Phase-modulated Signals Research Articles

Filtering properties of the tunable microwave photonic filter with stimulated Brillouin scattering

The filtering properties of a continuously tunable single-passband microwave photonic filter based on stimulated Brillouin scattering (SBS) are investigated. The filter utilizes the advantage of combining phase-modulated RF signal and dual-sideband suppressed-carrier pump signal to achieve the SBS-based tunable narrowband filtering. The effects of pump power on the out-of-band rejection (OBR) and 3-dB bandwidth, the optical fiber structure on the resonant sideband, and input RF signal power on the OBR and 3-dB bandwidth are analyzed theoretically and experimentally. The results show that the pump power has the potential of increasing the OBR and tuning 3-dB bandwidth, whereas the RF signal power has nearly no influence on the two parameters.

High-power magnetron transmitter as an RF source for superconducting linear accelerators

A concept of a high-power transmitter utilizing the Continuous Wave (CW) magnetrons, injection-locked by phase-modulated signals, and intended to operate within a wideband control feedback loop in phase and amplitude, is presented. This transmitter is proposed to drive Superconducting RF (SRF) cavities for intensity-frontier GeV-scale proton/ion linacs, such as the projected Fermilab proton linacs or linacs for Accelerator Driven System (ADS). The transmitter consists of two 2-cascade injection-locked magnetrons with outputs combined by a 3-dB hybrid. The transmitter performance was modelled using CW, S-Band, 1kW magnetrons. A wideband dynamic control of magnetrons, required for the superconducting linacs, was realized using the magnetrons, injection-locked by the phase-modulated signals. The capabilities of the magnetrons injection-locked by the phase-modulated signals and adequateness for feeding of SRF cavities have been verified by measurements of the magnetrons phase performance, by measurements of the transfer function magnitude characteristics of single and 2-cascade magnetrons in the phase modulation domain, and by measurements of spectra of carrier frequency of the magnetron. At the ratio of power of locking signal to output power of ≥−13dB (in 2-cascade scheme per magnetron) a phase modulation bandwidth is over 1.0MHz for injection-locked CW single magnetrons and a 2-cascade setup. The carrier frequency spectra (width of ~1Hz at the level of −60dBc) measured with the magnetron, injection-locked by a phase-modulated signal, did not demonstrate broadening at wide range of magnitude and frequency of the phase modulation. The wideband dynamic management of output power of the transmitter model has been first experimentally demonstrated using combined in power magnetrons, injection-locked by the phase-modulated signals. Experiments with the injection-locked magnetrons adequately emulated the wideband dynamic control with a feedback control system, which will allow to suppress all known parasitic modulation of the accelerating field in the SRF cavities. The magnetron transmitter concept, tests of the transmitter models and injection-locking of magnetrons by phase-modulated signals are discussed in this work.

Tunable Microwave Frequency Multiplication by Injection Locking of DFB Laser With a Weakly Phase Modulated Signal

We have demonstrated in this paper a novel tunable microwave frequency multiplication by injecting a weakly phase-modulated optical signal into a DFB laser diode. Signals with multiple weak sidebands are generated by cross-phase modulation of a continuous wave (CW) with short pulses from mode-locked fiber laser. Then, frequency multiplication is achieved by injection and phase locking a commercially available DFB laser to one of the harmonics of the phase modulated signal. The multiplication factor can be tuned by changing the frequency difference between the CW and the free oscillating wavelength of the DFB laser. The experimental results show that, with an original signal at a repetition rate of 1 GHz, a microwave signal with high spectral purity and stability is generated with a multiplication factor up to 60. The side-mode suppression ratio over 40 dB and phase noise lower than -90 dBc/Hz at 10 kHz are demonstrated over a continuous tuning range from 20 to 40.

Experimental Demonstration of Nonlinearity and Phase Noise Tolerant 16-QAM OFDM W-Band (75–110 GHz) Signal Over Fiber System

We propose a nonlinearity and phase noise tolerant orthogonal frequency division multiplexing (OFDM) W-band signal over fiber system based on phase modulation and photonic heterodyne up-conversion techniques. By heterodyne mixing the phase-modulated optical OFDM signal with a free-running laser in the photodiode, the constant envelope OFDM W-band wireless signal is obtained to suppress the nonlinear impairments. Moreover, the phase noises of the beating lasers appear as additive terms to the desired signal, and could be easily filtered out without complex phase noise estimation and compensation algorithms. In our experiment, 4 Gb/s QPSK and 8 Gb/s 16-QAM constant envelope OFDM W-band signals are transmitted over 22.8 km single mode fiber and 2.3 m air distance with achieved bit-error-rate performance below the forward error correction limit.

