# Evaluation of BLE Star Network for Wireless Wearable Prosthesis/Orthosis Controller +
## 2 Background
### Related Works  
BLE has been used for many applications since its release in 2010. Related works have studied some, but not all, of the configuration parameters considered here and typically under different test conditions or using earlier versions of BLE.  
[PERSON] et al. [25] connected two peripheral devices to one central node to study the relationship between MTU size and data loss, as well as the impact of the external environment. They used two TI CC2640 BLE microcontroller units (MCUs) for their peripheral nodes and seven different central devices (one Raspberry Pi, four iOS-based devices, and two Android-based devices) to study the influence of the operating system and BLE hardware on data loss. Additionally, they measured the packet loss and received signal strength vs. node-to-node distance and objects placed between the central and peripheral nodes. They proposed a data loss mitigation protocol of increasing the connection interval and data bundling.  
[PERSON] et al. [26] used a single BLE peripheral device to study the Quality of Service vis-a-vis throughput, packet error rate, and end-to-end delay. They determined that BLE can meet the Quality of Service requirements of specific medical applications. [PERSON] et al. [27] compared the current consumption and data throughput with various environmental interferences, comparing BLE 4.1 using the TI CC2650 SoC to Low Power Wi-Fi using the TI CC3200 for a multi-channel surface EMG acquisition system. They observed that Low Power Wi-Fi consumed seven times more current than BLE for low data rates, but there was a limitation of the throughput to 111.9 kbps for their BLE implementation. Note: With the release of BLE 5, higher throughputs are now achievable.  
To specifically study the influence of the environment and interference from other wireless devices, [PERSON] et al. [28] measured path loss (the attenuation of electromagnetic signals from transmitter to receiver) over distance in a hospital. They used nRF52840 SoC development kits running BLE 5.0. The received signal strength was measured at different locations in the hospital for a peripheral placed in a patient's room. A known number of BLE-, Wi-Fi- and ZigBee-enabled devices (personal and medical) were placed inside and outside of the main patient's room and surrounding patient rooms. The authors found that ranges of 6 m or more should utilize BLE 5.0's long-range mode to ensure reliable communication.  
Lastly, [PERSON] et al. [29] reviewed the BLE protocol and how various BLE parameters interact. The experimental and theoretical results detailing the number of connections that can be supported by a single central node, the relationship between connection interval and throughput, and power consumption are presented from different platforms such as the TI CC2241, Nordic Semiconductor nRF51822, and ST Microelectronic BlueNRG.  
None of the above cited works considered these various parameters together, as shown in this work. Additionally, these works used BLE version 4.x, with the exception of [28], which used BLE 5.0. Herein, BLE version 5.3 was used. This latter version has improvements in reliability and reductions in power consumption and latency.