13.6 Downlink CoMP Gains

The gain from CoMP on downlink performance is mainly in three major ways:

1. Inter-cell spatial domain coordination to suppress interference and/or improve the desired signal strength. This approach is sensitive to the channel state information accuracy therefore it poses tough requirements on the infrastructure.
2. Coordinate the radio resource management to optimize the resource assignment.
3. Mitigating the cell selection loss at the cell edge which is inherently there in distributed base station deployment with non-instantaneous cell selection mechanisms (due to handover margins and triggers).

The second way doesn't include precise spatial domain information; therefore it can provide moderate but robust gain and can work on ordinary infrastructure. CS/CB and DCS are mainly focusing on the second benefit while joint transmission is focusing on the first benefit. The third benefit can be significant at the cell edge (e.g. some implementations may operate with effective handover margins of 3–4 dB) but over time distributed solutions will also be optimized and will find ways to squeeze the effective handover margins. The CoMP gains mechanisms are shown in Table 13.6.

Table 13.6 Downlink CoMP gains with different CoMP options.

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Figure 13.8 summarizes the observed CoMP gains over Release 8 2 × 2 SU-MIMO, where several downlink CoMP schemes were simulated ...

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