## 3 Results of the Experimental Validation
### Determining the Less Error Prone Master Device's Location on the Backpack  
The Decawave DW1000, a fully integrated single-chip UWB, features a low-power transceiver IC, which is IEEE802.15.4-2011 compliant. Data rates of up to 6.8 Mbps are supported, and the communication range can be extended up to 290 m @ 110 kbps 10% PER. The frequency bands are between 3.5 GHz and 6.5 GHz, which allows limited soft-tissue penetration. On the transmit side, the maximum transmit power range should be set so that the EIRP at the antenna is as close as possible to the maximum allowable level of \(-41.3\) dBm/MHz to ensure that applicable regulatory standards such as FCC and ETSI can be met. On the receiver side, Automatic Gain Control (AGC) ensures optimum receiver performance by adjusting the receiver gain to the changing signal and environmental  
Figure 5: Current draw of five IMU devices, see text for detailed technical description. conditions. The level of the received signal is monitored so that automatic adjustments are made to ensure the optimum performance of the receiver. Regardless of all the optimal settings of the transmitter and receiver, and even for a short communication range, the signal-strength fluctuations, reflections or electromagnetic obstacles in the vicinity can greatly increase the number of communication-packet errors. Even in line-of-sight (LOS) conditions, the multipath reflections can provide an additional usable received signal or increase the packet loss rate, on the one hand. In non-LOS (NLOS) conditions between UWB modules, where there are obstacles in the LOS path, the range is reduced mainly due to the attenuation of the received signal. All these effects can occur with UWB modules attached to the human body, which also attenuates the GHz signals. While transferring accelerometer, gyroscope, magnetometer and insole payload data from the IMU units that are placed on various points of the body to the master unit, the placement of the master unit is of paramount importance. As an example, the master unit should not be placed inside a modern carbon-fibre housing that might be, for other reasons, a good choice for the exoskeletal controller. To experimentally test several different placements of the master unit while searching for an less error prone placement, the subject was fitted with a set of WSA consisting of five IMU units attached to the subject's right/left hip, right/left thigh, and pelvis, as shown in Figure 6. The main unit was attached to different locations of the backpack (Table 1 left), (1) at the bottom of the backpack, (2) at the bottom edge of the backpack, (3) at the bottom back of the backpack, (4) at the back of the backpack, (5) at the top edge of the backpack, (6) at the top of the backpack, (7) in a static position on the table 1.5 m behind the subject at a height of 0.7 m, and (8) firmly attached to the subject's back without the backpack. The laboratory test was conducted as a baseline, with the devices spaced 1.5 m apart. Tests (1) to (6) were performed during a walk in a public hall, while conditions (6) to (8) were checked when walking on a treadmill. Each session lasted for 10 min. The sampling rate was 100 Hz on each IMU unit and for each variable. Figure 6: Positions of the five IMU units were attached to the subject’s right/left hip, right/left thigh, and pelvis, while the Master Unit was placed at different locations on the backpack, as marked in the next figure. To begin the experiment, custom software written in Python was run on a portable aluminium-case computer located inside the backpack and connected via a USB cable to the main device located on the outside surface of the backpack. The backpack is made of 100% polyester fabric. The software captured the raw-data signals from the IMU sensors, counted the packet losses, and measured the received strength (RSSI) of the surrounding Wi-Fi signals. The sensor signals were post-processed using MATLAB software. The Table 1 shows the numerical values of packet loss in a percentage during the 600-s trials.