Disclosed is an apparatus for wireless communications. The apparatus includes a processing system configured to generate a single-channel frame, a bonded channel frame, or a MIMO channel frame. Each of the frame types includes a first portion and a second portion, said first portion being decodable by a first device operating according to a first protocol, said second portion not being decodable by the first device, wherein the first and second portions are decodable by a second device operating according to a second protocol; and an interface configured to output the frame for transmission. The second portion includes a first field including frequency-domain PRBS data for AGC, a second field including a time-domain sequence for timing of input sample window for FFT processing, and a third field including frequency-domain pilots for channel estimation. For MIMO, these fields for different transmit chains are transmitted in a time aligned manner.