1,063 research outputs found
Intelligent optical performance monitor using multi-task learning based artificial neural network
An intelligent optical performance monitor using multi-task learning based
artificial neural network (MTL-ANN) is designed for simultaneous OSNR
monitoring and modulation format identification (MFI). Signals' amplitude
histograms (AHs) after constant module algorithm are selected as the input
features for MTL-ANN. The experimental results of 20-Gbaud NRZ-OOK, PAM4 and
PAM8 signals demonstrate that MTL-ANN could achieve OSNR monitoring and MFI
simultaneously with higher accuracy and stability compared with single-task
learning based ANNs (STL-ANNs). The results show an MFI accuracy of 100% and
OSNR monitoring root-mean-square error of 0.63 dB for the three modulation
formats under consideration. Furthermore, the number of neuron needed for the
single MTL-ANN is almost the half of STL-ANN, which enables reduced-complexity
optical performance monitoring devices for real-time performance monitoring
A Blind Phase Stabilization Algorithm for Parallel Coherent Receivers
The impact from phase drifts in the different branches of parallel coherent receivers is investigated and it is shown how the spectrum is broadened when the receiver branches are not phase stabilized. Based on this, we propose a blind algorithm for compensating these phase drifts in digital signal processing by minimization of the spectral width. The algorithm performance is then evaluated by numerical simulations of quadrature phase-shift keying data using return-to-zero modulation. It is found that the algorithm is capable of identifying the phases with sufficient accuracy to make the residual effect of the phase mismatches negligible compared to the signal distortion by noise at a bit error rate of 0.001
Study of spread spectrum multiple access systems for satellite communications with overlay on current services
The feasibility of using spread spectrum techniques to provide a low-cost multiple access system for a very large number of low data terminals was investigated. Two applications of spread spectrum technology to very small aperture terminal (VSAT) satellite communication networks are presented. Two spread spectrum multiple access systems which use a form of noncoherent M-ary FSK (MFSK) as the primary modulation are described and the throughput analyzed. The analysis considers such factors as satellite power constraints and adjacent satellite interference. Also considered is the effect of on-board processing on the multiple access efficiency and the feasibility of overlaying low data rate spread spectrum signals on existing satellite traffic as a form of frequency reuse is investigated. The use of chirp is examined for spread spectrum communications. In a chirp communication system, each data bit is converted into one or more up or down sweeps of frequency, which spread the RF energy across a broad range of frequencies. Several different forms of chirp communication systems are considered, and a multiple-chirp coded system is proposed for overlay service. The mutual interference problem is examined in detail and a performance analysis undertaken for the case of a chirp data channel overlaid on a video channel
Spitzer Space Telescope Observations of the Magnetic Cataclysmic Variable AE Aqr
The magnetic cataclysmic variable AE Aquarii hosts a rapidly rotating white
dwarf which is thought to expel most of the material streaming onto it.
Observations of AE Aqr have been obtained in the wavelength range of 5 - 70
microns with the IRS, IRAC, and MIPS instruments on board the Spitzer Space
Telescope. The spectral energy distribution reveals a significant excess above
the K4V spectrum of the donor star with the flux increasing with wavelength
above 12.5 microns. Superposed on the energy distribution are several hydrogen
emission lines, identified as Pf alpha and Hu alpha, beta, gamma. The infrared
spectrum above 12.5 microns can be interpreted as synchrotron emission from
electrons accelerated to a power-law distribution dN=E^{-2.4}dE in expanding
clouds with an initial evolution timescale in seconds. However, too many
components must then be superposed to explain satisfactorily both the
mid-infrared continuum and the observed radio variability. Thermal emission
from cold circumbinary material can contribute, but it requires a disk
temperature profile intermediate between that produced by local viscous
dissipation in the disk and that characteristic of a passively irradiated disk.
Future high-time resolution observations spanning the optical to radio regime
could shed light on the acceleration process and the subsequent particle
evolution.Comment: 15 pages, 3 figures, accepted for publication in Ap
System architecture study of an orbital GPS user terminal
The generic RF and applications processing requirements for a GPS orbital navigator are considered. A line of demarcation between dedicated analog hardware, and software/processor implementation, maximizing the latter is discussed. A modular approach to R/PA design which permits several varieties of receiver to be constructed from basic components is described. It is a basic conclusion that software signal processing of the output of the baseband correlator is the best choice of transition from analog to digital signal processing. High performance sets requiring multiple channels are developed from a generic design by replicating the RF processing segment, and modifying the applications software to provide enhanced state propagation and estimation
Asynchronous multiuser decorrelating detector for AWGN channel
Decorrelating detector is one of the sub-optimum detectors for CDMA applications that generally has better performance than the conventional detector and is near-far resistant. Synchronous decorrelating detector employing DPSK modulation is considered and its simulation results are presented.
Attention is focussed on one-shot decorrelating detector for a two user case for asynchronous transmission, where each symbol interval is considered seperately. Initially the performance of the detector with exact estimation of the relative delay is analyzed and then the effect of inaccurate estimation on the probability of error is discussed
Data Provenance and Management in Radio Astronomy: A Stream Computing Approach
New approaches for data provenance and data management (DPDM) are required
for mega science projects like the Square Kilometer Array, characterized by
extremely large data volume and intense data rates, therefore demanding
innovative and highly efficient computational paradigms. In this context, we
explore a stream-computing approach with the emphasis on the use of
accelerators. In particular, we make use of a new generation of high
performance stream-based parallelization middleware known as InfoSphere
Streams. Its viability for managing and ensuring interoperability and integrity
of signal processing data pipelines is demonstrated in radio astronomy. IBM
InfoSphere Streams embraces the stream-computing paradigm. It is a shift from
conventional data mining techniques (involving analysis of existing data from
databases) towards real-time analytic processing. We discuss using InfoSphere
Streams for effective DPDM in radio astronomy and propose a way in which
InfoSphere Streams can be utilized for large antennae arrays. We present a
case-study: the InfoSphere Streams implementation of an autocorrelating
spectrometer, and using this example we discuss the advantages of the
stream-computing approach and the utilization of hardware accelerators
- …