DOI: 10.5281/zenodo.18153931
title: Two-Way Channel Frequency Response Dataset Obtained with MCPD technique

description: Overview

The dataset contains complex-valued two-way channel frequency response (CFR) measurements obtained using the phase-based ranging (PBR) technique. The dataset was created with the method developed in the paper [1], where the multi-carrier phase difference (MCPD) technique was integrated into the IEEE 802.15.4 time slotted channel hopping (TSCH) protocol, enabling distance estimation alongside communication. The dataset includes measurements from three setups under controlled indoor office conditions and provides both raw and interfered versions of the data.

Measurement Campaign Description

Measurements were performed in an office environment with two large magnetic boards providing strong reflective surfaces. The room contained typical office furniture and was unoccupied during the measurements. Four Wi-Fi access points were active in the 2.4 GHz band throughout the experiments. Two devices were placed in the center of the room on cardboard stands 50 cm above the table.

Three LoS configurations were measured:




Setup
LoS Distance
Description


Setup 1
2 m
Devices in direct LoS at 2 meters apart


Setup 2
3 m
Devices in direct LoS at 3 meters apart


Setup 3
4 m
Devices in direct LoS at 4 meters apart




Hardware and Firmware

The experiments used two VESNA devices equipped with AT86RF215 radios, which support IQ sampling. Devices were running Contiki-NG OS with a modified protocol stack enabling phase-based ranging as described in [1]. 

Measurement Method

In each setup, the devices exchanged data packets while simultaneously measuring the wireless channel using the MCPD technique. One device acted as the initiator (`init`), and the other as the reflector (`ref`). After each packet exchange, devices sampled the in-phase and quadrature (IQ) components of the continuous-wave (CW) tones exchanged across the 2.4 GHz ISM band. The resulting MCPD configuration:

- Frequency range: 2401.0 MHz to 2480.5 MHz - Frequency step: 0.5 MHz - Total tones: 160- Total bandwidth: 80 MHz

Calibration

Because low-cost radio hardware is used, the devices exhibit differences between their transmit and receive carrier frequencies, known as carrier frequency offset (CFO). Before the measurements, the devices were calibrated to minimize CFO, ensuring negligible frequency mismatch during operation.

Each distance estimate also includes a fixed hardware-induced bias resulting from additional propagation delays through the antennas, cables, and circuit board traces. In the setup, the bias was measured at **1.8 m**. Post-processing calibration is required to remove it from the final results.

Random Initial Phase Offsets

Standalone CFR measurements from `init` or `ref` contain random phase offsets because the phase-locked loop (PLL) of the radio initializes with an unknown phase at each frequency step. To eliminate the offsets, the one-way CFRs from both nodes are combined through element-wise multiplication. The operation cancels the random phase components across frequencies, providing phase-coherent measurements and enabling distance estimation through inverse Fourier transform analysis (or others). The detailed derivation of this method is presented in [1] and [2].

The used hardware inverts the reflector measurements [2], therefore they have to be inverted prior the usage. One can simply use the Python with NumPy library, that provides conjugate function

Two-way CFR drawbacks

The multiplication of two one-way CFRs in the frequency domain corresponds to the convolution of their respective one-way CIRs in the time domain, which introduces artefact peaks. As a result, the two-way CIR exhibits apparent multipath components that make the LoS peak estimation challenging.

As presented with the picture below, the one-way CIR peaks from 3.7 m (true LoS component) and peak at 8.4 m (multipath reflection) created an artefact at 5.9 m in the two-way CIR. Thus the LoS is no longer the highest peak in the two-way CIR.

(FIGURE IS DISPLAYED AS PREVIEW OF THE DATASET)

The problem can be addressed by converting the TWCFR back into the OWCFR through channel reconstruction. Details about channel reconstruction process can be found in [3].

References

[1] G. Morano, K. Guan, A. Hrovat, and T. Javornik, *"Phase-Based Distance Estimation Integrated With IEEE 802.15.4 TSCH Communication"*, IEEE Internet of Things Journal, vol. 11, no. 7, pp. 11 460–11 470, Apr. 2024, issn: 2327-4662. doi: 10.1109/JIOT.2023.3330933.

[2] G. Morano, A. Simončič, T. Kocevska, T. Javornik, and A. Hrovat, *"Distance- and Angle-Based Hybrid Localization Integrated in the IEEE 802.15.4 TSCH Communication Protocol"*, Sensors, vol. 24, no. 12, p. 3925, Jan. 2024, issn: 1424-8220. doi: 10.3390/s24123925.

[3] G. Morano, T. Javornik, A. Simončič, A. Švigelj and A. Hrovat, *"Interference Mitigation in One-Way Channel Reconstruction for Robust Phase-Based Ranging"*, IEEE Access, Early Access, 2025, issn: 2169-3536. doi: 10.1109/ACCESS.2025.3649293