NR SA Out of Coverage (OOC)

This tutorial is about Out of Coverage test. It would shows how you can put UE in out of test condition and check if UE gets recovered from the OOC states. In terms of user level operation, OOC is a very simple feature that would not attract much attention. But handling OOC is pretty important in terms of UE implementation. Usually UE manufacturer perform quite long list of test for OOC.

Step 1 : UE performs measurement for the cell

Step 2 : If it lost cell power (or measured cell power is lower than a certain threshold), UE tries to search another suitable cells among neighbouring cell

Step 3 : If UE failes to find any of suitable cell, it goes into OOC state. If it finds any suitable cell, I trigger the initial attach.

Step 4 : In certail time interval, UE wake up briefly and go Step 1.

NOTE : If these step repeats blindly when the suitable cells are not available, the battery would run out quickly. So the strategy to perform this process is very important on UE modem development. One of the most common trick to reduce the battery consuption is the increase the time interval at Step 4 every time UE fails to find suitable cell when it wake up. However, if you set too long time interval (backoff time), the time for UE to recover from OOC when the UE enters into the area with normal coverage. So well-define optimization is required and these optimization is up to UE implementation (not defined by 3GPP).

Table of Contents

• NR SA Out of Coverage (OOC)
• Test Setup
• Key Configuration Parameters
• Configuration
• Perform the Test

Test Setup

Test setup for this tutorial is as shown below.  This is just for low layer testing, you may not need any complicated IP layer setup.

• SIM Card used in this tutorial is the one delivered with the system as it is.
• If you want to change the configuration, The tutorial Configuration Guide would help

Key Configuration Parameters

Followings are important configuration parameters for this tutorial. You may click on the items for the descriptions from Amarisoft documents.

• tx_gain  (see this for tx_gain tutorial)

Configuration

I have used gnb-sa.cfg which is installed by default without any modification.

I am using the default mme (mme-ims.cfg), ims config as shown below.

Perform the Test

Power on UE and let it attach. You may wait until it gets into idle because OOC (Out Of Coverage) is mainly for idle mode test. If the cell goes out of coverage during the connected mode, call drop would happen.

Make it sure that UE is in idle mode and it indicates a relatively strong signal strength before the OOC test. If you are not using a phone that can display signal strength, you may use AT command to check the signal strength.

Check on the current cell power using tx_gain command. And then decrease the cell gain step by step until UE gets into Out Of Coverage states.

NOTE : How much power I need to decrease to put UE into OOC (Out of Coverage) state ?  The answer is 'it depends on UE implementation'. Do some experiements with your own DUT to find the right value.

If UE gets into OOC (Out Of Coverage) states, the signal indicator on the display would show 'No Signal' icon.

Stay in Out of Coverage for some time.  And then increase the cell power to normal

Wait until UE reattach to the cell.  How long you have to wait until UE reattach varies depending on how long the UE was in Out of Coverage status and UE implementation of Out of Coverage recovery algorithm.

Once the connection is recovered to In Service, you can confirm it with signal strength indicator on display.