Performance analysis of LMS adaptive prediction filters

The conditions required to implement real-time adaptive prediction filters that provide nearly optimal performance in realistic input conditions are delineated. The effects of signal bandwidth, input signal-to-noise ratio (SNR), noise correlation, and noise nonstationarity are explicitly considered. Analytical modeling, Monte Carlo simulations and experimental results obtained using a hardware implementation are utilized to provide performance bounds for specified input conditions. It is shown that there is a nonlinear degradation in the signal processing gain as a function of the input SNR that results from the statistical properties of the adaptive filter weights. The stochastic properties of the filter weights ensure that the performance of the adaptive filter is bounded by that of the optimal matched filter for known stationary input conditions     

A Robust Coded MIMO FH-CDMA Transceiver for Mobile Ad Hoc Networks

In this paper, we develop a coded MIMO FH-CDMA transceiver that is robust to partial-band jamming and the near-far problem for ad hoc networks with high mobility. Spatial and frequency diversity are achieved respectively by differential unitary space-time modulation (DUSTM) and coding/interleaving. Decision-feedback demodulation (DFD) and erasure insertion (EI) decoding are employed to mitigate fast Rayleigh fading and interference. A decision-directed adaptive estimator is also developed to estimate the required parameters in DFD and EI. The two proposed EI schemes are based on the Bayesian framework proposed by Baum and Pursley (1992) and a novel threshold test of the effective signal to noise and interference ratio (ESINR), respectively. Decoding error probability of the ESINR based EI is derived analytically. Performance of both EI schemes are examined under various interference conditions, and the effect of EI thresholds is carefully discussed. The Bayesian EI is shown to be insensitive to suboptimal threshold and achieves significantly better performance than error-only decoding. Furthermore, it is shown that analysis of the ESINR based EI scheme predicts the performance of the Bayesian EI when the interference is dominant.     

Ohmic contacts to semiconducting diamond

A solid-state reaction process for producing ohmic contacts to polished natural semiconducting diamond surfaces is discussed. The approach attempts to systematically characterize the processes which occur when metallic films of known thickness are deposited on a smooth diamond surface and annealed in the solid state under controlled conditions. Annealed tantalum/gold and titanium/gold deposits on {100} polished diamond surfaces reduced the resistance by seven orders of magnitude relative to the as-received samples. The interfaces were characterized using metallography, scanning electron microscopy, and secondary ion mass spectrometry     

Error probability performance prediction for multichannel reception of linearly modulated coherent systems on fading channels

This paper provides a framework for the analysis of error rate performance of maximal ratio combining multichannel reception of coherent linearly modulated systems over frequency-selective fading channels. Expressions for the error probability are developed, and the special cases for which closed-form or acceptable efficient numerical solutions are possible are delineated. A new efficient and accurate recursive method for the Ricean fading main resolved path case is presented for coherent quadrature amplitude modulation constellations. The effect of automatic gain control error on analysis of modulation schemes is demonstrated. Finally, numerical examples based on the maritime high-data-rate channel model are provided to demonstrate the usefulness of the framework.     

Adaptive interference suppression for CDMA overlay systems

It has been proposed that CDMA systems can be assigned to spectral bands which are presently occupied by narrowband users to further increase spectral capacity. Such CDMA overlay systems could provide new options for efficient utilization of the spectrum with minimal disruption to existing narrowband users, especially if adaptive interference suppression techniques are utilized in the spread spectrum receiver. Previous studies have defined the SNR improvement ratio which can be achieved for tone interferers and for narrowband interferers for which the center frequency of the interference is at the carrier frequency of the CDMA signal. In this paper the bit-error-rate (BER) performance of the mobile-to-base link of a CDMA system for a single narrowband user which occupies a significant portion of the CDMA bandwidth is evaluated. It is shown that the narrowband model used in previous studies does not apply in this case, especially for the large, effective, bandwidths which are characteristic of the interferers in the overlay system. The dependence of the BER on the filter order, the bandwidth of the interference, and its center frequency relative to the CDMA carrier frequency are defined. Additionally the increase in BER for a digital implementation of the adaptive suppression filter relative to the optimal Wiener filter is characterized with respect to the adaptive time constant and the quantization errors due to finite wordlength. It is shown that these implementation errors can be made negligible compared to the errors which are characteristic of the optimal Wiener filter. Analytic results are validated by simulation for typical system parameters     

