Embodiments herein relate to a receiver device; a method therein; a transmitter device and a method therein. The transmitter device is configured to transmit to the receiver device a device-to-device synchronization signal during a time window preceding the start of a resource pool. The transmitter device is further configured to transmit a discovery message during the resource pool. The discovery message includes the identity of the transmitter device for enabling the transmitter device and the receiver device to synchronize to each other.