WIRELESS CONNECTIVITY & SENSORS
User manual Thyone-I
11. Clear Channel Assessment
This section describes the Clear Channel Assessment (CCA) feature, often also called Listen Before Talk (LBT).
A radio transmitter performing a CCA assesses the channel and proceeds with transmission
only when the channel is free. This method provides a means for collision avoidance at the
cost of latency and throughput.
This function is disabled by default in the Thyone-I module meaning that the radio channel ac-
cess is performed using the so called ALOHA method. This means, send whenever you have
data to send resulting in a Poisson distribution for collision probability.
In addition to this, a CCA can be enabled which uses a channel access scheme called CSMA-
CA (carrier sense multiple access with collision avoidance). In this method, the transmitter with
data to send performs an energy measurement on the configured channel. If the measured en-
ergy is below a certain threshold, the channel is found to be free and the packet is transmitted.
In case the energy detected is beyond a certain threshold, the channel is found to be busy. In
this case, the module implements random back-offs and retries several times. If all the retries
fail, the host gets a channel busy status indicated.
To enable and configure this feature two parameters are used. First of all
which is
used to enable or disable the feature, where ’1’ means feature is enabled.
In addition to this a threshold
can be configured, which is used for deciding
either "channel is free" or "channel is busy". The
is defined as follows:
BusyT hreshold
dB
=
T hresholdBase
dB
+
CCA
_
T HRESHOLD
dB
Where ThresholdBase
dB
is a constant of -95 dB.
In the figure
below, level L1 indicates the noise floor. The level L2 represents the energy
level where the channel is still detected as free. L2 + 1 dB is the minimum energy level strong
enough to be detected as busy.
Figure 22: Channel busy thresholds
By default the value of
is "20" (0x14). This results in a BusyThreshold
dB
level
of -75dB. When the energy measurement of the radio module results in a level of more than
-75dB (i.e. -74dB and higher), the channel is considered as busy and the module will not send
the radio frame instantly.
Order code 2611011021000
123
Version 2.3 , July 2022
