## 4 Performance Results and Discussion
### Evaluation of the Results Regarding the Smart Sensor Use Case  
In Section 2, the Smart Sensors for Milling Processes use case has been discussed, motivating the utilization of 5G in combination with FRER for achieving reliable communication. Aside from this specific use case, highly reliable communication plays an important role in industrial communication. Data from wireless smart sensors or interconnected actuators in production can be used in a variety of cases. The communication requirements in Section 2 focus on use cases with a latency below 10 ms, a high reliability of 99.99%, and a data size between 128 and 1024 bytes. Table 2, an overview of the measurement results related to the use case requirements discussed in Section 2, is given. The industrial use-case requirements are met every time FRER is used, underlining its impact on communication reliability. In Setup 1 and Setup 2, it has been shown that the reduction of outliers in the communication caused by disturbances in one of the communication paths increases the reliability of the system and reduces the overall jitter and latency. Both setups meet the use case requirements when using FRER but do not meet the requirements with one single communication path. As shown in Table 2. Setup 1 achieved a latency of 8.28 ms using FRER and only 11.16 ms and 10.95 ms for the single path communication. Aside from the overall improvement of the communication quality, it can be seen that some single paths also meet the communication requirements, but with larger spikes in communication, for example, Path 2 in Setup 4 and Setup 5. Figure 15: Latency of the wireless transmission. (**a**) Latency for packets sent by 5G UE1 (mid-band SA), (**b**) latency for packets sent by 5G UE2 (mmW NSA), and (**c**) latency of the first packet arriving Switch 2. The only path meeting the communication requirements without spikes is the URLLC test system used in Setup 3. Further, the advantages of FRER in challenging industrial environments for radio signal propagation with moving objects and metal housings can be seen in Setup 4 with introduced disturbances. Having line of sight, Path 2 meets the industrial requirements in Setup 4, but as soon as disturbances due to blockage occur, the overall reliability is seen to be compromised, and the communication needs to rely on Path 1 to maintain reliable communication. Using FRER, the resilience of the communication regarding external influences such as the blocking of an antenna by a crane, metal housing, or a passing AGV has been increased, and so has the reliability. Such external disturbances can occur in industrial environments, especially for moving systems such as the wireless sensor mounted on a workpiece or tool inside a machine chamber or a moving object such as a crane or forklift. Overall, it has been shown that the requirements for the Smart Sensors for Milling Processes use case could be met using 5G and FRER even in environments with challenging radio propagation conditions on an industrial shop floor. Using single communication may be vulnerable to wireless communication-related disturbances. These may cause undesirable outliers, which lead to unmet reliability targets for the use case. Using both paths in parallel creates resilience towards those disturbances, increasing reliability. The requirements of the Smart Sensors for Milling Processes use cases, having 10 ms latency for 99.99% of messages is a common value for a number of industrial use cases. Fieldbus protocols such as PROFINET [32] have similar requirements; for example, PROFINET RT (Real Time), used for data exchanged directly via the Ethernet protocol, is used to implement applications in which the cycle times are in the >10 ms range [33,34]. While redundancy is costly in terms of extra hardware and spectrum usage for a wireless system, the benefits in terms of increased reliability become essential in many industrial applications as we have empirically evaluated for the investigated Smart Sensors for Milling Processes use case.