Continuous Phase Frequency Shift Keying Research Articles

New spectrally efficient spread spectrum signals based on atomic functions

Formulation of the problem. Spectrally efficient signals have become the basis of various radio interfaces in recent decades. Having several advantages in the occupied frequency band compared to phase shift keyed (PSK) signals, they are successfully used in mobile communication systems (GSM), and also find application in space communication and navigation systems. Recent studies in the field of "design" of spread spectrum signals (SSS) with PSK have shown the promise of using atomic functions (AF) to modernize the shape of the chip of video signal pseudo-random sequences (PRS), thus, the logical continuation is the approbation of atomic shapes of chips in the synthesis of continuous phase (CP) frequency shift keying (FSK) SSS, potentially providing bandwidth savings, which is a relevant scientific and applied task with a wide range of practical utility. Target. Present new spectral efficient formats of CPFSK signals generated by pseudo-random up- and fup-video signals based on chips from AF up(t ) and fup(t ) instead of rect-chips, as well as based on modification of the PRS filtering function, evaluate the spectral and correlation properties and advantages of new CPFSK-up(fup)-SSS; provide a comparative analysis of new CPFSK-SSS with widely used spectral efficient minimum shift keying (MSK) signals and their Gaussian variations (GMSK). Results. On the basis of pseudo-random up(fup) video signals generated by AF up(t ) and fup(t ), respectively, new spectrally efficient CPFSK-SSS formats are designed. Spectral and correlation illustrations of new signals are presented, estimates of their spectral efficiency are given and it is shown that they have better or parity indicators in terms of energy concentration in a fixed frequency band compared to MSK and GMSK. Practical significance. The new proposed spectrally efficient formats of CPFSK-SSS have the most important property in the form of the requirement of a smaller band of occupied frequencies at a single clock frequency of the generating video signal PRS, which makes it possible to put them into practice in information-measuring and communication radio electronic systems, in which high compactness of the spectrum and low level of side lobes are important.

Novel Wide-Range Frequency Offset Estimation and Compensation for Burst-mode CPFSK Upstream Signaling in TDM-Based Digital Coherent PON

The burst-mode continuous phase frequency shift-keying (CPFSK) transmitter that combines a directly modulated laser diode, an electro absorption modulator and a semiconductor optical amplifier is attractive as a cost-effective transmitter for phase modulation formats for digital signal processing (DSP)-based coherent passive optical network (PON) upstream signaling. However, since highly accurate wavelength controllers for the transmitters in optical network units (ONUs) create excessive cost burdens, large carrier frequency offsets (CFOs) must be expected. Thus, a CFO compensation method with wide compensation range is required. This paper proposes a novel CFO estimation and compensation method for burst-mode CPFSK signals in upstream PON signaling. The proposed method is based on a simple blind algorithm and does not require any training symbols. We demonstrate wide CFO compensation range, from −12 to 14 GHz, with high receiver sensitivity, less than −42.5 dBm for 10 Gbit/s binary CPFSK signals. This range far exceeds that of the conventional CFO compensation method using a blind algorithm. Moreover, the proposed method can enhance the convergence of finite impulse response (FIR) filters. The feasibility of the proposed CFO compensation technique is successfully demonstrated for burst-mode CPFSK signals.

Phase Noise Resilient Three-Level Continuous-Phase Modulation for DFT-Spread OFDM

