Continuous Phase Frequency Shift Keying Signals Research Articles

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.

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.

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.

Improved mapping policy for reducing error coefficient in CPFSK signals

An improved mapping policy is introduced that alternates between standard and inverted bit mapping functions at selected phase states to reduce the error coefficient of continuous phase frequency shift keying (CPFSK) signals. The proposed policy can be applied to many different forms of CPFSK signals. It is demonstrated that the mapping policy can significantly improve performance, particularly at lower to moderate SNR values.

Power spectra of FSK modulated laser fields

In a continuous phase frequency shift keying (CPFSK) coherent optical communication system, the optical signal is usually generated by modulating the bias current of a singlemode laser diode. This generation process is always accompanied by a simultaneous intensity modulation (IM) of the emitted light. The authors derive an exact expression for the power spectra of the optical CPFSK signal, taking this simultaneous IM effect into account. From the derived formula, the asymmetical shape of the power spectra observed earlier by other investigators is shown and explained.

Closed-form of the power spectral density for full response M-ary CPFSK modulation

In recent years, continuous phase modulation (CPM) scheme has gained increasing attention due to its attractive spectra properties. The continuous-phase frequency shift keying (CPFSK) modulation scheme has previously been studied and much effort has been spent to find simple analytical and numerical methods for computing the spectrum of CPFSK signals [1–16]. Some authors have derived formulas for the autocorrelation and power spectral density (PSD) functions of CPFSK signals, but the calculations are extremely laborious requiring numerical integration in two dimensions involving truncation errors. This paper presents a special method of analyzing the spectral properties of M-ary CPFSK for full response signaling. The autocorrelation function is presented in closed-form thereby avoiding truncation. The Fourier transform is used to find the power spectral density function, which is also expressed in closed-form. The effect of the system parameters, i.e. the size of the alphabet, the modulation index, and others on the system bandwidth and PSD are analyzed. The conditions under which the spectrum contains discrete lines are outlined. The continuous part of PSD is expressed in exponential form, and a large number of PSDs have been computed and plotted in a relatively short time and samples are presented in the paper. Finally, it is shown that systems with normalized modulation indices Δ = 1/ M offer superior performance in terms of bandwidth and power efficiency for different schemes.

Continuous Phase Frequency Shift Keying (CPFSK)

Binary data transmission using CPFSK signals is described. The structures of the modulator and the optimum coherent receiver are given and explained. The error rate analysis is presented by making high and low SNR approximations of the optimum receiver. It is shown that CPFSK offers an advantage of nearly 0.85 dB relative to the well known Binary Phase Shift Keying (BPSK)/Minimum Shift Keying (MSK). In the light of the modulation technique considered the trade-offs available among the transmitted power, channel bandwidth, and receiver complexity are discussed.

Nonlinear continuous phase frequency shift keying

A novel signal-space coded CPM (continuous phase modulated) signaling technique, called nonlinear CPFSK (continuous phase frequency shift keying) signaling, which guarantees the maximum constraint length allowed by the number of states is introduced. Nonlinear CPFSK signals use a suitably selected state transition matrix during all signaling intervals. The selected state transition matrix is realized by changing the modulation index of the signals, hence the modulation index used during any interval depends on the transmitted symbol as well as on the state of the system. Binary nonlinear CPFSK signaling schemes are constructed and analyzed. Numerical results indicate that nonlinear CPFSK signals can achieve attractive minimum distances compared with other existing CPM signaling formats.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Combined coded/multi-h CPFSK signaling

A continuous-phase frequency-shift-keying (CPFSK) signaling technique is suggested that combines convolutional encoding and multi-h signaling. In contrast to regular multi-h signaling, this technique changes the modulation index in a preselected pattern in order to maximize the minimum Euclidean distance. A rate-1/2 convolutional encoder along with a 2-h quaternary CPFSK modulator which uses two fixed modulation indexes is considered. Minimum Euclidean distances are calculated corresponding to the best encoder/mapper combinations for different modulation index patterns at attractive pairs of modulation indexes. Numerical results obtained for encoder memory lengths of one and two are used to illustrate that the minimum Euclidean distance of coded CPFSK signals can be significantly increased by combining with multi-h signaling. Modulation index patterns which perform significantly better than regular multi-h signals are determined. An error event analysis over the additive-white-Gaussian noise channel is carried out to investigate the actual error rate performance and to verify the theoretical results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design of coded CPFSK modulation systems for bandwidth and energy efficiency

Consideration is given to the problems related to the design of M-ary continuous-phase frequency-shift keying (CPFSK) systems with modulation index h=J/M, combined with eternal rate r binary convolution encoders. The following questions are raised and answered: (1) how should different encoder-modulator systems be compared and how can comparable systems be recognized from the system parameters, i.e. M, h, and r?; (2) what are the limits on the information rate per unit bandwidth, versus signal-to-noise ratio, when reliable transmission is required?; (3) how does one choose the system parameters M, h, and r when the overall system has to achieve a specified performance?; and (4) how does one design the external rate r binary convolutional encoder to put in front of the M-ary CPFSK modulation system with h=J/M? A simple approximation for the bandwidth of a CPFSK signal is given and shown to be sufficiently accurate for system design purposes. The design of the external convolutional encoder is carried out in a novel way that leads to fewer states in the combined encoder-modulator system and thus yields improved performance for a given demodulation-decoding complexity compared to previous approaches for the design of coded CPFSK systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>