Amarisoft

LTE - Carrier Aggregation

 

The purpose of this tutorial is to show you how to perform LTE Carrier Aggregation. Carrier Aggregation is a mechanism that aggregate the traffic at MAC layer which requires accurate synchronization among all the cell and scheduled by a common MAC scheduler. At high level, it happens in a few steps as follows.

In terms of 3GPP, Step 1 is optional but in live network Step 1 is always performed. In Amarisoft Callbox, user case choose whether to perform step 1 or not.

Regarding the total number of CC (PCC + SCCs) and the number of Layers for each cell, the capacity varies with the product type. Refer to the following table summarized from the datasheet (Click on the link to check out the full datasheet)

Product

Callbox mini

Callbox Classic

Callbox Advanced

Callbox Ultimate

Callbox Extreme

Max Number of LTE Cell

1

3

4

8

12

Max Number of NR Cell

1

3

4

8

12

Max Total Number of Cell

1

3

4

8

12

Σ(Bi*Li)

40

120

800

1600

2400

Bi : Bandwidth of Cell [i],  Li : Number of Layers of Cell[i]

 

 

Table of Contents

 

 

Test Setup

 

Test setup for this tutorial is as shown below. In this setup, it shows 4 SDR cards are connected with Antenna but not all the test in this tuturial requires the 4 sdr cards. You only have to connect antenna to the number of sdr cards that you need for each test.

TestSetup Callbox UE 4sdr 01

 

 

 

Key Configuration Parameters

 

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

 

 

 

Test 1 : 2CC CA - Inter band without Measurement

 

This test configures 2 cells as follows.

It performs following procedure

 

 

Configuration

 

In this test, I used enb-2cc.cfg without modification.

LTE CA Test 1 Config 01

I used the mme-ims.cfg config as it is.

LTE CA Test 1 Config 02

The configuration in enb-2cc.cfg  is as shown below.  

LTE CA Test 1 Config 03

LTE CA Test 1 Config 04

LTE CA Test 1 Config 05

This configuration is not mandatory, but I extended the timer so that eNB does not release the RRC before adding the SCC.

LTE CA Test 1 Config 06

 

 

Perform the Test

 

LTE CA Test 1 Run 01

NOTE : you may not always see the print for CC=1 because the print shown here is a sampled / averaged.  You may take it as success as long as you see the print for CC = 2.

LTE CA Test 1 Run 02

Run lteSim_server at the directory /root/mme and generate IP traffic as shown below (If you are not familiar with ltesim_server, check out this tutorial)

LTE CA Test 1 Run 03

LTE CA Test 1 Run 04

 

 

Log Analysis

Sample Log

 

In this section, you will see how to confirm if UE registration is complete from trace log. You can use the same method to find any issues (e.g, registration failure) for troubleshooting. When UE registration fails, you may use this tutorial to figure out the point of the failure and troubleshoot

NOTE : This section is just to check quickly some important points in the log, but it may be a little bit tricky to do the detailed log analysis (especially for lower layer log analysis). In that case, I strongly recommend you to use WebGUI for the log analysis. You may refer to WebGUI Tutorial

 

Before you try any carrier aggregation test, I strongly suggest you to check on UE capability for your UE and confirm that it support the band combination that you want to try.

LTE CA Test 1 Log 01

 

LTE CA Test 1 Log 02

 

LTE CA Test 1 Log 03

 

LTE CA Test 1 Log 04

 

LTE CA Test 1 Log 05

You see two separate DCIs are transmitted for each cells at the same subframe.

LTE CA Test 1 Log 06

Check PDSCHs and corresponding UCI with HARQ responses.

LTE CA Test 1 Log 07

 

LTE CA Test 1 Log 08

 

 

Test 2 : 2CC CA - with Measurement

 

This test configures 2 cells as follows.

It performs following procedure

 

 

Configuration

 

In this test I used the enb-2cc-meas.cfg which is copied and modified from enb-2cc.cfg

If you use other Network (e.g, other network simulator or real network), you have to make it sure to configure UE sim according to the settings on network side

LTE CA Test 2 Config 01

LTE CA Test 2 Config 02

Followings are the configurations in enb-2cc-meas.cfg

LTE CA Test 2 Config 03

LTE CA Test 2 Config 04

LTE CA Test 2 Config 05

LTE CA Test 2 Config 06

This is not mandatory change, but I extended this timer so that eNB does not release RRC too soon before adding SCC.

LTE CA Test 2 Config 07

 

 

Perform the Test

 

LTE CA Test 2 Run 01

NOTE : you may not always see the print for CC=1 because the print shown here is a sampled / averaged.  You may take it as success as long as you see the print for CC = 2.

LTE CA Test 2 Run 02

Run lteSim_server at the directory /root/mme and generate IP traffic as shown below (If you are not familiar with ltesim_server, check out this tutorial)

LTE CA Test 2 Run 03

LTE CA Test 2 Run 04

 

 

Log Analysis

Sample Log

In this section, you will see how to confirm if UE registration is complete from trace log. You can use the same method to find any issues (e.g, registration failure) for troubleshooting. When UE registration fails, you may use this tutorial to figure out the point of the failure and troubleshoot

NOTE : This section is just to check quickly some important points in the log, but it may be a little bit tricky to do the detailed log analysis (especially for lower layer log analysis). In that case, I strongly recommend you to use WebGUI for the log analysis. You may refer to WebGUI Tutorial

eNB configure Measurement Report condition.

LTE CA Test 2 Log 01

UE send measurement report. this is the trigger to add SCC. If eNB does not receive this message, SCC will not be added.

LTE CA Test 2 Log 02

Add SCC

LTE CA Test 2 Log 03

 

 

 

Test 3 : 2CC CA - DL+UL without Measurement

 

This test configures 3 cells as follows.

