What is baseband?
If you have rooted your phone and flashed custom ROMs you must have overcome the term baseband several times. Many times people confuse between kernel and baseband. In Android Kernel is the most important piece of software that controls almost every aspect of the device. The kernel has all the drivers for everything else, including camera, Bluetooth, and Wi-Fi, built into it. The baseband is merely a piece of firmware (a type of software), that controls the radio in your phone. The baseband is responsible for the network connectivity and other connectivity options.
Recently the latest baseband version “8x55A-AAABQOAZM-203028G-85” for Xperia Ray(ST18i) is leaked on the internet. This baseband provides better network stability and lesser battery drain as compared to the older 77 baseband. Here is a simple tutorial to flash the latest baseband on your Xperia Ray.