Impact of antenna separation on the link correlation of MIMO HetNet LTE-advanced networks

Since the angular spread is related to the propagation environment condition, MIMO channel capacity can be improved by increasing the antenna spacing. This paper evaluates the performance of link correlation for 2×2 MIMO deployments using horizontal and vertical UE and BS array configurations with various antenna separations at the UE and BS. The investigation makes use of measured 3D radiation patterns for the BS and UE antennas. This data is combined with state-of-the-art 3D ray-tracing predictions for a large number of macro and pico-cells locations. Results revealed that in order to achieve a correlation always in the range 0.25 to 0.75, the minimum required antenna spacing was around 0.5λ to 2λ for the UE, 2λ for the Pico-eNB and 10 λ for the Macro-eNB. MIMO performance (in terms of capacity) was seen to increase in pico-cells as a result of the higher angular spreads at the base station.