Minecraft (Pocket Edition) Multiplayer?

A friend and I wanted to play Minecraft together (over the same Wi-Fi) which did not work for reasons unknown to me. We tried again later (with different Wi-Fi connections) and suddenly it worked. Why is that and is there any way to fix the problem?

Either it is because you have to start a LAN game as soon as you are in the same connection, which would be new to me, or it is because your connection is too weak if you are both in the same WLAN, after all it will be double Connection required.