Coherent Demodulation Technique Research Articles

A low-complexity ISAC method for LFM-PSK signals using de-chirping and ISAC phase unwrapping techniques

Integrated Sensing and Communication (ISAC) has the potential to revolutionize wireless technology in areas such as autonomous vehicles, the Internet of Things, and unmanned aerial vehicle navigation technology. Nonetheless, conventional processing methods for Linear Frequency Modulation-Phase Shift Keying (LFM-PSK) signals predominantly depend on matched filtering, leading to high sampling rates and computational complexity. In response to these challenges, our research proposes a method to process LFM-PSK signals, which enables the use of de-chirping techniques. Applying the proposed ISAC unwrapping technique makes it possible to selectively recover the phase of the de-chirped LFM-PSK signal. Subsequently, the distance can be calculated by analyzing the slope of the recovered phase. Moreover, by adjusting the threshold in the ISAC unwrapping technique, communication information can be extracted by detecting phase hops associated with PSK. This method offers an attractive alternative to traditional methods such as matched filtering and coherent demodulation techniques. We derive the Cramér-Rao lower bound (CRLB) for ranging. Theoretical analysis and simulation indicate that our method effectively reduces the required sampling rate and provides higher-ranging performance than the matched filtering technique in radar sensing. In high signal-to-noise ratio scenarios, our proposed method delivers a ranging performance close to that of CRLB. Regarding communication, our method has the advantage of lower synchronization requirements, making it more feasible for practical engineering applications than the conventional coherent demodulation method. Furthermore, it also necessitates lower computational resources compared to matched filtering techniques. Importantly, our method allows high device sharing, promoting cost-effective ISAC implementation.

Speech enhancement based on modulation domain processing using coherent harmonic demodulation technique

This Letter presents a single-channel speech enhancement technique based on modulation domain signal processing. In the proposed approach, noise-dominant low-frequency (4–16 Hz) temporal modulation envelopes are discarded based on the modulation domain a priori signal-to-noise ratio criterion. Moreover, the authors have employed coherent harmonic demodulation method which ensures distortion-free filtering of modulators. The experiment results in various acoustic non-stationary noise scenario show that the proposed approach can significantly improve the speech quality and intelligibility while compared to the other existing state-of-the-art baseline techniques.

Characterization of the Phase and Amplitude Modulation of Injection-Locked VCSELs at 1550 nm Using Coherent Optical Demodulation

Experimental measurements of the optical amplitude and phase modulation from an injection-locked VCSEL at 1550 nm are reported. The use of a coherent optical demodulation technique, using a 90° optical hybrid, balanced photodiodes, and a high-speed oscilloscope, has enabled the complete modulation response to be recorded as a function of time. The VCSEL's response to current modulation was examined under various experimental parameters: over a wide frequency range, from kilohertz to gigahertz, for small and large current modulation and for different bias currents. Low-frequency (<;1 MHz) current modulation leads to temperature modulation, where the injection-locked VCSEL acts predominantly as a phase modulator, with a maximum depth of phase modulation, β, of 0.34 π rad. In the high-frequency (>100 MHz) electronic modulation regime, the VCSEL produces significant amplitude and phase modulation, with a maximum depth of amplitude modulation, m, of 35% and β = 0.47 π rad. The VCSEL's thermal response is much more efficient (requires less RF power) in producing phase modulation than its electronic response. The detailed experimental data on the optical phase modulation response of an injection-locked VCSEL are reported for the first time here and are useful for its many applications.

Investigation of cross-polarized heterodyne technique for measuring refractive index and thickness of glass panels

A new mathematical model of cross-polarized heterodyning is proposed for measuring glass panels. An optical system is presented for obtaining relative thickness variation and difference distribution of refractive indices simultaneously, and the dual-balanced coherent demodulation technique is used. The experiment results show that the transmittance of light beam can be less than 0.5% when the vibration amplitude of the glass panels is equal to 5 mm. It takes about 200 s to scan the whole glass sample with size of 1430 × 1360 mm 2. The resolution of the thickness variation is 0.3 μm, and the lateral sampling resolution is 1 mm.

Phase-sensitive reflection technique for characterization of a Fabry–Perot interferometer

Using a radio frequency coherent modulation and demodulation technique, we explicitly measure both the amplitude and the phase response of Fabry-Perot interferometers in reflection. This allows us to differentiate clearly between overcoupled and undercoupled cavities and allows a detailed measurement of the full width at half-maximum, the free spectral range, and the finesse of the cavities.

Measurement of epithermal neutrons by a coherent demodulation technique

Epithermal neutrons have been measured using a neutron dosimeter via a coherent demodulation technique. This dosimeter consists of CsI(Tl)-photodiode scintillation detectors, four of which are coupled to neutron-gamma converting foils of various sizes. Neutron-gamma converting foils of In, Au and Co materials were used, each of which has a large capture cross section which peaks in the epithermal neutron energy region. The type of foil was selected according to the material properties that best correspond to the energy of the epithermal neutrons to be measured. In addition, the proposed technique was applied using Au-foils in order to measure the Cd ratio. The validity of the proposed technique was examined using an 241Am–Be source placed in a testing stack of polyethylene blocks, and the results were compared with the theoretical values calculated by the Monte Carlo calculation. Finally, the dosimeter was applied for measuring epithermal neutrons and the Cd ratio in an experimental beam-tube of the TRIGA reactor.

