No Blues with Bluetooth!

Part 1: An Introduction…

Everybody knows what Bluetooth is. But when it comes to designing easy-to-use Bluetooth-enabled devices, there’s a lot to learn. In this new article series, longtime Circuit Cellar author Robert Lacoste dives deep into this ubiquitous wireless technology.

So here I am again, with a new bi-monthly feature article series entitled “No Blues with Bluetooth.” I suppose you’ve already guessed what I will be talking about.

Everybody knows…

Ok, now maybe you’re thinking that a full article series devoted to Bluetooth is a bit much. Everybody knows what Bluetooth is. Everybody knows how to activate it on their smartphone or tablet and connect any Bluetooth-enabled devices. Everybody knows that it’s usually painless, as Bluetooth is one of the most plug-and-play protocols on Earth.

And of course everybody knows that the list of Bluetooth devices is more than impressive: ear buds, speakers and cars of course, but also fitness trackers, blood pressure monitors, coffee machines, rings, shoes and flip-flops, basket or golf balls, strike detectors for fishermen, gloves, toothbrushes, trash cans, beds and pillows, cat flaps, water glasses, hairbrushes, toilet paper dispensers, egg trays, toasters—all of them have their Bluetooth variants! [2] And don’t forget non-smartphone Bluetooth applications, like electronic shelf labels, lightning mesh networks or industrial wireless links.

Moreover, as you are electronically addicted and as you read the best EE magazine, I am sure that you know that adding Bluetooth to an electronic project is quite easy and cheap. For example, using a Bluetooth module using AT commands over a UART, or maybe directly using one of the numerous Bluetooth system-on-chips (SoCs) available from companies like Texas Instruments, Nordic Semiconductors, Espressif, NXP, STM, Analog Devices and others. There have been plenty of such projects described in Circuit Cellar.

So why a full series on Bluetooth? Firstly, because there are plenty of interesting things to know about it. Secondly, because when you want or need to look under the hood, Bluetooth is far from easy stuff. In fact, whenever you want to design something easy to use for the end user, it’s a more complex task for the designer. In particular, think about compatibility: Devices may be built using fancy new Bluetooth versions, but you also want them to work with your grandmother’s 15-year-old phone. And it can—at least if you design it properly. Your new iPhone would for sure interwork with a 20-years old Bluetooth headset.

So I am going to discuss Bluetooth deeply. This month, I will start with a nearly non-technical overview of Bluetooth: its origins, who is managing it, its market share, its main versions, and some non-obvious details on Bluetooth features management. I will also introduce some nasty but good-to-know information on legal constraints and fees. Be sure that my follow-up articles will go deep into the technical side, as I am a technical guy.

Ready? Take a seat and enjoy this deep dive into Bluetooth!

Once upon a time

Why not start with history? The initial development of what was to become Bluetooth came from Dr. Jaap Haartsen, who worked at Ericsson’s Mobile Terminal Division in the ‘90s. At the time, portable consumer electronic products like printers or keyboards used RS-232 wires. In 1994, Haartsen worked on a solution to replace them with wireless links. Of course, mobile phones were already around, and using wireless to connect a mobile phone to its environment quickly appeared as a nice idea.

On the technology side, the approach developed by Haartsen used the 2.4GHz frequency band, which was already used by Wi-Fi. In order to mitigate interferences, he designed a so-called fast frequency hopping protocol, where small radio packets travel via a different frequency each time they’re sent. This is the basis of what eventually became Bluetooth; the technique was patented on September 17^th, 1997, by Haartsen on behalf of Ericsson. I strongly encourage you to read this patent (US6590928), as it provides all the key engineering aspects of this first Bluetooth version. This was the beginning of the adventure. The Bluetooth 1.0 specification was published a year later, in 1999—more on that in a minute.

Speaking of patents, another name must be cited here: Hedy Lamarr (1914-2000). Do you know her? She was a film star in the early days of Hollywood, but she was also an inventor [3]. During WWII, she and a friend of hers, the music composer George Antheil, developed and patented a radio guidance system for torpedoes that would change frequency frequently to avoid jamming. This patent from 1941 (US patent 2292387) is the first ever to use frequency hopping technology, the core of Bluetooth! So remember that Hedy Lamarr and George Antheil have something to do with Bluetooth—and not, as often cited, with Wi-Fi (which doesn’t use frequency hopping).

