Our EDMAC capability permits the users to access the M&C features of distant-end modems in a satellite link. This is accomplished by adding extra information to the user data in a manner that is completely transparent to the users.
On the transmit side, the user data is split into frames and 48 bits of overhead is added to each frame. At the start of each frame a 12 bit synchronization word is added. This allows the demodulator to find and lock to the start of frame. At regular intervals throughout the frame, additional data bytes and flag bits are added (a further 36 bits in total). It is these additional bytes that carry the M&C commands and response.
On the receive side, when the demodulator locks to the incoming carrier, it goes through the additional step of searching for, and locking to the synchronization word. This uniquely identifies the start of frame, and permits the extraction of the overhead bytes and flag bits at the correct position within the frame. In addition, the start of frame permits the de-scrambler to correctly recover the data. The user’s data is extracted, and sent through additional processing, in the normal manner. The extracted overhead bytes are examined to determine if they contain valid M&C bytes.