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With all of the other issues surrounding wireless communications, most of us take the radio spectrum for granted. Consider the many sectors who use wireless communications on a daily basis and it is easy to understand why networks are overloaded (and why the frequency spectrum is under extreme pressure). Mobile communications, computer data, radio stations, aircraft, taxis, and even astronauts rely on radios to keep in touch with one another.

Because this radio spectrum cannot be expanded, it is coming under increased pressure to carry more and more communications. The worldwide introduction of digital mobile communications is causing concerns of a spectrum drought on several continents. Of late, industry comments have shown that spectrum and bandwidth will become a tradable commodity in the near term, fetching high prices because of supply and demand.

Point-to-point fixed microwave services cater to trunked communications of digital data from point A to point B. Too much emphasis is placed on computer speed and last mile delivery. Much of this is done without any comprehension of the vital microwave links, which are the infrastructure trunking networks that join the ends. The particular application discussed in this article is used to trunk all of the telephone calls from the exchange to the mobile cell sites, and vice versa. This technology can be viewed as the cable equivalent in the land-line arena.

Virtual private networks (VPNs) make it possible for banks, hospitals, governments, emergency services, security, and military to handle communications needs and, therefore, bypass often slow or overloaded public networks. Wireless networks cater to the future by providing broadband and 3G trunking solutions. This technology is a wireless cable in the sky that, when compared to cable, can be deployed rapidly and at significantly less cost when compared to cable roll out. With this type of technology, rapid return on investment is achieved. And as higher data demand increases, traffic load system applications can be easily upgraded both in terms of time and expenditure.

Point-to-point microwave technology has been used since World War II. Significant commercial use came with the start of television broadcasting back in the 1950s. Since its inception, its application has been the transportation of pictures and sound between the studios and transmitter sites. Another application, however, is outside broadcasting. This segment would include broadcasts for golf, tennis, car racing and other sports and on-the-spot news.

These communications-type microwave systems were analog-based and were not originally designed for digital data communications. Today, basically all microwaves carrying digital data are analog-based, as well, and were not intended for digital data application. They use spectrum inefficiently because technology is lacking in this area. Because of this, frequency management regulators have had to assign frequency spectrum to work within these transmission constraints. Such regulators include the Federal Communications Commission (FCC), the European Transmission Standards Institute (ETSI), and the Australian Communications Authority (ACA). Technical regulators cannot change regulations without commercial equipment that offers options the regulators can consider. Once equipment becomes available, most regulators are willing to move forward.

There is constant pressure on the regulators to search for wireless spectrum solutions because of the demands on presently allocated bandwidth. That is why this fully digital design opens new opportunities and avenues for communications technology. Digital microwave also opens new avenues for revenue because of its efficient use of spectrum. This is particularly applicable to those who have purchased spectrum, as well as operators using government-licensed spectrum.

When applying digital transmission data to wireless spectrum, major hardware constraints come into play (especially at increasingly higher data rates). The major issues include the loss of data referred to as bit error rate (BER), jitter, spectral regrowth (the generation of spurious signals from the main data stream), band path interference from point to point in free space, and inherent signal fading. The rest of this article deals with technology designed to overcomes these factors when transporting signals from point to point.

The design concept, carried out in conjunction with the University of South Australia, had to meet three primary functions:

• The equipment design had to meet and exceed present technology and satisfy regulatory transmission requirements.

• It had to be compatible with existing equipment.

• It had to be economically competitive with existing technology.

All of the above requirements were met. Commercial application of the systems in use by the state police communications network have shown exceptional field performance reliability.

By applying digital signal processing (DSP) and phase linear design application, this technology brings to the industry a product that addresses several major impediments. It provides superior BER data recovery and improved fade margin performance, while dramatically reducing spectral regrowth. The net result is that this allows closer frequency channel assignments. As an indication of this efficiency, 2 Mbps of data can be transported in a bandwidth of 1.5 MHz using QPSK. Current technology uses up to 10 MHz of bandwidth. Two Mbps of data using 16-QAM modulation requires 850 kHz of bandwidth.

A bandwidth of 14 MHz would be used by 34 Mbps using 16-QAM. Current technology requires up to 28 MHz of bandwidth.

Because of the improved data recovery techniques, longer path lengths can be applied, and smaller antennas can be used (which would have significant cost savings on infrastructure networks). Mean time between failure (MTBF) will be of a high order, which further enhances network reliability.

The technology based on surface mount technology (SMT) requires minor intervention at the production level, which will allow high yield on productivity to meet market demand.

Control management is based on the simple network management protocol (SNMP). Thusly, control and monitoring functions, including frequency assignment, can be done by remote access. This adds the ability to allow global support worldwide. The only equipment required for installation in the field will be a personal computer. The system is totally modular and is serviced by module change, keeping field support to a minimum.

A new approach to microwave design has been presented, providing major world market potential for higher data rates, satellite up/down data applications, and possible future RF cable applications. Spectrum-efficient technology is a must for the new 3G wireless networks and rapidly expanding broadband networks. Current markets require rapid deployment capabilities to meet the explosive needs of the rural sector, the digital divide and mobile communications, as well as interactive television. Microwave networks answer this need in a cost-effective and timely manner when compared to cable deployment.

John Stannard, the founder of JNS Electronics Pty. Ltd, (www.jns.com.au) began his engineering career in Australia in television, moving on to medical electronics for Westinghouse USA before returning to Melbourne to establish his own firm in 1973. He is a Companion of the IREE and IEA and holds a Diploma of Aviation. He presently works as a consultant to the industry and can be contacted in at jns@jns.com.au.