The following uses an example to describe the method to determine the number of APs,
antenna positions, and channels.
A dormitory building has seven floors, with 20 rooms on each floor. Each room has four
users, and each user requires 2 Mbit/s bandwidth. Assuming that maximum number of
concurrent users is 30% of the total number of users, plan the indoor DAS system as follows:
1. Determine the required bandwidth.
– Bandwidth required on each floor = 20 x 4 x 2 x 0.3 = 48 Mbit/s
– Number of APs required on each floor = 48/20 = 2.4
2. Determine the number of APs.
– According to the preceding calculation result, each floor needs 3 APs, so a total of
21 APs are required in the seven-floor dormitory building.
– A 24-port PoE switch can be used as the aggregation switch and provides power to
APs.
– Determine the number of ACs based on the number of APs. ACs can be connected
to a BAS device in branched networking mode.
3. Determine the coverage areas (indoor coverage 50 m x 13 m).
– Dormitories are major coverage areas.
– Washrooms, toilets, and corridors are minor coverage areas.
4. Determine antenna installation positions, coverage radius, and interval between antennas
based on signal coverage requirements.
– Deploy an antenna between each four rooms so that radio signals need to penetrate
only one wall. The interval between antennas is 7.5 m.
– An additional antenna is deployed for the last dormitory at the end of the corridor to
ensure a good signal coverage. Washrooms, toilets, and corridors do not need
dedicated antennas.
5. Determine the indoor DAS system layout.
– If no 2G/3G indoor DAS system is deployed in the dormitory system, establish a
WLAN network.
– Install three APs on each floor. Each AP has two antennas, which are connected to
the AP through a two-way splitter.
– The coverage distance is 50 m, so 1/2-inch cables can be used to connect the APs
and antennas.
– Calculate the length of each cable.
– APs can be wall-mounted or installed in a cabinet. Choose the installation positions
that need the shortest cable length.
