Baseband is the term for equipment that assembles and disassembles user information for the satellite uplink and downlink. On the uplink side user information and traffic are encoded and modulated. On the downlink side, demodulated and decoded. Modem.
Almost all satellite communications ground segments employ digital technology, so modulation and demodulation is performed by the modem (similar in concept to a dial-up modem or cable modem, but intended for satellite transmission as opposed to the use of wires or cable). Modems also include forward error correction (FEC) to reduce the required amount of RF power from the HPA and from the satellite as well. Encoding and decoding.
- Performed on the data bits before they are applied to the FEC and modulation processes. Common examples include:
- Compression - to reduce the quantity of bits for the same amount of information, also tends to reduce the subjective quality of the sound or image.
- Multiplexing - to combine different streams of data into a single baseband bit stream, allowing one modem to provide the channel of transmission over the satellite.
- Encryption - to secure the information from monitoring or tampering during transmission. This is often provided at the user device (e.g. PC or encrypted telephone).
- Software - to manage the data flow and direction of delivery.