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How ANT+ Wireless Compatibility Works

ANT is an ultra-low power (ULP) wireless protocol for sending information wirelessly from one device to another, so that your phone, bike computer, heart rate monitor, power meter and other training devices can talk to each other and allow technology to make your cycling (and life) better than ever.   But how does it work?

– By Paul Smeulders –

Prior to founding ErgVideo, Paul Smeulders worked in the communications industry as an optical systems architect, hardware and software designer, and as a Professor of Electrical Engineering. His past and present roles uniquely qualify him to explain how compatibility of your various wireless gadgets is achieved, and how to decide which gadgets are compatible with one another.

The Shortest Answer I Can Give
If you ever met me and walked away thinking “That guy, no, he ISN’T detail-oriented at all.”
I wouldn’t believe you had met me and, you’d be the first person ever.

But this is the short story: The organization that created ANT+ has done consumers a huge favor by introducing and controlling the use of special icons that indicate proven compatibility of devices to a common set of standards.

In the past, you were limited to choosing, say, a heart rate strap and HRM watch from the same manufacturer, just to be sure it all worked. The watch might not have been as good as another brand, but the straps were known to be far better: more waterproof, longer battery life, whatever. You wished you could buy the best piece from each supplier, but couldn’t be sure the combination would work.

Now, with ANT+, you can do exactly that, with ease. Essentially, if you wonder if an ANT+ heart rate monitor will pick up your HR from some heart rate strap, you look for the ANT+ HR device conformance icon on both devices, even if the watch and strap are made by different companies. Do they match? Boom, you are good to go. The HRM conformance icon is shown below, left.

ergvideo16-ant-01iconsANT+ conformance icons for heart rate, speed, cadence, power, speed and cadence, and FE-C devices

Another example will help you decide if a wireless stationary bike trainer is compatible with the software you want to run, like ErgVideo. The ANT+ organization has created and standardized a communications and control protocol called “Fitness Equipment-Control” that ensures interoperability of “smart” trainers and controllers, which includes software apps. They evaluate the devices and software against standard tests, and when they pass, grant the developer/manufacturer permission to use the conformance icon on their product. So, in ErgVideo’s case, besides Wahoo Kickr and Snap, CompuTrainers and VeloTrons, you can simply look for trainers bearing the FE-C icon above, right, and rest assured that ErgVideo can control that trainer to deliver the full ErgVideo experience.


ergvideo16-ant-02multitrainerpromoThe list of compatible and supported devices is ever-growing, and ANT keeps a directory of compatible devices on their website here. I like to say that ANT+ is the Garanimals for gadgets!

Okay, you could quit now if you get it already, but if you read on, you’ll get added insight into how this came about and made life much easier for consumers, manufacturers, and product developers.

Standards make your gadgety-world go ‘round
Connections between devices, whether they are from your stereo amplifier to your speakers, your PC to your router, or your router/modem to the telecom network, all rely on some “interoperability or compatibility specification” to enable the connection and the resulting outcomes you want achieved: Sound, fast file transfers between your PC’s, or getting your PC to a show a webpage like PezCyclingNews.com, respectively, in my examples.


We know that we can’t connect an Ethernet cable directly into our 120V power receptacle in the wall. For one, the standard connecters don’t mate (this is always a great sign to stop trying…). While a hardware company can come up with its own ways to interconnect its own products, jumping off to connect to others’ usually means conforming to some well-known or “open” standard. Even in the case of interconnecting with their own equipment, the economics of using off-the shelf available parts (and software) for an open-standard interface is more attractive than fabricating custom devices to implement a proprietary, new interface.


