In the first part of the project, a review of the state of the art for wireless surface EMG systems has been conducted. The review has been directed checking the available standards for wireless communication that are compatible with the transmission of biosignals. In literature, several standards have been exploited for the transmission of biomedical signals. Among them, two possible candidates have been identified for the specific application of the project: the IEEE 802.11 and the IEEE 802.15.6. Both standards can reach data rate compatible with the application and can be exploited for wearable devices. Additionally, a search was performed among the patented devices with similar characteristics to the proposed project. It has been found that the most important companies that are producing clinical and research devices are increasing their interest in wireless surface EMG systems. Nevertheless no high-density wireless surface EMG system (>16 channels) implementing a standard communication protocol was found available on the market.
The most optimized communication standard for the proposed project was found to be the IEEE 802.15.6 that is specific for wireless body area networks. This standard can include a large variety of transmission bandwidths for different applications. The IEEE 802.15.6 has the advantage that may be used with much lower power transmission (10mW) compared to other standards.
Unfortunately, the standard is relatively new and, there are no commercially available hardware implementations that may be easily included in the proposed system. Therefore, its use requires the implementation of the entire standard in a prototype board.
For this reason, the project focused mostly on the improvement of an already existing system developed by the OT Bioelettronica in the last year. The system adopted is based on the well-established standard IEEE 802.11.
The second part of the project focused on the optimization of the features included in the standard IEEE 802.11 and on a simplified framework for the compression of the sampled surface EMG signals.
This implementation selected provides the flexibility to select the main transmission bandwidths (2.4 or 5 GHz), channels, data rate, Access Point/Station mode, modulation type, power management, security protocol, etc. The performance of the system was analyzed, in terms of interference, when multiple devices were active at the same time. The tests were done transmitting simulated data or previously collected surface EMG signals by OTB. Using the default parameters of the hardware implementation, the level of interference was quite high already with only two devices active at the same time. This resulted in a considerable reduction of data rate during the transmission and/or the packet loss of collected samples. For these reasons, several months were used optimizing the combination of the features in the wireless module in order to overcome some of these interference problems. This approach provided the possibility to reliably transmit sampled surface EMG signals from two wireless modules active at the same time, but it could not overcome the interference level when more modules were active. It was clear the necessity to include source coding of the sampled data in order to reduce the overall data rate and therefore decreasing the interference level among the wireless modules. Consequently, a low-complexity compression algorithm has been designed. This approach permited the use of four devices concurrently. This was an important outcome of the project since it provided the possibility to implement a network of four wireless modules that could sample high-density surface EMG data from four muscle groups at the same time in human subjects.
In the last part of the project, it was implemented a set of Matlab numerical simulations to understand the efficiency of a second generation of the wireless system using a simplified version of the IEEE 802.15.6 standard. These simulated preliminary results show that such implementation may provide the possibility to have more than four wireless devices recording and transmitting HD EMG at the same time on the human body.
The results of the project have been exploited in several ways. The project description has been shared at different congresses and events (ISEK 2018 in Dublin, Motor neuron meeting in Boulder, SISMES, ICNR2018, SIAMOC and OT Day 2017) with researchers and clinicians that are already using other OT Bioelettronica products.
