Wireless Broadband Technology Development
We've already talked about our desire to obtain ever-increasing bandwidth for Internet access. Cable modems and xDSL technologies are available today, but they have their limitations. We also looked at Internet satellite applications, which are still expensive, but they do provide high bandwidth services in remote areas that do not have xDSL or cable modem access.
Recall our early discussion of microwave in Chapter 1. Microwave transmission systems were traditionally used for long-haul backbone trunks until fiber arrived on the scene in the early 1980s, virtually replacing them altogether. Microwave technology just couldn't compete with fiber's signal transmission superiority.
Today, there has been resurgence in microwave technology; the emphasis is now with local access. Local Multipoint Distribution Service, Multichannel Multipoint Distribution Service, and Wireless Local Loop services may eventually provide wireless, high bandwidth access to residential and small business users without using a local loop.
Local Multipoint Distribution Service
Local Multipoint Distribution Service (LMDS) is a fixed wireless service capable of transmitting large amounts of data at a very high rate of speed. Microwave radios and antennas are used. One antenna is installed at the client side, and the other antenna is installed at the base or carrier side. The antennas must be line-of-sight directly facing each other and operate in the 25 GHz radio spectrum.
The LMDS base station antenna is generally placed on a high-rise building or tower, and the user's antenna is also placed on a building or tower that provides access.
Because of the cost of equipment and licensing fees, LMDS has not been widely implemented. Another limiting factor of LMDS is its range. Generally, LMDS provides 3 to 5 miles of coverage before the signal begins to degrade to an unusable level.
Multichannel Multipoint Distribution Service
Multichannel Multipoint Distribution Service (MMDS) is also a wireless service supporting up to 99 digital data streams, each transmitting 10 Mbps from a single base station or transmitter. MMDS operates in the 2.5 to 2.7 GHz range, which is substantially lower than the 25 GHz range for LMDS. Equipment for MMDS is therefore less costly than that for LMDS. MMDS can also transmit for more than 30 miles from its base station (depending upon power levels)significantly more than LMDS service.
The problem with MMDS service is the limited number of channels available. Only 200 MHz is allocated for MMDS use.
MMDS is currently being deployed with some success in large urban areas. These areas already have wired services but because of limited bandwidth copper facilities or high-cost fiber, customers are increasingly turning toward MMDS services to meet their needs.
MMDS and LMDS are both similar in design, but the frequency spectrum allocated for each is different. MMDS will be first in gaining market share with its lower cost and longer range. If MMDS pricing drops and demand for bandwidth remains high, MMDS technology may one day supply movies directly from movie houses to consumers and their home-theater equipment.
Wireless Local Loop
Wireless Local Loop (WLL) is another broadband wireless technology that supplements existing copper-wire services. The service operates in the 24 to 38 GHz range, which means signal distance is limited to a few miles. Like MMDS and LMDS, WLL requires a line-of-sight between antennas (Figure 10.4).
WLL antennas are placed on customer's roofs or small towers that are aimed at a WLL master tower providing service. In some test cases, WLL replaces traditional wiring altogether. For example, a remote community may all share in a T-3 (45 Mbps) that provides wireless connectivity for all of their voice, video, and data needs.
Figure 10.4 LMDS, MMDS, and WLL.
Three companies are presently looking to provide high bandwidth wireless access in hundreds of cities, using a different method of access. An airborne Internet called High Altitude Long Operation (HALO) would use lightweight planes to circle overhead. These planes would act as a relay station (just like a satellite does).
The big difference between Internet satellite and Internet aircraft is delay. A satellite hovering at 22,300 miles above the earth provides a noticeable delay, whereas an aircraft flying at an altitude of 52,000 feet provides minimal delay. The Internet aircraft flying altitude is above commercial aircraft altitudes and inclement weather.
Each city using Internet aircraft could be provided with three planes running 8-hour shifts. In theory, two pilots could split a shift for flying, or the aircraft could run in autopilot mode.
An example of such an aircraft is the Proteus project. The National Aeronautics and Space Administration (NASA) has teamed up with Scaled Composites, Inc., to develop such a plane. The Proteus plane is designed as a lightweight, high-altitude, long-duration telecommunications relay platform that can also provide atmospheric-sampling and earth-monitoring missions. The Proteus plane is designed to operate out of general aviation airports with minimal support and low operating costs.
Another example of Internet aircraft is the Internet blimp. A company called Sky Station International plans to fly a blimp powered by solar and fuel cells at an altitude of 13 miles. This unmanned blimp would provide wireless coverage to an area of 7,500 square miles in a geostationary position over a citywide area to provide Internet access (Figure 10.5).
Figure 10.5 Internet aircraft.
Another even more exotic method of Internet access is the airborne system being developed by AeroVironment and NASA. The Helios aircraft is a solar-powered, unmanned, lightweight plane that can fly for 6 months or more at 60,000 feet without landing. Solar panels provide power, and much of the plane's materials are made out of lightweight Styrofoam and Kevlar. Initial tests during the summer of 1998 and the summer of 2001 have proved to be very successful.
With all of the recent technological advancements using airborne vehicles, the Internet data of the future may be supplied primarily by aircraft or blimp and not by local loops, microwave towers, or cable.