A method is proposed for precisely analyzing the effects of the multiple access interference in the time-hopping ultra-wideband communication systems on the average symbol error rates. An exact analysis is derived for calculating the bit error probability of ultra-wideband systems operating in multiple access interference. The analytical expressions are validated by simulation and used to assess the accuracy of the Gaussian approximation, a widely adopted method for evaluating bit error rate performance. The Gaussian approximation is shown to be inaccurate for predicting bit error rates for medium and large signal-to-noise power ratio values. The different time-hopping modulation schemes are accurately assessed in terms of their sensitivities to the system parameters and the bit error rate.

This paper presents a unified description of phase noise and timing jitter of oscillators and PLLs based on diffusion theory. Analytical expressions for period jitter, cycle-to-cycle jitter, and absolute jitter are derived and related to the power spectral density of the excess phase and the relative single-sideband phase noise of the oscillator. In addition to white noise sources resulting in phase diffusion, the effects of flicker noise and noise in the control voltages including supply and substrate noise are considered. More specifically, the absolute rms jitter of a PLL is related to the white and the flicker noise of a free-running oscillator. For an experimental 60 GHz oscillator fabricated in a 0.25 μm SiGe:C BiCMOS technology a phase noise of -90 dBc/Hz is measured at 1 MHz offset. From this measurement, an absolute rms jitter contribution of 70 fs is predicted for a 5 MHz bandwidth PLL.

Understanding the properties of close-in phase noise is crucial for analyzing the effects of low-frequency, colored noise on the frequency stability of electrical oscillators. This paper shows these properties are distinctly different from those of far-out phase noise, which are commonly studied in the literature. Unlike far-out phase noise, the spectrum of close-in phase noise caused by several uncorrelated noise sources is not the same as the sum of the phase noise spectra caused by individual sources. Furthermore, in the absence of colored noise, this spectrum is not necessarily Lorentzian as generally believed. We show that the phase noise spectrum of a periodic signal with zero cycle-to-cycle jitter is always Lorentzian and demonstrate the appearance of 1/f⁴ phase noise due to a Lorentzian noise source. We also study two methods for suppressing the effects of low-frequency, colored noise on phase noise: signal symmetrization and noise-source switching. We show that the suppression of 1/f³ phase noise in single-ended ring oscillators is due to switching and not because of symmetrization. Symmetrization is effective only for the noise sources which are constantly “on”, such as the tail current source in differential ring oscillators. These findings provide effective guidelines for designing low-phase-noise oscillators.

1/f noise is present in several natural and artificial systems, and even though it was discovered several years ago, it is still not completely understood. Due to the lack of an universal model, the main methods of investigating a system where 1/f noise is present are numerical simulations and real measurements. The second method can lead to more adequate results, since it is free from numerical artifacts. In the case of real measurements, we need reliable, wide-band noise generators. Many ways of generating noise are known; most of them have several limitations on the frequency bandwidth or on spectral properties. We wanted to create a device which is easy to use, which can generate any kind of 1/f^α noise and whose bandwidth is wide enough to make our investigations. We used a DSP (ADSP2181) to numerically generate the desired noise, and a D/A converter to convert it to an analogue signal. The noise generation algorithm was based on the known method of filtering a Gaussian white noise with a series of first-order digital filters. We enhanced this method to get a better spectral shape and to compensate for the side effects of the digital-to-analogue conversion.

This paper deals with the compensation of the self-noise (jitter) in a nondata aided (blind) feedforward symbol timing estimator using two samples per symbol for linearly-modulated waveforms transmitted through AWGN channels. The main contribution of this paper is the derivation of an appropriate prefilter to achieve nearly jitter-free digital blind feedforward timing recovery. Computer simulations illustrate that the proposed prefiltering scheme improves significantly the performance at mid and high SNRs.

This paper describes a numerical design procedure for the design of optimal (in the minimum mean square channel estimation error sense) precoders for diversity systems with unitary codes where temporal correlation in the channel is present. The paper describes the use matrix differential calculus to derive the Jacobian (first derivative) of trace of the optimal (MMSE) estimation error covariance matrix with respect to the channel precoder matrix. This is used to define a gradient descent algorithm to minimise this error over all unit norm precoders. Simulation results using a per-survivor processing based receiver illustrate the improvement gained over unitary codes. The paper also shows by example that this does not necessarily lead on its own to optimal symbol detection error probability performance.

In this paper, we propose to use the EXIT chart to predict and optimise the performance of an equliser used in the context of turbo equalisation. More specifically, we will show how to choose certain parameters and an aproriate structure of the proposed equaliser in order to ensure an optimum exchange of extrinsic information between the equaliser and the decoder in the turbo process.

