Over the past ten years there has been much discussion surrounding the technology deployment model of utilizing a coaxial based (distributed antenna system) to transport cellular, PCS, Public Safety, the WLAN (Wireless LAN), and WMTS (Wireless Medical Telemetry Service). There also has been marketing surrounding this “architecture” as future proof.
Coaxial based/fiber based distributed antenna systems really have not changed a lot in the past ten plus years other than the ability to accommodate LTE and accommodate more and more the shift toward fiber.
However in looking at this “future proof” design it has to be understood that the WLAN is very dynamic in nature in terms of the technology marching forward. Since 1999 when 802.11b was approved; we now have since the 802.11 marched on with 802.11g,802.11a, 802.11i, 802.11e, 802.11n, 802.11ac…etc.
Some examples to take a look at.
Example One: The majority of all DAS designs are designed to accommodate a link budget and a certain signal level strength of negative (- 85dBm). (That is the signal strength of 5 bars on your cell phone.) While this signal level is fine for data (802.11b/g); it certainly will not meet the requirements of “wireless voice over IP”. So in this example if the DAS were designed for cellular, PCS, and 802.11b/g, and “wireless voice over IP” were added, a complete “new design” and redeployment is needed. “Wireless voice over IP requires a stronger signal strength in this case… – 65dBm.
Example Two: After 802.11b/g came the announcement of 802.11a. Going back to the link budget for a DAS…then now we have to add additional amplification. This will require “active” components to be a part of the DAS which can add to a risk of component failure.
Example Three: Adding WMTS requires multiple coaxial infrastructures and a new complete re-design. This required for the diversity requirement of WMTS.
Example Four: Providing the ability of MIMO for 802.11n. If we go back to Example One and Two, these designs will never be able to accommodate MIMO.
So at the end of the day it is probably much more cost effective, reliable, and less risk to implement a DAS for what it was intended to, and separate out the WLAN from the DAS.
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