Rssi and snr relationship help

What is the relationship between data rate, SNR, and RSSI? - Airheads Community

What is RSSI and its relation to a Wi-Fi network you use it can be determined differently and is based on signal strength and SNR margin. RSSI can help determine when the level of radio energy in the channel is lower than a certain point. What is RSSI and its relation to a Wi-Fi network you use it can be determined differently and is based on signal strength and SNR margin. RSSI can help determine when the level of radio energy in the channel is lower than a certain point. SNR is not actually a ratio but the difference in decibels between the we will try to explain the approximate correlation between signal (RSSI).

As long as the chosen modulation is based on the received signal quality, RSSI should still be a good metric for performance, right? True, but there seems to be a lot more to the story! First of all, RSSI is pure receive-side metric, while modulation happens at the transmitting side. To use the RSSI at one side of a link as a metric for the throughput of that link, means assuming the Wi-Fi link is symmetrical.

Until we start using Wi-Fi access points as smartphones, this is not very likely. While current access points often have three antennas sending at the maximum allowed power, many mobile devices are limited to one antenna and limit their output strength on purpose to save battery energy.

Furthermore, just how and when to switch between different modulations varies between Wi-Fi chipsets. For example, if a transmitted packet is not acknowledged, some Wi-Fi devices immediately fall back to a lower modulation while others will try to retransmit at the same modulation and only fall back after some retries. All this makes the relationship between RSSI and link throughput a lot less predictable!

Wireless fundamentals: Signal-to-Noise Ratio (SNR) and wireless signal strength - Cisco Meraki

In such tests we measure the real application-layer throughput on a fixed set of locations within a house environment. Since we store both the actual throughput result and the RSSI value for each measurement, we can easily correlate the two. The picture below shows data from such a test. Multiple access points all with similar characteristics are plotted.

At first glance, there seems to be a clear correlation between RSSI and throughput: This is definitely true. However, does this also mean we can predict the throughput based on the RSSI? In other words, can we assess the actual performance of an access point based on the reported RSSI values, like many tools do? Unfortunately, this is not the case.

For example, Cisco recommends 25 dB for their wireless voice telephony systems. Also, a larger margin i. Keep in mind that the corresponding level of performance only occurs at the boundary of each access point.

Users associating with access points at closer range will have higher SNR and better performance. When measuring SNRs, use the same client radio and antenna as the users will have if possible. A variance in antenna gain between the survey equipment and user device, for example, will likely result in users having a different SNR and performance than what you measured during the survey.

Changes made in the facility, such as the addition of walls and movement of large boxes will affect SNR too. This can be done easily with commercially-available tools.

Received signal strength indication

For example, the figure below is a screenshot taken from AirMagnet Survey, with the green and yellow colors indicating acceptable signal coverage areas of an If you find that the SNR is below the minimum value in some areas, such as the gray-shaded areas in the figure, consider installing additional access points or moving existing ones better distribute the signals and fill in the holes.

Concluding thoughts The use of a particular SNR value as a requirement for signal coverage is certainly a good practice, and the rules of thumb given in this tutorial are a good starting point. Be sure, however, to perform testing in your own environment to determine acceptable range boundary definitions.