The latest step in the continuing march toward ever higher radio frequencies, 38 GHz point-to-point digital services, is providing a set of interesting, unique products.
The 38 GHz technology has been proven in Europe and now a few American companies are introducing it and a variety of its applications in the United States. Personal communications services backbone offerings such as transport of messages from microcell to microcell, repeaters, network hubs and mobile telephone switching offices are some of the more important applications of the technology.
Recently, regulatory factors and advanced technology have combined to make 38 GHz a valuable telecommunications solution.
The applicable 38 GHz radios for PCS support up to 4 DS-1 (1.5 Mb/s, also known as T1) streams per link. These data rates can be supported at distances of up to five miles with high availability factors. The quality of the links is high; a bit error rate of 10-13 under unfaded conditions is achievable.
One of the advantages of the 38 GHz band is the innovative licensing structure the Federal Communications Commission has established. Rather than requiring individual link licenses, the FCC established area licenses. A licensed operator is given “ownership” of one or more 100 megahertz-wide blocks of spectrum in an applicant-defined area. Establishing a link merely requires notification, rather than application, coordination and licensing. These simplified requirements, along with the small size and light weight of the components, make for an extremely rapid installation.
In comparison to microwave systems operating at lower frequencies, 38 GHz millimeter wave systems have some advantages. The high operating frequency results in narrow beam widths (less than 2 degrees) with small antennas (1 or 2 feet in diameter), which are easier and less expensive to install.
Perhaps more valuable than the beam width is the very small Fresnel zone (the distance the line of sight must be from an obstacle to avoid diffraction problems) that comes from operating at 38 GHz.
These advantages of operating at high frequencies are a consequence of classical physics. They did not require a technical breakthrough. But being able to produce economical transceivers that would work at 38 GHz has required recent technology advances-millimeter wave power sources and low noise receivers. The combination of high gain antennas and solid-state electronics results in a large path margin (typically higher than 40 dB). Operational systems have experienced the designed link availability of 99.999 percent when properly designed (an average of less than 6 minutes of outage per year).
Although the current structure of the communications industry and telecommunications regulations in the United States makes 38 GHz important and useful for several applications, PCS/cell site interconnection is a natural for the technology.
Wireless PCS/cell site interconnections can offer many benefits over wireline connections. These can include:
Cost savings
Flexibility and speed
Reliability and quality
Proven technology
Cost savings
Wireless solutions can provide a significant cost advantage for PCS providers, who often face high expenses to bring complete systems on-line simultaneously in a number of markets. For example, WinStar Communications’ Wireless Fiber service is priced to cost as much as 10 percent to 15 percent below what the local exchange carriers charge for interconnection.
Flexibility and speed
One of the most compelling reasons for a PCS licensee to use a 38 GHz system for back-haul is the short installation time frame. Because 38 GHz providers do not need construction permits to install these wireless services, links can be installed very quickly. As PCS companies complete financing and system design, there will be a major effort to turn up systems quickly. Rapid site interconnection will contribute to the PCS provider’s ability to do this successfully.
Wireless links also provide the flexibility of allowing companies to easily move their PCS/cellular sites. If a site location needs to be adjusted after the initial deployment, the dishes on each end simply need to be realigned.
Optimal PCS network configurations will require a large number of PCS sites to be placed in non-traditional locations, such as on billboards along the highway. Precise positioning of sites will be critical, as cellular cell sites become smaller and the number of planned PCS sites grows. A 38 GHz wireless solution allows companies to place equipment in those sites that optimize network service delivery and economics, even if the sites do not have telecommunications.
Reliability and quality
Wireless Fiber for PCS uses a “spliceless” transmission path delivering quality that is comparable to conventional fiber installations-99.999 percent reliability, 10 years mean time between failure and 10-13 bit error rate.
Proven technology
The same technology underlying 38 GHz service has been used day-in and day-out for real world applications such as PCS in Europe. In Europe, the main application of 38 GHz technology has been provisioning cellular radio feed links between scattered base stations and central hubs. In fact, 38 GHz has been made a part of Global System for Mobile communications, the European cellular standard.
This technology gives PCS and cellular providers a quickly deployable solution to meet the demands of the highly competitive wireless communications services market.
David Ackerman is executive vice president of WinStar Telecommunications Group, which manufactures 38 GHz technology.
