M-QAM Signals Research Articles

Effect of interference of impulse noise induced by clipping on BER of M‐QAM signal in analog/digital hybrid optical transmission systems

The bit error rate (BER) of the M-QAM signal in analog/digital hybrid optical transmission (hybrid transmission) shows a floor-like feature due to impulse noise induced by clipping the subcarrier multiplexed signal at the laser threshold. This paper proposes a new BER analysis model, which is modified from our previous one based on Middleton's class A impulse noise model, and compares analytical results with experimental data. The analytical results agree particularly well with the experimental data for small optical modulation indexes (OMI) of the M-QAM signal; consequently, these results can be applied to estimating the bit error rate of the digital channel in hybrid transmission. There is also a tendency for the analysis results to diverge more greatly from the experimental data as the OMIs of the M-QAM signal increase. We also discuss the reasons for this divergence. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(8): 1–8, 1998

Reduction of nonlinear distortion in MQW semiconductor optical amplifier using light injection and its application in multichannel M-QAM signal transmission systems

By using an external light-injected multiple-quantum-well (MQW) semiconductor optical amplifier (SOA), we have demonstrated a 100-km optical fiber link that transports 77 channels of 64-QAM signals. This is equivalent to a system capacity of 2.3 Gb/s, while using a laser bandwidth of only 550 MHz. Under a requirement of carrier to noise and nonlinear distortion ratio of 30 dB per channel, the 1310-nm gain-peaked SOA input dynamic range was increased from 0 to 9 dB due to an injected light with 8.8 dBm and a wavelength of 1284 nm.

Optimal decision boundaries for M-QAM signal formats using neural classifiers

The application of neural classifiers for providing optimal decision boundaries of a warped and clustered M-QAM constellation affected by nonlinearity is analyzed in this paper. The classifier behavior, for the specific application, has been evaluated both by the carrier to noise ratio (CNR) degradation (DeltaC/N) due to nonlinearity for a target error rate P(c)=10(-3), and more thoroughly by classical figures of merit of the pattern recognition theory such as classification confidence and generalization capability. The influence of the probability distribution of the training examples and the effects of activation functions' sharpness (namely the temperature of the net) have also been investigated. The results, obtained on a simulation basis, indicate optimal matching with respect to upper bounds evaluated with some minor simplifying hypothesis, even if the overall method's effectiveness can be adequate only for mild nonlinearity conditions.

Effects of clipping-induced impulse noise in externally modulated multichannel AM/M-QAM video transmission systems

The effect of clipping-induced impulse noise in externally modulated multichannel AM/M-QAM video transmission systems is investigated. It is shown that the bit-error-rate of the M-QAM signals in the symmetric double-clipping events is, to the first order approximation, twice the single clipping events under the same conditions. The results are in good agreement with the experimental data for both 1319-nm and 1550-nm externally modulated laser transmitter-based systems.

Error performance of OFDM-QAM in subcarrier multiplexed fiber-optic transmission

Error performance of OFDM-QAM signals is analyzed for subcarrier multiplexed (SCM) fiber-optic video transmission, particularly for hybrid AM/OFDM systems. In comparison with conventional M-QAM signals, it is shown that the OFDM system provides significant performance improvements in terms of bit-error rate (BER), channel capacity, and operating range of the optical modulation depth, in the lightwave SCM environment where both the clipping impulse noise and Gaussian noise are present. As a result, the OFDM signals will introduce less interference effects on the nominal AM channels than the M-QAM signals under the same operating conditions.

33-channel 64-QAM signal transmission using a 1.3-μm semiconductor optical amplifier

From the network evolution point of view, optical amplifiers in a hybrid fiber coaxial (HFC) system may become extensively deployed at approximately the same time as when analog AM-VSB video signals are all replaced by digital M-QAM or M-VSB signals. This letter demonstrates the feasibility of using a 1.3-/spl mu/m semiconductor optical amplifier to transport 33 channels of 64-QAM signals with 30 Mbps/channel. A total system power budget of 20.3 dB was obtained.

