Distinguish between forward error correction and automatic repeat request in telemetry.

• A. FEC uses acknowledgments; ARQ uses redundant data.
• B. FEC and ARQ are identical in function.
• C. ARQ adds redundant data for error correction.
• D. Forward error correction adds redundant data to allow error correction at receiver; ARQ uses acknowledgments and retransmission.

Answer: (D)

In telemetry, error-control strategies split into two practical approaches: forward error correction and automatic repeat request. Forward error correction works by attaching redundant bits to the transmitted data so the receiver can detect and correct many errors on its own, without needing a resend. This lets the system recover from some corruption right at the receiver, reducing the need for retransmission and often lowering latency in error-prone channels.

Automatic repeat request relies on a feedback mechanism. The sender transmits data, the receiver checks integrity (often with a CRC), and if the data is good an acknowledgment goes back; if it’s bad, there’s no ACK or a negative signal, prompting the sender to retransmit. This approach fixes errors by retrying the exact data, not by correcting it with extra bits.

So the described distinction—FEC adding redundant data for local error correction at the receiver, and ARQ using acknowledgments and retransmission—matches how these two methods function.