Quaternary Phase-shift Keying Research Articles

New Accurate Approximation for Average Error Probability

This paper proposes new accurate approximations for average error probability (AEP) of a communication system employing either $M$ -phase-shift keying (PSK) or differential quaternary PSK with Gray coding (GC-DQPSK) modulation schemes over generalized fading channel. Firstly, new accurate approximations of error probability (EP) of both modulation schemes are derived over additive white Gaussian noise (AWGN) channel. Leveraging the trapezoidal integral method, a tight approximate expression of symbol error probability for $M$ -PSK modulation is presented, while new upper and lower bounds for Marcum $Q$ -function (MQF) of the first order, and subsequently those for bit error probability (BEP) under DQPSK scheme, are proposed. Next, these bounds are linearly combined to propose a highly refined and accurate BE P’s approximation. The key idea manifested in the decrease property of modified Bessel function $I_{v}$ , strongly related to MQF, with its argument $v$ . As an application, these approximations are used to tackle AEP’s approximation under $\kappa -\mu $ shadowed fading. Numerical results show the accuracy of the presented approximations compared to the exact ones.

ELF/VLF Communication Experiment by Modulated Heating of Ionospheric Auroral Electrojet at EISCAT

Amplitude modulation high-frequency (HF) radio waves at extremely low frequencies (ELF, 0.3-3 kHz) or very low frequencies (VLF, 3-30 kHz), heating the ionosphere, can nonlinearly modulate the auroral electrojet to produce ELF/VLF waves for long-distance communication. This article presents the results of the first ELF/VLF communication experiments being conducted at Tromsø, where the European Incoherent Scatter Scientific Association (EISCAT) HF facility is located. The ELF/VLF waves from the ionosphere are modulated by quaternary phase shift keying (QPSK) and used for communication. The ELF signals of 2017 Hz at 20 and 100 b/s, as well as VLF signals of 3517 Hz at 20, 100, and 400 b/s, received by a ground-based receiver (15 km away from the heater) were decoded, albeit with a high bit error rate (BER) for 3517 Hz at 20 b/s. With the decoding principle of QPSK, we attempted to find a solution to reduce the BER for future communication experiments. Based on the results of the ground experiment, the transmitted signals of 2017 Hz at 20 b/s were selected in the China Seismo-Electromagnetic Satellite (CSES) reception experiments. In a first, we demonstrate that ELF communication signals generated by the amplitude modulation heating of the ionosphere have been successfully received by the satellite and the ground-based receiver. These experimental results confirm that the ELF/VLF waves radiated by amplitude modulation heating of the auroral electrojet can be used for long-distance communication in future.

Multiplexed terrestrial free space optic system design using dual polarized multicarrier transmission technique

A hybrid technique for terrestrial free space optic (FSO) system has been proposed in this paper. The hybrid technique is a combination of 8 × 40 Gbps dense wavelength-division multiplexing and a multicarrier transmission (MCT) scheme such as coherent optical orthogonal frequency-division multiplexing (CO-OFDM). The prime design objective is to minimize the issues related to the terrestrial FSO-based system for atmospheric turbulence, bandwidth management, and receiver sensitivity. The cyclic prefix bits have been added with the data symbols of CO-OFDM, which minimizes the effect of nonlinearity due to atmosphere and reduces intersymbol interference. The dual-polarized quadrature phase-shift keying (DP-QPSK) sequence is used to modulate the subcarriers of the MCT system. DP-QPSK is very well known for its optical signal-to-noise ratio tolerance. It has been found that, by the incorporation of a hybrid scheme in the FSO system, a propagation range of 2.2 km in atmospheric turbulence regime for the targeted bit error rate (BER) of 3.8 × 10 − 3 or log of BER of −2.42 is achieved. A contrast performance comparison has also been carried out for the proposed hybrid system with different advanced modulation schemes such as differential quaternary phase-shift keying and four-level quadrature amplitude modulation. The Gamma-Gamma-type distribution function is considered for estimating the turbulence effect of the free space channel. Mathematical modeling related to the proposed system has also been incorporated for better analysis. This type of hybrid technique for the FSO system with the incorporation of DP-QPSK modulation format will give more technical feasibility to the modern communication system.