Industry and international “open” standards
The ITU website has a great definition:
“Open Standards” are standards made available to the general public and are developed (or approved) and maintained via a collaborative and consensus driven process. “Open Standards” facilitate interoperability and data exchange among different products or services and are intended for widespread adoption. —(International Telecommunications Union)

ergvideo16-ant-04itu-logo Standards bodies bring together the players in an industry, and often government representatives, to work together to define how their equipment will connect in ways the world needs. It’s amazing, and of course each player is rather hoping the adopted standard is closest to their own internal designs so changes are minor to conform to a new spec. Participants must state up-front their intellectual property holdings that might be fundamental in implementing a standard. They do not relinquish their patents or make them free, but they agree to license them on a fair, reasonable and non-discriminatory basis (FRAND). They can’t deny their competitors a license if they wish to implement the standard, and they cannot wield their patents as strike weapons to disadvantage some companies over others. Ultimately, it’s so one company cannot “control” through the patent courts an open standard like an ITU or IEEE or EIA standard.

ergvideo16-ant-05ieee_logoThe Ethernet connection between your PC and your modem is an open standard defined by the IEEE (Institute of Electrical and Electronics Engineers). Everything from the size, shape, number of wires on the connectors and cables, to the electrical voltages and currents and cable impedances, to how the digital information is modulated onto that cable as bits and bytes and packets and messages, to how the endpoints manage traffic on that cable, are all defined by the standard. Similarly, your home Wi-Fi is defined by the same organization, but instead of wires, connectors and voltages and currents, they define the frequency bands, the data modulation schemes, the intended reach and emitted power and so on. Here is where governments need a say on the committee, because they regulate the electromagnetic spectrum within their borders. Each country may restrict how much power anyone may emit in their own unregulated “consumer band” of frequencies, which is where Wi-fi and pretty much all your devices, other than your phone, operate.

So, any manufacturer can create equipment that connects over Ethernet or Wi-fi if they correctly implement the open standard at its minimum-required level. It’s in their business interests to do it right, because consumers will notice quickly whether their pc cannot connect at Starbuck’s and only sometimes at Tim Horton’s.

Representation of contents of an Ethernet frame. Data standards specifications are full of these!

Proprietary interconnect and interfaces
There is never anything forcing a manufacturer to adopt a standard. They are free to define their own interconnect and interfaces according to how they view the marketplace. They may see a business advantage in not revealing how their interconnect works, perhaps seeking to monopolize an application space. They can even take steps to discourage other products from interconnecting. Often, the first company with the first product works this way. They take on the entire development of the products end to end, from wires to application software. The consumer gets a single-source supplier, and she may consider that an excellent, simplifying quality. The market itself, and that player’s success within it, determines whether it’s a good idea or not.

There is however an interesting middle ground: proprietary with open parts that prime a business’ pump.

Single-owner closed interfaces with open parts
Suppose a company develops a great idea and takes upon itself all the costs for developing that idea and bringing it to market, but does not apply to the ITU or IEEE to adopt it as an open standard, because the company DOES want to own and control some strategic piece that helps solve a problem…AND they are 100% willing to help their customers solve it. They may have no direct interest in supplying the higher-level applications that need their technology, but want their tech to underpin the best solutions. So, they open just that strategic piece that enables the desired market activity. In the best of cases (like this one, wait for it…) they also take on the responsibility to test, verify, and approve the applications of all comer’s, so that interoperability (and thus quality and reliability) can be assured to their clients’ customers and, in turn, the underlying technology gets widely adopted and trusted.

So let’s start using the example of ANT and ANT+ as the “proprietary with parts open” standard, owned by Dynastream.

What ANT is, and how it works.
Well, it’s possible to read volumes and volumes of detail on this. Reading this article will not make you an expert, so don’t start acting like one: I will be making plenty of simplifications, and you will still think the article is too long!

ergvideo16-ant-07antpluslogoANT is a proprietary wireless communication system for connecting devices in near-field proximity using the unregulated 2.4GHz band (aka the “consumer band”). It is not an ITU, nor IEEE, nor any sort of open standard, so its owner is free to independently select licensees and partners. They develop chipsets and accompanying tech (like firmware, software, drivers) that implement this communications scheme and provide them for integration into a whole range of devices. Of course, ANT must comply with whatever regulations and standards govern the “consumer band”, but how it achieves the desired communications between devices is their own proprietary scheme.

ANT is optimized for local (within 30m) wireless networking among devices with modest data rates (600Kbps is the maximum rate that can be carried). It is targeted toward connecting “sensors” to devices that interpret, display, and use the measured quantities. The sensor and display devices are typically battery powered, so a real focus is on minimal power draw to enable long battery life. ANT competes with technology such as Bluetooth, BTLE, and ZigBee. Devices like bike speed sensors, power meters, and heart rate monitors all “fit” based on the required data rates, costs, common proximities and especially battery life. ANT+ is a specifically restricted subset of ANT, and an ANT+ network has restricted but completely-defined capabilities and functions compared to what a full ANT network could do.

