Question

LTE: Why RLC layer only used in ARQ Process and there is no involvement of this layer in HARQ Process?

Answer 1

Lets first understand both in short -

ARQ:
1. Works at RLC layer
2. If the received data has an error (as detected by ARQ) then it is discarded, and a new re-transmission is requested from the sender

HARQ:
1. Works at PHY layer but controlled by MAC layer
2. If the received data has an error then the Receiver buffers the data and requests a re-transmission from the sender. When the receiver receives the re-transmitted data, it then combines it with buffered data prior to channel decoding and error detection. This helps the performance of the re-transmissions.

Now as clear with the above explanation HARQ is one which operates at the lowest level and ARQ is just one level above and provide one more level of error detection on top of HARQ process. That is the whole concept why ARQ is at RLC and HARQ is MAC+PHY.

Comments

thanks salil.

Answer 2

In Adding to salili post......In Higher layer RLC- use a reliable error detection and correction technique i.e ARQ, even it is more time taking than HARQ. after passing through RLC, MAC does not require this ARQ prosses and in MAC processing require to save more time(becuase MAC have lots of process to do), so its use HARQ in place of ARQ... Please refer Salil post for the differences between HARQ and ARQ.

Comments

Thanks Biplab :)