[Xiaomi Mi A1 Guides, News, & Discussion] anshsharma240:
As we all know, MiA1 has a Snapdragon 625 processor that comes with the X9 LTE modem which supports Carrier Aggregation (2CA) but the OEM has not enabled it.

With the help of this guide you can enable carrier aggregation in your mia1 even without unlocked bootloader and root access.

Tools Required

1. Minimal ADB Drivers

2. QPST Flash Tools

3. QxDM Professional

4. LTE Band Calculator for Android

Steps to Follow

1. Install Minimal ADB Drivers, QPST Flash Tool & QXDM Professional on your PC.

2. Enable USB Debugging on your MiA1 .

3. Go to Phone dialer and dial " *#*#717717#*#* " to enable Diagnostic Mode(See Update Section below before Proceeding).

4. Connect your phone to PC via USB Cable then your PC will detect the device and automatically install the drivers.

5. Open Device Manager on PC and look for Ports(COM & LPT), under this you will see your device listed as "Qualcomm HS USB Diagnostics 9091 (COM*)".

6. Now, Run QPST as an administrator then goto Ports tab and check if your device is listed there and it's state is enabled.

7. Run QXDM as an administrator then goto Options tab and click on Communications. Now a new window will open, in that select your device COM Port under "Target Port" and make sure that your device is selected under "PortType", then click OK.

8. Select "NV Browser" from drop-down menu under View and select "RF LTE" under Category Filter.Now scroll and find something like "RFNV LTE B* CA BC CONFIG"("*" denotes the band).

9. As MiA1 only supports 2CA. we can CA using only two bands

For Ex: B1+B3, B3+B5, B3+B40, B5+B40, B5+B5, B40+B40 etc..

You can select any two band combination that is supported by your carrier and is available in you region.

10. Now Open LTE band Calculator on your phone and select two bands (e.g. B3+B40). you will see a value like "549755813892" or something else(it depends on your bands selection).

11. In QXDM select "RFNV LTE B3 CA BC CONFIG", click on "Read" then double-click on Input and clear the default value "0" and type the value that we have calculated using LTE Band Calculator in step 10 above, then click on "Write". Now,do the same with "RFNV LTE B40 CA BC CONFIG".

12. Wait for few seconds and then disconnect the phone from PC.

13. Now,Restart your phone and turn on data you will see 4g+ icon in status bar. That's it.

Things to Remember

* In step 10 choose bands that are available in your region and make sure, that your carrier supports CA over that bands.

* In step 11, change the value of bands selected in step 10.

* You have to try and test multiple combinations to get the stable CA state because in some bands network is unstable.

* If you lose signal after this process or if you want to revert back then just repeat step 11 and put default input value which is "0" for MiA1.

To check whether CA is working or not

1. Open Phone Dialer and dial "*#*#4636#*#*" to enter in Testing menu.

2. Tap on Phone Information and check "LTE physical channel configuration".

If CA is working, It will show you two connections Primary and Secondary along with their bandwidth, otherwise nothing.

I have configured intra-band CA over band 40 on Jio4G.

You can look at the screenshots attached below for difference with or without CA.

Update

USSD code is now working on latest June 2019 Security Patch.

USSD code is not working on March/April/May 2019 security patch.

If the USSD code doesn't work then you have to root your device first to enable diagnostic mode and after that, you can proceed further from step 5.

There are two ways to enable diagnostic mode after root which are as follows:

1. ADB

Enable "USB Debugging"on your phone.

Connect it to your PC/Laptop.

Open "Minimal ADB & Fastboot" Command Prompt with administrative rights.

Type adb devices and press enter.

Type adb shell and press enter.

Type su and press enter.

Type setprop sys.usb.config diag,adb and press enter.

2. Terminal Emulator App

Install any "Terminal Emulator" app from play store e.g. Termux

Enable "USB Debugging"on your phone.

Connect it to your PC/Laptop.

Open "Termux" .

Type su and press enter.

Type setprop sys.usb.config diag,adb and press enter.