Case Study of a DAS upgrade project: difficulties and minimizing risks

We usually consider an upgrade project fairly easy – especially if we are going to just upgrade the current system to a new one. However, that’s not how it turned out for a major healthcare campus DAS upgrade project we are currently working on.

This project turned out to be quite interesting from a logistical perspective. The usual limitations for a DAS project may come from electronics or materials delay for delivery or shortage of skilled workers at the site and maybe even restricted access to a building (public venue for example). None of the traditional limitations have taken the center stage.

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Restrictions imposed by the customer:

The customer mandated that we would have to keep the existing DAS running as we work on the new DAS.

We will get a swap-over window of a weekend to transition over to the new system. The whole campus has been broken into zones or groups. And we will build and cut-over the DAS one group at a time.

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Our Achilles Heel - Limitation of Space in IDF closets:

Spaces in IDF closets are considered premium real estate. These IDF closets are used for all equipment needed for the hospital – from networking to IoT and medical telemetry. Closets are very congested and finding space in there for new equipment is very difficult. Empty spaces are always filling up as time passes. So if the DAS design was done with a particular closet in the plan, and a few months later that space is no longer available we may have to re-design for that space-shortage. This lack of space for electronics mounting turned out to be our Achilles Heel.

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A quick history of the project:

We first deployed a campus-wide single carrier DAS almost 12 years ago. The customer now wants to upgrade the system to a multi-carrier DAS. Design is complete, we are getting close to the start date of the construction. As we were working on forecasting the deployment timeline, we realized the weakest link in our timeline will be caused by the lack of space required to mount or place the equipment. Let me elaborate…

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Details of Space Shortage:

Space shortage for this project can be divided into 2 types:

1. Shortage in IDF closet space for mounting electronics (i.e., remotes)

2. Shortage of space in DAS head-end room

Shortage of space in IDF Closet:

We can have one of the 3 scenarios in the IDF closet:

A. Plenty of space (no issue here)

B. No space available for the new electronics

C. Limited space, i.e., new electronics can be fit if we remove the existing DAS electronics

Scenarios B and C create additional downstream activities.

If there is no space in a closet (scenario B), but the design calls for placing electronics in that room, then basically the only option we have is to ‘redesign’ with available space in another room. This can change the link budget and the length of coaxial cable or fiber. If space is not available in a nearby location, then we may even have to change the type of electronics.

Scenario C presents a different set of difficulties. If the existing electronics (i.e., remote) have to be moved to make space for the new electronics (i.e., remotes) we will have to find a way to temporarily mount the new remote very close to the existing remote. This is because in order to keep the existing DAS running we cannot just remove the existing remote. We will still have to run coax and fiber to the new remote. We will have to keep slack in cable so that during the transition or swap-over window, we will have to remove the existing remote and permanently mount the new remote. This adds to the work during the short swap-over window. For these scenarios, we must make sure that we will have enough technicians during the swap-over windows to get these done.

Scenario C gets worse if we have to reuse the fiber strands currently attached to the existing remote for the new remote. That means we will have to wait for the swap-over window when we are allowed to turn the existing remote off, connect the fiber to the new remote and then start the CW testing.

As the number of scenario C goes up, action items during the swap-over window keep increasing.

Shortage of space in the head-end room:

The head-end room is currently full of head-end electronics for all the different zones. The multi-carrier DAS will need a new set of head-end electronics for each zone. This means we place the new head-electronics very close to the existing head-end rack, and during the swap-over window, we will have to turn off and remove the existing head-end, move the new head-end electronics on the existing rack space and make sure all the fiber jumpers are connected to the new head-end. Signal source integration and turn-up cannot start until this is done. All of these action items keep adding to the swap-over windows.

The number of activities for the swap-over window now becomes the weakest link. And this weakest link started with the limitation of space at the IDF closet and the head-end rooms.

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How to minimize the risk?

Knowing and quantifying all the action items during swap-over windows are the key to minimize risks.

Do a thorough construction walk with the design in hand.

This means:

1. Investigate the power and fiber availability in these rooms,

2. Count the fiber strands and update the count of fiber strands if needed.

3. Check out all the locations of the antennas and make sure they can be mounted at the designated locations.

4. Check to see if anything wall configuration on the floors has changed or not.

Identify rooms where space will be an issue.

Designate the issues with Scenario B or C labels. Determine the resolution for each issue:

1. If there is no space at all (Scenario B), find out the nearest available space where electronics can be mounted and complete the redesign.

2. Figure out cost and materials adjustment due to the redesign, and communicate that with the customer.

3. If there is limited space (Scenario C), figure out how the new electronics will be temporarily mounted during construction, and what will be the procedures for cutting it over (i.e., MOP).

4. Go through the same review exercise as step 3 above for the head-end room.

5. If you have to reuse the fiber (being used by existing electronics), add CW (Continuous Wave) testing to the list of activities during the swap-over windows.

6. Make a comprehensive list of activities that have to be completed during the swap-over windows.

7. Make sure you will have enough resources (human and testing gears) to complete all the activities during the swap-over window. DAS testing gears are usually quite expensive and make sure the availability of adequate testing gears does not become the weak link.

8. Log all of these in a spreadsheet so that they can be tracked effectively.