A wireless terminal comprises sidelink controlling circuitry and transmitting circuitry. The sidelink controlling circuitry is configured to select a reference source. The transmitting circuitry is configured to transmit sidelink synchronization signal (SLSS) based on the reference source. In a case that a timing reference is Global Navigation Satellite System (GNSS) and the GNSS is reliable according to a comparison with a threshold value, the sidelink controlling circuitry is configured to select GNSS as the reference source.