167,122 research outputs found
Direct bit detection receiver noise performance analysis for 32-PSK and 64-PSK modulated signals
Simple two channel receivers for 32-PSK and 64-PSK modulated signals have
been proposed which allow digital data (namely bits), to be recovered directly instead
of the traditional approach of symbol detection followed by symbol to bit mappings.
This allows for binary rather than M-ary receiver decisions, reduces the amount of
signal processing operations and permits parallel recovery of the bits. The noise
performance of these receivers quantified by the Bit Error Rate (BER) assuming an
Additive White Gaussion Noise interference model is evaluated as a function of E^/N^,
the signal to noise ratio, and transmitted phase angles of the signals. The performance
results of the direct bit detection receivers (DBDR) when compared to that of
conventional phase measurement receivers demonstrate that DBDR's are optimum in
BER sense. The simplicity of the receiver implementations and the BER of the
delivered data make DBDR's attractive for high speed, spectrally efficient digital
communication systems.http://archive.org/details/directbitdetecti00ahmeLieutenant Commander, Pakistan NavyApproved for public release; distribution is unlimited
Fibre segment interferometry using code-division multiplexed optical signal processing for strain sensing applications
A novel optical signal processing scheme for multiplexing fibre segment interferometers is proposed. The continuous-wave, homodyne technique combines code-division multiplexing with single-sideband modulation. It uses only one electro-optic phase modulator to achieve both range separation and quadrature interferometric phase measurement. This scheme is applied to fibre segment interferometry, where a number of long-gauge length interferometric fibre sensors are formed by subtracting pairs of signals from equidistantly placed, weak back reflectors. In this work we give a detailed account of the signal processing involved and, in particular, explore aspects such as electronic bandwidth requirements, noise, crosstalk and linearity, which are important design considerations. A signal bandwidth of ±20 kHz permits the resolution of phase change rates of 2.5 × 104 rad s-1 for each of the four 16.5 m long segments in our setup. We show that dynamic strain resolutions below 0.2 nanostrain Hz-0.5 at 2 m sensor gauge length are achievable, even with an inexpensive diode laser. When used in applications that require only relative strain change measurements, this scheme compares well to more established techniques and can provide high-fidelity yet cost-effective measurements
Adaptive Nonlinear RF Cancellation for Improved Isolation in Simultaneous Transmit-Receive Systems
This paper proposes an active radio frequency (RF) cancellation solution to
suppress the transmitter (TX) passband leakage signal in radio transceivers
supporting simultaneous transmission and reception. The proposed technique is
based on creating an opposite-phase baseband equivalent replica of the TX
leakage signal in the transceiver digital front-end through adaptive nonlinear
filtering of the known transmit data, to facilitate highly accurate
cancellation under a nonlinear TX power amplifier (PA). The active RF
cancellation is then accomplished by employing an auxiliary transmitter chain,
to generate the actual RF cancellation signal, and combining it with the
received signal at the receiver (RX) low noise amplifier (LNA) input. A
closed-loop parameter learning approach, based on the decorrelation principle,
is also developed to efficiently estimate the coefficients of the nonlinear
cancellation filter in the presence of a nonlinear TX PA with memory, finite
passive isolation, and a nonlinear RX LNA. The performance of the proposed
cancellation technique is evaluated through comprehensive RF measurements
adopting commercial LTE-Advanced transceiver hardware components. The results
show that the proposed technique can provide an additional suppression of up to
54 dB for the TX passband leakage signal at the RX LNA input, even at
considerably high transmit power levels and with wide transmission bandwidths.
