Planning Wi-Fi Channels for Large Events

Note

If you suspect Wi-Fi interference is the underlying problem, first read Troubleshooting Wireless Issues at an Event to diagnose the issue before redistributing channels.

Accommodating a Large Number of Robots at an Event

The wireless Control System is a point-to-point system. This means that each Driver Station-robot pair establishes its own Wi-Fi network at an event. If there are a large number of robots in a venue, then there will be a large number of wireless networks operating in the venue. If there are a large number of wireless networks operating in a small area, then there could be interference between the networks.

At smaller events with lower numbers (fewer than 30 or 40) of robots, the likelihood of significant interference caused by Robot-Driver Station activity is small. If there is not any other source of interference (such as Bluetooth devices operating on the field or wireless audio/video systems broadcasting on the same frequency) the FIRST Tech Challenge Control System should be able to operate properly.

At larger events (more than 30 or 40 robots) some steps might need to be taken before the event and during the event to help keep things running smoothly.

Wi-Fi Event Planning Guide

FIRST Tech Challenge has published a Wi-Fi Event Planning Guide that contains detailed steps a technical volunteer can take to help keep the wireless environment operating smoothly at larger events. Check the FIRST Tech Challenge community and resource library for the current version of this guide.

Distributing Robots Across Multiple Channels

Wi-Fi Channel Overlap

If an event will have a large number of robots (more than 40) in a small area, you should consider distributing the robots across multiple channels. Ideally, the lower the number of robots there are per channel, the less traffic and interference there will be per channel. Note that 2.4 GHz Wi-Fi channels that are less than 5 channel widths apart overlap.

Ideally, for 2.4 GHz Wi-Fi connections, you should distribute your robots on channels that are at least 5 channel widths apart. For example, if you were to configure one group of robots to channel 1 and a second group to channel 5, the two groups of robots would overlap slightly since the second channel is only 4 channel widths away from the first channel. If the second group of robots were moved from channel 5 to channel 6, then the two groups would no longer overlap since they are 5 channel widths apart.

Sometimes it might not be possible to space your robots 5 channel widths or greater apart. For example, one portion of the spectrum might be very noisy, and the robots are unable to operate on channels in or near that portion of the spectrum. In this case, it still might be beneficial to place the robots in groups on separate, overlapping channels. Even though the channels overlap slightly, placing the robots onto these channels might produce lower ping times and more responsive robots when compared to keeping all the robots on the same channel.

Factors to Consider when Selecting Wi-Fi Channels

If you would like to configure your robots to operate on more than one channel, here are some factors to consider when doing your planning.

  • How many robots will be present? The data rates for the control streams of the robot are low. If the wireless environment at your venue is clean, then a single channel should be able to support a pretty large number of robots. In testing, 46 pairs of Android devices ran reliably and responsively in a very tight area (approximately 14 feet by 14 feet).

    If your event will have a modest number of robots (less than 40), and if your wireless environment is clean, then you probably do not need to worry about moving robots around to different channels.

    If you do have a large group of robots, then you should consider dividing them up so you have a maximum of 35 to 40 robots per channel if possible. For example, if you have 70 robots, you can divide them into two groups of 35. You can also break up a large number of robots into even smaller groups and then place them onto multiple, overlapping channels if needed.

  • Are the target channels clear? Before you move your robots to a specific channel, you should do some tests on the channel to verify that it is clear.

    • Use Wi-Fi Analyzer or a similar tool. You can use a tool like Wi-Fi Analyzer to see how many access points are present on a channel. Remember, Wi-Fi Analyzer only shows you the visible (non-hidden) wireless networks. Also, Wi-Fi Analyzer does not show you how busy a channel is, it only shows you what visible Wi-Fi networks are on a channel.

    • Use a pair of Android devices to monitor ping times. If a target channel looks relatively clean, you should use a pair of Android devices running the FTC Driver Station and FTC Robot Controller apps to monitor the ping times on the target channel. You will need a pair of Android devices that support channel changing (such as approved FTC phones). Switch to the target channel and test to make sure you can select and run an OpMode (like the NullOp sample OpMode). If the average ping times for the test Android devices are low (less than 5 msec) then the channel is clear. If the average ping times are high (more than 50 msec) then there might be some type of interference on the channel.

