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Revolutionizing Indoor Cycling

May 26, 2023 by Sebastian Barnowski

Revolutionizing Indoor Cycling

North Pole Engineering, Core Health & Fitness and 4iiii Team Up to Create Next-Generation System Using ANT+ Frequency Diversity

Since 2008, North Pole Engineering has been a leader in the connected fitness space, revolutionizing the gym going experience by connecting wearables, fitness equipment and leaderboards seamlessly and reliably. As the use cases for this technology have grown, so too have the challenges, requiring innovative approaches and techniques. Recently, NPE (North Pole Engineering) teamed up with Core Health & Fitness and 4iiii to build a next generation system for indoor cycling studios. Connecting 40+ indoor bikes, power meters, watches, and heart rate monitors all while supporting no perceptible data dropouts at the console and the leaderboard.

Users love the connected indoor cycling experience. Cycle power meters bring a whole new dimension to what you can do with training, challenges, and gamification. But if the data is spotty, users get frustrated, and the joy is taken out of the experience. Maintaining high quality wireless communication with 40+ indoor bikes, a leaderboard, ANT+ power meters, heart rates devices all while allowing users to connect to the console with their Apple Watch posed a significant challenge. That is a lot of wireless traffic in a small space. NPE was key in making it all work,” said Travis Vaughan, Senior Director of Product at Core Health & Fitness. 

Figure 1. System Overview 

At the heart of the solution is the Schwinn console with NPE’s flagship GEM3NFC module, featuring ANT+, BLE and GymKit capabilities. The console, a battery powered device, transmits ANT+ fitness data to a leaderboard. It receives ANT+ power data from the 4iiii power meter. In addition, it supports heart rate monitor connectivity by allowing users to connect their Apple Watch via GymKit or a BLE/ ANT+ heart rate monitor. The 4iiii power meter on the crank supports ANT+ and BLE. The leaderboard uses NPE’s WASP receivers to aggregate ANT+ data from all devices. 


Figure 2. Schwinn Console by 4iiii 

ANT+ was chosen as the primary wireless technology for several reasons. As a broadcast technology it is ideally suited for leaderboard applications that require multiple bikes transmitting to one or more receivers. As a mature adopted standard, it makes it easier to connect sensors to displays in a predictable fashion. But ANT+, like many wireless technologies, has limitations in crowded environments. When more devices are added, interference between signals can occur causing data outages on the leaderboard and on the indoor bike console. To solve this issue, NPE worked within the ANT+ Alliance to develop and release the ANT+ Frequency Diversity Specification to address issues of interference in crowded spaces. This specification addresses interference issues between the sensor and the console, and between the console and the leaderboard. 

Figure 3. Signal Overlap Between Two Devices in the Time Domain 

“The Z-Bike with Schwinn console and 4iiii power meter integrating ANT+ Frequency Diversity works flawlessly. Users can easily pair BLE or ANT+ heart rate monitors, or their Apple Watch with a simple tap. Most importantly the data is solid. No more dropouts on the console, or on the leaderboard. Users are engaged with real-time feedback and come back to improve their performance in a group-based environment, said Vaughn. 

In simplest terms, Frequency Diversity involves transmitting data at two or more different frequencies. The first frequency stays the base ANT+ frequency, which is 2457MHz. The second frequency is chosen either randomly, or specifically to avoid other known interface sources such as Wi-Fi. Frequency Diversity also implements other collision avoidance mechanisms which are designed to move channels away from each other if they become overlapped.  

Solving interference at the console and at the leaderboard required two different approaches.  

The console had three design constraints.

  • Connectivity between the console and the power meter was 1:1 meaning each console/power meter pair was independent or any other. 
  • Console was battery operated. 
  • Console had a single radio requiring multi-connectivity for ANT+ and BLE. 

The first constraint meant that different frequencies on the second channel could be used to avoid interference between bikes. This effectively reduced the number of devices transmitting on the same frequency resulting in greatly reduced interference. The secondary frequency is chosen randomly by the console and negotiated with the power meter on start-up. If the performance of the channel is not sufficient at the chosen frequency, the console can choose another until it finds one that works correctly.  

The second and third constraints necessitated that a synchronous ANT channel be used for the main and secondary frequency. To support this, a synchronous mechanism known as dithering, was applied to the secondary channel. Dithering moves the ANT+ channel a small, random amount at regular intervals. This helps to dislodge any overlap if it has occurred, all without causing the receiver on the console to lose synchronization to the sensor. 


Figure 4. Dithering Coexistence Mechanism on Secondary Channel 

The leaderboard had two design constraints: 

  • Limited number of radios (2 to 4 depending on the Wasp type). 
  • Each radio scans at a single frequency for multiple ANT+ devices. 

As each radio will only scan at a single frequency, the secondary frequency needed to be the same for all bikes in the room. One radio could scan for the base ANT+ frequency, the second radio could scan for the secondary frequency. However, since the radios we always scanning, a synchronous channel was not necessary between the console and the leaderboard. A more effective asynchronous coexistence mechanism, known as re-slotting, was used to avoid interference. Re-slotting involves turning the secondary channel off then on at random intervals. As the secondary channel is turned back on, it will try to transmit in an open time slot.  


Figure 5. Re-Slotting Coexistence Mechanism on Secondary Channel 

Imagine walking into an indoor cycling studio and being able to seamlessly connect your wearable devices to the indoor bike, power meter, heart rate monitor, and leaderboard. That's the experience North Pole Engineering, Core Health & Fitness, and 4iiii have collaborated to create. The system, powered by ANT+ wireless technology, uses Frequency Diversity to ensure there are no data dropouts, even with over 40 devices all transmitting data in a small space. Thanks to this innovative approach, users can focus on improving their performance in a group-based environment, without any frustrating technical issues. With this technology, the possibilities for connected fitness are endless.