  Rapidly increasing traffic demand has forced indoor operators to deploy more
and more Wi-Fi access points (APs). As AP density increases, inter-AP
interference rises and may limit the capacity. Alternatively, cellular
technologies using centralized interference coordination can provide the same
capacity with the fewer number of APs at the price of more expensive equipment
and installation cost. It is still not obvious at what demand level more
sophisticated coordination pays off in terms of total system cost. To make this
comparison, we assess the required AP density of three candidate systems for a
given average demand: a Wi-Fi network, a conventional pico-cellular network
with frequency planning, and an advanced system employing multi-cell joint
processing. Numerical results show that dense Wi-Fi is the cheapest solution at
a relatively low demand level. However, the AP density grows quickly at a
critical demand level regardless of propagation conditions. Beyond this Wi-Fi
network limit, the conventional pico-cellular network works and is cheaper than
the joint processing in obstructed environments, e.g., furnished offices with
walls. In line of sight condition such as stadiums, the joint processing
becomes the most viable solution. The drawback is that extremely accurate
channel state information at transmitters is needed.
