An approach is provided for defining a 1 MHz preamble of a packet. The approach involves determining a preamble sequence of a packet, the preamble sequence having a determinable length. The approach also involves causing, at least in part, the preamble sequence to be divided into a predetermined number of blocks. The approach further involves causing, at least in part, a mathematical operation and a summation over the predetermined number of blocks and a corresponding number of received blocks. The approach also involves causing, at least in part, the summation to be maximized to determine the preamble sequence corresponds to one of a first bandwidth or a second bandwidth, the second bandwidth being greater than the first bandwidth, to determine a type of the packet.