A method for wireless communication at a base station, the method (1400, 1500) comprising: determining whether a transmission in a shared radio frequency spectrum band is a discovery signal transmission or an opportunistic transmission; and generating and transmitting a first type of synchronization signal in the shared radio frequency spectrum band when the transmission is determined to be a discovery signal transmission; or generating and transmitting a second type of synchronization signal in the shared radio frequency spectrum band when: the transmission is determined to be an opportunistic transmission; the opportunistic transmission is a second type of transmission; contention for access to the shared frequency spectrum band is won; and the opportunistic transmission is not a beginning subframe of a listen before talk, LBT, frame, or radio frame, wherein the second type of synchronization signal is different from the first type of synchronization signal; or generating and transmitting in the shared radio frequency spectrum band a third type of synchronization signal when: the transmission is an opportunistic transmission; contention for access to the shared frequency spectrum band is won; and the opportunistic transmission is a beginning subframe of a LBT frame or radio frame, wherein the third type of synchronization signal is different from the first type of synchronization signal and the second type of synchronization signal. determining whether a transmission in a shared radio frequency spectrum band is a discovery signal transmission or an opportunistic transmission; and generating and transmitting a first type of synchronization signal in the shared radio frequency spectrum band when the transmission is determined to be a discovery signal transmission; or generating and transmitting a second type of synchronization signal in the shared radio frequency spectrum band when: the transmission is determined to be an opportunistic transmission; the opportunistic transmission is a second type of transmission; contention for access to the shared frequency spectrum band is won; and the opportunistic transmission is not a beginning subframe of a listen before talk, LBT, frame, or radio frame, wherein the second type of synchronization signal is different from the first type of synchronization signal; or the transmission is determined to be an opportunistic transmission; the opportunistic transmission is a second type of transmission; contention for access to the shared frequency spectrum band is won; and the opportunistic transmission is not a beginning subframe of a listen before talk, LBT, frame, or radio frame, wherein the second type of synchronization signal is different from the first type of synchronization signal; or generating and transmitting in the shared radio frequency spectrum band a third type of synchronization signal when: the transmission is an opportunistic transmission; contention for access to the shared frequency spectrum band is won; and the opportunistic transmission is a beginning subframe of a LBT frame or radio frame, wherein the third type of synchronization signal is different from the first type of synchronization signal and the second type of synchronization signal. the transmission is an opportunistic transmission; contention for access to the shared frequency spectrum band is won; and the opportunistic transmission is a beginning subframe of a LBT frame or radio frame, wherein the third type of synchronization signal is different from the first type of synchronization signal and the second type of synchronization signal.