There are two distinct frequency planning strategies for Heterogeneous Network (HetNet) deployments where macrocells and small cells are overlaid:
1. Co-channel deployment, where macro and small cells use the same frequency carriers,
2. Dedicated Carrier deployment where macro cells and small cells use different frequency carriers.
The co-channel case can utilize the full system bandwidth at both macro and small cell layers but at a cost of higher inter-cell interference.
Enhanced ICIC features were defined in 3GPP Release 10 to address interference issues in Co-Channel HetNet.
The concept of Almost Blank Subframes was added in Release 10 to help protect transmissions to the UE when it is being served by one cell but there is another stronger signal that is interfering.