LTE CMAS

 

This tutorial shows how to test LTE CMAS on Amari Callbox with a commercial phone. CMAS stands for Commercial Mobile Alert System. It is a type of PWS (Public Warning System). Basic RAN Process of LTE CMAS is as follows :

• Transmit SIB12 with CMAS Message
• Transmit Paging to inform UE to decode the CMAS message

In real deployment, this process is controlled by CMAS server in core network side.  It is the CMAS server and Core Network which are triggering the whole CMAS process and RAN to transmit the message.

 

NOTE :  In 2G/3G, there was similar feature like PWS. It is called CBS (Cell Broadcasting System). The logic on core network side logic in CBS would be similar to PWS in LTE, but RAN side implementation of CBS is different from PWS in LTE. In LTE, we don't use any specifically dedicated channel for this and just use one of the existing channel (BCCH - PDSCH) whereas we use specially dedicated channel (CTCH - FACH-SCCPCH) for CBS.

NOTE :  Amarisoft does not support any of 2G/3G (i.e, GSM,CDMA,WCDMA,HSPA) and 2G/3G related function.

 

Table of Contents

• LTE CMAS
• Test Setup
• Key Configuration Parameters
• Configuration
• Perform the test
• Log Analysis
• RRC / NAS Signaling
• SIB 12
• Paging

 

Test Setup

Test setup for this tutorial is as shown below.  

• 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.

• pws_msgs : In this link, you would get the descriptions for all the items listed below. In the document, there are much more parameters (optional parameters) than the list below
• local_identifier
• message_identifier
• serial_number
• data_coding_scheme
• repetition_period
• warning_type
• warning_message
• warning_message_hex
• send_warning_indication
• warning_area_list

 

Configuration

I used the enb.default.cfg (LTE default configuration) as it is without changing any contents in it. Basically you can use any kind of enb configuration. eNB does not require any specific configuration for CMAS.

I also used mme-ims-cmas.cfg which was copied and modified from mme-ims.cfg.

In mme-ims-cmas.cfg I have added the following configuration. pws_msgs is the parameter where you can configure the details of CMAS.

 

Perform the test

Start LTE service and check basic cell configuration. Any cell configuration is OK as long as it is LTE cell.

Power on UE and let UE attach to the cell

Confirm that UE is attached to mme.

Send CMAS using pws_write command as shown below. (NOTE : The number '2' corresponds to the configuration parameter local_identifier of pws_msgs:[ ] in mme.cfg)

Check if you get CMAS message as shown below. You should hear alarm sound from the UE as well. Both text message and Alarm sound is requirement for the test.

You can stop cmas message using the following command. (NOTE : The number '2' corresponds to the configuration parameter local_identifier of pws_msgs:[ ] in mme.cfg)

 

Log Analysis

Sample Log

Since CMAS message is broadcast by SIB message, the first step for CMAS log analysis is to capture the log with BCCH and RRC enabled as shown below.

Set the layer as shown below for the convinience of the log analysis.

When you send the CMAS message message with pws_write command, Core Network send CMAS message as shown below.|

When Core Network send CMAS, eNB send Paging with cmas-indication

CMAS message is broadcast via sib12. This message is carrying all the contents configured by pws_msgs parameter in the configuration file. If you want to modify any part of sib12 for testing purpose, you should change the configuration of pws_msgs parameter in the configuration file.

 

RRC / NAS Signaling

 

SIB 12

: This is the SIB 12 message sent by eNB  to configure CMAS. (NOTE : You would see some IEs that has a specific assigned vale here, but consider it as just an example value. Those values should vary depending on test requirement)

{

  message c1: systemInformation: {

    criticalExtensions systemInformation-r8: {

      sib-TypeAndInfo {

        sib12-v920: {

          messageIdentifier-r9 '1112'H,

          serialNumber-r9 '3001'H,

          warningMessageSegmentType-r9 notLastSegment,

          warningMessageSegmentNumber-r9 0,

          warningMessageSegment-r9 '0174747A0E4ACF4161D0B0199C82E8E5391DD42ECFE7E1731900000000000000'H,

          dataCodingScheme-r9 '0F'H

        }

      }

 

Paging

: This is the Paging message sent by eNB  to Notify that CMAS is transmitted. (NOTE : You would see some IEs that has a specific assigned vale here, but consider it as just an example value. Those values should vary depending on test requirement)

 

{

  message c1: paging: {

    nonCriticalExtension {

      nonCriticalExtension {

        cmas-Indication-r9 true

      }

    }

  }

}