Microwave and Radio - Based Systems

In the 1950s, microwave radio was used extensively for long−distance telephone transmission. With the need to communicate over thousands of miles, the cost of stringing wires across the country was prohibitive. However, the equipment was both heavy and expensive. The radio equipment used vacuum tubes that were bulky as well as highly sensitive to heat. All of that changed dramatically when integrated circuits and transistors were used in the equipment. Now the equipment is not only lightweight, but also far more economical and easy to operate. In 1950, the typical microwave radio used 2,100 watts to generate three groups of radio channels (each group consists of 12 channels), yielding 36−voice−grade−channel capacity. Each voice grade channel operated at the standard 4 kHz. Today, equipment from many manufacturers (and Harris/Farinon, specifically) requires only 22 watts of output to generate 2,016 voice channels. Although there have been two orders of magnitude improvements in the quality of the voice transmission, the per−channel cost has plummeted from just over $1,000 to just under $37. This makes the transmission systems very attractive from a carrier's perspective. However, the use of private microwave radio has also blossomed over the years because of the cost and performance improvements.

Microwaves are radio waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF, and various sources use different boundaries. In all cases, microwave includes the entire SHF band at minimum, with RF engineering often putting the lower boundary at 1 GHz (30 cm), and the upper around 100 GHz (3 mm).

The major time delays are usually in getting through the regulatory process in a governmentally controlled environment. Several installations have taken over a year to be approved, only to have the radio system installed and running within a day or two. In many situations, microwave systems provide more reliable service than landlines, which are vulnerable to everything including flooding, rodent damage, backhoe cuts, and vandalism. Using a radio system, a developing country without a wired communications infrastructure can install a leading−edge telecommunications system within a matter of months. The cellular and Personal Communications Service (PCS) industries invested heavily in microwave radios to interconnect the components of their networks. In addition, a new use of microwave radio, called micro/millimeter wave radio, is bringing transmission directly into buildings through a new generation of tiny receiver dishes.

Cellular interconnection of microwave radio

            The PCS industry chose microwave radio technology for the interconnection and backhaul transport on its expanding network. The PCS suppliers and the cellular suppliers do not want to pay the local telephone company for monthly T1 access lines from the cell sites to the mobile switching sites. Therefore, to eliminate the monthly recurring charges, they have installed microwave radio systems in the 18 to 23 GHz frequency range. Tens of thousands of new cell sites and PCS sites have been constructed and will continue to be constructed over the next few years, further expanding the use of microwave radio systems in each of these sites. As third−generation, handheld devices make their way into the industry.

            Microwave also played a very crucial part of the PCS industry as the PCS systems use the 1.9 to 2.3 GHz frequency band. Fixed systems operators such as police, fire, electric utilities, and some municipal organization occupied these frequencies. To accommodate the move of these users from the 2 GHz frequency band, microwave was used to relocate the users to a new band, as mandated by the FCC.

            Microwave is heavily used in radio and television systems. Satellite TV relies on microwave repeaters on the satellite to retransmit TV signals to a receiving station. Microwave communication via satellite provides a more reliable signal than longer, land−based radio waves. It also improves the reception of the picture.

Action camera and microwave systems working together

Other Applications

A laptop computer with a credit card−sized PRISM radio chip set can now convert incoming microwave messages into binary code for computer processing and then convert them back into microwaves for transmission. Similarly, microwave transmission is used in LANs, on corporate or college campuses, in airports, and elsewhere. Whether it is collecting data, relaying conversations, or beaming messages from space, microwave makes the wireless revolution possible.

Laptop computers can now send and receive microwave radio transmissions.

No one can escape the wireless hype these days. The challenge is in wading through all the confusion and misleading statements to decide whether an application fits the need. If you can make sense of it all, you may find the solution to your connectivity needs.

What About Bandwidth?

Bandwidth is always a touchy subject. It can become a "never satisfied drain" on the corporate bottom line if due diligence is not practiced. There is a direct relationship to cost and total bandwidth. The more bandwidth needed, the greater the cost. Everyone would like as much bandwidth as possible, and at the same time wants it to be affordable. Many people make the mistake of buying more than they need, anticipating future growth. In this industry, prices keep falling as competition increases. If an organization needs an OC−3 (155 Mbps) today, then laying fiber is probably the most affordable solution. However, 155 Mbps microwave systems are available and the prices are constantly dropping, giving short−haul fiber a run for the money.

What About Reliability?

Having too much bandwidth is possible. Having too much reliability is just the opposite. Organizations lose significant amounts of money when the network connection is too slow, but far more when the link is down completely. One hour of network downtime can cost more than the profits and productivity achieved from a year of uptime. In this scenario, automatic backup is an absolute must. Buy the appropriate amount of bandwidth and make sure that the reliability is built in. Plan for the worst−case scenario! Consider an alternate backup plan. Use circuit−switched or packet−switched (frame−switched) alternative connections in case of an outage.

http://en.wikipedia.org/wiki/Microwave

Broadband Telecommunications Handbook(VPN 3GW MPLS MPLS VoIP SIP).pdf