Low complexity adaptive power and subcarrier allocation for OFDMA

The problem of low complexity sub-optimal power and subcarrier allocation for OFDMA systems is addressed in the paper. We propose a heuristic non-iterative method that is an extension of the ordered subcarrier selection algorithm recently proposed for a single user case to the OFDMA systems. The suggested method improves the average BER-performance of the system and it also provides fairness between the users in terms of the bit rates. Both the theoretical analysis and simulation results confirm efficiency of the proposed technique. Based on the proven lemma about inversion of power gains, we strengthen the suggested method by low complexity power loading that consists in equalization of the received signal-to-noise ratios of each user     

Heat treatment of granulated VT22 alloy

A standard regime of heat treatment has been developed for semifinished products of VT22 alloy manufactured by the conventional technology (casting + deformation). However, it gives a comparatively low level of crack resistance in the case of granular technology (hot isostatic pressing + deformation). In this connection it became necessary to refine the regime of heat treatment of the granulated VT22 alloy. The present work concerns the effect of different regimes of heat treatment on the size and shape of segregations of the ct-phase, investigated with the aim of improving the crack resistance characteristics of granulated VT22.     

Effect of prolonged heating on the thermal stability of phases inα +β titanium alloys

Conclusions With prolonged low-temperature heating, alloys VT3-1 and VT9 tend to the stable condition corresponding to the heating temperature. This is accompanied by a change in the quantity of phase and the concentration of -stabilizing elements in phase.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 42–46, May. 1977.     

Useful integrals for performance evaluation of communication systems in generalised η - μand κ - μ fading channels

The author obtains closed-form expressions for the averages of the Gaussian Q-function and product of two Gaussian Q-functions over the generalised η - μand κ distributions. These results can be useful in many practical applications when evaluating error rate performances of communication systems operating in radio channels modelled by the η - μand κdistributions. The formulas are obtained in terms of Appell?s (F/sub 1/(.) and F/sub 1/(.)) and Lauricella?s (F/sup 3//sub D/(.) and ϕF/sub 1/ (3)(.)) hypergeometric functions. As examples of application, the average symbol error rates of general order rectangular quadrature amplitude modulation (QAM) in η - μ and κ - μradio channels are evaluated.     

Spectral analysis of nonlinear amplifier based on the complex gainTaylor series expansion

A method of spectral analysis for a nonlinear amplifier driven by a Gaussian signal is presented. The technique is based on the Taylor series expansion of the complex gain of an amplifier. Therefore, it takes into account both amplitude-amplitude modulation (AM/AM) and amplitude-phase modulation (AM/PM) conversions and requires only an input signal autocorrelation (or power spectral density) and AM/AM and AM/PM measurements without any additional calculations     

Comments on “Comments on the peak factor of sampled andcontinuous signals”

The author comments that a signal, which does not satisfy the conditions of the sampling theorem, is used as a basis for the proof in the paper of Wulich (see ibid., vol.4, no.7, p.213-14, 2000). Therefore, the presented proof is incorrect     

On the relationship between peak factor of a multicarrier signal and aperiodic autocorrelation of the generating sequence

The well-known relationship between the peak-to-average power ratio (PAPR) of a multicarrier signal and the autocorrelation coefficients of the generating sequence is discussed. We emphasise that low values of the autocorrelation coefficients represent only a sufficient condition for a small value of the PAPR of the signal. Therefore, the autocorrelation coefficients of the generating sequences cannot serve as a basis for comparison of PAPR of the corresponding signals.     

Average symbol error probability of arbitrary rectangular quadrature amplitude modulation in generalised shadowed fading channels

A closed-form approximation of average symbol error probability of arbitrary rectangular quadrature amplitude modulation in a gamma-shadowed Nakagami fading radio channel is derived. The final result is obtained on the basis of an exponential approximation of the Gaussian Q-function. It is shown that the derived formula can also be used for error probability estimation in Nakagami-log-normal radio channels for a wide range of shadowing spread values. The numerical aspects of calculation are discussed.     

Nutritional disorders in workers and employees of an industrial enterprise in Tselinograd and the incidence of gastroduodenal diseases

Questioning of 877 subjects was conducted during prophylactic examination of workers at industrial enterprises in Tselinograd. Endoscopy and intragastral pH-metry were used to investigate the stomach and duodenum. Disorders in nutrition were proved more often in those with the disease diagnosed for the first time. The incidence rate of symptoms of diseases of the digestive organs depended on disorders in nutrition regimen, and was directly proportional to them. It has been shown that screening-questionnaire can be used for the study of nutrition factors in industrial workers during prophylactic examination. Gastroduodenal diseases, i.e. chronic gastritis with hyperacidity, and functional gastric diseases are most frequent.