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Chapter 5. Radio Wave > Noise Level

5.5. Noise Level

The performance of an indoor radio frequency transmission system is determined by the received signal strength and the noise floor. To compute equivalent noise floor at the input of a receiver, it is necessary to know the gains or losses at different receiver stages and the receiver antenna ambient noise temperature.

5.5.1. Antenna Ambient Noise Temperature

It is critical to know the noise level at the very front end of a receiver because the signal-to-noise ratio determined there cannot be further improved by subsequent electronics. For wired communication systems, the minimum noise level is determined by the thermal temperature of electronic components at the very front end. Sometimes the noise level of the environment could be higher than the receiver front end thermal noise level. For the indoor radio frequency channel, the similar logic of noise level determination applies except the noise level of the environment is related to the antenna ambient noise temperature. The ambient noise temperature is measured for the radio environment where the antenna is located and can be higher or lower than the temperature of the antenna. This situation is similar to that of the environment noise level, which can be higher or lower than the wired communication system. The receiver front-end noise level for the indoor radio frequency environment is determined by the higher of either environment or antenna temperature. For the indoor radio frequency environment, this usually is the room temperature which is between 17 and 27°C, 63 and 75°F, or 290 and 300°K. The noise power at a particular temperature is expressed by


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