MDS 05-4846A01, Rev. H
SD Series Technical Manual
57
Listen Before
Transmit (LBT)
Settings
The transceiver provides a legacy collision avoidance scheme called
Listen Before Transmit
(LBT). It employs P-Persistent CSMA protocol,
which senses channel usage and inhibits transmission if the channel is
currently in use. CSMA is an abbreviation for Carrier Sense Multiple
Access. This setting is superseded by Packet w/MAC and should only
be used in legacy systems and special use cases. Packet w/MAC is the
preferred method for collision avoidance.
NOTE:
The Listen Before Transmit (LBT) feature requires radios to
be configured for
Packet Mode
operation. Packet w/MAC
operation provides an alternative method for media access.
•
Listen Before Transmit
—Used to activate or deactivate LBT when the
radio is running in Packet Radio Mode.
•
LBT Behavior
—LBT can be configured to behave in one of two
ways; either
listen on the radio’s transmit frequency (TX)
or
listen
on the radio’s receive frequency (RX)
. Typically, Remote radios
are configured to
Listen on RX
(the default selection) to avoid colli-
sions with the Master unit. In split frequency operation,
Listen on
TX
may be preferred. Optimal choices depend on the data trans-
mission characteristics of the connected system.
•
Min/Max Channel Wait (ms)
—These settings refer to the time period
(in milliseconds) to wait after the channel is free before transmis-
sion is allowed.
Minimum wait time:
Normally, the minimum channel wait time
should not be changed from its default setting of
0 ms
unless per-
forming advanced operations, such as staggering the responses
from multiple Remotes.
Maximum wait time:
Normally, this setting should not be
changed from its default of
100 ms
unless performing advanced
operations. Some examples of when this may be beneficial
include:
• There is a need to stagger responses from several Remote
radios.
• The transmission latency from the time the channel is free is
too high, in which case a lower value can be entered.
• Collisions over the air are too high, in which case a higher
value can be entered.
