Anti-interference performance analysis of frequency-shift filter in scenario of multiple WPANs accessing HAN

In the scenario of multiple wireless personal area networks （WPANs） accessing the home area network （HAN）, the frequency-shift （FRESH）filter based on the cyclostationary theory is applied for the anti-interference at the 2. 4 GHz spectrum. The main architecture of multiple WPANs accessing the HAN is proposed. The medium access control（ MAC） -level coordination solution applied in the access point （AP）for the coexistence of different communication protocols within WPAN is discussed. The diagram of the adaptive FRESH filter is described. The anti-interference models of the FRESH filter in the scenario of multiple WPANs accessing the HAN are proposed. The minimum mean square error （MMSE）convergence property of the FRESH filter with the change in the data point number is analyzed. The simulation results indicate that the FRESH filter can effectively extract the signal of interest （SOI） from the interference with the partly overlapped spectrum. Thus, the excellent anti-interference performance of the FRESH filter is validated. Moreover, by both theoretical analysis and simulation, the MMSE convergent property of the FRESH filter is also proven.

Landau damping and frequency-shift of a quadrupole mode in a disc-shaped rubidium Bose–Einstein condensate

The damping and frequency-shift in Landau mechanism of a quadrupole mode in a disc-shaped rubidium Bose-Einstein condensate are investigated by using the Hartree-Fock-Bogoliubov approximation. The practical relaxations of the elementary excitations and the orthometric relation among them are taken into account to obtain advisable calculation formula for damping as well as frequency-shift. The first approximation of Gaussian distribution function is employed for the ground-state wavefunction to suitably eliminate the divergence of the analytic three-mode coupling matrix elements. According to these methods, both Landau damping rate and frequency-shift of the quadrupole mode are analytically calculated. In addition, all the theoretical results agree with the experimental ones.

A wideband frequency-shift keying demodulator for wireless neural stimulation microsystems

This paper presents a wideband frequency-shift keying （FSK） demodulator suitable for a digital data transmission chain of wireless neural stimulation microsystems such as cochlear implants and retinal prostheses. The demodulator circuit derives a constant frequency clock directly from an FSK carrier, and uses this clock to sample the data bits. The circuit occupies 0.03 mm^2 using a 0.6 μm, 2M/2P, standard CMOS process, and consumes 0.25 mW at 5 V. This circuit was experimentally tested at transmission speed of up to 2.5 Mbps while receiving a 5-10 MHz FSK carrier signal in a cochlear implant system.

Gravitational frequency-shift and deflection of light by quintessence

In this paper we investigate the gravitational frequency-shift and deflection of light in the Schwarzschild black hole space-time surrounded by quintessence. With the analytical and numerical methods, we find that the gravitational frequency-shift of light in the Schwarzschild black hole space-time surrounded by the quintessence increases as the values of the normalization factor c increases, but the gravitational frequency-shift of light decreases with the quintessential state parameter Wq increasing. We also calculate the deflection of light by quintessence and find that the deflection rate decreases as the values of the quintessential parameters c and Wq increase.

BLIND CHANNEL ESTIMATION OF SPACE-TIME FREQUENCY-SHIFT KEYING

The decoupled coherent Maximum Likelihood (ML) detection algorithm presented in this letter can sharply reduce the complexity of the receiver as well as provide better error performance under the precondition that channel should be estimated first. Considering the bandwidth inefficiency of Frequency Shift Keying (FSK), the acquisition of channel state information through training sequences will further decrease the transmission efficiency. This letter presents a blind channel estimation algorithm based on noise subspace theory which can acquire channel information without any training symbols. The simulation shows that the algorithm brings about fewer channel estimation errors while the frequency efficiency can be increased.

Modified frequency-shifted interferometer:encoding wavelength into phase

We propose a novel modified frequency-shifted interferometer, where a Mach–Zehnder interferometer is added in order to obtain wavelength information. We use the Hilbert transform to extract the wavelength information from the phase of the interference pattern and construct the relationship between phase and wavelength. The laser wavelength measurement experiment is used to verify the compound interferometer. Experimental results demonstrated that our method could obtain the wavelength from the phase, which is of great significance for demodulation of the fiber Bragg grating based on a frequency-shifted interferometer.

All-in-fiber amplification and compression of coherent frequency-shifted solitons tunable in the 1800–2000 nm range

We report an all-fiber, all-polarization maintaining(PM) source of widely tunable(1800–2000 nm) ultrashort pulses based on the amplification of coherent self-frequency-shifted solitons generated in a highly nonlinear fiber pumped with an Er-doped fiber laser. The system delivers sub-100 fs pulses with energies up to 8.6 nJ and is built entirely from PM optical fibers, without any free-space optics. The all-fiber alignment-free design significantly increases the suitability of such a source for field deployments.

