5G NR MAC Layer Failures: Root Causes and Solutions

Following are common 5G NR test cases at the MAC layer, including their failures, root causes, and potential solutions or suggestions.

Failure Case #1: Scheduling Request Failure

Root Causes:

• Congestion in uplink resources.
• Scheduling algorithm inefficiency.
• HARQ buffer overflow.

Solutions/Rectifications:

• Optimize the scheduling algorithm to prioritize resource allocation based on traffic types and QoS requirements.
• Increase the number of uplink resources and configure dynamic scheduling to adapt to varying traffic loads.
• Ensure proper buffer management to avoid overflows.

Failure Case #2: HARQ NACK-to-ACK Ratio Exceeds Threshold

Root Causes:

• Poor channel conditions.
• High error rates in physical layer transmission.
• Incorrect HARQ parameter settings.
• Software bugs in the HARQ process.

Solutions/Rectifications:

• Optimize HARQ process parameters like the number of retransmissions and timers.
• Improve link adaptation algorithms to select the best MCS (Modulation and Coding Scheme) for the current channel conditions.
• Use cross-layer optimizations between PHY and MAC layers to reduce errors.

Failure Case #3: MAC PDU (Protocol Data Unit) Loss or Corruption

Root Causes:

• Buffer overflow.
• Packet drop due to congestion.
• Incorrect link adaptation.
• Interference.

Solutions/Rectifications:

• Implement error detection and correction mechanisms such as CRC checks.
• Ensure adequate back-off and retransmission strategies to handle congestion.
• Perform load balancing to distribute traffic across multiple resources.

Failure Case #4: Resource Allocation Failures

Root Causes:

• Inefficient resource block allocation algorithms.
• Collision with other UEs (User Equipments).
• Misconfiguration of dynamic resource allocation parameters.

Solutions/Rectifications:

• Optimize dynamic resource allocation algorithms to minimize collisions and avoid resource exhaustion.
• Monitor traffic patterns and adjust resource allocation policies accordingly.
• Enhance Quality of Service (QoS) management to prioritize critical traffic.