# Communication Architecture in Mixed-Reality Simulations of Unmanned Systems
## 6 Addressing the Precision Aspects of the Proposed Architecture
### Hwe-Swe Communication Reachability  
Messages exchanged between the SWEs and HWEs need to be routed via the modem of the simulation platform. Thus, the RF signal characteristics of the message transmission between HWEs and SWEs are given by the signal characteristics between the HWE's modem and the modem of the  
Figure 6: Principle of the deployment of the network simulation into MR simulations.  
simulation platform, and do not reflect the positions of the HWE and SWE in the simulation. This can result in situations where an HWE-SWE pair can be close to each other in the simulation, but the entities would be mutually unreachable for message transmission in reality since the HWE is too far away from the simulation platform. Similarly, an HWE-SWE pair could be far from each other in the simulation; however, if the HWE is close to the simulation platform, its messages can be delivered. The main issues in the communication reachability of HWEs and SWEs that can occur are illustrated in Figure 7 and are as follows.  
1. Nodes SWE\({}_{1}\) and HWE\({}_{1}\)**should not be** mutually visible, but **they are**.
2. Nodes SWE\({}_{1}\) and HWE\({}_{3}\)**should be** mutually visible, but **they are not**.
3. Communication between nodes SWE\({}_{1}\) and HWE\({}_{4}\)**should not** interfere with the communication between nodes HWE\({}_{1}\) and HWE\({}_{2}\)**, **but it does**.  
We propose the following precautions that should be applied to address the identified issues and to achieve the high-fidelity simulation of the communications.  
1. A proper model of the RF signal propagation should be used for the message transmission between the HWE-SWE pairs to limit the message receivers to those that can be reached. This can be done during the message re-transmission issued by the simulation platform. The particular mechanism of the wireless network simulation that can be used to address this aspect is described in Section 5.3.
2. Range testing of the simulation scenarios needs to be limited to the area that is reachable for the signal of the particular simulation platform's modem. The modem has to be equipped with a high gain antenna to provide as large a testing area as possible. This way, no HWE can get outside of the range of the simulation platform and thus out of the range of any SWE (unless it is caused by the signal propagation model mentioned in the previous case).
3. Undesired signal interference caused by the simulation platform affects all communications in the reachable area of the platform's modem. It cannot be avoided; only its effects are limited. Two particular precautions can be taken. First, the transmit power of the platform's modem can be adjusted for every transmission and set to the minimal required power for a successful message reception; therefore, it does not influence nodes further away from the platform. For example, if the power is set to transmit a message to HWE\({}_{4}\) in Figure 7, HWE\({}_{6}\) would not be affected;  
Figure 7: Illustration of configurations that could cause imprecise modeling of HWE-SWE reachability. Circles represent the communication ranges of individual entities and of the simulation platform (embodied by the GCS).  
however, HWE\({}_{5}\) would still be. Second, the simulation platform's modem can be equipped with multiple directional antennas and a mechanism for using only selected ones for message transmissions based on the knowledge of positions of the target entities. However, the results of these two particular precautions have not been reported in the herein presented evaluation results. They are the subject of our future work.