What a name!: Before moving on from the history, are you curious why Bluetooth has such a strange name? According to Bluetooth.com, in 1996, Intel, Ericsson, and Nokia met and discussed a potential standardization of the invention [4]. Jim Kardach, from Intel, was then reading a historical novel about Vikings. In it, one of the key characters was Harald Gormsson (Figure 1), king of Norway in the 10th century. He’s known for uniting Denmark and Norway in 958. Could his name serve as a suitable temporary code name for a communication protocol that could modestly unite all wireless needs? Well, not exactly his name, but his nickname: Bluetooth. Seems that Harald “Bluetooth” Gormsson had a front tooth with a strange, bluish color. Later, the group looked for a more serious name, but they failed, and Bluetooth is still Bluetooth.

By the way, I’m sure you know the Bluetooth logo (Figure 2a). It comes from merging the old Nordic characters for “H” and “B,” the initials of our dear Harald Bluetooth (Figure 2b).

First products: So, Bluetooth 1.0 was specified in 1999. That same year, the first-ever product using Bluetooth was announced at COMDEX: A hands-free mobile headset and an accompanying Bluetooth-enabled mobile phone (Figures 3a and 3b). This phone, the Sony Ericsson T36, was actually launched on February 24^th, 2000. It was never mass-produced and was replaced a couple of months later by other Bluetooth-compatible models: Ericsson R520, T28, R320, and the well-known T39, which was sold in 2001. Only prototypes of the original T36 seem to exist—so if you have one, please send it to me.

FIGURE 3
The first Bluetooth-compatible phone was the Ericsson T36 (a). Nice first headset, isn’t it? (b)

The Bluetooth SIG

Bluetooth could have been a nice niche technology, but the target was far more ambitious. To maximize its reach, both in terms of applications and vendors, in 1998 Ericsson launched a dedicated working group with its partners IBM, Intel, Nokia, and Toshiba. This group, formally an association, is called the Bluetooth Special Interest Group (SIG) and is still more than active. Its job is to develop, specify, publish, and promote the Bluetooth standard. In its first two years of existence, more than 2,000 organizations joined the SIG, and today it has more than 39,000 member companies! By the way, all are publicly listed on the SIG website [5].

What are the other roles of the SIG? Bluetooth also means interoperability, so the SIG makes sure that using Bluetooth is painless for the end user. How? By putting in place rules and constraints for the designers. Basically, you, as a designer, will need to formally prove that your product is fully compliant with the Bluetooth specification before being authorized to say, “Hey, my product has Bluetooth.” This is the Bluetooth qualification process, and it is one of the key missions of the SIG. This subject is also linked to intellectual property management. I will present it briefly here below, but be sure I will devote a full article later on this subject.

Before we move on, a word on membership. Any company can join the SIG as a member [6]. There are two main membership levels: Adopter and Associate. An adopter is a user of Bluetooth technology, and there is no membership fee for that. An associate can be involved in the development of the Bluetooth standard itself, through working groups and committees. This is, in particular, an excellent way to know about upcoming Bluetooth versions before your competitors, or even to push Bluetooth in the direction you want. Associates also have some other benefits, as listed in Table 1. Being an associate comes, however, with an annual fee, which today is $10,340 for small companies. That’s why the vast majority of SIG members are only adopters.

Some market figures

So, Bluetooth is a standard specified by a private association, the SIG, and not a standard from an international agency like ETSI or IEEE. (There was some tentative work as the IEEE 802.15.1 standard, but this stops in 2005.) Nevertheless, Bluetooth is now 25 years old and is still more than alive. That’s already a big achievement, as few technologies have the same lifetime. Moreover, Bluetooth continues to grow in popularity year after year. In 2023, it is by far the most widespread wireless communication technology, at least in terms of number of units worldwide. We can look to the ”Bluetooth Market Update,” the SIG’s interesting annual publication, for some figures. The last one I have on hand is the 2023 version [7]; by the time you read this, the 2024 one will probably be available on the SIG website.

Just have a look at Figure 4. It shows the number of Bluetooth-compatible devices sold each year. Two things: Firstly, the curve is going up. Each year there are more new Bluetooth devices sold than in the previous year. Secondly, the numbers are huge. Look, for example, at 2023: That year, 5.4 billion Bluetooth devices were sold. Think about that. We are, more or less, 8 billion humans. From these 8 billion, remove the people too young, too old, or too poor to buy Bluetooth stuff. Let’s assume that, unfortunately, one out of two people on Earth need to keep their small income to survive, and that maybe 30% of those remaining are too young or too old. That means that these 5.4 billion Bluetooth devices were bought by 2.8 billion people. So, roughly each of the remaining people are buying two Bluetooth things per year. This is, of course, an average—people like you and me are probably buying 10 of them! Recall your 2023, and just make a list.

I also encourage you to download and read the Bluetooth Market Update document, which presents plenty of other interesting statistics. For example, see Figure 5. This one shows the split between so-called “platform devices” and “peripheral devices.” The former are basically hosts: smartphones, PCs, laptops, tablets, and so on. There are roughly 1.9 billion of them per year, and the curve is flat. The later are all the devices connected by Bluetooth to a host; they are far more numerous (3.5 billion in 2023), and increasing drastically year over year.

