The continuous-time peak-to-average power ratio of OFDM signals using complex modulation schemes

Computing the continuous-time peak-to-averagepower ratio (PAPR) of OFDM signals is computationally challenging. The pioneering work by Tellambura applies only to OFDM signals using real-valued modulation schemes. In this paper, a practical technique for evaluating the continuous-time PAPR of OFDM signals using complex modulation is presented. Using the proposed scheme, it is confirmed that the four-time oversampled discrete-time PAPR is a good approximation of the continuous-time PAPR even for complex OFDM signals. Furthermore, the proposed scheme is employed to verify some existing analytical bounds on continuous PAPR in the literature.     

In-Situ X-ray Diffraction Analysis of Metastable Austenite Containing Steels Under Mechanical Loading at a Wide Strain Rate Range

Metallurgical and Materials Transactions A - This paper presents and discusses the methodology and technical aspects of mechanical tests carried out at a wide strain rate range with simultaneous...     

Maximum-likelihood synchronization and channel estimation for OFDMA uplink transmissions

Maximum-likelihood estimation of the carrier frequency offset (CFO), timing error, and channel response of each active user in the uplink of an orthogonal frequency-division multiple-access system is investigated in this study, assuming that a training sequence is available. The exact solution to this problem turns out to be too complex for practical purposes as it involves a search over a multidimensional domain. However, making use of the alternating projection method, we replace the above search with a sequence of mono-dimensional searches. This results in an estimation algorithm of a reasonable complexity which is suitable for practical applications. As compared with other existing semi-blind methods, the proposed algorithm requires increased overhead but has more flexibility as it can be used with any subcarrier assignment scheme. Simulations indicate that the accuracy of the CFO estimates asymptotically achieves the Cramer-Rao bound.     

The design of digital all-pass filters using second-order cone programming (SOCP)

This brief proposes a new method for designing digital all-pass filters with a minimax design criterion using second-order cone programming (SOCP). Unlike other all-pass filter design methods, additional linear constraints can be readily incorporated. The overall design problem can be solved through a series of linear programming subproblems and the bisection search algorithm. The convergence of the algorithm is guaranteed. Nonlinear constraints such as the pole radius constraint of the filters can be formulated as additional SOCP constraints using Rouche's theorem. It was found that the pole radius constraint allows an additional tradeoff between the approximation error and the stability margin. The effectiveness of the proposed method is demonstrated by several design examples and comparison with conventional methods.     

Measuring the neighboring and environmental effects on residential property value: Using spatial weighting matrix

The relationship between house price and location is very complicated. Traditional theory mainly emphasizes the relationship between the effects of accessibility to central locations on housing prices and ignores location-specific attributes of housing. Previous studies at best examine only one or a few environmental amenities. However, little has been done on a high-rise, densely populated living environment. This paper thus aims to investigate the “neighboring and environmental characteristics” of a residential property on its market value in such unique setting. It uses a more advanced approach—i.e. a hedonic model with spatial adjustments—and applies GIS techniques. The findings are mostly consistent with our hypotheses. The traveling time from the apartment to the central business district is negatively correlated with housing price. Households are also willing to pay more for apartments with sea view and better air. However, greenbelt is not a significant variable on housing price and noise level is even found to be positively correlated with the price. This unexpected finding may be explained by the uniquely dense living environment in Hong Kong where households are willing to sacrifice serenity for convenience. The current research is adequately sophisticated and has contributed to a better understanding of the important theoretical question of how much a household is willing to spend on various environmental and neighbourhood attributes of an apartment.     

Buried ion-exchanged glass waveguides using field-assisted annealing

Theoretical and experimental studies on buried ion-exchanged waveguides using field-assisted annealing (FAA) in erbium-doped phosphate glasses are reported. The procedure for making buried waveguides with the use of a two-step process is demonstrated. An analytical model for the FAA process was developed to simulate the experimental conditions, and both the refractive index profiles and the effective buried depths of these waveguides are predicted. The mode intensity profiles as well as the buried depths are measured, and the measured data are in good agreement with the simulated results.     

An I/Q mismatch-free switched-capacitor complex sigma-delta Modulator

This paper presents a technique to suppress the mismatch between the in-phase (I) and quadrature-phase (Q) channels of a switched-capacitor complex sigma-delta modulator that is used for the analog-to-digital conversion of a real intermediate-frequency radio signal. The mismatch is suppressed through time sharing of the critical capacitors, i.e., the input sampling capacitor and the capacitor of the feedback digital-to-analog converter, between the I and Q channels. Circuit simulations verifying the proposed technique are presented.     

Zr4+/Ti4+ Codiffusion Characteristics in Lithium Niobate

Zr⁴⁺/Ti⁴⁺‐codoped LiNbO₃ plates were prepared by local codiffusion of stacked ZrO₂ and Ti metal films coated onto Z‐cut congruent LiNbO₃ substrates in wet O₂ at 1060°C. The metal and oxide films have different thicknesses and coating sequences. After diffusion, the Zr⁴⁺ doping effect on the refractive index of LiNbO₃ and the Li₂O out‐diffusion issue were studied by the prism coupling technique. The codiffusion characteristics of Zr⁴⁺ and Ti⁴⁺ were studied by secondary ion mass spectrometry. The results show that the Zr⁴⁺ doping has little contribution to the refractive index of the crystal. Li₂O out‐diffusion is not measurable. In the Zr⁴⁺‐only diffusion case, the diffusivity of Zr⁴⁺ is four times smaller than that of Ti⁴⁺. In the Zr⁴⁺/Ti⁴⁺ codiffusion case, the Ti⁴⁺ codiffusion assists the Zr⁴⁺ diffusion. The Zr⁴⁺ diffusivity increases linearly by two more times with the increase in initial Ti film thickness from 0 to 200 nm. On the other hand, the Zr⁴⁺ affects the Ti⁴⁺ diffusion little. Neither the ZrO₂ film thickness nor the coating sequence of Ti metal and ZrO₂ oxide films influences the diffusivity of the two ions. All the codiffusion characteristics are explained. A Zr⁴⁺/Ti⁴⁺ codiffusion model is suggested that consists of two independent diffusion equations with a Zr⁴⁺ diffusivity dependent of Ti⁴⁺ concentration and a constant Ti⁴⁺ diffusivity. In addition, the existence of a waveguide in the Zr⁴⁺/Ti⁴⁺‐codoped layer is verified experimentally, and the optical‐damage‐resistant feature of the waveguide is verified by two‐beam hologram recording experimental results.     

Surface plasmon coupling in hexagonal textured metallic microcavity

The coupling of surface plasmons to the photonic modes in hexagonal textured metallic microcavity was studied. Two types of sample structures (symmetric and asymmetric) were investigated. Both angle-resolved transmission and photoluminescent measurements showed the presence of surface plasmon modes for the textured metallic microcavity samples. For the asymmetric structured sample, the bandgap was observed at the Brillouin zone edge. The simulation of the photonic band structure using decoupled approximation for the standing wave modes agrees with the experimental result. We have derived the surface modes due to various interfaces in the microcavity. It was found that the surface plasmon modes from metal/air interface are most dominant, and was observed to couple strongly with both the transverse electric and transverse magnetic modes. Light extraction enhancement due to surface plasmon coupling was achieved with directional enhancement as much as 12 times compared with planar microcavity for the symmetric structured sample.