ARQ vs HARQ in 5G?

My friend: Hi Soumya, I have a question.

Me: Go ahead.

My friend: What is the difference between ARQ and HARQ in 5G?

Me: It is the same as in 4G. Automatic Repeat Request (ARQ) is a re-transmission protocol in which the receiver checks for errors within the received data and if an error is detected then the receiver discards the data and requests a re-transmission from the sender. ARQ is implemented in RLC layer and is slower than HARQ.

My Friend: So, what about HARQ?

Me: Hybrid ARQ (HARQ) is a re-transmission protocol in which the receiver checks for errors in the received data and if an error is detected then the receiver buffers the data and requests a re-transmission from the sender. A HARQ receiver is then able to combine the buffered data with the re-transmitted data for better decision. It is a combination of Forward Error Correction (FEC) and ARQ. HARQ is controlled by MAC.

My Friend: But, why do we have two protocols with same function?

Me: As HARQ depends on one bit for ACK/NACK, some errors can happen, so ARQ is fixing these errors to ensure more reliability in our system, actually they are complementing each other.

My friend: Thanks a lot.

Me: You are welcome.

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5G_ARQ_HARQ

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