14.3.7.1 Overview
Equipment using the AT86RF212B shall conform to the established regulations. With respect to the regulations in Europe, CSMA-CA based transmission according to IEEE 802.15.4 is not appropriate. In principle, transmission is subject to low duty cycles (0.1% to 1%). However, according to [6], equipment employing listen before talk (LBT) and adaptive frequency agility (AFA) does not have to comply with duty cycle conditions. Hence, LBT can be attractive in order to reduce network latency.
Minimum Listening Time
A device with LBT needs to comply with a minimum listening time, refer to Section 9.1.1.2 of [6]. Prior transmission, the device must listen for a receive signal at or above the LBT threshold level to determine whether the intended channel is available for use, unless transmission is pursuing acknowledgement.
A device using LBT needs to listen for a fixed period of at least 5ms. If the channel is free after this period, transmission may immediately commence (that is no CSMA is required). Otherwise, a new minimum listening period of a randomly selected time span between 5ms and 10ms is required. The time resolution shall be approximately 0.5ms. The last step needs to be repeated until a free channel is available.
LBT Threshold
According to [6], the maximum LBT threshold for an IEEE 802.15.4 signal is presumably -82dBm, assuming a channel spacing of 1MHz.