Method for optimizing the spacing between receiving antennas of an array usable for counteracting both interference and fading in cellular systems

摘要

The spacing between adjacent receiving antennas of an ULA located in a base station of a cellular communication system is optimized to both the channel and the interference space-time multipath. The spacing is lager than the canonical »/2 for introducing a certain degree of angular equivocation aimed to see the interferers (all or a certain number depending on the degree of freedom of the directivity function) as they were grouped together along an unique direction. In an ideal case of fixed interferers with null angular power spread, a given cellular planning and known aperture of the array, the optimal spacing ” opt between adjacent antennas is directly calculable in closed mathematical form in function of the equal angular separation ” ¸ between the DOAs of the interferers. When the restrictive hypotheses are neglected, the optimal spacing ” opt is calculable as the spacing that minimizes the spread between the N I wave numbers associated to the barycentric DOAs of the N I interfering cells. Moreover closed form solution can be dealt with on condition that N I interfering cells (with one broadside interfering cell) are considered; said angular separation between the interferers is assumed as being the average ” ¸ B among adjacent angular separations between barycentric DOAs weighted by the respective barycentric received power. Assuming a multipath channel with an arbitrary number of paths N p , the i th barycentric DOA is calculated by executing a weighted average extended to the N p × S directions of arrival of the N p paths by the S points of a grid indicative of the positions spanned by the i th interfering station inside its cell, weighting each DOA by the power received on that path. In a SIMO scenario with square cell planning according to the fixed or mobile WiMAX IEEE 802.16d802.16-2004/e, the value ” opt =1.8» is found as an optimum trade-off between beamforming and diversity (fig.5).