A wireless device of transmitting a data frame in a WLAN is provided. The wireless device includes: a MAC unit generating a data frame; a PHY unit transmitting a wireless signal of the data frame; and a processor being operably coupled to the MAC unit and the PHY unit and controlling a set of TXVECTOR parameters. The processor is configured for: generating the data frame, the data frame including a data field having a service field and a very high throughput signal information (VHT-SIG-B); and transmitting a wireless signal of the data frame via a operating channel bandwidth. The data field is scrambled with a scrambling sequence, the scrambling sequence is generated based on a initial scrambling sequence and a generator polynomial. The service field is determined based on the set of TXVECTOR parameters, the TXVECTOR parameters including an control information for the service field.