Inside Wireless: Noise Floor
Channel: RF elements s.r.o.
Date: 2019-09-30

In this Inside Wireless episode we talk about Noise Floor (NF). Noise is the signal a RF radio receives, but doesn’t understand. Noise floor tells us what is the strength of the noise in a given bandwidth and determines the Signal to Noise Ratio (SNR). SNR tells us how much stronger the useful signal is compared to the noise.

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There are two categories the noise sources can be divided into: 

1. Noise created by the radio itself due to the physics of the parts it is built from. There are many types of noise devices produce, such as thermal noise, flicker noise, shot noise, or burst noise. Sum of all these types of noise create the noise floor of a radio. In lab conditions, the noise floor is the jittery line at the bottom of the spectrum the radio works with. The useful signal is recognized by clearly higher level above the noise floor. 

2. Man-made noise. The devices located near your radio produce signals seen as noise by your radio and are received through the antenna. The man-made interference is usually much stronger than the noise created by the radio itself and is the biggest problem of fixed wireless networks. 

RF radio sees the signal quality primarily through the SNR given the strength of signal is between the noise floor and the maximum power. Interference decreases the SNR your radio is working with. Lower SNR means lower MCS rates seen as decreased overall throughput at the user end.

A frequent misunderstanding among WISPs is that the solution to interference is using an antenna with higher gain. Although higher gain antenna will increase the received signal strength, it can be harmful to the SNR at the same time. The sidelobes of an antenna decide how much added noise radio sees.

The traditional sector patch array antennas have huge sidelobes, so the added signal level due to higher gain is drowned in the added noise caused by the side lobes. 

The best way to avoid increasing noise floor your radio is working with, is to avoid collecting the surrounding interference. Using an antenna without sidelobes such as horn, you push the noise floor down, improving your SNR. Despite the horn might have smaller gain, the lack of sidelobes improves the SNR so eventually the link performs better than with higher gain antenna.

If the interference in the area is heavy, the improvement when using horns can be marginal, so it’s good to keep in mind that every link should be treated as a separate case. 

0:00 Intro
0:12 What is Noise Floor & SNR
0:25 Types of noise
1:20 Interference
1:29 Noise solution

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