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00:00Bluetooth is a fascinating technology. For example, when you play music on your wireless headphones,
00:07your smartphone transmits around a million ones and zeros to your headphones every second using
00:15Bluetooth. But how are a million or so ones and zeros wirelessly transmitted every single second
00:22between your smartphone and your wireless earbuds? In order to answer this question,
00:28we're going to explore the engineering behind Bluetooth and the principles of wireless
00:34communication. Before we get into the details and specifics of Bluetooth, let's start with an
00:41analogy. When you see a traffic light change color, you recognize what that color change means. The
00:48traffic light uses a section of the electromagnetic spectrum, or light, to convey information. The
00:54green light has a wavelength of around 540 nanometers, yellow around 570 nanometers, and red around 700
01:04nanometers. Your eyes can easily distinguish between these different wavelengths of light,
01:09and your brain interprets these different wavelengths and the information they convey.
01:15Your smartphone and wireless earbuds communicate using electromagnetic waves in a rather similar
01:22fashion, but utilizing a different section of the spectrum. Specifically, Bluetooth uses waves that are
01:29around 123 millimeters in wavelength. They're invisible to the human eye and can generally pass through
01:36obstructions like walls, rather like visible light passing through glass. When your smartphone sends a long
01:43string of binary ones and zeros to your earbuds, it communicates these ones and zeros by designating a
01:51wavelength of 121 millimeters as a 1 and a wavelength of 124 millimeters as a 0, similar to the 540 nanometer
02:02green and the 700 nanometer red colors of the traffic light. Your smartphone's antenna generates these two
02:09wavelengths and switches back and forth between them at an incredible rate of about a million times a second.
02:16With this process of switching between the two wavelengths, kind of like switching between the red and green
02:22traffic lights, your smartphone can communicate around a million ones and zeros every single second to
02:29your earbuds. And amazingly, engineers have designed the antenna and circuitry in your earbuds and smartphone to be
02:37attuned to sensing and transmitting these wavelengths back and forth to one another.
02:41Before we dive into further details on Bluetooth, let's briefly explore and clarify these visualizations,
02:51because they're potentially rather confusing. First of all, electromagnetic waves do not travel in a
02:58single direction in a sinusoidal fashion like this. In fact, the electromagnetic waves that are transmitted
03:06from your smartphone travel out in all directions like an expanding sphere. When your smartphone switches
03:13between frequencies, it's as if it were a light bulb that rapidly changes between two different frequencies
03:20of millimeter-length electromagnetic waves, which travel out as expanding spheres. As a result, your smartphone
03:28and wireless headphones can work in any direction. Thus, this visualization of a directional sinusoidal wave is
03:37lacking, yet there are still merits to the visualization. In order to give you a sense of how Bluetooth works,
03:44we're going to use four different visualizations that are all different perspectives of looking at the
03:50same invisible thing. Here we have the sinusoid waves, which give us a sense of the frequency and wavelength of the
03:58electromagnetic wave. What's moving up and down is not the wave itself, but rather it's the strength of the electric field.
04:07This perspective just shows us a directional sliver or ray of the expanding sphere with the electric field going up
04:16and down as the Bluetooth signal propagates outwards in all directions. If we were to measure the electric field
04:23at a single point in space, we would find that the strength of the electric field would increase and decrease
04:30sinusoidally and the number of peaks per second would be the frequency. Furthermore, we're ignoring the magnetic
04:38field component of the electromagnetic wave as including it would be too confusing. Let's move on to the second
04:45visualization. Here we have the traveling binary numbers, which give us a sense of the data being
04:52sent. However, it also doesn't show the spherical propagation of the electromagnetic waves or the
04:59changing frequency of the wave. Note that it's possible to send multiple bits at the same time,
05:06which we'll explore later. Third, we have the expanding spheres visualization, which gives a sense of the
05:14true near-omni-directional emission of electromagnetic waves from your smartphone and headphones. But it's
05:21difficult to show the frequency or the data that's being sent, and it's rather visually complex to process.
05:29And last, we have the simplified spheres, which help us see that these two devices are emitting and
05:36receiving electromagnetic waves along the same frequencies. But it doesn't show us much else.
05:42Different visualizations are useful in different scenarios, and with that covered, let's get back to the focus of this video.
05:51As mentioned, Bluetooth operates at around 123 millimeters of wavelength, but specifically, it operates between
05:59120.7 millimeters and 124.9 millimeters of wavelength in the electromagnetic spectrum. Note that these frequencies are more
06:11commonly referred to as having a 2.4 to 2.4835 gigahertz frequency bandwidth or range.
06:21Just as our eyes see within a range on the electromagnetic spectrum,
06:25Bluetooth antennas see or perceive within their own range of frequencies.
06:30Now, at any given time, there might be dozens of people using Bluetooth devices at the same time,
06:39in the same room. To accommodate so many users, this section of the electromagnetic spectrum is broken up
06:46into 79 different sections or channels, with each channel having a specific wavelength for a 1 and another for a 0.
06:55And at any given moment, your smartphone and earbuds communicate across just one of these channels.
