## 4 Discussion
High-speed transmission is implemented at 6.8 Mbps, with a QoS channel-noise scan supported by firmware. The data protocol as implemented in WSA has no delay issues compared to some other published approaches [41]. Susceptibility to radio interference could become a factor if the currently free frequency band becomes more crowded. WSA complies with the relevant standards for medical or health-related applications and devices such as biomedical class 2A for the clinical trial certification process and is in accordance with Directives 93/42 EEC, 2007/47 EC (e.g., standards EN60601, EN301489,EN62304). The tests were carried out in a certified laboratory within the framework of the EU-funded project CL ++ H2020 in the areas of EMI, electromagnetic immunity, ESD (electrostatic discharge) and electrical safety. A user manual, technical dosiser, risk analysis, software validation and usability report were produced. There are several requirements that must be met, such as safety, low transmit power, low specific absorption rate (SAR), EMC, size and weight of the device. For portable devices, energy efficiency is also an important factor, resulting in a low power consumption and a long battery life for the devices. The raw-data output from the IMU during the walking of an intact adult subject is shown in Figure 8. The sensors for this measurement were intentionally uncalibrated. The first column shows the data from the 3D gyroscope, the second column shows the data from the 3D accelerometer sensor, and the third column shows the data from the 3D magnetometer sensor. Each of the 15 plots in Figure 8 shows traces for the first-minute step on the left-hand side, and the right-hand side of each plot shows traces for the last-minute step. These are not calculated joint angles in the left and right legs. Using similar data with gradient-descent algorithms [42], we published a successful estimate of the IMU unit orientation based on an earlier version of WSA [9; 10]. By implementing modelling, IMU-based angular measurements are becoming the standard [43]. Gait analysis and a number of other clinical applications rely on these accelerometer data [44]. Among them, an indirect estimation of the ground reaction forces and moments is realistic in the cases that are not realistic with another method [45; 46]. Comparing the different traces in Figure 8, one can immediately see that the shapes for the first and last minutes of the walking are almost identical. It is important to note that the traces for the last minute are not shifted, i.e., they are not affected by drift. The drift could be primarily dependent on the MPU-9250 sensors. Other possible sources of interference could be in various aspects of the design of the electronic circuit of the IMU unit. Such ghost signals could not be found in the presented diagrams. Using the clear signals seen in Figure 8, we can visually distinguish the steps in the diagrams shown. But this user observation is only the first impression. Most importantly, this data can be used for intention-recognition algorithms as recently presented in [34]. Intention-recognition algorithms used in exoskeletons and bionic prostheses first divide the collected gait-related signals into steps, from one foot contact to the subsequent foot contact of the same leg. For each subject, the left- and right-leg data are processed independently. This is followed by a phase representation of the steps and a unification of the dimension of the sensory data for steps with different cadence. The overall architecture of the algorithm is divided into three modules: (1) a steady/transition module that identifies a step as either steady state or transition; (2) a steady-state module that classifies the locomotion task of a steady-state step, (3) a transition module that recognizes the initial and final locomotion modes of transition steps. By using the WSA presented in this work, the classification of steady-state steps achieved a mean accuracy of 98.7%, and the classification of transition steps achieved a mean accuracy of 95.6% [34].