PLUTO+ Localization - Final Project for Modern Communication System (ECSE-6560)

Author: Joseph Pizzimenti

Overview

This project implements an indoor wireless localization system inspired by the "SpotFi" research paper. It utilizes a PLUTO+ Software Defined Radio (SDR) with two receive antennas to estimate the Angle of Arrival (AoA) of an OFDM signal.

Unlike the Wi-Fi NIC-based approach of the SpotFi research paper, this project uses raw I/Q samples processed in MATLAB to perform direction finding on a single SDR with 2 receive antennas. It can handle multipath interference and is somewhat resiliant at further distances (as long as calibration is successful).

Hardware Requirements

• Receiver: 1x PLUTO+ SDR (with custom AD9361 firmware enabled for 2RX/2TX MIMO support, instructions below for use with custom firmware).
• Transmitter: 1x Analog Devices ADALM-PLUTO (Standard firmware is fine).
• Antennas: 2x matching antennas with their centers spaced about 9 cm apart (will vary depending on carrier frequency).
• Computer: Windows PC (for MATLAB Receiver) and Windows/Linux PC (for GNU Radio Transmitter).

Software Dependencies

This project relies on a specific stack of drivers, toolboxes, and external libraries. All components below are required.

1. System-Level Drivers (Windows)

MATLAB requires these underlying libraries to communicate with the SDR hardware via USB/Network.

• libiio (tested with v0.26): Download
• libad9361-iio (tested with v0.3): Download

Note: You must install the Development Headers (.h) and Libraries (.dll). If the installer does not add them to your system PATH automatically, you must add them manually or reference them in MATLAB (see Installation section).

2. MATLAB (Receiver Pipeline) (tested with MATLAB 2025b) - for Windows PC

• Required Add-Ons (Install via Home -> Add-Ons):
• Analog Devices, Inc. Transceiver Toolbox - (note: this is NOT the standard ADALM-PLUTO toolbox, it requires the following dependencies)
  • Simulink
  • Communications Toolbox
  • DSP System Toolbox
  • HDL Coder
  • Signal Processing Toolbox
  • Simulink Coder
• Phased Array System Toolbox

3. GNU Radio (Transmitter Pipeline) (tested with v3.10.12) - for other PC

• gr-iio (Standard iio blocks for PlutoSDR Sink).
• If using windows, other drivers may be required for SDR communication

Installation & Setup Guide

Step 1: Install System Drivers (Windows)

1. Download and run the installers for libiio and libad9361-iio.
2. Locate Headers: Locate where the .h files were installed.

• Location found on MY laptop: C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\
• Alternative: C:\Program Files\IIO\include
• If missing: You may need to manually download iio.h and ad9361.h from their respective GitHub repositories and place them in a known folder for MATLAB to reference.

Step 2: Configure MATLAB

The Analog Devices Transceiver Toolbox likely WILL NOT automatically find the required headers to run. You MUST point MATLAB to them at the top of your script:

% Add path to libiio/libad9361 headers
addpath('C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\');
% Add path to system DLLs (if not in PATH)
addpath('C:\Windows\System32');

Step 3: Flash PLUTO+ Firmware

The PLUTO+ comes with standard AD9363 firmware (1RX/1TX). You must unlock the AD9361 mode for MIMO support (2RX/2TX).

1. Download the PLUTO+ firmware from the plutoplus repo: Download plutosdr-fw.zip
2. Physically open up the PLUTO+ and move the DIP switches in the bottom right to be in the stock firmware position.
3. Plug in the PLUTO+ and drop the pluto.frm in the PLUTO device found in file explorer.
4. Press the eject button in the file explorer, and wait for the device to reappear.
5. SSH into the PLUTO+ (ssh [email protected], password: analog).
6. Run the following commands IN THIS EXACT ORDER!:

fw_setenv attr_name compatible
fw_setenv attr_val ad9361
fw_setenv mode 2r2t
pluto_reboot reset

Note: If these commands aren't run in this exact order or if at any point the device is unplugged, power flush the device and SSH back into the PLUTO+ to repeat these steps.

Usage

1. Start the Transmitter (GNU Radio with ADALM-PLUTO)

1. Open OFDMSignalGen.grc in GNU Radio Companion.
2. Ensure the PlutoSDR Sink is configured for:

• URI: ip:192.168.2.1 (or USB context defined by you in the firmware)
• LO Frequency: 1.56 GHz (or whatever frequency you choose)
• Sample Rate: 20 MSPS

3. Load the custom_ofdm_signal.bin file (generated by the MATLAB helper script to ensure known seed synchronization).
4. Run the flowgraph.

2. Run the Receiver (MATLAB with PLUTO+)

1. Connect the PLUTO+ to the Windows PC via USB (Ethernet may be more reliable, but USB was used for this experiment.
2. Open AngleTracking.m in the Receiver folder.
3. One-Time Calibration:

• Place the transmitter at the reference point you want to be 0 degrees from the receiver.
• Run Calibration.m to generate phase_cal.mat.

4. Start Localization:

• Run AngleTracking.m.
• The heatmap will display the estimated Angle of Arrival (AoA).

Files in Repository (by folder)

Receiver Folder

• AngleTracking.m: Main real-time localization script to find AoA
• Calibration.m: NECESSARY calibration script to calculate phase offsets between 2 RX ports. AngleTracking.m REQUIRES the result of this script to be present to run.

Simulation Folder

• Sim1_AoA_Test.m: Simulated Angle-of-Arrival testing with variable SNR
• Sim2_ToF_Test.m: Simulated Time-of-Flight testing with variable SNR

Testing Folder

• CSITest.m: Debug tool to visualize raw CSI magnitude and phase.
• CustomFirmwareTest2RX.m: A quick script written to test if the custom firmware functionality of the PLUTO+ (with 2*RX) is working.
• HighResNoiseFloorSweep.m: A script used to find the least noisy frequencies of the surrounding RF environment.

Transmitter Folder

• OFDMSignalGen.grc: GNU Radio flowgraph for the constant OFDM transmitter
• custom_ofdm_signal.bin: Pre-generated binary file (generated from generateOFDM.m) for transmission.
• generateOFDM.m: Generates the I/Q binary file with a fixed RNG seed.

Troubleshooting

"Expected ChannelMapping to be a scalar":

• Cause: MATLAB sees the device as a standard Pluto (1RX).
• Fix: Ensure you are connecting via ip:192.168.2.1 and that you have run the SSH unlock commands on the PLUTO+.

"Could not find file ad9361-wrapper.h":

• Cause: loadlibrary cannot find the header files.
• Fix: Verify the addpath command in the MATLAB script points to the folder containing ad9361.h and libiio.h.

MATLAB refuses to generate an sdrrx component for your PLUTO+

• Cause: The firmware was likely flashed incorrectly for the PLUTO+
• Fix: Run fw_printenv mode when SSHing into the SDR. It should say "mode=2r2t". Additionally, running fw_printenv attr_val should say "attr_val=ad9361". If they don't say this, repeat the firmware installation process carefully.

References

• SpotFi: Decimeter Level Localization Using WiFi
• Analog Devices Transceiver Toolbox
• A Hybrid AOA and TDOA-Based Localization Method Using Only Two Stations
• Antenna-Theory.com - Steering Vector