Method of handling normal bandwidth and narrow bandwidth coexistence

A method of handling coexistence of different bandwidth operations for a source station in a wireless communication system, comprising:

• transmitting a proprietary request frame using a normal bandwidth to a destination station of interest to join a narrow bandwidth operation, wherein the proprietary request frame indicates a service period of the narrow bandwidth operation;
• switching from a normal bandwidth operation to the narrow bandwidth operation after a proprietary response frame corresponding to the proprietary request frame using the normal bandwidth is received from the destination station;
• transmitting a proprietary frame for indicating end of the narrow bandwidth operation before termination of a transmit opportunity (TXOP) of the source station;
• checking whether a TXOP of the destination station during the narrow bandwidth operation is terminated;
• and
• transmitting a second contention-free end (CF-end) frame using the normal bandwidth to the destination station when the TXOP of the source station during the narrow bandwidth operation is not terminated, wherein the second CF-end frame indicates termination of the TXOP of the source station using the normal bandwidth, and transmitted by the source station with a transmission power level that is a sum of a standard transmission power level of the normal bandwidth operation and an amplification gain difference between the narrow bandwidth and normal bandwidth.