07:02For example, these are the frequencies for a 1 and a 0 in channel 38, whereas these are the frequencies for channel 54.
07:12Now, this begs the question. If dozens of devices are using the same wavelengths and possibly the same channel,
07:20how do your earbuds receive long strings of binary bits or messages from your phone exclusively?
07:28Well, first, the messages are assembled into packets. In each packet, the first 72 bits are the access codes
07:35that synchronize your smartphone and earbuds to make sure that it's your specific earbuds that receive the message.
07:42These access codes are similar to the address words on a postal letter or package.
07:48The next 54 bits are the header which provides details to the information being sent,
07:54which, in our analogy, can be equated to the size of the letter or the box.
07:58And the last 500 bits are the actual information or payload, kind of like the contents of our postal letter or box,
08:08which, in this case, are the digital ones and zeros that make up the audio that you're listening to.
08:14If you're wondering how audio can be represented by ones and zeros, take a look at this episode on Audio Codex.
08:21Okay, so now let's add more complexity to the mix. As mentioned, Bluetooth operates in a set of 79 different channels.
08:32However, when your smartphone and earbuds communicate, they don't stick to a single channel, but rather they
08:39hop around from channel to channel, kind of like channel surfing on your TV. In fact, this hopping between
08:47the 79 channels, which is called frequency hopping spread spectrum, happens 1600 times a second. And,
08:55after each hop, one packet of information composed of the address, header and payload is sent between
09:03your smartphone and earbuds. Your smartphone dictates the sequences of channels it will hop to,
09:10and your earbuds follow along. Furthermore, if one of the 79 channels is noisy due to
09:16interference or is crowded with other users, then your smartphone adapts and doesn't use that channel
09:24until the noise clears. This channel hopping also prevents anyone from eavesdropping on the information
09:30that's being sent between the two devices, because only your smartphone and earbuds know the sequence of
09:37channels that they will communicate across. Interestingly, because the information is divided and sent using
09:45packets, if your earbuds don't receive one of the thousands of packets, it says it didn't receive that
09:51particular one, and your smartphone sends the packet again. It might seem crazy or mind-blowing that the
10:00circuitry in your phone can generate pulses of electromagnetic waves a million times a second at very specific
10:08frequencies, and then have these pulses received and decoded by your earbuds. But, hey, it happens. Just think
10:17about how your screen has millions of pixels also emitting specific frequencies and strengths of the
10:23electromagnetic spectrum or light at around 30 to 60 or more times a second. Technology is fascinating.
10:32One quick side note. We would greatly appreciate it if you could take a second to like this video,
10:38subscribe to the channel, comment below, and share this video with others. A few seconds of your time can
10:46help us to create many more educational videos. Thank you. Okay, let's move on. One point of interest is that
10:55Bluetooth's frequency range of 2.4 gigahertz to 2.4835 gigahertz is shared by other industrial and medical
11:04devices. For example, your microwave is in this range and has a frequency of 2.45 gigahertz. In fact,
11:12when your microwave is on, it can cause your headphones to lose track of the ones and zeros being sent by your
11:19smartphone. Or, in other words, your headphones can lose signal. However, please don't think your
11:26Bluetooth headphones are dangerous because they emit a wavelength that's similar to your microwaves.
11:32That would be like comparing the light output from stadium floodlights to the light from your smartphone
11:38screen and saying that because they both use the same colors of light, they'll both cause damage
11:44when stared at from a foot away. Also, remember we mentioned that the electromagnetic waves from
11:50Bluetooth can easily travel through obstacles such as the walls of your house? However, the walls of
11:56the microwave are designed to block waves of this frequency. You can test this by putting your smartphone
12:03in the microwave. The Bluetooth signal from your smartphone to your headphones will be blocked and the
12:09connection lost. However, make sure not to turn on your microwave with any electronic devices inside of it.
12:16I repeat, do not turn on your microwave, otherwise it will damage whatever electronics you put into it.
12:24In addition to microwave ovens, 2.4 gigahertz Wi-Fi networks also operate within this range of the
12:32electromagnetic spectrum. Similar to Bluetooth, Wi-Fi networks divide this range or bandwidth into 14
12:41channels in order to accommodate multiple users communicating via Wi-Fi at the same time.
12:48You might be wondering, if there are a bunch of different devices all sharing similar frequencies,
12:54one of them being a microwave that, if poorly shielded, can emit stray electromagnetic waves,
13:01how is it possible for your smartphone and headphones to send megabits of data every second error-free?
13:09Well, as mentioned earlier, your smartphone does this by frequency hopping and utilizing packets.
13:16In addition to that, Bluetooth also utilizes bits for detecting errors and the circuitry in your
13:24smartphone filters out unwanted noise. For a non-technical understanding of this,
13:30let's go back to our traffic light analogy. When you're driving and you see a traffic light,
13:35it's not like that's the only thing you can see. Your eyes perceive a rather complex scene filled
13:42with tons of other objects. Your brain interprets this information-filled scene and picks out the
13:48information important to you, while ignoring all the objects that aren't. Similarly, your smartphone and
13:55wireless headphones have rather complicated circuitry inside a specialized Bluetooth microchip that's
14:03designed and tested by engineers, which filters out unwanted signals, checks for errors, coordinates the
14:10frequency hopping, and assembles the information into packets, thereby enabling reliable and secure communication.
