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Benford's Law deals, among other things, with the proportion of numbers whose first significant digit is a 1 (e.g., 0.00131 and 19668 both have first significant digit 1) in a variety of datasets. In these datasets, which arise in various compendiums or as mixtures of various sets of numbers, the proportion of numbers with first significant digit one is 0.3010 which is much higher than the commonsense value of 1/9. The reasons for this occurrence have been elusive. Mathematical attempts to explain this phenomenon have been relatively fruitless. Methods involving probability have been somewhat more successful. In this article we give some simple reasons for this occurrence and also give an example of a general mixture of distributions which exactly satisfies this Law. Various other examples and counterexamples are also given. KEY WORDS: Benford's Law; Law of the Stripey Hat; Significant digits.

Time series often contain observations of several variables and multivariate time series models are used to represent the relationship between these variables. There are many studies on vector autoregressive moving average (VARMA) models, but the representation of multiplicative seasonal VARMA models has not been seriously studied. In a multiplicative vector model, such as a seasonal VARMA model, the representation is not unique because of the noncommutative property of matrix multiplication. In this article, we carefully examine the consequences of different model representations on parameter estimation and forecasting through numerical illustrations, simulation, and the analysis of a housing starts and housing sales dataset. KEY WORDS: Estimation; Forecasting; Information criteria; Seasonality.

In this paper, we first derive the theoretical performance of a complementary code keying (CCK) code on an additive white Gaussian noise (AWGN) channel and over a multipath channel. To derive the error performance, we use the weight and cross-correlation distributions of the CCK code for optimal and suboptimal decoding, respectively, based on union bound. In addition, we propose a RAKE receiver for a CCK modem, which is suitable for a multipath environment with a large delay spread. The RAKE receiver principle is acceptable for modest multipath because it can coherently combine multipath components to provide signal-to-noise ratio (SNR) enhancement. However, as the delay spread is larger and the data rate of systems goes higher, intersymbol interference (ISI) generated due to multipath environments are increased. To handle the increasing ISI, the CCK modem needs an equalization technique to remove the ISI, together with RAKE processing. Thus, our proposed system is based on a channel matched filter (CMF) with a decision feedback equalizer (DFE). The CMF is applied for RAKE processing, whereas the DFE structure is used for ISI cancellation. In our system, ISI is calculated and removed by using a decoded CCK codeword. Index Terms--Complementary code keying (CCK), decision feedback equalizer (DFE), equalization, RAKE receiver.

This paper introduces a novel approach to data communication over the Global System for Mobile Communications (GSM) voice channel. It is based on the concept of 'symbols'--a set of predefined signals with finite bandwidths. Data are encoded into the symbols, and the symbols are voice coded as they were speech, modulated into the GSM signal, sent over the air, GSM demodulated, voice decoded, and converted back to data. The symbols are synthesized by a genetic algorithm with the aim of maintaining separability after passing them through the voice codec. This method enables data transfer over communication networks that do not have dedicated data channels and could also be used in conjunction with other data services to balance the system load between data and voice channels, allowing optimization of system resources. We present the full algorithmic structure of the system, which performs data communications over the GSM voice channel, and we also give the results of the performance tests. Index Terms--Data communications, genetic algorithms (GAs), mobile communications, vocoders.

We present examples based on actual and synthetic datasets to illustrate how simulation methods can mask identification problems in the estimation of discrete choice models such as mixed logit. Simulation methods approximate an integral (without a closed form) by taking draws from the underlying distribution of the random variable of integration. Our examples reveal how a low number of draws can generate estimates that appear identified, but in fact, are either not theoretically identified by the model or not empirically identified by the data. For the particular case of maximum simulated likelihood estimation, we investigate the underlying source of the problem by focusing on the shape of the simulated log-likelihood function under different conditions. JEL classification: C 15; C25 Keywords: Simulation methods; Discrete choice; Identification

Within Australia there is a growing interest in e-research and the use of cyberinfrastructure. There is also increasing recognition that the use of cyberinfrastructure is often inhibited, not by technical issues, but by so-called 'soft' issues, such as those related to work practices, intellectual property issues, the nature of research collaboration, and institutional imperatives. This paper reports on aspects of DART (Dataset Acquisition, Accessibility and Annotation e-Research Technologies), a current e-research project, specifically issues related to the broader questions of uptake and use of repositories by researchers. The paper concludes by discussing implications for libraries and for the design and promotion of repositories., In a study of changing research practices in Australia conducted for the Department of Education, Science and Training (DEST), Houghton et al conducted interviews and workshops with researchers from a [...]

In this paper, we demonstrate the first implementation of the integrated system-on-package (SOP) 60-GHz gigabit modulator and demodulator on liquid-crystal polymer (LCP). LCP provides an organic low-cost low dielectric-constant platform suitable for millimeter-wave passive design and packaging. Firstly, we demonstrate a 60-GHz planar bandpass filter and RF/baseband duplexer as the building blocks of the integrated module. Measurement results show ~3-dB insertion loss in the bandpass filter, as well as the RF path of the duplexer, and a higher than 30-dB isolation between the baseband and RF outputs. We utilize those building blocks in the design and implemented a hybrid 60-GHz antiparallel diode-pair-based 4x sub-harmonic mixer suitable for direct up or down conversion. Measurement results indicate a better than 17-dB insertion loss with 1.25-GHz baseband bandwidth for the 4 x mixer. Input 1-dB compression point of -2 dBm has been measured. Two subharmonic mixers are integrated back-to-back to perform the simultaneous binary phase-shift keying modulation and demodulation of the pseudorandom binary sequences. Eye diagrams show a better than 13-dB SNR for a data rate up to 1.5 Gb/s. 40-GHz versions of the 4 x subharmonic mixer and the back-to-back chain have also been implemented. Hence, we present the first integrated millimeter-wave gigabit SOP modulator and demodulator on LCP. Index Terms--Liquid crystal polymer (LCP), millimeter wave, modulator, subharmonic mixer, system-on-package (SOP).