In this paper, a novel waveform with low peak-to-average power ratio (PAPR) and high robustness against phase noise (PN) is presented. It follows the discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) signal model. This scheme, called 3MSK, is inspired by continuous-phase frequency shift keying (CPFSK), but it uses three frequencies in the baseband model – specifically, 0 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm f_{symbol}/4$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{symbol}$ </tex-math></inline-formula> is the symbol rate – which effectively constrains the phase transitions between consecutive symbols to 0 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm \pi /2$ </tex-math></inline-formula> rad. Motivated by the phase controlled model of modulation, different degrees of phase continuity can be achieved, allowing to reduce the out-of-band (OOB) emissions of the transmitted signal, while supporting receiver processing with low complexity. Furthermore, the signal characteristics are improved by generating an initial time-domain constant envelope signal at higher than the symbol rate. This helps to reach smooth phase transitions between 3MSK symbols, while the information is encoded in the phase transitions. Also the possibility of using excess bandwidth is investigated by transmitting additional non-zero frequency bins outside the active frequency bins of the basic DFT-s-OFDM model, which provides the capability to greatly reduce the PAPR. The most critical tradeoffs of the oversampled schemes are that improved PAPR is achieved with the cost of somewhat reduced link performance and, in case of excess band, also the spectrum efficiency is reduced. Due to the fact that the information is encoded in the phase transitions, a receiver model that tracks the phase variations without needing reference signals is developed. To this end, it is shown that this new modulation is well-suited for non-coherent receivers, even under strong phase noise (PN) conditions, thus allowing to reduce the overhead of reference signals. Evaluations of this physical-layer modulation and waveform scheme are performed in terms of transmitter metrics such as PAPR, OOB emissions and achievable output power after the power amplifier (PA), using a practical PA model. Finally, coded radio link evaluations are also provided, demonstrating that 3MSK has a similar bit error rate (BER) performance as that of traditional quadrature phase-shift keying (QPSK), but with significantly lower PAPR, higher achievable output power, and the possibility of using non-coherent receivers.

A Janus compatible software-defined underwater acoustic multiple-input multiple-output modem

This article describes the implementation of a multiple-input multiple-output acoustic communication link in shallow water conditions to enable a software-defined acoustic modem with a maximum transmission rate of 20 kbps in a 5-kHz bandwidth. The reliability improvement of a low-complexity Alamouti space–time block code is evaluated to improve the diversity in a high-rate transmission mode using single carrier modulation, as well as in a low-rate transmission mode relying on continuous-phase frequency-shift keying. Using measurements in realistic subsea conditions, the effect of the spatial channel correlation is demonstrated. It is found that for the space–time block code/continuous-phase frequency-shift keying, the spatial diversity is significantly degraded due to the high spatial correlation. In contrast, for the high-mode transmission rate, space–time block code with single carrier modulation offers a bit error rate improvement by a factor over hundred, in comparison to a single transmit element, demonstrating that the multiple-input multiple-output optimal code depends on the software-defined acoustic modem transmission mode.

High modulated soliton power propagation interaction with optical fiber and optical wireless communication channels

&lt;p&gt;&lt;span id="docs-internal-guid-52da184f-7fff-738a-f0e7-e8dd779e097b"&gt;&lt;span&gt;This paper has presented high modulated soliton power transmission interaction with optical fiber and optical wireless communication channels at flow rate of 40 Gbps and 20 km link range. The proposed modulation schemes are continuous phase frequency shift keying (CPFSK), Quadrature amplitude modulation (QAM), differential phase shift keying (DPSK), frequency shift keying (FSK), pulse amplitude modulation (PAM), minimum shift keying (MSK), and optical quadrature phase shift keying (OQPSK). CPFSK has presented better performance than other proposed modulation schemes for both optical fiber and optical wireless communication channels. The enhancement of optical signal/noise ratio at fiber/wireless channel, received electrical power and signal/noise ratio at optical receiver with increase of bits per symbol for different proposed modulation schemes except for CPFSK scheme. Therefore it is evident that CPFSK modulation scheme is more efficient and better performance than other modulation schemes for different communication channels. The obtained results are simulated with optisystem program version 13. &lt;/span&gt;&lt;/span&gt;&lt;/p&gt;

The key management of direct/external modulation semiconductor laser response systems for relative intensity noise control

