InMap-Pi - Indoors Signal Mapper (High precision measurement module for Raspberry Pi)

The project consists of a node application that communicates via Serial Port with a cell connectivity module (Quectel RM520N-GL) and allows extracting information regarding the cell signal quality through AT commands.

AT commands are wrapped around a very simple (async / promises interface) and results of the different commands are parsed into a JS object representations that aim to make the returned information more human-readable.

Then, the UI provided allows sending the measured data to a Backend server to link the measurements with a given measured Room.

Getting started

You may want to create an .env file if it does not exist already, set at least the following values depending on your SIM and deploying requirements

LOCAL_PORT="Your local port" # E.g., 3000 (where the browser page will be available)
SIM_PIN=1234 # The SIM PIN
BACKEND_SERVER="https://{yourServer}.../v1/API" # You may need to change the specific urls if the API changes a lot
FIXED_AUTH_TOKEN="YOUR TOKEN" 

• For execution: Run npm run prod for running the initialization of the 5G module through a sequence of AT commands and starting the web server locally.

• For development : Run npm run dev runs nodemon so that you can preview changes quickly.

Triggering Measurements

The application exposes a Web server that exposes REST endpoints to request the execution of various AT command sequences and obtain the results as JSON.

A simple web UI page has been created to interact with the Quectel module as a non-programmer user.

The GUI to trigger the measurements from the browser

Sample format of generated measurements

{
        "_id": "14b47432-b3a2-4224-99e1-2491562831fb",
        "roomId": "447df539-7f8b-470e-90ae-9377d282e12c",
        "timestamp": "2025-04-23T08:59:33.868Z",
        "position": {
            "x": 0,
            "y": 0,
            "z": 0
        },
        "version": 1,
        "measurementOwner": "ESOA",
        "measurementDevice": "RaspberryPi4B",
        "allMeasurements": {
            "signalStrength": {
                "rssi": 22,
                "rssiMeaning": "(-109 dBm to -53 dBm)",
                "channelBitErrorRate": 99,
                "channelBitErrorRateMeaning": "Not known or not detectable"
            },
            "qrsrp": [
                {
                    "prx": -108,
                    "drx": -121,
                    "rx2": "Invalid",
                    "rx3": "Invalid",
                    "radioAccessTech": "LTE"
                },
                {
                    "prx": -79,
                    "drx": -99,
                    "rx2": -105,
                    "rx3": -109,
                    "radioAccessTech": "NR5G"
                }
            ],
            "qrsrq": [
                {
                    "prx": -20,
                    "drx": -18,
                    "rx2": "Invalid",
                    "rx3": "Invalid",
                    "radioAccessTech": "LTE"
                },
                {
                    "prx": -10,
                    "drx": -14,
                    "rx2": -11,
                    "rx3": -11,
                    "radioAccessTech": "NR5G"
                }
            ],
            "sinr": [
                {
                    "prx": -5,
                    "drx": -3,
                    "rx2": "Invalid",
                    "rx3": "Invalid",
                    "radioAccessTech": "LTE"
                },
                {
                    "prx": 22,
                    "drx": 1,
                    "rx2": -1,
                    "rx3": -7,
                    "radioAccessTech": "NR5G"
                }
            ],
            "servingCell": {
                "state": "NOCONN",
                "stateExplanation": "UE is camping on a cell and has registered on the network and it is in idle mode",
                "mode": "EN-DC",
                "cells": [
                    {
                        "accessTechnology": "LTE",
                        "is_tdd": "\"FDD\"",
                        "mcc": "214",
                        "mnc": "07",
                        "cellId": "4472920",
                        "pcid": "149",
                        "earfcn": "2850",
                        "freq_band_ind": "7",
                        "ul_bandwidth": "5",
                        "dl_bandwidth": "5",
                        "tac": "6FC3",
                        "rsrp": -108,
                        "rsrq": -19,
                        "rssi": "-67",
                        "sinr": "8",
                        "sinr_computed": -4,
                        "cqi": 8,
                        "tx_power": "229",
                        "srxlev": "-"
                    },
                    {
                        "accessTechnology": "NR5G-NSA",
                        "mcc": "214",
                        "mnc": "07",
                        "pcid": "434",
                        "rsrp": -79,
                        "sinr": 22,
                        "rsrq": -10,
                        "arfcn": "636576",
                        "band": "78",
                        "nr_dl_bandwidth": "12",
                        "scs": "1"
                    }
                ]
            }
        },
        "measurementSession": "UNASSIGNED"
    }

Hardware employed

Raspberry PI 4B with Waveshare 5-inch Capacitive 5-Points Touch Display

Quectel RM520N-GL | Firmware Revision: RM520NGLAAR03A03M4G

Reference sheets 🗎

For installation of the components, I roughly relied on the Waveshare Wiki (RM520N-GL 5G HAT), although it is not very thorough. The organization of the page is quite horrible.

See RM520N-GL AT Commans Manual I added a copy of the manual to the repo for completeness. No copyright infringement intended though.

Limitations | Future work

• Only a subset of the AT commands are supported. Trying to use the sendATCommandAsync(<command>) with arbitrary commands may result on wrong parsing or the program hanging infinitely ( this is the case of advanced commands to perform HTTP requests). Problems have been identified for: AT+QHTTPCFG="contextid",1 that requires additional arguments passed in several lines.
• No support for parsing neighbouring cells (i.e. missing parsing for the command AT+QENG="neighbourcell").

Tech Stack

Troubleshooting

• The Raspberry PI has been set up to init without graphical interface, run startx in the command prompt if you need to use the GUI in the device.

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InMap - Indoors Signal Mapper Suite

🔗 Android App	🔗 Web visualizer	🔗 Precise measurement module for Raspberry-Pi