between major banks in Manhattan and their data centres which are often COWs can be lifesavers, and
across the Hudson River in New Jersey. Frequencies are so heavily utilised that
it is not uncommon for companies to share the same frequency but use it at
most mobile operators have an
different times of the day.
Microwave can be used as a network diversity option, particularly by
inventory of these stations for
providing access to carrier switching offices. A cable cut that disables local
their use
access can more than justify the expense of building a microwave facility.
The good news is that today‘s microwave radios provide very large amounts
of bandwidth, often in the tens and hundreds of megabytes per second. Radio Cellular on wheels
systems are very robust and can be cost-effective, particularly if they carry live In situations where traditional wire-line
production traffic in addition to waiting for a terrestrial network disruption. communications may be disrupted for an extended
The process of building a microwave link is relatively simple. In most cases period of time, such as what happened following
the equipment supplier can assist in this area, particularly with securing a Hurricane Katrina in the US Gulf states, a cellular
licence from the regulatory agency. And when designing a microwave service, station on wheels (COW) may be needed. COWs are
unblocked line of sight is essential. Make sure that nobody builds a building self-contained cellular base stations that can be rolled
between the two points on your microwave link! in and activated in a short period of time. In the case
of Katrina, many cellular base stations were damaged,
under water, or otherwise out of commission. COWs
can be lifesavers, and most mobile operators have an
inventory of these stations for their use.
Two-way mobile radio
Wireless clearly plays a big role in disaster recovery
operations, from the mobile two-way radios that
have been a staple of wireless for perhaps 60 years
now, to emergency-response equipment designed
to get mobile services back on the air. The two-way
radio is one of the most popular wireless devices for
emergency use, and both transmits and receives voice
signals in designated frequencies. Two-way radios are
available in mobile, stationary base and hand-held
portable configurations. Hand-held radios are often
called walkie-talkies or handie-talkies. A push-to-talk
or press-to-transmit button activates the transmitter.
Mobile phones are examples of two-way radios that
both transmit and receive at the same time (full-duplex
service). They use two different radio frequencies to
carry both sides of the conversation simultaneously.
Amateur (HAM) radio
Amateur radio operators use various modes of
transmission to communicate. Voice transmissions
are most common, with some, such as frequency
Unlicenced point-to-multipoint communications modulation (FM) offering high quality audio, and
Perhaps the most exciting use of wireless technology for network resilience others, such as single sideband (SSB) offering more
applications is point to multi-point (PtMP) systems. These systems deliver secure reliable communications, often over long distance,
high-speed internet and ethernet transmission in both indoor and the more when signals are marginal and bandwidth is restricted,
demanding outdoor environments. at the sacrifice of audio quality. Worldwide, amateur
PtMP services operate on licence-exempt frequencies, such as 900Mhz, radio operators must pass a licensing exam displaying
2.4Ghz and 5.8Ghz. Available systems typically combine ease of installation knowledge and understanding of key concepts. Unlike
with channel flexibility to provide a broadband internet solution usable by other RF spectrum users, radio amateurs may build or
many internet service providers (ISP/WISP) and network operators. Typical modify transmitting equipment for their own use within
data speeds range from 3Mbps to 60Mbps, depending on the vendor and the amateur spectrum without the need to obtain
application. Distances between outdoor devices range from ten to 25 miles, government certification of the equipment.
line of sight. Among the typical applications are broadband internet access,
internet access services for wireless internet service providers (WISP), last FRS and GMRS
mile extension for traditional wired internet service providers (ISP), IP video In addition to satellite phones, it may be more cost-
surveillance security systems, and wireless WAN/LAN networks. effective to have low-cost portable two-way radios for
Like other wireless technologies, a variety of interfaces are available, emergency communications within a facility. These
including T1/E1 and ethernet. Start-up costs are generally low, with central unit devices fall into two classes: Family Radio Service
costing around US$2,500 and remote antennas costing in the US$500 range. (FRS) and General Mobile Radio Service (GMRS).
e
In outdoor applications small antennas (about a foot long and four inches wide) Both service types can be configured in one radio, but
are installed on rooftops, and aimed and synchronised with the primary radio. GMRS requires completing a licence application. Both
For indoor applications, PtMP technology can connect multiple LAN subnets services, which are intended for individuals and not
within an office building and also provide a network bridge connecting various organisations, have several miles of range outdoors,
LANs in a multi-site or campus arrangement. As with outdoor systems, the and can also be useful for emergency communications
antennas must be strategically located to provide a clear, unblocked signal. within a facility or campus.
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