&lt;p&gt;&lt;span&gt;This study outlines the management of either direct or external modulation semiconductor laser systems for the key solution of bit rate up to 25 Gb/s under relative intensity noise (RIN) control. The bias and modulation peak currents based laser rate equations are optimized to achieve max Q factor and min bit error rate (BER) using first proposed model and optical/electrical signal power, optical/electrical signal to noise ratio are also enhanced using second proposed model. The percentage enhancement ratio in max. Q-factor and min. BER using first proposed model ranges from 53.25 % to 71.63 % in compared to the previous model. In the same way, by using second proposed model, the electrical signal power at optical receiver is enhanced within the range of 48.66 % to 68.88 % in compared to the previous model. Optical signal/noise ratio (OSNR) after optical fiber cable (OFC), signal/noise ratio (SNR) after electrical filter are measured with using different electrical pulse generators and electrical modulators at the optimization stage. The first proposed model reported better max. Q and min. BER values than the previous model. In addition to the second proposed model (direct modulation) has outlined better optical/electrical signal power than the previous model, while max. Q, min. BER values are kept constant. It is found that non return to zero pulse generator has presented better signal power than other pulse generators by using second proposed model. As well as the mixed of raised cosine pulse generator with external modulator reported max. Q, min. BER with other pulse generators by using first proposed model. OSNR at OFC is optimized by using continuous phase frequency shift keying (CPFSK) electrical modulator, While SNR at optical receiver is optimized by using phase shift keying (PSK) electrical modulator.&lt;/span&gt;&lt;/p&gt;

Hybrid CPFSK/OQPSK modulation transmission techniques’ performance efficiency with RZ line coding–based fiber systems in passive optical networks

&lt;p&gt;&lt;span&gt;This study shows hybrid continuous-phase frequency shift keying (CPFSK)/optical quadrature-phase shift keying (OQPSK) modulation transmission techniques’ performance efficiency with return-to-zero (RZ) line coding scheme–based fiber systems in passive optical networks. Max. Q factor/min. bit error rate variations versus modulation frequency and fiber length are studied in detail for various bits/symbol, based on hybrid proposed modulation transmission techniques. Also, optical power and received electrical power variations are simulated with fiber-length variations at a specified modulation frequency of 300 GHz. Max. Q Factor, min. BER, max. signal power, and min. noise power variations are based on hybrid modulation techniques for CPFSK/OQPSK of 32 bits/symbol and a modulation frequency of 500 GHz through a fiber length of 30 km.&lt;/span&gt;&lt;/p&gt;

Novel radar signal to efficiently utilise spectrum based on continuous‐phase frequency‐shift keying

Aiming at the problem of high side-band spectrum for a general frequency-shift keying (FSK) radar signal, this study introduces a novel radar FSK signal based on continuous-phase frequency-shift keying (CPFSK) used in communication systems. Theoretical analysis, simulation and physical application results show that the CPFSK radar signal efficiently controls the spectral containment, whose roll-off performance of the CPFSK is ∼20 dB better than that of normal FSK; meanwhile, the modified signal possesses good ambiguity and pulse compression performances for radar application.

A New CPFSK Demodulation Approach for Software Defined Radio

This paper proposes a new coherent Frequency-Shift Keying (FSK) demodulation technique for software defined radio platform, based on a new Digital Phase Locked Loop (DPLL) architecture. The proposed DPLL addresses the frequency dependence on classic DPLL architectures found in the literature. In classical approaches, the loop filter constants are dependent on the frequency level of the FSK transmitted symbols. The proposed approach applies a simpler feedback loop, with a single integrator and a phase detector architecture based on the small-angle approximation [Formula: see text], which resulted in a DPLL totally independent of frequency. The proposed demodulator has been implemented in Very High Speed Integrated Circuits (VHSIC) Hardware Description Language (VHDL) and evaluated for continuous-phase frequency shift keying (CPFSK) and Gaussian minimum shift keying (GMSK) signals. For CPFSK signals, the demodulator has been evaluated for 2, 4 and 8 frequency levels, with modulation indexes [Formula: see text], [Formula: see text] and [Formula: see text], respectively. For evaluation of GMSK signals, several Gaussian filter bandwidths were considered. In addition, a brief analysis for 2-CPFSK and GMSK is presented over multipath and carrier frequency offset. Results show that the proposed method presents a significantly reduced bit error rate when compared to other coherent methods presented in the literature.

