Phase-based UHF RFID approach for speed bag monitoring

This repository contains the materials used in the study

P. López-Matencio, F. J. González-Castaño and J. Vales-Alonso "Phase-based UHF RFID approach for speed bag monitoring," 2022 7th International Conference on Smart and Sustainable Technologies (SpliTech) Split / Bol, Croatia, 2022, pp. 1-4, https://doi.org/10.23919/SpliTech55088.2022.9854229

This work presents a new RFID-based application for sports activity monitoring. Specifically, the developed system aims to detect a boxing speed bag's periodic pattern of movements during a training session.

Operation overview

A speed bag is a light, air-filled, and small drop-shaped punching that may be anchored to the ceiling or a top-placed rebound platform

Figure 1: Speed bag RFID-based system scheme.

A typical workout with a speed bag may attack the bag for about 3 or 5 minutes and rest for one minute between rounds. The boxer has to repeatedly hit the bag during the session and use one or two hands while the bag moves fast. Therefore, the boxer must be very focused on the exercise and coordinate eye and hand movements to keep the speed of the bag. Monitoring the speed of the bag is challenging because the data must be obtained without hindering the execution of the exercise and without distracting the boxer. In our system, we are able to compute the oscillation frequency interrogating a passive tag attached to the bag.

Model approach

We assume the speedbag is in motion and the RFID antennas, TX and RX, are in the same plane.

The computation of the oscillation freequency is made thorugh the phase of the backscattered signal received in the reader's antenna. The Jupyter notebook LOSS_SPLIT.ipynb models the communication channel, the link budget (losses of the backscattered signal), and the phase and frequency of the received signal.

The following table contains the main parameters of out system model:

Parameter	Description
Frame interrogation protocol	FSA [ISO18000] with frame length 1 slot
Initial distance between Tx-Rx antennas ($d_0$)	in [1,10] m (at $\psi(t){=}\psi_0$ position)
Reader antenna	Patch panel (gain of 8 dBi)
Reader's antenna tilt ($\theta_1$)	Aimed to the center of the tag's antenna
Tag's antenna tilt ($\theta_2$)	Aimed to the center of the reader's antenna
Antenna azimuth	0, the tag's and reader's antennas are in a plane
Tag antenna	Half-wave dipole (gain of 2 dBi)
Tag power-up threshold ($\text{IC}_{th}$)	-19 dBm
Reader sensitivity threshold ($\text{S}_{th}$)	-80 dBm
Frequency	865.7 MHz
Transmission power	27 dBm
Backscatter-Link Frequency (BLF)	320 kHz
Noise level	-120.87 dBm
Channel model	Line-of-sight with Rician fading
Rician K-factor	3 dB
Tag attached material	Plastic
Tag modulation factor	0.25
On object gain penalty	1.1 dB
Vertical distance of the tag to the hook ($l$)	22 cm
Radius of the speedbag at tag's height ($h$)	27/π ≈ 8.6 cm
Angle of the tag's antenna with $x-\text{axis}$ ($\psi_0$)	21.34°
Mean oscillation frequency of the speedbag ($f$)	4 Hz
Time between tag's readings ($T_\text{reader}$)	1/35 s
EPC length	96 bits