QPSK Modulation in the O-Band Using a Single Dual-Drive Mach–Zehnder Silicon Modulator

Keeping up with bandwidth requirements in next generation short- and long-reach optical communication systems will require migrating from simple modulation formats such as on-off keying to more advanced formats such as quaternary phase-shift keying (QPSK). In this paper, we report the first demonstration of QPSK signal generation in the O-band using a silicon dual-drive Mach–Zehnder modulator (DD-MZM). The performance of the silicon DD-MZM is assessed at 20 Gb/s and compared against a similar DD-MZM based on LiNbO3, showing a limited implementation power penalty of only 1.5 dB.

Code shift keying based joint radar and communications for EMCON applications

Due to the explosion in the demand for broadband wireless services by consumers, wireless network service providers require increased frequency allocations from an already crowded frequency spectrum. In an effort to satisfy the increased frequency spectrum requirements of wireless communications networks, several methods have been proposed to allow communication systems and radars to co-exist within the same bandwidth or adjacent frequency bands while minimizing or preventing mutual interference. Most methods explored in the literature focus on the use of cognitive sensing and dynamic spectrum allocation. Other proposed methods to prevent mutual interference between radar and communications systems focus on waveform design. In this manuscript, a dual function communication and radar system with EMCON applications is investigated that uses Gold or Kasami codes in a code shift keying digital modulation scheme. The use of both binary phase shift keying (BPSK) and quaternary phase shift keying (QPSK) to modulate the code bits is investigated. The communications signal is used as the radar signal to implement a pseudo-random BPSK or QPSK coded radar. The symbol error rate (SER) of the communication system is determined through Monte Carlo simulations and compared to an SER upper bound for M-ary frequency shift keying. The radar signal's periodic autocorrelation function (PACF) and periodic ambiguity function are also examined demonstrating the schemes potential for use in a low probability of intercept radar application. The radar signal's characteristics are compared when using pseudo-random BPSK and QPSK modulations.

Hybrid-Domain Parallel Decision Feedback Equalization for Single-Carrier Block Transmission

To combat intersymbol interference (ISI) in single-carrier block transmission systems, the hybrid decision feedback equalizer (HDFE) is a low-complexity, symbol-by-symbol detector that combines a frequency-domain feedforward filter and a time-domain feedback filter. To mitigate the error propagation effect of HDFE while preserving the implementation advantages of frequency-domain equalization, we propose the parallel HDFE (P-HDFE) algorithm that operates, based on the reliability of the decision variable, as an ordinary HDFE or a sequence detector that consists of multiple HDFEs running in parallel. Our study shows that, at moderate to high signal-to-noise ratios (SNRs), P-HDFE outperforms HDFE with little increase in complexity. We analyze the symbol error rate of P-HDFE at high SNRs for the case of quaternary phase-shift keying and static ISI channels, accounting for error propagation and residual ISI. Simulations demonstrate the accuracy of the analysis.

Average SEP of AF Relaying in Nakagami-m Fading Environments

This paper is devoted to an investigation of an exact average symbol error probability (SEP) for amplify and forward (AF) relaying in independent Nakagami-m fading environments with a nonnegative integer plus one-half m, which covers many actual scenarios, such as one-side Gaussian distribution (m=0.5). Using moment generating function approach, the closed-form SEP is expressed in the form of Lauricella multivariate hypergeometric function. Four modulation modes are considered: rectangular quadrature amplitude modulation (QAM), M-ary phase shift keying (MPSK), M-ary differential phase shift keying (MDPSK), and π/4 differential quaternary phase shift keying (DQPSK). The result is very simple and general for a nonnegative integer plus one-half m, which covers the same range as integer m. The tightness of theoretical analysis is confirmed by computer simulation results.

Terrestrial Trunked Radio (TETRA) exposure of neuronal in vitro networks

Terrestrial Trunked Radio (TETRA) is a worldwide common mobile communication standard, used by authorities and organizations with security tasks. Previous studies reported on health effects of TETRA, with focus on the specific pulse frequency of 17.64Hz, which affects calcium efflux in neuronal cells. Likewise among others, it was reported that TETRA affects heart rate variability, neurophysiology and leads to headaches. In contrast, other studies conclude that TETRA does not affect calcium efflux of cells and has no effect on people's health.In the present study we examine whether TETRA short- and long-term exposure could affect the electrophysiology of neuronal in vitro networks. Experiments were performed with a carrier frequency of 395MHz, a pulse frequency of 17.64Hz and a differential quaternary phase-shift keying (π/4 DQPSK) modulation. Specific absorption rates (SAR) of 1.17W/kg and 2.21W/kg were applied.In conclusion, the present results do not indicate any effect of TETRA exposure on electrophysiology of neuronal in vitro networks, neither for short-term nor long-term exposure. This applies to the examined parameters spike rate, burst rate, burst duration and network synchrony.

