Minimize performance issues due to no phase sync in NSA

Hello Experts.

LTE anchor site (freq sync no phase sync).

I want to enable anchoring for inter site gNB TDD N78 layer.

So LTE cell from site 1 has X2 to site 2 n78(TDD).

As site 1 has no phase sync, there would be performance issues.

But I can minimize that by asking gNB only deliver data to 5G PDCP (dloverf1mode).

What is your opinion?

Why do you think there can be performance issues if there is no phase sync between LTE and NR cell?

Aggregation of 5G and LTE data should arrive UE within some time window.

So if the frame timing is different than it is unpredictable the performance…

5|G and LTE data is coordinated at PDCP layer.

There is way too much time available at PDCP layer to reorder packets, in comparison to delay that can come from out of phase frames.

Not so sure about that, but I will consider your comment. :slight_smile:

Indeed in 3x data split between LTE and NR is done at PDCP layer and t reordering at PDCP layer is like 300 msec.

300 ms is quite large, timer is around that value, right?

LTE anchor site is a site that provides the control plane for the 5G NR NSA (Non-Standalone) architecture, which means that the 5G data connection is established through the LTE layer. The LTE anchor site and the 5G NR site need to have frequency synchronization, but not necessarily phase synchronization. However, phase synchronization can improve the performance of some features, such as CoMP (Coordinated Multi-Point) and MIMO (Multiple-Input Multiple-Output).

Secondly, inter-site gNB TDD N78 layer is a layer of 5G NR base stations (gNBs) that operate in the n78 band (3.3-3.8 GHz TDD) and are connected to each other via X2 interface. This layer can provide higher data rates and capacity than the LTE layer, but it may have lower coverage and higher penetration losses.

Thirdly, DLoverF1mode is a feature that allows the gNB to deliver data to the 5G PDCP (Packet Data Convergence Protocol) layer directly, bypassing the LTE PDCP layer. This can reduce the latency and overhead of the data transmission, but it may also introduce some challenges, such as security, mobility, and QoS (Quality of Service) management.

Based on these information, my opinion is that enabling anchoring for inter-site gNB TDD N78 layer with an LTE anchor site that has no phase sync may be feasible, but it may also depend on other factors, such as the network topology, traffic demand, interference level, and user expectations. You may need to conduct some field tests and simulations to evaluate the performance and QoE of this configuration. You may also need to consider some trade-offs between the benefits and drawbacks of DLoverF1mode.

I hope this helps you with your question. :blush:

Nice comment, thank!!

Additionally f1 mode only also restricts the users under site 2 (site 2 also has LTE).

So total throughput for sure is gonna degrade.

So I have to use f1x2 mode means split between PDCP to RLC (LTE).