Simply put, all you need to do is to access the phone testing settings and enable the LTE to get it to work.
Follow this guide to enable LTE on your Nexus 4 in a few seconds -
- Open dialer and call *#*#4636#*#* which will take you to phone testing settings.
- Access "phone info"
- Change phone's cellular network type to LTE Only
- You're done!
Note enabling the 4G LTE may decrease signal performance and drain more battery. In order to revert back to the 3G, choose WCDMA. Note also, 4G site may not be in your country. Check the signal icon - there should be a 4G icon above it if it works.