14:18Before we move on to some higher-level engineering concepts, we'd like to take a few seconds to
14:25thank Keoxia for sponsoring this video. Many Bluetooth devices, such as mobile phones and tablets,
14:32use Keoxia Bix flash memory. Keoxia also manufactures a wide variety of SSDs and they have sponsored a couple of
14:41our videos that explore the inner workings behind how SSDs work. Here's a consumer-class SSD, versus this
14:50enterprise-class SSD. They look similar from the outside, but are entirely different on the inside.
14:57Keoxia provides these leading quality enterprise-class PCIe NVMe solid-state drives and they can fit in the same space,
15:08but have capacities up to a whopping 30TB and use a proprietary architecture built with their own
15:15controller, firmware, and Bix flash 3D TLC memory in order to deliver incredibly high sustained read and
15:24write performance and reliability. Check out Keoxia's SSDs using the link in the description.
15:31Let's move on to even more complicated details regarding Bluetooth. The scheme of sending a
15:38digital signal or a binary set of 1s and 0s by transmitting different frequencies of electromagnetic
15:46waves is called frequency shift keying. Frequency shifting means that we adjust the frequency and keying
15:54means that a 1 is assigned to one frequency and a 0 to another, just like our traffic light colors.
16:01Note that the comparison to a traffic light which emits one color and then another is a little
16:06inaccurate because your smartphone circuitry generates one frequency called a carrier wave.
16:13This circuitry shifts the carrier wave to a higher frequency when it wants to send a 1 or to a lower
16:20frequency when it wants to send a 0. This shifting of frequencies in order to send information is also
16:28called frequency modulation and it's closely related to FM radio. That being said, Bluetooth isn't
16:35limited to using just frequency shift keying, but rather it can also use other properties of
16:41electromagnetic waves to transmit information. A different method that has higher data transfer rates
16:47is called phase shift keying, which is significantly more complicated to explain, but we'll try.
16:54An electromagnetic wave's phase is a property that our eyes can't perceive and it shouldn't be confused
17:01with the amplitude or the frequency or the wavelength. Let's use an analogy. Imagine you're at the beach
17:08and you see the waves hitting the shore at a rate of one wave a second. Over a minute you would see 60 wave
17:15peaks reach and break on the shoreline. Changing the frequency would be changing how many wave peaks reach
17:22the shoreline every second and changing the amplitude would be changing the height of the peaks and troughs of the waves.
17:29However, phase shifting would be seen as breaking up the waves locations of the peaks and the troughs within a set of wavelengths.
17:37There are still 60 waves over an entire minute, meaning the frequency doesn't change, but as the phase shifts, it's as if the peaks and troughs
17:46shift forward or backward within a set of wavelengths. Bluetooth antennas and circuitry in your
17:53smartphone and wireless earbuds can be designed to emit and detect shifts in the phase of an electromagnetic wave,
18:01and binary values can be keyed or assigned to different levels of shifts in the phase of the wave.
18:08There are a few things to note with our examples and explanations. We've talked a lot about your smartphone
18:18sending information to your wireless earbuds. However, your earbuds also send data to your smartphone.
18:25For example, when you're on a phone call using your earbuds, the audio from the microphone in your
18:31wireless headphones is obviously sent back to your smartphone.
18:35In order for Bluetooth to accommodate this back-and-forth conversation, the smartphone and the
18:42headphones alternate transmitting and receiving data, while maintaining the frequency hopping schedule.
18:49During one 625-microsecond time slot, your smartphone will send one packet of data to your headphones along
18:57one channel, and then during the next 625-microsecond time slot, your headphones will send one packet of
19:04data to your smartphone along the next channel in the frequency hopping schedule.
19:11Also, as we mentioned earlier, a Bluetooth packet is composed of three sections. Access codes of 72 bits,
19:20a header of 54 bits, and for example, a payload of 500 bits. The number of bits in the access codes and
19:29header are pretty close to those mentioned. However, the size of the payload which is specified using the header
19:36can vary widely between 136 bits and 8168 bits, depending on the requirements of the data being sent.
19:46For example, simple commands from your headphones, like pause or play the music, would require far fewer
19:53bits than sending or receiving high-quality audio. An additional caveat is that the electromagnetic waves
20:01sent and received from the antenna in your smartphone and earbuds and the light from a traffic light share
20:08the aspect that they both function within the electromagnetic spectrum. However, the principles
20:14that govern how your smartphone and headphones generate and receive those electromagnetic waves are
20:20quite different from the principles around how traffic lights and your eyes work. It's kind of like how fire
20:27and an electric radiator both generate heat, but using vastly different methods. The principles behind
20:34Bluetooth fall under the category of antenna theory and will be explored in a separate episode.
20:40Thus far, we've made a few episodes that help to explain other parts of these wireless headphones,
20:48such as noise cancellation and the audio codec. And we've made even more episodes that dive into the
20:55different parts of your smartphone. Check them out to learn about these other fascinating technologies.
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