Designing DAS in Pilot Pollution Environment

For CDMA network, an indoor area with Pilot Pollution usually means it's an area with high signal strength, but low signal quality. This is a common phenomenon in high rise buildings in Houston (Houston, we have a problem!)

In CDMA network RSSI (Received Signal Strength Indicator) at a point is the total CDMA power received. So if at any point you are getting a RSSI of -65 dBm on a Sprint phone, that RSSI is the sum of RF Power received at that point point from all the Sprint base stations your handset can see or sniff.

Ec/Io on the other hand is an indicator of signal quality. Ec/Io at any point for a particular server (or base station) is the contribution of power from that base station divided by combined received power at that point from all base stations.

0 + 0 = 3

One of my favorite questions to ask to a new DAS engineer during interview is what is 0 dBm + 0 dBm. Say what? Answer is 3 dBm. And here's how:

0 dBm = 1 milliwatt

So 0 dBm + 0 dBm = 1 milliwatt + 1 milliwatt = 2 milliwatt

2 milliwatt = 10* Log(2) = 3 dBm

Therefore, 0 dBm + 0 dBm = 3 dBm.

Use of Info-graphics for DAS Project Management

I often get a "say-what?" look from a group of people when they come from a diverse background. While working on a healthcare DAS project, I had to give bi-weekly status update to the project stakeholders on the client side who came from diverse background - from IT, to facilities management, nursing department, infectious control, and even doctors. Talking about a DAS project can become little tricky in these situations. After a few of the bumpy sessions, I found that status update through infographics can be very effective.

Infographics is a fancy name for presenting your data visually. If you look around on the web though, infographics is mainly focused on being visually exciting and stimulating; and I don't blame the infographer, because just presenting table of data can be little boring. However, when I am using the graphics, I try to make sure that the background graphics adds value to the update I am presenting. So for example below, you can see how the major elements of the system is connected. Audience is also getting the updates on the different elements of the system. This can be fun, and presentation can be little more interesting than just presenting drab data. Audience from different background can have a better understanding of the system and how it's connected together. I also don't like to use a lot of slides when I am presenting to my clients. If a few slides are getting the point across then I am all for that.

By the way, I used Microsoft Excel and Paint for this presentation. Approximate time to put together the graphics was 20 minutes. Once I have the base graphics prepared status update boxes take just a few minutes to update.

Blue and White Coax for MIMO

Depending on the type of DAS platform (i.e., SOLiD, Andrew, MobileAccess) you are deploying, if it's a MIMO DAS you may have to pull parallel cable. For those who are not familiar with MIMO deployment, you will have to pull two sets of coaxial cable, splitters/couplers to a pair of antennas at the same location only 4-6 ft apart. In the field, this may become little complicated, because you don't want the parallel cables to get crossed. Installers usually mark the tip of the cables before pulling so that they can differentiate the cable sets.

One idea might be using cables of different color. So for example, you can pull a set of blue coax, and white coax as parallel network. I am strictly looking at it from the perspective of reducing confusion; however, logistically this may become a little complex - especially if the two colors of coax are produced by different manufacturers, etc.  

Cut me a slack...

During the DAS deployment phase, it's not unusual for cable pullers to leave some slack at the points where connectors will be installed. They do that with the thinking that having a little slack is much, much better than coming short on cable run at the point of, say, splitters or couplers. I had been in a project recently where the crew chief picked up a few crew from the local Union Hall to pull cables, and to make things simple and straightforward asked them to leave 5 ft slack at every connector point. This ended up costing us 15 ft of wasted cable per 2-way splitter or directional coupler (3 ports, 5 ft per port, a total of 15 ft). Waste doubled because this was a MIMO system. This waste is in addition to the waste we usually get from reaching the end of the spool. So when the crew chief asked for additional cable, we started suspecting the scale of the design first. We got more puzzled when we found that design was done according to the right scale. It took us almost over a week before we could figure out the principal cause.

A slackin' Situation

For this particular MIMO project, we had close to 376 antennas, 33 remotes, and 306 splitters/couplers. Just for the 5 ft slack at each connection point, the waste came out to be about 6,635 ft. From materials perspective, best thing to do is to connectorize as you go. In that case though, you may have to have crew who pulls cable and also knows how to put connectors on.

Walking-Coffin

We often use low tech thingy-ma-jiggy to build hi-tech network. One such device is - as the builder Jeremy Tesson fondly calls it - Walking-Coffin. Walking-Coffin may look like a transport vehicle for Fred Flintstone, but this was used to pull 2 sets of coax simultaneously for a neutral host MIMO DAS, where 2 parallel coax were going to 2 different antennas at a single location.

I also liked the way Jeremy accesorized the walking-coffin - a front end basket to carry around hardware and light tools, a hook to hang a dust pan. Cool!