Blind Nonlinearity Equalization by Machine-Learning-Based Clustering for Single- and Multichannel Coherent Optical OFDM

Fiber-induced intra- and interchannel nonlinearities are experimentally tackled using blind nonlinear equalization (NLE) by unsupervised machine-learning-based clustering (MLC) in ∼46-Gb/s single-channel and ∼20-Gb/s (middle-channel) multichannel coherent multicarrier signals (orthogonal frequency-division multiplexing (OFDM) based). To that end, we introduce, for the first time, hierarchical and fuzzy-logic C -means (FLC)-based clustering in optical communications. It is shown that among the two proposed MLC algorithms, FLC reveals the highest performance at optimum launched optical powers (LOPs), while at very high LOPs, hierarchical can compensate more effectively nonlinearities only for low-level modulation formats. When employing binary phase-shift keying and quaternary phase-shift keying, FLC outperforms K-means, fast-Newton support vector machines, supervised artificial neural networks, and NLE with deterministic Volterra analysis. In particular, for the middle channel of a QPSK wavelength-division multiplexing coherent optical OFDM system at optimum −5 dBm of LOP and 3200 km of transmission, FLC outperforms Volterra-NLE by 2.5 dB in Q-factor. However, for a 16-QAM single-channel system at 2000 km, the performance benefit of FLC over inverse Volterra-series transfer function reduces to ∼0.4 dB at a LOP of 2 dBm (optimum). Even when using novel sophisticated clustering designs in 16 clusters, no more than additional ∼0.3-dB Q-factor enhancement is observed. Finally, in contrast to the deterministic Volterra-NLE, MLC algorithms can partially tackle the stochastic parametric noise amplification .

High-Speed, High-Performance DQPSK Optical Links with Reduced Complexity VDFE Equalizers

Optical transmission technologies optimized for optical network segments sensitive to power consumption and cost, comprise modulation formats with direct detection technologies. Specifically, non-return to zero differential quaternary phase shift keying (NRZ-DQPSK) in deployed fiber plants, combined with high-performance, low-complexity electronic equalizers to compensate residual impairments at the receiver end, can be proved as a viable solution for high-performance, high-capacity optical links. Joint processing of the constructive and the destructive signals at the single-ended DQPSK receiver provides improved performance compared to the balanced configuration, however, at the expense of higher hardware requirements, a fact that may not be neglected especially in the case of high-speed optical links. To overcome this bottleneck, the use of partially joint constructive/destructive DQPSK equalization is investigated in this paper. Symbol-by-symbol equalization is performed by means of Volterra decision feedback-type equalizers, driven by a reduced subset of signals selected from the constructive and the destructive ports of the optical detectors. The proposed approach offers a low-complexity alternative for electronic equalization, without sacrificing much of the performance compared to the fully-deployed counterpart. The efficiency of the proposed equalizers is demonstrated by means of computer simulation in a typical optical transmission scenario.

Noncoherent detection of DQPSK in OFDM systems using predictive VA

Noncoherent detection of differential quaternary phase shift keying (DQPSK) signals in OFDM systems is efficiently implemented using a predictive Viterbi algorithm (VA) operating on a trellis with just ST = MP−1 states instead of MP states, where M denotes an M-ary PSK constellation and P denotes the order of the prediction filter. The prediction filter coefficients are generated based on the channel DFT alone making a high SNR approximation, since the estimation of the noise-variance using training symbols results in loss of throughput.

32 channel DQPSK DWDM-PON for local area network using dispersion compensation fiber

In the contest to improving optical channel rates in dense wavelength multiplexing (DWDM) service to realize 40Gb/s, different adjustment and coherent detection plans are being investigated. In this paper, we present differential quaternary phase-shift keying (DQPSK) balance for the arrangement of a 32-channel DWDM in a Local Area Network (LAN).