Generation of sub-100 fs pulses tunable from 1700 to 2100 nm from a compact frequency-shifted Er-fiber laser

We report generation of sub-100 fs pulses tunable from 1700 to 2100 nm via Raman soliton self-frequency shift.The nonlinear shift occurs in a highly nonlinear fiber, which is pumped by an Er-doped fiber laser. The whole system is fully fiberized, without the use of any free-space optics. Thanks to its exceptional simplicity, the setup can be considered as an alternative to mode-locked Tm-and Ho-doped fiber lasers.

The application of sample-and-hold circuits in the laser frequency-shifting

A new method of frequency-shifting for a diode laser is realized. Using a sample-and-hold circuit, the error signal can be held by the circuit during frequency shifting. It can avoid the restraint of locking or even lock-losing caused by the servo circuit when we input a step-up voltage into piezoelectric transition （PZT） to achieve laser frequency-shifting.

Landau Damping of Collective Modes in a Disc-Shaped Bose-Einstein Condensate

We investigate the Landau damping of collective modes in an anisotropic Bose Einstein condensate （BEC）, Based on divergence-free analytical solutions for the ground state wavefunction of the condensate and all eigenvalues and eigenfunctions for thermal excited quasiparticles, we make a detailed analytical calculation on coupling matrix elements. We evaluate the Landau damping of a quadrupole collective mode in the BEC with a disc-shaped trap and discuss its dependence on temperature and particle number of the system.

Parameter Estimation Approach of FSK/PSK Radar Signal

A parameter estimation approach of reconnaissance hybrid radar signal combined frequency-shift keying （FSK） and phase-shift keying （PSK） is presented. Firstly, the multi-phase difference is adopted to calculate the instantaneous frequency （IF） of FSK/PSK, then the frequency points of FSK are estimated from the histogram of IF. The code rate of PSK is extracted from the locations of phase discontinuity. Finally, the multi-phase difference of the square of the received signal is computed to estimate the code rate of FSK. The presented algorithm has higher accuracy of parameter estimation when the signal-to-noise ratio （SNR） is above 11 dB.

SOME BLIND FRESH EQUALIZATION ALGORITHMS WITH ANTI-INTERFERENCE CAPABILITIES

Some novel blind FREquency-SHift (FRESH) equalizer algorithms are proposed for the equalization of Finite Impulse Response (FIR) single channel with anti-interference capabilities. These algorithms based on FRESH filter can work well without any training sequence. Simulation results show that the equalizer algorithms can effectively reject many types of interferences and the performances of these new equalizer algorithms are superior to the conventional equalizer algorithms.

Generation of dual and quad‑optical frequency combs in the injected radiation free mode‑locked frequency‑shifted feedback laser

The results of an optoelectronic system—frequency-shifted feedback(FSF)laser experimental examination are presented.The considered FSF laser is seeded only with optical amplifer spontaneous emission(ASE)and operates in the mode-locked regime,whereby the output radiation is sequence of short pulses with a repetition rate determined by the delay time in its optical feedback circuit.In the frequency domain,the spectrum of such a pulse sequence is an optical frequency comb(OFC).These OFCs we call initial.We consider the possibility of tunable acousto-optic(AO)dual and quad-comb frequency spacing downconversion in the FSF laser seeded with ASE and operating in the mode-locked regime.The examined system applies a single frequency shifting loop with single AO tunable flter as the frequency shifter that is fed with several radio frequency signals simultaneously.The initial OFCs with frequency spacing of about 6.5 MHz may be obtained in the wide spectral range and their width,envelope shape and position in the optical spectrum may be tuned.The dual-combs are obtained with a pair of initial OFCs aroused by two various ultrasound waves in the acousto-optic tunable flter(AOTF).The dual-combs frequency spacing is determined by the frequency diference of the signals applied to the AOTF piezoelectric transducer and can be tuned simply.The quad-combs are obtained with three initial OFCs,forming a pair of dual-combs,appearing when three ultrasound frequencies feed the AOTF transducer.The quad-combs frequency spacing is defned by the diference between the frequency spacing of dual-combs.Quad-combs with more than 5000 spectral lines and tunable frequency spacing are observed.The successive frequency downconversion gives the possibility to reduce the OFC frequency spacing form several MHz for initial OFC to tens of kHz for quad-combs.