The authors propose two multirate teletraffic loss models in a two-link system that accommodates Poisson arriving calls from different service-classes with different bandwidth-per-call requirements. ...Each link has two thresholds which refer to the number of in-service calls in the link. The lowest threshold named support threshold, defines up to which point the link can support calls offloaded from the other link. The highest threshold, named offloading threshold, defines the point where the link starts offloading calls to the other link. Two different bandwidth sharing policies are considered: (i) the complete sharing policy, in which a call can be accepted in a link if there exist enough available bandwidth units and (ii) the bandwidth reservation policy, in which an integer number of bandwidth units is reserved to benefit calls of high bandwidth requirements. The two models do not have a product form solution for the steady state probabilities. However, they propose approximate formulas for the calculation of call blocking probabilities. The accuracy of the formulas is verified through simulation and found to be quite satisfactory.
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The packet-pair technique aims to estimate the capacity of a path (bottleneck bandwidth) from the dispersion of two equal-sized probing packets sent back to back. It has been also argued that the ...dispersion of longer packet bursts (packet trains) can estimate the available bandwidth of a path. This paper examines such packet-pair and packet-train dispersion techniques in depth. We first demonstrate that, in general, packet-pair bandwidth measurements follow a multimodal distribution and explain the causes of multiple local modes. The path capacity is a local mode, often different than the global mode of this distribution. We illustrate the effects of network load, cross-traffic packet-size variability, and probing packet size on the bandwidth distribution of packet pairs. We then switch to the dispersion of long packet trains. The mean of the packet-train dispersion distribution corresponds to a bandwidth metric that we refer to as average dispersion rate (ADR). We show that the ADR is a lower bound of the capacity and an upper bound of the available bandwidth of a path. Putting all of the pieces together, we present a capacity-estimation methodology that has been implemented in a tool called pathrate. We report on our experiences with pathrate after having measured hundreds of Internet paths over the last three years.
Determining the loop noise bandwidth and the coherent integration time is essential and important for the design of a reliable digital phase-locked loop (DPLL) in global navigation satellite system ...(GNSS) receivers. In general, designers set such parameters approximately by utilizing the well-known fact that the DPLL is stable if the normalized bandwidth, which is the product of the integration time and the noise bandwidth, is much less than one. However, actual limit points are not fixed at exactly one, and they vary with the loop filter order and implementation method. Furthermore, a lower limit on the normalized bandwidth may exist. This paper presents theoretical upper and lower limits for the normalized bandwidth of DPLL in GNSS receivers. The upper limit was obtained by examining the stability of DPLL with a special emphasis on the digital integration methods. The stability was investigated in terms of
-plane root loci with and without the consideration of the computational delay, which is a delay induced by the calculation of the discriminator and the loop filter. The lower limit was analyzed using the DPLL measurement error composed of the thermal noise, oscillator phase noise, and dynamic stress error. By utilizing the carrier-to-noise density ratio threshold which indicates the crossing point between the measurement error and the corresponding threshold, the lower limit of the normalized bandwidth is obtained.
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Millimeter-Wave (mm-Wave) frequencies are a front runner contender for the next generation body-centric wireless communications. In this paper, the design of a very low-profile antenna is presented ...for body-centric applications operating in the mm-Wave frequency band centered at 60 GHz. The antenna has an overall size of 14 × 10.5 × 1.15 mm 3 and is printed on a flexible printed circuit board. The performance of the antenna is evaluated in off-body, on-body, and bodyto-body communication scenarios using a realistic numerical phantom and verified through measurements. The antenna has a bandwidth of 9.8 GHz and offers a gain of 10.6 dBi in off-body (free space) configuration, while 12.1 dBi in on-body configuration. It also achieves an efficiency of 74% in off-body and 63% in on-body scenario. The small and flexible structure of the antenna along with excellent impedance matching, broad bandwidth, high gain, and good efficiency makes it a suitable candidate to attain simultaneous data transmission/reception at mm-Wave frequencies for the 5G body-centric applications.
Achieving a fractional bandwidth (FBW) of more than 60% has been a challenging problem for two-way symmetrical Doherty power amplifiers (TW-SDPAs) that are designed using a continuous-mode technique. ...As reported in the literature, these designed continuous-mode-based TW-SDPAs possess less than 52% FBW, which cannot satisfactorily meet the challenging, complex, and ever-evolving modulation schemes' demands. To overcome such a limitation, this article proposes a novel approach based on fuzzy logic techniques able to simplify and speed up the design of continuous-mode-based TW-SDPAs with the state-of-the-art FBW. In particular, the proposed technique uses the <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-means unsupervised learning clustering algorithm and the continuous-mode technique in a modeled fuzzy logic system environment. As a result, extensive impedance solution design space is readily made available and the optimal impedances required by the carrier and peaking subamplifiers for efficiently operating at the saturation and output-power-back-off (OPBO) levels are automatically obtained. For verification, a TW-SDPA was designed and measured. According to the measured results, the TW-SDPA operates within the 1.2-2.4-GHz frequency band corresponding to 66.7% FBW. As compared with the designed continuous-mode-based TW-SDPAs reported in the literature, this article indicates over 15% increment in FBW. Moreover, 41.59%-81.1% drain efficiency (DE) at saturation, 35%-63% DE at 6-dB OPBO, 42-45-dBm output power, and 7-10.52-dB gain were successfully achieved. Adjacent channel leakage ratio (ACLR) better than −46 dBc and average DE within 46%-55% were successfully recorded after linearization.
