on the medium if the medium is sensed u201c idle clear u201d then the sta is permitted to transmit if the medium is sensed as u201c busy u201d the sta has to defer its transmission in csma multiple stas may transmit simultaneously resulting in collisions it should be noted that as used herein a mobile device includes but is not limited to a dual mode smart phone a computer a laptop computer a notebook computer a personal digital assistant pda or any other device that can communicate using any part or portion of the wireless spectrum airwaves as shown in fig1 stations associate with an ap the ap with its associated stations forms a basic service set bss as an example if the ap and one or more of its associated stas transmit simultaneously after sensing the medium idle clear the frames packets transmitted by the ap and stas collide and are lost this type of collision occurs within the bss and is called an intra bss collision another type of collision is shown in fig2 ap 1 and ap 2 operate on the same channel frequency and overlap the intersection of the circles represents the interference range of ap 1 and ap 2 ap 1 transmits data frames to its associated stas e g to sta s 4 or sta s 1 ap 2 cannot hear ap 1 39 s transmission and thinks that the medium is idle ap 1 is a u201c hidden node u201d to ap 2 ap 2 may transmit frames to its associated sta s 5 while ap 1 is transmitting.