Error Control in Wireless Communication: ARQ and FEC Quiz Quiz

Explore the essential principles of error control in wireless communication, focusing on Automatic Repeat reQuest (ARQ) and Forward Error Correction (FEC) techniques. Assess your understanding of how these methods improve data reliability, their key differences, and their practical applications in wireless networks.

1. Automatic Repeat reQuest Mechanism

   In a wireless communication system, which process correctly describes how the Automatic Repeat reQuest (ARQ) protocol manages transmission errors?

   1. Data is retransmitted automatically at fixed time intervals, regardless of errors.
   2. The receiver requests retransmission when a data frame is detected as erroneous.
   3. The sender adds redundant bits to correct errors at the receiver.
   4. Errors are corrected by manually resending the entire data file.

   Explanation: In ARQ protocols, the receiver checks each received frame and asks for retransmission if an error is found, ensuring accurate data delivery. Unlike FEC, ARQ does not use redundant bits for error correction at the receiver, so the sender option is incorrect. Automatic retransmissions at fixed intervals without error checks would be inefficient and is not standard ARQ behavior. Correcting errors by manually resending entire data files is not part of ARQ and is highly impractical.

2. Identifying Forward Error Correction

   Which statement best describes how Forward Error Correction (FEC) operates in a wireless transmission scenario?

   1. The sender appends redundant information so the receiver can fix some errors without retransmission.
   2. The sender and receiver send repeated data to each other for verification.
   3. Errors are identified and corrected only after multiple acknowledgments.
   4. The receiver uses parity requests to ask the sender for error details.

   Explanation: FEC codes let the receiver detect and often correct errors directly using the extra redundancy added by the sender, making retransmissions unnecessary for many errors. Parity requests from the receiver are part of some ARQ systems but not FEC. Mutual repeated data exchange describes more complex protocols, not standard FEC. Correcting errors only after multiple acknowledgments confuses FEC with ARQ techniques.

3. Applications of Error Control Methods

   In which situation is Forward Error Correction typically preferred over ARQ in wireless communication?

   1. When feedback channels have higher capacity than forwarding channels.
   2. When errors are rare and network bandwidth is unlimited.
   3. When users prefer error-prone downloads for speed.
   4. When retransmissions are expensive or impossible, such as in satellite links.

   Explanation: FEC is favored when retransmitting data is costly or infeasible, like over satellite connections with long delays. When errors are rare and bandwidth is high, ARQ is usually more efficient due to its lower overhead. Prioritizing error-prone downloads is undesirable for reliable communication, making that distractor incorrect. High-capacity feedback channels do not directly suggest using FEC over ARQ.

4. ARQ Protocol Types

   What is a primary difference between Stop-and-Wait ARQ and Selective Repeat ARQ protocols in error control?

   1. Both retransmit all frames after an error, but at different time intervals.
   2. Selective Repeat ARQ can retransmit only the erroneous frames instead of all subsequent frames.
   3. Selective Repeat ARQ is only used in error-free networks.
   4. Stop-and-Wait ARQ uses forward error correction; Selective Repeat does not.

   Explanation: Selective Repeat ARQ enhances efficiency by retransmitting only the frames that were received incorrectly, unlike protocols that require sending all frames after a lost one. Both do not retransmit all frames—this is false for Selective Repeat. Neither ARQ protocol uses forward error correction; FEC is a different method. Selective Repeat can operate in the presence of errors, so the last distractor is incorrect.

5. Error Detection vs. Correction Roles

   When using ARQ in a wireless system, what is the main function of error-detecting codes such as checksums or CRC, as opposed to error-correcting codes?

   1. They automatically fix all detected errors without retransmission.
   2. They ensure that errors are ignored during transmission.
   3. They enable detection of errors in received frames, prompting retransmission if needed.
   4. They increase the speed of data transfer by compressing frames.

   Explanation: Error-detecting codes, like checksums or CRCs, allow the receiver to identify if data has been corrupted so that a request for retransmission can be sent in ARQ systems. They do not correct errors; that's the role of FEC schemes. Ignoring errors is not a goal of error-detecting codes. Compression and increased speed are unrelated to error detection; they're not provided by these codes.