Synchronization in wireless biomedical-sensor networks with Bluetooth Low Energy

Abstract

Bluetooth Low Energy (BLE) has reduced the energy consumption for sensor nodes drastically. One major reason for this improvement is a non-continuous connection between the nodes. But this causes also a nondeterministic data transmission time. Most synchronization protocols are influenced by this characteristic, with the result of less accuracy. In wireless body sensor networks this accuracy is often of vital importance. Therefore this paper evaluates different synchronization principles customized for BLE.For the evaluation measurements we used two BLE modules connected to one micro controller. This setup allowed us to calculate the error directly for the different principles. First we measured the send-receive time as a reference which influences most synchronization protocols. This time is directly affected by random transmission delays of BLE. Second we used the time difference between receiving and acknowledging a message as principle (A). The last principle (B) can only be used between nodes that use BLE that don’t require a constant connection, because it needs to connect and disconnect the nodes. After a new connection the “connected” events occur in the BLE nodes almost at the same time and can be used for synchronization. The reference measurement showed the worst results. The average delay was 4.76 ms with a standard deviation of 2.32 ms. Principle (A) showed average delays of 7.51 ms, which was almost exactly 1 connection interval in our setup. The standard deviation was 0.41 ms. Principle (B) showed the best results with an average time difference of 39.92 μs and a standard deviation of 14.19 μsThe results showed that with the principles (A) and (B) the synchronization of nodes can be highly improved compared to the reference. In future we will test the principles with synchronization protocols in real sensor nodes also with respect to the processor load.

PCO-Based BLE Mesh Accelerator

“…However, due to the distributed nature of PCO synchronization, our technique automatically forms an emergent network topology with automatic hop formation (see Figure 8). Compared to other synchronization schemes [5,[36][37][38][39], we achieve significantly higher synchronization accuracy at the cost of additional hardware. The presented accelerator is lightweight, but needs to be integrated into the PHY layer (radio ADC), which likely implies a new hardware design.…”

“…In [ 36 ], the authors achieve a synchronization accuracy of 37.78 ms by using a dedicated synchronization center microcontroller. In [ 37 ], the authors report a synchronization accuracy of 14.19 μs by using the establishment of a BLE connection event as the basis. In [ 38 ], the authors report a synchronization accuracy of 750 μs by forcing two BLE nodes to establish a connection at a fixed interval and using the time difference between connect events for estimation.…”

Fully portable and wireless universal brain–machine interfaces enabled by flexible scalp electronics and deep learning algorithm

“…The SKINTRONICS wireless telemetry unit uses a Bluetooth low-energy microcontroller (nRF52832, Nordic Semiconductor) due to its high throughput, low latency, low power draw and wireless range 39 . The BLE protocol supports wireless synchronization of multiple devices to support greater numbers of channels 50 . Considering each SKINTRONICS can support up to 8 channels, more devices can be synchronized for measuring multi-EEG signals at different locations.…”

Comparison between Two Time Synchronization and Data Alignment Methods for Multi-Channel Wearable Biosensor Systems Using BLE Protocol

“…Previously, several time synchronization methods have been introduced [23][24][25], specifically for use with BLE. In particular, the BLE beacon role or connection events tend to be feasible methods [26,27]. Using the beacon role, the central node periodically broadcasts clock information to the peripheral nodes to maintain high synchronization accuracy (drift of <1 µs/min [26]).…”

“…However, while broadcasting the clock information, the central node cannot receive data packets from peripheral nodes in real time. Alternatively, time synchronization can occur if multiple nodes are connected near-simultaneously (time synchronization differences of 39.92 ± 14.19 µs [27]). Again, this synchronization method cannot be maintained during data collection, as nodes would need to constantly disconnect and re-connect.…”