Abstract-Nonlinear distortion of OFDM signals can significantly increase the receiver symbol error rate (SER). Currently, distortion analyses rely on simulation, not yielding insight into the problem, or apply to specific nonlinearities only. In this letter, general analytic results are presented on the errors resulting from distortion. The results are applicable to smooth nonlinear distortion of an OFDM signal, which is the most common distortion. Simple analytical expressions are derived which allows a designer to determine the SER before performing simulations. Further, it is shown that the error on each OFDM subcarrier is approximately equally large.
SUMMARYWe demonstrate by measurements on a test circuit that a 5 GHz relaxation oscillator with accurate quadrature outputs and low phase-noise can be obtained, and that these favorable properties can be preserved while the mixing function is performed by this oscillator. This is useful either to measure the quadrature error at a low frequency, or to implement a low-intermediate frequency (IF) or zero-IF (homodyne) radio frequency front-end.
The corrosion behaviour of Cr(III) based conversion coatings on electrogalvanised steel was studied using polarisation and electrochemical impedance spectroscopy measurements in 0 . 01M NaCl solution (pH 6). The Cr(III) based conversion treatments were carried out in two different commercial trivalent chromium baths (pH 1 . 8-2 . 0). With an immersion time of 1 min, the thickness of the first type of Cr(III) based coating (blue) was about 94 nm and the thickness of the second type of coating (iridescent yellow) was about 250 nm; these thicknesses were determined by spectroscopic ellipsometry. As a comparison, a Cr(VI) based coating on electrogalvanised steel was also studied. The morphologies and compositions of the coatings were investigated by means of scanning electron microscopy, Fourier transform infrared spectroscopy and Auger electron spectroscopy. The Cr(III) coatings contained mainly a mixture of zinc oxides and chromium oxides/ hydroxides, and no Cr(VI) was detected in these coatings. The polarisation measurements in NaCl solution showed a retarded cathodic reaction for both the Cr(III) and the Cr(VI) based coatings. The corrosion resistance of the thicker Cr(III) coating was greater than that of the thinner Cr(III) coating. However, in the cases studied, the Cr(III) coatings still did not inhibit the corrosion of the electrogalvanised steel as effectively as did the Cr(VI) based coatings. The reason may be that the Cr(III) coatings do not possess the 'self-healing' properties that the Cr(VI) based coatings do. SE/S295
Drying effects on corrosion performance of Cr(VI)-and Cr(III)-treated electro-galvanized steel have been studied in NaCl solution using potentiodynamic measurements and electrochemical impedance spectroscopy (EIS). The Cr(VI) and the Cr(III) treated specimens were dried at three different temperatures: 60, 110 and 210°C. The surface layers were investigated using SEM, AES and XPS. The results show that the drying temperature not only affects the morphology of the surface layer, but also changes the chromium oxidation states in the layer. The corrosion protection given to the EG steel by Cr(VI) and Cr(III) pretreatments can be severely reduced if the pretreated surfaces are heated above 110°C. Both types of coating undergo some dehydration during heat treatments, which is undesirable for good corrosion protection. For Cr(VI) coatings, additional degradation mechanisms include widening of the cracks in the coating, and reduction of Cr(VI) to the Cr(III) oxidation state.
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