Friday, March 2, 2007

Patterns of cell-site development

Your cell phone’s ringing. What’s the first word you might say?

More than likely, it might be “Hello” or another cheerful one-word greeting. If you speak Spanish, you might say “Hola.”

Yet, the word Hola can also be used as a reminder of the pattern behind cell-site development. As a mnemonic tool, its letters would stand for the following.

H: High-altitude or high-elevation

O: One site

L: Low-altitude or low-elevation

A: Array of sites

With early forms of communication, height was always an advantage, since it allowed the sender to convey his message over the greatest distance. The Romans used mountaintops to post simple signs, whereas native tribes would communicate using puffs of smoke, drumbeats, or flashes of light.

Back in the 1950s, as long-distance telephonic traffic grew, AT&T (when it was still known as “Ma Bell”) used height to its advantage, by building microwave towers on remote mountaintops. These sites acted as the “backbone” for long-distance communications—until fiberoptics rendered this system obsolete in the 1970s.

The higher transmission speeds promised by fiberoptic opened the door for the first wireless-communication standard, based on analog transmission. As analog networks were introduced across the country in the 1980s and early 1990s, the HOLA pattern emerged again. Older microwave sites were converted first, to provide a new backbone. Then, carriers supplemented these high-elevation sites with monopoles at lower heights.

As call volume increases within a given cell, at some point even the tallest telecommunications tower will reach its processing limit. At that point, carriers generally have two options: increase the cell’s height (and power), or split the cell up into smaller areas served by towers or poles of lesser height.

Flashlights provide a handy means of illustrating cell-site development. If I want to illuminate the area around where I’m standing, I’d find the brightest light I could find, and put it up as high as I could reach, so that its pool of light would disperse over the greatest distance. Alternatively, I could cover the same area with smaller lights closer to the ground, arranging them so that their beams overlapped each other—leaving as few dark areas as possible. As towers reach their processing limit, smaller sites are built to handle the load.

Since its introduction in the early 1990s, digital cell sites have gotten progressively smaller. Two of the latest categories of sites to emerge have been described below.

Microcells generally consist of one to two panel antennas mounted on street signs, light standards or utility poles. In southern California, sites like these are being used by carriers to fill in coverage gaps in residential communities. They are also used to cover small stretches of road that could not be covered practically with a larger site at a higher elevation.

Picocells represent the latest in telecom-cell development. With equipment small enough to fit inside a suitcase, and antennas the size of a deck of cards, these cells are being installed in hard-to-cover, high-volume areas like airport concourses, shopping malls, subways and tunnels.

Therefore, as population density increases, so does the density of sites. As the density of sites increases, their broadcast radius decreases, as shown below.

(Note): Although a cell site’s radius depends upon its surrounding topography and its capacity to handle calls, cell sites in rural areas generally have a radius between five and eight miles, and cell sites in urban areas typically have a radius between two and five miles.


In the U.S. alone, more than 690,000 cellphone calls are made each second—more than one billion calls per day. According to the CTIA, there are approximately 184,000 cell sites in this country struggling to process this flood of information. The demand for more bandwidth to handle the transmission of higher levels of data (from analog calls to digital calls, text messages, photos and MP3s, to DVD-quality video) puts increasing pressure on engineers to develop new communication standards to better accommodate the volume of data flying through the air.

When a new standard is introduced, the HOLA pattern repeats itself: start high to cover as broad an area as possible and then subdivide into smaller cells as call-demand increases. This is illustrated in the following chart.

Chart created by The Heath Group.

At present, we are in a transitory state between CDMA/GSM and full-fledged adoption of WiMax. While CDMA and GSM continue to battle for the title of universal standard, in the end it may not matter. Neither protocol can keep up with our thirst for bandwidth. It's a little like arguing which Dixie cup to drink out of when you have a Big Gulp-sized thirst. The latest generations of broadband wireless, including prototypes of WiMax, may satiate this demand for now. Or, at least long enough until the next standard is developed.