Sporadic Creutzfeldt-Jakob disease in the United Kingdom: analysis of epidemiological surveillance data for 1970-96

OBJECTIVE: To identify changes in the occurrence of Creutzfeldt-Jakob disease that might be related to the epidemic of bovine spongiform encephalopathy. DESIGN: Epidemiological surveillance of the United Kingdom population for Creutzfeldt-Jakob disease based on (a) referral of suspected cases by neurologists, neuropathologists, and neurophysiologists and (b) death certificates. SETTING: England and Wales during 1970-84, and whole of the United Kingdom during 1985-96. SUBJECTS: All 662 patients identified as sporadic cases of Creutzfeldt-Jakob disease. MAIN OUTCOME MEASURES: Age distribution of patients, age specific time trends of disease, occupational exposure to cattle, potential exposure to causative agent of bovine spongiform encephalopathy. RESULTS: During 1970-96 there was an increase in the number of sporadic cases of Creutzfeldt-Jakob disease recorded yearly in England and Wales. The greatest increase was among people aged over 70. There was a statistically significant excess of cases among dairy farm workers and their spouses and among people at increased risk of contact with live cattle infected with bovine spongiform encephalopathy. During 1994-6 there were six deaths from sporadic Creutzfeldt-Jakob disease in the United Kingdom in patients aged under 30. CONCLUSIONS: The increase in the incidence of sporadic Creutzfeldt-Jakob disease and the high incidence in dairy farmers in the United Kingdom may be unrelated to bovine spongiform encephalopathy. The most striking change in the pattern of Creutzfeldt-Jakob disease in the United Kingdom after the epidemic of bovine spongiform encephalopathy is provided by the incidence in a group of exceptionally young patients with a consistent and unusual neuropathological profile. The outcome of mouse transmission studies and the future incidence of the disease in the United Kingdom and elsewhere, will be important in judging whether the agent causing bovine spongiform encephalopathy has infected humans.     

Space-path diversity in cdma using a compact array

This paper investigates the performance of a compact space-time diversity receiver for mobile communication systems. Expressions for the bit error rate and outage meanSnr are derived as a function of the channel covariance matrix. These results define the sensitivity of the performance of such a receiver to the environment (fading characteristics and angular spread) and the antenna array (geometry and coupling). Furthermore, these results are validated for a practical antenna system.     

CINR difference analysis of optimal combining versus maximal ratio combining

The statistical gain differences between two common spatial combining algorithms: optimum combining (OC) and maximal ratio combining (MRC) are analyzed using a gain ratio method. Using the receive carrier-to-interference plus noise ratio (CINR), the gain ratio ClNR/sub OC/ /CINR/sub MRC/ is evaluated in a flat Rayleigh fading communications system with multiple interferers. Exact analytical solutions are derived for the probability density function (PDF) and the average gain ratio with one interferer. When more than one interferer is present, the PDF of the gain ratio is illustrated using Monte Carlo simulations and its mean value is shown in basic integral form. An upper bound to the gain ratio is derived providing a simple means to determine when OC will exhibit significant gains over MRC.     

Potenziale und Herausforderungen in der Implementierung der organophilen Nanofiltration in der Spezialchemie

Organic solvent nanofiltration (OSN) is a suitable tool for process intensification. For specialty chemicals production within a multi‐purpose environment, there are some specific concerns regarding membranes and equipment design that have to be considered. Process development for OSN to date is hampered by a lack of system characteristics and detailed transport models. Here, we present a systematic investigation with different membrane materials and solvents in order to define guidelines for a fast membrane selection.