Mfsk signal detection using acousto‐optic joint transform correlator

Multiple frequency shift keying (MFSK) is a modulation suitable for transmitting digital data under fading conditions. A quantitative analysis of MFSK-with-diversity is presented. The MFSK signals on the several diversity channels are presumed to be perturbed independently by Rayleigh fading and additive white Gaussian noise. Also, it is assumed that fading is slow and that envelope, cross-correlation (matched filter) detection is used. The diversity combining method is chosen so that the receiver performs a likelihood-ratio test in deciding which one of K frequencies was transmitted. This optimum comibining method is to square and add the detected outputs of corresponding filters from each diversity channel. Theoretical error probability as a function of signal-energy-per-bit received is derived, and curves are plotted for two-, four-, and eight-frequency MFSK-with-diversity. Bandwidth requirements, as a function of type and order of diversity, are determined. Eight-frequency MFSK with triple diversity has a 21.8-db advantage over simple FSK for transmitting 6-bit characters with a 0.001 error probability.

The design, fabrication, and testing of an acousto-optic-based binary data recorder are described. The data to be recorded are applied to an acousto-optic (AO) Bragg cell illuminated by a pulsed laser diode, and the bit sequence present in the cell is imaged onto a linear detector array. Emphasis was placed on incorporating the optical system and the linear detector array with its control board into a rugged module of modest size capable of recording non-return-to-zero data at rates of 200 Mbits/s or greater. The design specifications of the AO cell and the pulsed laser were based on earlier analysis and proof-of-principle experiments. An in-house-built TI3AsS4 AO cell with a bandwidth of 260 MHz centered at 400 MHz gave 11% diffraction efficiency at the 810 nm wavelength used in the system. When used with a laser pulse of 4 ns full-width at half-maximum, this system had a maximum operating rate of 240 Mbits/s. The same optical system used with an AO cell with 500 MHz bandwidth and a 1.7 ns laser pulse had a maximum rate of 500 Mbits/s. The quality of the optical imaging did not appear to limit the performance, suggesting the possibility of either further increasing the data rate or reducing the size. Possible modifications to explore these options are discussed.

Accurate, low-noise, wideband phased array radar antennas depend on the use of true time delays between microwave elements. A photonic means of generating the required element-to-element phase shifts was developed by Toughlian and Zmuda for systems operating in the VHF frequency range, and extended by Monsay and Caccuitto for operation in the radar C band. The photonic beamformer is based on a heterodyne optical system, in which the reference beam acts as a probe of the acoustic wave in the acousto-optic (AO) cell. It is apparent that the benefits of this photonic system rely greatly on the ability of the probe beam to pick out just the right phase shift/time delay from the acoustic waveform in the AO cell. A basic limitation to system performance could come from intrinsic diffraction effects due to the finite beamwidth of the probe in the AO cell. In addition, the finite size of the photodetector in the system will have an effect on the final SNR. These effects have been studied in detail and their implications for design and performance of the photonic beamformer are discussed. © 1997 Society of Photo-Optical Instrumen- tation Engineers. (S0091-3286(97)01312-3)

This paper presents a multiple Frequency Shift Keying (FSK) transmission system which can simultaneously transmit power and data using magnetic resonance wireless power transfer (MR-WPT). The main challenge of this paper is that the MR-WPT with the Automatic Tuning Assist Circuit (ATAC) enables a multiple FSK communication toward moving objects. The proposed system with ATAC can maintain the resonant state even though the driving frequencies of the transmitter slightly differ from the resonant frequency. Therefore, this characteristic means that it enables simultaneous transmission of power and FSK modulated data at multiple frequencies without a sharp decline in power transmission efficiency. The proposed system is implemented, and it shows double bit data transmission at the same symbol rate with multiple FSK modulation.

Acousto-optic (AO) cells have been used to implement Fourier plane filtering in coherent optical processing systems. AO cells have large time-bandwidth products (>1000) and high frame rates (>10 kHz). The optical input to the AO cell at the Fourier plane consists of several plane waves travelling at different angles. The Bragg matching condition limits the input field of view of the AO cell in the Fourier plane. However, the finite acoustic wave vector spread, optical birefringence, and acoustic beam steering have been used to overcome this limitation. In this paper the relation between the SBW product of an image that can be processed by the AO cell and its time-bandwidth product is derived and experimentally verified. The AO cell in the Fourier plane is suitable for image morphology, and it is shown that the time-bandwidth product requirement for this application is independent of the size of the structuring element, enabling a comparatively large space-bandwidth input to be processed.

Dynamic behavior of an analog-to-digital converter (ADC) based on diffractive optical element(s) (DOE)(s) was studied and found to be in agreement with predictions. The analog signal was translated to an angular deflection of a laser beam by means of an acousto-optic (AO) cell. The number of bits in this experimental demonstration was three, using an eight-element DOE array. The maximum sample rate was found to be 2.5 MS/s, the limiting factor being the transit time for the acoustic wave across the width of the laser beam in the AO cell. The study is intended as a first dynamic demonstration of a proposed ADC scheme previously demonstrated in a quasi-static version. The full potential of the ADC scheme will require the use of a fast tunable diode laser to replace the AO deflection scheme used here.

A photonic means of generating the element-to-element phase shifts required for the operation of a true time delay radar beamformer was developed previously by Toughlian and Zmuda for systems operating in the VHF frequency range, and extended by Monsay for operation in the radar C band. The photonic beamformer is based on an acousto-optic (AO), heterodyne optical system in which the reference beam acts as a probe of the acoustic wave in the AO cell. The time delay of the acoustic waveform readout by the optical probe from various locations along the length of the AO cell can then be imposed directly on the microwave elements of the radar beamformer, providing the correct phase for each element at whatever frequency drives the AO cell. Fundamental systems-oriented calculations are reported. Results for both optical specifications and radar performance specifications are obtained based on a mathematical model of the photonic delay line previously developed by the author. These results address the use of the photonic delay line in a standard radar beamformer.

