A photonic crystal fiber (PCF) based high-temperature fiber-optic sensor is proposed and experimentally demonstrated. The sensor head is a Fabry-Perot cavity manufactured with a short section of endless single-mode photonic crystal fiber (ESM PCF). The interferometric spectrum of the Fabry-Perot interferometer is collected by a charge coupled device linear array based micro spectrometer. A high-resolution demodulation algorithm is used to interrogate the peak wavelengths. Experimental results show that the temperature range of 1200 °C and the temperature resolution of 1 °C are achieved.

High-temperature fiber-optic Fabry-Perot interferometric sensors.

In this study, the estimation of fast-fading long term evolution (LTE) downlink channels in high-speed applications of LTE advanced is investigated by the authors. A robust channel estimation and interpolation algorithm is essential in order to adequately track the fast time-varying channel response. In this contribution, the multipath fast-fading channel is modelled as a discrete, tapped-delay and finite impulse response filter. Using support vector machine regression (SVR), they develop an extended algorithm to jointly estimate the complex-valued channel frequency response in time and frequency domains, in the presence of fading and non-linear noise from the transmission of known pilot symbols. Furthermore, the channel estimates at the known pilot symbols are interpolated to the unknown data symbols by using the non-linear SVR approach exploiting kernel features. This study integrates both channel estimation at pilot symbols and interpolation at data symbol into the complex SVR interpolation method. The bit error rate and mean square error performances of the authors’ fast-fading channel estimation scheme is demonstrated via simulation for LTE downlink with 64-QAM modulation and 500 km/h velocity under non-linearities.

Joint interpolation for LTE downlink channel estimation in very high-mobility environments with support vector machine regression

Wireless communication systems utilizing orthogonal frequency division multiplexing (OFDM) transmissions are capable of delivering high data rates over multipath frequency selective channels. This paper deals with joint estimation/interpolation of wireless channel using pilot symbols transmitted concurrently with the data. We propose a low complexity, spectrally efficient minimum mean square error channel estimator which exploits the correlation structure of channel frequency response for reducing the complexity. Specifically, it is shown that if pilots are inserted appropriately across OFDM subcarriers, the proposed algorithm requires no matrix inversion, thereby significantly relieving the computational burden without deteriorating the performance. Moreover, the knowledge of channel correlation is also not required for the proposed estimator. Simulation results validate that the proposed technique outperforms existing low-complexity variants in terms of mean square error and computational complexity.

Structure-Based Low Complexity MMSE Channel Estimator for OFDM Wireless Systems

Orthogonal frequency-division multiplexing OFDM is widely used in modern communication systems thanks to the ease of its implementation as well as to a simple design of channel estimation methods. Pilot-based schemes are commonly employed to recover channel information and implement efficient channel equalisation. From the symbols transmitted over the pilot carriers, the channel coefficients for a whole OFDM are estimated. In this paper, we propose a method to compute in a closed form the mean square estimation error of different linear approximation and interpolation algorithms in the time-frequency domain. Specifically, by exploiting the linear relationship between the estimated channel coefficients for the whole frame and those relative to the pilots, the proposed approach permits to obtain the mean square error relative to all OFDM symbols in a frame. The method can be used for any linear frequency/time interpolation/approximation method and for any choice of pilot positions and channel statistics. Thanks to our derivations, several pilot-aided channel estimation and interpolation algorithms can be compared without resorting to burdensome computer simulations. In order to demonstrate the effectiveness of the method, the downlink of the long term evolution system is taken as a case study: some popular channel estimators have been selected and the best strategy in a realistic wireless scenario is investigated. The performance of the method is also verified by computing, by means of simulations, bit error rate BER curves for the long term evolution LTE multiple input multiple output MIMO downlink, using 2×2 and 4×4 Alamouti space-frequency coding configurations, in both uncoded and coded communications. Copyright © 2014 John Wiley & Sons, Ltd.

Time-frequency MSE analysis of linear channel estimation methods for the LTE downlink

This paper considers a novel virtual pilot-assisted channel estimation algorithm for multiple input multiple output single carrier frequency domain equalization (MIMO-SCFDE) systems over fast time-varying multipath channels. Given that the fast time-varying channels can no longer support the assumption that the channel frequency-domain response remains invariant for the duration of one SC-FDE symbol, most of the channel estimation methods cannot be directly applied to MIMO-SCFDE systems. We put forward an iterative interfrequency interference cancellation method for the time-varying multipath channels over one SC-FDE symbol. The proposed method utilizes the virtual pilot-assisted channel estimation and partial minimum-mean-square-error equalization to improve the accuracy of the estimation. Simulation results validate the improved performance of the proposed method for MIMO-SCFDE systems over fast time-varying multipath channels.

A Virtual Pilot-Assisted Channel Estimation Algorithm for MIMO-SCFDE Systems Over Fast Time-Varying Multipath Channels

We present an approach to model handwriting like curves with the cubic spline interpolation function. Different from NURBS such as Bezier and B-spline curve modeling, the huge complexity of the traditional spline interpolation have been obstructed and limited the application of spline curve modeling. We propose an efficient local cubic spline interpolation curve modeling algorithm and provide an approach to apply the algorithm to model arbitrary shape built from free form curves.

T. Nishizaki

Papers

Efficient Spline Interpolation Curve Modeling