A method of generating a code sequence in a wireless communication system is disclosed. The delta-phase detection method calculates phase differences between every two consecutive samples of the received signal, and counts the number of successive phase differences that are within a predetermined allowable detecting range. These expressions are based on the device physics but are in empirical form. The PF device has a filter structure for removal of particulates in the exhaust gas, and is selectively regenerated based on an amount of particulates trapped within the filter structure of the PF device.