Shift Keying Signals Research Articles

Simultaneous Generation of Wired and Wireless Signals Using a DP-MZM in a RoF System

We experimentally demonstrate a simultaneous generation of independent 10-Gbit/s wired on/off keying (OOK) signal and 20-Gbit/s wireless quadrature phase shift keying (QPSK) signal by using a dual-polarization Mach-Zehnder modulator (DP-MZM) in a millimeter-wave-band radio-over-fiber system at 30 GHz. The polarization directions of two signals are orthogonal, so there is not any interference between two polarizations in the photodiode. By using a 100/200-GHz interleaver, the power penalty after 15-km fiber transmission for the wireless QPSK signal can be reduced from 3.9 to 1.9 dB. As we know, this is the first time to use QPSK modulation format for the wireless signal in the simultaneous generation and delivery of wireless and wired signals by using a dual-polarization modulator.

A 2.4 GHz 2.9 mW Zigbee RF Receiver with Current-Reusing and Function-Reused Mixing Techniques

This study presents a low-power Zigbee receiver with a current-reusing structure and function-reused mixing techniques. To reduce the overall power consumption, a low noise amplifier (LNA) and a power amplifier (PA) share the biasing current with a voltage-controlled oscillator (VCO) in the receiving (RX) mode and transmitting (TX) mode, respectively. The function-reused mixer reuses the radio frequency trans-conductance (RF gm) stage to amplify the down-converted intermediate frequency (IF) signal, obtaining a free IF gain without extra power consumption. A peak detector circuit detects the receiving signal strength and auto-adjusts the biasing current to save power when a strong signal strength is detected. Meanwhile, the peak detector helps to provide a coarse gain control as part of the auto-gain-control function. As part of the IF gain range is shared by the multiple-feedback (MFB) low-pass filter, the number of programmable-gain IF amplifier stages can be reduced, which also means a decrease in power consumption. A prototype of this wireless sensor network (WSN) receiver was designed and fabricated using the TSMC 130 nm CMOS process under a supply voltage of 1 V. The entire receiver realizes a noise figure (NF) of 3.5 dB and a receiving sensitivity of −90 dBm for the 0.25 Mbps offset quadrature phase shift keying (O-QPSK) signal with a power consumption of 2.9 mW.

Analog 28 GHz LoS MIMO Relay System Using a 90° Hybrid Coupler

To enlarge the range of wireless fronthaul and backhaul communication links operating close to the millimeter-wave region, this letter presents a novel line-of-sight (LoS) multiple-input–multiple-output (MIMO) relay system. The analog relay system consists of a simple 90° hybrid coupler to separate two uncorrelated transmit data streams realizing a low complex and cheap system. The functional capability is proven within measurements of two independent 2 × 2 LoS MIMO links at 28 GHz connected by the relay system. A high decoupling of the two independent transmitted data streams of more than 27 dB after the 90° hybrid coupler and a high modulation error rate at the last receiver of around 22 dB could be reached for quadrature phase shift keying (QPSK) and 16-quadrature amplitude modulation (QAM) modulated signals.

Mark ratio modulation over pulse position modulation

• Mark ratio modulation over inverse PPM modulation is proposed for optical label switching. • Two signals are transmitted by one ASK modulation. • The mark ratio difference of PPM and inverse PPM is utilized to deliver an overlay signal. • The mark ratio modulation doesn’t degrade the PPM signal. Orthogonal modulation superimposes non-amplitude-modulated signals on Manchester coded or pulse position modulated amplitude shift keying (ASK) signals, allowing two traffic flows with different bit rates to be modulated on the same wavelength channel, and hence improving spectrum efficiency. Inspired by the orthogonal modulation, this paper proposes a novel modulation format, i.e., mark ratio modulation over pulse position modulation (PPM), which utilizes the mark ratio difference between the PPM symbols and the inverse PPM symbols to deliver an overlaid signal. Better than traditional orthogonal modulation, in the mark ratio modulation over PPM, both low-speed and high-speed traffic flows are modulated by ASK with no need to sacrifice the extinction ratio, while keeping the reception simple and easy. According to theoretical analysis and test, we found 4PPM is a good option, which can balance the trade-off between the PPM signal’s effective bit rate and the mark ratio modulated signal’s quality.