This paper reviews modulation recognition in the context of HF radio-communications. We investigate entropic distance measures and coherence measures for recognizing HF modulations. Preliminary results shown that it may be possible to identify a modulation and its transmit power level based on the entropic distance between it and another modulation. Coherence estimates may provide characteristic signatures that can be used to identify modulation types.

"Noise" had a glorious birth. While there were rumblings before 1905, it was Einstein's explanation of Brownian motion that started the field. His motivation was not the mere explanation of the erratic movement of pollen, but much bigger: that noise could establish the existence of atoms. Immediately after Einstein there was an incredible flurry of ideas of the most profound kind that continues to this day. But noise, considered by many as unwanted, and mistakenly defined as such by some, has little respectability. The term itself conjures up images of rejection. Yet, it is an idea that has served mankind in the most profound ways. It would be a dull gray world without noise. The story of noise is fascinating and while in its early stages its story was clearly told, its subsequent divergence into many subfields has often resulted in a lack of understanding of its historical origins and development. We try to give it some justice. We discuss who did what, when, and why, and the historical misconceptions. But most importantly, we aim to show that the story of noise is an exciting story worth telling.

A novel viewpoint based on the generalized approach to signal processing in the presence of noise and devoted to the collision resolution problem is introduced in this paper for wireless slotted random access sensor networks. Signal separation principles borrowed from signal processing problems are used. The received collided packets are not discarded in this approach but are exploited to extract each individual sensor node packet information. In particular, if k sensor nodes collide in a given time slot, they repeat their transmission for a total of k times so that k copies of the collided packets are received. Then the receiver has to resolve a k x k source-mixing problem and separate each individual sensor node. The generalized receiver does not introduce throughput penalties since it requires only k slots to transmit k colliding packets. In the course of analysis, we consider four channels models: ideal additive white Gaussian noise channel, in which the i-th sensor node’s gain is a deterministic but unknown constant; non-fading channel with power control but arbitrary phase, in which the amplitude of the i-th sensor node’s gain is constant (may be unknown), whereas the phase is random and uniformly distributed within the limits of the interval [0,2π]; Rayleigh fading channel, in which the phase is uniformly distributed within the limits of the interval [0,2π], whereas the amplitude is distributed with the parameter, σ_A and the amplitude and phase are independent; Rician fading channel, in which the phase is uniformly distributed within the limits of the interval [0,2π], whereas the amplitude is Rician distributed with the parameter A and σ_A and the amplitude and phase are independent. Performance issues that are related to the implementation of the collision detection algorithm based on the generalized approach to signal processing in the presence of noise demonstrate a great superiority in comparison with well-known methods. The protocol’s parameters are optimized to maximize the system throughput. Under the use of the generalized approach to signal processing in the presence of noise, the system throughput is higher in comparison with modern methods and algorithms.

This paper explores the use of genetic algorithms for the design of networks, where the demands on the network fluctuate in time. For varying network constraints, we find the best network using the standard genetic algorithm operators such as inversion, mutation and crossover. We also examine how the choice of genetic algorithm operators affects the quality of the best network found. Such networks typically contain redundancy in servers, where several servers perform the same task and pleiotropy, where servers perform multiple tasks. We explore this trade-off between pleiotropy versus redundancy on the cost versus reliability as a measure of the quality of the network.

We present an online algorithm to track multiple narrowband burst-type interferers in wideband communication systems. The arrivals/departures and the strengths of the interferers are identified with the use of HMM. This algorithm is targeted for wideband wireless systems which are overlaid on top of multiple narrowband services whose traffic can be bursty. This algorithm can be used to suppress or avoid interference for various kinds of communication systems including both single-carrier systems and multi-carrier systems such as OFDM. As an example, we apply the algorithm in a Direct-Sequence Spread-Spectrum system for interference suppression. Simulation results and analysis are presented. The simulation results show that our algorithm achieves very satisfactory performance in interference suppression compared to other NBI suppression methods in terms of both BER and robustness to the burst rate of the interferers.

The paper derives an optimal fixed interval smoother for the linear time invariant output estimation problem. The smoother employs forward and adjoint Kalman predictors. The suboptimal time-varying case is discussed which includes the use of forward and adjoint extended Kalman predictors within a nonlinear smoother. The efficacy of the smoother to tracking points within sequences of noisy images is investigated. The results of a simulation study are presented in which it is demonstrated that a Kalman filter can outperform a so-called matched filter, and a fixed interval smoother can provide a further performance improvement when the images are sufficiently noisy.

