FSK Systems Research Articles

Improved impulse noise modeling for indoor narrow-band power line communication

This paper presents a novel low-complexity fully parametric frequency-dependent impulse noise model for Narrow-Band PLC in the frequency band below 500 kHz. The statistical characterization of measured noise in terms of impulse temporal waveform and the average PSD allowed to confirm the limitations of the commonly used Middleton class-A model due to its flat PSD that is not matching measurements results. To improve the impulse noise model matching with measurement results, a two-state model using impulses in the form of damped sinusoids is proposed. Comparison of the time and frequency characteristics of the proposed model with measurement show the presence of modeled pulses with shapes close to the measured noise, as well as a good matching in the average PSD. Simulation results in using the proposed model for FSK and OFDM systems design show good accuracy to the measured noise, in terms of detector outputs in 2-FSK, bit error rates and fraction of errors per sub-band in the OFDM-based transmission.

Reduction of laser modulation bandwidth requirement in FSK systems using duobinary coding and differential detection

The duobinary signalling concept is applied to direct frequency modulation of a semiconductor laser. The main goal is the achievement of a low-cost high bit-rate transmission with reduced modulation bandwidth requirement of the laser diode. The simulation and experimental work demonstrate a laser modulation bandwidth reduction of about 50%. The system exhibits a high tolerance against fibre nonlinear effects, up to 20 dBm, and phase noise, up to 170 MHz of linewidth at 10 Gbit/s.

The Moments Approach for Performance Analysis of Optical FSK Systems Influenced by Phase Noise and Interchannel Interference

The moments approach is generally considered a systematic way to perform the analysis of coherent optical systems. Exact moments of the filtered signal corrupted by phase noise enable the construction of the Gaussian quadrature rule, which may be used to calculate the system error probability. In this paper, we extend the method to a wider class of systems to include the cases where the phase-noisy interchannel interference may be significant. We derive the essential equations in the matrix form to simplify the procedure as much as possible. To illustrate the results, we apply the moments method to two-channel optical heterodyne FSK system with dual-filter receiver structure, and evaluate the required channel spacing to have less than 1 dB additional penalty due to crosstalk.

The Moments Approach for Performance Analysis of Optical FSK Systems Influenced by Phase Noise and Interchannel Interference

The Moments Approach for Performance Analysis of Optical FSK Systems Influenced by Phase Noise and Interchannel Interference

Performance analysis of wide-band M-ary FSK systems in Rayleigh fading channels

Performance analysis schemes for wide-band M-ary frequency-shift keying systems with a limiter-discriminator-integrator receiver are presented along with analysis and simulation results for 4-ary and 8-ary systems. The probability distribution of clicks is required for performance analysis and is determined for Rayleigh fading channels.

Comparison of Certain Methods for Performance Evaluation of Coherent Optical FSK Systems

In this paper, we examine the use of different methods for performance evaluation of coherent optical FSK systems. Taylor expansion method (TE), numerical solution of Fokker-Planck (FP) equation and Gausian quadrature rule (GQR) are compared in terms of system error probability. A method for numerical solution of FP equation is proposed. Construction of GQR from moments and modified moments is considered and the numerical stability of GQR is investigated.

Exact analysis of postdetection combining for DPSK and NFSK systems over arbitrarily correlated Nakagami channels

Postdetection combining is a popular means to improve the bit error performance of DPSK and noncoherent FSK (NFSK) systems over fading channels. Nevertheless, the error performance of such systems in an arbitrarily correlated Nakagami environment is not available in the literature. The difficulty arises from inherent nonlinearity in noncoherent detection and from attempts to determine explicitly the probability density function of the total signal-to-noise ratio at the combiner output. We directly determine the error probability from the characteristic function of decision variables, resulting in closed-form solutions involving matrix differentiation. The performance calculation is further simplified by developing a recursive technique. The theory is illustrated by analyzing two feasible antenna arrays used in base stations for diversity reception, ending up with some findings of interest to system design.

Effect of nonuniform laser FM response on the performance of multichannel heterodyne FSK systems using optical amplifiers

A theoretical analysis is provided to evaluate the performance of optical frequency division multiplexed systems taking into considerations the combined effect of receiver noise, laser phase noise and nonuniform FM response characteristic of a practical DFB laser. To overcome the effect of nonuniform frequency modulation characteristic of semiconductor lasers, two different linecoding schemes are used for the laser driving signal. The crosstalk penalty due to the combined effect of nonuniform FM response and phase noise of lasers is evaluated. The improvement in receiver sensitivity due to optical preamplifier is also estimated. The computed results show that the performance of the system is highly degraded due to the effect of laser nonuniform fm response and can be reduced substantially by using linecoding. Further, there is considerable improvement in receiver sensitivity due to the use of an optical preamplifier in the absence of phase noise. In the presence of phase noise there is a reduction in receiver sensitivity.

