High-Spatial Resolution Raman-Distributed Optical Fiber Sensing Using Differential Pulsewidth Pair Detection

The sensing range of Brillouin optical time-domain analysis (BOTDA) is typically restricted to tens of kilometers by the fiber attenuation, pump depletion, and unwanted nonlinear effects. It limits the use of BOTDA in applications such as oil and gas pipeline monitoring that requires a sensing range up to hundreds of kilometers. In this work, a Raman amplification technique and a differential pulse-width pair (DPP) technique are employed to achieve high spatial resolution and long distance measurement. The Raman amplification technique involves three Raman pump configurations such as forward/backward and bi-directional pump with respect to different Brillouin pump pulses. Variations in pump and probe power, Raman propagation direction and injection location are explored to allow full control over signal amplification in any particular section of the total sensing fiber length. The signal-to-noise ratio (SNR) for a certain location along the length of the fiber can be enhanced to provide more useful localized information. In addition, a novel fitting algorithm based on artificial neural networks (ANNs) for Brillouin scattering spectrum is proposed for the estimation of Brillouin frequency shift with high accuracy. It is experimentally demonstrated for a sensing range of 100 km with a spatial resolution of 1 m and ANN based novel fitting algorithm.

Recently, the differential detection scheme has attracted considerable attention as a demodulated scheme for digital mobile communications because of its robustness in the frequency nonselective fading channel. A problem of the differential detection scheme is that its bit error rate (BER) performance in the additive white Gaussian noise (AWGN) channel is inferior to that of the coherent detection scheme. To solve this problem, many methods to improve BER performance of the differential detection in the AWGN channel have been proposed. However, those methods require complex signal processings.This paper proposes a novel differential detection scheme as a simpler improvement method which estimates the differential phase of the transmitted signal by a sequence estimation scheme using the Viterbi algorithm. The proposed scheme is simplified in a manner such that its signal processing is composed of only additions and subtractions on the phase information of the received signal. Results of computer simulation show that BER performance of the proposed scheme is close to that of the ideal coherent detection in the AWGN channel. In addition, the trellis diagram of the Viterbi algorithm can be reduced without performance degradation introducing the signal processing similar to the Scarece State Transition (SST) type Viterbi decoding. The proposed scheme also is useful in the case of the fast Rician fading channel and the slow Rayleigh fading channel.

A variety of schemes for performing differential detection in environments characterized by frequency offset are discussed. All of the schemes involve encoding the input phase information as a second-order difference and performing an analogous second-order differential detection at the receiver. Because of the back-to-back differential detection operations at the receiver, The performance of most of the schemes is considerably degraded relative to that of first-order differential detection schemes. However, the latter are quite sensitive to frequency offset and, in many instances, cannot be used at all. It is demonstrated that via a simple enhancement of using a 2 T s (instead of T s) delay in the second stage of the encoder and first stage of the decoder, the performance degradation can be significantly reduced. This result is significant in view of the fact that it comes without any penalty in implementation complexity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The paper presents a differential detection scheme for noncoherent detection of digital FM signals received over bandwidth restricted channels. The new differential detection scheme observes the phase of the FM signal at centres of signalling intervals to derive the differential phase. Differential encoding of transmitted data is required for preventing error propagation. Numerical results show that the new differential detector yields a superior performance in narrowband channels where conventional differential detection becomes unusable. Error probabilities and optimum BT values are presented assuming that bandlimiting is caused solely by IF filtering.

This paper addresses a multiple-symbol differential detection scheme for star 16QAM. At the outset, we analytically scrutinized conventional differential detection of star 16QAM. As a result, it emerged that the energy penalty of differential amplitude detection as compared with ideal coherent detection is larger than that of phase detection. Then to improve the overall performance of star 16QAM, we propose an MLSE algorithm for a large C/N as well as a suboptimum algorithm. Both of them allow multiple-symbol differential amplitude and phase detection. Their performances are also evaluated through computer simulation.KeywordsPhase DetectionEnergy PenaltyCoherent DetectionDifferential DetectionObservation SymbolThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Evolutionary gravitational Neocognitron neural network based differential spatial modulation detection scheme for uplink multiple user huge MIMO systems

Direct-sequence spread-spectrum (DSSS) with differential chip detection (DCD) schemes, chip model 1 and chip model 2, have been proposed in reference of A. Cavallini et al. (1997) and Q. Shi et al. (2002), respectively. The performances of these two DCD schemes have been studied via simulations in reference to M.M.K. Howlader and H, Chang (2003). In this paper, we derive the decision variables of these two DCD over additive white Gaussian noise (AWGN) and Rayleigh fading channel, and our results show that the noise variance in chip model 2 is twice of that in chip model 1.

We report all-optical object classification systems that are based on class-specific design of diffractive neural networks followed by a differential detection scheme. The blind inference accuracies achieved through this framework are significantly enhanced.