ANT communicates in a crowded radio-frequency space, because Wi-Fi and all your near-field consumer items like cordless phone extensions are transmitting in the same band (Yes, your Wi-Fi CAN interfere with your ANT+ devices!). Devices use narrower sub-bands in the 2.4 GHz band, so it’s a nice trick that some devices, based on traffic, can change sub-bands to hopefully find clear channels and reconnect. Otherwise you can manually, for example, force your Wi-Fi onto channels further away from the channels used by your ANT+ devices inside your home. ANT+ is at 2457MHz, and that is channel 10 on your Wi-Fi, you are best to avoid that combination. Selecting channel 1 to 6 for your Wi-Fi should be very effective to ensure no interference.

ergvideo16-ant-08-2_4ghzwifichannelsThe channels in 2.4GHz Wi-Fi showing ANT+ overlap (adapted from diagram by Michael Gauthier)

Now, you often have many ANT+ devices connected say, to your handlebar unit or your ErgVideo experience: Your trainer, a cadence unit, a HRM, and maybe a power meter and speed sensor might all be separate units. Your ANT+ devices do NOT need to find a clear sub-band for each one, and in fact, in ANT+ they all communicate on the same sub-band known as channel 57, or 2457MHz.

It doesn’t take long to accumulate quite a collection of ANT+ sensors, especially if you have a few bikes.

So how do multiple devices talk without interfering? Recall those days when two guys wore a similar HR strap and you didn’t know which one your watch was picking up? Arrrgh! ANT+ uses a “time division multiplexed” scheme wherein any transmitter is active for about 150 microseconds, blurts out a frame of about 12 bytes, and then turns itself off. It does this 4 times per second (it can change, and ANT can go much higher, with longer frames). Bits in that frame are represented using “Gaussian Frequency Shift Keying”, where a 0 is represented by a frequency slightly less than the carrier, and a 1, slightly more. These frequency shifts can be detected at receivers, and thus timed-sequences of 1’s and 0’s are interpreted from them. The transmitter is the piece that draws the most power from the battery. The battery lasts so long because the signal only needs to propagate a few meters, and the transmitter is only “on” for 4x150microseconds/second = 0.06% of the time.

Highly simplified binary FSK modulation, showing frequency changes representing 1’s or 0’s serially in time.

Now, each device detects when the others within range are transmitting, and arranges its own transmissions at times that won’t conflict with others. For example, if my HRM transmits at 0, 0.25, 0.5 and 0.75 seconds (ending at 0.00015, .25015, 0.50015 and 0.75015 seconds each) then my cadence meter can choose to send at 0.001, 0.251, 0.501, and 0.751 seconds and never interfere with my HRM’s transmission! The transmission “blurts” interleave with one another. As the space gets crowded with more devices, every device self-adjusts its own timing of transmissions to avoid collisions with all others!

The time division multiplex scheme: devices self-select where to synchronize their transmissions relative to other devices.

So, with the ANT devices, the communication scheme, and some low level data protocol pieces, Dynastream has a great way to ensure a network of devices can co-exist in a space where all data gets from various sources to their intended destinations unobstructed, cheaply and with long battery life. They make and sell the tech that embeds all that capability into other company’s devices, including the firmware to present a standard computer interface. Now, let’s talk about the ANT+ and the “open part”.

ANT+ and how interoperability is guaranteed
ANT provides connectivity that enables wireless data communication between devices. What gets communicated is completely up to a systems manufacturer: ANT can carry anything; that anything is only limited by maximum speed, reach, and power consumption. Frequency bands, repeat rates, encryption, frame sizes are all configurable and supported.

ANT+ is a specific, very narrow restriction of the rich ANT capabilities, where all the configurable comm-link parameters are fixed to known, common settings in all devices bearing the ANT+ icon. This ensures all ANT+ branded devices will connect on a common network when they are turned on. Configuration settings are baked-in.

