User's Manual

Spread Spectrum Wireless Data Transceiver User Manual
LUM0002AF Rev D Version 6.3 43
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NUMBER REPEATERS
In a MultiPoint network it is critical to transmission timing to configure this parameter correctly. The value
should be 0 if no Repeaters are in the network and 1 if any number of Repeaters are present. This
parameter should be set to the same value in all transceivers in a MultiPoint network. Number Repeaters
needs to be set to 1 when running Diagnostics from the Master.
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MASTER PACKET REPEAT
In a Point-to-MultiPoint network, Slaves do not acknowledge transmissions from the Master. If Slaves did
acknowledge all data transmissions, in a large network, the Master would soon become overwhelmed
with acknowledgments from the Slaves. Without acknowledgements, 100% confidence every Slave has
received every packet cannot be met. To address this issue, the user may modify the Master Packet
Repeat setting, assigning a value between 0 (the packet is transmitted once) to 9 (the packet is
transmitted 10 times). For networks with solid RF links, this parameter should be set to a low value such
as 1 or 2. If a network has some weak or marginal links it should be set with higher values. If a Slave
receives a good packet from a Master more than once it will discard the repeated packets. Similarly, once
a MultiPoint Repeater receives a good packet from the Master, it will discard any further repeated
packets. In turn, the Repeater will send the packet out to the next Repeater or Slaves the number of times
corresponding to its own Master Packet Repeat setting.
Increasing the Master Packet Repeat setting will increase the probability of a packet getting through, but
will also increase latency in the network because each packet from the Master or Repeater is being sent
multiple times. Therefore, it is important to find the optimal mix between network robustness, throughput,
and latency. In general, a setting of 2 to 3 will work well for most well designed networks.
Note: The Master Packet Repeat may be set to 0 if the user software is capable of, or requires
acknowledgment. In this case if a packet sent by the Master and not received by the Slave, the
user software will control the retries as needed.
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ASTER PACKET REPEAT IN MULTIPOINT NETWORKS WITH REPEATERS
The Master Packet Repeat parameter must also be set in MultiPoint Repeaters since a Repeater will
appear as a Master to a Slave. Therefore, the Repeater will send the packet out the number of times
corresponding to its own Master Packet Repeat parameter. If this parameter is set improperly the
reliability of the overall network may be diminished. For example, if a Master's Master Packet Repeat
setting is 3, the link between the Master and Repeater should be robust. If the Repeater's Master Packet
Repeat is set to 0, this could cause marginal communications between the Repeater and the Slaves. The