The city's experiment to blanket its 135 square miles with wireless high-speed Internet access has been hailed by supporters as one of the most innovative projects in the country. But some experts caution that significant technical and business issues must be hammered out before citywide wireless networks can become a reality.
Large cities such as Philadelphia and San Francisco see wireless broadband technology as a low-cost solution to providing broadband access to low-income residents.
They also believe that these Wi-Fi networks can help them save millions of dollars in operational costs by providing broadband connectivity for public-safety and other agencies within city government. Many believe the networks will help boost economic development by drawing more people to the city.
Philadelphia, which plans to have itsup and running by summer 2006, is the poster child of the municipal wireless movement.
While several smaller cities, such as Chaska, Minn., have deployed citywide Wi-Fi, the technology has not yet been tested in large metropolitan areas. Philadelphia will be the first major city to complete its network. Other large cities, including New York and San Francisco, are also looking to build their own Wi-Fi networks.
While supporters applaud Philadelphia for its vision, some experts warn that deploying Wi-Fi in dense urban areas may not be as easy as it sounds.
"Setting up a citywide network is definitely not as easy as putting up access points all over the place," said Doug Schremp, chief technology officer of , a consulting firm that designs and deploys networks. "There are some technical issues that need to be addressed, and cities really need to look at the operational and business issues that come with building and owning their own network."Building a do-it-yourself network
The idea of municipalities providing broadband service has been for the last couple of years, despite who view city-owned broadband networks as a threat to their businesses.
Some cities areto run fiber-optic lines directly to every home and business, which will increase broadband capacities well beyond those available from cable-modem and DSL service today. But these networks are very expensive to build, and many communities are looking at lower-cost, wireless technology instead.
While it would cost about $2,000 to $3,000 per household to run fiber, wireless can be deployed for about $20 to $25 per household. Philadelphia has about 590,000 households, according to the 2000 Census. Using that number, the city figures it will cost roughly $10 to $15 million to reach every household, according to its business plan.
Wi-Fi uses unlicensed broadcast spectrum, or airwaves, to deliver high-speed Internet access through a series of antennas positioned on telephone poles and other locations. Those antennas, in turn, are connected to the Internet. Depending on its location, each antenna can provide a coverage area with a radius of about 1,000 feet.
The spectrum crunch
Even though a wireless network can be built relatively inexpensively, experts say there are many challenges to providing reliable service.
One of the biggest technical issues that cities face in deploying municipal Wi-Fi is that it can suffer interference from other wireless devices trying to transmit signals in the same channel. Because wireless networks run on unregulated spectrum, many devices can interfere with transmission. For example, microwave ovens, hand-held phones, garage door openers and devices using Bluetooth applications all use the same 2.4MHz frequency used by Wi-Fi networks. What's more, thousands of computer users have installed their own Wi-Fi networks in their homes.
"The 2.4MHz spectrum is already very crowded," said Lindsay Schroth, a senior analyst at The Yankee Group. "When you have a large deployment such as Philadelphia also using that spectrum there's a lot of potential for overcrowding and interference."
Interference is a problem because it can greatly impact performance on the network by causing packets of transmission data to be dropped. The dropped packets have to be retransmitted, error rates increase and the routers that send the packets slow down their transmissions to compensate for the losses.
Cities such as Philadelphia say that they don't believe interference will be a big problem.
"We did a radio-frequency survey and didn't find any showstoppers," said Dianah Neff, chief technology officer for the city of Philadelphia. "We have 430 registered Wi-Fi