In wireless communication, the path loss is proportional to the square of the operating carrier frequency. As a result, the higher the frequency, the greater the path loss. Although path loss is affected by several parameters, including fading, shadowing, angle of arrival (AOA), and angle of departure (AOD). In comparison to lower frequencies, when the frequency is extremely high, it is easily absorbed by atmospheric gases, vapor, and rain. In the case of higher frequencies, however, the penetration loss is also greater. Path loss is proportional to the square of the carrier frequency according to the Friis free space path loss model. Path loss parameters are often divided into two categories: 1. Large Scale Path loss; 2. Small Scale Path loss. Large-scale path losses are basically due to the distance between transmitter and receiver and shadowing. Small-scale path losses are due to multipath fading, angle of arrival, etc.
Read More: about Friis Transmission pathloss formula
Try Online Simulator for Free Space Path Loss (FSPL)
The close-in (CI) path loss model is appropriate for current wireless systems operating at sub-6 GHz or higher, including millimeter-wave 5G.
.... (3)FSPL (d0) denotes free space path loss at a reference distance (typically 1 meter). The letter 'n' stands for path loss exponent. 'd' represents the total distance. The shadowing factor is denoted by χσ.
This allows us to calculate path loss for current bands like UWB with high precision. In 28 GHz transmission, for example, path loss at the first meter is roughly 32 dB. From there, path loss grows based on the environment's path loss exponent value.
Path loss increases as distance grows because the signal attenuates in the atmosphere. At equal distances, path loss is higher at higher frequencies than at lower frequencies. Similarly, path loss for LOS (Line of Sight) and NLOS (Non-Line of Sight) differs, as NLOS paths typically involve more reflections and longer travel distances. [Read More about LOS and NLOS Paths]
3.2. Small Scale Pathloss:
Factors like fading and angles of arrival (AOA/AOD) contribute to small-scale losses. In built-up areas, signals reflect off walls and foliage, traveling via multiple NLOS paths. This creates Multipath Components (MPCs) at the receiver. Fading occurs due to these MPCs interfering with each other. Common types include slow/fast fading and frequency selective fading. Fast fading occurs when the channel changes rapidly, while frequency selective fading varies across the frequency band.
4. Path loss exponent 'n':
The path loss exponent 'n' is a significant parameter. In an NLOS scenario, 'n' is typically higher than in a LOS scenario. It is also affected by frequency and antenna heights. It is found that with directional beamforming, the path loss exponent 'n' decreases. For example, the path loss exponent for 28 GHz directional communication is roughly 2.5, whereas for omnidirectional transmission it can reach 5 to 6.
However, we use the close-in path loss model for sub-6 GHz, SHF, and EHF transmissions.
Free Space Path Loss (FSPL) Calculator
Compute FSPL in dB, linear scale, and wavelength with multiple units and optional received power.
Inputs
Results
FSPL(dB): --
FSPL(linear): --
Wavelength λ: -- meters
Received Power Pr: -- dBm
Example Calculation
f = 3500 MHz, d = 1 km
FSPL(dB) = 20 log₁₀(1) + 20 log₁₀(3500) + 32.44
= 0 + 70.88 + 32.44
= 103.32 dB
Also read about
[1] Difference between AWGN and Rayleigh Fading
Effect of Rayleigh Fading
In wireless communication systems, digital information is transmitted by modulating a high-frequency carrier using techniques such as Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), or Phase Shift Keying (PSK). During propagation, the transmitted signal reaches the receiver through multiple paths created by reflections, scattering, and diffraction from buildings, vehicles, trees, and other surrounding objects. The received signal is therefore modeled as:
Here, h(t) denotes the Rayleigh fading channel, which represents the combined effect of multipath propagation, while w(t) represents Additive White Gaussian Noise (AWGN). In environments where no dominant line-of-sight (LOS) path exists, the multiple reflected signal components arrive at the receiver with different amplitudes, phases, and propagation delays. Depending on their relative phases, these components may combine constructively or destructively, producing rapid fluctuations in the received signal envelope known as deep fades.
Rayleigh fading significantly degrades the performance of ASK, FSK, and PSK modulation schemes by reducing the instantaneous received signal power. Consequently, the receiver experiences a lower Signal-to-Noise Ratio (SNR), which increases the Bit Error Rate (BER). Compared with an AWGN channel, Rayleigh fading produces a much slower improvement in BER as SNR increases because random multipath fading remains the dominant source of signal degradation. Among these modulation schemes, coherent PSK generally exhibits better robustness to fading than ASK, although all modulation techniques experience performance loss in severe multipath environments.
Modern wireless systems mitigate the effects of Rayleigh fading through channel equalization, diversity combining, MIMO, OFDM, adaptive modulation, and channel coding. These techniques exploit multipath diversity, compensate for channel distortions, and improve communication reliability in mobile, urban, and indoor wireless environments.