The statistical problem of estimating the bandwidth parameter of a Gauss-Markov process from a realization of fixed and finite duration T at selectable sampling interval Δ is addressed in this paper. As the observation time, T, is fixed and finite, the variance of estimated autocorrelation and continuous-time parameter does not vanish as Δ approaches 0. This necessitates a second order Taylor expansion in deriving the parameter estimator bias and variance, which produces significantly more accurate bias and variance results than a first order one does. Using likelihood ratio methods, we also show that even the large sample distributions of β estimator are better modeled by a gamma than by a normal form. According to the gradient change of the variance, a key result is that three sample regions, which are termed finite, large and very large, corresponding to substantial, gradual, and very slight decrease in variance of the parameter estimator respectively, are quantified. In terms of analysis BW, the three regions are (-23,-35), (-35,-55) and (-55,-∞) dB. The characterization of the trade off between the variance decrease and sampling rate results in a practical guideline for choosing sampling rate. To demonstrate the practical value of our results, we apply them to the noise prediction problems of a time invariant GM processes. Using moment generating functions, we are able to arrive at explicit and accurate relations between, the set of variables (Δ, T, β) and m-step prediction performance. In particular, we show that prediction performance is highly robust with respect to estimation accuracy of β. This is significant, in that it allows one to use a surprisingly small observation time, T , and still achieve nearly optimal performance associated with perfect knowledge of β.

The effects of the multimode content in a laser beam on the angle-of-arrival fluctuations are examined for free space optics (FSO) access systems. Multimode excitation is represented by coherent addition of Hermite-Gaussian higher order modes. Root mean square angle-of-arrival fluctuations are formulated using the previously reported multimode phase structure function, which is valid in weak atmospheric turbulence. Results are found for practical FSO links operating at 1550 nm and 850 nm wavelengths and for link spans of up to 5 km. In choosing the mode content, various sequential grouping of all possible mode combinations are used up to a certain order (n,m) mode. We start with the single fundamental mode (TEM₀₀) and span up to the highest order (n =10, m =10) mode. In this manner, different degrees of source coherence are also taken into account. Angle-of-arrival fluctuations are found to be in the range of several tens of μradians and almost insensitive to the mode content except for the cases when the mode group terminates with an odd mode. In such instances, the fluctuations rise to a few hundreds of μrad. Comparing our results with the field of view of a practical FSO receiver, which is several mrad, we conclude that the-angle-of arrival fluctuations due to multimode excitation will not influence the FSO link performance to a major extent.

The signal-to-noise ratio characterizing data transmission using modulation of the parameters of the mapping generating a chaotic sequence is estimated. It is shown that, in systems using a control parameter to introduce information, the output signal-to-noise ratio is reduced as compared to the input value. It is found that noise fluctuations in the information parameter measured depend on signal fluctuations at several adjacent sample points. A multichannel system is considered. It is noted that the increase in the number of channels results in the decrease in the output signal-to-noise ratio due to both addition of the noise components of the adjacent sample elements and exponential growth of errors in the reconstructed parameters of chaotic systems. A decrease in the output signal-to-noise ratio is found to be partly compensated by impeding unauthorized access to the information transmitted.

The paper presents a new approach to reconstruction of impulsively disturbed stereo audio signals. The problems of restoration of large blocks of missing samples are outlined. Present methods of removing of covariance defect are discussed. Model of stereophonic signal is defined and Kalman filter appropriate for this model is introduced. Modifications of the filter directing to the new method of reconstruction of block of missing samples are discussed. Projection based algorithm allows to recover samples of left (or right) stereo channel using additional information included in undistorted samples from the other channel.

Motion estimation (ME) is a computationally intensive task during video compression. Although diamond search (DS) is an efficient way to speed up block-matching process, skip mechanism (Skip-M) combined with DS will give further speed-up. However, how to choose threshold in this mechanism is essential to improvement magnitude. In this paper, we propose a scheme in which the threshold is chosen based on analysis of noise variance due to video devices. Simulation results show the proposed algorithm can remarkably reduce the time consumption with only marginal performance penalty.

In telecommunications, the incoming information signal is susceptible to attenuation, noise and jitter. Bit error rate, Q-factor, and signal to noise ratio are three key parameters that determine channel performance. Typical error detecting and correcting codes detect up to sixteen errors and correct up to eight within a block of information. Although this method monitors each channel without service interruption, the detection code has a limited error detection capability and requires several frames (or packets) to estimate bit error rate and thus it takes a relatively long time. Another method is based on “eye diagrams”; however, this requires costly equipment and off-line measurements in addition to service interruption. In this paper, we describe the mathematical background of statistical estimation of eye-diagrams and we present a circuit that automatically estimates BER, SNR, and Q-factor at each port without service interruption. This method is based on statistical sampling and therefore estimates are made in short intervals. In addition, we describe the functional block of a VLSI circuit that estimates the aforementioned performance parameters.