I have been trying to measure the PER between two nRF52840 DKs using BLE. To do so, I am using BLE Direct Test Mode to start a transmission on a 52840 DK and another development kit to listen for the broadcast and count the packages. The BLE DTM standard does not incorporate the possibility to count the number of sent packets on the transmitter side, so I am trying to calculate a theoretical amount of sent packages using the formula supplied by "BLUETOOTH CORE SPECIFICATION Version 5.4 | Vol 6, Part F page 3063".
To get to the packet length in bits i use the formula:
packet_len = pdu_payload_len + 8 + 8 + 32 + 24 + 8 * phy_bandwidth
with phy_bandwidth being the PHY mode [1Mbit/s | 2Mbit/s]
To get the LE Test packet length L in µs, I divide this amount by the phy_bandwidth:
L = packet_len / phy_bandwidth
I use L to calculate I(L) according to the specified formula of the core specification.
I then multiply I(L) with the amount of packets reported received by the receiver DK and divide by the time period the receiver was active.
package_error_rate = (1 - I(L) * packet_count / time_delta) * 100%
Unfortunately, using this method I calculate a PER of around 75% while the receiver and transmitter DKs are right next to each other. The transmitter is set to highest TX power in this scenario.
What could be the source of this problem? Is my approach of calculating the PER based on bandwidth and packet length incorrect?
Any help is much appreciated.
BASH:
pdu_payload_len=$(( packet_len_l6 + packet_len_higher * 16 )) # in bits phy_packet_len=$(( pdu_payload_len + 8 + 8 + 32 + 24 + 8 * phy_bandwidth )) # in bits #echo "$phy_packet_len" phy_packet_dur=$(echo "scale=0; $phy_packet_len / $phy_bandwidth" | bc) #in µs #echo "$phy_packet_dur" transmit_interval_dur=$(( ((phy_packet_dur + 249 + 624) / 625) * 625 )) ##echo "transmit_interval_dur: $transmit_interval_dur" PER=$(echo "scale=2; 100 - ($packet_count * $transmit_interval_dur) / ($delta * 10000)" | bc) #in %
