Why the price of DAS per sq. ft. basis can be misleading?
Our customers sometimes want to know the price of a DAS by square footage. Square footage price works in a lot of cases, but there are several limitations to produce such numbers for DAS projects and it can be misleading. We advise against it.
Two buildings with the same area may need different numbers of antennas and even different DAS. A lot of factors can shape the final number of antennas.
Assuming two buildings are getting same type of DAS platform or electronics, the number of antennas is usually a good indicator of the relative cost for the DAS. The higher number of antennas can indicate more electronics and passive materials (fiber or coaxial cable, splitters, couplers, connectors, etc.).
Following are some common factors that impact the number of antennas, size, and type of DAS.
Coverage Area:
The number of antennas is usually proportional to the area you are trying to cover. Greater the area of coverage, more antennas you will need. the actual number of antennas will be determined through engineering analysis.
Signal frequencies:
Signals with lower frequencies usually travel a longer distance than higher frequencies. The most common bands used for public safety are VHF, UHF, 700 & 800 bands. But a neutral host DAS in the U.S. will generally cover 700, 800, 1900, 2100, 2300, and 2500 bands. This is the reason a Public Safety DAS can be built with a lot fewer antennas than a neutral host cellular DAS.
Usually, the greatest frequencies become the weakest link in a DAS design. So when a public safety DAS can be designed for 800 MHz signal, we may have to design the neutral host for DAS 2500 MHz. 2500 MHz signals will travel quite a bit shorter distance than 800 MHz signals. This will translate into a higher density of antennas for a neutral host DAS than a public safety DAS; i.e., the bigger budget will be needed.
Number of inside walls:
The general rule is more walls signal runs into, less distance it will travel, which means more antennas will be needed. If the area of two floors is the same, the floor with more dense walls layout will require more antennas (i.e., higher budget).
Type of walls:
As the signal passes through the walls, it loses strength. The amount of lost signal depends on the type of wall. For example, the signal will lose more power going through a concrete wall than drywall. This means building with mostly concrete walls will need more antennas than a building with mostly dry walls even though the 2 buildings have the same size.
Signals coming in from outside:
When building a Carrier-grade DAS, engineers have to find out how much of outside signals are coming inside. When the Carrier or Mobile Network Operators (e.g., AT&T, Verizon, etc.) bring their signal sources to the DAS, they prefer to have DAS dominate the outside signal (that seeped in) by a factor of 4 to 10 times. The reason for this is that carriers want to make sure that when their users are using their phones, they take the signal from the indoor signal source via DAS - not the outside signal.
So if the signal from outside is strong, DAS will have to have more antennas to fight that signal. This, of course, can translate into a higher cost of DAS. This is another reason why the cost of DAS located in the middle of downtown is a lot more expensive than a DAS in similar size buildings but located outside the city.
Other external factors such as cable routing, time of work-hours, work restrictions (e.g. infectious control area in hospital buildings) can all make difference in pricing. These are the reasons, as DAS engineering company, we shy away from giving per square footage price.
Summary:
There are different factors that influence the final DAS type and configuration and ultimately cost. They are:
Greater the area of coverage, more antennas you will need, and hence higher the cost of DAS.
Signal frequencies: higher signal frequency takes more antennas to cover an area.
The number of inside walls: More walls inside a building will require more antennas to cover.
Type of walls: Building with concrete indoor walls will require more antennas than building with the same number of drywalls.
Signals coming in from outside: If the signals penetrating into the building has high strength, but low quality, you will need more antennas to overcome them. It often happens on higher floors in high-rise buildings.