CPFSK Signal Detection in White and Bursty Impulsive Noises

Designing communication techniques for non-Gaussian impulsive noise has been attracting considerable attention from the research community. In this paper, we focus on the continuous phase frequency shift keying (CPFSK) signal detection for both white and bursty impulsive noises. The independent and identically distributed (i.i.d.) symmetric $\alpha $ -stable ( ${S\alpha S}$ ) process and the stationary $m$ -order $\alpha $ -sub-Gaussian [ ${{\alpha \mathit {SG}}}(m)$ ] model are adopted to model the white and the bursty impulsive noises, respectively. At first, both coherent and non-coherent detections of CPFSK signals are investigated for white ${S\alpha S}$ noises. For the coherent sequence detection, the Viterbi algorithm is used by replacing the maximum likelihood (ML) measure with the myriad measure. In non-coherent detection, a multiple symbol aided scheme is proposed, for which both the ML and myriad measures are considered. Subsequently, the detection of CPFSK signals is further addressed in ${{\alpha \mathit {SG}}}(m)$ noise. For coherent detection, based on the Markov property of ${{\alpha \mathit {SG}}}(m)$ noise, we first express the likelihood function as the sum of branch measures, and the myriad measure is also provided to replace the ML measure. The multiple symbol-aided methods are also applied to the non-coherent detection in ${{\alpha \mathit {SG}}}(m)$ noise, and the corresponding ML and myriad measure-based algorithms are given as well. For the sake of comparison, the Gaussian measure is also considered. The simulation results show that the performance of the myriad measure-based algorithms can closely approach that of the ML measure-based algorithms for both coherent and non-coherent detection, and is much better than that of the Gaussian measure-based algorithms.

Energy and spectral efficiencies of [formula omitted]-CPFSK in fading and shadowing wireless channels

Designing an efficient digital communication system requires trade-offs among Spectral Efficiency (SE), Energy Efficiency (EE), and system complexity. In this paper, these metrics are analyzed for an M-ary Continuous Phase Frequency Shift Keying (M-CPFSK) system based on average mutual information and normalized bandwidth of the system. The analysis is presented for arbitrary value of modulation index h (0<h⩽1), number of frequency tones M, and observation length nTs of the receiver. The efficiency metrics are evaluated for Nakagami-m and Generalized-K (GK) channels corrupted by Additive White Gaussian Noise (AWGN). The bounds on SE and EE for these channels are derived and illustrated. Results show that the efficiency metrics are negatively impacted by fading and shadowing characteristics of channel. An increase in observation length of receiver for M-CPFSK can be used to improve SE and EE of the system. It is observed that increasing the observation length of the receiver although improves the energy efficiency metric, even when channel effects are severe, it will be at the cost of increased system complexity. The effects of system parameters on efficiency metrics are examined and it is shown that while M-CPFSK offers better EE as the modulation index h approaches unity, it increases the system bandwidth. SE and EE metrics as a function of M-CPFSK system parameters are examined and discussed.

Carrier synchronisation for multiple symbol Trellis‐coded CPFSK in burst‐mode transmission

A carrier synchronisation technique for multiple symbol Trellis-coded continuous phase frequency shift keying (MSTC-CPFSK) system in burst-mode transmission is proposed. For the synchronisation technique, a joint data-aided (DA) acquisition and phase-locked loop (PLL) tracking algorithm is presented. First, an all-zero sequence is utilised as a pilot for DA acquisition, where the modulated pilot waveform is a direct current (DC) signal, eliminating the operation of modulation removal; and then, a second-order PLL structure is introduced for tracking processing, and we make an analysis of the tracking performance by calculating the equivalent Cramer–Rao bound (ECRB) for the second-order PLL structure; subsequently, we extend the obtained result to any order PLL structures; moreover, the ECRB for the MSTC-CPFSK system is also derived through arithmetical calculation; finally, some numerical results are given to verify the performance of the authors presented synchronisation algorithm, and the simulations illustrate that their algorithm can improve the throughput compared with the classical DA-only algorithm.