A unique dataset obtained with combinations of minisodars and 915-MHz wind profilers at the Atmospheric Boundary Layer Experiments (ABLE) facility in Kansas was used to examine the detailed characteristics of the nocturnal low-level jet (LLJ). In contrast to instruments used in earlier studies, the ABLE instruments provide hourly, high-resolution vertical profiles of wind velocity from just above the surface to approximately 2 km above ground level (AGL). Furthermore, the 6-yr span of the dataset allowed the examination of interannual variability in jet properties with improved statistical reliability. It was found that LLJs occurred during 63% of the nighttime periods sampled. Although most of the observed jets were southerly, a substantial fraction (28%) was northerly. Wind maxima occurred most frequently at 200-400 m AGL, though some jets were found as low as 50 m, and the strongest jets tended to occur above 300 m. Comparison of LLJ heights at three locations within the ABLE domain and at one location outside the domain suggests that the jet is equipotential rather than terrain following. The occurrence of southerly LLJ varied annually in a way that suggests a connection between the tendency for jet formation and the large-scale circulation patterns associated with El Nino and La Nina, as well as with the Pacific decadal oscillation. Frequent and strong southerly jets that transport moisture downstream do not necessarily lead to more precipitation locally, however.

A report on neural network modeling for small dataset using both real and simulated datasets justified some of BartlettEs result is presented.

In an all-digital timing-adjustment system for digital modems, interpolation can be employed to recover samples that are synchronous with the data symbols. In this paper, a novel interpolation method is described for such systems. Instead of approximating a continuous-time signal with a conventional (algebraic) polynomial and computing the synchronized samples using a Farrow structure, a trigonometric polynomial is employed. It is demonstrated that this approach produces a particularly simple implementation structure, reduces computational delay and, for practical signals, can improve the interpolation performance. Moreover, to recover a synchronized sample from existing samples, given a timing offset, it is shown that the method can be optimized such that a recovered sample's interpolation error is minimized for that specific timing offset value. The input signal's spectrum is also taken into account. Simulation results indicate that the method can achieve the best performance among all state-of-the-art methods tested. In addition, the optimal interpolator can be implemented without increased hardware requirements. Index Terms--Fractional delay filter, interpolation, sample-rate conversion, synchronization, timing recovery, trigonometric polynomial.

Ever since the first dial-up modems appeared in the 1960s, their obsolescence has been repeatedly predicted. However, contrary to such predictions, dial-up modems thrived in the 1980s and 1990s as a result of the slow rollout of residential digital services and the unprecedented growth of internet and remote access. Since the first 300 b/s dial-up modem standard (V.21), modem speeds have increased steadily. Most recently, International Telecommunications Union (ITU) Recommendation V.90 (1998) takes advantage of the direct digital-network connection of an internet service provider (ISP) remote-access server to achieve speeds of more than 50 kb/s downstream (from ISP to a user). However, for upstream transmission (from a user to ISP), V.90 employs the older V.34 modulation (1994), which typically delivers on the order of 30 kb/s. A new ITU modem standard called V.92 increases upstream rates to above 40 kb/s, again by taking advantage of pulse code modulation connections. In this paper, we present the transmission scheme that has been adopted for V.92. It involves a generalization of Tomlinson-Harashima precoding. We predict that V.92 will be the last dial-up modem standard. However, we have to wonder whether we might be falling into the same trap into which many others have fallen in the past. The future will be the judge! Index Terms--Dial-up modem, pulse code modulation (PCM) modem, Tomlinson-Harashima precoding, V.90, V.92, 56k modem.

This correspondence analyzes the crest-factor behavior of an orthogonal frequency-division multiplexing (OFDM) modem. The behavior is characterized in terms of the complementary distribution function of the crest-factor (CDFC). The CDFC is a key parameter of OFDM systems, for example it provides limits on achievable information rates. Several approximations have been developed in the literature so far, but no true upper bounds dependent on the different constellations that are used in OFDM modulation have been derived. A new approach is given providing upper bounds that substitute for time-consuming simulations. Index Terms--Binary phase-shift keying (BPSK), Chernoff bound, crest-factor, Nyquist rate, orthogonal frequency-division multiplexing (OFDM), oversampling, peak-to-average power ratio (PAPR), peak-to-mean envelope power ratio (PMEPR), quadrature amplitude modulation (QAM).

The effects of the phase noise (PN) on orthogonal frequency-division multiplex modems are evaluated. Three receivers are studied: a coherent receiver, a common phase error correction receiver (which is a receiver specially designed to combat PN) and a differential receiver. The impact of the PN on the decision signal-to-noise ratio (SNR) of each of these receivers is computed as a function of the PN spectrum. The resulting formulas are extremely simple. The theory is applicable to a wide range of PN models, and unifies and extends previous results on the topic. The conditions under which the decision SNR yields correct symbol error rate predictions are discussed. Simulations are reported that confirm the results. Index Terms--Frequency-division multiplexing, phase noise.

Until the V.Fast modem standard is approved in 1994, modem chip makers will argue about the best means of increasing data rates beyond 14.4 kbits/s. But increased data rates are […]