The forecast for the skies over cities like Philadelphia, Portland, Chicago and San Francisco are for clouds, but not the white, fluffy kind. Cities like these are experimenting with their own data clouds—several WiFi hotspots clustered together to form a blanket, or meshed coverage across a particular neighborhood. Yet the downside (at least so far) has been that these clouds are not as all-consuming as San Francisco’s famous fog. Inevitably, hotspots are too far away or behind the wrong building to do a subscriber any good. As John Ness observes in a recent Newsweek article, “the irony of Wi-Fi convenience is that, without ubiquity, dependent users can pretty quickly become frustrated.”

Since most Wi-Fi antennas are already low to the ground (30 feet or less in most cases), the only practical remedy for seamless coverage is to broadcast from a higher elevation, and at higher speeds. At the present time, we are approaching a transition in digital communication from CDMA and GSM to the higher bandwidth and speed promised by WiMax. In terms of bandwidth, WiMax portends the ability for several users in the same area to watch DVD-quality video on the same channel at the same time.

In May of 2005, a Seattle-based company installed WiMax antennas and equipment atop the Space Needle, 605 feet above the ground. At this height, the Space Needle site will be able to transmit wireless Internet signals over a five-square-mile radius, at speeds more than sixty times faster than dial-up.

So, how high is high? Will we start installing ears on celestial bodies, as they orbit overhead? Maybe not, but other equally fanciful ideas are being considered now as possible replacements to the conventional land-based pole and dish.

One enterprising company, SpaceData, is trying to extend cell-phone coverage by installing antennas in weather balloons. According to the company, these balloons will fly at stratospheric heights, above the travel lanes of commercial aircraft. Antennas broadcasting from such a lofty height would be able to cover an area fifty miles or more across.

Yet as any little boy or girl knows, once you release a balloon’s tether, it is free—guided by wind currents until they eventually disintegrate. SpaceData hasn’t quite worked out the kinks in their design, but indicated that its balloons would be equipped with GPS, and that each balloon would be equipped with a mechanism that would jettison the cell antennas if it gets out of range; the antennas would then freefall by parachute to be retrieved later.

In a Wired Magazine article published in January of 2000, author George Johnson describes the vision of some computer scientists for a new wireless “web.”

“There will be a day, maybe as soon as 2010, when the Internet disappears, when computation and connectivity become so pervasive that you forget they are there. Today’s metaphor is the network—a vast expanse of nodes strung together with dark, gaping holes in between. But as the threads inevitably become more tightly drawn, the mesh will fill out the fabric, and then—with no voids whatsoever—into an all-pervasive presence, both powerful and unremarkable.”[i]

As each new year brings another advance in technology, it can now be said practically that we can share information anywhere, with anyone, anytime. The Internet is no longer a destination; it is an all-consuming fog of bits and bytes that we stumble through as we walk the paths of our daily routines.

If, as Johnson put it, today’s metaphor is the network, then tomorrow’s metaphor might be “data consciousness”—resulting from omnipresent access to every scrap of information. Spiritual leaders often talk about reaching a higher consciousness as they delve deeper into their devotional disciplines; we are heading towards a silicon-based consciousness, spread among the flash cards and hard drives of our phones and laptops, yet meshed together to form a shared memory.

In fact, as technology gets smaller and more sophisticated, we will increasingly turn to biological vocabulary to describe its form and function, and to frame its development within a context we can understand. Words like cells, virus, immune systems and feedback have all found digital corollaries.

It seems hard to believe that just twenty years ago, cell phones were a brick-sized novelty and letter-writing (not emails, text messages, or MySpace videos) was the preferred mode of communication. If the HOLA pattern continues to hold true, we will cycle through higher and higher pipelines of communication until there is no longer any delay whatsoever between ourselves and our information. It’s been said that information is the currency of the new economy; I believe it will become even more fundamental than that, as basic as a cup of water to a parched traveler, and as integral as the air we breathe.



[i] From “Only Connect”, written by George Johnson in Wired Magazine, Issue 8.01, January 2000. This article can be read in its entirety at http://www.wired.com/wired/archive/8.01/nets_pr.html.

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