Monitoring Your Robot’s Wi-Fi Connection

Started in the 2023-2024 season, Tech Tips are segments released in the FIRST Tech Challenge Team E-mail Blast. Sometimes the Tech Tips are included in whole in the email blast, but sometimes there is more content than is reasonable in the email blast so partial content is included in the blast with the rest of the content here.

One common question we get is how to determine the Wi-Fi signal strength between the Driver Station and the Robot. Because there are a lot of factors that can play into your robot performance on the field, it’s important to know that your robot is getting the strongest Wi-Fi signal possible. The FTC Driver Station App reports three related pieces of information: Signal Strength, Link Speed, and the Signal Bar Graph.

Wi-Fi Signal Strength

Wi-Fi signal strength is measured in dBm (decibel-milliWatts) and is always negative. Typically the range for Wi-Fi is -30dBm to -90dBm; -30dBm is the maximum possible signal strength, and -90dBm is considered too weak of a signal to support Wi-Fi communications. dBm is measured on a logarithmic scale, so comparing dBm values differs from what you would normally consider on a linear scale. Increments of 3dBm indicate doubling/halving signal strength, and increments of 10dBm indicate 10x change in signal strength. For example, a signal strength of -40dBm is twice as strong as a signal strength of -43dBm, and a signal strength of -67dBm is one-tenth the signal strength of -57dBm. Signal strengths around -40dBm are Amazing, but rarely achievable in match play. A strength of -60dBm is still considered Very Good. -67dBm is considered Good. -70dBm is considered Okay. Anything less than -80dBm is considered unusable.

To see the Signal Strength between your Driver Station and the Robot Controller, first ensure that the robot is connected within the Driver Station App. At the top of the Driver Station App is a readout that shows the connected network name, and under it are Ping times and the Channel number of the Wi-Fi connection. Tap that area of the app, and the display will change and instead show the signal strength under the connected network name. Tap again to swap back.

Knowing your Signal Strength can help you understand how metal on your robot might be affecting your Wi-Fi connection, understand how your robot’s signal may vary depending on the orientation of the robot to the Driver Station, and how external factors (like placing your Driver Station on a metal music stand) can degrade the signal strength. Remember that ensuring a strong Wi-Fi signal strength is just one factor in maintaining optimal robot health.

Link Speed and the Signal Bar Graph

Link Speed is the speed (in Mbps) at which a Wi-Fi connection can communicate, and it generally ranges from a snail-like 1Mbps through about 100Mbps, which is the maximum practical rate for an 802.11ac/b/g/n/w Wi-Fi network (when using a Control Hub and Driver Hub). It’s important to understand the difference between Signal Strength and Link Speed. Signal Strength is often used to describe how “loud” a connection is, and Link Speed is used to describe how “fast” a connection can communicate. Link Speed can also be a secondary indicator of how much “noise” or “interference” a communication channel has; the “louder” the signal and “clearer” the communication channel, the “faster” the devices can generally communicate. Wi-Fi link speeds are automatically renegotiated periodically and they’re most often affected by noise, channel congestion (too much happening at once), and distance.

A Wi-Fi channel is like a room where only one person/device is ever allowed to talk at a time. If each person/device can talk in short, fast bursts (fast link speed) then everyone has an opportunity to speak within a short duration of when they want to speak. However, if one or more devices are speaking slowly (slow link speed) then all devices have to wait for them to finish before they can talk REGARDLESS of their own link speeds - this invariably introduces communications lag. This example highlights the fact that even though it’s important for a given device to have a strong signal and a fast link speed, it’s important for ALL devices communicating on a channel to have a strong signal and fast link speed. As the idiom goes, it only takes one rotten apple to spoil the whole bunch.

Finally the Signal “Bar” Graph attempts to combine the Signal Strength and Link Speed into an easy to understand graphical meter. The more bars, the stronger and clearer the signal and the faster the communications.

Note

The Driver Hub has a known bug where the Link Speed indicator only shows the initially negotiated link speed, and the link speed indicated does not change when the Wi-Fi device renegotiates different link speeds. This means the Link Speed indicator and the Bar graph are not represented accurately on Driver Hubs, but are represented accurately on smartphones.

Got any questions about monitoring your robot’s Wi-Fi? Come start or join the conversation on the FTC Community Forums!