Photonic generation of arbitrarily phase-modulated microwave signals based on a single DDMZM

We propose and demonstrate a compact and cost-effective photonic approach to generate arbitrarily phase-modulated microwave signals using a conventional dual-drive Mach-Zehnder modulator (DDMZM). One arm (arm1) of the DDMZM is driven by a sinusoidal microwave signal whose power is optimized to suppress the optical carrier, while the other arm (arm2) of the DDMZM is driven by a coding signal. In this way, the phase-modulated optical carrier from the arm2 and the sidebands from the arm1 are combined together at the output of the DDMZM. Binary phase-coded microwave pulses which are free from the baseband frequency components can be generated when the coding signal is a three-level signal. In this case, the precise π phase shift of the microwave signal is independent of the amplitude of the coding signal. Moreover, arbitrarily phase-modulated microwave signals can be generated when an optical bandpass filter is attached after the DDMZM to achieve optical single-sideband modulation. The proposed approach is theoretically analyzed and experimentally verified. The binary phase-coded microwave pulses, quaternary phase-coded microwave signal, and linearly frequency-chirped microwave signal are experimentally generated. The simulated and the experimental results agree very well with each other.

Characterization of Class-F Power Amplifier With Wide Amplitude and Phase Bandwidth for Outphasing Architecture

A 2.14 GHz gallium nitride class-F power amplifier (PA) achieving both high efficiency and phase linearity over a wide frequency range is presented. The broadband PA is designed as one channel of outphasing architecture in cellular base-stations and analyzed in amplitude and phase domains. In amplitude domain, the PA exhibits measured maximum power added efficiency (PAE) of 80.1% with an output power of 40.7 dBm at 2 GHz. The PA achieves PAE higher than 55% over 500 MHz frequency range. The optimum second-harmonic load impedance enables the broadband operation. In phase domain, phase linearity of the PA is characterized by using phase modulation signals derived from single-carrier 10 MHz, two-carrier 40 MHz, and two-carrier 60 MHz long term evolution signals with 6.5 dB peak-to-average power ratio.

Quasi-light Storage for Optical Data Packets

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing of the signals is done in the electrical domain. Direct storage in the optical domain would avoid the transfer of the packets to the electrical and back to the optical domain in every network node and, therefore, increase the speed and possibly reduce the energy consumption of telecommunications. However, light consists of photons which propagate with the speed of light in vacuum. Thus, the storage of light is a big challenge. There exist some methods to slow down the speed of the light, or to store it in excitations of a medium. However, these methods cannot be used for the storage of optical data packets used in telecommunications networks. Here we show how the time-frequency-coherence, which holds for every signal and therefore for optical packets as well, can be exploited to build an optical memory. We will review the background and show in detail and through examples, how a frequency comb can be used for the copying of an optical packet which enters the memory. One of these time domain copies is then extracted from the memory by a time domain switch. We will show this method for intensity as well as for phase modulated signals.

Quasi-light Storage for Optical Data Packets

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing of the signals is done in the electrical domain. Direct storage in the optical domain would avoid the transfer of the packets to the electrical and back to the optical domain in every network node and, therefore, increase the speed and possibly reduce the energy consumption of telecommunications. However, light consists of photons which propagate with the speed of light in vacuum. Thus, the storage of light is a big challenge. There exist some methods to slow down the speed of the light, or to store it in excitations of a medium. However, these methods cannot be used for the storage of optical data packets used in telecommunications networks. Here we show how the time-frequency-coherence, which holds for every signal and therefore for optical packets as well, can be exploited to build an optical memory. We will review the background and show in detail and through examples, how a frequency comb can be used for the copying of an optical packet which enters the memory. One of these time domain copies is then extracted from the memory by a time domain switch. We will show this method for intensity as well as for phase modulated signals.

Performance Analysis and Image Processing of Phase-modulated Signal on Airborne Synthetic Aperture Ladar

In this study, the performance of three phase-modulated signals used in airborne Synthetic Aperture Ladar (SAL) is investigated. The transmitting and receiving modes and imaging processing methods for these signals are studied. Considering that the swath of the airborne SAL is very narrow, in order to reduce the AD sampling rate of the wideband signal, a phase-dechirping receiving mode is proposed for the phase-modulated signal based on the Linear Frequency Modulation (LFM) signal. The imaging simulation results for these three phase-modulated signals validate the effectiveness of the proposed method.

A simple and reliable sensor for accurate measurement of angular speed for low speed rotating machinery

This paper presents the theory and implementation of a novel sensor system for measuring the angular speed (AS) of a shaft rotating at a very low speed range, nearly zero speed. The sensor system consists mainly of an eccentric sleeve rotating with the shaft on which the angular speed to be measured, and an eddy current displacement sensor to obtain the profile of the sleeve for AS calculation. When the shaft rotates at constant speed the profile will be a pure sinusoidal trace. However, the profile will be a phase modulated signal when the shaft speed is varied. By applying a demodulating procedure, the AS can be obtained in a straightforward manner. The sensor system was validated experimentally based on a gearbox test rig and the result shows that the AS obtained are consistent with that obtained by a conventional encoder. However, the new sensor gives very smooth and stable traces of the AS, demonstrating its higher accuracy and reliability in obtaining the AS of the low speed operations with speed-up and down transients. In addition, the experiment also shows that it is easy and cost-effective to be realised in different applications such as condition monitoring and process control.