Analogous to multiple symbol differential detection of quadrature phase-shift-keying (QPSK), a multiple bit differential detection scheme is described for offset QPSK that also exhibits continuous improvement in performance with increasing observation interval. Being derived from maximum-likelihood (ML) considerations, the proposed scheme is purported to be the most power efficient scheme for such a modulation and detection method. Extension of the result to shaped offset QPSK is also possible.

We report a very efficient semianalytical approach for the performance evaluation of differential detection schemes for GMSK signals of the DECT standard. Precisely, for a given channel, the performance is determined by means of an analytical procedure which includes the saddlepoint approximation. We consider both static channels (with impulse response generated by the simulation program SIRCIM) and two-ray Rayleigh and log-normal fading channels. As a departure from previous works, our receiver includes an all-digital part after the analog differential detection scheme. The digital part includes: (1) a block for the estimation of both the optimum sampling phase and the nonlinear channel coefficients (by making use of the DECT training sequence), (2) a one-tap decision feedback (DF) equalizer, and (3) a block for the evaluation of the approximate optimum bias level (/spl gamma//sub e/) in the threshold detector. Both the DF equalizer coefficient and /spl gamma//sub e/ are based on the nonlinear channel coefficients estimate. For channels with a normalized delay spread up to 0.2, the use of the optimum threshold together with the DF equalizer permits a gain of about 2 dB at BER=10/sup -6/ with respect to a receiver without equalization and a zero-level decision threshold. In addition, we discover that, in indoor environments, the 2-bit GMSK detector performs roughly the same as the 1-bit detector. The threshold optimization is also effective in the presence of channels affected by fading. To support this statement, we report the performance of the 1-bit differential detection scheme combined with antenna selection diversity in the presence of a two-ray log-normal and Rayleigh fading channel.

High Resolution Differential Capacitance Detection Scheme for Micro Levitated Rotor Gyroscope

This paper presents a novel differential energy detection scheme for multi-carrier systems, which can form fast and reliable decision of spectrum availability even in very low signal-to-noise ratio (SNR) environment. For example, the proposed scheme can reach 90% in probability of detection (PD) and 10% in probability of false alarm (PFA) for the SNRs as low as -21 dB, while the observation length is equivalent to 2 multi-carrier symbol duration. The underlying initiative of the proposed scheme is applying order statistics on the clustered differential energy-spectral-density (ESD) in order to exploit the channel frequency diversity inherent in high data-rate communications. Specifically, to enjoy a good frequency diversity, the clustering operation is utilized to group uncorrelated subcarriers, while, the differential operation applied onto each cluster can effectively remove the noise floor and consequently overcome the impact of noise uncertainty while exploiting the frequency diversity. More importantly, the proposed scheme is designed to allow robustness in terms of both, time and frequency offsets. In order to analytically evaluate the proposed scheme, PFA and PD for Rayleigh fading channel are derived. The closed-form expressions show a clear relationship between the sensing performance and the cluster size, which is an indicator of the diversity gain. Moreover, we are able to observe up to 10 dB gain in the performance compared to the state-of-the-art spectrum sensing schemes.

Support vector machine (SVM) based differential pulse-width pair Brillouin optical time domain analyzer (DPP-BOTDA) has been proposed and experimentally demonstrated. With only one SVM model, temperature distribution along 5 km fiber under test has been successfully extracted from differential Brillouin gain spectrum (BGS) measured under different spatial resolution in DPP-BOTDA. The temperature accuracy by SVM is better than that by Lorentzian curve fitting (LCF), especially when the pump pulse width difference and the number of trace averaging used in the measurement are small, indicating larger tolerance of SVM to high spatial resolution and low signal-to-noise ratio. SVM is also more robust to a wide range of frequency scanning steps and has less accuracy degradation under large frequency scanning step. To extract temperature from 50 000 differential BGSs, 133.17 and 1.12 s are consumed by SVM-0.1 and SVM-1 °C, respectively, both of which are much shorter than that by LCF. The data processing time of SVM is further shortened with the help of principle component analysis for data dimension reduction. SVM for measurand extraction would be especially helpful in the scenario of DPP-BOTDA where high data sampling rate is required to resolve plenty of submeter scale sensing points.

We describe a new femtosecond time division interferometry technique for characterizing nonlinear index changes from different components of the χ(3) tensor. Pump probe interferometric measurements of nonlinear phase are performed using a time division multiplexed reference pulse. The n2∥ and n2⊥ components of the nonlinear index are measured by permuting the polarizations of the pulses and using a novel differential detection and modulation scheme. Measurements are demonstrated in an optical fiber.

Pre-correlation differential detection (PDD) scheme is studied for global navigation satellite systems (GNSS) receiver design. By performing a differential detection at the chip or sample level before correlation process, the effect of both data and residual carrier is eliminated which in turn allows for frequency independent code phase acquisition. Hence the search space and computational complexity is reduced to a large extent. The detection performance of this type of scheme is analysed in terms of receiver operating characteristic (ROC) curves and verified by simulation.