Look at http://en.wikipedia.org/wiki/List_of_WLAN_channels and you see you get 2 channels for 802.11n and 4 for 802.11b/g. Since most folk use the 802.11n setting you are assured that there are issues with WiFi in apartments.
Fix? Replace your router and devices to use the less used 5GHz WiFi. Since you are in a small space, you can place your WiFi router in the room you need access in.
Live in a condo & seriously think neighbors above me r continuously creating issues (believe them to be in tech). This a more than 8mos ongoing issue & have been able to resolve most issues only then 2 find another. My tablet which was my backup seems to have an issue getting an Internet Connection. Possible they r causing an interference from above? Notice radios or door open is when it occurs. Would a "spectrum analyzer" help me detect their interference & give me proof for the police should i need it? HELP!!!!