Abstract-Multiple reads of the same Flash memory cell with distinct word-line voltages provide enhanced precision for LDPC decoding. In this paper, the word-line voltages are optimized by maximizing the mutual information (MI) of the quantized channel. The enhanced precision from a few additional reads allows frame error rate (FER) performance to approach that of full-precision soft information and enables an LDPC code to significantly outperform a BCH code.A constant-ratio constraint provides a significant simplification in the optimization with no noticeable loss in performance.For a well-designed LDPC code, the quantization that maximizes the mutual information also minimizes the FER in our simulations. However, for an example LDPC code with a high error floor caused by small absorbing sets, the MMI quantization does not provide the lowest frame error rate. The best quantization in this case introduces more erasures than would be optimal for the channel MI in order to mitigate the absorbing sets of the poorly designed code.The paper also identifies a trade-off in LDPC code design when decoding is performed with multiple precision levels; the best code at one level of precision will typically not be the best code at a different level of precision.

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This paper presents the moment generating function (MGF)–based analysis of κ‐μ/gamma composite fading model, which is suitable for the indoor off‐body communication channel. In this paper, first of all, we derive an analytical expression for MGF of instantaneous signal‐to‐noise ratio. By using the derived MGF, the expressions of average symbol error rate (ASER)/average bit error rate (ABER) for binary and M‐ary modulation scheme are derived. Using the MGF approach, we also derive the expression of channel capacity for optimum rate adaption and channel inversion with fixed rate policy. The derived expressions for ABER/ASER and channel capacity are presented in the infinite series form. We further present the numerical results of error rate and channel capacity for different values of κ, μ, α, and β parameters. The result of ABER and channel capacity shows good agreement with the previously reported results as special cases that verify the derived expressions.

Oxidation of vanadyl sulfate by H2O2 involves multiple reactions at neutral pH conditions. The primary reaction was found to be oxidation of V(IV) to V(V) using 0.5 equivalent of H2O2, based on the loss of blue color and the visible spectrum. The loss of V(IV) and formation V(V) compounds were confirmed by ESR and 51V-NMR spectra, respectively. In the presence of excess H2O2 (more than two equivalents), the V(V) was converted into diperoxovanadate, the major end-product of these reactions, identified by changes in absorbance in ultraviolet region and by the specific chemical shift in NMR spectrum. The stoichiometric studies on the H2O2 consumed in this reaction support the occurrence of reactions of two-electron oxidation followed by complexing two molecules of H2O2. Addition of a variety of compounds--Tris, ethanol, mannitol, benzoate, formate (hydroxyl radical quenching), histidine, imidazole (singlet oxygen-consumption that also used V(IV) as the reducing source. This reaction requires concomitant oxidation of vanadyl by H2O2, favoured at low H2O2:V(IV) ratio. Another secondary reaction of oxygen release was found to occur during vanadyl oxidation by H2O2 in acidic medium in which the end-product was not diperoxovanadate but appears to be a mixture of VO3+ (-546 ppm), VO3+ (-531 ppm) and VO2+ (-512 ppm), as shown by the 51V-NMR spectrum. This reaction also occurred in phosphate-buffered medium but only on second addition of vanadyl. The compounds that stimulated the oxygen-consumption reaction were found to inhibit the oxygen-release reaction. A combination of these reactions occur depending on the proportion of the reactants (vanadyl and H2O2), the pH of the medium and the presence of some compounds that affect the secondary reactions.

Absfrcrcf -Voice Confenneing is an essential block of any multimedia system used for collaborative work. In a collaborative environment Floor ComoI is an important issue tbat is dealt by many; yet r i n g the number offloors is an open problem. In an audio conference, mixing streams from too many concurrent speakers degrades the voice quality. Therefore setting an upper bound for the number of streams woors) tbat may be mixed is sine qua non for providing quality conferencing service. In this paper we address the problem of setting the upper bound on number of floors for a system meant to support concurrent multi-party audio sessions on top of IP multicasting. A measure called "Loudness Number" tbat is used to manage the number of floors is briefly outlined to tbe extent of making this paper selfcontained. Our implementation at a functional level on a campuswide network of Window& systems has yielded satisfactory performance.

Real-time services have been supported by and large on circuitswitched networks. Recent trends favour services ported on packet-switched networks. For audio conferencing, we need to consider many issues -scalability, quality of the conference application, floor control and load on the clients/servers -to name a few. In this paper, we describe an audio service framework designed to provide a Virtual Conferencing Environment (VCE). The system is designed to accommodate a large number of end users speaking at the same time and spread across the Internet. The framework is based on Conference Servers [14], which facilitate the audio handling, while we exploit the SIP capabilities for signaling purposes. Client selection is based on a recent quantifier called "Loudness Number" that helps mimic a physical face-to-face conference. We deal with deployment issues of the proposed solution both in terms of scalability and interactivity, while explaining the techniques we use to reduce the traffic. We have implemented a Conference Server (CS) application on a campus-wide network at our Institute.

The authors investigate the spectral flatness measure (SFM)-based spectrum sensing technique for cognitive radios. This scheme exploits the fact that under Gaussian noise, the noise-only observations have flattened spectrum, i.e. more white, when compared with that of the observations containing the incumbent or primary signal; hence, an increased SFM under the null hypothesis. Under the null hypothesis, the authors derive the asymptotic distribution of the test statistic, and the asymptotically optimal detection threshold, with a constraint on the probability of false-alarm. Furthermore, the authors show that this test is robust to the noise variance uncertainty (NVU) and is related to a test based on the entropy in the observed sequence. Through extensive Monte-Carlo simulations, the authors show that the test based on SFM performs better than the existing energy detector and the blind detector, under realistic signal and fading models, all in the presence of NVU. The authors also highlight the practical utility of this technique based on experimental results.