Table of Contents
Advertisement
915U-2 Wireless I/O
Page 19
2.3 Radio
The following radio variants are available in the 915U-2 dependent on the country of
operation.
2.3.1 900 MHz Spread Spectrum radio
The radio operates in the 902-928 MHz ISM band and uses frequency hopping spread
spectrum modulation, which is a method of transmitting radio signals by rapidly
switching the carrier among many frequency channels, using a pseudo random
sequence known to both transmitter and receiver as Hop Sets.
There are two Hop sets and each one uses a different pseudo random sequence of
radio channels. Each Hop Set is made up of 50 channels, which cycle through to the
next channel after each transmission. (Some countries use fewer channels, e.g. New
Zealand).
The receiver is continually scanning all channels in the hop-set and when a valid data
packet is heard, it locks on to the channel and receives the data.
A spread-spectrum transmission offers some advantages over a fixed-frequency
transmission. These are - Spread-spectrum signals are more resistant to narrowband
interference, they are difficult to intercept or eavesdrop because of the pseudorandom
transmission sequences and transmissions can share a frequency band with other
types of conventional transmissions with minimal interference.
2.3.2 Meshing capability
The ELPRO WIBMesh protocol is based on the "Ad hoc On Demand Distance Vector"
(AODV) routing algorithm which is a routing protocol designed for ad hoc networks.
AODV is capable of unicast and multicast routing and is an on demand algorithm,
meaning that it builds and maintains these routes only as long as they are needed by
the source devices.
The Protocol creates a table, which shows the connection routes to other device in the
system. The Protocol uses sequence numbers to ensure the routes are kept as current
as possible. It is loop-free, self-starting, and can scale to a large numbers of nodes.
See section 3.4 "WIBMesh" for more details on configuration.
Page 19
915U-2 Wireless I/O
Advertisement
Table of Contents
