Deploying in Hallways vs. Deploying in Rooms

Having done a lot of Wi-Fi in the Multi-Dwelling Unit (MDU) space, I'm often asked by installers for Wi-Fi in apartment buildings and hotels as to why I always recommend putting access points in the apartments / guest rooms instead of in the hallway.

It is generally true that installing APs in hallways is generally far easier than installing APs in units.  After all, many hallways have drop ceilings making cabling and installation a snap.    Even when there are hard ceilings present, cabling soffits or access panels are often already in place or are fairly easy to install, making cabling possible.   If there isn't already low-voltage infrastructure (i.e. a spare CAT5e / CAT6a cable) available in each unit, getting cabling into the units can be impractical or cost-ineffective.  

However, from a performance standpoint, putting APs in line of sight of each other down a hallway is the worst thing you can do for the following reasons:

1. Talkback:  Client devices like smartphones and tablets have weak transmitters in order to maximize battery life.  Accordingly, while the AP may be strong enough to be heard by the client, the client often is not strong enough to be heard by the AP.  Hence, you want to put the APs as close to the clients as possible to best facilitate the client's ability to "talk back" to the AP. 
2. Attenuation:  The inside wall adjacent to the hallway tends to have high attenuation.  Why?  Everyone likes having the biggest windows looking out as possible.  Hence, the inside wall tends to have all of the metal appliances (refrigerators, dishwashers, ovens, etc.), mirrors, plumbing, steel fire doors, etc.    This serves to attenuate the signal from the hallways.  It is not uncommon to see signal penetration through the floor / ceiling be much better than signal penetration from the hallway into the unit.
3. Self-interference:   A long, thin hallway acts as a tunnel for Wi-Fi signals, focusing the signal and making it extend much further than it will laterally into the units.    Furthermore, even with the APs on different channels, there is always some level of adjacent channel interference.   When all of the APs are in line with each other, they will cause interference with each other.  The heavier the traffic load, the more interference there will be.

If you don't have the benefit of existing low-voltage cabling infrastructure, one trick often used is to run the cables down the corridor, penetrate above the doorway to the apartment / guest room, and mount the AP above the door.   While the AP may still not be ideally located within the center of the unit, having to penetrate the inside wall with signal is eliminated, placing the AP closer to the client devices and taking advantage of the building structure itself to further attenuate signals between the APs.