In SATCOM, which statement best differentiates MCPC from VCM?

• A. MCPC adapts modulation and coding per channel; VCM uses a single modulation and coding for all channels.
• B. MCPC uses a single modulation and coding for all channels; VCM adapts modulation and coding per channel or user to optimize efficiency.
• C. MCPC and VCM are the same; both adapt per user or channel.
• D. MCPC uses fixed coding for all channels; VCM uses fixed modulation for all channels.

Answer: (B)

The main idea is whether the modulation and coding are fixed for all channels on a carrier or can be varied for each channel or user. In MCPC, a single modulation and coding configuration is used for all channels on a transponder, so every channel shares the same data rate and protection level. VCM (Variable Coding and Modulation) allows the modulation order and coding rate to be adjusted per channel or per user, tailoring the scheme to individual link conditions to squeeze more efficiency from the same bandwidth. This per-channel tailoring lets some streams use higher-order modulation with lighter FEC when the link is good, while others use more robust schemes when needed. So the statement that MCPC uses a single modulation and coding for all channels, while VCM adapts modulation and coding per channel or per user to optimize efficiency, accurately reflects the difference.