| DAS & Wi-Fi Interoperability |
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by Todd Gibson Co-Founder and Co-Editor - WIIE First, what is a DAS? A DAS is a distributed antenna system that allows for a variety of RF signals to be combined & rebroadcasted out a single antenna system. It is not uncommon to find DAS implementations in large enterprises, universities, airports, high-rise buildings, and other large venues. The advantage of a DAS for the venue owner is increased revenue by allowing multiple carriers/service providers to share the same antenna to service the carrier's own customer base plus the DAS's ability to support private radio systems and public-safety radios. This creates a win-win for the venue owner and the customers/subscribers while the carrier has to typically share its revenue with the venue owner. In addition to allowing for multiple carriers into the venue owner's facility, it significantly reduces the amount of infrastructure cabling that would be required to support multiple carriers.
Now that Wi-Fi has proliferated widely into the same venues, Wi-Fi brings the same challenge to the venue owners in regards to the amount of equipment and infrastructure cabling that is required to support the Wi-Fi services. Wi-Fi also brings separate challenges as it only has 3 non-overlapping channels which create a wide array of potential service impacting issues in large, open venues due to channel planning/management. Typically DAS indoor antennas can extend approximately up to 150 feet (coax cable distance) from the IDF closet controller. In these types of venues, typically the RF planning approach is one of capacity vs. coverage which means that the antennas need to be implemented more densely across the facility. As this occurs, Wi-Fi coverage patters & channel planning is drastically impacted and will create a self-inflicted source of interference. As this occurs, it is near impossible to perform adequate channel planning as you need a certain power level for Wi-Fi due to its higher frequency and increased difficulties in floor/wall penetration. The more you increase the power for greater penetration, you reduce the spread of the antennas for capacity, and you have limit non-overlapping channels, the greater chance your Wi-Fi service on the DAS will suffer from cross channel interference, retransmissions and increased delay/jitter in the network. So, what is the solution? There are many DAS companies that have integrated Wi-Fi solutions/support into their platforms so all of the voice & data can share infrastructure. In reality, it is difficult to implement a carrier grade platform for cellular (voice & data) and Wi-Fi utilizing a DAS solution. In my opinion, the only real solution to incorporating rock solid cellular & Wi-Fi services is to deploy the infrastructure in parallel and do not integrate the Wi-Fi service with the DAS. |