Of course, you know that there are now no smartphones or tablets without Bluetooth. But these figures are still impressive, no?

Is Bluetooth free?

Thus, supporting Bluetooth is not a bad choice for your next project. Now the bad news. The SIG members have worked, and still work a lot, to develop Bluetooth, and few people work for free. A large part of the Bluetooth technology is patented, and the patent owners expect royalties for their inventions (even if they share them to build a standard). As an organization, the SIG also has a team to pay. It manages the Bluetooth patents and trademarks and must get some cash in. If you start to think that there is no free beer, at least for commercial projects, you may be right.

I’m not an expert here, but this cash management is done at two levels. Firstly, the chip companies pay royalties to the patent owners. This is due for each chip sold that integrates the intellectual property protected by a patent. This cash flow is invisible for the designer or end user; simply, the chips are more expensive because a part of the price is given back to the inventors.

Obviously, this royalty stuff isn’t just for Bluetooth. It’s the same for any patented technology, like Wi-Fi, cellular, USB, MP3, or HDMI. Want an order of magnitude? The overall royalty cost for a $400 cell phone seems to be no less than $120 [8]! You think you pay for hardware, but you also pay the inventors.

Ok, fair for the royalties, as you just pay them in the chip price. But there is another cost layer for Bluetooth: The SIG itself, as an organization, do own some intellectual property. In particular, I quote:

“The Bluetooth Special Interest Group (SIG) owns the Bluetooth word mark, figure mark, and combination mark (collectively, the Bluetooth Trademarks), and it protects the Bluetooth trademarks through the brand enforcement program.” [9]

The Bluetooth SIG has, in fact, put in place a quite stringent process to allow the use of these trademarks. Basically, you can’t even use the word Bluetooth if you don’t follow it, and of course, you can’t state publicly that your nice new product is Bluetooth-compatible. This process is the Bluetooth qualification process. I will have to devote a full article to this important aspect. Of course, such a process is a protection for the end users, as all Bluetooth-qualified devices will have good chances of working. But it’s also a cash cow for the SIG. In a nutshell, you will first have to join the SIG (free if you are an adopter). Then you will have to pay a so-called declaration fee ($11,040, to date). Then you may need to conduct some qualification tests and send all the results to the SIG, after which you are cleared to use the Bluetooth word and logo.

Regarding tests, it all depends on your design. Do you design a custom product using a Bluetooth SoC? This chip was already qualified on a given evaluation board and test software, but since you changed them, some tests would be needed. The details are a bit more complex, but you got the idea.

Requiring a qualification to ensure interoperability is not a bad thing. However, I’m a little more critical of this process as it requires each integrator to pay one time more than the declaration fee. Do you just integrate into your product a fully qualified Bluetooth module or USB dongle from a third party? If so, no qualification tests are needed at all, but you still need to pay the declaration fee. Even more, if your customer puts its brands on your product and resells it, they will also need to pay the declaration fee!

This is the current situation, confirmed by the SIG. But you have to know that it is now on the legal side. If you are interested, there is a law action ongoing between FCA USA, Inc (the manufacturers of Fiat, Chrysler, Dodge, and more) and the SIG on exactly that subject [10]. The SIG argues that a car manufacturer must follow the qualification process (and pay) for each new car that uses the “Bluetooth” word anywhere; Fiat-Chrysler argues that this name is now generic. I’m not at all a lawyer, but the subject is interesting, isn’t it?

Bluetooth versions

Of course, if you just want to play with Bluetooth, or even give away a couple of prototypes to your friends, there are few chances that the lawyers of the SIG will spend time with you. So enough legal stuff. Let’s finish with something a bit more technical: Bluetooth versions.

During these first 25 years, there have been no less than 14 Bluetooth versions (Figure 6). Bluetooth 1.0 was initially supporting a throughput of 2Mbps, enough for audio streaming. It was soon upgraded in 2004 to 3Mbps (Enhanced Data Rate, Bluetooth 2.0). Pushing the fast-forward button, a big change came in 2010 with Bluetooth 4.0 and the arrival of Bluetooth Low Energy (BLE). BLE is a significantly simplified Bluetooth protocol, limited initially to 1Mbps but compatible with ultra-low power devices. Since that date, there have been two flavors of Bluetooth: The older one (which I will call “classic Bluetooth”), still active in particular for audio, and BLE, targeting new applications. Both are Bluetooth, but they use drastically different protocols. Starting with my next article, I will present you BLE in detail. You may just like to know, for now, that it comes from a Nokia R&D project initially named Wibree.

