“…As a result, eICIC is mainly used in the co-channel deployment where the macrocell to small cell interference is a major issue, while DC is mainly suitable for the orthogonal deployment where the traffic flow splitting or the mobility management is a major issue. Other new emerging technologies in Cell Type 3 include dynamic small cell idle modes [21], [44], [45], dynamic Time Division Duplexing (TDD) transmission [18], [19], [20] (which have attracted a lot of momentum in both the academia and the industry in the last years), high-order MIMO techniques [46], [47], etc. Cell Type 4, finally, will push the technology frontier even further by using a very wide spectrum in high-frequency bands, e.g., mmWave [48], [49], [50], and exploiting massive MIMO techniques to achieve beam forming and spatial multiplexing [51], [52], etc.…”