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.
