Main Source Of Interference Research Articles

Clipped Diversity Combining for Channels with Partial-Band Interference--Part I: Clipped-Linear Combining

Clipped-linear diversity combining is analyzed for receivers without side information. Communication systems with noncoherent demodulation, binary and M -ary orthogonal signaling, and diversity transmission are considered. The main source of interference is additive Gaussian partial-band interference, but a nonzero quiescent noise level is also included in the analysis to account for wide-band noise sources. Some of the results apply to general (non-Gaussian) interference. The numerical results demonstrate that clipped-linear combining can perform well in terms of both narrow-band interference rejection capability and maximum signal-to-interference ratio requirement. A practical disadvantage of clipped-linear combining is that it relies on measurements of the signal output voltage.

Errors in atomic absorption spectrophotometric determination of Pb, Zn, Ni and Co in geologic materials

Errors in atomic absorption spectrophotometric determinations of Pb, Zn, Ni and Co may occur due to the presence of Fe, Al, Ca, Mg, Na and K in the sample solution. At low concentrations of trace element in solution (i.e., up to about 1 p.p.m.) and low concentrations of major elements (up to about 4,000 p.p.m. total cations), the main source of interference is enhancement due to background absorption; this may be corrected by the hydrogen continuum or by use of a non-absorbing wavelength. At higher concentrations of trace element the enhancement due to molecular absorption is partly or completely nullified through suppression caused by major element interference. Similarly, at higher concentrations of major elements, suppression occurs which is probably a function of atomizer efficiency. In these situations, correction for total molecular absorption results in a residual negative error. The errors in determination of Pb, Zn, Ni and Co in geological materials are often ignored in exploration geochemistry work. This restriction on the accuracy of the analytical data is becoming more important with the increasing use of exploration methods based on rock analyses. The errors may be minimized by ensuring that the concentration of both trace element and major element in solution is too low to cause significant suppression effects. Under these circumstances, reasonable results should be obtained through correction for background absorption.

A Generalized Nyquist Criterion and an Optimum Linear Receiver for a Pulse Modulation System

A pulse modulation system is modeled with M waveforms {s <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> (t)} <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sup> <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> , each of which is amplitude scaled and simultaneously transmitted over a single physical channel. An infinite pulse train is assumed with signal interval T, which is determined by bandwidth consideration of the channel. We restrict the receiver to be linear with M outputs, one for each signal waveform. At a high signal-to-noise ratio the main sources of interference at the input to the receiver are the intersymbol interference and crosstalk; by crosstalk we mean the interference between the different waveforms. It is desirable, therefore, for the receiver to eliminate both types of interference and to minimize the remaining error due to additive noise in the channel. This constraint on the intersymbol interference and crosstalk is defined as the generalized Nyquist criterion. The receiver which accomplishes the above is determined for a mean square error criterion. Finally, some examples are presented which demonstrate the ease with which the generalized Nyquist criterion can be used to design waveforms without intersymbol interference or crosstalk.