V.G. Kartashevskij – Dr. Sc. (Eng.), Professor, Dean of Faculty, Head of Department, Volga State University of Telecommunications and Informatics (Samara)
K.A. Bel\'skij – QA Analyst/Business Analyst, LLC «NetCracker» (Samara)
K.S. Slipenchuk – Deputy Head of Department, Volga State University of Telecommunications and Informatics (Samara)
In article the problem of processing of signals of orthogonal frequency multiplexing (OFDM) in channels with dispersion is considered. In the communication systems using the OFDM technology together with the quadrature amplitude modulation (QAM) for maintenance in a place of reception of orthogonality of harmonic oscillations on transfer protective intervals between the transferred symbols are formed. Introduction of protective intervals means loss of spectral system effectiveness, and the more a dispersion interval for fight against temporary dispersion, the it is more than loss of spectral efficiency. Really such losses can make to 20%.
For elimination of losses of spectral efficiency and for increase of a noise stability of reception in article it is offered to use estimation of the counting, characterizing OFDM a symbol, which in the scheme of reception move on the demodulator, representing the device of formation of FFT. As shown in article, it is expedient to make estimation of counting of OFDM of a symbol in the channel with dispersion and additive hindrances by criterion of maximum likelihood which realization is connected with the solution of the «return task».
The solution of the «return task» by method of regularization leads to the decision of system of the linear algebraic equations which coefficients decide by known values of counting of the pulse characteristic of the channel on dispersion and counting of an observed signal.
For the purpose of decrease of dimension of system of the linear equations it is offered to use algorithm «reception in general on a dispersion interval with consecutive formation of an assessment».
The integral procedure of this algorithm is use «feedback by an assessment».
Modeling of work of this algorithm showed its high noise stability in the wide range of change of the relation signal/noise in a reception place.
Formation of estimates with a small mean square error at low computing expenses allows to refuse protective intervals in structure of a channel signal when using this algorithm. This fact allows to increase significantly spectral system effectiveness of the communication using the OFDM technology.