OHPLM Okumura–Hata path-loss model

The Okumura-Hata path-loss model, also known as OHPLM, is a widely used empirical model for estimating the propagation loss of radio waves in urban and suburban environments. It was developed by Yoshihiko Okumura and obtained further refinements by the Hata and Cost 231 models. The OHPLM is often employed in the design and planning of wireless communication systems, including cellular networks, to predict the signal strength at various distances from a transmitter.

The path loss refers to the reduction in signal power as it propagates through the wireless medium due to factors such as distance, obstacles, and environmental conditions. Understanding and accurately estimating path loss are crucial for determining the coverage area, interference levels, and overall performance of wireless systems.

The OHPLM takes into account several parameters to calculate the path loss. These parameters include the frequency of operation, distance between the transmitter and receiver, antenna heights, and environment-specific factors such as terrain, building density, and frequency-dependent losses. By considering these variables, the model aims to provide a reasonable approximation of the path loss experienced in typical urban and suburban areas.

The OHPLM can be mathematically expressed as:

L = L₀ + 10n log₁₀(d) + C

Where:

• L is the path loss in decibels (dB)
• L₀ is the reference path loss at a reference distance
• n is the path loss exponent
• d is the distance between the transmitter and receiver
• C is an adjustment factor

The reference path loss L₀ is the path loss at a reference distance, usually taken as one kilometer. It represents the path loss at a close distance, where the effects of propagation are minimal. The reference path loss is typically obtained through measurements or simulations in the specific environment of interest.

The path loss exponent, denoted by n, characterizes the rate at which the signal power decays with distance. It depends on the frequency of operation and the environment under consideration. The path loss exponent is usually determined through extensive measurements and statistical analysis in various locations within the target area. It can vary depending on factors such as terrain type, building density, and clutter.

The adjustment factor, C, accounts for additional losses or gains that may not be captured by the distance and path loss exponent alone. It includes factors such as antenna heights, frequency-dependent losses, and other environmental effects specific to the propagation scenario. The adjustment factor is often determined through empirical fitting of measured data or by using pre-defined values based on previous studies.

The OHPLM has different variations depending on the frequency range of operation. The original model proposed by Okumura considered frequencies below 900 MHz. The Hata model extended the range up to 1500 MHz, while the Cost 231 model further expanded it to include frequencies up to 2000 MHz. These variations incorporate adjustments to the path loss exponent, reference path loss, and adjustment factor to accommodate the characteristics of different frequency bands.

In the OHPLM, the environment-specific factors are usually accounted for by using correction terms. These correction terms address the effects of urban or suburban environments, including the presence of buildings, trees, and other obstacles. They are applied to the reference path loss and vary depending on the specific conditions of the propagation scenario.

It's important to note that the OHPLM provides an average estimation of path loss and assumes a homogeneous environment. It does not capture the spatial variation or specific effects caused by irregular terrain, shadowing, diffraction, or multipath propagation. These factors can significantly influence the actual signal strength in real-world scenarios.

To validate the accuracy of the OHPLM, extensive field measurements and comparisons with actual propagation data are typically conducted. By comparing the predicted path loss from the model with the measured values, adjustments and refinements can be made to improve its accuracy in specific environments.

In conclusion, the Okumura-Hata path-loss model (OHPLM) is a widely used empirical model for estimating the path loss in urban and suburban environments. It considers parameters such as frequency, distance, antenna heights, and environment-specific factors to approximate the signal attenuation between a transmitter and receiver. While the model provides a useful tool for wireless system design and planning, it's important to validate its accuracy through measurements and consider additional factors that may influence the actual propagation conditions.