Yes, you need wifi. That's the only way to establish a connection with the 3DS. You need to ensure your hotspot is turned on (unless your device is rooted, then possibly this app will turn it on for you, from what I gather). Otherwise look at what I posted above. If you have any means of both hosting a web page, on any device, and having said device on the same network as your 3DS at the same time, then you can use it.
OK, but to which network I need to connect my 3ds and for starting a hotspot on my android, do I need internet on it?