A Phase Calibration Method for Millimeter-Wave Up-Converter Using Electro-Optic Sampling

A phase measurement method using electro-optic sampling of millimeter-wave 4-tone signals is presented for phase calibration of frequency converters. Phase lock loop (PLL) circuits with high comparison frequencies of 2.6 and 15 GHz are used to synchronize the millimeter-wave 4-tone signal with a short optical pulse for low-jitter equivalent time sampling. A 4-tone separate detection method using a lock-in amplifier is applied for precise phase measurement with high frequency resolution. In addition, a phase-correction scheme using 4-tone signals with different frequency spacings is introduced for wideband phase calibration. The error vector magnitude (EVM) of the 10.2-Gbaud quadrature phase shift keying (QPSK) signal with 292.5-GHz carrier frequency is evaluated to confirm the effectiveness of the wideband phase calibration.

Phase-sensitive amplification of a QPSK signal using a dispersion engineered silicon-graphene oxide hybrid waveguide.

We numerically investigate phase-sensitive amplification of a quadrature phase shift keying (QPSK) signal in a 35 µm dispersion engineered silicon-graphene oxide hybrid waveguide. The four-wave mixing efficiency is effectively enhanced by exploiting the ultrahigh Kerr nonlinearity and low loss of graphene oxide in the ultrawide wavelength range. A new structure of dispersion flat silicon-graphene oxide hybrid waveguide is proposed and used to achieve the phase regeneration of a QPSK signal using a dual-conjugated-pump degenerate scheme. The phase-dependent gain and phase-to-phase transfer functions are calculated to analyze the properties of a phase-sensitive amplifier (PSA). The constellation diagrams of the QPSK signal and the error vector magnitude are used to assess the regeneration capacity. The simulation results show that the proposed PSA with a good phase noise squeezing capability has potential applications in all-optical signal processing.

A Novel Envelope Detector Based on Unipolar Metal-Oxide TFTs

The lack of an envelope detector (ED) hinders the realization of bidirectional communication between radio frequency identification (RFID)/near field communication (NFC) tags and readers in metal-oxide thin film transistor (TFT) technology. To solve this, we present a novel ED implementation based on unipolar metal-oxide TFTs. The ED is fully integrated by n-type TFTs and has a novel topology. It can detect an amplitude shift keying (ASK) signal with a minimum modulation depth of 15% and a maximum envelope rate of 8kbit/s, and its minimum supply voltage reaches 2.5 V. These characteristics are greatly improved compared with those of previous works based on complementary organic or hybrid organic/metal-oxide TFTs.

Fractional-Order System Identification and Equalization in Massive MIMO Systems

In this paper, a new methodology for the identification and equalization of massive Multiple-Input Multiple-Output (MIMO) channels in fifth generation (5G) wireless communications is proposed. Channel equalization is performed in state-space, having estimated the channel using the fractional-order Multivariable Output Error State Space (MOESP) system identification algorithm. The proposed fractional-order algorithm is an improvement over its integer-order counterpart that is currently used for state-space channel identification/estimation and state-space channel equalization. When dealing with fractional-order calculus our work adopts the Riemann-Liouville definition. Our numerical results of channel identification having used a chirp signal to excite our massive MIMO system show a lower mean square error (MSE) in channel estimation using the proposed fractional-order MOESP identification algorithm when compared to integer-order MOESP identification algorithm of increased order. Furthermore, following equalization, transmission using Binary phase shift keying (BPSK), Quadrature phase shift keying (QPSK) and 256-Quadrature amplitude modulation (256-QAM) signals show that the symbol error rate (SER) as a function of signal to noise ratio (SNR) performance of the fractional-order equalization algorithm compares to that of the integer-order equalization algorithm. The proposed channel identification algorithm also provides a more parsimonious solution for modelling multipath fading, thus enabling the design of fractional-order equalizers. In addition, they may be used in other applications where high order filtering and more complex control algorithms which are difficult to tune would be needed. Finally, the work has other technological applications where there is a requirement for modelling and control of propagation processes in dispersive media.

