A wireless device receives message(s) configuring cell groups and transmissions of sounding reference signals (SRSs). Uplink transmission timing in a first cell group is derived employing a cell in the first cell group and uplink transmission timing in a second cell group is derived employing a second cell in the second cell group. A first signal is transmitted on a cell of the first cell group. A first subset of the SRSs are dropped and a second subset of the SRSs are transmitted.