Ring-TCM for fixed and fading channels: land-mobile satellite fading channels with QAM

The authors investigate ring-TCM codes suitable for M-QAM signal sets on nonfrequency-selective fading channels. A new range of nonrotational invariant (NRI) and rotational invariant (RI) fading-optimised ring-TCM codes suitable for rectangular M-QAM schemes is presented. The trade off between the code gain and the decoder complexity of these codes is analysed, and their actual performance under different fading channel conditions is evaluated. In addition, a comparison with the best fading-optimised TCM codes for M-QAM reported in the literature is carried out.

Near-optimal symbol-by-symbol detection schemes for flat Rayleigh fading

The optimal MAP detection algorithm for demodulation of M-QAM signaling in the frequency flat Rayleigh fading channel is proposed. A recursive structure is derived which allows for symbol-by-symbol metrics to be computed and data decisions to be made in an efficient manner. The complexity problem inherent to optimal detection schemes is addressed and approximations to optimal detection are considered which reduce complexity to practical levels yet still provide near-optimal performance levels. Reduced complexity algorithms are obtained through the use of decision feedback and thresholding which allow for higher order modulations such as 16-QAM to be implemented. Performance characterization of the algorithms presented are obtained via Monte Carlo simulation and results show that near-optimal bit error probability levels can be achieved. Extensions of the algorithms to include diversity combining techniques are also developed and shown to provide improved performance. Some theoretical derivations for optimal detection of 16-QAM in fading with diversity are also presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance limits on M-QAM transmission in hybrid multichannel AM/QAM fiber optic systems

Performance limits on M-QAM transmission in hybrid multichannel AM/QAM (amplitude modulated/quadrature amplitude modulated) fiber-optic systems are presented. It has been shown that for such hybrid analog/digital transmission over an optical fiber, the induced in-band clipping noise will significantly degrade the reception performance of M-QAM signals. Here the author determines the channel capacity and signal power (or optical modulation index) of M-QAM as limited by the presence of the clipping noise, which is non-Gaussian and impulsive, and discusses design tradeoffs for M-QAM channels in such cases.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new pattern jitter free frequency error detector

One method to enable fast acquisition of a phase-locked loop (PLL) in spite of large frequency offsets and small PLL bandwidths is to use an additional AFC (automatic frequency control) loop. A suitable frequency error detector (FED) for large frequency offsets is the well-known balanced quadricorrelator. This FED is shown to produce great pattern jitter if it is to work with digital modulated MQAM and MPSK signals (M>2) and random data. The authors describe how this pattern jitter for MQAM and MPSK signals can be overcome completely. Another understanding of the balance quadricorrelator is also given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Symbol error rate curves for M-QAM signals with multiple cochannel interferers

A recursive algorithm for determining the probability of symbol error in an M-QAM system, subject to multiple-cochannel interferers, is presented. In particular, a recursive formula is derived for determining the symbol-error-rate (SER) of an M-QAM system subject to both multiple-sinusoidal and similar, independent QAM interferers. The result is expected to prove useful in the analysis of such systems exposed to ever-increasing interference. >

Performance Signatures for Dual-Polarized Transmission of M-QAM Signals Over Fading Multipath Channels

Performance signatures for dual-polarized transmission of M-state quadrature amplitude-modulated signals over dispersive multipath digital radio channels are theoretically derived in this work. We report on two major findings. Firstly, we show that for the assumed propagation model, a cross-coupled interferer exhibits noiselike behavior and impacts on digital radio outage time in direct relation to its power level. Secondly, our theoretical finding is based on a new application of performance signature curves for two cross-coupled multipath channels. This treatment permits the prediction of multipath-induced digital radio outage for specified ratios of power in the copolarized and cross-coupled signals. Theoretical findings are qualitatively supported by measured performance signatures obtained from a laboratory simulation of the model.