4RF Aprisa SR+ User Manual - page 19
16 | About the Radio
Aprisa SR User Manual
Product Overview
Network Coverage and Capacity
In a simple point-to-multipoint network, an Aprisa SR, configured as a Base Station, will communicate with
multiple remote units in a given coverage area. With a link range of up to 60 km a typical deployment will
have 30 – 50 Remote Stations attached to the Base Station. However, geographic features, such as hills,
mountains, trees and foliage, or other path obstructions, such as buildings, tend to limit radio coverage.
Additionally, geography may reduce network capacity at the edge of the network where errors may occur
and require retransmission. However, the Aprisa SR uses Forward Error Correction (FEC) which greatly
improves the sensitivity performance of the radio resulting in less retries and minimal reduction in
capacity.
Ultimately, the overall performance of any specific network will be defined by a range of factors including
the geographic location, the number of Remote Stations in the Base Station coverage area and the traffic
profile across the network. Effective network design will distribute the total number of Remote Stations
across the available Base Stations to ensure optimal geographic coverage and network capacity.
Remote Messaging
Base Stations are fitted with omni-directional antennas and the Remote Stations use directional Yagi
antennas for higher gain. On start-up the Base Station transmits a registration message which is
recognized by the Remote Stations which respond with their own registration message. This allows the
Base Station to record the details of all the Remote Stations active in the network.
There are two message types in the Aprisa SR network, broadcast messages and unicast messages.
Broadcast messages are transmitted by the Base Station to the Remote Stations and unicast messages are
transmitted by the Remote Station to the Base Station.
All the Remote Stations, within the coverage area, will receive the messages broadcast from the Base
Station, but only the radio the message is intended for will action the message. Only the Base Station can
receive the unicast messages transmitted from the Remote Station. Unicast messages are ignored by other
Remote Stations which may be able to receive them. The Aprisa SR network is not designed for Remote
Stations to communicate with other Remote Stations.