English
Menu

Information Theory and Coding Basics

Which of the following correctly describes ARQ (automatic repeat request) and FEC (forward error correction), methods for dealing with errors in communication?

  1. AARQ corrects errors at the receiver alone, so no channel is needed to send notices back to the sender
  2. BFEC asks for retransmission when it detects an error, so delay tends to grow when there are many errors
  3. CFEC corrects errors at the receiver using redundant bits, so it can also be used for one-way broadcasting
Show answer and explanation

Answer: C. FEC corrects errors at the receiver using redundant bits, so it can also be used for one-way broadcasting

ARQ detects errors with a CRC or similar, tells the sender that the data could not be received and has them sent again; it needs a return channel and is delayed by the retransmissions. FEC sends redundant bits along with the data and corrects errors at the receiver alone, so it suits one-way broadcasting, communication with space probes where a round trip takes a long time, and communication that cannot tolerate delay. Real systems also often combine the two, correcting most errors with FEC and retransmitting the remaining ones with ARQ.

  • A. This is a property of FEC. ARQ asks for retransmission, so it needs a channel from the receiver back to the sender.
  • B. This is a property of ARQ. FEC corrects errors at the receiver without asking for retransmission.
  • C. Correct. Errors can be corrected at the receiver alone, so it works without a return channel.
Practice this topic Back to topic

Books on Information Theory and Coding Basics Ad

As an Amazon Associate I earn from qualifying purchases.

More Information Theory and Coding Basics questions

  1. In a binary symmetric channel, 0s and 1s are sent and each bit flips independently with probability 0.1. With the binary entropy function H(p) = −p log₂ p − (1 − p) log₂(1 − p), H(0.1) ≈ 0.469. Which of the following is closest to the channel capacity of this channel per transmission?
  2. Which of the following correctly states Shannon's channel coding theorem?
  3. To convert a Gray code into an ordinary binary number, the most significant bit is used as it is, and each lower bit is found as the exclusive OR of the binary bit already found one position higher and the Gray code bit in the same position. Which of the following is the 4-bit Gray code 1101 converted into binary?
  4. Let the amount of information obtained on being told that an event of probability p has occurred be −log₂ p bits. Which of the following is the amount of information obtained on being told that an event of probability 1/8 has occurred?
  5. Which of the following correctly describes a property of the amount of information (−log₂ p on being told that an event of probability p has occurred)?