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NR-ARQ (NR Automatic Repeat reQuest)

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NR-ARQ (New Radio Automatic Repeat reQuest) is a crucial mechanism within the 5G (fifth-generation) wireless communication standard. It is responsible for ensuring the reliable delivery of data by enabling automatic retransmission of lost or corrupted packets. Here's a detailed technical explanation of NR-ARQ:

1. ARQ in Wireless Communication:

  • ARQ (Automatic Repeat reQuest) is a set of protocols used to manage data transmission reliability in wireless communication networks.
  • It allows for the detection and retransmission of missing or erroneous data packets.

2. NR-ARQ in 5G:

  • NR-ARQ is the version of ARQ designed specifically for the 5G NR (New Radio) standard.
  • It is responsible for managing the reliability of data transfer between the User Equipment (UE) and the network's base station (gNodeB in 5G).

3. Packet Transmission Process:

  • When data is sent from the UE to the gNodeB or vice versa, it is divided into packets.
  • Each packet is assigned a unique identifier or sequence number.

4. Data Packet Reception:

  • Upon receiving a data packet, the recipient (UE or gNodeB) checks the integrity of the packet using error detection techniques.
  • If the packet is received correctly, it is acknowledged, and the recipient waits for the next packet.

5. Packet Loss or Corruption:

  • If a packet is lost or found to be corrupted during transmission, the recipient does not send an acknowledgment (ACK) but instead sends a negative acknowledgment (NACK) or a similar indication to the sender.

6. Retransmission Request:

  • Upon receiving a NACK or retransmission request, the sender (UE or gNodeB) retransmits the missing or corrupted packet.

7. Sequence Numbers:

  • NR-ARQ uses sequence numbers to keep track of the order in which data packets are sent and received.
  • This helps the sender and receiver ensure that packets are delivered in the correct order.

8. Number of Retransmissions:

  • NR-ARQ typically allows for a limited number of retransmission attempts for each packet.
  • If a packet cannot be successfully delivered after the maximum number of attempts, it may be discarded.

9. Timer-Based Retransmissions:

  • NR-ARQ often employs timers to control the timing of retransmission requests.
  • If a packet is not acknowledged within a certain time frame, it may trigger a retransmission.

10. Hybrid ARQ:

  • NR-ARQ can be combined with techniques like Hybrid ARQ (HARQ) to enhance reliability further.
  • HARQ allows for the incremental transmission of additional parity or redundancy bits to correct errors without requiring a complete retransmission.

11. Flow Control:

  • NR-ARQ includes flow control mechanisms to manage the rate of data transmission based on the receiver's capacity and feedback.

12. Signaling Overhead:

  • While NR-ARQ enhances reliability, it introduces some signaling overhead due to the exchange of ACKs, NACKs, and retransmission requests.

13. Robustness and Reliability:

  • NR-ARQ contributes to the robustness and reliability of 5G networks, ensuring that data is successfully delivered even in challenging wireless environments.

In summary, NR-ARQ (New Radio Automatic Repeat reQuest) is a fundamental mechanism in the 5G NR standard that ensures reliable data transmission by detecting and retransmitting lost or corrupted packets. It relies on sequence numbers, timers, and acknowledgments (ACKs and NACKs) to manage the flow of data and enhance the overall reliability of wireless communication in 5G networks.