Capacity formulas for smart antenna systems with spatial filtering for interference reduction

To enhance the capacity of cellular systems, the application of smart antennas at the base station has been proposed in the literature. With smart antennas, adaptive beamforming with directional reception and transmission becomes feasible. Consequently, smart antenna systems will significantly decrease interference power in cellular systems. Two basic approaches can be used to transform the reduced interference into actual capacity gains: space division multiple access (SDMA) and spatial filtering for interference reduction (SFIR). This paper is focusing on SFIR systems, where the reduced interference is utilized by reducing the frequency re-use distance and re-arranging the channel assignment such that each cell has available a higher number of channels, giving rise to higher Erlang capacity. This paper provides an analytical approach to assess the capacity achievable with smart antennas if SFIR is used. We consider the average C/I improvement and resulting tighter channel re-use, yielding improved call blocking performance. However, we also take into consideration the outage probability, which is a result of the dynamic nature of the interference.