Transmission of 128 Gb/s Optical QPSK Signal over FSO Channel under Different Weather Conditions and Pointing Errors

Free space optics (FSO) is a promising technology for high data rate transmission where data is transmitted wirelessly from one place to another. It has a variety of applications nowadays including indoor, outdoor, underwater, and deep space communications. However, the availability of link under various atmospheric conditions is a major concern. In this study, we evaluate the transmission of 128 Gb/s optical quadrature phase shift keying (QPSK) signal under different weather conditions and pointing errors. Simulation parameters such as FSO link range, atmospheric attenuation, pointing loss, and wavelength are taken into consideration. The system performance evaluation parameters including eye diagram, constellation, and received signal to noise ratio (SNR) are compared to find the best performance under different weather conditions. Numerical simulations show that the pointing errors up to 10 µrad and bad weather conditions up to 15 dB attenuation has sever effects on the system performance and we should use digital signal processing and equalization to enhance it.

Parameter Optimization of Generalized S Transform Based on Improved Genetic Algorithm

Background: For the traditional Fourier Transform (FT), it cannot effectively detect the frequency of non-stationary signals with time. Analyzing the local characteristics of time-varying signal by using FT is hard to achieve. Therefore, many time-frequency analysis methods which can meet different needs have been proposed on the basis of the traditional Fourier transform, like the Short Time Fourier Transform (STFT), the widely used Continuous Wavelet Transform (CWT), Wigner-Ville Distribution (WVD) and so on. However, the best time and frequency resolution cannot be achieved at the same time due to the uncertainty criterion. Methods: From the point of view of optimizing time-frequency performance, a new Generalized S Transform (GST) window function optimization method is proposed by combining time frequency aggregation with an improved genetic algorithm in this paper. Results: In the noiseless condition, the Linear Frequency Modulation (LFM), Nonlinear Frequency Modulation (NLFM) and binary Frequency Shift Keying (2FSK) signals are simulated. The simulation results prove that the method can improve the time-frequency concentration and decreasing Rényi entropy effectively. Compared with other four traditional time-frequency analysis methods, the improved GST has more advantages. Conclusion: In this paper, a new method of optimizing the window function in GST based on improved GA is proposed in this paper. Experiments on LFM, NLFM and 2FSK signals show that the proposed method not only has the advantages of high resolution, but also determines the optimal parameters via the time frequency focusing criterion and the Rényi entropy. Compared with the other four kinds of time-frequency analysis methods, the optimized GST based on improved GA in this paper has the best time-frequency focusing.

4 × 32-Gbps Block-Wise QPSK 1200-km SSMF Direct Detection Transmission Based on Delta-Sigma Virtual Carrier Generation

Direct detection (DD) is one of the most attractive solutions for short and medium reach optical fiber transmission in comprehensive consideration of digital signal processing (DSP), power consumption, and cost. Various single side band (SSB) DD techniques have been widely investigated to detect and process the complex signal. In this paper, we propose a novel approach which uses only high-speed digital input/outputs (IO) to generate both quadrature phase shift keying (QPSK) signal and virtual carrier signal. A transmission of 4 × 32 Gb/s QPSK signal over 1200-km standard single mode fiber (SSMF) in block-wise manner has been successfully demonstrated. Only a single polarization in-phase-and-quadrature (IQ) modulator and one single photodiode (PD) are used for each channel. Compared with conventional DSP of coherent detection, the DSP in the proposed scheme is also simplified that only fixed frequency compensation is required without additional phase noise elimination. The overall system complexity has been greatly reduced.

Analysis and Design of High-Order QAM Direct-Modulation Transmitter for High-Speed Point-to-Point mm-Wave Wireless Links

A novel high-speed wireless transmitter (TX) architecture is presented that directly transforms incoming data bits into high-order $4^{M}$ -quadrature amplitude modulation (QAM) constellation by adding multiple quadrature phase shift keying (QPSK) signals with appropriate amplitude ratios. The costly high-speed digital-to-analog converters (DACs) in conventional TXs are thus completely avoided, resulting in a highly integrated solution amenable to ultra-high speeds and operating frequencies. Design tradeoffs are analyzed in detail. Based on this article, a TX prototype at 115-GHz carrier frequency implementing the 16QAM direct-modulation scheme is fabricated in a 180-nm SiGe BiCMOS process ( $f_{\text {MAX}} = 270$ GHz). Wireless testing at a 20-cm distance with 25-dBi horn antennas on both transmitting and receiving side measures 20-Gb/s data rate with an error vector magnitude (EVM) of −15.8 dB and modulated output power of +1 dBm. The TX consumes 520 mW of power and occupies 3.17 mm2 of active area.

Research on MSK Demodulation Method for M-Sequence in IFF System

M-Sequence, short for Maximum Linear Feedback Shift Register Sequence, is widely used in identification friend or foe (IFF) system because of its good equalization and autocorrelation characteristics, and Minimum Shift Keying (MSK) signal has been paid more attention in military communication field because of its excellent signal characteristics. A new demodulation method for MSK modulation signal of M-Sequence is studied. The MSK signal is sampled by A/D converter, and an integration circuit is designed in the FPGA. The same M-Sequence is generated by the same M-Sequence source polynomial as the integrator coefficient. The peak value of the integrated signal is judged to determine the M-Sequence. When the symbol rate is 1 Mbps and the carrier rate is 1 Mbps and M-Sequence is 5 bits, the recognition time of the new method is less than 1 us, which is less than one fifth of the recognition time of the traditional demodulation method. This method simplifies the demodulation process and is easy to implement. It improves the recognition speed of M-Sequence in MSK modulation signal and provides some reference value for the development of IFF system.

Analysis of Spectral Sensing Using Angle-Time Cyclostationarity.

This work presents a novel spectral sensing method for the detection of signals presenting nonlinear phase variation over time. The introduced method is based on the angle-time cyclostationarity theory, which applies transformations to the signal to be sensed in order to mitigate the effects of nonlinear phase variation. The architecture is employed for sensing binary phase shift keying (BPSK) signals, being also compared with time cyclostationarity. The obtained simulation results clearly demonstrate the efficiency of the proposed approach, while presenting improved performance in terms of the detection rate of primary users increased by about 8 dB.

Experimental Mitigation of Atmospheric Turbulence Effect Using Pre-Signal Combining for Uni- and Bi-Directional Free-Space Optical Links With Two 100-Gbit/s OAM-Multiplexed Channels

In this paper, we experimentally demonstrate the mitigation of atmospheric turbulence effects using phase patterns that apply the inverse transmission matrix for pre-compensation in the 200-Gbit/s free-space orbital angular momentum (OAM) multiplexed optical link. In this link, two OAM channels are multiplexed, each carrying a 100-Gbit/s quadrature-phase shift keying (QPSK) signal. In the uni-directional (forward) link, a combination of two OAM modes is generated using a designed phase pattern in each of the two channels. After the two channels are multiplexed, each OAM mode will carry the combination of signals from both channels. Such beams could perform the inverse function of turbulence-induced crosstalk. We explore the link performances including crosstalk and bit error rate (BER) under 6 different turbulence realizations with a Fried parameter of 1-mm. We find the following: (a) the inter-channel crosstalk is reduced by up to 21 dB; (b) the inter-channel crosstalk is below −10 dB for the 6 turbulence realizations when the compensation is applied; (c) a BER below the FEC limit could be realized for the 6 turbulence realizations with an optical signal-to-noise ratio (OSNR) of 16.8 dB for the uni-directional link with the compensation. Moreover, the post-compensation is also investigated for the two 100-Gbit/s OAM-multiplexed backward channels in the bi-directional link. For the backward channels, the phase patterns are used to mitigate turbulence-induced crosstalk at the receiver for backward channels, and the inter-channel crosstalk is reduced by up to 16 dB.

Compact polarization diversity Kramers-Kronig coherent receiver on silicon chip.

We design and fabricate a compact silicon photonic integrated circuit (PIC) for polarization diversity heterodyne coherent detection. This PIC integrates two optical gratings for fiber coupling and polarization diversity, two germanium single-ended photodetectors (PDs), and three multimode interferometers (MMIs) for power splitting and optical hybrid. The device is highly compact with a footprint of 0.68mm × 0.9mm. We test this PIC with heterodyne detection experiments of polarization division multiplexed (PDM) 32Gbaud quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM) signals. The signal-signal beat interference due to square-law detection is separately mitigated with the Kramers-Kronig (KK) scheme for each of the two orthogonal polarizations. To our best knowledge, we report the first PDM-KK coherent receiver in PIC with a capability of detecting 256Gb/s 16QAM signals, which shows the most compact size among the silicon coherent receivers ever reported.

