CoMP

CoMP attacks the cell-edge problem by having neighbouring transmission points cooperate instead of compete. Out at the boundary between two cells, the signal you want and the interference from next door are nearly equal strength — terrible SINR. CoMP turns those nearby cells from a source of interference into collaborators.

It's not one technique but a family, and the distinction matters for what you can actually deploy:

• Coordinated Scheduling / Beamforming (CS/CB) — the cells coordinate when and where they transmit so they don't step on each other. The data still comes from one cell. Lighter on backhaul.
• Joint Transmission (JT) — multiple cells send the same data to the user at once, combining at the receiver. Much stronger gains, but it needs the data at every participating cell and tight synchronisation.
• Dynamic Point Selection — the network picks the best transmission point per subframe.

The reason CoMP has been used more sparingly than its theory promises is the cooperation cost: joint transmission especially demands fast inter-site coordination and accurate channel feedback, which strains real backhaul. It's conceptually a close cousin of cell-free MIMO, and the same coordination bottleneck holds both back in practice.