Concise SER Analysis of Differential Quaternary Phase Shift Keying with Gray Coding Over Composite Multipath Shadowing Channels

To effectively assess the symbol error rate (SER) performance achieved by π/4 differential quaternary phase shift keying (π/4-DQPSK) with Gray coding over Rician-Nakagami fading channels, a simple closed-form asymptotic SER formula is derived, which is much simpler than the existing exact SER expression. From the proposed simple closed-form formula, we can obtain some useful insights into the achievable error rate performance for the DQPSK modulation with Gray coding for various channel conditions in the high signal-to-noise ratio (SNR) regions.

Photonic aided bandpass sampling in coherent phase modulated radio-over-fiber links

We have experimentally presented a digital coherent receiver employing photonic aided bandpass sampling technology for phase-modulated radio-over-fiber (RoF) links. An optical intensity modulator (IM) is utilized as the bandpass sampler which performs encoded on–off keyed pulse sequence on the optical local oscillator. Quaternary Phase Shift Keying (QPSK) modulated data signal with 20MHz bandwidth at 5.2GHz, 10.2GHz and 15.2GHz RF carrier frequency is experimentally demonstrated to be successfully detected by using balanced photodiodes (BPDs) with only 800MHz analog bandwidth. It demonstrates that the required analog bandwidth of BPDs and ADCs can be dramatically reduced in a direct sampled coherent RoF communications system.

Distributed Aggregation of Spectrally Efficient Single- and Dual-Polarization Super-Channels by Optical Frequency Conversion in Fiber

Recently developed upgrade options for distributed ultra-dense frequency-division multiplexing toward large aggregation capacity are discussed. The concept, originally demonstrated for distributed coherent optical orthogonal frequency-division multiplexing, is based on optical frequency conversion in fiber. It enables precise frequency allocation of the successively multiplexed subcarriers within the super-channel without the need of absolute optical frequency control, i.e., allowing for use of free-running lasers at the individual multiplexing nodes. Follow-up experiments proved the applicability of this concept also to Nyquist wavelength-division multiplexing (WDM) with extremely small guard bands by successfully demonstrating the distributed aggregation of a spectrally efficient 400-Gb/s single-polarization zero-guard-band Nyquist-WDM super-channel using 4× 28-GBd 16-ary quadrature-amplitude modulation (16QAM) subcarriers. Recently, we further extended the concept to distributed generation of dual-polarization super-channels. This extension allowed for the distributed aggregation of a 400-Gb/s Nyquist-WDM super-channel using 4× 28-GBd polarization-division multiplexed quaternary phase-shift keying (PDM-QPSK) subcarriers. In this invited contribution, we review and compare in detail both experiments enabling 400-Gb/s aggregation capacity. Additionally, we discuss a viable option for operation under random fiber birefringence regardless of the polarization-dependent nature of the underlying optical frequency conversion process.

Mitigation of Fiber Nonlinearity Effects in Ultra High-Dense WDM System by Using Fractional Fourier Transform for 32 Channel System

The optical signal is severely degraded when transmitted in the fiber due to both the linear and nonlinear distortions. It is well known that, the linear distortions in single mode fiber include chromatic dispersion (CD) and polarization-mode dispersion (PMD) while self-phase modulation (SPM), cross phase modulation (XPM) and four-wave mixing (FWM) are considered the most among nonlinear distortions. A method called Fractional Fourier Transform (FRFT) has been applied to mitigate fiber nonlinearity impairments. In this work, 10 Gb/s optical fiber system with five spans, each of length 60 km, for three types of modulation formats (Return-to-Zero Differential Phase Shift Keying (RZ-DPSK), Return-to-Zero Differential Quaternary Phase Shift Keying (RZ-DQPSK) and Carrier-Suppressed Return-to-Zero (CSRZ)), single and multi-channel transmission systems are designed and simulated using “OptiSystem (2011) version 10.0” software package. The BER of thirty two channel systems (channel No.16) at bit rate 10 Gb/s per channel, 300 km link length of CSRZ modulation format with channel spacing of 50 GHz at SNR 10 dB without FRFT is 10-4.6 and 10-6.4 with FRFT. The BER of thirty two channel system (channel No.16) at bit rate 10 Gb/s per channel, 300 km link length of CSRZ modulation format with channel spacing of 25 GHz at SNR 10 dB without FRFT is 10- 2.56 and 10-3.24 with FRFT.

