Reduction of Separation Distance in MIMO Systems Using Polarization Diversity

Abstract

One of the promising techniques in communication systems is the Multiple Input –Multiple Output (MIMO) systems. The aim of these systems is increasing channel capacity, and the main problem in these systems is the required separation distance between antennas which must be greater than or equal to half wavelength. Satisfying this separation distance is difficult especially at low frequencies. In this paper we study the ability to reduce the total separation distance by using polarization diversity. Each two adjacent antenna are replaced by one dual polarized antenna. The obtained results show that the use of polarization diversity will reduce the required separation distance and the performance of the system will be better than that of classical system (without polarization diversity). This improvement is more useful at the system with greater number of antennas. Increasing the correlation between antennas due to the separation angle will reduce the channel capacity. The results also show that increasing the cross polarization discrimination XPD will increase channel capacity at low level of signal to noise ratio (SNR) and decrease it at high level of it if the attenuation for horizontally polarized signal is the same as that for vertically polarized signal (CPF=0), but if (CPF 0) then low values of XPD will improve channel capacity especially at high level of SNR. The results also prove that channel capacity inversely proportional with CPF at rural area (XPD 0), and when XPD=0 (urban area) the channel capacity linearly proportion with CPF at high level of SNR, and inversely proportional with CPF at low level of it.