More importantly, Dynastream defines very specific data-protocols that correspond to (and make sense only for) specific types of sensor devices and displays. They define WHAT information an HRM is supposed to transmit, and define exactly where within the data frames that information will be found, enabling the data to be coherently parsed when received. They insert an identifier in the frame that indicates “this frame came from an HRM” as well as which HRM, because each one has a unique numerical identifier. In the same way, they completely specify frames for speed sensors, power meters, and indeed now the FE-C stationary trainers.

These specifications are each called a “device profile” and every device that can bear the HR conformance icon, MUST implement the minimal functionality defined in the HR device profile, whether for a transmitter (strap) or receiver (watch, handlebar unit, computer application). To be sure, a test suite is provided, and before a product can legally bear the icon, it must be proven and tested by the ANT people.

The well-defined, fixed device profiles, vastly simplify every developer’s job in that they no longer need not program specific, different data protocols for every manufacturer offering devices in each application space. ANT+ enables them to all to start singing from the same song book.

And even with all of them singing at once, a receiver device can be configured to display data only from certain ones. For example, suppose I was on a room full of devices like 10 power meters, 4 cadence sensors, 12 HR straps, and 6 power trainers, and I wanted to see data only from my Power Meter #456. The display basically looks for the data “blurts” from that “paired device” by looking at the traffic and processing only the data frames from PM #456, ignoring frames from other non-power meter devices, and all other power meters that are not identifying as #456. The devices are not only sending currently measured data like power, they also periodically send battery status and manufacturer information as well. Advanced functionality like calibration commands can be sent back to devices that need it, and that too, is all defined in the device profile.

ErgVideo’s drag and drop studio set-up showing detection and pairing of many ANT+ and other devices all at once.


A display is not restricted to showing data from only single device paired to it. As in the case of ErgVideo, ALL the devices of interest that are active within range of the receiver (in our case an ANT+ usb stick) can be configured and displayed. ErgVideo is built to support up to 24 trainers, and the users’ individual ANT+ personal devices can also be received, displayed, and data logged in their performance output file.

ANT+ conformance icons, the Garanimals for Gadgets!
Remember that ANT+ is not fully “open” and is strictly controlled by its technology owner. It’s not at all a restriction that you could complain about, because they’re oversight provides an invaluable service to customers and developers: they measure and approve your product against a suite of conformance tests, after which you are granted permission to use the conformance icon on your product and its software. They make the process inexpensive and very smooth by providing the test suites against which you can measure your solution before formal submission. Personally, I really appreciate that the ANT+ gatekeepers provide a smooth and easy way for my customers to identify which trainers will be compatible with ErgVideo.

So, when you are looking at bits of ANT+ equipment, deciding on compatibility comes down to this: do the sensors and the display (software application) both bear the same ANT+ device-type conformance icon, either on the product or in its documentation or web info? If it’s an HRM and an HR strap, look for the HR icon on both devices (or in their marketing, or in the FW version promoted if it is an upgradable unit). If it is a cadence sensor, look for matching CAD icons on both. It’s like matching the tags on Garanimals!


ergvideo16-ant-01iconsANT+ conformance icons for heart rate, speed, cadence, power, speed and cadence, and FE-C devices

And of course, the question I get asked most: Will ErgVideo work with my smart trainer? The answer is: Wahoo Kickrs or SNAP, RacerMate CompuTrainers or VeloTrons, or wireless ANT+ trainers bearing the FE-C conformance icon. Currently, Tacx has several models bearing the FE-C icon, including Neo Smart, as does Elite, including their new Drivo.

Visit thisisant.com and have a look at their directory of compatible devices if you are ever in doubt.


ergvideo16-ant-14compatibilityErgVideo’s compatibility options just grew!

psmeulders-head16Paul Smeulders holds a Ph.D. in electrical engineering. Prior to founding ErgVIdeo.com, he worked in academia and the telecom industry as a software and hardware developer, designer and system architect for optical communications systems. He’s been riding bikes madly for 36 years, and is an NCCP certified coach in Road, Track and MTB. Today ErgVideo.com is his primary occupation, and he even lends “Steve in customer support” a hand from time to time. Travel is a thing for Paul, and if you wanted to meet him, you’d sign up for a trip with Velocious Cycling Adventures, for whom he acts as a guide and on-road coach.

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