When building out infrastructure into scattered rural communities is economically unfeasible, an obvious means to "get connected" would be to create a virtual or wireless network. Two technological developments coincide to increase the viability of wireless devices for Internet access in rural areas and in developing countries. The first is the advent of spread spectrum technology and the second is the decreasing cost of digital radios.
Spread spectrum technology employs frequency hopping, an idea that has its roots in the "Secret Communications System" patented by Vienna-born actress Hedy Lamarr and her friend George Antheil in 1942. Lamarr conceived of this idea as a means to allow the United States to use radio-controlled missiles against the Germans without the radio signals being intercepted or jammed. A simple radio signal sent to control a torpedo would have been easy to block. However, if the signal hopped from frequency to frequency at split-second intervals, anyone trying to listen in or jam it would hear only random noise. When both the sender and the receiver are hopping in tandem, the message would come through loud and clear.
Conventional wireless signals that transmit signals over a single frequency are easily susceptible to interference from other wireless users and from obstacles like buildings and trees. In addition, signals cannot share the same frequency. The deliberate variation of the frequency of the transmitted signal results in a much greater bandwidth thereby allowing many users to use the same frequency. The number of users per spectrum can be scaled up to millions even in urban congested areas. The digital radio firm Omnipoint, for example, utilizes spread spectrum wireless technology to potentially accommodate 490,000 users per square mile.
Signals transmitted using this technology require no license to operate in most countries. In the U.S., the FCC has designated Part 15 of the spectrum for transmission of signals. Only the design of the radios has to be licensed by the FCC. Cost is limited to the price of the radios as there is no communications charge, and no telephone company charge.
Spread spectrum technology can be used to gain High speed Internet access that bypasses the PSTN or cable company. Beyer, Vestrich, and Garcia-Luna-Aceves (1999) have created a viable schema for a rooftop community network that can be used by a geographically scattered rural community to create an Internet access infrastructure. Setting up such a network requires installing an Internet radio and a small antenna. The Internet radio acts as a hub as well as a modem by serving as a connection to the Internet as well as a repeater to forward to other users' traffic within the community network. The digital radio uses frequencies in the unlicensed spectrum, and contains a microcomputer that runs the Internet Radio Operating System (IROS) software. The IROS, much like the traffic police, controls the routing of packets between source and destination.
The antenna, which is three feet long and an inch in diameter, is mounted on the roof and connected to the Internet radio with a cable. The Internet radio, in turn, is connected to the user's computer, which is configured with the appropriate TCP/IP addresses, much like they are configured for dial-up access to the Internet. Being packet-based, it is an always-on connection that only uses resources when data is actually being transferred. Because of the limited frequencies that SS can use, the effective range is much smaller; often limited to less than 20 miles and requiring line of sight between radios. They can cover 10-mile distances at speeds up to 2 Mbps and can reach as far as 30 miles at slower speeds.
By taking advantage of the "bursty" nature of the Internet, members of a community network can share a single high speed Internet connection. This could be a cable, DSL or satellite broadband connection that leads into one residence that acts as the "Airhead." The Airhead is the Internet radio that serves as hub into the rest of the Internet, and as a virtual router to other users in the network. The Airhead in turn could divvy up the costs between the network users.
According to David Hughes, principle investigator of the NSF field tests using wireless spread spectrum technology, more than 60 companies have produced spread spectrum, no-license radio devices. Internet radios are still being produced primarily for the corporate consumer, however, and are priced between $2000 and $6000. Beyer et al estimate that current technology permits large-scale production of Internet radios that could be priced as low as $500. A chicken and egg situation prevails. The high price prevents attainment of a critical mass, yet without lowering prices Internet radios will remain out of reach for the mass market. Manufacturers of digital radios are also constrained by limitations imposed by the FCC. FCC regulations limit a transmitter's maximum output to one watt of power and limit the number of spectrum hops a signal can make.
The NSF has successfully implemented a number of Wireless Field Tests to demonstrate the potential of wireless spread spectrum technology in bringing Internet access to remote sparsely populated regions. One of their earliest successful attempts was the link between the Rocky Mountain Internet (RMI) POP in Alamosa and the Monte Vista Middle School, in Colorado. Under the guidance of David Hughes, Principal Investigator for the NSF Wireless Field Tests, a 14.2 mile 115 Kbps link between the two locations was set up to bring Internet access to the school and its 25 classrooms.
This link was set up using two FreeWave radios using spread spectrum technology within the 902-928 MHz range. An 8dBi gain antenna was installed on the rooftop of the building at the Alamosa end. The radio was placed in the computer room of RMI, Alamosa and connected via a 25-foot cable to the rooftop antenna. The radio was connected to the NSF Field test router, which was in turn connected to the RMI router. Large deciduous trees, which were higher than the antenna, surrounded downtown Alamosa and threatened to disrupt the radio signal.
At the Monte Vista end, an eight-foot omni antenna was set up on a 30-foot vertical mast on the roof of the one-story school building. The antenna was tuned to the 915 MHz radio range. The radio was placed up on the mast as close as possible to the antenna to prevent as much signal attenuation as possible. The following limitations were experienced: First, the original FreeWave radios only produced 300 milliwatts of power. Second, the distance between the radios was 14.2 miles. Third, the intervening distance between the two radios was filled with mature trees.
The project was successfully implemented at a total cost of $4,500. No monthly operating fees were incurred for the wireless substitute for local loop 56Kbps telco charges.
The significance of this project will be to develop a working model of how to permit US scientific and educational institutions to reach counterpart institutions in a large number of lesser developed nations with poor telecommunications infrastructures.
MMDS was originally licensed as a service to provide one-way wireless video programming. It is still referred to as "wireless cable" although the wireless cable industry could not compete with wired and satellite-based video programming providers. Recent revisions in FCC regulations permit MMDS spectrum to be used for bi-directional services, making it a viable channel for the provision of broadband Internet access. Several holders of MMDS licenses view MMDS as a means of reaching out to users who cannot make use of DSL or cable. MCI/WorldCom and Sprint collectively own licenses worth $3 billion, covering areas - some rural - populated by more than 50 million people. Sprint's MMDS service is delivered using land-based radio transmitters positioned at the tallest feasible location in a metropolitan area. A single transmitter can serve customers over an area totaling more than 3,000 square miles.
Customers obtain the MMDS signal using a small digital transceiver placed on their roof with line of sight to the transmitter. The digital receiver receives the signal and transfers it to a wireless modem, which communicates with their individual PC or Macintosh computer or Local Area Network (LAN).
Given the high cost of setting up a transmission tower, network economics will probably require a fairly large user base to spread fixed costs. According to the NTIA/USDA report (April 2000), MMDS will probably serve only those rural areas surrounding a non-rural town or a cluster of towns. It also mentions that MMDS has so far been deployed in towns with populations as low as 6,000.
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