, optimal bandwidth, and optimal joint power and bandwidth allocation for best localization of multiple targets. The well-known Cramer-Rao lower bound for target localization accuracy is used as a figure of merit and approximate solutions are found by minimizing a sequence of convex problems. Their quality is assessed through extensive numerical simulations and with the help of a lower-bound on the true solution. Simulations results reveal that bandwidth allocation policies have a definitely stronger impact on performance than power.

Abstract: This paper is concerned with the distributed finite-horizon fusion Kalman filtering problem for a class of networked multi-sensor fusion systems (NMFSs) in a bandwidth and energy constrained wireless sensor network. To satisfy the finite communication bandwidth, only partial components of each local vector estimate are allowed to be transmitted to the fusion center (FC) at a particular time, while each sensor intermittently sends information to the FC for reducing energy consumptions. At the FC end, a novel compensation strategy is proposed to compensate the untransmitted components of each local estimates, then a recursively distributed fusion Kalman filter (DFKF) is derived in the linear minimum variance sense. Notice that the designed DFKF update does not need to know the transmitting situation of each component at a particular time, which means that the proposed fusion estimation algorithm is easily implemented for the addressed NMFSs. Since the performance of the designed DFKF is dependent on the selecting probability of each component, some criteria for the choice of probabilities are derived such that the mean squared errors (MSEs) of the designed DFKF are bounded or convergent. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed method.

Abstract: In this paper, a novel hybrid time-frequency adaptive equalization algorithm based on a combination of frequency domain equalization (FDE) and decision-directed least mean square (DD-LMS) is proposed and experimentally demonstrated in a Nyquist single carrier visible light communication (VLC) system. Adopting this scheme, as well with 512-ary quadrature amplitude modulation (512-QAM) and wavelength multiplexing division (WDM), an aggregate data rate of 4.22-Gb/s is successfully achieved employing a single commercially available red-green-blue (RGB) light emitting diode (LED) with low bandwidth. The measured Q-factors for 3 wavelength channels are all above the Q-limit. To the best of our knowledge, this is the highest data rate ever achieved by employing a commercially available RGB-LED.

Abstract: Two- and four-pole 0.7-1.1-GHz tunable bandpass-to-bandstop filters with bandwidth control are presented. The bandpass-to-bandstop transformation and the bandwidth control are achieved by adjusting the coupling coefficients in an asymmetrically loaded microstrip resonator. The source/load and input/output coupling coefficients are controlled using an RF microelectromechanical systems (RF MEMS) switch and a series coupling varactor, respectively. The two- and four-pole filters are built on a Duroid substrate with e r=6.15 and h=25 mil. The tuning for the center frequency and the bandwidth is done using silicon varactor diodes, and RF MEMS switches are used for the bandpass-to-bandstop transformation. In the bandpass mode of the two-pole filter, a center frequency tuning of 0.78-1.10 GHz is achieved with a tunable 1-dB bandwidth of 68-120 MHz at 0.95 GHz. The rejection level of the two-pole bandstop mode is higher than 30 dB. The bandpass mode in the four-pole filter has a center frequency tuning of 0.76-1.08 GHz and a tunable 1-dB bandwidth of 64-115 MHz at 0.94 GHz. The rejection level of the four-pole bandstop mode is larger than 40 dB. The application areas are in wideband cognitive radios under high interference environments.