A signal transmission method, signal detection method and apparatuses thereof and communication system. The signal transmission apparatus includes a transmitting unit configured to transmit a synchronization signal (SS) block to a user equipment within a time window of a predetermined position in an SS block transmission period. Hence, UE cell search and measurement time is reduced, complexity at the UE is lowered, power consumption of the UE is lowered, cell handover is sped up, communication interruption is avoided, and currently at least one of existing problems is solved.