Cellular communications

Cell phones are practically everywhere in the US.  83% of American Adults own some kind of cell phone (Pew Internet, http://pewinternet.org/Reports/2011/Cell-Phones.aspx).  These are useful in emergency situations and 40% of American Adults have used them during an emergency.

Most cell phones are low power at .5 watts with an internal antenna.  However, the features of the frequency and other advances allow a single cell site to have a maximum range of 30 to 35 miles in optimal conditions with low user load.  In urban areas, maximum range doesn’t matter as it is more a factor of cell phone density (how many phones per square mile) and building penetration that influences how many cell sites are needed.

A factoid is that a cell tower is not in the center of one cell, but instead on the edge of three cells.  Cell towers are easily identified by the long narrow vertical antennas mounted to a triangular frame so they point in three distinct directions.

Cell sites can also overlap.  A large area may be served by a macrocell.  A high density area within the macrocell may be served by a microcell.  This could be a major interstate intersection, a shopping mall, or stadium — any place where a large number of cell phone users will gather and use their phones.  Individual buildings can install a femtocell, which is a small cellular base station that connects the cellular devices in a building to the cell network through an antenna on the roof or an internet connection.  This is especially useful where buildings are constructed with energy efficient features that block radio waves, or where important section of the build are underground.  Energy efficiency and heat blocking films applied to windows reduce the radio signal passing through the windows.  It is not uncommon to have a great cellular signal outside a building that drops to barely useable inside a building.

During disasters and other unique events, cellular companies bring in specialized units to restore or augment existing service.  Two common units are COWs (Cell on Wheels) and COLTs (Cell on Light Truck).  Cell service was bolstered on the National Mall during the last Presidential Inauguration.  The service providers new that people would making calls, and taking pictures and videos to upload during the swearing in ceremony.  This could have overloaded the existing cellular infrastructure that is designed around normal Mall traffic.

A subtle, yet important, shift from the cellular providers is the placement of branded Wifi hot spots in urban areas.  These Wifi hot spots available at no charge to their own customers shifts load from the cellular network to the wired broadband networks.  Phones from the major providers come preconfigured to prioritize the movement of data across the providers Wifi networks instead of the cellular network when available.  It is a way to load balance the overall system transparently to the users.

Faux G

Cellular systems can carry data as well as voice.  The International Telecommunication Union, Radiocommunication (ITU-R) is responsible for the cellular standards.  The ITU defines what can be called 4G.  Technically, the standard is the International Mobile Telecommunications-Advanced (IMT-A) standard but it is commonly marketed as 4G or LTE-Advanced.  IMT-A dictates minimum data transfer speeds of 100 Mbit/s while in motion and up to 1 Gbit/s while stationary.

You may have not yet experienced these speeds even if your device is labeled as 4G, yet many systems today tout 4G.  In late 2010, the ITU-R gave in to cellular vendors requests and allowed them to use the 4G name if the current system was substantially better then third generation systems and being built to meet the 4G standard.  Resulting from this change, companies went from 3G to 4G overnight because of shifts in the marketing department despite no major changes in the technology overnight.

It is important to take note of the possibility of 4G.  A T1 circuit is 1½ Mbit/s.  The minimum 4G standard of 100 Mbit/s is 66 times larger.  Take a look at the graphic posted on my blog Explaining Bandwidth at http://keith.robertory.com/?p=560 for a better understanding of this.  A cell phone running true 4G will have more bandwidth then an entire site serviced by a T1.  We are right on the verge of a major cellular service shift.  When setting up a site during a disaster, it is common to use one cellular data card (aka aircard) per computer.  With these faster speeds, we can use one cellular data card to be the head of the site’s network.

My team has already successfully setup a network in a disaster with one 4G aircard providing connectivity for 30 computers.  Granted it was rare that there were users on all 30 computers simultaneously surfing the net and streaming large files.  But, that’s the point during disasters — and really even day to day.  It isn’t about providing maximum bandwidth to each user all the time.  Instead, focus on load balancing to provide enough bandwidth to meet the combined average need ~90% of the time.  It is ok for the system to be a little slower during peak demand times.  Set the user’s expectations correctly, and your team will get through it.

A cellular connection could be used to back up a wireline circuit.  Advanced routers can handle multiple uplink connections with prioritization and failover settings.  This will provide redundancy.  It is better than two wireline circuits backing each other up when the backhoe cuts through the utility lines outside the building.  Redundancy is nice.  Diverse redundancy is better.

Your users in a disaster response will be on the computer only part of the time, with the rest of their time filled with other activities.  If a disaster responder travels to a location and spends the entire time behind a computer, then the question should be asked: could that person just stay in the office or at home to complete the same work?


Additional resources