We use computer simulations to support the development of the protocol. This involves simulating flying objects in various scenarios, which follow realistic flight paths and which "transmit" simulated radio packets on the one hand and "receive" radio packets on the other and assess whether a collision warning needs to be triggered or not.
To ensure that the flight paths are realistic, we compile data from real flights of different types of objects (paragliders, gliders, helicopters, etc.) in the form of IGC files provided by our development partners. The flight paths are combined in terms of time and location in order to obtain various test scenarios.
The simulations are visualized for visual inspection and evaluation.
To simulate a scenario, the computer runs through discrete steps with fixed time intervals, whereby in each step, among other things
- recalculates the location, speed and acceleration of each flying object,
- "to be transmitted" radio packets are compiled for each flying object according to the definition of the protocol
- and finally determining for each flying object whether each radio packet can be received and decoded and whether it leads to a collision warning according to the algorithm of the radio protocol.
The approach described makes it possible to run through the same scenarios again and again, adapt the protocol and check whether the adaptations lead to an improved generation of collision warnings. As a result, the number of real test flights to be carried out later to validate the protocol can be reduced, as optimized protocol variants are already being used.
In addition to the correctness of the collision warnings, further quality criteria can be observed during the simulation. These include, for example, the computing power used to create the radio packets and to detect possible collisions. The lowest possible computing power is desirable in order to be able to support devices (variometers) with limited hardware and a limited energy budget.
Possible parameters that can be varied in the simulations during the realization phase of the protocol include the content of the radio packets on the transmitter side, the time interval between transmissions, the modulation type, possibly the transmission power, and the algorithm for determining the collision warnings on the receiver side.
An important prerequisite for carrying out meaningful simulations is the use of a realistic simulation model. Take, for example, the assessment of whether a flying object can correctly receive and decode a radio packet from another flying object. In reality, this simple yes/no decision depends on a large number of sometimes complex issues, some of which are listed below:
- Transmitting power
- radiation characteristics of the transmitting antenna
- Possible shadowing, e.g. by the pilots (with paragliders) or the flying objects
- Distance to the receiver
- Radiation characteristics of the receiving antenna
- Sensitivity of the receiver
- Possible interference from simultaneously arriving packets
The simulation model is responsible for simulating these circumstances, whereby a compromise must be found between realism and effort. For example, it is not expedient to invest enormous effort in the exact determination of the radiation characteristics, as in practice these not only differ from device to device, but are also influenced by the alignment of the device during installation and by material in the vicinity of the device. Consequently, the simulation model will inevitably represent a simplified and generalized view of reality.
Much of the work we are carrying out in the initial phase of the project serves to create a basis for the simulations. For example, the recordings and evaluations of the data from the SDR recorder provide an insight into how the packets of current radio protocols arrive at an individual receiver, what signal strength they have and how they collide with each other. Data from the variometers may help to obtain an estimate of the directional characteristic of the antennas using statistical methods. And later test flights will help to refine the simulations and by re-running them to further improve the protocol.