User's Manual

UtiliNet® Endpoint User Guide 11-1-2006
Page 18 of 30
© Cellnet 2005
Line-Of-Sight
Like traditional radios, UtiliNet radios operate in the 900 MHz range of the radio frequency spectrum and,
therefore, fall into a class of communications equipment referred to as line-of-sight. As a general rule of
thumb, line-of-sight communications equipment requires a clear, unobstructed view from the source radio
to the destination radio in order for communications between the two to occur.
Network Design for 900 MHz Systems
Network design for 900 MHz system typically falls into two categories:
• The first category includes licensed channels that are generally trunking or MAS data systems.
This category, in most cases, requires that all remote fixed points and/or mobile points have line-
of-sight paths to a single repeater site typically located at the highest point in the geographic area
of coverage.
• The second category includes spread spectrum systems into which UtiliNet falls. However, unlike
other spread spectrum radios, UtiliNet radios utilize an OSI network layer. Each radio has store
and forward features that allow intermediate nodes or routers to route data packets in cases where
line-of-sight between the source and destination is not possible. A patented geographic addressing
scheme is the method used to route the data through the network nodes.
In any case, the design of a 900 MHz communications network becomes a matter of providing line-of-sight
paths between radios.
In most systems, the end points of the network are typically well defined and established. The data delivery
points (master sites) as well as the data gathering points (remote sites) are known. In order to design a
UtiliNet network that allows communications between the delivery points and the gathering points, a
design plan similar to the following should be used:
1. Using a GPS receiver or geological maps, record the latitude and longitude of each data
delivery/gathering point in the network.
2. Determine an approximate available antenna height for each site. This only needs to be an
approximation. In some cases, the site may have height limitations due to clearance problems or
aesthetics. In the 900 MHz frequency band, antenna height provides the largest gain in terms of
RF distance. In general, the higher that antennas may be mounted the better.
3. Use topographical maps or computer prediction programs to plot paths between known nodes to
get an indication of the ability of radios to communicate with one another over the average terrain
in the area. This procedure provides an approximation for required antenna height in order to clear
obstructions that may exist in the paths.
4. If path profiles are generated that indicate that certain sites DO NOT have line-of-sight paths to
any other site, use general area maps to identify where repeater or additional router locations
might be needed to insure line-of-sight paths from every radio to at least one other radio.
5. Field Survey - Regardless of the quality of maps or computer databases, predictions are still just
predictions. The only way to insure RF connectivity, regardless of the product or the frequency, is
to test the path.
Calculating Latitude/Longitude Coordinates
Each radio in the UtiliNet network is programmed with a unique latitudinal and longitudinal (lat/long)
coordinate. These lat/long coordinates are used by the network to make logical routing decisions (see
"Network Routing" on page 9-2 for more information). Because the network uses the lat/long information