Elevator shafts, stairwells

[oshea85]

I've got a hospital that is looking to deploy a voice application over a WLAN they want me to build.

Question: what does is take to cover the elevator shafts and stairwells?

From the pieces of this network I've already deployed, it doesn't look like the existing APs will do a good job of covering these areas.

I've always heard that you put an AP in the top of a shaft or stairwell with a patch or yagi antenna and let it rip.

Do I figure one AP/antenna per shaft/stairway? How far up and down can I go? My building is eleven stories.

Please, real-world-experience answers only. Thanks!

[JimGeier]

You're right, this is a tough issue. It seems that the directional antennas will be the best bet. Make sure you do a site survey to see if they will cover the needed area. Also consider using wireless repeaters (http://www.80211-planet.com/tutorials/article.php/1571601) to boost the signal from the directional antennas.

[dstern]

You might want to consider using a radiating (leaking) cable as an antenna. It's basically an antenna cable with slits in the outer conductor, allowing the signal to "leak" out.
You will have the same gain of about 3dBi (afair) at any point of the cable, making this an option for enclosed spaces, like tunnels, where there is a physically limited maximum distance a RF device can have from the antenna.
Have a look at http://www.rfsworld.com and check under Products -> Wireless Distributed Communication Systems

David

[NewBWiFiGuy]

Since the elevator has 110v power in it, you could actually install an AP on top with a tiny antenna either pointing down thru the roof, the light, or even inside the elivator. The AP could repeat off a signal from the AP installed at the top of the shaft.

Or, since there are flexible power wires already running in a bundle to the elevator you could run a long ethernet cable to the AP but your limited to 300ft give or take. Assuming your building is around 20ft per story you're still within 300ft.

Lots of data cable already runs to the elevator most likely (phone, control, monitoring) it shouldn't be hard to get a ethernet line run with that perhaps by the elevator support company. If you do it, I'd have them run two just for the hell of it.

[oshea85]

Intelligent responses, all. However....

In NYC, you can't (not by code at least) run a cable down a stairwell unless it's conductors for fire alarm/control. Can't run an exposed cable in an elevator shaft either.

The AP-on-top-of-the-car occurred to me some time ago, and what I found out is that the elevator companies run what's called a travelling cable to the car. They will not let you install another cable. It usually has about 50 pairs in it, but they're not data-grade, they're voice-grade; conductors are stranded to take the flexing, so attenuation becomes an issue. Although, I've gotten half-duplex 10BaseT to go over 440 feet on category-nothing voice riser that was chopped and spliced and terminated on 66-blocks.

This could work; I smell an experiment!

[Sam Cheung]

Perhaps the following may help:

Most elevators have power on elevator top for maintenance lighting you can tee off the power supply and power your AP. There are also maintenance lighting at bottom of elevator well and motor housing at the top (for cable drive lifts and elevators, not hydraulic ones).

[oshea85]

Has anyone ever tried to run Ethernet over the travelling cable in elevator cars?

[krook]

Probably not an ideal solution, but you could try DSL or HPNA if Ethernet won't work on the existing wires.

[oshea85]

Anyone have any new experiences they'd like to relate?

[Nunny]

Bump...

I know this thread is a couple years old now, but a forum search reveals this as the only thread here concerning elevators and stairs... and I'll give you one guess as to what I need to do in the near future.

Just wondering if anyone here has any new ideas or experiences on this subject.

Cheers,
Nunny

[wirelessoceans]

Nothing new but....

In most if not all states you cannot touch, manipulate, run cable in, attach access points to, or anything inside of an elevator shaft, you cannot leagally do any work their....AT ALL. If you need something done in an elevator you have to get city code compliance officers to ok the project and certified elevator technitians to install it. If you do not you could be arressted.

The best bet is to locate powerful ap's (maybe add amps as well) every three or so floor right outside the elevator shaft and site survey to see if coverage is sufficient. I have some hotels and MDU's that do happen to get elevator coverage (not by design) when the ap's are close enough to the shaft.

Stairwells are somewhat easier, depending on local code. If you are allowed to run riser through the stairwell then homerun a few POE AP's every few floors as needed. If you cannot run riser than I recommend the same technique as the elevator solution I gave earlier. It will cost more so charge more.

Unfortunatly these situations are pushing the limits of wi-fi and rf, and 802.11 was not designed for these circumstances. Good luck

[Nunny]

I had a feeling that would be the case.
Thanks for the help.

[spiderbite]

Actually, I incorporate the stairwells and elevator lobbies in my regular survey.

Once they are all turned up, there will be sufficient signal strength between floors to allow succesful roaming wether riding an elevator or walking the stairs.

Sometimes this requires the use of an actual ap specifically for this purpose and sometimes I get away with bleeding off an existing ap for something else.

Works like a champ....

[Nunny]

Spiderbite,

How, actually are you achieving that? Are you placing APs really close the stairwells and elevator shafts? And if so, per floor, every other floor? what types of antennas?

I currently have my entire hospital environment with excellent, full coverage on every floor. However the APs were placed for best overall coverage on a per-floor basis, and not necessarily placed right next to the stairwells or shafts... and and I'm not getting coverage in those areas (never really expected to per the nature of those areas).