Such novel cancellation solution can therefore substantially improve the TX-RX
isolation, hence reducing the requirements on passive isolation and RF
component linearity, as well as increasing the efficiency and flexibility of
the RF spectrum use in the emerging 5G radio networks.Comment: accepted to IEE
SARAS 2: A Spectral Radiometer for probing Cosmic Dawn and the Epoch of Reionization through detection of the global 21 cm signal
The global 21 cm signal from Cosmic Dawn (CD) and the Epoch of Reionization
(EoR), at redshifts , probes the nature of first sources of
radiation as well as physics of the Inter-Galactic Medium (IGM). Given that the
signal is predicted to be extremely weak, of wide fractional bandwidth, and
lies in a frequency range that is dominated by Galactic and Extragalactic
foregrounds as well as Radio Frequency Interference, detection of the signal is
a daunting task. Critical to the experiment is the manner in which the sky
signal is represented through the instrument. It is of utmost importance to
design a system whose spectral bandpass and additive spurious can be well
calibrated and any calibration residual does not mimic the signal. SARAS is an
ongoing experiment that aims to detect the global 21 cm signal. Here we present
the design philosophy of the SARAS 2 system and discuss its performance and
limitations based on laboratory and field measurements. Laboratory tests with
the antenna replaced with a variety of terminations, including a network model
for the antenna impedance, show that the gain calibration and modeling of
internal additives leave no residuals with Fourier amplitudes exceeding 2~mK,
or residual Gaussians of 25 MHz width with amplitudes exceeding 2~mK. Thus,
even accounting for reflection and radiation efficiency losses in the antenna,
the SARAS~2 system is capable of detection of complex 21-cm profiles at the
level predicted by currently favoured models for thermal baryon evolution.Comment: 44 pages, 17 figures; comments and suggestions are welcom
Demodulation of Spatial Carrier Images: Performance Analysis of Several Algorithms Using a Single Image
http://link.springer.com/article/10.1007%2Fs11340-013-9741-6#Optical full-field techniques have a great importance in modern experimental mechanics. Even if they are reasonably spread among the university laboratories, their diffusion in industrial companies remains very narrow for several reasons, especially a lack of metrological performance assessment. A full-field measurement can be characterized by its resolution, bias, measuring range, and by a specific quantity, the spatial resolution. The present paper proposes an original procedure to estimate in one single step the resolution, bias and spatial resolution for a given operator (decoding algorithms such as image correlation, low-pass filters, derivation tools ...). This procedure is based on the construction of a particular multi-frequential field, and a Bode diagram representation of the results. This analysis is applied to various phase demodulating algorithms suited to estimate in-plane displacements.GDR CNRS 2519 “Mesures de Champs et Identification en Mécanique des Solide
Video-rate or high-precision: A flexible range imaging camera
A range imaging camera produces an output similar to a digital photograph, but every pixel in the image contains distance information as well as intensity. This is useful for measuring the shape, size and location of objects in a scene, hence is well suited to certain machine vision applications.
Previously we demonstrated a heterodyne range imaging system operating in a relatively high resolution (512-by-512) pixels and high precision (0.4 mm best case) configuration, but with a slow measurement rate (one every 10 s). Although this high precision range imaging is useful for some applications, the low acquisition speed is limiting in many situations. The system’s frame rate and length of acquisition is fully configurable in software, which means the measurement rate can be increased by compromising precision and image resolution.
In this paper we demonstrate the flexibility of our range imaging system by showing examples of high precision ranging at slow acquisition speeds and video-rate ranging with reduced ranging precision and image resolution. We also show that the heterodyne approach and the use of more than four samples per beat cycle provides better linearity than the traditional homodyne quadrature detection approach. Finally, we comment on practical issues of frame rate and beat signal frequency selection
Beyond the fundamental noise limit in coherent optical fiber links
It is well known that temperature variations and acoustic noise affect
ultrastable frequency dissemination along optical fiber. Active stabilization
techniques are in general adopted to compensate for the fiber-induced phase
noise. However, despite this compensation, the ultimate link performances
remain limited by the so called delay-unsuppressed fiber noise that is related
to the propagation delay of the light in the fiber. In this paper, we
demonstrate a data post-processing approach which enables us to overcome this
limit. We implement a subtraction algorithm between the optical signal
delivered at the remote link end and the round-trip signal. In this way, a 6 dB
improvement beyond the fundamental limit imposed by delay-unsuppressed noise is
obtained. This result enhances the resolution of possible comparisons between
remote optical clocks by a factor of 2. We confirm the theoretical prediction
with experimental data obtained on a 47 km metropolitan fiber link, and propose
how to extend this method for frequency dissemination purposes as well
A Novel Adaptive Spectrum Noise Cancellation Approach for Enhancing Heartbeat Rate Monitoring in a Wearable Device
This paper presents a novel approach, Adaptive Spectrum Noise Cancellation (ASNC), for motion artifacts removal in Photoplethysmography (PPG) signals measured by an optical biosensor to obtain clean PPG waveforms for heartbeat rate calculation. One challenge faced by this optical sensing method is the inevitable noise induced by movement when the user is in motion, especially when the motion frequency is very close to the target heartbeat rate. The proposed ASNC utilizes the onboard accelerometer and gyroscope sensors to detect and remove the artifacts adaptively, thus obtaining accurate heartbeat rate measurement while in motion. The ASNC algorithm makes use of a commonly accepted spectrum analysis approaches in medical digital signal processing, discrete cosine transform, to carry out frequency domain analysis. Results obtained by the proposed ASNC have been compared to the classic algorithms, the adaptive threshold peak detection and adaptive noise cancellation. The mean (standard deviation) absolute error and mean relative error of heartbeat rate calculated by ASNC is 0.33 (0.57) beats·min-1 and 0.65%, by adaptive threshold peak detection algorithm is 2.29 (2.21) beats·min-1 and 8.38%, by adaptive noise cancellation algorithm is 1.70 (1.50) beats·min-1 and 2.02%. While all algorithms performed well with both simulated PPG data and clean PPG data collected from our Verity device in situations free of motion artifacts, ASNC provided better accuracy when motion artifacts increase, especially when motion frequency is very close to the heartbeat rate
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