Using state-of-the-art communication technology in WELMO

WELMO aims to develop and validate a new generation of low-cost low power miniaturized cooperative sensors neatly integrated in a vest, where the measured signals are aggregated and transmitted for further processing by a master sensor. The transmission of measurements from the vest to the cloud should occur seamlessly, therefore, the usage of wireless connectivity would be preferred.

In practice, an effective balance between two or more aspects has to be chosen. For the data transfer from the master sensor to an Android smartphone or a tablet, a choice had to be made between WiFi and Bluetooth LE (Low Energy).

The use of WiFi 802.11ac standard would be very efficient for high transfer speeds of up to 200 Mbps and generally longer distances, which is suitable for the WELMO vest. This design, however, would have yielded a higher power consumption. Furthermore, the master sensor and the Android device would have to be confined to a single WiFi network for the entire duration of the data transfer.

For most of the WiFi shortcomings, the novel Bluetooth 5 comes to the rescue. The use of Bluetooth gives users the flexibility to move around freely both in- and outdoors, while not exhausting either of the device’s batteries extensively. In terms of Bluetooth’s significantly lower throughput speeds, efficient methods for data transfer and compression have to be applied to enable real-time data transfer.

The sensor data acquired by the WELMO device consists of both EIT (Electrical Impedance Tomography) and lung sound sensor data, which results in an extensive amount of data to be sent via the wireless communication channel. So far, Bluetooth 4, 4.1, and 4.2, which are the predecessors of Bluetooth 5, have been largely designed for establishing wireless communication channels between IoT devices. Streaming larger amounts of data, however, has still been the task for Bluetooth Classic, which is considerably more power-consuming.

Fortunately, the latest technological advancements in Bluetooth enable the efficient utilization of the low-power data streaming implementation in the WELMO design as well. To name some, the DLE (Data Length Extension) feature introduced in Bluetooth 4.2 enables the transmission of almost 10x larger data packets, and the LE 2M PHY physical layer of Bluetooth 5 doubles the transmission speeds when compared to previous implementations. The throughput can be further increased by communicating directly over the Bluetooth’s L2CAP layer (supported on Android 10 operating system or newer), which makes it possible to bypass the transmission overhead associated with using the higher layer GATT framework for communications.

The enabling of the aforementioned Bluetooth 5 features on the WELMO device gives us theoretical throughput speeds of up to ~1300 Kbps, that together with applied lossy or lossless compression methods should be sufficient for real-time data transfer of high-quality sensor data.

Kristian Kajak

Artec Design LLC