SPATIAL DIVERSITY SIGNAL TRANSMISSION IN DIGITAL TROPOSCATTER STATIONS

Abstract

The article examines the possibility of increasing the normalized throughput of digital troposcatter stations on the way of using space-separated signal transmission. Shown is a block diagram of the transmitting path of a digital troposcatter station with space-separated signal transmission. Methods of separation at the reception of signals acting at the input of the space-time coding device of the transmission path of the microwave digital troposcatter station are analyzed. Three methods of signal addition are considered in detail: linear addition; auto selection; optimal (quasi-optimal) addition. Various variants of addition are analyzed: before the demodulator and after the demodulator. The calculation of the normalized channel capacity as a function of the signal-to-noise ratio for the case of two transmitting antennas with known and unknown channel matrices is carried out. It was found that with two transmitting antennas and an unknown channel matrix, the normalized bandwidth does not differ from the case of using one transmitting antenna. The effect of cross-polarization isolation on the normalized channel capacity is analyzed, when one transmitting antenna emits signals of horizontal polarization, and the second transmitting antenna emits signals of vertical polarization. The values of the error probability are obtained for spatially-separated signal transmission to two transmitting antennas for two laws of distribution of a random variable - Rayleigh and Rice. The Rice distribution law of a random variable, the error probability is expressed through the modified zero-order Bessel function. The calculated data are shown in the table. The calculation was carried out in two frequency ranges allowed for the use of troposcatter communication facilities and for a channel without fading and for a channel with intersymbol interference.