Performance Analysis of DWDM System for Different Modulation Schemes Using Variations in Channel Spacing

AbstractThis paper reflects the analytical study of dense wavelength division multiplexed optical network with different number of channels at various channel spacing in order to achieve higher data rates by means of few advanced modulation schemes. Bit error rate and quality factor are being analyzed with the variation in number of channels, channel spacing and transmission length of fiber. Advanced modulation schemes being compared here are carrier suppressed return to zero (CSRZ), duobinary return to zero (DRZ), modified duobinary return to zero (MDRZ), 33 % differential phase shift keying (33 % DPSK), 66 % DPSK and differential quaternary phase shift keying (DQPSK). It is keenly observed that CSRZ scheme with 100 GHz channel spacing serves best performance in terms of max. Q factor, min. BER and maximum transmission coverage upto 4,000 km for 16 and 32 channels DWDM system since CSRZ is high tolerant to nonlinear effects. On the other hand, MDRZ scheme with 75 GHz channel spacing exhibits transmission coverage upto 4,000 km and 4,500 km for 16 and 32 channels respectively, but with degraded signal due to effect of inter symbol interference (ISI).

Irregular Trellis for the Near-Capacity Unary Error Correction Coding of Symbol Values From an Infinite Set

Irregular joint source and channel coding (JSCC) scheme is proposed, which we refer to as the irregular unary error correction (IrUEC) code. This code operates on the basis of a single irregular trellis, instead of employing a set of separate regular trellises, as in previous irregular trellis-based codes. Our irregular trellis is designed with consideration of the UEC free distance, which we characterize for the first time in this paper. We conceive the serial concatenation of the proposed IrUEC code with an irregular unity rate code (IrURC) code and propose a new EXtrinsic Information Transfer (EXIT) chart matching algorithm for parametrizing these codes. This facilitates the creation of a narrow EXIT tunnel at a low $E_\text{b}/N_0$ value and provides near-capacity operation. Owing to this, our scheme is found to offer a low symbol error ratio (SER), which is within 0.4 dB of the discrete-input continuous-output memoryless channel (DCMC) capacity bound in a particular practical scenario, where gray-mapped quaternary phase shift keying (QPSK) modulation is employed for transmission over an uncorrelated narrowband Rayleigh-fading channel with an effective throughput of $0.508 \,\text{bit}\,{\text{s}}^{-1}\,{\text{Hz}}^{-1}$ . Furthermore, the proposed IrUEC–IrURC scheme offers a SER performance gain of 0.8 dB, compared to the best of several regular and irregular separate source and channel coding (SSCC) benchmarkers, which is achieved without any increase in transmission energy, bandwidth, transmit duration, or decoding complexity.

Frequency Offset Estimation With Multi-Steps Interpolation for Coherent Optical Systems

We investigate a frequency offset estimation (FOE) algorithm based on improved fast Fourier transform (FFT) for coherent optical systems. The algorithm implements FFT operation with a small number of samples and then adopts multi-steps interpolation with the increasing number of samples to improve the estimation accuracy gradually. In a 28-GBd coherent quaternary phase-shift keying system, simulation results show that the proposed algorithm reaches the same estimation accuracy with least-squares FOE algorithm that utilizes 64 time spans (LS-64) under the same total number of samples L. But the number of complex multiplications required by the proposed algorithm is just 7.26% and 6.75% of that required by LS-64 at L = 1024 and L = 2048, respectively.

Coherent ultra dense wavelength division multiplexing passive optical networks

In this paper, we firstly review the progress in ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON), by making use of the key attributes of this technology in the context of optical access and metro networks. Besides the inherit properties of coherent technology, we explore different modulation formats and pulse shaping. The performance is experimentally demonstrated through a 12×10Gb/s bidirectional UDWDM-PON over hybrid 80km standard single mode fiber (SSMF) and optical wireless link. High density, 6.25GHz grid, Nyquist shaped 16-ary quadrature amplitude modulation (16QAM) and digital frequency shifting are some of the properties exploited together in the tests. Also, bidirectional transmission in fiber, relevant in the context, is analyzed in terms of nonlinear and back-reflection effects on receiver sensitivity. In addition, as a basis for the discussion on market readiness, we experimentally demonstrate real-time detection of a Nyquist-shaped quaternary phase-shift keying (QPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array (FPGA).