The effect of error control coding in multichannel FSK coherent lightwave communication systems influenced by laser phase noise

It has been shown that coherent optical fiber receivers with a two-filter structure (TFS) consisting of a wide-band IF filter and a narrow-band postdetection filter are less susceptible to the influence of phase noise. However, the expanded IF bandwidth required to achieve optimum sensitivity performance is large, particularly in multichannel FSK systems. Forward error control coding can relax the laser linewidth requirement and improve receiver sensitivity. In this paper a multichannel asynchronous FSK scheme equipped with (31, k) Reed-Solomon codes is used to verify the coding benefit. A systematic error probability analysis is developed and a stable and accurate performance evaluation procedure is provided. The sensitivity penalties due to the combined phase noise and interchannel crosstalk for both coded and uncoded systems are calculated for comparison. The results show that the performance reduction due to phase noise can be largely alleviated by choosing a proper code rate and an optimum value of the expanded IF bandwidth.

Analysis of delay-and-multiply optical FSK receivers with line-coding and non-flat laser FM response

We present a theoretical analysis of the performance of coherent optical FSK systems when the driving laser signal is AMI or Manchester (biphase) line-coded to counteract the nonideal FM characteristic of the transmit laser diode, and the received signal is heterodyned and detected by a delay-and-multiply demodulator. The analysis takes into account IF filtering by assuming linear filtering of the noisy signal phase, accounting, for small linewidths, for laser phase noise in a straightforward and accurate manner. A simple equivalent baseband model of the system is derived for performance evaluation, applicable to both cases of large demodulator delay and when the delay tends to zero (ideal discriminator). Noise statistics include the clicks due to both signal and phase noise. The problem of performance evaluation is reduced to a classical intersymbol interference problem which is solved by mead of the method of Gauss quadrature rules. The analysis accurately predicts the effectiveness of AMI and Manchester line coding, depending on several system parameters such as linewidth, modulation index, IF bandwidth and laser FM response, and can be easily extended to other line coding techniques.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance evaluation of FSK and CPFSK optical communication systems: a stable and accurate method

The modified moments method for evaluating the performance of coherent optical FSK and CPFSK systems is presented. Since the classical procedure becomes ill-conditioned as the order of the moments increases, we consider the construction of Gaussian quadrature rules (GQR) from the modified moments. The analysis accounts for the influences of IF bandwidth, transmitter and local oscillator laser phase noise, postdetection filters, and additive Gaussian noise. It is found that the proposed approach is a highly reliable and efficient method for calculating the error probability. A comparison with results obtained from the Gaussian quadrature rule, Gaussian approximation method, and analytical approximation formulas shows that this technique is very accurate. Analytical expressions are derived for FSK and CPFSK receivers which include polarization and phase diversity techniques. The use of numerical programming to avoid many unnecessary computations is discussed. This evaluation method can be used to account for the effects of crosstalk in multichannel systems and the influence of error-control codes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bit error rate performance and power spectral density of a noncoherent hybrid frequency-phase modulation system

This paper studies the design and performance analysis of a noncoherent hybrid modulation scheme derived from multifrequency and multiphase signals, and referred to as joint frequency-phase modulation (JFPM). This modulation class includes many formats, which can be classified as efficient bandwidth-limited modulation or power-limited modulation techniques. A noncoherent receiver structure for JFPM signals is introduced, and an exact expression for the probability of a bit error over AWGN channels is obtained. The results show that noncoherent JFPM perform better than M-ary DPSK and/or noncoherent M-ary FSK systems. The power spectral density and the spectral efficiency of JFPM are analyzed. Fractional out-of-band power containment bandwidths are obtained numerically for different JFPM formats. These analytical results show that the power spectral density of JFPM does not contain a discrete component and the same bandwidth efficiency can be obtained by using different JFPM formats. Overall, JFPM can be classified as a bandwidth- and power-efficient modulation technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Theoretical analysis of coherent optical FSK systems with limiter-discriminator detection

