Research on different RF modulation

This page will be mostly about the research on different RF modulations and their properties. The whole point is for finding out the best solution for transmitting the fastest data between two radio modules. This will like be implemented in the ELRS AirPort feature or an individual MAVLink software-based flow control.

Facts:

#1 (G)FSK has the highest data rate compared to other modulation, but FLRC do decent on both the data rate and the range

source: https://www.semtech.com/uploads/design-support/SG-SEMTECH-WIRELESSRF.pdf

#2 Difference between some old RF modulations

source: https://www.electronicdesign.com/technologies/communications/article/21798737/electronic-design-understanding-modern-digital-modulation-techniques

#3 With sx1280, FLRC can transmit data to about 2.3km far with 260 kb/s which is as fast as half of the data maximum transmission speed on a RFD 900

source: https://cdn.rohde-schwarz.com/fr/general_37/local_webpages/SEMTECH_Journe_IoT_Rohde_Mars2018.pdf

#8 Not all the packets are send over FLRC

Seems like only F1000 and F500 here are using FLRC modulation

source: https://www.expresslrs.org/info/signal-health/

#9 ELRS Telem Packet Sends both DATA and LINK data, so that the actually telem data that is been sending out seem less than it looks like

source: https://www.expresslrs.org/info/telem-bandwidth/

#10 Telemetry ratio means the number of telemetry packets sent vs the total number of packets sent. For example, 1: 64 means in 64 packets, 63 are the RC packets and 1 is the telem packet. However, in airport, this ratio is fixed as 1:2 and that means an even amount of uplink/downlink

source:https://www.expresslrs.org/quick-start/pre-1stflight/?h=

#11 ELRS Modes Explained

For more info, watch CapnBry's video on ELRS modes here: https://www.youtube.com/watch?v=ymv9OJFWgJ4

#12 - ELRS TX/RX works independently from each other. In Airport, even if they are configured with different baud rate, they still bind and work well, but they transmit and receive the baud rate that is been set to them

#13 - How the ELRS Telemetry Bandwidth is calculated

Take the configuration of F500, 1:2 telem ratio as an example:

The interval in us for this setting is 2000us, then we know the packet frequency is 500 packets/s

The radio ratio is 1:2, the value is 2 here. The radio ratio means in 500 packets, only 250 of them are telemetry packets, and the other 250 are RC packets.

Burst is the attribute of how many DATA Telemetry packets are sent every one LINK Telemetry packet. When the telemetry burst is activated, that means we take the consideration of minimizing the number of LINK Telemetry into account. The LINK Telemetry instead of sends 1 by 1 along with DATA Telemetry, now it is been sent every 512 ms. This means roughly 127 DATA Packets are sent every half second.

Since 500Hz is not in Full Resolution frequency, the packet size is 5 per packet instead 10 per packet

Therefore, the final bandwidth of this configuration is 9921, which we usually configure the baud rate to 9600