Reconfigurable photonic generation of background-free microwave waveforms with multi-format

Photonic generation of background-free microwave waveforms with multi-format and parameter tunability is proposed and demonstrated. In the approach, the polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) is employed to modulate the linearly polarized lightwave. After properly adjusting the modulation indices of the PDM-MZM, background-free square and triangular waveforms will be obtained after heterodyne detection; by driving the polarization modulator with binary sequence, the structure can also generate background-free digital modulation signals, including amplitude shift keying (ASK), phase shift keying (PSK) and frequency shift keying (FSK) signals via the same structure. The approach is investigated by simulations. Square and triangular waveforms with repetition rate of 20 GHz are obtained, and digital modulation signals with modulation rate of 2 Gbit/s are generated. The proposed generator shows flexible tunability of carrier frequency, bit rate and modulation format. The stability of the structure is verified by phase drift, polarization error and RF driven voltage offset.

Sub-Nyquist Sampling of BPSK Signals via Feedback Structure

We consider the problem of sampling binary phase shift keying (BPSK) signals, which are widely used in communications and radar systems. Although sub-Nyquist sampling of such signals has been treated in various works, giant samples were needed. In this brief, a new sub-Nyquist sampling method based on a multichannel feedback structure is proposed for BPSK signals, which requires fewer samples. BPSK signals can be characterized by a finite number of parameters, namely, the carrier frequency, amplitude, locations of discontinuities, and phase of each symbol. Our feedback structure consists of a main channel and a feedback channel. The carrier frequency and amplitude can be estimated by the estimation of signal parameters by a rotational invariance technique algorithm in the main channel, while the phases and locations of discontinuities can be estimated by the annihilating filter in the feedback channel. The effectiveness of the proposed method is verified via simulations. In a noiseless situation, for a seven-segment BPSK signal lasting $1~{\mu } {s}$ with a 500-MHz carrier frequency, the equivalent sampling rate of the proposed method is only 3.8% of the carrier frequency, and much less than the Nyquist sampling rate of the signal. Finally, we analyze the effect of noise and present a robust reconstruction algorithm. Simulation results show that the proposed method exhibits better noise robustness than previous approaches.

Experimental demonstration of tunable de-aggregation from 16-QAM to 4-PAM for two wavelength multiplexed channels using wave mixing in a single nonlinear element to map constellation onto axes

We experimentally demonstrate tunable de-aggregation of two data carrying optical channels using nonlinear wave mixing. For each channel, the signal and its conjugate are coherently added and subtracted in order to map the constellation points onto real and imaginary axes, respectively. Each of two 10 and 15 Gbaud optical channels with a format of 16-quadrature amplitude modulation (16-QAM) are de-aggregated into two 4-level pulse amplitude modulation (4-PAM) signals. We use the same technique to de-aggregate quadrature phase shift keying (QPSK) signals into two binary phase shift keying (BPSK) signals at baud rates of 10 and 15 Gbaud for both channels. System performance is evaluated in terms of the optical signal-to-noise ratio (OSNR), and penalty of ∼0.7 dB is observed at bit error rate (BER) of 10−3.

Equivalent photonic switch for microwave frequency shift keying signal generation.

A photonic microwave frequency shift keying (FSK) signal generator is proposed and experimentally demonstrated based on an equivalent photonic switch (EPS). The EPS is constructed using a polarization-multiplexing dual-drive Mach-Zehnder modulator (PM-DMZM). By properly controlling the data sequences and RF signals applied to the PM-DMZM, microwave FSK signals with flexible frequency intervals can be obtained. The proposed FSK signal generator features the advantages of a simple structure, low loss, good stability, and great frequency tunability. In addition, the proposed setup can also be easily reconfigured to generate microwave amplitude shift keying and phase shift keying signals. The experimental results show that 2Gb/s at 5/14GHz and 1Gb/s at 6/20GHz microwave FSK signals are successfully generated, after transmission over 5km single-mode fiber. The required received optical power at 7% forward error correction threshold is only -14.48 dBm.