An operation method of a first device in a communication system may comprise: receiving, at a second device, a primary synchronization signal block (SSB) including first SSBs for the first device; feeding back to the second device an index of a first SSB with a highest received signal strength among the first SSBs of the first SSB set; receiving, at the second device, a second SSB set including the first SSBs for the first device and second SSBs for a third device; transmitting to the third device the second SSBs for the third device in the second SSB set; and forwarding an index of a second SSB with a highest received signal strength among the second SSBs to the second device, the index being received from the third device.