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Mobile Cell Phone Towers For Disaster Relief
cerberus4696 writes "According to today's Denver Post, Verizon recently premiered one of its new Cells On Light Trucks (COLTs), a complete, self-contained CDMA cell that can be moved to wherever it's needed, such as the scene of a natural disaster or a large public event. Since a standard CDMA cell can only handle a theoretical maximum of 62 calls at a time (usually less in practice), the network of permanent fixtures can quickly become overloaded in high-use situations. Verizon already uses a larger version of the system known as a Cell On Wheels (or COW; gotta love these acronyms), but as it takes three trucks and the better part of a day to deploy, nimbleness of response has apparently been an issue."
European GSM operators have been doing this for years.
Which is a good reason that Ham radio ops are still useful, particularly in disaster relief scenarios where much of the local infrastructure may have been destroyed.
But first you have to get us to stop talking about the weather and our rigs.
It sounds awfully low versus what I know about CDMA, but the system does have the ability to take advantage of many smaller cells in ways that GSM, at least until recently, couldn't. Clasically, GSM is even worse.
InfraLynx builds various vehicles now being used by the Homeland Security dept and the military. They have mobile cell towers, satellite uplinks, and all kinds of communications equipment.
i vers/
r alynx&btnG=Google+Search
2600 took some pictures. they are here http://www.2600.com/offthehook/2003/1001files/
another link:
http://iwce-mrt.com/ar/radio_infralynx_hummer_del
and the google page: http://www.google.com/search?hl=en&ie=UTF-8&q=inf
Sectorization refers to the practice, common with all cellular technologies, of dividing up the area around a cell site into regions, or sectors, each served by its own set of directional antennas. Three sector cells are extremely common; that's why so many towers have triangular platforms with a set of antennas on each side. There are usually three antennas on each side: one for transmit and two for receive, with the extra receive antenna providing spatial diversity.
Most CDMA cell sites in built-up areas have three (or six) sectors, operate on more than one 1.25 MHz RF channel, and use the newer CDMA 2000 1x standard. That can easily provide a total cell capacity of considerably more than 61 calls.
CDMA 2000 1x doubles the number of Walsh code channels (to 128) by adding a second set of traffic channels in quadrature to the original 64. Virtually all CDMA phones sold over the past few years do 1x.
Because of CDMA's inherent robustness, the same RF channel can be reused in adjacent cells and even adjacent sectors, greatly increasing the overall capacity of the spectrum in a given area. Because no careful frequency reuse plan is required, CDMA is also very well suited to the rapid deployment of cells in "hot spots" as described in this article.
Disclaimer: I work for Qualcomm.
Here's one company's version.
As past chief of a Fire Department I can tell you that a good, RELIABLE cell phone is critical to emergency management for the following reasons:
-Radio communications that Fire Departments/Ambulances/Police use are usually one or two half duplex channel. If you are lucky, you have four or five channels, but only one or two will get you in touch with you dispatcher (911 center). During a natural disaster, hundreds of units across your county could be trying to reach the 911 center at the same time. The existing communications systems available for emergency response become so overwhelmed during disasters that they become useless for communications (the worst example being NYPD and FDNY on 9-11). When radio systems do get overwhelmed, go to plan B: The cell phone.
-Radio communications are great for units that work together, but what happens when I need to talk to the people at a chemical manufacturing plant to best find out how to deal with a spill of their product? Or talk to the DOT about closing a road. Or even talk to the local Police (not on the same frequency). Or order as many pizzas as I can get my hands on to feed my Firefighter's? Or call the Humane Society to deal with the 57 cats that are homeless now that the crazy cat woman has finally burned her house down? Plan B: The cell phone
-Sensitive information (about a patient or fatality) should be handled discreetly. Many people listen to our transmission (and don't start a debate here, I am glad that people monitor the Fire and Police frequencies). As a medic if I need to talk to a doctor about a 15-year-old girl who has overdosed trying to commit suicide, I don't want that broadcasted to everyone in the county. Plan B: The cell phone.
Once upon a time (1990s) my local cell phone company actually entered our phones in to their systems as priority phones. Assuming that FD communications is more important than civilian communications, the system would kick off a civilian user to let the FD cell phone connect when the tower was full. I could never quite figure out how the tower would know my call was coming in if all of its receiving channels were full, but I never had a problem connecting a call so I never asked. I wish they still had that in place, because there have been many times recently that I haven't been able to connect with my cell phone when I needed to. My town (population of about 1000 year round residence, 5000 winter only residence) hosts a festival that yearly draws about 60,000 people. That is when I most need my cell phone to work, and it usually doesn't.
