|
 FREQUENTLY
ASKED QUESTIONS
1) What is Spread Spectrum?
Spread Spectrum is a special radio frequency
modulation technique that has been used for many years as a solution to offering
connectivity in point-to-point and point-to-multi-point data communications
applications. It was developed by the military for secure communications.
2) What is the operating range of Spread
Spectrum radio systems?
That depends on many things. Indoor propagation
is affected by the type of construction of the walls and floors. It depends on
where in the building the radios are mounted. A line of sight path has less loss
and therefore greater range than a path through walls. Metallic structures
attenuate signals much more than wood, cement or plaster. If the wave must be
propagated around corners by diffraction, the range can be severely restricted.
Typical spread spectrum systems have an indoor range of up to 2,000 feet
unobstructed, and up to 400 feet through standard walls. Outdoor propagation
depends on the factors mentioned above as well as on heights of antennas,
curvature of the earth, distance between two systems, density of foliage, and
size of any buildings or obstructions in the path. Typically, spread spectrum
systems have an outdoor range of up to 25 miles under ideal conditions.
3) Can multiple Spread Spectrum radio systems
be operated in the same physical area?
Normally yes, depending on data rate and
frequency of the system. Spread Spectrum radios operate in multiple frequencies,
which at data rates up to 20 Mbps can be set to allow from three to fifteen
systems to operate in the same vicinity. To assure maximum throughput, normal
configuration should be limited to no more than three systems in the same
vicinity.
4) Can systems be installed in a multi-point
configuration?
Most bridge or bridge/router Spread Spectrum
systems can be configured as either point-to-point or multi-point.
5) Can the actual radio equipment be
installed outside?
Yes, provided it is installed in special water
proof and climate-controlled enclosures. Radio units typically function in the
temperature range between -10F and +122F. Outside of these temperature ranges,
the performance of the systems begin to degrade.
6) Am I allowed by FCC rules to modify a
manufacturer's packaged Spread Spectrum radio system?
No. FCC rules clearly state that a manufacturer
must certify a packaged system. This certification specifies the type of radio,
cables, connectors, antennas and accessories that can be packaged for sale.
These certified systems cannot legally be modified in the U.S. by a manufacturer
or an end user. HOWEVER, NAS as a professional installer can legally modify and
customize a system, within certain limits.
7) How do I make sure my communications are
secure?
Much of today's technology for Spread Spectrum
radio was conceived for military applications with this exact problem in mind.
The unique spreading patterns in these systems are difficult to decode for a
receiver that doesn't know the specific pattern. For 802.11 communications,
implementation of Dynamic WEP, EAP/LEAP, and RADIUS servers are required for
complete security.
8) How much does a typical Spread Spectrum
radio system cost?
Systems vary in price depending on the data rate,
enhanced features and distance of the required link. Cost per megabit of data
rate decreases as the data rate of the system increases. A typical 11 Mbps long
distance point to point link would cost about $6,000. A similar 45 Mbps would
cost about $20,000; a 100 Mbps link about $45,000.
9) How do I find out more about what I need
for my application?
Contact NAS Wireless at:
NAS
Wireless
Wireless LAN (WLAN) Integrators
7172 Regional St., #313
Dublin, CA 94568
925.455.7170
925-455.2059 (fax)
info@naswireless.com
|
