This article explains what Minimum RSSI is and how to configure it in the UniFi Network application. We only recommend using this if you are familiar with basic RF theory as misconfiguration may result in performance degradation of your network.
How Minimum RSSI works
Received Signal Strength Indication (RSSI) is a value indicating the perceived signal level of a wireless client from the AP's perspective. The Minimum RSSI value is set individually on each AP and indicates the minimum signal level required for a client to remain connected.
The main purpose of this is to assist with a client's roaming between two nearby APs. It prevents a device from getting "stuck" connected to the initial AP at a weaker signal strength as opposed to roaming to a new AP that may be more optimal. Once the signal drops below the Minimum RSSI value set, the initial AP will kick the client so that it can reconnect to the new AP.
Once an AP kicks a client (by sending a de-authentication packet), it is up to the client to find a better AP to connect to. It may connect back to the same AP, especially if it is the only one within range. Since the signal strength still does not meet the Minimum RSSI, it will again be booted. Improper tuning can thus result in network instability. For this reason, it is important to realize that there is no one size fits all and you should carefully test your configuration to avoid introducing connectivity problems.
How to determine and configure Minimum RSSI
Minimum RSSI can be enabled within the UniFi Network Application by selecting an AP in UniFi Devices and then navigating to Settings in the side panel of the selected device. Once enabled, this can be manually set for your 2G and 5G radios independently.
You can view the Signal Strength for your current wireless clients by clicking on a device in the Client Devices tab. The signal is measured in units of dbm (decibels per milliwatt). You will notice that this is a negative number because the power is less than 1 mW:
- dbm = 10 log P1/1mW
- 0 dBm = 1 mW
- -10 dBm = 0.1 mW
- -20 dBm = 0.01 mW, and so forth
A value close to 0 indicates high signal quality, whereas a larger negative value indicates poor signal quality. Remember, you need to granularly select the appropriate value for each AP and avoid using a single value everywhere.
There are many factors that can affect the client's RSSI at the AP side including distance, building materials, objects, interference, etc. As much as we would love to give a recommendation, it really isn’t this simple. It’s safe to say -80dBm would be a starting point for standard home or office configurations, but there are too many environmental variables so you should have caution at all times.
The best method to determine appropriate Minimum RSSI values is to perform a site survey. This can be done by testing the signal strength of various wireless clients at different distances. Each device will have different antenna configurations and will thus perform differently in the same geographic location. You want to connect to a WiFi, make it specific to that AP (an override on that WiFi), and then roam to what you would consider the outer edge of the desired coverage area. Mark the client's RSSI, and then take a couple more points. The more data you gather, the better idea you’ll get for the minimum RSSI value to use.