A detailed theoretical analysis, based upon Rice's (1963) theory of clicks, for evaluating the error performance of heterodyne optical FSK receivers with limiter-discriminator detection and pre- and integrate-and-dump (I&D) post-detection filtering is developed, accounting for laser phase noise, intersymbol interference (ISI) and intermediate-frequency (IF) filtered carrier envelope fluctuation effects. From the analysis it turns out that the envelope fluctuations induced by phase noise may produce, for operating IF bandwidths, a much smoother transition to the bit error rate floor than expected when considering IF infinite bandwidth, thereby generating performance degradation right in the operating signal-to-noise ratio (SNR) region. The contribution to this degradation due to a change in the click statistics generated by the envelope fluctuations is found to be negligible. From the analysis, it is also found that the floor gets lower and approached more rapidly as the modulation index and the bandwidth get larger, until the known floor for infinite IF bandwidth is reached. Finally, general curves are presented for system performance relating bit error probability to optimum IF bandwidth, optimum modulation index, laser linewidth and receiver sensitivity. These curves represent the ultimate limit to performance of a heterodyne optical FSK receiver with limiter-discriminator detection and pre- and I&D post-detection filtering. >

Optical Heterodyne Limiter-discriminator and Discriminator FSK Systems

We present a rigorous model for heterodyne FSK systems with limiter-discriminator as well as with discriminator detection. The system performance is impaired by receiver noise as well as laser phase noise. A best sensitivity for the limiter discriminator system is 39.9 generated photo electrons for a 10 −9 bit error-rate whereas for the discriminator system it is 49.2 photo electrons. The system performances are compared to that of ASK and dual filter FSK systems. It is found that significant amounts of phase noise can be tolerated for all the systems provided that sufficient IF bandwidth is allocated and a large modulation index value is used (for the FSK systems)

Why FSK and CPFSK have identical linewidth requirements

CPFSK is the most widely used modulation scheme in coherent optical transmission. Theoretical analyses so far predicted a much more stringent linewidth requirement compared to ASK and FSK systems with noncoherent IF-detection. In this paper we present a unified linewidth analysis of ASK, FSK, CPFSK, and DPSK receivers, with leads to the conclusion that the linewidth performance of these different schemes is to a large extent identical. The inclusion of post-detection filtering in the analysis is critical for obtaining these results, which are supported by practical system measurements on a 1 Gbit/s phase diversity CPFSK receiver.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the thermal contribution to the FM response of DFB lasers: theory and experiment

Laser diodes exhibiting a dip-free FM response will be key devices for future coherent FSK systems. We studied (both theoretically and experimentally) the thermal contribution to the FM response of a laser. It turns out that the agreement is good enough to validate the Fourier transform approach. This enables us to propose schemes to reduce the thermal FM response: decrease the heat generated in the laser and/or its thermal resistance by episide-down mounting. >

Preamplifier implementation of ASK and limiter-discriminator FSK systems

Results for the sensitivity of preamplifier ASK and limiter-discriminator FSK systems are presented. The best sensitivities for a 10/sup -9/ error rate are 76 (ASK) and 79.8 (FSK) received photons. The FSK system allows easy threshold setting and simple optical filter design. Both types of system are suited for system design with significant phase noise.

Heterodyne and optically implemented dual-filter FSK systems: comparison based on a rigorous theory

The performance of heterodyne and optically implemented dual-filter FSK systems are compared based on a new rigorous theory that accounts for noise correlation (due to nonorthogonal signaling), laser phase noise, receiver noise, and amplifier spontaneous emission noise. Ideally, the two implementations have the same sensitivity with and without polarization control. The results emphasize the practical tradeoff between the heterodyne implementation (where receiver noise means that a low modulation index gives the best sensitivity) and the optical one (where the difficulty in making high-quality narrowband optical filters means that a larger modulation index gives the best sensitivity).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimal design of prefilters for binary FSK discriminators

Prefilters are derived for delay-line discriminators for FSK systems which allow these simple demodulators to give optimum, or matched filter performance. Filters are presented which allow the demodulator to give optimum performance even when the tone spacing is a multiple of the minimum orthogonal spacing. Finally, an architecture is suggested that incorporates a tapped-delay-line to synthesise these prefilters.

BER analysis on optical direct-detection FSK transmission systems using a Mach-Zehnder interferometer as a discriminator

This paper presents a BER analysis for two types of optical FSK transmission systems using a Mach-Zehnder interferometer as a discriminator. In one case the discriminator is assumed to be kept on the transmitter side and in the second case, on the receiver side. The analysis takes into account the linewidth of the source and other noises in the system. The discriminator disperses the input pulse, and an optimum filter required to produce a raised cosine output pulse spectrum is proposed. Such an optimum filter gives the minimum noise bandwidth without causing any ISI at the decision instant. The values of the equivalent noise-bandwidth factorsI 2 andI 3 of the filter vary between 0.563 to 0.822 and 0.086 to 0.193, respectively, when the interferometer delay timeτ is varied from zero to bit time. BER curves are given for various conditions of the FSK systems. To avoid an error floor the linewidth of the source should be <0.01/τ.