The direct sequence (DS) spread spectrum communication technique is widely regarded as one of the most effective methods of mitigating the effects of a repeating jammer in military communications systems. The proposed system coupled DS with multiple frequency shift keying (DS/MFSK). It is comprised of a transmitter and a receiver. Non-coherent demodulation is examined, as are the spreading sequences in question. The effect of AWGN and Rayleigh fading channels on the proposed approach's bit error rate (BER) is examined. The investigation demonstrates that even with an 8 dB signal-to-noise ratio, superior outcomes can be achieved; this study's suggested endeavor is to create a novel transceiver system built on the DS/MFSK modular architecture. MFSK modulation prevents multiple-access interference, while DS is typically employed to boost system efficiency across erratic fading. Test results show that reliability on the AWGN channel decreases a little while reliability is greatly enhanced by Rayleigh fading. Moreover, notable improvements in bandwidth efficiency are achieved.

As a driving aid system, automotive radar plays a more and more important role in reducing traffic accidents. In this paper, a simple and efficient automotive radar system based on MFSK (Multiple frequency shift keying) is designed, the system structure and implementation algorithm is presented. This system uses FPGA as the signal processing unit to ensure the response speed. In addition, the designed MFSK waveform algorithm achieved high precision and unambiguous measurement. The effectiveness of the system is verified by experiments and field measurements.

In this paper, a novel encoding concept using frequency diversity strategy and bispectrum-based signal processing is suggested for wireless communication systems. According to proposed approach, binary data (0s and 1s) is transmitted through a pair of mutually orthogonal triplet-signals containing phase coupled frequency tones. Phase coupling in each triplet-signal is given by group of three tones such that phase related to one frequency value is equal to the sum of phases related to other two frequencies. Novel third-order test statistics computed in the form of magnitude bispectrum peak values are suggested for detection and discrimination of received triplet-signals in noisy and fading communication radio channels. In order to discriminate triplet-signals at the receiver, the sensitivity of bispectrum to phase coupling is exploited. Bit error rate (BER) performance assessed for additive Gaussian channel noise and fast fading demonstrates considerable improving of noise and fading protection provided by suggested bispectrum-based technique comparing to the common multiple frequency shift keying (MFSK) scheme using common energy-based strategy for signal detection and discrimination.

A previously described holographic interconnection system uses an array of self-coherent but mutually incoherent sources to generate a set of overlapping holograms in a photorefractive crystal.1,2 In the current work, we assess the performance of this interconnection system experimentally. A linear array of self-coherent but mutually incoherent sources at visible wavelengths is generated by using an acousto-optic (AO) cell (TeO2) and custom analog electronics. Mutual incoherence is obtained by super-imposing a set of diffraction gratings (one for each source) at different frequencies in the AO cell, so that each diffraction grating yields a frequency shift in the corresponding diffracted beam. We present experimental results in Fe:LiNbO3 at 514.5 nm on the fidelity of the photorefractive interconnection in terms of diffraction efficiency, cross talk, and accuracy, as a function of both the number of multiplexed volume holograms and the degree of spatial overlap of the holograms. Some of these experimental results are compared with results obtained from simulation. The measured fidelity of this incoherent/coherent inter connection system is also compared to that of a fully coherent interconnection system.

We review the role of acousto-optic (AO) modulators in programmable real-time image processing. Using one AO cell, 1D high pass filtering and edge enhancement has recently been demonstrated. Two AO cells in tandem can be used to remove asymmetries for using one AO cell. We also show notch filtering characteristics of an AO cell by developing a technique to determine the spatial transfer functions numerically for various cases of beam incidence on an AO modulator. Normal incidence and incidence at twice the Bragg angle are investigated as examples.

Moire contours are seen on a curved surface viewed through a grating when the surface is illuminated with a matched grating. We have been able to replace both the projection and viewing physical gratings with gratings of variable spacing generated in acousto-optic (AO) cells and have been able to observe and record moire contours. The gratings are generated by amplitude modulating 70 MHz AO cells with a 1 to 10 MHz square wave. The gratings become visible on the curved object when the illuminating laser beam is strobed with 50 ns pulses by means of an AO modulator. We give data showing the variation in grating spacing with AO modulation frequency. Figures show the variation of the moire contour spacing with the AO modulation frequency and with target contour. The results for an angled flat plate target are compared with those in the literature.

Direct sequence code division multiple access (DS-CDMA) and M-ary frequency shift keying (MFSK) are two viable modulation schemes for broadband power line communication (PLC) channels, for multi-carrier and single carrier cases respectively. In this paper, we study the bit error rate (BER) performance of a synchronous DS-CDMA system and an MFSK system employing coherent detection for a PLC channel. The background noise present in PLC channel is assumed to follow Nakagami-m distribution as suggested by earlier works. Thereafter a comparison is drawn between the two modulation schemes. In order to draw the comparison at an equal level, we analyse the BER performances of the two systems having the same degree of transmitter/ receiver complexity along with the criteria of same bandwidth occupation, same transmission power as well as the same PLC channel characteristics. The study provides an insight as to how a small change in the parameter of a random variable (RV) describing the background power line noise has a marked influence on the BER performances of the two modulation schemes mentioned above. Also from the simulation results obtained it is quite evident that for a single user case, the MFSK system outperforms the DS-CDMA system at similar data rates.

Constrained optimization on the nonzero-order joint transform correlator constructed with the Mach–Zehnder configuration