Study of the methods for developing jamming-immune communications systems with the use of wavelet-modulated signals

The jamming-immune communications organization method is investigated. It is demonstrated that modulating wavelet functions with variable parameters are advantages over phase-modulated (PM) signals. The communications channel model has been constructed. The jamming immunity of PM wideband signals (WBSs), the WBSs modulated by the wavelet with constant parameters, and the WBSs modulated by the wavelet with variable parameters are comparatively analyzed. The imitation resistance is examined.

Application of dual-heterodyne mixing to optical phase-shift keying

Dual-heterodyne mixing has been developed to detect high-speed optical signal waveforms and measure not only the amplitude spectrum but also the phase spectrum. In the present study, this method was applied to a simple experiment that demodulated intensity-modulated terabit signals, and it successfully demodulated an 80 ps non monotonic optical pulse train of 12.5 Gbps 8 bit phase-modulated signals as arbitrary waveforms with dual-heterodyne mixing. These results will be the foundation for phase-shift-keying technology that increases future communication capacity.

Timing, Carrier, and Frame Synchronization of Burst-Mode CPM

In this paper, we propose a complete synchronization algorithm for continuous phase modulation (CPM) signals in burst-mode transmission over additive white Gaussian noise (AWGN) channels. The timing and carrier recovery are performed through a data-aided (DA) maximum likelihood algorithm, which jointly estimates symbol timing, carrier phase, and frequency offsets based on an optimized synchronization preamble. Our algorithm estimates the frequency offset via a one-dimensional grid search, after which symbol timing and carrier phase are computed via simple closed-form expressions. The mean-square error (MSE) of the algorithm's estimates reveals that it performs very close to the theoretical Cramer-Rao bound (CRB) for various CPMs at signal-to-noise ratios (SNRs) as low as 0 dB. Furthermore, we present a frame synchronization algorithm that detects the arrival of bursts and estimates the start-of-signal. We simulate the performance of the frame synchronization algorithm along with the timing and carrier recovery algorithm. The bit error rate results demonstrate near ideal synchronization performance for low SNRs and short preambles.

A Versatile Signal Generator Based on ARM for GPS Jamming

This paper proposed a versatile signal generator which employed an ARM CortexTM-M3 Core as the CPU, a direct digital synthesizer (DDS) chip and a mixer to make the phase modulated signal for GPS jamming. And due to the two parts of the generator, it could be used for intermediate frequency generating and the microwave frequency generating respectively as other two types of generators. With the system, a narrow-band jamming was demonstrated by spectrum and oscilloscope tests for the signals. And the infield test showed the effective range of the jamming was about 200 meters.

Ring resonator-based on-chip modulation transformer for high-performance phase-modulated microwave photonic links

In this paper, we propose and experimentally demonstrate a novel wideband on-chip photonic modulation transformer for phase-modulated microwave photonic links. The proposed device is able to transform phase-modulated optical signals into intensity-modulated versions (or vice versa) with nearly zero conversion of laser phase noise to intensity noise. It is constructed using waveguide-based ring resonators, which features simple architecture, stable operation, and easy reconfigurability. Beyond the stand-alone functionality, the proposed device can also be integrated with other functional building blocks of photonic integrated circuits (PICs) to create on-chip complex microwave photonic signal processors. As an application example, a PIC consisting of two such modulation transformers and a notch filter has been designed and realized in TriPleX(TM) waveguide technology. The realized device uses a 2 × 2 splitting circuit and 3 ring resonators with a free spectral range of 25 GHz, which are all equipped with continuous tuning elements. The device can perform phase-to-intensity modulation transform and carrier suppression simultaneously, which enables high-performance phase-modulated microwave photonics links (PM-MPLs). Associated with the bias-free and low-complexity advantages of the phase modulators, a single-fiber-span PM-MPL with a RF bandwidth of 12 GHz (3 dB-suppression band 6 to 18 GHz) has been demonstrated comprising the proposed PIC, where the achieved spurious-free dynamic range performance is comparable to that of Class-AB MPLs using low-biased Mach-Zehnder modulators.