A Multi-Gigabit CPFSK Polymer Microwave Fiber Communication Link in 40 nm CMOS

This paper presents a multi-gigabit communication link over a polymer microwave fiber (PMF). A polymer fiber is a light-weight and low-loss channel at millimeter-wave (mm-Wave) frequencies. PMF is a promising, robust and low-cost technology to complement copper or optical links for high-speed applications with transmission distances up to several meters. The high carrier frequency of 120 GHz ensures low bending losses for small bending radii and features a large absolute bandwidth, which can be exploited to achieve high data rates with a simple modulation scheme. The used continuous-phase frequency shift keying (CPFSK) modulation results in a power-efficient system at both the TX and the RX side. We report on 120 GHz 40 nm bulk CMOS TX and RX chips, the fiber and the coupling solution between the chips and the fiber. Data rates up to 12.7 Gbps over 1 meter, transmission lengths up to 7 meters at 2.5 Gbps and a link energy efficiency of 1.8 pJ/b/m for 4 meters and 7.4 Gbps are achieved for the complete communication link.

Noncoherent Multiple-Symbol Detector of Binary CPFSK in Physical-Layer Network Coding

It is well known that the binary continuous phase frequency shift keying (CPFSK) signal is power efficient with constant envelope, because it allows transmission with inexpensive and energy efficient nonlinear amplifiers. Recently, physical-layer network coding (PNC) using the binary CPFSK is considered as a potentially attractive solution to the dual needs of high throughput and high power efficiency in two-way relay wireless network. However, most recent studies on PNC have assumed that the carrier phases of the two transmitted signals arriving at the relay are ideally aligned. In fact, the carrier phase offset between the two node-signals always exists in practice. In this letter, a noncoherent multiple-symbol detector of binary CPFSK signals with unknown carrier phase offset in physical-layer network coding is proposed, which is based on the log-likelihood ratio test. It is shown by simulation that the algorithm with five symbol observation interval achieves 6.7 dB performance gain, compared with only one symbol observation interval.

Dispersion Compensation for 40-Gb/s Phase-Detected CPFSK Signal Using All-Optical Format Converter for Access Networks

We propose and simulate a dispersion compensator for a 40-Gb/s optical phase-detected signal, which is suitable for access networks. The compensator uses a chirp technique and consists of an asymmetric semiconductor optical amplifier-based Mach–Zehnder interferometer structure and a 40-GHz bandpass filter. A delay-line interferometer demodulator (DLI) is utilized for detection. The compensator converts non-return-to-zero ON–OFF-keying format to continuous-phase frequency-shift keying (CPFSK) so that the produced converted CPFSK format can offer more tolerance against positive and negative residual dispersion compared with the directly generated CPFSK. The chirp with a novel strategy, which is the creation of the out-of-place frequencies, instead of causing signal compression, compensates dispersion. This method can be defined for a CPFSK format composed of the upper sideband (USB) and lower sideband (LSB) signals. Contrary to an optical frequency discriminator receiver, there is no dispersion compensating part in a DLI receiver, but the out-of-place frequencies caused due to the chirp reduce the delay between the USB and LSB signals. We show that the positively chirped converted CPFSK tolerates 120 ps/nm of positive residual dispersion, at a 2-dB power penalty, which is $\sim 40$ / ps/nm more compared with the positive dispersion tolerance of directly generated CPFSK applying a 40-GHz optical bandpass filter.

