13.2 CoMP Concept

CoMP is based on coordinated or cooperative signal processing among multiple cells. Let us start with the most sophisticated CoMP concept, namely downlink multi-cell Joint Transmission (JT), as an illustrative example of how CoMP changes the view on interference in mobile communications.

On the left side of Figure 13.1, we see three cells simultaneously transmitting in a conventional (i.e. non-coordinated) way to three terminals on the same physical resources. For each of the terminals, this means that the desired signal from the assigned cell is impaired by interfering signals from the other two cells. In JT CoMP, one could now let all three cells transmit jointly to one of the terminals on the same resources in time and frequency. This may sound a bit like soft handover from Wideband Code Division Multiple Access (WCDMA), where two cells send the same signal with different scrambling codes to one terminal. In both CoMP and soft handover, the result is that signals which formerly were inter-cell interference are now useful signals adding up in at the receiver side. As shown in the centre plot of Figure 13.1, when certain physical resources are now transmitted towards the same user from different cells in single-user mode, the system becomes effectively a dynamic reuse factor 1/3 system as a single CoMP user now blocks resources in three cells. This is a similar effect as exploited with Inter-Cell Interference Coordination (ICIC) mechanisms, but instead of muting ...

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