Continuous Phase Frequency Shift Keying Systems Research Articles

Space–time codes for quaternary CPFSK systems with large number of receiver antennas

In this letter, novel space–time (ST) trellis codes are developed for quaternary continuous phase frequency shift keying (CPFSK) modulation systems (i.e., h = 1 2 ) with large number of receiver antennas in quasi-static fading channels. The ST codes are obtained from the code search algorithm applying the maximizing minimum squared Euclidean distance criterion (MMSEDC). The simulation results show that a significant performance gain can be obtained from the ST codes of the code search algorithms compared to the codes obtained from the delay diversity (DD) scheme for CPFSK modulation systems.

Analytical evaluation of transmission penalty due to group velocity dispersion, self-phase modulation, and amplifier noise in optical heterodyne CPFSK systems

An analytical bit error rate evaluation of an optical heterodyne continuous-phase frequency shift keying (CPFSK) transmission system affected by group-velocity dispersion (GVD), self-phase modulation (SPM), and erbium-doped fiber amplifier (EDFA) amplifier spontaneous emission noise (ASE) in a nonlinear fiber medium is carried out following a perturbative and a transfer matrix approach. The utility of both approaches has been exemplified by applying them to different dispersion compensation schemes in optical and electronic domains. The theoretical penalty estimates are found to have good agreement with both the reported experimental results and those obtained by the Q-value simulation.

Comparison of duobinary and 4-level continuous phase frequency shift keying signals for narrowband land mobile radio applications

The bit error rate performance of partial-response duobinary continuous-phase frequency shift keying (CPFSK), and full-response 4-level CPFSK are compared under the condition of equal RF spectral occupancy and equal data rate, for both Gaussian and Rayleigh fading channels. Incoherent limiter-discriminator detection is assumed for all cases. The spectral efficiency requirements of the FCC, for the allocated 220-222 MHz band for land mobile communications, are used to establish the system specifications. It is shown that 4-level CPFSK system significantly outperforms the 3-level duobinary CPFSK. This is due to the fact that the receiver bandwidth may be lowered for 4FSK thereby higher frequency deviation can be achieved resulting in higher SNR at the receiver which outweighs the noise margin advantage of duobinary system. Simulation systems are designed to measure the performance for both static and Rayleigh-fading narrowband channels.

Analysis of chromatic dispersion effect on coherent optical CPFSK system and performance improvement with the use of combinations of various optical fibers

The performance of a coherent optical continuous-phase frequency shift keying (CPFSK) system is evaluated theoretically including the combined effect of fiber chromatic dispersion, non-zero laser line width and receiver noises. The system limitations imposed by chromatic dispersion and laser phase noise are depicted. The system performance can be improved by shifting the zero-dispersion wavelength to the operating wavelength of the system and this shifting can be achieved efficiently by using a suitable combination of different types of optical fibers. Dispersion shifting characteristics are demonstrated using four kinds of fibers, namely: standard single-mode fiber (SMF), dispersion shifted fiber (DSF), dispersion compensated fiber (DCF) and large core fiber (LCF). The effect of dispersion shifting on the system performance is evaluated in terms of transmission distance and bit rate.

M-ary nonlinear continuous phase frequency shift keying

The authors present a new approach for designing a continuous phase frequency shift keying (CPFSK) system which is a nonlinear mapping of the M-ary symbols into the N-ary CPFSK. Using this approach they have designed an M-ary nonlinear CPFSK (NCPFSK) system of simple structure. The proposed M-ary NCPFSK system is a modification of the multi-h CPM (MHCPM) scheme. The proposed modulation gives improved performance over conventional modulation schemes.

Accurate performance modeling of subcarrier multiplexed fiber/radio systems: implications of laser nonlinear distortion and wide dynamic range

In this paper, we present an analytical approach to accurately assessing the performance of subcarrier multiplexed optical systems for the delivery of future mobile radio broadband services. The existence of a wide dynamic range of power levels in the return link, together with laser nonlinear distortion, represents a major problem and makes performance evaluation difficult. By modeling laser nonlinear distortion using Volterra series analysis, we show that the performance assessment of these systems becomes not only tractable, but also that they can be can be optimized based on the worst case condition. This analysis is performed here for the case of continuous phase frequency shift keying (CPFSK) modulation, for which we calculate the power spectral density (PSD) of the intermodulation products. The overall system performance is that investigated, and its dependence on laser bias and RIN is examined. As an illustrative example we consider a specific 50 channel CPFSK system occupying the bandwidth of 2 to 2.1 GHz.

Crosstalk and phase-noise effects in multi-channel coherent optical CP-FSK systems with tight IF filtering

Reported is a rigorous bit error rate analysis appropriate to continuous phase frequency shift keying (CP-FSK) coherent optical receivers with delay demodulation and an integrating IF filter with integration time less than or equal to the delay time. For an integration time equal to the delay time the model is extended to two optical channels. An important result of the analysis is that IF filtering for CP-FSK modulation reduces the phase swing due to modulation at the detector and this leads to a degradation in system performance with regard to phase noise, receiver noise, and crosstalk influence. For a modulation index of 0.5, for a single optical channel a minimum 2.4-dB penalty relative to matched filter detection is found. The required channel separation for CP-FSK systems appears to be significantly larger than for differential phase shift keying systems and phase noise enhances this effect.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Requirements for high-frequency LD FM response in an optical CPFSK heterodyne delay demodulation system

The required high-frequency laser diode (LD) FM responses for a continuous phase frequency shift keying (CPFSK) heterodyne delay modulation system were investigated. The degradations due to insufficient high-frequency FM response are evaluated, considering the FSK waveform distortion, which gives undesired phase error at the demodulation circuit. From the phase error, bit error rate (BER) degradation is calculated. The calculated results indicate that the delay-time adjustment for the demodulation circuit is effective in minimizing the power penalty. The theoretical evaluation, including the demodulation circuit optimization, explains the experimental results fairly well. Using the same evaluation procedure, required high-frequency LD FM responses are derived. The results, together with the required low-frequency FM responses, give guidelines for transmitter LD selection for coherent CPFSK systems. >

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>