Wireless Path Loss - 4 Factors to Consider for Transmission Range
When designing any system, engineers and system architects usually want to know how well the various components of the system will perform. In a microprocessor, logic or other digital system these questions usually are answered in terms of clock speeds, instructions per second or data throughput. With wireless communication, the most common performance questions involve range.
Unlike digital systems, trying to quantify the range performance of radio frequency (RF) communication systems can be difficult due to the large role the environment has on radio frequency signals. Buildings, trees, obstructions and lack of antenna height can all contribute to a decrease in signal strength at the receiving end. In order to estimate the communication distance (transmission range) for a system, four factors must be considered:
Transmit power. The power that is broadcast by the transmitter. This is usually measured in watts or milliwatts.
Receive sensitivity. A measure of the minimum signal strength that a receiver can discern.
Antenna gain. The amount of signal gain provided by the antennas.
Path loss. The signal decrease that occurs as the radio waves travel through the air or through obstacles.
Path loss or attenuation of RF signals occurs naturally with distance. Obstacles between the transmitter and receiver also attenuate signals. The amount of attenuation varies with the frequency of the RF signal and the obstructing materials’ type and density.
Generally speaking, the lower the frequency of transmission, the better the signal will travel through the air and through objects. If two radio systems had identical transmit power and receive sensitivity, but one system was at 900 MHz and the other at 2.4 GHz, then the 900 MHz radio would perform better because it has less path loss than a 2.4 GHz system. These parameters can be used to estimate the distance a system can communicate.
Knowing how strong the communication link is or just how close a system is to failure can be important in some situations. Link margin is a parameter that is used to measure how close the link is to failing. Link margin is the difference between the system gains and the system losses. Successful communication takes place when the link margin is greater than zero.
Link Margin = Transmit Power – Receiver Sensitivity + Antenna Gain – Path Loss
Comparing an RF communications system to human voice communication can help illustrate these principles. Transmit power represents the volume of the person speaking. Receive sensitivity represents the minimum volume required by the listener to discern the message. Antenna gain is equivalent to the use of a megaphone, and path loss is the attenuation that occurs as the voice travels over a distance or through obstacles.
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