Downlink cognitive interference alignment for heterogeneous networks

The deployment of small-cells along a macro-cell is considered to be an effective solution in order to increase the capacity and offload the traffic from the macro-cell system. In current heterogeneous configuration with large number of deployments, it is likely that the small-cells will coexist with macro cells over the same spectrum as additional spectrum licenses are difficult and expensive to acquire. The coexistence of these cells leads to considerable interference between the two systems. In this context, we propose an underlay downlink cognitive interference alignment approach in order to remove both the interference from small-cells to the macro-cell system and from macro-cell to the small-cells. In the proposed scheme the small-cells sense the unused resources in the space dimension of the macro-cell and then communicate without interfering with the macro-cell system. The simulation results show that the secondary system does not affect the performance of primary system. The proposed scheme also provides close to optimal performance with minor overheads.