This wasn't a problem 2 years ago when we originally installed, as our stairwells/elevators were not expected to need coverage. Now the wish is to have uninterrupted coverage as docs move between floors, so we're kind of backfilling in here... Due to the particular nature of the building construction, I don't believe it'll really be possible without spending a small fortune to double or triple AP coverage in those particular areas.

[spiderbite]

Yup!

When you did the original survey, these areas were not in consideration for seamless roaming coverage, much less the throughput you will need to double or treble the user density.

This is the most important thing you will have to keep in mind during your re-survey of the hospital – which by the way they will have to pay for since the scope of work has changed. Coverage is not throughput!!

During a survey for voice – I incorporate the footprint of the elevators and stairwells as part of the footprint of the floor. So it is easy to map out the cells needed but you can’t treat the elevators and stairwells as a separate entity. You need to weave a blanket of coverage that seeps into the stairwells and elevators.

The coverage needs to be at least marginal in the stairwells and elevators because when you turn them all on you create sort of a cloud that will allow the client to roam from floor to floor given that most people are not stationary (usually) in stairwells or elevators without being stuck on one AP from several floors up. Since they are moving, they will soon walk into a stronger signal on the next floor. But don’t have gaps for obvious reasons.

Not to tell you how to do your job, but I recommend you use very small cells based on user density and square footage.


Filling in the gaps trying to shoehorn coverage is not a good idea. First, you can fill in the coverage gaps but you will probably create another problem which is much worse. By turning up the power on existing AP’s or using new AP’s without a re-survey of the entire hospital you will create pockets of larger more powerful cells which will likely result in some AP’s having too many users associated while some AP’s go unused. In its worst form you may have clients from several floors away associated to AP’s whose throughput was reserved for the floor it was installed on.

This will result in poor load balancing which will present as disgruntled users wondering why the network is so slow. And you’re getting ready to at least double the user density.

The more users on the wireless infrastructure the more dialed in your survey needs to be.

It just so happens I am currently working on two hospitals. One’s up and running as of three days ago and I am ass deep in the other one. The following describes the current one:

The survey was done with Cisco 1231 G radios (I know – don’t ask) . It is seven floors in the main building and two floors in an adjacent building. 116 AP’s, most of which are 5 mW, a couple of 1 mW and a few 10 mW sprinkled in.

The radios were locked at 11 Mbps since that is the lowest data rate the customer wants. In the actual deployment the radios will be allowed to slide from 54 to 11 Mbps. The phones only operate at 11 Mbps anyway so…

I did the survey at 11 Mbps. There are roughly 12 to 14 AP’s per floor with a couple of 8’s here and there.

None of the AP’s are in a stairwell but there are several that are nearby.

Hope this helps…

[spiderbite]

Signal was great all over but when it came time to make a phone call the elevator moves too fast for roaming too occur seamlessly.

Unless you stop on each floor, and then the voice quality wasn't so hot...


Stairwells are fine though, cause people dont go that fast in stairwells.

Phone takes to long to decide to roam based on fixed settings that are unchangeable.

[golfnut]

Spider,

What type of VOIP phones are you using? Just curious as we're working on a similar project.

Thanks,

Greg

[spiderbite]

Its a spectralink something or other...The problem is that the phone has to incur a 6dBi signal loss before it decides to roam.

Apparently, the elevator stopping on each floor this works oK. When you go express, so to speak, it barfs really bad.

Now that I have you on the phone, let me ask you this...

There is a NEC code that FORBIDS putting anything that isnt elevator in the elevator shaft...which blows my plans to shine a directional antenna down the shaft..

I am thinking about placing an AP in the elevator compartment and making it a repeater. If, (big IF), the phone will associate to the repeater, then maybe the repeater will allieviate the roam issue from the elevator car. I know the throughput will be half but the calls only use about 250 350kbps on average..I should still be ok

My concerns are what will happen to the voice call when the repeater roams and will the phone freak out if the phone decides to pick up an external AP that is not the repeater. Also, I have to figure out how to make the repeater the more attractive target for the phone, maybe by using a higher power setting. I may have to remove some external AP's to let it travel a couple of floors at a time.

Keep in mind the site survey tool on the phone indicated that the was enough signal to maintain a call, however this is apparently not a good enough indicator to judge an actual voice call.


I would welcome your thoughts and anyone elses for that matter...

Thanks,

[golfnut]

Spider,

We're going to attempt this with a WLAN switch and thin APs which is supposed to provide better roaming / QoS and hopefully avoids the issue of the phone "hanging on" to a weak signal when a stronger one is nearby.

Haven't tried using a repeater with VOIP. Even if you have enough bandwidth, it's still transmitting at half-duplex which I think would affect the quality of the call.

Greg

[spiderbite]

Aside from the half duplex...

I have to enable Cisco extentions that the phone doesn't support.

the repeater only supports the Native Vlan...which isn't the phone Vlan...

and it doesn't support WDS which I am up to my pockets in...


I'm hosed.....