Popularity of metasurfaces has been continuously growing due to their attractive properties including the ability to effectively manipulate electromagnetic (EM) waves. Metasurfaces comprise optimized ...geometries of unit cells arranged as a periodic lattice to obtain a desired EM response. One of their emerging application areas is the stealth technology, in particular, realization of radar cross section (RCS) reduction. Despite potential benefits, a practical obstacle hindering widespread metasurface utilization is the lack of systematic design procedures. Conventional approaches are largely intuition-inspired and demand heavy designer's interaction while exploring the parameter space and pursuing optimum unit cell geometries. Not surprisingly, these are unable to identify truly optimum solutions. In this article, we introduce a novel machine-learning-based framework for automated and computationally efficient design of metasurfaces realizing broadband RCS reduction. Our methodology is a three-stage procedure that involves global surrogate-assisted optimization of the unit cells, followed by their local refinement. The last stage is direct EM-driven maximization of the RCS reduction bandwidth, facilitated by appropriate formulation of the objective function involving regularization terms. The appealing feature of the proposed framework is that it optimizes the RCS reduction bandwidth directly at the level of the entire metasurface as opposed to merely optimizing unit cell geometries. Computational feasibility of the optimization process, especially its last stage, is ensured by high-quality initial designs rendered during the first two stages. To corroborate the utility of our procedure, it has been applied to several metasurface designs reported in the literature, leading to the RCS reduction bandwidth improvement by 15%-25% when compared with the original designs. Furthermore, it was used to design a novel metasurface featuring over 100% of relative bandwidth. Although the procedure has been used in the context of RCS design, it can be generalized to handle metasurface development for other application areas.
The monitoring of acceleration is essential for a variety of applications ranging from inertial navigation to consumer electronics. Typical accelerometer operation involves the sensitive displacement ...measurement of a flexibly mounted test mass, which can be realized using capacitive, piezo-electric, tunnel-current or optical methods. Although optical detection provides superior displacement resolution, resilience to electromagnetic interference and long-range readout, current optical accelerometers either do not allow for chip-scale integration or utilize relatively bulky test mass sensors of low bandwidth. Here, we demonstrate an optomechanical accelerometer that makes use of ultrasensitive displacement readout using a photonic-crystal nanocavity monolithically integrated with a nanotethered test mass of high mechanical Q-factor. This device achieves an acceleration resolution of 10 µg Hz-1/2 with submilliwatt optical power, bandwidth greater than 20 kHz and a dynamic range of greater than 40 dB. Moreover, the nanogram test masses used here allow for strong optomechanical backaction, setting the stage for a new class of motional sensors.
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This communication presents substrate integrated coaxial resonator (SICR) based triple-mode bandpass filters designed for <inline-formula> <tex-math notation="LaTeX">K_{u} ...</tex-math></inline-formula>-band. A self-shielded SICR based third-order filter is realized using two planar coaxial resonators (SICR) embedded in a substrate integrated waveguide cavity (SIW). Merging the TEM based mode of two SICR's with TE 101 mode of SIW significantly enhances the bandwidth in a compact size. A novel topology realized using short circuited metallic via connecting to the top conducting plane through a metal strip demonstrates high degree of flexibility in positioning the transmission zeros to improve the selectivity as well as extend the out-of-band rejection of proposed filter. The three experimental prototypes devised for <inline-formula> <tex-math notation="LaTeX">K_{u} </tex-math></inline-formula>-band with fractional bandwidth more than 23% demonstrate multiple transmission zeros for good selectivity and out-of-band rejection with low insertion loss in a compact form factor.
The high-speed intrinsic modulation characteristics of a hybrid-modulation laser diode integrated with a passive waveguide was numerically analyzed. It was confirmed that the 3-dB intrinsic ...small-signal modulation bandwidth depended on the coupling coefficient of the corrugation grating κ at the distributed feedback (DFB) section and modulation amplitude ration ( MAR ) at the DFB and intra-cavity loss-modulation sections. The modulation bandwidth became wider when κ decreased and MAR increased. The maximum 3-dB E/O modulation bandwidth was more than 600 GHz when κ and MAR were from 40 to 80 cm -1 and 6.4 V. It remained more than 300 GHz when κ was from 40 to 200 cm -1 and MAR was from 3.2 to 6.4 V. Dynamic single-mode operation of the laser was demonstrated numerically with a 200-Gbit/s non-return-to-zero (NRZ) modulation signal. A clear eye-opened optical NRZ pattern with a minimum extinction ratio at the eye-opening area of more than 1.0 dB was confirmed in a wide operation range and at a higher bit rate up to 300 Gbit/s.
The paper presents the control strategy of stator current harmonic distortion performance improvement for doubly fed induction generator (DFIG) using bandwidth-based repetitive control (BRC) under ...generalized harmonic grid voltage. The control target is to eliminate the DFIG stator current 6n \pm 1 harmonic components; thus, sinusoidal stator output current can be injected into the power grid. Considering that the frequency deviation always occurs in the practical grid, the BRC regulator is designed on the basis of conventional repetitive control regulator with the introduction of control bandwidth. The closed-loop operation stability considering different bandwidth and gain parameter is also analyzed. Finally, the availability of the proposed BRC control strategy under generalized harmonic grid voltage is verified by experimental results.
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