    • If available, use a more sophisticated tool to monitor the target channels. If you have access to a more sophisticated tool like an Aircheck meter, you can use it to sweep a target channel. Use the tool to check for visible and hidden Wi-Fi networks, and to check how much Wi-Fi and non-Wi-Fi traffic is present on the channel. If the activity level is low on a target channel, then it should be safe to place your robots on the channel.

  • What type of Android devices will the teams be using? FTC-approved smartphones support channel changing using the FTC Robot Controller app. Approved Motorola smartphone models have included:

    • Motorola Moto G4 Play (4th Generation)

    • Motorola Moto G5

    • Motorola Moto G5 Plus

    • Motorola Moto E4 (USA versions only, includes SKUs XT1765, XT1765PP, XT1766, and XT1767)

    • Motorola Moto E5 (XT1920)

    • Motorola Moto E5 Play (XT1921)

Important

Approved hardware changes over time. For the current list of allowed phones and other hardware and software, teams should always refer to the current season’s FIRST Tech Challenge Competition Manual and its updates, rather than relying on the list above.

UnPairing Then Re-Pairing the Driver Station to the Robot Controller

After you have changed the channel on your Robot Controller Android device, you might have to unpair your Driver Station from the Robot Controller, and then re-pair the Driver Station back to the Robot Controller.

To unpair the Driver Station from the Robot Controller, launch the Settings menu from the Driver Station app and select the Pair with Robot Controller item.

Driver Station Settings menu with Pair with Robot Controller listed under Wifi Direct Configuration.

Select Pair with Robot Controller.

From the Pair with Controller screen, select None to unpair your phone.

Pair with Controller screen with the None option selected to stop pairing with any device.

Select “None” to unpair the device, then use the back arrow to return to the main screen.

Use the back arrow to return to the main Driver Station screen. The screen should now indicate that the Driver Station is not paired with any Wi-Fi Direct device.

Driver Station main screen showing Wifi Direct status as Not Paired.

The Driver Station is now unpaired from the Robot Controller.

To re-pair the two devices, launch the Settings menu from the Driver Station app again and select Pair with Robot Controller again. Find the listing for your Robot Controller Android device (in this example “ZTE-026”) and select this item.

Pair with Controller screen with a Robot Controller device selected from the list of available devices.

Select your target device (in this example ZTE-026), then use the back arrow to return to the main screen.

Note

Your Robot Controller smartphone Android device might prompt you to make sure you approve the connection request. On the Robot Controller device, tap the Accept button to approve the connection request.

Robot Controller screen showing an incoming connection invitation with the Accept button highlighted.

Tap Accept to approve the connection request.

Once you have accepted the connection request, the Driver Station screen should display that it has successfully connected to the Robot Controller.

Driver Station main screen showing Wifi Direct connected to the Robot Controller with a ping time displayed.

Once the connection request is accepted, the Driver Station connects to the Robot Controller.

Changing the Channel Using an Approved Motorola Smartphone

If you are using an approved Motorola smartphone as your Robot Controller, you can use the channel change function that is built into the FTC Robot Controller app to change the Wi-Fi Direct operating channel. From the Robot Controller app, launch the Settings menu and select the Change Wi-Fi Channel option.

Robot Controller app Settings menu showing the Change Wifi Channel option.

The Robot Controller app’s Settings menu, with the Change Wi-Fi Channel option.

In the Change Wi-Fi activity, select the target channel from the drop-down list of available channels.

Change Wifi Channel screen with a channel selection drop-down list and Change Channel button.

The Change Wi-Fi Channel screen, with the channel drop-down list and Change Channel button.

Once you have selected the desired target channel, push the Change Channel button to change the operating channel. If the operation is successful, you should see a toast appear, indicating that the channel was successfully changed.

Change Wifi Channel screen showing a confirmation message that the channel changed successfully.

A toast appears indicating that the channel change was successful.

Once the channel change has completed, use the Android back arrow button to return to the main screen. The Driver Station should be able to reconnect to the Robot Controller using the new operating channel.