Let's say I do not want (or cannot) use WiFi or Ethernet. However, I am connected to my RPi3 over UART serail cable. Is there any way to establish an SSH connection (or any other TCP/IP based connection) to Raspberry Pi from Windows 7 PC? Thanks!
You need to establish a network connection using PPP protocol. After that, just SSH using the IP address that was assigned while establishing a PPP connection.
Here are some links describing the process in more details, mostly on Raspberry Pi side:
Here is how to configure PPP connection at your Windows PC:
How to create a Windows script to automatically add PPP connection and connect it right away with one click - for that, you might need to create a PowerShell script or CMD script using the info from the following links: