1 Problem Description

In Project XXX, base station installation completes; the customer's spectrum is ready; five eLTE-IoT electricity meters are installed, but they cannot access the network. The following figure shows the location of these meters.

2 Analysis

2.1 Detailed Analysis and Troubleshooting Process

l   Check the power supply of the electricity meters, including voltage and power. If the voltage ranges from 200 V to 250 V and the output power is greater than 5 W, the meters can work properly. Power on the meters and find that the power supply is normal.

l   Check whether the versions of the meter communication modules are matched. The check result shows that the versions are matched.

l   Check whether the meters are in the blacklist state. If a meter is added to the blacklist, the meter cannot access the network within one hour. The preventative method is as follows:

Before changing the frequency of the base station, power off the meters. After the cell frequency is changed and the cell is successfully set up, power on the meters to prevent them from being added to the blacklist. Wait a maximum of 15 minutes. If the meters are added to the blacklist, it takes a long time to search for the network.

The preceding troubleshooting shows that the meters are added to the blacklist. After the preceding preventative operations are performed, the meters can access the network. The following figure shows the air interface access signaling of the meters.

However, shortly after the meters access the network, network connections are released due to the following causes:

The analysis shows that all meters are still using the default IP address 192.168.1.1, causing IP address conflicts and rejection by the core network. IP address conflicts indicate that a meter accessed the network before and the IP address is still saved in the meter.

To resolve the IP address conflicts, run the ADD DEVIC command on the core network side and reconfigure the meter IP addresses using the IPALLOCTYPE (STATIC) and ASSOCIATEDIP parameters.

The conclusion is as follows:

Holley electricity meters fail to access the network for the following causes:

l   A meter accessed the network before and a frequency change occurred. After the frequency change, the old frequency number was added to the blacklist. As a result, the meters had to wait one hour before being removed from the blacklist. The blacklist preventative mechanism is required for the meters to access the network again.

l   The meters failed to initiate an attach procedure after accessing the network because all meters are still using the default IP address 192.168.1.1, causing IP address conflicts and rejection by the core network.

2.2 Frequency Number Blacklist Mechanism

The frequency number blacklist mechanism used by the current module enables the possible selection of a correct frequency number for synchronization and attachment in case of exceptions.

A frequency number is added to the blacklist in the following scenarios:

l   An attach procedure is initiated but rejected. (Unknown Device)

l   A module is detached from the core network. (User Operation)

l   A radio link failure (RLF) occurs when an attach procedure is initiated on a frequency with no network access record.

l   d) The valid NetID (not 0xFFFF) set for the module is inconsistent with the PLEN in the system information of the cell on the frequency.

Conditions for removing a frequency number from the blacklist are as follows:

l   The module accesses the network on a frequency that is not listed in the blacklist

l   The frequency number is reconfigured using the AT command.

3 Solution

3.1 Description

l   Perform the following operations to prevent the meters from being added to the blacklist: (The blacklist mechanism will be optimized in future versions.)

Before changing the frequency of the base station, power off the meters. After the cell frequency is changed and the cell is successfully set up, power on the meters to prevent them from being added to the blacklist. Wait a maximum of 15 minutes. If the meters are added to the blacklist, it takes a long time to search for the network.

l   Resolve the IP conflict issue.

Allocate an IP address to each meter before delivery, or run the ADD DEVIC command on the core network side and reconfigure the meter IP addresses using the IPALLOCTYPE (STATIC) and ASSOCIATEDIP parameters.

3.2 Verification

After the preceding operations are performed, the meters can access the network and the attach procedure is successfully initiated. The module sends a login frame to the main base station.