I was looking for a cheap hotel not too far from the center and the congress. I got a hotel with friendly staff and a clean room. It's about 20min from the center(with public transports) and about 45min from the congress. From the tram-station/trainstation to the hotel it's about 10min walk. In the night I used the N3-Nightbus.
It's not a beautiful part of the town, but it was calm and quiet. Even if google-maps says that the wifi at this hotel is not free: it is.
- Free Wifi