Bluetooth Modulation and Multiple Access

Bluetooth uses simple single-carrier modulation (frequency and phase-shift keying) over very narrow channels, then relies on frequency hopping rather than fixed channels to share the spectrum. Where Wi-Fi slices time on a fixed channel for multiple access, Bluetooth hops to a new frequency each connection event.

Key Takeaways

• Bluetooth uses straightforward single-carrier modulation, frequency and phase-shift keying, over narrow channels
• Bluetooth Classic has 79 one-megahertz channels and BLE has 42, with a new frequency used each connection event
• The hopping is per connection event, not fast hopping within a single packet
• Bluetooth achieves multiple access through frequency hopping, whereas Wi-Fi does it by time-slicing a fixed channel

Video Transcript

Bluetooth uses basic digital modulation of various forms, both frequency and phase-shift keying. I'm not going to go into the details of that, but just understand these are single carrier modulation schemes, pretty straightforward. In contrast, Wi-Fi uses a lot of QAM, and some variants use OFDM on top of that. So a little more complicated modulation scheme, no big deal. I'm not trying to compare them as better or worse, I'm just saying this is what they are. Frequency and phase-shift keying, nothing wrong with that.

They use a very narrow channel to share their packets, but then they're using frequency hopping. So you saw all the channels in that previous spectrum diagram. Well, after they've connected, they're going to jump around among all of these different frequencies to share their data. As I mentioned, the Bluetooth Classic has 79 1 megahertz channels. The low energy has 42 megahertz channels. And then each connection event is going to use a new frequency. So it's not a fast frequency hopping, where they're hopping inside of a packet.

They share information back and forth. And then after a few hundred microseconds, or maybe a few milliseconds, depending on the protocol. And depending on what the device is negotiating, for LE they have some flexibility. They're going to jump to another frequency. Whereas Wi-Fi uses a fixed frequency channel and uses time to slice to enable multiple access, Bluetooth uses frequency hopping to enable multiple access.