APPLICATION OF EQUALIZERS TO REMOVE THE INTERMIMENTIAL INTERFERENCE IN TROPOSPHERIC COMMUNICATION CHANNELS

Abstract

The article explores the possibility of using equalizers to create controlled intersymbol interference as a way of dealing with such interference arising in the troposcatter channel. The frequency-selective fading in multipath propagation of radio signals leads to their distortion, causing interference with intersymbol interference in channels with variable parameters, such as the troposcatter channel. With an appropriate choice of waveforms can significantly reduce the effect of intersymbol interference. For this purpose in the article defines the function F(ξ), which describes the waveform, whose frequency response has steeper slopes than the “raised cosine”. The impulse function h(y) is written through the function F(ξ). To determine it the Fredholm integral equation with a symmetric core is solved. Formulas for the value of F(ξ) in the zero and higher approximations are obtained. The equalizer schemes that implement the required F(ξ) are given. The core of an integral equation is represented as a sum containing modified Bessel functions of the first kind of fractional order. A system of linear equations is obtained. The solution of which is the function F(ξ). This function F(ξ) was found by while holding a different number of members of the series. The inaccuracy of the calculated functions F(ξ) are found. In the article is the equalizer schemes which to implement the task of this research. Considered options for constructing equalizers according to the scheme with a test signal, without a test signal and adaptive with a transversal filter. The result obtained in the article using the QPSK modulation method can be extended to the case of multiple phase modulation. The use of the equalizer schemes described in the article is determined, as a rule, by the developer depending on the requirements for the characteristics and parameters of the digital troposcatter system.