Solutions for L.RRC.setupFail.NoReply without modifying T300

4G LTE
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Hi Experts.

Does anyone have a solution for L.RRC.setupFail.NoReply without changing T300?

Admin note: this post was updated with image below.

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If you investigate the worst-performing cells with the highest percentage of L.RRC.setupFail.NoReply, you’ll find they typically fall into two categories: either they are overshooting or located in areas with no signal dominance.

What is the value of the cellRadius parameter in your network?

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Additionally, UL interference may also contribute to this type of failure.

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To resolve the L.RRC.setupFail.NoReply issue without modifying T300, you can try the following solutions:

  1. Check signal strength: Ensure the UE has good signal quality and is not experiencing excessive interference.
  2. Network congestion: If the network is congested, it might be causing delays in the RRC setup. Try optimizing the network load.
  3. Check radio parameters: Review your RRC setup parameters like timer values, especially T304 and T308, to ensure they are appropriately configured for your network conditions.
  4. Verify carrier settings: Double-check the carrier configuration, including the RACH procedure, to ensure it’s properly tuned.

These adjustments might help mitigate the issue without needing to alter T300.

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RRC No Reply Failures are among the top RRC failures in most networks, primarily caused by weak uplink signals and users in poor radio conditions or overshooting cells.

To better understand this, consider the following:

  • The RRC Connection Request message is usually around 7 bytes in size.
  • The RRC Connection Setup Complete message, however, can include the entire NAS information (e.g., TAU or Attach Request) and varies in size, ranging from as small as 8 bytes to over 100 bytes.

Now, imagine a UE at the cell edge with limited power:

  1. When the UE sends the RRC Connection Request (7 bytes), it requires only a small number of resource blocks (RBs), resulting in higher power per carrier.
  2. However, when sending the RRC Connection Setup Complete (potentially 100 bytes), it needs a larger number of RBs, even with fragmentation. This reduces the average power per carrier.
  3. As a result, the eNB might fail to decode the message due to insufficient signal quality.

This explains why poor uplink conditions can significantly contribute to RRC No Reply Failures.

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You can improve it by increasing T300 timer, by coverage Optimization, Overshooting elimination, Coverage Enhancement & Power Control