When Population Density is a Plus

Back to Contents of Issue: June 2001

In April we told you about Japan's wireless P2P scene, which could lead to a new kind of person-to-person network. The idea is catching on.

by Sam Joseph

manDEVELOPMENTS in cellphones and other wireless technologies seem to be converging, if recent initiatives are anything to go by. The US's Defense Advanced Research Projects Agency (DARPA) is working on a "soldier's radio" designed to provide communication on the battlefield in the absence of relay towers and other communications infrastructure. The mobile-communications program intends to use high-capacity, low-power radios linked by a "self-configuring" network to keep soldiers connected with each other. The architecture has been described as a "mobile, ad hoc, peer-to-peer network" that uses frequency-hopping technology to avoid communication intercepts and location-finding capability. DARPA has plans to demonstrate the infantry radio concept in the field as early as next summer, but it's not the only one with this idea.

Cybiko Inc. and MeshNetworks are both working on similar concepts. The Cybiko is a Russian-developed handheld computer with a built-in short-wave radio that is already sweeping the American markets. As well as providing users with free text messaging to other Cybiko users within a 100-meter range, Illinois-based Cybiko is planning to add the capability to "hop" signals. Two Cybiko owners could thus communicate via a series of intermediate machines, owned by other people, in a peer-to-peer network. Florida-based MeshNetworks is working on infrastructure components to support just this kind of system, but questions remain about how signal routing will be handled, and whether you might end up not being able to use your own phone because two of your friends are using it to talk to each other. Imagine having to make an appointment to use your own mobile phone! Nonetheless, it seems that the concept of wireless P2P is out of the bag, and a little bit of speculation can lead to some very odd ideas, such as how the population density of a city can suddenly become a blessing instead of a curse.

Let us imagine that a Bluetooth-enabled phone was released and reached popularity levels matching those of existing cellphones. The standard Bluetooth transmission range is 10 meters, and it only takes a little math to work out how connected you would be in different cities based on cellphone ownership and population density. A quick look at the Population Density chart on the next page shows us that the differences can be significant. In Los Angeles, your Bluetooth phone could reach others only approximately 10 percent of the time, but metropolitan Tokyo's higher population density and cellphone usage levels gives you 64 percent connectivity -- better, but still pretty low. Focusing on the central 23 wards of Tokyo, we find connectivity reaching 89 percent, since on average the nearest person will be just 5 meters away (more like 5 centimeters or closer on the subway). Coverage of around 90 percent connectivity is not much worse than relying on a telco's communication tower, which never provides complete coverage itself; and remember, you're linking to other people's phones through nearby people, so it doesn't matter if you're underground, as long as there are enough people in between you and the person you want to contact.

Photograph courtesy of Bluetooth

One of the few places with a higher density of cellphone users is also in Asia: Seoul, South Korea, can achieve a hefty 94 percent coverage (See "Fast Country," page 32, December 2000). These kinds of figures work on the assumption that people are distributed randomly, which of course they are not, so there will be areas that will be not be covered by the "people net," so to speak; but add in a few 1-km--range base stations in underpopulated areas and the problem is solved. If the Bluetooth range increases, or some other technology is adopted, then things can change radically again. The Cybiko has a range of 50 to 100 meters indoors and 100 to 200 meters outdoors. If we re-work our sums for a 100-meter radius wireless device, then all the cities, including Los Angeles, end up with 100 percent coverage. If this sort of system catches on, then we can all look forward to a whole new way of communicating with each other.

Population Density
Location Users/km2 Coverage
Seoul 9285 94%
Central Tokyo 7049 89%
Metropolitan Tokyo 5618 64%
Helsinki 1966 45%
Los Angeles 352 10%

There are still outstanding problems to be solved, and it is not clear that current routing technology will prevent the wireless ad hoc approach from taking up so much of your phone's processing power that you can't use it for your own calls. There are all sorts of options, such as allocating resources that you think should be devoted to the common network, or allocating them to just your friends and family, or even charging for them (after all, it's your phone). There's also the question of how to find someone in this network; they might have a unique phone number, but what's the best path from your phone to their phone, and what happens when people in between get on a subway and the best route disappears?

Various ad hoc network routing schemes exist, but they are possible approaches rather than tried and tested solutions. The main group focusing on solving this problem is the Japanese Jnutella group, which recently released the first version of its software development kit, targeted at connecting not just phones, but PDAs, laptops, desktops -- basically any device that can be connected -- in one giant P2P network. Open source development efforts will take time to mature, but enthusiasm for such a framework in Japan is high and driving the project forward.

Meanwhile, centralized approaches, such as those employed by the existing telcos, are not likely to scale indefinitely as wireless communication ability is built into more and more devices, and many consumers will be attracted by the possibility of free text (and even voice) messages to people nearby. Early versions are likely to suffer from setbacks as the technology matures, but as the number of devices grows, there will be increasing pressure to find decentralized solutions. "Joseph's Law" tells us: "As soon as we develop a device powerful enough to track all of the infor-mation about all other devices, all of the devices end up with that power and we're back to square one."

The point is that we can track people's Web pages or cellphone numbers or preferences or shopping history in a centralized way, but the technology developed to support that centralized processing ends up being available to everybody, and then they generate so much more data that the centralized system falls down.

Just where all this wireless technology is going is not quite clear yet, but it's beginning to look like we're in for some massive decentralization, and maybe cheaper text messages as well.

Note: The function "email this page" is currently not supported for this page.