It performs following procedure

 

 

Configuration

 

In this test, I used enb-2cc-ul.cfg which is copied and modified from enb-2cc.cfg.

LTE CA Test 3 Config 01

I used the mme-ims.cfg config as it is.

LTE CA Test 1 Config 02

In UEsim, I am using ue-2cc-ul.cfg which is copied from ue-2cc.cfg (NOTE : If you are using the commercial UE, Skip the UEsim configuration shown here).

LTE CA Test 3 Config 03

 

The configuration in enb-2cc-ul.cfg  is as shown below.  

LTE CA Test 3 Config 04

LTE CA Test 3 Config 05

LTE CA Test 3 Config 06

This configuration is not mandatory, but I extended the timer so that eNB does not release the RRC before adding the SCC.

LTE CA Test 1 Config 06

 

Followings are the configuration on UEsim which is configured in ue-2cc-ul.cfg .(NOTE : If you are using the commercial UE, Skip the UEsim configuration shown here).

LTE CA Test 3 Config 07

LTE CA Test 3 Config 08

LTE CA Test 3 Config 09

 

 

Perform the Test

 

LTE CA Test 3 Run 01

LTE CA Test 3 Run 02

LTE CA Test 3 Run 03

 

 

Log Analysis

Sample Log

LTE CA Test 3 Log 01

LTE CA Test 3 Log 02

LTE CA Test 3 Log 03

LTE CA Test 3 Log 04

LTE CA Test 3 Log 06

LTE CA Test 3 Log 05

 

 

 

Test 4 : 2CC CA/FDD + NR NSA/FDD

 

This test configures 3 cells as follows.

It performs following procedure

 

 

Configuration

 

In this test, I used gnb-nsa-2LTE-1NR.cfg which is copied and modified from gnb-nsa.cfg.

LTE CA Test 4 Config 01

I used the mme-ims.cfg config as it is.

LTE CA Test 1 Config 02

 

The configuration in gnb-nsa-2LTE-1NR.cfg  is as shown below.  

LTE CA Test 4 Config 04

LTE CA Test 4 Config 05

LTE CA Test 4 Config 06

LTE CA Test 4 Config 07

LTE CA Test 4 Config 08

LTE CA Test 4 Config 09

LTE CA Test 4 Config 10

LTE CA Test 4 Config 11

 

 

Perform the Test

 

LTE CA Test 4 Run 01

LTE CA Test 4 Run 02

LTE CA Test 4 Run 03

 

 

Log Analysis

Sample Log

LTE CA Test 4 Log 01

LTE CA Test 4 Log 02

LTE CA Test 4 Log 03

LTE CA Test 4 Log 04

LTE CA Test 4 Log 05

LTE CA Test 4 Log 06

 

 

 

RRC / NAS Signaling

 

RrcConnectionReconfiguration

: This is the RrcConnectionReconfigurationmessage sent by eNB  to configure Carrier Aggregation. (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: rrcConnectionReconfiguration: {

    rrc-TransactionIdentifier 0,

    criticalExtensions c1: rrcConnectionReconfiguration-r8: {

      dedicatedInfoNASList {

        '...'H

      },

      radioResourceConfigDedicated {

        srb-ToAddModList {

          ...

        },

        physicalConfigDedicated {

          ...

        },

        drb-ToAddModList-r15 {

          ...

        }

      },

      nonCriticalExtension {

        nonCriticalExtension {

          nonCriticalExtension {

            sCellToAddModList-r10 {

              {

                sCellIndex-r10 1,

                cellIdentification-r10 {

                  physCellId-r10 2,

                  dl-CarrierFreq-r10 1575

                },

                radioResourceConfigCommonSCell-r10 {

                  nonUL-Configuration-r10 {

                    dl-Bandwidth-r10 n25,

                    antennaInfoCommon-r10 {

                      antennaPortsCount an1

                    },

                    phich-Config-r10 {

                      phich-Duration normal,

                      phich-Resource one

                    },

                    pdsch-ConfigCommon-r10 {

                      referenceSignalPower -18,

                      p-b 0

                    }

                  }

                },

                radioResourceConfigDedicatedSCell-r10 {

                  physicalConfigDedicatedSCell-r10 {

                    nonUL-Configuration-r10 {

                      antennaInfo-r10 {

                        transmissionMode-r10 tm1,

                        ue-TransmitAntennaSelection release: NULL

                      },

                      crossCarrierSchedulingConfig-r10 {

                        schedulingCellInfo-r10 own-r10: {

                          cif-Presence-r10 FALSE

                        }

                      },

                      pdsch-ConfigDedicated-r10 {

                        p-a dB0

                      }

                    },

                    ul-Configuration-r10 {

                      cqi-ReportConfigSCell-r10 {

                        cqi-ReportModeAperiodic-r10 rm20,

                        nomPDSCH-RS-EPRE-Offset-r10 0,

                        cqi-ReportPeriodicSCell-r10 release: NULL

                      }

                    },

                    cqi-ReportConfigSCell-v1250 {

                      altCQI-Table-r12 allSubframes

                    }

                  }

                }

              }

            },

            ...

            }

          }

        }

      }

    }

  }

}

 

 

 

 

FAQ

 

[Q1] Why I see less PDSCH scheduling on SCC ?

[A1] there are various factors affecting the scheduling on SCC. Some of the typical factors are as follows.

I would not comment anything about "Available Downlink Data" here. I am assuming in this comment that DL data is available high enough to utilize the full SCC resources or force_dl_schedule is enabled.

Bascally when the eNB is expecting PUCCH format other than format 3, it does not schedule PDSCH on SCC. So what you can do to work around the underscheduling issue on SCC would be one of the followings :

Followings are the list of configuration parameters that are related to this issue.