distance.cpp File Reference

Implementation of RSSI averaging and distance estimation utilities. More...

#include <math.h>
#include "distance.h"

Functions
void	updateRssiAvg (int rssi)
	Updates the running average of the received signal strength indicator (RSSI).
float	estimateDistanceMeters (float rssi, float txPower, float n)
	Estimates the distance (in meters) from RSSI using the log-distance path loss model.

Variables
bool	hasAvg = false
	Flag to indicate whether the RSSI average has been initialized.
float	rssiAvg = 0.0f
	Stores the current smoothed RSSI average.
float	txPower = -52.0f
	Transmitter power at 1 meter (in dBm).
float	nFactor = 2.5f
	Path-loss exponent (environmental factor).

Detailed Description

Implementation of RSSI averaging and distance estimation utilities.

This file provides definitions for global parameters and functions that help smooth RSSI (Received Signal Strength Indicator) values and estimate distance based on the log-distance path loss model.

The algorithm uses exponential smoothing for RSSI and applies the following formula for distance estimation:

where:

• is the estimated distance in meters,
• is the measured signal strength in dBm,
• is the RSSI at 1 meter reference distance,
• is the path-loss exponent.

Function Documentation

estimateDistanceMeters()

float estimateDistanceMeters	(	float	rssi,
		float	txPower,
		float	n )

Estimates the distance (in meters) from RSSI using the log-distance path loss model.

Estimate distance from RSSI using the log-distance path loss model.

Computes an approximate distance to the transmitter based on the difference between the measured RSSI and the known transmit power at 1 meter.

Parameters

[in]	rssi	Received signal strength indicator (in dBm).
[in]	txPower	Transmitter power at 1 meter (in dBm).
[in]	n	Path-loss exponent (environmental factor).

Returns

Estimated distance in meters.

updateRssiAvg()

void updateRssiAvg

(

int

rssi

)

Updates the running average of the received signal strength indicator (RSSI).

Update the exponential moving average of the RSSI.

Applies exponential smoothing with a fixed factor . This reduces noise in instantaneous RSSI readings.

Parameters

[in]

rssi

Current measured RSSI value (in dBm).

Variable Documentation

hasAvg

bool hasAvg = false

Flag to indicate whether the RSSI average has been initialized.

Flag indicating whether an RSSI average has been initialized.

nFactor

float nFactor = 2.5f

Path-loss exponent (environmental factor).

Typical values:

• ~2.0 in free space
• 2.7–4.0 in indoor/obstructed environments

Should be tuned experimentally for best accuracy.

rssiAvg

float rssiAvg = 0.0f

Stores the current smoothed RSSI average.

Exponential moving average of the RSSI value.

txPower

float txPower = -52.0f

Transmitter power at 1 meter (in dBm).

Reference transmit power (measured RSSI at 1 meter distance).

This value should be tuned based on calibration measurements.