Contribution of state modelling in efficient MAP symbol-by-symbol demodulation schemes for CPM-MIMO systems

In [1], a state space model was derived for the demodulation of Continuous Phase Modulation (CPM) signals, based on which the demodulation problem was solved through the symbol-by-symbol Bayesian estimation built around the MAP Symbol-by-symbol Detector (MAPSD). In this paper, a new state space model considered in the augmented state composed of the symbol and the phase state is proposed and the corresponding modified MAPSD demodulation scheme is presented. The main contribution of the paper however consists in deriving optimal and suboptimal symbol-by-symbol MAP detection schemes for MIMO systems operating with CPM signals. For this, a state model description of the corresponding demodulation problem is introduced based on which two CPM-MIMO Bayesian demodulators are proposed. The first one uses a Zero Forcing (ZF) pre-processing block to separate the different CPM signals followed by a bank of MAPSD based CPM demodulators. The second demodulator consists in a joint decision feedback (DF) CPM-MIMO MAPSD detector. Simulations confirm the good performance in term of BER of both proposed structures. Particularly, high BER's performance of the partially joint CPM-MIMO-MAPSD/DF is recorded and an emphasis is made on the implementation simplicity of this new detector with no constraint on the modulation index or the alphabet size.

RF Spatial Modulation Using Antenna Arrays

A new method of spatial linear modulation is presented for the RF signal modulation. The constant envelope and phase modulated signals are transmitted to an antenna array and then combined in space; the linear modulation is realized at the same time. The concentric antenna pairs are applied to eliminate the mismatch of phase delay among the modulated signals from different antenna pairs. The measurement results of an RF signal around 2.45 GHz modulated by a 3.84 Mbps QPSK signal are presented. The proposed spatial modulator is able to simplify RF transmitter design and achieve highly efficient power transmission.

All-Optical Photonic Microwave Phase Shifter Based on an Optical Filter With a Nonlinear Phase Response

A new photonic microwave phase shifting structure that can realize a continuous 0° to 360° phase shift with only little frequency dependent amplitude and phase variation over a wide frequency range is presented. It is based on controlling the amplitude and phase of the optical carrier and two antiphase RF modulation sidebands of two phase modulated optical signals by adjusting the wavelength of the optical carriers that fall on the rising and falling edges of an optical bandpass filter with a nonlinear phase response. The new photonic microwave phase shifter has a simple structure. It only requires one normal electro-optic phase modulator and one low-cost commercially available optical filter. It does not involve any electrical component, and has the advantages of small size, lightweight, and robust performance. Experimental results are presented which demonstrate the realization of a continuous 0° to 360° phase shift, with close to flat phase and amplitude response performance over a wideband microwave range.

Development of a digital receiver for range imaging atmospheric radar

In this paper, we describe a new digital receiver developed for a 1.3-GHz range imaging atmospheric radar. The digital receiver comprises a general-purpose software-defined radio receiver referred to as the Universal Software Radio Peripheral 2 (USRP2) and a commercial personal computer (PC). The receiver is designed to collect received signals at an intermediate frequency (IF) of 130MHz with a sample rate of 10MSs−1. The USRP2 digitizes IF received signals, produces IQ time series, and then transfers the IQ time series to the PC through Gigabit Ethernet. The PC receives the IQ time series, performs range sampling, carries out filtering in the range direction, decodes the phase-modulated received signals, integrates the received signals in time, and finally saves the processed data to the hard disk drive (HDD). Because only sequential data transfer from the USRP2 to the PC is available, the range sampling is triggered by transmitted pulses leaked to the receiver. For range imaging, the digital receiver performs real-time signal processing for each of the time series collected at different frequencies. Further, the receiver is able to decode phase-modulated oversampled signals. Because the program code for real-time signal processing is written in a popular programming language (C++) and widely used libraries, the signal processing is easy to implement, reconfigure, and reuse. From radar experiments using a 1-μs subpulse width and 1-MHz frequency span (i.e., 2-MHz frequency bandwidth), we demonstrate that range imaging in combination with oversampling, which was implemented for the first time by the digital receiver, is able to resolve the fine-scale structure of turbulence with a vertical scale as small as 100m or finer.

Double-Referential Holography and Spatial Quadrature Amplitude Modulation

We proposed a double-referential holography (DRH) that allows phase-detection without external additional beams. In the DRH, phantom beams, prepared in the same optical path as signal beams and preliminary multiplexed in a recording medium along with the signal, are used to produce interference fringes on an imager for converting a phase into an intensity distribution. The DRH enables stable and high-accuracy phase detection independent of the fluctuations and vibrations of the optical system owing to medium shift and temperature variation. Besides, the collinear arrangement of the signal and phantom beams leads to the compactness of the optical data storage system. We conducted an experiment using binary phase modulation signals for verifying the DRH operation. In addition, 38-level spatial quadrature amplitude modulation signals were successfully reproduced with the DRH by numerical simulation. Furthermore, we verified that the distributed phase-shifting method moderates the dynamic range consumption for the exposure of phantom beams.