Items of № 5, 2013

The Electrosvyaz Magazine is one of the leading science & technical magazines in Russia.


VoIP traffic management on voice (IVR) platforms

The article shows the main methods of customer service quality increasing by improving corporate telephony infrastructure.
The proposed approach allows to optimize customer service using maintenance based on IVR (Interactive voice response) system usage in a corporate telephony infrastructure.
The existing solutions of IVR systems are considered in this article. The advantages of the approach based on usage of free PBX and VoiceXML markup language are compared to existing solutions.
Key words: corporate telephone infrastructure, Interactive voice response, automatic exchange, telephone script.



Aspects of the preventive preparation of the telecommunication networks for the operation under emergency. Part II

In this part of the article, scenarios of the network operation under emergencies are discussed. The analysis of these scenarios and the development of preventive solutions of the network organization will provide for the highest possible level of the quality of service. In addition, analysis of typical scenarios allows us to elaborate recommendations for the design of the telecommunication network to meet the requirements for its operation in emergency situations.
Key words: emergency, telecommunication system, preventive preparation of the network, traffic, failure.



Synthesis of two-criterion liner precoders for MIMO systems№

The article describes two-criterion algorithms for liner precoding in MIMO systems. The first criterion used for synthesis of these algorithms is a maximization of capacity of MIMO system, the second criterion – maximization of distance between points of signal constellation at output of MIMO channel. The results of algorithms simulation are presented. It is showed that two-criterion algorithms have up to 17 dB gain in BER versus one-criterion algorithms diagonalizing the through MIMO system matrix. Also BER performance for the proposed two-criterion up to 4-5 dB better than that one for MIMO-BLAST system without liner precoding.
Key words: liner precoder, mimo system, precoding algorithm, virtual channel, channel loading, capacity.



Analysis of quadrature mismatch compensation’s methods for digital communication receivers

Quadrature signal processing is a widely used technique in modern communication devices. However, there is always some imbalance due to the analog front-end component’s tolerances. For instance, the amplitudes of quadrature components are not equal and I/Q branches not separate on 90˚ accurately. These imbalances may provide great effects for noise margin and the reception quality.
The methods of non-idealities compensation is presented and classified for the low-IF and Direct Conversion receivers. Nonidealities for compensation maintain amplitude and phase I/Q-imbalance, carrier frequency offset (CFO) and DC-offset. Key words: non-idealities compensation, front-end, reception quality. 



Joint estimation methods of DC component drift and amplitude-phase imbalance for QAM signal with additive background white noise

Two compensation methods of DC component drift and amplitude-phase imbalance for QAM signal with additive white noise have been examined: variational method and nonlinear filtration method. Both can be used to estimate signal parameters using either test sequence or previously detected information symbols. Estimation accuracy of these two methods has been analyzed for different signal-to-noise ratio (SNR). Computer simulation shows advantage of variational method over nonlinear filtration method.
Key words: estimation, nonlinear filtration, regularization algorithm, modified least squares method (LSM).



Requirements to the accuracy of implementation and tuning of quadrature fluctuations’ ring oscillators

Basing on the theoretical analysis of steady-state operation of transistor LC-quadrature oscillators using ring structure (QORS) with single resonator and two coupled resonators, inserted between two limiting amplifiers in the feedback ring, simple formulae, connecting demands to accuracy of quadrature oscillations generation with demands to accuracy of implementation and tuning of the resonant circuits, that are used in the QORS. Key words: quadrature oscillators using ring structure (QORS), connecting demands, feedback ring.



Programs for search of frequencies areas with a minimum level of parasitic spectral components in ranges of output fluctuations of DDS

Spurious signals at the output of direct digital frequency synthesizers (DDS) are considered. The main mechanisms of the spurious spectral components generation at the output of DDS were considered and a general formula for calculating of the spurious components frequencies at the output of multi-channel DDS is offered. The software for these frequencies calculation and for selection of the bands that are free from spurious signals is presented and described. Key words: direct digital frequency synthesizers (DDS), calculating, selection, spurious signals.


Design of high performance PLL frequency synthesizer

In this paper structural and parametric synthesis of PLL frequency synthesizers was offered. Classical method of structural synthesis based on the theory of optimal linear and nonlinear filtering did not work properly in the case of existence in a system external and internal signal and noise sources. To solve the problem two steps were proposed. Firstly, optimal filters were synthesized separately for external and internal signal and noise sources. Second step was the structural synthesis, which includes the properties of optimal filters obtained at first step.
Key words: Frequency synthesizer, PLL, phase noise, structural and parametric synthesis.



Noise stability of transmission system of optimum finite signals on a telephone communication channel

Calculation of a potential noise-immunity of system of a digital telephony from МАМ and QАМ, based on synthesis of the optimum finite signals which are matched with a telephone channel of communication and not calling an intersymbol interference is given. The new generalised formulas for a signal/noise ratio and an average probability the errors depending on such parameters, as transmission rate, number of levels of signals of MAM, QАМ and power SNR are gained. Outcomes can be used at the comparative analysis of a noise-immunity of modern intellectual modems.
Key words: system of a digital telephony, multilevel and quadrature peak on-off modulation, optimum finite signals, a transmission ratio on powers, a noise-immunity.



Characteristic features of HF ionospheric NVIS radio line propagation

Presented studies of the NVIS mode as a promising form of communication. The model of the NVIS propagation of HF broadband radio signals in multi ionospheric radio channel with the frequency dispersion and magnetoionic splitting is developed. Computer experiment for study the dispersion parameter in the HF radio channel is conducted. Theoretical and experimental research of the power delay profile using digital chirp ionosonde developed in VSTU are conducted. Key words: NVIS mode, HF radio channel, VSTU .


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