A high-sensitivity neutron dosimeter using the coherent demodulation technique

We have developed a high-sensitivity neutron dosimeter which incorporates an algorithm of the coherent demodulation technique. This dosimeter is constructed with five CsI(Tl)-p-i-n photodiode scintillation detectors four of which are coupled to neutron-gamma converting foils (Cd or Sm) of varying sizes. The sizes of the foil converters are varied to fit the sine function. When the five-channel dosimeter is exposed to neutrons, capture gammas are emitted in proportion to the size of the corresponding foil and the scintillation detectors' electrical responses vary accordingly. Through modulation-demodulation processing of the detector signals, the neutron fluence can be determined while rejecting the uniform influence of the gamma-ray background. The effectiveness of the dosimeter was confirmed in a mixed neutron/gamma field. A neutron fluence of 1.31/spl times/10/sup 4/ nvt was detected with an efficiency of 4.4% in a gamma background of 6.4 mR=1.6/spl times/10/sup -2/ mC/kg.

A novel gamma dosimeter applied a modified coherent demodulation technique

We have developed a novel gamma dosimeter in which a modified coherent demodulation technique is used for increasing the dosimetric sensitivity. The dosimeter probe consists of a 20 mm-thick collimating Pb-disk, five pairs of CsI(Tl) scintillator-photodiode detectors and five preamplifiers, which are housed in a cylindrical Al-tube. The disk placed just in front of five detectors has four circular-windows which differ in diameter so that the amounts of gamma component entering each detector are controlled. The gamma intensity (dose rate) is evaluated with the cross correlation power spectrum density between the count rate of detector signals and the area of the windows of the disk. The background component was statistically reduced to about 1/63, and then, gamma rays of 0.056mR/h= 1.44 × 10 −8C/kg/h could be detected against a background of 3.52mR/h = 90.8 × 10 −8C/kg/h.

A digital coherent receiver suitable for land-mobile satellite communications

Describes an advanced coherent demodulation technique suitable for land-mobile satellite communications. The proposed technique features a combined narrow/wide band dual open loop (DOL) carrier phase estimator, which effectively enables the coherent receiver to track fast phase fluctuations caused by fading, without degradation in phase slip characteristics. Additionally, an open loop phase estimator has inherent quick recovery performance. Its bit error rate (BER) performance is shown to be superior to that for existing detection schemes, achieving a 10/sup -2/ BER at 6.3 dB E/sub b//N/sub 0/ (0.9 dB greater than the theoretical E/sub b//N/sub 0/ condition for perfect carrier phase tracking) for QPSK over a Rician fading channel with the 10 dB Rician factor and the 1/16 baud rate fading pitch. The paper also describes a quick bit timing recovery scheme, with interpolation, featuring an open loop structure. Further, it presents an experimental digital modem developed through the use of digital signal processors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An advanced method for enhancement of dosimetric sensitivity

Abstract We have developed an advanced method for enhancement of the sensitivity of dosimeters, in which a modified algorithm of the coherent demodulation technique is introduced. A test gamma-dosimeter was produced, which consists of five pairs of CsI scintillator—photodiodes and four Pb plates, and many experiments were performed using 60 Co gamma sources. The background component was reduced to about 1 133 , and then, gamma rays of 0.06 mR/h = 1.55 × 10 −8 C/(kgh) could be detected against a background of 2.66 mR/h = 6.86 × 10 −7 C/(kgh).

A tritium monitoring system using the coherent demodulation technique

The present paper describes a new system for tritium monitoring by means of the coherent demodulation technique. The system consists of a gas mixer, a multi-microprocessor and an ionization chamber. A mixture of sample gas and pure air was fed to the ionization chamber, where the mixing ratio was modulated by a sine function. Demodulation was simultaneously performed by real-time power spectrum analysis of the sampled data. The background was efficiently separated, and a detection limit of 0.02 pCi·cm −3 was realized.

A simplified method for cross correlation power spectrum analysis

In this paper we describe a simplified method for real-time analysis of cross correlation power spectra. Exploiting the symmetrical and periodic nature of the reference function, it became possible to reduce the multiplication steps and hence to save computation time. This method was applied to the measurement of atmospheric tritium gas by means of the coherent demodulation technique, where a signal buried in high-level background noise can be efficiently determined.

The contributions of amplitude-and phase-sensitive detection to the synchronous demodulation in a RF SQUID magnetometer

It is known that the tank-circuit voltage of the rf SQUID carries information about the magnetic flux to be detected in amplitude and phase. The coherent demodulationtechnique utilizes mixing circuits to shift the rf tank voltage spectrum to dc without loss of any signal-information both in amplitude and phase (AM & Pm-detection). Vice versa such a combined detection can be devided into two several detection channels, amplitude sensitive detection (AM) and phase sensitive detection (PM). The contribution of each single mode to the combined detection AM & PM is analysed theoretically in the limit of small magnetic signals and measured in special rf circuits of the magnetometer, which apply PLL-techniques. The influence of feedback is also calculated. For refined studies of the interesting parameters the reference signal of the rf mixer allows to be phase-shifted by an arbitrary amount. All three modes of detections are sketched in diagrams as magnetometeroutput versus phase-shift of that reference signal. In addition, noise analysis is included and measured for vanishing signal. Basic formulas are derived for signal-to-noise ratios. A correlation coefficient is defined for recording correlated noise sources between AM and PM, whereby the possibility of S/N-improvement is pointed out. By computer support the graphs of equations are fitted to measured data with least mean-square deviation. More logical than functional circuit diagrams complete the insight into the treated basic ideas.