Radio; 900 Mhz Spread Spectrum Radio; Meshing Capability - Elpro Technologies 915U-2 User Manual

Page 20 915U-2 Wireless I/O

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 which is split into two sub-bands,
902-914 MHz (Low) and 915–928 MHz (High).
In America and Canada, the 915U-2 uses both high and low sub-bands - however in
other countries, i.e. Australia only the 915-928MHz band is available (Some countries
use fewer channels, e.g. New Zealand).
The radio uses frequency hopping spread spectrum modulation, which is a method of
transmitting radio signals by switching the carrier among many frequency channels,
using a pseudo random sequence called a hop set.
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.
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 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.
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