Where do I order one of these light truck cell towers?
Agree with another poster here... they rolled out a mobile cell site at the Pentagon on Sept 11, and handed out precharged mobile phones for the responders to use.
Here in New Zealand we have had mobile cell sites at popular New Years holiday spots (to handle surge capacity) when the country goes on holiday for a week or two at Xmas/New Year. They have been doing this a couple of years at least.
Whata so special about this one?
No matter how many cellular towers you have there is still the matter of the MSC (Mobile Switching Center) which is the hub of the system. The MSC is where mobile-to-mobile calls get routed between towers and mobile-offnet calls get routed to the LEC (Local Exchange Carrier) for local termination, or to the chosen IXC (Inter eXchange Carrier) for long-distance termination.
Most towers are simply spokes hubbed back to the MSC. If that connection to the MSC is lost the cell is pretty much useless. If the MSC loses its connection to the landline LEC and IXC networks then you can't originate/terminate calls outside that provider's network.
In many/most markets the mobile phone companies do not have direct interconnection to exchange traffic (calls) between each other. All calls between mobile carriers go through a LEC switch called the Access Tandem.
You will also fail to complete a call if the land-line infrastructure between the LEC and/or IXC switches is overloaded. I've seen networks which were only trunked to the Access Tandem and maybe 1-5 additional LEC switches (LSOs - Local Serving Offices). Its not hard at all to saturate the connectivity from the Access Tandem out to popular LSOs.
The long and short of it, there isn't any single magic bullet that will enable a telecommunications network to survive a 9/11 scale event. There are too many links in the chain that have to keep working. That being said there are steps that can be taken to make a network more resilient to such events, and often these actually save the provider a cost savings.
Australia uses CDMA too, since it's cheaper and more efficient to roll out than GSM, especially when trying to cover 1000s of K's of sparsely populated areas.
Unlike GSM, however, CDMA in Australia is (AFIAK) a Telstra-only service (Australia Telecom).
CDMA performs surprisingly well, almost matching the range of the old analogue AMPS towers we had circa 1999, and at a fraction of the cost (per base station).
Too bad the first (Qualcomm) phones they sold for it were crap - buggy firmware, expensive car kits.
If you're travelling in remote areas, CDMA is all you're going to get (if anything).
If there is existing infrastructure nearby, they can tap into local phone or data lines, and the BS may be even lucky enough to get use of a T1 line, or even DSL to send VOIP. 1.6 Mhz of bandwidth will support a couple of dozen voice channels, and depending on the grade of DSL, much the same.
If the local terrestrial infrastructure is nonexistent, inadequate, or severely damaged, then the choice becomes microwaves. While the microwave relay stations are old tech, microwave relays are still used for many things, and if the option is available, then it would provide an alternative means of transmitting data. If there is no microwave link nearby, it might be possible to position a second or even third mobile relay station to get the signal where it needs to go.
Failing a practical path via microwave or microwave relay via earth stations, there is always the option of setting up a satellite link to do the job. Expensive yes, but it will work just about anywhere you can find open sky.
The point is, there is almost always a way to get the job done.
> And now let the EEs shoot down my idea (not literally).
They probably won't
The other traffic channels are still available for soft and softer handoff. That's when two or more cells (or sectors within a cell) carry a single call simultaneously. The mobile combines the two cells' signals just as it would the multipath components from a single cell.
Also, the limits of the forward (base-to-mobile) and reverse (mobile-to-base) links may not be reached at the same time. CDMA 2000 1x introduced coherent modulation with a pilot on the reverse link, and this produced a significant improvement in real-world reverse link capacity.
Number of calls per cell is variable, it's apparently 992 calls for the entire GSM frequency range (which isn't implemented at a single cell). A better comparison might be number of channels/cell/MHz. Which for GSM seems to be around 6.5, and for 2G CDMA, around 12. So in reality you're looking at about half the number for GSM, though interference between GSM cells tends to be smaller, so it does depend very much on cell density and geography (and cost too, of course), probably then an average of about 30 calls/cell for GSM, with many factors affecting that though (62 is a strange number anyway, for CDMA it's variable number of calls per channel but less than 56, maybe the average is much much lower, and you expect a fair number of channels per cell...).