Why Repetition is used in 5G?

  • My friend: Hi Ibrahim, I have a question for you.

    • Me: Please, go ahead.
  • My friend: I was wondering why Repetition is used in 5G?

    • Me: Repetition is used to transmit the PDSCH transport blocks multiple times and this can be used in case of UE is having bad radio conditions and so the 5G BTS can configure the UE to use repetitions and once UE is again in good coverage, 5G BTS will release the repetitions not to consume extra resources with the same data. Also, note that repetitions are configured when UE is having a single transmission layer only.
  • My friend: But what is the advantage of using Repetition in bad coverage areas?

    • Me: Actually, it should improve the reliability and latency. Reliability is improved as multiple repetitions increases the probability of a successful reception at the UE side. Latency is improved as we avoid the re-transmission mechanism in case UE didn’t receive the data correctly from the first transmission. As in case the UE didn’t receive the data correctly, then the 5G BTS should wait for a HARQ feedback from the UE, then it reschedules the retransmission for the UE, which will take time and all this wasted time is avoided using the repetitions.
  • My friend: Humm, this seems nice. However, repetitions will consume more PDSCH resources, right?

    • Me: Yes, that’s right, but for UEs only in bad radio conditions. Also, take care as repetition will reduce the PDCCH load as the PDCCH is not required to provide a resource allocation for each individual transmission as re-transmissions will be reduced. So, it reduces system capacity by repeating the same data again, however it increases the reliability and latency in poor radio conditions which can be a good solution for URLLC cases for example.
  • My friend: Thank you very much. You made it very clear.

    • Me: You are most welcome.

Why Repetition is used in 5G?

Source: Ibrahim Sayed, PMP on LinkedIn: #5g #5gnr #5gtechnology | 16 comments

1 Like

Hello @Ibrahim_Sayed.

Is it new 3gpp feature for rel16?

How UE come to know when to use it is it by DCI?