Distinguishing CPFSK from QAM and PSK Modulations

Digital modulation classification is important for many civilian as well as military applications. In this paper, we propose a simple and robust feature to distinguish continuous-phase FSK from QAM and PSK modulations. The feature is based on product of two consecutive signal values and on time averaging of imaginary part of the product. Conditional probability density functions of the feature given modulation type are determined. In order to overcome the complexity of calculating probability density functions, central limit theorem for strictly stationary m-dependent sequences is used to obtain Gaussian approximations. After calculating probability density functions, thresholds are determined based on minimization of total probability of misclassification. Since threshold-based results are valid for special cases requiring knowledge of some parameters, we resort to usage of support vector machines for classification, which require little training and no a priori information except for carrier frequency. Following that joint effects on the performance of carrier offset, fast fading, and non-synchronized sampling are studied in the presence of additive white Gaussian noise. For comparison purposes, rectangular pulse shape is used. To prove practical usefulness, not only the performance is analyzed for root-raised cosine pulses but also for quite less oversampling of symbols than what is found in other approaches. In the course of doing that, the performance is compared with wavelet-based feature that uses support vector machines for modulation separation.

Improving the Performance of 40-Gbit/s CPFSK by Using XPM-Based Format Converter

We propose and simulate a novel all-optical modulation format converter to produce continuous-phase frequency-shift keying (CPFSK) at 40 Gb/s. The conversion is performed by an asymmetric semiconductor optical amplifier-based Mach-Zehnder interferometer. The converted CPFSK format is detected using an optical frequency discriminator demodulator. We show that as a result of the chirp imposed on the converted CPFSK format during the conversion, it offers more tolerance against positive and negative residual dispersion relative to the directly generated CPFSK. By considering a 2-dB power penalty, more than twice the positive dispersion tolerance of the directly generated CPFSK can be attained.

Simple timing recovery algorithm for binary CPFSK based on phase unwrapping

A reduced-complexity timing recovery method for binary continuous-phase frequency shift keying (CPFSK) is presented. The proposed algorithm is based on phase unwrapping and is easy to implement. Theoretical analysis and computer simulation both show that the new algorithm is able to perform close to the theoretical limit given by the modified Cramer–Rao bound (MCRB).

CPFSK Scheme With Multiple Modulation Indices in Optical OFDM Communication System

To improve spectrum efficiency (SE) of minimum-shift keying (MSK) in orthogonal frequency-division multiplexing (OFDM) system, MSK is extended to a continuous-phase frequency-shift-keying (CPFSK) scheme with multiple modulation indices h in this paper. We theoretically prove that the available h for the proposed multiple- h OFDM-CPFSK scheme is only the multiple of 1/2. Subsequently, a simple triple- h OFDM-CPFSK scheme with h = 0, 1/2, 1 is demonstrated as an example of the proposed multiple- h OFDM-CPFSK scheme. In our proof-of-concept experiment, a 10-Gb/s triple- h OFDM-CPFSK signal and a 10-Gb/s OFDM-MSK signal are successfully transported over 1000-km standard single-mode fiber. Electrical spectrum shows that the SE of the triple- h OFDM-CPFSK scheme is about twice as much as that of OFDM-MSK. Bit-error-rate performance of the 10-Gb/s triple- h OFDM-CPFSK signal and the 10-Gb/s OFDM-MSK signal after 300- and 1000-km transmissions demonstrates a robust performance of the triple- h OFDM-CPFSK scheme in long-haul high-speed transmission.

1.5-$\mu{\rm m}$ 10-Gb/s VCSEL Link for Optical Access Applications

We experimentally demonstrate the power budget improvement of a 10-Gb/s vertical-cavity surface-emitting laser (VCSEL) link by utilizing continuous-phase frequency-shift keying (CPFSK)/amplitude-shift keying (ASK) modulation format. We first measure the frequency modulation (FM) response of the VCSEL from 10 kHz to 10 GHz and then exploit dc-balanced line coding to utilize the flat region of the FM response. The CPFSK/ASK signals are generated by directly modulating the VCSEL and utilizing a delay interferometer (DI) for FSK-to-ASK conversion. We successfully transmit the signals over a 50-km dispersion-uncompensated link by optimizing the free-spectral range of the DI. Using the proposed scheme, we achieve > 5-dB improvement in the power budget compared with a conventional VCSEL link.