# Evaluation of BLE Star Network for Wireless Wearable Prosthesis/Orthosis Controller +
## 5 Discussion  
In this work, performance of a wireless biosensor network was studied in terms of power consumption, latency, and maximum network size for various BLE configurations using the nRF52840 SoC operating with BLE version 5.3. For a wireless, wearable EMG-driven prosthesis controller comprised of multiple peripheral devices, the results of this evaluation demonstrated that BLE version 5.3 would meet the latency requirements (as low as 10 ms, on average, for up to four peripherals) at a relatively low power consumption (<3 mA--representing, in our experiment, the sum of the currents consumed by the entire Adafruit Feather board, including the nRF52840 SoC, LEDs, and power management components). Additionally, these results were performed in a home office to mimic the expected environment in which a prosthesis/orthosis controller would operate. The decision to not control the test environment was deliberate to expose the test system to the various possible sources of interference that the wireless system may encounter in a user's home from RF sources such as Wi-Fi and BLE-enabled devices such as smart TVs, PCs, tablets, wireless headphones, and smart phones. With respect to the number of maximum peripheral connections, it was observed that in cases in which the event length is short (i.e., 2500 \(\upmu\)s), the maximum number of connections sustained failed to reach its theoretical maximum for connection intervals of 50 and 100 ms. At these greater connection intervals, larger amounts of data were being transmitted, filling the allocated buffers sooner than at the shorter connection intervals. Increasing the size of these buffers from their default value might alleviate this issue but at the risk of impacting other functionality, such as data processing and transmission to the PC via UART. To maximize the number of connections that can be sustained, future developers should focus on allocating sufficient storage of incoming data without interfering with other resources or functionality. When looking at the maximum number of peripheral connections, as the distance between the central and peripheral increased, the number of connections dropped significantly between the measurements at 0.5 m and 9 m. For prosthetic and orthotic applications, it is intended for the peripheral devices to be placed on the user's body and the central to be placed within their devices' control system. In most use cases, it is expected that the peripheral and central devices will be relatively close to one another, likely under one  
Figure 6: (**a**) Normalized latency measurements for the step input’s detection on the peripheral and (**b**) normalized latency measurements for the step input’s detection on the central node, computed by dividing the measured latency by the connection interval. There are 180 samples per histogram (10 trials per condition \(\times\) 6 connection intervals \(\times\) 3 event lengths). meter; in a typical configuration, it is expected that the peripheral would be placed on or near the muscles of the residual limb and the central placed within the prosthetic limb control system, so the limitations in the number of peripheral connections due to distance will be avoided. In the event that the distance between the central and peripheral exceeds a meter or two, fewer peripheral connections may be supported, which could be detrimental in scenarios where multiple peripherals are used. One possible solution to address this limitation is an increase in transmit power, which comes at the expense of greater power consumption. Measurements of the average power supply current showed that, for all event lengths considered, an average decrease of 16.13% was observed as the connection interval increased from 10 ms to 100 ms. With respect to the event length, few statistically significant differences were detected between event lengths of 2500 us and 5000 us. When comparing 2500 us and 7500 us, as well as 5000 us and 7500 us, more statistically significant differences were detected.