CODE DIVISION MULTIPLEXING IN BROADBAND TELECOMMUNICATION SYSTEM WITH MIMO (2X2) IMPLEMENTING MODIFIED GOLD’S PSEUDO-RANDOM SEQUENCE

Abstract

In modern telecommunication systems (TCS), multi-element MIMO antennas connected to different channels of information transmission are widely used. The propagation of a radio signal in urban areas causes a rather complicated dependence of the transmission coefficients and significant signal changes, which leads to the creation of a multipath signal at the input of the receiver, including the signal fading. Designing systems with MIMO 2x2, the signal polarization separation can be used when orthogonal signals with vertical and horizontal polarization are used. At the same time there are naturally cross — polarization obstacles. In systems with any number of antennas, spatial diversity may be used when the antennas are spaced over several wavelengths. In this case, the antennas should have as narrow a directional pattern as possible, which is increased by the size of the antennas, resulting in a very bulky system. In any case, the radiation patterns are overlapped and interference from adjacent channels gets into the channels. Of all the signal processing methods, the main feature of which is the high implementation complexity, one of the most appropriate to use is the code division of the channels. In this paper a telecommunication system with MIMO (2x2) is observed, which uses the code division multiplexing using spatial diverse antennas. For this purpose, a modified Gold’s pseudorandom sequence is used, which allows to form a QPSK signal and, accordingly, to provide 2 times reduced required bandwidth. The authors propose a system design scheme for the forming and processing of broadband noise signal. Keywords: telecommunication system, MIMO multi-element system, multipath signal, antenna, Gold’s code, noise signal, code division multiplexing.