Then Bluetooth 5.0 appeared in 2016, and provided new throughputs for BLE (125kbps, 500kbps, and 2Mbps, in addition to the original 1Mbps). I will explain why in detail in a dedicated article, but this version was a key building block for the innovations that are now coming to the market in 5.2 and 5.3. Mainly, it allowed a new way to distribute audio using BLE, and no longer Bluetooth Classic: LE Audio. There is also Bluetooth Mesh, coming from CSR and not actually linked to any version, but this would bring us too far for now.

The truth about Bluetooth « optional features »

Before closing this article, there is a fundamental thing that you must understand and keep in mind about Bluetooth versions. Each new version provides basically two things: bug corrections and new features. However, since Bluetooth 2.0, new features are always optional. This means that the designer can decide whether to support them or not, even if this is usually not communicated to the customer. Let’s take an example to make this 100% clear. From 4.0, BLE is 1Mbps. As explained, in 5.0, a new BLE mode running at 2MBps is specified. This is, like any new feature, optional. This means that a given fully 5.0-qualified product may or may not support this mode. And the same is true for every single new feature. The user thinks, “Super, 5.0 is faster”, but this may not be the case for a given product.

How does it work from a designer’s standpoint? A device simply lists the features it supports. As Bluetooth is all about interoperability, when two devices connect to each other, they will negotiate the link transparently. Something like:

Smartphone
“I am 5.0, and you?”

Device
“Super, I’m 5.2. I support 2Mbps, may we switch to 2Mbps?”

Smartphone
“I can’t. Please stay at 1Mbps.”

The good news is that it will work in any case, and will do so transparently. Which is great, unless your device actually needs 2Mbps. In that case, you would need to either downgrade the service, cancel the connection, or inform the user that the smartphone doesn’t support something you need. The problem is that the user is, unfortunately, not a Circuit Cellar reader. He bought a Bluetooth 5.0-compatible smartphone unaware that it might not support all the new features.

To make things crystal clear: It is indeed possible to sell a Bluetooth 5.4-qualified device with absolutely no new feature compared to, say, a Bluetooth 4.0 one. All known bugs would have been corrected, but the performances will be strictly the same, as no new options or features will be supported. Of course, a customer expects a better product when buying a new version but doesn’t know these interesting details. 

Stay tuned!

Here we are. I know that this feature article was far less technical than usual, but I thought such an overview was needed. I hope that you found it interesting. In my next article, I will start to dig into BLE with a presentation of the protocol stack and advertising mechanism. The following articles will discuss the BLE physical layer, the GATT protocol, test platforms, security, BLE hardware, the qualification process, 5.0 new modes, 5.1 and localization, 5.2 and LE audio, 5.3, 5.4, and so on.

Plenty of subjects, so probably plenty of articles to come. The next one will be in the upcoming June issue, but in the meantime, don’t hesitate to drop me an email if you want to either comment on or criticize this piece, or if you have any questions or proposals for the following ones. I will do my best to answer you either directly or through a follow-up article. Let’s be as interactive as possible!

RESOURCES
Bluetooth SIG | www.bluetooth.com

REFERENCES
[1] Robert Lacoste, “Let’s Understand Ground Stitching Vias.” Circuit Cellar 394, May 2023.
[2] Idiotic IoT Devices Nobody Asked For: https://gizmodo.com/15-idiotic-internet-of-things-devices-nobody-asked-for-1794330999
[3] Hedy Lamarr Wikipedia article: https://en.wikipedia.org/wiki/Hedy_Lamarr
[4] Origin of the Bluetooth name: https://www.bluetooth.com/about-us/bluetooth-origin/
[5] SIG member directory: https://www.bluetooth.com/develop-with-bluetooth/join/member-directory/
[6] SIG membership benefits: https://www.bluetooth.com/develop-with-bluetooth/join/membership-benefits/
[7] 2023 Bluetooth Market Update: https://www.bluetooth.com/2023-market-update/
[8] Medium—“Who own them and how much are the essential patents to make a telephone?”: https://medium.com/@Xataka/who-own-them-and-how-much-are-the-essential-patents-to-make-a-telephone-a7f35657b391
[9] Bluetooth.com—“All the Essentials You Need to Brand Your Bluetooth Product”: https://www.bluetooth.com/develop-with-bluetooth/marketing-branding/
[10] Moses Singer—“Bluetooth’s Trademark Infringement Action Distorted by First Sale Doctrine”: https://www.mosessinger.com/publications/bluetooths-trademark-infringement-action-distorted-by-first-sale-doctrine

PUBLISHED IN CIRCUIT CELLAR MAGAZINE • APRIL 2024 #405 – Get a PDF of the issue

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